Impulse photoconductance of thin-film polycrystalline silicon

Using optoelectronic correlation and sampling oscilloscope techniques we measured impulse photoconductance of polycrystalline-Si thin-film photoconductors excited by femtosecond dye-laser pulses. We studied as-deposited micrograin films as well as annealed, H-passivated, and H-passivated/annealed films. Results yielded photoexcited carrier mobilities of 6.8 and 104 cm2/V s, respectively in as-deposited and 1150 °C-annealed films. The photoconductance decays of as-deposited films showed an initial fast decay time of ∼22 ps followed by a primary decay time of ∼150 ps. Photoconductance decays of annealed films showed similar primary decay times but no initial fast decay transient. H passivation of both as-deposited and annealed films produced no changes in carrier mobilities. However, H passivation of as-deposited films eliminated the initial fast decay transient and increased the primary decay time to ∼800 ps. H passivation of annealed films increased decay time only slightly. Results suggest that grain boundaries control decays in as-deposited films but not in annealed films, and that H passivation does not reduce carrier scattering.