Special Issue "Current and Future Directions in Crystal Growth by Molecular Beam Epitaxy (MBE)"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (31 August 2017)

Special Issue Editor

Guest Editor
Dr. Paul J. Simmonds

Department of Physics, Boise State University, 1910 University Drive, Boise, ID 83725-1570, USA
Website | E-Mail
Interests: molecular beam epitaxy; III-V semiconductors; self-assembled nanostructures; quantum dots; tensile strain; epitaxial 2D materials

Special Issue Information

Dear Colleagues,

Since its development in the 1970s, MBE (molecular beam epitaxy) has become one of the most important and influential techniques for epitaxial crystal growth. Its versatility means that a wide range of families of crystalline materials, from metals to oxides, can be grown by MBE. Many of the major breakthroughs in semiconductor physics, from quantum wells to quantum dots, owe their origin to MBE research.
MBE continues to drive interdisciplinary innovation in materials science, physics, and electrical engineering, among other fields. The purposes of this Special Issue are: (1) to catalog some of the key recent advances in the synthesis and applications of crystalline materials made possible by MBE; and (2) to provide an outline for the future directions of this indispensable growth technique. To this end, we encourage research contributions on epitaxial growth by MBE that cover a broad range of disciplines, material systems, and applications. Some suggested topics are included in the keywords below, but research in other areas is also of significant interest.

Dr. Paul J. Simmonds
Guest Editor

Manuscript Submission Information

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Keywords

  • Thin films, strained-layer superlattices, and low-dimensional heterostructures
  • Nanostructures and self-assembly
  • Functional materials
  • Dissimilar materials integration
  • Van der Waals epitaxy: 2D materials and topological insulators

Published Papers (9 papers)

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Research

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Open AccessArticle Optical Characterization of AlAsSb Digital Alloy and Random Alloy on GaSb
Crystals 2017, 7(10), 313; doi:10.3390/cryst7100313
Received: 9 September 2017 / Revised: 13 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been
[...] Read more.
III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been widely adopted in preference to conventional random alloy growth because of the extra degree of control offered by the ordered alloying. In this article, we provide a comparative study of the optical characteristics of AlAsSb alloys grown lattice-matched to GaSb using both techniques. The sample grown by digital alloy technique showed stronger photoluminescence intensity, narrower peak linewidth, and larger carrier activation energy than the random alloy technique, indicating an improved optical quality with lower density of non-radiative recombination centers. In addition, a relatively long carrier lifetime was observed from the digital alloy sample, consistent with the results obtained from the photoluminescence study. Full article
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Open AccessFeature PaperArticle Gas Source Techniques for Molecular Beam Epitaxy of Highly Mismatched Ge Alloys
Crystals 2016, 6(12), 159; doi:10.3390/cryst6120159
Received: 21 October 2016 / Revised: 19 November 2016 / Accepted: 21 November 2016 / Published: 2 December 2016
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Abstract
Ge and its alloys are attractive candidates for a laser compatible with silicon integrated circuits. Dilute germanium carbide (Ge1−xCx) offers a particularly interesting prospect. By using a precursor gas with a Ge4C core, C can be preferentially
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Ge and its alloys are attractive candidates for a laser compatible with silicon integrated circuits. Dilute germanium carbide (Ge1−xCx) offers a particularly interesting prospect. By using a precursor gas with a Ge4C core, C can be preferentially incorporated in substitutional sites, suppressing interstitial and C cluster defects. We present a method of reproducible and upscalable gas synthesis of tetrakis(germyl)methane, or (H3Ge)4C, followed by the design of a hybrid gas/solid-source molecular beam epitaxy system and subsequent growth of defect-free Ge1−xCx by molecular beam epitaxy (MBE). Secondary ion mass spectroscopy, transmission electron microscopy and contactless electroreflectance confirm the presence of carbon with very high crystal quality resulting in a decrease in the direct bandgap energy. This technique has broad applicability to growth of highly mismatched alloys by MBE. Full article
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Open AccessArticle Temperature-Dependent X-ray Diffraction Measurements of Infrared Superlattices Grown by MBE
Crystals 2016, 6(11), 150; doi:10.3390/cryst6110150
Received: 11 October 2016 / Revised: 14 November 2016 / Accepted: 15 November 2016 / Published: 17 November 2016
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Abstract
Strained-layer superlattices (SLSs) are an active research topic in the molecular beam epitaxy (MBE) and infrared focal plane array communities. These structures undergo a >500 K temperature change between deposition and operation. As a result, the lattice constants of the substrate and superlattice
[...] Read more.
Strained-layer superlattices (SLSs) are an active research topic in the molecular beam epitaxy (MBE) and infrared focal plane array communities. These structures undergo a >500 K temperature change between deposition and operation. As a result, the lattice constants of the substrate and superlattice are expected to change by approximately 0.3%, and at approximately the same rate. However, we present the first temperature-dependent X-ray diffraction (XRD) measurements of SLS material on GaSb and show that the superlattice does not contract in the same manner as the substrate. In both InAs/InAs0.65Sb0.35 and In0.8Ga0.2As/InAs0.65Sb0.35 SLS structures, the apparent out-of-plane strain states of the superlattices switch from tensile at deposition to compressive at operation. These changes have ramifications for material characterization, defect generation, carrier lifetime, and overall device performance of superlattices grown by MBE. Full article
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Open AccessArticle Interplay Effect of Excitation and Temperature on Carrier Transfer between Vertically Aligned InAs/GaAs Quantum Dot Pairs
Crystals 2016, 6(11), 144; doi:10.3390/cryst6110144
Received: 1 September 2016 / Revised: 7 November 2016 / Accepted: 8 November 2016 / Published: 10 November 2016
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Abstract
Carrier transfer in vertically-coupled InAs/GaAs quantum dot (QD) pairs is investigated. Photoluminescence (PL) and PL excitation spectra measured at low temperature indicate that the PL peak intensity ratio between the emission from the two sets of QDs—i.e., the relative population of carriers between
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Carrier transfer in vertically-coupled InAs/GaAs quantum dot (QD) pairs is investigated. Photoluminescence (PL) and PL excitation spectra measured at low temperature indicate that the PL peak intensity ratio between the emission from the two sets of QDs—i.e., the relative population of carriers between the two layers of QDs—changes with increasing excitation intensity. Temperature-dependent PL reveals unexpected non-monotonic variations in the peak wavelength and linewidth of the seed layer of QDs with temperature. The PL intensity ratio exhibits a “W” behavior with respect to the temperature due to the interplay between temperature and excitation intensity on the inter-layer carrier transfer. Full article
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Review

