A Current Estimation Method for Bias-Temperature Stress of a-Si TFT Device

We have studied the time-dependence degradation of ON current of amorphous silicon thin-film transistors (a-Si:H TFTs), which is a function of stress duration, stress temperature, and stress bias. A simple method with stretched-exponential equation and current-voltage function is used to characterize and predict the TFT performance. Bias-temperature stress at different stress voltages has been performed on a-Si:H TFTs. A new method using ON current degradation to analyze TFT device performance is presented, which is different from the conventional threshold-voltage shift method. We have also observed that the beta value in the ON current degradation method compared to the threshold-voltage shift method, with a stretched-exponential stress time, is related to beta~beta₀-T_ST/T₀. Finally, we have also used the new equation to evaluate the performance of the gate-driver-on-array circuit in our products. If the limitation of the current for the pull-down device is 1times10^-6 A, then the operation time of the pull-down device can be estimated to about 1219 h when key pulled-down TFT is operating at 60degC.     

100 dpi 4-a-Si:H TFTs active-matrix organic polymer light-emitting display

In this paper, we report on 100 dpi four hydrogenated amorphous silicon thin-film transistors (4-a-Si:H TFTs) active-matrix organic polymer light-emitting display (AM-PLED). For this display, we have established the operational limitation of our 4-a-Si:H TFTs pixel electrode circuit by performing a load line analysis. Combining this result with the extracted pixel organic polymer light-emitting device (PLED) characteristics, we have found that the change of the AM-PLED pixel operating point, especially of a driving TFT, limits the operational range of AM-PLED pixel. The predicted results are compared with the measured data of 100 dpi monochromatic red light-emitting 4-a-Si:H TFTs AM-PLED. For our AM-PLED, we obtained luminance up to /spl sim/20 cd/m/sup 2/ and Commission Internationale de l'Eclairage color coordinates of (0.67, 0.33), which are calculated from the measured AM-PLED electroluminescence spectrum.     

Amorphous silicon back-plane electronics for OLED displays

This paper reviews design considerations along with measurement results pertinent to amorphous silicon (a-Si:H) thin-film transistor (TFT) drive circuits for active matrix organic light-emitting diode displays, and follows from work presented earlier (A. Nathan et al., 2002), (A. Nathan et al., 2003). We describe both pixel architectures and TFT circuit topologies that are amenable for vertically integrated, high aperture ratio pixels. Here, the organic light-emitting diode layer is integrated directly above the TFT circuit layer to provide an active pixel area that is at least 90% of the total pixel area with an aperture ratio that remains virtually independent of scaling. Both voltage-programmed and current-programmed drive circuits are considered. The latter provides compensation for shifts in device characteristics due to metastable shifts in the threshold voltage of the TFT. Integration of on-panel gate drivers is also discussed, where we present the architecture of an a-Si:H-based gate demultiplexer that is threshold voltage shift invariant. In addition, a programmable current mirror with good linearity and stability is presented. Programmable current sources are an essential requirement in the design of source driver output stages.     

Wurtzite GaN-based heterostructures by molecular beam epitaxy

Progress in plasma and reactive molecular beam epitaxy (PMBE and RMBE) grown n- and p-type GaN and GaN-AlGaN-based epitaxial films and optoelectronic devices is reviewed. The growth of GaN by RMBE (PMBE) is achieved by employing ammonia gas (plasma activated nitrogen) as the nitrogen source with resultant growth rates of about 2 μm/h (⩾1 μm/h). The structural, electrical, and optical properties of binary and ternary (Al,Ga)N and (In,Ga)N layers point to high quality. The GaN layers with Mg as the dopant atoms are p-type without any postgrowth treatment, but the hole concentrations are limited to mid 10¹⁷ cm^-3 although reports in the low 10¹⁸ cm^-3 dot the literature. The background carrier concentration, mobility, optical characteristics and ability to dope p-type depend significantly on the substrate temperature and V-III ratio employed, AlGaN-GaN, and GaN-InGaN electroluminescent devices have been realized but lack commercial quality. The AlGaN-GaN photodiodes by RMBE exhibited a maximum zero-bias responsivity of 0.12 A/W at 364 nm, which decreased by more than three orders of magnitude for wavelengths longer than 390 nm. A reverse bias of -10 V raised the responsivity to 0.15 A/W without any significant increase in noise. The noise equivalent noise power near zero bias is below the detection limit of the measurement setup. At a reverse bias of 28 V, the total noise equivalent power is 2.06×10^-11 W     

高效率非晶硅叠层太阳电池的研制

深入研究了a-Si/a-Si/a-SiGe三结叠层通讯卫星电池的制备技术.为了提高叠层电池的转换效率,提出改善n/i界面特性的缓冲层技术和高光敏性a-SiGe:H(F)薄膜的高氢气稀释比、低反应气压的淀积技术.通过工艺优化,研制出了AM1(100mW/cm~2)光照下转换效率为11.5%的a-Si/a-Si/a-SiGe三结叠层太阳电池.     

