MBE Growth of CuInSe2 on CdS: Initial Stages

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Abstract
Realization of the potentially high solar conversion efficiencies of CuInSe2/CdS heterojunctions has been hindered by a lack of knowledge and control of stoichiometry as well as cadmium diffusion in the CuInSe2 layer. In an attempt to understand these effects, we have used in situ Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) to study the early growth stages of CuInSe2 onto (0001B) CdS (T sub=300°C) using molecular beam epitaxy (MBE). We find that 25Å thick CuInSe2 layers show bulk-like AES and EELS spectra, although several atomic percent cadmium is always present on the surface. The energy loss peaks (12.0±0.5 eV and 21.5±0.5 eV) have widths of about 5–6 eV compared to about 3 eV for CdS loss peaks (instrument limited). In order to produce layers with no detectable cadmium at the surface, the CuInSe2 must be several hundred Ångstroms thick. The metallurgical junction formed at T sub=300°C is no wider than 10–20 Å, while the junction formed at T sub=400°C is about 40–50 Å wide.

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