An infrared detector having a hole barrier region adjacent to one side of an absorber region, an electron barrier region adjacent to the other side of the absorber region, and a semiconductor adjacent to the electron barrier

Bandara, Sumith V.

Gunapala, Sarath D.

Hill, Cory J.

Ting, David Z.

NASA Technical Reports Server

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(12) United States Patent 
Ting et al. 
(54) COMPLEMENTARY BARRIER INFRARED 
DETECTOR (CBIRD) 
(75) Inventors: David Z. Ting, Arcadia, CA (US); 
Sumith V. Bandara, Burke, VA (US); 
Cory J. Hill, Pasadena, CA (US); 
Sarath D. Gunapala, Stevenson Ranch, 
CA (US) 
(73) Assignee: California Institute of Technology, 
Pasadena, CA (US) 
(*) Notice: 	 Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 662 days. 
(21) Appl. No.: 12/501,167 
(22) Filed: 	 Jul. 10, 2009 
(65) 	 Prior Publication Data 
US 2010/0006822 Al 	 Jan. 14, 2010 
Related U.S. Application Data 
(60) Provisional application No. 61/134,577, filed on Jul. 
11, 2008. 
(51) Int. Cl. 
HOIL 31100 	 (2006.01) 
(52) U.S. Cl . .................... 257/21; 257/22; 257/E31.032; 
257/E31.033 
(58) Field of Classification Search .................... 257/21, 
257/22, E31.032, E31.033 
See application file for complete search history. 
(1o) Patent No.: 	 US 8,368,051 B2 
(45) Date of Patent: 	 Feb. 5, 2013 
(56) References Cited 
U.S. PATENT DOCUMENTS 
5,194,983 A * 	 3/1993 Voisin ........................... 359/245 
2002/0027238 Al * 	 3/2002 Lin et al ........................ 257/292 
OTHER PUBLICATIONS 
Darin Hoffman et al., "The Effect of Doping the M-Barrier in Very 
Long-Wave Type-II inAs/GaSb Heterodiodes", Applied Physics Let-
ters 93, 031107 (2008) pp. 1-3. 
Binh-Minh Nguyen et al., "Dark Current Suppression in Type II 
InAs/GaSb Superlattice Long Wavelength Infrared Photodiodes 
With M-Structure Barrier" Applied Physics Letters 91, 163511 
(2007) pp. 1-3. 
Binh-Minh Nguyen et al., `Background Limited Long Wavelength 
Infrared Type-II InAs/GaSb Superlattice Photodiodes Operating At 
110 K", Applied Physics Letters 93, 123502 (2008), pp. 1-3. 
M. Carras et al., "Interface Band gap Engineering in InAsSb 
Photodiodes", Applied Physics Letters 87, 102103 (2005) pp. 1-3. 
S. Maimon et al., ` nBn Detector, An Infrared Detector With Reduced 
Dark Current and Higher Operating Temperature",Applied Physics 
Letters 89, 151109 (2006), pp. 1-3. 
* cited by examiner 
Primary Examiner Tu-Tu Ho 
(74) Attorney, Agent, or Firm Kauth, Pomeroy, Peck & 
Bailey LLP 
(57) ABSTRACT 
An infrared detector having a hole barrier region adjacent to 
one side of an absorber region, an electron barrier region 
adjacent to the other side of the absorber region, and a semi-
conductor adjacent to the electron barrier. 
15 Claims, 2 Drawing Sheets 
108 
	
