Atomic transport in germanium and the mechanism of arsenic diffusion

The paper reviews some basic aspects of self- and foreign-atom diffusion in germanium (Ge) and provides new experimental results on the intrinsic and extrinsic diffusion of arsenic (As) in Ge. Experiments of As diffusion in Ge have been performed at temperatures between 640 and 920 °C utilizing a diluted Ge–As alloy as diffusion source. The As profiles were measured by means of the spreading resistance technique. Depending on the As concentration established at the surface, intrinsic and extrinsic As profiles were obtained. Arsenic diffusion in Ge is fully described on the basis of the vacancy mechanism taking into account singly negatively charged As-vacancy pairs. In contrast to a recent study of Vainonen-Ahlgren et al. (Appl. Phys. Lett. 77 (2000) 690), which claims that As diffusion is mediated by neutral and doubly negatively charged vacancies, we show that As diffusion is not sensitive to the properties of vacancies. From our experiments we determine an activation enthalpy of 2.70 eV and a pre-exponential factor of 30 cm2 s−1 for intrinsic As diffusion in Ge.