Editorial

3 pages, 169 KiB

Open AccessEditorial

Molecular Beam Epitaxy Growth of Quantum Wires and Quantum Dots

by Xiaohui Li, Qian Xu and Ziyang Zhang

Nanomaterials 2023, 13(6), 960; https://doi.org/10.3390/nano13060960 - 07 Mar 2023

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Molecular beam epitaxy technology has a significant advantage in semiconductor technology due to its strong controllability, especially for the preparation of materials such as quantum wires and quantum dots [...] Full article

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

Research

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11 pages, 491 KiB

Open AccessArticle

Temperature-Enhanced Exciton Emission from GaAs Cone–Shell Quantum Dots

by Christian Heyn, Leonardo Ranasinghe, Kristian Deneke, Ahmed Alshaikh and Robert H. Blick

Nanomaterials 2023, 13(24), 3121; https://doi.org/10.3390/nano13243121 - 12 Dec 2023

Viewed by 747

Abstract

The temperature-dependent intensities of the exciton (X) and biexciton (XX) peaks from single GaAs cone–shell quantum dots (QDs) are studied with micro photoluminescence (PL) at varied excitation power and QD size. The QDs are fabricated by filling self-assembled nanoholes, which are drilled in [...] Read more.

The temperature-dependent intensities of the exciton (X) and biexciton (XX) peaks from single GaAs cone–shell quantum dots (QDs) are studied with micro photoluminescence (PL) at varied excitation power and QD size. The QDs are fabricated by filling self-assembled nanoholes, which are drilled in an AlGaAs barrier by local droplet etching (LDE) during molecular beam epitaxy (MBE). This method allows the fabrication of strain-free QDs with sizes precisely controlled by the amount of material deposited for hole filling. Starting from the base temperature T = 3.2 K of the cryostat, single-dot PL measurements demonstrate a strong enhancement of the exciton emission up to a factor of five with increasing T. Both the maximum exciton intensity and the temperature

T_{x, m a x}

of the maximum intensity depend on excitation power and dot size. At an elevated excitation power,

T_{x, m a x}

becomes larger than 30 K. This allows an operation using an inexpensive and compact Stirling cryocooler. Above

T_{x, m a x}

, the exciton intensity decreases strongly until it disappears. The experimental data are quantitatively reproduced by a model which considers the competing processes of exciton generation, annihilation, and recombination. Exciton generation in the QDs is achieved by the sum of direct excitation in the dot, plus additional bulk excitons diffusing from the barrier layers into the dot. The thermally driven bulk-exciton diffusion from the barriers causes the temperature enhancement of the exciton emission. Above

T_{x, m a x}

, the intensity decreases due to exciton annihilation processes. In comparison to the exciton, the biexciton intensity shows only very weak enhancement, which is attributed to more efficient annihilation processes. 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, 5308 KiB

Open AccessArticle

Low Threshold Current and Polarization-Stabilized 795 nm Vertical-Cavity Surface-Emitting Lasers

by Qiuxue Fu, Yurun Sun, Suzhen Yu, Ancheng Wang, Jiajing Yin, Yongming Zhao and Jianrong Dong

Nanomaterials 2023, 13(6), 1120; https://doi.org/10.3390/nano13061120 - 21 Mar 2023

Cited by 1 | Viewed by 1327

Abstract

Low threshold current and polarization-stabilized 795 nm vertical-cavity surface-emitting lasers (VCSELs) are fabricated by integrating a surface grating of high polarization selectivity and high reflectivity. The rigorous coupled-wave analysis method is used to design the surface grating. For the devices with a grating [...] Read more.

