FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
PATENTS RULES, 2006
COMPLETE SPECIFICATION
(SECTION 10; RULE 13)
Title:
"LIGHT EMITTING DIODE MADE OF INDIUM-GALLIUM NITRIDE BASED LATERAL NANOWIRES & METHOD OF MANUFACTURE THEREOF USING QUANTUM WELL HETEROSTRUCTURES AND WET ETCHANTS"
Applicants:
>
IITB-MONASH RESEARCH ACADEMY, HAVING ITS OFFICE AT OLD CSE BUILDING, 2ND FLOOR, POWAI, MUMBAI- 400076, MAHARASHTRA, INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED :

TITLE: LIGHT EMITTING DIODE MADE OF INDIUM-GALLIUM NITRIDE BASED LATERAL NANOWIRES & METHOD OF MANUFACTURE THEREOF USING QUANTUM WELL HETEROSTRUCTURES AND WET ETCHANTS
. FIELD OF INVENTION
The present invention relates to a method for nanowire formation by natural selection during wet chemical etching. In particular, the method involves fabricating semi-conductor devices on the nanowires so formed. More particularly, the invention relates to Indium-Gallium nitride (InGaN) based lateral quantum wire light emitting diode (LED) for optoelectronics, e.g. highly efficient super-luminescent LEDs and lasers.
BACKGROUND OF INVENTION
A light-emitting diode (LED) is a basic pn-junction diode functioning as a two-', lead semiconductor light source, which emits light when activated. The electrons are able to ■ recombine with the holes within the diode when a requisite voltage is applied to its leads; thereby releasing energy in the form of photons. This effect is generally called as "electroluminescence", and the colour of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. LED is often small in area (less than 1 mm2) and integrated optical components may be used to shape the radiation pattern thereof. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths with high brightness. The recent developments in the field of LEDs permit their use for environment-friendly and task-specific lighting. LEDs have many advantages over incandescent light sources, for example, lower energy consumption, longer service-life, improved physical robustness, smaller size, and faster switching. At present, light-emitting diodes are used in applications as diverse as aviation 1 lighting, automotive headlamps, advertising, general lighting, traffic signals, and camera flashes. However, LEDs which are powerful enough for room lighting are still relatively expensive, and require more precise current and heat management than the compact fluorescent lamp sources of comparable output. LEDs have allowed new text and video displays, as well as sensors to be developed, while their high switching rates are also useful in advanced communications technology. The invention of p-doping techniques for GaN in the 1900's enabled the fabrication of blue LED. Blue LEDs are integral for the manufacture of white LEDs. The next revolution in lighting technology is expected to be the replacement of the age old incandescent sources with the white LEDs. Therefore, there is felt a need for a suitable wet-etching method to produce InGaN based light emitting nanostructures to improve the performance of InGaN based LEDs in order to overcome their present shortcomings and for their increased commercial exploitation.

It is very difficult to manufacture GaN-based optoelectronic devices due to their poor radiative efficiencies arising from structural defects such as dislocations, Auger recombination, carrier leakage and so on. The structural defects are selectively etched during the wet chemical etching process. The major problem of GaN based LEDs is that their efficiency drops, when the drive currents are high and this limits their commercial success as a solid state light alternative to CFLs. There is also a problem with existing LEDs that GaN-based optoelectronic devices are very difficult to manufacture due to the high defects density translating into reduced radiative efficiencies. During the wet etching process, these extended structural defects are etched only selectively. However the point defects, which rarely affect the optical efficiencies, cannot be completely removed.
The wet etching process has been used until now for roughening the top surface of LEDs or to smoothen the dry etched end facets and side walls of the semiconductor lasers. For example, the crystallographic wet etching technique was used to roughen the surface of LEDs in order to have more surface area such that the light extraction efficiency increases. However, it is necessary to find out possible uses of the wet etching technique to improve the emission efficiency of light emitting diodes having Indium-Gallium Nitride (InGaN) based heterostructure by leveraging the natural tendency of the etch method to remove preferentially the non-radiative threading dislocations.
P. Visconti, D. Huang, M. A. Reshchikov. F. Yun, Cingolani, D. J. Smith, J. Jasinki, W. Swider. Z, Liliental-Weber, and H. Morkoc [Mat. Sc. Engg. B93, 229 (2002)]_have observed that wet chemical etching with boiling Phosphoric acid (H3PO4) selectively removes the threading dislocations in GaN, thus resulting in hexagonal etch pits for Ga-polar samples.
C. Huh, K. S. Lee, E. J. Kang, and S. J. Park [J. Appl. Phys, 93, 9383 (2003)3 further substantiates that , the remaining material is also almost entirely free of these defects. Threading dislocations are one • of the major contributors of non-radiative recombination. Wet etching thus provides a method
for obtaining high quality materials. Additionally, the formation of the etch pits have been shown
to increase the light output efficiency of the LEDs probably due to increase in light extraction
efficiency.
W. Yang, Y. He, L. Liu, and X. Hu [Appl. Lett. 102, 241111 (2013li_M. C. Schmidt, K. C. Kim, H. Sato, N. Fellows, H. Masui, S. Nakamura, S. P. DenBaars, and J. S. Speck; Jpn. J. Appl. Phys. 46, L126 (2007) & H. Zhao, G. Liu, J. Zhang, J. D. Poplawsky, V. Dierolf, and N. Tansu; Optics Exp. 19, S4 A991 (2011)] have shown that the efficiency roll-off at high current densities in GaN based LEDs is a technological challenge that is yet to be comprehensively addressed. Plasmon couplings, use of

m-plane non-polar growth directions, ensuring low defect densities in the active region with good lattice match between the wells and barriers and mitigating carrier leakage are some of the . possible ways to alleviate the problem of droop in GaN LEDs.
Further, in the conventional GaN-based LEDs, L-l characteristics have a linear nature of the curve for lower current densities. For higher current densities the L-l plot starts to become sub-linear and the light output power falls. This is called as efficiency droop or simply "droop", which is an undesirable effect. Although, vertical nanowires (not lateral) formed in a GaN based heterostructure have been reported already, the nanowire dimensions were much larger.
M. T. Hardy, K. M. Kelchner, Y. Lin, P. S. Hsu, K. Fujito, H. Ohta, J. S. Speck, S. Nakamura, and S. P. DenBaars [Appl. Phys. Express. 2, 121004 (2009)] have proposed another approach to overcome droop by using optical gain in a material to enhance the light output in the LED, while not yet allowing it to lase by eliminating the feedback mechanism - the path of the superluminescent LEDs(SLEDs).
N. Dutta, and P. Deimel [Quantum Electron. 19,496 (1983)] have demonstrated that the feedback implies a mechanism to preferentially allow one or some of the many radiations of different wavelength emitted by the active region to grow stronger in intensity, while the non-favoured ones die out subsequently. By eliminating the necessity to match the resonant criterion, all modes of the emitted light survive to give a wide-band optical output. The noise features of LEDs are absent in SLEDs, while it offers better coupling to optical fibers.
Excitons are the bound states of the electron-hole (e-h) pair due to the unscreened Coulomb attraction between the oppositely charged carriers. The excitons are formed when the e-h pair ■ lowers its energy by an amount equal to the exciton binding energy. The larger the exciton binding energy, the greater is the stability of the exciton against thermal dissociation. The wide bandgap semiconductors like Gallium Nitride (GaN) and Zinc Oxide (ZnO) have large exciton binding energies (> 26 meV), which permit their existence at room temperature.
Indium Gallium Nitride (InGaN), the ternary alloy of Indium Nitride (InN) and GaN have been successfully utilized in the fabrication of light emitting diodes (LEDs) and lasers. The Ill-Nitrides including Gallium Nitride (GaN) belong to an actively studied class of materials due to their predominantly direct band-gaps with UV-Vis emission capabilities. However, they also represent a highly defective material system and obtaining device grade materials from this class of materials is a resource intensive as well as cost-intensive feat.

