The diffusion of Li was shown to be trap-limited at high doping levels. As in the case of other reactive impurity species, the intrinsic diffusivity of Li could be measured only in lightly Li-doped material that was of high purity; or exhibited weak pairing interactions. On the basis of charge-density profiles in Zn-doped GaAs, measured by using the capacitance-voltage technique, the intrinsic Li diffusivity could be described by an activation energy of 0.67eV and a pre-exponential factor of between 0.005 and 0.02cm2/s. However, in the case of Li-rich and nominally undoped starting material, diffusion was limited by the formation of complexes which involved several Li atoms and native defects. The most weakly bound Li atoms were released from the complexes at temperatures above 100C, and a dissociation energy of 1.20eV characterized the effective diffusion behavior. A previously reported 1.0eV migration energy for Li, in Li-saturated GaAs at high temperatures, was consistent with the present observations; within the assumed model of trap-limited diffusion.

K.Leosson, H.P.Gislason: Physical Review B, 1997, 56[15], 9506-11