SYNTHESIS OF CUBIC GaN SINGLE CRSYTALS BY THE K FLUX METHOD

氮化镓具有六方纤锌矿型结构（h-GaN），作为蓝光发光二极管和短波长激光二极管的材料引起了人们的兴趣。GaN具有立方锌混合型结构（c-GaN）的多晶型，但由于缺乏块状c-GaN单晶，c-GaN的详细性质尚未明确。本研究采用K助熔剂，在700℃、7 MPa、24 h条件下制备了颗粒状和片状氮化镓晶体。在气液界面处获得了尺寸约为1 mm的h-GaN血小板晶体。晶粒尺寸为50 μm，为c-GaN和h-GaN的混合物。Rietveld分析显示，颗粒状晶体含有40%的c-GaN。在600℃、24 h、7 MPa的N_2条件下，得到了粒径为30 μm、含95% c-GaN的颗粒状晶体。在700℃、24 h、4 MPa的N_2条件下制备的70% c-GaN颗粒晶体尺寸约为60 μm。c-GaN的生成随着温度和氮气压力的降低而增加。在700℃、96 h、4 MPa的N_2条件下，得到了最大尺寸为200 μm的颗粒状晶体。在650℃、96 h、4 MPa的N_2条件下合成的样品中获得了一颗尺寸为80 μm的无色透明c-GaN晶体。观察到（100）相的方形面和（111）相的等边三角形台阶，反映了立方结构的三轴对称性。在c-GaN晶体的阴极发光光谱中，c-GaN在3.209eV处的近带边发射峰与c-GaN薄膜的结果一致。peek的半值宽度为76 meV。采用K-Na助熔剂制备了颗粒状和片状GaN晶体。然而，用K- na通量制备的颗粒或板的c-GaN比例小于用K通量制备的颗粒或板。K-Ga熔体在W坩埚中，在650 ~ 680℃和4 ~ 7 MPa的氮气中未结晶。K-Ga金属间化合物部分熔体在610 ~ 630℃下得到了40 μm大小的颗粒状晶体。少

Gallium nitride, having the hexagonal wurtzite-type structure (h-GaN), has attracted an interest as a material for blue-light emitting diodes and short-wavelength laser diodes. GaN has a polymorph of the cubic zinc-blende-type structure (c-GaN), hut the detail properties on the c-GaN have not been clarified due to the lack at bulk c-GaN single crystals.In the present study, granular and platelet GaN crystals were prepared at 700℃ for 24 h and 7 MPa of N_2 by using a K flux. The platelet crystals of h-GaN with a size of about 1 mm were obtained at the vapor-liquid interface. The granular crystals with a size of 50 μm were characterized as a mixture of c-GaN and h-GaN. Rietveld analysis revealed that granular crystals contain 40% of c-GaN. The granular crystals of 30 μm containing 95% of c-GaN were obtained at 600℃,24 h and 7 MPa of N_2. The size of the granular crystals of 70% c-GaN, prepared at 700℃, 24 h and 4 MPa of N_2 was about 60 μm. The formation of c-GaN increased with decreasin … More g temperature and N_2 pressure.The granular crystals having the maximum size of 200 μm was obtained at 700℃, 96 h and 4 MPa of N_2. A colorless transparent c-GaN crystal with a size of 80 μm was picked up in the sample synthesized at 650℃,96 h and 4 MPa of N_2. Square facets of (100) phase and steps of equilateral triangle shape of (111) phase, reflecting the threefold-axis symmetry of cubic structure, were observed. A peak from near band-edge emission of c-GaN at 3.209eV observed in the cathodoluminescence spectrum of the c-GaN crystal was consistent with the results reported for c-GaN thin films. The half-value width of the peek was 76 meV.Granular and platelet GaN crystals were also synthesized by using a K-Na flux. However, the ratio of c-GaN is the granular or plates prepared with the K-Na flux was smaller than that prepared with the K flux. No crystal was obtained from K-Ga melt in a W crucible at 650 -680℃ and 4 -7 MPa of N_2. Granular crystals with a size of 40 μm were obtained from partial melt of K-Ga intermetallic compounds at 610 -630℃. Less