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Showing papers on "Schottky barrier published in 2003"


Journal ArticleDOI
Ali Javey1, Jing Guo2, Qian Wang1, Mark Lundstrom2, Hongjie Dai1 
07 Aug 2003-Nature
TL;DR: It is shown that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotube, greatly reduces or eliminates the barriers for transport through the valence band of nanot tubes.
Abstract: A common feature of the single-walled carbon-nanotube field-effect transistors fabricated to date has been the presence of a Schottky barrier at the nanotube–metal junctions1,2,3. These energy barriers severely limit transistor conductance in the ‘ON’ state, and reduce the current delivery capability—a key determinant of device performance. Here we show that contacting semiconducting single-walled nanotubes by palladium, a noble metal with high work function and good wetting interactions with nanotubes, greatly reduces or eliminates the barriers for transport through the valence band of nanotubes. In situ modification of the electrode work function by hydrogen is carried out to shed light on the nature of the contacts. With Pd contacts, the ‘ON’ states of semiconducting nanotubes can behave like ohmically contacted ballistic metallic tubes, exhibiting room-temperature conductance near the ballistic transport limit of 4e2/h (refs 4–6), high current-carrying capability (∼25 µA per tube), and Fabry–Perot interferences5 at low temperatures. Under high voltage operation, the current saturation appears to be set by backscattering of the charge carriers by optical phonons. High-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers are thus realized.

3,126 citations


Patent
24 Jun 2003
TL;DR: In this article, a gate electrode is formed on the gate insulating layer, and a source contact and a drain contact are disposed at the both sides of the gate contact and are electrically connected to the channel layer via openings.
Abstract: A zinc oxide (ZnO) field effect transistor exhibits large input amplitude by using a gate insulating layer. A channel layer and the gate insulating layer are sequentially laminated on a substrate. A gate electrode is formed on the gate insulating layer. A source contact and a drain contact are disposed at the both sides of the gate contact and are electrically connected to the channel layer via openings. The channel layer is formed from n-type ZnO. The gate insulating layer is made from aluminum nitride/aluminum gallium nitride (AlN/AlGaN) or magnesium zinc oxide (MgZnO), which exhibits excellent insulation characteristics, thus increasing the Schottky barrier and achieving large input amplitude. If the FET is operated in the enhancement mode, it is operable in a manner similar to a silicon metal oxide semiconductor field effect transistor (Si-MOS-type FET), resulting in the formation of an inversion layer.

1,048 citations


01 Mar 2003
TL;DR: It is shown that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance.

857 citations


Journal ArticleDOI
Marcus Freitag1, Yves Martin1, James A. Misewich1, Richard Martel1, Phaedon Avouris1 
TL;DR: In this article, a single carbon nanotube incorporated as the channel of an ambipolar field-effect transistor (FET) was observed to have an estimated quantum efficiency of >10%.
Abstract: We observe infrared laser excited photoconductivity from a single carbon nanotube incorporated as the channel of an ambipolar field-effect transistor (FET). Electron−hole pairs are generated within the nanotube molecule, and the carriers are separated by an applied electric field between the source and drain contacts. The photocurrent shows resonances whose energies are in agreement with the energies of exciton states of semiconducting nanotubes of the appropriate diameter. The photocurrent is maximized for photons polarized along the direction of the carbon nanotube. Thus, the nanotube FET acts as a polarized photodetector with a diameter 1000 times smaller than the wavelength of the light it detects and has an estimated quantum efficiency of >10%. A photovoltage is observed when an asymmetric band lineup due to two nonequivalent Schottky barriers or an asymmetric coupling of the gate to the nanotube is present.

633 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed to combine ohmic metal-tube contacts, high dielectric constant HfO2 films as gate insulators, and electrostatically doped nanotube segments as source/drain electrodes to obtain high ON currents, sub-threshold swings of ~ 70-80 mV/decade.
Abstract: High performance enhancement mode semiconducting carbon nanotube field-effect transistors (CNTFETs) are obtained by combining ohmic metal-tube contacts, high dielectric constant HfO2 films as gate insulators, and electrostatically doped nanotube segments as source/drain electrodes. The combination of these elements affords high ON currents, subthreshold swings of ~ 70-80 mV/decade, and allows for low OFF currents and suppressed ambipolar conduction. The doped source and drain approach resembles that of MOSFETs and can impart excellent OFF states to nanotube FETs under aggressive vertical scaling. This presents an important advantage over devices with metal source/drain, or devices commonly referred to as Schottky barrier FETs.

