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Epitaxial Thin Films: Properties and Applications
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Epitaxial Thin Films: Properties and Applications

A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Thin Films".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 20046

Special Issue Editor

Dr. Syed Burhanullah Qadri

E-Mail Website
Guest Editor
US Naval Research Laboratory, Washington D.C., USA
Interests: physics and material science

Special Issue Information

Dear Colleagues,

Epitaxial growth of thin films of materials has played a crucial role in a wide range of applications in electronics, optoelectronics, and magneto-optics. Among the various epitaxial growth techniques, liquid-phase epitaxy (LPE), metal organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), and most recently low temperature atomic layer epitaxy (ALEp) have been developed to deposit epitaxial films. These epitaxial films find a variety of applications in electronic, magneto-optic, optoelectronic, superconducting, ferroelectric, and pyroelectric and numerous other devices. These epitaxial growth techniques are also used to produce multilayer structures or superlattices with atomic-layer control, which is fundamental to nanoscale engineering. Comparative studies of the various epitaxy techniques suggest that no single technique can best satisfy the needs of all materials/devices. Therefore, suitable combinations are needed in microelectronics, optoelectronics, solar cells, thermophotovoltaics, thermo-electric, semiconductor electrochemical devices, magnetic/magneto-optical devices, and microelectromechanical systems. This Special Topic on Epitaxial Growth of Thin Films and Applications highlights the forefront of research in this interdisciplinary area spanning physics and material science.

Dr. Syed Burhanullah Qadri
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. Coatings 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 2600 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.

Published Papers (7 papers)

