Synthesis and structural properties of GaN powders

Gallium nitride (GaN) is a promising wide-band gap material for light emitting devices, such as blue, near ultraviolet, violet light emitting diodes and laser diodes [1], [2], [3], [4]. The band gap energy is Eg = 3.18 and 3.39 eV for cubic (zinc-blende structure) and hexagonal (wurtzite structure) symmetry at room temperature, respectively [5]. In addition, GaN exhibits high thermal conductivity and little radiation damage, so it can be applied to high power and high temperature microelectronic devices. However, the growth of high quality GaN layers is still a difficult task for the researchers since the GaN growth on foreign substrates leads to high dislocation density (≥10⁹ cm⁻²) due to severe mismatch both in lattice parameters and thermal expansion coefficients which ultimately affects the device performance and its lifetime. A trend for the future is, therefore, the development of GaN substrates for homoepitaxy by fabricating GaN bulk signal crystals and wafer. Sublimation [6] and high-pressure solution methods [7] are considered for crystal growth of GaN. The methods demand the availability of well-characterized GaN powder source with high purity and signal phase. In addition, GaN powders themselves could be used as high quality phosphors. So considerable effort has been directed towards the synthesis of GaN powders. The first synthesis GaN powders by reacting Ga₂O₃ with NH₃ gas in the temperature range of 600–1000 °C was reported by Lorenz and Binkowshi [8]. Many years later, Chu et al. have synthesized GaN powders using ammonolysis of gallium suboxide technique [9]. Recently, many reports are available on various aspects of GaN synthesis by reacting materials Ga with ammonia [10], [11], [12], [13]. In addition, many research groups have reported GaN powders were synthesized by reaction Ga₂O₃, GaAs, or GaOOH with NH₃ [14], [15], [16]. These techniques involve some critical experiment parameters such as the reaction temperature and the reaction period.

In this paper, the properties of GaN powders synthesized by nitriding Ga₂O₃ powders in the flow of NH₃ gas at 950 °C for 35 min were investigated by various characterization techniques such as X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM).