We study the dispersion properties of surface plasmon(SP) oscillations in a semi-bounded semiconductor plasma with the effects of the Coulomb exchange(CE) force associated with the spin polarization of electrons a...We study the dispersion properties of surface plasmon(SP) oscillations in a semi-bounded semiconductor plasma with the effects of the Coulomb exchange(CE) force associated with the spin polarization of electrons and holes as well as the effects of the Fermi degenerate pressure and the quantum Bohm potential.Starting from a quantum hydrodynamic model coupled to the Poisson equation,we derive the general dispersion relation for surface plasma waves.Previous results in this context are recovered.The dispersion properties of the surface waves are analyzed in some particular cases of interest and the relative influence of the quantum forces on these waves are also studied for a nano-sized Ga As semiconductor plasma.It is found that the CE effects significantly modify the behaviors of the SP waves.The present results are applicable to understand the propagation characteristics of surface waves in solid density plasmas.展开更多
Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the...Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the dynamic range of operation voltage, repetition frequencies and lifetime of switch. The unique feature of pseudospark switch is its hollow cathode geometry. The hollow cathode effect produced by the hollow cathode provides the protection of the switch for the triggering unit from erosion by high discharge plasma. In this paper, a zinc oxide (ZnO) surface flashover triggering is presented. This trigger unit possesses an excellent time delay (80 ns - 360 ns) and jitter (20 ns - 50 ns) at the switch voltage of 30 kV - 2 kV. The emitted plasma electron density is high enough to trigger switch reliably down to switch voltage of 440 V.展开更多
The ultrahigh vacuum scanning tunneling microscope(STM)was used to characterize the GaSb_(1-x)Bi_(x) films of a few nanometers thickness grown by the molecular beam epitaxy(MBE)on the GaSb buffer layer of 100 nm with ...The ultrahigh vacuum scanning tunneling microscope(STM)was used to characterize the GaSb_(1-x)Bi_(x) films of a few nanometers thickness grown by the molecular beam epitaxy(MBE)on the GaSb buffer layer of 100 nm with the GaSb(100)substrates.The thickness of the GaSb_(1-x)Bi_(x) layers of the samples are 5 and 10 nm,respectively.For comparison,the GaSb buffer was also characterized and its STM image displays terraces whose surfaces are basically atomically flat and their roughness is generally less than 1 monolayer(ML).The surface of 5 nm GaSb_(1-x)Bi_(x) film reserves the same terraced morphology as the buffer layer.In contrast,the morphology of the 10 nm GaSb_(1-x)Bi_(x) film changes to the mound-like island structures with a height of a few MLs.The result implies the growth mode transition from the two-dimensional mode as displayed by the 5 nm film to the Stranski-Krastinov mode as displayed by the 10 nm film.The statistical analysis with the scanning tunneling spectroscopy(STS)measurements indicates that both the incorporation and the inhomogeneity of Bi atoms increase with the thickness of the GaSb_(1-x)Bi_(x) layer.展开更多
Copper indium diselenide (CuInSe2) thin films were prepared by ion beam sputtering Cu, In and Se targets continuously on BK7 glass substrates and the three-layer film was then annealed in the same vacuum chamber. X-...Copper indium diselenide (CuInSe2) thin films were prepared by ion beam sputtering Cu, In and Se targets continuously on BK7 glass substrates and the three-layer film was then annealed in the same vacuum chamber. X-ray diffraction shows that the CuInSe2 thin films have a single chalcopyrite structure with preferential (112) orientation. Scanning electron microscopy reveals that the CIS thin films consist of uniform and densely packed grain clusters. Energy dispersive x-ray spectroscopy demonstrates that the elemental composition of CIS films approaches the stochiometric composition ratios of 1:1:2. Raman measurement shows that the main peak is at about 174cm^-1 and this peak is identified as the A1 vibrational mode from chaicopyrite ordered CulnSe2. Optical transmission and absorption spectroscopy measurement reveal an energy band gap of about 1.05 eV and an absorption coefficient of 10^5 cm^-1. The film resistivity is about 0.01 Ωcm.展开更多
