Contamination of CdS heteroepitaxial layers during vapour growth on GaAs substrates

Heteroepitaxial growth of CdS on semi-insulating GaAs substrates has been studied, using the (H 2 -CdS) vapour growth technique. High mobility single crystal layers were prepared on (111) A GaAs surfaces, with 1 to 15 μm thickness and 710-550 °C deposition temperature range. An investigation was made of the electrical properties of the layers. Mobilities up to 200 cm 2 /V-sec and 10 18 cm -3 typical carrier concentration were obtained at 700 °C. For low temperature deposit (550 °C) carrier concentration is lowered at 3 × 10 16 cm -3 with carrier mobilities in the 40 to 100 cm 2 /V-sec range. Relations between growth conditions and electrical characteristics of the CdS layers are analysed in terms of contamination by the substrate. A redistribution model of gallium and arsenic by the vapour phase during the growth is proposed and based on correlatives results given by ionic analysis, resistivity, and Hall effect measurements. Gallium and arsenic profiles were recorded at the heteroepitaxial interface and in the CdS layer. The role of a chemical reaction including substrate reactivity and formation of the gallium sulfide is suggested to explain these results.