双层复合栅介质膜的制备及电学性能研究

介电常数分别为2.6的聚甲基丙烯酸甲酯(PMMA)及介电常数为16的偏氟乙烯-三氟乙烯共聚物(P(VDF-TrFE))两种不同的有机绝缘材料,通过溶液旋涂的方法在P型硅衬底上制备了不同结构的复合栅介质膜并测试了它们的高频C-V特性及漏电特性。实验结果表明Si-PMMA-P(VDF-TrFE)-Ag结构绝缘膜上单位面积电容达到了35nF/cm2,40V电压下漏电流随着扫描次数的增加逐渐由7.29×10-7 A/cm2降低至3.44×10-7 A/cm2。而Si-P(VDF-TrFE)-PM-MA-Ag结构栅介质膜测得的单位面积电容仅为15nF/cm2,在相同电压下的单位面积漏电流为1.93×10-8 A/cm2。在此基础上分析了电子陷阱以及电场强度对双层栅绝缘膜C-V、I-V特性的影响。     

Photodegradation of organic light-emitting devices observed in nitrogen-filled environment

Degradation of organic light-emitting devices (OLEDs) upon ultraviolet (UV) irradiation has been studied by measuring luminance-voltage (L-V) and current-voltage (I-V) characteristics of the devices in a nitrogen-filled glove-box. Photo-oxidation or reaction is no longer the main origin of the degradation for the devices protected by nitrogen. Conventional double-layer OLEDs with tris(8-hydroxyquinoline) aluminum (Alq₃) as the electron transport material and single-layer devices containing Alq₃ as the only organic material exhibit different degradation behaviors: both L-V and I-V characteristics degrade severely for the irradiated double-layer devices, whereas whether I-V degrades or not in a single-layer device is closely related to the species of the charge carriers flowing in the device. By comparing electroluminescent and photoluminescent degradation behaviors of the single-Alq₃-layer devices, we conclude that lowered fluorescent quantum efficiency and hole current after UV irradiation are two origins of the degraded characteristics of the devices isolated from the moist environment.     

Morphology and current-voltage characteristics of nanostructured pentacene thin films probed by atomic force microscopy

Atomic force microscopy was used to study the growth modes (on SiO2, MoS2, and Au substrates) and the current-voltage (I-V) characteristics of organic semiconductor pentacene. Pentacene films grow on SiO2 substrate in a layer-by-layer manner with full coverage at an average thickness of 20 A and have the highest degree of molecular ordering with large dendritic grains among the pentacene films deposited on the three different substrates. Films grown on MoS2 substrate reveal two different growth modes, snowflake-like growth and granular growth, both of which seem to compete with each other. On the other hand, films deposited on Au substrate show granular structure for thinner coverages (no crystal structure) and dendritic growth for higher coverages (crystal structure). I-V measurements were performed with a platinum tip on a pentacene film deposited on a Au substrate. The I-V curves on pentacene film reveal symmetric tunneling type character. The field dependence of the current indicates that the main transport mechanism at high field intensities is hopping (Poole-Frenkel effect). From these measurements, we have estimated a field lowering coefficient of 9.77 x 10(-6) V-1/2 m1/2 and an ideality factor of 18 for pentacene.     

脉冲偏压下电弧离子镀等离子体负载的等效电路模型及其定量表征

为了解决电弧离子镀（AIP）工艺中脉冲偏压电源与AIP等离子体负载间的匹配问题，结合脉冲偏压下AIP工艺实验，运用等离子体鞘层理论、电路理论和仿真模拟技术，得到AIP等离子体负载本质上是由鞘层引起的容性负载，在电路中可以等效为电容和电阻相并联的单元；根据AIP等离子体鞘层演化的特性，将AIP等离子体负载的等效电容表征为与时间无关而只与脉冲偏压幅度和等离子体相关参数有关的量，AIP等离子体负载的等效电阻，可以在直流偏压下通过测量与脉冲偏压幅值对应的AIP等离子体负载电流来确定。经验证，本文建立的AIP等离子体负载的等效电路模型及其定量表征是有效的。     

