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Hongyu Tang
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7 records found
1
Journal article
(2025)
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Hongyu Tang, Weiqi Shi, Yifan Ding, Jiao Qi, Shuai Wu, Weiming Liu, Gaoyuan Wang, Jiajie Fan, Rongjun Zhang, Guoqi Zhang
The study focuses on the optical and electrical properties of Tungsten Ditelluride (WTe2), a type II Weyl semimetal, as well as the influence of its self-limiting oxide (SLO) layer that forms during natural oxidation. WTe2 exhibits promising applications in photodetection and energy harvesting due to its unique gapless linear dispersion and Berry-field-enhanced nonlinear optical effects. However, surface oxidation poses a challenge as it degrades the performance of WTe2. By employing spectroscopic ellipsometry and Raman spectroscopy, the progression of the oxide layer’s thickness and its impact on the optical constants of WTe2 were examined. The results revealed a rapid increase in oxide thickness within the first 24 h, and it reached saturation at ∼10 nm after 45 h of atmospheric exposure. Electrical properties were explored using Kelvin Probe Force Microscopy, uncovering a modification in surface potential and Fermi level following oxidation. Additionally, a SLO/WTe2 heterojunction device exhibited a wide region of positive and negative coexisting photocurrent, highlighting the potential for logical operations in ambient air. Finally, the mechanism of operation of the device is discussed. The electrical and optical properties of the pristine, partially oxidized and fully oxidized WTe2 are analyzed using density functional theory calculations. It shows that the SLO layer has a significant effect on the optical and electronic properties, which is instructive for future wavelength-modulated device optoelectronic logic operations.
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The study focuses on the optical and electrical properties of Tungsten Ditelluride (WTe2), a type II Weyl semimetal, as well as the influence of its self-limiting oxide (SLO) layer that forms during natural oxidation. WTe2 exhibits promising applications in photodetection and energy harvesting due to its unique gapless linear dispersion and Berry-field-enhanced nonlinear optical effects. However, surface oxidation poses a challenge as it degrades the performance of WTe2. By employing spectroscopic ellipsometry and Raman spectroscopy, the progression of the oxide layer’s thickness and its impact on the optical constants of WTe2 were examined. The results revealed a rapid increase in oxide thickness within the first 24 h, and it reached saturation at ∼10 nm after 45 h of atmospheric exposure. Electrical properties were explored using Kelvin Probe Force Microscopy, uncovering a modification in surface potential and Fermi level following oxidation. Additionally, a SLO/WTe2 heterojunction device exhibited a wide region of positive and negative coexisting photocurrent, highlighting the potential for logical operations in ambient air. Finally, the mechanism of operation of the device is discussed. The electrical and optical properties of the pristine, partially oxidized and fully oxidized WTe2 are analyzed using density functional theory calculations. It shows that the SLO layer has a significant effect on the optical and electronic properties, which is instructive for future wavelength-modulated device optoelectronic logic operations.
Journal article
(2025)
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Weiqi shi, Yifang Ding, Shaojun Fang, Hong Zhou, Jiao Qi, Jiajie Fan, Rongjun Zhang, Guoqi Zhang, Hongyu Tang
Van der Waals heterojunctions (vdWHs) have garnered significant attention for their promising applications in optoelectronics, attributed to their exceptional physical attributes. In this study, we present a straightforward approach to fabricating high-performance vdWHs photodetectors. Specifically, we prepared WSOx/WS2 vdWH photodetectors through the ozone oxidation of a WS2 thin films at 100 °C. To characterize the morphology and optical properties of both the WS2 and WSOx/WS2 thin films, we utilized atomic force microscopy (AFM) and Raman spectroscopy. Additionally, X-ray photoelectron spectroscopy (XPS) was employed to delve into the structural evolution by scrutinizing the bonding states of W, O, and S in the WS2 before and after the ozone oxidation process. The resultant WSOx/WS2 vdWH photodetectors exhibited impressive photoelectric performance at wavelengths of 475 nm and 532 nm. It demonstrated a high responsivity of 230.7 A/W, a remarkable specific detectivity of 1.794 × 1011 Jones, and a swift response speed of 60 ms at 475 nm. Furthermore, first-principles calculations based on density functional theory (DFT) were conducted to validate the oxidation kinetics of monolayer WS2, the type II energy band alignment, and the interlayer charge transfer within the WSOx/WS2 vdWH. This research contributes novel insights into the synthesis of two-dimensional transition metal oxides (TMOs)-transition metal dichalcogenides (TMDCs) heterostructures for photodetector applications.
