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Crystals
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Advances in Structural and Compositional Characterization for the Development of...
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Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (31 March 2019) | Viewed by 30904

Special Issue Editors

Prof. Dr. Katharina Lorenz

E-Mail Website
Guest Editor
Tecnologias Nucleares e Protecção Radiológica; Departamento de Engenharia e Ciências Nucleares
Interests: wide bandgap semiconductors; nanotechnology; ion beam analysis; ion beam modification
Dr. Andrés Redondo-Cubero

E-Mail Website
Guest Editor
Department of Applied Physics, Universidad Autónoma de Madrid, E-28049 Madrid, Spain
Interests: wide bandgap semiconductors; nanotechnology; ion beam analysis; ion beam modification; nanopatterning; crystalline structures

Special Issue Information

Dear Colleagues,

Wide bandgap semiconductors (WBGS) are the key to a new generation of electronic and optoelectronic devices with functionalities going beyond those of silicon devices. The overwhelming success of III-nitride based light emitting diodes (LEDs) and laser diodes used in solid state lighting applications and data storage is a prominent example. High power and high temperature electronic devices, today mainly built from SiC and GaN, find use in various fields from renewable energy generation, over electric vehicles, to transportation and space applications, just to name a few. Further fields of applications where WBGS are expected to play a prominent role include RF devices for space communications, sensors, quantum technologies, among others. In this scenario, emerging wide bandgap semiconductors such as ZnMg(Cd)O, Ga2O3 or diamond are about to reveal their full potential.

The performance of any device based on these novel materials will depend critically on the structural and compositional properties of the constituent semiconductor material. Advanced characterisation techniques are therefore needed to reveal the physical mechanisms leading to certain desired or unintended features such as certain microstructures, defects, strain, doping, etc. The objective of this Special Issue is therefore to highlight the importance of structural and compositional characterisation for the development of novel WBGS structures and devices and to give a series of representative examples of how advanced structural and compositional characterisation can help to control the desired properties and functions of materials and devices.

  • All wide bandgap semiconductors (WBGS) including nitrides, carbides, oxides, diamond and other emerging materials with different shapes and scales from bulk crystals to nanostructures;
  • Application of advanced structural and compositional characterisation to WBGS including X-Ray-based techniques, electron microscopy-based techniques, ion beam analysis techniques, nuclear probe techniques, imaging techniques, spectroscopies, surface sensitive techniques;
  • Micro and nanomechanical properties of WBGS;
  • In-situ characterisation;
  • Defects, dislocations, deformation, twins, and stress induced phenomena in WBGS;
  • Advances in materials modeling of WBGS;
  • Optimisation of growth procedures based on structural/compositional properties;
  • Doping;
  • Structural modification of WBGS including processing by etching, surface treatments, patterning, annealing, irradiation, implantation;
  • Fabrication and functionalisation;
  • WBGS device optimisation based on structural and compositional characterisation for applications in optoelectronics, high-power electronics, photonics, sensors, energy and other emerging technologies.

Prof. Dr. Katharina Lorenz
Dr. Andrés Redondo-Cubero
Guest Editors

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

  • Wide bandgap semiconductors
  • Heterostructures
  • Nanostructures
  • WBGS growth
  • Doping
  • Structural characterization
  • Compositional characterization
  • Defects, strain, microstructure
  • Materials processing and device fabrication
  • Relationship structural/compositional properties-device performance

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Published Papers (7 papers)

