Showing papers on "Schottky barrier published in 1970"

Reverse current-voltage characteristics of metal-silicide Schottky diodes

Abstract: The soft behavior of reverse biased Schottky barrier diodes has often been difficult to interpret quantitatively. The development of metal-silicide devices with diffused guard rings has made it possible to verify experimentally an advanced theoretical model. Reverse characteristics can now be accurately predicted over wide ranges of current, voltage, barrier height and temperature. The theoretical description accounts for anisotropy of effective masses, scattering by optical phonons, and quantum mechanical reflection and tunneling at the metal-semiconductor interface. These considerations yield practical Richardson constants equal to 112 for electrons and 32 for holes in silicon. Absence of true saturation in the reverse characteristic is caused by an electric field dependence of the effective barrier height. In addition to the usual image-force correction, the barrier height is lowered by a newly recognized effect attributed to an electrostatic dipole layer at the metal-semiconductor interface. Experimental devices have been fabricated using RhSi, ZrSi2, and PtSi contacts, forming barriers in both n- and p-type silicon. The resulting structures have been found to be extremely stable and uniform; furthermore, the metal-semiconductor interface, produced by solid-solid chemical reaction, is believed to be free from intervening layers of oxide and other contaminants. When necessary to eliminate field-enhancement at the electrode periphery, diffused guard rings have been incorporated into the structures. Agreement between experimental data and theory is obtained over nearly five orders of magnitude in reverse bias and eleven orders of magnitude in reverse current density, usually with an rms deviation of less than 10 per cent.

Theory of tunneling into interface states

Abstract: A theory of electron tunneling from the metal through the insulator and into the semiconductor of a MIS-structure is developed. Using a square well model, the interface states are represented by a distribution of δ-function potentials, and their wave functions calculated. Following the method of Bardeen, the tunneling matrix element and current are found and used with an extension of Shockley-Read recombination theory to determine a tunnelling time constant, τ To , similar to the surface recombination time constant, τ. Small signal solutions are calculated and presented in the form of equivalent circuits. For a single level state the equivalent circuit consists of the thick insulator, non-tunneling MIS-capacitor plus a tunneling current, j 1 , injected from the metal into the midpoint of the recombination RC circuit. j 1 is made up of three terms caused by modulation of the effective barrier height, and by modulation of the metal and trap occupancy functions. For τ To ⪡ τ , the case of an ideal Schottky barrier, the tunneling current is controlled by the recombination time, τ. If τ To > τ , the tunneling limited case, j 1 is controlled by τ To . This case is discussed in detail. The model's current and conductance characteristics are numerically calculated and graphically presented as a function of interface state density and distribution, interface potential, insulator thickness, and a.c. frequency.

Alternating Current Electrical Properties of Highly Doped Insulating Films

Abstract: Metal‐insulator‐metal systems are discussed in which the insulator is highly doped and in which Schottky barriers exist at the metal‐insulator interface. An equivalent circuit for the system is proposed and the ac electrical characteristics derived. It is shown that the capacitance is extremely temperature and frequency dependent. At high frequencies or low temperatures the capacitance is thickness dependent and equal to the geometric capacitance. At low frequencies and high temperatures it is thickness independent and equal to the Schottky barrier capacitance, which is determined by the doping density. Several methods of determining the activation energy of the donor centers from experimental capacitance versus frequency and temperature curves are suggested. The parallel equivalent conductance is also shown to be extremely frequency and temperature sensitive. It is found to have a pronounced maximum in both cases, which increases in magnitude and occurs at higher temperatures the thicker the insulator.

Microwave properties of Schottky-barrier field-effect transistors

Abstract: The microwave properties of silicon Schottky-barrier field-effect transistor(MESFET'S) with a gate-length of one micrometer are investigated. The scattering parameters of the transistors have been measured from 0.1 GHz up to 12 GHz. From the measured data an equivalent circuit is established which consist of an intrinsic transistor and extrinsic elements. Some of the elements of the intrinsic transistor, notably the transconductance, are strongly influenced by the saturation of the drift velocity. Best performance of the intrinsic transistor is obtained with highly doped and thin channels. The measured power-gain is in good agreement with theoretical values deduced from the equivalent circuit. The best device has a maximum frequency of oscillation fmax of 12 GHz. The investigation reveals that the extrinsic elements, especially the resistance of the gate-metallization and the gate-pad parasitics, degrade the power-gain considerably. Without them a value of fmax close to 20 GHz is predicted.

Capacitance Energy Level Spectroscopy of Deep-Lying Semiconductor Impurities Using Schottky Barriers

Abstract: The capacitance‐voltage (C‐V) relationship of a Schottky barrier diode is predicted for an energy distribution of impurity levels having spatially uniform concentration in an n‐type semiconductor. The model applies for forward and reverse bias voltages at modulation frequencies near dc and at modulation frequencies at which one or more of the deep doping levels cannot respond. Effects of partial ionization of impurity species and the effect of electrons in the depletion region are considered. It is predicted that the diode [d(1/C)/dV] versus V relationship exhibits sharp minima when the barrier height minus the applied bias is equal to the energy level relative to the conduction band edge of any of the predominant deep‐lying impurities in the semiconductor. The way in which deep lying impurities consequently affect a C‐V impurity profile analysis is discussed.

