Showing papers on "Schottky barrier published in 2000"

Band offsets of wide-band-gap oxides and implications for future electronic devices

Abstract: Wide-band-gap oxides such as SrTiO3 are shown to be critical tests of theories of Schottky barrier heights based on metal-induced gap states and charge neutrality levels. This theory is reviewed and used to calculate the Schottky barrier heights and band offsets for many important high dielectric constant oxides on Pt and Si. Good agreement with experiment is found for barrier heights. The band offsets for electrons on Si are found to be small for many key oxides such as SrTiO3 and Ta2O5 which limit their utility as gate oxides in future silicon field effect transistors. The calculations are extended to screen other proposed oxides such as BaZrO3. ZrO2, HfO2, La2O3, Y2O3, HfSiO4, and ZrSiO4. Predictions are also given for barrier heights of the ferroelectric oxides Pb1−xZrxTiO3 and SrBi2Ta2O9 which are used in nonvolatile memories.

Crossed Nanotube Junctions

Abstract: Junctions consisting of two crossed single-walled carbon nanotubes were fabricated with electrical contacts at each end of each nanotube. The individual nanotubes were identified as metallic (M) or semiconducting (S), based on their two-terminal conductances; MM, MS, and SS four-terminal devices were studied. The MM and SS junctions had high conductances, on the order of 0.1 e 2 / h (where e is the electron charge and h is Planck9s constant). For an MS junction, the semiconducting nanotube was depleted at the junction by the metallic nanotube, forming a rectifying Schottky barrier. We used two- and three-terminal experiments to fully characterize this junction.

Chemical Bonding and Fermi Level Pinning at Metal-Semiconductor Interfaces

Abstract: Since the time of Bardeen, Fermi level pinning at metal-semiconductor interfaces has traditionally been attributed to interface gap states. The present work shows that polarized chemical bonds at metal-semiconductor interfaces can lead to the apparent Fermi level pinning effect. Good agreement with various systematics of polycrystalline Schottky barrier height experiments has been found. These findings suggest that chemical bonding is a primary mechanism of the Schottky barrier height.

Role of fermi-level pinning in nanotube schottky diodes

Abstract: At semiconductor-metal junctions, the Schottky barrier height is generally fixed by "Fermi-level pinning." We find that when a semiconducting carbon nanotube is end contacted to a metal (the optimal geometry for nanodevices), the behavior is radically different. Even when the Fermi level is fully "pinned" at the interface, the turn-on voltage is that expected for an unpinned junction. Thus the threshold may be adjusted for optimal device performance, which is not possible in planar contacts. Similar behavior is expected at heterojunctions between nanotubes and semiconductors.

Barrier height inhomogeneities of epitaxial CoSi2 Schottky contacts on n-Si (100) and (111)

Abstract: The forward current–voltage characteristics of epitaxial CoSi 2 contacts grown by Ti-interlayer mediated epitaxy (TIME) scheme on n-type Si substrates of both (100) and (111) orientations are studied in the temperature range from 80 to 300 K At high temperatures (>220 K), the I–V characteristics obey the ideal thermionic emission model The Schottky barrier heights stay ∼061 eV and the ideality factors are close to unity At low temperatures, a change in the characteristics is observed around 10 −4 A/cm 2 , which is more significant for the contacts on Si (111) than for those on Si (100) Above this current, the I–V curves can also be fitted by the equation based on the thermionic emission theory, but the apparent barrier heights decrease and the ideality factors increase with decreasing temperature This abnormal behavior, as well as the curved Richardson plots, are interpreted by the assumption of a Gaussian distribution of barrier heights, which is in agreement with the statistical distribution obtained directly from ballistic electron emission microscopy (BEEM) measurements The excess current at small bias region is explained by coexistence of some small patches of reduced barrier height with the pinch-off model The CoSi 2 contacts on Si (111) contain more patches with larger parameter values than those on Si (100), which causes a significant difference in the I–V characteristics at low temperature

Organic electroluminescent devices: enhanced carrier injection using SAM derivatized ITO electrodes

