The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface p...The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface passivation layers and the gate insulators of the high-frequency GaN-based high-electron-mobility transistors were presented. Furthermore, the influences of dielectric thin films on the electrical properties of two-dimensional electron gas （2DEG） in the A1GaN/GaN hetero-structures were ana- lyzed. It was found that the additional in-plane biaxial tensile stress was another important factor besides the change in surface potential profile for the device perfor- mance improvement of the A1GaN/GaN HEMTs with dielectric thin films as both passivation layers and gate dielectrics. Then, two kinds of polar gate dielectric thin films, the ferroelectric LiNbO3 and the fluorinated A1203, were compared for the enhancement-mode GaN-based HEMTs, and an innovative process was proposed. At last, high-permittivity dielectric thin films were adopted as passivation layers to modulate the electric field and accordingly increase the breakdown voltage of GaN-based HEMTs. Moreover, the polyimide embedded with Cr particles effectively increased the breakdown voltage of GaNbased HEMTs. Finally, the effects of high-permittivity dielectric thin films on the potential distribution in the drift region were simulated, which showed an expanded electric field peak at the drain-side edge of gate electrode.展开更多
This paper investigates the electronic and optical properties for pure and Ce^3＋-doped CaS crystals by using the first-principles total energy calculations. The results show that CaS：Ce has a direct band gap of 2.16...This paper investigates the electronic and optical properties for pure and Ce^3＋-doped CaS crystals by using the first-principles total energy calculations. The results show that CaS：Ce has a direct band gap of 2.16 eV, and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states, respectively. Our results validate that the yellow emission from CaS：Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration. The Ce-S bond shows more covalent character than the Ca-S bond.展开更多
A single-stage single-switch high- frequency electronic ballast topology is presented. The circuit topology is the integration of a buck power- factor-correction （PFC） converter and a class E resonant inverter with ...A single-stage single-switch high- frequency electronic ballast topology is presented. The circuit topology is the integration of a buck power- factor-correction （PFC） converter and a class E resonant inverter with only one active power switch. The buck converter is operated in discontinuous conduction mode and at a fixed switching frequency, and constant duty cycle to achieve high power factor and it can be controlled easily. Detailed analysis of the operation and characteristics of the circuit is provided. Simulation results satisfy present standard requirements.展开更多
High-speed solar-blind short wavelength ultraviolet radiation detectors based onκ(ε)-Ga_(2)O_(3)layers with Pt contacts were demonstrated and their properties were studied in detail.Theκ(ε)-Ga_(2)O_(3)layers were ...High-speed solar-blind short wavelength ultraviolet radiation detectors based onκ(ε)-Ga_(2)O_(3)layers with Pt contacts were demonstrated and their properties were studied in detail.Theκ(ε)-Ga_(2)O_(3)layers were deposited by the halide vapor phase epitaxy on patterned GaN templates with sapphire substrates.The spectral dependencies of the photoelectric properties of struc-tures were analyzed in the wavelength interval 200-370 nm.The maximum photo to dark current ratio,responsivity,detectiv-ity and external quantum efficiency of structures were determined as:180.86 arb.un.,3.57 A/W,1.78×10^(12) Hz^(0.5)∙cm·W^(-1) and 2193.6%,respectively,at a wavelength of 200 nm and an applied voltage of 1 V.The enhancement of the photoresponse was caused by the decrease in the Schottky barrier at the Pt/κ(ε)-Ga_(2)O_(3)interface under ultraviolet exposure.The detectors demon-strated could functionalize in self-powered mode due to built-in electric field at the Pt/κ(ε)-Ga_(2)O_(3)interface.The responsivity and external quantum efficiency of the structures at a wavelength of 254 nm and zero applied voltage were 0.9 mA/W and 0.46%,respectively.The rise and decay times in self-powered mode did not exceed 100 ms.展开更多
In this work,metal–semiconductor–metal solar-blind ultraviolet photoconductors were fabricated based on theβ-Ga_(2)O_(3) thin films which were grown on the c-plane sapphire substrates by molecular beam epitaxy.Then...In this work,metal–semiconductor–metal solar-blind ultraviolet photoconductors were fabricated based on theβ-Ga_(2)O_(3) thin films which were grown on the c-plane sapphire substrates by molecular beam epitaxy.Then,the effects ofβ-Ga_(2)O_(3) annealing on both its material character-istics and the device photoconductivity were studied.Theβ-Ga_(2)O_(3) thin films were annealed at 800,900,1000,and 1100°C,respectively.Moreover,the annealing time was fixed at 2 h,and the annealing ambients were oxygen,nitro-gen,and vacuum(4.9×10^(-4 )Pa),respectively.The crys-talline quality and texture of theβ-Ga_(2)O_(3) thin films before and after annealing were investigated by X-ray diffraction(XRD),showing that higher annealing temperature can result in a weaker intensity of(402)diffraction peak and a lower device photoresponsivity.Furthermore,the vacuum-annealed sam-ple exhibits the highest photoresponsivity compared with the oxygen-and nitrogen-annealed samples at the same annealing temperature.In addition,the persistent photoconductivity effect is effectively restrained in the oxygen-annealed sample even with the lowest photoresponsivity.展开更多
