Effect of Polarized Light on the 1.8-, 3.3-, and 3.9-μ Radiation-Induced Absorption Bands in Silicon

Abstract

The effect of polarized light on the 1.8-, 3.3-, and 3.9-\ensuremath{\mu} radiation-induced absorption bands in silicon, which have been correlated with the divacancy, has been studied. It is found that an illumination with polarized light of energy corresponding to the 1.8- or 3.3-\ensuremath{\mu} band reduces the absorption coefficient of the band at a temperature below a critical temperature (32.5\ifmmode^\circ\else\textdegree\fi{}K for the 1.8-\ensuremath{\mu} band and 23\ifmmode^\circ\else\textdegree\fi{}K for the 3.3-\ensuremath{\mu} band). The phenomenon is attributed to the electronic reorientation of the divacancy achieved through an excited state by absorbing a photon. A net alignment of the defect can be observed only at a temperature at which the defect in the ground state is usually "frozen" in a particular orientation. From the temperature dependence of the recovery of the aligned defect in the dark, the activation energies of 0.076 and 0.056 eV are found to be required for the reorientation of the defects in the ground states causing the 1.8- and 3.3-\ensuremath{\mu} bands, respectively. The results indicate that the 1.8-\ensuremath{\mu} band arises from the neural divacancy only. An analysis of the temperature dependence of the reorientation effect has been made. It is indicated that the activation energy required for the reorientation in the excited state is very small, probably in the order of the thermal energy at \ensuremath{\sim}10\ifmmode^\circ\else\textdegree\fi{}K. No similar effect has been observed in the 3.9-\ensuremath{\mu} band, which is consistent with the fact that this band contributes photoconductivity.