Photovoltaic Infrared Devices in Epitaxial Narrow Gap Lead Chalcogenides on Silicon Substrates

Abstract

ABSTRACTWe review MBE growth of epitaxial IV-VI layers on Si(111) substrates and fabrication of photovoltaic infrared devices in the layers. Cut-off wavelengths are chemically tailored from 3 µm up to above 12 µm by using PbS, PbTe, Pb1−xEuxSe and Pb1−xSnxSe. An intermediate epitaxial stacked CaF2-BaF2 bilayer of 200 nm thickness serves to overcome the large lattice- and thermal expansion mismatch, and device quality IV-VI layers are obtained with layer thicknesses of only 2–4 µm. The layers are untwinned single crystal, exhibit perfectly smooth surfaces with surface defect concentrations down to 103 cm−2, and x-ray rocking curve line-width of ≈150 arcsec. Despite the large thermal expansion mismatch, the (111)-oriented layers withstand multiple cooling cycles down to 15K without problems.Although our IR-device fabrication technique is far from optimized, the sensitivities of our best photovoltaic sensors are comparable to MCT. IV-VI on Si IR sensors have the potential for a low cost technique of large IR focal plane arrays both for the 3–5 µm and 8–12 µm range because of the easy fabrication procedure and because uniformity problems are much less severe in IV-Vls due to the weaker dependence of the band-gap of Pb1−xSnxSe on composition x compared to MCT.