Formation Mechanism and Recombination-Enhanced Dissociation of a Hydrogen-Carbon Complex in Silicon
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FORMATION DISSOCIATION
MECHANISM AND RECOMBINATION -EN HAN CED OF A HYDROGEN-CARBON COMPLEX IN SILICON
YOICHI KAMrURA*, FUMIO HASHIMOTO*, AND MINORU YONETA** *Facultyof Engineering,Okayama University, Tsushimanaka 3-1-1, Okayama 700, Japan "**Facultyof Science, Okayama University of Science, Ridaichou 1-1, Okayama 700, Japan
ABSTRACT We have found that chemical etching induced an electron trap E3(0.15) into n-type Si. We attribute this trap to a hydrogen-carbon complex on the basis of available experimental data. By measuring DLTS depth profiles of the E3 trap, we propose a model of the formation mechanism of the hydrogen-carbon complex as follows. Hydrogen atoms are adsorbed on the Si surface to terminate Si dangling bonds during chemical etching, and after the etching some unstably adsorbed ones diffuse into the near-surface region of silicon and are trapped by carbon to form the complex. The E3 trap is stable up to 100'C in the dark but is annihilated by the illumination of band gap light around 250K only outside the depletion layer of the Schottky structure. This provides unambiguous experimental evidence for the recombination-enhanced dissociation, in which the electronic energy released by the electron-hole recombination at the E3 level is converted into local kinetic energy of hydrogen to be released from carbon.
INTRODUCTION Two different aspects of hydrogenation effects on semiconductors have recently received growing interest. One is the so-called passivation effect that atomic hydrogen neutralizes various electrically active defects and impurities by forming comlexes with them [1-3]. Hydrogen is normally injected by plasma treatments into the near-surface regions of semiconductor crystals. The other aspect is the dangling-bond termination effect of hydrogen at the Si surface [4]. In this case, hydrogen is introduced onto the Si surface on removing thermally or chemically oxidized surface layers by HF acid and rinsing them in ultrapure water. Using this technique, one can obtain very clean and atomically flat Si surfaces. The above two hydrogenation effects arc of course important from technological viewpoints, but they also provide several interesting fundamental research subjects concerning the behavior and properties of hydrogen in semiconductors. 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 hydrogen-carbon (H-C) complex acting as an electron trap E3(0.15) [5, 6]. The H-C complex is stable up to 100*C in the dark but is dissociated under band gap illumination even below 300K. In this paper, we propose models of the formation and annihilation mechanisms of the H-C complex on the basis of available experimental data.
EXPERIMENTAL PROCEDURE We used two kinds of phosphorus-doped silicon crystals, as listed in Table I. Many samples cut from the crystals were chemically etched and heated at 700"C in flowing 02 gas for 1 h to anneal some grow-in defects and also to
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