Surface mobility measurements in germanium

Measurements are reported of the surface mobility in accumulation layers of germanium at low temperatures, and results obtained are compared with the theoretical calculations of Schrieffer. Advantage is taken here of the relatively slow thermal release of charge from many of the surface states into the majority-carrier band at sufficiently low temperatures. By the use of the pulsed field-effect technique, a rapid decrease in majority-carrier concentration within the space-charge region is effected. The change in surface conductance measured at the onset of the pulse, before the deficit induced can be redistributed between the states and the majority-carrier band, then becomes a direct measure of the majority-carrier surface mobility. The results for n-type samples show that Schrieffer's corrections for electrons are overestimated. On the assumption that the theoretical values are valid for accumulation layers, it is concluded that the surface is not a completely diffuse scatterer.