Effect of Local Atomic Configuration on DX Energy Level
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EFFECT OF LOCAL ATOMIC CONFIGURATION ON DX ENERGY LEVEL T. BABA*, M. MIZUTA*, T. FUJISAWA**, J. YOSHINO** and H. KUKIMOTO** *Fundamental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, lbaraki 305, Japan **Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, 4259 Nagatsuda, Midori-ku, Yokohama, Kanagawa 227, Japan ABSTRACT The effects of specific local environments on DX centers were investigated for two different substitutional-site-donors of Si and Te in selectively-doped ordered-alloy samples. Capacitance transient technique under hydrostatic pressure was utilized for the determination of the DX energy-level structure. Downward movement of the energy levels for both Si- and Te-DX centers was observed when Al occupies the 2nd or 1st nearest neighbor site, respectively. A very large shift of the electron-emission activation-energy with pressure was found for the Te-DX centers surrounded by specific Al and Ga mixed-environments, whereas negligible shift for the Si-DX centers was observed regardless of the environment. These effects were discussed in relation to the lattice relaxation of the relevant DX centers. INTRODUCTION More than a decade has been passed since strange behaviors of n-type impurity, the DX center, in AIGaAs were discovered. In recent years, the origin of the DX center has been believed as a simple substitutional donor rather than the complex center consisting of a donor and a defect [1-5J. One of the important remaining issues is the lattice relaxation mechanism in real space. Recent findings of local-environment-specific energy level of the DX center together with theoretical prediction of multiplicity of the DLTS peak due to the large lattice relaxation scheme could make us possible to determine the relaxation mechanism by analyzing DLTS spectra of the DX center[6,7J. Local environment, especially the configuration of Al and Ga around a donor impurity, is apparently simpler for the group VI donors than for the group IV donors, if simple substitutional donor is assumed. In this regard, effect of local environment on the DX energy level of a Te donor was investigated and compared to that of the Si-DX center. The main concern of this paper is to evaluate the effect of Al on the energy level of the Te (V-site) DX center and compare it for the case of Si ( MI-site). We have found that the neighboring of Al (the first nearest site) to Te donors decreases the DX energy level just like the Si donor case previously reported. However, two types of the DX centers are classified by the pressure dependence. One shows negligible shift of the OLTS peak-temperature upon pressure application, similar to the case for the Si DX centers. The other type shows very large shift on pressure change. This difference is discussed in relation to the lattice relaxation mechanism. EXPERIMENTS In order to clarify the effect of local atomic configuration around Si and Te donors, we fabricated samples of ordered alloy (OA) structure, which consist of 1 monolayer of AlAs and 14 monolayers
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