S. Nakamura, M. Senoh, and T. Mukai [Jpn. Appl. Phys. 32, B, L8 (1993)]; S. Nakamura, M. Senoh, and T. Mukai [Appl. Phys. Lett. 62, 19, 2390 (1993)] & S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyoku, and Y. Sugimoto [Jpn. Appl. Phys. 35, L74 (1996)] have also taught that radiative recombination processes in semiconductors that involve excitons give rise to narrow emission peaks and greater efficiencies even at room temperature, provided that the excitons survive till such high temperatures.
K. Omae, Y. Kawakami, and S. Fujita [Phys. Rev. B 68, 085303 (2003)] have shown that the localized excitons engendered by the Indium clusters in InGaN make it possible to extract reasonably efficient light emission from the InGaN based opto-electronic devices in spite of the 1 presence of a high defect density in the material. These pseudo-confinement regions capture the excitons and prevent their movement towards the defects. Thus, the optical efficiencies presently observed in the LEDs and lasers can be enhanced manifolds, if the active region of the InGaN device is rid of the structural defects, since they promote non-radiative recombination. The presence of polarization fields in GaN tends to cause spatial separation of the e-h pairs and inhibits exciton formation. The exciton binding energy can be augmented by using quantum confinement, by enforcing greater overlap of the electron-hole wave-function and strain relaxation due to enhanced surface area. It has been demonstrated experimentally that InGaN-GaN quantum wells of dimensions smaller than the exciton Bohr radius (3.4 nm in InGaN) exhibit highly reduced piezoelectric fields, while allowing pronounced exciton localization effects.
. C. Huh, K. S. Lee, E. J. Kang, and S. J. Park [J. Appl. Phys, 93, 9383 (2003)]; S. Na, G. Y. Ha, D. S. Han, ' S. S. Kim, J. Y. Kim [J. H. Lim, D. J. Kim, K. I. Min, and S. J. Park [IEEE Photon Tech. Lett. 18, 14
(2006)3 & [T. Fujii, Y. Gao, R. Sharma, E. L. Hu, S. P. DenBaars, and S. Nakamura, Appl. Phys. Lett.
84,855(2004)].
The quantum confined features which are attractive for opto-electronic devices can be obtained in two ways: epitaxial growth or patterned dry etching. Vapour-Liquid-Solid (VLS) or Stranski-Krastanov growth methods are used in the bottom-up approach, while dry etching of the patterned heterostructure yield wires and dots in the top-down scheme. It was also demonstrated that the crystallographic wet chemical etching process was already used for surface texturing of the conventional GaN LEDs. D. A. Stocker, E. F. Schubert, and J. M. Redwing [Appl. Phys. Lett. 73, 2654 (1998)] has also observed that the crystallographic wet chemical etching process was also used for smoothening the surface after dry etching to reduce the surface damage.

W. Guo, M. Zhang, P. Bhattacharya, and J. Heo [Nano. Lett. 11, 1434 (2011)] have further proven that the vertical nanowires have been used for alleviation of the droop in GaN based devices. The low density of the nanowires is advantageous to study quantum mechanical phenomena, which becomes complicated if there is a forest of nanowires when grown in a bottom-up approach.
PRIOR ART
US6294475 Bl discloses a method of processing Ill-Nitride epitaxial layer system on a substrate. The process includes exposing non-c-plane surfaces of the Ill-nitride epitaxial layer system, for example by etching to a selected depth or cleaving, and crystallographic etching of the epitaxial layer system, in order to obtain crystallographic plane surfaces. The Ill-Nitride epitaxial layer system includes GaN. The etching step includes reactive ion etching in chlorine-based plasma, PEC etching in a KOH solution or cleaving, and the step of crystallographic etching includes immersing the epitaxial layer system in a crystallographic etching chemical, such as phosphoric acid, molten KOH, KOH dissolved in ethylene glycol, sodium hydroxide dissolved in ethylene glycol, tetraethyl ammonium hydroxide, ortetramethyl ammonium hydroxide.
EP2597687 A2 discloses a method for producing a GaN LED device, wherein a stack of layers comprising at least a GaN layer is texturized and comprises the steps of providing a substrate on ' its surface said stack of layers, depositing a resist layer directly on said stack, positioning a mask above said resist layer, said mask covering one or more first portions of said resist layer and not covering one or more second portions of said resist layer, exposing said second portions of said resist layer to a light source, removing the mask, bringing the resist layer in contact with a developer comprising potassium, wherein said developer removes said resist portions that have been exposed and texturizes the surface of at least the top layer of said stack by wet etching said surface, in the areas; situated underneath said resist portions that have been exposed.
US20140077158 A discloses a method provided for fabricating a light emitting diode (LED) using three-dimensional gallium nitride (GaN) pillar structures with planar surfaces. The method forms a plurality of GaN pillar structures, each with an n-doped GaN (n-GaN) pillar and planar sidewalls 1 perpendicular to the c-plane formed in either an m-plane or a-plane family. A multiple quantum well (MQW) layer is formed overlying the n-GaN pillar sidewalls, and a layer of p-doped GaN (p-GaN) is formed overlying the MQW layer. The plurality of GaN pillar structures are deposited on a first substrate, with the n-doped GaN pillar sidewalls aligned parallel to a top surface of the first substrate. A first end of each GaN pillar structure is connected to a first metal layer. The second end of each GaN pillar structure is etched to expose the n-GaN pillar second end and connected to a second metal layer.