Low-loss inductors built on PECVD intrinsic amorphous silicon for RF integrated circuits

The quality factor (Q) of inductors on silicon (Si) is limited by the series resistance of the metal at low frequency and by the substrate resistivity at high frequency. Oxide is generally used to isolate the useful signal of the inductor from the lossy substrate. However, stoichiometric silica (SiO2) is processed at a high temperature, which eliminates the possibility of post-CMOS integration. By contrast, plasma enhanced chemical vapour deposition (PECVD) amorphous Si can be deposited at a low temperature and is easily integrated with most Si-based processes. Intrinsic amorphous hydrogenated silicon (i-a-Si:H) also displays low conductivity. In this work, i-a-Si:H deposited at a low temperature (250?) is used in a novel approach as the isolation material for planar inductors on Si for RF integrated circuits. An improvementof more than 50% in Q is measured when 1.5 μm i-a-Si:H film is deposited on the Si substrate prior to fabrication of the inductor. This result demonstrates the influence of i-a-Si:H film on the RF performance of an inductor. Intrinsic a-Si:H is shown to be a promising material for the isolation of RF devices on low-resistivity Si.     

Characteristics of InGaN-AlGaN multiple-quantum-well laser diodes

We demonstrate room-temperature pulsed current-injected operation of InGaAlN heterostructure laser diodes with mirrors fabricated by chemically assisted ion beam etching. The multiple-quantum-well devices were grown by organometallic vapor phase epitaxy on c-face sapphire substrates. The emission wavelengths of the gain-guided laser diodes were in the range from 419 to 432 nm. The lowest threshold current density obtained was 20 kA/cm² with maximum output powers of 50 mW. Longitudinal Fabry-Perot modes are clearly resolved in the high-resolution optical spectrum of the lasers, with a spacing consistent with the cavity length. Cavity length studies on a set of samples indicate that the distributed losses in the structure are on the order of 30-40 cm^-1     

Cleaved and etched facet nitride laser diodes

Room-temperature (RT) pulsed operation of blue (420 nm) nitride-based multiquantum-well laser diodes grown on a-plane and c-plane sapphire substrates has been demonstrated. Structures investigated include etched and cleaved facets as well as doped and undoped quantum wells. A combination of atmospheric and low-pressure metal organic chemical vapor deposition using a modified two-flow horizontal reactor was employed. Threshold current densities as low as 12.6 kA/cm² were observed for 10×1200 μm lasers with uncoated reactive ion etched facets on c-plane sapphire. Cleaved facet lasers were also demonstrated with similar performance on a-plane sapphire. Laser diodes tested under pulsed conditions operated up to 6 h at RT. Lasing was achieved up to 95°C and up to a 150-ns pulselength (RT). Threshold current increased with temperature with a characteristic temperature T₀ of 114 K     

Static and dynamic analysis of organic and hybrid inverter circuits

This paper explores the possibility of organic-inorganic inverter circuits starting with independent designs of organic thin film transistors. Simulated I–V characteristics of all p/n devices are compared with experimental results that yield an average error of 0.8 % and 4.3 % for threshold voltage and mobility, respectively. Furthermore, static and dynamic responses of different inverters are compared, using CuPc–F₁₆CuPc, pentacene–C₆₀, pentacene–ZnO, pentacene–a-Si:H and pentacene–pentacene as driver and load combinations to address the effect of various materials and configurations. Analytical results for switching threshold and propagation delay have also been provided to validate the circuit simulation. Observations illustrate good balancing between pull up and pull down operation of pentacene with C₆₀, a-Si:H and ZnO due to the comparable mobility of p and n-type transistors. Moreover, pentacene–C₆₀ and all p-organic inverters demonstrate 38 % and 45 % reduction in propagation delay, respectively, even at smaller W/L ratios, as compared to CuPc–F₁₆CuPc combination, due to lower mobilities of CuPc and F₁₆CuPc devices. Although, pentacene–ZnO hybrid combination shows almost 35 % higher propagation delay as compared to a-Si:H, but still it is preferable due to several advantages related to fabrication, such as low process temperature.     

$hbox{CO}_{bf 2}$ Reforming of Aliphatic Hydrocarbons With Silent Discharge Plasma

CO₂ reforming of methane ( CH₄) and propane (C₃H₈) was performed with a silent discharge reactor (SDR). The reactor performance was evaluated in terms of energy efficiencies for the conversion of the substrates and formation of H₂ and CO. The reactivity of C₃H₈ was 2- to 3-fold higher than that of CH₄, and both of CH₄ and C₃H₈ were reformed in the order of 10¹⁶ molecules/J at 298 K. The energy efficiencies for the conversion of these substrates increased with their initial concentrations, but decreased with an increase in reactor energy density. On the other hand, the energy efficiencies for the conversion of CO₂, which were not affected by the hydrocarbon types, were lower than those for the hydrocarbon substrates. A positive temperature effect was observed in the conversion of the hydrocarbon substrates only at low reactor energy densities from 298 to 433 K.     

