0001] The present disclosure relates generally to a photodetector, and more specifically,
relates to a means for enhancing light absorption in the photodetector.
BACKGROUND
[0002] Background description includes information that may be useful in understanding
the present disclosure. It is not an admission that any of the information provided herein is prior
art or relevant to the presently claimed disclosure, or that any publication specifically or
implicitly referenced is prior art.
[0003] Recent era of high-speed photonic system demands photo detector to have large
bandwidth, gain and improved light enhancement competence with miniaturization of device.
Amongst the different light absorption enhancement methods being examined by the
investigators, plasmonic has acquired a lot of attention in the last decades. Fundamentally, the
conventional type metal-semiconductor-metal (MSM) photodetectors mainly include two
electrodes act as schottky diode in optical communication. When light is falling on the front
surface, it generates electron–hole pairs and produce output current. The major drawback of this
conventional photodetector is that when light is incident on the front surface then maximum
amount of the light is reflected back which results the light reflection losses and reduction in the
efficiency of the device.
[0004] To overcome this problem, plasmonic based photodetector using single layer nanogratings came into existence with gold material. These nano-gratings are used to couple more
light. So, using nano-gratings, minimization in the reflection losses can be achieved. Various
researchers obtained the plasmonic device using gold material with single and double layer of
rectangular nanogratings. On the other hand, gold is very costly when compared to other noble
material.
[0005] Therefore, there is a need in the industry to provide a cost-effective device that can
obtain higher light absorption and reduces optical losses.
3
OBJECTS OF THE PRESENT DISCLOSURE
[0006] An object of the present disclosure relates generally toametal-semiconductor-metal
detector, and more specifically, relates to a means for enhancing light absorption using double
layering of nano-gratings structure.
[0007] Another object of the present disclosureis to provide a plasmonic based
photodetector using double layer of trapezoidal nanograting structure that can be more efficient
for light absorption with surface plasmon resonance.
[0008] Another object of the present disclosureis to provide a photodetector that can use
silver material for nanograting structure that can be less costly and the damping rate can also be
less than other noble material.
[0009] Another object of the present disclosureis to provide a photodetector with nanogratings structure that can have superior light trapping characteristics.
[0010] Yet another object of the present disclosureis to provide a photodetect or that can use
GaAs material for substrate which can have direct band gap and higher electron mobility to
achieve higher light absorption with double nanograting structure.
SUMMARY
[0011] The present disclosure relates generally to ametal-semiconductor-metal detector,
and more specifically, relates to a means for enhancing light absorptionusing double layering of
nano-gratings structure.
[0012] In an aspect, the present disclosure provides a photodetector including: a first metal
layer placed at a first end of the photodetector, the first metal layer receives incident light waves,
wherein the first metal layer can be configured with one or more first grooves, each of the first
grooves having a quadrangular cross section, and each of the first grooves located at a predefined
distance from each other; anda second metal layer placed on a photonic semiconductor substrate,
the second metal layer configured with one or more second grooves, each of the second grooves
having a quadrangular cross-section, and each of the second grooves located at a predefined
distance from each other, wherein a gap can be created between the first metal layer and the
second metal layer, between the first grooves and corresponding second grooves, the gap adapted
to allow incident light waves to pass through to the substrate, andwherein the incident light
waves can be coupled at each of the first grooves and corresponding second grooves to form
4
coupled light waves such that the coupled light waves at the substrate have an absorption greater
than the incident light waves.
[0013] In an embodiment, the first metal layer and the second metal layer can be made of
metals selected from a group including gold, platinum, silver and a combination thereof.
[0014] In another embodiment, at least one of the first metal layer and the second metal
layer can be made of silver.
[0015] In another embodiment, the substrate includes gallium arsenide (GaAs) and any
combination thereof.
[0016] In another embodiment, the first metal layer and the second metal layer configured
to form double layered structure.
[0017] In another embodiment, the light absorption enhancement can be determined based
on the input parameters.
[0018] In another embodiment, the input parameters can be selected from a group
including shape, height, thickness of metal layer, input wavelength, substrate dimensions,
material and any combination thereof.
[0019] Various objects, features, aspects, and advantages of the inventive subject matter will
become more apparent from the following detailed description of preferred embodiments, along
with the accompanying drawing figures in which like numerals represent like components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The following drawings form part of the present specification and are included to
further illustrate aspects of the present disclosure. The disclosure may be better understood by
reference to the drawings in combination with the detailed description of the specific
embodiments presented herein.
