Research

Jump to: Review

13 pages, 2186 KiB

Open AccessArticle

Near Unity PLQY and High Stability of Barium Thiocyanate Based All-Inorganic Perovskites and Their Applications in White Light-Emitting Diodes

by Gopi Chandra Adhikari, Saroj Thapa, Yang Yue, Hongyang Zhu and Peifen Zhu

Photonics 2021, 8(6), 209; https://doi.org/10.3390/photonics8060209 - 09 Jun 2021

Cited by 10 | Viewed by 4054

Abstract

All-inorganic lead halide perovskite (CsPbX₃) nanocrystals (NCs) have emerged as a highly promising new generation of light emitters due to their extraordinary photophysical properties. However, the performance of these semiconducting NCs is undermined due to the inherent toxicity of lead and [...] Read more.

All-inorganic lead halide perovskite (CsPbX₃) nanocrystals (NCs) have emerged as a highly promising new generation of light emitters due to their extraordinary photophysical properties. However, the performance of these semiconducting NCs is undermined due to the inherent toxicity of lead and long-term environmental stability. Here, we report the addition of B-site cation and X-site anion (pseudo-halide) concurrently using Ba(SCN)₂ (≤50%) in CsPbX₃ NCs to reduce the lead and improve the photophysical properties and stability. The as-grown particles demonstrated an analogous structure with an almost identical lattice constant and a fluctuation of particle size without altering the morphology of particles. Photoluminescence quantum yield is enhanced up to near unity (~98%) by taking advantage of concomitant doping at the B- and X-site of the structure. Benefitted from the defect reductions and stronger bonding interaction between Pb²⁺ and SCN⁻ ions, Ba(SCN)₂-based NCs exhibit improved stability towards air and moisture compared to the host NCs. The doped NCs retain higher PLQY (as high as seven times) compared to the host NCs) when stored in an ambient atmosphere for more than 176 days. A novel 3D-printed multiplex color conversion layer was used to fabricate a white light-emitting diode (LED). The obtained white light shows a correlated color temperature of 6764 K, a color rendering index of 87, and luminous efficacy of radiation of 333 lm/W. In summary, this work proposes a facile route to treat sensitive lead halide perovskite NCs and to fabricate LEDs by using a low-cost large-scale 3-D printing method, which would serve as a foundation for fabricating high-quality optoelectronic devices for near future lighting technologies. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Graphical abstract

11 pages, 3142 KiB

Open AccessArticle

Efficient Carrier Recombination in InGaN Pyramidal µ-LEDs Obtained through Selective Area Growth

by Jie’an Jiang, Houqiang Xu, Li Chen, Long Yan, Jason Hoo, Shiping Guo, Yuheng Zeng, Wei Guo and Jichun Ye

Photonics 2021, 8(5), 157; https://doi.org/10.3390/photonics8050157 - 10 May 2021

Cited by 1 | Viewed by 2970

Abstract

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, [...] Read more.

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm² was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

9 pages, 2735 KiB

Open AccessCommunication

Size-Dependent Quantum Efficiency of Flip-Chip Light-Emitting Diodes at High Current Injection Conditions

by Xingfei Zhang, Yan Li, Zhicong Li, Zhenlin Miao, Meng Liang, Yiyun Zhang, Xiaoyan Yi, Guohong Wang and Jinmin Li

Photonics 2021, 8(4), 88; https://doi.org/10.3390/photonics8040088 - 24 Mar 2021

Cited by 3 | Viewed by 2370

Abstract

Versatile applications call for InGaN-based light-emitting diodes (LEDs) to operate at ultra-high current densities with high quantum efficiency. In this work, we investigated the size-dependent effects of the electrical and optical performance of LEDs as increasing the current density up to 100 A/cm [...] Read more.

