Regensburg 2002 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 11: Poster 1
HL 11.33: Poster
Montag, 11. März 2002, 17:00–19:30, Poster A
Photocurrent decay in microcrystalline silicon — •Rudolf Brüggemann1, Gottfried H. Bauer1, Steve Reynolds2, and Charles Main2 — 1Fachbereich Physik, Carl von Ossietzky Universität, D-26111 Oldenburg — 2School of Science and Engineering, University of Abertay Dundee, Dundee, Schottland UK
We measured the time-dependent photocurrent decay from the steady state in microcrystalline silicon from plasma-enhanced chemical vapor deposition and hot-wire chemical vapour deposition. Measurements were made over a wide range of steady-state photogeneration rates. We detail the variation with generation rate of the decay time, at which the initial photocurrent has dropped to 50 % or 1/e of its initial value. We studied samples exhibiting a range of photoconductive properties in terms of both the majority and minority carrier mobility-lifetime products. For our samples the shape of the transient photocurrent versus time shows power-law behavior with different power-law parameters. Interestingly, samples with a short steady-state photocarrier lifetime show a long decay time, together with a distinctly different power-law behavior when the decay time is plotted verus photogeneration rate. We relate the slow decay process to the much larger density of localized states in the band gap in the poor-quality samples. Trapped carriers are released, undergo emission and trapping processes and eventually recombine in these samples, on a much longer time-scale than in the high-quality samples. We also critically examine the estimation of drift mobilities from our decay experiments.