The synthesis,crystal structure and electrical conductivity properties of Fe-doped ZnO powders（in the range of 0.25-15 mol%） were reported in this paper.I-phase samples,which were indexed as single phase with a hexa...The synthesis,crystal structure and electrical conductivity properties of Fe-doped ZnO powders（in the range of 0.25-15 mol%） were reported in this paper.I-phase samples,which were indexed as single phase with a hexagonal（wurtzite） structure in the Fe-doped ZnO binary system,were determined by X-ray diffraction（XRD）.The solubility limit of Fe in the ZnO lattice is 3 mol% at 950℃.The above mixed phase was observed.And the impurity phase was determined as the cubic-ZnFe 2 O 4 phase when compared with standard XRD data using the PDF program.This study focused on single I-phase ZnO samples which were synthesized at 950℃ because the limit of the solubility range is the widest at this temperature.The lattice parameters a and c of the I-phase decreased with Fe-doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The grain size of the I-phase samples increased with heat treatment and doping concentration.The electrical conductivity of the pure ZnO and single I-phase samples was investigated using the four-probe dc method at 100-950℃ in air atmosphere.The electrical conductivity values of pure ZnO,0.25 and 3 mol% Fe-doped ZnO samples at 100℃ were 2×10-6,1.7×10-3 and 6.3×10-4 S.cm-1,and at 950℃ they were 3.4,8.5 and 4 S.cm-1,respectively.展开更多
Wurzite ZnS:Mn nanorods are synthesized via a solvothermal method by using ethylenediamine and water as mixed solvent.The diameters of the nanorods increase and the lengths decrease with the Mn concentration.High reso...Wurzite ZnS:Mn nanorods are synthesized via a solvothermal method by using ethylenediamine and water as mixed solvent.The diameters of the nanorods increase and the lengths decrease with the Mn concentration.High resolution transmission electron microscopic images illustrate that a few cubic ZnS:Mn nanoparticles arise along with hexagonal nanorods on high Mn concentration.The samples set off yellow-orange emission at 590 nm,characteristic of 4 T→ 6 A 1 transition of Mn 2+ at T d symmetry in ZnS.Electron spin resonance spectrum of the nanorods shows that high Mn concentrations produce a broad envelope,whereas six-line hyperfine appears for lower Mn concentrations.These results together with the magnetization curves indicate that all the ZnS:Mn samples are paramagnetic even down to 4 K,which suggests that the ZnS:Mn is not suitable for dilute magnetic semiconductor.展开更多
Well-aligned single-crystalline wurzite zinc oxide (ZnO) nanowire arrays were successfully fabricated on a Si substrate by a simple physical vapor-deposition (PVD) method at a relatively low temperature of about 500&#...Well-aligned single-crystalline wurzite zinc oxide (ZnO) nanowire arrays were successfully fabricated on a Si substrate by a simple physical vapor-deposition (PVD) method at a relatively low temperature of about 500°C. The as-fabricated nanowires were preferentially arranged along the [001] direction of ZnO. The photoluminescence spectrum of ZnO nanowire arrays showed two emission bands: a strong green emission at around 500 nm and a weak ultraviolet emission at 380 nm. The strong green light emission was related to the existence of the oxygen vacancies in ZnO crystals. Corresponding growth mechanism of the ZnO nanowires was briefly discussed.展开更多
We have analyzed the spin transport behaviour of four II-VI semiconductor nanowires by simulating spin polarized transport using a semi-classical Monte-Carlo approach. The different scattering mechanisms con- sidered ...We have analyzed the spin transport behaviour of four II-VI semiconductor nanowires by simulating spin polarized transport using a semi-classical Monte-Carlo approach. The different scattering mechanisms con- sidered are acoustic phonon scattering, surface roughness scattering, polar optical phonon scattering, and spin flip scattering. The II-VI materials used in our study are CdS, CdSe, ZnO and ZnS. The spin transport behaviour is first studied by varying the temperature （4-500 K） at a fixed diameter of 10 nm and also by varying the diameter （8-12 nm） at a fixed temperature of 300 K. For II-VI compounds, the dominant mechanism is for spin relaxation; D＇yakonovPerel and Elliot Yafet have been actively employed in the first order model to simulate the spin transport. The dependence of the spin relaxation length （SRL） on the diameter and temperature has been analyzed.展开更多