纳米多孔硅的电化学制备及性能研究

纳米多孔硅是一种潜在的化学和生物传感材料,本文采用电化学腐蚀法制备纳米多孔硅。采用SEM技术分析多孔硅的表面形貌,研究了腐蚀条件对多孔硅的孔隙率、厚度、I-V特性的影响。结果表明,多孔硅的孔隙率随着腐蚀电流密度和腐蚀时间的增加而呈线性增大趋势;其厚度随着腐蚀电流密度的增加而近似呈线性增大趋势,随腐蚀时间的成倍增加而显著增大;其I-V特性表现出非整流的欧姆接触。     

Electrical characterization of carbon monoxide sensitive high temperature sensor diode based on catalytic metal gate-insulator-silicon carbide structure

Field-effect gas sensors based on catalytic metal-insulator-silicon carbide (MISiC) devices are investigated. For the evaluation of the barrier height, the temperature dependence of the current-voltage (I-V) and the capacitance-voltage (C-V) characteristics of MISiC Schottky diodes were investigated in CO and O/sub 2/ atmospheres. Four methods were used to evaluate how a change in gas ambient influences the barrier height of the diode: a change of the intersection current at zero voltage in the forward direction of the I-V curve, a change of the temperature dependence in the forward direction and the reverse direction, respectively, of the I-V curve, and a change of the intersection voltage of 1/C/sup 2/ versus V plot. The four methods gave similar changes in the barrier height for the device in 8000 ppm CO and 4000 ppm O/sub 2/. The values of barrier height obtained from the I-V curves were here normalized by the ideality factor calculated from I-V measurements. The correlation between the barrier height change obtained from the I-V and the C-V measurements, respectively, is discussed regarding the ideality factor.     

Current rectification in a single silicon nanowire p-n junction

Diodes within individual silicon nanowires were fabricated by doping them during growth to produce p-n junctions. Electron beam lithography was then employed to contact p- and n-doped ends of these nanowires. The current-voltage (I-V) measurements showed diode-like characteristics with a typical threshold voltage (Vt) of about 1 V and an ideality factor (n) of about 3.6 in the quasi-neutral region. The reverse bias I-V measurement showed an exponential behavior, indicating tunneling as the current leakage mechanism.     

Josephson effects in Nb3Sn microbridges

We have studied Josephson effects in long narrow Nb3Sn microbridges at temperatures up to 17 K. These microbridges are formed by photolithographic techniques and subsequently subjected to controlled electrical discharges to modify the intrinsic Tcof the bridge region. The bridges exhibit 10 GHz micro wave steps in their I-V characteristics whose amplitudes are in excellent agreement with the Resistively Shunted Junction (RSJ) model. I-V characteristics (with and without microwaves) can be fit assuming an effective temperature approximately 15 K above the bath temperature. We have also investigated in detail structures in the I-V characteristics in the absence of microwaves. We show experimentally that phase-slip centers are induced at weak superconducting positions along the bridge when the S-N boundary of an expanding hot spot reaches within a thermal healing distance. The critical current of the phase-slip center thus formed exhibits a temperature dependence (1-T/Tc)^1/2instead of the usual mean field result (1-T/Tc)^3/2.     

五氧化二钽薄膜的I—V特性

采用直流脉冲反应磁控溅射方法制备了高介电常数五氧化二钽(Ta_2O_5)薄膜。利用Ta/Ta_2O_5/Ta的MIM电容结构分析了Ta_2O_5的电学性能,研究了上电极面积对I-V特性的影响、I-V曲线的对称性和零点偏移以及薄膜缺陷和基底粗糙度对MIM电学性能的影响。结果表明,随着上电极面积增大,电容的漏电流密度增大,击穿场强减小。氧化钽薄膜中缺陷的存在和粗糙度增大容易引起漏电流增大,击穿强度降低。当上电极直径为1mm时,MIM电容的性能最佳:击穿强度为2.22MV/cm,漏电流密度低于1×10~(-8)A/cm~2。     

Polymer-ultrathin graphite sheet-polymer composite structured flexible nonvolatile bistable organic memory devices

We present data, which were obtained before bending and after bending, for the electrical bistabilities, memory stabilities, and memory mechanisms of three-layer structured flexible bistable organic memory (BOM) devices, which were fabricated utilizing the ultrathin graphite sheets (UGS) sandwiched between insulating poly(methylmethacrylate) (PMMA) polymer layers. The UGS were formed by transferring UGS (about 30 layers) and using a simple spin-coating technique. Transmission electron microscopy (TEM) measurements were performed to investigate the microstructural properties of the PMMA/UGS/PMMA films. Current-voltage (I-V) measurements were carried out to investigate the electrical properties of the BOM devices containing the UGS embedded in the PMMA polymer. Current-time (I-t) and current-cycle measurements under flat and bent conditions were performed to investigate the memory stabilities of the BOM devices. The memory characteristics of the BOM maintained similar device efficiencies after bending and were stable during repeated bendings of the BOM devices. The mechanisms for these characteristics of the fabricated BOM are described on the basis of the I-V results.     