[0021] FIG. 1 illustrates an exemplary representation of a photodetector for enhanced light
absorption, in accordance with an embodiment of the present disclosure.
[0022] FIG. 2 illustrates a schematic view of plasmonic based photodetector with double
layering of trapezoidal nano-gratings using Opti-FDTD simulation tool, in accordance with an
embodiment of the present disclosure.
5
DETAILED DESCRIPTION
[0023] The following is a detailed description of embodiments of the disclosure depicted in
the accompanying drawings. The embodiments are in such detail as to clearly communicate the
disclosure. However, the amount of detail offered is not intended to limit the anticipated
variations of embodiments; on the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope of the present disclosure as
defined by the appended claims.
[0024] If the specification states a component or feature “may”, “can”, “could”, or “might”
be included or have a characteristic, that particular component or feature is not required to be
included or have the characteristic.
[0025] As used in the description herein and throughout the claims that follow, the
meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates
otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on”
unless the context clearly dictates otherwise.
[0026] The use of any and all examples, or exemplary language (e.g., “such as”) provided
with respect to certain embodiments herein is intended merely to better illuminate the invention
and does not pose a limitation on the scope of the invention otherwise claimed. No language in
the specification should be construed as indicating any non – claimed element essential to the
practice of the invention.
[0027] The present disclosure relates generally to ametal-semiconductor-metal detector,
and more specifically, relates to a means for enhancing light absorption using double layering of
nano-gratings structure.
[0028] In an aspect, the present disclosure relates to a photodetector including: a first metal
layer placed at a first end of the photodetector, the first metal layer receives incident light waves,
wherein the first metal layer can be configured with one or more first grooves, each of the first
grooves having a quadrangular cross section, and each of the first grooves located at a predefined
distance from each other; and a second metal layer placed on a photonic semiconductor
substrate, the second metal layer configured with one or more second grooves, each of the
second grooves having a quadrangular cross-section, and each of the second grooves located at a
predefined distance from each other, wherein a gap can be created between the first metal layer
and the second metal layer, between the first grooves and corresponding second grooves, the gap
6
adapted to allow incident light waves to pass through to the substrate, and wherein the incident
light waves can be coupled at each of the first grooves and corresponding second grooves to
form coupled light waves such that the coupled light waves at the substrate have an absorption
greater than the incident light waves.
[0029] In an embodiment, the first metal layer and the second metal layer can be made of
metals selected from a group including gold, platinum, silver and a combination thereof.
[0030] In another embodiment, at least one of the first metal layer and the second metal
layer can be made of silver.
[0031] In another embodiment, the substrate includes gallium arsenide (GaAs) and any
combination thereof.
[0032] In another embodiment, the first metal layer and the second metal layer configured
to form double layered structure.
[0033] In another embodiment, the light absorption enhancement can be determined based
on the input parameters.
[0034] In another embodiment, the input parameters can be selected from a group
including shape, height, thickness of metal layer, input wavelength, substrate dimensions,
material and any combination thereof.
[0035] FIG. 1 illustrates a schematic view of the plasmonic based photodetector structure,
in accordance with an embodiment of the present disclosure.
[0036] Referring to FIG.1, the plasmonic-based photodetector 100 can be provided with a
double layer of nano-gratings structure, the double layer of nano-gratings structure can include
four sections i.e. top metal layer(also referred to as first metal layer, herein) with one or more
grooves 102, sub wavelength aperture (SWA) 106 (also referred to as gap (106), herein), bottom
metal layer (also referred to as second metal layer, herein) with one or more grooves 104 and a
substrate 108. The nano-gratings structure can be of varying shapes like trapezoidal, rectangular
trapezoidal, ellipse, parabolic and any combination thereof. In an aspect, trapezoidal shape for
nano-gratings can be employed. Light trapping phenomenon is higher in trapezoidal nanogratings as compared to other shaped nano-gratings. Moreover, surface plasmon resonance can
be easily obtained with trapezoidal nanograting.The plasmonic based photodetector 100 with
double layering of nano-gratings can be operated at 1.4 μm wavelength for night vision
applications.