This paper reports that the polymer/organic heterojunction doped light-emitting diodes using a novel poly-TPD as hole transport material and doping both hole transport layer and emitter layer with the highly fluoresce...This paper reports that the polymer/organic heterojunction doped light-emitting diodes using a novel poly-TPD as hole transport material and doping both hole transport layer and emitter layer with the highly fluorescent rubrene and DCJTB has been successfully fabricated. The basic structure of the heterostructure is PTPD/Alq3. When hole transport layer and electron transport layer are doped simultaneously with different dopant, the electrol quantum efficiencies are about 3 times greater than that of the undoped device. Compared with undoped device and conventional TPD/Alq3 diode, the stability of the doping device is significantly improved. The process of emission for doped device may include carrier trapping as well as FSrster energy transfer.展开更多
Dye-sensitized solar cells（DSSCs） have attracted significant attention as alternatives to conventional silicon-based solar cells owing to their low-cost production,facile fabrication,excellent stability and high pow...Dye-sensitized solar cells（DSSCs） have attracted significant attention as alternatives to conventional silicon-based solar cells owing to their low-cost production,facile fabrication,excellent stability and high power conversion efficiency（PCE）.The dye molecule is one of the key components in DSSCs since it significant influence on the PCE,charge separation,light-harvesting,as well as the device stability.Among various dyes,easily tunable phenothiazine-based dyes hold a large proportion and achieve impressive photovoltaic performances.This class of dyes not only has superiorly non-planar butterfly structure but also possesses excellent electron donating ability and large π conjugated system.This review summarized recent developments in the phenothiazine dyes,including small molecule phenothiazine dyes,polymer phenothiazine dyes and phenothiazine dyes for co-sensitization,especially focused on the developments and design concepts of small molecule phenothiazine dyes,as well as the correlation between molecular structures and the photovoltaic performances.展开更多
Metal-organic chemical vapor deposition was applied to fabricate YBa2Cu3OT-a （YBCO） films on singlecrystal LaA103 （001） substrates for its high deposition rate, easy adjustment on film composition, and low require...Metal-organic chemical vapor deposition was applied to fabricate YBa2Cu3OT-a （YBCO） films on singlecrystal LaA103 （001） substrates for its high deposition rate, easy adjustment on film composition, and low requirement on vacuum apparatus. The effects of Cu（tmhd）2 concentra- tion in the precursor on the properties of YBCO films were systematically investigated. X-ray diffraction （XRD） reveals that the mole ratio of Cu/Ba in the precursor from 0.77 to 0.97 is helpful to improve the crystallization and out-of-plane orientation of YBCO films; however, it hardly affects the inplane texture. Scanning electron microscope （SEM） shows the dense, crack-free but rough surface, on which there are Cu-O and Ba-Cu-O outgrowths identified by energy-dispersive spectrometer （EDS）. As the mole ratio of Cu/Ba increasing, the average size of Ba-Cu-O precipitates keeps increasing and the film composition becomes inhomoge- neous at the mole ratio of Cu/Ba of 0.97. The 250 nm thick YBCO film prepared at the mole ratio of Cu/Ba of 0.91 shows the critical current density （Jc） of 4.0 MA.cm-2 （77 K, 0 T）.展开更多
This paper reports that ion implantation to a dose of 1 ×10^17 ions/cm^2 was performed on c-axis-orientated ZnO thin films deposited on （0001） sapphire substrates by the sol-gel technique. After ion implantatio...This paper reports that ion implantation to a dose of 1 ×10^17 ions/cm^2 was performed on c-axis-orientated ZnO thin films deposited on （0001） sapphire substrates by the sol-gel technique. After ion implantation, the as-implanted ZnO films were annealed in argon ambient at different temperatures from 600 - 900 ℃. The effects of ion implantation and post-implantation annealing on the structural and optical properties of the ZnO films were investigated by x-ray diffraction （XRD）, photoluminescence （PL）. It was found that the intensities of （002） peak and near band edge （NBE） exitonic ultraviolet emission increased with increasing annealing temperature from 600- 900 ℃. The defect related deep level emission （DLE） firstly increased with increasing annealing temperature from 600 - 750 ℃, and then decreased quickly with increasing annealing temperature. The recovery of the intensities of NBE and DLE occurs at ～850℃ and ～750℃ respectively. The relative PL intensity ratio of NBE to DLE showed that the quality of ZnO films increased continuously with increasing annealing temperature from 600 - 900 ℃.展开更多
