U.S. Patent Mar. 8, 2022

Sheet 19 of 31

US 11,271,023 B2

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US 11,271,023 B2

17

to the second conductor layer when the second electri-
cal potential is more positive than the first electrical
potential, and

wherein an electrical current produced by the electrons is

proportional to an amount of absorption of the infrared
photons in the photon absorption layer.

2. The quantum waveguide infrared photodetector of
claim 1, further comprising a mode confinement layer inter-
posed between the substrate and the semiconductor member
and bounded by surfaces of the substrate and the semicon-
ductor member.

3. The quantum waveguide infrared photodetector of
claim 2, further comprising a second mode confinement
layer disposed in semiconductor member, interposed
between the semiconductor member and the semiconductor
contact layer, and bounded by surfaces of the semiconductor
member and the semiconductor contact layer.

4, The quantum waveguide infrared photodetector of
claim 1, further comprising a core layer interposed between
the substrate and the semiconductor member.

5. The quantum waveguide infrared photodetector of
claim 4, further comprising a bottom cladding interposed
between the core layer and the substrate.

6. The quantum waveguide infrared photodetector of
claim 5, further comprising a mode confinement layer dis-
posed in core layer and interposed between the bottom
cladding and the semiconductor member.

7. The quantum waveguide infrared photodetector of
claim 6, wherein the mode confinement layer is bounded by

surfaces of the bottom cladding, the core layer, and the 3

semiconductor member.

8. The quantum waveguide infrared photodetector of
claim 1, further comprising a first electrical contact pad
disposed on the substrate and the first conductor layer and in

electrical communication with the first conductor layer, such 3

that the first electrical contact pad receives the first electrical
potential for electrically biasing the first conductor layer.

9. The quantum waveguide infrared photodetector of
claim 8, further comprising a second electrical contact pad
disposed on the substrate and the second conductor layer and
in electrical communication with the second conductor
layer, such that the second electrical contact pad receives the
second electrical potential for electrically biasing the second
conductor layer.

10. The quantum waveguide infrared photodetector of
claim 1, further comprising an electrical insulator disposed
on the semiconductor contact layer and the semiconductor
contact layer and that electrically insulates the first conduc-
tor layer from the second conductor layer.

11. The quantum waveguide infrared photodetector of
claim 1, further comprising an electrical bias supply in
electrical communication with the first conductor layer and

20

2

40

18
the second conductor layer, wherein the electrical bias
supply provides the first electrical potential to the first
conductor layer and the second electrical potential to the
second conductor layer.

12. The quantum waveguide infrared photodetector of
claim 11, further comprising a current meter in electrical
communication with the first conductor layer and the elec-
trical bias supply, wherein the current meter receives a
detector signal and determines the amount of electrical
current from the detector signal.

13. The quantum waveguide infrared photodetector of
claim 1, wherein the photon absorption layer comprises a
quantum well, quantum dots, or a quantum dash.

14. A process for detecting infrared photons by intersub-
band transitions in a semiconductor of a photon absorption
layer with the quantum waveguide infrared photodetector of
claim 1, the process comprising:

receiving, by the photon absorption layer, the infrared

photons;

propagating longitudinally the infrared photons along the

longitudinal length of the photon absorption layer;
converting, by the photon absorption layer, the infrared
photons into electrons by intersubband transitions in
the semiconductor of the photon absorption layer;
biasing the first conductor layer with the first electrical
potential;

biasing the second conductor layer with the second elec-

trical potential;

communicating the electrons from the photon absorption.

layer to the first conductor layer when the first electrical
potential is more positive than the second electrical
potential; and
communicating the electrons from the photon absorption.
layer to the second conductor layer when the second
electrical potential is more positive than the first elec-
trical potential to detect the infrared photons,

wherein an electrical current produced by the electrons is
proportional to the amount of absorption of the infrared
photons in the photon absorption layer.

15. The process of claim 14, further comprising commu-
nicating the electrons as a detector signal from the first
conductor layer to a current meter when the first electrical
potential is more positive than the second electrical poten-
tial.

16. The process of claim 14, further comprising commu-
nicating the electrons as a detector signal from the second
conductor layer to a current meter when the second electrical
potential is more positive than the first electrical potential

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US 11,271,023 B2

9

%) to 100 at. %, specifically from 25 at. % to 75 at. %, and
more specifically from 40 at. % to 60 at. %, based on a total
of all atoms in this layer. A thickness of barrier layer 214 can
be from 100 pm to 1 cm, specifically from 1 nm to 1 ym, and
more specifically from 2 nm to 500 nm. It is contemplated
that a width of barrier layer 214 can be from 1 nm to 1 cm,
specifically from 100 nm to 10 mm, and more specifically
from 1 ym to 100 pm. An electrical resistivity of barrier layer
214 can be from 10-!° Qm to 10!° Qm, specifically from
10-* Om to 10° Qm, and more specifically from 10-° Qm to
500 Qm. In an embodiment, barrier layer 214 is aluminum
gallium arsenide.

Core layer 215 provides optical confinement of quantum:
waveguide infrared photodetector 200 and selectively opti-
mizes optical overlap with photon absorption layer 208.
Core layer 215 can include silicon, quartz, gallium arsenide,
and the like. A thickness of core layer 215 can be from 1 nm.
to 1 cm, specifically from 100 nm to 1 mm, and more
specifically from 200 nm to 10 jm. It is contemplated that
a width of core layer 215 can be from 1 nm to 1 cm,
specifically from 100 nm to 10 mm, and more specifically
from 1 um to 100 pm. An electrical resistivity of core layer
215 can be from 10-!° Qm to 10!° Qm, specifically from
10-* Om to 10° Qm, and more specifically from 10-* m to
500 Qm. In an embodiment, core layer 215 is silicon. In
some embodiments, mode confinement layer 203 is disposed
in core layer 215, wherein substrate gap surface 204, semi-
conductor gap surface 205, and cladding air gap surface 217
are surfaces that provide a boundary for mode confinement
layer 203 that can be an air gap.

Bottom cladding 216 has a lower refractive index than
core layer 215 and low loss so the optical mode is efficiently
guided through photon absorption layer 208 without radiat-
ing toward substrate 201. Bottom cladding 216 can include

an oxidized material that forms substrate 201, e.g., silicon 3

dioxide and the like. A thickness of bottom cladding 216 can
be from I nm to | cm, specifically from 100 nm to 1 mm,
and more specifically from 1 1m to 20 um. It is contemplated
that width of bottom cladding 216 can be from 1 nm to 1 cm,
specifically from 500 nm to 1 mm, and more specifically
from 1 ym to 50 um. An electrical resistivity of bottom
cladding 216 can be from 10-!° Qm to 10"° Om, specifically
from 10-® Om to 10° Qm, and more specifically from 107°
Qm to 500 Qm. In an embodiment, bottom cladding 216 is
silicon dioxide,

Electrical contact pad 220 is electrically conductive and
provides an electrical interface to quantum waveguide infra-
red photodetector 200 for communicating detector signal
227 from quantum waveguide infrared photodetector 200
and for subjecting layers of quantum waveguide infrared
photodetector 200 to a potential difference via conductor
layer 213. Electrical contact pad 220 can include a stack of
metal layers (e.g., gold, nickel, germanium, and the like) or
other electrically conductive material (e.g., indium tin oxide
and the like) formatted as a semiconductor contact metal
stack. A thickness of electrical contact pad 220 can be from
1 nm to | cm, specifically from 10 nm to 1 mm, and more
specifically from 100 nm to 2 um. It is contemplated that a
width of electrical contact pad 220 can be from 1 nm to 1 cm,
specifically from 100 nm to 10 mm, and more specifically
from 1 jum to 100 pum. An electrical resistivity of electrical
contact pad 220 can be from 10°! Qm to 10'° Om, spe-
cifically from 10-® Qm to 10° Qm, and more specifically
from 10°> m to 500 Qm. In an embodiment, electrical
contact pad 220 is titanium and gold.

