Research On Epitaxial Growth Of GaN Based Green And White LED Devices

LED is widely used in landscape decoration, signal lighting, LCD backlighting, as well as solid-state lighting and other aspects in people's life. The advantages of LED are low power consumption, long life, health, environmental protection and so on.With the implementation of national energy sources strategy, energy-saving strategy has become a top priority of the whole energy sources strategy. Therefore, the new requirements to solid-state lighting, related scientific research and industry will be proposed. With the development of GaN-based materials, high-brightness, high-power blue and green LED has been developing rapidly. However, the lighting brightness and efficiency of the LEDs that can emit the middle wavelength range visible light are still relatively low, such as the green lighting LED. The light within this wavelength range can not be matched with other visible light to make solid-state lighting source with high quality.In this paper, on the basis of the luminous efficiency and brightness problem of the green lighting LED, the background and tendency in the researchs of non-tradition white light LED, the luminous intensity of the GaN-based material green lighting LED and the luminous mechanism analysis of the phosphor-free converted white LED are researched by the MOCVD epitaxial growth experiment method. Main contents of this paper are as follows:Firstly, the factors that LED luminous intensity and efficiency are influenced following the In component change in InGaN/GaN multiple quantum wells (MQWs) are analyzed. It is thought in this paper that with the increase in In composition, the lattice mismatch between InGaN and GaN becomes larger and piezoelectric polarization effects are enhanced when GaN-based materials grow on the C-plane sapphire. Due to a large polarization electric field in quantum well, the Quantum Confinement Stark effects (QCSE) and Quantum Confinement Franz-Keldysh effects (QCFK) are conspicuous. The energy band-bent of the wells and barriers is intensified, the wave functions of electrons and holes in the wells are separated in space, and the effective recombinations are reduced. Because of the relative band gap narrow effect, luminous spectra are red-shift and the luminous efficiency is reduced.Secondly, in order to improve the green LED luminous intensity and efficiency, the n-type InGaN layer and the superlattice like structure with 15 cycles are innovatively inserted under the active area of the LEDs, respectively. The experimental results show that the two strain modulation structures are useful to improve the luminous quality. The conception of doping matching is raised in this paper. The luminous quality of the green LED get remarkable improved, through the experiments of optimized doping matching and the In component gradient wells growth.Finally, the single-chip phosphor-free white LED is achieved by MOCVD method. Relaxation degree is enhanced by the strain modulation in the n-type InGaN layer with lower In component. InGaN phase separation appears in the quantum well, the In-rich areas and In-low areas are generated. The different fluctuations of the Indium composition correspond to the different localized states. When the carriers are injected into the active area, they are captured and recombinated by localized states which have different component in quantum wells. The lights are emitted with the different wavelengths which can be mixed into the white light. The white LED researched in this paper not only can directly emit white light from the same layer in active area, but also has much lower threshold voltage value compared with the traditional LEDs.