We propose a controllable high-efficiency electrostatic surface trap for cold polar molecules on a chip by using two insulator-embedded charged rings and a grounded conductor plate. We calculate Stark energy structure...We propose a controllable high-efficiency electrostatic surface trap for cold polar molecules on a chip by using two insulator-embedded charged rings and a grounded conductor plate. We calculate Stark energy structure pattern of ND3 molecules in an external electric field using the method of matrix diagonalization. We analyze how the voltages that are applied to the ring electrodes affect the depth of the efficient well and the controllability of the distance between the trap center and the surface of the chip. To obtain a better understanding, we simulate the dynamical loading and trapping processes of ND3 molecules in a |J, KM = |1,-1 state by using classical Monte–Carlo method. Our study shows that the loading efficiency of our trap can reach ~ 88%. Finally, we study the adiabatic cooling of cold molecules in our surface trap by linearly lowering the potential-well depth(i.e., lowering the trapping voltage), and find that the temperature of the trapped ND3 molecules can be adiabatically cooled from 34.5 m K to ~ 5.8 m K when the trapping voltage is reduced from-35 k V to-3 k V.展开更多
Pristine and Bi-doped lanthanum titanium oxide(La_(2)Ti_(2)O_(7))nanosheets have been synthesized as photocatalysts for overall solar water splitting.The surface hole trap is a critical factor that limits the photocat...Pristine and Bi-doped lanthanum titanium oxide(La_(2)Ti_(2)O_(7))nanosheets have been synthesized as photocatalysts for overall solar water splitting.The surface hole trap is a critical factor that limits the photocatalytic activity of pristine La_(2)Ti_(2)O_(7)-Deposition of cobalt phosphate(Co-Pi)and platinum(Pt)nanoparticles on La_(2)Ti_(2)O_(7) cannot remove the surface traps although they are essential for enabling the oxygen and hydrogen evolution reactions.It is interesting that doping bismuth(Bi)into La_(2)Ti_(2)O_(7) nanosheets has eliminated the surface traps due to surface enrichment of Bi.The Co-Pi/Bi-La_(2)Ti_(2)O_(7)/Pt nanosheets exhibit increasing photocatalytic activity toward overall water splitting with increasing the Bi-dopant level up to 5 at.%.Further increasing the Bi-dopant level leads to the formation of localized states above the valence band,leading to the lifetime reduction of photogenerated charge-carriers,and jeopardizing the photocatalytic activity.This work proposes an effective strategy to address the surface trapping and surface catalysis issues in the nanostructured metal oxide photocatalysts.展开更多
The reactive surface area, an important parameter controlling mineral reactions, affects the amount of mineralization trapping of CO2 which affects the long-term CO2 storage. The effect of the reactive surface area on...The reactive surface area, an important parameter controlling mineral reactions, affects the amount of mineralization trapping of CO2 which affects the long-term CO2 storage. The effect of the reactive surface area on the mineralization trapping of CO2 was numerically simulated for CO2 storage in saline aquifers. Three kinds of minerals, including anorthite, calcite and kaolinite, are involved in the mineral reactions. This paper models the relationship between the specific surface area and the grain diameter of anorthite based on experimental data from literature (Brantley and Mellott, 2000). When the reactive surface areas of anorthite and calcite decrease from 838 to 83.8 m^2/m^3, the percentage of mineralization trapping of CO: after 500 years decreases from 11.8% to 0.65%. The amount of dissolved anorthite and the amounts of precipitated kaolinite and calcite decrease significantly when the reactive surface areas ofanorthite and calcite decrease from 838 to 83.8 m2/m3. Calcite is initially dissolved in the brine and then precipitates during the geochemical reactions between CO2-H20 and the minerals. Different reactive surface areas of anorthite and calcite lead to different times from dissolution to precipitation. The pH of the brine decreases with decreasing reactive surface areas of anorthite and calcite which influences the acidity of the saline aquifer. The gas saturation between the upper and lower parts of the saline aquifer increases with decreasing reactive surface areas of anorthite and calcite. The mass density distribution of brine solution shows that the CO2^+brine solution region increases with decreasing reactive surface areas ofanorthite and calcite.展开更多