In accordance with the foregoing description of quantum
waveguide infrared photodetector 200, it should be appre-

40

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ciated that quantum waveguide infrared photodetector 200
includes a composite structure of a plurality of components
for the waveguide that guides infrared photons 224 longi-
tudinally in quantum waveguide infrared photodetector 200.
In an embodiment, with reference to FIG. 2 and FIG. 4, such
components include semiconductor contact layer 211, buffer
layer 210, barrier layer 209, photon absorption layer 208,
barrier layer 214, semiconductor contact layer 206, semi-
conductor member 202, mode confinement layer 203, and
optional electrical insulator 230. In an embodiment, with
reference to FIG. 3, such components also include core layer
215 and bottom cladding 216.

Infrared photons 224 are received by quantum waveguide
infrared photodetector 200 and propagate longitudinally
primarily in photon absorption layer 208 with a transverse
electromagnetic mode that is selectively confined by the
hybrid waveguide structure indicated in the immediate prior
paragraph to particular layers as indicated. FIG. 8 shows a
map of a magnitude of an electromagnetic field for a
transverse electromagnetic mode for infrared photons 224
propagating longitudinally in photon absorption layer 208
and layers proximate to photon absorption layer 208 for a
transverse cross-section of infrared photons 224. A wave-
length of infrared photons 224 can be in the near infrared to
far infrared region of the electromagnetic spectrum, e.g.,
from 700 nm to 1 mm, specifically from 1064 nm to 100 pm,
and more specifically from 2000 nm to 20 pm. Further,
infrared photons 224 may have electric and magnetic field
orientations in any direction. It is contemplated that infrared
photons 224 are converted to electrons 221 by absorption of
infrared photons 224 by photon absorption layer 208. An
infrared absorption band of photon absorption layer 208
depends upon layers proximate to photon absorption layer
208, wherein a composition and thickness of each layer in
combination provides for a wavelength range of absorption
and peak wavelength of absorption of photon absorption
layer 208. In this regard, the infrared absorption band of
photon absorption layer 208 can be 700 nm to 1 mm,
specifically from 1064 nm to 100 um, and more specifically
from 2000 nm to 20 um. A peak of the infrared absorption
band of photon absorption layer 208 can be from 700 nm to
1 mm, specifically from 1064 nm to 100 pm, and more
specifically from 2000 nm to 20 pm. Without wishing to be
bound by theory, it is believed that photon absorption layer
208 converts infrared photons 224 to electrons 221 by
exciting electrons from a lower energy state in the photon
absorption layer 208 to a higher energy state of the photon
absorption layer 208, where the lower energy state is bound,
and electrons cannot exit the photon absorption layer 208
under an applied electric field and the higher energy state is
coupled to the either semiconductor contact layer 206 or
semiconductor contact layer 211 and electrons can exit the
photon absorption layer 208 under an applied electric field

Electrons 221 produced from infrared photons 224 have

5 an energy provided by the potential difference subjected to

electrons 221 by the first electrical potential applied to first
conductor layer 213.1 and the second electrical potential
applied to second conductor layer 213.2. A voltage of the
first potential can be from -100 volt (V) to 100 V, specifi-
cally from -10 V to 10 V, and more specifically from -5 V
to 5 V.A voltage of the second potential can be from -100
volt (V) to 100 V, specifically from -10 V to 10 V, and more
specifically from -5 V to 5 V. Accordingly, an electrical
potential in photon absorption layer 208 to which infrared
photons 224 and nascent electrons 221 produced therefrom
can be from 0 V to 200 V, specifically from 0.1 V to 20 V,
and more specifically from 1 V to 10 V so that an energy of


U.S. Patent Mar. 8, 2022 Sheet 13 of 31 US 11,271,023 B2

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U.S. Patent Mar. 8, 2022 Sheet 4 of 31 US 11,271,023 B2

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US 11,271,023 B2

5

tum waveguide infrared photodetector 200 can include cur-
rent meter 226 in electrical communication with first con-
ductor layer 213.1 and electrical bias supply 225, wherein
current meter 226 receives detector signal 227 and deter-
mines the amount of electrical current from detector signal
227.

Components of quantum waveguide infrared photodetec-
tor 200 can be made from and include various materials.
Substrate 201 provides mechanical structure for other ele-
ments of quantum waveguide infrared photodetector 200
and provides electrical insulation for quantum waveguide
infrared photodetector 200. Substrate 201 can include sili-
con, quartz, gallium arsenide, and the like. A thickness of
substrate 201 can be from 1 nm to 10 mm, specifically from
1 pm to 2 mm, and more specifically from 50 um to 800 um.
It is contemplated that a diameter of substrate 201 can be
from 1 pm to 1 m, specifically from 1 mm to 500 mm, and
more specifically from 50 mm to 300 mm. An electrical
resistivity of substrate 201 can be from 107!° Qm to 10'°
Qm, specifically from 10-* Qm to 10° Qm, and more
specifically from 10° Qm to 500 Qm. Further, if substrate
201 is crystalline, a crystal axis orientation of substrate 201
can be in any direction. In an embodiment, substrate 201 is
silicon.

Semiconductor member 202 optimizes the guided optical
mode overlap with photon absorption layer 208. Semicon-
ductor member 202 can include silicon, quartz, gallium
arsenide, aluminum gallium arsenide, and the like. An
elemental composition of this layer can include gallium in

an amount from 1 atomic percent (at. %) to 100 at. %, 3

specifically from 25 at. % to 75 at. %, and more specifically
from 40 at. % to 60 at. %, based on a total of all atoms in
this layer; and arsenic in an amount from | atomic percent
(at. %) to 100 at. %, specifically from 25 at. % to 75 at. %,

and more specifically from 40 at. % to 60 at. %, based on a 3

total of all atoms in this layer. A thickness of semiconductor
member 202 can be from 1 nm to 1 em, specifically from 5
nm to 10 im, and more specifically from 100 nm to 5 um.
An electrical resistivity of semiconductor member 202 can
be from 107!° Qm to 10" Qm, specifically from 10-* Qm to
10° Qm, and more specifically from 10-> Qm to 500 Qm. In
an embodiment, semiconductor member 202 is gallium
arsenide. In some embodiments, mode confinement layer
203 is disposed in semiconductor member 202, wherein
semiconductor air gap surface 218 and semiconductor air
gap surface 219 are surfaces that provide a boundary for
mode confinement layer 203 that can be an air gap.

Mode confinement layer 203 provides a lower refractive
index than the waveguide core and has low loss so the
optical mode is efficiently guided through photon absorption
layer 208 without radiating infrared photons 224 toward
substrate 201. Mode confinement layer 203 can include an
air gap, aluminum gallium arsenide, and the like. An
elemental composition of this layer can include gallium in
an amount from 0 atomic percent (at. %) to 100 at. %,
specifically from 5 at. % to 95 at. %, and more specifically
from 10 at. % to 80 at. %, based on a total of gallium and
aluminum atoms in this layer; aluminum in an amount from
0 atomic percent (at. %) to 100 at. %, specifically from 5 at.
% to 95 at. %, and more specifically from 20 at. % to 90 at.
%, based on a total of gallium and aluminum atoms in this
layer; and arsenic in an amount from 1 atomic percent (at.
%) to 100 at. %, specifically from 25 at. % to 75 at. %, and
more specifically from 40 at. % to 60 at. %, based on a total
of all atoms in this layer. A thickness of mode confinement
layer 203 can be from 1 nm to 1 cm, specifically from 100
nm to 1 mm, and more specifically from 200 nm to 10 um.

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It is contemplated that a width of mode confinement layer
203 can be from 1 nm to 1 cm, specifically from 500 nm to
1 mm, and more specifically from 1 wm to 50 pm. An
electrical resistivity of mode confinement layer 203 can be
from 107'° Qm to 10'° Qm, specifically from 10-* Qm to
10° Qm, and more specifically from 10~° Qm to 500 Qm. In
an embodiment, mode confinement layer 203 is an air gap.
Substrate gap surface 204 and semiconductor gap surface
205 are surfaces that provide a boundary for mode confine-
ment layer 203.

