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

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

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

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

Schottky Detectors

Blocked Impurity Barrier (BIB ) Detectors

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)

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)

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)

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

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

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

Band Diagram of Si

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

Hydrogenic Model

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.

IVT Measurements BLIP temperature is 25 K at ± 0.9 V

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

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.

Thanks…