Low threshold current and polarization-stabilized 795 nm vertical-cavity surface-emitting lasers (VCSELs) are fabricated by integrating a surface grating of high polarization selectivity and high reflectivity. The rigorous coupled-wave analysis method is used to design the surface grating. For the devices with a grating period of 500 nm, a grating depth of ~150 nm, and a diameter of the surface grating region of 5 μm, a threshold current of 0.4 mA and an orthogonal polarization suppression ratio (OPSR) of 19.56 dB are obtained. The emission wavelength of 795 nm of a single transverse mode VCSEL is achieved at a temperature of 85 °C under an injection current of 0.9 mA. In addition, experiments demonstrate that the threshold and output power also depended on the size of the grating region. Full article

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

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7 pages, 2279 KiB

Open AccessCommunication

Dispersion Management Nonlinear Multimode Interference Mode-Locked Ytterbium Fiber Laser

by Shan Wang, Zhiguo Lv and Jintao Qiu

Nanomaterials 2023, 13(3), 535; https://doi.org/10.3390/nano13030535 - 28 Jan 2023

Cited by 1 | Viewed by 1259

Abstract

Dispersion management plays an important role in improving the output performance of a mode-locked fiber laser. Therefore, dispersion management is carried out by introducing the grating pair in our experiment. Through adjusting the distance between the grating pair, mode-locked pulses corresponding to different [...] Read more.

Dispersion management plays an important role in improving the output performance of a mode-locked fiber laser. Therefore, dispersion management is carried out by introducing the grating pair in our experiment. Through adjusting the distance between the grating pair, mode-locked pulses corresponding to different dispersion regimes can be realized, which typically range from soliton state in the anomalous dispersion regime to the dissipative soliton format in the normal dispersion regime. Furthermore, tunable spectrum distribution can be achieved by adjusting two intra-cavity polarization controllers. The proposed dispersion management method complements mode-locking techniques based on nonlinear multimode interference (NL-MMI). The laser can operate with self-start mode locking stably and is useful for practice applications. 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, 2829 KiB

Open AccessArticle

SiO₂ Passivated Graphene Saturable Absorber Mirrors for Ultrashort Pulse Generation

by Hongpei Wang, Cheng Jiang, Huiyuan Chu, Hao Dai, Beibei Fu, Shulong Lu and Ziyang Zhang

Nanomaterials 2023, 13(1), 111; https://doi.org/10.3390/nano13010111 - 26 Dec 2022

Cited by 3 | Viewed by 1288

Abstract

Owing to its broadband absorption, ultrafast recovery time, and excellent saturable absorption feature, graphene has been recognized as one of the best candidates as a high-performance saturable absorber (SA). However, the low absorption efficiency and reduced modulation depth severely limit the application of [...] Read more.

Owing to its broadband absorption, ultrafast recovery time, and excellent saturable absorption feature, graphene has been recognized as one of the best candidates as a high-performance saturable absorber (SA). However, the low absorption efficiency and reduced modulation depth severely limit the application of graphene-based SA in ultrafast fiber lasers. In this paper, a single-layer graphene saturable absorber mirror (SG-SAM) was coated by a quarter-wave SiO₂ passivated layer, and a significantly enhanced modulation depth and reduced saturation intensity were obtained simultaneously compared to the SG-SAM without the SiO₂ coating layer. In addition, long-term operational stability was found in the device due to the excellent isolation and protection of the graphene absorption layer from the external environment by the SiO₂ layer. The high performance of the SAM was further confirmed by the construction of a ring-cavity EDF laser generating mode-locked pulses with a central wavelength of 1563.7 nm, a repetition rate of 34.17 MHz, and a pulse width of 830 fs. 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, 12066 KiB

Open AccessArticle

Enhanced Photodetection Range from Visible to Shortwave Infrared Light by ReSe₂/MoTe₂ van der Waals Heterostructure

by Zhitao Lin, Wenbiao Zhu, Yonghong Zeng, Yiqing Shu, Haiguo Hu, Weicheng Chen and Jianqing Li

Nanomaterials 2022, 12(15), 2664; https://doi.org/10.3390/nano12152664 - 03 Aug 2022

Cited by 7 | Viewed by 1730

Abstract

Type II vertical heterojunction is a good solution for long-wavelength light detection. Here, we report a rhenium selenide/molybdenum telluride (n-ReSe₂/p-MoTe₂) photodetector for high-performance photodetection in the broadband spectral range of 405–2000 nm. Due to the low Schottky barrier contact [...] Read more.