408 citations


Journal ArticleDOI
06 Feb 2003-Nature
TL;DR: A multilayer photovoltaic device structure in which photon absorption instead occurs in photoreceptors deposited on the surface of an ultrathin metal–semiconductor junction Schottky diode is reported, which might provide the basis for durable low-cost solar cells using a variety of materials.
Abstract: There has been an active search for cost-effective photovoltaic devices since the development of the first solar cells in the 1950s (refs 1-3). In conventional solid-state solar cells, electron-hole pairs are created by light absorption in a semiconductor, with charge separation and collection accomplished under the influence of electric fields within the semiconductor. Here we report a multilayer photovoltaic device structure in which photon absorption instead occurs in photoreceptors deposited on the surface of an ultrathin metal-semiconductor junction Schottky diode. Photoexcited electrons are transferred to the metal and travel ballistically to--and over--the Schottky barrier, so providing the photocurrent output. Low-energy (approximately 1 eV) electrons have surprisingly long ballistic path lengths in noble metals, allowing a large fraction of the electrons to be collected. Unlike conventional cells, the semiconductor in this device serves only for majority charge transport and separation. Devices fabricated using a fluorescein photoreceptor on an Au/TiO2/Ti multilayer structure had typical open-circuit photovoltages of 600-800 mV and short-circuit photocurrents of 10-18 micro A cm(-2) under 100 mW cm(-2) visible band illumination: the internal quantum efficiency (electrons measured per photon absorbed) was 10 per cent. This alternative approach to photovoltaic energy conversion might provide the basis for durable low-cost solar cells using a variety of materials.

394 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that single-step tunneling is the dominant transport mechanism for electron spin polarization in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact.
Abstract: Electron-spin polarizations of 32% are obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact. An analysis of the transport data using the Rowell criteria demonstrates that single-step tunneling is the dominant transport mechanism. The current–voltage data show a clear zero-bias anomaly and phonon signatures corresponding to the GaAs-like and AlAs-like LO phonon modes of the AlGaAs barrier, providing further evidence for tunneling. These results provide experimental confirmation of several theoretical analyses, indicating that tunneling enables significant spin injection from a metal into a semiconductor.

319 citations


Journal ArticleDOI
TL;DR: In this article, the authors modeled grain boundaries in polycrystalline ZnO TFTs and performed simulation of the device by using a two-dimensional device simulator in order to determine the grain boundary effects on device performance.
Abstract: Thin-film transistors (TFTs) made of transparent channel semiconductors such as ZnO are of great technological importance because their insensitivity to visible light makes device structures simple. In fact, there have been several demonstrations of ZnO TFTs achieving reasonably good field effect mobilities of 1–10 cm2/V s, but the overall performance of ZnO TFTs has not been satisfactory, probably due to the presence of dense grain boundaries. We modeled grain boundaries in ZnO TFTs and performed simulation of a ZnO TFT by using a two-dimensional device simulator in order to determine the grain boundary effects on device performance. Polycrystalline ZnO TFT modeling was started by considering a single grain boundary in the middle of the TFT channel, formulated with a Gaussian defect distribution localized in the grain boundary. A double Schottky barrier was formed in the grain boundary, and its barrier height was analyzed as a function of defect density and gate bias. The simulation was extended to TFTs with many grain boundaries to quantitatively analyze the potential profiles that developed along the channel. One of the main differences between a polycrystalline ZnO TFT and a polycrystalline Si TFT is that the much smaller nanoscaled grains in a polycrystalline ZnO TFT induces a strong overlap of the double Schottky barriers with a higher activation energy in the crystallite and a lower barrier potential in the grain boundary at subthreshold or off-state region of its transfer characteristics. Through the simulation, we were able to estimate the density of total trap states localized in the grain boundaries for polycrystalline ZnO TFT by determining the apparent mobility and grain size in the device.