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Open AccessReview Brief Review of Epitaxy and Emission Properties of GaSb and Related Semiconductors
Crystals 2017, 7(11), 337; doi:10.3390/cryst7110337
Received: 31 August 2017 / Revised: 22 October 2017 / Accepted: 25 October 2017 / Published: 2 November 2017
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Abstract
Groups III–V semiconductors have received a great deal of attention because of their potential advantages for use in optoelectronic and electronic applications. Gallium antimonide (GaSb) and GaSb-related semiconductors, which exhibit high carrier mobility and a narrow band gap (0.725 eV at 300 K),
[...] Read more.
Groups III–V semiconductors have received a great deal of attention because of their potential advantages for use in optoelectronic and electronic applications. Gallium antimonide (GaSb) and GaSb-related semiconductors, which exhibit high carrier mobility and a narrow band gap (0.725 eV at 300 K), have been recognized as suitable candidates for high-performance optoelectronics in the mid-infrared range. However, the performances of the resulting devices are strongly dependent on the structural and emission properties of the materials. Enhancement of the crystal quality, adjustment of the alloy components, and improvement of the emission properties have therefore become the focus of research efforts toward GaSb semiconductors. Molecular beam epitaxy (MBE) is suitable for the large-scale production of GaSb, especially for high crystal quality and beneficial optical properties. We review the recent progress in the epitaxy of GaSb materials, including films and nanostructures composed of GaSb-related alloys and compounds. The emission properties of these materials and their relationships to the alloy components and material structures are also discussed. Specific examples are included to provide insight on the common general physical and optical properties and parameters involved in the synergistic epitaxy processes. In addition, the further directions for the epitaxy of GaSb materials are forecasted. Full article
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Open AccessReview Recent Advances on p-Type III-Nitride Nanowires by Molecular Beam Epitaxy
Crystals 2017, 7(9), 268; doi:10.3390/cryst7090268
Received: 18 August 2017 / Revised: 30 August 2017 / Accepted: 30 August 2017 / Published: 1 September 2017
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Abstract
p-Type doping represents a key step towards III-nitride (InN, GaN, AlN) optoelectronic devices. In the past, tremendous efforts have been devoted to obtaining high quality p-type III-nitrides, and extraordinary progress has been made in both materials and device aspects. In this
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p-Type doping represents a key step towards III-nitride (InN, GaN, AlN) optoelectronic devices. In the past, tremendous efforts have been devoted to obtaining high quality p-type III-nitrides, and extraordinary progress has been made in both materials and device aspects. In this article, we intend to discuss a small portion of these processes, focusing on the molecular beam epitaxy (MBE)-grown p-type InN and AlN—two bottleneck material systems that limit the development of III-nitride near-infrared and deep ultraviolet (UV) optoelectronic devices. We will show that by using MBE-grown nanowire structures, the long-lasting p-type doping challenges of InN and AlN can be largely addressed. New aspects of MBE growth of III-nitride nanostructures are also discussed. Full article
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Open AccessReview Novel Dilute Bismide, Epitaxy, Physical Properties and Device Application
Crystals 2017, 7(3), 63; doi:10.3390/cryst7030063
Received: 1 December 2016 / Revised: 2 February 2017 / Accepted: 15 February 2017 / Published: 24 February 2017
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Abstract
Dilute bismide in which a small amount of bismuth is incorporated to host III-Vs is the least studied III-V compound semiconductor and has received steadily increasing attention since 2000. In this paper, we review theoretical predictions of physical properties of bismide alloys, epitaxial
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Dilute bismide in which a small amount of bismuth is incorporated to host III-Vs is the least studied III-V compound semiconductor and has received steadily increasing attention since 2000. In this paper, we review theoretical predictions of physical properties of bismide alloys, epitaxial growth of bismide thin films and nanostructures, surface, structural, electric, transport and optic properties of various binaries and bismide alloys, and device applications. Full article
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Open AccessReview Topological Insulator Film Growth by Molecular Beam Epitaxy: A Review
Crystals 2016, 6(11), 154; doi:10.3390/cryst6110154
Received: 4 October 2016 / Revised: 16 November 2016 / Accepted: 18 November 2016 / Published: 23 November 2016
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Abstract
In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with
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In this article, we will review recent progress in the growth of topological insulator (TI) thin films by molecular beam epitaxy (MBE). The materials we focus on are the V2-VI3 family of TIs. These materials are ideally bulk insulating with surface states housing Dirac excitations which are spin-momentum locked. These surface states are interesting for fundamental physics studies (such as the search for Majorana fermions) as well as applications in spintronics and other fields. However, the majority of TI films and bulk crystals exhibit significant bulk conductivity, which obscures these states. In addition, many TI films have a high defect density. This review will discuss progress in reducing the bulk conductivity while increasing the crystal quality. We will describe in detail how growth parameters, substrate choice, and growth technique influence the resulting TI film properties for binary and ternary TIs. We then give an overview of progress in the growth of TI heterostructures. We close by discussing the bright future for TI film growth by MBE. Full article
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Other