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Research

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12 pages, 7117 KiB  
Article
Modelling of Optical Damage in Nanorippled ZnO Produced by Ion Irradiation
by Andrés Redondo-Cubero, Luis Vázquez, Denis Jalabert, Katharina Lorenz and Nebiha Ben Sedrine
Crystals 2019, 9(9), 453; https://doi.org/10.3390/cryst9090453 - 30 Aug 2019
Cited by 4 | Viewed by 2585
Abstract
Here, we report on the production of nanoripples on the surface of ZnO bulk substrates by ion beam erosion with 20 keV Ar+ ions at an oblique incidence (60°). The ripple patterns, analyzed by atomic force microscopy, follow a power law dependence [...] Read more.
Here, we report on the production of nanoripples on the surface of ZnO bulk substrates by ion beam erosion with 20 keV Ar+ ions at an oblique incidence (60°). The ripple patterns, analyzed by atomic force microscopy, follow a power law dependence for both the roughness and the wavelength. At high fluences these ripples show coarsening and asymmetric shapes, which become independent of the beam direction and evidence additional mechanisms for the pattern development. The shallow damaged layer is not fully amorphized by this process, as confirmed by medium energy ion scattering. A detailed study of the damage-induced changes on the optical properties was carried out by means of spectroscopic ellipsometry. Using a 3-layer model based on Tauc-Lorenz and critical point parameter band oscillators, the optical constants of the damaged layer were determined. The results showed a progressive reduction in the refractive index and enhanced absorption below the bandgap with the fluence. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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10 pages, 1583 KiB  
Article
Energy-Dependent RBS Channelling Analysis of Epitaxial ZnO Layers Grown on ZnO by RF-Magnetron Sputtering
by Florian Wittkämper, André Bikowski, Klaus Ellmer, Konrad Gärtner and Elke Wendler
Crystals 2019, 9(6), 290; https://doi.org/10.3390/cryst9060290 - 4 Jun 2019
Cited by 5 | Viewed by 3287
Abstract
The transparent conducting oxides ZnO and ZnO:Al are interesting materials for a wide range of applications. Several of these applications need a large area, single crystalline, and specially doped thin layers. A common technique for the fabrication of those layers is RF (radio [...] Read more.
The transparent conducting oxides ZnO and ZnO:Al are interesting materials for a wide range of applications. Several of these applications need a large area, single crystalline, and specially doped thin layers. A common technique for the fabrication of those layers is RF (radio frequency) -magnetron sputtering. The investigation of the crystal quality of such layers requires methods of analysis that are destruction free and that are able to obtain information about the concentration and type of defects versus depth. One such option is the Rutherford backscattering spectroscopy (RBS) in channelling mode. In this work, we exploit the channelling effect and its energy dependence, which are sensitive to the type of defects. By using appropriate software and measuring RBS channelling spectra with different beam energies, we were able to determine the depth distribution of point defects and dislocation loops. The presence of dislocation loops was proven using other previously applied analysis methods. The main advantage of RBS in channelling mode is the quantification of point defects, which can be important for defining the electrical and optical properties of such layers. The technique demonstrated is applicable to other defective crystals or thin crystalline layers. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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14 pages, 3500 KiB  
Article
Optimal Sr-Doped Free TiO2@SrTiO3 Heterostructured Nanowire Arrays for High-Efficiency Self-Powered Photoelectrochemical UV Photodetector Applications
by Shiming Ni, Fengyun Guo, Dongbo Wang, Shujie Jiao, Jinzhong Wang, Yong Zhang, Bao Wang and Liancheng Zhao
Crystals 2019, 9(3), 134; https://doi.org/10.3390/cryst9030134 - 6 Mar 2019
Cited by 8 | Viewed by 3707
Abstract
Due to their high performance, photoelectrochemical ultraviolet (UV) photodetectors have attracted much attention, but the recombination of photogenerated electrons at the interface of photoanode/electrolyte limited further improvement of photoelectrochemical UV photodetectors (PEC UVPDs). Modification of TiO2 photoanode by SrTiO3 could improve [...] Read more.
Due to their high performance, photoelectrochemical ultraviolet (UV) photodetectors have attracted much attention, but the recombination of photogenerated electrons at the interface of photoanode/electrolyte limited further improvement of photoelectrochemical UV photodetectors (PEC UVPDs). Modification of TiO2 photoanode by SrTiO3 could improve the performance of UVPD, because the energy barrier that is established at the TiO2–SrTiO3 interface could accelerate the separation of the photogenerated electrons-holes pair. However, the recombination center that is caused by the preparation of TiO2@SrTiO3 core-shell heterostructured nanostructure decreases the performance of PEC UVPDs, which is still an important problem that hindered its application in PEC UVPDs. In this paper, we presented a Sr-doped free TiO2@SrTiO3 core-shell heterostructured nanowire arrays as a photoanode for the self-powered PEC UVPD. This will not only accelerate the separation of the photogenerated electrons-holes pair, but it will also reduce the recombination of photogenerated electron-hole pairs in the photoanode. The intrinsic effect of SrTiO3 reaction time on the J variations of UVPDs is investigated in detail. An impressive responsivity of 0.358 A·W−1 was achieved at 360 nm for the UVPD based on TiO2@SrTiO3 core-shell heterostructured nanowire arrays, which heretofore is a considerably high photoresponsivity for self-powered photoelectrochemical UVPDs. Additionally, this UVPD also exhibits a high on/off ratio, fast response time, excellent visible-blind characteristic, and linear optical signal response. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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13 pages, 2602 KiB  