Field-induced interband tunneling effect transistor (FITET) with negative-differential transconductance and negative-differential conductance

The fabricated quantum-tunneling devices have a structure totally compatible with silicon-on-insulator CMOS device except for degenerate channel doping and the intentional omission of lightly doped drain (LDD) region. The key principle of the device operation is the field-induced interband tunneling effect, and thus the name of this quantum-tunneling device: FITET. In the transfer I-V characteristics of FITET, negative-differential transconductance (NDT) characteristics have been observed at room temperature. By controlling the critical device parameters to enhance field-effect such as gate oxide thickness, the peak-to-valley current ratio over 5 has been obtained at room temperature, and the negative-differential conductance (NDC) characteristics as well as NDT have been observed in the output I-V curves of the same FITET.     

Thermionic emission from the 2DEG assisted by image-charge-induced barrier lowering in AlInN/AlN/GaN heterostructures

The effect of image charges on current transport mechanisms investigated at the nanoscale in Al(1-x)In(x)N/GaN heterostructures was studied. Current-voltage (I-V) measurements were performed locally using a conductive AFM-tip as a nanoprobe and the conduction mechanism was modeled to explain the observed behavior. This model suggests that current transport is controlled by thermionic emission (TE) of the two-dimensional electron gas (2DEG) across the potential barrier at the heterointerface, where the image charges generated by the 2DEG induce a barrier lowering at the Al(1-x)In(x)N/GaN interface, enhancing electron transport. This barrier lowering depends on the 2DEG characteristics, such as 2DEG density n(2D), first subband energy E? and the average distance x? of the 2DEG from the interface. By fitting the experimental I-V curves with the present model the 2DEG density was evaluated. The obtained results were in very good agreement with the Hall measurements.     

Reproducibility of transmission line measurement of bipolar I-Vcharacteristics of MOSFETs

Reproducibility of transmission line (TL) measurement of bipolar current-voltage (I-V) characteristics of grounded gate MOSFET's has been examined. It is observed that the reproducibility is related to the duration of the pulses generated by the transmission line, and a longer pulse duration gives a better reproducibility. For a short pulse duration, it is more difficult to reproduce the I-V characteristics in the triggering region than in other regions (i.e., the pretriggering and snapback regions)     

金属/Hg1-xMnxTe接触的I-V特性研究

分别采用溅射和蒸发镀膜法在Hg1-xMnxTe试样表面形成了Au/Hg1-xMnxTe和Al/Hg1-xMnxTe接触,并用Aligent4155c I-V测试仪对其I-V特性进行了测量,随后对试样在10%NH4F:10%H2O2:H2O中进行了钝化处理,并对处理后的试样再次进行了I-V测量,对于测试结果用热电子发射-扩散理论进行了分析.结果表明:Au与Hg1-xMnxTe形成了良好的欧姆接触,而Al与Hg1-xMnxTe形成了具有整流特性的肖特基接触,其肖特基势垒的理论推算值为0.38eV.钝化处理后的试样,其表面漏电现象明显降低,Au/Hg1-xMnxTe接触的电流下降幅度在0.1V时最大,为76.1%;而Al/Hg1-xMnxTe接触在0.2V时最大,为93.2%.随着偏压的进一步增大,两种接触的电流减小的幅度都逐渐变小.     

Electric and magnetic properties of Eu1-xGdxS films and GdS-EuS film junctions

Polycrystalline Eu1-xGdxS films (0 < x < 0.35 and x = 1; thickness is 40 to 600 nm) were prepared by electron-beam and flash evaporation onto heated substrates. The electrical and magnetic properties of these films were investigated through resistivity and hysteresis measurements at temperatures between 4 and 300 K, with a magnetic field, B, of 0.4 Tesla. After a short discussion of intrinsic differences between the electric and magnetic behavior of films and single crystals, the first results on I-V characteristics of isomorphic GdS-EuS-GdS film junctions are presented. With increasing x and/or lattice-defect concentration, the Curie temperature, TC(x), increases to about 150 K, while the magnetization Js(x), strongly decreases (extrapolating to Js=0 at x=0.5). Typical properties of the GdS-EuS-GdS junctions are the N-type I-V characteristics and the attributed current oscillations at T ≪ TC, the change to Ohmic I-V characteristics for T approaching TC, and the large negative magnetoresistance, ranging up to ΔR/R/ΔB = -10 T^-1, at small B and T > TC, where ρ(T) passes a broad maximum.     

