Showing papers on "Schottky barrier published in 1996"

Silicon carbide high-power devices

Abstract: In recent years, silicon carbide has received increased attention because of its potential for high-power devices. The unique material properties of SiC, high electric breakdown field, high saturated electron drift velocity, and high thermal conductivity are what give this material its tremendous potential in the power device arena. 4H-SiC Schottky barrier diodes (1400 V) with forward current densities over 700 A/cm/sup 2/ at 2 V have been demonstrated. Packaged SITs have produced 57 W of output power at 500 MHz, SiC UMOSFETs (1200 V) are projected to have 15 times the current density of Si IGBTs (1200 V). Submicron gate length 4H-SiC MESFETs have achieved f/sub max/=32 GHz, f/sub T/=14.0 GHz, and power density=2.8 W/mm @ 1.8 GHz. The performances of a wide variety of SiC devices are compared to that of similar Si and GaAs devices and to theoretically expected results.

Schottky barriers and contact resistances on p‐type GaN

Abstract: We measured the Schottky barrier heights and specific contact resistivities of four different metals on p‐type GaN. The Schottky barrier heights of Pt, Ni, Au, and Ti were obtained from the current‐voltage characteristics to be 0.50, 0.50, 0.57, and 0.65 eV, respectively. The specific contact resistivities were 0.013, 0.015, 0.026, and 0.035 Ω⋅cm2, respectively. Our experimental results proved that the Schottky barrier heights and specific contact resistivities decrease with increase in metal work function as expected theoretically.

Schottky barrier properties of various metals on n-type GaN

Abstract: Schottky barriers of Ti, Cr, Au, Pd, Ni and Pt on n-type GaN epitaxial layers grown by low-pressure metal-organic chemical vapour deposition on sapphire have been fabricated and characterized. Measurements were carried out using current - voltage (I - V), current - voltage - temperature (I -V - T) and capacitance - voltage (C - V) techniques. A modified Norde plot was used as one of the analysis tools for the I - V - T measurements. The barrier heights, ideality factors and effective Richardson constants are presented. Barrier heights of 0.88, 0.92, 0.99 and 1.08 eV for Au, Pd, Ni and Pt respectively were obtained from the modified Norde plot. Contacts of Ti and Cr exhibited only slightly rectifying characteristics. These results show that the barrier height on n-GaN increases monotonically, but does not scale proportionately, with increasing metal workfunction.

Schottky contact and the thermal stability of Ni on n-type GaN

Abstract: The Schottky barrier height of Ni on n‐GaN has been measured to be 0.56 and 0.66 eV by capacitance–voltage (C–V) and current–density–temperature (J–T) methods, respectively. Gallium nickel (Ga4Ni3) is formed as Ni is deposited on the GaN film, which affects the barrier height markedly. The thermal stability of Ni on GaN is also investigated by annealing these specimens at various temperatures. Specimen annealing at temperatures above 200 °C leads to the formation of nickel nitrides Ni3N and Ni4N at the interface of Ni and GaN. These interfacial compounds change the measured barrier height to 1.0 and 0.8 eV by C–V and J–T methods, respectively. Comparisons of Schottky characteristics of Ni with those of Pt, Pd, Au, and Ti are also discussed.

On the existence of a distribution of barrier heights in Pd2Si/Si Schottky diodes

Abstract: The current–voltage characteristics of Pd2Si based Schottky diodes on both n‐ and p‐type silicon measured over a wide temperature range (52–295 K) have been interpreted on the basis of thermionic emission‐diffusion mechanism and the assumption of a Gaussian distribution of barrier heights. It is shown that while the occurrence of a distribution of barrier heights is responsible for the apparent decrease of the zero‐bias barrier height (φb0) and nonlinearity in the activation energy plot, the voltage dependence of the standard deviation causes the unusual increase of ideality factor (η) at low temperatures. Also, it is demonstrated that the forward bias shifts the mean barrier height towards the higher side and causes narrowing of the distribution as well. A simple method, involving the use of φb0 vs 1/T data, is suggested to gather evidence for the occurrence of a Gaussian distribution of barrier heights and obtain values of mean barrier height and standard deviation. The experimental results correspond t...