A chemical-assisted element direct-reaction method is developed to synthesize ZnSe compound semiconductor material at a relatively low temperature （-1000 ℃）. ZnSe polycrystal was obtained in the closed-tube systems...A chemical-assisted element direct-reaction method is developed to synthesize ZnSe compound semiconductor material at a relatively low temperature （-1000 ℃）. ZnSe polycrystal was obtained in the closed-tube systems with Zn-Se, Zn-Se-Zn（NHa）2CI2, ZnoSe-NH4CI and Zn-Se-ZnCI2. The as-synthesized samples were tested by X-ray diffraction （XRD）, thermogravimetric analysis （TGA） and analyzed by thermodynamic numerical method. The results demonstrate that the synthesis efficiency is higher than 99.96% for Zn-Se-ZnCl2 system at around 1000 ℃ for 3 weeks. It also exhibits that not only temperature, but also low apparent ratio of volume and surface area of the source materials and higher ZnCl2 content are required to achieve high synthesis efficiency. A SeCI transporting reaction synthesis process is proposed based on the thermodynamic analysis.展开更多
In thin film solar cells, the semiconductor materials usually contain multiple impurity/defect states as donor or acceptor dopants. The local charge neutrality （LCN） condition determines the equilibrium Fermi （EF）...In thin film solar cells, the semiconductor materials usually contain multiple impurity/defect states as donor or acceptor dopants. The local charge neutrality （LCN） condition determines the equilibrium Fermi （EF） level and concentration of electrons and holes. However, the equation of LCN is a transcendental equation of EF. It is impossible to find its analytical solution and we can only solve it by graphic or numerical method. A simple approximate graphic method （GM） used for estimation of majority carrier compensation of semiconductors with multiple donors and acceptors was proposed by Chin. By introducing the concept of ranking the dopants and the wrapping step function, dopants concentration and Fermi level could be obtained easily. In this paper, we analyze the graphic method and propose a new numeric graphic method （NGM） based on GM. In addition, comparison of NGM with NM and analytics of the accuracy of GM are presented. With numerical calculation, some procedures of GM extending the application of GM are improved.展开更多
We present an ultrasensitive ultraviolet （UV） detector based on a p-type ZnS nanoribbon （NR）/indium tin oxide （ITO） Schottky barrier diode （SBD）. The device exhibits a pseudo-photovoltaic behavior which can al...We present an ultrasensitive ultraviolet （UV） detector based on a p-type ZnS nanoribbon （NR）/indium tin oxide （ITO） Schottky barrier diode （SBD）. The device exhibits a pseudo-photovoltaic behavior which can allow the SBD to detect UV light irradiation with incident power of 6 × 10^-17 W （-85 photons/s on the NR） at room temperature, with excellent reproducibility and stability. The corresponding detectivity and photoconductive gain are calculated to be 3.1 × 10^20 cm.Hz1/2.W^-1 and 6.6 × 10^5, respectively. It is found that the presence of the trapping states at the p-ZnS NWITO interface plays a crucial role in determining the ultrahigh sensitivity of this nanoSBDs. Based on our theoretical calculation, even ultra-low photon fluxes on the order of several tens of photons could induce a significant change in interface potential and consequently cause a large photocurrent variation. The present study provides new opportunities for developiphigh-performance optoelectronic devices in the future.展开更多
Indium doped cadmium sulfide thin films （CdS：In） were produced by the spray pyrolysis technique on glass substrates. AC measurements were used to investigate the electrical properties of the films depending on Bric...Indium doped cadmium sulfide thin films （CdS：In） were produced by the spray pyrolysis technique on glass substrates. AC measurements were used to investigate the electrical properties of the films depending on Brick-layer model for polycrystalline materials. The measurements were performed at room temperature in the dark and room light in the frequency range from 20 Hz to 1 MHz using coplanar indium electrodes. The data were analyzed by using Bode plots for the impedance Z and dielectric loss tang with frequencyf It is found that the impedance has no dependence on frequency in the low frequency region but has 1/f dependence in the high frequency region. One dielectric loss peak is obtained, which means the presence of a single relaxation time, and hence the films are modeled by just one RC circuit which represents the grains. This means that there is just one conduction mechanism that is responsible for the conduction in the bulk, due to electronic transport through the grains. Real values of the impedance in the low frequency region and relaxation times for treated and as-deposited fihns were estimated.展开更多
Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques.Samples cut from the head(T04)and tail(W02)regions of a crystal ingot show distinct differe...Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques.Samples cut from the head(T04)and tail(W02)regions of a crystal ingot show distinct differences in Te inclusion distribution.Obvious difference is not observed in Fourier transform infrared(FTIR)spectra,UV-Vis-NIR transmittance spectra,and I-V measurements.However,carrier mobility of the tip sample is higher than that of the tail according to the laser beam induced current(LBIC)measurements.Low temperature photoluminescence(PL)measurement presents sharp emission peaks of D^(0)X and A^(0)X,and relatively large peak of D^(0)X(or A^(0)X)/Dcomplex for T04,indicating a better crystalline quality.Thermally stimulated current(TSC)spectrum shows higher density of shallow point defects,i.e.,Cd vacancies,In^(+)_(Cd),etc.,in W02 sample,which could be responsible for the deterioration of electron mobility.展开更多
Zinc chalcogenide which includes zinc selenide,zinc sulphide,zinc telluride and mixed crystals of these shows a great potential as an optoelectronic device material. Zinc selenotelluride is a suitable material for vis...Zinc chalcogenide which includes zinc selenide,zinc sulphide,zinc telluride and mixed crystals of these shows a great potential as an optoelectronic device material. Zinc selenotelluride is a suitable material for visible light emitting devices which are expected to cover the spectral range from yellow to blue. In our present study the composition controlled ZnSe1-xTex films with different Te content x = 0,0.2,0.4,0.6,0.8 and 1.0 were deposited by electron beam (EB) evaporation technique. GaAs films were deposited by vacuum evaporation route on indium tin oxide (ITO) substrates which were used as base for depositing the ZnSe1-xTex film. The band-gap energy change in the entire composition range was determined at room temperature by photoluminescence (PL) spectroscopy. The peak observed at about 2.56 eV shows the effect of solid solution formation between ZnSe and ZnTe which modifies the lattice and consequently the band edge emission characteristics. The heterostructures showed three peaks in the visible region of white light spectrum.展开更多
The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopoten...The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopotential method, as implemented in Quantum ESPRESSO. The exchange-correlation potential is treated with the local density approximation pz-LDA for these properties. Moreover, LDA＋U approximation is employed to treat the ＂d＂ orbital electrons properly. A comparative study of the band gap calculated within both LDA and LDA＋U schemes is presented. The analysis of results show considerable improvement in the calculation of band gap. The inclusion of compositional disorder increases the values of all elastic constants. In this study, it is found that elastic constants C11, C12, and C44 are mainly influenced by the compositional disorder. The obtained results are in good agreement with literature.展开更多
基金supported by the Research Foundation of Erciyes University (Kayseri,Turkey)
文摘The synthesis,crystal structure and electrical conductivity properties of Fe-doped ZnO powders（in the range of 0.25-15 mol%） were reported in this paper.I-phase samples,which were indexed as single phase with a hexagonal（wurtzite） structure in the Fe-doped ZnO binary system,were determined by X-ray diffraction（XRD）.The solubility limit of Fe in the ZnO lattice is 3 mol% at 950℃.The above mixed phase was observed.And the impurity phase was determined as the cubic-ZnFe 2 O 4 phase when compared with standard XRD data using the PDF program.This study focused on single I-phase ZnO samples which were synthesized at 950℃ because the limit of the solubility range is the widest at this temperature.The lattice parameters a and c of the I-phase decreased with Fe-doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The grain size of the I-phase samples increased with heat treatment and doping concentration.The electrical conductivity of the pure ZnO and single I-phase samples was investigated using the four-probe dc method at 100-950℃ in air atmosphere.The electrical conductivity values of pure ZnO,0.25 and 3 mol% Fe-doped ZnO samples at 100℃ were 2×10-6,1.7×10-3 and 6.3×10-4 S.cm-1,and at 950℃ they were 3.4,8.5 and 4 S.cm-1,respectively.
