Kaitian Zhang

Chongqing University

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Hongping Zhao

The Ohio State University

Vijay Gopal Thirupakuzi Vangipuram

The Ohio State University

Zhong Zheng

Chongqing University

Jinwoo Hwang

The Ohio State University

Liu Zhang

Zhejiang Sci-Tech University

K. Kash

Case Western Reserve University

Yuxuan Zhang

The Ohio State University

Yi Chai

Karyopharm Therapeutics (United States)

Xiaoyuan Lian

Chongqing University

Sujun Chen

East China Normal University

Cooperative Institutions

Chongqing University

The Ohio State University

University of Science and Technology of China

University at Buffalo, State University of New York

Chinese Academy of Sciences

Peking University

Central South University

Huazhong University of Science and Technology

Beijing Zhongke Science and Technology (China)

Gaozhou People's Hospital

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Suppressing Carbon Incorporation in Metal–Organic Chemical Vapor Deposition GaN Using High‐Offcut‐Angled Substrates

physica status solidi (RRL) - Rapid Research Letters (2023)

Vijay Gopal Thirupakuzi Vangipuram Kaitian Zhang Hongping Zhao

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 ).

Carbon fibers

10.1002/pssr.202300318

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Hybrid prediction method of blast furnace gas generation considering multi-operation modes in steel plants near the city

Sustainable Energy Technologies and Assessments (2023)

Kai Zhang Zhong Zheng Mingmei Zhu Hongsheng Chen Tairan Guo

Blast furnace gas

Mode (computer interface)

10.1016/j.seta.2023.103031

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Discovery of a Robust P‐Type Ultrawide Bandgap Oxide Semiconductor: LiGa₅O₈

Advanced Electronic Materials (2023)

Kaitian Zhang Vijay Gopal Thirupakuzi Vangipuram Hsien‐Lien Huang Jinwoo Hwang Hongping Zhao

Abstract LiGa 5 O 8 , an ultrawide bandgap semiconductor, is discovered to exhibit p ‐type conductivity at room temperature, making it the widest bandgap p ‐type oxide semiconductor known to date. Utilizing a mist–chemical vapor deposition (M–CVD) technique, successful growth of p ‐type LiGa 5 O 8 thin films on c ‐plane sapphire and GaN‐on‐sapphire substrates is achieved. Characterization through X‐ray diffraction and cross‐sectional scanning transmission electron microscopy (STEM) confirms the spinel cubic crystal structure of LiGa 5 O 8 . Comprehensive investigations into the effects of growth conditions on surface morphology, material composition, and p ‐type charge carrier transport are conducted. As‐grown LiGa 5 O 8 thin films exhibit a broad range of hole concentrations, ranging from 10 15 cm −3 to 10 18 cm −3 , depending on growth conditions. Elemental compositions of Li, Ga, and O are extracted using X‐ray photoemission spectroscopy (XPS). Both Li‐poor and Li‐rich LiGa 5 O 8 films demonstrate p ‐type conductivity. Optical absorption measurements reveal the bandgap of LiGa 5 O 8 films to be ≈5.36 eV. Additionally, temperature‐dependent Hall measurements of the p ‐type LiGa 5 O 8 thin films show robust p ‐conductivity down to 150 K. Results from this study promise the advancement of future power electronics based on ultrawide bandgap Ga 2 O 3 and related semiconductor material systems.

LIGA

Wide-bandgap semiconductor

10.1002/aelm.202300550

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Laser‐Assisted Metal–Organic Chemical Vapor Deposition of Gallium Nitride

physica status solidi (RRL) - Rapid Research Letters (2021)

Yuxuan Zhang Zhaoying Chen Kaitian Zhang Zixuan Feng Hongping Zhao

Ammonia (NH 3 ) is commonly used as group‐V precursor in gallium nitride (GaN) metal–organic chemical vapor deposition (MOCVD). The high background carbon (C) impurity in MOCVD GaN is related to the low decomposition efficiency of NH 3 , which represents one of the fundamental challenges hindering the development of high‐purity thick GaN for vertical high‐power device applications. This work uses a laser‐assisted MOCVD (LA‐MOCVD) growth technique to address the high‐C issue in MOCVD GaN. A carbon dioxide (CO 2 ) laser with a wavelength of 9.219 μm is utilized to facilitate NH 3 decomposition via resonant vibrational excitation. The LA‐MOCVD GaN growth rate (GR; as high as 10 μm h −1 ) shows a strong linear relationship with the trimethylgallium (TMGa) flow rate, indicating high effective V/III ratios and, hence, efficient NH 3 decomposition. [C] in LA‐MOCVD GaN films decreases monotonically, as the laser power increases. A low [C] at 5.5 × 10 15 cm −3 is achieved in the LA‐MOCVD GaN film grown with GR of 4 μm h −1 . LA‐MOCVD GaN films reveal high crystalline quality with room‐temperature mobility of >1000 cm 2 V −1 s −1 . LA‐MOCVD provides an enabling route to achieve high‐quality GaN epitaxy with low‐C and fast GR simultaneously. This technique can be extended for epitaxy of other nitride‐based semiconductors.

