231 results on '"Zhao, Hongping"'
Search Results
2. Weighted gene coexpression network analysis and machine learning for the determination of tfh cell and B cell infiltrating biomarkers in thymoma-associated myasthenia gravis
- Author
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Li, Zidong, Miao, Lu, Ren, Gang, Wang, Hailong, Shangguan, Lijuan, Zhao, Hongping, and Li, Xinyi
- Published
- 2024
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Catalog
3. Identification, evolution and expression analyses of the whole genome-wide PEBP gene family in Brassica napus L.
- Author
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Li, Yanling, Xiao, Lu, Zhao, Zhi, Zhao, Hongping, and Du, Dezhi
- Published
- 2023
- Full Text
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4. Broadband photodetectors with enhanced performance in UV–Vis–NIR band based on PbS quantum dots /ZnO film heterostructure
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Zhao, Hongping, Zhao, Man, and Jiang, Dayong
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- 2024
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5. A TransSE-ResNet Deep Learning Model with Multi-Head Attention Mechanism for Covid-19 Chest CT Image Classification
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Du, Ke, Yan, Jiaxing, Tang, Li, and Zhao, Hongping
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- 2023
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6. Design of AlGaN-Zn(Si,Ge)N2 quantum wells for high-efficiency ultraviolet light emitters.
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Hu, Chenxi, Kash, Kathleen, and Zhao, Hongping
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LIGHT emitting diodes ,ULTRAVIOLET radiation ,QUANTUM well devices ,SILICON alloys ,SEMICONDUCTOR lasers ,NITROGEN ,QUANTUM wells - Abstract
The effect of inserting a nm-scale layer of Zn(Si,Ge)N
2 into an AlGaN quantum well structure designed for light emission in the wavelength range from 255 to 305 nm is investigated here. The enhanced confinement of the hole within the quantum well results in an enhancement of the overlap of the hole and electron wave functions, resulting in an enhancement of the radiative recombination rate. In this theoretical calculation, for emission at a 270 nm wavelength, the enhancement in the wavefunction overlap can reach a factor of 7 when compared to an AlGaN quantum well device specifically engineered for optimal emission at the identical wavelength. Increases of almost an order of magnitude in both the peak spontaneous emission intensity and the radiative recombination rate are predicted. The peak emission wavelength can be tuned from 255 to 305 nm by adjusting the width and/or the composition of the inserted layer. The proposed structures provide a route to higher efficiency ultraviolet practical light emitting diodes and lasers. [ABSTRACT FROM AUTHOR] more...- Published
- 2024
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7. Three-dimensional photoluminescence imaging of threading dislocations in GaN by sub-band optical excitation.
- Author
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Daeumer, Matthias, Yoo, Jae-Hyuck, Xu, Zhiyu, Cho, Minkyu, Bakhtiary-Noodeh, Marzieh, Detchprohm, Theeradetch, Zhang, Yuxuan, Thirupakuzi Vangipuram, Vijay Gopal, Talesara, Vishank, Xu, Yibo, Letts, Edward, Key, Daryl, Li, Tian T., Shao, Qinghui, Dupuis, Russell, Shen, Shyh-Chiang, Lu, Wu, Zhao, Hongping, Hashimoto, Tadao, and Laurence, Ted A. more...
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POWER electronics ,CHEMICAL vapor deposition ,EPITAXIAL layers ,STRAY currents ,THREE-dimensional imaging - Abstract
GaN is rapidly gaining attention for implementation in power electronics but is still impacted by its high density of threading dislocations (TDs), which have been shown to facilitate current leakage through devices limiting their performance and reliability. Here, we discuss a novel implementation of photoluminescence (PL) imaging to study TDs in regions within vertically structured p-i-n GaN (PIN) diodes consisting of metalorganic chemical vapor deposition (MOCVD) epitaxial layers grown on ammonothermal GaN (am-GaN) substrates. PL imaging with a sub-bandgap excitation energy (3.1 eV) reveals TDs with excellent clarity in three dimensions within the am-GaN substrate. Galvanometric-driven PL imaging allows the microstructure of hundreds of devices to be characterized in a single session, enhancing the screening process through the addition of device specific TD location tracking and density mapping. The visibility, structural characteristics, luminescent nature and evolution of TDs through the GaN growth process are described, potentially providing the ability to define TD structures associated with leakage current. [ABSTRACT FROM AUTHOR] more...
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- 2025
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8. MOCVD growth of β-Ga2O3 with fast growth rates (>4.3 μm/h), low controllable doping, and superior transport properties.
- Author
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Yu, Dong Su, Meng, Lingyu, and Zhao, Hongping
- Subjects
CHEMICAL vapor deposition ,ELECTRON mobility ,THICK films ,ROUGH surfaces ,ELECTRONIC equipment - Abstract
Si-doped β-phase (010) Ga
2 O3 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-Ga2 O3 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 [H2 O]) were used for β-Ga2 O3 MOCVD growth. Our study revealed that the size and density of the 3D defects in the β-Ga2 O3 epi-films were significantly reduced when the O2 * was used. In addition, the use of off-axis (010) Ga2 O3 substrates with 2° off-cut angle leads to further reduction of defect formation in β-Ga2 O3 with fast growth rates. To suppress C incorporation in MOCVD β-Ga2 O3 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-Ga2 O3 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-Ga2 O3 grown using high O2 (O2 * ) flow rate of 2000 sccm. Results from this work will provide guidance on developing high-quality, thick β-Ga2 O3 films required for high power electronic devices with vertical configurations. [ABSTRACT FROM AUTHOR] more...- Published
- 2024
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9. Design and development of 1.5 kV vertical GaN pn diodes on HVPE substrate
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Talesara, Vishank, Zhang, Yuxuan, Chen, Zhaoying, Zhao, Hongping, and Lu, Wu
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- 2021
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10. MOCVD growth of (010) β-(AlxGa1−x)2O3 thin films
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Bhuiyan, A F M Anhar Uddin, Feng, Zixuan, Meng, Lingyu, and Zhao, Hongping
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- 2021
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11. Tutorial: Metalorganic chemical vapor deposition of β-Ga2O3 thin films, alloys, and heterostructures.