US8026156 discloses a method for fabricating a nitride-based compound layer, in which initially a GaN substrate is prepared. A mask layer with a predetermined pattern is formed on the GaN substrate to expose a partial area of the GaN substrate. Then, a buffer layer is formed on the partially exposed GaN substrate. The buffer layer is made of a material having a 10% or less lattice mismatch with GaN. Thereafter, the nitride-based compound is grown laterally from a top surface of the buffer layer toward a top surface of the mask layer and the nitride-based compound layer is vertically grown to a predetermined thickness. Also, the mask layer and the buffer layer are removed via wet-etching to separate the nitride-based compound layer from the GaN substrate.
However, none of these documents disclose application of pure GaN-based materials obtained by wet etching process to fundamentally change the material by getting rid of the above-mentioned defects naturally and minimizing the emission losses in the medium.
By minimizing the emission losses in the medium, the emission efficiency of the LEDs can be increased and by obviating above-mentioned material defects occurring during the wet etching process, an improved LED can be manufactured according to the process of the present invention.
Moreover, none of the above techniques teach making of lateral nanowires, as shown in accordance with the present invention. Because making lateral nanowires is extremely difficult, particularly making any such sparse system.
OBJECTS OF THE INVENTION
Some of the objects of the present invention - satisfied by at least one embodiment of the present invention - are as follows:
An object of the present invention is to provide a method for the formation of low-density lateral nano-wires of practically any dimension in a cost effective manner.
, Another object of the present invention is to provide a method for improving the emission efficiency of the GaN based LEDs in a cost-effective manner.
Still further object of the present invention is to provide a method for obtaining very pure GaN based materials through natural selection.
A further object of the present invention is a method for fabricating defect-free LEDs which have high optical efficiency.

Yet another object of the present invention is a method for fabricating LEDs which offer better coupling to optical fibres and wideband emission.
- Still further object of the present invention is to provide a method for fabricating super-luminescent LEDs which do not show droop characteristics.
A yet another object of the present invention is to provide a method for fabricating LED heterostructures with lateral nanowires for making highly efficient superluminescent LEDs
A still further object of the present invention is to simplify the process of realizing a GaN based blue nanowire laser.
Other objects and advantages of the present invention will become more apparent from the following description, when read with the accompanying figures of drawing, which are however , not intended to limit the scope of the present invention in any way.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method is provided for obtaining lateral nanowires in Ill-Nitrides, e.g. Indium-Gallium nitride (InGaN) based quantum well light emitting diode (LED) heterostructures/wherein the method comprises the following method steps:
(i) forming lateral quantum wires in a quantum well LED heterostructure by using natural
selection during an anisotropic wet chemical etching process; (ii) ascertaining the etch pits - which have started forming due to the extended defects
present in Ill-Nitrides - by using scanning electron microscope (SEM); (iii) merging the formed etch pits by etching for longer times to remove the majority of the
extended defects that hamper light emission; (iv) obtaining very narrow lateral nanowires by chemical etching of the defects by heating in
a wet etchant solution of boiling concentrated Phosphoric acid; (v) controlling the wire dimensions by varying the etching times; and (vi) allowing the obtained nanowires to stabilize;
wherein the wet etching changes the material by removing the defects naturally and by minimizing non-radiative losses in the semiconductor material by eliminating the threading dislocations by attacking them with the etchant solution at predetermined high etch temperatures to obtain etch pits and with longer etch times, the etch pits widen and adjacent pits nearly merge into each other to produce nanowires and the total number of nanowires per unit area increases.

1
. Typically, the wet etching process removes the defects naturally and by minimizing non-radiative losses in the semiconductor material by eliminating the screw dislocations present there, by attacking with the etchant solution at predetermined high etch temperatures to obtain etch pits and with longer etch times, the etch pits widen and adjacent pits nearly merge into each other to produce nanowires with a wall thickness of less than 10 nm and approximately 700 nm long and to increase the total number of nanowires per unit area.
Typically, the method uses quantum confinement effects for achieving the optimum performance of the devices, wherein the heterestructures consist of stacks of layers of different lattices matched with each other and some of the layers are formed thin by varying the layer thicknesses, such that the quantum effect is produced by restricting the size of the layers to induce the movements of charge carriers in the direction of their confinement.
Typically, the method is a crystallographic or anisotropic etching process.
Typically, the heterostructure is a p-i-n heterostructure with active regions formed by the metalorganic chemical vapour deposition (MOCVD) technique comprising the method steps of:
(a) Taking a sapphire substrate;
(b) Growing a 25 nm GaN buffer layer on the sapphire substrate;
(c) Growing a 1.5 u,m thick undoped GaN layer on the GaN buffer layer;
(d) Growing a 2u,m thick Mg-doped p-GaN layer on the undoped GaN layer, the Mg-doped p-GaN layer having a carrier concentration of ~ 1.2xl020cnr3,
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(e) Growing an electron blocking layer on the Mg-doped p-GaN layer, the electron blocking layer having an electron concentration of ~ 8xl019cm"3;
(f) Growing 6 InxGal-xN/lnyGal-yN (x=0.01, y=0.1) intrinsic quantum wells on the electron blocking layer;
(g) Growing a 100 nm thick Si-doped n-GaN layer with an electron concentration of ~ 1 x 1018 cm"3; and
(h) Growing a 15 nm thick n++GaN layer on the Si-doped n-GaN layer;
wherein, the method further comprises the steps of:
(i) ascertaining the etch pits formed due to the defects present in Ill-Nitrides by using
scanning electron microscope (SEM); (j) merging the formed etch pits by longer etching times thereby to remove the majority of
extended non-radiative defects that hamper light emission;

(k) obtaining very narrow lateral nanowires by chemical etching of the defects by heating in
a wet solution of boiling Phosphoric acid of 85% concentration; (I) controlling the nanowire dimensions by varying the etching times; and (m) allowing the obtained nanowires to stabilize.
Typically, the electron blocking layer is a 10 nm thick p-Alo.12Gao.8sN electron blocking layer. In accordance with the present invention, further a method is provided for producing a Laser by using the nanowires formed on the light emitting diode (LED) heterostructure as claimed in any of , the preceding claims.
In accordance with the present invention, there is also provided a light emitting diode (LED) made of Indium-Gallium nitride (InGaN) based quantum well heterostructures having lateral nanowires, which comprises:
(I) a sapphire substrate; a 25 nm GaN buffer layer grown on the sapphire substrate;
(II) a 1.5 fim thick undoped GaN layer grown on the GaN buffer layer;
(III) a 2u,m thick Mg-doped p-GaN layer grown on the undoped GaN layer, the Mg-doped p-GaN layer having a carrier concentration of ~ 1.2xl020cm"3;
(IV) an electron blocking layer grown on the Mg-doped p-GaN layer, the electron blocking layer having an electron concentration of ~ 8xl019cnrr3;
(V) 6 InxGal-xN/lnyGal-yN (x=0.01, y=0.1) intrinsic quantum wells grown on the electron blocking layer;
(VI) a 100 nm thick Si-doped n-GaN layer grown with an electron concentration of ~ 1 x 1018cm"3; and
(VII) a 15 nm thick n++GaN layer grown on the Si-doped n-GaN layer;
wherein, the electron blocking layer is a 10 nm thick p-Alo.nGao.ssN electron blocking layer and the etch pits are merged to produce lateral nanowires with a wall thickness of less than 10 nm and approximately 700 nm long and the total number of nanowires per unit area is substantially increased.
Typically, the nanowires act as a waveguide without any feedback to produce a super-luminescent behaviour.
In accordance with the present invention, there is also provided a Laser produced by converting the light emitting diode (LED) as claimed in claims 8 or 9, wherein the a feedback mechanism, e.g. a feedback cavity is coupled to the superluminescent active region of the light emitting diode (LED) heterostructure.

