Showing papers on "Schottky barrier published in 2005"

The Role of Metal-Nanotube Contact in the Performance of Carbon Nanotube Field-Effect Transistors

Abstract: Single-wall carbon nanotube field-effect transistors (CNFETs) have been shown to behave as Schottky barrier (SB) devices. It is not clear, however, what factors control the SB size. Here we present the first statistical analysis of this issue. We show that a large data set of more than 100 devices can be consistently accounted by a model that relates the on-current of a CNFET to a tunneling barrier whose height is determined by the nanotube diameter and the nature of the source/drain metal contacts. Our study permits identification of the desired combination of tube diameter and type of metal that provides the optimum performance of a CNFET.

Hysteretic current–voltage characteristics and resistance switching at an epitaxial oxide Schottky junction SrRuO3∕SrTi0.99Nb0.01O3

Abstract: Transport properties have been studied for a perovskite heterojunction consisting of SrRuO3 (SRO) film epitaxially grown on SrTi0.99Nb0.01O3 (Nb:STO) substrate. The SRO/Nb:STO interface exhibits rectifying current–voltage (I–V) characteristics agreeing with those of a Schottky junction composed of a deep work-function metal (SRO) and an n-type semiconductor (Nb:STO). A hysteresis appears in the I–V characteristics, where high resistance and low resistance states are induced by reverse and forward bias stresses, respectively. The resistance switching is also triggered by applying short voltage pulses of 1μs–10ms duration.

Comparing carbon nanotube transistors - the ideal choice: a novel tunneling device design

Abstract: Three different carbon nanotube (CN) field-effect transistor (CNFET) designs are compared by simulation and experiment. While a C-CNFET with a doping profile similar to a "conventional" (referred to as C-CNFET in the following) p-or n-MOSFET in principle exhibits superior device characteristics when compared with a Schottky barrier CNFET, we find that aggressively scaled C-CNFET devices suffer from "charge pile-up" in the channel. This effect which is also known to occur in floating body silicon transistors deteriorates the C-CNFET off-state substantially and ultimately limits the achievable on/off-current ratio. In order to overcome this obstacle we explore the possibility of using CNs as gate-controlled tunneling devices (T-CNFETs). The T-CNFET benefits from a steep inverse subthreshold slope and a well controlled off-state while at the same time delivering high performance on-state characteristics. According to our simulation, the T-CNFET is the ideal transistor design for an ultrathin body three-terminal device like the CNFET.

Metal-ferroelectric-metal heterostructures with Schottky contacts. I. Influence of the ferroelectric properties

Abstract: A model for metal-ferroelectric-metal heterostructures with Schottky contacts is proposed. The model adapts the general theories of metal-semiconductor rectifying contacts for the particular case of metal-ferroelectric contact by introducing the ferroelectric polarization as a sheet of surface charge located at a finite distance from the electrode interface, a deep trapping level of high concentration, and the static and dynamic values of the dielectric constant. Consequences of the proposed model on relevant quantities of the Schottky contact such as builtin voltage, charge density, and depletion width, as well as on the interpretation of the current-voltage and capacitance-voltage characteristics are discussed in detail.

Carbon nanotube Schottky diodes using Ti-Schottky and Pt-ohmic contacts for high frequency applications

Abstract: We have demonstrated Schottky diodes using semiconducting single-walled nanotubes (s-SWNTs) with titanium Schottky and platinum Ohmic contacts for high-frequency applications. The diodes are fabricated using angled evaporation of dissimilar metal contacts over an s-SWNT. The devices demonstrate rectifying behavior with large reverse bias breakdown voltages of greater than 15 V. To decrease the series resistance, multiple SWNTs are grown in parallel in a single device, and the metallic tubes are burnt-out selectively. At low biases these diodes showed ideality factors in the range of 1.5 to 1.9. Modeling of these diodes as direct detectors at room temperature at 2.5 terahertz (THz) frequency indicates noise equivalent powers (NEP) potentially comparable to that of the state-of-the-art gallium arsenide solid-state Schottky diodes, in the range of 10-13 W(square root)xHz.