Type II vertical heterojunction is a good solution for long-wavelength light detection. Here, we report a rhenium selenide/molybdenum telluride (n-ReSe₂/p-MoTe₂) photodetector for high-performance photodetection in the broadband spectral range of 405–2000 nm. Due to the low Schottky barrier contact of the ReSe₂/MoTe₂ heterojunction, the rectification ratio (RR) of ~10² at ±5 V is realized. Besides, the photodetector can obtain maximum responsivity (R = 1.05 A/W) and specific detectivity (D* = 6.66 × 10¹¹ Jones) under the illumination of 655 nm incident light. When the incident wavelength is 1550–2000 nm, a photocurrent is generated due to the interlayer transition of carriers. This compact system can provide an opportunity to realize broadband infrared photodetection. Full article

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

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13 pages, 4348 KiB

Open AccessArticle

Facile Synthesis of Monodispersed Titanium Nitride Quantum Dots for Harmonic Mode-Locking Generation in an Ultrafast Fiber Laser

by Ya-Tao Yang, Han-Wei Wu, Yuan Zou, Xue-Yang Fang, Shuang Li, Yu-Feng Song, Zhen-Hong Wang and Bin Zhang

Nanomaterials 2022, 12(13), 2280; https://doi.org/10.3390/nano12132280 - 01 Jul 2022

Cited by 10 | Viewed by 1915

Abstract

As a member of the transition metal nitride material family, titanium nitride (TiN) quantum dots (QDs) have attracted great attention in optical and electronic fields because of their excellent optoelectronic properties and favorable stability. Herein, TiN QDs were synthesized and served as a [...] Read more.

As a member of the transition metal nitride material family, titanium nitride (TiN) quantum dots (QDs) have attracted great attention in optical and electronic fields because of their excellent optoelectronic properties and favorable stability. Herein, TiN QDs were synthesized and served as a saturable absorber (SA) for an ultrafast fiber laser. Due to the strong nonlinear optical absorption characteristics with a modulation depth of ~33%, the typical fundamental mode-locked pulses and harmonics mode-locked pulses can be easily obtained in an ultrafast erbium-doped fiber laser with a TiN-QD SA. In addition, at the maximum pump power, harmonic mode-locked pulses with a repetition rate of ~1 GHz (164th order) and a pulse duration of ~1.45 ps are achieved. As far as we know, the repetition rate is the highest in the ultrafast fiber laser using TiN QDs as an SA. Thus, these experimental results indicate that TiN QDs can be considered a promising material, showing more potential in the category of ultrafast laser and nonlinear optics. Full article

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

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12 pages, 3726 KiB

Open AccessArticle

Double Perovskite Ba₂LaTaO₆ for Ultrafast Fiber Lasers in Anomalous and Normal Net Dispersion Regime

by Yiqing Shu, Mingqi An, Penglai Guo, Xun Yuan, Leiming Wu, Zhitao Lin, Weicheng Chen, Xiaohui Li and Jianqing Li

Nanomaterials 2022, 12(12), 2112; https://doi.org/10.3390/nano12122112 - 20 Jun 2022

Cited by 4 | Viewed by 1435

Abstract

Double perovskites (DPs) have been attracting attention in an assortment of optoelectronic applications, for they hold advantages such as high quantum efficiency, long carrier migration distance and strong linear and nonlinear absorptions. As specific kinds of perovskites (PVKs), DPs are gifted with orthorhombic [...] Read more.