Typically, the predetermined feedback is provided by using a lateral silicon nitride or other patterned organic polymer photo-resist grating of 6 or predetermined integer periods on one side and 7 or predetermined integer periods on the other side of the nanowire cavity to a allow a bandwidth collapse to produce sub-nm dimensions and to initiate the onset of the lasing action.
DESCRIPTION OF THE PRESENT INVENTION
The light emitting diode is one of the most promising optoelectronic devices, which presently merits further research and development to facilitate their increased application for commercial and environmental reasons, particularly in the light of the ever increasing energy requirement of the world populace. At present, a cost effective technology is not available, which uses the quantum confinement effects in an individual lateral nanowire for achieving the optimum performance from InGaN based LED heterostructures. A semiconductor heterostructure is a stack of layers of different semiconductors lattice matched to each other and of varying layer thicknesses such that some of the layers are so thin that quantum effects become prominent. The size restriction of the layers leads to the movements of charge carriers becoming restricted in direction of the confinement. Consequently the energy of the carriers changes from a continuous function to a discrete one in the direction of confinement. This is quantum confinement. The present invention provides an important technology in this field.
Although, the application of the wet chemical etching process has not been done previously for obtaining pure GaN-based materials, this process can be effectively used in accordance with the present invention for fabricating semiconductor devices, such as GaN based opto-electronics, particularly LEDs and lasers having higher emission efficiencies. Accordingly, very pure GaN-based materials could be obtained, that too very cost-effectively. Further, the purity of the material coupled with the quantum confinement effects in nanowires, facilitates in extracting an enhanced optical performance from the InGaN based LED heterostructure.
' It is already known that the heterostructure is a layered structure on a substrate (usually semiconductor material heterostructure), where size restricts the movements of the charge carriers forcing them into a quantum confinement. The quantum confinement also leads to the formation of a set of discrete energy levels at which the carriers can exist. The heterostructures have sharper density of states than the structures of more conventional bulkier sizes. In fact, a heterostructure is a sequential stack of different material layers deposited in such a way that there is electrical and material continuity across the interfaces and each layer is crystalline. The heterostructures can be advantageously used in fabricating semi-conductor devices, for example, GaN opto-electronics like Light emitting diodes, lasers, and super-luminescent light emitting

diodes as well as top-down electronics devices like transistors. In particular, the heterestructures are significant in fabricating short-wavelength light-emitting diodes and diode lasers. Whenever excitons are involved in an optical transition, it becomes an efficient process of light emission. An exciton is a binary of two particles, i.e. the electron and the hole, which are held together by means of a binding energy. The spatial extent of the exciton depends on the dielectric properties of the material in which it resides.
It has been successfully established by the present inventors that the light emission in the lateral nanowires of the InGaN material obtained by crystallographic etching have an excitonic origin. The present method of obtaining nanowires is novel in that the nanowires were obtained by using natural selection during an anisotropic or crystallographic wet chemical etching process. Then ascertaining by using SEM, the etch pits having started forming due to extended defects present in Ill-Nitrides and merging the etch pits formed by etching for longer times to remove these extended defects in the material which hamper light emission. In this way, the wire dimensions can be easily controlled by varying the etching times and the nanowires of practically any dimension can be obtained.
A super-luminescent LED denotes a super-linear nature of the light output power versus bias current (L-l) characteristics of the LED electroluminescent spectrum, which prevails even at high current densities. Therefore, the problem of droop is also completely eliminated by using lateral nanowires and a superluminescent light emission is obtained. The inventors observed no drop in performance of the LED by driving very high currents such that the devices broke down.
A superluminescent light emitting diode (SLED) is fabricated on a sub-10 nm lateral nanowire obtained naturally by etching the defects in a wet solution of heated Phosphoric acid. The 1 nanowires act as a waveguide without any feedback to give a super-luminescent behaviour. This superluminescent behaviour in the nanowires etched into the LED heterostructure leads to a lasing action, when a feedback mechanism is added to it. The losses in the nanowire are extremely low, which allows for a superluminescent performance due to material gain. Gain in a material arises when the losses in the form of non-radiative recombination, facet leakages and so on are reduced. By getting rid of the primary non-radiative centres, i.e., the screw dislocations, losses are being reduced drastically.
In accordance with the present invention, there is provided a cost-effective method for improving
the emission efficiency of GaN based LEDs. This method uses LEDs having InGaN based
heterostructures. Initially, the Scanning Electron Microscopy (SEM) was employed here for
'. ascertaining that the etch pits formed due to the defects present in the Ill-Nitrides including GaN,

are nearly merged to form very narrow nano-wires. Here, using a wet chemical etching in boiling Phosphoric acid, lateral nanowires of less than 10 nm widths in an InGaN based quantum well LED heterostructure are formed.
The hexagonal etch pits form at threading dislocation sites, where the anisotropic wet etching (orientation dependent etching) or crystallographic etching commences and with longer etch times, etch pits widen and adjacent pits nearly merge. It is to be noted that crystallographic etching is synonymous with "Anisotropic etching along crystal planes". During such wet etching processes, wet etchants etch crystalline materials at very different rates depending upon which crystal face is exposed to the etchant. The thin wall of the material remaining between two nearby hexagonal etch pits can be thus be constricted to widths of practically any dimension by controlling the etch times. Therefore, these narrow and defect-free regions of the quantum well LED heterostructures can be ideally used for making highly efficient superluminescent LEDs (SLEDs) or lasers. The immediate benefit of this approach is that excitons are able to withstand the thermal dissociation up to the room temperature.
This has been proved by sharp lines in the photoluminescence (PL) spectrum, increased binding energy of the excitons in the etched samples and unsaturated monotonic increase of PL intensity on increasing the excitation power of He-Cd laser source. Photoluminescence (PL) studies have shown an increase of the exciton binding energies from 20.8 eV in the non-etched sample to 45.9 eV with increased etching time. This corroborates the fact that the lateral width of the nanowire decreases with increase in etching time. Since decreasing width of nanowire leads to tighter coupling of the carrier wave-functions, it strengthens exciton binding. Subsequently, these nanowires were individually used for making the superluminescent LEDs, the efficiency of which does not reduce even when these are driven at very high current density and provide a very broad band spectrum. In fact, these superluminescent LEDs exhibit an exponential increase in their light output upon increasing the bias current.
An edge emitting LED is fabricated with the active region being the single lateral nanowire having a vertical quantum well structure. The top n-doped layer is intentionally kept thicker in order to avoid a complete removal of the n-region in the n-i-p LED heterostructure during the blanket wet etching.
The light output power versus bias current (L-l) characteristics at room temperature show no ' droop for higher current densities, for lower current densities, the light output is small and it increases super-linearly beyond a threshold current density of ~ 140 A/cm2, while the electroluminescent (EL) spectrum broadband.

