The Electronic States and Dynamical Properties of Hydrogen Bound to Carbon in Silicon
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THE ELECTRONIC STATES AND DYNAMICAL PROPERTIES OF HYDROGEN BOUND TO CARBON IN SILICON YOICHI KAMIURA*, FUMIO HASHIMOTO*, AND MINORU YONETA** *Facultyof Engineering,Okayama University, Tsushimanaka 3-1-1, Okayama 700, Japan "**Facultyof Science, Okayama University ofScience, Ridaichou 1-1, Okayama 700, Japan
ABSTRACT This paper demonstrates a unique action of hydrogen on defects and impurities in scmiconductors. Hydrogen injected into n-type Si by chemical etching or hydrogen plasma not only passivates phosphorus but also electrically activates carbon by forming a H-C complex acting as an electron trap E3(0.15). A model of the structure and electronic state of the H-C complex is proposed on the basis of available experimental data on the properties of the complex. The diffusion coefficient of isolated hydrogen below 300K is evaluated from its diffusion process to phosphorus after the photoinduccd dissociation of the H-C complex. Some differences in hydrogen diffusion between chemically etched and plasma hydrogenated crystals are discussed.
INTRODUCTION It has been widely recognized that atomic hydrogen passivates various electrically active defects and impurities [1-3]. However, other actions of hydrogen on defects and impurities have not been so extensively studied. Recently, we have found that hydrogen injected into n-type Si by chemical etching not only passivates phosphorus but also electrically activates a neutral impurity, carbon, by forming a H-C complex acting as an electron trap E3(0.15) [4]. The H-C complex is stable up to 100°C in the dark but is dissociated under band gap illumination even below 300K through the recombination-enhaneed reaction. The emitted free hydrogen diffuses to a phosphorus atom to passivate it. By analyzing this process, we have evaluated the hydrogen diffusion coefficient below 300K [5]. In this paper, we have first confirmed the above activation effect of hydrogen on carbon and the properties of the resultantly formed H-C complex by using another commonly used technique of hydrogen injection, or plasma hydrogenation. Next, we propose a model of the structure and electronic state of the H-C complex on the basis of available experimental data. Finally, we discuss some differences in hydrogen diffusion between chemically etched and plasma hydrogenated crystals.
EXPERIMENTAL PROCEDURE We used three kinds of silicon crystals containing different densities of phosphorus, oxygen, and carbon, as listed in Table I. Many samples cut from the crystals were chemically etched and heated at 700*C in flowing 02 gas for lh to anneal some grow-in defects and also to effuse hydrogen injected by the preceding chemical etching. The oxidized layers of the samples surface were removed by immersing them into HF acid. Subsequently, the samples were hydrogenated by chemical etching or hydrogen plasma. The chemical etching was carried out by immersing the samples into an acid mixture consisting of HNO3:HF = 10:1 at 20°C for 5 min. The hydrogen Mat. Res. Soc. Symp. Proc. Vol. 262. (0)1992 Materials Resea
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