Electronic state, atomic configuration and local motion of hydrogen aroundcarbon in silicon

We briefly review the experimental results on a hydrogen-carbon (H-C) compl ex in Si to present clear pictures on the electronic state and atomic confi guration of the complex and the local motion of hydrogen in the neighborhoo d of carbon in Si. Atomic hydrogen, which is injected into Si by chemical e tching or hydrogen-plasma irradiation, electrically activates a substitutio nal carbon atom by forming the H-C complex. It acts as an electron trap wit h a donor level at E-C-0.15 eV, which can be detected by deep-level transie nt spectroscopy (DLTS). The features of the DLTS peak splitting suggest the C-3V symmetry of the H-C complex and the antibonding character of the dono r state, and are consistent with a structural model, where a hydrogen atom occupies a bond-centered (BC) site between the carbon and silicon atoms. Th is model is also consistent with the results of recent theoretical calculat ions, The electronic state of the H-C complex is virtually identical to tha t of the isolated hydrogen in the BC site in the positive and neutral charg e states, but is slightly perturbed by carbon. The complex is unstable outs ide the depletion region of the Schottky junction. Therefore, it is conclud ed that the complex becomes unstable to be dissociated in the neutral charg e state by capturing an electron from the conduction band. Such charge-stat e dependent motion of hydrogen also characterizes the reorientation of the H-C complex as follows. The stress-induced alignment and subsequent relaxat ion of the H-C complex occur under < 111 > and < 110 > stresses. These proc esses correspond to the hydrogen jumps between the equivalent BC sites arou nd the carbon atom. This motion of hydrogen is greatly influenced by the ch arge state of the complex. The conclusion reached is that hydrogen moves mo re easily in the neutral charge state. Such a feature about the hydrogen mo tion is quite similar to that of the isolated hydrogen located in the BC si te. The charge-state dependent motion of hydrogen may be one of the unique properties of hydrogen in Si.