Transport and instabilities in microcrystalline silicon films

Coplanar transient photoconductivity and post-transit time-of-flight spectroscopy techniques are used to study carrier transport in microcrystalline silicon films prepared over a range of crystallinities. Although reduced deep defect densities are indicated in more highly crystalline films, this is thought to be an artefact of the shallow Fermi level position. Coplanar samples are susceptible to post-deposition oxidation and reversible adsorption of atmospheric gases, which alter the apparent density of states. A comparison of the results obtained using both techniques suggests that transport is anisotropic, with reduced band tailing (greater structural order) along the direction of film growth, a larger defect concentration around column boundaries, and a higher defect density within the amorphous tissue than in optimised single-component amorphous silicon films.