1. High Operating Temperature Split-off Band IR Detectors
Viraj Jayaweera
Department of Physics and Astronomy
Georgia State University

2. Outline Types of IR Detectors
Difference Between Mechanisms of Other types of detectors and Split-off Detector
Detector Structure and Experimental Results
Advantages for the Split-off detectors
Conclusion

3. Types of Infrared Detectors
IR Detectors
Photon Detectors
Thermal Detectors
Pyroelectric Detectors
Bolometer
Thermopile
Photo Conductive
Photovoltaic
QWIP (Quantum Well Infrared Photodetectors)
DWELL (Quantum Dots-in-a-Well Infrared Photodetectors)
T-QDIP (Tunneling Quantum Dot Infrared Photodetectors)
HIWIP (Homojunction Interfacial Workfunction Internal Photoemission)
HEIWIP (Heterojunction Interfacial Workfunction Internal Photoemission)

4. Detector Mechanisms Intrinsic (InSb, HgCdTe) Quantum Well
Conduction Band E
Conduction Band E k k
ESO
Heavy Hole Band
Light Hole Band
Heavy Hole Band
Light Hole Band
Split-off Band
Split-off Band
Intrinsic (InSb, HgCdTe)
Quantum Well

5. Split-off Mechanism
IR Photon excites holes from the light/heavy hole bands to the split-off band (Solid Arrow)
Excited holes may escape in split-off band or,
May scatter into the light/heavy hole bands and then escape
(Dashed Arrow)
Conduction Band E
Transition is entirely in hole bands
Carrier energies are continuous not quantized
Split-off response is inherently broadband k Ef
ΔL/H
Heavy Hole Band
Light Hole Band
ΔSO
Split-off Band

6. Response Mechanism I E
escape
Free Carrier Absorption
Light/Heavy Hole Band
Split-off Band k EF
ΔL/H
Heavy Hole Band
Light Hole Band
ΔSO
Split-off Band
The photoexcitation process consists of the standard
free carrier absorption.

7. Response Mechanism II
Light/Heavy Hole Band E k EF
ΔL/H
Split-off Absorption
Heavy Hole Band
Light Hole Band
scattering
ΔSO
Split-off Band
Split-off Band
direct photoabsorption to the split-off band, followed by a scattering to the light/heavy hole band.

8. Response Mechanism III
Light/Heavy Hole Band E k Ef
ΔL/H
Split-off Absorption
Heavy Hole Band
Light Hole Band
ΔSO
Split-off Band
Split-off Band
escape
Single indirect photoabsorption into the split-off band.

9. Response Mechanism IV
Light/Heavy Hole Band E k Ef
ΔL/H
Split-off Absorption
Heavy Hole Band
escape
Light Hole Band
scattering
ΔSO
Split-off Band
Split-off Band
indirect photoabsorption, followed by a scattering event to the light or heavy hole band.

10. Detector Structure (HE0204)i p+ hν Δ
After processing
Substrate
~1000 A
Metal
p GaAs
AlGaAs ++ +
n Periods
Top Contact
Barrier
Emitter

11. Detector Structure (HE0204)
400 μm
Au contact layers
Top Contact p++ GaAs
<2.5μm
~1.5mm
N Periods
GaAs (barrier)
p+ GaAs (emitter)
Homojunction
Heterojunction
AlGaAs (barrier)
p+ GaAs (emitter)
Bottom Contact p++ GaAs
Substrate

12. Absorption (HE0204)
Absorption
Wavelength (mm)

13. Split Off Response (HE0204)
Mechanism III
Mechanism II/IV
Responsivity (A/W)
Wavelength (mm)

14. Quantum Efficiency of Detector “1332”
50K
Reducing threshold to 10 µm should increase operating temperature to ~200 K
Increasing emitter doping should further increase T

15. Advantages h+ h+ h+ Δ Δ ESO ESO ESO Δ Δ Δ
Increased operating Temperature
Use of the split-off band provides increased absorption at short wavelengths
Increased escape due to high carrier energies
Increased gain due to impact ionization from high energy carriers h+ i p+ h+ i p+ h+ i p+ Δ Δ
Dark Current ~e-Δ/kT
ESO
ESO
ESO Δ Δ Δ

16. Advantages Different material will cover different split-off ranges
Antimonides – µm
Arsinides – µm
Phosphides – µm
Nitrides – µm

17. Conclusion SO detector shows improved response
Optimized devices should operate near room temperature for µm detector
Use of other materials will allow tailoring of the response range

18. End

19. Advantages over other 3-5 µm detectors
Arsenides will be used for this range
Have advantage of allowing integrated electronics
Present Detector
Advantage
Proposed Split-off Detector
InSb
77 K
Operating Temperature
300 K
HgCdTe K
~4% Bad Pixels (256x256)
Uniformity
~0.1% Bad Pixels (600x512)
PbSe
Threshold depends on Temperature
Better Stability
Threshold fixed by split-off energy

20. Advantages over other 8-14 µm detectors
Phosphides will be used for this range
Present Detector
Advantage
Proposed Split-off Detector
Quantum Wells
77 K
Narrow Response
Operating Temperature
Response width
200 K
Broadband Response
HgCdTe

21. Advantages over other 30-60 µm detectors
Nitrides will be used for this range
Nitrides are radiation hard, allowing high background operation
Present Detector
Advantage
Proposed Split-off Detector
BIB Detectors
4.2 K
Operating Temperature
77 K
Ge:Ga Extrinsic
Split-off detectors will be much faster than thermal detectors

22. Differences from other approaches
Intrinsic Detectors (InSb, HgCdTe)
Transition is entirely in hole bands
Quantum Wells
Carrier energies are continuous not quantized
SO Response is inherently broadband