SPECIAL TOPIC — Physics in micro-LED and quantum dots devices

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    A polarization mismatched p-GaN/p-Al0.25Ga0.75N/p-GaN structure to improve the hole injection for GaN based micro-LED with secondary etched mesa
    Yidan Zhang(张一丹), Chunshuang Chu(楚春双), Sheng Hang(杭升), Yonghui Zhang(张勇辉),Quan Zheng(郑权), Qing Li(李青), Wengang Bi(毕文刚), and Zihui Zhang(张紫辉)
    Chin. Phys. B, 2023, 32 (1): 018509.   DOI: 10.1088/1674-1056/ac9b35
    Abstract230)   HTML4)    PDF (1210KB)(116)      
    A low hole injection efficiency for InGaN/GaN micro-light-emitting diodes (μLEDs) has become one of the main bottlenecks affecting the improvement of the external quantum efficiency (EQE) and the optical power. In this work, we propose and fabricate a polarization mismatched p-GaN/p-Al$_{0.25}$Ga$_{0.75}$N/p-GaN structure for 445 nm GaN-based μLEDs with the size of $40 \times 40 $μm$^{2}$, which serves as the hole injection layer. The polarization-induced electric field in the p-GaN/p-Al$_{0.25}$Ga$_{0.75}$N/p-GaN structure provides holes with more energy and can facilitate the non-equilibrium holes to transport into the active region for radiative recombination. Meanwhile, a secondary etched mesa for μLEDs is also designed, which can effectively keep the holes apart from the defected region of the mesa sidewalls, and the surface nonradiative recombination can be suppressed. Therefore, the proposed μLED with the secondary etched mesa and the p-GaN/p-Al$_{0.25}$Ga$_{0.75}$N/p-GaN structure has the enhanced EQE and the improved optical power density when compared with the μLED without such designs.
    Review of a direct epitaxial approach to achieving micro-LEDs
    Yuefei Cai(蔡月飞), Jie Bai(白洁), and Tao Wang(王涛)
    Chin. Phys. B, 2023, 32 (1): 018508.   DOI: 10.1088/1674-1056/ac90b5
    Abstract318)   HTML10)    PDF (3004KB)(332)      
    There is a significantly increasing demand of developing augmented reality and virtual reality (AR and VR) devices, where micro-LEDs (μLEDs) with a dimension of ≤ 5 μ m are the key elements. Typically, μLEDs are fabricated by dry-etching technologies, unavoidably leading to a severe degradation in optical performance as a result of dry-etching induced damages. This becomes a particularly severe issue when the dimension of LEDs is ≤ 10 μ m. In order to address the fundamental challenge, the Sheffield team has proposed and then developed a direct epitaxial approach to achieving μLEDs, where the dry-etching technologies for the formation of μLED mesas are not needed anymore. This paper provides a review on this technology and then demonstrates a number of monolithically integrated devices on a single chip using this technology.
    Ion migration in metal halide perovskite QLEDs and its inhibition
    Yuhui Dong(董宇辉), Danni Yan(严丹妮), Shuai Yang(杨帅), Naiwei Wei(魏乃炜),Yousheng Zou(邹友生), and Haibo Zeng(曾海波)
    Chin. Phys. B, 2023, 32 (1): 018507.   DOI: 10.1088/1674-1056/aca7e8
    Abstract224)   HTML8)    PDF (4922KB)(161)      
    Benefiting from the excellent properties such as high photoluminescence quantum yield (PLQY), wide gamut range, and narrow emission linewidth, as well as low-temperature processability, metal halide perovskite quantum dots (QDs) have attracted wide attention from researchers. Despite tremendous progress has been made during the past several years, the commercialization of perovskite QDs-based LEDs (PeQLEDs) is still plagued by the instability. The ion migration in halide perovskites is recognized as the key factor causing the performance degradation of PeQLEDs. In this review, the elements species of ion migration, the effects of ion migration on device performance and stability, and effective strategies to hinder/mitigate ion migration in PeQLEDs are successively discussed. Finally, the forward insights on the future research are highlighted.
    Bottom-up approaches to microLEDs emitting red, green and blue light based on GaN nanowires and relaxed InGaN platelets
    Zhaoxia Bi(毕朝霞), Anders Gustafsson, and Lars Samuelson
    Chin. Phys. B, 2023, 32 (1): 018103.   DOI: 10.1088/1674-1056/aca9c2
    Abstract291)   HTML10)    PDF (3311KB)(226)      
    Miniaturization of light-emitting diodes (LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions, augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls. Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal-organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μ in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.
    Materials and device engineering to achieve high-performance quantum dots light emitting diodes for display applications
    Changfeng Han(韩长峰), Ruoxi Qian(钱若曦), Chaoyu Xiang(向超宇), and Lei Qian(钱磊)
    Chin. Phys. B, 2023, 32 (12): 128506.   DOI: 10.1088/1674-1056/acb916
    Abstract96)   HTML0)    PDF (1045KB)(61)      
    Quantum dots (QDs) have attracted wide attention from academia and industry because of their advantages such as high emitting efficiency, narrow half-peak width, and continuously adjustable emitting wavelength. QDs light emitting diodes (QLEDs) are expected to become the next generation commercial display technology. This paper reviews the progress of QLED from physical mechanism, materials, to device engineering. The strategies to improve QLED performance from the perspectives of quantum dot materials and device structures are summarized.