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Li Z.,Ningbo University | Li Z.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Lu Y.,Ningbo University | Lu Y.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | And 10 more authors.
Journal of Non-Crystalline Solids | Year: 2016

In this paper, the effect of Zr on the phase change properties of Ge2Sb2Te5 (GST) is systemically studied for phase-change random access memory. The sheet resistance ratio between amorphous and crystalline states achieves four to five orders of magnitude. The crystalline resistance, crystallization temperature (Tc) and the 10 years data-retention of Zr-GST films increase with the Zr concentration. Zr-GST films are crystallized into a single phase without phase separation due to the Zr bonding with Sb and Te. With the increasing annealing temperature, the transformation from face-centered cubic (fcc) to hexagonal is suppressed when the Zr atomic content is higher than 6%, which is ascribed to the lack formation of the Te-Te pairs. The wide band gap of the amorphous Zr-GST films is favorable to reduce the threshold current. The incorporating Zr atoms are embedded in the inner atomic-scale structure of the GST, which contributes to performance improvement of the GST material for phase-change random access memory. © 2016 Elsevier B.V.


Li X.,Ningbo University | Li X.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Chen J.,Shanghai JiaoTong University | Dai S.,Ningbo University | Dai S.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province
Optik | Year: 2016

We demonstrate a stable multiwavelength passively mode-locked erbium-doped fiber laser with ultra-narrow wavelength spacing and ultra-broad bandwidth. It is realized by exploiting an intracavity birefringence-induced comb filter and inhomogeneous loss mechanism based on nonlinear polarization rotation. Stable 808-line wavelength lasing with wavelength spacing of 0.07 nm and 3-dB bandwidth of 55.75 nm is achieved at room temperature. If 5-dB bandwidth of 86.15 nm is considered, the number of the lasing lines reaches 1248. In addition, the lasing wavelength lines and spacing could be flexibly tuned by modifying polarization-dependent cavity loss via properly rotating the waveplates. © 2016 Elsevier GmbH


Sun L.,Ningbo University | Sun L.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Chen F.,Ningbo University | Chen F.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | And 15 more authors.
Applied Physics A: Materials Science and Processing | Year: 2016

In this study, a series of Ge20TexSe(80−x) (x = 0, 5, 10, 20, 30, 60, 70) chalcogenide glasses were prepared using conventional melt-quenching technique. Through absorption spectra analysis, the optical Tauc gaps were derived in detail along the increase in the Te content which can be supported by structural changing of glass network shown by Raman spectra. The third-order optical nonlinearity of the glasses at mid-infrared wavelength of 3.1 μm was investigated by traditional Z-scan method. The nonlinear refractive index of the glasses increased with the increase in the Te content, typically the measured nonlinear refractive index of Ge20Se50Te30 glass increased to 8.2 ± 1.2 × 10−18 m2/W. The relationship between the nonlinear refractive index and the optical band gap was analyzed. © 2016, Springer-Verlag Berlin Heidelberg.


Ma Y.,Ningbo University | Ma Y.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Lu Y.,Ningbo University | Lu Y.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | And 11 more authors.
ECS Journal of Solid State Science and Technology | Year: 2016

In this paper, the phase change characteristics of Sb-Te-Se films were systematically studied by in-situ resistance-temperature measurement, X-ray diffraction (XRD), Raman scattering spectroscopy, X-ray photoelectron spectra (XPS), and Transmission electron microscopy (TEM). For preferred Sb56Te24Se20 and Sb55Te22Se23 films, the temperature for 10-year data retention can be up to 93.1 and 102.6C, which are higher than that of Ge2Sb2Te5 (GST, 82C). Both amorphous and crystalline resistivities increase with Se content. The resistance ratios between two states maintain almost 4 orders of magnitude. The microstructure of annealed Sb-Te-Se films exhibits uniform distribution of crystallized phases with rhombohedra Sb2SeTe2 and hexagonal Sb. The improvement in thermal stability of Sb-Te-Se films results from the atomic arrangements and consequently the complex cross bond system. © The Author(s) 2015.