燃煤电站烟气中汞脱除与减排技术

对现有环保设施的脱汞效果进行评价,简介燃烧前脱汞处理方法、烟气脱汞方法和涉及脱汞的多污染物脱除技术。已有的测试数据表明,SCR系统可将烟气中的元素态汞氧化为氧化态汞,使下游设备的脱汞能力提高;静电除尘器和布袋除尘器均能捕集烟气中的颗粒态汞和氧化态汞,后者效果更好;飞灰中的碳含量对除尘器脱汞效率有很大影响,碳含量越高,除尘器脱汞效率越高;现有的湿法烟气脱硫系统能够捕集烟气中的氧化态汞,但也能将氧化态汞还原成元素态汞。采用燃煤中添加溴化物的方法可以有效提高烟气中氧化态汞的比率,因此可提升现有设施的脱汞效率;多污染物控制技术能够实现SO_x、NO_x和汞等多污染物的联合脱除,将具有广阔的发展前景。     

Low-Threshold Stimulated Emission in ZnO Thin Films Grown by Atomic Layer Deposition

In this study, high-quality ZnO thin films were grown on sapphire substrates by atomic layer deposition (ALD), followed by high-temperature postdeposition annealing. A thin Al₂O₃ layer was subsequently deposited by ALD on the ZnO surface to reduce detrimental surface states. Photoluminescence measurements conducted in a backscattering configuration at room temperature show that the ZnO film exhibited stimulated emission with a low threshold intensity of 35.1 kW/ cm². This may be attributed to the high-quality ZnO film and Al₂O₃ surface passivation layer grown by ALD, as well as the Al doping effect caused by the thermal diffusion of Al from the sapphire into the ZnO. Results show that ZnO films grown by the ALD technique are applicable to next-generation short-wavelength photonic devices.     

Ultrafast response of As-implanted GaAs photoconductors

The photoconductive response of an optoelectronic switch fabricated from GaAs implanted with arsenic ions is measured to have a duration as short as 0.7 ps and a relaxation time as fast as 0.5 ps. The switching efficiency and relaxation time of the photoswitches using the As-implanted GaAs substrates are determined to be comparable to photoconductive devices employing GaAs grown by low-temperature molecular-beam epitaxy (LT-GaAs). For high dc-bias values, persistent photocurrent tails from transient leakage currents are found to be very prominent in bulk GaAs devices that were implanted with 10¹⁶ cm^-2 arsenic ions at 200 keV. This behavior has been determined to arise from substrate leakage current underneath the thin implanted layer, which recrystallizes and exhibits, as does LT-GaAs, arsenic-precipitate formation after annealing. In order to reduce this leakage current, multiple ion dosages with various implantation energies have been implemented. An epitaxial GaAs layer has also been implanted with arsenic ions, isolated from its semi-insulating substrate, and bonded onto a fused silica wafer in order to verify that the persistent tail response from the photoconductive switches was not actually due to the implanted region of the GaAs     

Analysis of 6-nm AlGaAs SQW low-confinement laser structures forvery high-power operation

This paper reports experimental results on single quantum-well separate confinement heterostructures (SQW SCH) with low-confinement factor, designed for very high-power operation. The maximum power output for AR/HR coated 3-mm-long devices, measured in very short pulsed conditions (100 ns/1 kHz), from 10-μm-wide stripes was as high as 6.4 W before catastrophic optical degradation. If scaled to continuous-wave (CW) conditions, this value would be 800-1100 MW, which would mean a factor of 22.7 times more than reported for the best devices with normal design for threshold minimization. The absorption coefficient for the symmetrical structure is as low as 1.1 cm^-1, in spite of the low trapping efficiency of carriers in the quantum well (QW). The maximum differential efficiency is 40% (both faces, uncoated devices) for symmetrical structure and 33% for the asymmetrical one (all measurements in pulsed conditions). Threshold current densities were 800 A/cm² for 5-mm-long devices in the symmetrical case and 2200 A/cm² in the asymmetrical one. The effects of inefficient carrier trapping in the QW on the threshold current densities and differential efficiency are discussed     

