PHOTOVOLTAIC INFRARED-SENSOR ARRAYS IN MONOLITHIC LEAD CHALCOGENIDES ON SILICON

MBE growth of epitaxial IV-VI lead salt layers on Si (111) substrates and fabrication of photovoltaic infrared devices in the layers is reviewed. IV-VI on Si IR sensors have potential as a low-cost technique of fabrication of large IR focal plane arrays for both the 3-5-mu-m and 8-12-mu-m ranges because of the easy fabrication procedure and because uniformity problems are much less severe in IV-VIs due to the weaker composition dependence of the bandgap compared with Cd(1-x)Hg(x)Te. Sensor arrays are fabricated i n 2-4-mu-m thick PbTe, PbS(1-x)Se(x) and Pb(1-x)Eu(x)Se for 3-5-mu-m and in Pb(1-x)Sn(x)Se for 8-12-mu-m cut-off. An intermediate epitaxial stacked 0.2-mu-m thick CaF2-BaF2 bilayer serves for compatibility and helps to overcome the large lattice and thermal expansion mismatch between the Si substrate and the IV-VI layer. Perfectly smooth surfaces with surface defect concentrations down to 103 cm-2, and x-ray rocking-curve linewidth of almost-equal-to 150 arcsec are obtained. Sensor arrays with 66 and 256 elements are described, the latter having been grown on standard Si chips with Al metallization.