Description:Field of Invention
The present invention relates to tunable opto-electronic properties of p-type Aluminum (Al) doped Tin-Oxide (Al:SnO) film. More particularly, the present invention relates to electron beam evaporation deposition method to be employed for the formation p-type Aluminum (Al) doped Tin--Oxide (Al:SnO) thin film which shows tunable opto-electronic properties.

The objectives of this invention
The objective of this invention is to engineered the optical, structural and electrical properties of Aluminum (Al) doped Tin-Oxide (Al:SnO) thin film by means of its compositional variation such as variation of Aluminum (Al)composition for its wide range of applications in optoelectronics devices.

Background of the invention
The compositional variation of Aluminum (Al) doped Tin-Oxide (Al:SnO) by using electron beam evaporation deposition method results into some change in its optoelectronic properties. Previous research has primarily focused on only oxygen mole fraction variation of Tin-Oxide by some other complex methods such as chemical vapor deposition(CVD), radio-frequency (RF) sputtering and spray pyrolysis(van Mol et al., 2006; Jadsadapattarakul et al., 2008; Guzmán-Caballero, Quevedo-López and Ramírez-Bon, 2019),however, some of these process such as chemical vapor deposition (CVD) require huge infrastructure to deal with toxic gases(Shi, 2015)whereas radio-frequency (RF) sputtering has low rate of deposition(Loch and Ehiasarian, 2017) whereas spray pyrolysis processes lacks precise control of variation of its constituents(Rukosuyev et al., 2018).So, there is need of some ease of deposition method to alter the composition of Aluminum (Al) doped Tin-Oxide (Al:SnO) to tune its optoelectronic properties. Therefore, electron beam evaporation deposition method have been proposed in order to alter the composition of Aluminum (Al) doped Tin-Oxide (Al:SnO) with a high degree of precision and control along with ease of fabrication as compared to other methods such as chemical vapor deposition (CVD) and radio-frequency (RF) sputtering.

Detailed of Prior Art
Earlier research work has predominantly focused on only oxygen mole fraction variation of Tin-Oxide by some other complex methods such as chemical vapor deposition (CVD) (US4853257A), RF (radio frequency) sputtering (US20030178751A1) andspray pyrolysis (US8182573B2). However, these processes lack precision in regulating the oxygen mole fraction variation of Tin-Oxide. Therefore, some difficulties are encountered in obtaining the desired optoelectronic properties of Tin-Oxide. External doping of Tin-Oxide thin films by atomic layer deposition (ALD) (US20180155372A1) and molecular beam epitaxy (MBE) (US4426237A) processes have been attempted in order tune its optoelectronic properties. But, these processes are highly expensive.Analyzing the background of the above inventions, a simple and economical method to alter the as Aluminum (Al) composition in Aluminum (Al) doped Tin-Oxide (Al:SnO) with a high degree of precision and ease of deposition is not much explored. Hence, deposition of Aluminum (Al) doped Tin-Oxide (Al:SnO) have been attempted with electron beam evaporation deposition method.

Summary of Invention
This patent discuss about the utility of electron-beam evaporation deposition method toalter the Aluminum (Al) composition in Aluminum (Al) doped Tin-Oxide (Al:SnO) with ease of fabrication at room temperature The structural, optical and electrical properties of Aluminum (Al) doped Tin-Oxide (Al:SnO) changes with variation in its Aluminum (Al) and oxygen mole fractions. Asimple as well as economical method having ease of fabrication for Aluminum (Al) doped Tin-Oxide (Al:SnO) thin film have been proposed and variation in its structural, optical and electrical properties have been discussed in order to find its usage in wide range of optoelectronic devices.
