STRAIN RELAXATION OF CDTE(100) LAYERS GROWN BY HOT-WALL EPITAXY ON GAAS(100) SUBSTRATES

The strain relaxation of CdTe(100) layers grown on GaAs(100) substrates by hot-wall epitaxy was investigated by measurement of optical properties, x-ray analysis, and transmission electron microscopy. It is considered from transmission electron microscopy observation that relaxation of most of the strain due to lattice mismatch occurred at the interface. However, a small amount of strain, of the order of 10-3, remained in layers thicker than 0.7 μm, and it was relaxed as the layer thickness increased. The residual strain of 4×10-4, which exists in layers thicker than 10 μm, was due to the difference between the thermal expansion coefficients of the layer and the substrate. Moreover, for layers thicker than 17 μm, split ground (n=1) and first excited (n=2) free-exciton states due to internal strain have for the first time been observed by photoluminescence and reflectance spectroscopy. The results show that CdTe layers with excellent crystallinity and homogeneity in strain are obtained.