Mechanisms of Impurity Deactivation in GaAs during Reactive Ion Etching.

The cause of carrier removal in GaAs due to plasma processing is found to consist of two mechanisms from a photoreflectance depth-profiling study. In the close vicinity of the surface, the Fermi level is pinned by the defects created by ion bombardment. In a much deeper region, electrical passivation of doped impurities themselves is playing the dominant role. Secondary-ion mass analysis confirmed that hydrogen diffusion is indeed responsible for the latter process. We suggest that the physically damaged surface layer acts as a sponge for even a trace amount of hydrogen in the processing environment.