Uses of Si (Silicon), Ge (Germanium) and GaAs (Gallium Arsenide)

Si: Silicon is used most frequently for the full range o electronic devices. It is readily available at low cost and has low reverse saturation currents, good temperature characteristics, and excellent breakdown voltage levels. 

Ge: Germanium is not used widely due to its temperature sensitivity and high reverse saturation current. It is still commercially available but is limited to some high speed applications (due to high mobility factor) and applications that use its sensitivity to light and heat (like- photo detectors and security systems)

GaAs: In 1990s the interest in Gallium Arsenide has grown in leaps and bounds. Its high speed characteristics are in more demand every day, with the features of low reverse saturation currents, excellent temperature sensitivities, and high breakdown voltages. The major area of its applications are in optoelectronics (more than 80%). As its manufacturing costs drop it will be most widely used in electronic devices. We can say that it is the semiconductor material of the future.