Epitaxial lead chalcogenide IR sensors on Si for 3-5 and 8-12μm

Abstract

Epitaxial IV-VI lead chalcogenide layers are grown on Si substrates with the aid of MBE-deposited stacked BaF2-CaF2 buffer films. The epitaxial buffer helps to overcome the large lattice and thermal expansion mismatch between IV-VIs and Si. Linear arrays of photovoltaic IR sensors fabricated in these layers cover cut-off wavelengths ranging from 3 mu m (PbS and Pb1-xEuxSe). The temperature coefficient of the band gap (cut-off wavelengths of the sensors) of PbSnSe-on-Si is smaller than in the bulk. This is explained by residual mechanical strain in the layers at cryogenic temperatures, while most of the strain due to the thermal expansion mismatch is relaxed at room temperature.