Semiconductor contact layer 206 extracts or injects elec-
trons 221 to or from photon absorption layer 208 and barrier
layer 214; to provide low resistance to conductor layer 213.
Semiconductor contact layer 206 can include silicon, gal-
lium arsenide, aluminum gallium arsenide, and the like. An
elemental composition of this layer can include gallium in
an amount from 0 atomic percent (at. %) to 100 at. %,
specifically from 5 at. % to 95 at. %, and more specifically
from 10 at. % to 80 at. %, based on a total of gallium and
aluminum atoms in this layer; aluminum in an amount from
0 atomic percent (at. %) to 100 at. %, specifically from 5 at.
% to 95 at. %, and more specifically from 20 at. % to 90 at.
%, based on a total of gallium and aluminum atoms in this
layer; and arsenic in an amount from 1 atomic percent (at

5 %) to 100 at. %, specifically from 25 at. % to 75 at. %, and

more specifically from 40 at. % to 60 at. %, based on a total
of all atoms in this layer. A thickness of semiconductor
contact layer 206 can be from 1 nm to 1 cm, specifically
from 10 nm to | mm, and more specifically from 100 nm to
1 jm. It is contemplated that a width of semiconductor
contact layer 206 can be from 1 nm to 1 cm, specifically
from 100 nm to 1 mm, and more specifically from 1 ym to
10 um. An electrical resistivity of semiconductor contact
layer 206 can be from 10-'° Om to 10'° Qm, specifically
from 10-* Qm to 10° Qm, and more specifically from 10->
Qm to 500 Qm. In an embodiment, semiconductor contact
layer 206 is gallium arsenide. Semiconductor contact sur-
face 207 is a surface of semiconductor contact layer 206 on
which barrier layer 214 and conductor layer 213 are formed.
Photon absorption layer 208 has a chosen composition
and thickness to selectively absorb infrared photons 224
incident to or propagating through quantum waveguide
infrared photodetector 200. Photon absorption layer 208 can
include a quantum well, quantum dot, or quantum dash,
wherein exemplary quantum wells include gallium, arsenic,
indium, aluminum and the like; exemplary quantum dots
include gallium, arsenic, indium, aluminum, and the lik
and exemplary quantum dashes include gallium, arsenic,
indium, aluminum, and the like. An elemental composition
of this layer can include gallium in an amount from 0 atomic
percent (at. %) to 100 at. %, specifically from 5 at. % to 95
at. %, and more specifically from 10 at. % to 80 at. %, based
ona total of gallium and indium atoms in this layer; indium
in an amount from 0 atomic percent (at. %) to 100 at. %,
specifically from 5 at. % to 95 at. %, and more specifically
from 20 at. % to 90 at. %, based on a total of gallium and
indium atoms in this layer; and arsenic in an amount from 1
atomic percent (at. %) to 100 at. %, specifically from 25 at
% to 75 at. %, and more specifically from 40 at. % to 60 at.
%, based on a total of all atoms in this layer. A thickness of
photon absorption layer 208 can be from 100 jum to 1 cm,
specifically from 1 nm to 100 nm, and more specifically
from 2 nm to 10 nm. It is contemplated that a width of
photon absorption layer 208 can be from 1 nm to 1 cm,
specifically from 100 nm to 10 mm, and more specifically
from 1 um to 100 um. An electrical resistivity of photon
absorption layer 208 can be from 10-?° Qm to 10’ Qm,



U.S. Patent

Mar. 8, 2022

Sheet 20 of 31

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U.S. Patent

Mar. 8, 2022

Sheet 26 of 31

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Mar. 8, 2022

Sheet 22 of 31

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specifically from 10TM* Qm to 10° Qm, and more specifically
from 10-* Qm to 500 Qm. Further, photon absorption layer
208 can absorb wavelengths from 100 nm to 100 Qm,
specifically from 1 jum to 20 um, more specifically from 2
fm to 15 um. In an embodiment, photon absorption layer
208 is a quantum well that includes indium gallium arsenide.

In an embodiment, quantum waveguide infrared photo-
detector 200 includes a single infrared absorbing layer 208,
rather than a plurality of infrared absorbing layers (e.g., ~40
layers) as in conventional devices. In some embodiments,
quantum waveguide infrared photodetector 200 includes a
plurality of absorption layers, wherein each photon absorp-
tion layer 208 has a different quantum well thickness to
increase optical bandwidth of quantum waveguide infrared
photodetector 200.

Barrier layer 209 supports selected electronic energy
states bound or quasi-bound by photon absorption layer 208
to correspond to an energy of infrared photons 224. Barrier
layer 209 can include aluminum gallium arsenide and the
like. An elemental composition of this layer can include
gallium in an amount from 0 atomic percent (at. %) to 100
at. %, specifically from 5 at. % to 95 at. %, and more
specifically from 10 at. % to 80 at. %, based on a total of
gallium and aluminum atoms in this layer; aluminum in an
amount from 0 atomic percent (at. %) to 100 at. %, specifi-
cally from 5 at. % to 95 at. %, and more specifically from
20 at. % to 90 at. %, based on a total of gallium and
aluminum atoms in this layer; and arsenic in an amount from

1 atomic percent (at. %) to 100 at. %, specifically from 25 3

at. % to 75 at. %, and more specifically from 40 at. % to 60
at. %, based on a total of all atoms in this layer. A thickness
of barrier layer 209 can be from 100 um to 1 cm, specifically
from 1 nm to 1 um, and more specifically from 2 nm to 500

nm. It is contemplated that a width of barrier layer 209 can 3

be from 1 nm to | cm, specifically from 100 nm to 10 mm,
and more specifically from 1 jum to 100 um. An electrical
resistivity of barrier layer 209 can be from 107° Qm to 10°°
Qm, specifically from 10-° Qm to 10° Qm, and more
specifically from 10-* Qm to 500 Qm. In an embodiment,
barrier layer 209 is aluminum gallium arsenide.

Buffer layer 210 provides a lower refractive index region
than the waveguide core and has low loss so the optical
mode of infrared photons 224 is efficiently guided without
radiating toward semiconductor contact layer 211 or second
conductor layer 213.2. Buffer layer 210 can include alumi-
num gallium arsenide and the like. An elemental composi-
tion of this layer can include gallium in an amount from 0
atomic percent (at. %) to 100 at. %, specifically from 5 at.
% to 95 at. %, and more specifically from 10 at. % to 80 at.
%, based on a total of gallium and aluminum atoms in this
layer; aluminum in an amount from 0 atomic percent (at. %)
to 100 at. %, specifically from 5 at. % to 95 at. %, and more
specifically from 20 at. % to 90 at. %, based on a total of
gallium and aluminum atoms in this layer; and arsenic in an
amount from | atomic percent (at. %) to 100 at. %, specifi-
cally from 25 at. % to 75 at. %, and more specifically from
40 at. % to 60 at. %, based ona total of all atoms in this layer.
A thickness of buffer layer 210 can be from 100 pm to 1 cm,
specifically from 1 nm to 10 um, and more specifically from
100 nm to 5 pm. It is contemplated that a width of buffer
layer 210 can be from 1 nm to 1 cm, specifically from 100
nm to 10 mm, and more specifically from 1 um to 100 wm.
An electrical resistivity of buffer layer 210 can be from
107!° Qm to 10! Qm, specifically from 10-* Qm to 10° Qm,
and more specifically from 10-> Qm to 500 Qm. In an
embodiment, buffer layer 210 is aluminum gallium arsenide.