The relative blue shift value of the primary peak of the EL spectrum from the nanowire LED (NW-LED) compared to the non-etched control LED is only 10 meV. The blue shift value is rather small considering that the lateral width of the nanowire is extremely narrow. The apparent anomaly can be explained with an infinite quantum well model coupled to the condition that the active region optical emission involves a lowering of the radiative emission energy due to binding energy of the exciton.
The method in accordance with the present invention uses crystallographic wet etching technique to fundamentally change the material by removing the extended defects naturally and by 1 minimizing the non-radiative losses in the medium or semiconductor material by eliminating the screw dislocations. The screw dislocations, which favour non-radiative recombination, are selectively attacked by the wet etchant at high temperatures to induce the anisotropic etching and they are removed. This leads to a reduction of the losses in the medium. So, a nearly defect-free material having high optical efficiency is obtained by this method.
It is also proposed to provide enough feedback by using a lateral silicon nitride grating of 6 periods on one side and 7 periods on the other side of the nanowire cavity, which allows a bandwidth collapse to sub-nm dimensions and the onset of lasing action. Therefore by coupling a feedback cavity to the superluminescent active region we propose to convert the LED device into a laser.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will be briefly described with reference to the accompanying drawings, which include:
Figure la shows the schematic of the light emitting diode (LED) heterostructure and the etching process in accordance with the present invention;
Figure lb shows the Scanning Electron Microscope (SEM) image of the etched sample;
Figure lc shows the SEM image of a single nanowire formed in accordance with the present invention;
Figure Id shows a 3-dimensional schematic of the nanowire in accordance with the present invention;

Figure le shows the atomic force microscopy (AFM) image of the sample etched in accordance with the present invention as shown in Figure lb;
Figure 2a shows another Scanning Electron Microscope (SEM) image of the GaN surface after etching in 85% concentrated H3P04;
Figure 2b shows the plot of the number of nanowires per unit area;
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Figure 2c shows the histogram of the number of nanowires of a particular length as a function of the etching time;
Figure 3a shows the photoluminescence (PL) spectrum plot of the sample C;
Figure 3b shows a power dependant PL spectrum of sample C;
Figure 3c shows the temperature dependant shift of the primary peak position of the PL spectrum of sample C;
Figure 3d shows the primary peak energy versus temperature plot of the PL spectrum as shown in Figure 3a;
Figure 3e shows the plot of the temperature dependant light output v/s excitation power density;
Figure 4 shows Scanning Electron Microscope (SEM) image of the nanowire light emitting diode in accordance with the present invention;
Figure 5a shows the temperature dependant output light power versus bias current (L-l) characteristics of the nanowire LED in accordance with the present invention;
Figure 5b shows the room temperature output light power versus bias current density characteristics of the nanowire in accordance with the present invention;
■ Figure 5c shows the bias dependant electroluminescence (EL) spectrum of the nanowire LED device in accordance with the present invention;
Figure 5d shows the full width at half maximum (FHWM) versus bias current density of the EL primary peak; and
Figure 5e shows the schematic explanation of the EL peak energy shift between the control LED
and the nanowire LED in accordance with the present invention. y

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The method in accordance with the present invention will now be described in more details with reference to the accompanying drawings without limiting the scope and ambit of the disclosure in any way.
Figure la shows the schematic of the light emitting diode (LED) heterostructure and the etching
process in accordance with the present invention. It is a p-i-n structure with active regions
consisting of six InxGal-xN/lnyGal-yN (x=0.01, y=0.1) intrinsic quantum wells grown on c-plane
sapphire substrate a by the metalorganic chemical vapour deposition (MOCVD) technique. It
consists of a 25 nm GaN buffer layer b grown on the sapphire substrate a, sequentially followed
by a 1.5 u.m thick undoped GaN layer c, a 2u.m thick Mg-doped p-GaN layer d having a carrier
concentration of ~ 1.2 x 1020cm3 and a 10 nm p-AlcmGaossN electron blocking layer e with
electron concentration of 8 x 1019cm~3. Thereafter, an active region f of six InxGal-xN/lnyGal-yN
(x=0.01, y=0.1) intrinsic quantum wells is grown and then a 100 nm thick Si-doped n-GaN layer g
' with an electron concentration of ~ 1 x 1018cm~3 is grown. Finally, a 15 nm thick n++GaN layer h is
grown thereon and 85% concentrated Phosphoric acid H3P04 is slowly heated to 200°C and the
temperature is now allowed to stabilize. This is labelled as unetched sample A. The InGaN based
LED heterostructures are now etched in the hot reagent for 5 and 8 minutes respectively and
labelled as samples B and C respectively. This figure further shows the anisotropic wet etches 10,
20, 30 near threading dislocations on both sides, which represent different wire widths WW
produced by wet etching for different time periods. Apparently, the physical widths of nanowire
reduce from sample B to C with increasing etch times [probably a couple of nanometers]. >
Figure lb shows the Scanning Electron Microscope (SEM) image of the etched sample after 8 minutes of etching. Here, the adjacent hexagonal etch pits in sample C, which are identifiable as 1 originating from screw type dislocations, and are almost on verge of merging with their adjacent etch pit.
Figure lc shows the SEM image of a single nanowire, the width of which is approximately 10 nm.
Here, the adjacent hexagonal etch pits in sample C, which are identifiable as originating from
screw type dislocations, have almost merged to result in a wall width (WW or 100) of
approximately (or less than) 10 nm and thickness of approximately 700 nm (Pa 1 = 674.0 nm
here). Although, the theoretical calculations suggest a wire width of 8 nm; the difference (10 nm ,
- 8 nm) could be explained by taking into consideration of the surface depletion effects, which
lead to narrowing of the wire dimension.