Current transport in Pd2Si/n-Si(100) Schottky barrier diodes at low temperatures

Abstract: The forward current-voltage (I–V) characteristics of Pd2Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height (ϕb0) and an increase of the ideality factor (η) with decreasing temperature. Further, the changes in ϕb0 and η become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and “T0-effect” fail to account for the temperature dependence of the barrier parameters. The 1n(Is/T2) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd2Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 104 A m−2 K−2 against the theoretical value of 1.12 × 106 A m−2 K−2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.

The growth and properties of Al and AlN films on GaN(0001)–(1×1)

Abstract: The growth, structure, and annealing behavior of Al films, formed by in situ vapor deposition on GaN(0001)–(1×1) near 25 °C, have been studied using Auger, electron energy loss, x ray and ultraviolet photoemission spectroscopies and low‐energy electron diffraction. Film growth occurs by a Stranski–Krastanov process with reaction at the immediate interface leading to metallic Ga. Annealing at ≳800 °C leads to release of N, which reacts with Al to form a (1×1)‐ordered layer of AlN, possibly alloyed with a small amount of Ga. The AlN layer has been characterized using the various spectroscopies, and the work function, band bending, and electron affinity of GaN and of the AlN overlayer have been obtained. The Al/GaN Schottky barrier height has been measured and compared with previous results for Ni/GaN.

Effect of surface inhomogeneities on the electrical characteristics of SiC Schottky contacts

Abstract: This paper reports analysis of the role of defects on the electrical characteristics of high-voltage 6H-SiC Schottky rectifiers. The measured reverse leakage current of high-voltage Ti and Pt rectifiers was found to be much higher than that predicted by thermionic emission theory and using a barrier height extracted from the C-V measurements. In this paper, a model based upon the presence of defects at the 6H-SiC/metal interface is used to explains this behavior. It is proposed that these defects result in lowering of the barrier height in the localized regions and thus, significantly affect the reverse I-V characteristics of the Schottky contacts. The presence of electrically active defects in the Schottky barrier area has been verified by EBIC studies.

Electrical conduction in platinum–gallium nitride Schottky diodes

Abstract: Gallium nitride is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Among the devices considered for high power generation is the ubiquitous field‐effect transistors which require Schottky barriers for modulating the channel mobile charge. It is in this context that we have undertaken an investigation of likely metal‐GaN contacts. Here we report on the electrical conduction and other properties of Pt–GaN Schottky diodes. These Schottky diodes were fabricated using n‐GaN grown by the molecular beam epitaxy method. Both capacitance–voltage and current–voltage measurements have been carried out as a function of temperature to gain insight into the processes involved in current conduction. Based on these measurements, physical mechanisms responsible for electrical conduction at low and high voltages and temperatures have been suggested. Schottky barrier height determined from the current–voltage and capacitance–voltage measurements is close to 1.10 eV.

BARRIER CHARACTERISTICS OF PtSi/p-Si SCHOTTKY DIODES AS DETERMINED FROM I-V-T MEASUREMENTS

Abstract: The current-voltage-temperature characteristics of PtSi/p-Si Schottky barrier diodes were measured in the temperature range 60–115 K. Deviation of the ideality factor from unity below 80 K may be modelled using the so-called T0 parameter with T0 = 18 K. It is also shown that the curvature in the Richardson plots may be remedied by using the flatband rather than the zero-bias saturation current density. Physically, the departure from ideality is interpreted in terms of an inhomogeneous Schottky contact. Here we determine a mean barrier height at T = 0 K, ƒ b 0 = 223 mV , with an (assumed) Gaussian distribution of standard deviation σ ƒ = 12.5 mV . These data are correlated with the zero-bias barrier height, ƒ j 0 = 192 mV (at T = 90 K), the photoresponse barrier height, ƒ ph = 205 mV , and the flatband barrier height, ƒ fb = 214 mV . Finally, the temperature coefficient of the flatband barrier was found to be −0.121 mVK−1, which is approximately equal to 1 2 (dE g i /dT) , thus suggesting that the Fermi level at the interface is pinned to the middle of the band gap.