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U.S. Patent 	 Feb. 5, 2013 	 Sheet 1 of 2 	 US 8,368,051 B2 
U.S. Patent 	 Feb. 5, 2013 	 Sheet 2 of 2 	 US 8 ,368,051 B2 
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US 8,368,051 B2 
1 
COMPLEMENTARY BARRIER INFRARED 
DETECTOR (CBIRD) 
PRIORITY CLAIM 
This application claims the benefit of U.S. Provisional 
Application No. 61/134,577, filed Jul. 11, 2008. 
GOVERNMENT INTEREST 
The invention claimed herein was made in the performance 
of work under a NASA contract, and is subject to the provi-
sions of Public Law 96-517 (35 USC 202) in which the 
Contractor has elected to retain title. 
FIELD 
The present invention relates to infrared detectors. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG.1 illustrates an infrared detector, with a representative 
energy band diagram, according to an embodiment. 
FIG. 2 illustrates an infrared detector, with an energy band 
diagram, according to another embodiment. 
DESCRIPTION OF EMBODIMENTS 
In the description that follows, the scope of the term "some 
embodiments" is not to be so limited as to mean more than 
one embodiment, but rather, the scope may include one 
embodiment, more than one embodiment, or perhaps all 
embodiments. 
FIG. 1 illustrates an infrared detector according to an 
embodiment, comprising infrared absorber region 102, hole 
barrier region 104 on one side of infrared absorber region 102, 
electron barrier region 106 on the other side of the infrared 
absorber region 102, and contact regions 108 and 110 in 
contact with hole barrier region 104 and electron barrier 
region 106, respectively. The illustration of the detector in 
FIG. 1 is pictorial in nature and is not necessarily drawn to 
scale. In practice, the various regions making up an embodi-
ment may be epitaxial layers grown on a substrate. 
The conduction and valence energy band levels for the 
infrared detector are illustrated below their corresponding 
regions, with the conduction band edge labeled with an E, 
and the valence band edge labeled with an E v. The dashed 
lines mark the various regions so as to provide a correspon-
dence from the energy band diagrams to regions 102, 104, 
106, 108, and 110. The regions and energy bands are not 
necessarily drawn to scale. 
For the part of the energy bands corresponding to infrared 
absorber region 102, the absorption of light is pictorially 
represented by the wavy lines with "Irv" above them to rep-
resent the photon energy, where h is Planck's constant and v 
is the frequency of the incoming infrared radiation. The 
absorption of a photon excites an electron from the valence 
band to the conduction band, which is represented by the 
vertical arrows pointing from the valence band to the conduc-
tion band. The illustrated solid circles near the conduction 
band represent electrons, and the illustrated hollow circles 
near the valence band represent holes. An arrow next to an 
electron or a hole pictorially represents the direction of the 
electron or hole under a bias voltage applied between contact 
regions 110 and 108, where contact region 108 is biased 
positively with respect to contact region 110. 
2 
Electrons are collected at contact region 108, and holes are 
collected at contact region 110. The bias voltage applied to 
contact regions 108 and 110 depends upon the type of mate-
rial used, and some embodiments may operate at zero bias 
5 voltage. For example, with contact region 110 comprising a 
p-doped semiconductor and contact region 108 comprising 
an n-doped semiconductor, contact region 108 may be posi-
tively biased with respect to contact region 110 for some 
embodiments. 
io 	 FIG. 1 illustrates a unipolar hole barrier in the valence 
energy band corresponding to hole barrier region 104, and a 
unipolar electron barrier in the conduction energy band cor-
responding to electron barrier region 106. The unipolar elec-
tron barrier region 106 blocks electrons from absorber region 
15 102, but allows the flow of holes from absorber region 102. 
Similarly, the unipolar hole barrier region 104 blocks holes 
from absorber region 102, but allows the flow of electrons 
from absorber region 102. Contact region 108 is adjacent to 
hole barrier region 104 for collecting electrons, and contact 
20 region 110 is adjacent to electron barrier region 106 for col-
lecting holes. Because of this placement, these complemen-
tary barriers do not impede the flow of photon-induced cur-
rent (photo-current), and it is believed that a number of 
benefits may result from their use. These benefits are dis- 
25 cussed below. 
A prior art infrared detector, such as for example an n -71-p 
detector, may suffer from generation-recombination (G-R) 
current due to the Shockley-Read-Hall (SRH) process taking 
place in the space-charge region, where for example in a 
30 n-7t-p detector a space-charge region is between the n-doped 
region and the 71 absorber region. Because wide band gap 
barriers (regions 104 and 106) in the embodiment of FIG. 1 
are adjacent to absorber region 102, a significant reduction in 
SHR generated dark current is expected. 
35 	 The use of wide band gap barriers is expected to help 
reduce thermally generated minority carriers in the diffusion 
wings from contributing to the photo current. For example, 
electron 112 represents a thermally generated electron, but 
because of electron barrier region 106, the probability of 
