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Dark current mechanisms and passivation of InAsSb infrared photodiodes on alternative substrates

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2005
Ersagun, Özlem
This thesis reports a detailed characterization of indium arsenide antimonide (InAs1- xSbx) photodetectors grown on gallium arsenide (GaAs) substrate by molecular beam epitaxy. A combination of polyimide and sulphur and a single layer of polyimide were used as passivation films in this study. Two different epilayer structures were used for assessing the detector performance and comparing the above passivation layers. For the first structure, the optical measurements revealed that Sb mole fraction was 0.13 and the cut-off wavelength was around 4.1 æm at 80 K. The Sb mole fraction of the second structure was 0.2, and the 77 K cut-off wavelength was 4.8 æm. Detailed electrical and optical characterizations were performed on 33x33 æm2 test diodes. The photodiodes yielded peak detectivities of ~3.65x1010 and ~1.22x1010 cmHz1/2/W at 80 K for the first and second structures, respectively. Considerable 1/f noise current related with trap-assisted tunneling mechanism was observed in both structures at 80 K. Dark current modeling study showed that the dark current was dominated by the shunt and trap-assisted tunneling mechanisms throughout the entire reverse bias voltages for both detectors. The dark current analysis of variable area detectors fabricated with both epilayer structures revealed that the reverse bias current was mainly generated by the surface leakage in small sized (33x33 æm2) detectors for both passivation layers. However, the surface current contribution was observed to be lower for the double layer (polyimide and sulphur) passivated detectors suggesting that it is a better passivation technique.