Special Issue "Advances in Epitaxial Materials"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 July 2019).

Special Issue Editor

Prof. Mike Leszczynski
E-Mail Website
Guest Editor
High Pressure Research Center of the Polish Academy of Sciences, Warsaw, Poland
Interests: semiconductors; epitaxy; defects in crystals; X-ray diffraction; electronic devices

Special Issue Information

Dear Colleagues,

Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate. The term epitaxy comes from the Greek roots “epi” (ἐπί), meaning "above", and “taxis” (τάξις), meaning "an ordered manner". For most technological applications, it is desired that the deposited material form a crystalline overlayer that has one well-defined orientation with respect to the substrate crystal structure (single-domain epitaxy).

At one extreme, we deal with homoepitaxy on perfect substrates, for example Si epitaxial layers on Si substrates. However, even in such cases, the properties (related to the presence of point defects) of the layer depend on growth parameters: Substrate off-orientation, growth rate, pressure, or temperature.

At the second extreme, we deal with polycrystalline layers on polycrystalline substrates. In that case, we have different epitaxy relation on each crystallite. Such case can happen in the technology of metal contacts and resistivity of these contacts can depend on epitaxial relations of the junction.

The most frequent case is somewhere between those two extrema. A good example is the growth of GaN layers on sapphire. In that case, the lattice mismatch is large (16%) and must be relaxed by a high density of misfit dislocations. However, for the useful optoelectronic devices (for example, blue LEDs for white lighting), it is necessary to have much lower density of dislocations. To achieve that, a number of technological tricks are used to filter dislocations, as low temperature buffer layers, strained interlayers, lateral epitaxy, and some others.

In heteroepitaxy, the basic information needed is on the critical thickness and strain for lattice relaxation by emission of dislocations, cracking or three-dimensional growth. However, these critical thickness and strain depend on several other parameters, for example, on density of dislocations in the substrate, point defect density in the layer, or growth temperature. This makes the problems of epitaxy fascinating, but, at the same time, very difficult to study.

Moreover, in epitaxy, we deal not only with complicated mechanisms of epitaxial growth, but also features specific for a reactor. For example, in nitride technology, it is not uncommon to switch-off the flow of TEGa, but the GaN is still growing. Additionally, the inhomegeneities of the epi-wafers are observed in nano-, micro-, and even mili-scales. This makes analysis of the wafers very laborious, and, unfortunately, very often done not thoroughly enough.

Future electronic and optoelectronic devices will be based not only on two-dimensional epi-wafers, but using lateral patterning, more sophisticated three-dimensional objects (quantum dots, wires) can be grown. This is a big challange as the growth conditions are very much different in that case, and the characterization of such structures is much more difficult.

All those and other issues of epitaxy will be dealt in this Special Issue. It is my pleasure to invite you to submit a manuscript for it. Full papers, communications, and reviews are all welcome.

Prof. Mike Leszczynski
Guest Editor

Manuscript Submission Information

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Keywords

  • epitaxy
  • lattice mismatch
  • lattice relaxation
  • misfit dislocations
  • semiconductors
  • metals
  • insulators

Published Papers (9 papers)

