近红外单光子探测器

该单光子探测器在实验中使用半导体制冷器制冷，雪崩二极管工作于盖革模式下，使用交流耦合方式提供门脉冲信号，通过延迟补偿和采样门控消除尖脉冲干扰，采用反馈门控减小后脉冲影响，优化电路参数减小暗计数.经实验测试与分析，温度在-62.5℃，门脉冲宽度为50ns，采样门控为10ns的条件下，最佳工作点的暗计数率小于4×10^-6ns^-1，量子效率约18%，噪声等效功率为2.4×10^-19W/Hz^1/2.     

AlGaN-Based Solar-Blind Schottky Photodetectors Fabricated on AlN/Sapphire Template

We report AlGaN-based back-illuminated solar-blind Schottky-type ultraviolet photodetectors with the cutoff- wavelength from 280nm to 292nm without bias. The devices show low dark current of 2.1× 10^-6A/cm^2 at the reverse bias of 5 V. The specific detectivity D＊ is estimated to be 3.3 × 10^12cmHz^1/2 W^-1 . To guarantee the performance of the photodetectors, the optimization of AlGaN growth and annealing condition for Schottky contacts were performed. The results show that high-temperature annealing method for Ni/Pt Schottky contacts is effective for the reduction of leakage current.     

Intrinsic Bistability and Critical Slowing in Tm^3＋/Yb^3＋ Codoped Laser Crystal with the Photon Avalanche Mechanism

We present theoretically a novel intrinsic optical bistability （IOB） in the Tm^3＋ /Yb^3＋ codoped system with a photon avalanche mechanism. Numerical simulations based on the rate equation model demonstrate distinct 10B hysteresis and critical slowing dynamics around the avalanche thresholds. Such an 10B characteristic in Tm^3＋ /Yb^3＋ eodoped crystal has potential applications in solid-state bistable optical displays and luminescence switchers in visible-infrared spectra.     

Influence of Dopant Concentration on Electroluminescent Performance of Organic White-Light-Emitting Device with Double-Emissive-Layered Structure

A novel phosphorescent organic white-light-emitting device （WOLED） with contiguration of ITO/NPB/CBP： TBPe：rubrene/Zn（BTZ）2：Ir（piq）2（acac）/Zn（BTZ）2/Mg：Ag is fabricated successfully, where the phosphorescent dye bis （1-（phenyl）isoquinoline） iridium （Ⅲ） acetylanetonate （Ir（piq）2 （acac）） doped into bis-（2-（2-hydroxyphenyl） benzothiazole）zinc （Zn（BTZ）2） （greenish-blue emitting material with electron transport character） as the red emitting layer, and fluorescent dye 2,5,8,11-tetra-tertbutylperylene （TBPe） and 5,6,11,12-tetraphenyl-naphthacene （rubrene） together doped into 4,4＇-N,N＇-dicarbazole-biphenyl （CBP） （ambipolar conductivity material） as the blue-orange emitting layer, respectively. The two emitting layers are sandwiched between the hole-transport layer N ,N＇-biphenyl-N , N＇-bis （1-naph thyl）-（1,1＇-biphenyl）-4, 4 Cdiamine （NP B） and electron-transport layer （Zn（BTZ）2 ） The optimum device turns on at the driving voltage of 4.5 V. A maximum external quantum efficiency of 1.53%. and brightness 15000 cd/m^2 are presented. The best point of the Commission Internationale de 1＇Eclairage （CIE） coordinates locates at （0.335, 0.338） at about 13 V. Moreover, we also discuss how to achieve the bright pure white light through optimizing the doping concentration of each dye from the viewpoint of energy transfer process.     

Organic Light-Emitting Diodes with Magnesium Doped CuPc as an Efficient Electron Injection Layer

Bright organic electroluminescent devices are developed using a metal-doped organic layer intervening between the cathode and the emitting layer. The typical device structure is a glass substrate/indium-tin oxide （ITO）/copper phthalocyanine （CuPc）/N,N＇-bis-（1-naphthl）-diphenyl-1,1＇-biphenyl-4,4＇-diamine （NPB）/Tris（8-quinolinolato） aluminum（Alq3）/Mg-doped CuPc/Ag. At a driving voltage of 11 V, the device with a layer of Mg-doped CuPc （1：2 in weight） shows a brightness of 4312cd/m^2 and a current efficiency of 2.52cd/A, while the reference device exhibits 514 cd/m^2 and 1.25 cd/A.     

