Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors （HEMTs）

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 10¹⁴cm^-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 10¹⁶cm^-3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current--voltage (I--V) characteristic, but has no effect on the transconductance in the saturation area.     

Chiral anomalies,low-energy theorems and the form factor of the VPP-interaction

It is shown that the account of form factors of the VPP interaction is very important for obtaining any low-energy theorems by a chiral effective lagrangian method. The connection of VPP form factors with chiral anomalies is analyzed.     

Investigation on threshold voltage of p-channel GaN MOSFETs based on p-GaN/AlGaN/GaN heterostructure

The threshold voltage (V_th) of the p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is investigated via Silvaco-Atlas simulations. The main factors which influence the threshold voltage of p-channel GaN MOSFETs are barrier height Φ_1,p, polarization charge density σ_b, and equivalent unite capacitance C_oc. It is found that the thinner thickness of p-GaN layer and oxide layer will acquire the more negative threshold voltage V_th, and threshold voltage |V_th| increases with the reduction in p-GaN doping concentration and the work-function of gate metal. Meanwhile, the increase in gate dielectric relative permittivity may cause the increase in threshold voltage |V_th|. Additionally, the parameter influencing output current most is the p-GaN doping concentration, and the maximum current density is 9.5 mA/mm with p-type doping concentration of 9.5×10¹⁶ cm^-3 at V_GS = -12 V and V_DS = -10 V.     

Performance Enhancement of Al Ga N/Ga N MIS-HEMTs Realized via Supercritical Nitridation Technology

This paper proposes a method of repairing interface defects by supercritical nitridation technology,in order to suppress the threshold voltage shift of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors(MIS-HEMTs).We find that supercritical NH₃ fluid has the characteristics of both liquid NH₃ and gaseous NH₃ simultaneously,i.e.,high penetration and high solubility,which penetrate the packaging of MIS-HEMTs.In addition,NH₂^-<...     

高k栅介质应变Si SOI MOSFET的阈值电压解析模型

在结合应变Si,高k栅和SOI结构三者的优点的基础上,提出了一种新型的高k栅介质应变Si全耗尽SOI MOSFET结构.通过求解二维泊松方程建立了该新结构的二维阈值电压模型,在该模型中考虑了影响阈值电压的主要参数.分析了阈值电压与弛豫层中的Ge组分、应变Si层厚度的关系.研究结果表明阈值电压随弛豫层中Ge组分的提高和应变Si层的厚度增加而降低.此外,还分析了阈值电压与高k栅介质的介电常数和应变Si层的掺杂浓度的关系.研究结果表明阈值电压随高k介质的介 关键词： 应变Si k栅')" href="#">高k栅 短沟道效应 漏致势垒降低     

铌镁酸铅-钛酸铅铁电阴极电子发射特性

研究了铌镁酸铅-钛酸铅铁电材料的铁电、介电性能对阴极发射阈值电压的影响, 以及铁电阴极发射电流与激励脉冲电压和抽取电压之间的关系, 并分析了其发射机理. 结果表明, 室温介电常数高、极化强度变化量大的弛豫铁电体0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃具有较小的发射阈值电压; 铁电阴极电子发射与快极化反转和等离子体的形成有关; 由极化反转所致电子发射的自发射电流随激励脉冲电压的增大呈幂律增长关系, 其发射电流开始于激励脉冲电压的下降沿; 在抽取电压较大时, 发射电流随抽取电压的增大呈线性增长关系, 说明大电流主要取决于抽取电压; 其发射电流开始于激励脉冲电压的上升沿, 与“三介点”处的场增强效应和等离子体的形成有关; 当抽取电压为2500 V 时, 得到的发射电流幅值为210 A, 相应的电流密度为447 A/cm².     

Nanoscale structuring of SrRuO3 thin film surfaces by scanning tunneling microscopy

Surface modifications through line etching of SrRuO₃ thin films have been carried out using a scanning tunneling microscope under ambient conditions. The line etching is found to be dependent on both bias voltage and scan speed for a given number of scan repetitions. We observe that an applied voltage above a threshold value is required for successful line etching. The depth of the etched lines is increasing with increasing bias voltage and scan repetitions as well as with decreasing scan speed. Moreover, sub-50 nm laterally confined mesa structures could be reproducibly etched on the SrRuO₃ thin film surfaces.     

