Transport Properties of Polycrystalline SiGe Thin Films Grown on SiO2

Abstract

ABSTRACTTransport properties of polycrystalline Si1−xGex (x = 0, 30, 50 and 70) thin films on SiO2 were studied by Hall measurements and transport properties of the TFTs fabricated on the films were characterized. Si1−xGex films were p-type in spite of non-doping. Room temperature hole densities of Si1−xGex films increased from 5 × 1013 to 5 × 1016 cm−3 as Ge concentration increased from 30 % to 70 %. The acceptor levels in Si1−xGex were located at 0.43, 0.40 and 0.34 eV for x=0.3, 0.5 and 0.7 from valence band, respectively. The high leakage current of SiGe-TFTs was observed and drain current could not be turned off even when the high gate voltage was applied. The acceptor density increased with increasing annealing temperature from 700 °C to 800 °C. The leakage currents were independent of the annealing temperature and is thought to originate from Ge-related defects in grain boundaries.