A COMPARISON OF THE OPTICAL, IR, ELECTRON-SPIN-RESONANCE AND CONDUCTIVITY PROPERTIES OF A-GE1-XCX-H WITH A-GE-H AND A-GE THIN-FILMS PREPARED BY RF-SPUTTERING

Amorphous germanium (a-Ge), hydrogenated amorphous germanium (a-Ge:H) and hydrogenated amorphous germanium carbide (a-Ge1-xC(x):H) films were prepared by r.f. sputtering at various r.f. power levels and ratios of gases. The Tauc-determined optical gaps of the films calculated are in the range 0.55-0.66 eV for a-Ge, 0.62-1.19 eV for a-Ge:H and higher than 0.95 eV for a-Ge1-xC(x):H. The slopes of the absorption curves of the films yield the usually observed values of the Urbach coefficients E0, namely 115 meV less-than-or-equal-to E0 less-than-or-equal-to 450 meV. The concentrations of Ge-H and C-H bands were determined from Fourier transform IR spectra. Auger spectroscopy was used to determine the C:Ge ratio of some samples. The electron spin resonance defect spin densities range from 2.8 x 10(17) to 7.84 x 10(20) spins cm-3. Dark conductivity and photoconductivity of the films were measured with an intensity of 50 mW cm-2 at the sample surface. These films are unsuitable for single-cell photovoltaic devices because their optical gaps are less than 1.2 eV.