Bonding at the CdSe/SiOx (x=0,1,2) interfaces

The chemistry occurring at the CdSe/Si, CdSe/SiO, and CdSe/SiO2 interfaces was investigated by looking at very thin tapered films (0–10 nm) of thermally evaporated CdSe with x-ray photoelectron spectroscopy. The analysis of the attenuation of the x-ray photoelectron signals along the tapered film was used to measure the electron mean free paths in as-deposited CdSe. The electron mean free path was found to increase with the photoelectron energy from 1.5 nm at 720 eV to 2.3 nm at 1200 eV. Our data suggest an island growth mechanism for CdSe on the Si substrate and a more uniform growth on silicon oxide. In the early growth, Se is first adsorbed on the surface creating sites where Cd subsequently adsorbs. Interdiffusion is observed for CdSe on the Si and SiO substrates after a vacuum anneal at 390 °C. The main result of this interdiffusion process is the formation of Si–Se bonds. Similar interdiffusion processes on thermal SiO2 substrates are expected but were too small to be detected.