Preparation Of Gallium Nitride Via Chemical Vapor Deposition Method And Its Optical Property Research

As a representative of the third generation semiconductor materials, gallium nitride(GaN) is widely researched. Since its unique optical and electrical properties, GaN showswide applications in optics and optoelectronics chemistry.In this paper, one-dimensional structures of gallium nitride nanorods, nanowires andchromium/indium doped gallium nitride nanowires were prepared in a tube furnace usingchemical vapor deposition (CVD) method, The influences of catalysts, different galliumsource, ammoniation temperature and annealing time on the structure and morphology ofproduct were investigated. Transmission electron microscopy (TEM), scanning electronmicroscopy (SEM), X ray diffraction (XRD), energy dispersive spectrum (EDS), Fouriertransform infrared spectroscopy (FTIR) and photoluminescence (PL) spectroscopy wereused to detect and analyze the samples. Also, the possible formation mechanism ofdifferent materials was discussed. The details and results are summarized as follows.Gallium nitride nanorods were prepared at1050℃and2h using gallium oxide as thegallium source, ammonia as the nitrogen source and silicon wafer as the substrate. Theeffect of catalyst on the structure and morphology of samples was studied by usingdifferent catalysts, such as nickel powder, indium powder and nickel nitrate, respectively.The results showed that when nickel nitrate was used as the catalyst, GaN nanorods wereprepared with the best morphology and the highest degree of crystallization. Based on theresults of SEM and EDS analysis, it could be deduced that GaN nanorods preparedwithout catalyst followed the vapor-solid growth mechanism, and GaN nanorods preparedwith catalyst followed the vapor-liquid-solid growth mechanism. The optical properties ofthe samples were investigated by the photoluminescence (PL) spectroscopy. It could befound that, GaN nanorods prepared with nickel nitrate as catalyst had a strong emissionpeak at369nm and a relatively weak emission peak at537nm. Compared with the PLspectra of the sample prepared without catalyst, the peak moved to the smaller wavelengthdirection obviously.GaN nanowires were prepared using ammonia as nitrogen source, silicon wafer assubstrate and different Ga sources, such as metal gallium, gallium oxide and gallium oxide hydroxide, respectively. The influences of catalyst (indium powder and nickel nitrate),ammoniation temperature (800,900,950,1000and1050℃) and annealing time (0.5,1,1.5,2and3h) on the products were investigated. The results showed that thedirectional growth of GaN nanowire arrays were obtained at1050℃and3h usinggallium oxide as the gallium source and nickel nitrate as the catalyst. The nanowires withdiameter of only30nm and the length of more than10μm show a hexagonal crystalstructure. PL analysis indicated that samples prepared with three different gallium sourcewere all show a characteristic peak of GaN at370nm, which was a slight red shiftcompared with that of bulk GaN. Also, PL result showed that GaN nanowires preparedwith gallium oxide as the gallium source had the minimum defects.Chromium doped GaN nanowires were prepared using gallium oxide as the galliumsource, chromium chloride as the chromium source and silicon wafer as the substrate. Theinfluences of chromium source weight (0.1,0.5and1g), ammoniation temperature (850,950and1050℃) and annealing time (1,1.5,2and3h) on GaN products wereinvestigated. It could be found that, a large number of straight Cr-doped GaN nanowireswere obtained at1050℃and3h and chromium source weight of0.5g. XRD and EDSanalysis confirmed the mass fraction of Cr in sampl was about2.8%. Since the catalystparticles were found on the head of nanowires, it could be concluded that the Cr-dopedGaN nanowires follwed the vapor-liquid-solid growth mechanism. The optical property ofCr-doped GaN samples was studied. Besides the intrinsic emission peak of GaN, therewas a weak emission peak at602nm, which might be caused by the doping.Indium doped GaN nanostructures were successfully prepared without catalyst or withnickel nitrate as the catalyst by using gallium oxide as the gallium source and indiumchloride as the indium source, respectively. Results showed that In-doped GaN with ahexagonal structure were all obtained under the two conditions. But without catalyst, GaNbulk materials or nanocones couled be obtained. When nickel nitrate was used as catalyst,a large number of straight In-doped GaN nanowires were obtained at1050℃and3h andindium source weight of0.5g. The indium content was close to2.7%. Compared with PLspectra of Cr doped GaN, the emission peak intensity at456nm was larger, whichindicated that In-doped GaN nanowires had more surface defects. Also, the PL spectra showed a weak emission peak at598nm, which might be due to the doping that expandedGaN optical response.A large number of straight gallium oxide hydroxide nanorods and zigzag shaped singlecrystalline nanorods with diameter range of100-200nm and length up to several tens ofmicrometers were successfully prepared using gallium oxide as the gallium source andnickel nitrate as the catalyst. The effects of catalyst (nickel and nickel nitrate) andreaction temperature (0.5and1.5h) influence on the sample were investigated.