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Research

Open AccessArticle
Growth Mechanism and Properties of Self-Assembled InN Nanocolumns on Al Covered Si(111) Substrates by PA-MBE
Materials 2019, 12(19), 3203; https://doi.org/10.3390/ma12193203 - 30 Sep 2019
Abstract
Self-assembled InN nanocolumns were grown at low temperatures by plasma-assisted molecular beam epitaxy with a high crystalline quality. The self-assembling procedure was carried out on AlN/Al layers on Si(111) substrates avoiding the masking process. The Al interlayer on the Si(111) substrate prevented the [...] Read more.
Self-assembled InN nanocolumns were grown at low temperatures by plasma-assisted molecular beam epitaxy with a high crystalline quality. The self-assembling procedure was carried out on AlN/Al layers on Si(111) substrates avoiding the masking process. The Al interlayer on the Si(111) substrate prevented the formation of amorphous SiN. We found that the growth mechanism at 400 C of InN nanocolumns started by a layer-layer (2D) nucleation, followed by the growth of 3D islands. This growth mechanism promoted the nanocolumn formation without strain. The nanocolumnar growth proceeded with cylindrical and conical shapes with heights between 250 and 380 nm. Detailed high-resolution transmission electron microscopy analysis showed that the InN nanocolumns have a hexagonal crystalline structure, free of dislocation and other defects. The analysis of the phonon modes also allowed us to identify the hexagonal structure of the nanocolumns. In addition, the photoluminescence spectrum showed an energy transition of 0.72 eV at 20 K for the InN nanocolumns, confirmed by photoreflectance spectroscopy. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
Indium Incorporation into InGaN Quantum Wells Grown on GaN Narrow Stripes
Materials 2019, 12(16), 2583; https://doi.org/10.3390/ma12162583 - 14 Aug 2019
Abstract
InGaN quantum wells were grown using metalorganic chemical vapor phase epitaxy (vertical and horizontal types of reactors) on stripes made on GaN substrate. The stripe width was 5, 10, 20, 50, and 100 µm and their height was 4 and 1 µm. InGaN [...] Read more.
InGaN quantum wells were grown using metalorganic chemical vapor phase epitaxy (vertical and horizontal types of reactors) on stripes made on GaN substrate. The stripe width was 5, 10, 20, 50, and 100 µm and their height was 4 and 1 µm. InGaN wells grown on stripes made in the direction perpendicular to the off-cut had a rough morphology and, therefore, this azimuth of stripes was not further explored. InGaN wells grown on the stripes made in the direction parallel to the GaN substrate off-cut had a step-flow-like morphology. For these samples (grown at low temperatures), we found out that the InGaN growth rate was higher for the narrower stripes. The higher growth rate induces a higher indium incorporation and a longer wavelength emission in photoluminescence measurements. This phenomenon is very clear for the 4 µm high stripes and less pronounced for the shallower 1 µm high stripes. The dependence of the emission wavelength on the stripe width paves a way to multicolor emitters. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
The Growth of Photoactive Porphyrin-Based MOF Thin Films Using the Liquid-Phase Epitaxy Approach and Their Optoelectronic Properties
Materials 2019, 12(15), 2457; https://doi.org/10.3390/ma12152457 - 01 Aug 2019
Abstract
This study reports on the optoelectronic properties of porphyrin-based metal–organic framework (MOF) thin films fabricated by a facile liquid-phase epitaxy approach. This approach affords the growth of MOF thin films that are free of morphological imperfections, more suitable for optoelectronic applications. Chemical modifications [...] Read more.
This study reports on the optoelectronic properties of porphyrin-based metal–organic framework (MOF) thin films fabricated by a facile liquid-phase epitaxy approach. This approach affords the growth of MOF thin films that are free of morphological imperfections, more suitable for optoelectronic applications. Chemical modifications such as the porphyrin ligand metallation have been found to preserve the morphology of the grown films making this approach particularly suitable for molecular alteration of MOF thin film optoelectronic properties without compromising its mesoscale morphology significantly. Particularly, the metallation of the ligand was found to be effective to tune the MOF bandgap. These porphyrin-based MOF thin films were shown to function effectively as donor layers in solar cells based on a Fullerene-C60 acceptor. The ability to fabricate MOF solar cells free of a liquid-phase acceptor greatly simplifies device fabrication and enables pairing of MOFs as light absorbers with a wide range of acceptors including non-fullerene acceptors. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessFeature PaperArticle
Metamorphic Integration of GaInAsSb Material on GaAs Substrates for Light Emitting Device Applications
Materials 2019, 12(11), 1743; https://doi.org/10.3390/ma12111743 - 29 May 2019
Abstract
The GaInAsSb material has been conventionally grown on lattice-matched GaSb substrates. In this work, we transplanted this material onto the GaAs substrates in molecular beam epitaxy (MBE). The threading dislocations (TDs) originating from the large lattice mismatch were efficiently suppressed by a novel [...] Read more.
