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Crystals
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Preparation and Characterization of Optoelectronic Functional Films
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Preparation and Characterization of Optoelectronic Functional Films

A special issue of Crystals (ISSN 2073-4352).

Deadline for manuscript submissions: 25 December 2024 | Viewed by 9509

Special Issue Editor

Prof. Dr. Liangyao Chen

E-Mail Website
Guest Editor
Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China
Interests: optical properties of materials; thin films; solar devices; ellipsometry; optical spectral analysis

Special Issue Information

Dear Colleagues,

This Special Issue will highlight recent advances and future perspectives in the field of optoelectronic functional materials constructed via many different techniques with the characterization of their variety of physical properties to stimulate and enhance applications in broad-ranging areas. The submission of original research articles related to functional materials engineered in the complex form of smart thin films, metal and alloy compositions, nanocomposites, meta-surface, and solar and photonic materials is highly encouraged. Research focusing on the applications of these materials is especially recommended for submission as well.

Prof. Dr. Liangyao Chen
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • functional materials
  • optical properties
  • composed material
  • metamaterials
  • metals and alloys

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Published Papers (6 papers)

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Research

13 pages, 2533 KiB  
Article
Effect of Molybdenum Concentration and Deposition Temperature on the Structure and Tribological Properties of the Diamond-like Carbon Films
by Hassan Zhairabany, Hesam Khaksar, Edgars Vanags and Liutauras Marcinauskas
Crystals 2024, 14(11), 962; https://doi.org/10.3390/cryst14110962 - 5 Nov 2024
Viewed by 587
Abstract
Two series of non-hydrogenated diamond-like carbon (DLC) films and molybdenum doped diamond-like carbon (Mo-DLC) films were grown on the silicon substrate using direct current magnetron sputtering. The influence of molybdenum doping (between 6.3 and 11.9 at.% of Mo), as well as the deposited [...] Read more.
Two series of non-hydrogenated diamond-like carbon (DLC) films and molybdenum doped diamond-like carbon (Mo-DLC) films were grown on the silicon substrate using direct current magnetron sputtering. The influence of molybdenum doping (between 6.3 and 11.9 at.% of Mo), as well as the deposited temperature (between 185 and 235 °C) on the surface morphology, elemental composition, bonding microstructure, friction force, and nanohardness of the films, were characterized by atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and a nanoindenter. It was found that the increase in the metal dopant concentration led to a higher metallicity and graphitization of the DLC films. The surface roughness and sp3/sp2 ratio were obtained as a function of the Mo concentration and formation temperature. The nanohardness of DLC films was improved by up to 75% with the addition of Mo. Meanwhile, the reduction in the deposition temperature decreased the nanohardness of the DLC films. The friction coefficient of the DLC films was slightly reduced with addition of the molybdenum. Full article
(This article belongs to the Special Issue Preparation and Characterization of Optoelectronic Functional Films)
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12 pages, 4683 KiB  
Article
Growth of Al-Cu Thin Films on LiNbO3 Substrates for Surface Acoustic Wave Devices Based on Combinatorial Radio Frequency Magnetron Sputtering
by Junseong Eom, Tae-Wong Kim, Peddathimula Puneetha, Jae-Cheol Park and Siva Pratap Reddy Mallem
Crystals 2024, 14(10), 844; https://doi.org/10.3390/cryst14100844 - 27 Sep 2024
Cited by 1 | Viewed by 509
Abstract
Al-Cu thin films were fabricated by RF magnetron sputtering from aluminum (Al) and copper (Cu) metal targets to improve the acoustic performance of SAW devices on LiNbO3 substrates. To optimize the electrode material for SAW devices, Al-Cu films with various compositions were [...] Read more.
Al-Cu thin films were fabricated by RF magnetron sputtering from aluminum (Al) and copper (Cu) metal targets to improve the acoustic performance of SAW devices on LiNbO3 substrates. To optimize the electrode material for SAW devices, Al-Cu films with various compositions were fabricated and their electrical, mechanical, and acoustic properties were comprehensively evaluated. The Al-Cu films exhibited a gradual decrease in resistivity with increasing Al content. The double-electrode SAW devices composed of Al-Cu films demonstrated a resonant frequency of 70 MHz and an average insertion loss of −16.1 dB, which was significantly lower than that of devices made with traditional Au or Al electrodes. Additionally, the SAW devices showed an increase in the FWHM values of the resonant frequency and a decrease in the insertion loss as the Al content in the IDT electrode decreased. These findings indicate that improving the performance of SAW devices can be achieved by reducing the density of the IDT electrodes, rather than focusing solely on their electrical characteristics. Full article
(This article belongs to the Special Issue Preparation and Characterization of Optoelectronic Functional Films)
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11 pages, 4972 KiB  
Article
Promoting Light Extraction Efficiency of Ultraviolet Light Emitting Diodes by Nanostructure Optimization
by Biaomin Li, Shihong Xia, Wei Guo, Zhenhai Yang, Yuheng Zeng, Zhizhong Yuan and Jichun Ye
Crystals 2022, 12(11), 1601; https://doi.org/10.3390/cryst12111601 - 10 Nov 2022
Cited by 3 | Viewed by 1758
Abstract
Ultraviolet (UV) light-emitting diodes (LEDs), as one of the more promising optoelectronic devices, are intrinsically limited by poor light extraction efficiencies (LEEs). To unlock the full potential of UV-LEDs, we propose a simple and effective strategy to promote the LEEs of UV-LEDs by [...] Read more.