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Bhuiyan, A. F. M. Anhar Uddin, Feng, Zixuan, Meng, Lingyu, and Zhao, Hongping
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THIN film deposition ,CHEMICAL vapor deposition ,THIN films ,GALLIUM alloys ,HETEROSTRUCTURES ,CRYSTAL orientation - Abstract
β-phase gallium oxide (Ga
2 O3 ) 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 Ga2 O3 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 Ga2 O3 thin films, (Alx Ga1−x )2 O3 alloys, and heterostructures along various crystal orientations and with different phases. This tutorial summarizes the recent progresses in the epitaxial growth of β-Ga2 O3 thin films via different growth methods, with a focus on the growth of Ga2 O3 and its compositional alloys by MOCVD. The challenges for the epitaxial development of β-Ga2 O3 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] more...- Published
- 2023
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12. Thin channel Ga2O3 MOSFET with 55 GHz fMAX and >100 V breakdown.
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Saha, Chinmoy Nath, Vaidya, Abhishek, Nipu, Noor Jahan, Meng, Lingyu, Yu, Dong Su, Zhao, Hongping, and Singisetti, Uttam
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METAL organic chemical vapor deposition ,MOLECULAR beam epitaxy ,BREAKDOWN voltage ,METAL oxide semiconductor field-effect transistors ,GALLIUM nitride - Abstract
This Letter reports a highly scaled 90 nm gate length β-Ga
2 O3 (Ga2 O3 ) T-gate MOSFET with a power gain cutoff frequency (fMAX ) of 55 GHz. The 60 nm thin epitaxial Ga2 O3 channel layer was grown by molecular beam epitaxy, while the highly doped (n++) source/drain regions were regrown using metal organic chemical vapor deposition. Maximum on current (IDS,MAX ) of 160 mA/mm and trans-conductance (gm ) around 36 mS/mm were measured at VDS = 10 V for LSD = 1.5 μ m device. Transconductance and on current are limited by high channel sheet resistance (Rsheet ). Gate/drain breakdown voltage of 125 V was measured for LGD = 1.2 μ m. We extracted 27 GHz current gain cutoff frequency (fT ) and 55 GHz fMAX for 20 V drain bias for unpassivated devices. While no current collapse was seen initially for both drain and gate lag measurements for 500 ns pulse, moderate current collapse was observed after DC, RF measurements caused by electrical stressing. We calculated a high fT . VBR product of 3.375 THz V, which is comparable to the state-of-the-art GaN HEMTs. This figure of merit suggests that Ga2 O3 could be a potential candidate for X-band application. [ABSTRACT FROM AUTHOR] more...- Published
- 2024
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13. Proton radiation effects on electronic defect states in MOCVD-grown (010) β-Ga2O3.
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McGlone, Joe F., Ghadi, Hemant, Cornuelle, Evan, Armstrong, Andrew, Burns, George, Feng, Zixuan, Uddin Bhuiyan, A. F. M. Anhar, Zhao, Hongping, Arehart, Aaron R., and Ringel, Steven A.
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DEEP level transient spectroscopy ,POLAR effects (Chemistry) ,IRRADIATION ,PROTONS ,CHEMICAL vapor deposition ,SCHOTTKY barrier diodes - Abstract
The impact of 1.8 MeV proton irradiation on metalorganic chemical vapor deposition grown (010) β -Ga
2 O3 Schottky diodes is presented. It is found that after a 10.8 × 10 13 cm − 2 proton fluence the Schottky barrier height of (1.40 ± 0.05 eV) and the ideality factor of (1.05 ± 0.05) are unaffected. Capacitance–voltage extracted net ionized doping curves indicate a carrier removal rate of 268 ± 10 cm − 1 . The defect states responsible for the observed carrier removal are studied through a combination of deep level transient and optical spectroscopies (DLTS/DLOS) as well as lighted capacitance–voltage (LCV) measurements. The dominating effect on the defect spectrum is due to the EC - 2.0 eV defect state observed in DLOS and LCV. This state accounts for ∼ 75 % of the total trap introduction rate and is the primary source of carrier removal from proton irradiation. Of the DLTS detected states, the EC - 0.72 eV state dominated but had a comparably smaller contribution to the trap introduction. These two traps have previously been correlated with acceptor-like gallium vacancy-related defects. Several other trap states at E C -0.36, E C -0.63, and E C -1.09 eV were newly detected after proton irradiation, and two pre-existing states at E C -1.2 and E C -4.4 eV showed a slight increase in concentration after irradiation, together accounting for the remainder of trap introduction. However, a pre-existing trap at EC - 0.40 eV was found to be insensitive to proton irradiation and, therefore, is likely of extrinsic origin. The comprehensive defect characterization of 1.8 MeV proton irradiation damage can aid the modeling and design for a range of radiation tolerant devices. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
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14. Investigation on the oil sorption capability of silkworm cocoon waste.
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Shao, Jiaxing, Jiang, Yueqi, Huang, Huiming, Zhao, HongPing, and Cheng, Lan
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VEGETABLE oils ,PETROLEUM waste ,LUBRICATING oils ,PETROLEUM ,SILKWORMS - Abstract
In this study, degummed and undegummed silkworm cocoon wastes were used to investigate their oil sorption capabilities for three kinds of oils, namely motor oil, vegetable oil, and crude oil. The laboratory-scale oil sorption results reveal that degummed silkworm cocoon waste has sorption capacities of 16.7, 15.8, and 14.2 g/g for motor oil, vegetable oil, and crude oil, respectively. It exhibits higher sorption capacities for these three oils compared with raw cocoons and cocoon scrap. These sorbents also exhibited excellent oil/water selectivity, retention capacity, and reusability. According to the large-scale experiment, the crude oil can be removed completely by degummed silkworm cocoon waste in 20 min, which shows that degummed silkworm cocoon waste could be considered a good alternative to synthetic sorbent materials applied to oil removal and recycling. [ABSTRACT FROM AUTHOR] more...
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- 2024
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15. High growth rate metal organic chemical vapor deposition grown Ga2O3 (010) Schottky diodes.
- Author
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Saha, Sudipto, Meng, Lingyu, Yu, Dong Su, Anhar Uddin Bhuiyan, A. F. M., Zhao, Hongping, and Singisetti, Uttam
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METAL organic chemical vapor deposition ,SCHOTTKY barrier diodes ,SCHOTTKY barrier ,CHEMICAL vapor deposition ,ELECTRONIC equipment ,THIN films ,BREAKDOWN voltage - Abstract
We report on the growth of Si-doped homoepitaxial β-Ga
2 O3 thin films on (010) Ga2 O3 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 Ga2 O3 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 Ga2 O3 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 Ga2 O3 epilayers for vertical power electronic devices. [ABSTRACT FROM AUTHOR] more...- Published
- 2024
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16. MOCVD Growth of β‑Ga2O3 on (001) Ga2O3 Substrates.
