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Carrier Lifetime Measurement of Short-Period InAs/GaSb Superlattices for the
Development of a High-Operating Temperature Mid-Infrared Detector
R. Mori1, 2
, T. Noe2, J. Kono
2
1 NanoJapan Program and Department of Applied Physics and Physico-Informatics, Keio
University
2 Department of Electrical and Computer Engineering, Rice University
The most widely used material systems for mid-infrared (IR) detection such as mercury
cadmium telluride (MCT) or quantum well infrared photodetectors (QWIP) require cryogenic
temperatures. Cryogens for cooling devices are not always available for some applications.
Therefore, a need exists to develop an uncooled mid-IR detector. Short-period InAs/GaSb
superlattices (SLs) are expected to be a promising material for uncooled IR detectors where the
band gap can be tuned to a particular IR range by the appropriate choice of SL period because of the
type-II band alignment of these SLs. A long carrier lifetime is required to amplify the
photocurrent to increase the sensitivity of devices that incorporate InAs/GaSb superlattices.
Although preliminary measurements of the lifetime have already been done, measurements that
indicate the full recovery to the original carrier ground state are required. In order to improve
these data, we have measured time-resolved reflectivity by using pump-probe spectroscopy. We
expect to observe a significantly long carrier lifetime and get more accurate results. Our
findings will inform sample growers’ design of this material system for mid-infrared detection.
Carrier Lifetime Measurement of Short-Period InAs/GaSb Superlattices for the Development of a High-Operating
Temperature Mid-Infrared Detector
Introduction Experimental Method Result and Conclusion
Future Work
R. Mori1, 2, T. Noe2, J. Kono2, 1 NanoJapan Program and Department of Applied Physics and Physico-Informatics, Keio University
2 Department of Electrical and Computer Engineering, Rice University
Theory • Material System
1. The most widely used material systems for mid-infrared detection require cryogenic for cooling
Not always available
2. A long carrier lifetime is required to amplify the photocurrent to increase the sensitivity of devices
A need exists to develop an uncooled mid-IR detector
A need exists to find a material that has a long carrier lifetime at room temperature
• Short-period InAs/GaSb superlattices(SLs) are expected to be a promising material
To decide the best structure of InAs/GaSb SLs by Measuring carrier lifetime
This material is based upon work supported by the National Science Foundation’s Partnerships for
International Research & Education Program (OISE-0968405)
Figure 1-a
(Figure 1-a) Based on a type-Ⅱ “broken gap” SL of InAs and GaSb: ü Can be designed to make room temperature operation possible ü Band gap can be tuned to a particular IR range by the appropriate choice of SL period (Figure 1-b) Five different SL structures produced by Moleculer Beam Epitaxy: ü Five samples with different layer thicknesses of InAs/GaSb
H1
InAs
GaSb GaSb GaSb
InAs
GaSb GaSb GaSb
InAs InAs
E1
E1
H1
Figure 1-b
24 Å GaSb
22 Å InAs
0.3 µm GaSb buffer N-type (Te-doped) GaSb (100)-
double side polished
• 46.0 Å • 49.5 Å • 56.0 Å • 61.0 Å • 71.0 Å
X 110 times ~0.5µm
Layer thickness of InAs/GaSb
Five Samples
Figure 2-a
• Measurement Principle (Figure 2-a) ü Reflectance (R) is changed with Pump ü Compare Reference with Signal to determine the carrier lifetime
• Continuous Wave (CW) Pump-Probe (Figure 2-b) ü Time-resolved pump-probe spectroscopy experiments ü To determine the interband recombination lifetime ü Can measure longer lifetime than traditional system
Figure 2-b
Probe Pump
Chirped Pulse Amplification Ti:Sapphire 1kHz
Optical Parametric Amplifier
Sample
CW
Beam Splitter
Reference
Photodiode
Signal
Ref
Oscilloscope
Figure 3-a
Purpose
24 Å GaSb 22 Å InAs …
Reference (Without Pump) Signal (With Pump) Pump (R+ΔR)I0 I0
t 0 τ
1
ΔR/R
1/e
exp(-t/τ）
Sample
I0 RI0
τ : carrier lifetime 1.2
1.0
0.8
0.6
0.4
0.2
0.0
DR
/R (
10-3
)
43210
Time (µs)
0.20.10.0
Trig
ger (
V)
t 1 =87.5 nst 2 =11.0 µs
Sample
Probe Probe
ü The average time of minority carriers’ recombination ü Defined by time constant
3x10-2
2
1
0
-1
-2
-3
R/R
(%)
2.52.01.51.00.50.0-0.5
Time (µs)
• Traditional pump-probe result(Figure 3-a) ü Very slow decay component exceeds 8 ns
• CW Pump-Probe result (Figure 3-b) ü Compare the previous research with this experiment ü There is more noise in this experiment
Figure 3-b
• Previous research ü Carrier lifetime is 87.5 ns ü t2 is very long time, but this identity is unknown
• This experiment ü Carrier lifetime is indecisive
Too noisy to determine a carrier lifetime
The signal is very low
Need a correct laser power and radius
• The cause of this result ü The energy density of Pump laser is too low ü There are something wrong between pump radius and probe radius
• Determine more precisely ultra-long carrier lifetime measurement with correct laser’s condition
arXiv:1106.0838
Contact Author: [email protected]
