We quantitatively investigate the third-order optical nonlinear response of Co-doped ZnO thin films prepared by magnetron sputtering using the Z-scan method. The two-photon absorption and optical Kerr effect are revea...We quantitatively investigate the third-order optical nonlinear response of Co-doped ZnO thin films prepared by magnetron sputtering using the Z-scan method. The two-photon absorption and optical Kerr effect are revealed to contribute to the third-order nonlinear response of the Co-doped ZnO films. The nonlinear absorption coefficient β is determined to be approximately 8.8 × 10-5 cm/W and the third-order nonlinear susceptibility X（3） is 2.93 × 10-6 esu. The defect-associated energy levels within the band gap are suggested to be responsible for the enhanced nonlinear response observed in Co-doped ZnO films.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
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
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
WNxfilms are deposited by reactive chemical vapor deposition at different amounts of nitrogen in gas mixtures.Experimental data demonstrate that nitrogen amount has a strong effect on microstructure, phase formation,t...WNxfilms are deposited by reactive chemical vapor deposition at different amounts of nitrogen in gas mixtures.Experimental data demonstrate that nitrogen amount has a strong effect on microstructure, phase formation,texture morphology, mechanical and optical properties of the WNxfilms. With increasing nitrogen a phase transition from a single WNxphase with low crystallinity structure to a well-mixed crystallized hexagonal WNxand face-centered-cubic W2N phases appears. Relatively smooth morphology at lower N2concentration changes to a really smooth morphology and then granular with coarse surface at higher N2concentration. The SEM observation clearly shows a columnar structure at lower N2concentration and a dense nanoplates one for higher nitrogen content. The hardness of WNxthin films mainly depends on the film microstructure. The absorbance peak position shifts to shorter wavelength continuously with increasing nitrogen amount and decreasing particle size.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
Fluorinated amorphous carbon films were deposited using microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) reactor with CF4 and C8H6 as source gas and were annealed in nitrogen ambience for the...Fluorinated amorphous carbon films were deposited using microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) reactor with CF4 and C8H6 as source gas and were annealed in nitrogen ambience for the investigating of their thermal stability .The relative concentration of C=C bond and optical bandgap were obtained by Fourier Transform Infrared (FTIR) spectroscopy and Ultraviolet-Visible (UV-VIS ) spectrum, respectively. It has been demonstrated that there is a close relationship between relative concentration of C=C bond and optical bandgap, and the films deposited at a higher microwave power have a lower optical bandgap and a better thermal stability.展开更多
From different reports, it （AZO） and indium-doped including usage areas. We nanocrystalline films with is realized that there is a need to consider all sides of aluminum-doped zinc oxide zinc oxide （IZO） thin film...From different reports, it （AZO） and indium-doped including usage areas. We nanocrystalline films with is realized that there is a need to consider all sides of aluminum-doped zinc oxide zinc oxide （IZO） thin films with their optical, luminescence and surface properties establish an assessment to carry out further information to summarize AZO and IZO impact of the layer number.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
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
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
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
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
Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide （DLSPPW） based 1/4 circle is calculated for a 90° bend model and a 270° bend ...Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide （DLSPPW） based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators （WRRs） and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.展开更多
Dual-band negative-index properties of the silver-SU-8-silver sandwich configuration, perforated with a square array of cross dipole apertures, are simulated and analyzed in the midinfrared region. The first and the s...Dual-band negative-index properties of the silver-SU-8-silver sandwich configuration, perforated with a square array of cross dipole apertures, are simulated and analyzed in the midinfrared region. The first and the second negative-index bands correspond to the （1,0） and （1,1） internal surface plasmon polariton （SPP） modes, respectively. The internal and external SPP modes acquired by the SPP dispersion relation of the metal/dielectric/metal model match well with the simulated transmission peaks. The effective parameters for the two negative-index bands are retrieved using simulated S parameters. The coupling effect between the （1,1） internal SPP mode and the localized resonance mode can be tuned by the arm length of cross dipole, which can weaken or destroy the negative electromagnetic response of the second negative-index band. The electric quadrupole mode of the second negative-index band accounts for its strong dependence on the dielectric loss of the interlayer.展开更多
