The Electronic Structure of a-Si,Ge:H Alloys

Abstract

ABSTRACTWe have carried out a detailed study of the energy distribution of deep defects for high quality glow discharge a-Si,Ge:H alloys using both thermal emission and optical Methods: drive-level capacitance profiling, transient photocapacitance and photocurrent plus modulation photocurrent spectroscopy. Four distinct bands of transitions involving defect states have been identified: two associated with thermal transitions, and the other two related to optical transitions. We have, for the first time, observed a negative signal in the photocapacitance spectra at photon energies near 1.2eV. This striking aspect verifies the presence of a distinct defect band above Ep from which electron thermal emission is greatly suppressed. Our Measurements also disclose a fairly narrow defect band below the Fermi level which contrasts with the defect properties observed in a-Si:H. Time resolved photocapacitance spectra indicate that this defect band exhibits configuration relaxation.