An experimental and theoretical study of Auger lineshapes in hydrogenated amorphous silicon structures

Abstract

Simple models of hydrogenated amorphous silicon (a-Si : H) consisting of hypothetical silane molecules with diamond or similar lattices were studied by the semi-empirical AMI method. Valence band densities of states (VBDOS) were calculated for the silane molecules with and without the removal of hydrogen atoms. Silicon L 1L 2.3V Auger spectra have also been obtained using X-ray excitation from disordered crystalline silicon (c-Si), and glow discharge produced a-Si : H. Comparisons have been made between the experimental L 1L 1.2V Auger spectra of samples with different amounts of hydrogen on the surface and the corresponding VBDOS calculations. Ignoring differences due to matrix elements, good agreement is obtained between the experimental and theoretical spectra and it is shown how the theoretical curves can help interpret changes in the experimental spectra after various treatments. The results provide confirmation that disordering of c-Si leads to an increase in the number of Si p-like defect states at the top of the VB. Furthermore, it is shown that hydrogenation plays an important role in stabilising defects in a-Si by tying off dangling bonds, removing the Si p-like states at the VB edge. This leads to the establishment of new electron energy levels in the VB, with different methods of hydrogenation leading to different bonding configurations. It is shown how the success of these methods provides the basis for subsequent studies of annealing, hydrogenation and photodegradation of a-Si : H alloys.