Defect re-distribution in amorphous silicon below equilibration temperature

Abstract

The effect of a Fermi level shift in an intrinsic energy distribution of gap states of amorphous silicon prepared by glow discharge is investigated with the aim of simulating the energy distribution of gap states near the i–n (p–i) interface in a p–i–n (n–i–p) device. Therefore we carried out experiments in which the Fermi level is moved to either the conduction or valence band edge in a ‘programmed’ intrinsic energy distribution of gap states by subjecting a metal/insulator/amorphous-silicon structure to n-type or p-type bias stress, respectively. Its effect on the energy distribution of gap states is measured by the charge version of deep level transient spectrometry. We observe that upon n-type (p-type) bias stress the energy distribution of gap states does not immediately adjust to the applied Fermi level shift, but that first an intermediate distribution is formed with a larger neutral dangling bond state contribution. In addition, it appears that the negatively charged dangling bond states are more resistant to p-type stress than the positively charged dangling bond to n-type stress.