Crystal Research and Technology
Cryst. Res. Technol. 42, 713 (2007) - Abstract -

Luminescence of GaN single crystals prepared by heating a Ga melt in Na–N2 atmosphere

Takahiro Yamada, Hisanori Yamane, Takenari Goto*, Takafumi Yao*, Yongzhao Yao**, and Takashi Sekiguchi**

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
*Center for Interdisciplinary Research, Tohoku University, 6-3 Aramaki, Aoba-ku, Sendai 980-8578, Japan
**Nanomaterials Laboratory, National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan

Keywords GaN, single crystal, Na flux method, photoluminescence, cathodoluminescence
PACS 71.55.Eq, 78.55.Cr, 78.60.Hf, 81.05.Ea, 81.10.Dn
DOI 10.1002/crat.200610893

Colorless transparent prismatic crystals (0.5-2.0 mm long) and hopper crystals (1.0-2.5 mm long) of GaN were prepared by heating a Ga melt at 800°C in Na vapor under N2 pressures of 7.0 MPa for 300 h. The photoluminescence (PL) spectrum of a prismatic crystal at 4 K showed the emission peaks of neutral donor-bound exciton and free exciton at 3.472 eV and 3.478 eV, respectively, in the near band edge region. The full-width at half-maximum (FWHM) of donor-bound exciton peak was 1.9 meV. The emission peaks of a donor–acceptor pair transition and its phonon replicas were observed in a lower energy range (2.9-3.3 eV). The emission peaks of the donor–acceptor pair transition and phonon replicas were also observed in the cathodoluminescence (CL) spectrum at 20 K. The donor-bound exciton PL peak of a hopper crystal at 4 K was at 3.474 eV (2.1 meV higher), having a FWHM of 6.1 meV which was over 3 times larger than that of the prismatic crystal. A strong broad band with a maximum intensity around 1.96 eV was observed for the hopper crystals in the CL spectrum at room temperature.




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