- Author
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Meng, Lingyu, Yu, Dongsu, Huang, Hsien-Lien, Chae, Chris, Hwang, Jinwoo, and Zhao, Hongping
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- 2024
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17. Wet and dry etching of ultrawide bandgap LiGa5O8 and LiGaO2.
- Author
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Thirupakuzi Vangipuram, Vijay Gopal, Zhang, Kaitian, and Zhao, Hongping
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PLASMA etching ,VAPOR-plating ,EPITAXY ,THIN films ,SURFACE morphology ,DILUTION ,SILICON nitride films - Abstract
Crystalline thin films of LiGa
5 O8 have recently been realized through epitaxial growth via mist-chemical vapor deposition. The single crystal, spinel cubic LiGa5 O8 films show promising fundamental material properties and, therefore, make LiGa5 O8 a potential enabling material for power electronics. In this work, chemical resistance and etch susceptibility were investigated for the first time on crystalline LiGa5 O8 thin films with various wet chemistries. It was found that LiGa5 O8 is very chemically resistive to acid solutions, with no apparent etching effects observed when placed in concentrated acid solutions of HCl, H2 SO4 , HF, or H3 PO4 at room temperature. In contrast, orthorhombic (010) LiGaO2 shows effective etching in HCl solutions at varying dilution concentrations, with etch rates measured between 8.6 [1000:1 (DI water: HCl concentration)] and 6092 nm/min (37 wt. % HCl). The inductively coupled plasma reactive ion etching (ICP-RIE) of LiGa5 O8 using BCl3 /Ar and CF4 /Ar/O2 gas chemistries was investigated. The etching rate and surface morphology of etched surfaces were examined as a function of RIE and ICP power. Using a CF4 /Ar/O2 gas chemistry with an RIE power of 75 W and an ICP power of 300 W resulted in smooth etched planar surfaces while maintaining an etch rate of ∼24.6 nm/min. Similar dry etching studies were performed for LiGaO2 . It was found that the BCl3 /Ar gas chemistry was better suited for LiGaO2 etching, with similar surface morphology quality being obtained after etching as prior etching when a RIE power of 15 W and an ICP power of 400 W is utilized. [ABSTRACT FROM AUTHOR] more...- Published
- 2024
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18. In situ MOCVD growth and band offsets of Al2O3 dielectric on β-Ga2O3 and β-(AlxGa1−x)2O3 thin films.
- Author
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Bhuiyan, A F M Anhar Uddin, Meng, Lingyu, Huang, Hsien-Lien, Hwang, Jinwoo, and Zhao, Hongping
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INDIUM gallium zinc oxide ,THIN films ,SCANNING transmission electron microscopy ,DIELECTRIC films ,ALUMINUM oxide ,X-ray photoelectron spectroscopy ,CHEMICAL vapor deposition ,DIELECTRIC devices - Abstract
The in situ metalorganic chemical vapor deposition (MOCVD) growth of Al
2 O3 dielectrics on β-Ga2 O3 and β-(Alx Ga1−x )2 O3 films is investigated as a function of crystal orientations and Al compositions of β-(Alx Ga1−x )2 O3 films. The interface and film qualities of Al2 O3 dielectrics are evaluated by high-resolution x-ray diffraction and scanning transmission electron microscopy imaging, which indicate the growth of high-quality amorphous Al2 O3 dielectrics with abrupt interfaces on (010), (100), and ( 2 ¯ 01) oriented β-(Alx Ga1−x )2 O3 films. The surface stoichiometries of Al2 O3 deposited on all orientations of β-(Alx Ga1−x )2 O3 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) Al2 O3 dielectrics. The evolution of band offsets at both in situ MOCVD and ex situ ALD deposited Al2 O3 /β-(Alx Ga1−x )2 O3 is determined as a function of Al composition, indicating the influence of the deposition method, orientation, and Al composition of β-(Alx Ga1−x )2 O3 films on resulting band alignments. Type II band alignments are determined at the MOCVD grown Al2 O3 /β-(Alx Ga1−x )2 O3 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 Al2 O3 deposited on differently oriented β-Ga2 O3 and β-(Alx Ga1−x )2 O3 films will potentially contribute to the design and fabrication of future high-performance β-Ga2 O3 and β-(Alx Ga1−x )2 O3 based transistors using MOCVD in situ deposited Al2 O3 as a gate dielectric. [ABSTRACT FROM AUTHOR] more...- Published
- 2022
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19. Quantum dots-reinforced luminescent silkworm silk with superior mechanical properties and highly stable fluorescence
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Cheng, Lan, Zhao, Hongping, Huang, Huiming, Li, Bo, Li, Robert K. Y., Feng, Xi-Qiao, and Dai, Fangyin
- Published
- 2019
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20. Robust composite silk fibers pulled out of silkworms directly fed with nanoparticles
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Wu, GuoHua, Song, Peng, Zhang, DongYang, Liu, ZeYu, Li, Long, Huang, HuiMing, Zhao, HongPing, Wang, NanNan, and Zhu, YanQiu
- Published
- 2017
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21. Characterization of silkworm larvae growth and properties of silk fibres after direct feeding of copper or silver nanoparticles
- Author
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Cheng, Lan, Huang, Huiming, Chen, Shaoyong, Wang, Wenlu, Dai, Fangyin, and Zhao, Hongping
- Published
- 2017
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22. Experimental determination of the band offsets at the UWBG p-LiGa5O8/Ga2O3 interface.
- Author
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Zhang, Kaitian, Thirupakuzi Vangipuram, Vijay Gopal, Chae, Christopher, Hwang, Jinwoo, and Zhao, Hongping
- Abstract
LiGa
5 O8 , a recently discovered ultrawide bandgap semiconductor exhibiting p-type conductivity at room temperature, is grown on (010) β-Ga2ubscript>O 3 substrate. Utilizing a mist chemical vapor deposition method, LiGa5 O8 thin film grown on insulating Ga2 O3 substrate exhibits hole concentration ∼2.31 × 1018 cm−3 and hole mobility ∼2.07 cm2 /V s. The resulting heterostructure is characterized comprehensively. A smooth, uniform film growth was observed by scanning electron microscopy and atomic force microscopy imaging. Cross-sectional scanning transmission electron microscopy and x-ray diffraction confirm the growth of spinel cubic crystal structure of LiGa5 O8 along the [110] direction. Moreover, the valence and conduction band offsets at p-LiGa5 O8 /β-Ga2 O3 heterointerface were determined via x-ray photoelectron spectroscopy. The determined band alignments at LiGa5 O8 /β-Ga2 O3 interface reveal the formation of a type-II (staggered) heterojunction. The experimental measurements provide valuable parameters of the band offsets at the heterointerface, addressing a crucial aspect for future power electronic device design and fabrication based on β-Ga2 O3 ultrawide bandgap semiconductors. [ABSTRACT FROM AUTHOR] more...- Published
- 2024
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23. Suppressing Carbon Incorporation in Metal–Organic Chemical Vapor Deposition GaN Using High‐Offcut‐Angled Substrates.