314 citations


Journal ArticleDOI
TL;DR: In this paper, a spin polarization of 32% was obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact.
Abstract: Electron spin polarizations of 32% are obtained in a GaAs quantum well via electrical injection through a reverse-biased Fe/AlGaAs Schottky contact. An analysis of the transport data using the Rowell criteria demonstrates that single step tunneling is the dominant transport mechanism. The current-voltage data show a clear zero-bias anomaly and phonon signatures corresponding to the GaAs-like and AlAs-like longitudinal-optical phonon modes of the AlGaAs barrier, providing further evidence for tunneling. These results provide experimental confirmation of several theoretical analyses indicating that tunneling enables significant spin injection from a metal into a semiconductor.

282 citations


Journal ArticleDOI
TL;DR: In this article, the properties of the contacts between single-walled carbon nanotubes (SWNTs) and Au electrodes were studied using scanning Kelvin probe and electrostatic force microscopies.
Abstract: The properties of the contacts between single-walled carbon nanotubes (SWNTs) and Au electrodes are studied using scanning Kelvin probe and electrostatic force microscopies. Contact potential differences and local dipoles at the SWNT/Au interface are determined under various conditions involving gas adsorption and surface passivation. In particular, the effects of the coadsorption of alkanethiol, S, and O2 are explored in detail. We find that the coadsorbates alter the energy-level line-up at the contacts and induce significant shifts of the SWNT bands relative to the metal Fermi level. This behavior is explained by considering the response of the local Au work function to the presence of the nanotube and of the coadsorbates as well as the effects of the adsorbate dipoles near the contacts. Finally, we use coadsorption to control the Schottky barrier height at the nanotube-Au contacts.

238 citations


Journal ArticleDOI
R. Ayouchi1
TL;DR: In this article, structural, optical, chemical and electrical properties of thin films of ZnO obtained by spray pyrolysis over Pt or silica substrates are determined at temperature ranges between 223 and 373 K.

Journal ArticleDOI
TL;DR: Au and Ag Schottky contacts on the epiready (0001)Zn surface of bulk n-ZnO crystals show Schotty barrier heights of 0.65-0.70 eV from capacitance-voltage measurements, activation energies for reverse saturation currents of 0 3 −0.4 eV and saturation current densities ranging from 10−5 A cm−2 on surfaces etched in HCl to 8×10−7 A¾2 on solvent cleaned samples.
Abstract: Au and Ag Schottky contacts on the epiready (0001)Zn surface of bulk n-ZnO crystals show Schottky barrier heights of 0.65–0.70 eV from capacitance–voltage measurements, activation energies for reverse saturation currents of 0.3–0.4 eV and saturation current densities ranging from 10−5 A cm−2 on surfaces etched in HCl to 8×10−7 A cm−2 on solvent cleaned samples. The diode ideality factors were in the range 1.6–1.8 under all conditions. The properties of both the Au and the Ag Schottky diodes were degraded by heating in vacuum to temperatures even as low as 365 K. The degradation mechanisms during annealing were different in each case, with the Au showing reaction with the ZnO surface and the Ag contacts showing localized delamination. Mechanical polishing of the ZnO surface prior to contact deposition produced a high-resistivity damaged layer with prominent deep level defects present with activation energies of 0.55 and 0.65 eV.

Patent
Sei-Hyung Ryu1
24 Apr 2003
TL;DR: The Schottky diode may have an active area less than the active area of a built-in body diode of the DMOSFET as mentioned in this paper, and it may have a turn-on voltage lower than that of the body diodes.
Abstract: Silicon carbide semiconductor devices and methods of fabricating silicon carbide semiconductor devices have a silicon carbide DMOSFET and an integral silicon carbide Schottky diode configured to at least partially bypass a built in diode of the DMOSFET. The Schottky diode may be a junction barrier Schottky diode and may have a turn-on voltage lower than a turn-on voltage of a built-in body diode of the DMOSFET. The Schottky diode may have an active area less than an active area of the DMOSFET.

Journal ArticleDOI
13 Jun 2003-Science
TL;DR: This work shows with the structure specifics of heteroepitaxy that the electrostatic boundary conditions can be set in a distinct interface phase that acts as a “Coulomb buffer” that will functionalize the barrier-height concept itself.
Abstract: The barrier height for electron exchange at a dielectric-semiconductor interface has long been interpreted in terms of Schottky9s theory with modifications from gap states induced in the semiconductor by the bulk termination. Rather, we show with the structure specifics of heteroepitaxy that the electrostatic boundary conditions can be set in a distinct interface phase that acts as a “Coulomb buffer.” This Coulomb buffer is tunable and will functionalize the barrier-height concept itself.

