NEW DEVELOPMENT ON THE CONTROL OF HOMOEPITAXIAL AND HETEROEPITAXIAL GROWTH OF CDTE AND HGCDTE BY MBE

It is reported that rotation twins as well as reflection twins are easily formed in CdTe and HgCdTe grown by MBE in the (111) orientation. Twinning can be avoided by carefully controlling the substrate preparation and by applying very stringent growth conditions, mostly for the stability of Hg pressure and the real surface temperature of the substrate, which is extremely difficult to control when the substrate rotates. A comparison between HgCdTe twinned layers and twin-free layers has shown that electrically active acceptors and high hole mobility are associated with the presence of reflection twins and/or mercury-rich alloy zones due to Hg overpressure during the growth. Twin-free HgCdTe layers can exhibit etch pit density count two orders of magnitude lower than twinned layers. Twin-free CdTe layers have been grown on GaAs and Si substrates. Excellent thickness uniformities have been reported: 0.24% for the standard deviation of a 2-inch diameter CdTe layer grown on GaAs(100) and 2.3% for a 5-inch diameter CdTe grown on Si(100).