We review the concept of congruence of null geodesics, the Raychaudhuri equation for the expansion, its harmonic oscillator version and associated “quantum” propagator, the role of the equation in the derivation of ...We review the concept of congruence of null geodesics, the Raychaudhuri equation for the expansion, its harmonic oscillator version and associated “quantum” propagator, the role of the equation in the derivation of the Penrose singularity theorem, the definition of trapped surfaces, and the derivation of the theorem itself.展开更多
NiO has a perfect-aligned energy level with CH3 NH3 Pb I3 perovskite such that it serves as a hole transport layer(HTL),but Ni O-based perovskite solar cells(PSCs)still suffer from low efficiency due to the poor inter...NiO has a perfect-aligned energy level with CH3 NH3 Pb I3 perovskite such that it serves as a hole transport layer(HTL),but Ni O-based perovskite solar cells(PSCs)still suffer from low efficiency due to the poor interface contact between the perovskite layer and the Ni O HTL,and haphazardly stacked perovskite grains.Herein,poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1,3}-thiadiazole)](PFBT)is introduced between the Ni O and perovskite layers in the form of a polymer aggregate to enhance perovskite crystallinity and decrease the interface charge recombination between perovskite and Ni O in PSCs,resulting in an improved performance.Moreover,PFBT modified perovskite films showed sharper,smoother,and more compact crystalline grains with fewer grain boundaries,leading to the decreased nonradiative recombination.This study offers a simple strategy to achieve highly efficient PSCs with the incorporation of polymer semiconductor aggregates to passivate the interface between the perovskite and Ni O layers.展开更多
All-inorganic CsPbI_3 quantum dots(QDs) have demonstrated promising potential in photovoltaic(PV) applications. However, these colloidal perovskites are vulnerable to the deterioration of surface trap states, leading ...All-inorganic CsPbI_3 quantum dots(QDs) have demonstrated promising potential in photovoltaic(PV) applications. However, these colloidal perovskites are vulnerable to the deterioration of surface trap states, leading to a degradation in efficiency and stability. To address these issues, a facile yet effective strategy of introducing hydroiodic acid(HI) into the synthesis procedure is established to achieve high-quality QDs and devices. Through an in-depth experimental analysis, the introduction of HI was found to convert PbI_2 into highly coordinated [PbI_m]~(2-m), enabling control of the nucleation numbers and growth kinetics. Combined optical and structural investigations illustrate that such a synthesis technique is beneficial for achieving enhanced crystallinity and a reduced density of crystallographic defects. Finally, the effect of HI is further reflected on the PV performance. The optimal device demonstrated a significantly improved power conversion efficiency of 15.72% along with enhanced storage stability. This technique illuminates a novel and simple methodology to regulate the formed species during synthesis, shedding light on ofurther understanding solar cell performance, and aiding the design of future novel synthesis protocols for high-performance optoelectronic devices.展开更多
A prevailing understanding on electrochemical activation of photoelectrodes is that electrochemical treatment leads to increased charge carrier densities thereby improved photoelectrode performances.Contrary to this u...A prevailing understanding on electrochemical activation of photoelectrodes is that electrochemical treatment leads to increased charge carrier densities thereby improved photoelectrode performances.Contrary to this understanding,in this study enhanced photoactivity of WO_(3) photoanode upon electrochemical treatment is ascribed to an extraordinary mechanism of surface trap passivation.The associated mechanism is analyzed by in situ optical spectroscopy,using which the optical property changes of WO_(3) electrode during electrochemical treatment are monitored.The results suggest surface W^(5+)species,the origin of surface traps on WO_(3) photoanodes,are converted to W^(6+) ions by electrochemical treatment.This study demonstrates the particular ability of the electrochemical strategy to passivate surface traps of photoanodes,and also shows the advantages of in situ optical spectroscopy to investigate the real-time electronic structure variations of electrodes during electrochemical treatment.展开更多
