Density of states study of sputtered and evaporated a-Si: H by space-charge-limited current technique

The density of states (DOS) in sputtered and evaporated a-Si: H has been determined from space-charge-limited current (SCLC) measurements on samples with a Cr/a-Si/a-Si: H/a-Si/Cr sandwich configuration. In the current-voltage characteristics of sputtered films, a non-Ohmic region due to one-carrier SCLC conduction is followed by a sharp increase in current at higher fields. This increase is attributed to switching phenomena caused by the formation of a current filament in the film. The DOS near the Fermi level of sp-a-Si: H films varies between 7 × 1015 and 1 × 1017 cm−3 eV−1, and, as observed in gd-a-Si: H, depends strongly on the film thickness in the measured range of 0·6-2·0 μm. The DOS for evaporated films is comparatively low–around 1017 cm−3 eV-−1 –showing that dangling bonds can be saturated by incorporation of sufficient atomic hydrogen into the films.