Influence of oxygen incorporation on the properties of magnetron sputtered hydrogenated amorphous germanium films

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Abstract
Hydrogenated amorphous germanium‐oxygen alloy films (a‐Ge1−x O x :H) with 10−5≤x≤0.4 were prepared by reactive dc‐magnetron sputtering at substrate temperatures of 320 and 420 K in an Ar/H2/O2 atmosphere. No influence of the added oxygen on any material properties could be detected for an oxygen partial pressure p(O2)≤3×10−4 mTorr corresponding to x≤10−4 (unintentional contamination regime). Between 2×10−4≤x≤5×10−3 the dark conductivity of the films linearly increases with x(doping regime). In this regime the optical gap and the hydrogen content remain unchanged, while midgap absorption and Urbach energy weakly increase indicating the increase of network disorder and defect density due to the Fermi level shift caused by the oxygen doping. Maximum conductivity of 8×10−3 Ω−1 cm−1 is achieved for x≊0.02. For x≳0.05 the conductivity and the hydrogen content drop, defect density and Urbach energy strongly increase, and the pronounced increase of the optical gap points to the formation of an alloy (alloy regime).