It has been reported that the gate leakage currents are described by the Frenkel-Poole emission(FPE) model,at temperatures higher than 250 K.However,the gate leakage currents of our passivated devices do not accord wi...It has been reported that the gate leakage currents are described by the Frenkel-Poole emission(FPE) model,at temperatures higher than 250 K.However,the gate leakage currents of our passivated devices do not accord with the FPE model.Therefore,a modified FPE model is developed in which an additional leakage current,besides the gate(ⅠⅡ),is added.Based on the samples with different passivations,the ⅠⅡcaused by a large number of surface traps is separated from total gate currents,and is found to be linear with respect to(φB-Vg)0.5.Compared with these from the FPE model,the calculated results from the modified model agree well with the Ig-Vgmeasurements at temperatures ranging from 295 K to 475 K.展开更多
Direct current(DC) reverse step voltage stress is applied on the gate of an AlGaN/GaN high-electron mobility transistor(HEMT).Experiments show that parameters degenerate under stress.Large-signal parasitic source/...Direct current(DC) reverse step voltage stress is applied on the gate of an AlGaN/GaN high-electron mobility transistor(HEMT).Experiments show that parameters degenerate under stress.Large-signal parasitic source/drain resistance(RS/RD) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test(DUT).Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon,and surface state recovery is the major reason for the recovery of device parameters.展开更多
Drain-modulated generation current IDMGinduced by interface traps in an n-type metal-oxide-semiconductor fieldeffect transistor(n MOSFET) is investigated. The formation of IDMGascribes to the change of the Si surfac...Drain-modulated generation current IDMGinduced by interface traps in an n-type metal-oxide-semiconductor fieldeffect transistor(n MOSFET) is investigated. The formation of IDMGascribes to the change of the Si surface potential φs.This change makes the channel suffer transformation from the inversion state, depletion I state to depletion II state. The simulation result agrees with the experiment in the inversion and depletion I states. In the depletion II state, the theoretical curve goes into saturation, while the experimental curve drops quickly as VDincreases. The reason for this unconformity is that the drain-to-gate voltage VDGlessens φs around the drain corner and controls the falling edge of the IDMG curve.The experiments of gate-modulated generation and recombination currents are also applied to verify the reasonability of the mechanism. Based on this mechanism, a theoretical model of the IDMGfalling edge is set up in which IDMGhas an exponential attenuation relation with VDG. Finally, the critical fitting coefficient t of the experimental curves is extracted. It is found that t = 80 m V = 3k T /q. This result fully shows the accuracy of the above mechanism.展开更多
A novel structure of 4H-SiC MESFETs is proposed that focuses on surface trap suppression.Characteristics of the device have been investigated based on physical models for material properties and improved trap models.B...A novel structure of 4H-SiC MESFETs is proposed that focuses on surface trap suppression.Characteristics of the device have been investigated based on physical models for material properties and improved trap models.By comparing with the performance of the well-utilized buried-gate incorporated with a field-plate (BG-FP) structure,it is shown that the proposed structure improves device properties in comprehensive aspects. A p-type spacer layer introduced in the channel layer suppresses the surface trap effect and reduces the gate-drain capacitance(C_(gd)) under a large drain voltage.A p-type spacer layer incorporated with a field-plate improves the electric field distribution on the gate edge while the spacer layer induces less C_(gd) than a conventional FP.For microwave applications,4H-SiC MESFET for the proposed structure has a larger gate-lag ratio in the saturation region due to better surface trap isolation from the conductive channel.For high power applications,the proposed structure is able to endure higher operating voltage as well.The maximum saturation current density of 460 mA/mm is yielded.Also,the gate-lag ratio under a drain voltage of 20 V is close to 90%.In addition,5%and 17.8%improvements in f_T and f_(max) are obtained compared with a BG-FP MESFET in AC simulation,respectively.Parameters and dimensions of the proposed structure are optimized to make the best of the device for microwave applications and to provide a reference for device design.展开更多
