Piezospectroscopy study of the trigonal FeIn pair center in silicon

Abstract

The electronic structure of an iron- and indium-related center in silicon has been studied by Fourier transmission infrared spectroscopy, employing uniaxial stress and polarization spectroscopy. The center gives rise to an excitation spectrum centered at about 6550 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and is closely related to the orthorhombic FeIn pair center with an excitation spectrum at about 6100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The two spectra are always observed in our Fe and In codoped samples, and show metastability properties similar to those that have been reported previously for the trigonal and orthorhombic FeIn pair centers. In this paper, uniaxial stress results are reported which show unambiguously that the ${6550\ensuremath{-}\mathrm{c}\mathrm{m}}^{\mathrm{\ensuremath{-}}1}$ spectrum involves a center with trigonal symmetry. The polarization properties of the stress split lines show that the initial state of the transitions transforms as the ${\ensuremath{\Gamma}}_{4}$ irreducible representation of the ${C}_{3v}$ point group which is identical to the one previously deduced for the trigonal FeIn center by electron paramagnetic resonance. One of the excitation lines shows interesting polarization rules, which are discussed in detail and explained as a superposition of a \ensuremath{\sigma} and a \ensuremath{\pi} dipole at a ${C}_{3v}$ center. The origin of the spectrum is tentatively assigned to transitions from the deep ground state to shallowlike hole states. The symmetry assignment of the center and its ground state gives strong evidence that the center studied is indeed the trigonal version of the FeIn pair center.