Ion-beam modification of metastable gallium oxide polymorphs
TL;DR: In this paper, structural changes under the action of Al+ irradiation have been investigated by X-ray diffraction for polymorphic Ga2O3 layers grown by halide vapor phase epitaxy on c-plane sapphire and consisting predominantly of α-phase with inclusions of e(κ)-phase.
About: This article is published in Materials Letters.The article was published on 2021-11-01 and is currently open access. It has received 11 citations till now. The article focuses on the topics: Ion beam & Phase (matter).
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TL;DR: In this paper , a single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated and a novel mode of lateral polymorphic regrowth was detected.
Abstract: Polymorphs are common in nature and can be stabilized by applying external pressure in materials. The pressure and strain can also be induced by the gradually accumulated radiation disorder. However, in semiconductors, the radiation disorder accumulation typically results in the amorphization instead of engaging polymorphism. By studying these phenomena in gallium oxide we found that the amorphization may be prominently suppressed by the monoclinic to orthorhombic phase transition. Utilizing this discovery, a highly oriented single-phase orthorhombic film on the top of the monoclinic gallium oxide substrate was fabricated. Exploring this system, a novel mode of the lateral polymorphic regrowth, not previously observed in solids, was detected. In combination, these data envisage a new direction of research on polymorphs in Ga_{2}O_{3} and, potentially, for similar polymorphic families in other materials.
25 citations
TL;DR: In this article , the effect of ion-beam-induced defect formation and physical characteristics of wide and ultra-wide bandgap semiconductors are studied and the mechanisms of ion induced defect formation are not well-studied and understood.
13 citations
TL;DR: In this paper , a detailed review of Ga 2 O 3 based power devices with detailed discussion on the basic parameters such as V br , R on and leakage current along with the factors critically affecting them is presented.
Abstract: Silicon based power devices have limited capabilities in terms of voltage handling and switching speeds, leading to rampant research in the field of next generation wide bandgap semiconductors like SiC, GaN, and Ga 2 O 3 . Amongst these, gallium oxide with its ultra-wide bandgap of 4.6-4.9 eV and high breakdown field (approx. 8 MV cm -1 ) turns out to be a potential replacement. Availability of large size, high-quality wafers at moderate costs make it desirable even from industrial viewpoint. Ga 2 O 3 power diodes having breakdown voltages (V br ) of hundreds of Volts have been reported. However, they suffer from very high on-resistance (R on ) leading to increased switching losses and decreased switching speed. This timely review analyses the recent progress made in Ga 2 O 3 based power devices with detailed discussion on the basic parameters such as V br , R on and leakage current along with the factors critically affecting them. Special focus is laid on the impeccable value-additive extreme environment applications. Open challenges plaguing the field such as trade-off between achieving high V br and low R on simultaneously, shortcomings in the material itself and the need for new physics to explain the high energy carrier transport is also explored along with the future prospects required to achieve true power-saving and commercialization. • Physics behind power device parameters and effect on the performance is explained. • Extensive outlook is provided on the current status of Ga 2 O 3 based power devices. • Effects of temperature, defects, growth methods on power devices are discussed. • High radiation hardness of Ga 2 O 3 and its extreme environmental uses are emphasized. • Open challenges and future prospects of Ga 2 O 3 based power devices are elucidated.
10 citations
TL;DR: In this paper , a hot-wall mist chemical vapor deposition (mist-CVD) method has been shown to be effective for the growth of pure α-and β-phase Ga2O3 thin films on the α-Al 2O3 substrate.
Abstract: Alpha (α)- and beta (β)-phase gallium oxide (Ga2O3), emerging as ultrawide-band gap semiconductors, have been paid a great deal of attention in optoelectronics and high-performance power semiconductor devices owing to their ultrawide band gap ranging from 4.4 to 5.3 eV. The hot-wall mist chemical vapor deposition (mist-CVD) method has been shown to be effective for the growth of pure α- and β-phase Ga2O3 thin films on the α-Al2O3 substrate. However, challenges to preserve their intrinsic properties at a critical growth temperature for robust applications still remain a concern. Here, we report a convenient route to grow a mixed α- and β-phase Ga2O3 ultrathin film on the α-Al2O3 substrate via mist-CVD using a mixture of the gallium precursor and oxygen gas at growth temperatures, ranging from 470 to 700 °C. The influence of growth temperature on the film characteristics was systematically investigated. The results revealed that the as-grown Ga2O3 film possesses a mixed α- and β-phase with an average value of dislocation density of 1010 cm–2 for all growth temperatures, indicating a high lattice mismatch between the film and the substrate. At 600 °C, the ultrathin and smooth Ga2O3 film exhibited a good surface roughness of 1.84 nm and an excellent optical band gap of 5.2 eV. The results here suggest that the mixed α- and β-phase Ga2O3 ultrathin film can have great potential in developing future high-power electronic devices.