Threshold switching uniformity in In_2Se_3 nanowire-based phase change memory

The uniformity of threshold voltage and threshold current in the In2Se3nanowire-based phase change memory(PCM)devices is investigated. Based on the trap-limited transport model, amorphous layer thickness, trap density, and trap depth are considered to clarify their influences upon the threshold voltage and threshold current through simulations.     

Bias stress effect in low-voltage organic thin-film transistors

The bias stress effect in pentacene organic thin-film transistors has been investigated. The transistors utilize a thin gate dielectric based on an organic self-assembled monolayer and thus can be operated at low voltages. The bias stress-induced threshold voltage shift has been analyzed for different drain-source voltages. By fitting the time-dependent threshold voltage shift to a stretched exponential function, both the maximum (equilibrium) threshold voltage shift and the time constant of the threshold voltage shift were determined for each drain-source voltage. It was found that both the equilibrium threshold voltage shift and the time constant decrease significantly with increasing drain-source voltage. This suggests that when a drain-source voltage is applied to the transistor during gate bias stress, the tilting of the HOMO and LUMO bands along the channel creates a pathway for the fast release of trapped carriers.     

薄膜热处理对ZnO薄膜晶体管性能的提高

制备了两种以SiO2为绝缘层的底栅ZnO薄膜晶体管,分别以未退火和退火处理的ZnO薄膜作为有源层.与未退火处理的ZnO薄膜晶体管相比,退火处理的ZnO薄膜晶体管的饱和迁移率由2.3 cm2/(V·s)增大至3.12 cm2/(V·s),阈值电压由20.8V减小至9.9V,亚阈值摆幅由2.6 V/dec减小至1.9 V/...     

A new microcontroller-based RADFET dosimeter reader

A new reader for radiation dose measurements using RADFET (pMOSFET) dosemeters has been developed. The threshold voltage (V_T) of the pMOSFETs is measured using a “one-point” method that determines V_T as the gate voltage for a given drain current. Using V_T, the absorbed dose, which is directly proportional to the threshold voltage shift, is calculated. The reader is based on a low cost 8-bit PIC 18F4520 microcontroller (MCU), and works independently of a personal computer, uses a touch screen and stores the data in microcontroller memory. Good agreement in threshold voltage values, obtained using a high-quality source-measure unit and the reader, was obtained. In addition, the reader can be used for threshold voltage measurement with other types of MOSFETs, especially in long duration experiments, as well as for the real-time measurements in radiotherapy, either as an autonomous system or integrated in a larger monitoring configuration.     

Quasi-two-dimensional threshold voltage model for junctionless cylindrical surrounding gate metal-oxide-semiconductor field-effect transistor with dual-material gate

Based on the quasi-two-dimensional(2D) solution of Poisson’s equation in two continuous channel regions, an analytical threshold voltage model for short-channel junctionless dual-material cylindrical surrounding-gate(JLDMCSG) metal-oxide-semiconductor field-effect transistor(MOSFET) is developed. Using the derived model, channel potential distribution, horizontal electrical field distribution, and threshold voltage roll-off of JLDMCSG MOSFET are investigated. Compared with junctionless single-material CSG(JLSGCSG) MOSFET, JLDMCSG MOSFET can effectively suppress short-channel effects and simultaneously improve carrier transport efficiency. It is also revealed that threshold voltage rolloff of JLDMCSG can be significantly reduced by adopting both a small oxide thickness and a small silicon channel radius. The model is verified by comparing its calculated results with that obtained from three-dimensional(3D) numerical device simulator ISE.     

Dependence of the threshold voltage in indium-phosphide pore formation on the electrolyte composition

Results of the experimental determination of the threshold voltage of pore formation for n-InP (100) crystals with a charge-carrier density of 2.3 × 10¹⁸ cm^?3 are presented. The threshold voltage of pore formation is shown to be a function of the electrolyte composition, in particular, of the acid concentration in the electrolyte solution. A 5% solution of hydrochloric acid is the most suitable etchant for obtaining high-quality porous indium phosphide films. It is possible to obtain a nanoporous layer that consists of pores 40 nm in diameter spaced by 5–10 nm. The porosity in this case is 45%.     

