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Undoped β-Ga2O3 single crystals were grown by the floating zone technique under several mixtures of N2 and O2 gas and 2 atm pressure. Polarized reflectance spectra in the 50–1200 cm—1 region showed all 12 IR active modes, with an additional background due to free carrier reflection. By least-squares fitting, the resonance frequency, the oscillator strength, the damping constant for each lattice oscillator, and the plasma frequency and damping factor of the free carriers were determined. Electrical measurements of the conductivity and the Hall-coefficient were correlated with the electrical parameters estimated from the optical data. The increase in the carrier concentration with decreasing oxygen partial pressure is accompanied by a decrease in carrier mobility, so that the conductivity does not vary significantly with the oxygen partial pressure.
V�llora et al. (2002) studied this question.