7
[0037] In an embodiment, nano-gratings are basically used for light coupling and can be
also called as wave collector. Light can be incident on the metal surface where top gratings 102
are used to couple the maximum light and transmit through the sub wavelength aperture 106. The
transmitted light can be coupled with bottom gratings 104 wherein the bottom gratings 104 can
distribute the incoming light inside the substrate 108 in wider area. Maximum light distribution
occurs, which increase the light absorption within the plasmonic based photodetector and
increase the efficiency as in output form. In this structure, bottom grating 104 plays an important,
the bottom grating 104 can distribute the enhanced light through the sub wavelength aperture 106
to a wider area in the substrate 108. It can be observed that light distribution with bottom
gratings 104 can be higher.
[0038] In another embodiment, the first metal layer and the second metal layer can be
made of metals selected from a group comprising gold, platinum, silver and a combination
thereof. In an aspect, the surface of the top metal layer with one or more grooves 102 includes
silver material. Intra-band transitions (eV) of silver material can be 3.9 i.e., higher than energy of
photons. So, silver can be promising material for plasmonic applications. The best choice of
material for plasmonic applications can be one that has the minimum losses means less damping
rate and intra-band transitions (eV) can be greater than energy of the plasmons (1.8eV to 3.1eV).
Plasmonic based photodetector 100 using double layering of trapezoidal nano-gratings with
silver material can reduce the optical losses and absorb the maximum light in the near-infrared
region.Table.1 represents that the damping rate of silver material less than other material.
Material Damping rate (eV) Intraband transitions (eV)
Silver 0.02 3.9
Gold 0.07 2.3
Aluminum 0.13 1.41
Table 1. Noble material with damping rate and Intraband transitions
[0039] In an embodiment, the double layer of trapezoidal nano-gratings can be configured
to capture large amount of light or enhance the light trapping for more light absorption. Silver
can be used on the top and bottom nano-gratings 102, 104. The silver has low cost, low damping
rate and higher intra-band transitions characteristics and gallium arsenide (GaAs) can be used for
8
substrate 108.Plasmonic based photodetectors can utilize the concept of sub wavelength
plasmonic nano structures for high response and better sensitivity. In this nanostructure design,
electromagnetic (EM) field confinement can occur as compared to other focusing methods like
dielectric lens etc
[0040] As the size of the electronic devices is decreasing day by day, to reduce the size of
the optical components, the plasmonic study can be used and plasmonicbased photodetector 100
can be a promising device. By employing the abovementioned steps in plasmonic device, higher
absorption in near-infrared region at 1.4μm wavelength can be achieved. The plasmonic based
photodetector can be used in night vision applications.
[0041] In another embodiment, to analyse the performance of the plasmonic based
photodetector, light absorption enhancement factor (LAEF) can be used to determine the
performance of the plasmonic based photodetector. Light absorption enhancement factor is
defined as theratio of power transmittance with nano-gratings to power transmittance without
nanograting. To obtain the LAEF factor, the optiwave finite-difference time-domain (OptiFDTD) simulation software,which calculate the LAEF on the basis of input parameters can be
used.
[0042] The nano-gratings shape can have superior light trapping characteristics because of
surface plasmon resonance. GaAs material can be used as substrate, which can have direct band
gap and higher electron mobility. In this way, higher light absorption with double nano-gratings
can be achieved. The bottom gratings can play an important role to capture thelight.
[0043] FIG. 2 illustrates a schematic view of plasmonic based photodetector with
doublelayering of trapezoidal nano-gratings using Opti-FDTD simulation tool, in accordance
with an embodiment of the present disclosure.
[0044] Referring to FIG.2, the plasmonic based photodetector 200 with double layering of
trapezoidal nanograting structure can be simulated using Opti-FDTD tool with defined input
parameters and achieved a high LAEF. The plasmonic based photodetector 200 includes a first
metal layer placed at a first end of the photodetector, the first metal layer receives incident light
waves, the first metal layer can be configured with one or more first grooves102, each of grooves
having a quadrangular cross section, and each of the grooves102can be located at a predefined
distance from each other. The second metal layer placed on a photonic semiconductor
substrate108, the second metal layer configured with one or more second grooves104, each of
9
the second grooves 104 having a quadrangular cross-section, and each of second grooves 104
located at a predefined distance from each other.