The two frequently observed phenomena,photoluminescence(PL)blinking and quantum-confined Stark effect(QCSE)-induced spectral diffusion,are not conducive to the applications of colloidal quantum dots(QDs).It remains el...The two frequently observed phenomena,photoluminescence(PL)blinking and quantum-confined Stark effect(QCSE)-induced spectral diffusion,are not conducive to the applications of colloidal quantum dots(QDs).It remains elusive how these two phenomena are linked to each other.Unraveling the potential link between blinking and QCSE could facilitate the adoption of appropriate strategies that can simultaneously suppress both PL blinking and spectral diffusion.In this work,we investigated the blinking mechanism and QCSE of single CdSe/CdS/ZnS QDs in the presence of positive and negative surface charges using single-dot PL spectroscopy.We found that the negative surface charges can simultaneously suppress PL blinking and spectral diffusion of single QDs.On the other hand,the positive surface charges could change the blinking mechanisms of QDs from Auger-blinking to band-edge carrier(BC)-blinking.Two types of QCSE were observed,and a significant QCSE-induced spectral broadening of 5.25 nm was measured,which could be attributed to the hopping of surface charges between different surface-trap sites.Based on these findings,several theoretical models are proposed to explain various phenomena observed.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10674047,10804031,10904037,10904060,10974055,11034002,and61205198)the National Key Basic Research and Development Program of China(Grant Nos.2006CB921604 and 2011CB921602)+2 种基金the Basic Key Program of Shanghai Municipality,China(Grant No.07JC14017)the Fundamental Research Funds for the Central Universitiesthe Shanghai Leading Academic Discipline Project,China(Grant No.B408)
文摘We propose a controllable high-efficiency electrostatic surface trap for cold polar molecules on a chip by using two insulator-embedded charged rings and a grounded conductor plate. We calculate Stark energy structure pattern of ND3 molecules in an external electric field using the method of matrix diagonalization. We analyze how the voltages that are applied to the ring electrodes affect the depth of the efficient well and the controllability of the distance between the trap center and the surface of the chip. To obtain a better understanding, we simulate the dynamical loading and trapping processes of ND3 molecules in a |J, KM = |1,-1 state by using classical Monte–Carlo method. Our study shows that the loading efficiency of our trap can reach ~ 88%. Finally, we study the adiabatic cooling of cold molecules in our surface trap by linearly lowering the potential-well depth(i.e., lowering the trapping voltage), and find that the temperature of the trapped ND3 molecules can be adiabatically cooled from 34.5 m K to ~ 5.8 m K when the trapping voltage is reduced from-35 k V to-3 k V.
基金supported by the National Natural Science Foundation of China(Nos.51972010 and 51472013)the Natural Science Foundation of Jiangsu Province(Youth Fund,Nos.BK20190640 and BK20190641)the Fundamental Research Funds for the Central Universities(No.2019XKQYMS11)。
文摘Pristine and Bi-doped lanthanum titanium oxide(La_(2)Ti_(2)O_(7))nanosheets have been synthesized as photocatalysts for overall solar water splitting.The surface hole trap is a critical factor that limits the photocatalytic activity of pristine La_(2)Ti_(2)O_(7)-Deposition of cobalt phosphate(Co-Pi)and platinum(Pt)nanoparticles on La_(2)Ti_(2)O_(7) cannot remove the surface traps although they are essential for enabling the oxygen and hydrogen evolution reactions.It is interesting that doping bismuth(Bi)into La_(2)Ti_(2)O_(7) nanosheets has eliminated the surface traps due to surface enrichment of Bi.The Co-Pi/Bi-La_(2)Ti_(2)O_(7)/Pt nanosheets exhibit increasing photocatalytic activity toward overall water splitting with increasing the Bi-dopant level up to 5 at.%.Further increasing the Bi-dopant level leads to the formation of localized states above the valence band,leading to the lifetime reduction of photogenerated charge-carriers,and jeopardizing the photocatalytic activity.This work proposes an effective strategy to address the surface trapping and surface catalysis issues in the nanostructured metal oxide photocatalysts.
