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In this work, we explored the growth regime of (100) β-Ga2O3 homoepitaxial films on substrates with different miscut angles (1°, 2°, and 4°) in the MOVPE system. Under a low O2/Ga ratio growth condition, step-flow growth of (100) β-Ga2O3 homoepitaxial films can be maintained up to 3 μm on substrates with different miscut angles. Moreover, the results reveal that the growth rate decreases slightly with decreasing miscut angles, which matches estimation of the Burton–Cabrera–Frank theory and can be explained by the model of adsorption–desorption. By comparing the miscut-dependent growth rates, we give experimental evidence on the fundamental difference between the growth of (100) β-Ga2O3 films by MOVPE and MBE. In addition, a transport model is proposed to explain the desorption process in terms of the boundary layer and the kinetic resistance. [ABSTRACT FROM AUTHOR]

In this study, in situ synchrotron x-ray diffraction was used to investigate a high-temperature phase transition in tensile-strained epitaxial NaNbO3/(110)DyScO3 films. A ferro-to-ferroelectric phase transition was found in the temperature range between 230 and 350 °C, with a very pronounced thermal hysteresis. While at room temperature the well known monoclinic a1a2 in-plane ferroelectric phase is present, here, a slightly disturbed orthorhombic ferroelectric a1/a2 phase with exclusive in-plane polarization was found at high temperatures. This phase appeared in four variants, indicating the occurrence of four types of superdomains. The orthorhombic symmetry and the corresponding domain morphology observed at high temperatures showed a striking similarity to K0.9Na0.1NbO3 thin films grown on a (110) NdScO3 substrate. [ABSTRACT FROM AUTHOR]

This work investigated the metalorganic vapor-phase epitaxy (MOVPE) of (100) β-Ga2O3 films with the aim of meeting the requirements to act as drift layers for high-power electronic devices. A height-adjustable showerhead achieving a close distance to the susceptor (1.5 cm) was demonstrated to be a critical factor in increasing the stability of the Ga wetting layer (or Ga adlayer) on the surface and reducing parasitic particles. A film thickness of up to 3 μm has been achieved while keeping the root mean square below 0.7 nm. Record carrier mobilities of 155 cm2 V−1 s−1 (2.2 μm) and 163 cm2 V−1 s−1 (3 μm) at room temperature were measured for (100) β-Ga2O3 films with carrier concentrations of 5.7 × 1016 and 7.1 × 1016 cm−3, respectively. Analysis of temperature-dependent Hall mobility and carrier concentration data revealed a low background compensating acceptor concentration of 4 × 1015 cm−3. [ABSTRACT FROM AUTHOR]

Beta gallium oxide (β-Ga2O3) is a promising ultra-wide bandgap semiconductor with attractive physical properties for next-generation high-power devices, radio frequency electronics, and solar-blind ultraviolet radiation detectors. Here, we present an overview and perspective on the development of MOVPE-grown (100) β-Ga2O3 thin films and its role in supplementing high-power electronics. We review the development path of the growth process on (100) β-Ga2O3 thin films with a discussion regarding the solved and remaining challenges. The structural defect formation mechanism, substrate treatment strategies, and different growth windows are analyzed to optimize the grown film to fulfill the requirements for device fabrication. Toward industrial applications, MOVPE-grown β-Ga2O3 thin films are evaluated in two aspects: thick layers with smooth surface roughness and the electrical properties in terms of high carrier mobility and low doping concentration. Based on the reviewed results, we propose strategies in substrate preparation treatments and supportive tools such as the machine learning approaches for future growth process optimization and envision the rising interest of the β-Ga2O3-related alloy, β-(AlxGa1−x)2O3. [ABSTRACT FROM AUTHOR]

Here, we investigate the effect of post-metallization anneal temperature on Ti/Au ohmic contact performance for (100)-oriented Ga2O3. A low contact resistance of ∼2.49 × 10−5 Ω·cm2 is achieved at an optimal anneal temperature of ∼420 °C for (100) Ga2O3. This is lower than the widely-used temperature of 470 °C for (010)-oriented Ga2O3. However, drastic degradation of the (100)-oriented contact resistance to ∼1.36 × 10−3 Ω·cm2 is observed when the anneal temperature was increased to 520 °C. Microscopy at the degraded ohmic contact revealed that the reacted Ti–TiOx interfacial layer has greatly expanded to 25–30 nm thickness and GaAu2 inclusions have formed between (310)-Ga2O3 planes and the Ti–TiOx layer. This degraded interface, which corresponds to the deterioration of ohmic contact properties, likely results from excess in-diffusion of Au and out-diffusion of Ga, concurrent with the expansion of the Ti–TiOx layer. These results demonstrate the critical influence of Ga2O3 anisotropy on the optimal post-metallization anneal temperature. Moreover, the observed Ti/Au contact degradation occurs for relatively moderate anneal conditions (520 °C for 1 min in N2), pointing to the urgent necessity of developing alternative metallization schemes for gallium oxide, including the use of Au-free electrodes. [ABSTRACT FROM AUTHOR]