We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole ...We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole （BT） and 4,7-bis（2-thienyl）-2,1,3-benzothiadiazole （DBT） as green and red light-emitting units, respectively. For the single copolymer/InGaN hybrid device, the Commission Internationale de 1＇Eclairage （CIE） coordinates, color temperature Tc and color rendering index Ra at 20mA are （0.323,0.329）, 5960K and 86, respectively. In comparison with the performance of red eopolymer PFO-DBT15 （DOF：DBT=85：15 with DOF being 9＇9- dioctylfluorene） and green copolymer PFO-BT35 （DOF：BT=-65：35） blend/InGaN hybrid white devices, it is concluded that the chemically doped copolymer hybridized device shows a higher emission intensity and spectral stability at a high driving current than the polymer blend.展开更多
We fabricate an inverted bottom-emission organic light emitting diode （IBOLED） employing two n-doped layers, i.e., 5 nm lithium carbonate doped PTCDA （1：2 Li2CO3：PTCDA） with 5 nm Li2CO3 doped BCP （1：4 Li2CO3：...We fabricate an inverted bottom-emission organic light emitting diode （IBOLED） employing two n-doped layers, i.e., 5 nm lithium carbonate doped PTCDA （1：2 Li2CO3：PTCDA） with 5 nm Li2CO3 doped BCP （1：4 Li2CO3：BCP） on top, where PTCDA and BCP stand for 3, 4, 9, 10 perylenetetracarboxylic dianhydride and bathcuporine, respectively. Compared to the IBOED using a layer of 10 nm 1：4 Li2CO3：BCP, the one utilizing the two-layer combination of 5 nm 1：2 Li2CO3：PTCDA and 5 nm 1：4 Li2CO3：BCP shows decreasing operation voltage and thereby increasing power efficiency, mainly attributed to the higher electron conductivity of 1：2 Li2CO3：PTCDA than that of 1：4 Li2CO3：BCP. The mechanism of the electron transport through the interface of 1：2 Li2CO3：PTCDA and 1：4 Li2CO3：BCP is also discussed. We provide a simply and effective structure to enhance the current conduction for IBOLEDs.展开更多
基金Supported by National Basic Research Program of China under Grant Nos 2011CB922200 and 2013CB922303
文摘We quantitatively investigate the third-order optical nonlinear response of Co-doped ZnO thin films prepared by magnetron sputtering using the Z-scan method. The two-photon absorption and optical Kerr effect are revealed to contribute to the third-order nonlinear response of the Co-doped ZnO films. The nonlinear absorption coefficient β is determined to be approximately 8.8 × 10-5 cm/W and the third-order nonlinear susceptibility X（3） is 2.93 × 10-6 esu. The defect-associated energy levels within the band gap are suggested to be responsible for the enhanced nonlinear response observed in Co-doped ZnO films.
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.
文摘WNxfilms are deposited by reactive chemical vapor deposition at different amounts of nitrogen in gas mixtures.Experimental data demonstrate that nitrogen amount has a strong effect on microstructure, phase formation,texture morphology, mechanical and optical properties of the WNxfilms. With increasing nitrogen a phase transition from a single WNxphase with low crystallinity structure to a well-mixed crystallized hexagonal WNxand face-centered-cubic W2N phases appears. Relatively smooth morphology at lower N2concentration changes to a really smooth morphology and then granular with coarse surface at higher N2concentration. The SEM observation clearly shows a columnar structure at lower N2concentration and a dense nanoplates one for higher nitrogen content. The hardness of WNxthin films mainly depends on the film microstructure. The absorbance peak position shifts to shorter wavelength continuously with increasing nitrogen amount and decreasing particle size.
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.
文摘Fluorinated amorphous carbon films were deposited using microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) reactor with CF4 and C8H6 as source gas and were annealed in nitrogen ambience for the investigating of their thermal stability .The relative concentration of C=C bond and optical bandgap were obtained by Fourier Transform Infrared (FTIR) spectroscopy and Ultraviolet-Visible (UV-VIS ) spectrum, respectively. It has been demonstrated that there is a close relationship between relative concentration of C=C bond and optical bandgap, and the films deposited at a higher microwave power have a lower optical bandgap and a better thermal stability.
