Suppression of indium out-diffusion during molecular beam epitaxy growth of CdTe on InSb substrates

While HgCdTe remains the workhorse material for high-performance infrared (IR) detectors, there is still an ever-increasing demand for devices with lower costs and minimal defect densities. Epitaxial HgCdTe is typically grown on either low-cost Si substrates utilizing a CdTe virtual substrate with a large lattice mismatch or high-cost bulk CdZnTe substrates. Although high-quality CdTe epilayers can be successfully grown by molecular beam epitaxy on lattice-matched InSb (100) and (211)B substrates, InSb substrates are not used due to In out-diffusion and contamination concerns. This paper reports a comparison study of the different MBE processes of CdTe growth on InSb substrates. A compound CdTe cell and two individual elemental Cd and Te effusion cells were used under different growth conditions, Cd-rich vs Te-rich. CdTe epilayers grown on InSb under Cd-rich conditions using single elemental Cd and Te cells were shown to be of higher quality with significantly reduced In out-diffusion in regard to the standard CdTe growth process under Te-rich conditions using a compound CdTe cell and a Te cell. High-quality CdTe epilayers were achieved with a high-resolution x-ray diffraction FWHM linewidth of 35 arcsec and In concentrations below 1015 cm−3 determined from secondary ion mass spectrometry. A heavy Cd soak of the InSb surface prior to growth initiation of the CdTe layer may also suppress the out-diffusion of In and the subsequent formation of the In–Te alloy. The increase in CdTe epilayer quality under Cd-rich conditions using elemental Cd and Te cells is found to be consistent for both (100) and (211) orientations.