DEVELOPMENTS IN THE BULK GROWTH OF CD1-XZNXTE FOR SUBSTRATES

Single crystals of CdTe or dilute alloys of Cd1-yZnyTe (Y < 0.04) and CdTe1-2Sez (z < 0.04) with low defect density, high purity, and large single-crystal area (>30 cm2) are required as substrates for high-quality epitaxial Hg1-xCdxTe thin films in the infrared (IR) detector industry. Bridgman or gradient freeze is the most common technique used for commercial production of these materials because of its success in producing large-area substrates of good quality and reproducibility. For epitaxial growth of Hg1-xZnxTe, which has been of considerable interest in recent years as an IR detector material, the substrate of choice has been Cd0.80Zn0.20Te, for lattice matching with long-wavelength Hg1-xZnxTe epitaxial layers (x = 0.15). The primary focus of this paper is on CdZnTe, which is currently the preferred substrate material and most widely used for both HgCdTe and HgZnTe epitaxy. This paper reviews the current status of bulk substrate technology for IR detector applications, highlighting critical issues and essential research areas for further improvement of these materials.