Germanium films were deposited on GaAs (100) substrates at temperatures between room temperature (RT) and 500°C using ultra high vacuum (UHV) E-beam and sputtering deposition methods. The Ge film deposited in UHV at 100°C was amorphous and had a flat absorbance curve over the range investigated, 4000 - 500 cm-1, with a value of 0.03 at 1000 cm1 (10μm). Films deposited by E-beam at RT and 50°C had comparably low absorbances, but they contained a peak at 830 cm-1, which was possibly due to absorption by a Ge-O bond. The amorphous film deposited at 150°C and the single crystal films deposited at 400 and 500°C by E-beam had larger absorbances caused by free carrier absorption. The amorphous Ge sputtered film deposited at RT had a relatively low absorbance, but it contained the absorption peak attributed to Ge-O. The absorbance increased dramatically when it was annealed at 400 or 500°C due to the rapid out diffusion of Ga and As through the relatively open structure.