Electron Blocking Layer Free Full-Color InGaN/GaN White Light-Emitting Diodes
Electron Blocking Layer Free Full-Color InGaN/GaN White Light-Emitting Diodes
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无电子阻挡层全色 InGaN/GaN 白色发光二极管
DOI：
10.1149/ma2020-02422743mtgabs
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发表时间：
2020
期刊：
影响因子：
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通讯作者：
Nguyen, Hieu Pham
中科院分区：
文献类型：
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作者：
Jain, Barsha;Velpula, Ravi Teja;Bui, Ha Quoc;Patel, Moulik;Nguyen, Hieu Pham
氮化铟(InGaN)化合物半导体合金已被广泛研究和应用于白光发光二极管(LED)[1，2]。与传统的平面结构相比，由于有效的侧向应力松弛，III-氮化物纳米线可以显示出显著的优势，包括极大地降低位错密度和极化场。此外，在有源区引入量子点/盘的纳米线LED可以产生更好的载流子限制，有望成为发射可调的高效率LED[2]。然而，在进一步提高量子效率和光输出功率方面，纳米线LED仍然面临着一些挑战，包括有源区载流子限制效率低下、载流子分布不均匀和电子溢出。LED中电子阻挡层(EBL)的集成在一定程度上缓解了电子泄漏问题，但如果设计不当，也会降低向有源区的空穴注入，导致较差的空穴传输问题。因此，没有EBL的LED，具有高效的载流子限制能力，可以忽略有源区的载流子泄漏是最佳选择[3]。在本工作中，我们展示了无EBL的高性能无磷InGaN/GaN纳米线白光LED。在富氮条件下，利用射频等离子体辅助分子束外延(Veeco Gen II MBE)在Si(111)衬底上生长了该结构，并制作了器件进行了表征。提出的LED结构(LED3)由一个200 nm厚的n-GaN纳米线模板、10个3 nm GaN量子垒(QB)/3 nm InGaN量子阱(QW)的有源区多量子阱(MQW)和一个100 nm厚的p-GaN组成。此外，我们还加入了30 nm的n-In0。2Ga0。N-GaN和有源区之间的8N量子阱，以控制电子溢出。此外，为了利用从有源区逸出的电子，第二个10 nm的p-In0。1Ga0。在有源区和p-GaN之间引入了9N量子阱。这种第二量子阱降低了p-GaN的电子损耗，并贡献了蓝光发射，从而相对控制了LED器件的白光发射。拟议结构的示意图如图1(A)所示。与传统的LED结构(LED1：200 nm n-GaN，10 MQW(3 Nm)/MQBS(3 Nm)，100 nm p-GaN)和基于EBL的结构(LED2：200 nm n-GaN，10 MQW(3 Nm)/MQBS(3 Nm)，10 nm p-Al0)进行了比较。1Ga0。9N EBL，100 nm p-GaN)，以了解所建议的LED结构的增强性能。结果表明，与传统的和基于EBL的InGaN/GaN LED相比，所提出的LED在更少的电子泄漏、更高的空穴注入、更高的内量子效率(IQE)、外量子效率(EQE)和输出光功率方面具有更好的性能。该器件具有较高的IQE(58.5%)和高稳定的发射特性。图1(B)和1(C)中示出了LED的相对等效光功率和输出光功率。这种独特的无EBL纳米线LED结构是实现普通照明和显示应用中的大功率无磷LED的一种很有前途的方法。
Indium gallium nitride (InGaN) compound semiconductor alloys have been intensively studied and utilized for white light-emitting diodes (LEDs)[1, 2]. Compared to conventional planar structures, III-nitride nanowires can exhibit significant advantages including greatly reduced dislocation densities and polarization fields, due to the effective lateral stress relaxation. Additionally, the nanowire LEDs with the incorporation of quantum dots/disks in the active region may lead to superior carrier confinement, promising for high efficiency LEDs with tunable emission [2]. However, nanowire LEDs still contain several challenges to further improve the quantum efficiency and light output power, which includes inefficient carrier confinement in the active region, nonuniform carrier distribution, and electron overflow. The integration of an electron blocking layer (EBL) in the LED mitigates electron leakage problem to an extent but it also lowers the hole injection into the active region if not designed properly causing poor hole transport problem. Hence, the LED without EBL, with efficient carrier confinement capability, negligible carrier leakage from active region is the optimal choice [3].In this work, we have demonstrated EBL free high-performance phosphor-free InGaN/GaN nanowire white LEDs. The proposed structure is grown on Si (111) substrate by RF plasma-assisted MBE (Veeco Gen II MBE) under nitrogen-rich condition, then fabricated devices for characterization. The proposed LED structure (LED3) consists of a 200 nm thick n-GaN nanowire template, 10 multiple quantum wells (MQWs) of 3 nm GaN quantum barrier (QB)/3 nm InGaN quantum well (QW) in the active region and a 100 nm thick p-GaN. In addition, we have incorporated 30 nm n-In0. 2Ga0. 8N QW between the n-GaN and the active region to control electron overflow. Moreover, to utilize the electrons escaped from the active region, a second 10 nm p-In0. 1Ga0. 9N QW is introduced between the active region and p-GaN. This second QW reduces electron loss to the p-GaN and contributes blue light emission to relatively control the white light emission from the LED device. The schematic diagram of the proposed structure is shown in Fig. 1 (a). A comparison has been made with the conventional LED structure (LED1: 200 nm n-GaN, 10 MQWs (3 nm)/MQBs (3 nm), 100 nm p-GaN) and EBL based structure (LED2: 200 nm n-GaN, 10 MQWs (3 nm)/MQBs (3 nm), 10 nm p-Al0. 1Ga0. 9N EBL, 100 nm p-GaN) to understand the enhanced performance of the proposed LED structure. As a result, we observed that proposed LED has better performance in terms of less electron leakage, high hole injection, improved internal quantum efficiency (IQE), external quantum efficiency (EQE) and output optical power as compared to other conventional and EBL based InGaN/GaN LEDs. The resulting device exhibits high IQE of 58.5% with highly stable emission characteristics. The relative EQE and output optical power of the LEDs are shown in Figs. 1 (b) and 1 (c). Such unique EBL free nanowire LED structure is a promising approach to achieve high-power phosphor-free LEDs for general illumination and display applications.