β-Ga2O3 has drawn much attention in the field of power and radio frequency electronics, due to an ultrawide bandgap energy of ∼4.9 eV and a high breakdown field strength of ~8 MV/ cm (Poncé et al, 2020 Physical Review Research.2 033102). The in-plane lattice mismatch of 2.4% between the (-201) plane of β-Ga2O3 and the (0002) plane of wurtzite AlN is beneficial for the formation of an AlN/β-Ga2O3 heterostructure (Sun et al, 2017 Appl. Phys. Lett.111 162105), which is a potential candidate for β-Ga2O3-based high electron mobility transistors (HEMTs). In this study, the Schrödinger-Poisson equations are solved to calculate the AlN/β-Ga2O3 conduction band profile and the 2DEG sheet density, based on the supposition that the 2DEG originates from door-like surface states distributed evenly below the AlN conduction band. The main scattering mechanisms in AlN/β-Ga2O3 heterostructures, i.e. the ionized impurity scattering, interface roughness scattering, acoustic deformation-potential scattering and polar optical phonon scattering are calculated using the Boltzmann transport theory, moreover, the relative importance of different scattering mechanisms is evaluated. The results show that at room temperature, the 2DEG sheet density increases with increasing AlN thickness, and reaches 1.0×1013cm-2 at an AlN thickness of 6 nm. With the increase of the 2DEG sheet density, the ionized impurity scattering limited mobility increases, but other scattering mechanisms limited mobilities decrease. The interface roughness scattering dominates the mobility at low and moderate temperatures (T<148 K), and the polar optical phonon scattering dominates the mobility at temperatures above 148 K. The room-temperature mobility is 368.6 cm2/Vs for the AlN/β-Ga2O3 heterostructure with an AlN thickness of 6 nm.
由于β-Ga2O3具有~ 4.9 eV的超宽带隙能量和~8 MV/ cm的高击穿场强，在功率和射频电子领域引起了广泛的关注(ponc等人，2020物理评论研究，2 033102)。β-Ga2O3的(-201)面与纤锌矿AlN的(0002)面之间存在2.4%的面内晶格失配，有利于形成AlN/β-Ga2O3异质结构(Sun et al .， 2017)。理论物理。Lett. 111 162105)，它是基于β- ga2o3的高电子迁移率晶体管(HEMTs)的潜在候选者。在本研究中，基于假设2DEG来源于均匀分布于AlN导带下方的门状表面态，求解Schrödinger-Poisson方程，计算AlN/β-Ga2O3导带剖面和2DEG片密度。利用玻尔兹曼输运理论计算了AlN/β-Ga2O3异质结构中的主要散射机制，即电离杂质散射、界面粗糙度散射、声变形势散射和极性光学声子散射，并对不同散射机制的相对重要性进行了评价。结果表明:在室温下，随着AlN厚度的增加，2DEG片密度逐渐增大，当AlN厚度为6 nm时达到1.0×1013cm-2;随着2DEG片密度的增加，离子杂质散射限制迁移率增加，而其他散射机制限制迁移率降低。AlN厚度为6 nm的AlN/β-Ga2O3异质结构在低温和中温(T2/Vs)下的迁移率主要由界面粗糙度散射决定。
{"title":"Studies on Mechanism of Electron Transport in AlN/β-Ga2O3 Heterostructures","authors":"Zhou Zhanhui, Li Qun, He Xiaomin","doi":"10.7498/aps.72.20221545","DOIUrl":"https://doi.org/10.7498/aps.72.20221545","url":null,"abstract":"β-Ga<sub>2</sub>O<sub>3</sub> has drawn much attention in the field of power and radio frequency electronics, due to an ultrawide bandgap energy of ∼4.9 eV and a high breakdown field strength of ~8 MV/ cm (Poncé et al, 2020 <i>Physical Review Research.</i> <b>2</b> 033102). The in-plane lattice mismatch of 2.4% between the (-201) plane of β-Ga<sub>2</sub>O<sub>3</sub> and the (0002) plane of wurtzite AlN is beneficial for the formation of an AlN/β-Ga<sub>2</sub>O<sub>3</sub> heterostructure (Sun et al, 2017<i> Appl. Phys. Lett.</i> <b>111</b> 162105), which is a potential candidate for β-Ga<sub>2</sub>O<sub>3</sub>-based high electron mobility transistors (HEMTs). In this study, the Schrödinger-Poisson equations are solved to calculate the AlN/β-Ga<sub>2</sub>O<sub>3</sub> conduction band profile and the 2DEG sheet density, based on the supposition that the 2DEG originates from door-like surface states distributed evenly below the AlN conduction band. The main scattering mechanisms in AlN/β-Ga<sub>2</sub>O<sub>3</sub> heterostructures, i.e. the ionized impurity scattering, interface roughness scattering, acoustic deformation-potential scattering and polar optical phonon scattering are calculated using the Boltzmann transport theory, moreover, the relative importance of different scattering mechanisms is evaluated. The results show that at room temperature, the 2DEG sheet density increases with increasing AlN thickness, and reaches 1.0×10<sup>13</sup>cm<sup>-2</sup> at an AlN thickness of 6 nm. With the increase of the 2DEG sheet density, the ionized impurity scattering limited mobility increases, but other scattering mechanisms limited mobilities decrease. The interface roughness scattering dominates the mobility at low and moderate temperatures (T<148 K), and the polar optical phonon scattering dominates the mobility at temperatures above 148 K. The room-temperature mobility is 368.6 cm<sup>2</sup>/Vs for the AlN/β-Ga<sub>2</sub>O<sub>3</sub> heterostructure with an AlN thickness of 6 nm.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"1 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77159046","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shi Lu-lin, Cheng Rui, Wang Zhao, Cao Shi-Quan, Yang Jie, Zhou Ze-Xian, Chen Yan-Hong, Wang Guo-Dong, Hui De-Xuan, Jin Xue-Jian, Wu Xiao-Xia, Lei Yu, Wang Yu-Yu, Su Mao-Gen