Carbon nanotube Schottky diode and directionally dependent field-effect transistor using asymmetrical contacts

Abstract: We demonstrate the fabrication and operation of a carbon nanotube (CNT) based Schottky diode by using a Pd contact (high-work-function metal) and an Al contact (low-work-function metal) at the two ends of a single-wall CNT. We show that it is possible to tune the rectification current-voltage (I-V) characteristics of the CNT through the use of a back gate. In contrast to standard back gate field-effect transistors (FET) using same-metal source drain contacts, the asymmetrically contacted CNT operates as a directionally dependent CNT FET when gated. While measuring at source-drain reverse bias, the device displays semiconducting characteristics whereas at forward bias, the device is nonsemiconducting.

Enhancement mode III-nitride FET

Abstract: A III-nitride switch includes a recessed gate contact to produce a nominally off, or an enhancement mode, device. By providing a recessed gate contact, a conduction channel formed at the interface of two III-nitride materials is interrupted when the gate electrode is inactive to prevent current flow in the device. The gate electrode can be a schottky contact or an insulated metal contact. Two gate electrodes can be provided to form a bi-directional switch with nominally off characteristics. The recesses formed with the gate electrode can have sloped sides. The gate electrodes can be formed in a number of geometries in conjunction with current carrying electrodes of the device.

Silicon nanowires as enhancement-mode Schottky barrier field-effect transistors

Abstract: Silicon nanowire field-effect transistors (SiNWFETs) have been fabricated with a highly simplified integration scheme to function as Schottky barrier transistors with excellent enhancement-mode characteristics and a high on/off current ratio ~107. SiNWFETs show significant improvement in the thermal emission leakage (~6 × 10−13 A µm−1) compared to reference FETs with a larger channel width (~7 × 10−10 A µm−1). The drain current level depends substantially on the contact metal work function as determined by examining devices with different source/drain contacts of Ti (≈4.33 eV) and Cr (≈4.50 eV). The different conduction mechanisms for accumulation- and inversion-mode operation are discussed and compared with two-dimensional numerical simulation results.

Effect of hydrogen peroxide treatment on the characteristics of Pt Schottky contact on n-type ZnO

Abstract: We report on the formation of good Pt Schottky contacts on the Zn-terminated n-type ZnO (0001) surfaces (∼2×1017cm−3) using surface treatment with a hydrogen peroxide solution. The Pt contacts on organic solvent-cleaned ZnO (0001) show leaky behavior with a high leakage current of ∼−0.05A under −5V reverse bias voltage, whereas the hydrogen peroxide-treated contacts show Schottky behavior with very low leakage current of ∼−6.5×10−8A under −5V reverse bias voltage. Schottky barrier heights estimated from current-voltage and capacitance-voltage characteristics are 0.89 and 0.93eV, respectively. Room-temperature photoluminescence results show that the hydrogen peroxide treatment is fairly effective in removing deep-level defects near the ZnO surface region. In addition, the preliminary deep-level transient spectroscopy result is also presented.

Schottky barrier diodes for millimeter wave detection in a foundry CMOS process

Abstract: CoSi/sub 2/-Si Schottky barrier diodes on an n-well and on a p-well/substrate are fabricated without a guard ring in a 130-nm foundry CMOS process. The nand p-type diodes with an area of 16/spl times/0.32/spl times/0.32 /spl mu/m/sup 2/ achieve cutoff frequencies of /spl sim/1.5 and /spl sim/1.2 THz at 0-V bias, respectively. These are the highest cutoff frequencies for Schottky diodes fabricated in foundry silicon processes. The leakage currents at 1.0-V reverse bias vary between 0.4 to 10 nA for the n-type diodes. The break down voltage for these diodes is around 15 V. It should be possible to use these in millimeter wave and far infrared detection.

