Abstract
The distribution of localized states in a-Si: H above the Fermi energy has been determined by phase-shift analysis of modulated photocurrents. By use of a novel experimental technique the modulation frequency range could be greatly extended compared to conventional mechanical light chopping, revealing the gap-state distribution over an energy interval from 0•25 to 0•7 eV below the conduction-band edge. A shoulder at 0•35 eV and a peak at 0•55 eV below the band edge have been detected. Defect creation by strong illumination increases the peak and quenches the shoulder, indicating a shallow-state-deep-state conversion, and also proves the high sensitivity of this method. Data taken over a large temperature range from 110 to 480 K indicate an energy shift of the dominant electron-transport path with temperature.