Article
Modification of TiO2 Nanowire Arrays with Sn Doping as Photoanode for Highly Efficient Dye-Sensitized Solar Cells
by Shiming Ni, Fengyun Guo, Dongbo Wang, Shujie Jiao, Jinzhong Wang, Yong Zhang, Bao Wang, Pu Feng and Liancheng Zhao
Crystals 2019, 9(2), 113; https://doi.org/10.3390/cryst9020113 - 21 Feb 2019
Cited by 27 | Viewed by 4207
Abstract
The dye-sensitized solar cell (DSSC) is one candidate among the third-generation solar cells. The performance of most DSSCs based on TiO2 photoanode was limited by the low electron mobility within TiO2. To produce a much higher power conversion efficiency, Sn-doped [...] Read more.
The dye-sensitized solar cell (DSSC) is one candidate among the third-generation solar cells. The performance of most DSSCs based on TiO2 photoanode was limited by the low electron mobility within TiO2. To produce a much higher power conversion efficiency, Sn-doped TiO2 nanowire arrays were successfully prepared using a simple hydrothermal process. It was found that Sn doping augments electron mobility well and raises the flat band potential to improve the performance of DSSCs. The power conversion efficiency (η) of a DSSC based on the reasonable Sn-doped TiO2, N719 dye, platinized counter electrode and iodide/triiodide electrolyte reaches 8.75%. Furthermore, with an anatase TiO2 light scattering layer, a DSSC based on the Sn-doped TiO2 NWAs exhibits a remarkable power conversion efficiency of 9.43%, which is especially useful in weak light conditions. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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16 pages, 6414 KiB  
Article
Influence of Pressure on the Mechanical and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals
by Hongbo Qin, Tianfeng Kuang, Xinghe Luan, Wangyun Li, Jing Xiao, Ping Zhang, Daoguo Yang and Guoqi Zhang
Crystals 2018, 8(11), 428; https://doi.org/10.3390/cryst8110428 - 14 Nov 2018
Cited by 4 | Viewed by 5510
Abstract
The mechanical and electronic properties of two GaN crystals, wurtzite and zinc-blende GaN, under various hydrostatic pressures were investigated using first principles calculations. The results show that the lattice constants of the two GaN crystals calculated in this study are close to previous [...] Read more.
The mechanical and electronic properties of two GaN crystals, wurtzite and zinc-blende GaN, under various hydrostatic pressures were investigated using first principles calculations. The results show that the lattice constants of the two GaN crystals calculated in this study are close to previous experimental results, and the two GaN crystals are stable under hydrostatic pressures up to 40 GPa. The pressure presents extremely similar trend effect on the volumes of unit cells and average Ga-N bond lengths of the two GaN crystals. The bulk modulus increases while the shear modulus decreases with the increase in pressure, resulting in the significant increase of the ratios of bulk moduli to shear moduli for the two GaN polycrystals. Different with the monotonic changes of bulk and shear moduli, the elastic moduli of the two GaN polycrystals may increase at first and then decrease with increasing pressure. The two GaN crystals are brittle materials at zero pressure, while they may exhibit ductile behaviour under high pressures. Moreover, the increase in pressure raises the elastic anisotropy of GaN crystals, and the anisotropy factors of the two GaN single crystals are quite different. Different with the obvious directional dependences of elastic modulus, shear modulus and Poisson’s ratio of the two GaN single crystals, there is no anisotropy for bulk modulus, especially for that of zinc-blende GaN. Furthermore, the band gaps of GaN crystals increase with increasing pressure, and zinc-blende GaN has a larger pressure coefficient. To further understand the pressure effect on the band gap, the band structure and density of states (DOSs) of GaN crystals were also analysed in this study. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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9 pages, 7693 KiB  
Article
Study of Nanoscratching Process of GaAs Using Molecular Dynamics
by Defu Yi, Jianyong Li and Pengzhe Zhu
Crystals 2018, 8(8), 321; https://doi.org/10.3390/cryst8080321 - 11 Aug 2018
Cited by 15 | Viewed by 4512
Abstract
In this paper, molecular dynamics method was employed to investigate the nanoscratching process of gallium arsenide (GaAs) in order to gain insights into the material deformation and removal mechanisms in chemical mechanical polishing of GaAs. By analyzing the distribution of hydrostatic pressure and [...] Read more.
In this paper, molecular dynamics method was employed to investigate the nanoscratching process of gallium arsenide (GaAs) in order to gain insights into the material deformation and removal mechanisms in chemical mechanical polishing of GaAs. By analyzing the distribution of hydrostatic pressure and coordination number of GaAs atoms, it was found that phase transformation and amorphization were the dominant deformation mechanisms of GaAs in the scratching process. Furthermore, anisotropic effect in nanoscratching of GaAs was observed. The diverse deformation behaviors of GaAs with different crystal orientations were due to differences in the atomic structure of GaAs. The scratching resistance of GaAs(001) surface was the biggest, while the friction coefficient of GaAs(111) surface was the smallest. These findings shed light on the mechanical wear mechanism in chemical mechanical polishing of GaAs. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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Review

