1. p- type Si Homojunction Interfacial Workfunction Internal Photoemission Dual-Band Detector Responding in Near- and Far-Infrared Regions
G. Ariyawansa Department of Physics and Astronomy Georgia State University

2. Outline Introduction Types of Junction Detectors
Homojunction Detectors
Heterojunction Detectors
Schottky Detectors
Blocked Impurity Barrier (BIB) Detectors
Si HIWIP Detector Structure
Dual-Band Detection
Impurity Transitions and Hydrogenic Model
IVT Measurements and Arrhenious Calculations
Summary and Future Studies

3. Introduction
Multi-band IR detection is useful in numerous applications such as,
Mine Detection: The use of images in two different spectral bands can aid in the detection and reduce the number of false positives.
Military Applications: The NIR portion could be used to detect the muzzle flash while the FIR portion can be useful for determining troops and operating vehicles.
Remote Sensing: Taking the difference in the spectral information of the signal for the two bands.
Other applications: Environmental Monitoring, Medical Diagnosis, Space Astronomy Applications, Spectroscopy …
Interfacial workfunction detectors:
FIR detector designs
Broad response
Tailarable wavelength threshold
Dual-band detection

4. Types of Junction Detectors
Homojunction Detectors
Heterojunction Detectors
Schottky Detectors
Blocked Impurity Barrier (BIB ) Detectors

5. Schottky Detectors

6. Blocked Impurity Barrier (BIB ) Detectors

7. Three Types of Homojunction Detector Structures
Type I - Nd < Nc ( ECn+ > EF )
Nd : Doping of Emitter Nc : Mott’s critical concentration D h n
Diffusion e
Thermal
Impurity Band C E F
n (Emitter) +
Tunneling
Field i
i (Barrier)
D = (ECn+ - EF) + DEC
JAP 77, 915, (1995)

8. Three Types of Homojunction Detector Structures
Type II - Nc < Nd < N0 ( ECn+ < EF < ECi )
Nd : Doping concentration of the Emitter/ Absorber
Nc : Mott’s critical concentration
N0 : Critical concentration D h n e
Impurity Band C + F
n (Emitter) E
i (Barrier) i
Field E
D = Eci - EF E
Fermi level is above the conduction band edge of the emitter
Emitter becomes metallic
Infrared absorption is due to free carriers
JAP 77, 915, (1995)

9. Three Types of Homojunction Detector Structures
Type III - Nd > N0 ( EF > ECi )
i (n )
Bias F h n e ++ - E
Nd : Doping concentration of
the Emitter/ Absorber
N0 : Critical concentration
Fermi level is above the conduction band edge of the barrier
Conduction band edge of the Emitter and the barrier become degenerate
Space charge region at the n++ - i interface forms the barrier
Barrier height depends on the concentration and the applied field
JAP 77, 915, (1995)

10. Si HIWIP- Detector Structure
Doping
Ntc = 1.5 X 1019 cm-3
Ne = 3 X 1018 cm-3
Nb = 1 X 1010 cm-3
Nbc = 1.5 X 1019 cm-3

11. Dual-Band Detection
NIR response : Interband transitions in the Si barrier
FIR response : Intraband transitions in the structure

12. Near-IR Response
E2TO, E1TO : Phonon assisted exciton transitions at the bang edge.

13. Band Diagram of Si

14. Near-/Far- IR Dual Band Response @ 5.3 K
The NIR photons are absorbed in the barrier giving rise to a transition of carriers (electron-hole pair) between conduction and valence band of the GaAs barrier.
Incident MIR/FIR photons undergo free carrier absorption in the emitter.
Threshold wavelength varies with the applied bias

15. Hydrogenic Model

16. Near-/Far- IR Dual Band Response @ 30 K
Labeled peaks are related to impurity transitions of Boron in Si.
Numbers assigned are in meV and numbers in parenthesis are reported values.
The strength of the peak increases with the bias and the temperature.

17. IVT Measurements
BLIP temperature is 25 K at ± 0.9 V

18. Arrhenious Calculations
Arrhenious calculations are not valid out of the bias range from ~ -0.5V to 0.5V
This results consistent with spectral results.

19. Conclusion and Future Studies
A single emitter Si HIWIP dual-band detector can detect NIR and MIR/FIR radiation.
Interband transitions in Si lead to NIR response while FIR response is due to intraband transitions in the structure.
High performance of the detector demonstrate the potential applications where the detection in both NIR and FIR are important.
Future Studies >>>>
Developing a dual band detector covering UV and FIR regions.
Band tuning based on operational conditions.

20. Thanks…