Determination of doping factor, mobility ratio and excess concentration using photovoltages at extreme band bendings

Abstract

Photovoltages (surface photovoltage plus Dember voltage) were calculated and plotted, taking into consideration the influence of charge exchange between a continuum of surface states and the semiconductor. For moderate band bendings the photovoltage depends on several parameters which renders their reliable determination very difficult. For extreme band bendings, however, only doping factor, mobility ratio and relative excess concentration enter into given formulas. It is shown how by means of field-modulated photovoltage measurements using short pulses of light these three parameters could be determined reliably. Ge-samples with real surfaces were used. Good agreement between parameters determined in this way and otherwise indicates validity of the model and the approximations used in this work. The mobility ratio was found constant up to excess concentrations of about 10 14 cm −3. Possible extension of such measurements to semiconductors whose doping factors are very different from unity and applications are shortly discussed.