9 citations
TL;DR: In this article , Halide Vapor Phase Epitaxy (HVPE) was used to grow very thick κ-Ga2O3 on GaN/sapphire templates.
Abstract: Thick (23 µm) films of κ-Ga2O3 were grown by Halide Vapor Phase Epitaxy (HVPE) on GaN/sapphire templates at 630 °C. X-ray analysis confirmed the formation of single-phase κ-Ga2O3 with half-widths of the high-resolution x-ray diffraction (004), (006), and (008) symmetric reflections of 4.5 arc min and asymmetric (027) reflection of 14 arc min. Orthorhombic κ-Ga2O3 polymorph formation was confirmed from analysis of the Kikuchi diffraction pattern in electron backscattering diffraction. Secondary electron imaging indicated a reasonably flat surface morphology with a few (area density ∼103 cm−2) approximately circular (diameter ∼50–100 µm) uncoalesced regions, containing κ-Ga2O3 columns with in-plane dimensions and a height of about 10 µm. Micro-cathodoluminescence (MCL) spectra showed a wide 2–3.5 eV band that could be deconvoluted into narrower bands peaked at 2.59, 2.66, 2.86, and 3.12 eV. Ni Schottky diodes prepared on the films showed good rectification but a high series resistance. The films had a thin near-surface region dominated by Ec − 0.7 eV deep centers and a deeper region (∼2 µm from the surface) dominated by shallow donors with concentrations of ≤1016 cm−3. Photocurrent and photocapacitance spectra showed the presence of deep compensating acceptors with optical ionization energies of ∼1.35 and 2.3 eV, the latter being close to the energy of one of the MCL bands. Deep level transient spectroscopy revealed deep traps with energies near 0.3, 0.6, 0.7, 0.8, and 1 eV from the conduction band edge. The results show the potential of HVPE to grow very thick κ-Ga2O3 on GaN/sapphire templates.
8 citations
References
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01 Jun 2010-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: SRIM as discussed by the authors is a software package concerning the stopping of ion/atom collisions, and individual interatomic potentials have been included for all ion and atom collisions in the SRIM package.
Abstract: SRIM is a software package concerning the S topping and R ange of I ons in M atter. Since its introduction in 1985, major upgrades are made about every six years. Currently, more than 700 scientific citations are made to SRIM every year. For SRIM-2010 , the following major improvements have been made: (1) About 2800 new experimental stopping powers were added to the database, increasing it to over 28,000 stopping values. (2) Improved corrections were made for the stopping of ions in compounds. (3) New heavy ion stopping calculations have led to significant improvements on SRIM stopping accuracy. (4) A self-contained SRIM module has been included to allow SRIM stopping and range values to be controlled and read by other software applications. (5) Individual interatomic potentials have been included for all ion/atom collisions, and these potentials are now included in the SRIM package. A full catalog of stopping power plots can be downloaded at www.SRIM.org . Over 500 plots show the accuracy of the stopping and ranges produced by SRIM along with 27,000 experimental data points. References to the citations which reported the experimental data are included.
6,906 citations
TL;DR: The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed in this article.
Abstract: Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics, solar blind UV photodetectors, solar cells, and sensors with capabilities beyond existing technologies due to its large bandgap. It is usually reported that there are five different polymorphs of Ga2O3, namely, the monoclinic (β-Ga2O3), rhombohedral (α), defective spinel (γ), cubic (δ), or orthorhombic (e) structures. Of these, the β-polymorph is the stable form under normal conditions and has been the most widely studied and utilized. Since melt growth techniques can be used to grow bulk crystals of β-GaO3, the cost of producing larger area, uniform substrates is potentially lower compared to the vapor growth techniques used to manufacture bulk crystals of GaN and SiC. The performance of technologically important high voltage rectifiers and enhancement-mode Metal-Oxide Field Effect Transistors benefit from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. However, the absence of clear demonstrations of p-type doping in Ga2O3, which may be a fundamental issue resulting from the band structure, makes it very difficult to simultaneously achieve low turn-on voltages and ultra-high breakdown. The purpose of this review is to summarize recent advances in the growth, processing, and device performance of the most widely studied polymorph, β-Ga2O3. The role of defects and impurities on the transport and optical properties of bulk, epitaxial, and nanostructures material, the difficulty in p-type doping, and the development of processing techniques like etching, contact formation, dielectrics for gate formation, and passivation are discussed. Areas where continued development is needed to fully exploit the properties of Ga2O3 are identified.
