Theoretical Interpretations of the Gap State Density Determined from the Field Effect and Capacitance-Voltage Characteristics of Amorphous Semiconductors

An exact theory for the calculation of the electronic density of bulk gap states in amorphous semiconductors from field effect and capacitance-voltage measurements is presented. The analytical expression for the density of the gap states is given as a function of the surface potential of amorphous semiconductors. It is also shown that the influence of surface states on the measured gap states can be completely eliminated by combining a capacitance-voltage method with a field effect technique.