Performance Improvement of GaN Based Schottky Barrier Ultraviolet Photodetector by Adding a Thin A1GaN Window Layer

We propose a new structure of GaN based Schottky barrier ultraviolet photodetector, in which a thin n-type A1GaN window layer is added on the conventional n^--GaN/n^＋-GaN device structure. The performance of the Schottky barrier ultraviolet photodetector is found to be improved by the new structure. The simulation result shows that the new structure can reduce the negative effect of surface states on the performance of Schottky barrier GaN photodetectors, improving the quantum efficiency and decreasing the dark current. The investigations suggest that the new photodetector can exhibit a better responsivity by choosing a suitably high carrier concentration and thin thickness for the A1GaN window layer.     

Experiments of Multi-Level Read-Only Recording Using Readout Signal Wave-Shape Modulation

An innovative multilevel read-only recording method is proposed. In this method, a short pit/land is deliberately inserted to the original land/pit. This modifies the wave-shape of readout signM. Taking the wave-shape as the symbol of level detection, a signal wave-shape modulation （SWSM） multilevel method is realized. This method is carried out and validated on the DVD read-only manufacture and readout system. A capacity of 15 GB can be expected, and a bit error rate of 10-4 is achieved. The capacity can meet the demand of high definition movie publication. This method also provides a potential multi-level solution for other storage formats and systems.     

Ultra-Stable Rubidium-Stabilized External-Cavity Diode Laser Based on the Modulation Transfer Spectroscopy Technique

We construct an ultra-stable external-cavity diode laser via modulation transfer spectroscopy referencing on a hyperfine component of the ST Rb D2 lines at 780 nm. The Doppler-free dispersion-like modulation transfer signal is obtained with high signal-to-noise-ratio. The instability of the laser frequency is measured by beating with an optical frequency comb which is phase-locked to an ultra-stable oven controlled crystal oscillator. The Allan deviation is 3.9 × 10-13 at I s averaging time and 9.8 ×10-14 at 90s averaging time.     

Fiber optical communications devices

Both low attenuation silica optical fibers with peak transmission in the wavelength regions of 0.85 μm, and 1.05 μm, and improved lasers at both wavelengths are now available. In this review paper, the principal components for emission, modulation and detection are described. The characteristics of both semiconductor lasers, made of GaAs and related compounds, emitting at 0.85 μm or 1.05 μm and high neodymium-content lasers are discussed. For modulation, current modulation of GaAs lasers and external electro-optic modulation are considered. Concerning detection, the realisation of Si photodetectors suitable at 0.85 μm and the new photodetectors at 1.05 μm from Ga_1−x In _x As are reviewed.     

Polymer White-Light-Emitting Diodes with High Work Function Cathode Based on a Novel Phosphorescent Chelating Copolymer

Polymer white-light-emitting diodes are fabricated based on the blend of poly[9,9-di-（2-ethylhexyl）-fluorenyl-2, 7- diyl]-end capped with polysilsesquioxane （PFO） and a chelating copolymer of poly[（9,9-bis（3′-（N,N-dimethylamino） propyl）-2, 7-fluorene-alt-2, 7-（9,9-dioctylfluorene） ）-co- [2, 7-（9,9-dioctlyfluorene）-alt-5,5-bis（2-（4-methyl-l-naphtha- lene） pyridine-C^2,N） iridium （III） acethylacetonate]] （PFN-NaIr）. The device with the sole aluminium cathode is able to produce a comparably white electroluminescence efficiency of 1.31 cd/A to that of the device using low work function cathodes （such as Ba, Ca, etc.）. The CIE coordinates of the white light emission consisting of red, green and blue three components are nearly at （0.34, 0.35）. The mechanism of the white light emission from the device with the AI cathode is investigated, which is related to the efficient injection of electrons through the interface of PFN-Nalr/AI.     

Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in ^85Rb

An atomic clock system based on coherent population trapping （CPT） resonance in 85Rb is reported, while most past works about the CPT clock are in ST Rb. A new modulation method （full-hyperfine-frequency-splitting modulation） is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in SSRb. The experimental results show that the short-term frequency stability of the CPT clock in SSRb is in the order of 10^-10/s and the long-term frequency stability can achieve 1.5 × 10^-11/80000s, which performs as well as 87 Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of SSRb indicates that an atomic clock based on CPT in SSRb should be a promising candidate for making the chip scale atomic clock.     

Efficient Top-Emitting Polymer Light-Emitting Diodes Using Chromium as Anode

We demonstrate a high eftlciency top-emitting polymer light-emitting diode （TPLED） with chromium （Cr） taking as the anode. The TPLED structure is Cr/poly-3, 4-ethylenedioxythiophene （PEDOT：PSS）/poly [2-（4-3＇,7＇- dimethyloctyloxy）-phenyl]-p-phenylenevinylene） （P-PP V） /Ba/Ag. The Cr （ 100 nm） anode is prepared by sputterdepositing in a vacuum chamber. It is found that the device emissive properties are affected dramatically by the thickness of both PEDOT：PSS and the Ag cathode. Optimized thicknesses of PEDOT：PSS and Ag layer are 60nm and 15nm, respectively. The diode exhibits excellent electroluminescence （EL） properties, such as a turn-on voltage of 3.32 V, luminous eftlciency of 4.41 cd/A and luminance of 6989cd/m^2 at driving voltage of about 9 V.     

Electroluminescence from Multilayered Diamond/CeF3/SiO2 Films

We report a thin film electroluminescent device with a three-layer structure （diamond/CeF3/SiO2 films）, which has a luminance of 1.5 cd/m^2 at dc voltage 215 V. The electroluminescence spectrum at room temperature shows that the main peaks locate at 527 and 593nm, which are attributed to isolated emission centers of Ce^3＋ ions.     

Fast‐response organic–inorganic hybrid light‐emitting diode

We demonstrated important changes produced on the modulation frequency of hybrid organic–inorganic light‐emitting diodes to examine the applicability as a light source for visible optical communications. The fabricated device structure was 4,4′‐bis[N ‐(1‐napthyl)‐N ‐phenyl‐amino]biphenyl/4,4′‐(bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl:4,4′‐bis[9‐dicarbazolyl]‐2,2′‐biphenyl/ZnS/LiF/MgAg. This device showed an improvement in the modulation frequency using ZnS instead of an organic material, tris(8‐hydroxyquinoline)aluminum. A maximum cutoff frequency of 20.6 MHz was achieved.

     

Efficient Solution-Processed Blue Electrophosphorescent Devices Based on a Novel Small-Molecule Host

Efficient blue small molecular phosphorescent fight-emitting diodes with a blue phosphorescent dye bis（3,5- difluoro-2-（2-pyridyl）-phenyl-（2-carboxypride） iridium （Ⅲ） （Flrpic） doped into a novel small-molecule host 9,9- bis[4-（3,6-di-tert-butylcarbazol-9-yl）phenyl] fluorene （TBCPF） as the light-emitting layer have been fabricated by spin-coating. The host TBCPF can form homogeneous amorphous films by spin-coating and has triplet energy higher than that of the blue phosphorescent dye Flrpic. All the devices with different Flrpic concentration in the emitting layer give emission from Flrpic indicating complete energy transfer from TBCPF to Flrpic. The device shows the best performance with a peak brightness of 8050 cd/m^2 at 10.2 V and the maximum current efficiency up to 3.52 cd/A, when the Flrpic doped concentration is as high as 16%.     