Growth of a ZnO/GaN heterostructure is carried out using pulsed laser deposition. By etching the ZnO layer from the ZnO/GaN structure, the photoluminescence (PL) of the associated GaN layer shows that the donor- acc...Growth of a ZnO/GaN heterostructure is carried out using pulsed laser deposition. By etching the ZnO layer from the ZnO/GaN structure, the photoluminescence (PL) of the associated GaN layer shows that the donor- acceptor luminescence of CaN shifts to about 3.27eV, which is consistent with the electroluminescence (EL) of n-ZnO/p-GaN already reported. XPS shows that oxygen diffuses into the CaN crystal lattice from the surface to 20nm depth. The PL spectra at different temperatures and excitation densities show that oxygen plays the role of potential fluctuation. The associated PL results of the interface in these LEDs could be helpful to understand the mechanism of EL spectra for ZnO/CaN p-n junctions.展开更多
High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a- plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied...High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a- plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2at.% and the lowest resistivity can reach 1.92 ×10-4Ω·cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.展开更多
Pure zinc blende GaAs nanowires were grown by metal organic chemical vapor deposition on GaAs(111)B substrates via Au catalyzed vapor-liquid-solid mechanism. The diameter, size distribution, and density of Au partic...Pure zinc blende GaAs nanowires were grown by metal organic chemical vapor deposition on GaAs(111)B substrates via Au catalyzed vapor-liquid-solid mechanism. The diameter, size distribution, and density of Au particles can be changed by varying the Au film thickness. We find that the grown nanowires are of rod-like shapes and pure zinc blende structure; moreover, the growth rate depends on the density of Au particles and it is independent of its diameters. It can be concluded that the nanowire was grown with main contributions from the direct impingement of vapor species onto the Au-Ga droplets and contributions from adatom diffusion can be negligible. The results indicate that the droplet acts as a catalyst rather than an adatom collector.展开更多
Ta-doped ZnO transparent conductive films are deposited on glass substrates by rf sputtering at 300℃. The influence of the post-annealing temperature on the structural, morphologic, electrical, and optical properties...Ta-doped ZnO transparent conductive films are deposited on glass substrates by rf sputtering at 300℃. The influence of the post-annealing temperature on the structural, morphologic, electrical, and optical properties of the films is investigated by x-ray diffraction, Hall measurement, and optical transmission spectroscopy. The lowest resistivity of 3.5 ×10^-4 Ω·cm is obtained from the film annealed at 400℃in N2. The average optical transmittance of the films is over 90%. The optical bandgap is found to decrease with the increase of the annealing temperature.展开更多
Effects of dopant properties on microstructures and the electrical characteristics of poly (3-hexylthiophene) (P3HT) films are studied by doping 0.1 wt% 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4?T...Effects of dopant properties on microstructures and the electrical characteristics of poly (3-hexylthiophene) (P3HT) films are studied by doping 0.1 wt% 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4?TCNQ), 6,6-phenyl-C61butyric acid methyl ester (PCBM) and N,N'?Diphenyl-N,N'-(m-tolyl)-benzidine (TPD) into P3HT, respectively. The introductions of various dopants in small quantities increase the field-effect mobility and the I on/Ioff ratio of P3HT thin-film transistors. However, each of dopants shows various effects on the crystalline order and the molecular orientation of P3HT films and the performance of P3HT thin-film transistors. These can be attributed to the various size, shape and energy-level properties of the dopants.展开更多
Different TiOx thin films prepared by graded or sufficient oxidization of Ti are applied with Pt or Ag electrode in metal?insulator-metal (MIM) structures for studying the properties and mechanisms of resistive swi...Different TiOx thin films prepared by graded or sufficient oxidization of Ti are applied with Pt or Ag electrode in metal?insulator-metal (MIM) structures for studying the properties and mechanisms of resistive switching. The differences on the mobile oxygen vacancies in TiOx films and different work functions of the electrode films result in different insulator-metal interface states, which are displayed as ohmic-like or non-ohmic contact. Based on the interface states, the electrical models for MIM devices are analyzed and extracted. The electrode-limited effect and the bulk-limited effect can be unified to explain the mechanisms for resistive switching behavior as the dominant effect respectively in various conditions. All the current-voltage curves of the four kinds of specimens measured in the experiments can be explained and proved in accordance with the theory.展开更多