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Semiconductor contact layer 211 extracts or injects elec-
trons 221 to or from photon absorption layer 208 and barrier
layer 209 to provide low resistance to second conductor
layer 213.2. Semiconductor contact layer 211 can include
aluminum gallium arsenide and the like. An elemental
composition of this layer can include gallium in an amount
from 0 atomic percent (at. %) to 100 at. %, specifically from
5 at. % to 95 at. %, and more specifically from 10 at. % to
80 at. %, based on a total of gallium and aluminum atoms in
this layer; aluminum in an amount from 0 atomic percent (at
%) to 100 at. %, specifically from 5 at. % to 95 at. %, and
more specifically from 20 at. % to 90 at. %, based on a total
of gallium and aluminum atoms in this layer; and arsenic in
an amount from 1 atomic percent (at. %) to 100 at. %,

5. specifically from 25 at. % to 75 at. %, and more specifically

from 40 at. % to 60 at. %, based on a total of all atoms in
this layer. A thickness of semiconductor contact layer 211
can be from 1 nm to 1 cm, specifically from 1 nm to 10 um,
and more specifically from 10 nm to I jum. It is contemplated
that a width of semiconductor contact layer 211 can be from
1 nm to | cm, specifically from 100 nm to 10 mm, and more
specifically from 1 um to 100 jum. An electrical resistivity of
semiconductor contact layer 211 can be from 107'° Qm to
10° Qm, specifically from 10-* um to 10° Qm, and more

specifically from 10-* Qm to 500 Qm. In an embodiment,

semiconductor contact layer 211 is gallium arsenide. Top
contact surface 212 is a surface of semiconductor contact
layer 211 on which second conductor layer 213.2 is formed.
Conductor layer 213 is electrically conductive and pro-
vides an electrical interface to quantum waveguide infrared
photodetector 200 for communicating detector signal 227
from quantum waveguide infrared photodetector 200 and for
subjecting layers of quantum waveguide infrared photode-
tector 200 to a potential difference. Conductor layer 213 can
include a metal (e.g., gold, nickel, germanium, and the like)
or other electrically conductive material (e.g., indium tin
oxide and the like). A thickness of conductor layer 213 can
be from | nm to 1 cm, specifically from 10 nm to 1 mm, and
more specifically from 100 nm to 2 um. It is contemplated
that a width of conductor layer 213 can be from 1 nm to 1
cm, specifically from 100 nm to 10 mm, and more specifi-
cally from 1 jum to 100 pm. An electrical resistivity of
conductor layer 213 can be from 10-'° Qm to 10'¢ t m,
specifically from 10-* Qm to 10° Qm, and more specifically

5 from 10-* Qm to 500 Qm. In an embodiment, conductor

layer 213 is nickel, gold-germanium eutectic alloy, nickel,
and gold. Conductor layer 213 can be made of a plurality of
stacked layers that, e.g., include an order of layers stacked
as follows: nickel, a gold/germanium alloy, nickel, and gold.
Other combinations of metals can be used for conductor
layer 213. Stacking layers in conductor layer 213 can be
referred to as a semiconductor contact metal stack that
differs depending on a type of dopant and semiconductor
composition of such layers.

Barrier layer 214 supports selected electronic energy
states bound by photon absorption layer 208 to correspond
to an energy of infrared photons 224. Barrier layer 214 can
include aluminum gallium arsenide and the like. An elemen-
tal composition of this layer can include gallium in an
amount from 0 atomic percent (at. %) to 100 at. %, specifi-
cally from 5 at. % to 95 at. %, and more specifically from
10 at. % to 80 at. %, based on a total of gallium and
aluminum atoms in this layer; aluminum in an amount from
0 atomic percent (at. %) to 100 at. %, specifically from 5 at.

5 % to 95 at. %, and more specifically from 20 at. % to 90 at.

%, based on a total of gallium and aluminum atoms in this
layer; and arsenic in an amount from 1 atomic percent (at


U.S. Patent Mar. 8, 2022 Sheet 17 of 31 US 11,271,023 B2

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U.S. Patent Mar. 8, 2022 Sheet 9 of 31 US 11,271,023 B2

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FIG. 9



US 11,271,023 B2

1

QUANTUM WAVEGUIDE INFRARED
PHOTODETECTOR

CROSS REFERENCE TO RELATED
APPLICATIONS

The application claims priority to U.S. Provisional Patent
Application Ser. No. 62/877,932 filed Jul. 24, 2019, the
disclosure of which is incorporated herein by reference in its
entirety.

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with United States Government
support from the National Institute of Standards and Tech-
nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in the
invention. Licensing inquiries may be directed to the Tech-
nology Partnerships Office, NIST, Gaithersburg, Md.,
20899; voice (301) 975-2573; email tpo@nist.gov; refer-
ence NIST Docket Number 19-042US1.

BRIEF DESCRIPTION

Disclosed is a quantum waveguide infrared photodetector
for detecting infrared photons by intersubband transitions in
a semiconductor of a photon absorption layer, the quantum
waveguide infrared photodetector comprising: the photon

absorption layer that receives infrared photons propagating 3

longitudinally along a longitudinal length of the photon
absorption layer, converts the infrared photons into elec-
trons, and communicates the electrons to a conductor layer;
a barrier layer on which the photon absorption layer is

disposed; a semiconductor contact layer on which the barrier 3

layer is disposed; a semiconductor member on which the
semiconductor contact layer is disposed; a substrate on
which the semiconductor member is disposed; a barrier layer
disposed on the photon absorption layer: a buffer layer
disposed on the barrier layer; a semiconductor contact layer
disposed on the buffer layer; a first conductor layer disposed
on the semiconductor contact layer and that receives a first
electrical potential; and a second conductor layer disposed
on the semiconductor contact layer and that receives a
second electrical potential, wherein electrons produced by
the photon absorption layer in response to receipt of the
infrared photons are communicated from the photon absorp-
tion layer: to the first conductor layer when the first electrical
potential is more positive than the second electrical poten-
tial, and to the second conductor layer when the second
electrical potential is more positive than the first electrical
potential, an electrical current produced by the electrons is
proportional to an amount of absorption of the infrared
photons in the photon absorption layer.

Disclosed is a process for detecting infrared photons by
intersubband transitions in a semiconductor of a photon
absorption layer with the quantum waveguide infrared pho-
todetector of claim 1, the process comprising: receiving, by
the photon absorption layer, the infrared photons; propagat-
ing longitudinally the infrared photons along the longitudi-
nal length of the photon absorption layer; converting, by the
photon absorption layer, the infrared photons into electrons
by intersubband transitions in the semiconductor of the
photon absorption layer; biasing the first conductor layer
with the first electrical potential; biasing the second con-
ductor layer with the second electrical potential; communi-
cating the electrons from the photon absorption layer to the

3

40

&

2

first conductor layer when the first electrical potential is
more positive than the second electrical potential; and
communicating the electrons from the photon absorption
layer to the second conductor layer when the second elec-
trical potential is more positive than the first electrical
potential to detect the infrared photons, wherein an electrical
current produced by the electrons is proportional to the
amount of absorption of the infrared photons in the photon
absorption layer.

BRIEF DESCRIPTION OF THE DRAWINGS.

The following description should not be considered lim-
iting in any way. With reference to the accompanying

s drawings, like elements are numbered alike.

FIG. 1 shows a plan view of an embodiment of quantum
waveguide infrared photodetector 200;

FIG. 2 shows a cross-section along line A-A in panel A
and a cross-section along line B-B of an embodiment of
quantum waveguide infrared photodetector 200 show in
FIG. 1;

FIG. 3 shows a cross-section along line A-A in panel A
and a cross-section along line B-B of an embodiment of
quantum waveguide infrared photodetector 200 show in

s FIG. 1;

FIG. 4 shows a cross-section along line A-A in panel A
and a cross-section along line B-B of an embodiment of
quantum waveguide infrared photodetector 200 show in
FIG. 1;

FIG. 5 shows a cross-section along line A-A in panel A
and a cross-section along line B-B of an embodiment of
quantum waveguide infrared photodetector 200 show in
FIG. 1;

FIG. 6 shows a plan view of an embodiment of quantum
waveguide infrared photodetector 200;

FIG. 7 shows an embodiment of quantum waveguide
infrared photodetector 200 with electrons received by con-
ductor layer 213.1 in panel A due to electrical biasing with
electrical bias supply 225 and electrons received by con-
ductor layer 213.2 in panel B due to electrical biasing with
electrical bias supply 225;

FIG. 8 shows a map of a magnitude of an electromagnetic
field of a transverse electromagnetic mode for infrared
photons propagating longitudinally in photon absorption

5 layer 208 and layers proximate to photon absorption layer

208 for a transverse cross-section of an embodiment of
quantum waveguide infrared photodetector 200;

FIG. 9 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 10 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 11 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 12 shows steps involved in making quantum wave-

5 guide infrared photodetector 200 show in FIG. 2;

FIG. 13 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 14 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 15 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 16 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;

FIG. 17 shows steps involved in making quantum wave-

5 guide infrared photodetector 200 show in FIG. 2;

FIG. 18 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 2;


U.S. Patent Mar. 8, 2022 Sheet 29 of 31 US 11,271,023 B2
step 341
ar en
208
w4—E
206
202
me
200 on
at
\ i 1
step 312 "00S
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206
202
mo
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step 313 coeane a
ai 7 tt fp
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1 a
FIG. 29 23 20.


