Temperature-dependent hole transport for pentacene thin-film transistors with a SiO2 gate dielectric modified by (NH4)2Sx treatment

The effect of a SiO₂ gate dielectric modified by (NH₄)₂S_x treatment on the temperature-dependent hole transport behavior for pentacene-based organic thin-film transistors (OTFTs) is studied. (NH₄)₂S_x treatment leads to the formation of SSi bonds (i.e., the formation of a sulfurated layer) on the SiO₂ surface that serves to reduce the SiO₂ capacitance, increasing the value of the hole mobility in OTFTs. The temperature-dependent hole transport is dominated by the multiple trapping model. It is shown that (NH₄)₂S_x treatment leads to a reduction in the activation energy, resulting from the formation of a sulfurated layer at the pentacene/SiO₂ interface that serves to suppress the pentacene-SiO₂ interaction. (NH₄)₂S_x treatment provides an opportunity to realize the stable and reliable carrier conduction behavior for OTFTs.     

On the correlation of postannealing induced phase transition in pentacene with carrier transport

Postannealing effects on pentacene thin film transistors (TFTs) are discussed correlating the pentacene film morphology, the crystalline polymorph, and the electronic transport. The bulk phase thermally induced in pentacene during postannealing treatment is found to be another main cause detrimental to the carrier transport of TFTs. In addition, it turns out that encapsulation of the TFTs using polyvinyl alcohol helps to improve the thermal stability by retarding the onset of the bulk phase in pentacene.     

Structural phase transition in pentacene caused by molecular doping and its effect on charge carrier mobility

The structural properties and charge carrier mobility of pentacene doped by 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and 2,2-(perfluoronaphthalene-2,6-diylidene) dimalononitrile (F6-TCNNQ) are studied by X-ray diffraction, scanning electron microscopy, field effect transistor measurements, and space charge limited currents (SCLC). We observe the presence of polycrystalline and amorphous domains within the doped pentacene film grown under co-deposition conditions. The appearance of the amorphous phase is induced by the molecular dopants F4-TCNQ and F6-TCNNQ. A strong drop of crystallite size is obtained at a doping concentration of around 7 and 4 wt.%, respectively. The loss of the polycrystalline structure is correlated to a strong decrease of the charge carrier mobility in pentacene in horizontal and vertical film structures. We discuss typical scenarios of charge transport for polycrystalline and amorphous thin films in order to explain the observed loss of mobility originated by the doping induced structural phase transition. In this way an optimum doping concentration for highest conductivity with acceptable mobility is determined which can help to improve the performance of organic solar cells and organic high-frequency rectification diodes.     

Growth of CdGeAs2 single crystals by the chemical vapor transport method

We have grown CdGeAs₂ single crystals by chemical vapor transport (CVT), a method not previously applied for this compound. The crystallographic data of this chalcopyrite (cell parametersa ₀ = 5.9456 ± 0.0001Å, c₀ = 11.2131 ± 0.0007Å) and its electrical transport properties are reported. Predominantly n-type crystals are obtained (at RTn = 1 · 10¹⁷cm?3, μⁿ = 2000 cm²(Vs)^?1). Vacuum heat treatment at 500° C yields a type conversion fromn- to p-type. In all p-type samples the minority carrier mobility is calculated to be larger than 10000 cm²(Vs)^?1.     

Conductivity modulation enhanced lateral IGBT with SiO2 shielded layer anode by SIMOX technology on SOI substrate

New Lateral IGBT with SiO2 shielded layer anode on SOI substrate is proposed and discussed. Compared to the conventional LIGBT, the proposed device offers a conductivity modulation enhanced effect due to the SiO2 shielded layer anode structure which can be formed by SIMOX technology. Simulation results show that, for the proposed LIGBT, during conducting state, the electron-hole plasma concentrations in n-drift region are several times larger than that of conventional LIGBT; the conducting current is up to 37% larger than that of conventional one. The SiO2 shielded layer anode conductivity modulation enhanced effect do not sacrifice other characteristics of device, such as breakdown and switching, but is compatible to other optimized technologies.     

Conductivity modulation enhanced lateral IGBT with SiO2 shielded layer anode by SIMOX technology on SOI substrate

A new lateral insulated-gate bipolar transistor (LIGBT) with a SiO2 shielded layer anode on SOI substrate is proposed and discussed.Compared to the conventional LIGBT,the proposed device offers an enhanced conductivity modulation effect due to the SiO2 shielded layer anode structure which can be formed by SIMOX technology.Simulation results show that,for the proposed LIGBT,during the conducting state,the electron-hole plasma concentrations in the n-drift region are several times larger than those of the conventional LIGBT; the conducting current is up to 37% larger than that of the conventional one.The enhanced conductivity modulation effect by SiO2 shielded layer anode does not sacrifice other characteristics of the device,such as breakdown and switching,but is compatible with other optimized technologies.     

