An official website of the United States government
β-Ga2O3 and its alloys are promising for next-generation high-power electronic devices, but realizing high-quality thick epitaxial layers with smooth morphology at high growth rates remains a major challenge. In this study, we systematically investigated the metalorganic chemical vapor deposition (MOCVD) growth of β-Ga2O3 on edge-defined film-fed growth (EFG, Sn doped) and vertical bridgman (VB, Fe doped) (001) β-Ga2O3 substrates. (001) β-Ga2O3 films grown on both substrates show similar cracking issue. Films grown on EFG substrates show lower atomic force microscopy roughness as compared to those grown on VB substrates. X-ray diffraction (XRD) measurements indicate lower crystalline quality in films grown on VB substrates compared to films grown on EFG substrates. XRD rocking curves also illustrate that films grown on VB substrates have higher structural anisotropy. From cross-sectional scanning transmission electron microscopy (STEM) imaging, surface reconstruction occurred at the growth interface for both EFG and VB substrates. MOCVD growth of β-(Al0.0625Ga0.9375)2O3 on (001) β-Ga2O3 substrates indicate crack-free layers can be grown up to 6 μm at a growth rate of 4.5 μm/h. STEM atomic-scale analysis revealed a uniform Al-distributed interfacial layer at the growth interface followed with an Al-segregated region aligning along the (1¯01) plane. Electrical measurements revealed low mobility in thick (001) AlGaO layers which is due to crystal rotation and Al segregation. These results provide understanding of MOCVD growth of (001) β-Ga2O3 and (001) β-(AlxGa1−x)2O3 films at fast growth rates and insights into the interplay of growth chemistry, substrate selection, and alloy incorporation.
more »
« less
Demonstration of thick phase-pure β-Ga2O3 on a c-plane sapphire substrate using MOCVD
We demonstrated a metal-organic chemical vapor deposition (MOCVD) of smooth, thick, and monoclinic phase-pure gallium oxide (Ga2O3) on c-plane sapphire using silicon-oxygen bonding (SiOx) as a phase stabilizer. The corundum (α), monoclinic (β), and orthorhombic (ε) phases of Ga2O3 with a bandgap in the 4.4 – 5.1 eV range, are promising materials for power semiconductor devices and deep ultraviolet (UV) solar-blind photodetectors. The MOCVD systems are extensively used for homoepitaxial growth of β-Ga2O3 on (001), (100), (010), and (¯2 01) β-Ga2O3 substrates. These substrates are rare/expensive and have very low thermal conductivity; thus, are not suitable for high-power semiconductor devices. The c-plane sapphire is typically used as a substrate for high-power devices. The β-Ga2O3 grows in the (¯2 01) direction on sapphire. In this direction, the presence of high-density oxygen dangling bonds, frequent stacking faults, twinning, and other phases and planes impede the heteroepitaxy of thick β-Ga2O3. Previously phase stabilizations with SiOx have been reported for tetragonal and monoclinic hafnia. We were able to grow ~580nm thick β-Ga2O3 on sapphire by MOCVD at 750 oC through phase stabilization using silane. The samples grown with silane have a reduction in the surface roughness and resistivity from 10.7 nm to 4.4 nm and from 371.75 Ω.cm to 135.64 Ω.cm, respectively. These samples show a pure-monoclinic phase determined by x-ray diffraction (XRD); have tensile strain determined by Raman strain mapping. These results show that a thick, phase-pure -Ga2O3 can be grown on c-plane sapphire which can be suitable for creating power devices with better thermal management.
more »
« less
- PAR ID:
- 10431786
- Editor(s):
- Teherani, Ferechteh H.; Rogers, David J.
