GaP/Si(001) interface study by XPS in combination with Ar gas cluster ion beam sputtering

The study of the chemical composition of buried interfaces by X-ray photoelectron spectroscopy (XPS) is limited by the inelastic mean free path of emitted photoelectrons (PE). Soft X-ray sources (AlKa) are generally suitable for careful probing of surfaces or very thin films. Here we applied gas cluster ion beam sputtering in combination with in-situ XPS (GCIB-XPS) to analyze buried GaP/Si(0 0 1) heterointerfaces. The GCIB method was used to dig a crater into the 20 nm thick GaP(0 0 1) film. We found optimal parameters for GCIB sputtering and achieved interface layers without severe damage. Destructive effects, i.e. broadening of core level peaks, could not be completely avoided, however, and the formation of metallic Ga on the GaP surface was observed. PE spectra of the sputtered heterostructures were compared with corresponding reference spectra of sputtered bulk crystals. Interface contributions to the intensity of phosphorus and sillicon core level peaks were revealed: interface components are shifted to high binding energies of P 2p Si 2p core levels. Similar results were obtained on 4 nm thick GaP/Si(0 0 1) by XPS. Finally, a top-to-bottom concept for buried semiconductor interfaces studies by GCIB-XPS is demonstrated.