Transport properties of polycrystalline SiGe thin films grown on SiO2

Transport 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 x 10(13) to 5 x 10(16) cm(-3) as Ge concentration increased from 30% to 70%. The acceptor level, 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 degrees C to 800 degrees C. The leakage currents were independent of the annealing temperature and is thought to originate from Ge-related defects in grain boundaries.