Abstract: Taking as a device model ITO|TPD|Alq3|Al (where TPD is N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine and Alq3 is tris(quinolin-8-olato)aluminium) it is shown that control and improvement of carrier injection may be achieved using self-assembled monolayers (SAMs) to manipulate the Schottky energy barrier at the ITO–TPD interface. By using polar adsorbate molecules with the dipole oriented outward from the surface an artificial dipolar layer is formed and the work function is increased, and viceversa. With this method the threshold voltage for light emission (turn-on) can be reduced by 4 V and the maximum luminance increased by a factor of 3.5, giving an overall performance superior to that using the more stable Ag/Mg counter electrode. The SAMs effect is confirmed using a Scanning Kelvin Probe (SKP) to profile the relative work function of half-coated ITO samples. Increases in work function in excess of 0.3 eV are observed, in line with predictions using the calculated molecular dipoles of the SAM molecules.

Monolithically integrated trench mosfet and schottky diode

Abstract: A monolithically integrated Schottky diode together with a high performance trenched gate MOSFET. A MOS enhanced Schottky diode structure (210) is interspersed throughout the trench MOSFET cell array (206, 212) to enhance the performance characteristics of the MOSFET switch. The forward voltage drop is reduced by taking advantage of the low barrier height of the Schottky structure. In a specific embodiment, the width of the trench is adjusted such that depletion in the drift region of the Schottky is influenced and controlled by the adjacent MOS structure to increase the reverse voltage capability of the Schottky diode.

High frequency conductivity of the high-mobility two-dimensional electron gas

Abstract: We measure the real and imaginary conductivity sigma(k = 0,omega) of a high-mobility two-dimensional electron gas (2DEG) system at frequencies below and above the momentum scattering rate. The imaginary part of the 2DEG impedance is observed to be inductive, consistent with the Drude model. Using this kinetic inductance, we construct a transmission line by capacitively coupling the 2DEG to an Al Schottky barrier gate separated by 5000 A from the 2DEG. The measured wave velocity and temperature-dependent damping of this transmission line are in good agreement with a simple Drude model. Exciting these modes is equivalent to exciting a 2D plasma mode strongly modified by the interaction between the 2DEG and the gate.

Dependence of Ni/AlGaN Schottky barrier height on Al mole fraction

Abstract: The dependence of the Schottky barrier height of Ni/AlxGa1−xN contact on the Al mole fraction up to x=0.23 was studied. The barrier heights were measured by I–V, capacitance–voltage, and the internal photoemission method. The Al mole fractions were estimated from the AlGaN band gap energies measured by photoluminescence. In the range of x<0.2 a linear relationship between the barrier height and Al mole fraction was obtained. This was consistent with the slope predicted by the Schottky rule. For x=0.23, the measured barrier height was lower than predicted. We believed this was due to crystalline defects at the Ni/AlGaN interface.

Effects of thin oxide in metal-semiconductor and metal-insulator-semiconductor epi-GaAs Schottky diodes

Abstract: The current–voltage (I–V) and capacitance–voltage (C–V) characteristics of metal–insulator–semiconductor (MIS) GaAs Schottky diodes are investigated and compared with metal–semiconductor (MS) diodes. The MIS diode showed nonideal behavior of I–V characteristics with an ideality factor of 1.17 and a barrier height of 0.97 eV. The energy distribution of interface states density was determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height, though it is small. The reduction in the saturation current in the MIS case is caused by a thin oxide layer and is due to the combination of increased barrier height and a decrease in the Richardson constant. The carrier concentration anomaly observed between the MIS and MS diodes measured from reverse bias C–V measurements is explained via oxide $(\beta-Ga_2O_3)$ traps due to the Ga-vacancy by deep level transient spectroscopy (DLTS) measurement.

A unified simulation of Schottky and ohmic contacts

Abstract: The Schottky contact is an important consideration in the development of semiconductor devices. This paper shows that a practical Schottky contact model is available for a unified device simulation of Schottky and ohmic contacts. The present model includes the thermionic emission at the metal/semiconductor interface and the spatially distributed tunneling calculated at each semiconductor around the interface. Simulation results of rectifying characteristics of Schottky barrier diodes (SBD's) and resistances under high impurity concentration conditions are reasonable, compared with measurements. As examples of application to actual devices, the influence of the contact resistance on salicided MOSFETs with source/drain extension and the immunity of Schottky barrier tunnel transistors (SBTTs) from the short-channel effect (SCE) are demonstrated.

