Distribution and Cross-Sections of Fast States on Germanium Surfaces

The existence of traps, or "fast" states, on a semiconductor surface, becomes apparent from three physical experiments: measurements of field effect, of surface photovoltage, and of surface recombination velocity s. Results of combined measurements of these three quantities on etched surfaces of p- and n-type germanium have been presented in the preceding paper. The present paper is concerned with the conclusions which may be drawn from these experiments as to the distribution in energy of these surface traps, and -the distribution of cross-sections for transitions between the traps and the conduction and valence bands. The statistics of trapping at a surface level has been developed by Brattain and Bardeen and by Stevenson and Keyes, following the work on body trapping centers of Hall" and of Shockley and Read. It is known that surface traps are numerous on a mechanically damaged surface' or on a surface that has been bombarded but not annealed; 1 2 3 4 3 6 8 1041 1042 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1956