Study On MOCVD Growth And Properties Of III-Ⅴ Nitrides And High Brightness Blue LED Wafers

GaN based Ⅲ-Ⅴ nitrides have potential applications on high brightness LEDs, shortwavelength lasers, ultraviolet detectors, high temperature and high power electronicdevices. Study on physics issues and technologies of nitrides open a new area of 3thgeneration semiconductor.More than ten companies in America and Japan reported to have developed thenitrides growth technology since Nichia company in Japan first realized thecommercialization of GaN based blue LED in 1994.In this thesis,GaN and its ternary were grown by a home-made atmosphere pressuremetalorganic chemical vapor deposition (MOCVD) and Thomas Swan 6×2" MOCVDsystems. High bright blue LED wafers were obtained by optimizing the nitrides growthtechnology and wafer structure. Some encouraging results are following as:1. We present the idea of using a buffer layer of deviation from stoichiometry formaterials growth on large lattice mismatch substrates. This idea was realized in nitridesgrowth in this thesis. The epilayer crystalline quality was improved and the dislocationdensity was decreased by using GaN low and high temperature buffer layers of deviationfrom stoichiometry. The RBS/channeling spectra exhibited that the minimum yield χminof GaN layers was just only 1.5%. The leak electric current of GaN based LED wasobviously decreased and lower than 1μA at 5 volt reverse voltage by using this new buffertechnology.2. Optimum nitridation condition can improve the optical and electrical properties ofGaN layers obviously. However, the quality of GaN layers degenerated when thenitridation condition was not proper. It was suggested the reason that the epilayer surfacebecame rough by nitridation was due to the three dimensional growth mode.3. Our research results indicated that the blue PL luminescence band in unintentionaldoped GaN layers obviously related with the compensation ratio of unintentional dopedGaN, and was described to the transition from the free electron in conduction band toacceptor levels (eA luminescence).4. Our research results indicated that the intensity of yellow band emission in GaN:Sifilms was largely influenced by the parasitic reactions in the gas phase. A decreased growthrate of GaN:Si with increasing SiH4/TMGa ratio was described. Si-doped GaN films withcarrier concentration from 1×1017cm-3 to 4×1019cm-3 can be obtained.5. The doping dose of Mg was very important to obtain high hole concentration GaNlayer. Deep donors related with Mg would form if much high Mg doping dose were used.The GaN based LED wafers whose turn-on voltage was lower than 3.6 volt were obtainedby optimum the Mg doping dose and the thermally annealed condition.6. A study indicated that H2 in precursors carrier gas obviously result in increasing thegrowth rate of InxGa1-xN films, while a deep energy level emission probably appeared.7. An appropriate In/Ga ratio was necessary to increase the indium mole fraction inInxGa1-xN layers.8. InGaN layers with the indium mole fraction of 0.26 can be obtained. The band edgeemission of this InGaN layer was 545nm. The minimum yields χmin of RBS/channeling forIn0.04Ga0.96N films was only 4.1%.9. The GaN based blue LED with the turn-on voltage of lower 3.6 volt, the leakelectric current of lower 1μA at 5 volt reverse voltage and the output power of 2.9 mWcan be stably obtained even the chip processing of LED was not optimum. The blue LEDwafers have been realized commercialization.This work was supported by 863 program in China.