Figure Id shows a 3-dimensional schematic of the nanowire showing the sloping wall of non- etched material left behind. This wall has sloping faces and it constitutes a nanowire having vertical quantum wells. It is expected that surface depletion effects will further reduce the
dimensions of the nanowire.
Figure le shows the atomic force microscopic (AFM) image of the sample etched for 8 minutes, which clearly shows the formations of nanowires in the regions where two adjacent etch pits have merged. The presence of dislocations provides an impetus to start the crystallographic etching, where the hot H3PO4 attacks the defect and creates etch pits. As the time elapses, the pits widen and nearby pits nearly merge. Etching time provides a handle to control the width of the nanowire. It is concluded from this AFM image that at least top 15 nm of the top n-type layer survives in sample C. The red colour profile shown on right in Figure le shows that the nanowire dimension at the quantum well is approximately 10 nm.
Figure 2a shows another Scanning Electron Microscope (SEM) image of the GaN surface after etching in 85% concentrated H3PO4, showing a, (5 and y types of etch pits. The a-type pits are thought to have originated from screw dislocations, p-type from edge dislocations and y-type from mixed threading dislocations [Refer: L Lu, Z. Y. Gao, B. Chen, F. J. Xu, S. Huang, Z. L Miao, Y. Hao, Z. J. Yang, G. Y. Zhang, X. P. Zhang, J. Xu and D. P. Yu in J. App. Phys. 104,123525, 2008]. It is to be noted that the screw dislocations are the primary reason for the non-radiative losses in light-emitting devices.
Figure 2b shows the plot of the number of nanowires per unit area formed with increasing etching time.
' Figure 2c shows the histogram of the number of nanowires of a particular length as a function of the etching time. As the etching is prolonged, the total number of nanowires per unit area increases, which are narrow enough to allow observation of quantum effects. Longer nanowires also result by increasing the etching times.
Figure 3a shows the photoluminescence (PL) plot of the sample C (etched for 8 minutes) at 10K. These photoluminescence (PL) studies dependent on the temperature were performed in a closed cycle Helium cryostat with 325 nm He-Cd laser as the band-gap excitation source.
Figure 3b shows a power dependant PL spectrum of sample C at 300K. In this figure, the evolution of the yellow emission with excitation power density is shown inset on the right side at top and the monochromatic increase of intensity of the primary peak with excitation power is shown inset on the right side at bottom. It is apparent from the power dependent PL spectrum at room

temperature for sample C inset at the top of this figure that the yellow emission intensity tends to saturate with the excitation power density being increased from 50.8 W/cm2to 228 W/cm2. This is different from the blue emission having a monotonic increase in intensity with increasing power density of the excitation source, as shown in the inset at the bottom of this figure. This confirms the defect related origin of the yellow emission. The narrow line-width of the primary peak up to room temperature, the unsaturated PL intensity with increasing power density of the excitation source as well as the temperature-induced blue shift indicates its excitonic genesis in sample C.
Figure 3c shows the temperature dependant shift of the primary peak position of the PL spectrum of sample C. Here, the primary peak initially shows a red shift, followed by a blue shift in the temperature ranges from 100K and 200K. The temperature-dependent band-gap narrowing effect is shown only above 225K. At low temperatures having minimal thermal agitation, the photo-generated excitons are rendered relatively immobile in the local minima. However, their mobility increases with increasing temperature. As a result, they tend to settle into the band-edge global minima possibly caused by Indium fluctuations, which leads to the perceived red shift in the PL peak energy. However, with further rise in temperature, they move out of the local energy minima towards the above band-gap quantum confined energy states and induce the anomalous blue shift of the PL peak. These localized bound states arise from quantum confinement. So, total blue shift indicates the presence of bound localized states and thereby is an indicator of the density of nanowires in the region of sample being probed with the laser light. For still higher temperatures, the thermal bandgap narrowing takes over to give the Varshni-like temperature shift of the PL peak energy. It is observed that the magnitude of the blue shift (indicated by the energy range between the two turning points in Figure 3d) increases with increasing etching time, implying that the density of the localized states increases as the nanowires become narrower, thus leading to the enhanced density of quantum nanowires on the surface. The primary peak energy of the PL has blue shift in sample B and red shift for sample C, as compared to that in sample A.
The exciton binding energies are obtained from the Arrhenius plot of the integrated PL intensity for all the samples [Refer: H. Morkoc, Handbook of Nitride Semiconductors and Devices, Vol. 2: Electronic and Optical Processes in Nitrides (Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, 2008)]. The binding energy increases from 20.8 meV for the sample A having the primary peak located at 2.82 eV to 45.9 meV in the case of sample C with the primary peak at 2.81 eV. The binding energy of excitons increases with enhanced confinement owing to better coupling between the electron-hole wave-functions in homogeneous confined structures.

Figure 3d shows the primary peak energy versus temperature plot of the PL spectrum in Figure 3a. It has an S-shape indicating the presence of bound localized states.
Figure 3e shows the plot of the integrated PL light output intensity versus excitation power density, indicating an abrupt increase of output intensity for excitation intensities above 200 W/cm2 for lower temperatures. Here, the luminescence does not decrease substantially for the primary peak. The increase of the luminescence with the excitation power confirms the excitonic , origin thereof. This is also quantitatively similar to L-l of the nanowire devices shown later.
Figure 4 shows Scanning Electron Microscope image of the nanowire light emitting diode. The n-contact is the Ohmic contact to the top n-region. The nanowires were imaged on sample C and their coordinates were ascertained before writing the mesa structures and global alignment marks on the surface using electron-beam-lithography. Subsequently the inductively coupled reactive ion etching (ICP-RIE) was done to expose the p-layer. The Ni/Au (20 nm/20 nm) Ohmic stack was deposited on the patterned sample followed by lift-off and annealing at 500°C for 1 minute in 02 for the Ohmic p-contact. Following the p-Ohmic formation, local alignment marks
were made on the mesa structure. The Ohmic contact to the n-layer of the nanowire consists of a
narrow protrusion of length 4 u.m and width 1 u.m from a larger contact pad having a dimension
of 50pm x 50um. The n-Ohmic stack of Ti/AI/Ni/Au (25nm/100nm/30nm/100nm) was
deposited by electron beam evaporator and annealed at 800°C in N2 for 90 seconds after metal
lift-off.
Figure 5a shows the temperature dependant continuous wave-plot of the light output power versus bias current density (L-l) characteristics of the nanowire LED. The inset shows the L-l plot of the control LED at room temperature fabricated with the non-etched as-grown heterostructure. It is observed that the light output at lower temperature is higher than that at room temperature. However, the difference between the room temperature and L-l plots at 10 K is small, which is different from the conventional GaN-based quantum well LEDs. It is obvious that if the active region material is nearly free of the non-radiative defects, such as screw dislocations, then the light output will not differ much between low and room temperature operation, because the . main reason for poor optical performance at high temperature is the non-radiative recombination facilitated by defects. The L-l characteristic do not reveal any droop up to a current density of 400 A/cm2 at room temperature.
Figure 5b shows the room temperature output light power versus bias current density characteristics of the nanowire and control LED are denoted by solid lines, while the external quantum efficiency versus bias current density is denoted by dashed lines. It is observed that the