基金supported by the National Natural Science Foundation of China (Grant No. 50906043)the Tsinghua University Initiative Scientific Research Program(2009THZ02232)The first author did this study while at Geoscience Australia sponsored by CAGS (China-Australia Geological Storage of CO2Project)
文摘The reactive surface area, an important parameter controlling mineral reactions, affects the amount of mineralization trapping of CO2 which affects the long-term CO2 storage. The effect of the reactive surface area on the mineralization trapping of CO2 was numerically simulated for CO2 storage in saline aquifers. Three kinds of minerals, including anorthite, calcite and kaolinite, are involved in the mineral reactions. This paper models the relationship between the specific surface area and the grain diameter of anorthite based on experimental data from literature (Brantley and Mellott, 2000). When the reactive surface areas of anorthite and calcite decrease from 838 to 83.8 m^2/m^3, the percentage of mineralization trapping of CO: after 500 years decreases from 11.8% to 0.65%. The amount of dissolved anorthite and the amounts of precipitated kaolinite and calcite decrease significantly when the reactive surface areas ofanorthite and calcite decrease from 838 to 83.8 m2/m3. Calcite is initially dissolved in the brine and then precipitates during the geochemical reactions between CO2-H20 and the minerals. Different reactive surface areas of anorthite and calcite lead to different times from dissolution to precipitation. The pH of the brine decreases with decreasing reactive surface areas of anorthite and calcite which influences the acidity of the saline aquifer. The gas saturation between the upper and lower parts of the saline aquifer increases with decreasing reactive surface areas of anorthite and calcite. The mass density distribution of brine solution shows that the CO2^+brine solution region increases with decreasing reactive surface areas ofanorthite and calcite.
文摘We review the concept of congruence of null geodesics, the Raychaudhuri equation for the expansion, its harmonic oscillator version and associated “quantum” propagator, the role of the equation in the derivation of the Penrose singularity theorem, the definition of trapped surfaces, and the derivation of the theorem itself.
基金National Natural Science Foundation of China(61875072)National Postdoctoral Program for Innovative Talents(BX20190135)+2 种基金the Special Project of the Province-University Co-constructing Program of Jilin Province(SXGJXX2017-3)Project of Graduate Innovation Fund of Jilin University(101832018C018)International Cooperation and Exchange Project of Jilin Province(20170414002GH,20180414001GH)for the support to the work。
文摘NiO has a perfect-aligned energy level with CH3 NH3 Pb I3 perovskite such that it serves as a hole transport layer(HTL),but Ni O-based perovskite solar cells(PSCs)still suffer from low efficiency due to the poor interface contact between the perovskite layer and the Ni O HTL,and haphazardly stacked perovskite grains.Herein,poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1,3}-thiadiazole)](PFBT)is introduced between the Ni O and perovskite layers in the form of a polymer aggregate to enhance perovskite crystallinity and decrease the interface charge recombination between perovskite and Ni O in PSCs,resulting in an improved performance.Moreover,PFBT modified perovskite films showed sharper,smoother,and more compact crystalline grains with fewer grain boundaries,leading to the decreased nonradiative recombination.This study offers a simple strategy to achieve highly efficient PSCs with the incorporation of polymer semiconductor aggregates to passivate the interface between the perovskite and Ni O layers.
