Vapor Phase Synthesis and Characterization of Gallium Nitride Powders

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Vapor Phase Synthesis and Characterization of Gallium Nitride Powders

Kazuhiko Hara, Yoshinori Matsuo and Yuuki Matsuno Imaging Science and Engineering Laboratory, Tokyo Institute of Technology 4259 Nagatsuda-cho, Midori-ku, Yokohama 226-8503, Japan ABSTRACT GaN crystalline powders have been synthesized by the reaction of a Ga vapor with an ammonia gas at the reaction temperature Tr = 900 - 1100 °C in an atmospheric-pressure open-tube reactor. The size of GaN particles ranges from 0.2 to 2 µm. It was found that the structural and luminescent properties depend strongly on Tr. The mean size of the GaN particles increased as Tr is raised. The GaN powders exhibited photoluminescence (PL) dominated by the band edge emissions. Thermal quenching is relatively significant for the powders synthesized at lower Tr. This is presumably due to enhanced non-radiative recombination at the surface because of their smaller particle size.

INTRODUCTION High luminescent efficiency and resistance against deterioration of GaN-based materials, which have been demonstrated by their light-emitting devices, are very attractive features for the development of powder phosphors for wide-area flat panel display devices. To this effect, we aim at synthesizing undoped GaN powders with high crystalline quality for the novel matrix of powder phosphors. Although there are numerous publications on the growth of GaN films, reports on the synthesis of GaN powders are very limited. GaN powders have been synthesized by the nitridation of Ga [1-3] or Ga compounds [1,4], which yielded GaN crystalline particles of micrometer size. However, the relationship between the synthesis conditions and the properties of powders was not systematically examined in these studies. This paper describes the preparation of undoped GaN powders by the method utilizing the reaction of a Ga vapor with an ammonia gas under atmospheric pressure. Focusing on the dependence on the reaction temperature, the structural and luminescent properties of the powders were characterized.

EXPERIMENTAL DETAILS The synthesis system developed for this study, as schematically shown in figure 1, consists of a vertical quartz reactor of 1 m long with 40 mm in inner diameter. The 7N-pure Ga source was placed in a boron nitride crucible and was heated by rf induction in a flow of getter-purified N2 gas (0.5 slm). The surface temperature of the molten Ga was monitored by a pyrometer and was kept at about 1300 °C during the synthesis. About 0.3 g of Ga was vaporized in 1 hour under this condition. The Ga vapor was mixed with a flow of 5N-pure NH3 (0.5 slm) and N2 (0.5 slm), and then, transported to the reaction zone maintained at the reaction temperature of Tr = 900 1100 °C by a 600 mm long tubular furnace. The temperature profile in the furnace at Tr = 1000 °C is shown in the figure. After the synthesis process, powders were filtered at the outlet of the G3.31.1

Pyrometer

Filter Exhaust ←

Position (mm)

600

Furnace

300

Ga 0 600

800 1000

Temperature (°C)

RF coil

NH3+ N2 →

Figure 1. Schemat

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