Evidence for the Improved Defect-Pool Model for Gap States in Amorphous Silicon from Charge DLTS Experiments on Undoped a -Si:H

Results of the first charge deep level transient spectroscopy (DLTS) measurements on undoped a-Si:H are presented. The ability of the charge DLTS technique to resolve the gap-state distribution and to monitor directly its evolution after preequilibrium preparation by bias annealing is demonstrated. Three groups of gap states with mean energies of 0.63, 0.82, and 1.25 eV are observed. The condition for their creation as well as the energy values are in a good agreement with the D⁺, D⁰, and D^- states of the improved defect-pool model.