The Study Of GaN-based Optoelectronic Material Growth Method

Due to the advantageous properties, III-Nitride semiconductor materials and itsapplications are becoming more and more important. Semiconductor lightingengineering, based on blue, green and ultraviolet LEDs, is leading a new industrialrevolution. GaN based blue LEDs have been commercialized successfully, which arewidely used in fields of landscape lamp, backlight and lighting lamp. Meanwhile, GaNbased microwave power devices are being gradually commercialized.With the progress in research and application on III-Nitride devices, GaN basedoptoelectronic devices and microwave power devices have great demand on materialproperties. For LEDs, to increase quantum efficiency, decrease non-radiativerecombination,and reduce trap-induced photon absorption, epitaxial technique with highcrystal quality and low defect density, high performance p-type doping technique andhigh efficiency and uniformity multiple quantum-well structure manufacturingtechnique are required. For microwave power devices, to increase breakdown voltage,improve power density and reduce parasitic effects, the same demands are needed.Based on the above background, several key issues related to the application ofIII-nitride semiconductor devices have been studied in this thesis, which include highquality GaN, AlN and alloy growth methods on sapphire substrate, high performancep-type doping, InGaN/GaN multiple quantum-well structure prepatation, and MOCVDsystems for realizing above processing. The major contributions and achievements areshown in the following:1. MOCVD system developmentIt includes two parts: participating in the development of independent intellectualproperty rights MOCVD system, and improving gas-supply system during application.2. Research on epitaxial technique based on GaN-class materialsVia research on epitaxial technique and processing for GaN-class materials, it isconcluded that in the growth of epitaxial for big mismatch materials(GaN, AlN, AlGaN,etc), surface ehanced reaction pulse methodGsuper lattice structure to stress-modulationand stress match-and-modulation starting from nucleation layer growth are the keyfactors to obtain high crystal quality and low defect density epitaxial materials. In thisthesis, the epitaxial structure and processing of GaN-class materials are optimized basedon stress matching.Micro-morphology at different stage during GaN materials epitaxial growth havebeen analyzed, and the main factors that affect material crystal quality are obtained.Optimized processing for super thin AlN nucleation layer and annealing technique forbuffer layer have been proposed. It can significantly improve the crystal quality ofepitaxial material.By analyzing the difficulties during AlN epitaxial material growth, pulsedsurface-enhancement reaction technique is proposed and crucial processing factors are optimized. High-quality AlN epitaxial material with XRDM002RRC FWHM38arcsecM102RRC FWHM198arcsec are obtained. The characteristic parameters are ininternational top-class level.By analyzing the morphology of AlGaN with different Al content, crucial factorsfor stress matching during high-quality epitaxial processing have been determined.Super lattice insert layer, based on stress modulation, have been proposed. Viaoptimization of insert layer structure and content, high quality and low defect densityAlGaN epitaxial material with different Al content have been obtained.3. Study on p-type doping technique for GaN-class materialsThe growth temperature, Ga/Mg mole ratio and annealing processing for p-typeGaN fabrication are optimized. By utilizing air-annealing, p-GaN epitaxial withresistance less than1Ω·cm are obtained.By using uniform doping technique, p-Al0.25Ga0.75N with resistance of4.37Ω·cm isrealized. Based on surface enhancement reaction MOCVD, plused δ-doping p-AlGaNprocessing has been investigated, and p-Al0.25Ga0.75N with resistance of1.92Ω·cm hasbe obtained.4. Investigation on the growth of GaN-based multiple quantum-well structureTo solve the effective doping of In and processing stability, multi quantum-wellstructure and processing with well cladding layer and anneal process have beenproposed. The fabrication processing characterized by high In doping efficiency andhigh wavelength stability has been realized. Trapezoid quantum-well structure, whichcan improve luminous efficiency has been preliminary achieved. This processing is ofgreat value to the stability and yield of commercial LEDs.In order to solve problem of YL and low wavelength uniformity due to thefluctuation of MOCVD gas-supply and process temperature, a new type of gas-supplysystem for MO source module has been designed. Related processing with highwavelength uniformility have been realized, which builds up a good basis for high yieldLED epitaxial wafer.To overcome polarization-induced low lighting recombination efficiency,InGaN/GaN multi-quantum well structure with In doped barrier and low temperatureGaN cladding layer has been designed and realized, and the related processing has beenoptimized. Combine with quantum well annealing process, it is demonstrated that theluminous efficiency has a significant increase of15.61%.High brightness blue LEDs, which are based on the above research, have beentransferred to industry in2007. Nowadays, the company has great capability of100’000epitaxial wafers and2.5billion LED chips per year.