Migrations of Interstitial Atoms in Semiconductors (Surface Diffusion and Kick-Out Mechanism)
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MIGRATIONS OF INTERSTITIAL ATOMS IN SEMICONDUCTORS (SURFACE DIFFUSION AND KICK-OUT MECHANISM) TAKAO WADA ,AKIHIRO TAKEDA , MASAYA ICHIMURA , and MICHIHIKO TAKEDA *Nagoya Institute of Technology, Showa, Nagoya, 466, Japan **Government Industrial Research Institute, Nagoya, 462, Japan
ABSTRACT Ge and Zn atoms were introduced into the unirradiated regions of Si at 150 0 C and GaAs wafers at 50°C, respectively by using the electron-beam doping method. The surfaces of Si and GaAs substrates were covered partially by the overlayers of Ge and Zn sheets, respectively. The only surfaces of the Ge and Zn sheets were irradiated 17locally 1 8 with high at 2energy electrons 7MeV with the fluences of 5xlO1 - lxlO electrons cm . Even at a distance of "40mm from the irradiated overlayers in the Si and GaAs substrates, Ge and Zn atoms respectively, whose interstitials may migrate the unirradiated regions, were detected by SIMS measurements. PL signal due to band-toacceptor (ZnG) transition at 1.48eV becomes observable after annealing at 0 800 C for 20mn in the unirradiated GaAs region, which is separated from Zn sheet by nearly 10mm. I. INTRODUCTION When a crystal is irradiated with energetic electrons and the transmitted energy to a knocked atom is larger than a threshold energy Td, the atom is displaced from its regular site into an interstitial position and a Frenkel (vacancy-interstitial) pair is created [1]. We do have some firm information about the interstitial, but it has not yet been firmly identified. Watkins has observed the formation of aluminium interstitials in Al-doped Si irradiated at 4.2K. The production rate of these Al interstitials was considerably larger than the production rate expected if these interstitials were produced by direct encounters with energetic electrons. Watkins [2] has indicated that the presence of these Al interstitials can only be the result of long-range migration of Si interstitials with subsequent exchange with substitutional Al, giving Al interstitials. Nagata et al. [3] have estimated gallium surface diffusion distances in the molecular-beam epitaxial (MBE) growth of (001) oriented GaAs films under both Ga-and As-stable conditions. And the surface diffusion length of Ga on GaAs (111) B has been obtained [4] as a function of reciprocal growth temperature by taking account of the supersaturation ratio of adatoms on the terrace for MBE growth. Electron beam doping (EBD) [5-8], oxidation [9] and epitaxy [10-11], which utilize high-energy electronirradiation, have recently reported by the authors and others. For EBD, Ushaped diffusion profiles of impurities in substrates have been explained by considering the "kick-out" mechanism and the surface diffusion [6]. In the present paper, we study the introduction of Ge and Zn atoms into the unirradiated regions of Si at 150'C and GaAs wafers at 50 0 C, respectively by using the EBD method. Table I
Impurity sheets and substrates used in the experiments. Material
Impurity sheet Substrate
Purity, conduction type, resistivity, orientation, thickne
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