Epitaxial YBCO films were deposited on （100） LaAlO3 single-crystal substrates by metalorganic deposition of metal trifluoroacetate precursors with different concentrations. All the YBCO films have Tc around 91 K and...Epitaxial YBCO films were deposited on （100） LaAlO3 single-crystal substrates by metalorganic deposition of metal trifluoroacetate precursors with different concentrations. All the YBCO films have Tc around 91 K and Jc excess 2 MA/cm^2 at 77 K in zero field. XRD θ-2θscans show all the films have c-axis normal orientation. The FWHM （full width at half-maximum intensity） values of X-ray ω-scans of （005） reflection are 0.379°, 0.283°, and 0.543° for the YBCO thin films deposited with precursor solution concentrations of 1.52, 1.0, and 0.75 mol/L, respectively. With the concentration of the precursors decreasing, the thickness of the films decreases linearly. SEM micrographs show that porosities in the films become bigger with the precursor solution concentration decreasing. The big porosities in the film with the lowest concentration precursor deteriorate the superconducting property and make it have a wider superconducting transition and a lower Jc.展开更多
We report the preparation of p-type ZnO thin films on （0001） sapphire substrates by a combination of sol-gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperatu...We report the preparation of p-type ZnO thin films on （0001） sapphire substrates by a combination of sol-gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperature indicate that the N-implanted ZnO：Al films annealed at 600℃ have converted to p-type conduction with a hole concentration of 1.6 × 1018 cm^-3, a hole mobility of 3.67cm^2/V· s and a minimum resistivity of 4.80 cm-Ω. Ion-beam induced damage recovery has been investigated by x-ray diffraction （XRD）, photoluminescence （PL） and optical transmittance measurements. Results show that diffraction peaks and PL intensities are decreased by N ion implantation, but they nearly recover after annealing at 600℃. Our results demonstrate a promising approach to fabricate p-type ZnO at a low cost.展开更多
FeSiAl alloys ribbons synthesized by melt-quench were annealed in vacuum at 873 K for 60 rain. The flaky powders were prepared by milling the annealed ribbons for 70 h. After milling, the powders were heat treated at ...FeSiAl alloys ribbons synthesized by melt-quench were annealed in vacuum at 873 K for 60 rain. The flaky powders were prepared by milling the annealed ribbons for 70 h. After milling, the powders were heat treated at 573 K for 90 rain. The ordering degree of the powders lattice structure was analyzed by X-ray diffraction （XRD）. The measurement of specific saturation magnetization was carried out by vibrating samples magnetometer （VSM）. Complex permittivity and complex permeability in the frequency band of 0.5-18 GHz were measured with the vector network analyzer. The ordering degree of the superlattice structure increased from 0.2＇7 to 0.49. Complex permittivity and complex permeability decreased with increasing Si content. After ordering, the specific saturation magnetization decreased from 134.2 to 85.0 A.m2.kg-1. For use in anti-EMI material, the total contents of Si and Al in FeSiAl alloys should be controlled at a low level.展开更多
This paper performs the density functional theory calculations to obtain some factors influencing the response of pyrochlores Gd2B207 （B = Ti, Sn, Zr） to ion irradiation-induced amorphization. The 48f oxygen positio...This paper performs the density functional theory calculations to obtain some factors influencing the response of pyrochlores Gd2B207 （B = Ti, Sn, Zr） to ion irradiation-induced amorphization. The 48f oxygen position parameter x, cohesive energy, bond type and defect-formation energy are discussed. The results show that parameter x can be used to indicate the disordering tendencies within a given pyrochlore family. Bond type, cohesive energy and defect-formation energies can be used to explain some experimental observations, but they are not determined exclusively by radiation ＂resistance＂ for a different pyrochlore family.展开更多
In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysi...In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.展开更多
Single-layer YBa2Cu3O7-δ（YBCO） films with the thickness of over 600 nm were fabricated by modified metal organic deposition using trifluoroacetate metal organic deposition（TFA-MOD） method on LaAlO3（LAO） substra...Single-layer YBa2Cu3O7-δ（YBCO） films with the thickness of over 600 nm were fabricated by modified metal organic deposition using trifluoroacetate metal organic deposition（TFA-MOD） method on LaAlO3（LAO） substrates. Polyvinylbutyral（PVB） was added into the precursor solution to enhance the thickness of the single layer. The pyrolysis process was shortened to about 3 h due to the reduction of the fluorine content in the precursor solution.The effects of heating rate during the crystallization process on the microstructure and Jcvalues of YBCO films were investigated. The α-axis-oriented YBCO crystals dominate when the heating rate is lower than 20 °C·min^-1, while faster heating rate of 43 °C·min^-1 results in pure c-axis epitaxial growth. The Jcvalues of YBCO films increase linearly with heating rate increasing due to the increase of c-axis YBCO growth, and the critical current（Ic） value of 100 A·cm^-1 within a single-layer YBCO film is achieved.展开更多
Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated fo...Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.展开更多