control LED has a pronounced droop. Here, the exponential nature of the L-l curve at about room temperature without any abrupt changes in slope demonstrate a superluminescent behaviour. Therefore, in nanowire LED devices, the light output intensity is probably less than the detection limits of the power-meter for lower current densities. The slope efficiency of the nanowire device, defined as the slope of the experimental L-1 plot, increases while that of the . control LED shows a pronounced droop for similar current densities and going negative for higher current densities as can be observed from Figure 5b. The bias dependent electroluminescence (EL) from the nanowire LED has an initial blue shift in the peak energy due to filling of higher energy states.
Figure 5c shows the bias dependant electroluminescence (EL) spectrum of the nanowire LED device at 300K. Further increase in bias current density results in red shift as a result of the device heating as seen here.
Figure 5d shows the full width at half maximum (FHWM) versus bias current density of the EL primary peak. The line width increases initially with increase in bias current, probably because of band filling effect as seen here. However, the FWHM drops with further increase in the bias current as expected [Refer: M. T. Hardy, K. M. Kelchner, Y. Lin, P. S. Hsu, K. Fujito, H. Ohta, J. S. Speck, S. Nakamura, and S. P. DenBaars, Appl. Phys. Express. 2, 121004 (2009)]. For bias currents higher than 13.5 mA, the FWHM increases again possibly due to heating effects. The observed blue shift of the NW-LED EL peak with respect to the control LED EL peak, matches the theoretically obtained quantization energy for an infinitely bounded quantum well. The NW has the air dielectric on both sides as the additional confining potential walls. Hence, the NW system can be considered to be having an infinite potential well in the lateral dimension and the finite confining potential due to the vertical heterostructure.
Figure 5e shows the schematic explanation of the EL peak energy shift between the control LED 1 and the nanowire LED. Ei is the confinement energy due to the quantum well in the LED heterostructure. The confinement energy of the nanowire LED should have led to a large blue shift of the EL energy peak, i.e. E2; however the binding energy of the exciton compensates a part of the blue shift. The overall observed blue shift in the EL peak is now smaller as compared to the situation where we consider the additional confinement due to nanowire formation. Here, the schematic explains the reason behind the small difference in the observed excitonic emission from the nanowire and the control LED, although the nanowire widths are narrow. The schematic incorporates the binding energies of 20.8 meV and 45.9 meV in the control LED and the NW LED respectively which partly compensates the expected large energy shift due to the additional confinement induced by the NW formation. The control LED gives EL peak energy of

2.84 eV, being 20.8 meV below the conduction band edge taking into account the exciton binding
energy in the unetched sample. The confinement energy for an InGaN-based NW of lateral
width 8 nm is approximately 30 meV. Thus, the ground state emission energy of the NW-LED
would be located at 2.89 eV. The EL emission energy can be calculated as 2.84 eV by
considering the exciton binding energy of 45.9 eV associated with the primary PL peak in the
sample etched for 8 minutes. This is fairly in conformity with the observed EL peak energy
of 2.85 eV. In the present embodiment, well-known technique of wet etching is used for making
naturally formed nanowires in an InGaN-based LED heterostructure, wherein the wire dimension
can be varied by controlling the etching duration. The tightly confined electron-hole pairs in such
narrow essentially defect-free wires tend to form stable excitons as compared to those present >
in the conventional quantum well LED heterostructure, The nano-fabricated LEDs have super-linear response at current densities up to 400 A/cm2. The light output power versus bias current density plot also shows a little variation with temperature as expected in a predominantly defect-free nanowire LED.
The nano-wire formation technique without using the resource intensive growth methods demonstrated here provides inexpensive and simple quantum confined structures in technologically important class of Ill-nitrides. Various other devices, such as high electron mobility transistors and lasers, where material defects need to be minimized, can be made from these naturally selected lateral nanowires.
METHOD OF FABRICATION OF NANOWIRES ACCORDING TO THE INVENTION
The wet chemical etching process is used in constricting the thin wall of material remaining between two nearby hexagonal etch pits into the widths of practically any dimension by , controlling the etching time. These narrow and defect free regions of the quantum well LED heterostructure are the ideal candidates for making highly efficient superluminescent LEDs.
The formation of lateral nanowires of widths less than 10 nm in an InGaN-based quantum well LED heterostructure was successfully demonstrated by wet chemical etching in boiling Phosphoric acid. Photoluminescence (PL) study of the etched samples show an increase of the exciton binding energy with increasing etching time to corroborate that the nanowire lateral width decreases with etch time.
The edge emitting LED is fabricated with the active region being the lateral nanowire having a vertical quantum well structure. The light output power versus bias current (L-l) characteristics at room temperature shows no droop for higher current densities, for lower current densities the

I
light output is small and it increases super-linearly beyond a threshold current density of ~ 140 A/cm2 while the electroluminescent spectrum is broadband.
APPLICATIONS OF THE INVENTION
Further, the nanowires formed on the LED heterostructures can also be used to make a laser cavity. The nanowire LED already fabricated shows signs of gain in the material and this can be utilized to achieve optical resonance in the form of a laser by further adding a resonant cavity/mirrors parallel to the end facets of the nanowire.
Superluminescent light emitting diodes are useful in optical communication systems. They offer 1 better coupling to optical fibres and wideband emission. The material of the nanowires is almost defect-free and hence has high optical efficiencies. Since the surface to volume ratio increases in the nanowires, the light extraction efficiency of LEDs is also enhanced. The capability to fabricate a laser on the etched nanowire by simply adding a dielectric grating greatly simplifies the process of realising a GaN-based blue laser. Blue lasers are technologically important for various civilian and defense purposes.
TECHNICAL ADVANTAGE & ECONOMIC SIGNIFICANCE OF THE INVENTION
Some of the technical advantages of the device proposed in accordance with the present invention are as under:
The method to obtain nanowires in accordance with the present invention is novel, because nanowires are obtained naturally by merging etch pits formed by removing the defects in the material. The nanowire dimensions can also be controlled by controlling the etching times. Thus, the method provides a useful handle to obtain nanowires of practically any dimension. The material of the nanowires so obtained is almost defect-free.
Previously, in the absence of the method according to the present invention, growing such high quality material necessitated the use of expensive methods like MBE (molecular beam epitaxy). Although, the process of fabrication of superluminescent LEDs is traditionally challenging, the present invention demonstrates the possibility of making superluminescent LEDs without using any complicated fabrication techniques or expensive equipment.
Similarly, blue lasers are extremely challenging to fabricate due to the large number of layers required and the tendency of Gallium Nitride based materials to form defects. However, by the method of realization of the blue laser in accordance with the present invention, the number of

layers is drastically reduced; as a result, a higher efficiency is attainable, which allows lower threshold currents.
Therefore, the wet etching technique used in accordance with the present invention, which facilitates removal of existing defects, can lead to exceptional reduction in the threshold current.
Based on above technical advantages of the superluminescent light emitting diodes, these can be used successfully in optical communication systems and optical coherence tomography. These > LEDs also offer better coupling to fibres and thus are useful in fibre coupled lighting and gyroscope applications.
Similarly, blue laser communication systems would also be able to enhance the bandwidth tremendously, thereby increasing their many applications, such as underwater communications, inter-satellite communication systems and so on.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", shall be understood to implies including a described element, integer or method step, or group of elements, integers or method steps, however, does not imply excluding any other element, integer or step, or group of elements, integers or method steps.
The use of the expression "a", "at least" or "at least one" shall imply using one or more elements or ingredients or quantities, as used in the embodiment of the disclosure in order to achieve one or more of the intended objects or results of the present invention.
The exemplary embodiments described in this specification are intended merely to provide an understanding of various manners in which this embodiment may be used and to further enable the skilled person in the relevant art to practice this invention. The description provided herein is purely by way of example and illustration. The various features and advantageous details are explained with reference to this non-limiting embodiment in the above description in accordance with the present invention. The descriptions of well-known components and manufacturing and processing techniques are consciously omitted in this specification, so as not to unnecessarily 1 obscure the specification.
Although the embodiments presented in this disclosure have been described in terms of its preferred embodiments, the skilled person in the art would readily recognize that these embodiments can be applied with modifications possible within the spirit and scope of the present invention as described in this specification.