1,535 citations
TL;DR: In this paper, the volume expansivity, bulk modulus, and specific heat at constant volume are computed as a function of temperature within the quasi-harmonic approximation of the spinel structure.
Abstract: First-principles calculations are made for five Ga2O3 polymorphs. The structure of e-Ga2O3 with the space group Pna 21 (No. 33, orthorhombic), which is sometimes called κ-Ga2O3 in the literature, is consistent with experimental reports. The structure of γ-Ga2O3 is optimized within 14 inequivalent configurations of defective spinel structures. Phonon dispersion curves of four polymorphs are obtained. The volume expansivity, bulk modulus, and specific heat at constant volume are computed as a function of temperature within the quasi-harmonic approximation. The Helmholtz free energies of the polymorphs are thus compared. The expansivity shows a relationship of β
243 citations
TL;DR: In this paper, high-resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD) was carried out on Ga2O3 epilayers grown at low temperature (650 °C) by vapor phase epitaxy in order to investigate the real structure at the nanoscale.
Abstract: A comprehensive study by high-resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD) was carried out on Ga2O3 epilayers grown at low temperature (650 °C) by vapor phase epitaxy in order to investigate the real structure at the nanoscale. Initial XRD measurements showed that the films were of the so-called e phase; i.e. they exhibited hexagonal P63mc space group symmetry, characterized by disordered and partial occupation of the Ga sites. This work clarifies the crystal structure of Ga2O3 layers deposited at low temperature at the nanoscale: TEM investigation demonstrates that the Ga atoms and vacancies are not randomly distributed, but actually possess ordering, with (110)-twinned domains of 5–10 nm size. Each domain has orthorhombic structure with Pna21 space group symmetry, referred to as κ-Ga2O3. Further XRD analysis carried out on thicker samples (9–10 μm) confirmed this finding and provided refined structural parameters. The six (110)-type twinned ordered domains together – if the domain size falls below the actual resolution of the probing techniques – can be misinterpreted as the disordered structure with its P63mc space group symmetry usually referred to as e-Ga2O3 in the current literature. The crystal structure of these Ga2O3 layers consists of an ABAC oxygen close-packed stacking, where Ga atoms occupy octahedral and tetrahedral sites in between, forming two types of polyhedral layers parallel to (001). The edge-sharing octahedra and the corner-sharing tetrahedra form zig-zag ribbons along the [100] direction. Anti-phase boundaries are common inside the domains. The polar character of the structure is confirmed, in agreement with the characteristics of the Pna21 space group and previous observations.
193 citations
TL;DR: The crystal structure and ferroelectric properties of ε-Ga2O3 deposited by low-temperature MOCVD on (0001)-sapphire were investigated by single-crystal X-ray diffraction and the dynamic hysteresis measurement technique.
Abstract: The crystal structure and ferroelectric properties of e-Ga2O3 deposited by low-temperature MOCVD on (0001)-sapphire were investigated by single-crystal X-ray diffraction and the dynamic hysteresis measurement technique. A thorough investigation of this relatively unknown polymorph of Ga2O3 showed that it is composed of layers of both octahedrally and tetrahedrally coordinated Ga3+ sites, which appear to be occupied with a 66% probability. The refinement of the crystal structure in the noncentrosymmetric space group P63mc pointed out the presence of uncompensated electrical dipoles suggesting ferroelectric properties, which were finally demonstrated by independent measurements of the ferroelectric hysteresis. A clear epitaxial relation is observed with respect to the c-oriented sapphire substrate, with the Ga2O3 [10–10] direction being parallel to the Al2O3 direction [11–20], yielding a lattice mismatch of about 4.1%.
167 citations