基金supported by the National Natural Science Foundation of China (Grant No.50721091)
文摘Wurzite ZnS:Mn nanorods are synthesized via a solvothermal method by using ethylenediamine and water as mixed solvent.The diameters of the nanorods increase and the lengths decrease with the Mn concentration.High resolution transmission electron microscopic images illustrate that a few cubic ZnS:Mn nanoparticles arise along with hexagonal nanorods on high Mn concentration.The samples set off yellow-orange emission at 590 nm,characteristic of 4 T→ 6 A 1 transition of Mn 2+ at T d symmetry in ZnS.Electron spin resonance spectrum of the nanorods shows that high Mn concentrations produce a broad envelope,whereas six-line hyperfine appears for lower Mn concentrations.These results together with the magnetization curves indicate that all the ZnS:Mn samples are paramagnetic even down to 4 K,which suggests that the ZnS:Mn is not suitable for dilute magnetic semiconductor.
基金Supported by the Program for Science & Technology Innovation Talents in Universi-ties of Henan Province (Grant No. 2008 HASTIT002)
文摘Well-aligned single-crystalline wurzite zinc oxide (ZnO) nanowire arrays were successfully fabricated on a Si substrate by a simple physical vapor-deposition (PVD) method at a relatively low temperature of about 500°C. The as-fabricated nanowires were preferentially arranged along the [001] direction of ZnO. The photoluminescence spectrum of ZnO nanowire arrays showed two emission bands: a strong green emission at around 500 nm and a weak ultraviolet emission at 380 nm. The strong green light emission was related to the existence of the oxygen vacancies in ZnO crystals. Corresponding growth mechanism of the ZnO nanowires was briefly discussed.
文摘We have analyzed the spin transport behaviour of four II-VI semiconductor nanowires by simulating spin polarized transport using a semi-classical Monte-Carlo approach. The different scattering mechanisms con- sidered are acoustic phonon scattering, surface roughness scattering, polar optical phonon scattering, and spin flip scattering. The II-VI materials used in our study are CdS, CdSe, ZnO and ZnS. The spin transport behaviour is first studied by varying the temperature （4-500 K） at a fixed diameter of 10 nm and also by varying the diameter （8-12 nm） at a fixed temperature of 300 K. For II-VI compounds, the dominant mechanism is for spin relaxation; D＇yakonovPerel and Elliot Yafet have been actively employed in the first order model to simulate the spin transport. The dependence of the spin relaxation length （SRL） on the diameter and temperature has been analyzed.
基金supports of the National Natural Science Foundation of Chinathe National 973 Project (No. 2011CB610406)+1 种基金the Research Fund of Young Teachers for the Doctoral Program of Higher Education of China (No. 20106102120016)the Independent Subject of State Key Laboratory of Solidification Processing (74-QP-2011)
文摘A chemical-assisted element direct-reaction method is developed to synthesize ZnSe compound semiconductor material at a relatively low temperature （-1000 ℃）. ZnSe polycrystal was obtained in the closed-tube systems with Zn-Se, Zn-Se-Zn（NHa）2CI2, ZnoSe-NH4CI and Zn-Se-ZnCI2. The as-synthesized samples were tested by X-ray diffraction （XRD）, thermogravimetric analysis （TGA） and analyzed by thermodynamic numerical method. The results demonstrate that the synthesis efficiency is higher than 99.96% for Zn-Se-ZnCl2 system at around 1000 ℃ for 3 weeks. It also exhibits that not only temperature, but also low apparent ratio of volume and surface area of the source materials and higher ZnCl2 content are required to achieve high synthesis efficiency. A SeCI transporting reaction synthesis process is proposed based on the thermodynamic analysis.
文摘In thin film solar cells, the semiconductor materials usually contain multiple impurity/defect states as donor or acceptor dopants. The local charge neutrality （LCN） condition determines the equilibrium Fermi （EF） level and concentration of electrons and holes. However, the equation of LCN is a transcendental equation of EF. It is impossible to find its analytical solution and we can only solve it by graphic or numerical method. A simple approximate graphic method （GM） used for estimation of majority carrier compensation of semiconductors with multiple donors and acceptors was proposed by Chin. By introducing the concept of ranking the dopants and the wrapping step function, dopants concentration and Fermi level could be obtained easily. In this paper, we analyze the graphic method and propose a new numeric graphic method （NGM） based on GM. In addition, comparison of NGM with NM and analytics of the accuracy of GM are presented. With numerical calculation, some procedures of GM extending the application of GM are improved.
