An analytic model for gate-all-around silicon nanowire tunneling field effect transistors

An analytical model of gate-all-around(GAA) silicon nanowire tunneling field effect transistors(NW-TFETs) is developted based on the surface potential solutions in the channel direction and considering the band to band tunneling(BTBT) efficiency. The three-dimensional Poisson equation is solved to obtain the surface potential distributions in the partition regions along the channel direction for the NW-TFET, and a tunneling current model using Kane’s expression is developed. The validity of the developed model is shown by the good agreement between the model predictions and the TCAD simulation results.     

单根砷掺杂氧化锌纳米线场效应晶体管的电学及光学特性

采用化学气相沉积（CVD）的方法在砷化镓基底上合成直径为20 nm左右、长约数十微米的氧化锌纳米线,然后采用热扩散的方法,将生长于砷化镓基底之上的氧化锌纳米线通过600 ℃,30 min的有氧退火处理后,获得了砷掺杂的氧化锌纳米线.将获得的掺杂后的氧化锌纳米线采用电子束曝光以及真空溅射镀膜的方法将钛/金合金作为接触电极引出,从而构建成场效应晶体管.文中研究了单根氧化锌纳米线砷掺杂前后的电学特性,证实了通过砷掺杂来获得p型的氧化锌纳米线的可行性.构建的p型砷掺杂氧化锌场效应晶体管的跨导为35 nA/V,载流 关键词： p型ZnO纳米线 砷掺杂 场效应晶体管 光致发光     

Effects of surface roughness on the electrical characteristics of ZnO nanowire field effect transistors

We have systematically investigated the effects of surface roughness on the electrical characteristics of ZnO nanowire field effect transistors (FETs) before and after passivation by poly (methyl metahacrylate) (PMMA), a polymer-insulating layer. To control the surface morphology of ZnO nanowires, ZnO nanowires were grown by the vapor transport method on two different substrates, namely, an Au-catalyzed sapphire and an Au-catalyzed ZnO film/sapphire. ZnO nanowires grown on the Au-catalyzed sapphire substrate had smooth surfaces, whereas those grown on the Au-catalyzed ZnO film had rough surfaces. Electrical characteristics such as the threshold voltage shift and transconductance before and after passivation were strongly affected by the surface morphology of ZnO nanowires.     

Review of gallium oxide based field-effect transistors and Schottky barrier diodes

Gallium oxide(Ga_2O_3), a typical ultra wide bandgap semiconductor, with a bandgap of ~4.9 e V, critical breakdown field of 8 MV/cm, and Baliga's figure of merit of 3444, is promising to be used in high-power and high-voltage devices.Recently, a keen interest in employing Ga_2O_3 in power devices has been aroused. Many researches have verified that Ga_2O_3 is an ideal candidate for fabricating power devices. In this review, we summarized the recent progress of field-effect transistors(FETs) and Schottky barrier diodes(SBDs) based on Ga_2O_3, which may provide a guideline for Ga_2O_3 to be preferably used in power devices fabrication.     

Excitons in the preionization electric field of a Schottky barrier

The low-temperature (T=80 K) exciton reflectance spectra of CdS crystals in the electric field of a Schottky barrier are investigated. An anomalous Stark shift of a hydrogenic exciton state is detected in the preionization limit. An analysis of the spectra within the theory of a nonlocal dielectric response in a spatially inhomogeneous medium reveals the character of the subbarrier electric field distribution. Fiz. Tverd. Tela (St. Petersburg) 40, 879–880 (May 1998)     

Analysis of thermionic emission from electrodeposited Ni–Si Schottky barriers

Ni–Si Schottky barriers are fabricated by electrodeposition using n on n+ Si substrates. I–V, C–V and low temperature I–V measurements are presented. A high-quality Schottky barrier with extremely low reverse leakage current is revealed. The results are shown to fit an inhomogeneous barrier model for thermionic emission over a Schottky barrier proposed by Werner and Guttler [J.H. Werner, H.H. Guttler, Barrier inhomogeneities at Schottky contacts, J. Appl. Phys. 69 (3) (1991) 1522–1533]. A mean value of 0.76 V and a standard deviation of 66 mV is obtained for the Schottky barrier height at room temperature with a linear bias dependence. X-ray diffraction and scanning electron microscopy measurements reveal a polycrystalline Ni film with grains that span from the Ni–Si interface to the top of the Ni layer. The variation in Ni orientation is suggested as a possible source of the spatial distribution of the Schottky barrier height.     

Phonon-assisted tunneling in Schottky barriers

Experimental current-voltage characteristics and their temperature dependencies for AlGaAs Schottky barrier structures are shown to be in agreement with the recent theory of phonon-assisted tunneling.     

