- NSF-PAR ID:
- 10339267
- Date Published:
- Journal Name:
- Applied Physics Reviews
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 1931-9401
- Page Range / eLocation ID:
- 011315
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Gallium oxide (Ga 2 O 3 ) and its most stable modification, monoclinic β-Ga 2 O 3 , is emerging as a primary material for power electronic devices, gas sensors and optical devices due to a high breakdown voltage, large bandgap, and optical transparency combined with electrical conductivity. Growth of β-Ga 2 O 3 is challenging and most methods require very high temperatures. Nanowires of β-Ga 2 O 3 have been investigated extensively as they might be advantageous for devices such as nanowire field effect transistors, and gas sensors benefiting from a large surface to volume ratio, among others. Here, we report a synthesis approach using a sulfide precursor (Ga 2 S 3 ), which requires relatively low substrate temperatures and short growth times to produce high-quality single crystalline β-Ga 2 O 3 nanowires in high yields. Even though Au- or Ag-rich nanoparticles are invariably observed at the nanowire tips, they merely serve as nucleation seeds while the nanowire growth proceeds via supply and local oxidation of gallium at the substrate interface. Absorption and cathodoluminescence spectroscopy on individual nanowires confirms a wide bandgap of 4.63 eV and strong luminescence with a maximum ∼2.7 eV. Determining the growth process, morphology, composition and optoelectronic properties on the single nanowire level is key to further application of the β-Ga 2 O 3 nanowires in electronic devices.more » « less
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In this paper, the short circuit ruggedness of Gallium Oxide (Ga 2 O 3 ) vertical FinFET is studied using Technology Computer-Aided-Design (TCAD) simulations. Ga 2 O 3 is an emerging ultra-wide bandgap material and Ga 2 O 3 vertical FinFET can achieve the normally-off operation for high voltage applications. Ga 2 O 3 has a relatively low thermal conductivity and, thus, it is critical to explore the design space of Ga 2 O 3 vertical FinFETs to achieve an acceptable short-circuit capability for power applications. In this study, appropriate TCAD models and parameters calibrated to experimental data are used. For the first time, the breakdown voltage simulation accuracy of Ga 2 O 3 vertical FinFETs is studied systematically. It is found that a background carrier generation rate between 10 5 cm −3 s −1 and 10 12 cm −3 s −1 is required in simulation to obtain correct results. The calibrated and robust setup is then used to study the short circuit withstand time (SCWT) of an 800 V-rated Ga 2 O 3 vertical FinFET with different inter-fin architectures. It is found that, due to the high thermal resistance in Ga 2 O 3 , to achieve an SCWT >1 μ s, low gate overdrive is needed which increases R on,sp by 66% and that Ga 2 O 3 might melt before the occurrence of thermal runaway. These results provide important guidance for developing rugged Ga 2 O 3 power transistors.more » « less
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Deep level defect states in β-, α-, and ɛ -Ga 2 O 3 crystals and films: Impact on device performance
A review is given of reported trap states in the bandgaps of different polymorphs of the emerging ultrawide bandgap semiconductor Ga2O3. The commonly observed defect levels span the entire bandgap range in the three stable (β) or meta-stable polymorphs (α and ɛ) and are assigned either to impurities such as Fe or to native defects and their complexes. In the latter case, the defects can occur during crystal growth or by exposure to radiation. Such crystalline defects can adversely affect material properties critical to device operation of transistors and photodetectors, including gain, optical output, threshold voltage by reducing carrier mobility, and effective carrier concentration. The trapping effects lead to degraded device operating speed and are characterized by long recovery transients. There is still significant work to be done to correlate experimental results based on deep level transient spectroscopy and related optical spectroscopy techniques to density functional theory and the dominant impurities present in the various synthesis methods to understand the microscopic nature of defects in Ga2O3.
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Abstract We report on the tunable and enhanced dielectric properties of tungsten (W) incorporated gallium oxide (Ga2O3) polycrystalline electroceramics for energy and power electronic device applications. The W‐incorporated Ga2O3(Ga2−2xWxO3, 0.00 ≤ x ≤ 0.20; GWO) compounds were synthesized by the high‐temperature solid‐state chemical reaction method by varying the W‐content. The fundamental aspects of the dielectric properties in correlation with the crystal structure, phase, and microstructure of the GWO polycrystalline compounds has been investigated in detail. A detailed study performed ascertains the W‐induced changes in the dielectric constant, loss tangent (tan
δ ) and ac conductivity. It was found that the dielectric constant increases with addition of W in the system as a function of temperature (25°C‐500°C). Frequency dependence (102‐106 Hz) of the dielectric constant follows the modified Debye model with a relaxation time of ∼20 to 90 μs and a spreading factor of 0.39 to 0.65. The dielectric constant of GWO is temperature independent almost until ∼300°C, and then increases rapidly in the range of 300°C to 500°C. W‐induced enhancement in the dielectric constant of GWO is fully evident in the frequency and temperature dependent dielectric studies. The frequency and temperature dependent tanδ reveals the typical behavior of relaxation loses in GWO. Small polaron hopping mechanism is evident in the frequency dependent electrical transport properties of GWO. The remarkable effect of W‐incorporation on the dielectric and electrical transport properties of Ga2O3is explained by a two‐layer heterogeneous model consisting of thick grains separated by very thin grain boundaries along with the formation of a Ga2O3‐WO3composite was able to account for the observed temperature and frequency dependent electrical properties in GWO. The results demonstrate that the structure, electrical and dielectric properties can be tailored by tuning W‐content in the GWO compounds. -
Gallium oxide (Ga2O3) is a highly promising ultrawide‐bandgap semiconductor for power electronics that emerged about a decade ago. Epitaxial growth Ga2O3at the small scale is demonstrated. In order to develop scalable manufacturing of high‐performance epitaxial structures, in‐depth understanding of the fundamental growth processes, control parameters, and mechanism is imperative. This review discusses the recent progress in epitaxial growth of β‐Ga2O3films and highlights challenges in obtaining high growth rate, low defects, and high carrier mobilities. Compared with the other epitaxy methods, metal–organic chemical vapor deposition (MOCVD) offers a wider growth window and precursor selection option, to minimize the tradeoff between crystal quality and growth rate. Growth rate is inversely proportional to temperature, within a certain temperature window, because of the unavoidable premature gas‐phase reactions and desorption of the highly volatile gallium suboxide (Ga2O) at elevated temperatures. Growth defects, background impurity incorporation, and carrier mobilities can be affected by the choice of MOCVD precursors, nucleation, and adsorption/desorption/diffusion of adatoms on substrate surfaces of different orientations, including the effect of growing on cleavage and noncleavage planes. This review summarizes the current status of the epitaxial growth of β‐Ga2O3and analyzes the major factors that enhance mobility and reduce background doping concentration. The insights gained help advance the manufacturability of device‐grade epitaxial thin films.