The structure, electrical transport, and optical properties of GaSe films fabricated by means of radio-frequency (RF) magnetron sputtering in Ar were investigated. The as-sputtered GaSe films were amorphous, and their...The structure, electrical transport, and optical properties of GaSe films fabricated by means of radio-frequency (RF) magnetron sputtering in Ar were investigated. The as-sputtered GaSe films were amorphous, and their optical energy gap Eg are 1.9~2.6 eV. The effect of the synthesis conditions on the optical and electrical properties of the GaSe films has also been studied展开更多
Transparent conductive cadmium indium oxide films (CdIn2O4) were prepared by r.f. reactive sputtering from Cd-In alloy targets under an Ar-O2 atmosphere. Electrical conductivity of the order of 105Ω-1.m-1 and the opt...Transparent conductive cadmium indium oxide films (CdIn2O4) were prepared by r.f. reactive sputtering from Cd-In alloy targets under an Ar-O2 atmosphere. Electrical conductivity of the order of 105Ω-1.m-1 and the optical transmission as high as 94% are easily attained by postdeposition annealing treatment. The effects of oxygen concentration in the reactive gas mixture and post-deposition annealing treatment on the optical transmittance as well as optical parameters, such as refractive index (n), extinction coefficient (k), real part (ε') and imaginary part (ε') of the dielectric constant, were studied in the visible and near-infrared region. The highfrequency dielectric constant ε∞ the plasma frequency ωP, and the conduction band effective mass mc of different samples were also investigated展开更多
Transparent zinc oxide(ZnO) thin films are fabricated by a simple sol-gel spin-coating technique on glass substrates with different solution concentrations(0.3-1.2 M) using zinc acetate dehydrate [Zn(CH_3COO)_2&...Transparent zinc oxide(ZnO) thin films are fabricated by a simple sol-gel spin-coating technique on glass substrates with different solution concentrations(0.3-1.2 M) using zinc acetate dehydrate [Zn(CH_3COO)_2·2H_2O] as precursor and isopropanol and monoethanolamine(MEA) as solvent and stabilizer, respectively. The molar ratio of zinc acetate dehydrate to MEA is 1.0. X-ray diffraction, ultraviolet-visible spectroscopy and photoluminescence spectroscopy are employed to investigate the effect of solution concentration on the structural and optical properties of the ZnO thin films. The obtained results of all thin films are discussed in detail and are compared with other experimental data.展开更多
The optical reflectance and transmittance spectra in the wavelength range of 300-2500 nm are used to compute the absorption coefficient of zinc oxide films annealed at different post-annealing temperatures 400, 500 an...The optical reflectance and transmittance spectra in the wavelength range of 300-2500 nm are used to compute the absorption coefficient of zinc oxide films annealed at different post-annealing temperatures 400, 500 and 600°C.The values of the cross point between the curves of the real and imaginary parts of the optical conductivity ɑ_1 and ɑ_1 with energy axis of films exhibit values that correspond to optical gaps and are about 3.25-3.3 eV. The maxima of peaks in plots dR/dλ and dT/dλ versus wavelength of films exhibit optical gaps at about 3.12-3.25 eV.The values of the fundamental indirect band gap obtained from the Tauc model are at about 3.14-3.2 eV. It can be seen that films annealed at 600°C have the minimum indirect optical band gap at about 3.15 eV. The films annealed at 600°C have Urbach's energy minimum of 1.38 eV and hence have minimum disorder. The dispersion energy d of films annealed at 500°C has the minimum value of 43 eV.展开更多
Zn_(0.8)Cd_(0.2)O thin films prepared using the spin-coating method were investigated. X-ray diffraction, scanning electron microscopy, and UV-Vis spectrophotometry were employed to illustrate the effects of the p...Zn_(0.8)Cd_(0.2)O thin films prepared using the spin-coating method were investigated. X-ray diffraction, scanning electron microscopy, and UV-Vis spectrophotometry were employed to illustrate the effects of the pre-heating temperature on the crystalline structure, surface morphology and transmission spectra of Zn_(0.8)Cd_(0.2)O thin films. When the thin films were pre-heated at 150 ℃, polycrystalline Zn O thin films were obtained. When the thin films were pre-heated at temperatures of 200 ℃ or higher, preferential growth of Zn O nanocrystals along the c-axis was observed. Transmission spectra showed that thin films with high transmission in the visible light range were prepared and effective bandgap energies of these thin films decreased from 3.19 e V to 3.08 e V when the pre-heating temperature increased from 150 ℃ to 300 ℃.展开更多
