H2-induced changes in electrical conductance of β-Ga2O3 thin-film systems
TL;DR: In this article, the changes in conductance of polycrystalline, undoped β-Ga2O3 thin films in the temperature range of 400-650° C are described.
Abstract: H2-induced changes of electrical conductivity in polycrystalline, undoped β-Ga2O3 thin films in the temperature range of 400–650° C are described. The sheet conductance of these films depends reversibly, according to a power law σ□ ∼ p
1/3, on the partial pressure of hydrogen in the ambient atmosphere of the Ga2O3 film. A bulk vacancy mechanism is excluded by experiments and it is shown that the interaction is based on a surface effect. Changes in conductance are discussed to result from the formation of an accumulation layer due to chemisorption on the grain surfaces. Typical coverages are determined to be approximately 10−4 ML for pH2=0.05 bar and T=600° C. A possible explanation of the σ□ ∼ p
1/3 power law is provided.
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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, a review of β-Ga2O3 at the research level that spans from the material preparation through characterization to final devices is presented, including material preparation (bulk crystals, epi-layers, surfaces), an exploration of optical, electrical, thermal and mechanical properties, as well as device design / fabrication with resulted functionality suitable for different fields of applications.
Abstract: β-Ga2O3 is an emerging, ultra-wide bandgap (energy gap of 4.85 eV) transparent semiconducting oxide (TSO), which attracted recently much scientific and technological attention. Unique properties of that compound combined with its advanced development in growth and characterization place β-Ga2O3 in the frontline of future applications in electronics (Schottky barrier diodes, field-effect transistors), optoelectronics (solar- and visible-blind photodetectors, flame detectors, light emitting diodes), and sensing systems (gas sensors, nuclear radiation detectors). A capability of growing large bulk single crystals directly from the melt and epi-layers by a diversity of epitaxial techniques, as well as explored material properties and underlying physics, define a solid background for a device fabrication, which, indeed, has been boosted in recent years. This required, however, enormous efforts in different areas of science and technology that constitutes a chain linking together engineering, metrology and theory. The present review includes material preparation (bulk crystals, epi-layers, surfaces), an exploration of optical, electrical, thermal and mechanical properties, as well as device design / fabrication with resulted functionality suitable for different fields of applications. The review summarizes all of these aspects of β-Ga2O3 at the research level that spans from the material preparation through characterization to final devices.
242 citations
TL;DR: In this paper, the fundamental understanding of the semiconductor physics and chemistry of Ga2O3 in terms of electronic band structures, optical properties, and the chemistry of defects and impurity doping is provided.
Abstract: Gallium oxide (Ga2O3) is an emerging wide bandgap semiconductor that has attracted a large amount of interest due to its ultra-large bandgap of 4.8 eV, a high breakdown field of 8 MV/cm, and high thermal stability. These properties enable Ga2O3 a promising material for a large range of applications, such as high power electronic devices and solar-blind ultraviolet (UV) photodetectors. In the past few years, a significant process has been made for the growth of high-quality bulk crystals and thin films and device optimizations for power electronics and solar blind UV detection. However, many challenges remain, including the difficulty in p-type doping, a large density of unintentional electron carriers and defects/impurities, and issues with the device process (contact, dielectrics, and surface passivation), and so on. The purpose of this article is to provide a timely review on the fundamental understanding of the semiconductor physics and chemistry of Ga2O3 in terms of electronic band structures, optical properties, and chemistry of defects and impurity doping. Recent progress and perspectives on epitaxial thin film growth, chemical and physical properties of defects and impurities, p-type doping, and ternary alloys with In2O3 and Al2O3 will be discussed.
240 citations
TL;DR: Based on semi-empirical quantum-chemical calculations, the electronic band structure of β-Ga2O3 was presented and the formation and properties of oxygen vacancies were analyzed as discussed by the authors.
Abstract: Based on semiempirical quantum-chemical calculations, the electronic band structure of β-Ga2O3 is presented and the formation and properties of oxygen vacancies are analyzed. The equilibrium geometries and formation energies of neutral and doubly ionized vacancies were calculated. Using the calculated donor level positions of the vacancies, the high temperature n-type conduction is explained. The vacancy concentration is obtained by fitting to the experimental resistivity and electron mobility.
