Study On Epitaxy Of Ganandalgan Grown On Sapphire,Silicon And SiC Substrate By Mocvd

Gallium Nitride (GaN) has adventages such as its high breakdown field, goodthermal conductivity, corrosion resistance, and radiation hardness. There exist2DEGwith high density and high mobility in AlGaN/GaN interface. Therefore, theAlGaN/GaN heterojuntion is the ideal material for the development of microwavedevices and power electronic devices. AlGaN/GaN heterojuntion is often preparedby hetero-epitaxy due to the difficulty of homo-epitaxy. The AlGaN/GaNheterostructure prepared for microwave devices is usually grown on SiC substrate orsapphire substrate. However the AlGaN/GaN heterostructure used for powerelectronic devices is prepared on Si substrate. This dissertation is mainly concernedwith the optimation of epitaxy of AlGaN/GaN heterostructure grown on differentsubstrate by MOCVD (Metalorganic Chemical Vapor Deposition，MOCVD).Themain contents are as follows:1. Inorder to improve the electrical properties of AlGaN/GaN, the growthparameters of highly resistive GaN buffer is optimized. The influence of chamberpressure, species of carrier gas and nucleation layer thickness on electrical propertiesof GaN buffer is investigated. The optimized growth parameters are the growth timeof nucleation layer is170s with N2as carrier gas and pressure of500torr. The highlyresistive GaN buffer prepared with these parameters is as high as1.98×1010Ω/□.2. Inorder to improve the interface quality of AlGaN/GaN, Fe doping of GaN isstudied. The effect of Cp2Fe flow and growth time of Fe-doped GaN on the crystalquality and the electrical properties of GaN are investigated. The optimized growthparameters are growth time of Fe-doped GaN is30min with Cp2Fe flow of68μmol/min. The highly resistive GaN buffer prepared with these parameters is ashigh as1×1010Ω/□, and the thickness is2μm。3. Inorder to improve the crystal quality of GaN grown on Si substrate, theeffect of AlN buffer layer on the crystal quality of GaN is investigated. The influencefactor of morphology and growth rate is systematically investigated so as to optimizethe growth parameters of AlN. The optimized growth parameters of AlN buffer layerare chamber pressure of300torr, TMAl flow of76μmol/min, V/III of1700, H2flowof16slm. The GaN with better crystal quality is grown on optimized AlN bufferlayer. XRD ω scan shows that FWHM of (0002) is681arcsec; FWHM of (10-12) is728arcsec.4. Inorder to improve the mobility and sheet carrier concentration, theAlGaN/GaN structure is optimized. The effect of GaN templates with differentgrowth parameters of nucleation on electrical properties of heterostructure isinvestigated. It is found that the carrier mobility of heterostructure grown on GaN template which is grown with optimized growth parameters is relatively high. Themobility is1230cm2/(V s). On the other hand, the effect of V/III of Fe-doped GaNand growth time of Fe-doped GaN on the electric properties of heterostructure isinvestigated. The mobility and sheet carrier concentration of heterostructure arerelatively higher when the GaN buffer is grown with V/III of1870and doping timeof30min. The influence of thickness of AlN interlayer and AlGaN barrier layer onheterostructure is investigated. It is found that the heterostructure with AlN growthtime of60s and AlGaN growth time of420s has relatively better electric properties.The optmized heterostructure’s carrier mobility is1560cm2/(V s) and the sheetcarrier concentration is1.1×1013cm2/(V s).5. The GaN film is grown on SiC substrate. The crystal quality, surfacemorphology and c-axis lattice are measured to characterise the quality of GaN. Inorder to investigate the effect of SiC on GaN, the SiC is characterised by XRDdouble-crystal ω scan. The XRD double-crystal ω scan shows that FWHM of (0002)is681arcsec; FWHM of (10-12) is728arcsec. The surface roughness is0.524nm.Thec-axis lattice parameter is0.5182nm.