Structural and optical properties of nanometric titanium oxide(TixOy) films obtained by cathodic arc plasma deposition were investigated. Phase analysis by x-ray diffraction and Fouriertransform infrared spectroscop...Structural and optical properties of nanometric titanium oxide(TixOy) films obtained by cathodic arc plasma deposition were investigated. Phase analysis by x-ray diffraction and Fouriertransform infrared spectroscopy showed the presence of anatase, rutile, Ti_2O_3, Ti_4O_7 and amorphous phases. Scanning electron microscopy images showed well-developed surface morphology with nano-patterns. Spectroscopic ellipsometry revealed film thicknesses of 53 and50 nm, variable refractive indices dependent on the light wavelength and close to zero extinction coefficients for wavelengths higher than 500 nm. On the basis of ultraviolet–visible spectroscopy data and using the Tauc equation, band gap values for direct and indirect electron transitions were determined.展开更多
Azobenzene polymer films doped with and without Ag nanoparticles are prepared. The photoinduced reorientation process is investigated by using an Nd:YVO4 pump beam at 532 nm and a low semiconductor laser beam at 650 ...Azobenzene polymer films doped with and without Ag nanoparticles are prepared. The photoinduced reorientation process is investigated by using an Nd:YVO4 pump beam at 532 nm and a low semiconductor laser beam at 650 nm. The reorientation rate of azo polymer films is enhanced in the presence of Ag nanoparticles, and the rate of the azo polymer film with Ag concentration of 2.2 μg/ml is larger than that of the azo polymer films with Ag concentrations of 1.1 μg/ml and 4.4 μg/ml. The third-order nonlinear optical properties of the Ag/azo composite film are obtained by the Z-scan technique at a wavelength of 532 nm, and the measured nonlinear refractive index is 9.258×10-9 esu. It is shown that the main mechanisms involved in the large nonlinear optical responses come from the local field enhancement of Ag nanoparticles and the nonlinear effect of the azo polymer matrix.展开更多
A slanted columnar TiO2 sculptured anisotropic thin film (ATF) is prepared via the glancing angle deposition technique and used as the phase retardation plate. The tilted nanocolumn microstructures of thin film indu...A slanted columnar TiO2 sculptured anisotropic thin film (ATF) is prepared via the glancing angle deposition technique and used as the phase retardation plate. The tilted nanocolumn microstructures of thin film induce the optical anisotropy. With the biaxial birefringent model, the optical constants dispersion equations of TiO2 ATF are derived by fitting the transmittance spectra for s-and p-polarized waves measured at normal and oblique incidence within 400 nm–1200 nm. The phase shift of polarized light after reflection and/or transmission through the TiO2 ATF is analyzed with the characteristic matrix employing the extracted structure parameters. The theoretical studies reasonably well accord with the experimental results measured with spectroscopic ellipsometry. In addition, the dependences of the phase shift on the coating physical thickness and oblique incidence angle are also discussed. Birefringence of the biaxial ATF provides a sophisticated phase modulation by varying incidence angles over a broad range to have a wide-angle phase shift.展开更多
Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for a...Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for applied magnetic fields of only 10 Oe, become ferromagnetic for excess electrons and larger magnetic fields. They are semimetallic. Thin films are ferromagnetic and semiconductors. Over the time, many experiments have been performed on both systems and the physics in each system is consistent. Band structure computations either yield ferromagnetic semimetals or ferromagnetic semiconducting thin films. There seems to be two incompatible worlds, those of single crystals and those of thin films. In the present work, the author compares directly the various measurements and calculations and gives reasons for their different results.展开更多
