一种改进的MOS器件热载流子退化模型

An improved hot carrier injection （HCI） degradation model was proposed based on interface trap generation and oxide charge injection theory. It was evident that the degradation behavior of electric parameters such as Idlin, Idsat, Gm and Vt fitted well with this model. Devices were prepared with 0.35μm technology and different LDD processes. Idlin and Idsat after HCI stress were analyzed with the improved model. The effects of interface trap generation and oxide charge injection on device degradation were extracted, and the charge injection site could be obtained by this method. The work provides important information to device designers and process engineers.     

Influences of Injection Barrier and Mobility on Recombination Rate and Zone in OLEDs

The luminous efficiency of organic light-emitting devices depends on the recombination probability of electrons injected at the cathode and holes at the anode. A theoretical model to calculate the distribution of current densities and the recombination rate in organic single layer devices is presented taking into account the charge injection process at each electrode, charge transport and recombination in organic layer. The calculated results indicate that efficient single-layer devices are possible by adjusting the barrier heights at two electrodes and the carrier mobilities. Lowering the barrier heights can improve the electroluminescent（EL） efficiency pronouncedly in many cases, and efficient devices are still possible using an ohmic contact to inject the low mobility carrier, and a contact limited contact to inject the high mobility carrier. All in all, high EL efficiency needs to consider sufficient recombination, enough injected carriers and well transport.     

Surface traps-related nonvolatile resistive switching memory effect in a single SnO2:Sm nanowire

For nanostructure SnO2,it is very difficult for its electric properties to accurately control due to the presence of abundant surface states.The introduction of Sm can improve the traps in surface space charge region of SnO2 nanowires,resulting in a controllable storage charge effect.For the single nanowire-based two-terminal device,two surface state-related back-to-back diodes are formed.At a relatively large voltage,electrons can be injected into the traps in surface space charge region from negative electrode,resulting in a decrease of surface barrier connected with negative electrode,and contrarily electrons can be extracted from the traps in surface space charge region into positive electrode,resulting in an increase of surface barrier connected with positive electrode.The reversible injection and extraction induce a nonvolatile resistive switching memory effect.     

关于三极场发射显示器样机中夹心式层状阴极电极的制作研究

Based on an effective screen-printing process,a novel sandwich layered cathode electrode was developed on a cathode faceplate.The ZnO electrode was sandwiched between an indium tin oxide(ITO) electrode layer and a silver electrode layer,and the carbon nanotube was prepared directly on the exposed ITO electrode layer surface.The cathode potential could be conducted to the carbon nanotube with the sandwich layered cathode electrode.Using the carbon nanotube as a field emitter,a triode field emission display prototype with a sandwich layered cathode electrode was fabricated,which possessed a better field emission characteristic,higher luminous brightness and better emission image luminance uniformity.The turn-on electric field was 1.88 V/μm and the measured maximum field emission current was 2273.6μA at 3.19 V/μm.By the method of adjusting the field emission current,the electron-emitting uniform capacity of the carbon nanotube cold cathode could be modified, and the emission image luminance uniformity and the emission current stability of triode field emission display prototype was also be improved significantly.The emission current fluctuation of the sandwich layered cathode electrode type field emission display was less than 1.1%.Furthermore,the total manufacture cost of the triode field emission display prototype was low.     

High-efficiency and reduced efficiency roll-off of top-emitting organic light-emitting diodes

Top-emitting organic light-emitting diodes (TEOLEDs) have attracted extensive attention for their high brightness and flat-panel display. However, the efficiency roll-off at high brightness is the issue that needs to be resolved for further practical applications using TEOLED devices. Herein, a serial of high-efficiency tandem TEOLED introducing a fullerene/zinc-phthalocyanine organic semiconductor heterojunction as a charge generation layer is demonstrated. With unique photovoltaic properties, the charge generation layer can absorb part of the photons emitted by the emission layer (Ir(ppy)3) and generate electrons and holes. By optimizing the thickness of the charge generation layer, the pure green electroluminescent TEOLED device manufactured has a high brightness of 156 000 cd/cm2 and a maximum current efficiency of 86 cd/A. Importantly, relying on the energy between the photovoltaic and the microcavity effects, only 1.5% of the efficiency roll-off is obtained at 1 000—10 000 cd/cm2. Introducing fullerene/zinc-phthalocyanine as the charge-generating layer provides a promising alternative for developing high-efficiency tandem TEOLED devices.     