Ion energy loss in the interaction between highly charged ions and dense plasmas near the Bohr velocity energy region is one of the important physical problems in the field of high-energy density physics driven by intense heavy ion beams. Based on the 320 kV experimental platform at the Institute of Modern Physics, Chinese Academy of Sciences, an experimental setup is newly built for the research of interaction between ions and laser-produced plasmas near the Bohr velocity, where the ion energy loss and charge state distribution can be experimentally investigated. This paper introduces the new setup in detail, including: the generation and controlling of pulsed ions beam ( ≥ 200 ns); the preparation of high-density laser plasma target (1017 ~ 1021 cm-3); the diagnostics of plasmas and the developed high energy resolution ion measurement system (＜1%). In the experiment, the charge distribution was measured where the Xe15+ ions with 4 MeV penetrated through the laser-produced Al plasma target. The charge-state analysis device observed that the different resutls without and with the plasmas, in which the outgoing Xe ions charge-state changes correspondingly from the 15+ to 10+, thus the electron capture process is believed dominates. In addition, the proton energy loss was measred too by using the magnetic spectrometer, and the experimental energy loss is about 2.0 keV which is significantly higher than those theoretical predictions by a factor of 30%. In our consideration, the possible reason can be deduced to that in the near Bohr velocity energy regime, the first-order Born approximation condition is not valid, thus the Bethe and SSM models fail to represent the experimental results. In future, a systematic study will be performed based on our ions-plasmas ineteraction setups and the energy loss and charge state data will be introduced.
{"title":"Experimental setup for interaction between highly charged ions and Laser-produced plasma near the Bohr velocity energy region","authors":"Shi Lu-lin, Cheng Rui, Wang Zhao, Cao Shi-Quan, Yang Jie, Zhou Ze-Xian, Chen Yan-Hong, Wang Guo-Dong, Hui De-Xuan, Jin Xue-Jian, Wu Xiao-Xia, Lei Yu, Wang Yu-Yu, Su Mao-Gen","doi":"10.7498/aps.72.20230214","DOIUrl":"https://doi.org/10.7498/aps.72.20230214","url":null,"abstract":"Ion energy loss in the interaction between highly charged ions and dense plasmas near the Bohr velocity energy region is one of the important physical problems in the field of high-energy density physics driven by intense heavy ion beams. Based on the 320 kV experimental platform at the Institute of Modern Physics, Chinese Academy of Sciences, an experimental setup is newly built for the research of interaction between ions and laser-produced plasmas near the Bohr velocity, where the ion energy loss and charge state distribution can be experimentally investigated. This paper introduces the new setup in detail, including: the generation and controlling of pulsed ions beam ( ≥ 200 ns); the preparation of high-density laser plasma target (1017 ~ 1021 cm-3); the diagnostics of plasmas and the developed high energy resolution ion measurement system (＜1%). In the experiment, the charge distribution was measured where the Xe15+ ions with 4 MeV penetrated through the laser-produced Al plasma target. The charge-state analysis device observed that the different resutls without and with the plasmas, in which the outgoing Xe ions charge-state changes correspondingly from the 15+ to 10+, thus the electron capture process is believed dominates. In addition, the proton energy loss was measred too by using the magnetic spectrometer, and the experimental energy loss is about 2.0 keV which is significantly higher than those theoretical predictions by a factor of 30%. In our consideration, the possible reason can be deduced to that in the near Bohr velocity energy regime, the first-order Born approximation condition is not valid, thus the Bethe and SSM models fail to represent the experimental results. In future, a systematic study will be performed based on our ions-plasmas ineteraction setups and the energy loss and charge state data will be introduced.