Following are the comments for the queries raised by Prof. Pawel E. Tomaszewski on our published paper entitled "Structural, Optical, and Electrical Properties of Zn-Doped CdO Thin Films Fabricated by a Simplified Sp...Following are the comments for the queries raised by Prof. Pawel E. Tomaszewski on our published paper entitled "Structural, Optical, and Electrical Properties of Zn-Doped CdO Thin Films Fabricated by a Simplified Spray Pyrolysis Technique" by K. Usharani and A.R. Balu published in Acta Metall. Sin.展开更多
Thin films of zinc-doped cadmium oxide with different Zn-doping levels(0, 2, 4, 6, and 8 at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using perfume atomizer at rela...Thin films of zinc-doped cadmium oxide with different Zn-doping levels(0, 2, 4, 6, and 8 at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using perfume atomizer at relatively low substrate temperature(375 °C) compared with the conventional spray method. The effect of Zn doping on the structural,morphological, optical, and electrical properties of the films was investigated. XRD patterns revealed that all the films are polycrystalline in nature having cubic crystal structure with a preferential orientation along the(1 1 1) plane irrespective of Zn-doping level. Zn-doping level causes a slight shift in the(1 1 1) diffraction peak toward higher angle. The crystallite size of the films was found to be in the range of 28–37 nm. The band gap value increases with Zn doping and reaches a maximum of 2.65 eV for the film coated with 6 at% Zn doping and for further higher doping concentration it decreases.Electrical studies indicate that Zn doping causes a reduction in the resistivity of the films and a minimum resistivity of15.69 X cm is observed for the film coated with 6 at% Zn.展开更多
The commented paper [1] presents the results on structural, optical, and electrical properties of Zn-doped CdO thin films. Unfortunately, there are several mistakes and errors not found by any of referees. It is neces...The commented paper [1] presents the results on structural, optical, and electrical properties of Zn-doped CdO thin films. Unfortunately, there are several mistakes and errors not found by any of referees. It is necessary to show these mistakes or misleading statements to avoid their use in the future papers by authors and other peoples.展开更多
In this study,we report the annealing effects on the physical properties of Sn_3Sb_2S_6 thin films.Sn_3Sb_2S_6 thin films were prepared onto non-heated glass substrates via thermal evaporation technique.The as-deposit...In this study,we report the annealing effects on the physical properties of Sn_3Sb_2S_6 thin films.Sn_3Sb_2S_6 thin films were prepared onto non-heated glass substrates via thermal evaporation technique.The as-deposited films were annealed in air for 1 h in the temperature range from 100 to 300 °C.X-ray diffraction results show that the crystallinity of the thin films increased after annealing.The microstructure parameters crystallite size,dislocation density,lattice strain and stacking fault probability were calculated.The optical properties were obtained from the analysis of the experimental recorded transmittance and reflectance spectral data over the wavelength range 300–1800 nm.High absorption coefficient(10~5cm^(-1)) reached to the visible and near-IR spectral range.A decrease in optical band gap from 1.92 to 1.71 e V by increasing the air annealing temperature was observed.Oscillator energy E_o and dispersion energy E_d of the films after annealing were estimated according to the model of Wemple–Di Domenico single oscillator.Spitzer–Fan model was applied to determine the electron free carrier susceptibility and the ratio of carrier concentration to the effective mass.The layers annealed at temperatures 〉150 ℃ undergo abrupt changes in their electrical properties and exhibit a resistive hysteresis behavior.These properties confer to the material interest perspectives for its application in diverse advanced technologies such as photovoltaic applications and optical storage.展开更多
We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron tran...We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200/times 200 ×μm^2 square mesa.展开更多
We report our recent progress of investigations on InGaN-based blue-violet laser diodes (LDs). The roomtemperature (RT) cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown o...We report our recent progress of investigations on InGaN-based blue-violet laser diodes (LDs). The roomtemperature (RT) cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing (FS) GaN substrate by metal organic chemical vapor deposition (MOCVD). The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well (MQW), respectively.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
Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 μm at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy...Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 μm at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 × 10^-6 A/cm^2 at 0 V bias and 2.24 × 10^-4 A/cm^2 at a reverse bias of 5 V. At a wavelength of 1.55 μm, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 μm diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.展开更多
We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulatio...We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 μm and a cavity length of 1200 μm are fabricated and tested in the pulsed regime under different temperatures. It is found that T0 of the QD lasers is as high as 532 K in the temperature range from 10°C to 60°C. In addition, the aging test for the lasers under continuous wave operation at 100°C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.展开更多
We fabricate 1.5 μm InGaAsP/InP tunnel injection multiple?quantum-well (TI-MQW) Fabry-Perot (F-P) ridge lasers. The laser heterostructures, including an inner cladding layer and an InP tunnel barrier layer, are ...We fabricate 1.5 μm InGaAsP/InP tunnel injection multiple?quantum-well (TI-MQW) Fabry-Perot (F-P) ridge lasers. The laser heterostructures, including an inner cladding layer and an InP tunnel barrier layer, are grown by metal-organic chemical-vapor deposition (MOCVD). Characteristic temperature T0 of 160 K at 20°C is obtained for 500?μm?long lasers. T0 is measured as high as 88 K in the temperature range of 15?75°C. Cavity length dependence of T0 is investigated.展开更多
The s-polarized surface plasmon polaritons (SPPs) at the interface between dielectric and metamaterial are studied, and the dispersion relations of SPPs are also presented. Using the prism coupling mechanism, we obt...The s-polarized surface plasmon polaritons (SPPs) at the interface between dielectric and metamaterial are studied, and the dispersion relations of SPPs are also presented. Using the prism coupling mechanism, we obtain the attenuated total reflection (ATR) spectra in the frequency regime based on the Otto configuration. It is found that the thickness of the dielectric in the configuration and the small damping of the metamaterial affect the coupling strength significantly without changing the coupling frequency. Furthermore, the optimized thickness of the dielectric decreases with a larger damping, and the coefficient F of the metamaterial also determines the coupling frequency and strength.展开更多
文摘The structure, electrical transport, and optical properties of GaSe films fabricated by means of radio-frequency (RF) magnetron sputtering in Ar were investigated. The as-sputtered GaSe films were amorphous, and their optical energy gap Eg are 1.9~2.6 eV. The effect of the synthesis conditions on the optical and electrical properties of the GaSe films has also been studied
文摘Transparent conductive cadmium indium oxide films (CdIn2O4) were prepared by r.f. reactive sputtering from Cd-In alloy targets under an Ar-O2 atmosphere. Electrical conductivity of the order of 105Ω-1.m-1 and the optical transmission as high as 94% are easily attained by postdeposition annealing treatment. The effects of oxygen concentration in the reactive gas mixture and post-deposition annealing treatment on the optical transmittance as well as optical parameters, such as refractive index (n), extinction coefficient (k), real part (ε') and imaginary part (ε') of the dielectric constant, were studied in the visible and near-infrared region. The highfrequency dielectric constant ε∞ the plasma frequency ωP, and the conduction band effective mass mc of different samples were also investigated
文摘Transparent zinc oxide(ZnO) thin films are fabricated by a simple sol-gel spin-coating technique on glass substrates with different solution concentrations(0.3-1.2 M) using zinc acetate dehydrate [Zn(CH_3COO)_2·2H_2O] as precursor and isopropanol and monoethanolamine(MEA) as solvent and stabilizer, respectively. The molar ratio of zinc acetate dehydrate to MEA is 1.0. X-ray diffraction, ultraviolet-visible spectroscopy and photoluminescence spectroscopy are employed to investigate the effect of solution concentration on the structural and optical properties of the ZnO thin films. The obtained results of all thin films are discussed in detail and are compared with other experimental data.
