Auger lineshape analysis of semiconductors and transition-metal oxides

Ganesh Narayan Raikar

This work deals with the experimental investigation of the surfaces of some of the technologically important semiconductors such as a-Si:H, InP, Zn3P2, CdS and FeS2, and transition-metal oxides such as Fe2O3, CO3O4, NiO and CuO, using Auger lineshape analysis (ALA) with a view to assessing its suitability to extract the local density of states (LDOS) information. In addition, ALA has also been used as a probe of the local chemical environment. Chemical bonding effects are reflected in both the shape and intensity of the Auger peaks. The Auger process samples only the occupied DOS and the CVV lineshapes should reflect a fold of the ground state DOS when hole-hole interaction and other complicating effects are small. Although other spectroscopic techniques such as Xray photo-electron spectroscopy (XPS) and electron energy loss spectroscopy (EELS) (also called core loss spectroscopy (CLS)) have been occasionally utilised in this work, the primary emphasis is placed on ALA. The van Cittert iterative deconvolution technique has been used to recover the intrinsic Auger lineshape from the experimental data. This technique has been extensively tested on both the synthetic data as well as real data from copper and aluminium and the results are in good agreement with the published literature. Interpretation of the deconvoluted data has been in terms of one electron theoretical DOS and/or the data from XPS and SXE (soft X-ray emission). In addition, the Cini-Sawatzky theory has also been used via the effective hole-hole interaction, Ueff' to distinguish between "bandlike" and "quasiatomic" like Auger lineshapes. Oxygen chemisorption is studied on InP, Zn3P2 and FeS2 and substantial changes are observed in the CVV Auger lineshapes. These changes are related to changes in the chemical environment of the surface atoms and associated changes in the valence band DOS. The new peaks that arise on the low kinetic energy side of the P L2,3VV Auger line in InP and ZnsP2 are accounted for in terms of both the interatomic and the molecular orbital (MO) transitions. The splitting of Fe M2, 3VV Auger line in FeS2 upon chemisorption has been explained in terms of the "autoionisation" process. The valence band density of states (VBDOS) of InP and ZnsP2 has also been studied using XPS. Some of the discrepancies in the previous interpretation of the XPS data of ZnsP2 have been addressed. The main objectives of extracting local density of states and chemical information have been fulfilled to a great extent. Many of the surfaces studied in this work have not been analysed in this way previously. The main conclusion of this work is that ALA can be used successfully on a broad range of semiconductor materials to obtain band structural and chemical information.

Auger lineshape analysis of semiconductors and transition-metal oxides

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