Detailed description of the invention
The Aluminum (Al) doped Tin-Oxide (Al:SnO) thin films have been deposited on quartz glass substrate using a customized e-beam evaporation chamber shown by schematic diagram in figure 1. Quartz glass substrates are cleaned ultrasonically with acetone and isopropanol first. Subsequently substrates are dipped into the de-ionized water and finally dried with nitrogen gun.Cleaned substrate is placed into the substrate holder inside the e-beam chamber and vacuum level of 1×10-6 mbar is achieved by two steps, using roughing and high vacuum pumps (Turbo Molecular Pump) sequentially. The high vacuum pump is allowed to operate for sometime to ensure the base pressure in the order of 1×10-6 mbar inside the e-beam chamber. After evacuating the chamber to a base pressure of 10-6 mbar, oxygen gas (99.999% purity) is purged into the chamber through MFC (Mass Flow Controller) to maintain the flow rate of 4sccm (standard cubic centimetres per minute). Now, the e-beam is generated and focused on the crucible containing Tin (Sn) metal pellets (99.99%, purity) to be evaporated. The electron-beam (e-beam) evaporated Tin (Sn) reacts with the oxygen gas in the vicinity of quartz glass substrate initially to form Tin-Oxide (SnO) film. The growth rate of deposition Tin (Sn) was maintained at 1 Angstrom/second and the flow rate (4sccm) of Oxygen was optimized to create an Oxygen deficient condition inside e-beam chamber for partial oxidation of Tin to form Tin-Oxidei.e., stannous oxide(SnO). The deposition Tin (Sn) metal and oxygen was carried out for 1000 second. Thereafter, Aluminum (Al) metal pellets (99.99%, purity) was placed in crucible inside e-beam chamber and was evaporated by the action electron-beam (e-beam) technique to form Aluminum (Al) doped Tin-Oxide (Al:SnO). The growth rate of deposition was maintained at 0.1 Angstrom/second. The deposition of Aluminum (Al) was carried for 50 second. Similarly, deposition of Aluminum (Al) were carried out for 100 second, 150 second and 200 second to form four different types of Aluminum (Al) doped Tin-Oxide (Al:SnO) which have been named here as Type-I, Type-II, Type-III and Type-IV respectively. Type-I corresponds to Aluminum (Al) doped Tin-Oxide (Al:SnO) samples in which Aluminum (Al) was deposited for 50 seconds, Type-II corresponds to Aluminum (Al) doped Tin-Oxide (Al:SnO) samples in which Aluminum (Al) was deposited for 100 seconds, Type-III corresponds to Aluminum (Al) doped Tin-Oxide (Al:SnO) samples in which Aluminum (Al) was deposited for 150 seconds, and Type-IV corresponds to Aluminum (Al) doped Tin-Oxide (Al:SnO) samples in which Aluminum (Al) was deposited for 200 seconds. It is important to note here that all growth processes related to the formation Aluminum (Al) doped Tin-Oxide (Al:SnO) film have been carried out room temperature.
The optical and electrical characterization of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) have been performed.
The optical characterization of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) have been carried out using UV-VIS-NIR spectrophotometer. The figure 2 shows that the absorbance of Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest absorbance and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has lowest absorbance. The absorbance is calculated as logarithmic function of T (transmittance) which is expressed by equation 1.
(1)
Where A is absorbance and T is transmittance of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples.
Thereafter, Hall measurement of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) have been performed in order to find out nature of sample, its carrier concentration, Hall mobility and sheet resistivity using equations given below. The equation 2 represents the formula for calculation Hall coefficient, equation 3represents the formula for calculation of carrier concentration and equation 4represents the formula for calculation of Hall mobility of Aluminum (Al) doped Tin-Oxide (Al:SnO).
Hall coefficient of Aluminum (Al) doped Tin-Oxide (Al:SnO) sample,
(2)
Hole carrier concentrationof Aluminum (Al) doped Tin-Oxide (Al:SnO) sample,
(3)
Hall mobilityof Aluminum (Al) doped Tin-Oxide (Al:SnO) sample,
(4)
WhereRHis Hall coefficient ofAluminum (Al) doped Tin-Oxide (Al:SnO) sample, pis hole carrierconcentration of Aluminum (Al) doped Tin-Oxide (Al:SnO) sample,? is resistivityof Aluminum (Al) doped Tin-Oxide (Al:SnO) sampleandqis electronic charge( Coulombs)and d is the thickness of Aluminum (Al) doped Tin-Oxide (Al:SnO) coating on quartz glass substrate.Iis the current and B is the applied magnetic field.
The resistivity ofAluminum (Al) doped Tin-Oxide (Al:SnO) sample is given by equation 5.
(5)
Where dis the thickness of Aluminum (Al) doped Tin-Oxide (Al:SnO) coating on quartz glass substrate.RS is sheet resistance of Aluminum (Al) doped Tin-Oxide (Al:SnO) thin film on quartz glass substrate.
