The in-diffusion of As vacancies, and their interaction with the mid-gap electron trap, EL2, during unprotected and proximity high-temperature annealing was modelled. By fitting existing data, it was found that the diffusive capture of VAs by EL2 was inhibited by a large (greater than 1eV) repulsive barrier of unknown origin. When taken together with other published results, the model indicated that the diffusivity of VAs was described by:

D(cm2/s) = 0.004 exp[-1.8(eV)/kT]

However, this value was thought to be uncertain by at least an order of magnitude. A new discovery was the existence of a strong repulsive barrier between VAs and EL2. This inhibited their interaction, and was of the order of 1.2eV. When interpreted as being a Coulomb barrier, it required that EL2 (or a portion of EL2) should carry a positive charge. In order to keep EL2 neutral, there would then have to be a compensating acceptor in EL2.

K.M.Luken, R.A.Morrow: Journal of Applied Physics, 1996, 79[3], 1388-90