Chemical Optimization of Self-Assembled Carbon Nanotube Transistors

Abstract: We present the improvement of carbon nanotube field effects transistors (CNTFETs) performances by chemical tuning of the nanotube/substrate and nanotube/electrode interfaces. Our work is based on a method of selective placement of individual single walled carbon nanotubes (SWNTs) by patterned aminosilane monolayer and its use for the fabrication of self-assembled nanotube transistors. This method brings a relevant solution to the problem of systematic connection of self-organized nanotubes. The aminosilane monolayer reactivity can be used to improve carrier injection and doping level of the SWNT. We show that the Schottky barrier height at the nanotube/metal interface can be diminished in a continuous fashion down to an almost ohmic contact through these chemical treatments. Moreover, sensitivity to 20 ppb of triethylamine is demonstrated for self-assembled CNTFETs, thus opening new prospects for gas sensors taking advantages of the chemical functionality of the aminosilane used for assembling the CNTFETs.

n-Type field-effect transistors made of an individual nitrogen-doped multiwalled carbon nanotube.

Abstract: We report on the fabrication and characterization of field-effect transistor based on an individual multiwalled nitrogen-doped carbon nanotube. Our measurements show that the N-doped carbon nanotubes have n-type properties. The contact properties of the tube and Pt electrodes are also studied in detail. Temperature dependence of two-terminal transport experiments suggests that transport is dominated by thermionic emission and tunneling through a 0.2 eV Schottky contact barrier.

Tuning of NiSi/Si Schottky barrier heights by sulfur segregation during Ni silicidation

Abstract: The Schottky barrier height (SBH) of NiSi on Si(100) was tuned in a controlled manner by the segregation of sulfur (S) to the silicide∕silicon interface. S was implanted into silicon prior to silicidation. During subsequent Ni silicidation, the segregation of S at the NiSi∕Si interface leads to the change of the SBH. The SBH of NiSi decreased gradually on n-Si(100) from 0.65eV to 0.07eV and increased correspondingly on p-Si(100).

Grain boundary effect on the dielectric properties of CaCu3Ti4O12 ceramics

Abstract: The electrical properties of CaCu3Ti4O12 ceramic materials, showing an enormously large dielectric constant, were investigated. It was found that the grain boundary plays an important role in the giant dielectric behaviour of these ceramics. Measurement of the electrical current density (J) versus the electrical field (E) was carried out. A good linear relationship between lnJ and E1/2 was found, which demonstrates that the Schottky barrier should exist at the grain boundary. A double Schottky barrier model composed of a depletion layer and a negative charge sheet was proposed, analogous to the barrier model for ZnO varistors. An activation energy value of about 0.6 eV was obtained from the data of the characteristic frequency corresponding to the peak of the imaginary part of the dielectric permittivity versus temperature, which may be attributed to the activation of to in the depletion layer.

Characterization of in-grown stacking faults in 4H–SiC (0001) epitaxial layers and its impacts on high-voltage Schottky barrier diodes

Abstract: The density, shape and structure of in-grown stacking faults in 4H–SiC (0001) epitaxial layers have been characterized by cathodeluminescence, photoluminescence and high-resolution transmission electron microscopy. These analyses indicate that in-grown stacking faults are of 8H structure, and are generated mostly near the epilayer/substrate interface during chemical vapor deposition. The impact of the stacking faults on the performance of 4H–SiC (0001) Schottky barrier diodes has been investigated. It is revealed that the stacking faults cause the lowering of Schottky barrier height as well as the decrease of breakdown voltage.

Methods of fabricating nitride-based transistors with a cap layer and a recessed gate

Abstract: An anneal of a gate recess prior to formation of a gate contact, such as a Schottky contact, may reduce gate leakage and/or provide a high quality gate contact in a semiconductor device, such as a transistor. The use of an encapsulation layer during the anneal may further reduce damage to the semiconductor in the gate recess of the transistor. The anneal may be provided, for example, by an anneal of ohmic contacts of the device. Thus, high quality gate and ohmic contacts may be provided with reduced degradation of the gate region that may result from providing a recessed gate structure as a result of etch damage in forming the recess.