Variations in I-V characteristics of oxide semiconductors induced by oxidizing gases

Abstract: Current (I)-voltage (V) characteristics of porous sintered discs of semiconductive ZnO- and SnO2-based materials have been investigated in air, 100 ppm NO2, 800 ppm O3 and 1 H2 in the temperature range 200–700°C. All the oxide discs tested exhibited nonlinear I-V characteristics of varistor-type in every atmosphere. The breakdown voltage shifted to a high electric field upon exposure to NO2 and O3, compared with that in air, presenting a striking contrast to the behavior in 1.0% H2. It was revealed that pure ZnO and SnO2 themselves exhibited a relatively large shift in breakdown voltage when exposed to the oxidizing gases. Addition of Bi2O3 to SnO2 resulted in a slight increase in the sensitivity to NO2 and O3 but in a relatively large increase in the H2 sensitivity at 600°C. It was also found that the breakdown voltage increased with increasing the sweep rate of the electric field, suggesting some influence of the Joule's heating of a specimen during measurement on the I-V characteristics at slow sweep rates. However, the magnitude of the gas-induced shift in breakdown voltage was not so affected by the sweep rate, but rather increased at 12.3 V s−1. From these results, it was confirmed that the behavior of chemisorbed species on the surface of oxide particles near grain boundaries determined by the height of the double Schottky barrier and then the gas-sensitive non-linear I-V characteristics.

Stable electroluminescence from reverse biased n-type porous silicon-aluminum schottky junction device

Abstract: We report the realization of a bright and stable electroluminescent Schottky diode based on aluminum‐porous silicon junction. White light, visible in normal daylight, is emitted when a reverse bias is applied to the device, promoting the junction breakdown. The device has a fast (100 ns) rise time of the light emission. An excellent stability, tested over more than one month of continuous operation at a high bias level, is achieved by the complete encapsulation of the active porous silicon under a transparent alumina layer. The external power efficiency of light emission is 0.01%.

Schottky barrier rectifiers and methods of forming same

Abstract: A Schottky rectifier (10) includes MOS-filled trenches and an anode electrode at a face of a semiconductor substrate and an optimally nonuniformly doped drift (12d) region therein which in combination provide high blocking voltage capability with low reverse-biased leakage current and low forward voltage drop. The nonuniformly doped drift (12d) region contains a concentration of first conductivity type dopants therein which increases monotonically in a direction away from a Schottky rectifying function formed between the anode electrode (18) and the drift region (12d). A profile of the doping concentration in the drift region is preferably a linear or step graded profile with a concentration of less than about 5x1016 cm-3 (e.g., 1x1016 cm-3) at the Schottky rectifying junction and a concentration of about ten times greater (e.g., 3x1017 cm-3) at a junction between the drift region (12d) and a cathode region (12c). The thickness of the insulating regions (16) (e.g., SiO?2?) in the MOS-filled trenches is also greater than about 1000 A to simultaneously inhibit field crowding and increase the breakdown voltage of the device. The nonuniformly doped drift region (12d) is preferably formed by epitaxial growth from the cathode region (12c) and doped in-situ.

The bias-dependence change of barrier height of Schottky diodes under forward bias by including the series resistance effect

Abstract: Schottky barrier height shifts depending on the interfacial layer as well as a change of the interface state charge with the forward bias while considering the presence of bulk (semiconductor) series resistance are discussed both theoretically and experimentally. It has been concluded that the barrier height shift or increase in Schottky diodes is mainly due to the potential change across the interfacial layer and the occupation of the interface states as a result of the applied forward voltage. One assumes that the barrier height is controlled by the density distribution of the interface states in equilibrium with the semiconductor and the applied voltage. In nonideal Schottky diodes, the values of the voltage drops across the interfacial layer, the depletion layer and the bulk resistance are given in terms of the bias dependent ideality factor, n, different from those in literature. These values are determined by a formula obtained for Vi and Vs by means of change of the interface charge with bias.

