Berlin 2008 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
HL: Fachverband Halbleiterphysik
HL 54: Si/Ge
HL 54.11: Vortrag
Freitag, 29. Februar 2008, 13:15–13:30, EW 202
Electrical and optical properties of laser-crystallized polycrystalline silicon-germanium thin films — •Moshe Weizman1, Lars-Peter Scheller1, Norbert Nickel1, and Baojie Yan2 — 1Hahn-Meitner-Institut Berlin, Kekuléstr. 5, 12489 Berlin, Germany — 2United Solar Ovonic Corporation 1100 West Maple Road Troy, MI 48084, USA
The SiGe thin films investigated in this study were deposited on quartz by glow-discharge decomposition of a mixture of disilane, germane, and hydrogen and subsequently crystallized employing a XeCl excimer laser. Our investigations reveal that the grain boundaries in the poly-SiGe films critically influence the electrical and optical behavior of this material. Hall effect and electron spin resonance (ESR) measurements show evidence for the formation of a defect band on grain boundaries due to dangling bonds. This defect band appears preferably in Ge rich alloys with a critical dangling bond concentration of about 5 · 1018 cm−3 and causes high metallic-like conductivities at low temperatures. Optical absorption measured with photothermal deflection spectroscopy (PDS) reveals a direct band gap characteristic that suggests the absorption occurs primarily at the grain boundaries. Sub-bandgap absorption indicates that the position of the neutrally charged dangling bond D0 is about 150 meV above the valance band, which is probably the reason the Fermi level is pinned at the lower half of the bandgap and the layers exhibit p-type conductivity. We will discuss these surprising properties in terms of solar cell potential applications