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Research

10 pages, 9943 KiB  
Article
Evidence of Delta Phase of Fe in MBE-Grown Thin Epitaxial Films on GaAs
by Ramasis Goswami and Syed B. Qadri
Coatings 2022, 12(6), 771; https://doi.org/10.3390/coatings12060771 - 03 Jun 2022
Viewed by 1453
Abstract
Fe/GaAs is an important system for the study of spin injection behavior that can vary with the nature and interfaces of Fe films. Here, we investigate the effect of interfacial strain on the microstructure, interfaces and phase-formation behavior in epitaxially grown Fe films. [...] Read more.
Fe/GaAs is an important system for the study of spin injection behavior that can vary with the nature and interfaces of Fe films. Here, we investigate the effect of interfacial strain on the microstructure, interfaces and phase-formation behavior in epitaxially grown Fe films. To vary the strain, we have characterized Fe films of various thicknesses ranging from 10 to 1000 nm which were grown using molecular beam epitaxy on GaAs (011) and AlGaAs (001) substrates. High resolution X-ray diffraction studies revealed that films with higher thicknesses exhibited an equilibrium α-Fe phase, while the films with less than 10 nm thicknesses indicated the presence of δ-Fe. Transmission electron microscopy revealed the interface for 10-nm-thick films had strain lobes with no interfacial phase formation for films deposited at room temperature. At a higher deposition temperature of 175 °C, similar strain lobes were observed for a 10-nm-thick film. Extended annealing at 200 °C transformed the metastable δ-Fe phase to an equilibrium α-Fe. However, at higher temperature, the interface contained an intermixing layer of (FeAl)GaAs. We demonstrate that the interfacial strain plays a major role in stabilizing the metastable δ-Fe on GaAs. Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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8 pages, 3121 KiB  
Article
N+ Irradiation and Substrate-Induced Variability in the Metamagnetic Phase Transition of FeRh Films
by Steven P. Bennett, Samuel W. LaGasse, Marc Currie, Olaf Van’t Erve, Joseph C. Prestigiacomo, Cory D. Cress and Syed B. Qadri
Coatings 2021, 11(6), 661; https://doi.org/10.3390/coatings11060661 - 31 May 2021
Cited by 4 | Viewed by 3448
Abstract
Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often Tc > 400 K), both ion irradiation and strained epitaxial growth have [...] Read more.
Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often Tc > 400 K), both ion irradiation and strained epitaxial growth have been used to bring it to applicable temperatures. Nevertheless, cross sample variability is pervasive in these studies. Here we explore the optical and magnetic properties of 35 nm thick FeRh grown by magnetron sputter deposition simultaneously on two different single crystal substrates: epitaxially on MgO (001) and highly strained with large lattice mismatch on Al2O3 (1000). We then irradiate the epitaxial film with 5 keV N+ ions to introduce disorder (and to a lesser extent, modify chemical composition) without effecting the surface morphology. We find that the phase-transitional properties of both films are strikingly different due to the large lattice mismatch, despite being grown in tandem with nominally identical growth conditions including Fe/Rh stoichiometry, pressure, and temperature. We observe that N+ implantation lowers Tc by ~60 K, yielding a sample with nominally the same transition temperature as the non-epitaxial film on sapphire, yet with a significantly increased magnetic moment, a larger magnetization change and a more abrupt transition profile. We attribute these differences to the Volmer-Weber type growth mode induced by the sapphire substrate and the resulting rougher surface morphology. Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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13 pages, 5710 KiB  
Article
Epitaxial Growth of Single Crystal YAG for Optical Devices
by Syed N. Qadri, Woohong Kim, Shyam Bayya, L. Brandon Shaw, Syed B. Qadri, Joseph Kolis, Bradley Stadelman and Jasbinder Sanghera
Coatings 2021, 11(6), 644; https://doi.org/10.3390/coatings11060644 - 27 May 2021
Cited by 1 | Viewed by 2894
Abstract
We report the latest progress on fabrication of rare earth doped single crystal yttrium aluminum garnet (YAG) core/undoped YAG cladded fibers. Rare-earth doped single crystal core fibers were grown with laser heated pedestal growth methods. In a second step, epitaxial methods were used [...] Read more.
We report the latest progress on fabrication of rare earth doped single crystal yttrium aluminum garnet (YAG) core/undoped YAG cladded fibers. Rare-earth doped single crystal core fibers were grown with laser heated pedestal growth methods. In a second step, epitaxial methods were used to grow a single crystalline undoped YAG cladding onto the core fiber. Hydrothermal and liquid phase epitaxy methods utilize the core doped fiber as the seed. X-ray diffraction of cladding reveals an equilibrium (110) morphology. Energy-dispersive X-ray spectroscopy analysis shows there is minimal diffusion of rare-earth dopants into the cladding structure. The use of scandium doping is shown to substitute at the Al3+ site, thereby allowing an additional tunability of refractive index of core structure material besides conventional Y3+ site dopants. The use of these epitaxial growth methods enables material compatibility, tuning of refractive index, and conformal growth of cladding structures onto core fibers for optical devices. Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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8 pages, 2064 KiB  
Article
Stable Electron Concentration Si-doped β-Ga2O3 Films Homoepitaxial Growth by MOCVD
by Teng Jiao, Zeming Li, Wei Chen, Xin Dong, Zhengda Li, Zhaoti Diao, Yuantao Zhang and Baolin Zhang
Coatings 2021, 11(5), 589; https://doi.org/10.3390/coatings11050589 - 17 May 2021
Cited by 13 | Viewed by 2938
Abstract
To obtain high-quality n-type doped β-Ga2O3 films, silane was used as an n-type dopant to grow Si-doped β-Ga2O3 films on (100) β-Ga2O3 substrates by metal-organic chemical vapor deposition (MOCVD). The electron concentrations of the [...] Read more.
