Preparation And Investigation Of GaN Epilayer And LED Based On Sic Substrate

GaN and its compound (Al,Ga,In)N have a direct bandgap which vary from0.64eV to6.2eV, correspond with the visible spectrum perfectly, is widely used in light emitting diode (LED), laser diode (LD), solar cells, ultraviolet photodetectors and so on. However, due to the extreme high melting point and saturated vapor pressure, GaN generally heterepitaxy on foreign substrates such as SiC, Al2O3because of lacking of GaN substrate. A smaller lattice mismatch and the same same cleavage facets with GaN, a high thermal conductivity and electrical conduction make SiC substrate admired as one of the most suitable substrate for GaN epixity. However, SiC substrate surface always covered with a layer of oxide film, and3.4%lattice mismatch and huge thermal mismatch between GaN and SiC will introduce a large number of dislocations and cracks in the GaN epitaxial film, which will degrade the quality of the GaN layers.In this paper, we employ Thomos Swan MOCVD system to study the influence of GaN epilayer properties by in situ pretreatment of the substrate and in situ SiNx insertion layer, and discuss the formation mechanism, the N face GaN is also concerned. Finally, we prepare the vertical structure Ga-face and N-face GaN-based LED.The properties of GaN epitaxial layers by in situ SiH4pre-treated SiC substrate were studied systemically. It was found SiH4can react with the SiO2by forming volatilized SiO which will desorb from the SiC surface, by controlling the treating time, SiC surface shows an optimum Si-H surface termination. Moreover, our experiments demonstrated that the SiH4pre-treatment can distinctly influence the AlGaN nucleation layer and the GaN basic characteristics.The properties of GaN epilayers by in situ H2pre-treated SiC substrate were studied. It was found that in situ H2treatment brought an as-like porous SiC surface, and the subsequent initial epitaxial GaN is similar as lateral epitaxial growth, which improved the quality of GaN.In situ SiNx insertion layer was employed to prepare GaN epilayers on SiC substrate in MOCVD, the introduction of SiNx insertion layer can effectively reduce the dislocation density and release tensile stress. Ultimately, a more than5μm thick, high-quality, crack-free n-type GaN epilayer was obtained, by which we prepared a vertical structure of the LED, the LED has a very steep interface, and the temperature-induced S-shape PL shift was caused by a change in the carrier dynamics with increasing temperature due to inhomogeneity and carrier localization in the MQWs.The N face GaN epilayer was prepared on the C face SiC substrate by MOCVD system, and the basic character of the N face GaN was investegated. A large number of Ga vacancies was formed a hot phosphoric acid solution etching, which brought a yellow luminescence in the room temperature photo luminescence spectra. Lastly, a vertical structure of the N face LED was prepared, and we can detect an effective light emitting at the current of650mA...