Based on the advantages of SOI technology, the frequency performance of SiGe HBT with SOI structure has been simulated. Compared with bulk SiGe HBT, the results show that the buried oxide layer （BOX） can reduce coll...Based on the advantages of SOI technology, the frequency performance of SiGe HBT with SOI structure has been simulated. Compared with bulk SiGe HBT, the results show that the buried oxide layer （BOX） can reduce collector-base capacitance CCB with the maximum value 89.3%, substrate-base capacitance CSB with 94. 6%, and the maximum oscillation frequency is improved by 2.7. The SOl structure improves the frequency performance of SiGe HBT, which is adaptable to high-speed and high power applications.展开更多
A theoretical relationship between the wavelet transform and the fast fourier transformation(FFT) methods in broadband wireless signal is proposed for solving the direction of arrivals(DOAs) estimation problem. This l...A theoretical relationship between the wavelet transform and the fast fourier transformation(FFT) methods in broadband wireless signal is proposed for solving the direction of arrivals(DOAs) estimation problem. This leads naturally to the derivation of minimum variance distortionless response(MVDR) algorithm, which combines the benefits of subspace methods with those of wavelet, and spatially smoothed versions are utilized which exhibits good performance against correlated signals. We test the method's performance by simulating and comparing the performance of proposed algorithm, FFT MVDR and MVDR with correlated signals, and an improved performance is obtained.展开更多
High-resistivity β-Ga203 thin films were grown on Si-doped n-type conductive β-Ga203 single crystals by molecular beam epitaxy （MBE）. Vertical-type Schottky diodes were fabricated, and the electrical properties of...High-resistivity β-Ga203 thin films were grown on Si-doped n-type conductive β-Ga203 single crystals by molecular beam epitaxy （MBE）. Vertical-type Schottky diodes were fabricated, and the electrical properties of the Schottky diodes were studied in this letter. The ideality factor and the series resistance of the Schottky diodes were estimated to be about 1.4 and 4.6 x 10^6 %. The ionized donor concentration and the spreading voltage in the Schottky diodes region are about 4 x 10^18 cm-3 and 7.6 V, respectively. The ultra-violet （UV） photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination. A photoresponsivity of 1.8 A/W and an external quantum efficiency of 8.7 x 10%2% were observed at forward bias voltage of 3.8 V, the proper driving voltage of read-out integrated circuit for UV camera. The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β-Ga203 thin films and the n-type conductive β-Ga203 single-crystal substrate.展开更多
In this work,Bi2Te3 films（250 nm） are fabricated on Si O2/Si substrates by radio frequency（RF） magnetron sputtering at room temperature,and the prepared films are annealed over the temperature range of 200 °C...In this work,Bi2Te3 films（250 nm） are fabricated on Si O2/Si substrates by radio frequency（RF） magnetron sputtering at room temperature,and the prepared films are annealed over the temperature range of 200 °C to 400 °C.Crystallinity and electrical properties of the films can be tuned correspondingly.The power factors of Bi2Te3 films of 0.85 μW/K2 cm to 11.43 μW/K2 cm were achieved after annealing.The infrared reflectance measurements from 2.5 μm to 5.0 μm demonstrate that there is also a slight red-shift of the plasma oscillation frequency in the Bi2Te3 films.By means of plasmonic calculations,we attribute the red-shift of absorption peaks to the reduction of carrier concentration and the change of effective mass of Bi2Te3 films with the increased annealing temperature.展开更多
基金financially supported by the National Nature Science Foundation of China(No.50932002)the Research Foundation for the Doctoral Program of Higher Education of China(No.2012018530003)
文摘The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface passivation layers and the gate insulators of the high-frequency GaN-based high-electron-mobility transistors were presented. Furthermore, the influences of dielectric thin films on the electrical properties of two-dimensional electron gas （2DEG） in the A1GaN/GaN hetero-structures were ana- lyzed. It was found that the additional in-plane biaxial tensile stress was another important factor besides the change in surface potential profile for the device perfor- mance improvement of the A1GaN/GaN HEMTs with dielectric thin films as both passivation layers and gate dielectrics. Then, two kinds of polar gate dielectric thin films, the ferroelectric LiNbO3 and the fluorinated A1203, were compared for the enhancement-mode GaN-based HEMTs, and an innovative process was proposed. At last, high-permittivity dielectric thin films were adopted as passivation layers to modulate the electric field and accordingly increase the breakdown voltage of GaN-based HEMTs. Moreover, the polyimide embedded with Cr particles effectively increased the breakdown voltage of GaNbased HEMTs. Finally, the effects of high-permittivity dielectric thin films on the potential distribution in the drift region were simulated, which showed an expanded electric field peak at the drain-side edge of gate electrode.
