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12 pages, 4031 KiB

Open AccessEditor’s ChoiceArticle

Explorations on Growth of Blue-Green-Yellow-Red InGaN Quantum Dots by Plasma-Assisted Molecular Beam Epitaxy

by Xue Zhang, Zhiwei Xing, Wenxian Yang, Haibing Qiu, Ying Gu, Yuta Suzuki, Sakuya Kaneko, Yuki Matsuda, Shinji Izumi, Yuichi Nakamura, Yong Cai, Lifeng Bian, Shulong Lu and Atsushi Tackeuchi

Nanomaterials 2022, 12(5), 800; https://doi.org/10.3390/nano12050800 - 26 Feb 2022

Cited by 6 | Viewed by 2965

Abstract

Self-assembled growth of blue-green-yellow-red InGaN quantum dots (QDs) on GaN templates using plasma-assisted molecular beam epitaxy were investigated. We concluded that growth conditions, including small N₂ flow and high growth temperature are beneficial to the formation of InGaN QDs and improve the crystal quality. The lower In/Ga flux ratio and lower growth temperature are favorable for the formation of QDs of long emission wavelength. Moreover, the nitrogen modulation epitaxy method can extend the wavelength of QDs from green to red. As a result, visible light emissions from 460 nm to 622 nm have been achieved. Furthermore, a 505 nm green light-emitting diode (LED) based on InGaN/GaN MQDs was prepared. The LED has a low external quantum efficiency of 0.14% and shows an efficiency droop with increasing injection current. However, electroluminescence spectra exhibited a strong wavelength stability, with a negligible shift of less than 1.0 nm as injection current density increased from 8 A/cm² to 160 A/cm², owing to the screening of polarization-related electric field in QDs. Full article

(This article belongs to the Special Issue Molecular Beam Epitaxy Growth of Quantum Wires and Quantum Dots)

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10 pages, 1346 KiB

Open AccessArticle

Carrier Dynamics in InGaN/GaN-Based Green LED under Different Excitation Sources

by Jianfei Li, Duo Chen, Kuilong Li, Qiang Wang, Mengyao Shi, Chen Cheng and Jiancai Leng

Crystals 2021, 11(9), 1061; https://doi.org/10.3390/cryst11091061 - 2 Sep 2021

Cited by 7 | Viewed by 3689

Abstract

The excitation power and temperature dependence of the photoluminescence (PL) and electroluminescence (EL) spectra were studied in green InGaN/GaN multiple quantum well (MQW)-based light-emitting diodes (LED). An examination of the PL-325, PL-405, and EL spectra at identical optical or electrical generation rates at room temperature showed that the normalized spectra exhibited different characteristic peaks. In addition, the temperature behavior of the peak energy was S-shaped for the PL-405 spectrum, while it was V-shaped for the EL spectrum. These measurement results demonstrate that the excitation source can affect the carrier dynamics about the generation (injection), transfer, and distribution of carriers. Full article

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15 pages, 4961 KiB

Open AccessArticle

Investigation of Photonic-Crystal-Structured p-GaN Nanorods Fabricated by Polystyrene Nanosphere Lithography Method to Improve the Light Extraction Efficiency of InGaN/GaN Green Light-Emitting Diodes

by Po-Hsun Lei, Po-Chun Yang and Po-Chun Huang

Materials 2021, 14(9), 2200; https://doi.org/10.3390/ma14092200 - 25 Apr 2021

Cited by 9 | Viewed by 2775

Abstract

We fabricated the photonic-crystal-structured p-GaN (PC-structured p-GaN) nanorods using the modified polystyrene nanosphere (PS NS) lithography method for InGaN/GaN green light-emitting diodes (LEDs) to enhance the light extraction efficiency (LEE). A modified PS NS lithography method including two-times spin-coating processes and the post-spin-coating heating treatment was used to obtain a self-assembly close-packed PS NS array of monolayer as a mask and then a partially dry etching process was applied to PS NS, SiO₂, and p-GaN to form PC-structured p-GaN nanorods on the InGaN/GaN green LEDs. The light output intensity and LEE of InGaN/GaN green LEDs with the PC-structured p-GaN nanorods depend on the period, diameter, and height of PC-structured p-GaN nanorods. RSoft FullWAVE software based on the three-dimension finite-difference time-domain (FDTD) algorithm was used to calculate the LEE of InGaN/GaN green LEDs with PC-structured p-GaN nanorods of the varied period, diameter, and height. The optimal period, diameter, and height of PC-structured p-GaN nanorods are 150, 350, and 110 nm. The InGaN/GaN green LEDs with optimal PC-structured p-GaN nanorods exhibit an enhancement of 41% of emission intensity under the driving current of 20 mA as compared to conventional LED. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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5 pages, 1085 KiB

Open AccessProceeding Paper

Structural Modifications in Free-Standing InGaN/GaN LEDs after Femtosecond Laser Lift-Off

by Steffen Bornemann, Nursidik Yulianto, Tobias Meyer, Jan Gülink, Christoph Margenfeld, Michael Seibt, Hutomo Suryo Wasisto and Andreas Waag

Proceedings 2018, 2(13), 897; https://doi.org/10.3390/proceedings2130897 - 29 Nov 2018

Cited by 4 | Viewed by 2358

Abstract

A laser lift-off (LLO) process has been developed for detaching thin InGaN/GaN lightemitting diodes (LED) from their original sapphire substrates by applying an ultrafast laser. LLO is usually based on intense UV irradiation, which is transmitted through the sapphire substrate and subsequently absorbed at the interface to the epitaxially grown GaN stack. Here, we present a successful implementation of a two-step LLO process with 350 fs short pulses in the green spectral range (520 nm) based on a two-photon absorption mechanism. Cathodo- and electroluminescence experiments have proven the functionality of the LLO-based chips. The impact of radiation on the material quality was analysed with scanning (SEM) and transmission electron microscopy (TEM), revealing structural modifications inside the GaN layer in some cases. Full article

(This article belongs to the Proceedings of EUROSENSORS 2018)

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12 pages, 2670 KiB

Open AccessArticle

An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits

by Mengling Liu, Jie Zhao, Shengjun Zhou, Yilin Gao, Jinfeng Hu, Xingtong Liu and Xinghuo Ding

Nanomaterials 2018, 8(7), 450; https://doi.org/10.3390/nano8070450 - 21 Jun 2018

Cited by 30 | Viewed by 7025

Abstract

Despite the fact that an InGaN/GaN superlattice (SL) is useful for enhancing the performance of a GaN-based light-emitting diode (LED), its role in improving the efficiency of green LEDs remains an open question. Here, we investigate the influence of a V-pits-embedded InGaN/GaN SL on optical and electrical properties of GaN-based green LEDs. We recorded a sequence of light emission properties of InGaN/GaN multiple quantum wells (MQWs) grown on a 0- and 24-pair InGaN/GaN SL by using scanning electron microscopy (SEM) in combination with a room temperature cathodoluminescence (CL) measurement, which demonstrated the presence of a potential barrier formed by the V-pits around threading dislocations (TDs). We find that an increase in V-pit diameter would lead to the increase of V-pit potential barrier height. Our experimental data suggest that a V-pits-embedded, 24-pair InGaN/GaN SL can effectively suppress the lateral diffusion of carriers into non-recombination centers. As a result, the external quantum efficiency (EQE) of green LEDs is improved by 29.6% at an injection current of 20 mA after implementing the V-pits-embedded InGaN/GaN SL layer. In addition, a lower reverse leakage current was achieved with larger V-pits. Full article

(This article belongs to the Special Issue Optoelectronic Nanodevices)

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