A Langmuir adsorption model of the Si incorporation mechanism into metalorganic vapor-phase epitaxy grown (100) β-Ga2O3 thin films is proposed in terms of the competitive surface adsorption process between Si and Ga atoms. The outcome of the model can describe the major feature of the doping process and indicate a growth rate-dependent doping behavior, which is validated experimentally and further generalized to different growth conditions and different substrate orientations. [ABSTRACT FROM AUTHOR]

Two inch diameter, highly conducting (Si-doped) bulk β-Ga2O3 single crystals with the cylinder length up to one inch were grown by the Czochralski method. The obtained crystals revealed high structural quality characterized by narrow x-ray rocking curves (FWHM ≤ 25 arc sec) and high surface smoothness (RMS < 200 pm) of the epi-ready wafers. The free electron concentration and Hall mobility at room temperature were in the range of 1.6–9 × 1018 cm−3 and 118 – 52 cm2 V−1 s−1, respectively, which are not affected by a heat treatment at temperatures up to 1000 °C in an oxidizing atmosphere. Temperature-dependent electrical properties of the crystals revealed a degenerated semiconducting state. Both high structural quality and electrical properties make the crystals well suited as substrates for homoepitaxy and electronic device fabrication in the vertical configuration. [ABSTRACT FROM AUTHOR]

A high growth rate process above 1 µm/h was achieved for Si-doped (100) β-Ga2O3 homoepitaxial films grown via metalorganic vapor phase epitaxy (MOVPE) while maintaining high crystalline perfection up to a film thickness of 3 µm. The main growth parameters were investigated to increase the growth rate and maintain the step-flow growth mode, wherein the enhanced diffusion channel due to the formation of a Ga adlayer was proposed to be the possible growth mechanism. Si doping allowed precise control of the n-type conductivity of the films with electron concentrations ranging from 1.5 × 1017 to 1.5 × 1019 cm−3 and corresponding mobilities from 144 to 21 cm2 V−1 s−1, as revealed by Hall effect measurements at room temperature. Secondary ion mass spectrometry confirmed homogeneous Si doping through the film and a one-to-one correlation between the Si concentration and the electron concentration. Low defect density in the films was determined by x-ray diffraction measurements. The demonstration of a high growth rate process of β-Ga2O3 films with μm level thickness and smooth surface morphology via MOVPE is critical for high power electronics with vertical device architecture. [ABSTRACT FROM AUTHOR]

In this work, we train a hybrid deep-learning model (fDNN, Forest Deep Neural Network) to predict the doping level measured from the Hall Effect measurement at room temperature and to investigate the doping behavior of Si dopant in both (100) and (010) β-Ga2O3 thin film grown by the metalorganic vapor phase epitaxy (MOVPE). The model reveals that a hidden parameter, the Si supplied per nm (mol/nm), has a dominant influence on the doping process compared with other process parameters. An empirical relation is concluded from this model to estimate the doping level of the grown film with the Si supplied per nm (mol/nm) as the primary variable for both (100) and (010) β-Ga2O3 thin film. The outcome of the work indicates the similarity between the doping behavior of (100) and (010) β-Ga2O3 thin film via MOVPE and the generality of the results to different deposition systems. [ABSTRACT FROM AUTHOR]

Epitaxially strained NaNbO3 films were grown by liquid-delivery spin metal-organic chemical vapour deposition on several oxide substrates, inducing tensile and compressive lattice strain. High-resolution X-ray diffraction measurements reveal that coherently grown compressively strained NaNbO3 films on NdGaO3 exhibit the orthorhombic c phase. With increasing in-plane strain a first structural phase transition to the monoclinic r phase and, further on, for films grown under tensile strain on rare earth scandates, a second phase transition to the aa phase, are observed. Our results are in good agreement with the pathway of phase transitions predicted by Diéguez, Rabe & Vanderbilt [ Phys. Rev. B, (2005), 72, 144101] for NaNbO3 films. [ABSTRACT FROM AUTHOR]

The dielectric function and interband critical points of compressively strained ferroelectric K 0.85 Na 0.15 NbO 3 thin film grown by metal-organic vapor phase epitaxy (MOVPE) are studied in broad spectral and temperature ranges by spectroscopic ellipsometry (SE). The temperature dependence of the measured pseudodielectric functions is strongly affected by a structural phase transition from the monoclinic M c -phase to the orthorhombic c-phase at about 428 K. Using a parametric optical constant model, the corresponding dielectric functions as well as the interband optical transitions of the film are determined in the spectral range of 0.73-6.00 eV. Standard critical point (SCP) analysis of the 2 nd derivatives of the dielectric functions identified three and four critical points for monoclinic and orthorhombic symmetries, respectively. A systematic redshift of the threshold energies with increasing temperatures was observed.