Negative- U property of interstitial hydrogen in GaAs

We identify the donor level of interstitial hydrogen in GaAs, which is characterized by the activation enthalpy E_C−E_t=0.13 eV. This level is the marker of two different but closely related defect structures, which are indistinguishable as far as their emission properties are concerned; however, discernible on the basis of their different dynamical behaviors are revealed by annealing studies. We interpret the two structures as regular bond center hydrogen H(BC) and bond center hydrogen H(BC^′), which is perturbed by the local strain from a neighbor point defect. We demonstrate negative-U properties of the perturbed structure and infer that the corresponding acceptor H(T^′) lies deep in the band gap. These results for interstitial hydrogen in GaAs are in every aspect analogous to the properties of interstitial hydrogen in Si.