Luminescent Efficiency in Single-layer Organic Electrophosphorescent Devices

Based on the charge injection and recombination processes and the triplet-triplet annihilation process, a model to calculate the electro.luminescent（EL） efficiency is presented. The influences of the applied electric field on the injection efficiency, recombination efficiency and electroluminescent efficiency are discussed. It is found that： （1） The injection efficiency is increasing while the recombination efficiency is decreasing with the applied electric field increasing. （2） The EL efficiency is enhanced at low electric field slowly but is decreasing at high electric field with the increase of applied voltage. （3） The EL efficiency is decreasing with the increase of the host-guest molecular distance （R）. So, it is concluded that the EL efficiency in single-layer organic electrophosphorescent devices is dominated by injection efficiency at lower electric field and recombination efficiency at higher electric field.     

Electronic properties of InAs-based metal-insulator-semiconductor (MIS) structures

Special features of electronic processes in InAs-based MIS structures operating in the charge injection mode were investigated. These structures are used as photodetectors in the spectral range of 2.5–3.05 μm. A double-layer system consisting of an anodic oxide layer and a low-temperature silicon dioxide layer was used as an insulator. It was shown that fluorine-containing components, which were introduced into electrolyte, reduced the value of the built-in charge and the surface-state density to minimal measurable values of ≲2×10¹⁰ cm⁻² eV⁻¹. Physical and chemical characteristics of the surface states at the InAs-insulator interface and the possible causes of their absence were discussed on the basis of the phase composition data of anodic oxide obtained by X-ray photoelectron spectroscopy. An anomalous field generation was observed under the nonequilibrium depletion of the semiconductor. The processes of tunneling generation, which are important at large amplitudes of the depletion pulse, were considered. The noise behavior of MIS structures under a nonequilibrium depletion was investigated. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 9, 2001, pp. 1111–1119. Original Russian Text Copyright ? 2001 by Kuryshev, Kovchavtsev, Valisheva.     

硅化物阻挡层对高压漏扩展MOS晶体管的影响

Silicide-block-film effects on drain-extended MOS （DEMOS） transistors were comparatively investigated, by means of different film stack stoichiometric SiO2 and silicon-rich oxide （SRO）. The electrical properties of the as-deposited films were evaluated by extracting source/drain series resistance. It was found that the block film plays a role like a field plate, which has significant influence on the electric field beneath. Similar to hot-carrier- injection （HCI） induced degradation for devices, the block film initially charged in fabrication process also strongly affects the device characteristics and limits the safe operating area.     

Compact analytical model for single gate AlInSb/InSb high electron mobility transistors

We have developed a 2D analytical model for the single gate Al In Sb/In Sb HEMT device by solving the Poisson equation using the parabolic approximation method.The developed model analyses the device performance by calculating the parameters such as surface potential,electric field distribution and drain current.The high mobility of the Al In Sb/In Sb quantum makes this HEMT ideal for high frequency,high power applications.The working of the single gate Al In Sb/In Sb HEMT device is studied by considering the variation of gate source voltage,drain source voltage,and channel length under the gate region and temperature.The carrier transport efficiency is improved by uniform electric field along the channel and the peak values near the source and drain regions.The results from the analytical model are compared with that of numerical simulations(TCAD) and a good agreement between them is achieved.     

Structure design and film process optimization for metal-gate stress in 20 nm nMOS devices

The optimizations to metal gate structure and film process were extensively investigated for great metalgate stress(MGS) in 20 nm high-k/metal-gate-last(HKVMG-last) nMOS devices.The characteristics of advanced MGS technologies on device performances were studied through a process and device simulation by TCAD tools. The metal gate electrode with different stress values(0 to—6 GPa) was implemented in the device simulation along with other traditional process-induced-strain(PIS) technologies like e-SiC and nitride capping layer.The MGS demonstrated a great enhancing effect on channel carriers transporting in the device as device pitch scaling down.In addition,the novel structure for a tilted gate electrode was proposed and relationships between the tilt angle and channel stress were investigated.Also with a new method of fully stressed replacement metal gate(FSRMG) and using plane-shape-HfO to substitute U-shape-HfO,the effect of MGS was improved.For greater film stress in the metal gate,the process conditions for physical vapor deposition(PVD) TiN-x- were optimized.The maximum compressive stress of—6.5 GPa TiN_x was achieved with thinner film and greater RF power as well as about 6 sccm N ratio.     