Double perovskites (DPs) have been attracting attention in an assortment of optoelectronic applications, for they hold advantages such as high quantum efficiency, long carrier migration distance and strong linear and nonlinear absorptions. As specific kinds of perovskites (PVKs), DPs are gifted with orthorhombic crystal structures which provide rich conversion combinations and broaden the space for research and application. However, few works have been reported about DPs in ultrafast photonics applications. In this article, a DP with chemical formula of Ba₂LaTaO₆ (BLT) was successfully synthesized by high-temperature solid phase method. The microstructures and morphologies were observed, and the linear and nonlinear absorption were characterized. By first using BLT as a novel saturable absorber in both normal and anomalous dispersion region fiber lasers, dual-wavelength soliton and dissipative soliton were successfully operated at C-band. This study affirms BLT’s nonlinear optical properties, lays the foundation for optical research on BLT, and meanwhile provides a meaningful reference for future development of pulsed lasers based on DPs. Full article

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

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8 pages, 2112 KiB

Open AccessArticle

Broadband Quantum Dot Superluminescent Diode with Simultaneous Three-State Emission

by Cheng Jiang, Hongpei Wang, Hongmei Chen, Hao Dai, Ziyang Zhang, Xiaohui Li and Zhonghui Yao

Nanomaterials 2022, 12(9), 1431; https://doi.org/10.3390/nano12091431 - 22 Apr 2022

Cited by 3 | Viewed by 1577

Abstract

Semiconductor superluminescent light-emitting diodes (SLEDs) have emerged as ideal and vital broadband light sources with extensive applications, such as optical fiber-based sensors, biomedical sensing/imaging, wavelength-division multiplexing system testing and optoelectronic systems, etc. Self-assembled quantum dots (SAQDs) are very promising candidates for the realization [...] Read more.

Semiconductor superluminescent light-emitting diodes (SLEDs) have emerged as ideal and vital broadband light sources with extensive applications, such as optical fiber-based sensors, biomedical sensing/imaging, wavelength-division multiplexing system testing and optoelectronic systems, etc. Self-assembled quantum dots (SAQDs) are very promising candidates for the realization of broadband SLED due to their intrinsic large inhomogeneous spectral broadening. Introducing excited states (ESs) emission could further increase the spectral bandwidth. However, almost all QD-based SLEDs are limited to the ground state (GS) or GS and first excited state (ES₁) emission. In this work, multiple five-QD-layer structures with large dot size inhomogeneous distribution were grown by optimizing the molecular beam epitaxy (MBE) growth conditions. Based on that, with the assistance of a carefully designed mirror-coating process to accurately control the cavity mirror loss of GS and ESs, respectively, a broadband QD-SLED with three simultaneous states of GS, ES₁ and second excited-state (ES₂) emission has been realized, exhibiting a large spectral width of 91 nm with a small spectral dip of 1.3 dB and a high continuous wave (CW) output power of 40 mW. These results pave the way for a new fabrication technique for high-performance QD-based low-coherent light sources. Full article

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

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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 4 | Viewed by 2072

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 [...] Read more.

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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9 pages, 3522 KiB

Open AccessArticle

Growth Behaviors of GaN on Stripes of Patterned c-Plane GaN Substrate

by Peng Wu, Jianping Liu, Lingrong Jiang, Lei Hu, Xiaoyu Ren, Aiqin Tian, Wei Zhou, Masao Ikeda and Hui Yang

Nanomaterials 2022, 12(3), 478; https://doi.org/10.3390/nano12030478 - 29 Jan 2022

Cited by 3 | Viewed by 1973

Abstract

Growth behaviors of GaN on patterned GaN substrate were studied herein. Spiral and nucleation growth were observed after miscut-induced atomic steps disappeared. The morphology of nucleation growth at different temperature is explained by a multi-nucleation regime introducing critical supersaturation. Simulated results based on [...] Read more.