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Van der Waals heterojunctions (vdWHs) have garnered significant attention for their promising applications in optoelectronics, attributed to their exceptional physical attributes. In this study, we present a straightforward approach to fabricating high-performance vdWHs photodetectors. Specifically, we prepared WSOx/WS2 vdWH photodetectors through the ozone oxidation of a WS2 thin films at 100 °C. To characterize the morphology and optical properties of both the WS2 and WSOx/WS2 thin films, we utilized atomic force microscopy (AFM) and Raman spectroscopy. Additionally, X-ray photoelectron spectroscopy (XPS) was employed to delve into the structural evolution by scrutinizing the bonding states of W, O, and S in the WS2 before and after the ozone oxidation process. The resultant WSOx/WS2 vdWH photodetectors exhibited impressive photoelectric performance at wavelengths of 475 nm and 532 nm. It demonstrated a high responsivity of 230.7 A/W, a remarkable specific detectivity of 1.794 × 1011 Jones, and a swift response speed of 60 ms at 475 nm. Furthermore, first-principles calculations based on density functional theory (DFT) were conducted to validate the oxidation kinetics of monolayer WS2, the type II energy band alignment, and the interlayer charge transfer within the WSOx/WS2 vdWH. This research contributes novel insights into the synthesis of two-dimensional transition metal oxides (TMOs)-transition metal dichalcogenides (TMDCs) heterostructures for photodetector applications.
Journal article
(2024)
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Zhoudong Yang, Xinyue Wang, Yuanhui Zuo, Zhuorui Tang, Hongyu Tang, Rongjun Zhang, Xuejun Fan, Guoqi Zhang, Jiajie Fan, More Authors...
4H-SiC is widely used in power electronics owing to its superior physical properties. However, temperature-induced stresses compromise the reliability of 4H-SiC power devices in high-temperature applications, warranting precise, and nondestructive stress characterization responsive to temperature variations. Herein, a temperature-dependent predictive model is proposed for analyzing the Raman shift–stress in 4H-SiC. The 4H-SiC epitaxial samples prepared via chemical vapor deposition are characterized using in situ variable-temperature Raman spectroscopy, resulting in a temperature correction factor of approximately −0.021 cm−1 K−1, which is integrated into the conventional Raman shift–stress relationship to assess stress variations induced by temperature variations. The elastic modulus tensor of 4H-SiC at various temperatures determined using molecular dynamics simulations indicates a linear reduction in modulus with increasing temperature. This variable temperature modulus is incorporated into the Raman shift–stress relationship. Furthermore, a finite element method is used for model simplification to perform stress calculations in three axial directions. The experimental results confirm the consistency between calculated and experimental values with a 10% error range under the uniaxial stress condition. The study findings provide valuable insights into assessing stress evolution in 4H-SiC under temperature variations based on Raman spectroscopy, thereby advancing the application of spectroscopic techniques in material stress detection.
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4H-SiC is widely used in power electronics owing to its superior physical properties. However, temperature-induced stresses compromise the reliability of 4H-SiC power devices in high-temperature applications, warranting precise, and nondestructive stress characterization responsive to temperature variations. Herein, a temperature-dependent predictive model is proposed for analyzing the Raman shift–stress in 4H-SiC. The 4H-SiC epitaxial samples prepared via chemical vapor deposition are characterized using in situ variable-temperature Raman spectroscopy, resulting in a temperature correction factor of approximately −0.021 cm−1 K−1, which is integrated into the conventional Raman shift–stress relationship to assess stress variations induced by temperature variations. The elastic modulus tensor of 4H-SiC at various temperatures determined using molecular dynamics simulations indicates a linear reduction in modulus with increasing temperature. This variable temperature modulus is incorporated into the Raman shift–stress relationship. Furthermore, a finite element method is used for model simplification to perform stress calculations in three axial directions. The experimental results confirm the consistency between calculated and experimental values with a 10% error range under the uniaxial stress condition. The study findings provide valuable insights into assessing stress evolution in 4H-SiC under temperature variations based on Raman spectroscopy, thereby advancing the application of spectroscopic techniques in material stress detection.
Tungsten disulfide (WS2) has recently attracted considerable attention owing to its excellent physical, chemical, electronic, and optical properties, leading to increased research into its applications in electronic and optoelectronic devices. However, the oxidation of 2D material affects significantly its optical and electronic properties during storage or processing. This study employs density functional theory (DFT) to analyze the effects of natural and thermal oxidation on the optical and electronic properties of WS2 monolayer. First, the climbing-image nudged elastic band (cNEB) method is applied to analyze transitional states and the potential barriers of WS2 oxidation. It reveals that primarily involves the bonding of oxygen atoms with sulfur atoms, whereas thermal oxidation introduces both oxygen substitutions and generates oxygen vacancies. Second, the electron band structures after natural and thermal oxidation are comparably analyzed, which reveals that natural and thermal oxidation both can narrow the bandgap. Lastly, we investigate the optical properties of WS2 monolayer under different oxidation conditions. The results demonstrate that natural oxidation results in weakened light absorption and a blue shift relative to the pristine WS2, whereas thermal oxidation enhances absorption and induces a red shift. These findings underscore the importance of carefully managing oxidation conditions to effectively modulate the optoelectronic properties of WS2.
