MBE Growth of PbSe/CaF_2/Si(111) Heterostructures

Despite the large thermal expansion mismatch between PbSe and silicon high quality epitaxial layers of PbSe can be grown on (111)-oriented silicon substrates when fluoride buffer layers are used. Such heteroepitaxial growth offers a number of benefits that can lead to fabrication of improved infrared sensor arrays. In this work, we show that high quality PbSe/CaF_2/Si(111) heterostructures can be grown using just one growth chamber of a molecular beam epitaxy system. The PbSe epilayers show mobilities as high as 23,200 cm^2V^-1s^-1 and electron concentrations of 1- 2x10^17 cm^-3 at 77 K. P-type layers were obtained by controlling selenium vacancy concentrations using a selenium flux provided by an EPI valved-cracker source. In addition, we present reflection high- energy electron diffraction intensity oscillation data that confirm layer-by-layer growth modes for both CaF₂ and PbSe. We also present x-ray photoelectron spectroscopy data which show that the PbSe/CaF₂ interface consists of a thin transition layer dominated by Pb-F and Ca-Se bonds.