A comprehensive guide to the formation of epitaxial III-Nitrides and epitaxial Ge3N4 on germanium substrates--and solid phase epitaxy of germanium on silicon substrates--this work presents a simple but effective method for growing epitaxial III-Nitride layers on crystalline germanium surfaces. Beside epitaxial III-Nitride growth, a method is introduced to obtain epitaxial Ge3N4 on germanium. Finally a novel method to produce high-quality germanium layers on silicon is introduced, allowing interactions between germanium devices and silicon technology. This study provides researchers with a detailed look at the formation of crystalline nitrides on germanium, germanium on silicon, Schottky contacts on germanium, and electrochemical measurements.