EPR of interstitial hydrogen in silicon: Uniaxial stress experiments

This paper deals with an electron paramagnetic resonance (EPR) study of the Si-AA9 EPR center, which has been previously identified as arising from a [111] bond-centered (BC) interstitial hydrogen in the neutral charge state (H-0) and is a hydrogenic analog of the anomalous state of muonium (Mu*) in silicon. Hydrogen was implanted into a high purity silicon sample by means of a cyclotron at 80 K. A uniaxial stress of similar to 2000 kg cm(-2) was applied to the [110] axis of the sample in the dark in the temperature range from 170 K to 77 K, and the stress was then removed. It was found that a preferential alignment of the defect had been frozen in at 77 K for both the H+ and H-0 states. Thermally activated recovery for alignment of the H+ in the BC position reveals an activation energy for reorientation of (0.43+/-0.02) eV with a pre-exponential factor of 1/tau=2.3x10(12) s(-1). For equilibrium alignment of the H+ in the BC position (at 140 K) the component of the piezospectroscopic B tensor was also determined to be B approximate to-2 eV. The fact that uniaxial stress (in the dark) produces alignment of the nonparamagnetic state of the AA9 center is the first experimental evidence that H+ is indeed situated in the BC position on the [111] axis, while a negative sign of the B tensor is direct confirmation that nearest to hydrogen, silicon atoms are outwardly relaxed.