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We report on the growth of Si-doped homoepitaxial β-Ga2O3 thin films on (010) Ga2O3 substrates via metal-organic chemical vapor deposition (MOCVD) utilizing triethylgallium (TEGa) and trimethylgallium (TMGa) precursors. The epitaxial growth achieved an impressive 9.5 μm thickness at 3 μm/h using TMGa, a significant advance in material growth for electronic device fabrication. This paper systematically studies the Schottky barrier diodes fabricated on the three MOCVD-grown films, each exhibiting variations in the epilayer thickness, doping levels, and growth rates. The diode from the 2 μm thick Ga2O3 epilayer with TEGa precursor demonstrates promising forward current densities, the lowest specific on-resistance, and the lowest ideality factor, endorsing TEGa's potential for MOCVD growth. Conversely, the diode from the 9.5 μm thick Ga2O3 layer with TMGa precursor exhibits excellent characteristics in terms of lowest leakage current, highest on-off ratio, and highest reverse breakdown voltage of −510 V without any electric field management, emphasizing TMGa's suitability for achieving high growth rates in Ga2O3 epilayers for vertical power electronic devices. [ABSTRACT FROM AUTHOR]

β-phase gallium oxide (Ga2O3) is an emerging ultrawide bandgap (UWBG) semiconductor with a bandgap energy of ∼ 4.8 eV and a predicted high critical electric field strength of ∼8 MV/cm, enabling promising applications in next generation high power electronics and deep ultraviolet optoelectronics. The advantages of Ga2O3 also stem from its availability of single crystal bulk native substrates synthesized from melt, and its well-controllable n-type doping from both bulk growth and thin film epitaxy. Among several thin film growth methods, metalorganic chemical vapor deposition (MOCVD) has been demonstrated as an enabling technology for developing high-quality epitaxy of Ga2O3 thin films, (AlxGa1−x)2O3 alloys, and heterostructures along various crystal orientations and with different phases. This tutorial summarizes the recent progresses in the epitaxial growth of β-Ga2O3 thin films via different growth methods, with a focus on the growth of Ga2O3 and its compositional alloys by MOCVD. The challenges for the epitaxial development of β-Ga2O3 are discussed, along with the opportunities of future works to enhance the state-of-the-art device performance based on this emerging UWBG semiconductor material system. [ABSTRACT FROM AUTHOR]

The in situ metalorganic chemical vapor deposition (MOCVD) growth of Al2O3 dielectrics on β-Ga2O3 and β-(AlxGa1−x)2O3 films is investigated as a function of crystal orientations and Al compositions of β-(AlxGa1−x)2O3 films. The interface and film qualities of Al2O3 dielectrics are evaluated by high-resolution x-ray diffraction and scanning transmission electron microscopy imaging, which indicate the growth of high-quality amorphous Al2O3 dielectrics with abrupt interfaces on (010), (100), and ( 2 ¯ 01) oriented β-(AlxGa1−x)2O3 films. The surface stoichiometries of Al2O3 deposited on all orientations of β-(AlxGa1−x)2O3 are found to be well maintained with a bandgap energy of 6.91 eV as evaluated by high-resolution x-ray photoelectron spectroscopy, which is consistent with the atomic layer deposited (ALD) Al2O3 dielectrics. The evolution of band offsets at both in situ MOCVD and ex situ ALD deposited Al2O3/β-(AlxGa1−x)2O3 is determined as a function of Al composition, indicating the influence of the deposition method, orientation, and Al composition of β-(AlxGa1−x)2O3 films on resulting band alignments. Type II band alignments are determined at the MOCVD grown Al2O3/β-(AlxGa1−x)2O3 interfaces for the (010) and (100) orientations, whereas type I band alignments with relatively low conduction band offsets are observed along the ( 2 ¯ 01) orientation. The results from this study on MOCVD growth and band offsets of amorphous Al2O3 deposited on differently oriented β-Ga2O3 and β-(AlxGa1−x)2O3 films will potentially contribute to the design and fabrication of future high-performance β-Ga2O3 and β-(AlxGa1−x)2O3 based transistors using MOCVD in situ deposited Al2O3 as a gate dielectric. [ABSTRACT FROM AUTHOR]

