A new I-V model for stress-induced leakage current includinginelastic tunneling

A new I-V model to quantitatively represent stress-induced leakage current (SILC) is presented and compared with the experimental I-V characteristics. The trap-assisted tunneling model is modified so as to include the energy relaxation of tunneling electrons, which has been experimentally verified by applying the carrier separation technique to MOSFETs with the SILC component. The energy relaxation is treated in the new model as the change in the energy level of traps before and after the capture of electrons during two-step tunneling. It is demonstrated that this model successfully represents the experimental I-V characteristics of the SILC component and, particularly, the low apparent barrier height in the Fowler-Nordheim (FN) plot of the SILC component. The calculated low barrier height is attributed to the dominance of direct tunneling mechanism on both tunneling into traps and out of traps. The impact of the energy relaxation during tunneling, used in the present model, on the I-V characteristics is discussed in terms of the trap distribution inside the gate oxide, compared with conventional elastic tunneling model     

双层有机电致发光器件有机层厚度优化的数值研究

在陷阱电荷限制电流传导理论的基础上,提出了双层有机电致发光器件的数值模型,研究了结构为“阳极/空穴输运层( HTL) /发光层( EML) /阴极”的器件中电流密度和量子效率随有机层的特征陷阱能量、陷阱密度和载流子迁移率的依赖关系.研究发现,对于给定的HTL 和EML 的特征陷阱能量、陷阱密度和载流子迁移率,存在一个最优的HTL 和EML 之间的厚度比率,在此最优厚度比下,器件的电流密度和量子效率达到最大.通过有机层厚度的优化,器件的电流密度和量子效率可提高多达两个数量级.另外,还研究了最优厚度比随有机层特征陷阱能量、总陷阱密度和载流子迁移率之间的     

双层有机电致发光器件有机层厚度优化的数值研究

在陷阱电荷限制电流传导理论的基础上,提出了双层有机电致发光器件的数值模型,研究了结构为"阳极/空穴输运层(HTL)/发光层(EML)/阴极"的器件中电流密度和量子效率随有机层的特征陷阱能量、陷阱密度和载流子迁移率的依赖关系. 研究发现,对于给定的HTL和EML的特征陷阱能量、陷阱密度和载流子迁移率,存在一个最优的HTL和EML之间的厚度比率,在此最优厚度比下,器件的电流密度和量子效率达到最大.通过有机层厚度的优化,器件的电流密度和量子效率可提高多达两个数量级.另外,还研究了最优厚度比随有机层特征陷阱能量、总陷阱密度和载流子迁移率之间的定量关系.     

聚合物发光器件中输运特性的模拟分析

对聚合物发光二极管 I- V特性的测量发现 ,被测器件内存在着类似于某些无机器件中的负阻现象和“迟滞回线”状场致漂移的伏安特性 .模拟分析表明 ,一种反向势垒的存在及其击穿 ,应是引起负阻现象的原因 .缺陷态的存在及其电荷填充的变化 ,是导致 I- V特性曲线随偏压扫描方向变化的主要原因 .而低场下的接触性能决定着发光二级管载流子的输运性质 :若为非欧姆接触 ,则 I- V曲线可用 F- N隧穿模型来描述 ;若为欧姆接触 ,则应用陷阱电荷限制电流 (TCL)模型来描述     

有机发光器件中缺陷态行为表现

对有机发光二极管（OLED）的I-V特性曲线,用有内建电场Ei的修正F-N模型,或陷阱电荷限制电流（TCL）模型进行了模拟分析,均观察到缺陷态对器件特性的影响。对修正F-N模型拟合,Ei不是常数而是随电场变化的,对满足TCL模型的OLED器件,其I-V特性呈现类似于无机半导本器件中的“迟滞回线”状,而且随测试次数的变化呈现可恢复的变化。这些均说明OLED中存在着缺陷态,用缺陷态上电荷填充状态的变化对上述现象进行了解释。     

Carrier transport mechanism in La-incorporated high-k dielectric/metal gate stack MOSFETs

In this paper, carrier transport mechanism of MOSFETs with HfLaSiON was analyzed. It was shown that gate current is consisted of Schottky emission, Frenkel-Poole (F-P) emission and Fowler-Nordheim (F-N) tunneling components. Schottky barrier height is calculated to be 0.829 eV from Schottky emission model. Fowler-Nordheim tunneling barrier height was 0.941 eV at high electric field regions and the trap energy level extracted using Frenkel-Poole emission model was 0.907 eV. From the deviation of weak temperature dependence for gate leakage current at low electric field region, TAT mechanism is also considered.     

MOSFET degradation due to stressing of thin oxide

Oxide and interface traps in 100 Å SiO2created by Fowler-Nordheim tunneling current have been investigated using capacitor C-V, I-V, and transistor I-V measurements. The net oxide trapped charge is initially positive due to hole trapping near the anode interface and, at sufficiently high fluence, it becomes negative due to the trapping of electrons with a centroid of 60 Å from the injector (cathode) interface. Interface traps (Surface states) are created by tunneling electrons flowing to and from the substrate. The interface-trap energy distribution gives a distinct peak at 0.65 eV above the valence band edge. The positive charge trapping and interface traps generation saturate at high electron fluence, but not the electron trap generation. The generation rates for electron traps and interface traps are weak functions of tunneling current density over the range tested. The interface traps cause degradations in subthreshold current slope and surface electron mobility. The threshold-voltage shift can be either positive or negative under the combined influence of the oxide charges and the interface charges.     