[0045] In an embodiment, the sub wavelength aperture 106 can be created between the first
metal layer and the second metal layer, between the first grooves 102 and the second
grooves104. The sub wavelength aperture106 can be adapted to allow incident light waves to
pass through to the substrate108. The incident light waves can be coupled at each of the first
grooves102 and corresponding second grooves 104 to form coupled light waves such that the
coupled light waves transmitted at the substrate 108 have an absorption greater than the incident
light waves.
[0046] In an embodiment, plasmonic based photodetector 200 with double layering of
trapezoidal nanograting structure can be simulated using Opti-FDTD tool. Opti-FDTD can be
one of the most commonly used methods, highly integrated, and user-friendly software that can
allow computer aided design and simulation of advanced passive photonic components. It can
allow modelling and analysis of sub-micron or sub wavelength designs with accuracy. The OptiFDTD software package is based on the FDTD method.
[0047] The FDTD method can be established as a powerful engineering tool for design of
integrated and diffractive optical devices. Due to its unique combination of features such as, the
ability to model light propagation, scattering and diffraction, and reflection and polarization
effects. It can also model material anisotropy and dispersion without any pre-assumption of field
behaviour such as, the slowly varying amplitude approximation.
[0048] In an embodiment, input vertical plane202can beused to provide the input light
wavelength which lies in near-infrared region as from Opti-FDTD simulation tool. The
plasmonic based photodetector parameters used may be in nano-meter scale for miniaturization
of optical components and high responsivity of the device. To obtain the LAEF factor, the OptiFDTD simulation software calculate the LAEF on the basis of input parameters. Input
parameters which are used during simulations can be given in Table 2.
Parameters Value
Nanograting shape Trapezoidal
Nanograting top/bottom height 60nm/40nm
Input wavelength 1.1 μm-1.55μm
10
Subwavelength aperture height 60nm
Substrate material GaAS
Number of nano-gratings 4
Substrate wafer dimensions(width/height) 1250nm/360nm
Table 2. Input parameters used during simulation
[0049] However, these are just exemplary values, and that the actual values can be a wide
range, and the values included here are just for illustrative purposesother values and integer
multiples are possible as well.
[0050] Table. 3 depicts the LAEF of the proposed design which indicates the higher LAEF
i.e., 3.538 at 1.4μm. This table compare the result with rectangular nanograting of silver material
achieved the LAEF i.e., 2.2345. From this that light trapping can be analysed superior with
trapezoidal nano-gratings as compared to rectangular. Higher absorption achieved with the
resonance phenomenon in case of trapezoidal nano-gratings.
Input Wavelength
(µm)
LAEF with Rectangular LAEF with Trapezoidal
1.1 0.887 0.357
1.2 0.1763 1.833
1.3 0.878 2.5162
1.33 1.189 2.823
1.4 2.2435 3.538
1.5 0.7979 1.755
1.55 0.7897 1.416
Table. 3 Comparison between LAEF
[0051] The numerical analysis of the metal surfaces with different nanograting shapes can
be implemented and their performances arecompared. However, these are just exemplary values,
and that the actual values can be a wide range, and the values included here are just for
illustrative purposes other values and integer multiples are possible as well.
11
[0052] In an embodiment, material employed in the plasmonic based photodetector for
nano-gratings can be less costly as compared to gold and damping rate can also be less than other
noble material. Moreover, nano-gratings shape can have superior light trapping characteristics
because of surface plasmon resonance. GaAs material can be used as substrate which can have
direct band gap and higher electron mobility. In this way, higher light absorption with double
nano-gratings can be achieved because bottom gratings play an important role to capture thelight.
[0053] The plasmonic based photodetector can be used for night vision applications because
it operates in near infrared region (1.1 µm- 1.55µm) and can give the higher output in terms of
LAEF. Maximum output is obtained with trapezoidal groove shape-based photodetector with
maximum LAEF can be 3.538.However, these are just exemplary values, other values and
integer multiples are possible as well.
[0054] The present invention, in various embodiments, includes components, methods,
processes, systems and/or apparatus substantially as depicted and described herein, including
various embodiments, sub-combinations, and subsets thereof. Those of skill in the art will
understand how to make and use the present invention after understanding the present disclosure.
The present invention, in various embodiments, includes providing devices and processes in the
absence of items not depicted and/or described herein or in various embodiments hereof,
including in the absence of such items as may have been used in previous devices or processes,
e.g. for improving performance, achieving ease and\or reducing cost of implementation.
