Defects in irradiated silicon: EPR and electron-nuclear double resonance of interstitial boron

Abstract

An EPR spectrum, labeled Si-$G28$, is identified as arising from neutral interstitial boron in silicon. It is produced by 1.5-MeV electron irradiation at 20.4\ifmmode^\circ\else\textdegree\fi{}K, presumably when a substitutional boron atom traps a mobile interstitial silicon atom which is produced in the original damage event. Three possible models are discussed which are consistent with the EPR and electron-nuclear double-resonance results: (a) a bent Si-B-Si bonded interstitialcy; (b) a similar Si-Si-B interstitialcy; or (c) a Jahn-Teller distortion of the boron from the hexagonal interstitial site in the silicon lattice. Uniaxial stress in the presence of light at low temperatures produces alignment in one of the distortional degrees of freedom for the defect. This is interpreted as stress alteration of the capture matrix elements for electrons into the differently distorted configurations. Polarized light is also found to produce alignment in the absence of stress into a second degree of freedom for the defect. Thermally activated recovery from this alignment reveals an activation energy for reorientation of 0.6 eV. Interstitial boron is unstable at room temperature, disappearing in \ensuremath{\sim} 30 min with an activation energy also of \ensuremath{\sim} 0.6 eV. It is suggested that annealing may result from long-range migration of the interstitial boron with the one-jump diffusional process being identical to the 0.6-eV reorientational process. This is a natural consequence of models (a) or (c). The reorientation stimulated by light at 4.2\ifmmode^\circ\else\textdegree\fi{}K, therefore, indicates that athermal migration may be induced by the light. An attempt to test this using 1.06-\ensuremath{\mu}m YAIG:Nd laser illumination was inconclusive.