- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Strain-Induced Metastable Phase Stabilization in Ga2O3 Thin Films
摘要： It is well known that metastable and transient structures in bulk can be stabilized in thin films via epitaxial strain (heteroepitaxy) and appropriate growth conditions that are often far from equilibrium. However, the mechanism of heteroepitaxy, particularly how the nominally unstable or metastable phase gets stabilized, remains largely unclear. This is especially intriguing for thin film Ga2O3, where multiple crystal phases may exist under varied growth conditions with spatial and dimensional constraints. Herein, the development and distribution of epitaxial strain at the Ga2O3/Al2O3 film-substrate interfaces is revealed down to the atomic resolution along different orientations, with an aberration-corrected scanning transmission electron microscope (STEM). Just a few layers of metastable α-Ga2O3 structure were found to accommodate the misfit strain in direct contact with the substrate. Following an epitaxial α-Ga2O3 structure of about couple unit cells, several layers (4~5) of transient phase appear as the intermediate structure to release the misfit strain. Subsequent to this transient crystal phase, the nominally unstable κ-Ga2O3 phase is stabilized as the major thin film phase form. We show that the epitaxial strain is gracefully accommodated by rearrangement of the oxygen polyhedra. When the structure is under large compressive strain, Ga3+ ions occupy only the oxygen octahedral sites to form a dense structure. With gradual release of the compressive strain, more and more Ga3+ ions occupy the oxygen tetrahedral sites, leading to volumetric expansion and the phase transformation. The structure of the transition phase is identified by high resolution electron microscopy (HREM) observation, complemented by the density functional theory (DFT) calculations. This study provides insights from the atomic scale and their implications for the design of functional thin film materials using epitaxial engineering.
关键词： κ-Ga2O3,misfit strain,α-Ga2O3,metastable phase,aberration-corrected scanning transmission electron microscopy
更新于2025-09-23 15:23:52
-
Temperature-Dependent Electrical Characteristics of β-Ga <sub/>2</sub> O <sub/>3</sub> Diodes with W Schottky Contacts up to 500°C
摘要： The development of thermally stable contacts capable of high temperature operation are necessary for Ga2O3 high power rectifiers. We have measured the electrical characteristics of sputter-deposited W Schottky contacts with Au overlayers for reducing sheet resistance on n-type Ga2O3 before and after device operation up to 500°C. Assuming thermionic emission is dominant, the extracted barrier height decreases with measurement temperature from 0.97 eV (25°C) to 0.39 eV (500°C) while showing little change from its initial value of 0.97 eV after cooling down from each respective operation temperature. The room temperature value is comparable to that obtained by determining the energy difference between binding energy of the Ga 3d core level and the valence band of the Ga2O3 when W is present, 0.80 ± 0.2 eV in this case. The Richardson constant was 54.05 A.cm?2.K?2 for W and the effective Schottky barrier height at zero bias (eφb0) was 0.92 eV from temperature-dependent current-voltage characteristics. The temperature coefficient for reverse breakdown voltage was 0.16 V/K for W/Au and 0.12 V/K for Ni/Au. The W-based contacts are more thermally stable than conventional Ni-based Schottkies on Ga2O3 but do show evidence of Ga migration through the contact after 500°C device operation.
关键词： electrical characteristics,thermal stability,high temperature operation,Ga2O3,Schottky contacts
更新于2025-09-23 15:23:52
-
Mechanism Behind the Easy Exfoliation of Ga <sub/>2</sub> O <sub/>3</sub> Ultra-Thin Film Along (100) Surface
摘要： The transparent wide band gap semiconductor β-Ga2O3 has gained wide attention due to its suitability to a wide range of applications. Despite not being a van der Waals material and having highly strong ionic bonding, the material can be mechanically cleaved and exfoliated easily along favorable surfaces to make ultra-thin layers and used in device fabrications. One of the interesting properties of this material is that thin layers preserve the pristine bulk-like electronic properties, which makes it even more promising for applications in power devices. However, very little is known about the mechanism why such ultra-thin film or even single bilayer exfoliation is favorable from the bulk. In this letter, we have explained the mechanism of such phenomenon by detailed analyses of different types of Ga–O bonding character. The protocol of methodology used and developed in this study can be utilized in general to understand bond breaking and forming of other complex materials as well. This understanding will give us a better control to fabricate thin film 2D devices.
关键词： density functional theory,bond energy,computational physics,2D Ga2O3,easy exfoliation,surface energy
更新于2025-09-23 15:23:52
-
Red-light Emission of Li-doped Ga2O3 One-dimensional Nanostructures and the Luminescence Mechanism
摘要： Li-doped Ga2O3 one-dimensional nanostructures were synthesized by thermal evaporation. The observation results of morphology show that there are plenty of one-dimensional nanostructures in the sample. Raman spectra of samples show excellent crystallinity and the Raman peaks of the Li-doped Ga2O3 have red-shifted compared to the “undoped” Ga2O3 in the low wavenumber section. Comparing the photoluminescence behavior of the two samples at room temperature, they were found to have blue light emission peaks, but the emission peak of Li-doped Ga2O3 is blue-shifted. Additionally, there is a strong red light emission peak centered at 692 nm in the spectrum of Li-doped Ga2O3.
关键词： Li-doped,Nanostructures,Photoluminescence,Ga2O3,Raman spectrum
更新于2025-09-23 15:23:52
-
Self-trapping and ordering of heavy holes in the wide band-gap semiconductor
摘要： Scanning tunneling microscopy (STM) has been utilized for imaging and manipulation of self-trapped holes on the surface of the wide band-gap semiconductor β-Ga2O3. A positively charged surface layer comprised of localized holes with 1013 cm?2 density has been observed for n-doped samples. We show that the surface layer can be populated by hole pumping from the STM tip. A transition between the glassy phase and ordered striped phase of self-trapped holes has also been observed. Our analysis indicates that the saturated two-dimensional density of self-trapped holes may be determined by balance of self-trapping and Coulomb repulsion energies.