[0055] It should be apparent to those skilled in the art that many more modifications besides
those already described are possible without departing from the inventive concepts herein. The
inventive subject matter, therefore, is not to be restricted except in the spirit of the appended
claims. Moreover, in interpreting both the specification and the claims, all terms should be
interpreted in the broadest possible manner consistent with the context. In particular, the terms
“comprises” and “comprising” should be interpreted as referring to elements, components, or
steps in a non-exclusive manner, indicating that the referenced elements, components, or steps
may be present, or utilized, or combined with other elements, components, or steps that are not
expressly referenced. Where the specification claims refer to at least one of something selected
from the group consisting of A, B, C … and N, the text should be interpreted as requiring only
one element from the group, not A plus N, or B plus N, etc. The foregoing description of the
specific embodiments will so fully reveal the general nature of the embodiments herein that
12
others can, by applying current knowledge, readily modify and/or adapt for various applications
such specific embodiments without departing from the generic concept, and, therefore, such
adaptations and modifications should and are intended to be comprehended within the meaning
and range of equivalents of the disclosed embodiments. It is to be understood that the
phraseology or terminology employed herein is for the purpose of description and not of
limitation. Therefore, while the embodiments herein have been described in terms of preferred
embodiments, those skilled in the art will recognize that the embodiments herein can be
practiced with modification within the spirit and scope of the appended claims.
[0056] While various embodiments of the present disclosure have been illustrated and
described herein, it will be clear that the disclosure is not limited to these embodiments only.
Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to
those skilled in the art, without departing from the spirit and scope of the disclosure, as described
in the claims.
ADVANTAGES OF THE PRESENT DISCLOSURE
[0057] The present disclosure provides a plasmonic based photodetector using double
layering of trapezoidal nanogratingthat can be more efficient for light absorption with surface
plasmon resonance.
[0058] The present disclosure provides silver material employed in the photodetector for
nanograting thatcan be less costly and damping rate can also be less than other noble material.
[0059] The present disclosure provides a photodetector with nano-gratings structure that can
have superior light trapping characteristics because of surface plasmon resonance. GaAs material
can be used as substrate which can have direct band gap and higher electron mobility to achieve
higher light absorption with double nano-gratings.
[0060] The present disclosure provides a photodetect or that can use GaAs material as
substrate which has direct band gap and higher electron mobility to achieve the higher light
absorption

We Claim:

1. A photodetector (100) comprising:
a first metal layer placed at a first end of the photodetector (100), the first metal
layer receives incident light waves, wherein the first metal layer is configured with a
plurality of first grooves (102), each of the plurality of first grooves (102) having a
quadrangular cross section, and each of said plurality of first grooves (102) located at a
predefined distance from each other; and
a second metal layer placed on a photonic semiconductor substrate (108), the
second metal layer configured with a plurality of second grooves (104), each of the
plurality of second grooves (104) having a quadrangular cross-section, and each of said
plurality of second grooves (104) located at a predefined distance from each other,
wherein a gap (106) is created between the first metal layer and the second metal layer,
between the plurality of first grooves (102) and corresponding plurality of second
grooves (104), the gap (106) adapted to allow incident light waves to pass through to the
substrate, and
wherein the incident light waves are coupled at each of the first grooves (102) and
corresponding second grooves (104) to form coupled light waves such that the coupled
light waves at the substrate (108) have an absorption greater than the incident light
waves.
2. The photodetector as claimed in claim 1, wherein the first metal layer and the second
metal layer are made of metals selected from a group comprising gold, platinum, silver
and a combination thereof.
3. The photodetector as claimed in claim 2, wherein at least one of the first metal layer and
the second metal layer is made of silver.
4. The photodetector as claimed in claim 1, wherein the substrate comprises gallium
arsenide (GaAs) and any combination thereof.
5. The photodetector as claimed in claim 1, wherein the first metal layer and the second
metal layer configured to form double layered structure.
6. The photodetector as claimed in claim 1, wherein the light absorption enhancement is
determined based on the input parameters.
14
7. The photodetector as claimed in claim 6, wherein the input parameters are selected from
a group comprising shape, height, thickness of metal layer, input wavelength, substrate
dimensions, material and any combination thereof.