| With the wide applications of light-emitting diode (LED) from the indicator light and the display in the beginning to the backlight of LCD screen, indoor and outdoor lighting, et al, LED's brightness is highly required. Nowadays, white light LEDs, excited by the blue LED mixed with phosphors, are used as ordinary lighting indoor or outdoor. Its luminous efficiency and low brightness are the most important issues.The purpose of this research is to improve the luminous efficiency of LED. First, the analysis of the impact factors on LED's the internal quantum efficiency (IQE) and external quantum efficiency (EQE) has been made from different aspects. Then, a detailed research has been made on various effective methods which can improve LED's IQE and EQE. Finally, a detailed study was made on the impact of barrier layers of multiple quantum wells (MQWs) doped by Indium. With X-ray diffraction and photoluminescence spectra, differences in crystalline quality, MQWs'structure characteristics and photoluminescence wavelength (intensity, FWHM) have been studied among partly indium-doped , all indium-doped barrier structure and conventional barrier structure in MQWs.The optical properties of the devices made by conventional LED chip technology were tested.Based on the previous study, a deep research on the influences of LED's luminous efficiency with a smaller gradient indium flows in MQW's all over the barrier layer. Considering the energy band diagrams of the two MQW structures, it is found that , in indium-doped MQW ,the bend in energy band has been reduced, and quantum confinement Stark effect(QCSE) has been weaken. On the contrary, the efficiency of electron blocking and holes injection has been improved, respectively. The wave-functions of electron and hole have overlapped. All these play an active role in increasing the LED's luminous efficiency. The experiment results show that LED brightness can be increased by 16.5% with all quantum barriers doped by indium lightly. |
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