文摘This paper investigates the electronic and optical properties for pure and Ce^3＋-doped CaS crystals by using the first-principles total energy calculations. The results show that CaS：Ce has a direct band gap of 2.16 eV, and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states, respectively. Our results validate that the yellow emission from CaS：Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration. The Ce-S bond shows more covalent character than the Ca-S bond.
文摘A single-stage single-switch high- frequency electronic ballast topology is presented. The circuit topology is the integration of a buck power- factor-correction （PFC） converter and a class E resonant inverter with only one active power switch. The buck converter is operated in discontinuous conduction mode and at a fixed switching frequency, and constant duty cycle to achieve high power factor and it can be controlled easily. Detailed analysis of the operation and characteristics of the circuit is provided. Simulation results satisfy present standard requirements.
基金Research of the photoelectric properties of theκ(ε)-Ga_(2)O_(3)films was supported by the Russian Science Foundation,grant number 20-79-10043-P.Fabrication of the ultraviolet detectors based on theκ(ε)-Ga_(2)O_(3)layers was supported by the grant under the Decree of the Government of the Rus-sian Federation No.220 of 09 April 2010(Agreement No.075-15-2022-1132 of 01 July 2022)Research of the structural prop-erties of theκ(ε)-Ga_(2)O_(3)was supported by the St.Petersburg State University,grant number 94034685.
文摘High-speed solar-blind short wavelength ultraviolet radiation detectors based onκ(ε)-Ga_(2)O_(3)layers with Pt contacts were demonstrated and their properties were studied in detail.Theκ(ε)-Ga_(2)O_(3)layers were deposited by the halide vapor phase epitaxy on patterned GaN templates with sapphire substrates.The spectral dependencies of the photoelectric properties of struc-tures were analyzed in the wavelength interval 200-370 nm.The maximum photo to dark current ratio,responsivity,detectiv-ity and external quantum efficiency of structures were determined as:180.86 arb.un.,3.57 A/W,1.78×10^(12) Hz^(0.5)∙cm·W^(-1) and 2193.6%,respectively,at a wavelength of 200 nm and an applied voltage of 1 V.The enhancement of the photoresponse was caused by the decrease in the Schottky barrier at the Pt/κ(ε)-Ga_(2)O_(3)interface under ultraviolet exposure.The detectors demon-strated could functionalize in self-powered mode due to built-in electric field at the Pt/κ(ε)-Ga_(2)O_(3)interface.The responsivity and external quantum efficiency of the structures at a wavelength of 254 nm and zero applied voltage were 0.9 mA/W and 0.46%,respectively.The rise and decay times in self-powered mode did not exceed 100 ms.
基金the National Natural Science Foundation of China(No.61223002)the Research Foundation for the Doctoral Program of Higher Education of China(No.2012018530003)。
文摘In this work,metal–semiconductor–metal solar-blind ultraviolet photoconductors were fabricated based on theβ-Ga_(2)O_(3) thin films which were grown on the c-plane sapphire substrates by molecular beam epitaxy.Then,the effects ofβ-Ga_(2)O_(3) annealing on both its material character-istics and the device photoconductivity were studied.Theβ-Ga_(2)O_(3) thin films were annealed at 800,900,1000,and 1100°C,respectively.Moreover,the annealing time was fixed at 2 h,and the annealing ambients were oxygen,nitro-gen,and vacuum(4.9×10^(-4 )Pa),respectively.The crys-talline quality and texture of theβ-Ga_(2)O_(3) thin films before and after annealing were investigated by X-ray diffraction(XRD),showing that higher annealing temperature can result in a weaker intensity of(402)diffraction peak and a lower device photoresponsivity.Furthermore,the vacuum-annealed sam-ple exhibits the highest photoresponsivity compared with the oxygen-and nitrogen-annealed samples at the same annealing temperature.In addition,the persistent photoconductivity effect is effectively restrained in the oxygen-annealed sample even with the lowest photoresponsivity.
