Theoretical Study of LED Operating in Noncarrier Injection Mode

Wu, Chaoxing; Wang, Kun; Guo, Tailiang

doi:10.3390/nano12152532

Cited by 11 publications

(3 citation statements)

References 17 publications

(23 reference statements)

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“…[7][8][9][10][11][12] However, effective electrical connection between the electrode array and the nano-LED array is challenging. [13][14][15][16][17] Recently, an operation mode for nano-LEDs, namely, noncarrier injection (NCI) mode, [18][19][20][21][22][23][24] has been demonstrated. For LEDs operating in the NCI mode, the LED chips are sandwiched between insulating layers, and the periodic electroluminescence (EL) can be obtained under an alternating current (AC).…”

Section: Introductionmentioning

confidence: 99%

Device Simulation on GaN‐LED Operating in Noncarrier Injection Mode for Performance Improvement by Enhancing the Tunneling Effect in Multiquantum Wells

Wang

Liao

et al. 2023

Adv Elect Materials

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Noncarrier injection (NCI) operation mode is an emerging driving mode for nanoscale light‐emitting diodes (LEDs) for application in nanopixel light‐emitting displays. However, the luminescence intensity of the NCI‐LED with traditional epitaxial structure is relatively low because of the absence of external carrier injection. Therefore, improving the luminescence intensity by optimizing the epitaxial structure of the LED is an important technical measure. In this work, the tunneling behavior of the NCI‐LED under reverse bias, which plays a key role in increasing the luminescence intensity, is studied through modeling and simulation. The dynamic variation of carrier concentration in each voltage cycle is studied to explore the working process of the NCI‐LED. Results show that the luminescence output of the NCI‐LED is highly sensitive to doping concentrations, and reducing the number of multiquantum wells can increase the probability of interband tunneling so as to improve dramatically the carrier number contributing to luminescence. This simulation work can deepen the understanding of the NCI mode and serve as an important guidance for the rational design of the NCI‐LEDs.

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Section: Introductionmentioning

confidence: 99%

Device Simulation on GaN‐LED Operating in Noncarrier Injection Mode for Performance Improvement by Enhancing the Tunneling Effect in Multiquantum Wells

Wang

Liao

et al. 2023

Adv Elect Materials

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“…源矩阵驱动两种 [11,12] 。但无论是采用何种驱动方式，外电极与 LED 芯片必须要存在良好的电学接触以保证高效的载流子注入。因此，实现外延基板上的巨量微纳 LED 芯片与显示背板上驱动结构之间精准的空间对准以保证 LED 芯片与驱动电极形成良好的电气连接是核心关键技术之一 [13] 。由于微纳 LED 尺寸只有几百纳米到几十微米，且需要对准的 LED 芯片数量高达百万甚至上亿颗之多，要实现 LED 芯片与驱动电路的高性能电学接触也愈发困难，这成为阻碍微纳 LED 走向大规模商业化应用的瓶颈。另一方面，驱动电极与微纳 LED 之间不可避免地会有接触电阻并由此产生焦耳热，影响器件工作性能。虽然电极与微纳 LED 之间的界面处理能最大程度地消除接触电阻，但是随着 LED 尺寸缩小至亚微米，界面处理难度将显著加大，并有可能影响器件发光性能 [14][15][16] 。 2020 年福州大学郭太良、吴朝兴团队提出了一种交流驱动的无外部载流子注入微米 LED 器件与纳米 LED 器件(无注入型微纳 LED) ，即电极与 LED 芯片之间无电学接触无外部载流子注入 [17,18] 。该工作模式有望消除接触电阻带来的影响以及降低对金属键合的高精度要求。但是，有关无注入微纳 LED 的理论研究只是停留在对内部载流子输运的定量描述，并没有具体的物理和数学模型。由于传统 LED 复合发光的载流子来源于外部，现有的载流子输运模型(即传统的 PN 结模型)无法直接应用于无注入型 LED。另一方面，无注入型 LED 器件由于隔绝了外部载流子的注入，将面临着发光效率低、驱动电压高和需要高频交流电等问题，急需用于器件优化的理论指导 [19]…”

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Carrier transport model of non-carrier-injection light-emitting diode

Jiancheng¹,

Wu²,

Guo³

2023

Acta Phys. Sin.