The GaInAsSb material has been conventionally grown on lattice-matched GaSb substrates. In this work, we transplanted this material onto the GaAs substrates in molecular beam epitaxy (MBE). The threading dislocations (TDs) originating from the large lattice mismatch were efficiently suppressed by a novel metamorphic buffer layer design, which included the interfacial misfit (IMF) arrays at the GaSb/GaAs interface and strained GaInSb/GaSb multi-quantum wells (MQWs) acting as dislocation filtering layers (DFLs). Cross-sectional transmission electron microscopy (TEM) images revealed that a large part of the dislocations was bonded on the GaAs/GaSb interface due to the IMF arrays, and the four repetitions of the DFL regions can block most of the remaining threading dislocations. Etch pit density (EPD) measurements indicated that the dislocation density in the GaInAsSb material on top of the buffer layer was reduced to the order of 106 /cm2, which was among the lowest for this compound material grown on GaAs. The light emitting diodes (LEDs) based on the GaInAsSb P-N structures on GaAs exhibited strong electro-luminescence (EL) in the 2.0–2.5 µm range. The successful metamorphic growth of GaInAsSb on GaAs with low dislocation densities paved the way for the integration of various GaInAsSb based light emitting devices on the more cost-effective GaAs platform. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
Optimization of MBE Growth Conditions of In0.52Al0.48As Waveguide Layers for InGaAs/InAlAs/InP Quantum Cascade Lasers
Materials 2019, 12(10), 1621; https://doi.org/10.3390/ma12101621 - 17 May 2019
Abstract
We investigate molecular beam epitaxy (MBE) growth conditions of micrometers-thick In0.52Al0.48As designed for waveguide of InGaAs/InAlAs/InP quantum cascade lasers. The effects of growth temperature and V/III ratio on the surface morphology and defect structure were studied. The growth conditions [...] Read more.
We investigate molecular beam epitaxy (MBE) growth conditions of micrometers-thick In0.52Al0.48As designed for waveguide of InGaAs/InAlAs/InP quantum cascade lasers. The effects of growth temperature and V/III ratio on the surface morphology and defect structure were studied. The growth conditions which were developed for the growth of cascaded In0.53Ga0.47As/In0.52Al0.48As active region, e.g., growth temperature of Tg = 520 °C and V/III ratio of 12, turned out to be not optimum for the growth of thick In0.52Al0.48As waveguide layers. It has been observed that, after exceeding ~1 µm thickness, the quality of In0.52Al0.48As layers deteriorates. The in-situ optical reflectometry showed increasing surface roughness caused by defect forming, which was further confirmed by high resolution X-ray reciprocal space mapping, optical microscopy and atomic force microscopy. The presented optimization of growth conditions of In0.52Al0.48As waveguide layer led to the growth of defect free material, with good optical quality. This has been achieved by decreasing the growth temperature to Tg = 480 °C with appropriate increasing V/III ratio. At the same time, the growth conditions of the cascade active region of the laser were left unchanged. The lasers grown using new recipes have shown lower threshold currents and improved slope efficiency. We relate this performance improvement to reduction of the electron scattering on the interface roughness and decreased waveguide absorption losses. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
Epitaxial Non c-Axis Twin-Free Bi2Sr2CaCu2O8+δ Thin Films for Future THz Devices
Materials 2019, 12(7), 1124; https://doi.org/10.3390/ma12071124 - 05 Apr 2019
Abstract
Thin films of (117) Bi2Sr2Ca2CuO8+δ (Bi-2212) were grown by Molecular Organic Chemical Vapor Deposition (MOCVD) on (110) SrTiO3 and (110) LaAlO3 substrates. Substrates were vicinal with off angles up to 20°. Films are 3D [...] Read more.
Thin films of (117) Bi2Sr2Ca2CuO8+δ (Bi-2212) were grown by Molecular Organic Chemical Vapor Deposition (MOCVD) on (110) SrTiO3 and (110) LaAlO3 substrates. Substrates were vicinal with off angles up to 20°. Films are 3D epitaxial and X-ray diffraction φ-ψ scans demonstrate that, while the films grown on a flat substrate are composed of twinned grains, the films on vicinal substrate are twin-free. A higher quality is obtained if growth is performed at two temperatures: Growth starts at 550–600 °C and continues at 700–750 °C. The twin-free film grown by the two-temperature method shows a zero-resistance critical temperature of 37 and 32 K when the measuring current is applied in-plane parallel and perpendicular to [001] direction of the substrate. Twin-free non c-axis thin films are promising for fabrication of novel planar THz devices. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
CH4 Adsorption Probability on GaN(0001) and (000−1) during Metalorganic Vapor Phase Epitaxy and Its Relationship to Carbon Contamination in the Films
Materials 2019, 12(6), 972; https://doi.org/10.3390/ma12060972 - 23 Mar 2019
Cited by 1
Abstract
Suppression of carbon contamination in GaN films grown using metalorganic vapor phase epitaxy (MOVPE) is a crucial issue in its application to high power and high frequency electronic devices. To know how to reduce the C concentration in the films, a sequential analysis [...] Read more.