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Tungsten disulfide (WS2) has recently attracted considerable attention owing to its excellent physical, chemical, electronic, and optical properties, leading to increased research into its applications in electronic and optoelectronic devices. However, the oxidation of 2D material affects significantly its optical and electronic properties during storage or processing. This study employs density functional theory (DFT) to analyze the effects of natural and thermal oxidation on the optical and electronic properties of WS2 monolayer. First, the climbing-image nudged elastic band (cNEB) method is applied to analyze transitional states and the potential barriers of WS2 oxidation. It reveals that primarily involves the bonding of oxygen atoms with sulfur atoms, whereas thermal oxidation introduces both oxygen substitutions and generates oxygen vacancies. Second, the electron band structures after natural and thermal oxidation are comparably analyzed, which reveals that natural and thermal oxidation both can narrow the bandgap. Lastly, we investigate the optical properties of WS2 monolayer under different oxidation conditions. The results demonstrate that natural oxidation results in weakened light absorption and a blue shift relative to the pristine WS2, whereas thermal oxidation enhances absorption and induces a red shift. These findings underscore the importance of carefully managing oxidation conditions to effectively modulate the optoelectronic properties of WS2.
Journal article
(2024)
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Zhuorui Tang, Shibo Zhao, Jian Li, Yuanhui Zuo, Jing Tian, Hongyu Tang, Jiajie Fan, Guoqi Zhang
This work addresses a novel technique for selecting the best process parameters for the 4H–SiC epitaxial layer in a horizontal hot-wall chemical vapor reactor using a transient multi-physical (thermal-fluid-chemical) simulation model and combined with a machine-learning model. An experiment was performed to validate the feasibility of the numerical model. Secondly, a single-factor analysis was conducted to investigate the effects of process parameters, including the deposition temperature, inlet-flow volume, rotational speed of the susceptor, and cavity pressure, on the quality of the 4H–SiC epitaxial layer. Finally, a machine learning algorithm, the ant colony optimization-back propagation neural network (ACO–BPNN), was employed to develop the input/output model and optimize process parameters for obtaining a high-quality epitaxial layer and reducing the optimization cycle and costs. Notably, the optimized process was validated by real experiments, where the error between calculation and experiment is 4.03 % for deposition rate and 0.49 % for coefficient of variation, respectively. The results highlight the model as reliable and lay the foundation for the CVD growth of the 4H–SiC epitaxial layer.
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This work addresses a novel technique for selecting the best process parameters for the 4H–SiC epitaxial layer in a horizontal hot-wall chemical vapor reactor using a transient multi-physical (thermal-fluid-chemical) simulation model and combined with a machine-learning model. An experiment was performed to validate the feasibility of the numerical model. Secondly, a single-factor analysis was conducted to investigate the effects of process parameters, including the deposition temperature, inlet-flow volume, rotational speed of the susceptor, and cavity pressure, on the quality of the 4H–SiC epitaxial layer. Finally, a machine learning algorithm, the ant colony optimization-back propagation neural network (ACO–BPNN), was employed to develop the input/output model and optimize process parameters for obtaining a high-quality epitaxial layer and reducing the optimization cycle and costs. Notably, the optimized process was validated by real experiments, where the error between calculation and experiment is 4.03 % for deposition rate and 0.49 % for coefficient of variation, respectively. The results highlight the model as reliable and lay the foundation for the CVD growth of the 4H–SiC epitaxial layer.
The silicon carbide (SiC) epitaxial growth process is crucial in chip manufacturing. The distribution of the flow and temperature fields in the reactor chamber influences the epitaxial layer uniformity. Therefore, this study optimizes the distribution of the flow and temperature fields inside the reactor to enhance the quality of the epitaxial layer. COMSOL Multiphysics is used to model the horizontal chemical vapor deposition (CVD) reactor chamber, and the flow and temperature fields inside the reactor chamber are analyzed. Factors influencing the uniformity of flow field distribution include the reactant gas distribution and the gas-inlet tunnel’s diameter and position. The flow field uniformity is represented by the relative standard deviation of the velocity. Parameters impacting the temperature field uniformity include the position and pitch of the heating coil and the graphite column width. The heating efficiency of the substrate and temperature uniformity are expressed by the average temperature and standard deviation of the temperature, respectively. Support vector machine (SVM) is used to establish the relationship between design variables and the objective function, and the multi-objective particle swarm optimization (MOPSO) algorithm is used to optimize the reactor. The proposed approach improves the uniformity of the flow and temperature fields and the heating efficiency of the substrate.