- Author
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Thirupakuzi Vangipuram, Vijay Gopal, Zhang, Kaitian, and Zhao, Hongping
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CHEMICAL vapor deposition ,GALLIUM nitride ,MASS spectrometry - Abstract
Carbon (C) is a common impurity that acts as a compensator within GaN grown via metal–organic chemical vapor deposition (MOCVD). Reducing C in GaN will help reduce the compensation level and provide a route to achieve GaN with reliably low effective doping for high‐power device applications. GaN grown with fast growth rates on bulk GaN with various offcut angles via conventional‐MOCVD (C‐MOCVD) and laser‐assisted MOCVD (LA‐MOCVD) is compared and analyzed. C‐incorporation effects are compared through quantitative secondary‐ion mass spectroscopy analysis in GaN grown on GaN substrate with offcut angles of 4° and 0.3° toward m‐plane over a wide range of growth rates by C‐MOCVD and LA‐MOCVD. For both growth techniques investigated, a significant reduction in C‐incorporation is observed when a high‐offcut‐angle (4°) substrate is used as compared to a lower‐offcut‐angle (0.3°) substrate. With C‐MOCVD, at the fastest growth condition investigated (17.26 μm h−1 at 0.3°‐offcut, 15.25 μm h−1 at 4°‐offcut), a reduction in [C] by 21.2X is observed with an increase in the offcut angle from 0.3° to 4°. A 82.6X reduction in [C] is observed with the similar fast growth condition via LA‐MOCVD on GaN with 4° offcut angle (9.78 μm h−1) as compared to C‐MOCVD at 0.3° offcut angle (17.26 μm h−1). [ABSTRACT FROM AUTHOR] more...
- Published
- 2024
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24. Effect of varying threading dislocation densities on the optical properties of InGaN/GaN quantum wells with intentionally created V-shaped pits.
- Author
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Zhang, Kaitian, Hu, Chenxi, Thirupakuzi Vangipuram, Vijay Gopal, Meng, Lingyu, Chae, Christopher, Zhu, Menglin, Hwang, Jinwoo, Kash, Kathleen, and Zhao, Hongping
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DISLOCATION density ,OPACITY (Optics) ,INDIUM gallium nitride ,QUANTUM wells ,OPTICAL properties ,GALLIUM nitride ,SCREW dislocations - Abstract
The effect of varying threading dislocation densities on the internal quantum efficiencies (IQEs) of InGaN quantum wells (QWs), with and without intentionally created "V-pits," is reported here. InGaN QW samples grown on GaN-on-sapphire templates with threading dislocation densities of <1 × 10
8 and <1 × 109 cm−2 are compared, with and without GaN/InGaN superlattice (SL) layers incorporated to intentionally open up the threading dislocation cores and form large-size "V-pits." The formation of "V-pits" is confirmed by cross-sectional transmission electron microscopy to initiate from threading dislocations in the SL layers. The densities of the pits are confirmed by plan-view SEM to agree with the substrate threading dislocation densities. The experimental room temperature IQEs of the "V-pit" QW samples are enhanced to 15% ± 1% compared to 6% ± 2% for conventional QW samples. Both conventional and "V-pit" samples show insensitivity to the magnitude of the dislocation densities with respect to IQE performance, while the "V-pit" samples show shifts in the peak emission wavelengths compared to the conventional samples, attributed to strain modulation. This study provides additional understanding of the causes of the observed insensitivity of the IQEs to different threading dislocation densities. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
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25. Synergistic Effects of Chiral Morphology and Reconfiguration in Cattail Leaves
- Author
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Zhao, Zilong, Huang, Weixi, Li, Bingwei, Chen, Kexing, Chen, Kuifu, Zhao, Hongping, and Feng, Xiqiao
- Published
- 2015
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26. Chemical vapor deposition of m-plane and c-plane InN nanowires on Si (100) substrate
- Author
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Rafique, Subrina, Han, Lu, and Zhao, Hongping
- Published
- 2015
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27. Optical phonon modes, static and high-frequency dielectric constants, and effective electron mass parameter in cubic In2O3.
- Author
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Stokey, Megan, Korlacki, Rafał, Knight, Sean, Ruder, Alexander, Hilfiker, Matthew, Galazka, Zbigniew, Irmscher, Klaus, Zhang, Yuxuan, Zhao, Hongping, Darakchieva, Vanya, and Schubert, Mathias
- Subjects
PERMITTIVITY ,HALL effect ,PHONONS ,DRUDE theory ,POLARONS - Abstract
A complete set of all optical phonon modes predicted by symmetry for bixbyite structure indium oxide is reported here from a combination of far-infrared and infrared spectroscopic ellipsometry, as well as first principles calculations. Dielectric function spectra measured on high quality, marginally electrically conductive melt grown single bulk crystals are obtained on a wavelength-by-wavelength (also known as point-by-point) basis and by numerical reduction of a subtle free charge carrier Drude model contribution. A four-parameter semi-quantum model is applied to determine all 16 pairs of infrared-active transverse and longitudinal optical phonon modes, including the high-frequency dielectric constant, ε ∞ = 4.05 ± 0.05. The Lyddane–Sachs–Teller relation then gives access to the static dielectric constant, ε DC = 10.55 ± 0.07. All experimental results are in excellent agreement with our density functional theory calculations and with previously reported values, where existent. We also perform optical Hall effect measurements and determine for the unintentionally doped n -type sample a free electron density of n = (2.81 ± 0.01) × 10 17 cm − 3 , a mobility of μ = (112 ± 3) cm 2 /(Vs), and an effective mass parameter of (0.208 ± 0.006) m e. Density and mobility parameters compare very well with the results of electrical Hall effect measurements. Our effective mass parameter, which is measured independently of any other experimental technique, represents the bottom curvature of the Γ point in In 2 O 3 in agreement with previous extrapolations. We use terahertz spectroscopic ellipsometry to measure the quasi-static response of In 2 O 3 , and our model validates the static dielectric constant obtained from the Lyddane–Sachs–Teller relation. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
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28. Free-Standing β-Ga2O3 Thin Diaphragms
- Author
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Zheng, Xu-Qian, Lee, Jaesung, Rafique, Subrina, Han, Lu, Zorman, Christian A., Zhao, Hongping, and Feng, Philip X.-L.