Au与p-CZT晶体的接触特性及其CZT表面处理状态的影响

对不同腐蚀、钝化表面处理的CZT晶片与Au接触的I-V特性进行了研究.用XPS分析了钝化前后CZT晶体表面成分,发现钝化后CZT晶片表面形成厚度为3.1nm的TeO2氧化层.用Agilent 4339B高阻仪进行未腐蚀、腐蚀与腐蚀钝化的CZT晶片I-V特性测试,结果表明腐蚀和腐蚀钝化均能不同程度提高Au/p-CZT接触的势垒高度,相应地减小了漏电流.     

Modelling current transport through DNA (deoxyribonucleic acid) molecules using equivalent circuits

The current transport properties of DNA molecules are of considerable interest. The key reason for this appears to be linked to the universality of DNA molecules in living organisms, their self-assembly properties, and potential applications as nanoscale devices. The modelling of the I-V characteristics of a DNA molecule using equivalent circuits is reported. The advantages of the proposed model are that non-linear current behaviour can be included together with potential piece-wise solutions. The model includes the use of transistors to mimic current discontinuities at transition points. The simulated results closely resemble measured I-V curves and do not invoke resonant tunneling which contradicts observed temperature dependences. An equivalent-circuit model which includes the use of active devices is shown to be effective way to mimic non-linear current transport in biological molecules.     

Transport phenomena and conduction mechanism of single-walled carbon nanotubes (SWNTs) at Y- and crossed-junctions

This letter illustrates the transport phenomena associated with single-walled carbon nanotube (SWNT) junctions of Y- and cross-configurations. Localized gating effect exhibited by Y- and crossed-junctions suggests the resemblance of their electrical characteristics with ambipolar and unipolar p-type FETs, respectively. Temperature dependence of the I-V characteristics reveals that the conduction mechanism in the said SWNT junctions is governed by thermionic emission at temperatures above 100 K and by tunneling at T < 100 K. In-depth analysis of current transport through the crossed- and Y-junction SWNTs is significant in view of their predominant influence on the electrical performance of carbon nanotube networks (CNT-mat).     

退火处理对Zno/Si异质结光电转换特性的影响

采用直流反应溅射方法在p型Si(100)衬底上生长掺Al的ZnO薄膜,并研究退火处理对ZnO薄膜性质的影响。XRD测量结果表明,ZnO薄膜为六方纤锌矿结构,退火后薄膜的晶粒长大,晶界减少;暗态I-V特性曲线表明,ZnO/Si异质结具有明显的整流特性,退火后由于晶粒间界减少和空位浓度降低使反向漏电流降低1个量级;此外,退火处理能在一定程度上改善异质结的光伏效应,使其转换效率提高。     

Simple analytical model of bias dependence of the photocurrent of metal-semiconductor-metal photodetectors

The current-voltage (I-V) characteristics of metal-semiconductor-metal (MSM) photodetectors under various light intensities are examined. The current shows an initial increase followed by saturation and a subsequent sharp increase as bias increases. We propose a theoretical model for bias dependence in all regions of operation except for breakdown, based on drift collection of carriers in the depleted regions under the contacts and diffusion and recombination in the undepleted region. This is based on the solution of the diffusion equation in the undepleted area between the two contacts of the MSM structure. The solution is subject to boundary conditions on excess minority carriers at the cathode end and continuity of current at the anode end. The latter is written in terms of a parameter, denoted as effective diffusion length, which describes the collection efficiency of carriers at the anode. The closed-form solution thus derived corroborates with physical expectations in several limiting cases. To compare theory with experiment, we propose methods to extract parameters that are used to normalize the I-V curves and calculate depletion widths under different light intensities, from current- and capacitance-voltage measurements. A close match between experimental and theoretical results is observed, and possible breakdown mechanisms are discussed.