Heteroepitaxial PbTe-on-Si pn-junction IR-sensors: correlations between material and device properties

Abstract

Epitaxial IV–VI narrow band gap semiconductors on Si(1 1 1) substrates exhibit high structural quality despite the large lattice and thermal expansion mismatch. Test arrays with photovoltaic n +–p PbTe infrared sensors (cut-off wavelength 5.5 μm at 80 K ) of different sizes were fabricated and analyzed. The sensitivities are generation–recombination (g–r)-limited in the 90– 200 K range. The g–r carrier lifetimes in the depletion region are determined from the R 0 A-products (inverse noise current densities). The corresponding carrier diffusion lengths are correlated with the material properties, namely low-temperature saturation Hall mobilities and X-ray rocking curve line widths. It turns out that all these parameters are determined by the density of the threading dislocations, and each dislocation crossing the active area gives rise to a shunt resistance. At lower temperatures, the R 0 A-products saturate and the ideality factors increase above a value of 2. This behaviour suggests that, as in the case of Schottky barriers of metal–semiconductor junctions of IV–VIs, fluctuations of the built-in electric field occur near the dislocation cores which cross the active areas of the devices.