Study On The Preparation And Properties Of Aluminum Oxide Passivation Of GaN-based Blue LED

Since the birth of GaN-based light-emitting diodes, the technology and application of LED are developing fast. High-power GaN-based LED has an expansive application prospect in all-solid-state white lighting illumination, which is considered to be the most promising to replace incandescent and fluorescent lamps, as the third generation of solid-state illumination source. However, with the increase of drive current and the chip size, some problems, for example, the increase in leakage current, the drop in illuminating efficiency, the reduction in reliability and so on, can be caused, we need to conduct a study in the aspect of the chip architecture design and so on to solve them. Passivation technology directly influence the reliability of devices, so it is an important Step for production of high brightness, high power and high reliability LED devices. Currently, the silicon oxides or nitrides are the most widely used passivation materials of LED chips. However, with the development of technology research, the new structure of vertical structure chips, thin film chips, and flip-chips have gradually become the development direction of the next generation of LED chips, which put forward new requirements to the passivation materials. According to the design requirements of these new structure LED chips and the compatibility with other process of making the devices, the traditional passivation materials are not yet sufficient for design. So, the selection of a suitable passivation material is the crucial issues to fabricate these devices. As a new type of functional thin film material, aluminum oxide film promises well as new type surface passivation of LED devices due to its high transmittance, large refractive index, good insulation, strong anti-radiation, excellent corrosion-resistance and high hardness an so on. So more and more attention is paid to the study of its preparation process and related properties. Since magnetron sputtering is an extremely effective thin film deposition method of high-speed, low-temperature and low-damage, we deposit aluminum oxide films by RF reactive magnetron sputtering, and study their preparation and properties in theory and experiments. In this paper, Al2O3thin films have been deposited on Sapphire-based GaN substrates by using R.F reactive magnetron sputtering method and sputtering the aluminum target, focusing on the effect of sputtering parameters and annealing conditions on the surface morphology, light transmittance, refractive index and corrosion resistance properties of Al2O3thin films. By improving the preparation process and optimizing the growth parameters, high-quality, high-performance alumina passivation layers are obtained, which make preparations for the passivation films deposited on the vertical film structure LED chips.The results of experiment have indicated that, it can be obtained the optimal deposition conditions of Al2O3thin films by R.F reactive magnetron sputtering on room temperature, the sputtering power, argon oxygen ratio and working gas pressure are150W,200/60sccm,0.6Pa, respectively. At these conditions, Al2O3thin films with relatively high deposition rate show layer by layer growth mode and smooth surface and dense structure. The refractive index of the film is1.65close to the ideal single-layer passivation layer refractive index and the light transmittance of film reaches91%at455nm Blue-ray characteristic wavelength. Although corrosion resistance is not very satisfactory, the corrosion rate of the film in the BOE is the lowest relatively. By selecting and optimizing the annealing scheme, it is found that the optimized thermal annealing scheme of Al2O3films is annealing for60min at500℃. At these conditions, Heat-annealed Al2O3films at these conditions have smaller surface roughness, the refractive index of1.658and the higher light transmittance at455nm wavelength of94.74%and, most importantly, the corrosion resistance of Al2O3films annealed has greatly improved, and the corrosion rate is0.09nm/s. we therefore conclude that, after proper heat treatment, Al2O3films deposited by R.F reactive magnetron sputtering under the optimized conditions can meet the requirements of the vertical film structure LED devices and be compatible with other process of device fabrication.