Dynamic oxide voltage relaxation spectroscopy

A new method for trap characterization of oxidized silicon is described. The Dynamic Oxide Voltage Relaxation Spectroscopy (DOVRS) is an improved version of the formerly proposed Oxide Voltage Relaxation Spectroscopy (OVRS) technique which applies a periodic long duration constant current for tunneling injection. It has been demonstrated that the new technique can be used not only to separate and identify the oxide trap from interface trap, but also to separate and determine the centroid from the oxide trap density generated in the MOS system by the tunneling current stress. In the pulse constant current mode, the OVRS measurement can be completed instead of using the double current-voltage technique. Thus the new method results in more accurate and quicker measurements of the oxide trap centroid. Analytical expressions for computing the paramaters of the interface and oxide traps are derived. The effect of the channel carrier mobility on the spectroscopy is also considered. Two types of oxide and two types of interface traps were observed at a pulse constant Fowler-Nordheim current stress by the new method of DOVRS     

Electrical characterization of polymer-based FETs fabricated by spin-coating poly(3-alkylthiophene)s

The current-voltage (I-V) characteristics of two different polymer thin-film transistors (TFTs), based on spin-coating of poly(3-hexylthiophene)-P3HT and poly(3-hexadecylthiophene)-P3HDT, are studied. A model is developed to interpret the results and to explain the differences between these two polymers. Various parameters of the semiconducting polymers, including bulk mobility, field-effect mobility, trap density, and unintentional dopant concentration are estimated. The model takes into account the domination of the bulk current over the channel current in the subthreshold regime as well as the effects of the depletion layer as parasitic resistances in series with the channel resistance. Furthermore, the effects of the films thickness on the electrical characteristics of these TFTs are discussed. Compared to the P3HT, the P3HDT-based TFT has a lower subthreshold slope, higher on current ratio, and higher field-effect mobility.     

Detailed evaluation of in-operando potentials in OLED devices: A combined experimental and drift-diffusion study

We report on a technique to determine in-operando transport properties of Organic Light Emitting Diodes (OLEDs). Two types of OLEDs that solely differ in the emission layer but obviously exhibit a different potential distribution are investigated in this study. If the emission layer consists of the isomer TH-A a large shift in onset voltage can be observed in case of layer thickness variation of the emission layer. In case of the isomer TH-B a thickness variation has no impact on the onset voltage. Therefore the voltage developments per layer are determined with the help of IV measurements on a set of devices with varying layer thickness. From an empirical point of view the voltage behaviour in each layer follows a simple power law. A drift-diffusion model is developed that well describes the current density dependent evolution of coefficient and exponent of the power law. From the model we are able to derive the carrier injection mechanism into the respective layer as well as the injection barrier height. Also the carrier mobility is determined. Finally we are able to show that the existence of a large injection barrier can not explain the observed onset voltage shifts in case of TH-A. Instead an electric field at or close to the interface is necessary to describe the TH-A behaviour.     

The effect of Fowler-Nordheim tunneling current stress on mobilityin n-channel MOSFETs

The electron effective mobility in n-channel MOSFETs has been investigated under Fowler-Nordheim (F-N) tunneling current stress at room temperature. With F-N current stress, mobilities become smaller than of the prestress mobilities over the whole region of inversion carrier density N_inv, and the N_inv -dependence of the mobility almost disappears     

Electrical characteristics of GaAs MIS Schottky diodes

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of GaAs metal-insulator-semiconductor (MIS) Schottky barrier diodes are investigated over a wide temperature range and compared with MS diodes. The effects of the insulating layer on barrier height and carrier transport are delineated by an activation energy analysis. Excess currents observed at low forward and reverse bias have also been analyzed and their cause identified. A capacitance anomaly consistently noticed in MIS Schottky barriers is resolved by stipulating a non-uniform interfacial layer, and a self-consistent model of the GaAs MIS Schottky barrier is developed by analyzing I-V and C-V data of both MIS and MS diodes.     

Effect of carrier injection into MESFET substrates : comparison of MESFET on a semi-insulating buffer,MESFET on a P substrate,and substrate-less MESFET

The carrier injection from the active-layer of the submicron-gate-lengthMesfet into the buffer-layer, or substrate in general, is studied by means of a two-dimensional computer simulation in which the energy conservation equation is simultaneously solved with the carrier conservation equation and Poisson’s equation. The mobility, electron temperature and energy relaxation time are treated as energy dependent parameters. This model is capable of simulating the non-stationary conditions associated with the submicron-gate-length devices. The effect of the carrier injection on the I-V characteristics as well as on the small-signal parameters is investigated by simulating twoMesfet structures; the first is aMesfet on a perfect buffer-layer while the second is a symmetricalMesfet which has no substrate. It is found out that the drain current is increased by the carrier injection, whereas the transconductance is reduced due to the increase of the device dynamic range. TheMesfet with an interfacial potential barrier is also simulated. It exhibits characteristics intermediate between those of the other two devices.     