Wang G.,Ningbo University | Wang G.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Shen X.,Ningbo University | Shen X.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | And 8 more authors.
Thin Solid Films | Year: 2016

The structural stability of carbon (C) incorporated Sb2Te films was investigated during crystallization process. Variations in the transition temperature for the as-deposited films during crystallization show that these films exhibit their enhanced amorphous stability due to C incorporation, while more C content will lead to a difference in the degree of disorder in the crystalline state. XPS data reveals that C atoms do not bond with Sb and Te atoms and only present in the form of [Formula presented] bonds. According to XRD and TEM results, C atoms presents amorphous and this can increase the degree of disorder in the crystalline films. The Sb2Te nanocrystals were surrounded by an amorphous C phase. A subsequent Raman analysis further provides the direct evidence of improvement in the degree of disorder in the crystalline state. The laser-induced crystallization process of C37.4(Sb2Te)62.6 reveals that the degree of disorder in the crystalline state is relatively high and the reliability during the repetitive laser melt-quenching cycles is confirmed with fast crystallization as well as a low melting point of only 353 °C. Increasing degree of disorder in the Sb2Te films by C addition can improve the phase-change behavior and make this film suitable for data storage applications. © 2016 Elsevier B.V.


Zhang P.,Ningbo University | Zhang P.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Zhao Z.,Ningbo University | Zhao Z.,Jiaxing University | And 12 more authors.
Optical Materials Express | Year: 2016

Ge20As20Se15Te45 chalcogenide glass was fabricated and systematically studied. This glass exhibits broad transmission range, high linear and non-linear refractive index, and good thermal stability. The low glass transition temperature allowed for the thermal nanoimprint to be accomplished directly on the bulk Ge20As20Se15Te45 glass to produce photonic crystals with a hybrid soft stamp. By optimizing the imprint conditions, uniform gratings with 500 nm depth grooves were fabricated by direct resist-free thermal nanoimprint lithography. © 2016 Optical Society of America.


Li G.,Ningbo University | Xu T.,Ningbo University | Xu T.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Dai S.,Ningbo University | And 5 more authors.
Kuei Suan Jen Hsueh Pao/Journal of the Chinese Ceramic Society | Year: 2016

Series of GaxSb40-xS60 chalcogenide glasses were synthesized by a melt-quenching method. The thermal and optical properties of sample glasses were determined by the Archimedes principle, X-ray diffraction, thermal expansion, ultra violet-visible-near infrared absorption spectroscopy, and Fourier transform infrared spectroscopy, respectively. The structures of the samples with different compositions were analyzed by Raman spectroscopy. The results show that all of the glasses have good thermal stability and spectral properties. The density decreases slightly, the glass transition temperature improves, and the thermal expansion coefficient reduces with increasing the content of gallium. Besides, there is a slightly augmentation of optic band gap and a regularly blue-shifted of IR absorption cutting-off edge. Since all of the chalcogenide glasses have a high transmittance in a wide spectrum range of 0.8-14.0 μm (covering three main commutation bands and thermal infrared band), they are thus a promising material for mid-infrared application. According to the Raman spectra, the formation of [GaS4] tetrahedral units promote and the [SbS3] pyramid units suppress with the increase of gallium content. The relationship between optical properties and the structure in the chalcogenide glasses was summarized. © 2016, Editorial Department of Journal of the Chinese Ceramic Society. All right reserved.


Zhang X.-D.,Ningbo University | Zhang X.-D.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Wu Y.-H.,Ningbo University | Wu Y.-H.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | And 12 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2016