High mobility Ge-on-insulator p-channel MOSFETs using Pt germanide Schottky source/drain

Abstract: We demonstrate, for the first time, successful operation of Schottky-barrier source/drain (S/D) germanium-on-insulator (GOI) MOSFETs, where a buried oxide and a silicon substrate are used as a gate dielectric and a bottom gate electrode, respectively. Excellent performance of p-type MOSFETs using Pt germanide S/D is presented in the accumulation mode. The hole mobility enhancement of 50%/spl sim/40% against the universal hole mobility of Si MOSFETs is obtained for the accumulated GOI channel with the SiO/sub 2/-Ge interface.

Oxygen-induced p-type doping of a long individual single-walled carbon nanotube

Abstract: The effect of oxygen adsorption on a nanotube-based field effect transistor have been controversial as to whether it induces p-type doping of the nanotube body or the work function increase in the metal electrode. Here we report a transport measurement showing that a long individual single-walled nanotube can be doped as p-type upon oxygen adsorption. We discuss that, despite the fact that the charge transfer between the nanotube and O2 adsorbator has not been agreed to date, the effect of oxygen adsorption should still be interpreted as inducing p-type doping in the nanotube body. The n-type doping by NH3 adsorption is also measured for the purpose of comparison. Based on these observations, we suggest that, while the Schottky barrier management could be more effective for the transistor with a short nanotube, the doping effect could be more influential in devices with longer nanotubes.

Electrode dependence of resistance switching in polycrystalline NiO films

Abstract: We investigated resistance switching in top-electrode/NiO∕Pt structures where the top electrode was Au, Pt, Ti, or Al. For Pt∕NiO∕Pt and Au∕NiO∕Pt structures with ohmic contacts, the effective electric field inside the film was high enough to induce trapping or detrapping at defect states and thus resistance switching. For a Ti∕NiO∕Pt structure with well-defined Schottky contact at Ti∕NiO interface accompanied by an appreciable voltage drop, the effective electric field inside the NiO film was not enough to induce resistance switching. For an Al∕NiO∕Pt structure with a low Schottky barrier at the Al∕NiO interface, resistance switching could be induced at a higher voltage since the voltage drop at the Al∕NiO interface was not negligible but small.

High-performance 50-nm-gate-length Schottky-source/drain MOSFETs with dopant-segregation junctions

Abstract: High-performance operation was achieved in a novel Schottky-source/drain MOSFET (SBT: Schottky barrier transistor), which has dopant-segregation (DS) Schottky source/drain. Sub-100 nm complementary DS-SBTs were fabricated using the CoSi/sub 2/ process, which was fully compatible with the current CMOS technology. Excellent CMOS performance was obtained without any channel-mobility degradation, and CMOS ring oscillator was successfully demonstrated. In addition, >20 % improvement in drive current over the conventional n-MOSFETs was confirmed in the n-type DS-SBTs around the gate length of 50 nm.

A comparison study of symmetric ultrathin-body double-gate devices with metal source/drain and doped source/drain

Abstract: We have performed a simulation study of symmetric ultrathin-body double-gate (SUTBDG) devices with metal source/drain (S/D) structures designed for low-operating-power applications. A relatively high S/D Schottky barrier strongly influences the threshold voltages of the devices. The drive current (I/sub ON/) is dominated by barrier tunneling for nonnegative SBHs. Both electrons and holes may contribute to the off-state current (I/sub OFF/). Tunneling from the drain terminal limits the minimum obtainable I/sub OFF/. Germanium channel devices with metal S/D and a given I/sub OFF/ have smaller I/sub ON/ than similar silicon devices. With low nonnegative Schottky barrier heights (SBHs), metal S/D devices can outperform doped S/D devices, if the device performance degradation due to series resistances and parasitic capacitances is taken into account. Based on realistic device design rules, we have determined the upper bounds of S/D SBHs that allow metal S/D devices to offer improved performance over doped S/D devices with different body thicknesses.

