Piezoelectric effects and electronic structures of InAs/GaAs quantum dots grown along （111） and （011） directions are investigated in this paper. The finite element method is used. Electronic energy levels are calc...Piezoelectric effects and electronic structures of InAs/GaAs quantum dots grown along （111） and （011） directions are investigated in this paper. The finite element method is used. Electronic energy levels are calculated by solving the three-dimensional effective mass Schrodinger equation including a strain modified confinement potential and piezoelectric effects. The difference in electronic structure between quantum dots grown along the （111） direction and the （011） direction are compared. The cubic and truncated pyramidal shaped quantum dots are adopted.展开更多
The development of two-dimensional(2D)semiconductors has attracted widespread attentions in the scientific community and industry due to their ultra-thin thickness,unique structure,excellent optoelectronic properties ...The development of two-dimensional(2D)semiconductors has attracted widespread attentions in the scientific community and industry due to their ultra-thin thickness,unique structure,excellent optoelectronic properties and novel physics.The excellent flexibility and outstanding mechanical strength of 2D semiconductors provide opportunities for fabricated strain-sensitive devices and utilized strain tuning their electronic and optic–electric performance.The strain-engineered one-dimensional materials have been well investigated,while there is a long way to go for 2D semiconductors.In this review,starting with the fundamental theories of piezoelectric and piezoresistive effect resulted by strain,following we reviewed the recent simulation works of strain engineering in novel 2D semiconductors,such as Janus 2D and 2D-Xene structures.Moreover,recent advances in experimental observation of strain tuning PL spectra and transport behavior of 2D semiconductors are summarized.Furthermore,the applications of strain-engineered 2D semiconductors in sensors,photodetectors and nanogenerators are also highlighted.At last,we in-depth discussed future research directions of strain-engineered 2D semiconductor and related electronics and optoelectronics device applications.展开更多
The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are ...The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are shown and the dispersion relation is calculated. The results show that, by introducing the inter-coupling between the different piezoelectric segments, which is accomplished by serially connecting every n piezoelectric segment into supercells, some tunable Bragg band gaps can accordingly be opened in the low frequency region. The investigation could provide a new guideline for the tunable phononic crystal under passive control.展开更多
Piezoelectric materials have been analyzed for over 100 years,due to their ability to convert mechanical vibrations into electric charge or electric fields into a mechanical strain for sensor,energy harvesting,and act...Piezoelectric materials have been analyzed for over 100 years,due to their ability to convert mechanical vibrations into electric charge or electric fields into a mechanical strain for sensor,energy harvesting,and actuator applications.A more recent development is the coupling of piezoelectricity and electro-chemistry,termed piezo-electro-chemistry,whereby the piezoelectrically induced electric charge or voltage under a mechanical stress can influence electro-chemical reactions.There is growing interest in such coupled systems,with a corresponding growth in the number of associated publications and patents.This review focuses on recent development of the piezo-electro-chemical coupling multiple systems based on various piezoelectric materials.It provides an overview of the basic characteristics of piezoelectric materials and comparison of operating conditions and their overall electro-chemical performance.The reported piezo-electro-chemical mechanisms are examined in detail.Comparisons are made between the ranges of material morphologies employed,and typical operating conditions are discussed.In addition,potential future directions and applications for the development of piezo-electro-chemical hybrid systems are described.This review provides a comprehensive overview of recent studies on how piezoelectric materials and devices have been applied to control electro-chemical processes,with an aim to inspire and direct future efforts in this emerging research field.展开更多
Based on the new modified couple stress theory and considering the flexoelectric effect of the piezoelectric layers,the Euler Bernoulli nano-beam model of composite laminated materials driven by electrostatically fixe...Based on the new modified couple stress theory and considering the flexoelectric effect of the piezoelectric layers,the Euler Bernoulli nano-beam model of composite laminated materials driven by electrostatically fixed supports at both ends is established. The nonlinear differential governing equations and boundary conditions are derived by the Hamilton principle. The generalized differential quadrature method(GDQM) and the Newton Raphson method are used to numerically solve the differential governing equations. The influence of flexoelectric effect on the static and the dynamic pull-in characteristics of laminated nano-beams is analyzed. The results of the numerical calculation are in a good agreement with those in the literature when the model degenerated into a nanobeam model without flexoelectric effect. The stacking sequence,length scale parameter l and piezoelectric layer applied voltage V_(p) of the composite will affect the pull-in voltage,frequency and time-domain response of the structure. Given that the flexoelectric effect will reduce the pull-in voltage and dimensionless natural frequency of the structure,the maximum dimensionless displacement at the midpoint of the beam and the period of time-domain response should be increased.展开更多