Suppression of carbon contamination in GaN films grown using metalorganic vapor phase epitaxy (MOVPE) is a crucial issue in its application to high power and high frequency electronic devices. To know how to reduce the C concentration in the films, a sequential analysis based on first principles calculations is performed. Thus, surface reconstruction and the adsorption of the CH4 produced by the decomposition of the Ga source, Ga(CH3)3, and its incorporation into the GaN sub-surface layers are investigated. In this sequential analysis, the dataset of the adsorption probability of CH4 on reconstructed surfaces is indispensable, as is the energy of the C impurity in the GaN sub-surface layers. The C adsorption probability is obtained based on steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic ensemble-based, non-phenomenological framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium. This framework is suitable especially when one studies the adsorption behavior of an impurity molecule because the conventional approach, the chemical potential control method, cannot be applied to a quantitative analysis for such a system. The proposed sequential model successfully explains the influence of the growth orientation, GaN(0001) and (000−1), on the incorporation of C into the film. This model can contribute to the suppression of the C contamination in GaN MOVPE. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
Structure and Electron Mobility of ScN Films Grown on α-Al2O3(1102) Substrates
Materials 2018, 11(12), 2449; https://doi.org/10.3390/ma11122449 - 03 Dec 2018
Cited by 2
Abstract
Scandium nitride (ScN) films were grown on α-Al2O3( 1 1 ¯ 02 ) substrates using the molecular beam epitaxy method, and the heteroepitaxial growth of ScN on α-Al2O3( 1 1 ¯ 02 ) and their [...] Read more.
Scandium nitride (ScN) films were grown on α-Al2O3( 1 1 ¯ 02 ) substrates using the molecular beam epitaxy method, and the heteroepitaxial growth of ScN on α-Al2O3( 1 1 ¯ 02 ) and their electric properties were studied. Epitaxial ScN films with an orientation relationship (100)ScN || ( 1 1 ¯ 02 )α-Al2O3 and [001]ScN || [ 11 2 ¯ 0 ]α-Al2O3 were grown on α-Al2O3( 1 1 ¯ 02 ) substrates. Their crystalline orientation anisotropy was found to be small. In addition, [100] of the ScN films were tilted along [ 1 ¯ 101 ] of α-Al2O3( 1 1 ¯ 02 ) in the initial stage of growth. The tilt angle between the film growth direction and [100] of ScN was 1.4–2.0° and increased with growth temperature. The crystallinity of the ScN films also improved with the increasing growth temperature. The film with the highest Hall mobility was obtained at the boundary growth conditions determined by the relationship between the crystallinity and the nonstoichiometric composition because the film with the highest crystallinity was obtained under the Sc-rich growth condition. The decreased Hall mobility with a simultaneous improvement in film crystallinity was caused by the increased carrier scattering by the ionized donors originating from the nonstoichiometric composition. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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Open AccessArticle
Investigating Metal–Insulator Transition and Structural Phase Transformation in the (010)-VO2/(001)-YSZ Epitaxial Thin Films
Materials 2018, 11(9), 1713; https://doi.org/10.3390/ma11091713 - 13 Sep 2018
Cited by 1
Abstract
The VO2 thin films with sharp metal–insulator transition (MIT) were epitaxially grown on (001)-oriented Yttria-stabilized zirconia substrates (YSZ) using radio-frequency (RF) magnetron sputtering techniques. The MIT and structural phase transition (SPT) were comprehensively investigated under in situ temperature conditions. The amplitude of [...] Read more.
The VO2 thin films with sharp metal–insulator transition (MIT) were epitaxially grown on (001)-oriented Yttria-stabilized zirconia substrates (YSZ) using radio-frequency (RF) magnetron sputtering techniques. The MIT and structural phase transition (SPT) were comprehensively investigated under in situ temperature conditions. The amplitude of MIT is in the order of magnitude of 104, and critical temperature is 342 K during the heating cycle. It is interesting that both electron concentration and mobility are changed by two orders of magnitude across the MIT. This research is distinctively different from previous studies, which found that the electron concentration solely contributes to the amplitude of the MIT, although the electron mobility does not. Analysis of the SPT showed that the (010)-VO2/(001)-YSZ epitaxial thin film presents a special multi-domain structure, which is probably due to the symmetry matching and lattice mismatch between the VO2 and YSZ substrate. The VO2 film experiences the SPT from the M1 phase at low temperature to a rutile phase at a high temperature. Moreover, the SPT occurs at the same critical temperature as that of the MIT. This work may shed light on a new MIT behavior and may potentially pave the way for preparing high-quality VO2 thin films on cost-effective YSZ substrates for photoelectronic applications. Full article
(This article belongs to the Special Issue Advances in Epitaxial Materials)
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