Interdiffusion and chemical trapping at InP(110) interfaces with Au, Al, Ni, Cu, and Ti

We have studied UHV-cleaved (110) surfaces of InP covered with a large variety of metal layers and interlayers, using Auger-electron spectroscopy in conjunction with Ar+-ion sputtering. All measurements were made under identical experimental conditions, other than the thickness or type of the metal films, in order to minimize ion-beam-induced distortion of the data. We find that In and especially P are segregated at unreactive metal surfaces such as Au or Cu. Very thin interlayers of "reactive" metals between Au and InP completely reverse the out-diffused distribution of the phosphorus, which is accumulated at the interface due to chemical trapping by the reactive-metal interlayers. Indium out-diffusion is found to be unaffected by these interlayers while Au in-diffusion depends sensitively on the type of metal interlayer. The results are correlated with soft-x-ray photoemission spectroscopy (SXPS) measurements to reveal the diffusant spatial distribution on a microscopic scale while illustrating the relative limitations of the SXPS technique. The contrasting effects of the unreactive versus reactive-metal interfaces are correlated with Schottky-barrier heights and with energy-level calculations of associated surface defects.