The mechanical electric coupling effect of piezoelectric materials and devices is discussed and a brief review on the evolution of the technique is pr...The mechanical electric coupling effect of piezoelectric materials and devices is discussed and a brief review on the evolution of the technique is presented.On such basis,as a first step toward the formulation of finite elements for analysis of piezoelectric devices,a multivariate variation principle is presented.As has been revealed by the present work,an important particularization thereof is the Allik Hughes functional.展开更多
Columnar nanocrystalline aluminum nitride(cnc-AlN) thin films with(002) orientation and uniform texture have been deposited successfully on large silicon wafers by RF reactive magnetron sputtering.At the optimum sputt...Columnar nanocrystalline aluminum nitride(cnc-AlN) thin films with(002) orientation and uniform texture have been deposited successfully on large silicon wafers by RF reactive magnetron sputtering.At the optimum sputtering parameters, the deposited cnc-AlN thin films show a c-axis preferred orientation with a crystallite size of about 28 nm and surface roughness(RMS) of about 1.29 nm. The cnc-AlN thin films were well transparent with an optical band gap about 4.8 e V, and the residual compressive stress and the defect density in the film have been revealed by Ramon spectroscopy. Moreover, piezoelectric performances of the cnc-AlN thin films executed effectively in a film bulk acoustic resonator structure.展开更多
In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step...In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step-stress） are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] （Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415）. However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.展开更多
Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease...Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT.展开更多
In this work, we present a theoretical and experimental study on the drain current 1/f noise in the AIGaN/GaN high electron mobility transistor （HEMT）. Based on both mobility fluctuation and carrier number fluctuati...In this work, we present a theoretical and experimental study on the drain current 1/f noise in the AIGaN/GaN high electron mobility transistor （HEMT）. Based on both mobility fluctuation and carrier number fluctuation in a two- dimensional electron gas （2DEG） channel of AlGaN/GaN HEMT, a unified drain current 1/f noise model containing a piezoelectric polarization effect and hot carrier effect is built. The drain current 1/f noise induced by the piezoelectric polarization effect is distinguished from that induced by the hot carrier effect through experiments and simulations. The simulation results are in good agreement with the experimental results. Experiments show that after hot carrier injection, the drain current 1/f noise increases four orders of magnitude and the electrical parameter degradation Agm/gm reaches 54.9%. The drain current 1/f noise degradation induced by the piezoelectric effect reaches one order of magnitude; the electrical parameter degradation Agm/gm is 11.8%. This indicates that drain current 1/f noise of the GaN-based HEMT device is sensitive to the hot carrier effect and piezoelectric effect. This study provides a useful reliability characterization tool for the A1GaN/GaN HEMTs.展开更多
This paper describes an optical voltage transducer （OVT） for the 35 kV electric power system based on modular interference in dual-mode highly elliptical-core polarization maintenance fiber （E-Core PMF）. The tempe...This paper describes an optical voltage transducer （OVT） for the 35 kV electric power system based on modular interference in dual-mode highly elliptical-core polarization maintenance fiber （E-Core PMF）. The temperature and environmental perturb- bation can be compensated automatically. In the scheme, a quartz crystal cylinder wrapped with highly elliptical-core fiber plays the role of voltage sensor head. The two interference output lobes＇ intensity from the E-core PMF is modulated with the converse piezoelectric effect of quartz crystal. A PZT wrapped with E-core PMF at ground potential serves as the static modular phase difference control and temperature compensation unit. The experiment results indicate that the OVT designed in this paper has satisfying performance and could successfully rejects the temperature perturbation.展开更多
基金Project supported by the National High Technology Research and Development Program of China (Grant No.2009AA03Z405)the National Natural Science Foundation of China (Grant Nos.60908028 and 60971068)
文摘Piezoelectric effects and electronic structures of InAs/GaAs quantum dots grown along （111） and （011） directions are investigated in this paper. The finite element method is used. Electronic energy levels are calculated by solving the three-dimensional effective mass Schrodinger equation including a strain modified confinement potential and piezoelectric effects. The difference in electronic structure between quantum dots grown along the （111） direction and the （011） direction are compared. The cubic and truncated pyramidal shaped quantum dots are adopted.
