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Advances in Photodiodes 428At the same time these PDs are characterized by rather low values of the differential resistance -area product R 0 A at room temperature. This seems to be the main reason that InAs infrared photodetectors operate in sub-BLIP regime (Rogalsky, 1995). Further improvement in their performance is possible with a decrease in dark current and supression of Auger recombination. Preparation of photodiodes and experimental techniquesHomojunction PDs were prepared by short-term (20-30 min) diffusion of Cd into n-InAs substrates at T=875 K. The substrates of n-type conductivity were cut from single-crystal ingots grown in joint-stock company "Pure metals plant" (Svetlovodsk, Ukraine). The damaged surface layers were removed by using dynamic chemical-mechanical polishing in 2% Br 2 -CH 3 OH solution. Their structural quality was controlled by X-ray diffraction method. In the chemically polished substrates the rocking curves half-width was 25-27 '' . Electrical parameters were controlled by van der Pauw technique at 295 K. The carrier concentration and mobility were found to be n=(2÷3)×10 16 cm -3 and µ n =(2÷2.5)×10 4 cm 2 /V×s, respectively. The density of dislocations was in the range (2÷4)×10 4 cm 2 . The substrates with the diffused p-type layer had mirror-like surfaces free of structural damages such as inclusions of impurity atoms. They were characterized by the rocking curve halfwidth of 32-35 '' . Typical profiles of Cd atoms in a substrate are shown in Fig.1. As seen, at low values of depth x they can be approximated by two exponential dependences (shown by solid lines in Fig. 1). Similar profiles of impurity atoms were previously observed in GaAs (Grigor'ev & Kudykina, 1997) and explained by generation of non-equilibrium vacancies at the substrate's surface. In such a case, an impyrity profile is determined by distribution of vacancies under the surface. The junction depth was determined from the probe thermo-emf measurements during careful chemical etching of diffused layers. Mesa structures were prepared on (111)A side of substrates by chemical etching in 2% Br 2 -HBr solution. In order to eleiminate the surface leakage current mesas were passivated by etching in HNO 3 -based solution followed by deposition of anode oxide doped with fluorine with thickness of 0.3 m. After passivation they were covered by thin layer of ZnTe thermally deposited in a vacuum chamber at temperature 150 o C. The heterojunction p + -InAsSbP/n-InAs PDs were prepared by LPE technique in IOFFE Physico-Technical Institute, St.-Petersbur Russia (Zotova, 1991;Matveev, 1997;Matveev, 2002). For this purpose, lattice matched InAsSbP epitaxial layers of approximately 3 μm thickness were grown on (111)B surfaces of InAs substrates. The quaternary InAsSbP compound had energy gap of 0.43 eV at T = 297 K. The epilayers were doped to about 10 18 cm -3 by addition of Zn to the melt. The substrates were n-type single crystals with electron concentration n=(2÷3)×10 16 cm -3 . In homojunction and heterojunction PDs mesa struc...

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Native defects in HgCdTe, including dislocations and defect complexes, can act as Shockley-Read-Hall (SRH) centers due to their effect on the carrier lifetime. There is a large literature concerning the links of deep defects to the carrier lifetime in