| Gallium Nitride (GaN) is an excellent promising direct wide bandgapsemiconductor material and also is one of the most advanced semiconductors in theworld due to its excellent property of light and electrology, its outstanding mechanismpropoty and heat stability. (physics, chemistry , mechanical and heat stability.It can beused for light emitting diodes and also used for fluorescent light lamp or incandescentlamp. In addition, GaN is also appropriate for a potential application of fuel batteries.The spectrum scope from glow to ultraviolet light are overcastted by the band gap ofboth GaN and alloy. The commodity is swiftly realized as soon as the light emittingdiodes and laser came into existence. Up to the present, it can be widely applied tolight emitting devices, such as blue, near ultraviolet, violet light emitting diodes, laserand high temperature / high power microelectronic devices , At the same time, it can beused as a new eco-friendly material and applied into environmental protection. It isbecoming the hotspot for semiconductor materials and also ideal for performancesuperiority of optoelectronic devices. While the research years indicate that theinfluence of GaN powder are gradually being attached much importance to the aspectof fabricating of photoelectricity,high temperature and high power microelectronicdevices, and also exerts a function of origination in the course of developing highqulity GaN films or GaN nanowires, that preparation of GaN powders are exerting anmore and more important affection on the growth of mast GaN films and theapplication of optics technique of nano-dimension considered by S.H.Lee et al,moreover, GaN itself can also serve as fluorescent light powder of high quality..Sublimation and high-pressure solution methods are considered as effective methodsfor crystal growth of GaN. The methods demand the availability of well-characterizedGaN powder source with high purity and signal phase. So considerable effort has beendirected towards the synthesis of highly-qualified GaN powders. In 1993, GaNpowders have been synthesized for the first time by a novel hot mechanical alloyingprocess by P. Millet et al, but this method is time-consuming and can only get GaNpowder of low purity. In 1996, ultra-pure GaN powders have also been synthesized bythe direct current arc plasma method by H.D.Li et al, using Ga,both mixture of N2 andNH3 as reaction material, but the increase of purity can not make up theuncontrollability and complication in the operation.In this dissertation, a novel two-step method of synthesizing GaN powder ischiefly discussed, By means of a two-step combination of sol-gel process withhigh–temperature ammoniating , gallium oxide (Ga2O3) gel formed by usingGa(OC2H5)3 as a new precursor are used as the gallium source, and ammonia(99.99%)is used as the nitrogen source, GaN powders are synthesized by nitriding Ga2O3 gel inthe flow of NH3 gas at different temperature for 20 min.The results of experiment and characterization indicate that the optimal conditionof fabrication of GaN powders using two-step method of sol-gel and high nitridationtemperature is associated with a different technology that gel can be fabricated bysol-gel. In this experiment, four different proportionings are used to fabricate gel bymeans of combination of Ga(OC2H5)3 as precursor with anhydrous C2H5OH, that is tosay, the proportioning of Ga(OC2H5)3 and anhydrous C2H5OH respectively is : (1)2:40;(2)2:70;(3)2:100;(4)2:130 . The results of experiment and characterizationalso indicate that the optimal condition of GaN powders in the two proportioning of(1)2:40 and(2)2:70 synthesized by reactioning gel with the flowing NH3 is 20minat 950℃, however, in the other two proportioning of (3)2:100 and(4)2:130, theoptimal condition of GaN powders synthesized by the reaction of gel with the flowingNH3 is 20min at 1000℃, at the same time, the optimal condition GaN powderssynthesized directly by the reaction β-Ga2O3 with the flowing NH3 that areinvestigated is 20min at 950℃. and all this experiment go along at constant pressure.Measurement results indicate that the synthesised GaN by different conditions is of asingle-phase hexagonl wurtzite structure. In any unintentionally doped sample, C andO are inescapable. When the sample is investigated by XPS, C and O are found, but Ois attributed to chemisorbed oxygen. Blue light emission is as a major peak in PLspectrum, and the emission is attributed to the transition from shallow donor level tothe acceptor carbon. When the morphology of GaN are investigated, the GaN powderssynthesized by this method is a single, short rod-like crystal and its size is about150nm in the two proportioning of (1)2:40 and(2)2:70,otherwise,it is about450nm in the other two proportioning of (1)2:100 and(2)2:130. The influenceson formation,morphology,structure and size of crystal of the same and differentproportioning condition at different nitridation temperature are positively discussed,and the research results indicate that the pattern,surface morphology,size andgranularity of GaN microcrystal under the same nitridation time are influenced bydifferent preparation condition of sol-gel and different nitridation temperature of gel,moreover, the optimal condition of preparation of GaN powders is influenced by thedifferent proportioning of reaction precursor.The mechanism of growth of GaN powder is also studied.The free energy ofreaction Ga2O3 gel and NH3 is positive and, thus, indication that they would not occurin the mechanism of growth studied. The reaction is favorable only if Ga2O is formedin this process. In the course of high nitridation temperature, When nitridationtemperature exceeded 600℃, NH3 is decomposed into NH2, NH, N2, N, H2 and H, so itcan be used as N source and the sample of GaN gel as Ga source. When thetemperature exceed 850℃, Ga2O3 deoxidized by H2 first converts into Ga2O, O2-inGa2O powders is then replaced by N3-. Along with time increases, GaN particles arecoagulated and crystal nuclei are formed, and then large grains are formed gradually. |
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