Microsphere resonators based on chalcogenide glasses combine the superior optical properties of microsphere resonators (such as high Q-factors and small mode volumes) and excellent material properties of chalcogenide glasses in the infrared spectrum (such as good transmissivities, high refractive indices, and low phonon energies), and thus have promising applications in the fields of low-threshold infrared lasers, nonlinear Raman amplifiers/lasers, and narrow bandwidth infrared filters. In this work, the infrared microsphere resonators are built by using a novel chalcogenide glass composition of 75 GeS2-15 Ga2S3-10 CsI (Ge-Ga-S), doped with 1.3 wt% Tm. Compared with previously reported chalcogenide microsphere resonators fabricated with As2S3 and gallium lanthanum sulfide (Ga-La-S) glasses, the proposed Ge-Ga-S glass does not contain the toxic element of As nor the expensive rare earth element of La, and thus is more environmentally friendly and cost-effective for fabricators and users. We first fabricate bulk Ge-Ga-S glasses by using the facility in our laboratory. After measuring the absorption and fluorescence spectra of bulk glasses, they are crushed into powders and the powders are blown downwards through an inert-gas-filled vertical furnace (temperature set at 1000 ℃). Molten glass powders are transformed into high-quality microspheres in the furnace due to surface tension. Thousands of microspheres with diameters ranging from 50 to 200 m can be made in one fabrication process. By using optical microscopy and scanning electron microscopy, a microsphere with high surface quality is selected for further optical characterization. The selected microsphere has a diameter of 72.84 μm, an eccentricity less than 1% (about 80 nm), and a Q-factor of 1.296×104. A silica fiber taper with a waist-diameter of 1.93 μm is fabricated as the coupling mechanism for the microsphere resonator. The coupling between the microsphere and the micro fiber taper is realized with the aid of nano-positioning stages. An 808 nm laser diode is used as a pump light source, which is sent into one end of the fiber taper and is evanescently coupled into the microsphere. Spontaneous emissions of fluorescent light are then generated in the microsphere, whose spectral characteristics are measured by using an optical spectrum analyzer. It can be clearly noted from the measurement results that the typical fluorescence spectrum of the Tm3+-doped Ge-Ga-S glass is modified by whispering gallery mode (WGM) patterns as periodic intensity peaks/valleys are apparently present in the measured spectral curves. The locations of those experimentally measured spectral peaks/valleys are in good agreement with WGM mode calculated results through using the Mie scattering theory, which verifies that the proposed Ge-Ga-S glass can be used to build high-quality infrared microsphere resonators. The largest deviation between the experimentally measured spectral peaks/valleys and theoretically calculated WGM modes is about 0.047%. Minor deviation is present because the experimentally fabricated microsphere has a small difference from an ideal sphere (with an eccentricity of about 1% in this work). Longer processing time of glass powders in the vertical furnace or a post-thermal treatment could help improve the sphericity of microspheres. © 2016 Chinese Physical Society.


Wei F.,Ningbo University | Wei F.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Zhang W.,Ningbo University | Zhang W.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | And 12 more authors.
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2015

The plane wave expansion method (PWE) is adopted to calculate chalcogenide photonic crystal bandgap, and finite difference time domain (FDTD) method is used to simulate transmission characteristics for 60° bent chalcogenide photonic crystal waveguide. Two symmetric air-holes are introduced in outer edge of line defects in the 60° bent region, in order to improve the transmission efficiency by adjusting the radii of the air-holes. The simulation result shows that transmission bandwidth is widened from the initial 60 nm to 161 nm while the radius of the air-holes is 0.54R, however, the transmission efficiency fluctuates violently. Then some more air-holes are introduced in the central line defect in bent region. It is noticed that when 3 air-holes with radius of 0.48R are added, not only the transmission efficiency is improvement, but also the transmission bandwidth is widened to 340 nm. Continuous bend of 60° waveguide structure optimization is similar to that of single one, and the result shows that the transmission efficiency in continuous bend of waveguide can be significantly improved. © 2015, Science Press. All right reserved.


Pan S.,Ningbo University | Pan S.,Key Laboratory of Photoelectric Materials and Devices of Zhejiang Province | Wang Q.,CAS Shanghai Institute of Ceramics | Li H.,CAS Shanghai Institute of Ceramics | And 3 more authors.
Radiation Measurements | Year: 2016

Eu2+:CeBr3 crystals were grown by vertical Bridgman growth method and slight aliovalent doping of Eu2+ in the CeBr3 crystal did not change the crystal structure. The X-ray stimulated luminescence, photoluminescence, decay kinetics and scintillation properties were investigated at room temperature. The X-ray stimulated luminescence spectra exhibited wide broad emission bands from 3.54 eV to 2.95 eV in the Eu2+:CeBr3 crystal with high content of 620 ppm of Eu2+, which were the overlap of the emission bands ascribed to 5d → 4f transition of Ce3+ and 4f65 d1 → 4f7 transition of Eu2+, respectively. When the content of Eu2+ was decreased to 70 ppm, another emission band centered at 2.29 eV was observed. The photoluminescence spectra showed the energy transfer from Ce3+ to Eu2+. This decreased the Ce3+ emission intensity but enhanced the Eu2+ emission intensity. The photoluminescence decay time of Ce3+ emission decreased from 14 ns to 10 ns when the content of Eu2+ increased from 70 ppm to 620 ppm. The decay time of the emission of 525 nm did not change with the excitation wavelength and Eu2+ content, which could be assigned to the excitons that were bound on Eu2+ related centers. The light output of the Eu:CeBr3 crystal under the excitation of 241Am radioactive source was less than 20.2% of Tl:NaI crystal. © 2016 Elsevier Ltd. All rights reserved.

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