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"27 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84213310","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The research on the macroscopic properties of neutron stars has great significance for revealing the internal composition and structure of neutron stars. We have analyzed the influence of δ mesons on the equation of states, the maximum masses, the tidal Love numbers and the tidal deformabilities for the conventional neutron stars and the hyperon stars within the relativistic mean field theory. It is found that the presence of δ mesons can strengthen the tidal deformabilities of the low and medium-mass conventional neutron stars (or hyperon stars). However, the strengthening trends of the tidal deformabilities with δ mesons are gradually weakened as the increase of the masses for the conventional neutron (or hyperon stars). Especially for massive hyperon stars, the tidal deformabilities with δ mesons is weaker than the corresponding values without δ mesons. Moreover, the presence of hyperons can reduce the tidal deformabilities of stars with the same mass. For the stars containing δ mesons, only the tidal deformabilities in the hyperon stars with Λ, Σ and Ξ hyperons can satisfy both constraints of GW170817 and GW190814 events under the parameters selected in the paper. As the date on gravitational waves associated with the neutron stars gradually increase, which will provide a possible way for judging the hyperon species in the hyperon stars.
{"title":"Study on the tidal deformabilities of neutron stars in the relativistic mean field approach with δ mesons","authors":"Diao Bin, Xu Yan, Huang Xiu-Lin, Wang Yi-Bo","doi":"10.7498/aps.72.20221599","DOIUrl":"https://doi.org/10.7498/aps.72.20221599","url":null,"abstract":"The research on the macroscopic properties of neutron stars has great significance for revealing the internal composition and structure of neutron stars. We have analyzed the influence of δ mesons on the equation of states, the maximum masses, the tidal Love numbers and the tidal deformabilities for the conventional neutron stars and the hyperon stars within the relativistic mean field theory. It is found that the presence of δ mesons can strengthen the tidal deformabilities of the low and medium-mass conventional neutron stars (or hyperon stars). However, the strengthening trends of the tidal deformabilities with δ mesons are gradually weakened as the increase of the masses for the conventional neutron (or hyperon stars). Especially for massive hyperon stars, the tidal deformabilities with δ mesons is weaker than the corresponding values without δ mesons. Moreover, the presence of hyperons can reduce the tidal deformabilities of stars with the same mass. For the stars containing δ mesons, only the tidal deformabilities in the hyperon stars with Λ, Σ and Ξ hyperons can satisfy both constraints of GW170817 and GW190814 events under the parameters selected in the paper. As the date on gravitational waves associated with the neutron stars gradually increase, which will provide a possible way for judging the hyperon species in the hyperon stars.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"16 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84326489","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
By using non-equilibrium Green's function method, we investigate the thermoelectric properties of the molecular junctions based on acene-linked graphene nanoribbons. In this paper, effects of the length of the acene molecule, the contact position between the acene molecule and graphene nanoribbon electrodes on the thermoelectric parameters is mainly considered. It is found that the phonon contribution is dominant in the thermal conductance corresponding to the maximum of the thermoelectric figure of merit (ZTmax). As the length of the acene molecules increases, the phonon thermal conductance decreases monotonically, and eventually becomes almost independent of the acene molecules’ length. When the acene molecules are in contact with the middle (upper) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is highest. However, when the acene molecules are in contact with the middle (middle) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is lowest. When the temperature increases, ZTmax has an monotonously increasing tendency, regardless of the contact position. With the increase of the length of the acene molecules, the chemical potential corresponding to ZTmax becomes closer to the intrinsic Fermi level. The above findings may provide the valuable reference for the future design of thermoelectric devices based on the acene molecular junctions.
