微型发光二极管（Micro-LED）被认为是下一代显示技术。与传统有机发光二极管（OLED）、液晶显示（LCD）等显示技术相比，Micro-LED在分辨率、亮度、对比度、响应速度、寿命、功耗等方面具有显著优势，符合以虚拟现实/增强现实（VR/AR）为代表的新型显示的要求。但是，Micro-LED还存在一些问题，一方面尺寸效应的作用机制仍然不明确，没有高效率的超小尺寸Micro-LED器件报道；另一方面红光Micro-LED效率低，导致难以制作出高质量全彩Micro-LED显示屏。本论文面向微显示应用需求，制备了超小尺寸InGaN红绿蓝光Micro-LED，并对不同颜色器件的尺寸效应进行了分析，为InGaN材料实现全彩微显示奠定了基础。论文工作取得的主要结果如下：1. 通过激光直写光刻技术，制备了1-20 μm蓝绿光Micro-LED，1 μm蓝光和绿光器件的外量子效率分别可达13.02%和9.57%。基于“死区”模型拟合出蓝光和绿光Micro-LED的死区宽度分别约0.18 μm和0.15 μm，通过时间分辨光致发光（TRPL），确认了绿光Micro-LED尺寸效应较小的原因在于更高的载流子局域化程度。2. 通过交替通断源外延方法，制备了基于高密度InGaN自组装量子点的橙红光LED，其光致发光（PL）波长可达613 nm，内量子效率（IQE）可达13%，5 μm尺寸Micro-LED器件在电流密度0.3 A/cm2下外量子效率（EQE）达到峰值2.80%，对应发光波长570 nm。进一步，在量子点有源区下方引入应力调控结构，制备了波长更长的红光量子点Micro-LED，其5 μm尺寸器件在电流密度10 A/cm2下发光波长可达630 nm，对应EQE 0.03%。3. 通过引入AlN盖层，补偿了高In组分InGaN/GaN量子阱（QW）的晶格失配，并提升了长波长下的发光效率。基于GaN自支撑同质衬底（FGS），实现芯片尺寸1 μm的InGaN基红光Micro-LED。器件在50 A/cm2下EQE达到峰值0.86%，对应发光波长614 nm。相比基于图形化蓝宝石衬底的Micro-LED器件，基于FGS的器件表现出了更长的发光波长（>600 nm）和更好的阵列发光均匀性。
Micro-sized light-emitting diode (Micro-LED) is considered the next generation display technology. Compared with traditional display technologies, such as organic light-emitting diode (OLED) and liquid crystal display (LCD), Micro-LED has significant advantages in resolution, brightness, contrast, response speed, lifespan and power consumption, meeting the new requirements of new display devices represented by virtual reality and augmented reality (AR/VR). However, Micro-LEDs still have many problems. On the one hand, the mechanism of size-dependent effect is still unclear, and there are no reports of high-quality ultra-small sized Micro-LEDs devices. On the other hand, the luminescence efficiency of red Micro-LED is poor, making it difficult to produce high-quality full-color micro displays. This paper focuses on the needs of micro display applications, and prepare ultra-small blue, green and red InGaN Micro-LEDs. The size effects of different color devices are analyzed, laying the foundation for achieving full color micro displays using InGaN materials. The main results of this paper are as follows:Firstly, by using laser direct writing lithography, we have prepared blue and green 1-20 μm Micro-LEDs with the highest efficiency among reported devices. The external quantum efficiencies (EQE) of 1-μm blue and green devices can reach 13.02% and 9.57%, respectively. Based on the “dead zone” numerical fitting, it was pointed out that the “dead zone” widths of blue and green Micro-LEDs are approximately 0.18 μm and 0.15 μm, respectively. Through time resolved photoluminescence (TRPL), it was confirmed that the smaller size effect of green Micro-LEDs is due to the higher degree of carrier localization.Secondly, amber LEDs based on high-density InGaN self-assembled quantum dots (QDs) were prepared by precursor-alternate-admittance method, with a photo-luminescence (PL) wavelength of 613 nm and an internal quantum efficiency (IQE) of 13%. The external quantum efficiency (EQE) of the 5 μm Micro-LED device reached a peak of 2.80% at 0.3 A/cm2, corresponding to a luminous wavelength of 570 nm. Furthermore, QD Micro-LEDs with longer emission wavelength were prepared by introducing a stress-controlled structure below the QD active region. The peak wavelength of 5-μm devices could reach 630 nm at 10 A/cm2, corresponding to an EQE of 0.03%。Finally, by introducing an AlN insert layer, the lattice mismatch between high In component InGaN/GaN quantum wells (QW) is compensated, and the luminescence efficiency at long wavelengths is improved. Based on GaN freestanding substrate (FGS), we achieved the world's first InGaN red Micro-LEDs with chip size of 1 μm. The peak EQE of 1-μm device is 0.86%, corresponding to a peak emission wavelength of 614 nm and a working current density of 50 A/cm2. Compared to patterned sapphire substrates (PSS), Micro-LED devices grown on FGS exhibit longer emission wavelengths (>600 nm) and better array emission uniformity.
