Improvement of External Quantum Efficiency and Efficiency Droop of InGaN-based Green Light-emitting Diodes by Band Structure Engineering

• Main Authors: Fan, Jia-Rong, 范嘉榮
• Other Authors: Kuo, Hao-chung
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/23714443189386723586

碩士 === 國立交通大學 === 光電工程研究所 === 102 === In this thesis, we want to design the epitaxial structure of InGaN-based green light-emitting diodes (LEDs) to improve the holes transport, electron leakage, and polarization field which could enhance the external quantum efficiency and alleviate the efficiency droop behavior. In our experiment ways, we used Advanced Physical Models of Semiconductor Devices (APSYS) simulation software to design our structure and calculate the band diagram and carrier distribution. From the simulation have a good result, we further fabricate the green LEDs sample with design structure by Metal-Organic Chemical Vapor Deposition(MOCVD) and measure the electrical characteristics by Electroluminescence (EL) instrument. The following of three parts are our design structure introduction and discussion. First, we designed a Indium graded-composition quantum barrier (GQB) with indium composition decreasing along the (0001) direction from 7% to 0% for c-plane InGaN/GaN green LEDs. The simulation results demonstrated that GQB can effectively enhance the transport capability of holes as well as electrics confinement and reduce polarization field. Consequently, the GQB LEDs have better external quantum efficiency and alleviated the efficiency droop behavior as compared with conventional LED by EL measurement. Second, we designed a Indium graded-composition last barrier (GLB) and Step Indium composition Last barrier(Step LB) with indium composition increasing along the (0001) direction from 0% to 5% for c-plane InGaN/GaN green LED. The simulation results showed that the GLB and Step LB structure can improve the effective barrier high of electrons and holes and reduce the electrics field in the last well. As a result, the holes transport in MQWs was enhanced and confine more carrier in the well to increase the radiative recombination efficiency at high current density. Consequently, the GLB and Step LB LEDs have better external quantum efficiency and alleviated the efficiency droop behavior as compared with conventional LED by EL measurement. Third, we have designed AlInGaN/GaN super-lattice electrics blocking layer for c-plane InGaN/GaN green LED. The simulation results showed that the AlInGaN/GaN SL EBL can reduce the electrics field in the last GaN barrier and improve the effective barrier high of electrons and holes. As a result, the holes transport in MQWs was enhanced and confine more carrier in the well to increase the radiative recombination efficiency at high current density. Consequently, the AlInGaN/GaN SL EBL have better external quantum efficiency and alleviated the efficiency droop behavior as compared with conventional LED by EL measurement.