Trimethylgallium

10.1002/pssr.202100202

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Citations (18)

Band Structure Engineering Based on InGaN/ZnGeN₂ Heterostructure Quantum Wells for Visible Light Emitters

Crystal Growth & Design (2021)

Md Rezaul Karim Benthara Hewage Dinushi Jayatunga Kaitian Zhang Menglin Zhu Jinwoo Hwang

Band structure engineering based on InGaN/ZnGeN2 heterostructure quantum wells (QWs) is proposed to address the long-standing charge separation challenge in visible light emitters using polar InGaN QWs as active media. A nanometer-scale layer of ZnGeN2 is successfully incorporated in InGaN QWs via metalorganic chemical vapor deposition. Understanding the structural properties of the heterostructure QWs reveals that the growth conditions for the GaN barrier layers play an important role in the QW properties. Specifically, the structural quality of the QWs is improved by increasing the thickness and the growth temperature of the GaN barrier layers. Due to the large band offset at the InGaN/ZnGeN2 heterointerface, the position and thickness of the ZnGeN2 sub-layer within the InGaN QWs determine the potential minima and thus the carrier wave functions in both conduction and valence bands. This work demonstrates the effectiveness of emission wavelength tunability of InGaN/ZnGeN2/InGaN heterostructure QWs via tuning of the ZnGeN2 sub-layer properties. More significantly, the peak emission of InGaN/ZnGeN2/InGaN heterostructure QWs can be extended to longer wavelengths without increasing the In composition or the QW thickness. Results from this work provide a new route for addressing the low quantum efficiency of conventional InGaN QWs emitting at green and longer wavelengths.

Band offset

Barrier layer

Wide-bandgap semiconductor

10.1021/acs.cgd.1c00630

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Citations (5)

Effect of varying threading dislocation densities on the optical properties of InGaN/GaN quantum wells with intentionally created V-shaped pits

Journal of Vacuum Science & Technology B Nanotechnology and Microelectronics Materials Processing Measurement and Phenomena (2023)

Kaitian Zhang Chenxi Hu Vijay Gopal Thirupakuzi Vangipuram Lingyu Meng Christopher Chae

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 × 108 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.

Threading (protein sequence)

10.1116/6.0003141

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Citations (1)

Atomic Scale Defect Formation and Evolution at LiGa5O8/β-Ga2O3 and Ga2O3/Ni/Au Interfaces

Microscopy and Microanalysis (2024)

Christopher Chae Kaitian Zhang Daram N. Ramdin Vijay Gopal Thirupakuzi Vangipuram L. J. Brillson

Atomic units

10.1093/mam/ozae044.529

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Experimental determination of the band offsets at the UWBG p-LiGa5O8/Ga2O3 interface

Applied Physics Letters (2024)

Kaitian Zhang Vijay Gopal Thirupakuzi Vangipuram Christopher Chae Jinwoo Hwang Hongping Zhao

LiGa5O8, a recently discovered ultrawide bandgap semiconductor exhibiting p-type conductivity at room temperature, is grown on (010) β-Ga2O3 substrate. Utilizing a mist chemical vapor deposition method, LiGa5O8 thin film grown on insulating Ga2O3 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 LiGa5O8 along the [110] direction. Moreover, the valence and conduction band offsets at p-LiGa5O8/β-Ga2O3 heterointerface were determined via x-ray photoelectron spectroscopy. The determined band alignments at LiGa5O8/β-Ga2O3 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-Ga2O3 ultrawide bandgap semiconductors.

Interface (matter)

10.1063/5.0200125

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Biofabrication, characterization and unveiling the biological potential of zinc oxide nanoparticles from bacterium Bacillus pacificus KR A1

Surfaces and Interfaces (2024)

Durairaj Karthick Rajan Jinzheng Wu Li Hao Kaitian Zhang Shubing Zhang

Biofabrication

Characterization

Bacillus (shape)

10.1016/j.surfin.2024.105382

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Design of InGaN-ZnSnGa2N4 quantum wells for high-efficiency amber light emitting diodes

Journal of Vacuum Science & Technology A Vacuum Surfaces and Films (2023)

Kaitian Zhang Chenxi Hu Vijay Gopal Thirupakuzi Vangipuram K. Kash Hongping Zhao

A novel type-II InGaN-ZnSnGa2N4 quantum well (QW) structure is proposed based on recent experimental achievements for the successful epitaxy of ZnSnN2-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 ZnSnGa2N4 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-ZnSnGa2N4 QW is numerically simulated based on the experimentally measured band offsets between ZnSnGa2N4 and GaN. With the InGaN-ZnSnGa2N4 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-ZnSnGa2N4 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-ZnSnGa2N4 QW as compared to that of the conventional InGaN QW. This InGaN-ZnSnGa2N4 QW structure design can be promising to pave a new way to achieve high efficiency amber LEDs.

10.1116/6.0002524

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Citations (1)