It is important to note that all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples obtained from Hall measurement shows p-type nature.
The hole carrier concentration all four sample (Type-I, Type-II, Type-III and Type-IV) of Aluminum (Al) doped Tin-Oxide (Al:SnO) were obtained to be 2.1 x 1017cm-3,4.2 x 1018cm-3, 9.1 x 1018cm-3 and 1.2 x 1019cm-3, respectively.In terms of hole carrier concentration, Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest hole carrier concentration and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has relatively lowest hole carrier concentration.
The Hall mobility all four sample (Type-I, Type-II, Type-III and Type-IV) of Aluminum (Al) doped Tin-Oxide (Al:SnO) were obtained to be 12.4 cm2/Vs ,9.2 cm2/Vs,7.3 cm2/Vsand5.2 cm2/Vs,respectively.In terms of Hall mobility, Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest Hall mobility and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has lowest Hall mobility.
The resistivity of all four sample (Type-I, Type-II, Type-III and Type-IV) of Aluminum (Al) doped Tin-Oxide (Al:SnO) were obtained to be 5.9×10-3 O-cm, 2.1×10-3 O-cm, 8.6×10-4 O-cm and 1.4×10-4 O-cm, respectively, using four point probe method.In terms of resistivity, Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest resistivity and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has relatively lowestresistivity.
The Hall measurement of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) have been tabulated in Table 1 as ready references.
Brief description of Drawing
Figure 1Schematic diagram of electron-beam process for formation of Aluminum (Al) doped Tin-Oxide (Al:SnO).
Figure 2Absorbance spectra of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples.
Table 1 Carrier concentration, Hall mobility and sheet resistivity and nature of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples obtained using Hall measurement.
Detailed description of the drawing
Figure 1 shows schematic diagram of electron-beam process for formation of Aluminum (Al) doped Tin-Oxide (Al:SnO).Electron beam is generated from filament inside the vacuum chamber. These electron beams are focused on molybdenum crucible, due to which Tin pellets present in crucible get melted and forms Tin vapor which reacts with the oxygen atoms present in the chamber to SnO samples on quartz glass substrates placed inside the electron-beam chamber. Thereafter, electron beam is now focused on another crucible containing Aluminum (Al) pellets to form the Aluminum (Al)vapor which react withSnO to form Aluminum (Al) doped Tin-Oxide (Al:SnO).
Figure 2 shows absorbance spectra of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples. It has been obtained from UV-VIS-NIR spectrophotometry.It represent photon absorbing ability of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples for the different wavelength of photons. Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest absorbance and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has lowest absorbance.
Table 1 shows data of all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples obtained from Hall measurement. Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest Hall mobility and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has relatively lowest Hall mobility.In terms of hole carrier concentration, Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest hole carrier concentration and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has relatively lowest hole carrier concentration, whereas Type-I Aluminum (Al) doped Tin-Oxide (Al:SnO) sample has relatively highest sheet resistivity and Type-IV Aluminum (Al) doped Tin-Oxide (Al:SnO) has relatively lowest sheet resistivity. It is important to note that all four types of Aluminum (Al) doped Tin-Oxide (Al:SnO) samples obtained from Hall measurement shows p-type nature.
5 Claims & 2 Figures , Claims:Claims:
1. A method for the growth ofp-type Aluminum (Al) doped Tin-Oxide (Al:SnO) thin film comprises of following steps:
(a) Electron beam evaporation (e-beam) deposition carried out at room temperature for the formation p-type Aluminum (Al) doped Tin-Oxide (Al:SnO) thin film samples.
(b) Fabricated samples of Aluminum (Al) doped Tin-Oxide shows p type nature and different absorbance, carrier concentration, Hall mobility and resistivity.
2. The method as claimed in claim 1, wherein tunable opto-electronic properties includes absorbance, carrier concentration, Hall mobility and sheet resistivity.
3. The method as claimed in claim 1, wherein room temperature denotes 27 0C inside the electron-beam chamber.
4. The method as claimed in claim 1, wherein the flow rate of oxygen maintained at 4 sccm inside the electron-beam chamber.
5. The method as claimed in claim 1, wherein the deposition time of Aluminum (Al) has been altered here as 50 seconds, 100 seconds, 150 second and 200 seconds to obtained p-type Aluminum (Al) doped Tin--Oxide (Al:SnO) thin film samples.