文摘The optical reflectance and transmittance spectra in the wavelength range of 300-2500 nm are used to compute the absorption coefficient of zinc oxide films annealed at different post-annealing temperatures 400, 500 and 600°C.The values of the cross point between the curves of the real and imaginary parts of the optical conductivity ɑ_1 and ɑ_1 with energy axis of films exhibit values that correspond to optical gaps and are about 3.25-3.3 eV. The maxima of peaks in plots dR/dλ and dT/dλ versus wavelength of films exhibit optical gaps at about 3.12-3.25 eV.The values of the fundamental indirect band gap obtained from the Tauc model are at about 3.14-3.2 eV. It can be seen that films annealed at 600°C have the minimum indirect optical band gap at about 3.15 eV. The films annealed at 600°C have Urbach's energy minimum of 1.38 eV and hence have minimum disorder. The dispersion energy d of films annealed at 500°C has the minimum value of 43 eV.
基金Funded by the National Natural Science Foundation of China(No.51461135004)the Doctoral Fund of Ministry of Education Priority Development Project(No.20130143130002)+1 种基金the Key Technology Innovation Project of Hubei Province(2013AAA005)the Scientific Leadership training Program of Hubei Province
文摘Zn_(0.8)Cd_(0.2)O thin films prepared using the spin-coating method were investigated. X-ray diffraction, scanning electron microscopy, and UV-Vis spectrophotometry were employed to illustrate the effects of the pre-heating temperature on the crystalline structure, surface morphology and transmission spectra of Zn_(0.8)Cd_(0.2)O thin films. When the thin films were pre-heated at 150 ℃, polycrystalline Zn O thin films were obtained. When the thin films were pre-heated at temperatures of 200 ℃ or higher, preferential growth of Zn O nanocrystals along the c-axis was observed. Transmission spectra showed that thin films with high transmission in the visible light range were prepared and effective bandgap energies of these thin films decreased from 3.19 e V to 3.08 e V when the pre-heating temperature increased from 150 ℃ to 300 ℃.
基金by the Ministry of Education,Science and Technological Development of the Republic of Serbia(grant 172026)COST action MP1306
文摘Structural and optical properties of nanometric titanium oxide(TixOy) films obtained by cathodic arc plasma deposition were investigated. Phase analysis by x-ray diffraction and Fouriertransform infrared spectroscopy showed the presence of anatase, rutile, Ti_2O_3, Ti_4O_7 and amorphous phases. Scanning electron microscopy images showed well-developed surface morphology with nano-patterns. Spectroscopic ellipsometry revealed film thicknesses of 53 and50 nm, variable refractive indices dependent on the light wavelength and close to zero extinction coefficients for wavelengths higher than 500 nm. On the basis of ultraviolet–visible spectroscopy data and using the Tauc equation, band gap values for direct and indirect electron transitions were determined.
文摘Azobenzene polymer films doped with and without Ag nanoparticles are prepared. The photoinduced reorientation process is investigated by using an Nd:YVO4 pump beam at 532 nm and a low semiconductor laser beam at 650 nm. The reorientation rate of azo polymer films is enhanced in the presence of Ag nanoparticles, and the rate of the azo polymer film with Ag concentration of 2.2 μg/ml is larger than that of the azo polymer films with Ag concentrations of 1.1 μg/ml and 4.4 μg/ml. The third-order nonlinear optical properties of the Ag/azo composite film are obtained by the Z-scan technique at a wavelength of 532 nm, and the measured nonlinear refractive index is 9.258×10-9 esu. It is shown that the main mechanisms involved in the large nonlinear optical responses come from the local field enhancement of Ag nanoparticles and the nonlinear effect of the azo polymer matrix.
