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

We briefly review the experimental results on a hydrogen-carbon (H-C) complex in Si to present clear pictures on the electronic state and atomic configuration of the complex and the local motion of hydrogen in the neighborhood of carbon in Si. Atomic hydrogen, which is injected into Si by chemical etching or hydrogen-plasma irradiation, electrically activates a substitutional carbon atom by forming the H-C complex. It acts as an electron trap with a donor level at E-C-0.15 eV, which can be detected by deep-level transient 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 donor state, and are consistent with a structural model, where a hydrogen atom occupies a bond-centered (BC) site between the carbon and silicon atoms. This model is also consistent with the results of recent theoretical calculations, The electronic state of the H-C complex is virtually identical to that of the isolated hydrogen in the BC site in the positive and neutral charge states, but is slightly perturbed by carbon. The complex is unstable outside the depletion region of the Schottky junction. Therefore, it is concluded that the complex becomes unstable to be dissociated in the neutral charge state by capturing an electron from the conduction band. Such charge-state dependent motion of hydrogen also characterizes the reorientation of the H-C complex as follows. The stress-induced alignment and subsequent relaxation of the H-C complex occur under < 111 > and < 110 > stresses. These processes correspond to the hydrogen jumps between the equivalent BC sites around the carbon atom. This motion of hydrogen is greatly influenced by the charge state of the complex. The conclusion reached is that hydrogen moves more easily in the neutral charge state. Such a feature about the hydrogen motion is quite similar to that of the isolated hydrogen located in the BC site. The charge-state dependent motion of hydrogen may be one of the unique properties of hydrogen in Si.