Schottky barriers on n-GaN grown on SiC

Abstract: Characteristics of Schottky barriers fabricated on n-type GaN were investigated. The barriers were formed by vacuum thermal evaporation of Cr, Au, and Ni. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the barriers were measured in a wide temperature and current density range. Fundamental parameters (barrier height and built-in potential) of the Schottky barriers were determined. The dependence of the barrier ideality factor on doping concentration in GaN was measured. Correlation between the barrier height and metal work function was observed. The electron affinity for GaN was determined using both C-V and I-V characteristics. The current flow mechanism through the barriers is discussed.

Near-ideal platinum-gan schottky diodes

Abstract: Fabrication and characterisation of nearly ideal Pt/n-GaN Schottky barrier diodes are described. The n-GaN employed was grown by the reactive molecular beam epitaxy method. The capacitance/voltage (C/V) characteristics indicate marginal trap density in the semiconductor, and the current/voltage (I/V) characteristics give an ideality factor very close to unity. Barrier height deduced both from I/V and C/V measurements are /spl sim/1.10 eV provided the influence of scattering is considered negligible. This confirms again the near absence of interface traps in the diodes, and suggests that the effective mass of an electron in GaN is 0.2/spl plusmn/0.02.

Effect of series resistance on the forward current-voltage characteristics of Schottky diodes in the presence of interfacial layer

Abstract: In order to make an accurate determination of Schottky diode parameters such as the ideality factor, the barrier height and the series resistance [using forward current-voltage ( I - V ) characteristics in the presence of an interfacial layer], a novel calculation method has been developed by taking into account the applied voltage drop across the interfacial layer ( V i ). The parameters obtained by accounting for the voltage drop V i have been compared with those obtained without considering the above voltage drop. To examine the consistency of this approach, the comparison has been made by means of Schottky diodes fabricated on a n -type semiconductor substrate with different bulk thickness. It is shown that the voltage drop across the interfacial layer will increase the ideality factor and the voltage dependence of the I - V characteristics. In addition, it is shown that the series resistance value increases as the semiconductor bulk thickness has been increased.

Electronic Structure of Passive Films Formed on Molybdenum‐Containing Ferritic Stainless Steels

Abstract: The effect of molybdenum on the electronic structure of the passive films formed on ferritic (Fe-Cr and Fe-Cr-Mo) stainless steels is examined by capacitance and photoelectrochemical measurements. The capacitance study is supported by a mathematical analysis of the Schottky barrier developed at the semiconductor-electrolyte interface in the case of a semiconductor with multiple bulk electronic states in the bandgap. The numerical simulations, based on the more general Mott-Schottky relation proposed, are in good agreement with the experimental results. It can be concluded that the capacitance behavior of the passive films is related to the contributions of a shallow donor level very close to the conduction band and a deep donor level at about 0.4 eV below the conduction band. The addition of molybdenum decreases the donor density of the deep level. Photoeffects observed for subbandgap photon energies reveal that this deep donor level behaves like a trapping electronic state situated in the space-charge zone of the passive film. On the basis of the results obtained, the crystallographic factors determining the nature of the donor species are discussed.

PtSi–n–Si Schottky‐barrier photodetectors with stable spectral responsivity in the 120–250 nm spectral range

Abstract: Front‐illuminated PtSi–n–Si Schottky barrier photodiodes have been developed for the ultraviolet and vacuum ultraviolet spectral range. Their spectral responsivity was determined in the 120–500 nm spectral range by use of a cryogenic electrical substitution radiometer operated with spectrally dispersed synchrotron radiation. For wavelengths below 250 nm, the spectral responsivity is about 0.03 A/W, comparable to that of GaAsP Schottky photodiodes. Unlike the GaAsP diodes, the new PtSi–n–Si diodes have a spatially uniform response which is virtually stable after prolonged exposure to short wavelength radiation. Even after a radiant exposure of 150 mJ cm−2 at wavelength 120 nm, the relative reduction in spectral responsivity remains below 0.2%. Due to these features, this type of photodiode is a promising candidate for use as secondary detector standard in the ultraviolet and vacuum ultraviolet spectral ranges.

