Growth Pressure Controlled Nucleation Epitaxy of Pure Phase ε- and β-Ga2O3 Films on Al2O3 via Metal–Organic Chemical Vapor Deposition (original) (raw)
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ACS Omega
Alpha (α)-and beta (β)-phase gallium oxide (Ga 2 O 3), emerging as ultrawideband 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 αand β-phase Ga 2 O 3 thin films on the α-Al 2 O 3 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 αand β-phase Ga 2 O 3 ultrathin film on the α-Al 2 O 3 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 Ga 2 O 3 film possesses a mixed αand β-phase with an average value of dislocation density of 10 10 cm −2 for all growth temperatures, indicating a high lattice mismatch between the film and the substrate. At 600°C , the ultrathin and smooth Ga 2 O 3 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 αand β-phase Ga 2 O 3 ultrathin film can have great potential in developing future high-power electronic devices.
Thin Solid Films, 2020
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Experimental and Theoretical Validation of Ga2O3 Thin Films Deposited by Physical Vapor Deposition
2019 International Semiconductor Conference (CAS), 2019
In this work, we have shown that betagallium oxide (Ga2O3) thin films of differing thickness could be obtained by physical vapor deposition method, employing proper annealing conditions. These enable us to compare the variation of optical properties like transparency, band gap in these phases. Apart from these, our analysis of transmittance spectra of beta-Ga2O3 indicated the reduction of structural disorders (amorphous to crystalline) with increase in annealing temperature. The calculated band gap based on Density Functional Theory (DFT) for bulk beta-Ga2O3 thin films ~ 4.9 eV (direct) at room temperature is in excellent agreement with our experimentally measured values. This work will serve as design guidance for the new Ga2O3 based thin film electronics.
Chemical Vapor Deposition of Ga2O3 Thin Films on Si Substrates
Bulletin of The Korean Chemical Society, 2002
Amorphous Ga 2 O 3 films have been grown on Si(100) substrates by metal organic chemical vapor deposition (MOCVD) using gallium isopropoxide, Ga(O i Pr) 3 , as single precursor. Deposition was carried out in the substrate temperature range 400-800 °C. X-ray photoelectron spectroscopy (XPS) analysis revealed deposition of stoichiometric Ga 2 O 3 thin films at 500-600 °C. XPS depth profiling by Ar + ion sputtering indicated that carbon contamination exists mostly in the surface region with less than 3.5% content in the film. Microscopic images of the films by scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed formation of grains of approximately 20-40 nm in size on the film surfaces. The root-mean-square surface roughness from an AFM image was ∼10 A. The interfacial layer of the Ga 2 O 3 /Si was measured to be ∼35 A thick by cross-sectional transmission electron microscopy (TEM). From the analysis of gaseous products of the CVD reaction by gas chromatography-m...
Low temperature Ga2O3 atomic layer deposition using gallium tri-isopropoxide and water
Thin Solid Films, 2013
Ga 2 O 3 atomic layer deposition (ALD) was carried out using gallium tri-isopropoxide (GTIP) as a gallium source and H 2 O as an oxygen source at a low temperature (150°C). The Ga 2 O 3 ALD films show amorphous, smooth, and transparent behavior. The growth behavior and a variety of optical, structural, and electrical properties were investigated by various measurements. The growth behavior of Ga 2 O 3 ALD using GTIP reveals a typical ALD process, and Ga 2 O 3 films on glass substrates show outstanding transmittance (over 90%). The Ga:O ratio was measured as 1:1.7 by the Rutherford backscattering spectrometry, and auger electron spectroscopy confirmed that there was no carbon impurity (under the detection limit). The surface morphology was investigated through an atomic force microscope analysis, and all of the films deposited at 150, 200, and 250°C showed smooth and featureless characteristics. Ga 2 O 3 ALD thin film shows excellent leakage current (1 × 10 −11 A at 1 MV/cm) and a very suitable breakdown field (6.5-7.6 MV/cm) as compared to previously reported Ga 2 O 3 films. Also, the dielectric constant of the films is similar to that of conventional Ga 2 O 3 films (about 9.23).
Homoepitaxial growth of β-Ga2O3layers by metal-organic vapor phase epitaxy
physica status solidi (a), 2013
Epitaxial b-Ga 2 O 3 layers have been grown on b-Ga 2 O 3 (100) substrates using metal-organic vapor phase epitaxy. Trimethylgallium and pure oxygen or water were used as precursors for gallium and oxygen, respectively. By using pure oxygen as oxidant, we obtained nano-crystals in form of wires or agglomerates although the growth parameters were varied in wide range. With water as an oxidant, smooth homoepitaxial b-Ga 2 O 3 layers were obtained under suitable conditions. Based on thermodynamical considerations of the gas phase and published ab initio data on the catalytic action of the (100) surface of b-Ga 2 O 3 we discuss the adsorption and incorporation processes that promote epitaxial layer growth. The structural properties of the b-Ga 2 O 3 epitaxial layers were characterized by X-ray diffraction pattern and high resolution transmission electron microscopy. As-grown layers exhibited sharp peaks that were assigned to the monocline gallium oxide phase and odd reflections that could be assigned to stacking faults and twin boundaries, also confirmed by TEM. Shifts of the layer peak towards smaller 2u values with respect to the Bragg reflection for the bulk peaks have been observed. After post growth thermal treatment in oxygen-containing atmosphere the reflections of the layers do shift back to the position of the bulk b-Ga 2 O 3 peaks, which was attributed to significant reduction of lattice defects in the grown layers after thermal treatment.
