Similarity of Vacancy Creation Mechanisms in Si Doped GaAs and Ga Doped ZnSe Observed by a Monoenergetic Positron Beam
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SIMILARITY OF VACANCY CREATION MECHANISMS IN Si DOPED GaAs AND Ga DOPED ZnSe OBSERVED BY A MONOENERGETIC POSITRON BEAM
S. TANIGAWA', J. L. LEE*, L WEI%, M. KAWABE', T. MIYAJLMA*", H. OKUYAMA", K. AKIMOTO"" and Y. MORr*" "Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305, Japan "'Electronics and Telecommunications Research Institute, P. 0. Box 8, Daedok Science Town, Daejon, Korea "'Research Center, Sony Corporation, 174 Fujitsuka, Hodogaya-ku, Yokohama 240, Japan
ABSTRACT The impurity effects on the creation of vacancies in GaAs and in ZnSe were investigated by monoenergetic positron beam measurements. In the case of the Si-doped MBE grown GaAs, the doping of Si atoms was found to enhance the creation of Ga site vacancies. The concentration of Ga vacancies was found to be proportional to the doped Si concentration. The observed linear relation between both concentrations supports the theoretical prediction on the creation of Ga vacancies in terms of the change in the Fermi-level position by the Si doping into GaAs and also suggests that Si atoms diffuse in GaAs as a neutral complex of Ga vacancy-Si pair rather than that of Si-Si pair. In the case of the Ga-doped MBE grown ZnSe, Zn vacancies were found to be generated in proportion to the concentration of doped Ga atoms. The observed similarity of the vacancy creation in the Si-doped GaAs and in the Ga-doped ZnSe can be well explained by the consideration of the charge neutrality condition around impurities. INTRODUCTION The free carrier concentration in MBE-grown Si-doped GaAs increases linearly with Si concentration up to 7x1018 cm3, and then decreases rapidly[l ]. This has been considered as a compensation of a donor (Si,.) with acceptors (Si and/or V..)[2, 31. Two representative models have been proposed to account for the Si diffusion in GaAs. Greiner and Gibbons[2] have shown that the diffusion constant of Si atoms is dependent upon the concentration of Si. From this and the high degree of compensation, they have suggested that Si atoms diffuse as neutral pairs of Si .- SiA. Deppe el aL [31, however, have shown that the Si diffusion rate in GaAs is not simply concentration dependent, but depends on the crystal Fermi level and the concentration of an ionized Ga vacancy Vs,,. Because of the dependence on both of the As vapor pressure and the Fermi level, they suggested that the Si atoms diffuse as a donor on the column III sublattice employing column III vacancies, namely Si,, - Vc. Although the impurity diffusion mechanism has been thought to be directly related to the concentration of point defects such as Ga vacancies V and Ga interstitials lIc, no experimental works have been carried out because of lack of tools for the direct detection of those defects. The similar compensation effect is also an important problem in the doped ZnSe. ZnSe is a promising material for the fabrication of blue light emitting laser diodes. It has been difficult to realize such a device because of the difficulty of controlling both the conductiontype and
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