Generalized approach to the parameter extraction from I - V characteristics of Schottky diodes

Abstract: Two approaches for Schottky barrier parameter evaluation are presented and compared. The first method extracts the barrier height, the ideality factor and the series resistance also for the structures that have no linear part in the forward direction of the curve. This enables one to take into consideration also the reverse part of I - V curves that is normally omitted and the information lost. The second, more general, approach takes into account an inhomogeneity of the Schottky barrier and extracts the parameters of the barrier height distribution. It is shown that for this case it is possible to substitute the ideality factor, which is a non-physical parameter, by a barrier height distribution with the mean value and the standard deviation . Using this method a single I - V measurement is sufficient for determining the barrier height distribution.

Reverse leakage current calculations for SiC Schottky contacts

Abstract: Reverse leakage current calculations are a function of Schottky barrier height and temperature have been performed for metal gates on n-type 6H-SiC. These calculations were performed using a WKB evaluation of the tunneling probability through a reverse biased Schottky barrier and numerically integrating over all energies to find the reverse current density. This method is shown to yield much better agreement with previously published reverse leakage currents on 6H-SiC than can be obtained using thermionic emission theory.

Series resistance calculation for the Metal-Insulator-Semiconductor Schottky barrier diodes

Abstract: An accurate way of determining the series resistance Rs of Schottky Barrier Diodes (SBDs) with and without the interfacial oxide layer using forward current-voltage (I–V) characteristics is discussed both theoretically and experimentally by taking into account the applied voltage drop across the interfacial layerVi. For the experimental discussion, the forward biasI–V characteristics of the SBDs with and without the oxide layer fabricated by LEC (the Liquid-Encapsulated Czochralski) GaAs were performed. The SBD without the oxide layer was fabricated to confirm a novel calculation method. For the theoretical discussion, an expression ofVi was obtained by considering effects of the layer thickness and the interface state density parameters on forward biasI–V of the SBDs. The valueRs of the SBD with interfacial oxide layer was seen to be larger than that of the SBD without the interfacial oxide layer due to contribution of this layer to the series resistance. According to the obtained theoretical formula, the value ofVi for the SBD with the oxide layer was calculated and it was subtracted from the applied voltage values V and then the value ofRs was recalculated. Thus, it has been shown that this new value ofRs is in much closer agreement with that determined for the SBD without the oxide layer as predicted. Furthermore, the curves of the interface states energy distribution of each sample are determined. It was concluded that the shape of the density distribution curve and order of magnitude of the density of the interface states in the considered energy range are in close agreement with those obtained by others for Au/n-GaAs Schottky diodes by Schottky capacitance spectroscopy.

High barrier metallic polymer/p-type silicon schottky diodes

Abstract: A metallic polypyrrole film has been formed on a p-type Si substrate by means of an anodization process An investigation of the formed polymer/pSi Schottky diodes has been made The polypyrrole polymer provides a good rectifying contact to the p-Si semiconductor The current-voltage (barrier height Φb0 = 084 eV) and capacitance-voltage (Φb0 = 094 eV) characteristics of the devices are significantly improved with increasing Φb0 and decreasing the ideality factor (n = 120) after a polymer melt processing step These values of Φb0 are significantly larger than those of conventional Schottky diodes Furthermore this study shows that owing to its room temperature processing the high barrier-metallic polypyrrole/pSi structures can be useful for deep level characterisation of p-Si

Spin-valve effects in nickel/silicon/nickel junctions

Abstract: We report on fabrication and characterization of a planar spin-valve device which has two sets of interdigited nanoscale Ni fingers as two electrodes in Schottky contact with Si. The finger width is 75 nm for one set and 150 nm for the other. A large length-to-width ratio of the fingers results in a single domain magnetization and a sharp magneto-resistance (MR) response. The switching field of the finger is determined by the finger width and spacing due to magnetostatic interaction. MR measurements reveal spin-valve effects in the Ni/Si/Ni junctions with MR changes of 0.3-0.6% at room temperature. The effects are discussed within a spin-valve model.

