The evaluation of germanium surface treatments

Abstract

Studies have been made of the variations of electrical surface properties with surface treatment. The variables measured are the field effect mobility and the surface recombination velocity. A report is presented of the results with various etch systems, the influence of contamination in the etch or rinse water (some contaminants are found seriously to alter the characteristics with as low as 0.5 p.p.m.) and the variation of surface properties during heat treatment. A method has been developed for rapid estimation of surface barrier, density of fast states and reproducibility of the surface (with the large number of variables associated with surface treatments, rapidity in accumulation and interpretation of data is essential). These parameters (surface barrier, etc.) are obtained from the measurements discussed above and a set of calibration curves developed for the purpose. The method requires the energy levels of the fast states to be independent of surface treatment (or another set of calibration curves be developed for the new set of energies) but is self-checking with respect to this energy level parameter. Of those treatments used to date, the only one which has not been comparable in energy levels produced is the electrolytically etched surface, and a more exact analysis by W allis and W ang( 4) has indicated also that here the energy levels are at considerably different values. The experimental results are interpreted in terms of fast state density and surface barrier using this method. Evidence will be presented that under certain treatments water vapor can change the density of recombination centers.