Direct observation of the hysteretic Fermi level modulation in monolayer MoS2 field effect transistors

The hysteresis in the transfer curve of MoS₂ has significant impact on the device performance. However, the hysteresis mechanism is still not clear. Here, we investigate the hysteresis of the monolayer MoS₂ by probing the local Fermi level variations as a function of the back gate voltage in different atmosphere using the Kelvin probe microscopy. While the Fermi level of the MoS₂ in air is much lower than that in vacuum, both the MoS₂ devices in vacuum and air show large Fermi level hysteresis. The Fermi level hysteresis direction is clock-wise, identical to that observed in the transfer curves. Both the hysteresis in Fermi level and transfer curve can be explained consistently by taking into account the charge trapping. Our findings confirm that carrier density modulation in MoS₂ plays a vital role in the hysteresis, and provide insight into the hysteresis mechanism for the optimization of the device performance.     

Optical modulation of the effective channel thickness in GaAs field effect transistors with a Schottky gate (MESFETs)

Using a model relating the change in drain current with modulation of the effective channel thickness upon IR illumination of GaAs field effect transistors with a Schottky gate (MESFETs), it is shown that it is possible to determine the change in channel thickness and the concentration profile for deep centers in an FET channel. Profiles are given for the distribution of deep centers in the channels of GaAs MESFETs with different noise temperatures. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 349–353, May–June, 2006.     

Modification of Al/Si interface and Schottky barrier height with chemical treatment

The influence of different chemical treatments on the electrical behaviour of n- and p-type Al/Si Schottky junctions was studied. A Schottky barrier height of 0.91 eV was achieved on p-type Si probably due to the unpinning of the Fermi-level at the Al/Si interface. This is one of the highest barrier height values reported so far for a solid-state Schottky junction prepared to p-Si. A doping level reduction was observed in the vicinity of the Si surface for wafers with native oxide and for those boiled in acetone or annealed in forming gas. It was observed unexpectedly that the reactive plasma etch used for the formation of mesa structures decreases the apparent Schottky barrier height. The relation between the sum of n- and p-type Schottky barrier heights and forbidden gap is discussed.     

Excitons in ZnP2 crystals in the electric field of a Schottky barrier

A study is made of the effect of electric fields on the exciton states of β-ZnP₂ crystals (T=77 K) in structures with Schottky barriers formed by depositing semitransparent electrically-conducting InSnO₂ films on the crystal surface. The observed changes in the exciton optical reflection spectra when an electrical potential is applied to a barrier are explained by the shift and broadening of the exciton level caused by the Stark effect. The experimental data are compared with calculations based on a theory of exciton optical reflection from planar spatially nonuniform structures. Fiz. Tverd. Tela (St. Petersburg) 40, 884–886 (May 1998)     

InAs quantum dot field effect transistors

We have studied single electron and hole storage in self-assembled InAs quantum dots (QDs) embedded in GaAs/n-AlGaAs field effect transistors (QD-FETs). We prepared two types of QD-FETs. A single electron and a photo-generated single hole can be stored in each QD in Type 1. In the new Type II, single-electron discharge processes can be controlled by a surface gate voltage (V_g) as well as single-electron storage processes. We demonstrate possible application to novel photo devices and quantum dot memory devices.     

Si and Mg pair-doped interlayers for improving performance of AlGaN/GaN heterostructure field effect transistors grown on Si substrate

We report a novel structure of AlGaN/GaN heterostructure field effect transistors(HFETs) with a Si and Mg pairdoped interlayer grown on Si substrate. By optimizing the doping concentrations of the pair-doped interlayers, the mobility of 2DEG increases by twice for the conventional structure under 5 K due to the improved crystalline quality of the conduction channel. The proposed HFET shows a four orders lower off-state leakage current, resulting in a much higher on/off ratio(～ 109). Further temperature-dependent performance of Schottky diodes revealed that the inhibition of shallow surface traps in proposed HFETs should be the main reason for the suppression of leakage current.     

Self-connected horizontal silicon nanowire field effect transistor

We propose a technique to fabricate self-connected horizontal Si nanowire (NW) field effect transistors (FETs) by a self-assembly mechanism. We show direct growth of Si NWs between two predefined metallic electrodes along the SiO₂ gate oxide using the vapour–liquid–solid (VLS) growth mode. In our approach, the gold catalyst layer is covered by the contact metal, giving rise to selective and localized catalytic activity and growth of NWs from the gold edges. The diameter of the NWs can be adjusted by the thickness of the catalyst layer. Using such a process, we demonstrate field effect operation on the conductivity of a non-intentionally doped 20 nm diameter Si NW. This technique can be implemented in three dimensions, paving the way to three-dimensionalD integration using vertical stacks of self-connected FETs.     

Schottky barriers in carbon nanotube heterojunctions

Electronic properties of heterojunctions between metallic and semiconducting single-wall carbon nanotubes are investigated. Ineffective screening of the long-range Coulomb interaction in one-dimensional nanotube systems drastically modifies the charge transfer phenomena compared to conventional semiconductor heterostructures. The length of depletion region varies over a wide range sensitively depending on the doping strength. The Schottky barrier gives rise to an asymmetry of the I-V characteristics of heterojunctions, in agreement with recent experimental results by Yao et al. and Fuhrer et al. Dynamic charge buildup near the junction results in a steplike growth of the current at reverse bias.