文摘This paper reports that the polymer/organic heterojunction doped light-emitting diodes using a novel poly-TPD as hole transport material and doping both hole transport layer and emitter layer with the highly fluorescent rubrene and DCJTB has been successfully fabricated. The basic structure of the heterostructure is PTPD/Alq3. When hole transport layer and electron transport layer are doped simultaneously with different dopant, the electrol quantum efficiencies are about 3 times greater than that of the undoped device. Compared with undoped device and conventional TPD/Alq3 diode, the stability of the doping device is significantly improved. The process of emission for doped device may include carrier trapping as well as FSrster energy transfer.
基金the National Natural Science Foundation of China(Nos.21572030,21272033,21402023)Fundamental Research Funds for the Central Universities(No.ZYGX2014J026)for financial support
文摘Dye-sensitized solar cells（DSSCs） have attracted significant attention as alternatives to conventional silicon-based solar cells owing to their low-cost production,facile fabrication,excellent stability and high power conversion efficiency（PCE）.The dye molecule is one of the key components in DSSCs since it significant influence on the PCE,charge separation,light-harvesting,as well as the device stability.Among various dyes,easily tunable phenothiazine-based dyes hold a large proportion and achieve impressive photovoltaic performances.This class of dyes not only has superiorly non-planar butterfly structure but also possesses excellent electron donating ability and large π conjugated system.This review summarized recent developments in the phenothiazine dyes,including small molecule phenothiazine dyes,polymer phenothiazine dyes and phenothiazine dyes for co-sensitization,especially focused on the developments and design concepts of small molecule phenothiazine dyes,as well as the correlation between molecular structures and the photovoltaic performances.
基金financially supported by the Sichuan Youth Science and Technology Innovation Research Team(No.2011JTD0006)the Fundamental Research Funds for the Central Universities(Nos.ZYGX2012J039 and ZYGX2011Z002)
文摘Metal-organic chemical vapor deposition was applied to fabricate YBa2Cu3OT-a （YBCO） films on singlecrystal LaA103 （001） substrates for its high deposition rate, easy adjustment on film composition, and low requirement on vacuum apparatus. The effects of Cu（tmhd）2 concentra- tion in the precursor on the properties of YBCO films were systematically investigated. X-ray diffraction （XRD） reveals that the mole ratio of Cu/Ba in the precursor from 0.77 to 0.97 is helpful to improve the crystallization and out-of-plane orientation of YBCO films; however, it hardly affects the inplane texture. Scanning electron microscope （SEM） shows the dense, crack-free but rough surface, on which there are Cu-O and Ba-Cu-O outgrowths identified by energy-dispersive spectrometer （EDS）. As the mole ratio of Cu/Ba increasing, the average size of Ba-Cu-O precipitates keeps increasing and the film composition becomes inhomoge- neous at the mole ratio of Cu/Ba of 0.97. The 250 nm thick YBCO film prepared at the mole ratio of Cu/Ba of 0.91 shows the critical current density （Jc） of 4.0 MA.cm-2 （77 K, 0 T）.
文摘This paper reports that ion implantation to a dose of 1 ×10^17 ions/cm^2 was performed on c-axis-orientated ZnO thin films deposited on （0001） sapphire substrates by the sol-gel technique. After ion implantation, the as-implanted ZnO films were annealed in argon ambient at different temperatures from 600 - 900 ℃. The effects of ion implantation and post-implantation annealing on the structural and optical properties of the ZnO films were investigated by x-ray diffraction （XRD）, photoluminescence （PL）. It was found that the intensities of （002） peak and near band edge （NBE） exitonic ultraviolet emission increased with increasing annealing temperature from 600- 900 ℃. The defect related deep level emission （DLE） firstly increased with increasing annealing temperature from 600 - 750 ℃, and then decreased quickly with increasing annealing temperature. The recovery of the intensities of NBE and DLE occurs at ～850℃ and ～750℃ respectively. The relative PL intensity ratio of NBE to DLE showed that the quality of ZnO films increased continuously with increasing annealing temperature from 600 - 900 ℃.