U.S. Patent Mar. 8, 2022 Sheet 6 of 31 US 11,271,023 B2

RO
0
\ mA
* | re
213.4
” 26 [ ——
232] | ——— Lm
21 wT
206
1317 | ——— ns
2061 ! \ Lem,
a7 BN
Le A

FIG. 6


U.S. Patent Mar. 8, 2022 Sheet 5 of 31 US 11,271,023 B2

200

'
210 z
i m4
a Z
nace aaaeain aa
z
i
V z
20
_
FIG. 5A
a ma 2242
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3h
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ar, carn
. tg 20
Bets —\ pet
oe “to eS le 206
= = 1-02
L003
Cant

FIG. 5B


U.S. Patent Mar. 8, 2022 Sheet 18 of 31 US 11,271,023 B2

step 310

230 220

FIG. 18


U.S. Patent Mar. 8, 2022 Sheet 8 of 31 US 11,271,023 B2

AiGaAs

2 (microns)

x (enicrons)

FIG. 8


U.S. Patent Mar. 8, 2022 Sheet 24 of 31 US 11,271,023 B2

step 298 0b

6
m=
02
rie

>,
=—-

step 299

eT

we
mn

=>,
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Mr,

FIG, 24


a2 United States Patent

Stanton

US0112710:

(10) Patent No US 11,271,023 B2
(45) Date of Patent: Mar. 8, 2022

(54)

(71)

(72)
(73)

(21)
(22)
(65)

(60)

(51)

(52)

mn

QUANTUM WAVEGUIDE INFRARED
PHOTODETECTOR

Applicant: Government of the United States of
America, as represented by the
Secretary of Commerce, Gaithersburg,
MD (US)

Inventor: Eric John Stanton, Boulder, CO (US)

Assignee: GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS
REPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
USC. 154(b) by 29 days.

Appl. No.: 16/919,515

Filed: Sul. 2, 2020

Prior Publication Data
US 2021/0028214 Al Jan. 28, 2021

Related U.S. Application Data

Provisional application No. 62/877,932, filed on Jul
24, 2019.

Int. Cl.
HOIL 31/103 (2006.01)
HOIL 27/146 (2006.01)
HOIL 31/0232 (2014.01)
HOIL 31/0352 (2006.01)
US. Cl.

CPC .. HOLL 27/14625 (2013.01); HOIL 27/14669
(2013.01); HOIL 31/02327 (2013.01); HOIL
31/035218 (2013.01)

aT

(58) Field of Classification Search
CPC aren HOLL 27/14625; HOIL 31/02327; HO1L
31/035218; HOIL 27/14669; HO1L
31/02027; HOIL 31/101; HOIL 31/102;
HOIL 31/103; HOIL 31/107; HOIL
31/1075

See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS

5,937,274 A * 8/1999 Kondow HOIL 2102392
438/47

2004/0046176 Al* 3/2004 Kim HOIL 31/101
287/83

2021/0210646 Al* 7/2021 Maros HOLL 31/03048

* cited by examiner

Primary Examiner —Fduardo A Rodela
(74) Attorney, Agent, or Firm — Office of Chief Counsel
for National Institute of Standards and Technology

(7) ABSTRACT

A quantum waveguide infrared photodetector includes: a
photon absorption layer that receives infrared photons
propagating longitudinally along a longitudinal length of the
photon absorption layer, converts the infrared photons into
electrons, and communicates the electrons to a conductor
layer; a first conductor layer that receives a first electrical
potential; and a second conductor layer that receives a
second electrical potential, wherein electrons produced by
the photon absorption layer are communicated from the
photon absorption layer: to the first conductor layer when
the first electrical potential is more positive than the second
electrical potential, and to the second conductor layer when
the second electrical potential is more positive than the first
electrical potential, an electrical current produced by the
electrons is proportional to an amount of absorption of the
infrared photons in the photon absorption layer.

16 Claims, 31 Drawing Sheets



U.S. Patent

step 303

Mar. 8, 2022 Sheet 11 of 31

US 11,271,023 B2

a

try

228 708

TM
=
t

SS
Ss
ss

28

>,
in

me S$
Ew Ss
Pretty tyr tyr tet

FIG. 11


U.S. Patent Mar. 8, 2022 Sheet 10 of 31 US 11,271,023 B2

=!

s
mc
i/
>~,
i
|
pomp
|
|
|

FIG. 10


U.S. Patent Mar. 8, 2022 Sheet 31 of 31 US 11,271,023 B2

step 347
ot 220 213.2 70
309 : #210
nat Tagg el3t 7
Va n L. mt / Se 213.2
U—E =
027 i 1
a Zé \
mu “aan

FIG. 31


U.S. Patent Mar. 8, 2022 Sheet 30 of 31 US 11,271,023 B2

20
sep3!h 00 whe 1
NN coe 8
tN | og
\ m4 a8 / IT
6
2 |
mi PAmInN
234 202134
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34
at mo onR2
— at stg ot
step 316 16 SV a
a3 vad 139
6
mo i
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mt pal
FIG. 30 2134 999 218.


U.S. Patent Mar. 8, 2022 Sheet 7 of 31 US 11,271,023 B2

200 oe
~ al | _ TN
"
a
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ae a
281K 04-4
i 06 r
207 ; —
NY st Lot a
WF |
mht ct
2132 \ 492
MA 4 22
a yy 4

FIG. 7A FIG. 7B


U.S. Patent Mar. 8, 2022 Sheet 21 of 31 US 11,271,023 B2

200 213.2
att
see “Ny es
mw F
Aa) 2192
e—E L
| FE j
rege
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step 308 SN Yah
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EE L,
w-F Y
3: A
20

FIG. 21


US 11,271,023 B2

13

for making quantum waveguide infrared photodetector 200
shown in FIG. 5, a process for making quantum waveguide
infrared photodetector 200 includes providing substrate 201
(step 300); etching substrate 201 to form mode confinement
layer 203 by patterning the substrate 201 with photoresist
and etching with sulfur hexafluoride (step 301); forming first
ply 228 (step 302) by disposing layers of gallium arsenide
and aluminum gallium arsenide with molecular beam epi-
taxy ona gallium arsenide substrate; bonding first ply 228 to
second ply 229 (step 303) by hydrophobic direct bonding;
removing first ply substrate 223 (step 304) by wet etching
with ammonium hydroxide, hydrochloric acid, and water;
etching semiconductor contact layer 206, barrier layer 214,
photon absorption layer 208, barrier layer 209, bufler layer
210, and semiconductor contact layer 211 (step 305) by
patterning with photoresist and exposure to silicon tetra-
chloride plasma; forming conductor layer 213 (step 306) by
electron beam evaporation; forming electrical insulator 230
(step 307) by spinning and exposing a photosensitive dielec-
tric with a pattern: removing a portion of electrical insulator
230 (step 308) by dry ashing with oxygen plasma; forming
electrical contact pad 220 (step 309) by electron beam
evaporation; and removing a section of layers adjoining the
quantum waveguide infrared photodetector 200 (step 310)
by etching with silicon tetrachloride plasma.

In an embodiment, with reference to FIG. 23 and FIG. 24,
the process for making quantum waveguide infrared photo-
detector 200 includes forming a preliminary bonded inter-
face with a patterned air gap trench at the interface (step

298) by etching the first wafer, growing a multilayer film on 3

the second wafer, and then bonding the first wafer to the
second wafer; and forming a planar thin membrane (step
299) by removing the substrate from the second wafer and
leaving the multilayer film bonded to the first wafer.

