Photovoltaic IV-VI on silicon infrared devices for thermal imaging applications

Narrow gap IV-VI (e.g. Pb(1-x)Sn(x)Se and PbTe) layers grown epitaxially on Si(lll)-substrates by MBE exhibit high quality despite the large lattice and thermal expansion mismatch. A CaF(2), buffer layer is employed for compatibility. Due to easy glide of misfit dislocations in the IV-VI layers, thermal strains relax even at cryogenic temperatures and after many temperature cyclings. The high permittivities of the IV-Vis effectively shield the electric fields from charged defects. This makes the materials rather forgiving higher quality devices are obtained from lower quality material. We review the state of the development and describe ways to further improve device performance by lowering the dislocation densities in the lattice mismatched layers. This is achieved by temperature rampings, which drive out the threading dislocations from the active parts of the sensors. Presently densities of 1 x 10(6) cm(-2) in layers of a few micrometer thickness are obtained. These densities are sufficiently low in order not to dominate the leakage currents in real devices even at 80K temperature. Due to the rather low temperatures used during the MBE and delineation (below 450 degrees C), sensor arrays rue obtained by postprocessing even on active Si-substrates. We describe the development stage of a 96 x 128 array with 75 un pitch on a Si substrate containing active read-out circuits.