PHOTOVOLTAIC LEAD-CHALCOGENIDE ON SILICON INFRARED-SENSOR ARRAYS

MBE growth and infrared device fabrication with epitaxial IV-VI layers on Si substrates are reviewed. Epitaxy on Si substrates is achieved u sing a stacked BaF2/CaF2 or CaF2 buffer layer. With buffers containing no BaF2, standard photolithographic delineation with wet-etching tech niques can be used. Photovoltaic IV-VI sensors with cutoff wavelengths ranging from 3 to 14 mum are fabricated in PbS, PbSe1-xSx, PbEu1-xSex , PbTe, or Pb1-xSnSe layers on Si (111) substrates. They offer the pos sibility for low-cost infrared focal plane arrays with sensitivities s imilar to Hg1-xCdxTe, but with much less demanding material processing steps. A 13-mm-long linear array with 10.5-mum cutoff wavelength has inhomogeneities in cutoff below 0.1 mum. Some arrays were grown on pre fabricated active Si substrates containing the whole readout circuits. First thermal images using these chips are demonstrated. The induced mechanical strain resulting from the different thermal expansion of IV -VIs and Si relaxes down to cryogenic temperatures even after many tem perature cycles because of dislocation glide in the main {100} glide p lanes.