Low-temperature epitaxy of Ge films by sputter deposition

Abstract

The crystallographic structure and orientation of Ge films formed by sputter deposition onto Ge (111) substrates have been investigated as a function of various deposition parameters. Important parameters affecting the film structure include growth rate, substrate temperature, substrate-surface cleanliness, and sputtering-gas purity. The structure of the sputter-deposited films was examined by HEED, while the substrate surface was characterized by HEED, LEED, and Auger electron spectroscopy. Results show that epitaxy of Ge can be obtained by sputter deposition at substrate temperatures as low as 100 °C, provided the deposition conditions are properly optimized. A plot of the film structure as a function of substrate temperature and growth rate defines the three regions of crystallinity (amorphous, polycrystalline, and single crystalline), indicating the existence of a triple point. The amorphous-polycrystalline and epitaxial transitions occur at temperatures considerably lower than those reported by previous investigations. Thermal regeneration of the substrate surface results in a considerable reduction of the transition temperatures. Oxygen in the sputtering atmosphere plays a significant role in determining the epitaxial temperature.