We prepare the gallium oxide (β-Ga2O3) nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and research their oxygen sensing under UV illumination with different oxygen pressures. X...We prepare the gallium oxide (β-Ga2O3) nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and research their oxygen sensing under UV illumination with different oxygen pressures. X-ray diffraction reveals that the synthesized product is monoclinic gallium oxide, it is further confirmed by electron diffraction of transmission electron microscope, and its morphology through the observation using scanning electron microscope reveals thatβ-Ga2O3 nanobelts with a breadth less than lOOnm and length of severai micrometers are synthesized under low oxygen pressure, while the nano/microbelts are synthesized under high oxygen pressure. Room-temperature oxygen sensing is tested under at 254 nm illumination and it is found that the current decreases quickly first and then slowly with oxygen pressure from low to high.展开更多
InAs infrared-sensitive solar cells are fabricated by using the films grown by the liquid phase epitaxy technique. The film microstructures are characterized by x-ray diffraction and scanning electronic microscopy. Th...InAs infrared-sensitive solar cells are fabricated by using the films grown by the liquid phase epitaxy technique. The film microstructures are characterized by x-ray diffraction and scanning electronic microscopy. The current-voltage characteristics of the solar cells in the dark and under AM1.5 illumination at 300 K and 77 K are discussed. The conversion efficiency of p-InAs/n-sub InAs cells decreases when the thickness of the p-type film changes from 1.7 μm to 3.5 μm, which is caused by the reduced effective photons near p?n junction. The p-InAs/n-InAs/n-sub InAs solar cell with the conversion efficiency of 7.43% in 1-2.5 μm under AM1.5 at 77 K is obtained. The short circuit current density increases dramatically with decreasing temperature due to the weakened effect of phonon scattering.展开更多
A novel PMMA/PMGI/ZEP520 trilayer resist electron beam lithograph (EBL) technology is successfully developed and used to fabricate the 150 nm gate-length In0.7Ga0.3As/In0.52Al0.48As Pseudomorphic HEMT on an InP subs...A novel PMMA/PMGI/ZEP520 trilayer resist electron beam lithograph (EBL) technology is successfully developed and used to fabricate the 150 nm gate-length In0.7Ga0.3As/In0.52Al0.48As Pseudomorphic HEMT on an InP substrate, of which the material structure is successfully designed and optimized. A perfect profile of T?gate is successfully obtained. These fabricated devices demonstrate excellent dc and rf characteristics: the transconductance Gm, maximum saturation drain?to-source current IDSS, threshold voltage VT, maximum current gain frequency fT derived from h21, maximum frequency of oscillation derived from maximum available power gain/maximum stable gain and from unilateral power?gain of metamorphic InGaAs/InAlAs high electron mobility transistors (HEMTs) are 470 mS/mm, 560 mA/mm, -1.0 V, 76 GHz, 135 GHz and 436 GHz, respectively. The excellent high frequency performances promise the possibility of metamorphic HEMTs for millimeter-wave applications.展开更多
基金financial support of Arak University under research Project No.96/5834UGC-SAP(DRS,Phase Ⅲ)[with Sanction order No.F.510/3/DRS-III/2015(SAPI)]UGC-MRP[with F.No.43-539/2014(SR) and FD Diary No.3668] for support
文摘We study the dispersion properties of surface plasmon(SP) oscillations in a semi-bounded semiconductor plasma with the effects of the Coulomb exchange(CE) force associated with the spin polarization of electrons and holes as well as the effects of the Fermi degenerate pressure and the quantum Bohm potential.Starting from a quantum hydrodynamic model coupled to the Poisson equation,we derive the general dispersion relation for surface plasma waves.Previous results in this context are recovered.The dispersion properties of the surface waves are analyzed in some particular cases of interest and the relative influence of the quantum forces on these waves are also studied for a nano-sized Ga As semiconductor plasma.It is found that the CE effects significantly modify the behaviors of the SP waves.The present results are applicable to understand the propagation characteristics of surface waves in solid density plasmas.