- Published
- 2017
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29. Probing unintentional Fe impurity incorporation in MOCVD homoepitaxy GaN: Toward GaN vertical power devices.
- Author
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Zhang, Yuxuan, Chen, Zhaoying, Li, Wenbo, Lee, Hyunsoo, Karim, Md Rezaul, Arehart, Aaron R., Ringel, Steven A., Rajan, Siddharth, and Zhao, Hongping
- Subjects
SECONDARY ion mass spectrometry ,CHEMICAL vapor deposition ,HALL effect ,ELECTRON mobility ,MOLECULAR beam epitaxy ,EPITAXY - Abstract
Unintentional impurity incorporation in GaN drift layers represents a challenging issue that can limit their potential performance in vertical power devices. In this paper, we focus on studying the origins of Fe impurity incorporation in metal-organic chemical vapor deposition (MOCVD) grown GaN materials. Acting as a compensator in n-type GaN drift layers, Fe impurities can reduce the electron mobility in GaN and limit the lowest controllable doping level. Two sources, the sample cleaning process and growth susceptor, were identified as the main mechanisms of Fe incorporation in the MOCVD GaN growth process. It was found that solvent cleaning of the wafer can introduce significant Fe contamination at the growth interface, which would slowly be incorporated into the GaN epilayer, thus causing background Fe impurity as high as 10
17 cm−3 level. Moreover, the Fe impurity in the coating material on the susceptor can introduce additional Fe impurity during the growth process. Our studies revealed that the Fe impurity level could be significantly suppressed by more than two orders when an alternative cleaning process was used and the susceptor surface was fully covered by substrates. Characterization of the Fe impurity concentrations was performed via secondary ion mass spectrometry. The trap level (EC − 0.57) eV from deep-level transient spectroscopy that had previously been attributed to Fe confirmed the carrier compensation effect from Fe. Room temperature Hall mobility as high as 1007 cm2 /V s was achieved on the MOCVD grown low-Fe GaN. Results from this work will provide guidance for achieving high purity GaN toward high performance GaN vertical power devices. [ABSTRACT FROM AUTHOR] more...- Published
- 2020
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30. Deep level defects and cation sublattice disorder in ZnGeN2.
- Author
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Haseman, Micah S., Karim, Md Rezaul, Ramdin, Daram, Noesges, Brenton A., Feinberg, Ella, Jayatunga, Benthara Hewage Dinushi, Lambrecht, Walter R. L., Zhu, Menglin, Hwang, Jinwoo, Kash, Kathleen, Zhao, Hongping, and Brillson, Leonard J. more...
- Subjects
CATHODOLUMINESCENCE ,SURFACE photovoltage ,CHEMICAL vapor deposition ,DIFFRACTION patterns ,X-ray photoelectron spectroscopy ,RADIANT intensity - Abstract
III-nitrides have revolutionized lighting technology and power electronics. Expanding the nitride semiconductor family to include heterovalent ternary nitrides opens up new and exciting opportunities for device design that may help overcome some of the limitations of the binary nitrides. However, the more complex cation sublattice also gives rise to new interactions with both native point defects and defect complexes that can introduce disorder on the cation sublattice. Here, depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy measurements of defect energy levels in ZnGeN
2 combined with transmission electron microscopy and x-ray diffraction reveal optical signatures of mid-gap states that can be associated with cation sublattice disorder. The energies of these characteristic optical signatures in ZnGeN2 thin films grown by metal–organic chemical vapor deposition are in good agreement with multiple, closely spaced band-like defect levels predicted by density functional theory. We correlated spatially resolved optical and atomic composition measurements using spatially resolved x-ray photoelectron spectroscopy with systematically varied growth conditions on the same ZnGeN2 films. The resultant elemental maps vs defect spectral energies and intensities suggest that cation antisite complexes (ZnGe –GeZn ) form preferentially vs isolated native point defects and introduce a mid-gap band of defect levels that dominate electron–hole pair recombination. Complexing of ZnGe and GeZn antisites manifests as disorder in the cation sub-lattice and leads to the formation of wurtzitic ZnGeN2 as indicated by transmission electron microscopy diffraction patterns and x-ray diffraction reciprocal space maps. These findings emphasize the importance of growth and processing conditions to control cation place exchange. [ABSTRACT FROM AUTHOR] more...- Published
- 2020
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31. Tunable bandgap and Si-doping in N-polar AlGaN on C-face 4H-SiC via molecular beam epitaxy.
- Author
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Mondal, Shubham, Wang, Ding, Anhar Uddin Bhuiyan, A F M, Hu, Mingtao, Reddeppa, Maddaka, Wang, Ping, Zhao, Hongping, and Mi, Zetian
- Subjects
MOLECULAR beam epitaxy ,MODULATION-doped field-effect transistors ,LIGHT emitting diodes ,SEMICONDUCTOR lasers ,WIDE gap semiconductors ,OPTOELECTRONIC devices - Abstract
N-polar AlGaN is an emerging wide-bandgap semiconductor for next-generation high electron mobility transistors and ultraviolet light emitting diodes and lasers. Here, we demonstrate the growth and characterization of high-quality N-polar AlGaN films on C-face 4H-silicon carbide (SiC) substrates by molecular beam epitaxy. On optimization of the growth conditions, N-polar AlGaN films exhibit a crack free, atomically smooth surface (rms roughness ∼ 0.9 nm), and high crystal quality with low density of defects and dislocations. The N-polar crystallographic orientation of the epitaxially grown AlGaN film is unambiguously confirmed by wet chemical etching. We demonstrate precise compositional tunability of the N-polar AlGaN films over a wide range of Al content and a high internal quantum efficiency ∼74% for the 65% Al content AlGaN film at room temperature. Furthermore, controllable silicon (Si) doping in high Al content (65%) N-polar AlGaN films has been demonstrated with the highest mobility value ∼65 cm
2 /V-s observed corresponding to an electron concentration of 1.1 × 1017 cm−3 , whereas a relatively high mobility value of 18 cm2 /V-s is sustained for an electron concentration of 3.2 × 1019 cm−3 , with an exceptionally low resistivity value of 0.009 Ω·cm. The polarity-controlled epitaxy of AlGaN on SiC presents a viable approach for achieving high-quality N-polar III-nitride semiconductors that can be harnessed for a wide range of emerging electronic and optoelectronic device applications. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
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32. 7.86 kV GaN-on-GaN PN power diode with BaTiO3 for electrical field management.