40 electron 112 tunneling through hole barrier region 106 to 
contact region 108 is very small. Furthermore, photo-gener-
ated electrons in absorber region 102 diffusing in a direction 
toward contact region 110 are deflected back by electron 
barrier region 106 with very high probability; and photo- 
45 generatedholes in absorberregion 102 diffusing in a direction 
toward contact region 108 are deflected back by hole barrier 
region 104 with very high probability. 
For some embodiments, contact regions 108 and 110 may 
comprise material so as to have a wider band gap than 
5o absorber region 102, thereby acting as a window to allow 
longer wavelength radiation to reach absorber region 102. For 
some embodiments, contact regions 108 and 110 may com-
prise material so as to have smaller band gaps than hole 
barrier region 104 and electron barrier region 106, so as to 
55 facilitate in making ohmic contacts to reduce contact resis-
tance. For some embodiments, both contact regions 108 and 
110 may be doped as either n-type or p-type. Some embodi-
ments may not include one or both of these contact regions, in 
which case electrical contact is made directly to one or both of 
60 the barrier regions. 
For some embodiments, some or all of regions 102, 104, 
and 106 may be superlattices. For some embodiments, 
absorber region 102 may be a superlattice designed for Auger 
suppression to further reduced dark current. Some or all of 
65 these superlattices may be chirped, and some of the regions 
may be graded by introducing an alloy composition grading. 
Some embodiments may have band offsets between some of 
US 8,368,051 B2 
3 
the various regions. For example, one or both of the absorber-
barrier interfaces may have staggered band offsets, or the 
barrier-contact interfaces may have nested band offsets, 
where the offsets are such that electrons and holes may flow 
unimpeded by these types of band offsets when contact region 
104 is biased positively with respect to contact region 106. 
The doping levels of the barrier regions and absorber region 
102 may be adjusted to control various device properties. 
Energy band diagrams, including the Fermi level, for a 
specific example of an embodiment in which electrical con-
tact is made directly to the hole barrier region are illustrated in 
FIG. 2. As in FIG. 1, a simplified view of the various regions 
making up an embodiment are shown with their correspond-
ing energy band levels, but because electrical contact is made 
directly to hole barrier region 204, a contact region corre-
sponding to contact region 108 is not needed. 
For the embodiment of FIG. 2, contact region 210 has a 
widerband gap than absorber region 202 and is doped n-type. 
Electron barrier region 206 for the embodiment of FIG. 2 is 
doped p-type. Having an n-type contact region next to elec-
tron barrier region 206 creates a second p-n junction (the first 
being the one between hole barrier region 204 and absorber 
region 202) over which an applied voltage bias drop may be 
developed. This reduces the voltage drop over absorber 
region 202, thereby reducing dark current generation in 
absorber region 202. 
For the embodiment of FIG. 2, absorber region 202, hole 
barrier region 204, and electron barrier region 206 are super-
lattice structures. Contact region 210 for collecting holes 
comprises InAsSb. These regions are shown in HG. 2 with 
their corresponding energy bands, where the y-axis is energy 
in electron volts (eV), and the x-axis denotes distance in 
microns, and where the origin of the x-axis is taken at the left 
hand side of hole barrier region of 204. Note that the embodi-
ment illustrated in FIG. 2 does not have a contact layer for 
collecting electrons, but rather an ohmic contact may be made 
directly to hole barrier region 204 for collecting electrons. As 
illustrated in FIG. 2, the layer 210 could be made of a material 
such that the conduction band of the layer 210 overlaps with 
the valence band of the electron barrier 206 to facilitate the 
removal of excess holes from the absorber region 202. 
In the particular embodiment of FIG. 2, absorber region 
202 is a 600 period (44 A, 21 A) InAs/GaSb superlattice 
structure. That is, a structure comprising a 44 A thick InAs 
layer adjacent to a 21 A thick GaSb layer is repeated 600 
times along the x-axis. Hole barrier region 204 is an 80 period 
(46 A, 12 A) InAs/A1Sb superlattice, and electron barrier 
region 206 is a 60 period (22 A, 21 A) InAs/GaSb superlat-
tice. For the particular embodiment of FIG. 2, hole barrier 
region 204 and electron barrier region 206 are designed to 
have, respectively, an approximately zero conduction sub-
band offset with respect to absorber region 202 and an 
approximately zero valence sub-band offset with respect to 
absorber region 202. Hole barrier region 204 is nominally 
doped at n=1.1016 CM-3 absorber region 202 is nominally 
doped at p=1.1016 CM-3  and electron barrier region 206 is 
nominally doped at p=1.1016 CM-3.  Contact region 210 is an 
n=1.1018 CM-3  doped InAso 9 ,Sb, 09  layer. The particular 
embodiment illustrated in FIG. 2 was grown on a 50-mm 
diameter Te-doped GaSb (100) substrate in a molecular beam 
epitaxial chamber. These parameters are cited merely as an 
example embodiment. 
For some embodiments, contact region 210 may serve as a 
bottom contact layer, and hole barrier region 204 may serve as 
a top contact layer. For a positive bias applied to hole barrier 