The process for making quantum waveguide infrared 3

photodetector 200 also can include providing a substrate
(step 311) with epitaxially grown layers that form the entire
quantum waveguide infrared photodetector 200; etching
semiconductor contact layer 206, barrier layer 214, photon
absorption layer 208, barrier layer 209, buffer layer 210, and
semiconductor contact layer 211 (step 305) by patterning
with photoresist and exposure to silicon tetrachloride
plasma; forming conductor layer 213 (step 306) by electron
beam evaporation; forming electrical insulator 230 (step
307) by spinning and exposing a photosensitive dielectric
with a pattern; removing a portion of electrical insulator 230
(step 308) by dry ashing with oxygen plasma; forming
electrical contact pad 220 (step 309) by electron beam
evaporation; and removing a section of layers adjoining the
quantum waveguide infrared photodetector 200 (step 310)
by etching with silicon tetrachloride plasma.

Quantum waveguide infrared photodetector 200 has
numerous advantageous and unexpected benefits and uses.
In an embodiment, a process for detecting infrared photons
by intersubband transitions in a semiconductor of photon
absorption layer 208 with quantum waveguide infrared
photodetector 200 includes: receiving, by photon absorption
layer 208, infrared photons 224; propagating longitudinally
infrared photons 224 along the longitudinal length of photon
absorption layer 208; converting, by photon absorption layer
208, infrared photons 224 into electrons 221 by intersub-
band transitions in the semiconductor of photon absorption
layer 208; biasing first conductor layer 213.1 with the first
electrical potential; biasing second conductor layer 213.2
with the second electrical potential; communicating elec-
trons 221 from photon absorption layer 208 to first conduc-
tor layer 213.1 when the first electrical potential is more

S

3

40

14

positive than the second electrical potential; and communi-
cating electrons 221 from photon absorption layer 208 to
second conductor layer 213.2 when the second electrical
potential is more positive than the first electrical potential to
detect the infrared photons, wherein an electrical current
produced by electrons 221 is proportional to the amount of
absorption of infrared photons 224 in photon absorption
layer 208. The process also can include communicating
electrons 221 as detector signal 227 from first conductor
layer 213.1 to current meter 226 when the first electrical
potential is more positive than the second electrical poten-
tial. The process also can include communicating the elec-
trons 221 as detector signal 227 from second conductor layer
213.2 to current meter 226 when the second electrical

5 potential is more positive than the first electrical potential. A

fluence of infrared photons 224 received by quantum wave-
guide infrared photodetector 200 can be determined from
detector signal 227 by measuring and integrating the elec-
trical current produced by the quantum waveguide infrared
photodetector 200 under a voltage bias over time.
Quantum waveguide infrared photodetector 200 and pro-
cesses disclosed herein have numerous beneficial uses,
including room temperature infrared detection at high speed,
high sensitivity, and in a compact package. Advantageously,

5 quantum waveguide infrared photodetector 200 overcomes

limitations of technical deficiencies of conventional com-
positions such as low absorption per quantum well, leading
to large numbers of quantum wells and associated high dark
current and noise current. Further, the quantum waveguide
infrared photodetector reduces the cross-sectional area of the
photon absorbing layer 208 in the direction of current flow
and subsequently the current noise.

Quantum waveguide infrared photodetector 200 and pro-
cesses herein unexpectedly produce higher detection sensi-
tivity with lower current noise than conventional technolo-
gies at the same temperature. Moreover, quantum
waveguide infrared photodetector 200 provides equivalent
detection sensitivity and current noise at a higher tempera-
ture, e.g., room temperature, compared to cryogenic tem-
perature operation of conventional technologies. Conven-
tional technologies include surface normal irradiated
quantum well infrared photodetectors (QWIPs), quantum
dot infrared photodetectors (QDIPs), quantum cascade
detectors (QCDs), inter-band cascade detectors (ICDs), mer-

5 cury-cadmium-telluride detectors (MCTs), deuterated L-ala-

nine doped triglycine sulfate (DLaTGS), and pyroelectric
detectors. These conventional detectors work for lower-
speed detection applications. Beneficially, quantum wave-
guide infrared photodetector 200 has comparatively higher
performance than these conventional technologies in terms
of detection speed, sensitivity, and noise level and a lower
cost to fabricate and produce. Additionally, a QWIP with
surface normal detection can be formatted into infrared focal
plane arrays for infrared cameras. Quantum waveguide

‘5 infrared photodetector 200 detects light incident on a single

detector element in the plane of the material growth and uses
an absorbing region for intersubband transition in a quantum
well and waveguiding has been developed for photodiodes
using inter-band absorption. Unexpectedly, quantum wave-
guide infrared photodetector 200 has high efficiency with
high index contrast on a silicon substrate. Quantum wave-
guide infrared photodetector 200 is made by wafer bonding
photodetector material to a separate wafer rather than fab-
ricating the detector on a native substrate on which QWIP

5 layers are grown. As a result, quantum waveguide infrared

photodetector 200 can be formed with a decrease in the
number of quantum wells and a decrease in the cross-


US 11,271,023 B2

15
sectional area of current flow compared with conventional
devices, while maintaining at least as high optical absorption
efficiency as conventional devices. Accordingly, quantum
waveguide infrared photodetector 200 has greater respon-
sivity, less dark current noise, and greater signal-to-noise
ratio than conventional devices.
‘The articles and processes herein are illustrated further by
the following Example, which is non-limiting.

EXAMPLE

16
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. “Or” means “and/or.” It should further be noted that the
terms “first.” “second,” “primary,” “secondary,” and the like
herein do not denote any order, quantity, or importance, but
rather are used to distinguish one element from another. The
modifier “about” used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by

10 the context (e.g.. it includes the degree of error associated
with measurement of the particular quantity). The conjunc-
Layers for an exemplary quantum waveguide infrared tion “or” is used to link objects of a list or alternatives and
photodetector 200 are listed in the Table. A primary absorb- is not disjunctive; rather the elements can be used separately
ing region includes Ing ,GapoAs layers proximate to or can be combined together under appropriate circum-
AlpsGay.¢As layers, wherein the configuration absorbs 15 stances.
infrared light near 5.0 um wavelength with a bandwidth of
about 100 nm. Changing a thickness of the Ing ;Gap.As What is claimed is:
layer to match an energy difference between the 1. A quantum waveguide infrared photodetector for
Ing ;Gap.gAs quantum well and adjacent Al.,Gay¢As bar- detecting infrared photons by intersubband transitions in a
rier layer provides selective absorption of a different central semiconductor of a photon absorption layer, the quantum
absorption wavelength. waveguide infrared photodetector comprising:
TABLE
Thickness Doping
Element Material (am) (em)
semiconductor member 202 GaAs 900 Intrinsic
semiconductor contact layer 206 GaAs 200 2x 1018
bamtier layer 214 Ao sGo As 40 Intrinsic
photon absorption layer 208 Ing 1Gay gAs. 0.5 Intrinsic
photon absot layer 208 Ing :Gag.gAs 2.85 2x 10!8
photon absorption layer 208 Ing Gay gAs. 0.5 Intrinsic
barrier layer 209 Alp. «Gilg gAS 400 Intrinsic
buffer layer 210 Alos wo 04G402 ro 06 AS 200 Intrinsic
buffer layer 210 AlosGag 24s 3000 Intrinsic
semiconductor contact layer 211 GaAs 50 2x 108
semiconductor etch stop layer 222 AlogGag 24s 150 Intrinsic
first ply substrate 223 GaAs substrate 625 x 10° Intrinsic
While one or more embodiments have been shown and the photon absorption layer that receives infrared photons
described, modifications and substitutions may be made propagating longitudinally along a longitudinal length
thereto without departing from the spirit and scope of the of the photon absorption layer, converts the infrared
invention. Accordingly, it is to be understood that the present photons into electrons, and communicates the electrons
invention has been described by way of illustrations and not
invent . 3 to a conductor layer:
limitation, Embodiments herein can be used independently a barrier layer on which the photon absorption layer is
or can be combined. disposed. P prion iy
All ranges disclosed herein are inclusive of the endpoints, 45 isposed; .
and the endpoints are independently combinable with each a first semiconductor contact layer on which the barrier
other. The ranges are continuous and thus contain every layer is disposed;
value and subset thereof in the range. Unless otherwise a semiconductor member on which the semiconductor
stated or contextually inapplicable, all percentages, when contact layer is disposed;
expressing a quantity, are weight percentages. The suffix 50 a substrate on which the semiconductor member is dis-
“(s)” as used herein is intended to include both the singular posed;
and the plural of the term that it modifies, thereby including a barrier layer disposed on the photon absorption layer;
at least one of that term (¢.g., the colorant(s) includes at least a buffer layer disposed on the barrier layer;
one colorants). “Optional” or “optionally” means that the a second semiconductor contact layer disposed on the
subsequently described event or circumstance can or cannot 55 buffer layer;
occur, and that the description includes instances where the a first conductor layer disposed on the first semiconductor
event occurs and instances where it does not. As used herein, contact layer and that receives a first electrical poten-
“combination” is inclusive of blends, mixtures, alloys, reac- tial; and
tion products, and the like. a second conductor layer disposed on the second semi-
As used herein, “a combination thereof” refers to a 60 conductor contact layer and that receives a second
combination comprising at least one of the named constitu- electrical potential,
ents, components, compounds, or elements, optionally wherein electrons produced by the photon absorption
together with one or more of the same class of constituents, layer in response to receipt of the infrared photons are
components, compounds, or elements. communicated from the photon absorption layer:
All references are incorporated herein by reference. 65 to the first conductor layer when the first electrical