- Author
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Xu, Yibo, Vangipuram, Vijay Gopal Thirupakuzi, Talesara, Vishank, Cheng, Junao, Zhang, Yuxuan, Hashimoto, Tadao, Letts, Edward, Key, Daryl, Zhao, Hongping, and Lu, Wu
- Subjects
BREAKDOWN voltage ,ELECTRON mobility ,DIELECTRIC materials ,DIODES ,GALLIUM nitride ,PERMITTIVITY - Abstract
Devices based on gallium nitride (GaN) have great potential for high power switching applications due to the high breakdown field and high electron mobility. In this work, we present a vertical GaN-on-GaN PN power diode using high dielectric constant material, BaTiO
3 , for electrical field management and high breakdown voltages, in together with an optimized guard-ring and field plate design. Numerical simulation shows that with high-k dielectrics implemented, the peak electrical field at the PN interface is mitigated from 3.5 to 3.1 MV/cm under a reverse bias of −9.05 kV. The device design with BaTiO3 shows a breakdown voltage of 9.65 kV or about 600 V improvement. The fabricated diodes with a 57 μm thick drift layer demonstrate a breakdown voltage of 7.86 kV on a bulk GaN substrate. The device has an on-resistance of 2.8 mΩ cm 2 and a Baliga figure of merit of 22 GW/ cm 2 . [ABSTRACT FROM AUTHOR] more...- Published
- 2023
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33. Al Incorporation up to 99% in Metalorganic Chemical Vapor Deposition‐Grown Monoclinic (AlxGa1–x)2O3 Films Using Trimethylgallium.
- Author
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Bhuiyan, A F M Anhar Uddin, Meng, Lingyu, Huang, Hsien-Lien, Chae, Christopher, Hwang, Jinwoo, and Zhao, Hongping
- Subjects
SCANNING transmission electron microscopy ,CHEMICAL vapor deposition ,THIN films ,X-ray diffraction - Abstract
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] more...
- Published
- 2023
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34. Electrical characteristics of in situ Mg-doped β-Ga2O3 current-blocking layer for vertical devices.
- Author
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Saha, Sudipto, Meng, Lingyu, Bhuiyan, A. F. M. Anhar Uddin, Sharma, Ankit, Saha, Chinmoy Nath, Zhao, Hongping, and Singisetti, Uttam
- Subjects
CHEMICAL vapor deposition ,MASS spectrometry ,DOPING agents (Chemistry) - Abstract
The lack of p-type doping has impeded the development of vertical gallium oxide (Ga
2 O3 ) devices. Current blocking layers (CBLs) using implanted deep acceptors have been used to demonstrate vertical devices. This paper presents a pioneering demonstration of in situ Mg-doped β-Ga2 O3 CBLs grown using metal–organic chemical vapor deposition. The Mg-doping density during growth was calibrated by quantitative secondary ion mass spectroscopy. Electrical test structures were designed with in situ Mg doped layers with various targeted Mg doping concentrations. The effectiveness of the CBL is characterized by using temperature-dependent current–voltage measurements using n-Mg-doped-n structures, providing crucial insight into the underlying mechanisms. Pulsed measurements show similar blocking characteristics as DC. To further validate the experimental results, a TCAD simulation is performed, and the electrically active effective doping is found to be dependent on the Mg-doping density, offering an alternate perspective on the optimization of CBL performance. Breakdown measurements show a peak 4 MV/cm field strength. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
35. α‑Tertiary Primary Amine Synthesis via Photocatalytic C(sp3)–H Aminoalkylation.
- Author
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Zhao, Hongping, Hu, Yuanyuan, Zheng, Songlin, and Yuan, Weiming
- Published
- 2023
- Full Text
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36. Trap characterization of high-growth-rate laser-assisted MOCVD GaN.
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Li, Wenbo, Zhang, Yuxuan, Chen, Zhaoying, Zhao, Hongping, Ringel, Steven A., and Arehart, Aaron R.
- Subjects
GALLIUM nitride ,CHEMICAL vapor deposition ,OPTICAL spectroscopy ,PITFALL traps ,POINT defects ,OPTICAL tweezers ,ELECTRON traps ,GALLIUM - Abstract
A detailed study comparing defect incorporation between laser-assisted metal-organic chemical vapor deposition (MOCVD)-grown GaN and conventional low- and high-growth-rate MOCVD GaN was conducted. Using deep-level transient and optical spectroscopy, traps throughout the bandgap were characterized where traps were found at E
C -0.25 eV, EC -0.57 eV, EC -0.72 eV, EC -0.9 eV, EC -1.35 eV, EC -2.6 eV, and EC -3.28 eV in all three samples. This indicates no new traps were observed in the laser-assisted MOCVD GaN sample. Overall, the trap concentrations in the laser-assisted MOCVD sample were ∼2× higher than the optimal low-growth-rate sample, but this is primarily due to the increase in gallium vacancy EC -2.6 eV and carbon-related EC -3.28 eV trap concentrations. The EC -0.9 eV trap concentration was ∼2× higher in the laser-assisted sample, so proton irradiation experiments were conducted to identify the physical source of this level. The results indicated this was a native point defect likely related to gallium interstitials. Overall, this study shows that the laser-assisted MOCVD growth method is promising for future thick, high-quality GaN epilayers after further growth optimizations. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
37. Temperature dependent characteristics of β-Ga2O3 FinFETs by MacEtch.
- Author
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Ren, Zhongjie, Huang, Hsien-Chih, Lee, Hanwool, Chan, Clarence, Roberts, Henry C., Wu, Xihang, Waseem, Aadil, Bhuiyan, A F M Anhar Uddin, Zhao, Hongping, Zhu, Wenjuan, and Li, Xiuling
- Subjects
METAL oxide semiconductor field-effect transistors ,FIELD-effect transistors ,DEBYE temperatures ,THRESHOLD voltage ,THERMAL stability ,HIGH temperatures - Abstract
Understanding the thermal stability and degradation mechanism of β-Ga
2 O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial for their high-power electronics applications. This work examines the high temperature performance of the junctionless lateral β-Ga2 O3 FinFET grown on a native β-Ga2 O3 substrate, fabricated by metal-assisted chemical etching with Al2 O3 gate oxide and Ti/Au gate metal. The thermal exposure effect on threshold voltage (Vth ), subthreshold swing (SS), hysteresis, and specific on-resistance (Ron,sp ), as a function of temperature up to 298 °C, is measured and analyzed. SS and Ron,sp increased with increasing temperatures, similar to the planar MOSFETs, while a more severe negative shift of Vth was observed for the high aspect-ratio FinFETs here. Despite employing a much thicker epilayer (∼2 μm) for the channel, the high temperature performance of Ion /Ioff ratios and SS of the FinFET in this work remains comparable to that of the planar β-Ga2 O3 MOSFETs reported using epilayers ∼10–30× thinner. This work paves the way for further investigation into the stability and promise of β-Ga2 O3 FinFETs compared to their planar counterparts. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
