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.     

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.     

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.     

Performance of Organic Field Effect Transistors with Self-Improved Cu/Organic Interfaces

We fabricate pentacene-based organic field effect transistors （OFETs） with Cu as source and drain （S-D） electrodes. The fabricated devices stored for ten hours under ambient atmospheric conditions exhibit superior performance compared with the as-prepared devices. The field-effect mobility increases from 0. 012 to 0.03 cm^2 V^-1 s^-1, and the threshold voltage downshifts from -14 to -9 V. The on/off current ratios are close to the order of 10^4. The improved performance of the stored devices is attributed to the formation of thin Cu oxide at the Cu electrodes/organic interfaces. These results suggest a simple and available way to optimize device properties and to reduce fabrication cost for OFETs.     

Improved Performance of Organic Thin Film Transistor with an Inorganic Oxide/Polymer Double-Layer Insulator

We employ the Ta2Os/PVP （poly-4-vinylphenol） double-layer gate insulator to improve the performance of pentacene thin-film transistors. It is found that the double-layer insulator has low leakage current, smooth surface and considerably high capacitance. Compared to Ta205 insulator layers, the device with the Ta2Os/PVP doublelayer insulator exhibits an enhancement of the field-effect mobility from 0.21 to 0.54 cm2/Vs, and the decreasing threshold voltage from 4.38 V to -2.5 V. The results suggest that the Ta2Os/PVP double-layer insulator is a potential gate insulator for fabricating OTFTs with good electrical performance.     

A Charge-Trap Memory Device with a Composition-Modulated Zr-Silicate High-k Dielectric Multilayer Structure

We report a novel charge-trap memory device with a composition-modulated Zr-silicate high-k dielectric mul- tilayer structure prepared by using the pulsed laser deposition technique. The device employs amorphous （ZrO2）0.5（SiO2）0.5 as the tunneling and blocking oxide layers, and ZrO2 nanocrystals as the trapping storage layer. Zr02 nanocrystals are precipitated from the phase separation of （ZrO2）0.5（SiO2）0.2 films annealed at 800℃, and isolated from each other within the amorphous （ZrO2）0.5（SiO2）0.5 matrix. Our charge trapping device shows a memory window of 2.6 V and a stored electron density of 1×10^13/cm2.     

Photovoltaic and Electroluminescence Bifunctional Devices with Starburst Amine and Rare-Earth-Complexes

We fabricate the organic photovoltaic （PV） devices, in which 4,4＇,4＂-tris-（2-methylphenylphenylamino）triphenylamine （m-MTDATA） and rare earth （RE） （dibenzoylmethanato）a（bathohenanthroline） （RE（DBM）abath） （RE = Nd or Pr） are used as electron donor and acceptor, and investigate their PV properties. The PV diode fabricated in the optimum processing conditions shows the open-circuit voltage of 1.91 V, short-circuit current of 0.1 mA/cm^2, fill factor of 0.38, and the overall power conversion efficiency of 1.9% when it is irradiated under UV light （4 m W/cm^2）. The photocurrent density exhibits an increase of 20% at least when a very thin LiF layer is inserted between the RE-complexes and the A1 cathode. A strong electroluminescence from the interface is also observed and the maximum luminance of a yellow emission resulted from the exciplex is 580 cd/m^2 at 17 V bias.     

Characteristics of a Cataphoresis He-Ca+ Recombination Laser

A cataphoretic input of calcium vapour into the active volume of pulsed He-Ca^＋ laser is designed and made. The recombination laser at 373.3 nm and the R-M transition laser at 854.6 nm are achieved experimentally with modified Blumlein circuit by high-frequency longitudinal pulsed discharge. The dependences of work parameters such as the pulse frequency, the power supply voltage and the helium pressure on laser output characteristics at 373.3nm line are measured and discussed. The maximum laser output power of 136mW and the specific power of 5.9 m W/cm^3 are obtained, respectively.     

