The excitation spectrum of the trigonal and the orthorhombic FeIn centres in silicon

Excitation spectra of trigonal and orthorhombic FeIn pairs in silicon have been studied by Fourier transform spectroscopy. The spectra were identified as due to hole transitions from the deep ground state to shallow hole states. The orthorhombic configuration is stable but population of the metastable trigonal configuration was obtained by above-bandgap excitation. For the orthorhombic and trigonal centre, the positions of the 0/- FeIn levels were estimated to be 390 meV and 320 meV below the conduction band minima. Arguments are given that for the trigonal centre iron resides on the nearest-neighbour interstitial position.