基金The project supported by the National Nature Science Foundation of China(No.10035020)
文摘Accurate and reliable triggering is one of the most important issues with high power pseudospark switch, because it not only has an impact on the design of discharge chamber of switch, but also has an influence on the dynamic range of operation voltage, repetition frequencies and lifetime of switch. The unique feature of pseudospark switch is its hollow cathode geometry. The hollow cathode effect produced by the hollow cathode provides the protection of the switch for the triggering unit from erosion by high discharge plasma. In this paper, a zinc oxide (ZnO) surface flashover triggering is presented. This trigger unit possesses an excellent time delay (80 ns - 360 ns) and jitter (20 ns - 50 ns) at the switch voltage of 30 kV - 2 kV. The emitted plasma electron density is high enough to trigger switch reliably down to switch voltage of 440 V.
基金supported by the National Natural Science Foundation of China(Nos.61474073,61874069 and 61804157).
文摘The ultrahigh vacuum scanning tunneling microscope(STM)was used to characterize the GaSb_(1-x)Bi_(x) films of a few nanometers thickness grown by the molecular beam epitaxy(MBE)on the GaSb buffer layer of 100 nm with the GaSb(100)substrates.The thickness of the GaSb_(1-x)Bi_(x) layers of the samples are 5 and 10 nm,respectively.For comparison,the GaSb buffer was also characterized and its STM image displays terraces whose surfaces are basically atomically flat and their roughness is generally less than 1 monolayer(ML).The surface of 5 nm GaSb_(1-x)Bi_(x) film reserves the same terraced morphology as the buffer layer.In contrast,the morphology of the 10 nm GaSb_(1-x)Bi_(x) film changes to the mound-like island structures with a height of a few MLs.The result implies the growth mode transition from the two-dimensional mode as displayed by the 5 nm film to the Stranski-Krastinov mode as displayed by the 10 nm film.The statistical analysis with the scanning tunneling spectroscopy(STS)measurements indicates that both the incorporation and the inhomogeneity of Bi atoms increase with the thickness of the GaSb_(1-x)Bi_(x) layer.
基金Supported by the Natural Science Foundation of Guangdong Province under Grant No 7009409, and Program of Science and Technology of Shenzhen under Grant No 200729.
文摘Copper indium diselenide (CuInSe2) thin films were prepared by ion beam sputtering Cu, In and Se targets continuously on BK7 glass substrates and the three-layer film was then annealed in the same vacuum chamber. X-ray diffraction shows that the CuInSe2 thin films have a single chalcopyrite structure with preferential (112) orientation. Scanning electron microscopy reveals that the CIS thin films consist of uniform and densely packed grain clusters. Energy dispersive x-ray spectroscopy demonstrates that the elemental composition of CIS films approaches the stochiometric composition ratios of 1:1:2. Raman measurement shows that the main peak is at about 174cm^-1 and this peak is identified as the A1 vibrational mode from chaicopyrite ordered CulnSe2. Optical transmission and absorption spectroscopy measurement reveal an energy band gap of about 1.05 eV and an absorption coefficient of 10^5 cm^-1. The film resistivity is about 0.01 Ωcm.