Growths of monoclinic (AlxGa1−x)2O3 thin films up to 99% Al contents are demonstrated via metalorganic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa) as the Ga precursor. The utilization of TMGa, rather than triethylgallium, enables a significant improvement of the growth rates (>2.5 μm h−1) of β‐(AlxGa1−x)2O3 thin films on (010), (100), and (2¯01) β‐Ga2O3 substrates. By systematically tuning the precursor molar flow rates, growth of coherently strained phase pure β‐(AlxGa1−x)2O3 films is demonstrated by comprehensive material characterizations via high‐resolution X‐ray diffraction (XRD) and atomic‐resolution scanning transmission electron microscopy (STEM) imaging. Monoclinic (AlxGa1−x)2O3 films with Al contents up to 99, 29, and 16% are achieved on (100), (010), and (2¯01) β‐Ga2O3 substrates, respectively. Beyond 29% of Al incorporation, the (010) (AlxGa1−x)2O3 films exhibit β‐ to γ‐phase segregation. β‐(AlxGa1−x)2O3 films grown on (2¯01) β‐Ga2O3 show local segregation of Al along (100) plane. Record‐high Al incorporations up to 99% in monoclinic (AlxGa1−x)2O3 grown on (100) Ga2O3 are confirmed from XRD, STEM, electron nanodiffraction, and X‐ray photoelectron spectroscopy measurements. These results indicate great promises of MOCVD development of β‐(AlxGa1−x)2O3 films and heterostructures with high Al content and growth rates using TMGa for next‐generation high‐power and high‐frequency electronic devices. [ABSTRACT FROM AUTHOR]

In this Letter, the role of background carbon in metalorganic chemical vapor deposition (MOCVD) β-Ga2O3 growth using trimethylgallium (TMGa) as the Ga precursor was investigated. The quantitative C and H incorporations in MOCVD β-Ga2O3 thin films grown at different growth rates and temperatures were measured via quantitative secondary ion mass spectroscopy (SIMS). The SIMS results revealed both [C] and [H] increase as the TMGa molar flow rate/growth rate increases or growth temperature decreases. The intentional Si incorporation in MOCVD β-Ga2O3 thin films decreases as the growth rate increases or the growth temperature decreases. For films grown at relatively fast growth rates (GRs) (TMGa > 58 μmol/min, GR > 2.8 μm/h) or relatively low temperature (<950 °C), the [C] increases faster than that of the [H]. The experimental results from this study demonstrate the previously predicted theory—H can effectively passivate the compensation effect of C in n-type β-Ga2O3. The extracted net doping concentration from quantitative SIMS {[Si]-([C]-[H])} agrees well with the free carrier concentration measured from Hall measurement. The revealing of the role of C compensation in MOCVD β-Ga2O3 and the effect of H incorporation will provide guidance on designing material synthesis for targeted device applications. [ABSTRACT FROM AUTHOR]

Phase pure β-(AlxGa1−x)2O3 thin films are grown on (001) oriented β-Ga2O3 substrates via metalorganic chemical vapor deposition. By systematically tuning the precursor molar flow rates, the epitaxial growth of coherently strained β-(AlxGa1−x)2O3 films is demonstrated with up to 25% Al compositions as evaluated by high resolution x-ray diffraction. The asymmetrical reciprocal space mapping confirms the growth of coherent β-(AlxGa1−x)2O3 films (x < 25%) on (001) β-Ga2O3 substrates. However, the alloy inhomogeneity with local segregation of Al along the ( 2 ̄ 01) plane is observed from atomic resolution STEM imaging, resulting in wavy and inhomogeneous interfaces in the β-(AlxGa1−x)2O3/β-Ga2O3 superlattice structure. Room temperature Raman spectra of β-(AlxGa1−x)2O3 films show similar characteristics peaks as the (001) β-Ga2O3 substrate without obvious Raman shifts for films with different Al compositions. Atom probe tomography was used to investigate the atomic level structural chemistry with increasing Al content in the β-(AlxGa1−x)2O3 films. A monotonous increase in chemical heterogeneity is observed from the in-plane Al/Ga distributions, which was further confirmed via statistical frequency distribution analysis. Although the films exhibit alloy fluctuations, n-type doping demonstrates good electrical properties for films with various Al compositions. The determined valence and conduction band offsets at β-(AlxGa1−x)2O3/β-Ga2O3 heterojunctions using x-ray photoelectron spectroscopy reveal the formation of type-II (staggered) band alignment. [ABSTRACT FROM AUTHOR]

Epitaxial growth of κ-phase Ga2O3 thin films is investigated on c-plane sapphire, GaN- and AlN-on-sapphire, and (100) oriented yttria stabilized zirconia (YSZ) substrates via metalorganic chemical vapor deposition. The structural and surface morphological properties are investigated by comprehensive material characterization. Phase pure κ-Ga2O3 films are successfully grown on GaN-, AlN-on-sapphire, and YSZ substrates through a systematical tuning of growth parameters including the precursor molar flow rates, chamber pressure, and growth temperature, whereas the growth on c-sapphire substrates leads to a mixture of β- and κ-polymorphs of Ga2O3 under the investigated growth conditions. The influence of the crystalline structure, surface morphology, and roughness of κ-Ga2O3 films grown on different substrates are investigated as a function of precursor flow rate. High-resolution scanning transmission electron microscopy imaging of κ-Ga2O3 films reveals abrupt interfaces between the epitaxial film and the sapphire, GaN, and YSZ substrates. The growth of single crystal orthorhombic κ-Ga2O3 films is confirmed by analyzing the scanning transmission electron microscopy nanodiffraction pattern. The chemical composition, surface stoichiometry, and bandgap energies of κ-Ga2O3 thin films grown on different substrates are studied by high-resolution x-ray photoelectron spectroscopy (XPS) measurements. The type-II (staggered) band alignments at three interfaces between κ-Ga2O3 and c-sapphire, AlN, and YSZ substrates are determined by XPS, with an exception of κ-Ga2O3/GaN interface, which shows type-I (straddling) band alignment. [ABSTRACT FROM AUTHOR]

