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 Cd1-xHgxTe. Sensor arrays are fabricated in 2-4 mu m thick PbTe, PbS1-xSex and Pb1-xEuxSe for 3-5 mu m and in Pb1-xSnxSe 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 approximately=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.