While considerable emphasis has been placed on the specific features of the preferred embodiment described here, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiments without departing from the principles of the invention. These and other changes in the preferred embodiment of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to ' be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We claim:
1. A method of obtaining lateral nanowires in Ill-Nitrides, e.g. Indium-Gallium nitride (InGaN)
based quantum well light emitting diode (LED) heterostructures, wherein the method comprises
the following method steps:
(i) forming lateral quantum wires in a quantum well LED heterostructure by using natural
selection during an anisotropic wet chemical etching process; (ii) ascertaining the etch pits - which have started forming due to the extended defects
present in Ill-Nitrides - by using scanning electron microscope (SEM); (iii) merging the formed etch pits by etching for longer times to remove the majority of said
extended defects that hamper light emission; (iv) obtaining very narrow lateral nanowires by chemical etching of said defects by heating in
a wet etchant solution of boiling concentrated Phosphoric acid; (v) controlling the wire dimensions by varying the etching times; and (vi) allowing the obtained nanowires to stabilize;
wherein the wet etching changes the material by removing said defects naturally and by minimizing non-radiative losses in the semiconductor material by eliminating the threading dislocations by attacking them with said etchant solution at predetermined high etch temperatures to obtain etch pits and with longer etch times, said etch pits widen and adjacent pits nearly merge into each other to produce nanowires and the total number of nanowires per unit area increases.
2. A method as claimed in claim 1, wherein the wet etching process removes said defects naturally and by minimizing non-radiative losses in said semiconductor material by eliminating the screw dislocations present there, by attacking with said etchant solution at predetermined high etch temperatures to obtain etch pits and with longer etch times, said etch pits widen and adjacent pits nearly merge into each other to produce nanowires with a wall thickness of less than 10 nm and approximately 700 nm long and to increase the total number of nanowires per unit area.
3. A method as claimed in claim 1, wherein said method uses quantum confinement effects
for achieving the optimum performance of the device, wherein said heterostructures consist of stacks of layers of different lattices matched with each other and some of the layers are formed thin by varying the layer thicknesses, such that the quantum effect is produced by restricting the size of the layers to induce the movements of charge carriers in the direction of their ' confinement.

4. A method as claimed in claim 1, wherein said method is a crystallographic or anisotropic
r
etching process.
5. A method for producing a light emitting diode (LED) heterostructure as claimed in claim 1,
wherein said heterostructure is a p-i-n heterostructure with active regions formed by the
metalorganic chemical vapour deposition (MOCVD) technique comprising the method steps of:
(a) Taking a sapphire substrate;
(b) Growing a 25 nm GaN buffer layer on said sapphire substrate;
(c) Growing a 1.5 |um thick undoped GaN layer on said GaN buffer layer;
(d) Growing a 2u.m thick Mg-doped p-GaN layer on said undoped GaN layer, said Mg-doped p-GaN layer having a carrier concentration of ~ 1.2xl020cm~3,
(e) Growing an electron blocking layer on said Mg-doped p-GaN layer, said electron blocking layer having an electron concentration of 8xl019cm~3;
(f) Growing 6 InxGal-xN/lnyGal-yN (x=0.01, y=0.1) intrinsic quantum wells on said electron blocking layer;
(g) Growing a 100 nm thick Si-doped n-GaN layer with an electron concentration of ~ 1 x 1018cm"3; and
(h) Growing a 15 nm thick n++GaN layer on said Si-doped n-GaN layer;
wherein, the method further comprises the steps of:
(i) ascertaining the etch pits formed due to the defects present in Ill-Nitrides by using
scanning electron microscope (SEM); (j) merging the formed etch pits by longer etching times to remove the majority of said
extended non-radiative defects that hamper light emission; (k) obtaining very narrow lateral nanowires by chemical etching of said defects by heating
in a wet solution of boiling Phosphoric acid of 85% concentration; (I) controlling the nanowire dimensions by varying the etching times; and (m) allowing the obtained nanowires to stabilize.
6. A method for producing a light emitting diode (LED) heterostructure as claimed in claim 1,
wherein said electron blocking layer is a 10 nm thick p-Alo.12Gao.88N electron blocking layer.
'. 7. ' A method for producing a Laser by using the nanowires formed on the light emitting ' diode (LED) heterostructure as claimed in any of the preceding claims.

8. A light emitting diode (LED) made of Indium-Gallium nitride (InGaN) based quantum well
heterestructures having lateral nanowires, which comprises:
(I) a sapphire substrate; a 25 nm GaN buffer layer grown on said sapphire substrate;
(II) a 1.5 u.m thick undoped GaN layer grown on said GaN buffer layer;
(III) a 2u.m thick Mg-doped p-GaN layer grown on said undoped GaN layer, said Mg-doped p-GaN layer having a carrier concentration of ~ 1.2xl020cm-3;
(IV) an electron blocking layer grown on said Mg-doped p-GaN layer, said electron blocking layer having an electron concentration of ~ 8xl019cm"3;
(V) 6 InxGal-xN/lnyGal-yN (x=0.01, y=0.1) intrinsic quantum wells grown on said electron blocking layer;
(VI) a 100 nm thick Si-doped n-GaN layer grown with an electron concentration of ~ 1 x 1018crrf3; and
(VII) a 15 nm thick n++GaN layer grown on said Si-doped n-GaN layer;
wherein, said electron blocking layer is a 10 nm thick p-Alo.12Gao.88N electron blocking layer and the etch pits are merged to produce lateral nanowires with a wall thickness of less than 10 nm and approximately 700 nm long and the total number of nanowires per unit area is substantially increased.
, 9. Light emitting diode (LED) as claimed in claim 8, wherein the nanowires act as a
waveguide without any feedback to produce a super-luminescent behaviour.
10. A Laser produced by converting the light emitting diode (LED) as claimed in claims 8 or 9, wherein said a feedback mechanism, e.g. a feedback cavity is coupled to the superluminescent active region of said light emitting diode (LED) heterostructure.
11. Laser, as claimed in anyone of the claims 8 to 10, wherein predetermined feedback is provided by using a lateral silicon nitride or other patterned organic polymer photo-resist grating of 6 or predetermined integer periods on one side and 7 or predetermined periods on the other side of the nanowire cavity to a allow a bandwidth collapse to produce sub-nm dimensions and to initiate the onset of the lasing action.
1