{"title":"A study on the thermoelectric properties of acene molecular junctions","authors":"Xie Zhong-Xiang, 周五星, Yu Xia, Jia Pin-Zhen, Chen Xue-Kun, Deng Yuan-Xiang, Zhang Yong, Zhou Wu-Xing","doi":"10.7498/aps.72.20230354","DOIUrl":"https://doi.org/10.7498/aps.72.20230354","url":null,"abstract":"By using non-equilibrium Green's function method, we investigate the thermoelectric properties of the molecular junctions based on acene-linked graphene nanoribbons. In this paper, effects of the length of the acene molecule, the contact position between the acene molecule and graphene nanoribbon electrodes on the thermoelectric parameters is mainly considered. It is found that the phonon contribution is dominant in the thermal conductance corresponding to the maximum of the thermoelectric figure of merit (ZTmax). As the length of the acene molecules increases, the phonon thermal conductance decreases monotonically, and eventually becomes almost independent of the acene molecules’ length. When the acene molecules are in contact with the middle (upper) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is highest. However, when the acene molecules are in contact with the middle (middle) part of the left (right) electrode of graphene nanoribbons, the corresponding ZTmax is lowest. When the temperature increases, ZTmax has an monotonously increasing tendency, regardless of the contact position. With the increase of the length of the acene molecules, the chemical potential corresponding to ZTmax becomes closer to the intrinsic Fermi level. The above findings may provide the valuable reference for the future design of thermoelectric devices based on the acene molecular junctions.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"47 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83967127","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Liu Zhong-Lei, Cao Jin-Ming, Wang Zhi, Zhao Yu-Hong
The perovskite crystal structure determines the appearance of ferroelectricity and the determination of the polarization direction of ferroelectric ceramics. When the polarization direction has a certain order, different domain structures will combine to form a multiparticle system with a specific morphology, the topological structures that exist in ferroelectrics. In this study, the domain structure of potassium sodium niobate (K0.5Na0.5NbO3) thin films under different hysteresis electric fields and thicknesses was observed by the phase field method. According to the different switching paths of the domain structure under the electric field, the domain is divided into fast and slow switching process. Based on this, a method is proposed to first determine the domain switching state of the desired experiment and then conduct directional observation. Through the analysis of the domain structures combined with the polarization vector, a clear multi-domain combined vortex-antivortex pair topological structure was observed for the first time in K0.5Na0.5NbO3 films. The vortex structure was further analyzed for its switching process, and it was observed that this vortex topological microstructure can make the domain more likely to switch, so that more small-scale polarization vectors can be ordered to form the desired multiparticle system topology. This polarization vector ordering is similar to the microscopic phase boundary formed by the specific polarization directions on both sides of the morphotropic phase boundary (MPB) for the improvement of the dielectric properties of ferroelectric materials.
{"title":"Exploring Ferroelectric Vortex Topology and morphotropic Phase Boundaries by Phase Field Method","authors":"Liu Zhong-Lei, Cao Jin-Ming, Wang Zhi, Zhao Yu-Hong","doi":"10.7498/aps.72.20221898","DOIUrl":"https://doi.org/10.7498/aps.72.20221898","url":null,"abstract":"The perovskite crystal structure determines the appearance of ferroelectricity and the determination of the polarization direction of ferroelectric ceramics. When the polarization direction has a certain order, different domain structures will combine to form a multiparticle system with a specific morphology, the topological structures that exist in ferroelectrics. In this study, the domain structure of potassium sodium niobate (K0.5Na0.5NbO3) thin films under different hysteresis electric fields and thicknesses was observed by the phase field method. According to the different switching paths of the domain structure under the electric field, the domain is divided into fast and slow switching process. Based on this, a method is proposed to first determine the domain switching state of the desired experiment and then conduct directional observation. Through the analysis of the domain structures combined with the polarization vector, a clear multi-domain combined vortex-antivortex pair topological structure was observed for the first time in K0.5Na0.5NbO3 films. The vortex structure was further analyzed for its switching process, and it was observed that this vortex topological microstructure can make the domain more likely to switch, so that more small-scale polarization vectors can be ordered to form the desired multiparticle system topology. This polarization vector ordering is similar to the microscopic phase boundary formed by the specific polarization directions on both sides of the morphotropic phase boundary (MPB) for the improvement of the dielectric properties of ferroelectric materials.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"25 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74000656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Heng-Di Wen, Yue Liu, Liang Zhen, Yang Li, Cheng-Yan Xu
Two-dimensional material heterojunction device with unique photoelectric properties due to its nanoscale thickness and van der Waals contact surface. In this paper, a MoS2/MoTe2 vertical vdWs heterojunction device with Gate-tunable is constructed. The Kelvin probe force microscopy (KPFM) technology is combined with the electric transport measurement technology, which reveals the charge transport behavior of the MoS2/MoTe2 heterojunction under dark and light conditions, including the bipolarity characteristics of the transition from n-n+ junction to p-n junction. This paper comprehensively and systematically explains the charge transport mechanism of heterojunction, including the charge transmission process of n-n+ junction and p-n junction under positive and negative bias conditions, the transformation of nodule behavior with gate voltage, the influence of barriers on charge transmission, the different rectification characteristics between n-n+ junction and p-n junction, the major role of source and leakage bias voltage on band tunneling, and the influence of photogenerated carriers on electrical transmission. The method in this paper can be generalized to other two-dimensional heterojunction systems and provides an important reference and reference for improving the performance of two-dimensional semiconductor devices and their applications in the future.
