Numerical Study on Blue InGaN Light-Emitting Diodes with Asymmetric Active Region

• Main Authors: Chih-Teng Liao, 廖志騰
• Other Authors: Yen-Kuang Kuo
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/70374411650733650414

碩士 === 國立彰化師範大學 === 光電科技研究所 === 97 === High-luminescence and high-efficiency blue InGaN light-emitting diodes are of foremost importance for applications in illumination market, such as the outdoor display and solid-state lighting. However, several mechanisms which degenerate the optical performance, including light extraction efficiency, current crowding effect, high operation voltage, efficiency droop, and piezoelectric effect, should be solved to achieve high-power blue InGaN light-emitting diodes. In this thesis, I numerically investigate the effect of piezoelectric effect and efficiency droop on the optical performance of the blue InGaN light-emiting diodes. In addition, the optimum design of the structure is proposed to enhance the optical characteristics of the blue InGaN light-emitting diodes. In chapter 1, I introduce a brief content about my research. On the other hand, the polarization-related effect and efficiency droop about the blue InGaN–based light-emitting diodes are also introduced. In chapter 2, the structure of the blue InGaN light-emitting diode under study and the physical parameters such as the bandgap energy, bowing parameter, band-offset ratio, polarization effect, and SRH lifetime of the III-nitride alloys used in my simulation are introduced. In chapter 3, the effect of staggered quantum well upon the blue InGaN light-emitting diodes is numerically studied. The blue InGaN light-emitting diodes with various staggered quantum wells are theoretically investigated. According to the simulation result, the best optical characteristic is obtained when the staggered-quantum-well is designed as In0.20Ga0.80N (1.4 nm)-In0.26Ga0.74N (1.6 nm) for the blue light-emitting diodes. It is because of the enhanced overlap of electron and hole wavefunctions, increased hole injection efficiency, and suppressed electron leakage for the blue InGaN light-emitting diodes. In chapter 4, for the blue InGaN light-emitting diodes, the effect of the asymmetric barriers is investigated. The idea of asymmetric barriers is proposed to reduce the efficiency droop phenomenon and to improve the internal quantum efficiency. After theoretical calculation, the lighting performance of the blue InGaN light-emitting diodes is effectively improved by using the asymmetric barriers. Besides, the physical explanations for the improvement in device performance are discussed in detail. Finally, the thesis is concluded in chapter 5.