Photodetectors using resonance and method of making
View Patent ↗An infrared photodetector comprising: a thin contact layer substantially transparent to infrared light; an absorption layer positioned such that light admitted through the substantially transparent thin contact area passes through the absorption layer; the absorption layer being configured to utilize resonance to increase absorption efficiency; at least one reflective side wall adjacent to the absorption layer being substantially non-parallel to the incident light operating to reflect light into the absorption layer for absorption of infrared radiation; and a top contact layer positioned adjacent to the active layer. A method of designing a photodetector comprising selecting a type of material based upon the wavelength range to be detected; determining a configuration geometry; calculating the electromagnetic field distributions using a computer simulated design of the configuration geometry, and determining a quantum efficiency spectrum at the desired wavelength or wavelength range; whereby the effectiveness of the photodetector is simulated prior to fabrication.
1. A computer implemented method for designing a photodetector utilizing a 3-dimensional simulation comprising:
selecting a type of material from which to construct a photodetector based upon a desired wavelength or wavelength range to be detected;
determining at least one configuration geometry for the photodetector;
determining 3-dimensional electromagnetic field distributions using a computer simulation for the at least one configuration geometry,
using a computer, determining a quantum efficiency spectrum at the desired wavelength or wavelength range for the at least one configuration geometry; and
selecting a 3-dimensional configuration geometry based upon the computer determined quantum efficiency spectrum;
whereby effectiveness of the photodetector is simulated using a computer to perform a 3-dimensional simulation to determine the quantum efficiency spectrum prior to fabrication.
2. The method of claim 1 wherein the electromagnetic field distributions of a plurality of configuration geometries are determined using a computer simulation comprising a 3-dimensional finite element electromagnetic simulation, and wherein quantum efficiencies of the plurality of configuration geometries are determined at a predetermined wavelength range in order to determine an optimal configuration geometry.
3. The method of claim 1 wherein the step of selecting a type of material comprises:
calculating Eigen values and energies of the material structure; and
calculating an absorption coefficient of the material based upon the Eigen energies;
and wherein the step of determining a configuration geometry comprises:
inputting into the computer, parameters for a material to be used;
defining material properties of all geometrical objects in the configuration geometry;
and
defining physical relations among all geometrical boundaries.
4. The method of claim 3 wherein the calculating of the absorption coefficient is determined by
α
(
λ
)
=
∑
n
N
D
W
L
π
e
2
ℏ
2
ɛ
h
ɛ
0
m
*
c
f
n
ρ
n
(
λ
)
where N D is doping density, W is well width, L is length of a quantum well period, e is electric charge, h is the Plank's constant, ∈ h is relative permittivity in z direction, ∈ 0 is permittivity in free space, m* is electron effective mass, c is the speed of light in vacuum, f n is oscillator strength for optical transition from ground state to nth excited state, and ρ n is line width of nth optical transition.
5. The method of claim 1 wherein the photodetector is a quantum well infrared photodetector with a GaAs substrate and wherein optical absorption at a particular location is linearly proportional to the light intensity at that location, and wherein light is detected in a wavelength range from 3 to 15 microns and wherein quantum efficiency (η) for a prism-shaped photodetector is determined by
η
=
1
P
0
∫
V
ⅆ
I
(
r
->
)
,
=
1
P
0
∫
V
α
I
(
r
->
)
ⅆ
3
r
,
=
α
A
2
c
ɛ
0
E
0
2
∫
V
nc
ɛ
0
2
E
z
(
r
->
)
2
ⅆ
3
r
,
=
n
α
AE
0
2
∫
V
E
z
(
r
->
)
2
ⅆ
3
r
,
where P o is optical power incident normally on a detector area A, V is the detector active volume, I is optical intensity associated with E z , α is absorption coefficient, r is spatial coordinate, n is material reflective index, ∈ o is permittivity of free space, c is the speed of light, E 0 is electric field in free space, E z is electric polarization perpendicular to the layers and wherein quantum efficiency η for a prism-shaped photodetector is determined by
η
=
t
s
η
int
=
t
s
1
p
[
t
+
ⅇ
-
α
p
2
α
(
1
-
ⅇ
2
α
t
)
]
where t s is substrate transmission coefficient, p is pixel pitch, α is absorption coefficient, t is QWIP material thickness.
6. The method of claim 5 wherein quantum efficiency of the photodetector is calculated from a volume integral of |E z | 2 in presence of a finite α.
7. The method of claim 1 wherein the photodetector has a pyramidal configuration with four inclined sidewalls and quantum efficiency is
η
=
t
s
exp
(
-
α
p
)
α
2
p
2
{
1
+
α
p
+
2
α
2
t
(
p
-
t
)
exp
(
α
p
)
+
[
α
(
2
t
-
p
)
-
1
]
exp
(
2
αt
)
}
where t s is substrate transmission coefficient, p is pixel pitch, α is absorption coefficient, t is QWIP material thickness.
8. The method of claim 1 wherein the selecting of a type of material from which to construct the photodetector comprises calculating Eigen functions & Eigen energies of materials to obtain absorption coefficients of materials and selecting a material based upon absorption characteristics of the material.
9. The method of claim 1 wherein the determining of the electromagnetic field distributions using a computer simulation comprises designing a detector physical geometry on a computer using a three-dimensional computer aided design program; the photodetector comprising components of different materials that are treated as subdomains;
inputting input parameters of materials for each subdomain used in the computer simulation; and
defining material properties of subdomains and physical relations between boundaries of the sub domains.
10. The method of claim 1 wherein the determining of a quantum efficiency spectrum at the desired wavelength or wavelength range for the at least one configuration geometry comprises using the electromagnetic field distributions for a plurality of configurations and computing the quantum efficiency for a plurality of configurations.
11. The method of claim 1 wherein the determining a quantum efficiency spectrum at the desired wavelength or wavelength range for the at least one configuration geometry comprises integrating the electromagnetic field according to a formula
η
=
n
α
AE
0
2
∫
V
E
z
(
r
->
)
2
ⅆ
3
r
where n is refractive index of the detector material, “alpha” is absorption coefficient of detector material, A is detector area, E 0 is incident electric field of light in free space, V is detector active volume, E z is electric field vertical to the material layers, r is spatial coordinate; and wherein to solve for E z numerically a numerical finite element solver is utilized.