{"title":"Charge transmission of MoS2/MoTe2 vertical heterojunction and it's modulation","authors":"Heng-Di Wen, Yue Liu, Liang Zhen, Yang Li, Cheng-Yan Xu","doi":"10.7498/aps.72.20221768","DOIUrl":"https://doi.org/10.7498/aps.72.20221768","url":null,"abstract":"Two-dimensional material heterojunction device with unique photoelectric properties due to its nanoscale thickness and van der Waals contact surface. In this paper, a MoS2/MoTe2 vertical vdWs heterojunction device with Gate-tunable is constructed. The Kelvin probe force microscopy (KPFM) technology is combined with the electric transport measurement technology, which reveals the charge transport behavior of the MoS2/MoTe2 heterojunction under dark and light conditions, including the bipolarity characteristics of the transition from n-n+ junction to p-n junction. This paper comprehensively and systematically explains the charge transport mechanism of heterojunction, including the charge transmission process of n-n+ junction and p-n junction under positive and negative bias conditions, the transformation of nodule behavior with gate voltage, the influence of barriers on charge transmission, the different rectification characteristics between n-n+ junction and p-n junction, the major role of source and leakage bias voltage on band tunneling, and the influence of photogenerated carriers on electrical transmission. The method in this paper can be generalized to other two-dimensional heterojunction systems and provides an important reference and reference for improving the performance of two-dimensional semiconductor devices and their applications in the future.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"59 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73092164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cheng Ai-Qiang, Wang Shuai, Xu Zu-Yin, He Jin, Zhang Tian-Cheng, Bao Hua-Guang, Ding Da-Zhi
With the rapid development of wireless communications, GaN HEMTs, which have various advantages of high power density, high electron mobility, and high breakdown threshold, have attracted increasing attention. Microwave power amplifiers based on GaN HEMTs are widely used in many fields, such as communication, medical, and detection instruments. In the accurate design of GaN microwave power amplifiers, reliable RF large signal models are vitally important. In this paper, a scalable large-signal model based on EEHEMT model is proposed to describe the properties of multifinger AlGaN/GaN high electrom mobility transistors (HEMTs) accurately. A series of scaling rules are established for the intrinsic parameters of the device, including drain-source current Ids, input capacitance Cgs and Cgd, which take into account both the gate width of a single finger and the number of gate fingers. With the proposed scalable large-signal model, the performances of the L-band GaN high-efficiency power amplifier with the length of gate of 14.4mm is analyzed. This amplifier demonstrates outstanding performance with the output power up to 46.5dBm and the drain efficiency of over 70% covering the entire frequency range from 1120MHz to 1340MHz. Great agreement between the simulations and experiments is achieved, demonstrating the excellent accuracy of the proposed model. Moreover, the proposed model can further predict the performance of high-order harmonics, providing an effective tool for the design of advanced high-power and high-efficiency microwave power amplifiers. Certainly, the EEHEMT model lacks the ability to characterize the dynamical behavior induced by trap and self-heating effects. Thus, for further consideration, scaling models for the thermal resistance and heat capacity will be investigated to broaden the applicability of the proposed model in the case of continuous waves.