Metalorganic chemical vapor deposition (MOCVD) growths of β-Ga2O3 on on-axis (100) Ga2O3 substrates are comprehensively investigated. Key MOCVD growth parameters including growth temperature, pressure, group VI/III molar flow rate ratio, and carrier gas flow rate are mapped. The dependence of the growth conditions is correlated with surface morphology, growth rate, and electron transport properties of the MOCVD grown (100) β-Ga2O3 thin films. Lower shroud gas (argon) flow is found to enhance the surface smoothness with higher room temperature (RT) electron Hall mobility. The growth rate of the films decreases but with an increase of electron mobility as the VI/III molar flow rate ratio increases. Although no significant variation on the surface morphologies is observed at different growth temperatures, the general trend of electron Hall mobilities are found to increase with increasing growth temperature. The growth rates reduce significantly with uniform surface morphologies as the chamber pressure increases. By tuning the silane flow rate, the controllable carrier concentration of (100) β-Ga2O3 thin films between low-1017 cm−3 and low-1018 cm−3 was achieved. Under optimized growth condition, an (100) β-Ga2O3 thin film with RMS roughness value of 1.64 nm and a RT mobility of 24 cm2/Vs at a carrier concentration of 7.0 × 1017 cm−3 are demonstrated. The mobilities are primarily limited by the twin lamellae and stacking faults defects generated from the growth interface. Atomic resolution scanning transmission electron microscopy reveals the formation of twin boundary defects in the films, resulting in the degradation of crystalline quality. Results from this work provide fundamental understanding of the MOCVD epitaxy of (100) β-Ga2O3 on on-axis Ga2O3 substrates and the dependence of the material properties on growth conditions. The limitation of electron transport properties of the (100) β-Ga2O3 thin films below 25 cm2/Vs is attributed to the formation of incoherent boundaries (twin lamellae) and stacking faults grown along the on-axis (100) crystal orientation. [ABSTRACT FROM AUTHOR]

High crystalline quality thick β-Ga2O3 drift layers are essential for multi-kV vertical power devices. Low-pressure chemical vapor deposition (LPCVD) is suitable for achieving high growth rates. This paper presents a systematic study of the Schottky barrier diodes fabricated on four different Si-doped homoepitaxial β-Ga2O3 thin films grown on Sn-doped (010) and (001) β-Ga2O3 substrates by LPCVD with a fast growth rate varying from 13 to 21 μm/h. A higher temperature growth results in the highest reported growth rate to date. Room temperature current density–voltage data for different Schottky diodes are presented, and diode characteristics, such as ideality factor, barrier height, specific on-resistance, and breakdown voltage are studied. Temperature dependence (25–250 °C) of the ideality factor, barrier height, and specific on-resistance is also analyzed from the J–V–T characteristics of the fabricated Schottky diodes. [ABSTRACT FROM AUTHOR]

Single α-phase (AlxGa1−x)2O3 thin films are grown on m-plane sapphire (α-Al2O3) substrates via metalorganic chemical vapor deposition. By systematically tuning the growth parameters including the precursor molar flow rates, chamber pressure, and growth temperature, the epitaxial growth of high-quality phase pure α-(AlxGa1−x)2O3 films (0 ≤ x ≤ 1) is demonstrated with smooth surface morphologies and alloy homogeneities by comprehensive material characterization. The asymmetrical reciprocal space mapping reveals fully relaxed films for α-(AlxGa1−x)2O3 films with x ≤ 0.5. The coherent growth of α-(AlxGa1−x)2O3/α-Al2O3 superlattice structures is demonstrated with abrupt interfaces and uniform Al distribution for higher Al compositions at x = 0.78 in the α-(AlxGa1−x)2O3 layer. The influence of growth parameters, such as growth temperature and chamber pressure, on the phase stabilization and Al incorporation in the α-(AlxGa1−x)2O3 films is investigated. While lower growth temperatures facilitate the phase stabilization of α-Ga2O3 thin films, lower chamber pressure leads to higher Al incorporation in α-(AlxGa1−x)2O3 films. High resolution x-ray photoelectron spectroscopy was utilized for determining the Al compositions and bandgaps of α-(AlxGa1−x)2O3. Furthermore, the evolution of the valance and conduction band offsets at α-Al2O3/α-(AlxGa1−x)2O3 heterojunctions is evaluated with the variation of Al compositions, which reveals the formation of type-I (straddling) band alignment between α-Al2O3 and α-(AlxGa1−x)2O3. [ABSTRACT FROM AUTHOR]