Additional observations on the gallium-X center in neutron-irradiated Si:Ga

In a previous paper we reported the formation of the gallium-X center by neutron irradiation of gallium-doped silicon. Since that report we have investigated a variety of other neutron-irradiated Si:Ga samples using float-zone crystals grown by three different vendors and irradiated at four different reactors. The behavior of Ga-X as a function of irradiation conditions, annealing temperatures (up to 800 °C) and various material properties has been studied by Fourier-transform infrared absorption spectroscopy and temperature dependent Hall-effect measurements. Ga-X was not observed in any of the as-grown samples but was definitely present in every irradiated sample. In all cases it first appears after a 400 °C anneal, reaches maximum concentration after a 600 °C anneal, and then decreases at higher anneal temperatures. The maximum Ga-X concentration observed in any sample appears to be dependent on the carbon concentration in that sample and not on the irradiation conditions. A more detailed Ga-X absorption spectrum was obtained showing lines not previously reported. A binding energy of 57.18±0.03 meV is deduced for the Ga-X ground state.