Electrical and microscopic characterization of ZnO films on p-SiC substrates

ZnO/p- SiC heterojunctions were fabricated by thermal evaporation from ZnO high quality powder (99.99%) onto 4H and 6H p-SiC polytypes. We find that, despite the low cost technique employed for the deposition of the ZnO film, the devices exhibited breakdown voltages in excess of 100 V, high rectification ratio (forward to reverse current ratio, I_F/I_R) and low leakage current, respectively, 2×10⁵ and 4.5×10⁻⁷ A/cm² (for the 4H p-SiC based device) and 5×10⁴ and 5×10⁻⁷ A/cm² (for the 6H p-SiC based device). The current-voltage (I×V) characteristics were also measured at the nanometer scale by means of conductive atomic force microscopy. A simple Schottky diode model and conductance divided by current versus conductance plots (G/I×G plots) was used to analyze device characteristics. This analysis shows that, when probing at the nanometric scale, fluctuations of the effective barrier height and/or surface states across individual grains or grain boundaries cause deviations from linear G/I×G plots. These fluctuations are smeared out when probing at the macroscale and thus it becomes possible to obtain linear plots and extract diode parameters.     

High-Density Stacked Ru Nanocrystals for Nonvolatile Memory Application

Stacked ruthenium （Ru） nanocrystals （NCs） are formed by rapid thermal annealing for the whole gate stacks and embedded in memory structure, which is compatible with conventional CMOS technology. Ru NCs with high density （3 × 10^12 cm-2）, small size （2 4nm） and good uniformity both in aerial distribution and morphology are formed. Attributed to the higher surface trap density, a memory window of 5.2 V is obtained with stacked Ru NCs in comparison to that of 3.5 V with single-layer samples. The stacked Ru NCs device also exhibits much better retention performance because of Coulomb blockade and vertical uniformity between stacked Ru NCs.     

Effects of Proton Irradiation on a CMOS Image Sensor

We perform 9 MeV proton irradiation of a complementary metal oxide semiconductor （CMOS） image sensor at doses from 1 × 10^9 to 4 × 10^10 cm^-2. In general, the average brightness of dark output images increases with an increasing dose, and reaches the maximum at 1 × 10^10 cm^-2. The captured colour images become very blurry at 4 × 10^10 cm^-2. These can be explained by change of concentrations of irradiation-induced electron-hole pairs and vacancies in the various layers of CMOS image sensor calculated by the TRIM simulation programme with dose.     

Three-Step Growth Optimization of AlN Epilayers by MOCVD

A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low temperature （LT） A1N nucleation layer （NL）, and two high temperature （HT） A1N layers with different V/Ⅲ ratios. Our results reveal that the optimal NL temperature is 840-880℃, and there exists a proper growth switching from low to high V/Ⅲ ratio for further reducing threading dislocations （TDs）. The screw-type TD density of the optimized AIN film is just 7.86×10^6 cm^-2, about three orders lower than its edge-type one of 2×10^9 cm^-2 estimated by high-resolution x-ray diffraction （HRXRD） and cross-sectional transmission electron microscopy （TEM）.     

Enhanced Green Electrophosphorescence from Oxadiazole-Functionalized Iridium Complex-Doped Devices Using Poly（9,9-Dioctylfluorene） Instead of Poly（N-Vinylcarbazole） as a Host Matrix

Optoelectronic properties of the oxadiazole-functionalized iridium complex-doped polymer light-emitting devices （PLEDs） are demonstrated with two different polymeric host matrices at the dopant concentrations 1-8%. The devices using a blend of poly（9,9-dioctylttuorene）（PFO） and 2-（4-biphenyl）-5-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as a host matrix exhibited a maximum luminance efficiency of 11.3 cd/A at 17. 6 mA/cm^2. In contrast, the devices using a blend of poly（N-vinylcarbazole） （PVK） and PBD as a host matrix reveal only a peak luminance efficiency of 6.Scd/A at 4.1 mA/cm^2. The significantly enhanced electrophosphorescent emissions are observed in the devices with the PFO-PBD blend as a host matrix. This indicates that choice of polymers in the host matrices is crucial to achieve highly efficient phosphorescent dye-doped PLEDs.     

Demonstration of Mo Soft X-Ray Lasers with a Grazing Incidence Pumping Scheme in the XL-II Facility

A Ni-like Mo soft x-ray laser （SXRLs） operating at 18.9nm has been demonstrated by employing a grazing incidence pumping scheme with 120m^3 in the 200ps pre-pulse and 140mJ in the 200fs main pulse. The SXRL gain is estimated to be 1.5-3cm^-1 when a grazing incidence angle of 14° is applied. Numerical simulations are also performed to investigate the dynamics of the ion distribution. It is found that a high intensity at 2.4× 10^14 W/cm^2 of the 200fs main pulse could heat the pre-plasma rapidly to an appropriate temperature for population inversion, and could compensate for the shortage of the total pump energy to a certain extent.     