Optically and thermally detected deep levels in n-type Schottky and p+-n GaN diodes

Abstract: N-Schottky and p+–n GaN junctions are currently used for different technologies. A comparison of the deep levels found throughout the entire band gap of n-GaN grown by metal-organic chemical vapor deposition under both configurations is presented. Both deep level optical spectroscopy and deep level transient spectroscopy measurements are used allowing the observation of both majority and minority carrier traps. Deep levels at Ec−Et=0.58–0.62, 1.35, 2.57–2.64, and 3.22 eV are observed for both diode configurations, with concentrations in the ∼1014–1016 cm−3 range. The 0.58–0.62 eV level appears correlated with residual Mg impurities in the n side of the p+–n diode measured by secondary-ion-mass spectroscopy, while the 1.35 eV level concentration increases by a factor of ∼4 for the Schottky junction possibly correlating with the carbon profile. The 2.57–2.64 eV level is a minority carrier hole trap in n-GaN, likely related to the yellow photoluminescence band, and is detected both optically from the conduct...

Analysis and modeling of AlxGa1−xN-based Schottky barrier photodiodes

Abstract: Schottky barrier photovoltaic detectors have been fabricated on n-AlxGa1−xN(0⩽x⩽0.35) and p-GaN epitaxial layers grown on sapphire. Their characteristics have been analyzed and modeled, in order to determine the physical mechanisms that limit their performance. The influence of material properties on device parameters is discussed. Our analysis considers front and back illumination and distinguishes between devices fabricated on ideal high-quality material and state-of-the-art heteroepitaxial AlxGa1−xN. In the former case, low doping levels are advisable to achieve high responsivity and a sharp spectral cutoff. The epitaxial layer should be thin (<0.5 μm) to optimize the ultraviolet/visible contrast. In present devices fabricated on heteroepitaxial AlxGa1−xN, the responsivity is limited by the diffusion length. In this case, thick AlxGa1−xN layers are advisable, because the reduction in the dislocation density results in lower leakage currents, larger diffusion length, and higher responsivity. In order to...

SiO 2 -Passivated Lateral-Geometry GaN Transparent Schottky-Barrier Detectors

Abstract: We report on a transparent Schottky-barrier ultraviolet detector on GaN layers over sapphire substrates. Using SiO2 surface passivation, reverse leakage currents were reduced to a value as low as 1 pA at 5 V reverse bias for 200 μm diameter device. The device exhibits a high internal gain, about 50, at low forward biases. The response time (about 15 ns) is RC limited, even in the internal gain regime. A record low level of the noise spectral density, 5×10−23 A2/Hz, was measured at 10 Hz. We attribute this low noise level to the reduced reverse leakage current.

Simulation of Schottky barrier MOSFETs with a coupled quantum injection/Monte Carlo technique

Abstract: A full-band Monte Carlo device simulator has been used to analyze the performance of sub-0.1 /spl mu/m Schottky barrier MOSFETs. In these devices, the source and drain contacts are realized with metal silicide, and the injection of carriers is controlled by gate voltage modulation of tunneling through the source barrier. A simple model treating the silicide regions as metals, coupled with an Airy function approach for tunneling through the barrier, provides injecting boundary conditions for the Monte Carlo procedure. Simulations were carried out considering a p-channel device with 270 /spl Aring/ gate length for which measurements are available. Our results show that in these structures there is not a strong interaction with the oxide interface as in conventional MOS devices and carriers are injected at fairly wide angles from the source into the bulk of the device. The Monte Carlo simulations not only give good agreement with current-voltage (I-V) curves, but also easily reproduce the subthreshold behavior since all the computational power is devoted to simulation of channel particles. The simulations also clarify why these structures exhibit a large amount of leakage in subthreshold regime, due to both thermionic and tunneling emission. Computational experiments suggest ways to modify the doping profile to reduce to some extent the leakage.

