Design And Optimization Of High-Voltage GaN-Based Light-Emitting Diodes

As the efficiency,brightness and life of GaN-based LEDs have been further improved,GaN-based LEDs are replacing traditional lighting sources in areas like general lighting and backlight in liquid crystal displays.The injection current or area of LED must be increased,if we want to increase the power of LED and to promote the usage of LED.However,that will inevitably decrease the current spreading ability and efficiency of LED.High-voltage(HV)LED,which divides a chip into a few independent micro-chips,operating at small injection current and high voltage.Therefore,compared with traditional high-power LED,high-voltage LED has greater current spreading ability and efficiency.In this thesis,the improvement of optical and electrical performances of direct current(DC)and alternating current(AC)GaN-based high-voltage LED and the perfection of the design parameters of the DC and AC GaN-based high-voltage LED are investigated as follows:(1)There is luster inconsistency problem in the GaN-based LED with naturally textured p-GaN,which will decrease image recognition rate and accuracy during the wire bonding.An optimized textured p-GaN technology was designed to avoid luster inconsistency problem and to increase light extraction efficiency at the same time.(2)Inter-finger electrode structure was designed to tackle the bottleneck faced by the current spreading ability of GaN-based LED.In the contrastive simulation of electrode structure for GaN-based LEDs with traditional pad and inter-finger electrode structures,it was found that inter-finger electrode structure was superior in increasing the current spreading ability of GaN-based LED.The variant I-V characteristics measurement and high-temperature/current test of GaN-based LED were conducted to investigate the physical mechanism behind the forward tunneling cureent and the effect of the high-temperature/current stress on the forward tunneling current.(3)The light coupling propagation phenomenon between two adjacent LED cells within the high-voltage LED was explored by an analytical model developed by mathematical formulations.The oblique angle of the isolation trench of high-voltage LED was optimized to enable smooth and reliable interconnection between adjacent LED cells.The effect of the width of the isolation trench on the high-voltage LED was investigated.(4)A type of DC and six types of AC high-voltage LEDs were designed and fabricated to investigate the improvement of the performance of high-voltage LED.The performances between DC and AC high-voltage LEDs were compared.The number and size of LED cell of AC high-voltage LED were optimized to improve the performance of the AC LED.