The optical properties of thick sputtered films (∼30μ) of amorphous Ge, grown with different substrate temperatures (0ˇ-Ts-350°C), were obtained between 0·05 and 4·5 eV by a combination of reflectance, transmittance and ellipsometric measurements. The refractive index at 0·15 eV decreases monotonically with increasing Ts, or equivalently, with increasing density, and is 4·13±0·05 eV in the highest density films. The absorption edge is approximately exponential (102≲α≲104 cm-1) but shifts monotonically to higher energy and increases in slope with increasing Ts. Similarly, the peak in ε2 grows by about 10% and shifts by about 0·15 eV to higher energies, reaching a maximum of about 23 at 2·90±0·05 eV in the high density films. The peak in the transition strength ω2ε2 occurs at 4·2±0·2 eV in all films, but increases in magnitude with increasing Ts. The sum rules for neff(ω) and ε0,eff(ω) are evaluated for ▄ω≲5 eV and vary monotonically with Ts. These trends are neither compatible with Galeener's void resonance theory nor with changes in the oxygen content of the films, determined by the examination of absorption peaks at 0·053 eV and 0·09 eV. An explanation, suggested here and expanded in I, is based on the observed changes in the structure of the network and voids.
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