‘The use of the terms “a” and “an” and “the” and similar
referents in the context of describing the invention (espe-

potential is more positive than the second electrical
potential, and


U.S. Patent Mar. 8, 2022 Sheet 27 of 31 US 11,271,023 B2
\ 24 2
step 306 / a
: aN
00 at L
213.1 . 213.2
td =)
2620 =: iam
2-7 = 2 — J : { ;
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FIG. 27 34 20 2494


U.S. Patent Mar. 8, 2022 Sheet 3 of 31 US 11,271,023 B2

200
NN 213.2 a2 9
Pr a
210 Le
us
Sti conemmepemmemaeaae fo
\ 24 wi:
202
15
16
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FIG. 3A
at nia ar
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ma {-
aT, os one 24
281——j a a
i
ONE he
hh tt tah i
A i {et
2 Wyn = sy oe tu\ YD
203 of 4 215 HN 29


U.S. Patent Mar. 8, 2022 Sheet 14 of 31 US 11,271,023 B2

step 306
a a at rn
\—= |
mat 208 2134 jae

Ho:

06—E - Wee
ot
02 qe Ay |. H
Ht aS
nna mek
013

L-2ti

H0

008

008

04

06

002

|
3M

FIG. 14


U.S. Patent Mar. 8, 2022 Sheet 16 of 31 US 11,271,023 B2

steo 308
vi 132 ag
Pua F _—_ 2132
7 7@:
206 pi : rj
m— 7 i
ae \

230

FIG. 16


U.S. Patent Mar. 8, 2022 Sheet 2 of 31 US 11,271,023 B2

20

-—+
29
| 24
FE coeen comme ae /.
\ a4
06
002
a ee
< is a ;
03 204 2
205 i
FIG. 2A
7
ids, i 200
4
214 H a
207 + mi
ae Neng lid a
| ’, y = [74
> ed SNe 126
m0
mt

7 {
Ly 205 a 203
FIG. 2B


US 11,271,023 B2

11

electrons 221 can be from 0 electron volts (eV) to 200 eV,
specifically from 0.1 eV to 20 eV, and more specifically from
1 eV to 10 eV.

Electrons 221 communicated from photon absorption
layer 208 to conductor layer 213 or electrical contact pad
220 are issued from quantum waveguide infrared photode-
tector 200 as detector signal 227. Detector signal 227 can be
an electrical current from 1 pico ampere (pA) to 10 ampere
(A), specifically from 10 pA to 1 A, and more specifically
from 100 pA to 10 mA.

Quantum waveguide infrared photodetector 200 can
include additional optical and electronic components includ-
ing mirrors, lenses, optical fiber, electrical communication
lines (¢.g., coaxial cable) and the like.

It should be appreciated that quantum waveguide infrared
photodetector 200 can be configured with layers formed on
a gallium arsenide substrate and bonded to a silicon sub-
strate. With reference to FIG. 2, the silicon substrate can
include an etched trench to isolate optical properties of the
waveguide in quantum waveguide infrared photodetector
200 from the silicon substrate and provide a lower cladding
of air, wherein this structure provides a high index of
refraction contrast for the guided optical mode. With refer-
ence to FIG. 3, quantum waveguide infrared photodetector
200 can include the waveguide on a silicon substrate
coupled to the GaAs-based waveguide to tailor the optical
confinement laterally. The waveguide core can include sili-
con or another material for selective absorption of wave-
lengths of infrared photons 224, wherein the material can

have low optical loss. A length of quantum waveguide 3

infrared photodetector 200 can be selectively shortened so
optical loss requirement can be minimized. A lower cladding
shown in FIG. 3 can include a variety of materials that can
ease fabrication such as including the substrate waveguide

of silicon with a lower cladding of silicon dioxide. With 3

reference to FIG. 4, quantum waveguide infrared photode-
tector 200 can include a double bonding fabrication step to
form a GaAs waveguide to provide longer wavelength
detection and to tailor the confinement of optical modes
independent of a ridge width (the combined widths of
photon absorption layer 208, barrier layer 209, buffer layer
210, semiconductor contact layer 211, and barrier layer 214)
of quantum waveguide infrared photodetector 200. Dimen-
sions of quantum waveguide infrared photodetector 200 can
control wavelength of operation via absorption of infrared
photons 224. In an embodiment, quantum waveguide infra-
red photodetector 200 with a suspended configuration shown
in FIG. 4 can operate at 5.0 um wavelength with a ridge
width of (3.01.0) jum and a separation between the photon
absorption layer 208, the barrier layer 209, the buffer layer
210, the semiconductor contact layer 211, and the barrier
layer 214 and conductor layer 213.1 and conductor layer
213.3 of (2.5#0.5) um. The conductor layer 213.2 can be
narrower than the photon absorption layer 208, the barrier
layer 209, the buffer layer 210, the semiconductor contact
layer 211, and the barrier layer 214 by about 1.0 um, to give
a 500 nm offset on each side. The Si trench can be etched,
e.g.. to be 1.0 um deep and as wide as (8.0+2.0) jum.
Quantum waveguide infrared photodetector 200 can be
made in various ways. In an embodiment, a process for
making quantum waveguide infrared photodetector 200
includes forming substrate 201 by providing a silicon wafer
or a wafer of another material such as quartz or gallium
arsenide; forming semiconductor member 202 on semicon-
ductor contact layer 206 by contacting semiconductor con-
tact layer 206 with a gaseous composition of gallium and
arsenide atoms; forming mode confinement layer 203 by

2

40

&

12

etching substrate 201 with a dry or wet etch chemistry in a
patterned region that is wider than photon absorption layer
208, barrier layer 209, buffer layer 210, semiconductor
contact layer 211, and barrier layer 214; forming substrate
gap surface 204 by etching substrate 201 with a dry or wet
etch chemistry in a pattemed region that is wider than
photon absorption layer 208, barrier layer 209, buffer layer
210, semiconductor contact layer 211, and barrier layer 214;
forming semiconductor gap surface 205 by bonding to
substrate 201 using a direct or interlayer surface bonding
technique such as hydrophobic direct bonding; forming
semiconductor contact layer 206 by contacting barrier layer
214 with a gaseous composition of gallium and arsenide
atoms; forming semiconductor contact surface 207 by etch-

5 ing photon absorption layer 208, barrier layer 209, buffer

layer 210, semiconductor contact layer 211, and barrier layer
214 with a dry or wet etch chemistry in a patterned region;
forming photon absorption layer 208 by contacting barrier
layer 209 with a gaseous composition of gallium and
arsenide atoms and sometimes indium or aluminum atoms;
forming barrier layer 209 by contacting buffer layer 210 with
a gaseous composition of gallium, arsenide, and aluminum
atoms; forming buffer layer 210 by contacting semiconduc-
tor contact layer 211 with a gaseous composition of gallium,