Journal ArticleDOI
TL;DR: In this article, the authors show that carbon nanotube Schottky-barrier transistors exhibit scaling that is qualitatively different than conventional transistors, which depends in an unexpected way on both the thickness and the dielectric constant of the gate oxide.
Abstract: We show that carbon nanotube Schottky-barrier transistors exhibit scaling that is qualitatively different than conventional transistors The performance depends in an unexpected way on both the thickness and the dielectric constant of the gate oxide Experimental measurements and theoretical calculations for ambipolar devices provide a consistent understanding of the novel scaling, which reflects the very different device physics of a Schottky-barrier transistor with a quasi-one-dimensional channel contacting a sharp edge A simple analytic model gives explicit scaling expressions for key device parameters such as subthreshold slope, turn-on voltage, and transconductance

Journal ArticleDOI
21 May 2003
TL;DR: These results demonstrate that spin injecting contacts can be formed using a very familiar and widely employed contact methodology, providing a ready pathway for the integration of spin transport into semiconductor processing.
Abstract: The use of carrier spin as a new degree-of-freedom in semiconductor devices offers new functionality and performance. However, efforts to implement semiconductor spintronics have been crippled by the lack of an efficient and practical means to electrically inject spin polarized carriers into a semiconductor device heterostructure. This paper summarizes progress toward that end using magnetic semiconductors and ferromagnetic metals as spin injecting contacts. We describe a very successful approach which employs a ferromagnetic metal/tunnel barrier contact, where the tunnel barrier is simply a tailored Schottky barrier which forms naturally between the ferromagnetic metal and the semiconductor itself. Initial efforts have demonstrated electron spin polarizations of at least 32% in GaAs quantum-well LED heterostructures. Significantly higher spin injection efficiencies are anticipated in optimized structures. These results demonstrate that spin injecting contacts can be formed using a very familiar and widely employed contact methodology, providing a ready pathway for the integration of spin transport into semiconductor processing.

Journal ArticleDOI
TL;DR: In this paper, the first 4H-SiC Schottky barrier diode (SBD) blocking over 10 kV was demonstrated using 115-spl mu/m n-type epilayers doped to 5.6 /spl times/ 10/sup 14/ cm/sup -3/ through the use of a multistep junction termination extension.
Abstract: This letter reports the demonstration of the first 4H-SiC Schottky barrier diode (SBD) blocking over 10 kV based on 115-/spl mu/m n-type epilayers doped to 5.6 /spl times/ 10/sup 14/ cm/sup -3/ through the use of a multistep junction termination extension. The blocking voltage substantially surpasses the former 4H-SiC SBD record of 4.9 kV. A current density of 48 A/cm/sup 2/ is achieved with a forward voltage drop of 6 V. The Schottky barrier height, ideality factor, and electron mobility for this very thick epilayer are reported. The SBD's specific-on resistance is also reported.

Journal ArticleDOI
TL;DR: In this paper, the Schottky contact was used to measure the charge collection efficiency of a semiconductor epitaxial 4H-SiC detector with different micropipe densities from CREE.
Abstract: Particle detectors were made using semiconductor epitaxial 4H–SiC as the detection medium. The investigated detectors are formed by Schottky contact (Au) on the epitaxial layer and an ohmic contact on the back side of 4H–SiC substrates with different micropipe densities from CREE. For radiation hardness studies, the detectors have been irradiated with protons ( 24 GeV /c ) at a fluence of about 10 14 cm −2 and with electrons (8.2 MeV ) and gamma-rays ( 60 Co source) at doses ranging from 0 to 40 Mrad . We present experimental data on the charge collection properties by using 5.48, 4.14 and 2.00 MeV α-particles impinging on the Schottky contact. Hundred percent charge collection efficiency (CCE) is demonstrated for reverse voltages higher than the one needed to have a depletion region equal to the α-particle projected range, even after the irradiation at the highest dose. By comparing measured CCE values with the outcomes of drift–diffusion simulations, values are inferred for the hole lifetime, τp, within the neutral region of the charge carrier generation layer. τp was found to decrease with increasing radiation levels, ranging from 300 ns in non-irradiated detectors to 3 ns in the most irradiated ones. The diffusion contribution of the minority charge carriers to CCE is pointed out.