文摘From different reports, it （AZO） and indium-doped including usage areas. We nanocrystalline films with is realized that there is a need to consider all sides of aluminum-doped zinc oxide zinc oxide （IZO） thin films with their optical, luminescence and surface properties establish an assessment to carry out further information to summarize AZO and IZO impact of the layer number.
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.
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.
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 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.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10821062 and 10804004, the National Basic Research Program of China under Grant Nos 2007CB307001and 2009CB930504, and the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No 200800011023.
文摘Based on full 3D finite element method simulations, the transmission of a dielectric-loaded surface plasmon polariton waveguide （DLSPPW） based 1/4 circle is calculated for a 90° bend model and a 270° bend model, respectively. It is found that the 270° bend model gives almost pure bending loss while the 90° bend model contains additional coupling loss. The models are applied to deduce the loss and unloaded quality factor of DLSPPW based waveguide ring resonators （WRRs） and the results of the 270° bend model agree well with direct simulating results of the WRRs. Thus the 270° bend model gives a fast and simple way to calculate bending loss and it is helpful for WRR design because no wavelength scan is needed.
基金Supported in part by the National Natural Science Foundation of China under Grant No 60778041, and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China under Grant No 07KJA51001.
文摘Dual-band negative-index properties of the silver-SU-8-silver sandwich configuration, perforated with a square array of cross dipole apertures, are simulated and analyzed in the midinfrared region. The first and the second negative-index bands correspond to the （1,0） and （1,1） internal surface plasmon polariton （SPP） modes, respectively. The internal and external SPP modes acquired by the SPP dispersion relation of the metal/dielectric/metal model match well with the simulated transmission peaks. The effective parameters for the two negative-index bands are retrieved using simulated S parameters. The coupling effect between the （1,1） internal SPP mode and the localized resonance mode can be tuned by the arm length of cross dipole, which can weaken or destroy the negative electromagnetic response of the second negative-index band. The electric quadrupole mode of the second negative-index band accounts for its strong dependence on the dielectric loss of the interlayer.
基金Supported by the Natural Science Foundation of Guangdong Province under Grant No 06300928 and 8251063101000007.
文摘We report an efficient white-light emission based on a single copolymer/InGaN hybrid light-emitting diode. The single copolymer consists of a conjugated polyfluorene backbone by incorporating 2,1,3-benzothiadiazole （BT） and 4,7-bis（2-thienyl）-2,1,3-benzothiadiazole （DBT） as green and red light-emitting units, respectively. For the single copolymer/InGaN hybrid device, the Commission Internationale de 1＇Eclairage （CIE） coordinates, color temperature Tc and color rendering index Ra at 20mA are （0.323,0.329）, 5960K and 86, respectively. In comparison with the performance of red eopolymer PFO-DBT15 （DOF：DBT=85：15 with DOF being 9＇9- dioctylfluorene） and green copolymer PFO-BT35 （DOF：BT=-65：35） blend/InGaN hybrid white devices, it is concluded that the chemically doped copolymer hybridized device shows a higher emission intensity and spectral stability at a high driving current than the polymer blend.
基金Supported by the National Natural Science Foundation of China under Grant No 50803014.
文摘We fabricate an inverted bottom-emission organic light emitting diode （IBOLED） employing two n-doped layers, i.e., 5 nm lithium carbonate doped PTCDA （1：2 Li2CO3：PTCDA） with 5 nm Li2CO3 doped BCP （1：4 Li2CO3：BCP） on top, where PTCDA and BCP stand for 3, 4, 9, 10 perylenetetracarboxylic dianhydride and bathcuporine, respectively. Compared to the IBOED using a layer of 10 nm 1：4 Li2CO3：BCP, the one utilizing the two-layer combination of 5 nm 1：2 Li2CO3：PTCDA and 5 nm 1：4 Li2CO3：BCP shows decreasing operation voltage and thereby increasing power efficiency, mainly attributed to the higher electron conductivity of 1：2 Li2CO3：PTCDA than that of 1：4 Li2CO3：BCP. The mechanism of the electron transport through the interface of 1：2 Li2CO3：PTCDA and 1：4 Li2CO3：BCP is also discussed. We provide a simply and effective structure to enhance the current conduction for IBOLEDs.