An investigation of acceptor-doped grain boundaries in ?

Abstract: Grain boundary (GB) doped exhibits interesting electroceramic phenomena including varistor and barrier layer capacitor behaviour. We present here our investigation of GB acceptor-doped using analytical electron microscopy including electron holography. Mn was diffused into sintered polycrystalline to attain GBs which are rich in Mn. The presence and spatial extent of Mn at the GBs were analysed using x-ray emission spectroscopy (XES) and parallel electron energy loss spectroscopy (PEELS). The valence state of Mn was determined using PEELS to be predominantly +2. Finally, transmission high-energy electron holography was utilized to directly image and quantify the electrostatic potential and associated space-charge across the GBs directly. The holography results reveal a negatively charged GB with positive space-charge, indicating that Mn with a valence of +2 resides as an acceptor dopant on the Ti site at the GB core. The barrier height and local charge density distribution, including the Debye length, of the double Schottky barrier at the GB are derived from these holography results. This investigation demonstrates the usefulness of electron holography as a bulk-sensitive technique to probe the statics and dynamics of electrostatic field distribution and electrical charge across interfaces in technologically useful materials, and the need to employ diverse analytical techniques for such an investigation.

Thin film diamond photodiode for ultraviolet light detection

Abstract: A photodiode has been constructed from lightly boron doped, Si supported, thin film chemically vapor deposited (CVD) diamond which shows over five orders of magnitude discrimination between deep UV (≤220 nm) and visible light A thin (10 nm) gold Schottky barrier with an associated Ti–Ag–Au ohmic contact was used to create a rectifying device with low (≤2 pA) dark currents when reversed biased This structure showed a sharp cut off in photoresponse at 220 nm, the band gap energy of diamond Conversely, a photoconductive device fabricated from similar (nominally undoped) material gave a broader UV photoresponse and displayed high dark currents; the superior performance of the diode structure on fine grain material is discussed

Systematic investigation of the effects of organic film structure on light emitting diode performance

Abstract: We present a systematic investigation of the effects of organic film structure on light emitting diode (LED) performance. Metal/organic film/metal LEDs were fabricated using a five ring, poly(phenylene vinylene) related oligomer as the active layer. The structure of the vacuum evaporated oligomer films was varied from amorphous to polycrystalline by changing the substrate temperature during deposition. The intrinsic properties of the oligomer films and the LED performance were measured. The measured intrinsic film properties include: optical absorption, photoluminescence (PL) spectra, PL lifetime, PL efficiency, and effective carrier mobility. The measured device characteristics include current–voltage, capacitance–voltage, electroluminescence (EL) efficiency, and the contact metal/organic film Schottky barrier heights. The optical absorption and PL properties of the films are weakly dependent on film structure but the effective carrier mobility decreases with increasing crystallinity. The EL quantum effi...

Formation of Schottky barriers at interfaces between metals and molecular semiconductors of p‐ and n‐type conductances

Abstract: In order to clarify electronic structures of molecular semiconductor/metal interfaces, a Schottky–Mott rule is examined for vacuum‐sublimed films of two kinds of porphyrins, which have similar chemical structures, but opposite conductance types. The result shows that Schottky barrier heights are simply determined by the difference in work function between the porphyrin solids and metals irrespective of the conductance types of the porphyrin semiconductors, indicative of negligible influence of surface states on the Schottky barrier formation. Measurements of photocurrent generation efficiencies at these Schottky junctions indicate that a surface recombination process is not a major deactivation route for electron‐hole pairs generated in the molecular semiconductors by light.