Combined Measurements of Field Effect, Surface Photo-Voltage and Photoconductivity

This and the succeeding paper are concerned with studies of the properties of fast surface states on etched germanium surfaces. The experiments involve simultaneous measurement of a number of different physical surface properties. The theory, which will be presented in the second paper, interprets the results in terms of a distribution of fast surface states in the energy gap. The distribution function, and the cross-sections for transitions from the states into the conduction and valence bands, may then be deduced from the experimental results. Early experiments 1 on contact potential of germanium, and on the change of contact potential with light, indicated that there are two kinds of surface charge associated with a germanium surface, over and above the holes and electrons that are distributed through the surface space-charge region. One kind of surface charge, usually called "charge 1019 1020 T H E BELL SYSTEM T E C H N I C A L J O U R N A L , S E P T E M B E R 1 9 5 6 in fast traps" can follow a change in the space-charge region very fast in comparison with the light-chopping time used in that work (Moo sec); the other kind, imagined to be more closely connected with adsorbed chemical material, can only change rather slowly. In a previous paper by the authors 2 it was pointed out that the Brattain-Bardeen experiments, taken by themselves, do not furnish unambiguous information concerning the distribution of these " f a s t " traps, but that such information might be obtained by performing, simultaneously, other measurements on the germanium surface.