Influence of Energy Level Matching on Device Performances of Organic Light-emitting Diodes

Through experiments and computer simulation, the influence of the energy levels of organic materials and electrode materials in the organic light-emitting diodes (OLEDs) on the device performances is discussed. Results show that the device performances are influenced by not only the carrier injection barriers at the electrode interface but also the harriers at the organic heterojunction interface. This result is helpful to the selection of the organic materials and their arrangement in the optimal design of OLEDs.     

Electric‐Field‐Assisted Charge Generation and Separation Process in Transition Metal Oxide‐Based Interconnectors for Tandem Organic Light‐Emitting Diodes

The charge generation and separation process in transition metal oxide (TMO)‐based interconnectors for tandem organic light‐emitting diodes (OLEDs) is explored using data on electrical and spectral emission properties, interface energetics, and capacitance characteristics. The TMO‐based interconnector is composed of MoO₃ and cesium azide (CsN₃)‐doped 4,7‐diphenyl‐1,10‐phenanthroline (BPhen) layers, where CsN₃ is employed to replace the reactive metals as an n‐dopant due to its air stability and low deposition temperature. Experimental evidences identify that spontaneous electron transfer occurs in a vacuum‐deposited MoO₃ layer from various defect states to the conduction band via thermal diffusion. The external electric‐field induces the charge separation through tunneling of generated electrons and holes from MoO₃ into the neighboring CsN₃‐doped BPhen and hole‐transporting layers, respectively. Moreover, the impacts of constituent materials on the functional effectiveness of TMO‐based interconnectors and their influences on carrier recombination processes for light emission have also been addressed.     

Tailoring Electron‐Transfer Barriers for Zinc Oxide/C60 Fullerene Interfaces

The interfacial electronic structure between oxide thin films and organic semiconductors remains a key parameter for optimum functionality and performance of next‐generation organic/hybrid electronics. By tailoring defect concentrations in transparent conductive ZnO films, we demonstrate the importance of controlling the electron transfer barrier at the interface with organic acceptor molecules such as C₆₀. A combination of electron spectroscopy, density functional theory computations, and device characterization is used to determine band alignment and electron injection barriers. Extensive experimental and first principles calculations reveal the controllable formation of hybridized interface states and charge transfer between shallow donor defects in the oxide layer and the molecular adsorbate. Importantly, it is shown that removal of shallow donor intragap states causes a larger barrier for electron injection. Thus, hybrid interface states constitute an important gateway for nearly barrier‐free charge carrier injection. These findings open new avenues to understand and tailor interfaces between organic semiconductors and transparent oxides, of critical importance for novel optoelectronic devices and applications in energy‐conversion and sensor technologies.     

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.     

Study of rectifying property of ITO/PI/TIPS-pentacene/Au diodes by electric field induced optical second harmonic generation

By using time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurement, we studied the rectifying property of organic double-layer diodes with a structure of indium-tin-oxide/polyimide/6,13-Bis(triisopropylsilylethynyl)-pentacene/gold (ITO/PI/TIPS-pentacene/Au). Upon application of a step voltage to the diodes, the TR-EFISHG probed the electric field changes induced in the TIPS-pentacene layer by hole injection from the ITO electrode, followed by the hole accumulation at the PI/TIPS-pentacene interface. Consequently, the electric field distributions in the diodes before and after the carrier injection were traced with accumulated charges at the PI/TIPS-pentacene interface, depending on the DC biasing applied to the diodes. Analyzing the carrier behavior in ITO/PI/TIPS-pentacene/Au on the basis of a Maxwell–Wagner model, we discussed the rectifying property of the diodes in terms of DC biasing effect, i.e., threshold-voltage shift, and concluded that space charge limited current process that flows across the PI layer governs the rectification of the diodes. Using the TR-EFISHG measurement is an effective way to study the rectifying property of organic double-layer diodes.     

