Measurement of deep levels in hydrogenated amorphous silicon by transient voltage spectroscopy

Abstract

Electronic defect levels in amorphous silicon Schottky diodes have been measured by capacitance transient spectroscopy performed in the constant capacitance mode. In hydrogenated amorphous silicon deep levels are continuously distributed in energy and of sufficient density to dominate the electrical properties. The constant capacitance mode, applied for the first time to an amorphous semiconductor, offers significant advantages over the transient capacitance mode for measuring the bulk density of gap states. For example, numerical solution of Poisson’s equation for only the steady-state charge distribution is required to analyze the transient response of a diode after a trap-filling voltage pulse. The technique has been used to record time-resolved transients, which saturate with respect to pulse width, and the analysis yields deep level distributions in the range of 1017 eV−1 cm−3 over the energy interval from 0.6 to 0.9 eV below the conduction-band mobility edge.