文摘We present an ultrasensitive ultraviolet （UV） detector based on a p-type ZnS nanoribbon （NR）/indium tin oxide （ITO） Schottky barrier diode （SBD）. The device exhibits a pseudo-photovoltaic behavior which can allow the SBD to detect UV light irradiation with incident power of 6 × 10^-17 W （-85 photons/s on the NR） at room temperature, with excellent reproducibility and stability. The corresponding detectivity and photoconductive gain are calculated to be 3.1 × 10^20 cm.Hz1/2.W^-1 and 6.6 × 10^5, respectively. It is found that the presence of the trapping states at the p-ZnS NWITO interface plays a crucial role in determining the ultrahigh sensitivity of this nanoSBDs. Based on our theoretical calculation, even ultra-low photon fluxes on the order of several tens of photons could induce a significant change in interface potential and consequently cause a large photocurrent variation. The present study provides new opportunities for developiphigh-performance optoelectronic devices in the future.
文摘Indium doped cadmium sulfide thin films （CdS：In） were produced by the spray pyrolysis technique on glass substrates. AC measurements were used to investigate the electrical properties of the films depending on Brick-layer model for polycrystalline materials. The measurements were performed at room temperature in the dark and room light in the frequency range from 20 Hz to 1 MHz using coplanar indium electrodes. The data were analyzed by using Bode plots for the impedance Z and dielectric loss tang with frequencyf It is found that the impedance has no dependence on frequency in the low frequency region but has 1/f dependence in the high frequency region. One dielectric loss peak is obtained, which means the presence of a single relaxation time, and hence the films are modeled by just one RC circuit which represents the grains. This means that there is just one conduction mechanism that is responsible for the conduction in the bulk, due to electronic transport through the grains. Real values of the impedance in the low frequency region and relaxation times for treated and as-deposited fihns were estimated.
基金Project supported by the National Natural Science Foundations of China(Grant Nos.51502244,51702271,U1631116,and 51372205)the National Key Research and Development Program of China(Grant Nos.2016YFF0101301 and 2016YFE0115200)+2 种基金the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University,China(Grant No.SKLSP201741)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.2016KJXX-09)the Fundamental Research Funds for the Central Universities,China(Grant No.3102015BJ(II)ZS014)
文摘Photoelectric properties of CdZnTe:In samples with distinctive defect distributions are investigated using various techniques.Samples cut from the head(T04)and tail(W02)regions of a crystal ingot show distinct differences in Te inclusion distribution.Obvious difference is not observed in Fourier transform infrared(FTIR)spectra,UV-Vis-NIR transmittance spectra,and I-V measurements.However,carrier mobility of the tip sample is higher than that of the tail according to the laser beam induced current(LBIC)measurements.Low temperature photoluminescence(PL)measurement presents sharp emission peaks of D^(0)X and A^(0)X,and relatively large peak of D^(0)X(or A^(0)X)/Dcomplex for T04,indicating a better crystalline quality.Thermally stimulated current(TSC)spectrum shows higher density of shallow point defects,i.e.,Cd vacancies,In^(+)_(Cd),etc.,in W02 sample,which could be responsible for the deterioration of electron mobility.
文摘Zinc chalcogenide which includes zinc selenide,zinc sulphide,zinc telluride and mixed crystals of these shows a great potential as an optoelectronic device material. Zinc selenotelluride is a suitable material for visible light emitting devices which are expected to cover the spectral range from yellow to blue. In our present study the composition controlled ZnSe1-xTex films with different Te content x = 0,0.2,0.4,0.6,0.8 and 1.0 were deposited by electron beam (EB) evaporation technique. GaAs films were deposited by vacuum evaporation route on indium tin oxide (ITO) substrates which were used as base for depositing the ZnSe1-xTex film. The band-gap energy change in the entire composition range was determined at room temperature by photoluminescence (PL) spectroscopy. The peak observed at about 2.56 eV shows the effect of solid solution formation between ZnSe and ZnTe which modifies the lattice and consequently the band edge emission characteristics. The heterostructures showed three peaks in the visible region of white light spectrum.
文摘The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopotential method, as implemented in Quantum ESPRESSO. The exchange-correlation potential is treated with the local density approximation pz-LDA for these properties. Moreover, LDA＋U approximation is employed to treat the ＂d＂ orbital electrons properly. A comparative study of the band gap calculated within both LDA and LDA＋U schemes is presented. The analysis of results show considerable improvement in the calculation of band gap. The inclusion of compositional disorder increases the values of all elastic constants. In this study, it is found that elastic constants C11, C12, and C44 are mainly influenced by the compositional disorder. The obtained results are in good agreement with literature.