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Non-carrier-injection light-emitting diodes (NCI-LEDs) are expected to be widely used in next generation micro-display technologies, including Micro-LEDs and nano-pixel light-emitting displays due to their simple device structure. However, because there is no charge carrier injection from external electrodes, carrier transport behavior of the NCI-LED cannot be described by using the traditional PN junction and LED theory. Therefore, establishing a carrier-transport model for the NCI-LED is of great significance for understanding its working mechanism and for improving device performance. In this paper, carrier transport mathematical model of the NCI-LED is established and the mechanical behavior of charge-carrier transport is analyzed quantitatively. Based on the mathematical model, the working mechanism of the NCI-LED is explained, the carrier transport characteristics of the device are obtained. Additionally, the key features, including the length of the induced charge region, the forward biased voltage across the internal PN junction, and the reverse biased voltage across the internal PN junction are studied. Their relationships with the applied frequency of the applied driving voltage are revealed. It is found that both the forward and reverse biases of the internal PN junction increase with the driving frequency. When the driving frequency reaches a certain value, the forward and reverse bias of the PN junction would be maintained at a maximum value. Moreover, the length of the induced charge region decreases with the increase of the driving frequency, and when the frequency reaches a certain value, the induced charge region would always be in the state of exhaustion. According to the mathematical model, suggestions for the device optimization design are provided: (1) Reducing the doping concentration of the induced charge regions can effectively increase the voltage drop across the internal LED; (2) Employing the tunneling effect occurring in the reverse-biased PN junction can effectively improve the electroluminescence intensity; (3) Using square-wave driving voltage can obtain a larger voltage drop across the internal LED and increase the electroluminescence intensity. This work on the carrier transport model is expected to provide a clear physical image for understanding the working mechanism of NCI-LED, and to provide a theoretical guidance for optimizing the device structure.

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“…Considering the absence of carriers injected from the external electrode, revealing the source of carriers that can support stably periodic electroluminescence is important. Until now, various electroluminescence devices using self-supported LED chips, nano-LEDs, phosphors, two-dimensional materials, organic light-emitting diodes, and QD-based light-emitting diodes that do not require external charge injection have been widely reported. − Because of the ultrasmall size of QDs in three dimensions, the mechanisms to explain the source of charge are not suitable for the insulator/QDs/insulator structure. The existing explanation for the insulator/QDs/insulator device is as follows.…”

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In-Well Ionization from Monolayer Quantum Dots for Non-Carrier-Injection Electroluminescence

Shen

Wang

et al. 2022

J. Phys. Chem. Lett.

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Quantum dot (QD) light-emitting devices operating in non-carrier-injection (NCI) mode have attracted intense interest. Revealing the source of carriers that support the periodic electroluminescence is important because there is no injection of carriers from the external electrode. Electrons/holes generated by well-to-well multiple ionization in adjacent QDs are generally recognized as the carrier source for electroluminescence, and the stacked QD layers are necessary. In this work, NCI electroluminescence (NCI-EL) from monolayer QDs is successfully demonstrated, which cannot be properly explained by the previously proposed mechanism of multiple ionization. A working mechanism related to periodic in-well ionization is proposed, in which electrons tunnel directly from the valence band of QDs to the conduction band to form free electrons and holes. The effects of driving voltage amplitude, frequency, and QD size on the NCI-EL performance are investigated. Finite element simulation is used to clarify the ionization process. We believe this work can extend the working mechanism model of NCI-EL from QDs and provide guidance for promoting QD-based light-emitting device performance.

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Theoretical Study of LED Operating in Noncarrier Injection Mode

Cited by 11 publications

References 17 publications

Device Simulation on GaN‐LED Operating in Noncarrier Injection Mode for Performance Improvement by Enhancing the Tunneling Effect in Multiquantum Wells

Device Simulation on GaN‐LED Operating in Noncarrier Injection Mode for Performance Improvement by Enhancing the Tunneling Effect in Multiquantum Wells

Carrier transport model of non-carrier-injection light-emitting diode

In-Well Ionization from Monolayer Quantum Dots for Non-Carrier-Injection Electroluminescence

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