Schottky barrier effects in the photocurrent of sol–gel derived lead zirconate titanate thin film capacitors

Abstract: We studied the photoresponse of Pb(Zr0.53Ti0.47)O3 (PZT) thin films by measuring the current–voltage (I–V) curve at several ferroelectric polarization states illuminated by a monochromatic 3.5 eV UV light. The photocurrent in Pt/PZT/Pt capacitors was sensitive to the polarization state, and the poling voltage-dependent photocurrent showed very asymmetric hysteresis behavior. The capacitance that is dependent upon the thickness of the samples was first measured. Then, the capacitance of the interfacial layer at a state with no interdiffusion between Pt and PZT film was extrapolated by using an equivalent circuit model. The result of the extrapolation was 28.1 μF/cm2.

Gas-sensitive characteristics of metal/semiconductor polymer Schottky device

Abstract: Metal/polymer Schottky barrier diodes have been fabricated using electrochemically prepared films of polyaniline as the semiconductor and aluminium as the metal. Polyaniline was doped with HCl at room temperature to form a p-type semiconductor. On a sandwich-type device, the junction at Al/polyaniline showed rectifying behavior, and was used as a sensor for the detection of methane gas. The current–voltage ( I – V ) and capacitance–voltage ( C – V ) characteristics have been studied at room temperature, and the shifts in the I – V and C – V dependence of the diodes were measured with different concentrations of gas for different time intervals. The data have been analysed and interpreted on the basis of the thermionic emission mechanism.

Evaluation of Schottky contact parameters in metal–semiconductor–metal photodiode structures

Abstract: The electrical behavior of metal–semiconductor–metal (MSM) Schottky barrier photodiode structures is analyzed by means of current–voltage measurements at different temperatures. The reverse characteristics of the Schottky contact are examined by taking into account the barrier height dependence on the electric field and tunneling through the barrier. It is shown that, under these conditions, the logarithmic dependence of the reverse current on the reverse bias is a linear function and allows us to evaluate the barrier height, saturation current density, and junction ideality factor of the MSM-photodiode Schottky contact. The results are well consistent with experiment.

Electrical characteristics of CoSi2/n-Si(100) Schottky barrier contacts formed by solid state reaction.

Abstract: The Schottky barrier height (SBH) of CoSi 2 contacts formed by solid state reaction of Co, Co/Ti, Ti/Co and Ti/Co/SiO 2 on n-Si(1 0 0) substrates has been measured in the temperature range from 80 to 300 K with the use of current– and capacitance–voltage techniques. The forward I – V characteristics are analyzed on the basis of the standard thermionic emission model and the assumption of a Gaussian distribution of the barrier heights. The difference in SBHs determined from the I – V and C – V data is temperature dependent. From this difference, the standard deviation and its temperature coefficient are derived and are in the range of 58–78 meV and −0.07 to −0.14 meV K −1 , respectively. The Richardson plots, modified according to the Gaussian distribution model, have a good linearity over the whole temperature range for all samples. The corresponding activation energy is in good agreement with the barrier height determined from the C – V data. The SBH of the CoSi 2 contacts grown from Co and Ti bimetallic layers is lower than that grown from a Co layer only. The temperature coefficient of the SBH varies from approximately −0.16 meV K −1 for polycrystalline CoSi 2 to ∼0 meV K −1 for epitaxial CoSi 2 contacts, thus suggesting different interfacial Fermi level pinning at the CoSi 2 /Si contacts grown from different multilayer structures.

Mechanisms for the reduction of the Schottky barrier heights of high-quality nonalloyed Pt contacts on surface-treated p-GaN

Abstract: X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical bonding and electronic properties of the interfaces between Pt and p-GaN layers that were two-step surface treated using a buffered-oxide etch solution, and hence, to understand the surface-treatment time dependence of the Schottky barrier height (SBH). Current–voltage (I–V) measurements show that the effective SBH decreases with increasing surface-treatment time. The XPS results show that as the treatment time increases, the Ga 2p and Pt 4f core levels for the 20-min-treated samples shift toward the lower-binding-energy side by 0.6 and 1.5 eV, respectively, compared to the 0.5-min-treated one. It is further shown that the intensity of the oxygen core-level peak decreases with increasing treatment time. Based on the I–V and XPS results, the observed reduction of the effective SBHs is attributed to the combined effects of the effective removal of the native oxide and the shift of the surface Fermi level toward the valence-band ...

