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472 results on '"Zhang, Zi-Hui"'

161. Enhanced performance of an AlGaN-based deep ultraviolet light-emitting diode using a p^+-GaN/SiO_2/ITO tunnel junction

Author

Che, Jiamang, Shao, Hua, Chu, Chunshuang, Li, Qingqing, Zhang, Yonghui, Sun, Xiaowei, and Zhang, Zi-Hui

Abstract

In this work, a 280-nm-wavelength deep-ultraviolet light-emitting diode (DUV LED) with a p^+-GaN/SiO_2/ITO tunnel junction is fabricated and investigated. Due to the decreased tunnel region width and enhanced electric field intensity in the 1-nm-thick SiO_2 layer, the interband tunneling efficiency and the corresponding hole injection efficiency are promoted. Therefore, the external quantum efficiency (EQE) for the proposed device is increased when compared with a traditional DUV LED. In addition, an improved current spreading effect is observed for our proposed device. As a result, improved wall-plug efficiency (WPE) is obtained owing to the increased optical power and decreased forward operating voltage. Meanwhile, the enhanced electric field intensity in the SiO_2 layer reduces the voltage drop in the p-n junction region for the proposed device, and thus the leakage current is reduced.

Published
2022

163. Investigation into the impact of bulk defects in the drift layer on the electrical properties of GaN-based trench Schottky barrier diodes

Author

Gao, Xuchen, He, Feng, Huang, Fuping, Wang, Zhizhong, Chu, Chunshuang, Tian, Kangkai, Zhang, Yonghui, and Zhang, Zi-Hui

Abstract

Using numerical simulation tools, this work systematically investigates the impact of bulk defects in the drift layer on GaN-based trench metal–insulator–semiconductor barrier-controlled Schottky rectifiers. Investigations show that in forward conduction, the acceptor-type defects significantly increase the on-resistance (Ron.sp). When the device is in reverse blocking mode, donor-type defects tend to weaken the charge-coupling effect, leading to early breakdown of the device, while acceptor-type defects show the opposite feature. In addition, our report identifies that the reverse blocking effect is significantly impacted when the defects are located in the region with maximum electric field magnitude. We also find that the acceptor-type traps generate a remarkable charging/discharging effect, which will destabilize the dynamic forward conduction process. Hence, we numerically prove that bulk defects should be avoided in actual power diodes.

Published
2024
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164. Advantage of SiO2 Intermediate Layer on the Electron Injection for Ti/n-Al0.60Ga0.40N Structure.

Author

Shao, Hua, Che, Jiamang, Kou, Jianquan, Chu, Chunshuang, Tian, Kangkai, Zhang, Yonghui, Bi, Wengang, and Zhang, Zi-Hui

Subjects
SCHOTTKY barrier, ALUMINUM gallium nitride, ELECTRONS, CONDUCTION bands
Abstract

In this work, and experimentally propose inserting an SiO2 intermediate layer between the Ti and n-AlGaN layer to improve the electron injection efficiency. When the SiO2 intermediate layer is adopted, the SiO2 layer can share a part of the applied voltage and then weakens the surface depletion effect, which is confirmed by the capacitance–voltage measurement. Furthermore, the energy bending of the SiO2 layer pushes the affinity of Ti to be even higher than the conduction band of the Al0.60Ga0.40N layer, which then screens the Schottky barrier and favors the election injection. The influence of the thickness of the SiO2 intermediate layer is also investigated in this work. When the SiO2 layer becomes thick, the tunneling capability of the electrons will be significantly limited due to the increased tunnel region width, leading to increased forward voltage. [ABSTRACT FROM AUTHOR]

Published
2020
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165. Highly efficient Mn-doped CsPb(Cl/Br)3 quantum dots for white light-emitting diodes.

Author

Sun, Chun, Wang, Le, Su, Sijing, Gao, Zhiyuan, Wu, Hua, Zhang, Zi-hui, and Bi, Wengang

Subjects
LIGHT emitting diodes, QUANTUM dots, SURFACE preparation, MANGANESE, PHOTOLUMINESCENCE, BROMINE, ENGINEERING
Abstract

White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) have attracted much attention and rely on mixing several colors of perovskites. However, this inevitably leads to a non-uniform light distribution and serious light loss. Here, a novel strategy was demonstrated to obtain white emission by combining the orange and blue emission from CsPb/Mn(Cl/Br)3 QDs. Notably, highly efficient white emission with a photoluminescence quantum yield of 94% was achieved by an anion exchange surface engineering (AESE) strategy. After AESE treatment the surface traps can be eliminated, resulting in improved exciton and Mn2+ emission. A prototype WLED device was fabricated and exhibited excellent optical stability, demonstrating great potential for perovskite QDs in the field of optoelectronics. [ABSTRACT FROM AUTHOR]

Published
2020
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188. One Stone, Two Birds: High-Efficiency Blue-Emitting Perovskite Nanocrystals for LED and Security Ink Applications