Versatile applications call for InGaN-based light-emitting diodes (LEDs) to operate at ultra-high current densities with high quantum efficiency. In this work, we investigated the size-dependent effects of the electrical and optical performance of LEDs as increasing the current density up to 100 A/cm², which demonstrated that mini-strip flip-chip LEDs were superior option to achieve better performance. In detail, at a current density of 100 A/cm², the light output power density of these mini-strip LEDs was improved by about 6.1 W/cm², leading to an improvement in the wall-plug efficiency by 4.23%, while the operating temperature was reduced by 11.3 °C, as compared with the large-sized LEDs. This could be attributed to the increase in the sidewall light extraction, alleviated current crowding effect, and improved heat dissipation. This work suggests an array of mini-strip LEDs would provide an option in achieving higher luminescent efficiency at ultrahigh current injection conditions for various applications. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

7 pages, 2169 KiB

Open AccessCommunication

Development of Micron Sized Photonic Devices Based on Deep GaN Etching

by Karim Dogheche, Bandar Alshehri, Galles Patriache and Elhadj Dogheche

Photonics 2021, 8(3), 68; https://doi.org/10.3390/photonics8030068 - 02 Mar 2021

Cited by 4 | Viewed by 2866

Abstract

In order to design and development efficient III-nitride based optoelectronic devices, technological processes require a major effort. We propose here a detailed review focussing on the etching procedure as a key step for enabling high date rate performances. In our reported research activity, [...] Read more.

In order to design and development efficient III-nitride based optoelectronic devices, technological processes require a major effort. We propose here a detailed review focussing on the etching procedure as a key step for enabling high date rate performances. In our reported research activity, dry etching of an InGaN/GaN heterogeneous structure was investigated by using an inductively coupled plasma reactive ion etching (ICP-RIE). We considered different combinations of etch mask (Ni, SiO₂, resist), focussing on the optimization of the deep etching process. A GaN mesa process with an etching depth up to 6 µm was performed in Cl₂/Ar-based plasmas using ICP reactors for LEDs dimen sions ranging from 5 to 150 µm². Our strategy was directed toward the mesa formation for vertical-type diode applications, where etch depths are relatively large. Etch characteristics were studied as a function of ICP parameters (RF power, chamber pressure, fixed total flow rate). Surface morphology, etch rates and sidewall profiles observed into InGaN/GaN structures were compared under different types of etching masks. For deep etching up to few microns into the GaN template, we state that a Ni or SiO₂ mask is more suitable to obtain a good selectivity and vertical etch profiles. The optimized etch rate was about 200nm/min under moderate ICP conditions. We applied these conditions for the fabrication of micro/nano LEDs dedicated to LiFi applications. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

10 pages, 3759 KiB

Open AccessArticle

The Optical Properties of InGaN/GaN Nanorods Fabricated on (-201) β-Ga₂O₃ Substrate for Vertical Light Emitting Diodes

by Jie Zhao, Weijiang Li, Lulu Wang, Xuecheng Wei, Junxi Wang and Tongbo Wei

Photonics 2021, 8(2), 42; https://doi.org/10.3390/photonics8020042 - 06 Feb 2021

Cited by 2 | Viewed by 2812

Abstract

We fabricated InGaN/GaN nanorod light emitting diode (LED) on (-201) β-Ga₂O₃ substrate via the SiO₂ nanosphere lithography and dry-etching techniques. The InGaN/GaN nanorod LED grown on β-Ga₂O₃ can effectively suppress quantum confined Stark effect (QCSE) compared [...] Read more.

We fabricated InGaN/GaN nanorod light emitting diode (LED) on (-201) β-Ga₂O₃ substrate via the SiO₂ nanosphere lithography and dry-etching techniques. The InGaN/GaN nanorod LED grown on β-Ga₂O₃ can effectively suppress quantum confined Stark effect (QCSE) compared to planar LED on account of the strain relaxation. With the enhancement of excitation power density, the photoluminescence (PL) peak shows a large blue-shift for the planar LED, while for the nanorod LED, the peak position shift is small. Furthermore, the simulations also show that the light extraction efficiency (LEE) of the nanorod LED is approximately seven times as high as that of the planar LED. Obviously, the InGaN/GaN/β-Ga₂O₃ nanorod LED is conducive to improving the optical performance relative to planar LED, and the present work may lay the groundwork for future development of the GaN-based vertical light emitting diodes (VLEDs) on β-Ga₂O₃ substrate. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

6 pages, 3875 KiB

Open AccessEditor’s ChoiceCommunication

Effect of Si Doping on the Performance of GaN Schottky Barrier Ultraviolet Photodetector Grown on Si Substrate

by Fangzhou Liang, Wen Chen, Meixin Feng, Yingnan Huang, Jianxun Liu, Xiujian Sun, Xiaoning Zhan, Qian Sun, Qibao Wu and Hui Yang

Photonics 2021, 8(2), 28; https://doi.org/10.3390/photonics8020028 - 23 Jan 2021

Cited by 8 | Viewed by 2762

Abstract

GaN Schottky barrier ultraviolet photodetectors with unintentionally doped GaN and lightly Si-doped n⁻-GaN absorption layers were successfully fabricated, respectively. The high-quality GaN films on the Si substrate both have a fairly low dislocation density and point defect concentration. More importantly, the [...] Read more.

