Analysis of Faceted Growth Hillocks in MOCVD Grown Epitaxial HgCdTe on GaAs with a Nuclear Microprobe

Abstract

Hg_1−xCd_xTe epitaxial layers on GaAs substrates grown by Metal Organic Chemical Vapour Deposition (MOCVD) display growth defects resembling pyramidal faceted hillocks which appear to originate from defects originally present on the substrate. For <100> oriented GaAs substrates and normal growth conditions, these growth defects have an areal density of 1–1000 mm^-2. The size of the hillocks depends on the layer thickness and they have the potential to degrade performance of optoelectronic devices fabricated in the epitaxial layers. Nuclear microprobe analysis, performed with a 2 MeV He⁺ beam focused to less than 5 μm in diameter, has allowed the hillocks to be imaged with the technique of Channeling Contrast Microscopy (CCM). Channeling spectra, obtained by Rutherford Backseat tering Spectrometry (RBS) of the hillocks themselves, showed that the χ_min was 13 %. This was similar to the χ_min of the high quality single crystal surrounding material. The CCM images also revealed extensive regions of poor channeling, with shapes that suggested that the regions originally arose from scratches in the substrate. These poor channeling regions were not readily observable by other techniques.