{"title":"A large signal scaling model of high power GaN microwave device","authors":"Cheng Ai-Qiang, Wang Shuai, Xu Zu-Yin, He Jin, Zhang Tian-Cheng, Bao Hua-Guang, Ding Da-Zhi","doi":"10.7498/aps.72.20230440","DOIUrl":"https://doi.org/10.7498/aps.72.20230440","url":null,"abstract":"With the rapid development of wireless communications, GaN HEMTs, which have various advantages of high power density, high electron mobility, and high breakdown threshold, have attracted increasing attention. Microwave power amplifiers based on GaN HEMTs are widely used in many fields, such as communication, medical, and detection instruments. In the accurate design of GaN microwave power amplifiers, reliable RF large signal models are vitally important. In this paper, a scalable large-signal model based on EEHEMT model is proposed to describe the properties of multifinger AlGaN/GaN high electrom mobility transistors (HEMTs) accurately. A series of scaling rules are established for the intrinsic parameters of the device, including drain-source current Ids, input capacitance Cgs and Cgd, which take into account both the gate width of a single finger and the number of gate fingers. With the proposed scalable large-signal model, the performances of the L-band GaN high-efficiency power amplifier with the length of gate of 14.4mm is analyzed. This amplifier demonstrates outstanding performance with the output power up to 46.5dBm and the drain efficiency of over 70% covering the entire frequency range from 1120MHz to 1340MHz. Great agreement between the simulations and experiments is achieved, demonstrating the excellent accuracy of the proposed model. Moreover, the proposed model can further predict the performance of high-order harmonics, providing an effective tool for the design of advanced high-power and high-efficiency microwave power amplifiers. Certainly, the EEHEMT model lacks the ability to characterize the dynamical behavior induced by trap and self-heating effects. Thus, for further consideration, scaling models for the thermal resistance and heat capacity will be investigated to broaden the applicability of the proposed model in the case of continuous waves.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"31 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75861189","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pan Zhi-Peng, Li Wei, Lv Jia-Gang, Nie Yu-Wei, Zhong Li, Liu Su-ping, Ma Xiao-Yu
As the key part of Vertical Cavity Surface Emitting Laser (VCSEL), active region will seriously affect the threshold and efficiency of the device. To obtain appropriate laser wavelength and material gain, the In0.18Ga0.82As strain compensated quantum well is optimized design. The relationship between the lasing wavelength of multiple quantum wells (MQWs) and the thickness is calculated. Take into account the influence between the active region temperature and the lasing wavelength, the thickness of the quantum well is chose as 6 nm, the quantum barrier thickness is chose as 8 nm, corresponding to the lasing wavelength of 929 nm. The material gain characteristics of the MQWs under different temperature are simulated by Rsoft. The material gain exceeds 3300 /cm at 300 K, and the temperature drift coefficient of the peak wavelength is 0.3 nm/K. In this paper, Al0.09Ga0.91As and Al0.89Ga0.11As are selected as high and low refractive index materials of Distributed Braagg Reflector (DBR), and 20 nm graded layer is inserted between two types of materials. The influence of the graded layer thickness of DBR on the valence band barrier and reflection spectrum is calculated and analyzed. The increase of graded layer thickness can lead to the decrease of band barrier peak and the decrease of reflection spectrum bandwidth. The reflection spectrum and phase spectrum of P-DBR and N-DBR are calculated by the transmission matrix mode (TMM), the reflectance of DBR is over 99% and the phase shift is zero at 940 nm. The optical field distribution of the whole VCSEL structure is simulated, in which the standing wave peak overlaps with the active region, and the maximum gain can be obtained. Based on the finite element method (FEM), the effect of oxidation confined layer on the injection current is simulated. The current in the active region is effectively limited to the position corresponding to the oxidation confined hole, and its current density is stronger and more uniform. The optical field distribution in different modes of PC-VCSEL is simulated, different modes have different resonant wavelengths. The quality factor Q in different modes of VCSEL and Photonic Crystal-Vertical Cavity Surface Emitting Laser (PC-VCSEL) is calculated, Q of the fundamental mode is higher than higher transverse mode. It is demonstrated that the photonic crystal air hole structure can realize the output of basic transverse mode by increasing the loss of high order transverse mode. VCSEL and PC-VCSEL with oxidation hole size of 22 μm are successfully fabricated, in which the photonic crystal period is 5 μm, the air pore diameter is 2.5 μm and the etching depth is 2 μm. Under continuous current test, the maximum slope efficiency of VCSEL is 0.66 mW/mA, the output power is 9.3 mW at 22 mA, and the lasing wavelength is 948.64 nm at 20 mA injection current. Multiple wavelengths and large spectrum width is observed in the spectrum of VSCEL, which is an obvious multi-transverse mode. The maxi