region 204 with respect to contact region 210, the voltage 
drop is can take place over the junction formed by electron 
4 
barrier region 206 and contact region 210. This junction is 
away from absorber region 202, thereby mitigating dark cur-
rent generation. In general, for a non-negative bias applied to 
hole barrier region 204 with respect to contact region 210, 
5 photo generated minority carriers (electrons) in absorber 
region 202 diffuse or drift towards hole barrier region 204 to 
be collected by a contact applied to hole barrier region 204. 
The excess hole population redistributes by dielectric relax-
ation, and may recombine with electrons injected into 
10 
absorber region 202 from contact region 210. 
Various modifications may be made to the disclosed 
embodiments without departing from the scope of the inven-
tion as claimed below. 
15 
What is claimed is: 
1. A detector comprising: 
a p-type absorber region to generate electrons and holes in 
response to electromagnetic radiation; 
20 	 a unipolar hole barrier region having inner and outer ends 
and disposed such that the inner end is positioned adja-
cent to the absorber region; 
a first n-type contact region disposed adjacent to the outer 
end of the hole barrier comprising a semiconductor 
25 material that allows the un-impeded flow of minority 
carriers from the absorber region; 
a unipolar electron barrier region having inner and outer 
ends and disposed such that the inner end is positioned 
adjacent to the absorber region; and 
30 	 a second contact region disposed adjacent to the outer end 
of the electron barrier, comprising a semiconductor 
material that allows the un-impeded flow of majority 
carriers from the absorber region 
wherein the absorber region, the unipolar hole barrier 
35 region and the unipolar electron barrier region are all 
substantially lattice-matched to a semiconductor sub-
strate; and 
wherein the energy band gap of the barriers between the 
absorber and the contacts are selected such that the 
40 undesirable generation-recombination (G-R) dark cur-
rent produced through the Shockley-Read-Hail (SRH) 
processes is reduced. 
2. The detector as set forth in claim 1, wherein the absorber 
region, the hole barrier region, and the electron barrier region 
45 are selected from the group consisting of a bulk semiconduc-
tor and a superlattice semiconductor. 
3. The detector as set forth in claim 2, wherein the absorber 
region comprises an InAs/GaSb superlattice semiconductor. 
4. The detector as set forth in claim 3, wherein the hole 
5o barrier region comprises an InAs/A1Sb superlattice semicon-
ductor. 
5. The detector as set forth in claim 4, wherein the electron 
barrier region comprises an InAs/GaSb superlattice semicon-
ductor. 
55 	 6. The detector as set forth in claim 5, wherein the absorber 
region is a 600 period (44 A, 21 A) superlattice semiconduc-
tor. 
7. The detector as set forth in claim 6, wherein the absorber 
region is a 600 period (44 A, 21 A) superlattice, the hole 
6o barrier region is an 80 period (46 A, 12 A) superlattice, and 
the electron barrier region is a 60 period (22 A, 21 A) super-
lattice. 
8. The detector as set forth in claim 1, wherein the first 
contact region has a wider band gap than that of the absorber 
65 region. 
9. The detector as set forth in claim 1, wherein the electron 
barrier region comprises a p-type doped semiconductor. 
US 8,368,051 B2 
5 
10. The detector as set forth in claim 9, wherein the hole 
barrier region comprises an n-type doped semiconductor, and 
the absorber region comprises a p-typed doped semiconduc-
tor. 
11. The detector as set forth in claim 1, wherein the elec-
tromagnetic radiation is infrared. 
12. The detector as set forth in claim 1, wherein the first 
n-type contact is formed by the unipolar hole barrier. 
13. The detector as set forth in claim 1, wherein the second 
contact is a p-type contact. 
14. The detector as set forth in claim 1, wherein the second 
contact is an n-type contact in a broken gap alignment to the 
electron barrier. 
15. A detector comprising: 
an n-type absorberregion to generate electrons and holes in 
response to electromagnetic radiation; 
• unipolar electron barrier region having inner and outer 
ends and disposed such that the inner end is positioned 
adjacent to the absorber region; 
• first p-type contact region disposed adjacent to the outer 
end of the electron barrier, comprising a semiconductor 
6 
material that allows the un-impeded flow of minority 
carriers from the absorber region; 
• unipolar hole barrier region having inner and outer ends 
and disposed such that the inner end is positioned adja-
5 cent to the absorber region; and 
• second contact region disposed adjacent to the outer end 
of the hole barrier, comprising a semiconductor material 
that allows the un-impeded flow of majority carriers 
from the absorber region; 
io 	 wherein the absorber region, the unipolar hole barrier 
region and the unipolar electron barrier region are all 
substantially lattice-matched to a semiconductor sub-
strate; and 
wherein the energy band gap of the barriers between the 
15 absorber and the contacts are selected such that the 
undesirable generation-recombination (G-R) dark cur-
rent produced through the Shockley-Read-Hall (SRH) 
processes is reduced. 


Complementary barrier infrared detector (CBIRD)

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