Piezospectroscopy study of the trigonal FeIn pair center in silicon

The electronic structure of an iron- and indium-related center in silicon h as been studied by Fourier transmission infrared spectroscopy, employing un iaxial stress and polarization spectroscopy. The center gives rise to an ex citation spectrum centered at about 6550 cm(-1), and is closely related to the orthorhombic FeIn pair center with an excitation spectrum at about 6100 cm(-1). The two spectra are always observed in our Fe and In codoped sampl es, and show metastability properties similar to those that have been repor ted previously for the trigonal and orthorhombic FeIn pair centers. In this paper, uniaxial stress results are reported which show unambiguously that the 6550-cm(-1) spectrum involves a center with trigonal symmetry. The pola rization properties of the stress split lines show that the initial state o f the transitions transforms as the Gamma(4) irreducible representation of the C-3v point group which is identical to the one previously deduced for t he trigonal FeIn center by electron paramagnetic resonance. One of the exci tation lines shows interesting polarization rules, which are discussed in d erail and explained as a superposition of a sigma and a 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 assignm ent of the center and its ground state gives strong evidence that the cente r studied is indeed the trigonal version of the FeIn pair center. [S0163-18 29(99)04023-0].