基金by the Natural Science Foundation of Anhui Province under Grant Nos 070414184 and 070412034.
文摘Growth of a ZnO/GaN heterostructure is carried out using pulsed laser deposition. By etching the ZnO layer from the ZnO/GaN structure, the photoluminescence (PL) of the associated GaN layer shows that the donor- acceptor luminescence of CaN shifts to about 3.27eV, which is consistent with the electroluminescence (EL) of n-ZnO/p-GaN already reported. XPS shows that oxygen diffuses into the CaN crystal lattice from the surface to 20nm depth. The PL spectra at different temperatures and excitation densities show that oxygen plays the role of potential fluctuation. The associated PL results of the interface in these LEDs could be helpful to understand the mechanism of EL spectra for ZnO/CaN p-n junctions.
基金Supported by the National Natural Science Foundation of China under Grant No 10804017, the Natural Science Foundation of Jiangsu Province under Grant No BK2007118, Research Fund for the Doctoral Program of Higher Education of China under Grant No 20070286037, Cyanine-Project Foundation of Jiangsu Province under Grant No 1107020060, Foundation for Climax Talents Plan in Six-Big Fields of Jiangsu Province under Grant No 1107020070, and New Century Excellent Talents in University (NCET-05-0452).
文摘High-quality Ga-doped ZnO (ZnO:Ga) single crystalline films with various Ga concentrations are grown on a- plane sapphire substrates using molecular-beam epitaxy. The site configuration of doped Ga atoms is studied by means of x-ray absorption spectroscopy. It is found that nearly all Ga can substitute into ZnO lattice as electrically active donors, a generating high density of free carriers with about one electron per Ga dopant when the Ga concentration is no more than 2%. However, further increasing the Ga doping concentration leads to a decrease of the conductivity due to partial segregation of Ga atoms to the minor phase of the spinel ZnGa2O4 or other intermediate phase. It seems that the maximum solubility of Ga in the ZnO single crystalline film is about 2at.% and the lowest resistivity can reach 1.92 ×10-4Ω·cm at room temperature, close to the best value reported. In contrast to ZnO:Ga thin film with 1% or 2% Ga doping, the film with 4% Ga doping exhibits a metal semiconductor transition at 80 K. The scattering mechanism of conducting electrons in single crystalline ZnO:Ga thin film is discussed.
文摘Pure zinc blende GaAs nanowires were grown by metal organic chemical vapor deposition on GaAs(111)B substrates via Au catalyzed vapor-liquid-solid mechanism. The diameter, size distribution, and density of Au particles can be changed by varying the Au film thickness. We find that the grown nanowires are of rod-like shapes and pure zinc blende structure; moreover, the growth rate depends on the density of Au particles and it is independent of its diameters. It can be concluded that the nanowire was grown with main contributions from the direct impingement of vapor species onto the Au-Ga droplets and contributions from adatom diffusion can be negligible. The results indicate that the droplet acts as a catalyst rather than an adatom collector.
文摘Ta-doped ZnO transparent conductive films are deposited on glass substrates by rf sputtering at 300℃. The influence of the post-annealing temperature on the structural, morphologic, electrical, and optical properties of the films is investigated by x-ray diffraction, Hall measurement, and optical transmission spectroscopy. The lowest resistivity of 3.5 ×10^-4 Ω·cm is obtained from the film annealed at 400℃in N2. The average optical transmittance of the films is over 90%. The optical bandgap is found to decrease with the increase of the annealing temperature.
文摘Effects of dopant properties on microstructures and the electrical characteristics of poly (3-hexylthiophene) (P3HT) films are studied by doping 0.1 wt% 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4?TCNQ), 6,6-phenyl-C61butyric acid methyl ester (PCBM) and N,N'?Diphenyl-N,N'-(m-tolyl)-benzidine (TPD) into P3HT, respectively. The introductions of various dopants in small quantities increase the field-effect mobility and the I on/Ioff ratio of P3HT thin-film transistors. However, each of dopants shows various effects on the crystalline order and the molecular orientation of P3HT films and the performance of P3HT thin-film transistors. These can be attributed to the various size, shape and energy-level properties of the dopants.