Journal ArticleDOI
TL;DR: In this article, single-walled boron nitride nanotubes (BNNTs) were used to construct a field effect transistor (FET) with gate-induced barrier modulation.
Abstract: We have fabricated electronic devices based on single-walled boron nitride nanotubes (BNNTs). Our measurements indicate that all BNNTs are semiconducting, and p-doped. Temperature dependence of two terminal transport experiments suggests that at low drain fields, transport is dominated by thermionic emission over 250–300 meV Schottky contact barriers. Gate-induced barrier modulation was observed in vertically scaled devices, resulting in field-effect transistor operation.

Journal ArticleDOI
TL;DR: The Schottky barrier height is proportional to the metal work function, indicating that the Fermi level is not pinned at the GaN surface as discussed by the authors, which is a discrepancy between the work function of the metal and the resulting barrier height.
Abstract: Platinum, gold, and silver formed abrupt, unreacted, smooth, and epitaxial metal–semiconductor interfaces when deposited from the vapor onto clean, n-type GaN(0001) films. The Schottky barrier heights, determined from data acquired using x-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, capacitance–voltage, and current–voltage measurements agreed to within the experimental error for each contact metal and had the values of 1.2±0.1, 0.9±0.1, and 0.6±0.1 eV for Pt, Au, and Ag, respectively. The band bending and the electron affinity at the clean n-GaN surface were 0.3±0.1 and 3.1±0.1 eV, respectively. The barrier height is proportional to the metal work function, indicating that the Fermi level is not pinned at the GaN surface. However, discrepancies to the Schottky–Mott model were found as evidenced by a proportionality factor of 0.44 between the work function of the metal and the resulting Schottky barrier height. The sum of these discrepancies constitute the interface dipole contr...

Patent
04 Aug 2003
TL;DR: A semiconductor device including a schottky device and a trench type semiconductor switching device such as a MOSFET formed in a common die as mentioned in this paper is an example of such a device.
Abstract: A semiconductor device including a schottky device and a trench type semiconductor switching device such as a MOSFET formed in a common die.

Journal ArticleDOI
Lei Fu1, Yunai Liu1, PingAn Hu1, Kai Xiao1, Gui Yu1, Daoben Zhu1 
TL;DR: In this article, a Schottky junction diode was fabricated using individual Ga2O3 nanoribbons, and the measured current−voltage characteristic exhibited clear rectifying behavior with a turn-on voltage of 0.5 V and a rectification ratio of 2.5 × 104 at ±2 V.
Abstract: Semiconductive Ga2O3 nanoribbons have been synthesized via hydrogen-assisted thermal evaporation at 1000 °C. The width of the nanoribbons could be controlled by adjusting the content of hydrogen in a mixture of carrier gases. The room-temperature photoluminescence spectrum reveals that there exists a strong blue emission band centered at 430 nm. The blue emission is mainly attributed to the oxygen vacancies in the Ga2O3 nanoribbons. We have fabricated a Schottky junction diode, utilizing individual Ga2O3 nanoribbons, and studied its electrical transport properties. The measured current−voltage characteristic exhibited clear rectifying behavior with a turn-on voltage of 0.5 V and a rectification ratio of 2.5 × 104 at ±2 V.

Journal ArticleDOI
TL;DR: In this article, a GaN LED with a Schottky diode was shown to increase the electrostatic discharge threshold from 450 to 1300 V. Although the reverse current and the forward turn-on voltage were both higher for the GaN LEDs with the diode.
Abstract: GaN Schottky diodes were built internally inside the GaN green LEDs by using etching and redeposition techniques. By properly selecting the etching areas underneath the bonding pads, one can minimize the optical loss due to the etching process. Although the reverse current and the forward turn-on voltage were both higher for the GaN LED with a Schottky diode, it was found that the internal Schottky diode could significantly increase the electrostatic discharge threshold from 450 to 1300 V.