文摘Epitaxial YBCO films were deposited on （100） LaAlO3 single-crystal substrates by metalorganic deposition of metal trifluoroacetate precursors with different concentrations. All the YBCO films have Tc around 91 K and Jc excess 2 MA/cm^2 at 77 K in zero field. XRD θ-2θscans show all the films have c-axis normal orientation. The FWHM （full width at half-maximum intensity） values of X-ray ω-scans of （005） reflection are 0.379°, 0.283°, and 0.543° for the YBCO thin films deposited with precursor solution concentrations of 1.52, 1.0, and 0.75 mol/L, respectively. With the concentration of the precursors decreasing, the thickness of the films decreases linearly. SEM micrographs show that porosities in the films become bigger with the precursor solution concentration decreasing. The big porosities in the film with the lowest concentration precursor deteriorate the superconducting property and make it have a wider superconducting transition and a lower Jc.
基金Project supported by the Program for New Century Excellent Talents in University (Grant No NCET-04-0899)Special Foundation for University Subject Construction, Department of Education of Guangdong Province, China (Grant No [2006] 11)
文摘We report the preparation of p-type ZnO thin films on （0001） sapphire substrates by a combination of sol-gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperature indicate that the N-implanted ZnO：Al films annealed at 600℃ have converted to p-type conduction with a hole concentration of 1.6 × 1018 cm^-3, a hole mobility of 3.67cm^2/V· s and a minimum resistivity of 4.80 cm-Ω. Ion-beam induced damage recovery has been investigated by x-ray diffraction （XRD）, photoluminescence （PL） and optical transmittance measurements. Results show that diffraction peaks and PL intensities are decreased by N ion implantation, but they nearly recover after annealing at 600℃. Our results demonstrate a promising approach to fabricate p-type ZnO at a low cost.
文摘FeSiAl alloys ribbons synthesized by melt-quench were annealed in vacuum at 873 K for 60 rain. The flaky powders were prepared by milling the annealed ribbons for 70 h. After milling, the powders were heat treated at 573 K for 90 rain. The ordering degree of the powders lattice structure was analyzed by X-ray diffraction （XRD）. The measurement of specific saturation magnetization was carried out by vibrating samples magnetometer （VSM）. Complex permittivity and complex permeability in the frequency band of 0.5-18 GHz were measured with the vector network analyzer. The ordering degree of the superlattice structure increased from 0.2＇7 to 0.49. Complex permittivity and complex permeability decreased with increasing Si content. After ordering, the specific saturation magnetization decreased from 134.2 to 85.0 A.m2.kg-1. For use in anti-EMI material, the total contents of Si and Al in FeSiAl alloys should be controlled at a low level.
文摘This paper performs the density functional theory calculations to obtain some factors influencing the response of pyrochlores Gd2B207 （B = Ti, Sn, Zr） to ion irradiation-induced amorphization. The 48f oxygen position parameter x, cohesive energy, bond type and defect-formation energy are discussed. The results show that parameter x can be used to indicate the disordering tendencies within a given pyrochlore family. Bond type, cohesive energy and defect-formation energies can be used to explain some experimental observations, but they are not determined exclusively by radiation ＂resistance＂ for a different pyrochlore family.
基金Project supported by the National Basic Research Program of China(Grant No.2007CB310407)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(Grant No.61021061)+1 种基金the National Natural Youth Fund of China(Grant No.61001025)National Programs for Science and Technology Development of Guangdong Province,China(Grant No.2010B090400314)
文摘In this paper, M-type hexagonal barium ferrite powders are synthesized using the sol-gel method. A dried precursor heated in air is analyzed in the temperature range from 50 to 1200 ℃ using thermo-gravimetric analysis and differential scanning calorimetry. The effects of the additives and the cacinating temperature on the magnetic properties are investigated, and the results show that single-phase barium ferrite powders can be formed. After heat-treating at 950 ℃ for 4h with 3 wt% additive, the coercivity and saturation magnetization are found to be 440 Oe and 57.9 emu/g, respectively.
基金financially supported by the National Natural Science Foundation of China (No.51002024)the Sichuan Youth Science and Technology Innovation Research Team (No.2011JTD0006)+1 种基金the Program for Cooperation of Industry, Education and Academy of Guangdong Province, China (No. 2012B091100298)the Fundamental Research Funds for the Central Universities (Nos.ZYGX2012J039, ZYGX2011Z002, and ZYGX2012J035)
文摘Single-layer YBa2Cu3O7-δ（YBCO） films with the thickness of over 600 nm were fabricated by modified metal organic deposition using trifluoroacetate metal organic deposition（TFA-MOD） method on LaAlO3（LAO） substrates. Polyvinylbutyral（PVB） was added into the precursor solution to enhance the thickness of the single layer. The pyrolysis process was shortened to about 3 h due to the reduction of the fluorine content in the precursor solution.The effects of heating rate during the crystallization process on the microstructure and Jcvalues of YBCO films were investigated. The α-axis-oriented YBCO crystals dominate when the heating rate is lower than 20 °C·min^-1, while faster heating rate of 43 °C·min^-1 results in pure c-axis epitaxial growth. The Jcvalues of YBCO films increase linearly with heating rate increasing due to the increase of c-axis YBCO growth, and the critical current（Ic） value of 100 A·cm^-1 within a single-layer YBCO film is achieved.