Hydration effects in the photoassisted wet chemical etching ofgallium nitride

In this paper, we report a pH dependent study of the wet chemical etching of unintentionally doped n-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated from a 253.7-nm mercury line source, etching of GaN is found to take place in aqueous potassium hydroxide (KOH) solutions of pH values ranging from 11 to 15. The measured GaN etch rate reveals a peak value of 90 nm/min at pH=14.25 and drops rapidly on both sides of the peak position. The etch effect ceases in KOH/ethanol solutions of similar molarities. These observations are attributed to a hydration related phenomenon in which competing effects from free water molecules (H₂O)_f and hydroxyl ions (OH^-) result in a peak etch rate. Our analysis indicates the slowly falling tail of the GaN etch rate in the dilute pH regime is characterized by a (H₂O)_f dominant process while the fast variation of etch rate at pH>14 is due to a competition between (H₂O)f and OH^-. PACS numbers: 68.55.Jk, 73.50.Pz, 81.65.Cf, 81.65.Hq     

Highly efficient diode-pumped 3-μm Er3+:BaY2F8 laser

A systematic investigation on a series of monoclinic Er³⁺ :BaY₂F₈ crystals with different dopant concentrations (C_Er=5%-30%) and crystal orientations was conducted to optimize the laser performance in this new 3-μm laser medium by laser diode pumping. The highest slope efficiency of 32% near the quantum defect (35%) was obtained with a 10% doped Er³⁺:BaY₂F₈ crystal with the orientation (010) and a length of 3.5 mm. A maximum output power of 160 mW was achieved at an absorbed pump power of 550 mW at a wavelength of 970 nm     

Electrodeposited iridium oxide for neural stimulation and recordingelectrodes

Iridium oxide films formed by electrodeposition onto noniridium metal substrates are compared with activated iridium oxide films (AIROFs) as a low impedance, high charge capacity coating for neural stimulation and recording electrodes. The electrodeposited iridium oxide films (EIROFs) were deposited on Au, Pt, PtIr, and 316 LVM stainless steel substrates from a solution of IrCl₄, oxalic acid, and K ₂CO₃. A deposition protocol involving 50 potential sweeps at 50 mV/s between limits of 0.0 V and 0.55 V (versus Ag|AgCl) followed by potential pulsing between the same limits produced adherent films with a charge storage capacity of >25 mC/cm². Characterization by cyclic voltammetry and impedance spectroscopy revealed no differences in the electrochemical behavior of EIROF on non-Ir substrates and AIROF. The mechanical stability of the oxides was evaluated by ultrasonication in distilled water followed by dehydration and rehydration. Stability under charge injection was evaluated using 200 μs, 5.9 A/cm² (1.2 mC/cm²) cathodal pulses. Loss of iridium oxide charge capacity was comparable for AIROFs and the EIROFs, ranging from 1% to 8% of the capacity immediately after activation or deposition. The EIROFs were deposited and evaluated on silicon microprobe electrodes and on metallized polyimide electrodes being developed for neural recording and stimulation applications     

Selenium-based amorphous silicon flat-panel digital X-ray imager for protein crystallography

This work proposes a large-area detector for protein crystallography based on an amorphous silicon (a-Si:H) thin film transistor (TFT) pixel-array backplane and an overlying amorphous selenium (a-Se) photoconductor for direct conversion of incident X-rays into an image charge. To achieve high sensitivity, avalanche multiplication in a-Se is adopted to make the detector sensitive to each incident X-ray. The use of a-Si:H technology enables large-area imaging of protein diffraction patterns at less expense compared to existing charge coupled device (CCD) and imaging plate (IP) detectors. In addition, a theoretical analysis shows that the detector exhibits fast readout speed (readout time <1 s), high dynamic range (~10˚), high sensitivity (~1 X-ray photon), and high detective quantum efficiency (~.7), thus validating its suitability for protein crystallography.     

Emission mechanism in rubrene-doped molecular organiclight-emitting diodes: direct carrier recombination at luminescentcenters

The emission mechanism in molecularly doped organic light-emitting diodes, where the emitting layer is composed of N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as the host and 5,6,11,12-tetraphenylnaphthacene (rubrene) as the dopant, is investigated in terms of energy transfer and direct carrier recombination. Hole trapping by rubrene is identified by current versus voltage and mobility measurements in single-layered devices. Shallow traps are formed and are found to be filled by injected holes at electric field above 2×10⁵ V/cm. Electroluminescence observed in single-layered devices indicate that electrons can be injected directly into the hole transporter, TPD. In double-layered devices composed of TPD and tris-(8-hydroxyquinolinato) aluminum(III) (Alq₃), the penetration depth of electrons into undoped TPD is determined to be ⩽5 nm from the Alq₃ interface. Upon doping with rubrene, the emission zone is extended to 20 nm due to the increase in the electron penetration depth. This is attributed to the transition of the electron hopping sites from TPD to rubrene molecules. At high-rubrene concentration, electron transport occurs via hopping on the rubrene molecules. The dominant emission mechanism in rubrene-doped TPD is attributed to the electron-hole recombination at the dopant molecule. This is maximized by hole trapping and electron transport of rubrene