193 citations
TL;DR: In this paper, a Ga2O3-based gas sensor was used to detect O2 and CO gases in a working temperature range of 100-500°C with a peak response at 300-400°C for O2 gas and 200-400-degree C for CO gas.
Abstract: Gallium oxide nanowires were synthesized by a chemical thermal evaporation method using gallium metal as a source material. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterizations indicate that the obtained nanowires are well-crystallized single phase monoclinic Ga2O3. Multiple nanowire gas sensors were fabricated by dispensing the Ga2O3 nanowires on an interdigitated Pt-electrode. The Ga2O3 nanowire gas sensors show reversible response to O2 and CO gases in a working temperature range of 100–500 °C. A peak response is found at 300 °C for O2 gas and the peak response appears at 200 °C for CO gas. For both kinds of gases, the sensor response increases empirically with an increase of gas concentration. The results demonstrate the possibility of using the Ga2O3-based gas sensor at low working temperature field.
153 citations
References
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Book•
01 Jan 1972
1,443 citations
[...]
01 Jan 1973
TL;DR: The structure of the second edition of this handbook has not undergone any major changes; however, certain corrections and improvements have been made in the content of certain chapters.
Abstract: In the comparatively short amount of time since the publi- cation of the first edition of this handbook in 1969, the authors continued to work on the collection and treatment of data on oxide properties that have appeared in the literature. The numerous responses that we have received during this time have given in- disputable evidence of the value of such a reference book to scientists, production engineers, and instructors, and these com- ments have also provided grounds for publishing a new edition of this book. In preparing the second edition, the authors reviewed crit- ically the material in the first edition of the handbook, updated obsolete information, and added new material to certain chapters. Of major assistance in defining the scope of the revision were the comments of Prof. S. G. Tresvyatskii, Prof. A. I. Avgustinik, Prof. E. K. Keler, Prof. K. K. Strelov, Dr. A. N. Borisenko, Dr. D. S. Rutman, and many others, to whom the authors wish to ex- press their deep gratitude. The structure of the second edition of this handbook has not undergone any major changes; however, certain corrections and improvements have been made in the content of certain chapters.
1,333 citations
Book•
01 Jan 1989
TL;DR: Silicon Based Chemical Sensors as mentioned in this paper : Gas Sensors based on Semiconductor Powders are used for solid state chemical sensor applications, and they have been shown to be useful in many applications.
Abstract: Introduction. Solid State Background. Solid/Gas Interfaces. Solid/Liquid Interfaces. Catalysis Background. Membrane Background. Biosensor Principles. Principles of Chemfet Operation. Silicon Based Chemical Sensors. Thin Film Gas Sensors. SolidElectrolytes-Devices. Gas Sensors Based on Semiconductor Powders. Application of Solid State Chemical Sensors.
953 citations
789 citations
TL;DR: The crystal structure of β•Ga2O3 has been determined from single-crystal 3D x-ray diffraction data as mentioned in this paper, and the most probable space group to which the crystal belongs is C2h3-C2/m.
Abstract: The crystal structure of β‐Ga2O3 has been determined from single‐crystal three‐dimensional x‐ray diffraction data. The monoclinic crystal has cell dimensions a=12.23±0.02, b=3.04±0.01, c=5.80±0.01 A and β=103.7±0.3° as originally reported by Kohn, Katz, and Broder [Am. Mineral. 42, 398 (1957)]. There are 4 Ga2O3 in the unit cell. The most probable space group to which the crystal belongs is C2h3—C2/m; the atoms are in five sets of special positions 4i: (000, ½½0)±(x0z). There are two kinds of coordination for Ga3+ ions in this structure, namely tetrahedral and octahedral. Average interionic distances are: tetrahedral Ga–O, 1.83 A; octahedral Ga–O, 2.00 A; tetrahedron edge O–O, 3.02 A; and octahedron edge O–O, 2.84 A. Because of the reduced coordination of half of the metal ions, the density of β‐Ga2O3 is lower than that of α‐Ga2O3 which has the α‐corundum structure. Also the closest approach of two Ga3+ ions in β‐Ga2O3 is 3.04 A which is considerably larger than the closest approach of metal ions in the s...
732 citations