VAPOR PHASE SYNTHESIS AND CHARACTERIZATION OF GALLIUM-NITRIDE-BASED POWDERS

(1)在常压开管反应器中，Ga蒸气与氨气在反应温度T_r=900 ~ 1100℃下反应合成GaN结晶粉末。随着T_r的增大，GaN颗粒的平均尺寸增大。在900℃下合成的粉体由多种多面体颗粒组成，大部分颗粒尺寸在0.2 ~ 0.4 μm之间。随着T_r的增大，颗粒趋向于变大。当T_r=1100℃时，晶粒分布更为分散，达到0.3 ~ 2.0 μm。(2) x射线衍射发现，在T_r≥1050℃时合成的粉末主要由六边形GaN颗粒组成，而在T_r≤1000℃时合成的粉末主要由立方态GaN （c-GaN）颗粒组成。在1000℃和900℃下合成的样品，通过理论计算得到的粉末中c-GaN的含量分别为7%和23%。(3) GaN粉末表现出以带边发光为主的光致发光（PL）。在较高T_r下合成的GaN粉末在293 K时的综合PL强度约为24 K时的3%，表明其非辐射中心浓度较低。在较低T_r下合成的粉末具有较明显的热猝灭作用。这可能是由于它们的颗粒尺寸较小，在表面增强了非辐射复合。(4)安装铟坩埚后，合成了Ga_<1-x>In_xN合金粉末。在800℃合成的样品中，铟的含量χ = 0.04。χ随T_r的增大而减小；当T_r=1100℃时，未掺杂铟。在1000℃下合成的χ=0.02的样品比在1100℃下合成的样品显示出更强的PL，表明合金波动引起的载流子局部化现象有效地抑制了表面的非辐射复合。

(1) GaN crystalline powders were synthesized by the reaction of a Ga vapor with an ammonia gas at the reaction temperature T_r=900-1100℃ in an atmospheric-pressure open-tube reactor. The mean size of the GaN particles increased as T_r is raised. The powder synthesized at 900℃ consists of particles of various polyhedra, most of which have size of 0.2-0.4 μm. As T_r is raised, the particles tend to become larger. The size distribution also becomes much spread and reaches 0.3〜2.0 μm for T_r=1100℃.(2) It was found by X-ray diffraction that the powders consist primarily of hexagonal GaN particles for T_r【greater than or equal】1050℃, whereas those synthesized at T_r【less than or equal】1000℃ contain cubic GaN (c-GaN) particles. The fractions of c-GaN in the powders determined based on theoretical calculations ware about 7 and 23% for the samples synthesized at 1000 and 900℃, respectively.(3) The GaN powders exhibited photoluminescence (PL) dominated by the band edge emissions. The integrated PL intensity at 293 K is about 3 % of that obtained at 24 K for the GaN powders synthesized at higher T_r, indicating a low concentration of non-radiative centers. Thermal quenching is relatively significant for the powders synthesized at lower T_r. This is presumably due to enhanced non-radiative recombination at the surface because of their smaller particle size.(4) Ga_<1-x>In_xN alloy powders were synthesized after installing a crucible for indium. The indium content, χ, of 0.04 was obtained for the sample synthesized at 800℃. χ decreased with raising T_r ; no indium was incorporated when T_r=1100℃. The sample with χ=0.02, which was synthesized at 1000℃, showed more intense PL than that synthesized at 1100℃, suggesting that carrier localization phenomena induced by the alloy fluctuation effectively suppress non-radiative recombination at the surface.