To obtain high-quality n-type doped β-Ga2O3 films, silane was used as an n-type dopant to grow Si-doped β-Ga2O3 films on (100) β-Ga2O3 substrates by metal-organic chemical vapor deposition (MOCVD). The electron concentrations of the Si-doped β-Ga2O3 films obtained through experiments can be stably controlled in the range of 6.5 × 1016 cm−3 to 2.6 × 1019 cm−3, and the ionization energy of Si donors is about 30 meV, as determined by analysis and calculation. The full width at half maxima of the rocking curves of the (400) crystal plane of all doped films was less than 500 arcsec, thus showing high crystal quality, while the increase of the doping concentration increased the defect density in the β-Ga2O3 films, which had an adverse effect on the crystal quality and surface morphology of the films. Compared with heteroepitaxial Si-doped β-Ga2O3 films, homoepitaxial Si-doped β-Ga2O3 films exhibited higher quality, lower defect density, and more stable electron concentration, which make them more conductive for preparing Ga2O3-based power devices. Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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9 pages, 25572 KiB  
Article
Microstructure and Interfaces of Ultra-Thin Epitaxial AlN Films Grown by Plasma-Enhanced Atomic Layer Deposition at Relatively Low Temperatures
by Ramasis Goswami, Syed Qadri, Neeraj Nepal and Charles Eddy, Jr.
Coatings 2021, 11(4), 482; https://doi.org/10.3390/coatings11040482 - 20 Apr 2021
Cited by 3 | Viewed by 2646
Abstract
We demonstrate the growth of ultra-thin AlN films on Si (111) and on a GaN/sapphire (0001) substrate using atomic layer epitaxy in the temperature range of 360 to 420 °C. Transmission electron microscopy and X-ray diffraction were used to characterize the interfaces, fine [...] Read more.
We demonstrate the growth of ultra-thin AlN films on Si (111) and on a GaN/sapphire (0001) substrate using atomic layer epitaxy in the temperature range of 360 to 420 °C. Transmission electron microscopy and X-ray diffraction were used to characterize the interfaces, fine scale microstructure, and the crystalline quality of thin films. Films were deposited epitaxily on Si (111) with a hexagonal structure, while on the GaN/sapphire (0001) substrate, the AlN film is epitaxial and has been deposited in a metastable zinc-blende cubic phase. Transmission electron microscopy reveals that the interface is not sharp, containing an intermixing layer with cubic AlN. We show that the substrate, particularly the strain, plays a major role in dictating the crystal structure of AlN. The strain, estimated in the observed orientation relation, is significantly lower for cubic AlN on hexagonal GaN as compared to the hexagonal AlN on hexagonal GaN. On the Si (111) substrate, on the other hand, the strain in the observed orientation relation is 0.8% for hexagonal AlN, which is substantially lower than the strain estimated for the cubic AlN on Si(111). Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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9 pages, 1911 KiB  
Article
Development of a Fluorine-Free Polymer-Assisted-Deposition Route for YBa2Cu3O7−x Superconducting Films
by Mircea Nasui, Ramona Bianca Sonher, Traian Petrisor, Jr., Sorin Varodi, Cornelia Pop, Lelia Ciontea and Traian Petrisor
Coatings 2020, 10(10), 966; https://doi.org/10.3390/coatings10100966 - 11 Oct 2020
Cited by 3 | Viewed by 1932
Abstract
Polymer assisted deposition (PAD) was used as an environmentally friendly, non-fluorine, growth method for superconducting YBa2Cu3O7−x (YBCO) films. The kinetics of the thermal decomposition of the precursor powder was studied by thermogravimetry coupled with mass spectrometry (TG-QMS). [...] Read more.
Polymer assisted deposition (PAD) was used as an environmentally friendly, non-fluorine, growth method for superconducting YBa2Cu3O7−x (YBCO) films. The kinetics of the thermal decomposition of the precursor powder was studied by thermogravimetry coupled with mass spectrometry (TG-QMS). YBCO films were spin coated on (100) SrTiO3 (STO) single crystalline substrates, followed by a single step thermal treatment under wet and dry O2 and O2/N2 mixture. The as-obtained films were epitaxially grown having a [001]YBCO||[001]STO out-of-plane epitaxial relationship and exhibited good superconducting properties with Tc (R = 0) > 88 K, transition widths, ΔT ≈ 2 K and critical current densities as high as 2.3 MA/cm2 at 77 K and self magnetic field. Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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12 pages, 4825 KiB  
Article
Reactive Sputtering Deposition of Epitaxial TiC Film on Si (100) Substrate
by Yu-Siang Fang, Thi Hien Do, Kun-An Chiu, Wei-Chun Chen and Li Chang
Coatings 2020, 10(7), 647; https://doi.org/10.3390/coatings10070647 - 05 Jul 2020
Cited by 10 | Viewed by 3302
Abstract
Epitaxial (100) TiC film deposition on Si (100) substrate by direct current magnetron reactive sputtering of a metallic Ti target with 3%–6% CH4 in Ar gas was investigated. X-ray diffraction and cross-sectional scanning transmission electron microscopy (STEM) reveal that epitaxial cubic TiC [...] Read more.
Epitaxial (100) TiC film deposition on Si (100) substrate by direct current magnetron reactive sputtering of a metallic Ti target with 3%–6% CH4 in Ar gas was investigated. X-ray diffraction and cross-sectional scanning transmission electron microscopy (STEM) reveal that epitaxial cubic TiC can be grown on the Si substrate by domain matching epitaxy in 5/4 ratio with the epitaxial relationship of TiC (100)[0 1 ¯ 1] // Si (100)[0 1 ¯ 1]. For sputtering with 3% and 4% CH4, the deposited films are found to consist of both TiC and metallic Ti phases. Increasing the CH4 flow ratio to 5% results in a deposited film completely consisting of TiC without metallic Ti phase. The crystallinity of the deposited TiC is also improved with increasing the CH4 ratio to 5%. X-ray photoelectron spectroscopy shows that the [C]/[Ti] atomic ratio in TiC is nearly close to 1 for growth with 5% CH4 flow ratio and above. The measured electrical resistivities of the deposited films also increase from 41 to 153 μΩ·cm with increasing the CH4 ratio from 3% to 6%. With film growth beyond 50 nm thickness, it is shown that some disoriented TiC grains are formed. Full article
(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)
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