Traps in AlGaN/GaN/SiC heterostructures studied by deep level transient spectroscopy

Abstract: AlGaN∕GaN∕SiC Schottky barrier diodes (SBDs), with and without Si3N4 passivation, have been characterized by temperature-dependent current-voltage and capacitance-voltage measurements, and deep level transient spectroscopy (DLTS). A dominant trap A1, with activation energy of 1.0 eV and apparent capture cross section of 2×10−12cm2, has been observed in both unpassivated and passivated SBDs. Based on the well-known logarithmic dependence of DLTS peak height with filling pulse width for a line-defect related trap, A1, which is commonly observed in thin GaN layers grown by various techniques, is believed to be associated with threading dislocations. At high temperatures, the DLTS signal sometimes becomes negative, likely due to an artificial surface-state effect.

Schottky barrier height modulation using dopant segregation in Schottky-barrier SOI-MOSFETs

Abstract: The effect of dopant segregation (DS) on the electrical behavior of silicon-on-insulator Schottky barrier MOSFETs (SB-MOSFETs) is investigated. Ion implantation with arsenic and boron and subsequent silicidation is used to create highly n- and p-doped interface layers at the silicide-silicon interface. As a result, a strong band bending occurs at the silicide-silicon interface giving rise to a lowering of the effective Schottky barrier height. In turn, an increased electron as well as hole injection into the channel leads to improvements of the off- and on-state of the SB-MOSFETs. Using dopant segregation n-type as well as p-type SB-MOSFETs with nickel silicide source/drain electrodes have been fabricated exhibiting an inverse sub-threshold slope close to the thermal limit and showing one order of magnitude higher on-currents if compared to SB-MOSFETs without DS. In essence, the use of dopant segregation allows the fabrication of high performance Schottky barrier MOSFETs.

Current transport in Zn/p-Si(1 0 0) Schottky barrier diodes at high temperatures

Abstract: In this study, we have performed behavior of the non-ideal forward bias current–voltage (I–V) and the reverse bias capacitance–voltage (C–V) characteristics of Zn/p-Si (metal–semiconductor) Schottky barrier diode (SBDs) with thin interfacial insulator layer. The forward bias I–V and reverse bias C–V characteristics of SBDs have been studied at the temperatures range of 300–400 K. SBD parameters such as ideality factor n, the series resistance (RS) determined Cheung's functions and Schottky barrier height, Φ b , are investigated as functions of temperature. The ideality factor n and RS were strongly temperature dependent and changed linearly with temperature and inverse temperature, respectively. The zero-bias barrier heights Φ b 0 ( I – V ) calculated from I–V measurements show an unusual behavior that it was found to increase linearly with the increasing temperature. However, the barrier height Φ b ( C – V ) calculated from C–V measurements at 500 kHz frequency decreased linearly with the increasing temperature. The correlation between Φ b 0 ( I – V ) and Φ b ( C – V ) barrier heights have been explained by taking into account ideality factors n and the tunneling factor ( α χ 1 / 2 δ ) in the current transport mechanism. Also, the temperature dependence of energy distribution of interface state density ( N SS ) was determined from the forward I–V measurements by taking into account the bias dependence of the effective barrier height. The higher values of n and RS were attributed to the presence of a native insulator on Si surface and to high density of interface states localized at semiconductor–native oxide layer (Si/SiO2) interface.

Temperature dependence of electrical parameters of the Au/n-InP Schottky barrier diodes

Abstract: The temperature dependence of current–voltage (I–V) and capacitance–voltage (C–V) characteristics of the Au/n-InP Schottky barrier diodes has been measured in the temperature range of 80–320 K. The forward I–V characteristics are analysed on the basis of standard thermionic emission (TE) theory and the assumption of a Gaussian distribution of the barrier heights (BHs). It has been shown that the ideality factor decreases while the barrier height increases with increasing temperatures, on the basis of TE theory. Furthermore, the homogeneous BH value of approximately 0.524 eV for the device has been obtained from the linear relationship between the temperature-dependent experimentally effective BHs and ideality factors. The modified Richardson plot, according to inhomogeneity of the BHs, has a good linearity over the temperature range. The value of Richardson constant A* has been found to be 5.97 A cm−2 K−2, which is close to the theoretical value of 9.4 A cm−2 K−2 for n-InP. Moreover, the temperature coefficient of the BH is found to be −3.16 × 10−4 eV K−1 for Au/n-InP.