Carrier freezeout in n-on-p Hg0.7Cd0.3Te photodiode and acceptor level determination

0.7 Cd_0.3Te photodiodes at temperatures lower than 25 K. The freezeout was seen under the conditions that interband tunneling dominates the current in the photodiode and that avalanche ionization does not take place. These conditions are fulfilled at temperatures lower than 25 K and reverse bias voltages around 3 V. An acceptor level of about 4 meV was determined for p-type Hg_0.7Cd_0.3Te with N_A-N_D∼10¹⁶ cm^-3 from the temperature dependence of the photodiode resistance governed by carrier freezeout. The difficulties in observation of carrier freezeout in Hg_1-xCd_xTe with a larger composition ratio x or higher doping concentration are discussed. Received: 21 November 1996/Accepted: 15 April 1997     

PERFORMANCE INVESTIGATION OF MULTISTEP AVALANCHE CHAMBER

We have designed and operated a test module of multistep avalanche chamber with effective detection area of 9 by 9 cm². Argon-acetone mixture gas is provided by a simple gas mixing system, and mixture ratio can be modulated by gas flow. The performance of the chamber has been investigated by use of ⁵⁵Fe 5.9 keV X-ray source at acetone concentration in argon of 2.7％, and the effect of acetone concentration to the chamber has been measured.     

Defect generation in polycrystalline Cu(In,Ga)Se2 by high-energy electron irradiation

We investigate the degradation of ZnO/CdS/ Cu(In,Ga)Se₂ heterojunction solar cells for space applications and the defect generation in polycrystalline Cu(In,Ga)Se₂ thin films by irradiation with 1-MeV electrons with fluences J_e up to J_e=5᎒¹⁸ cm^-2. Notable degradation of the solar cell performance starts at fluences of J_e=10¹⁷ cm^-2 where the open circuit voltage decreases by about 5% while short circuit current and fill factor remain essentially unaffected. Thus, Cu(In,Ga)Se₂ solar cells withstand electron fluences which are higher by one order of magnitude or more when compared to other technologies. A model describes the absolute open circuit voltage loss considering the increase of space charge recombination by electron irradiation-induced defects. Defect analysis by admittance spectroscopy shows that acceptor defects with an energy distance of approximately 300 meV from the valence band are generated at a rate %=0.017 (ǂ.01) cm^-1.     

High-Speed and Large-Scale Electromagnetically Actuated Resonant MEMS Optical Scanner

A high speed electromagnetically actuated resonant micro-electromechanical systems (MEMS) optical scanner with large mirror area of 6×4mm² has beendeveloped. The MEMS optical scanner chip is fabricated using bulk silicon micromachining process and electroplating technique, and can generate the maximum optical deflection angle of ±6.8°circ at the 2.95kHz resonant frequency with a quality factor of 197 in air under the low power consumption of 50mW, when it is immersed in a constant 510.2mT magnetic field parallel to the coil plane. In addition, the surface roughness of less than 20nm for scanning mirror has been measured and the optical reflectivity of mirror atwavelength of 1550nm is high up to 85%. The results show that the device can satisfy the demands of mm-sized scanning systems in optical communications.     

Red organic light-emitting devices with dotted-line doped emitting layers

High efficiency red organic light-emitting devices (OLEDs) with several dotted-line doped layers (DLDLs) were fabricated by using an ultra-high vacuum organic molecular-beam deposition system. The red OLEDs consisted of indium-tin-oxide (ITO)/N, N′-diphenyl-N, N′-bis(1-naphthyl)-(1, 1′-biphenyl)-4, 4′-diamine (α-NPD): 40 nm/tris(8-hydroxyquinoline)aluminum (Alq₃)+4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetra-methyljuloldyl-9-enyl)-4H-pyran (DCJTB); 3%wt.: x nm/(Alq₃+DCJTB; 3%wt./ Alq₃)_n−1: (30−x) nm/ Alq₃: 30 nm/Mg:Ag with n of 2, 4, 6, or 8, and x=30/(2n−1). The luminance yield of the device with 8 DLDLs was 75% higher than that of the device with a common doped layer. This was attributed to more formation of the excitons formed in a wider region resulting from the existence of the DLDLs. The dominant mechanisms of the dopant emission for the devices with DLDLs were described on the basis of the sequential carrier trapping process.