38. The role of carbon and C-H neutralization in MOCVD β-Ga2O3 using TMGa as precursor.
- Author
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Meng, Lingyu, Bhuiyan, A F M Anhar Uddin, and Zhao, Hongping
- Subjects
CHEMICAL vapor deposition ,CARRIER density ,MASS spectrometry ,THIN films ,LOW temperatures - Abstract
In this Letter, the role of background carbon in metalorganic chemical vapor deposition (MOCVD) β-Ga
2 O3 growth using trimethylgallium (TMGa) as the Ga precursor was investigated. The quantitative C and H incorporations in MOCVD β-Ga2 O3 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-Ga2 O3 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-Ga2 O3 . 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-Ga2 O3 and the effect of H incorporation will provide guidance on designing material synthesis for targeted device applications. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
39. Design of InGaN-ZnSnGa2N4 quantum wells for high-efficiency amber light emitting diodes.
- Author
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Zhang, Kaitian, Hu, Chenxi, Thirupakuzi Vangipuram, Vijay Gopal, Kash, Kathleen, and Zhao, Hongping
- Subjects
QUANTUM wells ,LIGHT emitting diodes ,INDIUM gallium nitride ,ION recombination ,CONDUCTION bands ,VALENCE bands ,CONDUCTION electrons - Abstract
A novel type-II InGaN-ZnSnGa
2 N4 quantum well (QW) structure is proposed based on recent experimental achievements for the successful epitaxy of ZnSnNbscript>2-GaN alloys and the determination of their band offsets with GaN. The simulation results indicate that this structure is promising as the active region for high-efficiency InGaN-based amber (λ ∼ 590 nm) light-emitting diodes (LEDs). The hole wavefunction in the valence band is better confined with the insertion of a monolayer scale of ZnSnGa 2 N4 into the InGaN QW while the electron wavefunction in the conduction band is better confined with the incorporation of an AlGaN layer in the GaN quantum barrier. The band structure of the InGaN-ZnSnGa2 N4 QW is numerically simulated based on the experimentally measured band offsets between ZnSnGa2 N4 and GaN. With the InGaN-ZnSnGa2 N4 QW design, a low In content (20%) is required in the InGaN layer to reach a peak emission wavelength of ∼590 nm, yet an In composition of 25% is needed to reach the same emission wavelength for a conventional InGaN QW with the same layer thicknesses. Moreover, the electron-hole wavefunction overlap (Гe1−hh1 ) for the InGaN-ZnSnGa2 N4 QW design reaches 18% for an emission wavelength at ∼590 nm. This result is much improved over the conventional InGaN QW overlap of 5% emitting at the same wavelength. The increase in electron-hole wavefunction overlap results in an approximately 14 times enhancement in the predicted spontaneous emission radiative recombination rate of the InGaN-ZnSnGa2 N4 QW as compared to that of the conventional InGaN QW. This InGaN-ZnSnGa2 N4 QW structure design can be promising to pave a new way to achieve high efficiency amber LEDs. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
40. Scaled β-Ga2O3 thin channel MOSFET with 5.4 MV/cm average breakdown field and near 50 GHz fMAX.
- Author
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Saha, Chinmoy Nath, Vaidya, Abhishek, Bhuiyan, A. F. M. Anhar Uddin, Meng, Lingyu, Sharma, Shivam, Zhao, Hongping, and Singisetti, Uttam
- Subjects
METAL organic chemical vapor deposition ,METAL oxide semiconductor field-effect transistors ,BREAKDOWN voltage ,SILICON nitride ,INDIUM gallium zinc oxide ,LENGTH measurement - Abstract
This Letter reports a high performance β -Ga
2 O3 thin channel MOSFET with T gate and degenerately doped (n++) source/drain contacts regrown by metal organic chemical vapor deposition. Highly scaled T-gate with a gate length of 160–200 nm was fabricated to achieve enhanced RF performance and passivated with 200 nm silicon nitride. Peak drain current (ID,MAX ) of 285 mA/mm and peak transconductance (gm ) of 52 mS/mm were measured at 10 V drain bias with 23.5 Ω mm on resistance (RON ). Metal/n++ contact resistance of 0.078 Ω mm was extracted from transfer length measurements. RON is possibly dominated by interface resistance between channel and highly doped n++ regrown layer. A gate-to-drain breakdown voltage of 192 V is measured for LGD = 355 nm resulting in average breakdown field (EAVG ) of 5.4 MV/cm. This EAVG is the highest reported among all sub-micron gate length lateral FETs. Current gain cut off frequency (fT ) of 11 GHz and record power gain cut off frequency (fMAX ) of approximately 48 GHz were extracted from small signal measurements. fT is limited by DC-RF dispersion due to interface traps which needs further investigation. The fT ·VBR product is 2.112 THz V for 192 V breakdown voltage. Device surpasses the switching figure of merit of Silicon and competitive with mature wide bandgap devices. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
41. Metalorganic vapor phase epitaxy and characterizations of nearly-lattice-matched AlInN alloys on GaN/sapphire templates and free-standing GaN substrates
- Author
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Liu, Guangyu, Zhang, Jing, Li, Xiao-Hang, Huang, G.S., Paskova, Tanya, Evans, Keith R., Zhao, Hongping, and Tansu, Nelson