{"title":"Design and Fabrication of 940 nm VCSEL Single-emitter Device","authors":"Pan Zhi-Peng, Li Wei, Lv Jia-Gang, Nie Yu-Wei, Zhong Li, Liu Su-ping, Ma Xiao-Yu","doi":"10.7498/aps.72.20230297","DOIUrl":"https://doi.org/10.7498/aps.72.20230297","url":null,"abstract":"As the key part of Vertical Cavity Surface Emitting Laser (VCSEL), active region will seriously affect the threshold and efficiency of the device. To obtain appropriate laser wavelength and material gain, the In0.18Ga0.82As strain compensated quantum well is optimized design. The relationship between the lasing wavelength of multiple quantum wells (MQWs) and the thickness is calculated. Take into account the influence between the active region temperature and the lasing wavelength, the thickness of the quantum well is chose as 6 nm, the quantum barrier thickness is chose as 8 nm, corresponding to the lasing wavelength of 929 nm. The material gain characteristics of the MQWs under different temperature are simulated by Rsoft. The material gain exceeds 3300 /cm at 300 K, and the temperature drift coefficient of the peak wavelength is 0.3 nm/K. In this paper, Al0.09Ga0.91As and Al0.89Ga0.11As are selected as high and low refractive index materials of Distributed Braagg Reflector (DBR), and 20 nm graded layer is inserted between two types of materials. The influence of the graded layer thickness of DBR on the valence band barrier and reflection spectrum is calculated and analyzed. The increase of graded layer thickness can lead to the decrease of band barrier peak and the decrease of reflection spectrum bandwidth. The reflection spectrum and phase spectrum of P-DBR and N-DBR are calculated by the transmission matrix mode (TMM), the reflectance of DBR is over 99% and the phase shift is zero at 940 nm. The optical field distribution of the whole VCSEL structure is simulated, in which the standing wave peak overlaps with the active region, and the maximum gain can be obtained. Based on the finite element method (FEM), the effect of oxidation confined layer on the injection current is simulated. The current in the active region is effectively limited to the position corresponding to the oxidation confined hole, and its current density is stronger and more uniform. The optical field distribution in different modes of PC-VCSEL is simulated, different modes have different resonant wavelengths. The quality factor Q in different modes of VCSEL and Photonic Crystal-Vertical Cavity Surface Emitting Laser (PC-VCSEL) is calculated, Q of the fundamental mode is higher than higher transverse mode. It is demonstrated that the photonic crystal air hole structure can realize the output of basic transverse mode by increasing the loss of high order transverse mode. VCSEL and PC-VCSEL with oxidation hole size of 22 μm are successfully fabricated, in which the photonic crystal period is 5 μm, the air pore diameter is 2.5 μm and the etching depth is 2 μm. Under continuous current test, the maximum slope efficiency of VCSEL is 0.66 mW/mA, the output power is 9.3 mW at 22 mA, and the lasing wavelength is 948.64 nm at 20 mA injection current. Multiple wavelengths and large spectrum width is observed in the spectrum of VSCEL, which is an obvious multi-transverse mode. The maxi","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"96 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75941294","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Xu Lei, Li Pei-Ling, Lyu Zhao-Zheng, Shen Jie, Qu Fan-Ming, Liu Guang Tong, Lu Li
Topological superconductors have attracted increased research interest because they have been proposed to host non-abelian Ising Anyon Majorana zero modes, which can be used to construct fault-tolerant quantum computers. This paper mainly reviews the electrical transport methods for detecting the presence of Majorana zero modes. First, the basic concepts of topological superconductivity, Majorana zero modes and non-Abelian statistics are introduced, followed by a summary of various schemes for implementing topological superconductivity. Experimental methods for detecting topological superconductivity or Majorana zero modes using low-temperature transport methods, including electron tunneling spectroscopy, Coulomb blockade spectroscopy and non-local conductance detection, which are widely used in superconductor/nanowire hybrid systems, are then discussed. On the other hand, measurements of the (inverse) AC Josephson effect and current (energy) phase relationships are also reviewed to identify MZM in Josephson devices. Meanwhile, to deepen our understanding of MZM, the trivial mechanisms for interpreting the experimental data observed in the above experiments are provided. Finally, a brief summary and outlook of the electrical transport methods of Majorana zero modes are presented.
