Abstract
The electrical properties, deep level spectra, optical transmission, and luminescence spectra were measured on freestanding GaN crystals grown by hydride vapor phase epitaxy. The samples are semi-insulating n type with room temperature resistivity of 3.8×109Ωcm and high electron mobility of 715cm2∕Vs. The Fermi level in these samples is pinned by a Fe-related level near Ec−0.57eV that could be due to the Fe2+∕Fe3+ transition. This level manifests itself also as a strong blue luminescence band peaked near 2.85eV. An additional Fe-related band with optical threshold near 1.6eV is observed in optical transmission spectra. The samples are paramagnetic, suggesting an absence of significant Fe precipitation.
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