Photoluminescence of CdTe crystals grown by physical-vapor transport

High-quality CdTe crystals with resistivities higher than 10⁸ Ω cm were grown by the physical-vapor transport (PVT) technique. Indium, aluminum, and the transition-metal scandium were introduced at the nominal level of about 6 ppm to the source material. Low-temperature photoluminescence (PL) has been employed to identify the origins of PL emissions of the crystals. The emission peaks at 1.584 eV and 1.581 eV were found only in the In-doped crystal. The result suggests that the luminescence line at 1.584 eV is associated with Cd-vacancy/In complex. The intensity of the broadband centered at 1.43 eV decreases strongly with introduction of Sc.     

The study of lateral carrier transport in structures with InGaN quantum dots in the active region

GaN-based structures with InGaN quantum dots in the active region, which emit in the blue and green spectral ranges, are studied. The structures grown by both the conventional method and with the use of special procedures of the growth of the active region were compared. The use of these special growth modes stimulates the activated phase decomposition, which leads to the formation of quantum dots with substantially larger localization depth of electrons. It is shown that the formation of such deep quantum dots, like the formation of larger inhomogeneities of the active region, substantially suppresses the lateral carrier transport. This effect improves the characteristics of light-emitting diode structures at a low injection level and increases the temperature stability of quantum efficiency.     

横向剪切原理在投影栅去基频中的应用

基于投影栅的3维面形测量中,包裹相位的提取过程中不可避免地会引入载频分量。为了准确地还原受物体3维形貌所调制的真实相位,必须要消除载频相位,采用剪切原理消除投影栅中的载频,首先通过对光场作剪切转化为相位梯度分布的新光场,再联合最小二乘解包裹算法进行相位展开,并与现有的方法进行了对比。结果表明,该方法能够有效地消除载频,减小重建误差,且其算法简单,可使重构相位值更接近待测的真实相位值。该方法在投影栅去载频的研究中是可行和有效的。     

载波调制法提高保偏光纤偏振耦合检测的信噪比

保偏光纤偏振耦合系统能有效检测保偏光纤中偏振耦合点的空间位置及耦合强度,因而可被广泛地应用于应力、应变、温度和位置的分布式传感中。由于噪声影响,测试系统中的信噪比和耦合强度检测灵敏度会下降。为了改善系统信噪比,提高保偏光纤中弱耦合点的检测能力,将铌酸锂外调制技术应用于白光干涉保偏光纤耦合测试系统。调制后的信号经光电探测器接收,用数字解调算法进行数据处理。实验结果表明:在电机扫描速度为0.75 mm/s,调制频率为9.1 kHz,采样率为140 kHz时,载波调制时信噪比提高了8 dB,解调耗时仅1.12 s。     

Nanoparticle ordering by dewetting of Co on SiO2

Most metals on SiO₂ have a finite contact angle and are therefore subject to dewetting during thermal processing. The resulting dewetting morphology is determined primarily by nucleation and growth or instabilities. The dewetting mechanism implies a disordered spatial arrangement for homogeneous nucleation, but an ordered one for instabilities such as spinodal decomposition. Here, we show that the morphology of laser-melted ultrathin Co film (4-nm thick) can be attributed to dewetting via an instability. Dewetting leads to breakup of the continuous Co film into nanoparticles with a monomodal size distribution with an average particle diameter of 75 nm±23 nm. These nanoparticles have short-range order (SRO) of 130 nm in their separation. This result has important implications for nanomanufacturing with a robust spacing or size selection of nanoparticles in addition to spatial ordering.     

Growth of CdS crystals by the physical vapor transport method

Based on the physical vapor transport (PVT) method, the growth of large-size CdS crystals inside a vertical semi-closed tube is studied. Firstly, in order to ensure 1D diffusion-advection transport, multi-thin tubes are used in the growth tube. The XRD spectra of the CdS crystal grown in this configuration indicates that the crystal quality has clearly been improved, where the FWHM is 58.5 arcsec. Secondly, theoretical and experimental growth rates under different total pressures are compared; the results show that the experiential growth rate equation is valid for our semi-tube growth, and it could be used to estimate the growth rate and maximum growth time under different total pressures.     

PVT法CdS单晶生长

Based on the physical vapor transport （PVT） method, the growth of large-size CdS crystals inside a vertical semi-closed tube is studied. Firstly, in order to ensure 1D diffusion-advection transport, multi-thin tubes are used in the growth tube. The XRD spectra of the CdS crystal grown in this configuration indicates that the crystal quality has clearly been improved, where the FWHM is 58.5 arcsec. Secondly, theoretical and experimental growth rates under different total pressures are compared; the results show that the experiential growth rate equation is valid for our semi-tube growth, and it could be used to estimate the growth rate and maximum growth time under different total pressures.     