- Date Published:
- Journal Name:
- Proc. SPIE 12422, Oxide-based Materials and Devices
- Volume:
- XIV
- Page Range / eLocation ID:
- 15
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract In this work, high-quality Ge-doped (2̅01) β-Ga2O3 thin films were heteroepitaxially grown on c-plane sapphire substrates with offcut angles of 0°, 2°, 6°, and 8° using low-pressure chemical vapor deposition (LPCVD). Increasing the sapphire offcut promoted step-flow growth, resulting in improved terrace alignment, reduced surface roughness, and enhanced crystalline quality. Phase-pure monoclinic β-Ga2O3 with strong (2̅01) preferential orientation was confirmed by X-ray diffraction and Raman spectroscopy, while X-ray photoelectron spectroscopy revealed a near-stoichiometric composition with an O/Ga ratio of 1.48. Electrical transport properties exhibited a strong dependence on the substrate offcut angle, with room-temperature Hall mobility increasing from 15 to 117 cm2/V·s as the offcut angle increased from 0° to 6°, across carrier concentrations spanning 1.43 × 1017 to 2.75 × 1018 cm–3. The 6° offcut sample achieved a room-temperature mobility of 117 cm2/V·s at a carrier concentration of 1.43 × 1017 cm–3 and a peak low-temperature mobility of 337 cm2/V·s at 128 K with a carrier concentration of 8.96 × 1016 cm–3, representing the highest reported room-temperature and low-temperature mobilities for Ge-doped β-Ga2O3 films grown on sapphire substrates. Carrier concentration and mobility data were analyzed using charge-neutrality and Boltzmann transport models incorporating donor activation together with polar optical phonon, ionized impurity, neutral impurity, acoustic deformation potential, and dislocation scattering mechanisms. The fitting revealed shallow donor activation energies of 12.5–19 meV, a deeper donor level at 80 meV, low acceptor compensation (<5 × 1015 cm–3), and threading dislocation densities on the order of 109 cm–2. These results establish sapphire offcut engineering as an effective pathway for achieving high-mobility, LPCVD-grown Ge-doped β-Ga2O3 heteroepitaxy on scalable foreign substrates, which is critical for the development of high-performance β-Ga2O3 power devices.more » « less
-
Si-doped β-phase (010) Ga2O3 epi-films with fast growth rates were comprehensively investigated using trimethylgallium (TMGa) as the Ga precursor via metalorganic chemical vapor deposition (MOCVD). Two main challenges facing the MOCVD growth of thick (010) β-Ga2O3 films with fast growth rates include high impurity carbon (C) incorporation and rough surface morphologies due to the formation of imbedded 3D pyramid-shaped structures. In this work, two different categories of oxygen source (high-purity O2 > 99.9999% and O2* with 10 ppm of [H2O]) were used for β-Ga2O3 MOCVD growth. Our study revealed that the size and density of the 3D defects in the β-Ga2O3 epi-films were significantly reduced when the O2* was used. In addition, the use of off-axis (010) Ga2O3 substrates with 2° off-cut angle leads to further reduction of defect formation in β-Ga2O3 with fast growth rates. To suppress C incorporation in MOCVD β-Ga2O3 grown with high TMGa flow rates, our findings indicate that high O2 (or O2*) flow rates are essential. Superior room temperature electron mobilities as high as 110–190 cm2/V·s were achieved for β-Ga2O3 grown using O2* (2000 sccm) with a growth rate of 4.5 μm/h (film thickness of 6.3 μm) within the doping range of 1.3 × 1018–7 × 1015 cm−3. The C incorporation is significantly suppressed from ∼1018 cm−3 to <5 × 1016 cm−3 ([C] detection limit) for β-Ga2O3 grown using high O2 (O2*) flow rate of 2000 sccm. Results from this work will provide guidance on developing high-quality, thick β-Ga2O3 films required for high power electronic devices with vertical configurations.more » « less
-
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-Ga 2 O 3 . Epitaxial β-Ga 2 O 3 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-Ga 2 O 3 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-Ga 2 O 3 substrates, indicative of similar dislocation densities for epilayers and substrates. Hence, hot-wall MOCVD is proposed as a prospective growth method to be further explored for the fabrication of β-Ga 2 O 3 .more » « less
-
Growing a thick high-quality epitaxial layer on the β-Ga2O3 substrate is crucial in commercializing β-Ga2O3 devices. Metal organic chemical vapor deposition (MOCVD) is also well-established for the large-scale commercial growth of β-Ga2O3 and related heterostructures. This paper presents a systematic study of the Schottky barrier diodes fabricated on two different Si-doped homoepitaxial β-Ga2O3 thin films grown on Sn-doped (001) and (010) β-Ga2O3 substrates by MOCVD. X-ray diffraction analysis of the MOCVD-grown sample, room temperature current density–voltage data for different Schottky diodes, and C–V measurements are presented. Diode characteristics, such as ideality factor, barrier height, specific on-resistance, and breakdown voltage, are studied. Temperature dependence (170–360 K) of the ideality factor, barrier height, and Poole–Frenkel reverse leakage mechanism are also analyzed from the J–V–T characteristics of the fabricated Schottky diodes.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Conference Paper:
- https://doi.org/10.1117/12.2661097
