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

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Abstract
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.