{"title":"Detecting Majorana zero mode with transport measurements","authors":"Xu Lei, Li Pei-Ling, Lyu Zhao-Zheng, Shen Jie, Qu Fan-Ming, Liu Guang Tong, Lu Li","doi":"10.7498/aps.72.20230951","DOIUrl":"https://doi.org/10.7498/aps.72.20230951","url":null,"abstract":"Topological superconductors have attracted increased research interest because they have been proposed to host non-abelian Ising Anyon Majorana zero modes, which can be used to construct fault-tolerant quantum computers. This paper mainly reviews the electrical transport methods for detecting the presence of Majorana zero modes. First, the basic concepts of topological superconductivity, Majorana zero modes and non-Abelian statistics are introduced, followed by a summary of various schemes for implementing topological superconductivity. Experimental methods for detecting topological superconductivity or Majorana zero modes using low-temperature transport methods, including electron tunneling spectroscopy, Coulomb blockade spectroscopy and non-local conductance detection, which are widely used in superconductor/nanowire hybrid systems, are then discussed. On the other hand, measurements of the (inverse) AC Josephson effect and current (energy) phase relationships are also reviewed to identify MZM in Josephson devices. Meanwhile, to deepen our understanding of MZM, the trivial mechanisms for interpreting the experimental data observed in the above experiments are provided. Finally, a brief summary and outlook of the electrical transport methods of Majorana zero modes are presented.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"78 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76093361","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fluorination of graphene is one of the most effective methods to improve the corrosion protection of graphene coatings. In this paper, the diffusion and penetration behaviors of O atoms on fully fluorinated graphene (CF) and partially fluorinated graphene (C4F) were investigated using the NEB transition state search method. The effects of F atoms on the corrosion resistance of fluorinated graphene films were analyzed either. The results show that the adsorption of F atoms can effectively inhibit the diffusion of O atoms on graphene. On C4F, the F atoms are distributed in a para-top position, which greatly increases the surface diffusion energy barrier of O atoms. Moreover, it is difficult for the adsorbed O atoms to diffuse to different sp2 C rings through the obstruction of F atoms. The energy barrier of the horizontal diffusion of O atoms even reaches 2.69 eV in CF. And with the increase of F atoms, the stable structure of graphene is gradually destroyed, the barrier ability of C-atom layer for penetration behaviors of O atoms is greatly reduced. Furthermore, the interfacial adhesion work of pure graphene, CF and C4F films with Cu(111) surfaces were calculated, as well as the electronic structures of the composite interface using first-principles calculations. The interfacial adhesion work of the Cu/G, Cu/C4F and Cu/CF interfaces are 2.626J/m2、3.529J/m2and 3.559J/m2, respectively. The calculations show that the bonding of C4F and C4F with Cu substrate are more strong than pure graphene with Cu substrate, and the interfacial adhesion work increase with increasing of F atom adsorption concentration. The calculation of the density of states also conform stronger interaction between Cu and C atoms of the Cu/C4F interface than that of the Cu/CF interface. Bader charge analysis show increased charge transfer at both the Cu/C4F and Cu/CF interfaces comparing with the Cu/G interface, and Cu/C4F interface has more charge transfer, in which Cu-C bonds are formed.
{"title":"First-principles calculations on O-atom diffusion on fluorinated graphene","authors":"Hailin Yang, Qili Chen, Xing Gu, Ning Lin","doi":"10.7498/aps.72.20221630","DOIUrl":"https://doi.org/10.7498/aps.72.20221630","url":null,"abstract":"Fluorination of graphene is one of the most effective methods to improve the corrosion protection of graphene coatings. In this paper, the diffusion and penetration behaviors of O atoms on fully fluorinated graphene (CF) and partially fluorinated graphene (C4F) were investigated using the NEB transition state search method. The effects of F atoms on the corrosion resistance of fluorinated graphene films were analyzed either. The results show that the adsorption of F atoms can effectively inhibit the diffusion of O atoms on graphene. On C4F, the F atoms are distributed in a para-top position, which greatly increases the surface diffusion energy barrier of O atoms. Moreover, it is difficult for the adsorbed O atoms to diffuse to different sp2 C rings through the obstruction of F atoms. The energy barrier of the horizontal diffusion of O atoms even reaches 2.69 eV in CF. And with the increase of F atoms, the stable structure of graphene is gradually destroyed, the barrier ability of C-atom layer for penetration behaviors of O atoms is greatly reduced. Furthermore, the interfacial adhesion work of pure graphene, CF and C4F films with Cu(111) surfaces were calculated, as well as the electronic structures of the composite interface using first-principles calculations. The interfacial adhesion work of the Cu/G, Cu/C4F and Cu/CF interfaces are 2.626J/m2、3.529J/m2and 3.559J/m2, respectively. The calculations show that the bonding of C4F and C4F with Cu substrate are more strong than pure graphene with Cu substrate, and the interfacial adhesion work increase with increasing of F atom adsorption concentration. The calculation of the density of states also conform stronger interaction between Cu and C atoms of the Cu/C4F interface than that of the Cu/CF interface. Bader charge analysis show increased charge transfer at both the Cu/C4F and Cu/CF interfaces comparing with the Cu/G interface, and Cu/C4F interface has more charge transfer, in which Cu-C bonds are formed.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"234 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76115412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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