| GaN-based materials have been widely used or shown great application potential in power devices, LD devices and LED devices because of their large band gap, good chemical and thermal stability, high saturated electron drift velocity and large breakdown electric field strength. However, their epitaxial growth process and device structure still need to be further optimized. In this thesis, the effect of three-dimensional(3D)growth processes on crystal quality and properties of the Ga N epitaxial layer grown on sapphire substrates via Metal-organic Chemical Vapor Deposition(MOCVD) technique was studied, and its growth mechanism was discussed. Meanwhile, the influence of quantum well thickness of In Ga N/Ga N multiple quantum well on photoluminescence and the related physical mechanism were studied by means of theoretical simulation and experimental research.The main research results are as follows.GaN epitaxial layers were grown on sapphire substrates at different growth temperatures(1060 ℃-1080 ℃) and V/III ratios(1335-763) inthree dimensional growth process, respectively. Dislocation density,surface morphologies, optical properties, electrical properties and residual stress have been characterized by high-resolution X-ray diffraction(HRXRD), atomic force microscopy(AFM), photoluminescence spectroscopy(PL), Hall measurement and Raman spectroscopy,respectively. When 3D growth temperatures of 1060, 1070 and 1080 ℃were employed to grow Ga N epilayers, edge dislocation densities in Ga N samples were calculated to be 5.09×108, 3.58×108and 5.56×108/cm3,respectively, showing an initially increasing and then decreasing trend,while their screw dislocation densities changed inconspicuously, namely1.06×108, 0.98×108, and 1.01×108/cm3, respectively. Moreover, the residual stresses in the Ga N samples decreased from 0.86 to 0.65 GPa as the growth temperature increased from 1060 to 1080 ℃. When the V/III ratio in three-dimensional growth process decreased from 1335 to 763,the edge dislocation density of the epitaxial layers gradually decreased from 5.93×108to 3.32×108/cm3, while their screw dislocation density did not change significantly. The PL intensity gradually increased. Carriers concentration decreased from 8.31×1017to 5.60×1016/cm3 and carriers mobility increased from 212 to 267 cm2/vs. The difference in crystal quality and properties for Ga N epilayers grown at different 3D temperatures and V/III ratios might be ascribed to variable growth rate and consolidation rate of islands. The optimized 3D growth temperatureand V/III ratio are 1070 ℃ and 763 within the rang of study, respectively.The photoluminescence of In Ga N/Ga N multi-quantum well structures with different well thicknesses(1.5, 2.0, 2.5, 3.2, 4.0 and 5.0 nm) were simulated by means of software Si LENSe. As quantum well thickness increased from 1.5 to 5.0 nm at the same excitation power density, the quantum confined Stark effect in quantum wells was strengthened, which resulted in a red-shift of peak wavelength. For the same quantum well structure, as the excitation power density increased from 1.4 to 100W/cm2, the shielding electric field caused by photo-generated carriers gradually increased, the quantum confined Stark effect was weakened in quantum wells, leading to a blue-shift of the peak wavelength. In addition,In Ga N/Ga N multiple quantum well structures with different quantum well thicknesses(2.5 and 3.2 nm) were grown on sapphire substrates via a MOCVD growth technique. The influence of well thickness on their optical properties was studied systematically via PL spectroscopy. The results showed that the peak wavelength red shifted when well thickness increased from 2.5 to 3.2 nm at the same excitation power density. For the same sample, as the excitation power density increased from 1.4 to 47.0W/cm2, the peak wavelength blue shifted. These results were consistent with those from simulative calculation. |
PDF Full Text Request