关键词： β-Ga2O3,scanning tunneling microscopy,self-trapping,heavy holes,charge ordering,Wigner-Mott regime
更新于2025-09-23 15:23:52
-
Evaluation of Low-Temperature Saturation Velocity in β -(Al?Ga???)?O?/Ga?O? Modulation-Doped Field-Effect Transistors
摘要： We report on the high-field transport characteristics and saturation velocity in a modulation-doped β-(AlxGa1?x)2O3/Ga2O3 heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm2/V·s at room temperature to 1520 cm2/V·s at 50 K. The high electron mobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current–voltage measurements and small-signal radio frequency (RF) measurements. The measured velocity–field profile suggested a saturation velocity above 1.1 × 107 cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The current gain cutoff frequency (ft) and maximum oscillation frequency (fmax) showed significant increases from 4.0/11.8 GHz at room temperature to 17.4/40.8 GHz at 50 K for the device with gate length of LG = 0.61 μm. The analysis of the low temperature ft based on device simulations indicated a peak velocity of 1.2 × 107 cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in β-Ga2O3 make it a promising candidate for high-power and high-frequency device applications.
关键词： mobility,β-Ga2O3,modulation-doped field-effect transistor (MODFET),2-D electron gas (2DEG),saturation velocity,high breakdown field
更新于2025-09-23 15:22:29
-
An Overview of the Ultrawide Bandgap Ga2O3 Semiconductor-Based Schottky Barrier Diode for Power Electronics Application
摘要： Gallium oxide (Ga2O3) is a new semiconductor material which has the advantage of ultrawide bandgap, high breakdown electric field, and large Baliga’s figure of merit (BFOM), so it is a promising candidate for the next-generation high-power devices including Schottky barrier diode (SBD). In this paper, the basic physical properties of Ga2O3 semiconductor have been analyzed. And the recent investigations on the Ga2O3-based SBD have been reviewed. Meanwhile, various methods for improving the performances including breakdown voltage and on-resistance have been summarized and compared. Finally, the prospect of Ga2O3-based SBD for power electronics application has been analyzed.
关键词： Breakdown electric field,Baliga’s figure of merit,On-resistance,Ultrawide bandgap semiconductor,Gallium oxide (Ga2O3),Power device,Schottky barrier diode (SBD)
更新于2025-09-23 15:22:29
-
Puzzling robust 2D metallic conductivity in undoped β-Ga2O3 thin films
摘要： Here, we report the analogy of an extremely stable topological-like ultra-wide bandgap insulator, a solid that is a pure insulator in its bulk but has a metallic conductive surface, presenting a two-dimensional conductive channel at its surface that challenges our current thinking about semiconductor conductivity engineering. Nominally undoped epitaxial b-Ga2O3 thin films without any detectable defect (after a range of state-of-the-art techniques) showed the unexpectedly low resistivity of 3 × 10^-2 Ωcm which was found to be also resistant to high dose proton irradiation (2 MeV, 5 × 10^15 cm^-2 dose) and was largely invariant (metallic) over the phenomenal temperature range of 2 K up to 850 K. The unique resilience and stability of the electrical properties under thermal and highly ionizing radiation stressing, combined with the extended transparency range (thanks to the ultra-wide bandgap) and the already known toughness under high electrical field could open up new perspectives for use as expanded spectral range transparent electrodes (e.g., for UV harvesting solar cells or UV LEDs/lasers) and robust Ohmic contacts for use in extreme environments/applications and for novel optoelectronic and power device concepts.
关键词： Electron accumulation,Wide bandgap insulator,Transport properties,Ga2O3
更新于2025-09-23 15:22:29
-
Shallow and deep trap levels in X-ray irradiated β-Ga2O3: Mg
摘要： The results of the investigation of thermostimulated luminescence (TSL) and photoconductivity (PC) of the X-ray irradiated undoped and Mg2+ doped β-Ga2O3 single crystals are presented. Three low-temperature peaks at 116 K, 147 K and 165 K are observed on the TSL glow curves of undoped crystals. The high-temperature TSL peaks at 354 K and 385 K are dominant in Mg2+ doped crystals. The correlation between doping with Mg2+ ions and the local energy levels of the intrinsic structural defects of β-Ga2O3, which are responsible for the TSL peaks and PC, is established. The nature of TSL peaks and the appropriate photoconductivity excitation bands are discussed.
关键词： Photoconductivity,β-Ga2O3,Single crystal,Activation energy,Trap levels,Thermostimulated luminescence
更新于2025-09-23 15:22:29
-
Application of halide vapor phase epitaxy for the growth of ultra-wide band gap Ga <sub/>2</sub> O <sub/>3</sub>
摘要： Halide vapor phase epitaxy (HVPE) is widely used in the semiconductor industry for the growth of Si, GaAs, GaN, etc. HVPE is a non-organic chemical vapor deposition (CVD) technique, characterized by high quality growth of epitaxial layers with fast growth rate, which is versatile for the fabrication of both substrates and devices with wide applications. In this paper, we review the usage of HVPE for the growth and device applications of Ga2O3, with detailed discussions on a variety of technological aspects of HVPE. It is concluded that HVPE is a promising candidate for the epitaxy of large-area Ga2O3 substrates and for the fabrication of high power β-Ga2O3 devices.
关键词： halide vapor phase epitaxy,Schottky barrier diodes,epitaxy growth,Ga2O3
更新于2025-09-23 15:22:29