文摘Different TiOx thin films prepared by graded or sufficient oxidization of Ti are applied with Pt or Ag electrode in metal?insulator-metal (MIM) structures for studying the properties and mechanisms of resistive switching. The differences on the mobile oxygen vacancies in TiOx films and different work functions of the electrode films result in different insulator-metal interface states, which are displayed as ohmic-like or non-ohmic contact. Based on the interface states, the electrical models for MIM devices are analyzed and extracted. The electrode-limited effect and the bulk-limited effect can be unified to explain the mechanisms for resistive switching behavior as the dominant effect respectively in various conditions. All the current-voltage curves of the four kinds of specimens measured in the experiments can be explained and proved in accordance with the theory.
文摘We prepare the gallium oxide (β-Ga2O3) nanomaterials from gallium and oxygen by thermal evaporation in the argon atmosphere and research their oxygen sensing under UV illumination with different oxygen pressures. X-ray diffraction reveals that the synthesized product is monoclinic gallium oxide, it is further confirmed by electron diffraction of transmission electron microscope, and its morphology through the observation using scanning electron microscope reveals thatβ-Ga2O3 nanobelts with a breadth less than lOOnm and length of severai micrometers are synthesized under low oxygen pressure, while the nano/microbelts are synthesized under high oxygen pressure. Room-temperature oxygen sensing is tested under at 254 nm illumination and it is found that the current decreases quickly first and then slowly with oxygen pressure from low to high.
基金Supported by the National Basic Research Program of China under Grant No 2010CB933700, the National Natural Science Foundation of China under Grant Nos 10804117 and 60221502, the Natural Science Foundation of Shanghai under Grant No 08ZR1421900, and the Knowledge Innovation Project in Chinese Academy of Sciences.
文摘InAs infrared-sensitive solar cells are fabricated by using the films grown by the liquid phase epitaxy technique. The film microstructures are characterized by x-ray diffraction and scanning electronic microscopy. The current-voltage characteristics of the solar cells in the dark and under AM1.5 illumination at 300 K and 77 K are discussed. The conversion efficiency of p-InAs/n-sub InAs cells decreases when the thickness of the p-type film changes from 1.7 μm to 3.5 μm, which is caused by the reduced effective photons near p?n junction. The p-InAs/n-InAs/n-sub InAs solar cell with the conversion efficiency of 7.43% in 1-2.5 μm under AM1.5 at 77 K is obtained. The short circuit current density increases dramatically with decreasing temperature due to the weakened effect of phonon scattering.
基金Supported by the National Natural Science Foundation of China under Grant No 60806024, and the Fundamental Research Funds for Central University under Grant No XDJK2009C020.
文摘A novel PMMA/PMGI/ZEP520 trilayer resist electron beam lithograph (EBL) technology is successfully developed and used to fabricate the 150 nm gate-length In0.7Ga0.3As/In0.52Al0.48As Pseudomorphic HEMT on an InP substrate, of which the material structure is successfully designed and optimized. A perfect profile of T?gate is successfully obtained. These fabricated devices demonstrate excellent dc and rf characteristics: the transconductance Gm, maximum saturation drain?to-source current IDSS, threshold voltage VT, maximum current gain frequency fT derived from h21, maximum frequency of oscillation derived from maximum available power gain/maximum stable gain and from unilateral power?gain of metamorphic InGaAs/InAlAs high electron mobility transistors (HEMTs) are 470 mS/mm, 560 mA/mm, -1.0 V, 76 GHz, 135 GHz and 436 GHz, respectively. The excellent high frequency performances promise the possibility of metamorphic HEMTs for millimeter-wave applications.