基金Project supported by the National Natural Science Foundation of China(Grant No.61205211)
文摘A slanted columnar TiO2 sculptured anisotropic thin film (ATF) is prepared via the glancing angle deposition technique and used as the phase retardation plate. The tilted nanocolumn microstructures of thin film induce the optical anisotropy. With the biaxial birefringent model, the optical constants dispersion equations of TiO2 ATF are derived by fitting the transmittance spectra for s-and p-polarized waves measured at normal and oblique incidence within 400 nm–1200 nm. The phase shift of polarized light after reflection and/or transmission through the TiO2 ATF is analyzed with the characteristic matrix employing the extracted structure parameters. The theoretical studies reasonably well accord with the experimental results measured with spectroscopic ellipsometry. In addition, the dependences of the phase shift on the coating physical thickness and oblique incidence angle are also discussed. Birefringence of the biaxial ATF provides a sophisticated phase modulation by varying incidence angles over a broad range to have a wide-angle phase shift.
文摘Since about 10 years, there is a controversy about physics and chemistry of GdN between stoichiometric (tested) large single crystals and off-stoichiometric thin films. GdN single crystals are anti-ferromagnetic for applied magnetic fields of only 10 Oe, become ferromagnetic for excess electrons and larger magnetic fields. They are semimetallic. Thin films are ferromagnetic and semiconductors. Over the time, many experiments have been performed on both systems and the physics in each system is consistent. Band structure computations either yield ferromagnetic semimetals or ferromagnetic semiconducting thin films. There seems to be two incompatible worlds, those of single crystals and those of thin films. In the present work, the author compares directly the various measurements and calculations and gives reasons for their different results.
文摘Following are the comments for the queries raised by Prof. Pawel E. Tomaszewski on our published paper entitled "Structural, Optical, and Electrical Properties of Zn-Doped CdO Thin Films Fabricated by a Simplified Spray Pyrolysis Technique" by K. Usharani and A.R. Balu published in Acta Metall. Sin.
文摘Thin films of zinc-doped cadmium oxide with different Zn-doping levels(0, 2, 4, 6, and 8 at%) were deposited on glass substrates by employing an inexpensive, simplified spray technique using perfume atomizer at relatively low substrate temperature(375 °C) compared with the conventional spray method. The effect of Zn doping on the structural,morphological, optical, and electrical properties of the films was investigated. XRD patterns revealed that all the films are polycrystalline in nature having cubic crystal structure with a preferential orientation along the(1 1 1) plane irrespective of Zn-doping level. Zn-doping level causes a slight shift in the(1 1 1) diffraction peak toward higher angle. The crystallite size of the films was found to be in the range of 28–37 nm. The band gap value increases with Zn doping and reaches a maximum of 2.65 eV for the film coated with 6 at% Zn doping and for further higher doping concentration it decreases.Electrical studies indicate that Zn doping causes a reduction in the resistivity of the films and a minimum resistivity of15.69 X cm is observed for the film coated with 6 at% Zn.
文摘The commented paper [1] presents the results on structural, optical, and electrical properties of Zn-doped CdO thin films. Unfortunately, there are several mistakes and errors not found by any of referees. It is necessary to show these mistakes or misleading statements to avoid their use in the future papers by authors and other peoples.
文摘In this study,we report the annealing effects on the physical properties of Sn_3Sb_2S_6 thin films.Sn_3Sb_2S_6 thin films were prepared onto non-heated glass substrates via thermal evaporation technique.The as-deposited films were annealed in air for 1 h in the temperature range from 100 to 300 °C.X-ray diffraction results show that the crystallinity of the thin films increased after annealing.The microstructure parameters crystallite size,dislocation density,lattice strain and stacking fault probability were calculated.The optical properties were obtained from the analysis of the experimental recorded transmittance and reflectance spectral data over the wavelength range 300–1800 nm.High absorption coefficient(10~5cm^(-1)) reached to the visible and near-IR spectral range.A decrease in optical band gap from 1.92 to 1.71 e V by increasing the air annealing temperature was observed.Oscillator energy E_o and dispersion energy E_d of the films after annealing were estimated according to the model of Wemple–Di Domenico single oscillator.Spitzer–Fan model was applied to determine the electron free carrier susceptibility and the ratio of carrier concentration to the effective mass.The layers annealed at temperatures 〉150 ℃ undergo abrupt changes in their electrical properties and exhibit a resistive hysteresis behavior.These properties confer to the material interest perspectives for its application in diverse advanced technologies such as photovoltaic applications and optical storage.
