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

Catalyzed epoxy systems have been studied consisting of an ED 20 epoxy diane oligomer ED 20, a curing catalyst (dicyandiamide (DCDA)), and an accelerator (an asymmetric urea based on toluene diiso cyanate). The chemical composition and structure of the catalyzed epoxy systems have been established by IR and NMR spectroscopy in the initial and cured states. The influence of the composition of the complex catalyst system of curing on the mechanisms of chemical transformation of epoxy system has been consid ered. It is shown that the products of interaction of epoxydiane oligomers with DCDA in the presence of the accelerator-asymmetric urea of Dyhard UR500 brand-is a complex system consisting of chains of poly esters produced by a chain growth mechanism and amine sites, as well as interaction products of epoxy groups with imines, isocyanates, and hydroxyl groups with nitriles.

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