Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 14: Si/Ge
HL 14.1: Vortrag
Montag, 26. März 2007, 16:00–16:15, H14
Defect band formation at grain boundaries in laser-crystallized polycrystalline SiGe thin films — •M. Weizman1, L.-P. Scheller1, N. 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
Polycrystalline silicon-germanium (poly-SiGe) alloys are considered as a promising material for thin film solar cells due to their enhanced optical absorption in comparison to poly-Si. The SiGe thin films investigated in this study were fabricated on glass substrates by the following steps. Initially, amorphous silicon-germanium films (a-Si1−xGex:H) were deposited by glow-discharge decomposition of a mixture of disilane, germane, and hydrogen to a thickness of 100 to 255 nm. The Ge content, x, of the resulting samples was varied over the entire range 0 < x < 1. At the second processing step, the amorphous samples were crystallized employing a XeCl excimer laser. Electron spin resonance (ESR) measurements done on these samples at low temperatures (5 < T < 60 K) reveal that at a critical Ge content of about x = 0.5 the ESR signal vanishes completely for the Ge rich alloys and instead a broad signal caused by electron cyclotron resonance (ECR) appears. This result is interpreted as the formation of a defect band at the grain boundaries at a critical dangling bound defect density which is in the range of 5 · 1018 cm−3. Angle resolved measurements of the ECR signal as well as conductivity measurements are also presented in order to support this hypothesis.