KEY PARAMETERS FOR FURTHER REDUCTION OF GAP STATES IN A-GE-H AND ITS IMPROVED STABILITY UNDER KEV-ELECTRON IRRADIATION

The influence of various deposition parameters on the properties of dc -magnetron sputtered a-Ge:H is studied. The lowest Urbach energy of 45 meV is obtained for films of saturated hydrogen concentration of 6 at % prepared at an argon pressure of 0.5 mTorr and a substrate temperatu re around 450 K. The decrease of the target to substrate - distance fr om 17 cm to 8 cm results in a further reduction of the defect density and the Urbach energy to 7X10(16) cm(-3) and 40 meV (determined by PDS ), respectively. The saturation value of the defect density created un der keV-electron irradiation is 3X10(17) cm(-3), which is close to the value for device quality a-Si:H and a factor of ten less than for fil ms prepared at the larger distance.