Properties of HgTe-CdTe superlattices grown on GaAs substrates by molecular beam epitaxy

(100)- and (111)-oriented HgTe-CdTe superlattices were grown on (100)-oriented GaAs by molecular beam epitaxy. Low substrate temperatures (150-1700C) were required to minimize interdiffusion and improve crystal quality. High resolution x-ray step scans of the superlattice diffraction region show narrow, distinct principle and satellite peaks out to sixth order. The intensities and positions of these peaks are theoretically fitted to quantitatively determine superlattice period, HgTe/CdTe layer thickness ratios, strain, and statistical variation in layer thicknesses. Optical absorption spectra were measured as a function of temperature. The highest crystal quality superlattices exhibit sharp absorption edges with positive temperature coefficients in reasonable agreement with theory. Many superlattices exhibit addition higher energy absorption features with temperature dependences similar to the lower energy fundamental absorption edge. The higher energy absorption features are associated with optical transitions involving higher order (n = 2,3) superlattive minibands. These superlattices have high electron mobilities at low temperatures. The effects of doping on the electrical properties will be discussed