基金financially supported by the National Key Research and Development Program of China (No. 2021YFB3800101 and 2022YFE0110300)National Natural Science Foundation of China (No. U19A2089, 52261145696, 52073198, 92163114, and 22161142003)+3 种基金Natural Science Foundation of Jiangsu Province (BK20211598)“111” projectthe Young Elite Scientist Sponsorship Program by CASTCollaborative Innovation Center of Suzhou Nano Science and Technology, Soochow University。
文摘All-inorganic CsPbI_3 quantum dots(QDs) have demonstrated promising potential in photovoltaic(PV) applications. However, these colloidal perovskites are vulnerable to the deterioration of surface trap states, leading to a degradation in efficiency and stability. To address these issues, a facile yet effective strategy of introducing hydroiodic acid(HI) into the synthesis procedure is established to achieve high-quality QDs and devices. Through an in-depth experimental analysis, the introduction of HI was found to convert PbI_2 into highly coordinated [PbI_m]~(2-m), enabling control of the nucleation numbers and growth kinetics. Combined optical and structural investigations illustrate that such a synthesis technique is beneficial for achieving enhanced crystallinity and a reduced density of crystallographic defects. Finally, the effect of HI is further reflected on the PV performance. The optimal device demonstrated a significantly improved power conversion efficiency of 15.72% along with enhanced storage stability. This technique illuminates a novel and simple methodology to regulate the formed species during synthesis, shedding light on ofurther understanding solar cell performance, and aiding the design of future novel synthesis protocols for high-performance optoelectronic devices.
基金supported by the National Natural Science Foundation of China(51902153,51972165)the Ministry of Education of Singapore Tier 1(RG193/17,RG79/20(2020-T1-001-045))。
文摘A prevailing understanding on electrochemical activation of photoelectrodes is that electrochemical treatment leads to increased charge carrier densities thereby improved photoelectrode performances.Contrary to this understanding,in this study enhanced photoactivity of WO_(3) photoanode upon electrochemical treatment is ascribed to an extraordinary mechanism of surface trap passivation.The associated mechanism is analyzed by in situ optical spectroscopy,using which the optical property changes of WO_(3) electrode during electrochemical treatment are monitored.The results suggest surface W^(5+)species,the origin of surface traps on WO_(3) photoanodes,are converted to W^(6+) ions by electrochemical treatment.This study demonstrates the particular ability of the electrochemical strategy to passivate surface traps of photoanodes,and also shows the advantages of in situ optical spectroscopy to investigate the real-time electronic structure variations of electrodes during electrochemical treatment.
基金supported by the National Natural Science Foundation of China(Grant No.61306113)
文摘It has been reported that the gate leakage currents are described by the Frenkel-Poole emission(FPE) model,at temperatures higher than 250 K.However,the gate leakage currents of our passivated devices do not accord with the FPE model.Therefore,a modified FPE model is developed in which an additional leakage current,besides the gate(ⅠⅡ),is added.Based on the samples with different passivations,the ⅠⅡcaused by a large number of surface traps is separated from total gate currents,and is found to be linear with respect to(φB-Vg)0.5.Compared with these from the FPE model,the calculated results from the modified model agree well with the Ig-Vgmeasurements at temperatures ranging from 295 K to 475 K.
基金Project supported by the Key Science and Technology Foundation of Guangdong Province,China (Grant Nos. 2011A080801005 and 2010A080802001)the Guiding Project on the Integration of Industry,Education and Research of Guangdong Province,China (Grant No. 00802440123641045)the Strategic Emerging Industries,the Special Fund for LED Industry Projects of Guangdong Province,China (Grant No. 2012A080304003)
文摘Direct current(DC) reverse step voltage stress is applied on the gate of an AlGaN/GaN high-electron mobility transistor(HEMT).Experiments show that parameters degenerate under stress.Large-signal parasitic source/drain resistance(RS/RD) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test(DUT).Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon,and surface state recovery is the major reason for the recovery of device parameters.
