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8 April 1999 Carrier transport mechanisms in narrow-gap photodiodes
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Carrier transport mechanisms in photodiodes from narrow-gap HgCdTe and PbSnTe semiconductors for long wavelength infra- red and medium wavelength infra-red applications are discussed in connection with their use in hybrid multielement arrays for T approximately equals 77 - 150 K temperature range. It is shown that the bulk diffusion and thermal generation-recombination (GR) currents in depletion region determine carrier transport mechanisms in these photodiodes at zero bias. The transport mechanisms are changed for reverse-biased voltages at which diodes are operating with silicon read-out devices in hybrid arrays. In this case the dark current is determined not only by the GR recombination (Schockley-Read-Hall (SRH) recombination) via the centers in the gap, but preferentially by two non-thermal mechanisms: (1) interband tunneling via the traps in the gap, and (2) direct band-to-band tunneling. The last one is important only at rather high electron concentrations n >= 1016 cm-3 or n >= 2(DOT)1018 cm-3 in HgCdTe and PbSnTe photodiodes, respectively and at large reverse-bias (V >= 0.2 V) voltages. The parameters of the traps (density of states, energy level position, capture cross section) have been estimated from the fit of calculated transport characteristics to the measured dependences on bias and temperature in the photodiodes of both investigated compounds. One level of traps in the gap for SRH recombination and trap-assisted tunneling mechanisms were used in fitting procedure. The best fit was obtained for the model in which the level of the traps was near the middle or slightly shifted from the middle of the gap towards the conduction band edge.
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Fiodor F. Sizov, Joanna V. Gumenjuk-Sichevskaya, and Vladimir V. Tetyorkin "Carrier transport mechanisms in narrow-gap photodiodes", Proc. SPIE 3725, International Conference on Solid State Crystals '98: Epilayers and Heterostructures in Optoelectronics and Semiconductor Technology, (8 April 1999);

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