Berlin 2008 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 54: Si/Ge
HL 54.9: Talk
Friday, February 29, 2008, 12:45–13:00, EW 202
Grain boundary conduction in undoped laser-crystallized polycrystalline silicon-germanium thin films — •Lars-Peter Scheller1, Moshe Weizman1, Norbert H. Nickel1, and B. Yan2 — 1Hahn-Meitner-Institut Berlin, Kekuléstr. 5, 12489 Berlin, Germany — 2United Solar Ovonic Corporation, 1100 West Maple Road Troy, MI 48084, USA
Due to its enhanced optical absorption in the IR and visible spectral range polycrystalline silicon-germanium (poly-SiGe) is a promising absorber material for future thin film and tandem solar cells.
In this study the electrical transport properties of laser-crystallized poly-Si1−xGex thin films (0 ≤ x ≤ 1) on quartz were investigated by temperature dependent Hall and conductivity measurements. All intentionally undoped samples showed p-type conduction that in some cases was accompanied by an astonishing high conductivity in the range of 0.1 to 10 (Ωcm)−1. Depending on the germanium content and the used crystallization procedure, three different transport mechanisms were identified: a) thermally activated transport with an activation energy of approximately 350 meV, b) Mott’s variable range hopping and c) a nearly temperature independent metallic like transport. In addition, a subsequent remote hydrogen plasma treatment led to a pronounced decrease in the conductivity and a transition from metallic to activated transport. This surprising behavior is explained in terms of carrier transport in a defect band induced by Ge dangling bond defects at the grain boundaries.