X-RAY PHOTOELECTRON SPECTROSCOPIC CORE-LEVEL SHIFTS OF PHOSPHORUS IN PHOSPHATES AND NATIVE OXIDE LAYERS ON INP(100) - APPLICATIONS OF THE AUGER PARAMETER CONCEPT

Solid phosphorus compounds have been investigated by X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy. The core level shifts have been separated into initial and final state shifts by employing the Auger parameter concept. Although strong chemical trends in general dictated the shifts, the significant differences between compounds with fourfold oxygen coordination could essentially be attributed to environmental effects. We have been able to demonstrate that the extra-atomic or environmental contributions to the shifts of relaxation and initial state terms may be semiquantitatively estimated by dielectric screening and the Madelung potential models, respectively. The investigations were extended to native oxide layers on InP(100). The chemical state plots have been found to provide information on the nature of the layers beyond a conventional XPS analysis. In a similar way to that for bulk samples, the initial state-related shift contributions indicate the condensation of phosphates in the layers, and the Auger parameter shifts are sensitive to the composition of the layers and to substrate screening.