A hole trap which was related to H and C was found in p-type crystalline material, after H and D injection, by means of chemical etching and plasma exposure. Deep-level transient spectroscopy showed that this center was located at 0.33eV above the valence band, and exhibited no Poole-Frenkel effect in electric fields of less than 6000V/cm. Depth profiling, using deep-level transient spectroscopy, indicated that this center was distributed between 1 and 7 from the surface; with densities of 1011 to 1013/cm3, depending upon the hydrogenation method. On the other hand, secondary ion mass spectroscopy revealed that most of the D which was injected existed within a much shallower region that was less than 60nm from the surface, with densities of 1018 to 1020/cm3. It was concluded that most of the injected H remained in the near-surface region, probably in the form of molecules and larger clusters, and that only a minority diffused into the bulk in atomic form so as to form an electrically active complex with C. Annealing experiments were used to investigate the thermal stability of the complex. It was found that it was stable in the dark at temperatures of up to 100C. Above this, it was completely annihilated; according to first-order kinetics with an activation energy of about 1.7eV. Illumination with band-gap light (with and without reverse bias) at room temperature, or at 50C, had no effect upon the stability of the trap. This contrasted with the photo-induced annihilation of a recently observed electron trap that was also related to H and C and which exhibited a comparable thermal stability. These similarities and differences suggested that the previously observed electron trap, and the presently observed hole trap, arose from 2 different defects (with similar origins and structures) and were tentatively proposed to be the electronic states of bond-centered and C anti-bonding configurations, respectively, of H in H-C complexes.

Y.Kamiura, M.Tsutsue, Y.Yamashita, F.Hashimoto, K.Okuno: Journal of Applied Physics, 1995, 78[7], 4478-86