Author

Sun, Chun, Gao, Zhiyuan, Liu, Hanxin, Wang, Le, Deng, Yuchen, Li, Peng, Li, Huanrong, Zhang, Zi-Hui, Fan, Chao, and Bi, Wengang

Abstract

Blue-emitting perovskite nanocrystals (NCs) are known to exhibit low photoluminescence (PL) quantum yield (QY) compared to green- and red-emitting counterparts, which is due to the presence of localized trap states on the surface. Here, we demonstrate a new method to synthesize high-efficiency blue-emitting perovskite NCs by anion exchange of 0D and 3D perovskite NCs. The remarkable enhancement of the PL QY is caused by surface reconstruction and subsequent suppression of nonradiative recombination centers of 3D perovskite NCs during the anion exchange. Remarkably, these high-efficiency NCs have two appealing applications. First, they can be applied in backlight display, where the GaN light-emitting diode is usually used as the blue emission source. We found that the as-prepared NCs were facile to tune their emission peaks and possessed narrow linewidths. As a downconverter, the NCs realize an ultrapure blue light for backlight display. Second, benefiting from the existence of 0D perovskite, anticounterfeiting inks can also be achieved based on these blue-emitting perovskite NCs. The encoding/reading strategy relies on the conversion of 0D perovskites. These findings provide new opportunities for blue-emitting perovskite NCs and broaden their application.

Published
2024
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197. Investigations on AlGaN‐Based Deep‐Ultraviolet Light‐Emitting Diodes With Si‐Doped Quantum Barriers of Different Doping Concentrations.

Author

Tian, Kangkai, Chen, Qian, Chu, Chunshuang, Fang, Mengqian, Li, Luping, Zhang, Yonghui, Bi, Wengang, Chen, Changqing, Zhang, Zi‐Hui, and Dai, Jiangnan

Subjects
LIGHT emitting diodes, SILICON, DOPING agents (Chemistry), QUANTUM wells, POLARIZATION (Electricity)
Abstract

In this work, we investigate the impact of Si doped AlGaN quantum barriers on the optical powers for [0001] oriented III‐nitride based deep‐ultraviolet light‐emitting diodes (DUV LEDs). The polarization‐induced electric field in the active region is screened as the result of Si‐doped quantum barriers, which gives rise to the improved spatial overlap between electron and hole wave functions. The polarization screening effect within the quantum wells is further proven by the observation of the blue shift for the wavelength. However, the hole distribution across the active region can be significantly retarded if the Si dosage in the quantum barriers is too high. Therefore, the improved radiative recombination within the active region can be realized provided that the Si dosage in the quantum barriers is moderately adjusted to guarantee both the better hole injection efficiency and the screened polarization effect in the multiple quantum wells. [ABSTRACT FROM AUTHOR]

Published
2018
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199. Numerical Investigations on the n+-GaN/AlGaN/p+-GaN Tunnel Junction for III-Nitride UV Light-Emitting Diodes.

Author

Li, Luping, Zhang, Yonghui, Tian, Kangkai, Chu, Chunshuang, Fang, Mengqian, Meng, Ruilin, Shi, Qiang, Zhang, Zi‐Hui, and Bi, Wengang

Subjects
LIGHT emitting diodes, NITRIDES, TUNNEL junction devices, ELECTRIC fields, ELECTRIC conductivity, LIGHT sources
Abstract

In this report, a parametric investigation on the n+-GaN/AlGaN/p+-GaN tunnel junction is made for III-nitride based ultraviolet light emitting diodes (UV LEDs). It is found that, on one hand, by using various Al compositions and AlGaN layer thicknesses, the n+-GaN/AlGaN/p+-GaN tunnel junction can modify the electric field therein, which will affect the carrier tunneling probability and the current-voltage characteristics. On the other hand, the Al composition and the AlGaN layer thickness also have a strong impact on the tunnel region width, which will affect the current flowing path and then influence the hole distribution apart from the p-type ohmic contact. This work conducts a comprehensive analysis and presents an in-depth understanding regarding the n+-GaN/AlGaN/p+-GaN tunnel junction, so that the hole concentration and the internal quantum efficiency can be significantly improved for III-nitride UV LEDs. [ABSTRACT FROM AUTHOR]

Published
2017
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200. Nonradiative recombination — critical in choosing quantum well number for InGaN/GaN light-emitting diodes

Author

Zhang, Yi Ping, primary, Zhang, Zi-Hui, additional, Liu, Wei, additional, Tan, Swee Tiam, additional, Ju, Zhen Gang, additional, Zhang, Xue Liang, additional, Ji, Yun, additional, Wang, Lian Cheng, additional, Kyaw, Zabu, additional, Hasanov, Namig, additional, Zhu, Bin Bin, additional, Lu, Shun Peng, additional, Sun, Xiao Wei, additional, and Demir, Hilmi Volkan, additional

Published
2014
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