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16 pages, 3290 KiB  
Review
Recent Advances on Carrier and Exciton Self-Trapping in Strontium Titanate: Understanding the Luminescence Emissions
by Miguel L. Crespillo, Joseph T. Graham, Fernando Agulló-López, Yanwen Zhang and William J. Weber
Crystals 2019, 9(2), 95; https://doi.org/10.3390/cryst9020095 - 13 Feb 2019
Cited by 38 | Viewed by 6325
Abstract
An up-to-date review on recent results for self-trapping of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and [...] Read more.
An up-to-date review on recent results for self-trapping of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and exciton self-trapping on the luminescence emissions under a variety of excitation sources with special emphasis on experiments with laser pulses and energetic ion-beams. In spite of the extensive research effort, a definitive identification of such localized states, as well as a suitable understanding of their operative light emission mechanisms, has remained lacking or controversial. However, promising advances have been recently achieved and are the objective of the present review. In particular, significant theoretical advances in the understanding of electron and hole self-trapping are discussed. Also, relevant experimental advances in the kinetics of light emission associated with electron-hole recombination have been obtained through time-resolved experiments using picosecond (ps) laser pulses. The luminescence emission mechanisms and the light decay processes from the self-trapped excitons are also reviewed. Recent results suggest that the blue emission at 2.8 eV, often associated with oxygen vacancies, is related to a transition from unbound conduction levels to the ground singlet state of the STE. The stabilization of small electron polarons by oxygen vacancies and its connection with luminescence emission are discussed in detail. Through ion-beam irradiation experiments, it has recently been established that the electrons associated with the vacancy constitute electron polaron states (Ti3+) trapped in the close vicinity of the empty oxygen sites. These experimental results have allowed for the optical identification of the oxygen vacancy center through a red luminescence emission centered at 2.0 eV. Ab-initio calculations have provided strong support for those experimental findings. Finally, the use of Cr-doped STO has offered a way to monitor the interplay between the chromium centers and oxygen vacancies as trapping sites for the electron and hole partners resulting from the electronic excitation. Full article
(This article belongs to the Special Issue Advances in Structural and Compositional Characterization for the Development of Wide Bandgap Semiconductors)
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