Investigation of crystallinity of germanium thin films vacuum deposited on GaAs

We investigated the cyrstalline quality of Ge thin films vacuum deposited on heated (100) GaAs substrates. Ge was evaporated using an electron beam and deposited to thicknesses of 100 and 500 nm, which were measured by a Dektak stylus-type instrument. These results were compared with the predictions of a cosine distribution law derived for the deposition system and found to be in relatively good agreement. The crystalline quality of the films was studied using scanning electron microscopy. Results have shown that epitaxy was strongly dependent on the substrate temperature, surface cleanliness and post-deposition annealing. Epitaxy was reproducibly achieved at a substrate temperature ofT_s=450 °C. All films deposited atT_s=350 or 400 °C were polycrystalline or amorphous, except one grown atT_s=350 °C, which proved to be monocrystalline. It is speculated that an anomalously clean and smooth substrate surface was responsible for this crystalline quality of films. In addition, it has been shown that post-deposition annealing of the films improved their crystallinity.