Determination of thickness and composition of thin Al{sub x}Ga{sub 1-x}As layers on GaAs by total electron yield (TEY)

Abstract

The measurement of the total electron yield (TEY) emitted from a solid specimen when irradiated by monochromatic x-rays is used for quantitative information on the specimen. For this purpose one has to determine the increase of TEY in the course of a variation of the photon energy from below to above the absorption edges of the specimen elements. These increases are the analytical quantities and are correlated with the composition of the specimen. The detected electrons are photo, Auger and secondary electrons. Most of them lost some of their original kinetic energy due to inelastic collisions along their path from the atom of origin to the surface. Low energy electrons are especially found in the secondary electron peak with electron energies of less than 20eV. Electrically nonconductive specimens under x-irradiation tend to positive surface charging. Thus, the relatively high flux of secondary electrons is more or less rejected by the grounded electron detector entrance. The amount of rejected secondary electrons depends on the charging potential. In order to avoid this charging dependent contribution to the TEY-increase the electron detector entrance is set to a negative bias and prevents generally low energy electrons from detection. It is the aim of themore » present investigations to extend the field of application of TEY from quantitative analysis of bulk specimens to thin films and to compare the results obtained by TEY with results from x-ray fluorescence analysis (XRF), electron probe micro analysis (EPMA) and x-ray photoelectron spectrometry (XPS). This comparison allows to demonstrate the application of TEY. For verification of the theoretical considerations, Al{sub x}Ga{sub 1-x}As layers on GaAs have been chosen. Values of layer thicknesses were in the range from 20 to 120 nm. An essential feature of TEY for this specific application is the escape depth of the electrons of approximately 100nm. 7 refs., 9 figs., 5 tabs.« less