INFLUENCE OF OXYGEN INCORPORATION ON THE PROPERTIES OF MAGNETRON SPUTTERED HYDROGENATED AMORPHOUS-GERMANIUM FILMS

Hydrogenated amorphous germanium-oxygen alloy films (a-Ge1-xOx:H) with 10(-5) less-than-or-equal-to x less-than-or-equal-to 0.4 were prepare d by reactive dc-magnetron sputtering at substrate temperatures of 320 and 420 K in an Ar/H-2/O2 atmosphere. No influence of the added oxyge n on any material properties could be detected for an oxygen partial p ressure p(O2) less-than-or-equal-to 3 x 10(-4) mTorr corresponding to x less-than-or-equal-to 10(-4) (unintentional contamination regime). B etween 2 x 10(-4) less-than-or-equal-to x less-than-or-equal-to 5 x 10 (-3) the dark conductivity of the films linearly increases with x (dop ing regime). In this regime the optical gap and the hydrogen content r emain unchanged, while midgap absorption and Urbach energy weakly incr ease indicating the increase of network disorder and defect density du e to the Fermi level shift caused by the oxygen doping. Maximum conduc tivity of 8 x 10(-3) OMEGA-1 cm-1 is achieved for x almost-equal-to 0. 02. For x > 0.05 the conductivity and the hydrogen content drop, defec t density and Urbach energy strongly increase, and the pronounced incr ease of the optical gap points to the formation of an alloy (alloy reg ime).