GaN Schottky barrier ultraviolet photodetectors with unintentionally doped GaN and lightly Si-doped n⁻-GaN absorption layers were successfully fabricated, respectively. The high-quality GaN films on the Si substrate both have a fairly low dislocation density and point defect concentration. More importantly, the effect of Si doping on the performance of the GaN-on-Si Schottky barrier ultraviolet photodetector was studied. It was found that light Si doping in the absorption layer can significantly increase the responsivity under reverse bias, which might be attributed to the persistent photoconductivity that originates from the lowering of the Schottky barrier height. In addition, the devices with unintentionally doped GaN demonstrated a relatively high-speed photo response. We briefly studied the mechanism of changes in Schottky barrier, dark current and the characteristic of response time. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

13 pages, 2278 KiB

Open AccessArticle

AlGaN-Delta-GaN Quantum Well for DUV LEDs

by Cheng Liu, Bryan Melanson and Jing Zhang

Photonics 2020, 7(4), 87; https://doi.org/10.3390/photonics7040087 - 03 Oct 2020

Cited by 14 | Viewed by 2619

Abstract

AlGaN-delta-GaN quantum well (QW) structures have been demonstrated to be good candidates for the realization of high-efficiency deep-ultraviolet (DUV) light-emitting diodes (LEDs). However, such heterostructures are still not fully understood. This study focuses on investigation of the optical properties and efficiency of the [...] Read more.

AlGaN-delta-GaN quantum well (QW) structures have been demonstrated to be good candidates for the realization of high-efficiency deep-ultraviolet (DUV) light-emitting diodes (LEDs). However, such heterostructures are still not fully understood. This study focuses on investigation of the optical properties and efficiency of the AlGaN-delta-GaN QW structures using self-consistent six-band k⸱p modelling and finite difference time domain (FDTD) simulations. Structures with different Al contents in the Al_xGa_1−xN sub-QW and Al_yGa_1−yN barrier regions are examined in detail. Results show that the emission wavelength (λ) can be engineered through manipulation of delta-GaN layer thickness, sub-QW Al content (x), and barrier Al content (y), while maintaining a large spontaneous emission rate corresponding to around 90% radiative recombination efficiency (

η_{R A D}

). In addition, due to the dominant transverse-electric (TE)-polarized emission from the AlGaN-delta-GaN QW structure, the light extraction efficiency (

η_{E X T})

is greatly enhanced when compared to a conventional AlGaN QW. Combined with the large

η_{R A D}

, this leads to the significant enhancement of external quantum efficiency (

η_{E Q E})

, indicating that AlGaN-delta-GaN structures could be a promising solution for high-efficiency DUV LEDs. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Graphical abstract

13 pages, 2806 KiB

Open AccessArticle

Insights of Hysteresis Behaviors in Perovskite Solar Cells from a Mixed Drift-Diffusion Model Coupled with Recombination

by Chongqiu Yang, Xiaobiao Shan and Tao Xie

Photonics 2020, 7(3), 47; https://doi.org/10.3390/photonics7030047 - 03 Jul 2020

Cited by 10 | Viewed by 4437

Abstract

Hysteresis in perovskite solar cells is a notorious issue limiting its development in stability, reproducibility and efficiency. Ions’ migration coupled with charges’ recombination are indispensable factors to generate the hysteretic curves on the basis of experimental and theoretical calculation studies, however, the underlying [...] Read more.