链式氧化制备SiO2膜的研究

研究了应用链式扩散设备对经过制绒、清洗、扩散和刻蚀处理后的单晶P型硅片进行热氧化SiO2膜的生长。采用准稳态光电导衰减法(QSSPC)在室温条件下对氧化前后硅片的少子寿命进行测试,探讨了氧化工艺条件对少子寿命、SiO2薄膜质量的影响机理,并对氧化工艺进行了优化。实验结果表明:在氧气流量为20L/min,带速为13i/m,氧化工艺区阶梯式温度设置为600、800、800、800、800、800、850和900℃时,链式氧化后硅片少子寿命达到42.5μs,SiO2膜的厚度适合,结构致密;在不影响减反效果的情况下,获得了良好的钝化效果。     

Surface enhancement of CdSe by SiO2

The effect of SiO2 on the surface of thin-film CdSe (both vacuum deposited) is reported. An enhancement of the semiconductor-film conductance was observed which was dependent on the SiO2-film thickness.     

Effects of hydrogen on majority carrier transport and minority carrier lifetimes in long-wavelength infrared HgCdTe on Si

We present extended results on the use of a hydrogen plasma to passivate the effects of defects in long-wave ir HgCdTe/Si. Annealed and as-grown epilayers, in situ doped with indium, were exposed to a hydrogen plasma generated in an electron cyclotron resonance (ECR) reactor. Secondary ion mass spectrometry was used to measure the extent of hydrogen incorporation into the epilayers. Hall and photoconductive lifetime measurements were used to assess the efficacy of passivation. The passivation of defects responsible for the scattering and recombination of electrical carriers was observed for most ECR conditions over a range of dislocation densities.     

A novel 4H-SiC MESFET by lateral insulator region to improve the DC and RF characteristics

In this paper, a novel recessed gate metal–semiconductor field-effect transistor (RG-MESFET) is presented by modifying the depletion region and the electric field. The proposed structure improves the breakdown voltage, drain current and high frequency characteristics by embedding a lateral insulator region between drain and gate while is placed laterally into the metal gate and a silicon well exactly under the insulator region. We called this new structure as modified recess gate MESFET (MRG-MESFET). The radio frequency and direct current (DC) characteristics of the proposed structure is studied using numerical simulations and compared with a conventional MESFET (C-MESFET). The breakdown voltage, drain current DC transconductance and maximum power density of the proposed structure increase by 27%, 16.5%, 15% and 48%, respectively, relative to the C-MESFET. Also, the gate-source capacitance and the minimum noise figure of the proposed structure improve relative to the C-MESFET. The proposed structure can be used for high breakdown voltage, high saturation drain current, high DC transconductance, high power, high frequency, and low noise applications.     

TD-SCDMA系统中的一种接纳控制策略

研究了TD-SCDMA系统中的接纳控制策略,并提出了一种基于路径损耗辅助的接纳算法.该算法通过测忖量路径损耗,在不同时隙内对用户进行资源分配,可以有效平衡时隙间负载,消除远近效应,保持系统稳定.仿真结果表明,该算法能够有效改善系统性能.     

Nonlinear PID control to improve the control performance of 2 axes pneumatic artificial muscle manipulator using neural network

The application of a robot to rehabilitation has become a matter of great concern because of the requirement of functional recovery therapy of arm or limb. A novel pneumatic artificial muscle (PAM) actuator which has achieved increased popularity to provide the inherent safety and mobility assistance to humans performing tasks and another advantages such as high strength and power/weight ratio, low cost, compactness, ease of maintenance, cleanliness, readily available and cheap power source and so on. However, the complex nonlinear dynamics of the PAM manipulator makes it a challenging and appealing system for modeling and control design. The problems with the time variance, compliance, high hysteresis and nonlinearity of pneumatic systems have made it difficult to realize precise position control. In order to realize satisfactory control performance, the effect of nonlinear factors contained in the PAM manipulator must be considered.The purpose of this study is to improve the control performance of 2 axes PAM manipulator using a nonlinear PID controller. Superb mixture of conventional PID controller and the neural network, which has powerful capability of learning, adaptation and tackling nonlinearity, brings us a novel nonlinear PID controller using neural network. This proposed controller is appropriate for a kind of plants with nonlinearity uncertainties and disturbances. The experiments were carried out in practical 2 axes PAM manipulator and the effectiveness of the proposed control algorithm was demonstrated through the experiments, which suggests its superior performance and disturbance rejection.