Mapping charge carrier density in organic thin-film transistors by time-resolved photoluminescence lifetime studies

The device performance of organic transistors is strongly influenced by the charge carrier distribution. A range of factors effect this distribution, including injection barriers at the metal-semiconductor interface, the morphology of the organic film, and charge traps at the dielectric/organic interface or at grain boundaries. In our comprehensive experimental and analytical work we demonstrate a method to characterize the charge carrier density in organic thin-film transistors using time-resolved photoluminescence spectroscopy. We developed a numerical model that describes the electrical and optical responses consistently. We determined the densities of free and trapped holes at the interface between the organic layer and the SiO₂ gate dielectric by comparison to electrical measurements. Furthermore by applying fluorescence lifetime imaging microscopy we determine the local charge carrier distribution between source and drain electrodes of the transistor for different biasing conditions. We observe the expected hole density gradient from source to drain electrode.     

基于有机p型掺杂电荷产生层制备叠层式白光OLED的研究

基于新型有机p型掺杂的电荷产生层,制备了叠层式白光有机发光二极管(OLED).有机p型掺杂层具有很高的导电率,可以在不影响器件电学特性的前提下,通过改变该层的厚度来优化白光OLED的器件性能,调节器件的光色.与传统白光OLED相比,文章研究的叠层式白光OLED制备工艺简单、电荷产生效率高,可应用于平板显示与固态照明.     

Effects of substrate topography on current injection and light emission properties of organic light emitting devices

Substrate topography plays a critical role in the function of nano-scale materials and devices. We study small molecular organic light emitting devices (OLEDs) deposited onto non-planar substrates, where the substrate’s radius of curvature in some regions approaches the thickness of the active device layers. As a result, the electric field profile inside the organic charge transport layers is modified, influencing carrier injection, transport, and light emission properties. Experiments and numerical modeling suggest that charge balance and electroluminescence efficiency potentially can be improved in electron injection-limited OLED architectures via substrate geometry. These findings elucidate the optoelectronic behavior (and degradation) of OLEDs on imperfect substrates, and suggest a strategy based on substrate topography for controlling device behavior.     

The Role of Transition Metal Oxides in Charge‐Generation Layers for Stacked Organic Light‐Emitting Diodes

The mechanism of charge generation in transition metal oxide (TMO)‐based charge‐generation layers (CGL) used in stacked organic light‐emitting diodes (OLEDs) is reported upon. An interconnecting unit between two vertically stacked OLEDs, consisting of an abrupt heterointerface between a Cs₂CO₃‐doped 4,7‐diphenyl‐1,10‐phenanthroline layer and a WO₃ film is investigated. Minimum thicknesses are determined for these layers to allow for simultaneous operation of both sub‐OLEDs in the stacked device. Luminance–current density–voltage measurements, angular dependent spectral emission characteristics, and optical device simulations lead to minimum thicknesses of the n‐type doped layer and the TMO layer of 5 and 2.5 nm, respectively. Using data on interface energetic determined by ultraviolet photoelectron and inverse photoemission spectroscopy, it is shown that the actual charge generation occurs between the WO₃ layer and its neighboring hole‐transport material, 4,4',4”‐tris(N‐carbazolyl)‐triphenyl amine. The role of the adjacent n‐type doped electron transport layer is only to facilitate electron injection from the TMO into the adjacent sub‐OLED.     

Tandem organic light-emitting diodes with buffer- modified C60/pentacene as charge generation layer

Buffer-modified C60/pentacene as charge generation layer (CGL) is investigated to achieve effective performance of charge generation. Undoped green electroluminescent tandem organic light-emitting diodes (OLEDs) with multiple identical emissive units and using buffer-modified C60/pentacene organic semiconductor heterojunction (OHJ) as CGL are demonstrated to exhibit better current density and brightness, compared with conventional single-unit devices. The current density and brightness both can be significantly improved with increasing the thickness of Al. However, excessive thickness of Al seriously decreases the transmittance of films and damages the interface. As a result, the maximum current efficiency of 1.43 cd.A-1 at 30 mA.cm-2 can be achieved for tandem OLEDs with optimal thickness of Al. These results clearly demonstrate that Cs2CO3/Al is an effective buffer for C60/pentacene-based tandem OLEDs.