TEM investigation of defects in arsenic doped layers grown in-situ by MBE

Abstract

A study concerning the effect of growth condition on As incorporation and formation of defects using transmission electron microscopy (TEM) is presented. It is well known that devices in a narrow bandgap HgCdTe material system could suffer from tunneling currents and generation recombination processes, especially at cryogenic temperatures, due to material defects. For in-situ As doped p-on-n device structures grown by molecular beam epitaxy (MBE), extended defects and in particular twinning in a p-type layer grown under Hg-rich conditions is believed to reduce the zero bias dynamic impedance of devices and significantly impact recombination of carriers in the space charge region. Using TEM we have studied defects formed in As-doped layers grown under Hg- and Te-rich conditions. Samples grown under high II/VI flux ratio at growth temperature of 170 C have a high density of columnar twin defects, whereas no twin defects were seen for layers grown under optimal growth conditions at 190 C. A very high flux of As, however, was required to incorporate As into the layers at growth temperature of 190 C.