Nearly Efficiency-Droop-Free AlGaN-Based Ultraviolet Light-Emitting Diodes with a Specifically Designed Superlattice p-Type Electron Blocking Layer for High Mg Doping Efficiency

Zhang, Zi Hui; Chen, Sung Wen Huang; Chu, Chunshuang; Tian, Kangkai; Fang, Mengqian; Zhang, Yonghui; Bi, Wengang; Kuo, Hao Chung

doi:10.1186/s11671-018-2539-9

Cited by 66 publications

(49 citation statements)

References 28 publications

(35 reference statements)

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“…AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) can be widely used in the fields of solid-state lighting, medicine, biochemistry, and so on. Therefore, more and more efforts have been devoted to improve the crystal quality of the materials [ 1 – 4 ], the p-type doping techniques, and the optimization of the device structures [ 5 – 9 ]. Miyake et al demonstrated that the AlN crystal quality can be improved significantly by high-temperature annealing [ 3 ].…”

Section: Introductionmentioning

confidence: 99%

Influence of Quantum-Well Width on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes at Different Temperatures

et al. 2018

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The influence of quantum-well (QW) width on electroluminescence properties of AlGaN deep ultraviolet light-emitting diodes (DUV LEDs) was studied at different temperatures. The maximum external quantum efficiency (EQE) ratios of LED with 3.5 nm QW to that with 2 nm increased from 6.8 at room temperature (RT) to 8.2 at 5 K. However, the ratios for LED with 3.5 nm QW to that with 5 nm QW decreased from 4.8 at RT to 1.6 at 5 K. The different changes of EQE ratios were attributed to the decrease of non-radiative recombination and the increase of volume of the active region. From theoretical analysis, the LED with 2-nm wells had a shallowest barrier for electron overflow due to the quantum-confined effect, whereas the LED with 5-nm wells showed the least overlap of electron and hole due to the large internal field. Therefore, the LED with 3.5 nm QW had the highest maximum EQE at the same temperature. As temperature decreased, the current for maximum EQE decreased for all the LEDs, which was believed to be due to the increase of electron which overflowed out of QWs and the decrease of hole concentration. The results were helpful for understanding the combination of polarization effect and electron overflow in DUV LEDs.

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Section: Introductionmentioning

confidence: 99%

Influence of Quantum-Well Width on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes at Different Temperatures

et al. 2018

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“…As has been proposed by other groups, the electron leakage for DUV LEDs can be reduced after enhancing the hole injection [19][20][21]. However, the proposals may affect the crystalline condition for the subsequently grown p-type layer.…”

Section: Resultsmentioning

confidence: 87%

“…As reported, the efficiency droop decreases from 54% to 34% when an n-AlN/AlGaN EBL is utilized [19]. The Al 0.45 Ga 0.55 N/Al 0.60 Ga 0.40 N superlattice p-EBL also helps to reduce the efficiency droop from 24% to 4% [20]. The multiple quantum wells (MQWs) with Mg doped quantum barriers can achieve the alleviated efficiency droop [21].…”

Section: Introductionmentioning

confidence: 87%

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On the Impact of Electron Leakage on the Efficiency Droop for AlGaN Based Deep Ultraviolet Light Emitting Diodes

et al. 2020

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In this work, we have investigated the origin of efficiency droop for AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs). We find that the efficiency droop is likely to be caused by the electron leakage for DUV LEDs studied in this work. The electron leakage arises from the unbalanced electron and hole injection efficiencies. The correlation between the efficiency droop and the electron leakage can be numerically calculated by manipulating the conduction band barrier height of the p-AlGaN electron blocking layer (p-EBL) for the proposed DUV LEDs. For the purpose of demonstrating that the efficiency droop for DUV LEDs can be experimentally decreased by reducing the electron leakage, a p +-GaN/In 0.15 Ga 0.85 N/n +-GaN tunnel junction on DUV LED is grown by using metal organic chemical vapor deposition (MOCVD) technology. The tunnel junction helps to enhance the hole injection, thus decreasing the electron leakage and the efficiency droop. Moreover, the parasitic emission in the p-type hole injection layer is no longer observed thanks to the decreased electron leakage level.

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“…Additionally, because ionized impurities in the materials have a scattering effect on carriers and thus reduce carrier mobility, the undoped GaN layer in the multi-layer stacking structure allows for higher electron mobility than the traditional n-AlGaN layer, which will enhance the current spreading capability of the devices. To further explore the internal mechanisms of a multi-layer stacked n-AlGaN/u-GaN structure that promotes uniform current spreading, the partial conduction band energy and electron concentration in the AlGaN/GaN structure, and the hole concentration in the first quantum well of both samples, were calculated by the advanced physical model of semiconductor devices (APSYS) [34], which includes the tunneling and heterojunction models. The operating temperature, the Shockley-Read-Hall recombination lifetime, and the screening factor were set to 300 K, 100 ns, and 20%, respectively.…”

Section: Methodsmentioning

confidence: 99%

Using a Multi-Layer Stacked AlGaN/GaN Structure to Improve the Current Spreading Performance of Ultraviolet Light-Emitting Diodes

Wang

Zhang

et al. 2020

Materials

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To obtain excellent current spreading performance of ultraviolet light-emitting diodes (UVLEDs), a 60-period stacked Si modulation-doped n-AlGaN/u-GaN structure is proposed to replace the traditional n-AlGaN structure. The high-resolution X-ray diffraction ω-scan rocking curves show that the periodic growth of AlGaN and GaN layers plays a positive role in reducing dislocation density. Compared with the conventional UV light-emitting diodes (LEDs), light emission micrographs of devices with a multi-layer stacked n-AlGaN/u-GaN structure reveal higher brightness and a more uniform distribution. In addition, the output power and external quantum efficiency under a 20-mA injection current are increased by 22% and 26.5%, respectively. Experimental and simulation results indicate that a multi-layer stacking structure can alleviate the current crowding effect in four ways:(1) a reduction in dislocation density; (2) replacement of quasi-two-dimensional electron transport with electronic bulk transport to enhance electron mobility; (3) an increase in electron concentration without improving the impurity concentration; and (4) a weakening of the electron scattering effect by reducing the impurity concentration.

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Nearly Efficiency-Droop-Free AlGaN-Based Ultraviolet Light-Emitting Diodes with a Specifically Designed Superlattice p-Type Electron Blocking Layer for High Mg Doping Efficiency

Cited by 66 publications

References 28 publications

Influence of Quantum-Well Width on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes at Different Temperatures

Influence of Quantum-Well Width on the Electroluminescence Properties of AlGaN Deep Ultraviolet Light-Emitting Diodes at Different Temperatures

On the Impact of Electron Leakage on the Efficiency Droop for AlGaN Based Deep Ultraviolet Light Emitting Diodes

Using a Multi-Layer Stacked AlGaN/GaN Structure to Improve the Current Spreading Performance of Ultraviolet Light-Emitting Diodes

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