Nanomedicine & nanotechnology open access, 2021
The structure, morphology and optical properties of β-Ga 2 O 3 thin films grown on GaN at various substrate temperature by ozone molecular beam epitaxy (MBE) are investigated in this work. (-201)-oriented β-Ga 2 O 3 thin films are formed on c-plane GaN template substrate. When the substrate temperature increases, the crystal quality of β-Ga 2 O 3 thin film improves, and a high-crystalline-quality β-Ga 2 O 3 thin film is obtained at the substrate temperature of 700 °C. The Φ scans of X-ray diffraction is utilized to characterize the β-Ga 2 O 3 thin film, from the result we find that the β-Ga 2 O 3 thin film has a six-fold domain structure, attributed to the epitaxial relationships (β-Ga 2 O 3 [010] // GaN [11-20] and β-Ga 2 O 3 [102] // GaN [1-100]). Base on the morphology, it can be seen that the β-Ga2O3 thin film follows the island-growth model, and the size of the island increases as the substrate temperature increases. Furthermore, it is found that the defect related luminescence decreases with the increase of substrate temperature by analyzing the CL spectra, implying the improvement of crystal quality. The presented optimized β-Ga2O3 thin film grown on GaN template substrate should effectively promote the development of high reliable performance self-powered ultraviolet (UV) photodetector based on the Ga2O3/GaN heterojunction.
Fast growth rate of epitaxial β–Ga2O3 by close coupled showerhead MOCVD
Journal of Crystal Growth, 2017
We report on the growth of epitaxial Ga 2 O 3 thin films on c-plane sapphire substrates using a close coupled showerhead MOCVD reactor. Ga(DPM) 3 (DPM=dipivaloylmethanate), triethylgallium (TEGa) and trimethylgallium (TMGa) metal organic (MO) precursors were used as Ga sources and molecular oxygen was used for oxidation. Films grown from each of the Ga sources had high growth rates, with up to 10 m/hr achieved using a TMGa precursor at a substrate temperature of 900 ºC. As confirmed by X-ray diffraction, the films grown from each of the Ga sources were the monoclinic (01) oriented Ga 2 O 3 phase. The optical bandgap of the films was also estimated to be ~ 4.9 eV. The fast growth rate of Ga 2 O 3 thin films obtained using various Ga-precursors has been achieved due to the close couple showerhead design of the MOCVD reactor as well as the separate injection of oxygen and MO precursors, preventing the premature oxidation of the MO sources. These results suggest a pathway to overcoming the long-standing challenge of realizing fast growth rates for Ga 2 O 3 using the MOCVD method.
Epitaxial growth of β-Ga2O3 by hot-wall MOCVD
AIP Advances
The hot-wall metalorganic chemical vapor deposition (MOCVD) concept, previously shown to enable superior material quality and high performance devices based on wide bandgap semiconductors, such as Ga(Al)N and SiC, has been applied to the epitaxial growth of β-Ga2O3. Epitaxial β-Ga2O3 layers at high growth rates (above 1 μm/h), at low reagent flows, and at reduced growth temperatures (740 °C) are demonstrated. A high crystalline quality epitaxial material on a c-plane sapphire substrate is attained as corroborated by a combination of x-ray diffraction, high-resolution scanning transmission electron microscopy, and spectroscopic ellipsometry measurements. The hot-wall MOCVD process is transferred to homoepitaxy, and single-crystalline homoepitaxial β-Ga2O3 layers are demonstrated with a [Formula: see text]01 rocking curve width of 118 arc sec, which is comparable to those of the edge-defined film-fed grown ([Formula: see text]01) β-Ga2O3 substrates, indicative of similar dislocation d...
Point and extended defects in heteroepitaxial β−Ga2O3 films
Physical Review Materials, 2020
Ga 2 O 3 is emerging as an excellent potential semiconductor for high power and optoelectronic devices. However, the successful development of Ga 2 O 3 in a wide range of applications requires a full understanding of the role and nature of its point and extended defects. In this work, high quality epitaxial Ga 2 O 3 films were grown on sapphire substrates by metal-organic chemical vapor deposition and fully characterized in terms of structural, optical, and electrical properties. Then defects in the films were investigated by a combination of depth-resolved Doppler broadening and lifetime of positron annihilation spectroscopies and thermally stimulated emission (TSE). Positron annihilation techniques can provide information about the nature and concentration of defects in the films, while TSE reveals the energy level of defects in the bandgap. Despite very good structural properties, the films exhibit short positron diffusion length, which is an indication of high defect density and long positron lifetime, a sign for the formation of Ga vacancy related defects and large vacancy clusters. These defects act as deep and shallow traps for charge carriers as revealed from TSE, which explains the reason behind the difficulty of developing conductive Ga 2 O 3 films on non-native substrates. Positron lifetime measurements also show nonuniform distribution of vacancy clusters throughout the film depth. Further, the work investigates the modification of defect nature and properties through thermal treatment in various environments. It demonstrates the sensitivity of Ga 2 O 3 microstructures to the growth and thermal treatment environments and the significant effect of modifying defect structure on the bandgap and optical and electrical properties of Ga 2 O 3 .