LPE HgCdTe on sapphire status and advancements

Abstract

With the evolution of infrared arrays to over four million pixels, larger formats have demanded higher quality mercury cadmium telluride (MCT) wafers. Since single defects can easily degrade multiple diodes, high operability requires very homogeneous and nearly flawless epitaxial surfaces. Subsequent photolithography and hybridization also demand unprecedented levels of substrate flatness and low imperfections. To consistently and reliably produce large area arrays, Insaco Inc., The Boeing Company, and Rockwell International Corporation have developed major quality improvement procedures which address all three components of the infrared material wafer architecture. Centered on the producible alternative to cadmium telluride for epitaxy (PACE) process, technological advancements encompassed sapphire substrates, organometallic vapor phase epitaxy (OMVPE), cadmium telluride (CdTe) buffer layer growth, and liquid phase epitaxial (LPE) mercury cadmium telluride growth. Processed material from these runs mated to Conexant™ fabricated multiplexers have successfully produced 1024 1024 and the first 2048 2048 IR short-wave (2.5 m at 80 K) hybrid focal plane arrays. Operabilities in these implanted n-on-p junction devices reach 99.98% with near 70% quantum efficiency in the astronomy ‘K’ band (2.2–2.4 microns).