Ultraviolet (UV) light-emitting diodes (LEDs), as one of the more promising optoelectronic devices, are intrinsically limited by poor light extraction efficiencies (LEEs). To unlock the full potential of UV-LEDs, we propose a simple and effective strategy to promote the LEEs of UV-LEDs by screening and tailoring suitable optical structures/designs through rigorous numerical simulations. The photonic crystals (PCs) and/or nano-patterned sapphire substrates (NPSSs) equipped with the nano-pillar, nano-cone, nano-oval, and their derivates, are particularly investigated. The simulated results show that individual PC with an average transmittance of 28% is more efficient than that of individual NPSS (24.8%). By coupling PC and NPSS structures, a higher LEE with an average transmittance approaching 29% is obtained, much higher than that of the flat one (23.6%). The involved mechanisms are clarified and confirm that the promotion of optical performance of the nanostructured devices should be attributed to the widened response angles (from 0 to 60°), rather than the enhanced transmittances in the small angles within 30°. Full article
(This article belongs to the Special Issue Preparation and Characterization of Optoelectronic Functional Films)
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19 pages, 4046 KiB  
Article
Resonant Tunneling of Electrons and Holes through the InxGa1−xN/GaN Parabolic Quantum Well/LED Structure
by Hind Althib
Crystals 2022, 12(8), 1166; https://doi.org/10.3390/cryst12081166 - 19 Aug 2022
Cited by 1 | Viewed by 2288
Abstract
Models describing the tunneling of electrons and holes through parabolic InxGa1−xN/GaN quantum well/LED structures with respect to strain were developed. The transmission coefficient, tunneling lifetime, and efficiency of LED structures were evaluated by solving the Schrödinger equation. The effects [...] Read more.
Models describing the tunneling of electrons and holes through parabolic InxGa1−xN/GaN quantum well/LED structures with respect to strain were developed. The transmission coefficient, tunneling lifetime, and efficiency of LED structures were evaluated by solving the Schrödinger equation. The effects of the mole fraction on the structure strain, resonant tunneling and tunneling lifetime, and LH–HH splitting were characterized. The value of LH–HH splitting increased and remained higher than the Fermi energy; therefore, only the HH band was dominant in terms of the valence band properties. The results indicate that an increase in the mole fraction can lead to efficiency droop. Full article
(This article belongs to the Special Issue Preparation and Characterization of Optoelectronic Functional Films)
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9 pages, 1760 KiB  
Article
The Mechanisms of AlGaN Device Buffer Layer Growth and Crystalline Quality Improvement: Restraint of Gallium Residues, Mismatch Stress Relief, and Control of Aluminum Atom Migration Length
by Baibin Wang, Jing Yang, Degang Zhao, Yuheng Zhang, Zhenzhuo Zhang, Feng Liang, Ping Chen and Zongshun Liu
Crystals 2022, 12(8), 1131; https://doi.org/10.3390/cryst12081131 - 12 Aug 2022
Cited by 4 | Viewed by 1845
Abstract
The mechanisms of AlGaN device buffer layer growth were studied. Gallium residues in the reactor chamber may be harmful to the quality of the AlN strain modulation layer, which eventually worsens the AlGaN buffer layer. By restraining the gallium residues, the crystalline quality [...] Read more.
The mechanisms of AlGaN device buffer layer growth were studied. Gallium residues in the reactor chamber may be harmful to the quality of the AlN strain modulation layer, which eventually worsens the AlGaN buffer layer. By restraining the gallium residues, the crystalline quality of the AlGaN layer is markedly improved. In addition, enhancing stress relief in nucleation and coalescence stages will reduce the edge dislocations induced by strain relaxation in the 2D growth stage. A slower precursor flow rate can promote the stress relief in nucleation and coalescence stages. By comparison, a suitable suppression of Al atoms’ surface migration can decrease surface roughness, which can be realized by increasing the precursor flow rate. Eventually, we obtained a AlGaN buffer layer having both low edge dislocation density and a flat surface using a two-step growth method. Full article
(This article belongs to the Special Issue Preparation and Characterization of Optoelectronic Functional Films)
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10 pages, 2999 KiB  
Article
Effect of High Temperature Treatment on the Photoluminescence of InGaN Multiple Quantum Wells
by Yachen Wang, Feng Liang, Degang Zhao, Yuhao Ben, Jing Yang, Zongshun Liu and Ping Chen
Crystals 2022, 12(6), 839; https://doi.org/10.3390/cryst12060839 - 14 Jun 2022
Cited by 2 | Viewed by 2097
Abstract
In this work, the photoluminescence (PL) properties of three as-grown InGaN/GaN multiple quantum well (MQW) structures which are heat-treated under different temperatures with nitrogen (N2) atmosphere are investigated. Temperature-dependent photoluminescence (PL) analysis was used to characterize the depth of localized states [...] Read more.
In this work, the photoluminescence (PL) properties of three as-grown InGaN/GaN multiple quantum well (MQW) structures which are heat-treated under different temperatures with nitrogen (N2) atmosphere are investigated. Temperature-dependent photoluminescence (PL) analysis was used to characterize the depth of localized states and defect density formed in MQWs. By fitting the positions of luminescence peaks with an LSE model, we find that deeper localized states are formed in the MQWs after high-temperature treatment. The experimental results show that the luminescence intensity of the sample heat-treated at 880 °C is significantly improved, which may be due to the shielding effect of In clusters on defects. While the luminescence efficiency decreases because of the higher defect density caused by the decomposition of the InGaN QW layer when the sample is heat-treated at 1020 °C. Moreover, the atomic force microscope results show that the increase in heat-treatment temperature leads to an increase in the width of surface steps due to the rearrangement of surface atoms in a high-temperature environment. Full article
(This article belongs to the Special Issue Preparation and Characterization of Optoelectronic Functional Films)
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