Size Reduction and Rare Earth Doping of GaN Powders through Ball Milling
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1202-I09-12
Size Reduction and Rare Earth Doping of GaN Powders through Ball Milling Xiaomei Guo1, Tiju Thomas2, Kewen K. Li1, Jifa Qi3, Yanyun Wang1, Xuesheng Chen4, Jingwen Zhang1, Michael G. Spencer2, Hua Zhao5, Yingyin K. Zou1, Hua Jiang1, Baldassare Di Bartolo5 1 Boston Applied Technologies, Inc., Woburn, MA 2 School of Electrical and Computer Engineering, Cornell University, Ithaca, NY 3 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 4 Department of Physics and Astronomy, Wheaton College, Norton, MA 5 Department of Physics, Boston College, Chestnut Hill, MA
ABSTRACT Ball milling of ammonothermally synthesized GaN powders was performed in an ethanol solution for a variety of durations, resulting in average particle sizes of nanometer. The ball milled powders showed an obviously brightened color and improved dispersability, indicating reduced levels of aggregation. X-ray diffraction (XRD) peaks of the ball milled GaN powders were significantly broadened compared to those of the assynthesized powders. The broadening of the XRD peaks was partially attributed to the reduction in the average particle size, which was confirmed through SEM analyses. On the other hand, rare earth doping of commercial GaN powders was also achieved through a ball mill assisted solid state reaction process. Rare earth salts were mixed with GaN powder by ball milling. The as-milled powders were heat treated under different conditions to facilitate the dopant diffusion. Luminescence properties of the rare earth doped GaN powders at near infrared range were investigated and the results were discussed.
INTRODUCTION One of the major issues encountered with high power lasers is the management of the heat generated during lasing. Gallium nitride (GaN) possesses high heat conductivity (1.3 W cm-1 ºC-1), making it a promising candidate for high power applications. However, it is extremely difficult and costly to produce single crystal GaN with sufficient size and optical quality. Polycrystalline laser hosts offer several remarkable advantages over conventional single crystal ones: higher active ions doping concentrations, larger sizes, more complex shapes, and much lower fabrication costs due to shortened fabrication process and high volume production capability [1]. Therefore, exploration in fabricating GaN ceramic laser host has been an intensively researched area in recent years. Proper particle size and good size uniformity of starting powders are key factors to achieving desirable optical transparency in GaN ceramics since its crystallographic anisotropy effect can be reduced as the crystallite size falls into the submicron range [2].
However, mono-dispersed nanoparticle syntheses of GaN have remained a challenging task. The difficulties confronted by researchers include impurity removal, yield, size uniformity and crystallinity, etc.. Wu et al. have produced GaN powders with high yield and high purity using an ammonothermal process [3]. However, the obtained powders are in micron si
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