- Published
- 2012
- Full Text
- View/download PDF
42. Ultrafast growth rate and high mobility In2O3 films grown on c-sapphire via low pressure chemical vapor deposition.
- Author
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Zhang, Yuxuan, Karim, Md Rezaul, Feng, Zixuan, and Zhao, Hongping
- Subjects
CHEMICAL vapor deposition ,INDIUM oxide ,OPTOELECTRONIC devices ,SCHOTTKY barrier diodes ,MOLECULAR beam epitaxy ,SEMICONDUCTOR doping - Abstract
In this study, the growth of unintentionally doped semiconductor indium oxide with ultrafast growth rates on c-plane sapphire by low pressure chemical vapor deposition (LPCVD) was demonstrated. The effect of key growth parameters, such as oxygen flow rate and distance between the substrate to the indium source, on the growth rate, crystalline quality, surface morphology, as well as carrier transport properties were studied. The growth rate is highly dependent on the oxygen flow rate and the distance between the indium source and the substrate: (i) the growth rate reaches 113 μm/h with an oxygen flow rate of 75 sccm under the investigated growth condition; and (ii) it decreases exponentially with the increase of distance between the indium source and the substrate. X-ray diffraction characterization of the as-grown films indicates that the increase of oxygen flow rate leads to the suppression of (100) facet formation, significantly influencing the film morphology. The LPCVD growth conditions also determine the background doping and carrier mobility. With an oxygen flow rate of 75 sccm, a high electron mobility of 126 cm
2 V−1 s−1 with a bulk concentration of 3.9 × 1017 cm−3 was obtained. Results from this work provide guidance on LPCVD growth of In2 O3 with targeted growth rate, surface morphology, carrier concentration, and mobility. [ABSTRACT FROM AUTHOR] more...- Published
- 2019
- Full Text
- View/download PDF
43. Degradation of dyes using hollow copper microspheres as catalyst
- Author
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Xia, Lixin, Zhao, Hongping, Liu, Guangye, Hu, Xinhu, Liu, Yuan, Li, Jushi, Yang, Donghui, and Wang, Xiaofang
- Published
- 2011
- Full Text
- View/download PDF
44. Investigation of carbon incorporation in laser-assisted MOCVD of GaN.
- Author
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Zhang, Yuxuan, Thirupakuzi Vangipuram, Vijay Gopal, Zhang, Kaitian, and Zhao, Hongping
- Subjects
GALLIUM nitride ,CHEMICAL vapor deposition - Abstract
Background carbon (C) impurity incorporation in metalorganic chemical vapor deposition (MOCVD) grown gallium nitride (GaN) represents one of the major issues in further improving GaN vertical power device performance. This work presents a laser-assisted MOCVD (LA-MOCVD) technique to address the high-C issue in MOCVD homoepitaxial GaN under different growth rate (R
g ) regimes and studies the correlations between [C] and Rg . [C] in LA-MOCVD GaN is reduced by 50%–90% as compared to the conventional MOCVD GaN for a wide growth rate range between 1 and 16 μm/h. A mass-transport based model is developed to understand the C incorporation at different Rg regimes. The results obtained from the developed model are in good agreement with experimental data. The model further reveals that LA-MOCVD effectively suppresses C incorporation by reducing the active C species in the gas phase. Moreover, high step velocity in step flow growth mode can facilitate C incorporation at fast Rg , exhibiting steeper C increase. The theoretical model indicates that [C] can be suppressed below 1016 cm−3 with a fast growth rate (Rg ) of 10 μm/h by utilizing higher power LA-MOCVD and freestanding GaN substrates with larger off-cut angles. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
45. Metalorganic chemical vapor deposition of β-(AlxGa1−x)2O3 thin films on (001) β-Ga2O3 substrates.
- Author
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Uddin Bhuiyan, A F M Anhar, Meng, Lingyu, Huang, Hsien-Lien, Sarker, Jith, Chae, Chris, Mazumder, Baishakhi, Hwang, Jinwoo, and Zhao, Hongping
- Subjects
CHEMICAL vapor deposition ,THIN films ,ATOM-probe tomography ,GALLIUM alloys ,X-ray photoelectron spectroscopy ,CONDUCTION bands ,DIAMOND films - Abstract
Phase pure β-(Al
x Ga1−x )2 O3 thin films are grown on (001) oriented β-Ga2 O3 substrates via metalorganic chemical vapor deposition. By systematically tuning the precursor molar flow rates, the epitaxial growth of coherently strained β-(Alx Ga1−x )2 O3 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-(Alx Ga1−x )2 O3 films (x < 25%) on (001) β-Ga2 O3 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-(Alx Ga1−x )2 O3 /β-Ga2 O3 superlattice structure. Room temperature Raman spectra of β-(Alx Ga1−x )2 O3 films show similar characteristics peaks as the (001) β-Ga2 O3 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-(Alx Ga1−x )2 O3 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-(Alx Ga1−x )2 O3 /β-Ga2 O3 heterojunctions using x-ray photoelectron spectroscopy reveal the formation of type-II (staggered) band alignment. [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
46. Vertical GaN-on-GaN pn power diodes with Baliga figure of merit of 27 GW/cm2.
- Author
-
Talesara, Vishank, Zhang, Yuxuan, Vangipuram, Vijay Gopal Thirupakuzi, Zhao, Hongping, and Lu, Wu
- Subjects
DIODES ,BREAKDOWN voltage ,HIGH voltages ,OHMIC contacts ,GALLIUM nitride ,LOW voltage systems - Abstract
High power vertical GaN devices are in great demand recently due to their potential on extremely high-power conversion efficiency. Here, we show vertical GaN p–n power diodes fabricated on bulk GaN substrates with an optimized guard ring structure for electrical field management and high breakdown voltage. By using a low doped (∼10
15 cm−3 ) 28 μm thick drift layer in combination with optimized ohmic contacts, a breakdown voltage (VB ) of 4.9 kV and a low specific on-resistance (RON ) of 0.9 mΩ cm2 were achieved. In combination with the high breakdown voltage and low specific on-resistance, the device demonstrated a Baliga figure of merit (V2 B /RON ) of 27 GW/cm2 . [ABSTRACT FROM AUTHOR] more...- Published
- 2023
- Full Text
- View/download PDF
47. Three-component reductive conjugate addition/aldol tandem reaction enabled by nickel/photoredox dual catalysis.
- Author
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Zhao, Hongping and Yuan, Weiming
- Published
- 2023
- Full Text
- View/download PDF
48. The effect of c-di-GMP (3′–5′-cyclic diguanylic acid) on the biofilm formation and adherence of Streptococcus mutans
- Author
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Yan, Wenjuan, Qu, Tiejun, Zhao, Hongping, Su, Lingyun, Yu, Qing, Gao, Jie, and Wu, Buling
- Published
- 2010
- Full Text
- View/download PDF
49. A one-step facile synthesis of Ag–Ni core–shell nanoparticles in water-in-oil microemulsions
- Author
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Xia, Lixin, Hu, Xinhu, Kang, Xiaobo, Zhao, Hongping, Sun, Mengtao, and Cihen, Xiaowei
- Published
- 2010
- Full Text
- View/download PDF
50. Current injection efficiency induced efficiency-droop in InGaN quantum well light-emitting diodes
- Author
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Zhao, Hongping, Liu, Guangyu, Arif, Ronald A., and Tansu, Nelson
- Published
- 2010
- Full Text
- View/download PDF
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