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Open AccessLetter Formation of GaAs/GaSb Core-Shell Heterostructured Nanowires Grown by Molecular-Beam Epitaxy
Crystals 2017, 7(4), 94; doi:10.3390/cryst7040094
Received: 28 February 2017 / Revised: 21 March 2017 / Accepted: 22 March 2017 / Published: 24 March 2017
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Abstract
In this paper, we demonstrated the growth of GaAs/GaSb core-shell heterostructured nanowires on GaAs substrates, with the assistance of Au catalysts by molecular-beam epitaxy. Time-evolution experiments were designed to study the formation of GaSb shells with different growth times. It was found that,
[...] Read more.
In this paper, we demonstrated the growth of GaAs/GaSb core-shell heterostructured nanowires on GaAs substrates, with the assistance of Au catalysts by molecular-beam epitaxy. Time-evolution experiments were designed to study the formation of GaSb shells with different growth times. It was found that, by comparing the morphology of nanowires for various growth times, lateral growth was taking a dominant position since GaSb growth began and bulgy GaSb particles formed on the nanowire tips during the growth. The movement of catalyst Au droplets was witnessed, thus, the radial growth was enhanced by sidewall nucleation under the vapor-solid mechanism due to the lack of driving force for axial growth. Moreover, compositional and structural characteristics of the GaAs/GaSb core-shell heterostructured nanowires were investigated by electron microscopy. Differing from the commonly anticipated result, GaSb shells took a wurzite structure instead of a zinc-blende structure to form the GaAs/GaSb wurzite/wurzite core-shell heterostructured nanowires, which is of interest to the research of band-gap engineering. This study provides a significant insight into the formation of core-shell heterostructured nanowires. Full article
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