基金Project supported by the National Natural Science Foundation of China(Grant No.61306131)the Research Project of Education Department of Shaanxi Province,China(Grant No.2013JK1095)
文摘Drain-modulated generation current IDMGinduced by interface traps in an n-type metal-oxide-semiconductor fieldeffect transistor(n MOSFET) is investigated. The formation of IDMGascribes to the change of the Si surface potential φs.This change makes the channel suffer transformation from the inversion state, depletion I state to depletion II state. The simulation result agrees with the experiment in the inversion and depletion I states. In the depletion II state, the theoretical curve goes into saturation, while the experimental curve drops quickly as VDincreases. The reason for this unconformity is that the drain-to-gate voltage VDGlessens φs around the drain corner and controls the falling edge of the IDMG curve.The experiments of gate-modulated generation and recombination currents are also applied to verify the reasonability of the mechanism. Based on this mechanism, a theoretical model of the IDMGfalling edge is set up in which IDMGhas an exponential attenuation relation with VDG. Finally, the critical fitting coefficient t of the experimental curves is extracted. It is found that t = 80 m V = 3k T /q. This result fully shows the accuracy of the above mechanism.
基金Project supported by the Pre-research Foundation of China(No.51308030201)the Special Foundation,China(No.9140A080509DZ0106)the Fundamental Research Funds for the Central Universities,China
文摘A novel structure of 4H-SiC MESFETs is proposed that focuses on surface trap suppression.Characteristics of the device have been investigated based on physical models for material properties and improved trap models.By comparing with the performance of the well-utilized buried-gate incorporated with a field-plate (BG-FP) structure,it is shown that the proposed structure improves device properties in comprehensive aspects. A p-type spacer layer introduced in the channel layer suppresses the surface trap effect and reduces the gate-drain capacitance(C_(gd)) under a large drain voltage.A p-type spacer layer incorporated with a field-plate improves the electric field distribution on the gate edge while the spacer layer induces less C_(gd) than a conventional FP.For microwave applications,4H-SiC MESFET for the proposed structure has a larger gate-lag ratio in the saturation region due to better surface trap isolation from the conductive channel.For high power applications,the proposed structure is able to endure higher operating voltage as well.The maximum saturation current density of 460 mA/mm is yielded.Also,the gate-lag ratio under a drain voltage of 20 V is close to 90%.In addition,5%and 17.8%improvements in f_T and f_(max) are obtained compared with a BG-FP MESFET in AC simulation,respectively.Parameters and dimensions of the proposed structure are optimized to make the best of the device for microwave applications and to provide a reference for device design.
基金the National Key Research and Development Program of China(No.2017YFA0304203)the National Natural Science Foundation of China(Nos.62127817,62075120,62075122,61875109,91950109,and 62105193),NSFCSTINT(No.62011530133)+3 种基金PCSIRT(No.IRT_17R70)Natural Science Foundation of Shanxi Province(No.201901D111010(ZD))Research Project Supported by Shanxi Scholarship Council of China(No.HGKY2019002)PTIT,Shanxi“1331 Project”,and 111 project(No.D18001).
文摘The two frequently observed phenomena,photoluminescence(PL)blinking and quantum-confined Stark effect(QCSE)-induced spectral diffusion,are not conducive to the applications of colloidal quantum dots(QDs).It remains elusive how these two phenomena are linked to each other.Unraveling the potential link between blinking and QCSE could facilitate the adoption of appropriate strategies that can simultaneously suppress both PL blinking and spectral diffusion.In this work,we investigated the blinking mechanism and QCSE of single CdSe/CdS/ZnS QDs in the presence of positive and negative surface charges using single-dot PL spectroscopy.We found that the negative surface charges can simultaneously suppress PL blinking and spectral diffusion of single QDs.On the other hand,the positive surface charges could change the blinking mechanisms of QDs from Auger-blinking to band-edge carrier(BC)-blinking.Two types of QCSE were observed,and a significant QCSE-induced spectral broadening of 5.25 nm was measured,which could be attributed to the hopping of surface charges between different surface-trap sites.Based on these findings,several theoretical models are proposed to explain various phenomena observed.