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The silicon carbide (SiC) epitaxial growth process is crucial in chip manufacturing. The distribution of the flow and temperature fields in the reactor chamber influences the epitaxial layer uniformity. Therefore, this study optimizes the distribution of the flow and temperature fields inside the reactor to enhance the quality of the epitaxial layer. COMSOL Multiphysics is used to model the horizontal chemical vapor deposition (CVD) reactor chamber, and the flow and temperature fields inside the reactor chamber are analyzed. Factors influencing the uniformity of flow field distribution include the reactant gas distribution and the gas-inlet tunnel’s diameter and position. The flow field uniformity is represented by the relative standard deviation of the velocity. Parameters impacting the temperature field uniformity include the position and pitch of the heating coil and the graphite column width. The heating efficiency of the substrate and temperature uniformity are expressed by the average temperature and standard deviation of the temperature, respectively. Support vector machine (SVM) is used to establish the relationship between design variables and the objective function, and the multi-objective particle swarm optimization (MOPSO) algorithm is used to optimize the reactor. The proposed approach improves the uniformity of the flow and temperature fields and the heating efficiency of the substrate.
The silicon carbide (SiC) epitaxial growth process is crucial in chip manufacturing. The growth rate and uniformity of epitaxial film are two critical evaluation criteria of epitaxial process. In order to obtain a higher growth rate and more uniform epitaxial film, it is necessary to improve the SiC epitaxial growth process. The traditional method to improve the epitaxial growth process is the “trial and error method”, but this method will consume a lot of time and economic costs. Therefore, it is necessary to find an efficient way to simulate the epitaxial growth process of SiC. This work uses computer aided Multiphysics simulation method to study the growth of SiC epitaxial films in a horizontal hot-wall chemical vapor deposition (CVD) reaction chamber. Firstly, a three-dimensional model of a horizontal hot-wall CVD reaction chamber is established, in which the MTS (methyltrichlorosilane)/H2 is used to deposit SiC epitaxial films on large-area substrates. The effects of temperature, gas flow distribution ratio, and pallet speed on the growth rate and uniformity of SiC epitaxial films are studied. The results show that: 1) In the range of 1500K-1600K, the higher temperature brings the higher growth rate of SiC epitaxial film. 2) The gas flow ratio of three groups of air inlets can simultaneously affect the growth rate and uniformity of the SiC epitaxial film. With the greater the airflow at the middle air inlet, the higher growth rate and the lower film uniformity will be obtained. 3) The tray rotation speed does not affect the film growth rate, but the higher of film uniformity will be achieved under the higher tray rotation speed. The simulation results agree well with the experimental results, which proves that the Multiphysics simulation method is feasible and can be used for further optimization of the epitaxial growth process of SiC.
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The silicon carbide (SiC) epitaxial growth process is crucial in chip manufacturing. The growth rate and uniformity of epitaxial film are two critical evaluation criteria of epitaxial process. In order to obtain a higher growth rate and more uniform epitaxial film, it is necessary to improve the SiC epitaxial growth process. The traditional method to improve the epitaxial growth process is the “trial and error method”, but this method will consume a lot of time and economic costs. Therefore, it is necessary to find an efficient way to simulate the epitaxial growth process of SiC. This work uses computer aided Multiphysics simulation method to study the growth of SiC epitaxial films in a horizontal hot-wall chemical vapor deposition (CVD) reaction chamber. Firstly, a three-dimensional model of a horizontal hot-wall CVD reaction chamber is established, in which the MTS (methyltrichlorosilane)/H2 is used to deposit SiC epitaxial films on large-area substrates. The effects of temperature, gas flow distribution ratio, and pallet speed on the growth rate and uniformity of SiC epitaxial films are studied. The results show that: 1) In the range of 1500K-1600K, the higher temperature brings the higher growth rate of SiC epitaxial film. 2) The gas flow ratio of three groups of air inlets can simultaneously affect the growth rate and uniformity of the SiC epitaxial film. With the greater the airflow at the middle air inlet, the higher growth rate and the lower film uniformity will be obtained. 3) The tray rotation speed does not affect the film growth rate, but the higher of film uniformity will be achieved under the higher tray rotation speed. The simulation results agree well with the experimental results, which proves that the Multiphysics simulation method is feasible and can be used for further optimization of the epitaxial growth process of SiC.