基金supported by the National Natural Science Foundation of China(51572025,51627801,61435010 and 51702219)the State Key Research Development Program of China(2019YFB2203503)+3 种基金Guangdong Basic and Applied Basic Research Foundation(2019A1515110209)the Science and Technology Innovation Commission of Shenzhen(JCYJ20170818093453105,JCYJ20180305125345378)National Foundation of China(41422050303)Beijing Municipal Science&Technology Commission and the Fundamental Research Funds for Central Universities.
文摘The development of two-dimensional(2D)semiconductors has attracted widespread attentions in the scientific community and industry due to their ultra-thin thickness,unique structure,excellent optoelectronic properties and novel physics.The excellent flexibility and outstanding mechanical strength of 2D semiconductors provide opportunities for fabricated strain-sensitive devices and utilized strain tuning their electronic and optic–electric performance.The strain-engineered one-dimensional materials have been well investigated,while there is a long way to go for 2D semiconductors.In this review,starting with the fundamental theories of piezoelectric and piezoresistive effect resulted by strain,following we reviewed the recent simulation works of strain engineering in novel 2D semiconductors,such as Janus 2D and 2D-Xene structures.Moreover,recent advances in experimental observation of strain tuning PL spectra and transport behavior of 2D semiconductors are summarized.Furthermore,the applications of strain-engineered 2D semiconductors in sensors,photodetectors and nanogenerators are also highlighted.At last,we in-depth discussed future research directions of strain-engineered 2D semiconductor and related electronics and optoelectronics device applications.
基金Supported by the National Natural Science Foundation of China under Grant No 11274121
文摘The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are shown and the dispersion relation is calculated. The results show that, by introducing the inter-coupling between the different piezoelectric segments, which is accomplished by serially connecting every n piezoelectric segment into supercells, some tunable Bragg band gaps can accordingly be opened in the low frequency region. The investigation could provide a new guideline for the tunable phononic crystal under passive control.
基金supported by the National Key R&D Project from Minister of Science and Technology in China (No. 2016YFA0202701)the National Natural Science Foundation of China (No. 51472055)+4 种基金External Cooperation Program of BIC, Chinese Academy of Sciences (No. 121411KYS820150028)the 2015 Annual Beijing Talents Fund (No. 2015000021223ZK32)Qingdao National Laboratory for Marine Science and Technology (No. 2017ASKJ01)the University of Chinese Academy of Sciences (Grant No. Y8540XX2D2)the ‘thousands talents’ program for the pioneer researcher and his innovation team, China。
文摘Piezoelectric materials have been analyzed for over 100 years,due to their ability to convert mechanical vibrations into electric charge or electric fields into a mechanical strain for sensor,energy harvesting,and actuator applications.A more recent development is the coupling of piezoelectricity and electro-chemistry,termed piezo-electro-chemistry,whereby the piezoelectrically induced electric charge or voltage under a mechanical stress can influence electro-chemical reactions.There is growing interest in such coupled systems,with a corresponding growth in the number of associated publications and patents.This review focuses on recent development of the piezo-electro-chemical coupling multiple systems based on various piezoelectric materials.It provides an overview of the basic characteristics of piezoelectric materials and comparison of operating conditions and their overall electro-chemical performance.The reported piezo-electro-chemical mechanisms are examined in detail.Comparisons are made between the ranges of material morphologies employed,and typical operating conditions are discussed.In addition,potential future directions and applications for the development of piezo-electro-chemical hybrid systems are described.This review provides a comprehensive overview of recent studies on how piezoelectric materials and devices have been applied to control electro-chemical processes,with an aim to inspire and direct future efforts in this emerging research field.
文摘Based on the new modified couple stress theory and considering the flexoelectric effect of the piezoelectric layers,the Euler Bernoulli nano-beam model of composite laminated materials driven by electrostatically fixed supports at both ends is established. The nonlinear differential governing equations and boundary conditions are derived by the Hamilton principle. The generalized differential quadrature method(GDQM) and the Newton Raphson method are used to numerically solve the differential governing equations. The influence of flexoelectric effect on the static and the dynamic pull-in characteristics of laminated nano-beams is analyzed. The results of the numerical calculation are in a good agreement with those in the literature when the model degenerated into a nanobeam model without flexoelectric effect. The stacking sequence,length scale parameter l and piezoelectric layer applied voltage V_(p) of the composite will affect the pull-in voltage,frequency and time-domain response of the structure. Given that the flexoelectric effect will reduce the pull-in voltage and dimensionless natural frequency of the structure,the maximum dimensionless displacement at the midpoint of the beam and the period of time-domain response should be increased.
