| There has been considerable interest in Gallium Nitride recently owing to its large band-gap and excellent physical properties such as high electron mobility and very high thermal conductivity. GaN material is extensively fabricated laser diodes、light-emitting diodes (including green、blue、UV) and high temperature-power devices. The Si substrate is cheap, large size, high thermal conductivity and easy processing advantages thus become a promising substrate which may carry on the batch production of LED after sapphire and silicon carbide. Wurtzite structure (0001) GaN will produce a large number of dislocations because of the large lattice mismatch, is20.4%, with diamond structure Si (111) substrate. The high thermal mismatch between GaN and Si is nearly56%. During the cooling process after the end of epitaxial growth, the epitaxial layer will bear a heavy piece of stress. In recent years, the growth GaN on Si substrate materials had obtained significant progress, and the technology is mature with each passing day, but still has some problems to be solved urgently, such as the improvement of epi-wafer quality and the efficiency of chip.Focused on the Si-based GaN materials growth, improving the wavelength uniformity and enhancing the light intensity were studied. This dissertation is investigated systematically by using PL mapping test system, fluorescence microscopy, double crystal X-ray diffraction etc. On the basis of the improved Thomas Swan MOCVD in our laboratory, there are a seriers of process adjustments on the epitaxial growth as follows:1、In the N type GaN inserted a1000A InGaN layer with8%Indium fractions, study the effect of its different insertion position with0.27μm,0.4μm,0.53μm and1μm on wavelength uniformity. The effect of the location on quantum well is different, too close or too far away will be adversely affected.2、Study the effect of the optimization of interlayer composition of In size and growth conditions on quantum well In fractions on the basis of without changing the behind quantum wells growth conditions. At the same time improve carrier uniformity expansion by optimizing the preparation layer In components. After optimization, the epitaxial wafer gains the results:the main wavelength is521.46nm, with6.38nm standard deviation, and half peak width is33.35nm.3、Study the effet of growth interruption and carrier gas type of cap layer growth on the photoluminescence of quantum well."Stop30s" will make the quantum well InGaN decomposite, while1000H2to grow cap layer would make InGaN quantum well severe catabolism resulting in uantum well uniformity under FL microscopy. Thus the nitrogen carrier gas with H2affects more than stop growth on quantum-well.4、We compared the effect of different well width of quantum well structures on wavelength uniformity, half peak width and PL intensity and other optical characteristics. The quantum well layer thickness varies several nanometers could make photoluminescence change. Thinning well layer, wavelength increases, and the uniformity is better. But the thin well’s PL intensity decreased, this may be affected by non-radiative ceners at the interface.5、Under the condition of big NH3to growth MQWs, we explored wavelength uniformity and light intensity variations by fixing In/Ga ratio, small TMIn/(TMIn+TEGa), fixing In while changing Ga, and fixing Ga while changing In. Considering light intensity, growth rate, and wavelength uniformity, various growth conditions have good results.At last, the influence of roughening area on external quantum efficiency has been investigated, which is based on GaN LED on Si substrate having an n-side-up vertical electrode structure by wafer-bonding technology. The experimental results show that: Compared to the conventional LED, The EQE can be increased by6%after enlargement of N-face roughening area through graphic etching. The enhancement is attributed to the appearance of an additional escape cone for light extraction enabled by surface texture. |
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