Matrix dependent Auger peak shifts and the oxidation of GaAs

Abstract

Ranke and Jacobi 1 observed significant shifts in energy (‘somewhat less than 5 eV’) of the Ga LMM core-core Auger transition, and a marked change in peak shape, upon oxidation of GaAs. A variety of oxidized GaAs surfaces (anodic, 3:1:1 etched, UHV oxidised) have been studied by depth profiling and associated techniques, in both 4-grid and CMA Auger spectrometers, to specify these matrix induced effects on the Auger transitions more precisely, and to deduce from them changes in the local chemical environment. The main results of this study are summarised as follows. 1. 1. Under typical modulation conditions required for 4-grid analysis of weak Ga LMM transitions (ie > 10 eV peak to peak) modulation distortion occurs resulting in enhanced shifts up to 5 eV, and peak shape changes similar to those observed by Ranke and Jacobi 1, 1975. 2. 2. In the absence of modulation distortion (<5 eV peak to peak), the Ga LMM peak shifted 2.2 eV to lower kinetic energy upon oxidation of GaAs, whereas the As LMM peak shows zero shift. 3. 3. The arsenic concentration was reduced in the oxide compared with the GaAs, in accord with the results of Ranke and Jacobi 1. The results coupled with recent more extensive observation by Wagner 2, 1975 show that large matrix induced shifts in core-core Auger spectra are not uncommon. The physical basis for this phenomena and its implications for general chemical environment analysis by Auger spectroscopy will be discussed.