The surface of material which had been implanted with 100keV Se ions was encapsulated with As-doped amorphous hydrogenated Si to a thickness of about 80nm. Crystallization of the encapsulant upon annealing at 1000C was hindered by doping with As atoms to a concentration of 2 x1020/cm3. However, the encapsulant could be crystallized when the concentration of the As dopant atoms was lowered. The crystallized encapsulant had many grain boundaries, and the diffusion rate of impurities was thereby increased. The GaAs surface decomposed markedly via the boundary of the Si/GaAs structure, and As and Ga vacancies were produced at the GaAs surface. A number of Si atoms also diffused into the GaAs crystal. An As-vacancy rich region formed near to the surface, and the Ga vacancy diffused into the GaAs because the diffusivity of the As vacancy in GaAs was much lower than that of the Ga vacancy. The Si atoms gave a flat profile, with a steep slope at the surface, because of the distribution of the vacancies. That is, the Si atoms preferentially occupied vacant As sites in the VAs-rich region or vacant Ga sites in the VGa region. A series of reactions,

SeAs+ + (SiGa+ + SiAs-) + VGa- - (SeAs+ + SiAs-) + (SiGa+ + VGa-)

(SiAs- + SeAs+) + (VGa- + SiGa+)

increased the diffusion rate of the implanted Se atoms. Thus, the activation efficiency improved with increasing concentration of As atoms in the encapsulant, and the diffusion rate was reduced because the content of Si atoms and vacancies in GaAs was decreased.

K.Yokota, K.Nishida, A.Yutani, S.Tamura, Y.Horino, A.Chayahara, M.Satho, K.Hirai, H.Takano, M.Kumagaya: Japanese Journal of Applied Physics, 1993, 32[1-10], 4418-24