Nobuhiko Ishii

A simple molecular orbital calculation of ESR g-values for amorphous Si1−xCx, Si1−xGex and Ge1−xCx

Abstract g-values of the ESR signals due to dangling bonds in Si 1−x C x , Si 1−x Ge x and Ge 1−x C x alloy systems have been calculated for a cluster by using the extended Huckel theory, and compared with the observed g-values. It is revealed that g-values for dangling bonds on Si or Ge atoms are affected by the surrounding C atoms in Si 1−x C x or Ge 1−x C x alloy systems. In Si 1−x Ge x alloy system, however, the influence of the environment on the g-values of Si and Ge dangling bonds is rather small.

Density-functional-theory calculations of isotropic hyperfine coupling constants of radicals

Abstract Isotropic hyperfine coupling constants for the radicals BH 2 , CH 2 − , NH 2 , OH 2 + , BH 3 − , CH 3 , NH 3 + , H 2 CO + and CH 2 CH are calculated using density-functional theory with a gradient-corrected local-spin-density approximation and a Slater-type-orbital basis set. The agreement between the calculated and observed results is fairly good. The effect of rare-gas atoms surrounding radicals on the isotropic hyperfine coupling constants is also discussed.

Calculation of phonon density of states for amorphous Si

Abstract The phonon density of states is calculated for amorphous Si clusters with various bond angle and bond length fluctuations. From these results we conclude that the broadening of the width of the TO-like peak is due to the bond angle fluctuation, whereas the bond length fluctuation has a rather small effect on the phonon density of states.

Density functional theory calculations of isotropic hyperfine coupling constants of atoms and monohydrides

Abstract Isotropic hyperfine coupling constants of atoms (H, B, C, N, O, F) and monohydrides (CH, NH, OH) are calculated using density functional theory with a gradient-corrected local-spin-density approximation and a Slater-type-orbital basis set. The agreement between the calculated and observed results is fairly good. It is important to use a Slater-type orbital basis set which satisfies the cusp condition for electron density in order to obtain reliable results.

P-related defects in P-doped a-Si:H

Abstract The electronic states of a weak Si-P bond are calculated by applying a simple LCAO MO method to a small cluster of atoms. The energy level of the antibonding state of the weak Si-P bond appears above that of the Si dangling bond in the gap. The ESR hyperfine lines observed in P-doped a -Si:H can be attributed to an electron in this antibonding state. The change of the length of the Si-P bond according to its charged state is suggested to be a possible origin of the Staebler-Wronski effect.

Defects in magnetron-sputtered a-Gel−χNχ:H

Abstract Electron spin resonance (ESR) signals of a-Ge l − χ N χ :H films can be approximately decomposed into two components, suggesting that these two components arise from Ge dangling bonds in the Ge-rich and from N-rich phase-separated regions. Light-induced ESR signals are observed both at 77 K (≥ 0.29) and room temperature (≥ 0.32).

Cluster-model calculations of hyperfine coupling constants of dangling bond and weak bond in a-Si : H

Abstract We have calculated the 29 Si hyperfine coupling constants (hfccs) for neutral Si dangling bond ( D 0 ), that is, neutral threefold-coordinated Si atom and charged weak Si Si bonds ( W − and W + ) using the density-functional theory. The hfccs calculated for D 0 and W − are in fairly good agreement with the results estimated from the hyperfine structure of the g = 2.0055-line in the ESR signal and that of the g = 2.0043-component of the light-induced ESR (LESR) signal, respectively, in a -Si : H. In addition, the magnitude of the hfcc calculated for W + is less than the upper bound of the hfcc estimated for the g = 2.01-component of the LESR signal.

Cluster-model calculations of hyperfine parameters and g values for defects in a-Si:H

Abstract We have calculated the 29 Si hyperfine parameters using the density-functional theory and g values using an iterative extended Huckel theory for defects in Si clusters. We confirm from these calculations that the ESR signal with g=2.0055 and the g=2.0043- and 2.012-components of the light-induced ESR signal in a-Si:H originate from neutral threefold-coordinated Si atoms and negatively and positively charged weak Si–Si bonds, respectively.