S arsenide, and aluminum atoms; forming semiconductor con-

tact layer 211 by contacting semiconductor etch stop layer
222 with a gaseous composition of gallium and arsenide
atoms and sometimes aluminum atoms; forming top contact
surface 212 by etching semiconductor etch stop layer 222
with a dry or wet etch chemistry either patterned or not
patterned; forming conductor layer 213 by physical or
chemical vapor deposition over a patterned sacrificial layer;
forming barrier layer 214 by contacting photon absorption
layer 208 with a gaseous composition of gallium, arsenide,
and aluminum atoms; forming core layer 215 by bonding
core layer 215 to bottom cladding 216 using a direct or
interlayer surface bonding technique (c.g., hydrophobic
direct bonding) and etching core layer 215 with a dry or wet
etch chemistry (e.g., boron trichloride plasma) in a patterned
region; forming bottom cladding 216 by performing wet or
dry thermal oxidation of substrate 201; forming cladding air
gap surface 217 by etching core layer 215 with a dry or wet
etch chemistry in a patterned region; forming semiconductor
air gap surface 218 by etching semiconductor member 202

5 with a dry or wet etch chemistry in a patterned region;

forming semiconductor air gap surface 219 by bonding
semiconductor contact layer 206 to semiconductor member
202 using a direct or interlayer surface bonding technique;
and forming electrical contact pad 220 by forming electrical
contact pad 220 using physical or chemical vapor deposition
over a patterned sacrificial layer. The process also can
include forming semiconductor etch stop layer 222 on
gallium arsenide substrate 223 by contacting gallium
arsenide substrate 223 with a gaseous composition of gal-

5 lium, arsenide, and aluminum atoms, semiconductor etch

stop layer 222 is an etch stop layer for selectively stopping
an etchant from etching layers on which semiconductor etch
stop layer 222 is disposed. Moreover, layers of first ply 228
can be formed on first ply substrate 223 that can be removed
by etching.

In an embodiment, with reference to FIG. 9 to FIG. 18 for
making quantum waveguide infrared photodetector 200
shown in FIG. 2, with reference to FIG. 19 to FIG. 22 for
making quantum waveguide infrared photodetector 200

5 shown in FIG. 3, with reference to FIG. 23 to FIG. 28 for

making quantum waveguide infrared photodetector 200
shown in FIG. 4, and with reference to FIG. 29 to FIG. 31


U.S. Patent Mar. 8, 2022 Sheet 25 of 31 US 11,271,023 B2

step 304

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US 11,271,023 B2

Sheet 1 of 31

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FIG. 1

Mar. 8, 2022

U.S. Patent

200


US 11,271,023 B2

3

FIG. 19 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 3;

FIG. 20 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 3;

FIG. 21 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 3:

FIG, 22 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 3;

FIG, 23 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 4:

FIG, 24 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 4;

FIG. 25 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 4:

FIG. 26 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 4:

FIG. 27 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 4;

FIG. 28 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 4:

FIG. 29 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 5;

FIG, 30 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 5: and

FIG. 31 shows steps involved in making quantum wave-
guide infrared photodetector 200 show in FIG. 5.

DETAILED DESCRIPTION

A detailed description of one or more embodiments is 3

presented herein by way of exemplification and not limita-
tion.

It has been discovered that quantum waveguide infrared
photodetector 200 provides a greater signal-to-noise ratio

compared with conventional infrared detectors. Beneficially, 3

quantum waveguide infrared photodetector 200 receives
infrared photons injected in absorbing regions of quantum
waveguide infrared photodetector 200 in a plane of material
layers of quantum waveguide infrared photodetector 200
instead of surface normal to the material layers of quantum
waveguide infrared photodetector 200 as conventional
detectors do. Unexpectedly, quantum waveguide infrared
photodetector 200 provides room-temperature detection of
infrared light with high sensitivity and high speed and can be
a detector for infrared absorption spectroscopy, optical
coherence tomography, light detection and ranging, com-
munications, and the like.

Quantum waveguide infrared photodetector 200 detects
infrared photons 224 by intersubband transitions in a semi-
conductor of photon absorption layer 208. In an embodi-
ment, with reference to FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG.
5, FIG. 6, and FIG. 7, quantum waveguide infrared photo-
detector 200 includes: photon absorption layer 208 that
receives infrared photons 224 propagating longitudinally
along a longitudinal length (indicated in FIG. 1 as being in
a direction along X-axis) of photon absorption layer 208,
converts infrared photons 224 into electrons 221, and com-
municates electrons 221 to conductor layer 213; barrier layer
214 on which photon absorption layer 208 is disposed;
semiconductor contact layer 206 on which barrier layer 214
is disposed; semiconductor member 202 on which semicon-
ductor contact layer 206 is disposed; a substrate 201 on
which semiconductor member 202 is disposed; a barrier
layer 209 disposed on photon absorption layer 208; a buffer
layer 210 disposed on barrier layer 209; a semiconductor
contact layer 211 disposed on buffer layer 210; a first
conductor layer 213.1 disposed on semiconductor contact

20

2

40

&

4

layer 206 and that receives a first electrical potential; and a
second conductor layer 213.2 disposed on semiconductor
contact layer 211 and that receives a second electrical
potential, wherein electrons 221 produced by photon absorp-
tion layer 208 in response to receipt of infrared photons 224
are communicated from photon absorption layer 208: to first
conductor layer 213.1 (as electrons 221.1) when the first
electrical potential is more positive than the second electri-
cal potential, and to second conductor layer 213.2 (as
electrons 221.2) when the second electrical potential is more
positive than the first electrical potential. an electrical cur
rent produced by electrons 221 is proportional to an amount
of absorption of infrared photons 224 in photon absorption
layer 208.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes mode confinement layer 203
interposed between substrate 201 and semiconductor mem-
ber 202 and bounded by surfaces of substrate 201 and
semiconductor member 202.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes core layer 215 interposed
between substrate 201 and semiconductor member 202.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes bottom cladding 216 inter-
posed between core layer 215 and substrate 201.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes mode confinement layer 203
disposed in core layer 215 and interposed between bottom
cladding 216 and semiconductor member 202.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes mode confinement layer 203 is
bounded by surfaces of bottom cladding 216, core layer 215,
and semiconductor member 202.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes second mode confinement
layer 203.2 disposed in semiconductor member 202, inter-
posed between semiconductor member 202 and semicon-
ductor contact layer 206, and bounded by surfaces of semi-
conductor member 202 and semiconductor contact layer
206,

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes first electrical contact pad
220.1 disposed on substrate 201 and first conductor layer
213.1 and in electrical communication with first conductor
layer 213.1, such that first electrical contact pad 220.1
receives the first electrical potential for electrically biasing
first conductor layer 213.1.

In an embodiment, quantum waveguide infrared photo-
detector 200 further includes second electrical contact pad
220.2 disposed on substrate 201 and second conductor layer
213.2 and in electrical communication with second conduc-
tor layer 213.2, such that second electrical contact pad 220.2
receives the second electrical potential for electrically bias-
ing second conductor layer 213.2.

In an embodiment, with reference to FIG. 16, quantum
waveguide infrared photodetector 200 further includes elec-
trical insulator 230 disposed on semiconductor contact layer
211 and semiconductor contact layer 206 and that electri-
cally insulates first conductor layer 213.1 from second
conductor layer 213.2.

In an embodiment, with reference to FIG. 7, quantum
waveguide infrared photodetector 200 further includes elec-
trical bias supply 225 in electrical communication with first
conductor layer 213.1 and second conductor layer 213.2,

5 wherein electrical bias supply 225 provides the first electri-

cal potential to first conductor layer 213.1 and the second
electrical potential to second conductor layer 213.2. Quan-


U.S. Patent Mar. 8, 2022 Sheet 28 of 31 US 11,271,023 B2
step 309
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U.S. Patent

step 304

Mar. 8, 2022

Sheet 12 of 31

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U.S. Patent Mar. 8, 2022 Sheet 15 of 31 US 11,271,023 B2

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