Obliquely deposited amorphous Ge films. I. Optical properties

The dependence of deposition and annealing temperature is studied of the absorption coefficient, fundamental absorption edge, refractive index, extinction coefficient, reflectivity, and real and imaginary parts of the complex dielectric constant in the spectral range 0.4 to 6.2 eV of obliquely deposited a-Ge films. Normal incidence room temperature deposited films exhibit a reasonably sharp absorption edge at ≈0.56 eV and a low frequency refractive index of 4.2. Deposition at oblique incidence results in sharpening and shifting of the absorption edge to higher energies and a decrease in the optical absorption, refractive index, and extinction coefficient. Similar changes are observed with increasing temperature of deposition or annealing. The magnitude of the changes decreases with increasing angle of incidence. The observed effects are understood in terms of changes brought about by the deposition conditions in the apparent density and concentration of voids and dangling bonds. The spectral dependence of the optical constants exhibits marked variation in the low energy (up to 2.5 eV) region with increasing obliqueness. With increasing energy, the difference between the optical constants of normal and oblique incidence deposited films decreases to negligible values (Above ≈4.0 eV).