Surface recombination and sulfide passivation of GaN

Abstract: The surface recombination velocity in n-type heteroepitaxial GaN(0001) is shown to decrease dramatically when the surface is chemically treated with aqueous and alcoholic solutions of inorganic sulfides, such as ammonium or sodium sulfide (NH4)2Sx and Na2S). The room-temperature excitonic photoluminescence (PL) intensity increases by a factor of four to six after treatment, and improvements persist for at least seven months in room air. Various other chemicals commonly used in device processing are investigated and shown to change the PL intensity by factors ranging from 0.7 to 2.5, buffered oxide etching being the most beneficial. Schottky barrier diodes using gold as the contact metal are fabricated using a sulfide treatment prior to evaporation. The barrier height from capacitance-voltage measurements is as high as 1.63 ± 0.07 V, the highest value ever achieved on n-GaN. This result is evidence that the effect of surface states on the Fermi level has been substantially reduced by the treatment.

A 2.8kV, Forward Drop JBS Diode with Low Leakage

Abstract: High voltage Schottky-, Junction Barrier Schottky (JBS)- and PiN-diodes with an implanted JTE termination have been fabricated on the same 4H-SiC wafer. Blocking voltages of 2.5-2.8 kV were reached for JBS and PiN diodes while the Schottky diodes reach about 2.0 kV. It is shown that the JBS design increases the blocking voltage effectively compared to the Schottky device with less than 10% increase in on-state static losses. Also, a comparison of static losses to a PiN diode gives a decrease of 40% for the JBS. The leakage current is also lowered by two decades compared to the Schottky device at its blocking voltage. Temperature measurements show that the low leakage current is maintained up to at least 225 °C.

Selective high-resolution electrodeposition on semiconductor defect patterns.

Abstract: We report a new principle and technique that allows one to electrodeposit material patterns of arbitrary shape down to the submicrometer scale. We demonstrate that an electrochemical metal deposition reaction can be initiated selectively at surface defects created in a p-type Si(100) substrate by Si (++) focused ion beam bombardment. The key principle is that, for cathodic electrochemical polarization of p-type material in the dark, breakdown of the blocking Schottky barrier at the semiconductor/electrolyte interface occurs at significantly lower voltages at implanted locations than for an unimplanted surface. This difference in the threshold voltages is exploited to achieve selective electrochemical deposition.

Schottky effect model of electrical activity of metallic precipitates in silicon

Abstract: A quantitative model of the electrical activity of metallic precipitates in Si is formulated with an emphasis on the Schottky junction effects of the precipitate–Si system. Carrier diffusion and carrier drift in the Si space charge region are accounted for. Carrier recombination is attributed to the thermionic emission mechanism of charge transport across the Schottky junction rather than the surface recombination. It is shown that the precipitates can have a very large minority carrier capture cross-section. Under weak carrier generation conditions, the supply of minority carriers is found to be the limiting factor of the recombination process. The plausibility of the model is demonstrated by a comparison of calculated and available experimental results.

Characterization of shallow silicided junctions for sub-quarter micron ULSI technology. Extraction of silicidation induced Schottky contact area

Abstract: The current-voltage (I-V) characteristics of shallow silicided p/sup +/-n and n/sup +/-p junctions are presented. In the former the diode behavior was same as in nonsilicided junction, while drastic change in diode I-V was observed in the latter. The formation of Schottky contact was conclusively shown to be the root cause of the modified I-V behavior of n/sup +/-p junction in the forward bias region. Poole-Frenkel barrier lowering predominantly influenced the reverse leakage current, masking thereby the effect of Schottky contact. The leakage current in n/sup +/-p diodes was higher than in nonsilicided diodes by two orders of magnitude and this is consistent with the formation of Schottky contact via titanium or titanium-silicide penetrating into the p-substrate and generating trap sites. There is no increase in the leakage current and no formation of Schottky contact in case of the p/sup +/-n junction. The Schottky contact amounting to less than 0.01% of the total junction area and not amenable for SEM or TEM observation was extracted for the first time by simultaneous characterization of forward and reverse characteristics of silicided n/sup +/-p diode.