Growth behaviors of GaN on patterned GaN substrate were studied herein. Spiral and nucleation growth were observed after miscut-induced atomic steps disappeared. The morphology of nucleation growth at different temperature is explained by a multi-nucleation regime introducing critical supersaturation. Simulated results based on a step motion model successfully explain the growth behaviors on stripes. These findings can be applied to control the surface kinetics of devices such as laser diodes grown on patterned substrate. Full article

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

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Review

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53 pages, 14342 KiB

Open AccessReview

Mid-Infrared Optoelectronic Devices Based on Two-Dimensional Materials beyond Graphene: Status and Trends

by Rui Cao, Sidi Fan, Peng Yin, Chunyang Ma, Yonghong Zeng, Huide Wang, Karim Khan, Swelm Wageh, Ahmed A. Al-Ghamd, Ayesha Khan Tareen, Abdullah G. Al-Sehemi, Zhe Shi, Jing Xiao and Han Zhang

Nanomaterials 2022, 12(13), 2260; https://doi.org/10.3390/nano12132260 - 01 Jul 2022

Cited by 17 | Viewed by 5109

Abstract

Since atomically thin two-dimensional (2D) graphene was successfully synthesized in 2004, it has garnered considerable interest due to its advanced properties. However, the weak optical absorption and zero bandgap strictly limit its further development in optoelectronic applications. In this regard, other 2D materials, [...] Read more.

Since atomically thin two-dimensional (2D) graphene was successfully synthesized in 2004, it has garnered considerable interest due to its advanced properties. However, the weak optical absorption and zero bandgap strictly limit its further development in optoelectronic applications. In this regard, other 2D materials, including black phosphorus (BP), transition metal dichalcogenides (TMDCs), 2D Te nanoflakes, and so forth, possess advantage properties, such as tunable bandgap, high carrier mobility, ultra-broadband optical absorption, and response, enable 2D materials to hold great potential for next-generation optoelectronic devices, in particular, mid-infrared (MIR) band, which has attracted much attention due to its intensive applications, such as target acquisition, remote sensing, optical communication, and night vision. Motivated by this, this article will focus on the recent progress of semiconducting 2D materials in MIR optoelectronic devices that present a suitable category of 2D materials for light emission devices, modulators, and photodetectors in the MIR band. The challenges encountered and prospects are summarized at the end. We believe that milestone investigations of 2D materials beyond graphene-based MIR optoelectronic devices will emerge soon, and their positive contribution to the nano device commercialization is highly expected. Full article

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

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33 pages, 11449 KiB

Open AccessReview

Recent Developments of Quantum Dot Materials for High Speed and Ultrafast Lasers

by Zhonghui Yao, Cheng Jiang, Xu Wang, Hongmei Chen, Hongpei Wang, Liang Qin and Ziyang Zhang

Nanomaterials 2022, 12(7), 1058; https://doi.org/10.3390/nano12071058 - 24 Mar 2022

Cited by 7 | Viewed by 3243

Abstract

Owing to their high integration and functionality, nanometer-scale optoelectronic devices based on III-V semiconductor materials are emerging as an enabling technology for fiber-optic communication applications. Semiconductor quantum dots (QDs) with the three-dimensional carrier confinement offer potential advantages to such optoelectronic devices in terms [...] Read more.

Owing to their high integration and functionality, nanometer-scale optoelectronic devices based on III-V semiconductor materials are emerging as an enabling technology for fiber-optic communication applications. Semiconductor quantum dots (QDs) with the three-dimensional carrier confinement offer potential advantages to such optoelectronic devices in terms of high modulation bandwidth, low threshold current density, temperature insensitivity, reduced saturation fluence, and wavelength flexibility. In this paper, we review the development of the molecular beam epitaxial (MBE) growth methods, material properties, and device characteristics of semiconductor QDs. Two kinds of III-V QD-based lasers for optical communication are summarized: one is the active electrical pumped lasers, such as the Fabry–Perot lasers, the distributed feedback lasers, and the vertical cavity surface emitting lasers, and the other is the passive lasers and the instance of the semiconductor saturable absorber mirrors mode-locked lasers. By analyzing the pros and cons of the different QD lasers by their structures, mechanisms, and performance, the challenges that arise when using these devices for the applications of fiber-optic communication have been presented. Full article

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

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