Hysteresis in perovskite solar cells is a notorious issue limiting its development in stability, reproducibility and efficiency. Ions’ migration coupled with charges’ recombination are indispensable factors to generate the hysteretic curves on the basis of experimental and theoretical calculation studies, however, the underlying physical characteristics are rarely clarified. Here, a mixed electronic-ionic drift-diffusion model combined with bulk and interfacial recombination is investigated. Positive and negative ion species could drift to and accumulate at interfaces between the perovskite/transport layers, influencing internal electric potential profiles and delaying the charges’ ejection to the transport layers. The charges might recombine spontaneously or trap-assisted, reducing the total amount of electrons and holes collected in the external circuit, leading to a diminished photocurrent. Moreover, our calculations indicate that an appropriate measurement protocol is really essential to evaluate the device performance precisely and to suppress J–V hysteresis. Meanwhile, a negligible hysteretic loop could be obtained by balancing the material properties of the transport layers and restraining the ions mobility in the perovskite layer. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Graphical abstract

Review

Jump to: Research

25 pages, 5580 KiB

Open AccessReview

Recent Progress of Electrically Pumped AlGaN Diode Lasers in the UV-B and -C Bands

by Syed M. N. Hasan, Weicheng You, Md Saiful Islam Sumon and Shamsul Arafin

Photonics 2021, 8(7), 267; https://doi.org/10.3390/photonics8070267 - 08 Jul 2021

Cited by 13 | Viewed by 5532

Abstract

The development of electrically pumped semiconductor diode lasers emitting at the ultraviolet (UV)-B and -C spectral bands has been an active area of research over the past several years, motivated by a wide range of emerging applications. III-Nitride materials and their alloys, in [...] Read more.

The development of electrically pumped semiconductor diode lasers emitting at the ultraviolet (UV)-B and -C spectral bands has been an active area of research over the past several years, motivated by a wide range of emerging applications. III-Nitride materials and their alloys, in particular AlGaN, are the material of choice for the development of this ultrashort-wavelength laser technology. Despite significant progress in AlGaN-based light-emitting diodes (LEDs), the technological advancement and innovation in diode lasers at these spectral bands is lagging due to several technical challenges. Here, the authors review the progress of AlGaN electrically-pumped lasers with respect to very recent achievements made by the scientific community. The devices based on both thin films and nanowires demonstrated to date will be discussed in this review. The state-of-the-art growth technologies, such as molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD); and various foreign substrates/templates used for the laser demonstrations will be highlighted. We will also outline technical challenges associated with the laser development, which must be overcome in order to achieve a critical technological breakthrough and fully realize the potential of these lasers. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

19 pages, 3961 KiB

Open AccessReview

Perspectives on UVC LED: Its Progress and Application

by Tsung-Chi Hsu, Yu-Tsai Teng, Yen-Wei Yeh, Xiaotong Fan, Kuo-Hsiung Chu, Su-Hui Lin, Kuo-Kuang Yeh, Po-Tsung Lee, Yue Lin, Zhong Chen, Tingzhu Wu and Hao-Chung Kuo

Photonics 2021, 8(6), 196; https://doi.org/10.3390/photonics8060196 - 31 May 2021

Cited by 54 | Viewed by 10664

Abstract

High-quality epitaxial layers are directly related to internal quantum efficiency. The methods used to design such epitaxial layers are reviewed in this article. The ultraviolet C (UVC) light-emitting diode (LED) epitaxial layer structure exhibits electron leakage; therefore, many research groups have proposed the [...] Read more.

High-quality epitaxial layers are directly related to internal quantum efficiency. The methods used to design such epitaxial layers are reviewed in this article. The ultraviolet C (UVC) light-emitting diode (LED) epitaxial layer structure exhibits electron leakage; therefore, many research groups have proposed the design of blocking layers and carrier transportation to generate high electron–hole recombination rates. This also aids in increasing the internal quantum efficiency. The cap layer, p-GaN, exhibits high absorption in deep UV radiation; thus, a small thickness is usually chosen. Flip chip design is more popular for such devices in the UV band, and the main factors for consideration are light extraction and heat transportation. However, the choice of encapsulation materials is important, because unsuitable encapsulation materials will be degraded by ultraviolet light irradiation. A suitable package design can account for light extraction and heat transportation. Finally, an atomic layer deposition Al₂O₃ film has been proposed as a mesa passivation layer. It can provide a low reverse current leakage. Moreover, it can help increase the quantum efficiency, enhance the moisture resistance, and improve reliability. UVC LED applications can be used in sterilization, water purification, air purification, and medical and military fields. Full article

(This article belongs to the Special Issue Wide Bandgap Semiconductor Photonic Devices)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Wide Bandgap Semiconductor Photonic Devices

Share This Special Issue

Special Issue Editors

Special Issue Information

Published Papers (10 papers)

Research

Review

Further Information

Guidelines

MDPI Initiatives

Follow MDPI