Impulse photoconductance of thin-film polycrystalline silicon

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Abstract
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.