TRANSIENT AND STEADY-STATE OPTOELECTRONIC PROPERTIES OF MU-C-SI-H

Steady-state and transient photoconductivity measurements have been carried out on hydrogenated microcrystalline silicon films (mu-c-Si:H). The subgap absorption was determined by the constant photocurrent method (CPM). In addition, the dark conductivity activation energy and Raman spectra have been measured. In comparison with a hydrogenated amorphous silicon (a-Si:H) sample, mu-c-Si:H has a higher photo- and dark conductivity, a longer response time, a higher subgap absorption coefficient, and a smaller activation energy. These findings are consistent with Fermi level pinning near the conduction band caused by defect states in the grain boundary regions. After light soaking, the increase in subgap absorption (in absolute values) in mu-c-Si:H is larger than in a-Si:H. This change is tentatively explained by the increase of the density of grain boundary defects. The concomitant decrease in photoconductivity is ascribed to changes of the defect density in both the grain boundaries and the amorphous matrix.