高效GaN基绿光LED研究

High efficiency green light emitting diodes have attracted a great attention for application as key components in high-power white light illumination, full color display and so on. However, the electro-optic conversion efficiency is very low, about 20% in the present. The key points are droop under the high current density, wavelength shifts with increasing current and so on. Based on the investigation of green nitride light emitting diodes, we will study the high efficiency green light emitting diodes. We will investigate the modification of the piezoelectric fields in the InGaN/GaN multiple quantum wells, investigate the P-type doping to enhance the hole concentration, and investigate the performance change of the green nitride light emitting diodes under high current density. The energy band of the active region will be modified to reduce the strain at the interface between the barrier and the well, then enhancing the wave function overlap of the hole and electron to obtain a high radiative efficiency. Nonpolar and semipolar growth of high-indium-content quantum wells will be extensively investigated for the elimination or reduction of polarization-related electric fields. The high density mobile three-dimensional hole gas obtained by polarization doping will be studied and applied to the green light emitting diodes to obtain a sufficient hole injection. The In-Mg co-doped p-type GaN epilayers will be grown and researched to get high hole concentration. The aims of the project are to realizing internal quantum efficiency of 50%, with the peak wavelength above 520 nm, and the hole concentration exceeding 2E18 /cm^3, then fabricated green light emitting diodes with proprietary intellectual property rights.

基于富铟的InGaN/GaN绿光结构材料一直是固态显示、照明领域的一个难点，被称为“Green Gap”。目前高效绿光发光二极管（LED）的电光转换效率仅为20%。本项目将开展高效氮化镓基绿光LED材料和机理的研究。针对富铟的激子局域化现象，开展团簇原子输运及复合的理论计算和模拟，并进行高铟组分InGaN/GaN量子阱内强压电极化电场的调控。研究基于非极性材料的结构性质、应力状况、面内极化特征、光电性质及其随结构和外场参数的变化规律。开展研究“3D空穴”即界面极化电荷向材料内部输运的机制，以获得新机制下高空穴浓度的金属极性面p型共掺杂材料，并开展大电流注入下外场条件下对富铟材料体系输运复合性能的影响的系统研究。实现发光波长大于520 nm，内量子效率大于50%的高效绿光LED，空穴浓度大于2E18/cm^3。实现大电流密度下高光色品并具有自主知识产权的高效氮化物绿光LED。

本课题研究团队经过5年的创新研究，在InGaN基绿光LED的外延结构设计、材料生长、器件工艺和测试分析等方面解决了一系列关键的科学与技术问题，研制成功了高光效的氮化物绿光LED，完成了课题的研究内容，达到了预定的研究目标，取得了如下的主要成果：.1)通过优化设计了新型富In组分多量子阱能带结构、采用复合电子阻挡层、利用微纳六棱锥结构制备出半极性面InGaN/GaN等方式，降低了绿光LED多量子阱内压电极化电场强度，525 nm InGaN基LED内量子效率达到66.4%，在350mA下器件输出功率达到308.6 mW。.2)优化了p-GaN的Mg掺杂生长条件及金属极性面AlGaN的3D极化诱导空穴气p型掺杂技术；构建了应力调制氮化物中Mg杂质激活能的物理模型；利用In-Mg共掺实现了高空穴浓度的p型掺杂技术，获得了空穴浓度为2.3E^18 /cm^3的p型掺杂。.3)开展了高In组分氮化物材料的外延生长，发现了H2生长气氛下富In组分InGaN量子阱中局域态演化及缺陷湮灭的物理机制；进行了纳米PSS的制备和GaN外延生长，得到表面粗糙度0.1nm的GaN表面，490nm LED功率转换效率达到53.5%。.4)提出了表面等离激元增强绿光发光的新机制，实现了表面等离激元绿光LED的发光强度增强4.35倍，自发辐射速率增强3.8倍；545nm绿光LED内量子效率增强至34.7%，出光效率增强至30.1%。.5)探索了纳米柱结构LED的微腔导波模式分布及光场分布，发现了阳极氧化铝（AAO）准光子晶体、图形化多孔阵列Ni/Au半透明电极、火山口型图形化衬底等的光引出机制，改善了绿光LED的发光效率，实现了绿光LED出光效率最大提升116%。.6)提出并实现了集成结温传感的LED芯片及封装，解释了不同结温和大注入电流下绿光LED的色漂移等光电性能变化规律；利用H2的侧壁钝化技术，解决了绿光LED的侧壁漏电问题。获得了纳米柱绿光LED有源区内69.8％的应变弛豫，实现了大电流下绿光LED发光波长的稳定。建立了有机/III-V纳米复合结构半导体带边发射的能量转移物理模型；发现了不同背景载流子浓度下Pt/Au/AlInGaN肖特基接触的载流子输运机制。