Germanium pMOSFETs with Schottky-barrier germanide S/D, high-/spl kappa/ gate dielectric and metal gate

Abstract: Schottky-barrier source/drain (S/D) germanium p-channel MOSFETs are demonstrated for the first time with HfAlO gate dielectric, HfN-TaN metal gate and self-aligned NiGe S/D. The drain drivability is improved over the silicon counterpart with PtSi S/D by as much as /spl sim/5 times due to the lower hole Schottky barrier of the NiGe-Ge contact than that of PtSi-Si contact as well as the higher mobility of Ge channel than that of Si.

Tunneling-assisted Poole-Frenkel conduction mechanism in HfO2 thin films

Abstract: Tunneling-assisted Poole-Frenkel (TAPF) mechanism, which represents electron tunneling from a metal electrode to traps in a nearby insulator layer followed by detrapping of the electrons from the traps by virtue of a lowered potential well due to an applied electric field, is suggested in this study to precisely describe the electrical conduction behavior of a Pt∕HfO2∕Si capacitor. The current density versus the applied electric-field curves of the TAPF conduction show a similar electric-field dependency to that of the Poole-Frenkel (PF) conduction. However, unlike the PF mechanism, the activation energy of the leakage current density corresponds to the value of the Schottky barrier height (SBH) of a metal/insulator junction minus a lowered potential-well height by the applied electric field in the TAPF mechanism. In addition, the SBH of the Pt∕HfO2 junction is calculated considering a high space-charge density (>∼1018cm−3) in the HfO2 layer. The measured activation energy for the electrical conduction fr...

Semiconductor device and manufacturing method thereof

Abstract: PROBLEM TO BE SOLVED: To eliminate the problem wherein reliability is deteriorated, when peeling between a protective film and an electrode film takes place due to reaction between solder and the electrode film, at the soldering of connections or between flux and the electrode film at soldering work. SOLUTION: The semiconductor device is a Schottky junction type semiconductor device having an n semiconductor layer 2; an insulating film 4 formed on the n-type semiconductor layer 2; a first electrode film 7 forming the n-type semiconductor layer 2 and a Schottky barrier through the opening of the insulating film 4; a second electrode film 8 which is formed on the first electrode film 7 and extends on the insulating film 4; the protective film 5 which is formed on the second electrode film layer 8 and extends on the insulating film 4; a fourth electrode film 10 which contacts the second electrode film 8 through the opening of the protective film 5 and extends on the protective film 5; and a third electrode film 9 which is formed on the fourth electrode film 10 and can be connected with soldering. Reliability in a reverse direction can be improved. The semiconductor device can be also applied to ohmic electrode, such as a p-n junction diode. COPYRIGHT: (C)2006,JPO&NCIPI

Thermally stable visible-blind diamond photodiode using tungsten carbide Schottky contact

Abstract: We have developed a thermally stable, deep-ultraviolet (DUV) photodiode using tungsten carbide (WC) Schottky and Ti/WC ohmic contacts for a boron-doped homoepitaxial p-diamond epilayer. Effects of thermal annealing in an argon ambient on the electrical and photoresponse properties were investigated. Annealing at temperatures up to 550°C improves the rectifying current-voltage characteristics, resulting in a dramatic enhancement of DUV responsivity at 220nm by a factor of 4×103. A blind ratio as large as 105 between DUV and visible light has been achieved at a reverse bias as small as 1V. Development of the thermally stable WC-based Schottky and ohmic contacts provides a route for stable operation of a diamond photodetector at high temperatures.