Terahertz Quantum Cascade Laser at 3.39THz

We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region, From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced cascade period thickness is consistent with the result of x-ray diffraction. The test device is lasing at 3.39THz and operating up to lOOK in pulsed mode. At IOK, the maximum output power is greater than 1 mW with a threshold current density of 738 A/cm^2.     

Hydrogen Sensors Based on AlGaN/AlN/GaN Schottky Diodes

Pt/AlGaN/AlN/GaN Schottky diodes are fabricated and characterized for hydrogen sensing. The Pt Schottky contact and the Ti/Al/Ni/Au ohmic contact are formed by evaporation. Both the forward and reverse currents of the device increase greatly when exposed to hydrogen gas. A shift of 0.3 V at 300 K is obtained at a fixed forward current after switching from N2 to 10%H2＋N2. The sensor responses under different concentrations from 50ppm H2 to 10%H2＋N2 at 373K are investigated. Time dependences of the device forward current at 0.5 V forward bias in N2 and air atmosphere at 300 and 373K are compared. Oxygen in air azcelerates the desorption of the hydrogen and the recovery of the sensor. Finally, the decrease of the Schottky barrier height and sensitivity Of the sensor are calculated.     

Photoinduced Birefringence and Broadband All-Optical Photonic Switch in a Bacteriorhodopsin/Polymer Composite Film

Photoinduced birefringence with large optical nonlinearity in a bacteriorhodopsin/polymer composite film is observed. A high refractive index change of 8.5×10^-5 photoinduced by 476nm pumping beam is reached at the low intensity of 6.5mW/cm². Based on it, a broadband all-optical photonicswitch is realized with an optical controlling switch system. Because of controlling beam's selectivity in switching, the transporting beams of different wavelengths with different intensities and shapes can be modulated by adjusting the wavelength and intensity of the controlling beam.     

Atomic Diffusion in Cu/Si （111） and Cu/SiO2/Si （111） Systems by Neutral Cluster Beam Deposition

The Cu films are deposited on two kinds of p-type Si （111） substrates by ionized duster beam （ICB） technique. The interface reaction and atomic diffusion of Cu/Si （111） and Cu/SiO2/Si （111） systems are studied at different annealing temperatures by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results are obtained： For the Cu/Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs when annealed at 230℃. The diffusion coefficients of the samples annealed at 230℃ and 500℃ are 8.5 ×10^-15 cm^2.s^-1 and 3.0 ×10^-14 cm^2.s^-1, respectively. The formation of the copper-silicide phase is observed by XRD, and its intensity becomes stronger with the increase of annealing temperature. For the Cu/SiO2//Si （111） samples prepared by neutral dusters, the interdiffusion of Cu and Si atoms occurs and copper silicides are formed when annealed at 450℃. The diffusion coefficients of Cu in Si are calculated to be 6.0 ×10^-16 cm^2.s^-1 at 450℃, due to the fact that the existence of the SiO2 layer suppresses the interdiffusion of Cu and Si.     

压力对GdoBr:Eu晶场参数的影响

 在室温下测量了GdoBr:Eu的常压和高压荧光谱，光谱范围在13 000~21 500 cm^-1之间，压力至12 GPa。由光谱数据得到了Eu³⁺晶场能级随压力的变化曲线。⁷F_0～5能级随压力的变化规律比较复杂，而⁵D_0~2各能均随压力的升高几乎线性地降低。在基态谱项⁷F的49个状态上进行了晶场拟合计算，所得常压下的5个非零晶场参数分别为：B₀²＝-1 124.0 cm^-1，B₀⁴＝-969.6 cm^-1，B₄⁴＝827.9 cm^-1，B₀⁶＝889.6 cm^-1，B₄⁶＝377.0 cm^-1。高压下的计算结果表明，B₀⁴、B₀⁶这两个晶场参数随压力的增加而增大，B₄⁶随压力的增加而减小，而B₀²、B₄⁴随压力的变化有些起伏。晶场强度在8 GPa以下随压力增加而减小，其后开始变强。     

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.