Disorientation kinetics of the B 80 4 centers in single crystal silicon

Using exciton spectroscopy methods, it was established that ₈₀ ⁴ centers can be oriented under uniaxial compression conditions not only in the [111] axis direction, but in the $[bar 111]$ and $[1bar 11]$ directions as well. Disorientation of the ₈₀ ⁴ centers was studied in detail, a kinetic equation adequately describing this process is presented, and an expression for the characteristic reorientation time as a function of the temperature was obtained. It was found that the reorientation rate obeys the Arrhenius law with an activation energy of about 1.54 eV. The experimental results are explained proceeding from a hypothesis that the ₈₀ ⁴ center is identical to a ring hexavacancy. A mechanism of the ₈₀ ⁴ center (hexavacancy) reorientation is proposed within the framework of this model, according to which the hexavacancies are thermally excited into the first metastable state and then pass to a ring state with different orientation. Involving the spatial displacement of hexavacancies during reorientation, this process has to be accompanied by the Brownian motion of the hexavacancies. A correlation was found between the direction of orientation of the ₈₀ ⁴ centers (hexavacancies) and the relative change in the 〈11〉bond length under uniaxial compression conditions. This result is interpreted in terms of the hexavacancy geometry.