Transport properties of thermal oxide films grown on polycrystalline silicon—Modeling and experiments

A theoretical model considering the effects of Fowler-Nordheim tunneling, image-force lowering, first-order trapping kinetics, impact ionization, and asperity-induced field enhancement has been developed to investigate the ramp-voltage-stressed I-V characteristics of the oxide films thermally grown on the polycrystalline silicon. From the ramp-voltage-stressed I-V measurements, the important physical parameters such as average field-enhancement factor, effective total trapping density, trap capture cross section, recombination capture cross section, and dielectric breakdown field can be extracted. Under a ramp voltage stress, it is shown that the serious asperity effect can lead to a larger leakage current and a weaker dielectric breakdown field, but the serious trapping effect may reduce the leakage current and enlarge the dielectric breakdown field. Moreover, dry O2oxidation at a higher temperature and steam oxidation at a lower temperature can result in a better quality poly-oxide because the asperity-induced field enhancement is weakened and the electron trapping effect is slightly increased. Besides, high-temperature dry O2oxidation can result in a smaller asperity effect as compared with steam oxidation, and the quality of the poly-oxide is deteriorated when the poly-Si substrate is heavily doped because the asperity effect is enhanced.     

Tunnel emission into an insulating film with traps

The effect of space charge and traps on the current density of electrons tunnelling from a metal into the conduction band of an insulating film is calculated for the case of very low free carrier mobility in the insulator. It is shown that free carrier space charge is ineffective in lowering the tunnelling current even for extremely low free carrier mobility but that a high trap density can severely limit the tunnel current density.     

Chemical reaction concerns of gate metal with gate dielectric in Tagate MOS devices: an effect of self-sealing barrier configurationinterposed between Ta and SiO2

Chemical reaction of gate metal with gate dielectric for Ta gate MOS devices has been experimentally investigated both by electrical and physical measurements: capacitance-voltage (C-V), current-voltage (I-V), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), electron diffraction measurements. In spite of the chemical reaction of Ta with SiO₂ consuming ~1-nm-thick in gate oxide, the interface trap densities of ~2×10¹⁰ cm^-2 eV ^-1 at midgap and ideal channel mobility characteristics have been observed in the Ta gate MOS devices with 5.5-nm-thick thermal oxide gate dielectric. Considering the experimental data with theoretical calculation based on thermodynamics together, a barrier layer model has been developed for the Ta gate MOS systems. The physical mechanism involved is probably self-sealing barrier layer formation resulting from the chemical reaction kinetics in the free-energy change of Ta-Si-O system     

总剂量辐照SiO2/6H-SiC引起的界面势垒变化

辐照会引起MOS器件电介质氧化物与半导体界面势垒变化,影响其工作性能和可靠性。测量了n型6H-SiC MOS电容辐照105rad(Si)剂量前后的I-V曲线,通过Fowler-Nordheim(F-N)隧道电流拟合,得到了界面势垒的大小,辐照前的为2.596 eV,辐照后降为1.492eV。界面势垒变化主要是由辐照产生的界面态引起的。     

Evidence of space-charge-limited current in amorphous silicon Schottky diodes

Palladium/amorphous silicon (a-SiHx) Schottky barrier diodes have been found to exhibit superlinear dark forward current-voltage (I-V) characteristics over the temperature range 30 to 130°C. The results are consistent with expected behavior for space-charge-limited current in the presence of distributed traps. The trap parameters are deduced from I-V data.     

Au/(Si/SiO2)/p-Si结构中电流输运机制的研究

用射频磁控溅射法制备了Si/SiO2薄膜,利用Au/(Si/SiO2)/p-Si结构的I-V特性曲线对其输运机制进行了分析。结果表明,在较高的正向电场下,载流子主要是以电场协助隧穿(Fowler-Nordheim隧穿)方式通过氧化层,而在低场范围内和反向电场下,电流的产生则以热电子发射的方式为主。     

Modeling of the electrical characteristics of an organic field effect transistor in presence of the bending effects

An analytical model incorporating the density of trap states for a bendable organic field effect transistor (OFET) is presented in this paper. The aim of this work is to propose a novel modeling framework to quantitatively characterize the bending effects on the electrical properties of an OFET in the linear and saturation regimes. In this model, the exponentially distributed shallow trap states are introduced into the Poisson equation to describe the carrier transports in the channel. The carrier mobility takes into account the low field mobility enhancement under gradual channel approximation and high field degradation. As a result, the generalized current-voltage transistor equations are derived for the first time to reflect the transconductance relationships of the OFET with trap states. In addition, an electro-mechanical coupling relationship is established per the metaphorical analogy between inorganic and organic semiconductor energy band models to quantify the stress-induced variations of the carrier mobility, and the threshold voltage. It is revealed that the before- and after-bending transconductances, predicted from the derived analytical model, are in good agreement with the experimental data measured from DNTT-based OFET bending tests.