Impact of film thickness on threshold voltage of polysilicon TFTs

The threshold voltage is a key parameter in the silicon MOSFETS design and operation. In this paper, we study the factors that contribute to the changes of threshold voltage of thin-film LPCVD polysilicon transistors when varying the thickness of the active layer.The results show that the threshold voltage depends strongly on the film thickness. For high thicknesses, the threshold voltage is shown to be determined by the trapped holes at grain boundaries. The variation of this parameter with film thickness can be attributed to inter-granular trap states density variation in the film.For low thicknesses, a simple electrostatic model of the study structure, associated with a numerical method of solving 2D-Poisson's equations, shows that the changes of threshold voltage of polysilicon TFT depends on grain-boundary properties and charge-coupling between the front and back gates. Based on this consideration, the usual threshold voltage expression is modified. The results so obtained are compared with the available experimental data, which show a satisfactory match thus justifying the validity of the proposed relation.     

Coulomb Blockade of a Mesoscopic RLC Circuit

The quantum theory of the mesoscopic RLC circuit and the condition for Coulomb blockade are given by using canonical quantization and a unitary transformation from the classical equation of motion. Our results show that there is a threshold voltage _T in the circuit. The threshold voltage is related not only to the junction capacitance and inductance, but also to the resistance of the circuit. Generally speaking, the larger the resistance, the larger the threshold voltage. This clarifies the phenomenon of the Coulomb blockade of the dissipative mesoscopic circuit.     

Photon-induced switching and tunneling phenomena in a YBCO thin film junction

In the persistent photoconductivity (PPC) phenomenon, illumination of a YBa₂Cu₃O_6.5 thin film junction with a 1mW He−Ne laser leads to the decrease of the critical voltage (similar to the threshold voltage). The decrease of the critical voltage was reversed by illumination with incandescent light. The critical voltage across the junction was experimentally decreased and increased by alternating illumination between He−Ne laser and incandescent light. We also observed visible quenching of the photo-induced state using a 5mW He−Ne laser. Finally, the threshold behavior of the junction was destroyed by illuminating it with incandescent light.     

Influence of tetrabutylammonium hexafluorophosphate (TBAPF6) doping level on the performance of organic light emitting diodes based on PVK:PBD blend films

The effect of doping level of tetrabutylammonium hexafluorophosphate (TBAPF₆) on the performance of single-layer organic light emitting diodes (OLEDs) with ITO/PVK:PBD:TBAPF₆/Al structure were investigated where indium tin oxide (ITO) was used as anode, poly(9-vinylcarbazole) (PVK) as hole-transporting polymeric host, 2-(4-biphenylyl)-5-phenyl-1,3,4-oxadiazole (PBD) as electron-transporting molecule and aluminium (Al) as cathode. It was found that the doped devices underwent a unique transition at the first voltage scan as indicated by drastically increasing of current at certain applied voltage. After the transition, the threshold voltage for current injection as well as the turn-on voltage decreased significantly as compared to the undoped device. The current injection threshold voltage and turn-on voltage decreased with the increase of TBAPF₆ doping level. More importantly, a relatively low current injection threshold voltage of 3 V has been achieved by doping a significant amount of TBAPF₆ (weight ratio greater than five) in the single-layer OLED based on PVK:PBD blend films with high work function Al metal as cathode. The significant improvement was attributed to the reduction of both electron and hole injection energy barriers caused by accumulation of ionic species at the interface.     

Shapiro effect in mesoscopic LC circuit

In this paper we consider the movement of an electron in the single electron tunnel process through a mesoscopic capacitor. The results show that, due to the Coulomb force, there is a threshold voltage V_t in the mesoscopic LC circuit. When the external voltage is lower than the threshold voltage, the tunnel current value is zero, and the Coulomb blockade phenomenon arises. Furthermore, considering that the mesoscopic dimension is comparable to the coherence length in which charge carriers retain the phase remembrance, a weak coupling can be produced through the proximity effect of the normal metal electrons of both electrodes of a mesoscopic capacitor. By varying the external voltage, we can observe the Shapiro current step on the current－voltage characteristic curve of a mesoscopic LC circuit.     

Gas molecule dissociation effect on rf discharge burning in low pressure ammonia

This Letter outlines the experimental study of molecule dissociation effect on rf capacitive discharge burning. We show that for each ammonia pressure value there exists some threshold rf voltage value below which the dissociation degree does not exceed 3%, but at higher rf voltage it grows to 30%. Increasing NH₃ dissociation degree accelerates the discharge current growth against rf voltage. The rf discharge remains in a weak-current α-mode at low as well as at high dissociation degree because all ammonia dissociation products possess ionization potentials exceeding that for NH₃.