Patent
18 Aug 2003
TL;DR: In this article, the authors describe one-chip micro-integrated optoelectronic sensors and methods for fabricating and using the same, including an optical emission source, optical filter and a photodetector.
Abstract: This disclosure describes one-chip micro-integrated optoelectronic sensors and methods for fabricating and using the same. The sensors may include an optical emission source, optical filter and a photodetector fabricated on the same transparent substrate using the same technological processes. Optical emission may occur when a bias voltage is applied across a metal-insulator-semiconductor Schottky contact or a p-n junction. The photodetector may be a Schottky contact or a p-n junction in a semiconductor. Some sensors can be fabricated on optically transparent substrate and employ back-side illumination. In the other sensors provided, the substrate is not transparent and emission occurs from the edge of a p-n junction or through a transparent electrode. The sensors may be used to measure optical absorption, optical reflection, scattering or fluorescence. The sensors may be fabricated and operated to provide a selected spectrum of light emitted and a multi-quantum well heterostructure may be fabricated to filter light reaching the photodetector.

Journal ArticleDOI
TL;DR: In this article, the effect of high-energy radiation exposure on device characteristics is discussed taking into account possible contact inhomogeneities arising from dislocations and interfacial defects, and the effects observed in the Schottky diode I-V and C-V characteristics indicate that the total-dose radiation hardness of GaN devices may be limited by susceptibility of the metal-GaN interface to radiation-induced damage.
Abstract: The effect of /spl gamma/-ray exposure on the electrical characteristics of nickel/n-GaN Schottky barrier diodes has been investigated using current-voltage (I-V), capacitance-voltage (C-V), and deep-level transient spectroscopy (DLTS) measurements. The results indicate that /spl gamma/-irradiation induces an increase in the effective Schottky barrier height extracted from C-V measurements. Increasing radiation dose was found to degrade the reverse leakage current, whereas its effect on the forward I-V characteristics was negligible. Low temperature (/spl les/50) post-irradiation annealing after a cumulative irradiation dose of 21 Mrad(Si) was found to restore the reverse I-V characteristics to pre-irradiation levels without significantly affecting the radiation-induced changes in C-V and forward I-V characteristics. Three shallow radiation-induced defect centers with thermal activation energies of 88 104 and 144 meV were detected by DLTS with a combined production rate of 2.12 /spl times/ 10/sup -3/ cm/sup -1/. These centers are likely to be related to nitrogen-vacancies. The effect of high-energy radiation exposure on device characteristics is discussed taking into account possible contact inhomogeneities arising from dislocations and interfacial defects. The DLTS results indicate that GaN has an intrinsically low susceptibility to radiation-induced material degradation, yet the effects observed in the Schottky diode I-V and C-V characteristics indicate that the total-dose radiation hardness of GaN devices may be limited by susceptibility of the metal-GaN interface to radiation-induced damage.

Journal ArticleDOI
TL;DR: In this paper, the optical band gap and optical constants (absorption coefficient, refractive index and extinction coefficient) of polycrystalline thin films of PbS have been determined by absorbance and transmittance measurements using Fourier transform infrared spectrophotometer.
Abstract: The narrow gap lead chalcogenides and related solid solutions have been the materials of considerable technological importance. Their unusual and unique characteristics make them a preferred subject for solid state research and development. The high quality polycrystalline thin films of PbS have been deposited onto ultra-clean glass substrates by vacuum evaporation technique. The as-deposited films were annealed in vacuum at 350 K. The optical, electrical and structural investigations on PbS thin films have been carried out. The optical band gap and optical constants (absorption coefficient, refractive index and extinction coefficient) of the films were determined by absorbance and transmittance measurements using Fourier transform infrared spectrophotometer. The DC conductivity and activation energy of the films were measured in temperature range 300–380 K. The schottky junction of PbS with indium was made and the barrier height and ideality factor were determined using current–voltage characteristics. The sample quality, crystal structure and lattice parameter of the films were determined from X-ray diffraction pattern.

Journal ArticleDOI
Jing Guo1, Jing Wang1, Eric Polizzi1, Supriyo Datta1, Mark Lundstrom1 
01 Dec 2003
TL;DR: In this article, the electrostatics of nanowire transistors are studied by solving the Poisson equation selfconsistently with the equilibrium carrier statistics of the nanowires.
Abstract: The electrostatics of nanowire transistors are studied by solving the Poisson equation self-consistently with the equilibrium carrier statistics of the nanowire. For a one-dimensional, intrinsic nanowire channel, charge transfer from the metal contacts is important. We examine how the charge transfer depends on the insulator and the metal/semiconductor Schottky barrier height. We also show that charge density on the nanowire is a sensitive function of the contact geometry. For a nanowire transistor with large gate underlaps, charge transferred from bulk electrodes can effectively "dope" the intrinsic, ungated region and allow the transistor to operate. Reducing the gate oxide thickness and the source/drain contact size decreases the length by which the source/drain electric field penetrates into the channel, thereby, improving the transistor characteristics.