文摘The mechanical electric coupling effect of piezoelectric materials and devices is discussed and a brief review on the evolution of the technique is presented.On such basis,as a first step toward the formulation of finite elements for analysis of piezoelectric devices,a multivariate variation principle is presented.As has been revealed by the present work,an important particularization thereof is the Allik Hughes functional.
文摘Columnar nanocrystalline aluminum nitride(cnc-AlN) thin films with(002) orientation and uniform texture have been deposited successfully on large silicon wafers by RF reactive magnetron sputtering.At the optimum sputtering parameters, the deposited cnc-AlN thin films show a c-axis preferred orientation with a crystallite size of about 28 nm and surface roughness(RMS) of about 1.29 nm. The cnc-AlN thin films were well transparent with an optical band gap about 4.8 e V, and the residual compressive stress and the defect density in the film have been revealed by Ramon spectroscopy. Moreover, piezoelectric performances of the cnc-AlN thin films executed effectively in a film bulk acoustic resonator structure.
基金Project supported by the National Basic Research Program of China (Grant No. 2011CBA00600)the National Natural Science Foundation of China (Grant No. 61106106)the Fundamental Research Funds for the Central Universities (Grant No. K50510250006)
文摘In spite of their extraordinary performance, AlGaN/GaN high electron mobility transistors （HEMTs） still lack solid reliability. Devices under accelerated DC stress tests （off-state, VDS = 0 state, and on-state step-stress） are investigated to help us identify the degradation mechanisms of the AlGaN/GaN HEMTs. All our findings are consistent with the degradation mechanism based on crystallographic-defect formation due to the inverse piezoelectric effects in Ref. [1] （Joh J and del Alamo J A 2006 IEEE IDEM Tech. Digest p. 415）. However, under the on-state condition, the devices are suffering from both inverse piezoelectric effects and hot electron effects, and so to improve the reliability of the devices both effects should be taken into consideration.
基金Project supported by the Program for New Century Excellent Talents in University (Grant No.NCET-12-0915)
文摘Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AIGaN/GaN high electron mobility transistor （HEMT）. It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments. We postulate that defects may be randomly induced within the A1GaN barrier by the high electric field during each voltage step. But once the critical voltage is reached, the trap concentration will increase sharply due to the inverse piezoelectric effect. A leakage path may be introduced by excessive defect, and this may result in the permanent degradation of the A1GaN/GaN HEMT.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.61076101,61204092,61334002,and JJ0500102508)
文摘In this work, we present a theoretical and experimental study on the drain current 1/f noise in the AIGaN/GaN high electron mobility transistor （HEMT）. Based on both mobility fluctuation and carrier number fluctuation in a two- dimensional electron gas （2DEG） channel of AlGaN/GaN HEMT, a unified drain current 1/f noise model containing a piezoelectric polarization effect and hot carrier effect is built. The drain current 1/f noise induced by the piezoelectric polarization effect is distinguished from that induced by the hot carrier effect through experiments and simulations. The simulation results are in good agreement with the experimental results. Experiments show that after hot carrier injection, the drain current 1/f noise increases four orders of magnitude and the electrical parameter degradation Agm/gm reaches 54.9%. The drain current 1/f noise degradation induced by the piezoelectric effect reaches one order of magnitude; the electrical parameter degradation Agm/gm is 11.8%. This indicates that drain current 1/f noise of the GaN-based HEMT device is sensitive to the hot carrier effect and piezoelectric effect. This study provides a useful reliability characterization tool for the A1GaN/GaN HEMTs.
基金supported by the National Natural Science Foundation of China under Grant No. 50477001.
文摘This paper describes an optical voltage transducer （OVT） for the 35 kV electric power system based on modular interference in dual-mode highly elliptical-core polarization maintenance fiber （E-Core PMF）. The temperature and environmental perturb- bation can be compensated automatically. In the scheme, a quartz crystal cylinder wrapped with highly elliptical-core fiber plays the role of voltage sensor head. The two interference output lobes＇ intensity from the E-core PMF is modulated with the converse piezoelectric effect of quartz crystal. A PZT wrapped with E-core PMF at ground potential serves as the static modular phase difference control and temperature compensation unit. The experiment results indicate that the OVT designed in this paper has satisfying performance and could successfully rejects the temperature perturbation.