基金Supported by the National Science Fund for Distinguished Young Scholars of China under Grant No 60525406, the National Natural Science Foundation of China under Grant Nos 60736031, 60806018, 60906026 and 10990100, the National Basic Research Program of China under Grant No 2006CB604903, and the National High-tcch R&D Program of China under Grant Nos 2007AA03Z446 and 2009AA03Z403.
文摘We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200/times 200 ×μm^2 square mesa.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60976045, 60506001, 60776047 and 60836003, and the National Basic Research Program of China under Grant No 2007CB936700.
文摘We report our recent progress of investigations on InGaN-based blue-violet laser diodes (LDs). The roomtemperature (RT) cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing (FS) GaN substrate by metal organic chemical vapor deposition (MOCVD). The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well (MQW), respectively.
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.
文摘Top-illuminated metamorphic InGaAs p-i-n photodetectors (PDs) with 50% cut-off wavelength of 1.75 μm at room temperature are fabricated on GaAs substrates. The PDs are grown by a solid-source molecular beam epitaxy system. The large lattice mismatch strain is accommodated by growth of a linearly graded buffer layer to create a high quality virtual InP substrate indium content in the metamorphic buffer layer linearly changes from 2% to 60%. The dark current densities are typically 5 × 10^-6 A/cm^2 at 0 V bias and 2.24 × 10^-4 A/cm^2 at a reverse bias of 5 V. At a wavelength of 1.55 μm, the PDs have an optical responsivity of 0.48 A/W, a linear photoresponse up to 5 mW optical power at -4 V bias. The measured -3 dB bandwidth of a 32 μm diameter device is 7 GHz. This work proves that InGaAs buffer layers grown by solid source MBE are promising candidates for GaAs-based long wavelength devices.
基金Supported by the National High-Technology Research and Development Program of China under Grant No 2006AA03Z401, One-Hundred Talents Program of Chinese Academy of Sciences, and the National Natural Science Foundation of China under Grant No 60876033.
文摘We report the molecular beam epitaxy growth of 1.3 μm InAs/GaAs quantum-dot (QD) lasers with high characteristic temperature T0. The active region of the lasers consists of five-layer InAs QDs with p-type modulation doping. Devices with a stripe width of 4 μm and a cavity length of 1200 μm are fabricated and tested in the pulsed regime under different temperatures. It is found that T0 of the QD lasers is as high as 532 K in the temperature range from 10°C to 60°C. In addition, the aging test for the lasers under continuous wave operation at 100°C for 72 h shows almost no degradation, indicating the high crystal quality of the devices.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60736036, 60706009, 60777021 and 60702006, the National Basic Research Program of China under Grant Nos 2006CB604901 and 2006CB604902, and the National High-Tech Research and Development Program of China under Grant No 2007AA03Z419, 2007AA03Z417 and 2009AA03Z442.
文摘We fabricate 1.5 μm InGaAsP/InP tunnel injection multiple?quantum-well (TI-MQW) Fabry-Perot (F-P) ridge lasers. The laser heterostructures, including an inner cladding layer and an InP tunnel barrier layer, are grown by metal-organic chemical-vapor deposition (MOCVD). Characteristic temperature T0 of 160 K at 20°C is obtained for 500?μm?long lasers. T0 is measured as high as 88 K in the temperature range of 15?75°C. Cavity length dependence of T0 is investigated.
基金Supported by the National Natural Science Foundation of China under Grant No 10775055.
文摘The s-polarized surface plasmon polaritons (SPPs) at the interface between dielectric and metamaterial are studied, and the dispersion relations of SPPs are also presented. Using the prism coupling mechanism, we obtain the attenuated total reflection (ATR) spectra in the frequency regime based on the Otto configuration. It is found that the thickness of the dielectric in the configuration and the small damping of the metamaterial affect the coupling strength significantly without changing the coupling frequency. Furthermore, the optimized thickness of the dielectric decreases with a larger damping, and the coefficient F of the metamaterial also determines the coupling frequency and strength.