Journal ArticleDOI
TL;DR: In this article, the barrier heights of Ir, Ni, and Re Schottky contacts on strained Al0.25Ga0.75N/GaN heterostructures were characterized using capacitance-voltage (C-V) and I-V techniques.
Abstract: Ir, Ni, and Re Schottky contacts on strained Al0.25Ga0.75N/GaN heterostructures are characterized using capacitance–voltage (C–V) and I–V techniques. Based on the measured C–V characteristics, two dimensional electron gas sheet carrier concentrations at the AlGaN/GaN interface and barrier heights of Ir, Ni, and Re Schottky contacts are calculated. The barrier heights of 1.12, 1.27, and 1.68 eV are obtained for Ir, Ni, and Re Schottky contacts, respectively. The results show that the barrier heights of Schottky contacts on strained AlGaN/GaN heterostructures are strongly dependent on the metal work functions. However, contrary to Schottky contacts on bulk AlGaN or GaN, the barrier height on strained AlGaN/GaN heterostructures is lower for a Schottky contact with a higher metal work function. This is attributed to the stronger wave function coupling between electrons in the Schottky metal and surface donor electrons. The I–V characteristics for Ir, Ni, and Re Schottky contacts confirm the results obtained b...

Journal ArticleDOI
TL;DR: In this paper, the Schottky barrier height at the interface between Pd and TiO 2 induced by H 2 was larger in N 2 than in air, and also under reverse bias than forward bias conditions.
Abstract: TiO 2 thin films have been prepared by anodic oxidation of Ti plates at different temperatures, and H 2 sensing properties of the obtained TiO 2 thin film sensors equipped with a Pt and Ti electrode have been investigated both in air and N 2 under forward and reverse bias conditions. The TiO 2 thin film prepared by the anodic oxidation at 20 °C had a large number of sub-micron pores, and exhibited the highest sensitivity and reversible response to H 2 both in air and N 2 under forward and reverse bias conditions. The current–voltage ( I – V ) characteristic of the sensor was roughly Ohmic in 0.8% H 2 balanced with N 2 , while it was non-Ohmic in other environments studied. In addition, the change in the Schottky barrier height at the interface between Pd and TiO 2 induced by H 2 was larger in N 2 than in air, and also under reverse bias than forward bias conditions. The reversible and concentration-dependent H 2 sensitivity of the sensor in N 2 was suggested to arise mainly from the change in the Schottky barrier height induced by dissolution of H atoms in the Pd bulk.

Journal ArticleDOI
Jin-Ping Ao1, Daigo Kikuta1, Naotaka Kubota1, Yoshiki Naoi1, Yasuo Ohno1 
TL;DR: In this article, a copper gate AlGaN/GaN high electron mobility transistors (HEMTs) with low gate leakage current was demonstrated, and the Schottky barrier height of Cu on n-GaN was 0.18 eV higher than that of Ni/Au.
Abstract: Copper (Cu) gate AlGaN/GaN high electron mobility transistors (HEMTs) with low gate leakage current were demonstrated. For comparison, nickel/gold (Ni/Au) gate devices were also fabricated with the same process conditions except the gate metals. Comparable extrinsic transconductance was obtained for the two kinds of devices. At gate voltage of -15 V, typical gate leakage currents are found to be as low as 3.5/spl times/10/sup -8/ A for a Cu-gate device with gate length of 2 /spl mu/m and width of 50 /spl mu/m, which is much lower than that of Ni/Au-gate device. No adhesion problem occurred during these experiments. Gate resistance of Cu-gate is found to be about 60% as that of NiAu. The Schottky barrier height of Cu on n-GaN is 0.18 eV higher than that of Ni/Au obtained from Schottky diode experiments. No Cu diffusion was found at the Cu and AlGaN interface by secondary ion mass spectrometry determination. These results indicate that copper is a promising candidate as gate metallization for high-performance power AlGaN/GaN HEMT.