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HL: Fachverband Halbleiterphysik
HL 14: Si/Ge
HL 14.4: Vortrag
Montag, 26. März 2007, 16:45–17:00, H14
Metallic conduction in undoped laser-crystallized polycrystalline silicon-germanium thin films — •L.-P. Scheller1, M. Weizman1, 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
Due to its enhanced optical absorption in the IR and visible spectral range polycrystalline silicon-germanium (poly-SiGe) could become a promising new absorber material for future thin film and tandem solar cells.
The poly-SiGe samples investigated in this study were fabricated in the following way. First, amorphous undoped SiGe (a-SiGe:H) films with a germanium content between 33% and 100% were deposited on quartz substrates. Then, these a-SiGe:H samples were laser-crystallized with a pulsed XeCl excimer laser both by a step-by-step process and by a single laser pulse. Carrier transport in these samples was investigated by Hall and conductivity measurements in a temperature range of 20 K to 300 K.
Although the amorphous base material is undoped, many samples show p-type conduction with astonishing high conductivities in the range of 0.1 to 10 (Ωcm)−1. In addition, the Ge-rich samples exhibit metallic behavior with nearly constant conductivity down to 20 K. Further, a subsequent remote hydrogen plasma treatment leads to a pronounced decrease in conductivity. This surprising behavior is explained in terms of carrier transport in a defect band induced by dangling bond defects at the grain boundaries.