The Study of Si, Se and O-Implanted GaAs by Slow Positrons
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THE STUDY OF Si, Se AND O-IMPLANTED GaAs BY SLOW POSITRONS S. Fujii, S. Shikata', L. Wei** and S. Tanigawa'" Opto-Electronics R&D Laboratories Sumitomo Electric Industries Ltd., 1 Taya-cho Sakae-ku Yokohama 244, JAPAN "Itami Research Laboratories, Sumitomo Electric Industries Ltd., 1-1-1 Koyakita Itami 664, JAPAN "Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305 JAPAN.
ABSTRACT Variable-energy (0-30keV) positron beam studies have been carried out on 200 keV Seimplanted and 70 keV Si-implanted GaAs specimens before and after annealing for electrical activation. From the measurements of Doppler broadened profiles as a function of incident positron energy, it was found that vacancy clusters with high concentration were introduced in the annealed specimen after Se implantation. From the parallel measurement of electrical characteristics, a higher activation efficiency was found for the higher concentration of vacancy clusters. That fact implies that electrons supplied by the activation of Se also convert the charge state of As vacancies from positive to negative. In contrast, no vacancy clusters were introduced in the Si-implanted GaAs. On the other hand, oxygen clustering was found in annealed specimen after 0 implantation. INTRODUCTION Silicon ion implantation into GaAs is widely used in the formation of a channel layer in metal semiconductor (MES) field effect transistors(FET). For the substitutional gate formation process in MESFET fabrication, the usual method of activation annealing is to deposit dielectric film, preventing the evaporation of arsenic, followed by annealing under arsine ambient. It is well known that Ga diffuses out into dielectric films such as SiO 2, SiN, and SiOxNy[1, 2]. It has been reported that for phosphosilicate glass and SiOxNy, Ga out-diffusion, and thus the formation of Ga vacancies, enhances the electrical activation of implanted Si, whereas the opposite phenomena was observed for SiO 2 in another experiment[2]. On the other hand, Se has emerged as a potential candidate for n-type dopants in MBE grown AlGaAs/GaAs heterostructures, because of its role in the reduction of DX centers leading to high performance cryo HEMT device characteristics[3]. In ion implantation technology, Se seems to be a desirable dopant for the formation of a thin channel layer because of its heavy mass and single site substitution. Nevertheless, Se is known as a dopant of low activation efficiency. Also oxygen ion implantation into GaAs is widely used for the formation of an isolation layer in GaAs-AlGaAs Heterojunction Bipolar Transistors(HBT). It is known that after annealing between 450 and 550 'C, activated oxygen occupies a substitutional site and forms a deep double electron trap[4,5]. Therefore, techniques which enable us to determine the vacancy type defects are expected to yield informations on activation mechanism. Recently, positron annihilation has proved to be the only method in studying vacancy type defects in semiconductors directly[6]. Utilizing slow positron beams, th
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