Heteroepitaxial growth of n-type CdSe on GaAs(0 0 1) by pulsed laser deposition: Studies of film-substrate interdiffusion and indium diffusion

Epitaxial CdSe films were grown on (0 0 1)-oriented and 2°-miscut GaAs wafers at platen temperatures (T_p) of 250-425°C by ArF (193 nm) pulsed excimer laser ablation of a stoichiometric CdSe target in vacuum and low-pressure Ar gas. The substrates were bonded to the platen with indium solder or silver paint. Auger electron spectroscopy (AES) combined with ion sputtering and energy dispersive X-ray fluorescent spectroscopy were employed to investigate film-substrate interdiffusion, the presence of indium or silver in the films, and CdSe film stoichiometry, all as functions of the film-growth conditions. Extensive interdiffusion took place at the film-substrate interface for CdSe films grown at T_p ≥ 355°C but was greatly reduced at T_p = 250°C. Tilting the substrate to be approximately parallel to the ablation plume as well as increasing the ambient gas pressure also reduced film-substrate interdiffusion. Indium was found in films deposited at T_p ≥ 355°C while no In was detected in films deposited at T_p = 250°C. AES depth profiling showed that the In concentration was highest at the CdSe film surface and that the Cd concentration varied inversely with the In concentration. At higher In concentrations the Se concentration also varied inversely with the In concentration in the near-surface region, implying that In clusters or interstitials may exist in addition to substitutional indium. In the absence of indium diffusion the CdSe films were nearly stoichiometric. No silver was found in any film.