基金financially supported by the National Nature Science Foundation of China (No. 61223002)Sichuan Youth Science and Technology Innovation Research Team Funding (No. 2011JTD0006)
文摘Surface acoustic wave（SAW） resonators with Pt/AlN/Si and Pt/AlN/Pt/Si configurations were fabricated by lift-off photolithography techniques. High-temperature performances of both configurations were investigated for temperature sensor applications. AlN films grown on Ptcoated Si substrates exhibit a lower（002） preferred orientation than those grown on Si substrates. The center frequencies of Pt/AlN/Si and Pt/AlN/Pt/Si configurations at room temperature are 424.1 and 456.4 MHz, respectively.The SAW was limited by Pt bottom electrodes to propagate in AlN layer. The temperature coefficient of frequency（TCF） values of Pt/AlN/Si and Pt/AlN/Pt/Si configurations are-51.6 × 10^-6 and-69.2 × 10^-6℃^-1, respectively.Compared with that of Pt/AlN/Si configuration, the TCF value of Pt/AlN/Pt/Si configuration decreases by 34.1 %.AlN resonator with the Pt floating bottom electrodes provides a large, quasi-constant temperature sensitivity which is suitable for temperature sensor applications.
文摘Based on the advantages of SOI technology, the frequency performance of SiGe HBT with SOI structure has been simulated. Compared with bulk SiGe HBT, the results show that the buried oxide layer （BOX） can reduce collector-base capacitance CCB with the maximum value 89.3%, substrate-base capacitance CSB with 94. 6%, and the maximum oscillation frequency is improved by 2.7. The SOl structure improves the frequency performance of SiGe HBT, which is adaptable to high-speed and high power applications.
基金supported by the Chinese Natural Science Foundation 61401075Central University Business Fee ZYGX2015J106
文摘A theoretical relationship between the wavelet transform and the fast fourier transformation(FFT) methods in broadband wireless signal is proposed for solving the direction of arrivals(DOAs) estimation problem. This leads naturally to the derivation of minimum variance distortionless response(MVDR) algorithm, which combines the benefits of subspace methods with those of wavelet, and spatially smoothed versions are utilized which exhibits good performance against correlated signals. We test the method's performance by simulating and comparing the performance of proposed algorithm, FFT MVDR and MVDR with correlated signals, and an improved performance is obtained.
基金supported by the National Nature Science Foundation of China(Grant No.61223002)the Science and Technology Commission of Shanghai Municipality,China(Grant No.13111103700)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.2012018530003)
文摘High-resistivity β-Ga203 thin films were grown on Si-doped n-type conductive β-Ga203 single crystals by molecular beam epitaxy （MBE）. Vertical-type Schottky diodes were fabricated, and the electrical properties of the Schottky diodes were studied in this letter. The ideality factor and the series resistance of the Schottky diodes were estimated to be about 1.4 and 4.6 x 10^6 %. The ionized donor concentration and the spreading voltage in the Schottky diodes region are about 4 x 10^18 cm-3 and 7.6 V, respectively. The ultra-violet （UV） photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination. A photoresponsivity of 1.8 A/W and an external quantum efficiency of 8.7 x 10%2% were observed at forward bias voltage of 3.8 V, the proper driving voltage of read-out integrated circuit for UV camera. The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β-Ga203 thin films and the n-type conductive β-Ga203 single-crystal substrate.
基金supported by the National Natural Science Foundation of China under Grant No.51025208Program for Changjiang Scholars and Innovative Research Team in University under Grant No.IRT1309
文摘In this work,Bi2Te3 films（250 nm） are fabricated on Si O2/Si substrates by radio frequency（RF） magnetron sputtering at room temperature,and the prepared films are annealed over the temperature range of 200 °C to 400 °C.Crystallinity and electrical properties of the films can be tuned correspondingly.The power factors of Bi2Te3 films of 0.85 μW/K2 cm to 11.43 μW/K2 cm were achieved after annealing.The infrared reflectance measurements from 2.5 μm to 5.0 μm demonstrate that there is also a slight red-shift of the plasma oscillation frequency in the Bi2Te3 films.By means of plasmonic calculations,we attribute the red-shift of absorption peaks to the reduction of carrier concentration and the change of effective mass of Bi2Te3 films with the increased annealing temperature.
