DENSITY-OF-STATES DETERMINATION OF AMORPHOUS-SILICON FROM SPACE-CHARGE-LIMITED PHOTOCURRENTS

The density-of-states around midgap g(E) of undoped amorphous silicon (a-Si:H) has been determined by measuring the space-charge-limited photocurrent (SCLPC) of a-Si:H Schottky diodes under blue light (λ=450 nm) illumination. In this novel technique, a single type of photogenerated carrier is utilized as the source of space charge to dispense with highly doped layers required in the conventional space-charge-limited current (SCLC) technique. Conditions for the uniform formation of space charge are discussed and checked by the satisfaction of a scaling law for samples with different thicknesses. The g(E) deduced from the SCLPC is found to be similar to that from the SCLC technique.