Blue Led High-power Gan Quito Quantum Well Structure Performance Optimization Design

As a wide-band gap III-V compound semiconductor, gallium nitride can be used as an emitter. However, it is difficult to prepare the gallium nitride bulk single crystal, and the epitaxy has been developed in industry by using MOCVD on the different substrates, such as sapphire, silicon carbide and silicon. For the light-emitting diode, the most widely used substrate is sapphire because of the maturely technology and cost. As the sapphire substrate is an insulating material, to weld N electrode, we should etch the epitaxy film from P type gallium nitride to N type gallium nitride material. For this structure, the N and P electrodes are on the same side, therefore, the current crowding effect will be produced for GaN-based LED under the current injection and results in the joule heat, lifetime reduction, wavelength shift. Therefore, by optimizing the mesa patterns, the performance of GaN/InGaN LEDs can be efficiently improved. Additionally, the hall effect is bad to the device luminous efficiency as existence of the transverse current. This thesis is aimed at those problems. The main works of this paper as follows:Firstly, we build three dimensional sapphire substrate GaN-based multiple quantum well structure light-emitting diode model by the semiconductor device simulate software which is named as the Advanced Physical Models of Semiconductor Devices (APSYS). The GaN/InGaN LEDs have a mesa pattern with P and N electrodes on the diagonal at20mA injection current. Firstly, we simulated the properties of GaN/InGaN LEDs by changing the In component in barriers and width of wells and barriers, respectively. Then, we analyzed current voltage (IV) performance and internal quantum efficiency, and discussed the spontaneous emission spectral intensity and red shift phenomena. By comparing with the conventional quantum well parameter LED, the optimized LED structures have better photoelectric properties with a voltage reduction of18.43%, light intensity enhancement of11.46%and red-shift phenomenon reduction of5nm at a well width of2nm, barrier width of4nm, and In component of0.08in barriers at drive current of20mA. The obtained results may be benefit to the design of the high performance LED.Secondly, as the electrons and holes’mobility is quite different, and the device will have more concentration light emission, this will lead to the uneven distribution of junction temperature, and affect reliability of the device. In order to improve the performance of the GaN/InGaN LEDs, we simulated the properties of GaN-based LED by doping different concentration N-type impurity in carriers’material. All of the IV performance, internal quantum efficiency, spontaneous emission spectral intensity and electron and hole concentration distribution show that with the impurity concentration increasing, those performance increases, but when the concentration becomes larger, those performance decreases, and the best concentration is5E+16.Finally, as the mesa patterns can not only optimize current crowding effect, but also reduce the effect of the hall effect which is disadvantageous to the device at a certain degree. Therefore, the performance of the GaN/InGaN LEDs with three mesa structures, i.e. the opposite angle electrodes shape, inter-digital shape and "Tian Zi Xing" shape, has been studied. The results show that the GaN-based LED with "Tian Zi Xing" mesa shape designed by the author has excellent opto-electric properties, and for the "Tian Zi Xing" mesa pattern the GaN-based LED has much better performance with the electrode shape width equal to20um.