Behavior of Cesium Oxide as a Low Work‐Function Coating

Abstract: A detailed picture of the behavior of cesium oxide as a low work‐function coating on III‐V semiconductors and on silver has been obtained. Measurement of required cesium and oxygen exposure for optimum photoyield shows that the compound normally formed is close to CS2O, with variations in required exposure for very thin and very thick layers. By making simultaneous Kelvin work‐function, photoyield‐threshold, and thickness measurements, it was possible to establish that the CS2O, an n‐type semiconductor, forms a heterojunction or Schottky barrier with its substrate. This provides a band bending which produces a gradual lowering of the vacuum level with increasing thickness to an ultimate work function of 0.6 eV. The photoyield and dark current from the substrate are limited by the interfacial barrier at the heterojunction. This barrier is 1.00±0.05 eV for a silver substrate and 1.23±0.03 eV for GaSb. The band‐bending distance in the CS2O is about 50 A and the hot electron scattering distance is 9 A. These data have been used in an improved calculation of the maximum Γ escape probability and requisite CS2O thickness for electron emission from III‐V semiconductors of different bandgaps. Electron emission from CS2O induced by an oxygen overpressure was also measured. CSOH is compared with CS2O as a work‐function lowering coating.

Effects of image force and tunneling on current transport in metal-semiconductor (Schottky barrier) contacts

Abstract: Image force lowering of the potential energy barrier is included in a theoretical calculation of current transport in metal-semiconductor (Schottky barrier) contacts. Thermionic and thermionic-field (tunnel) emission are analyzed in a normalized formulation to yield the current (I) vs. voltage (V) relationship. Quantum-mechanical reflection of carriers near the top of the image force rounded barrier is included in the theory by the use of Kemble's transmission probability which incorporates the one-dimensional WKB-type tunneling approximation into a transmission probability applicable both above and below the top of the barrier. Carrier distributions in the semiconductor and in the metal are described by Maxwell-Boltzmann statistics. For any given combination of three dimensionless input parameters E b kT , kT E 00 , and E 00 E 11 , which correspond to bias, temperature and donor concentration respectively, two dimensionless output parameters I f I m (current) and the diode n value (inverse slope of the semilog I vs. V relationship) are determined. Computer solutions are presented in both graphical and tabular form. The results permit a straightforward calculation of the barrier height and the semiconductor donor concentration from experimental I−V data. In comparison with the predictions of current transport models that neglect image force lowering, the present work shows that inclusion of image force leads to a significant increase in the predicted magnitude of the current density and to minor changes in the magnitude of the diode n value. Corrections to the predictions of models that neglect image force arise primarily from enhanced thermionic emission over the image force lowered barrier rather than from enhanced tunnel emission through the image force narrowed barrier. The Kemble transmission probability may be defined in terms of a characteristic transmission energy, Et, which is useful when thermionic emission dominates the conduction process to the extent that quantum-mechanical tunneling and reflection may be considered as a perturbation on thermionic emission. When this occurs Et can be used to estimate the magnitude of the perturbation.

The physics of Schottky barriers

Abstract: A review is given of the physical processes which determine the height of the barrier and the current-voltage relationship in a metal-semiconductor Schottky barrier.

Characteristics of aluminum-silicon schottky barrier diode

Abstract: Aluminum n -type silicon Schottky barrier diodes with near-ideal characteristics have recently been developed. In this paper the characteristics of such a Schottky barrier are discussed. The I–V characteristics agree well with the theoretical thermionic emission model. The barrier height is determined from the saturation current, temperature dependence of forward current, and photoemission to be0.69±0.01eV. The switching measurements show no minority carrier storage, as expected. The low-frequency noise is very low and is comparable to the best p-n junction and guard-ring Schottky barrier. These desirable features, coupled with the simple process of the Al- n Si Schottky barrier, make them attractive in a variety of applications.

Low-frequency excess noise in metal—Silicon Schottky barrier diodes

Abstract: Theoretical models for the generation-recombination noise and trapping noise in metal-semiconductor Schottky barrier diodes are developed. Low-frequency excess noise in Schottky barrier diodes is found to be dominated by the modulation of the barrier height φB caused by fluctuation in the charge state of traps or generation-recombination centers. This noise mechanism does not occur in p-n junctions. The bias and the temperature dependence of the generation-recombination noise is critically compared with the experimental data for forward diode current ranges from 3 to 300 µA and operating temperatures from -25° to 100°C. Trapping noise in Schottky barrier diodes is observed at low temperatures in diodes not intentionally doped with deep level impurities. The experimental results on trapping noise can be described by assuming that the trap states have a constant capture cross section and are uniformly distributed in space, as well as in energy. The surface potential at the diode periphery also has an important effect on the Schottky barrier diode noise. The best low-frequency noise behavior is found when the surface is at the flat-band condition. An accumulated surface is always associated with a large amount of low-frequency excess noise.

Titanium-silicon Schottky barrier diodes

Abstract: Schottky barriers have been formed by vacuum evaporation of titanium onto chemically cleaned n- and p-type silicon. The barrier heights of the contacts were found to 0.50 and 0.61 eV for n- and p-type barriers, respectively. The barrier heights were determined from measurements of the 1 C 2 vs . V characteristics, the reverse saturation current density, and the activation energy of the reverse current. The effects of fabrication technique on diode properties are discussed. It is found that p-type diodes can be fabricated using standard oxide passivation techniques, without severe degradation of most diode properties; n-type diodes are severely degraded by the presence of silicon dioxide at the periphery of the diode, but this problem can be completely eliminated by the use of a diffused p-type ‘guard-ring’. Noise measurements are also presented for the p-type oxide-passivated diodes and for the n-type ‘guard-ring’ diodes; these diodes are found to have essentially ideal noise behavior above a few kHz.

Dependence of Schottky Barrier Height on Donor Concentration

Abstract: Schottky barrier heights of Au contacts to n‐type Si with either etch‐polished or vacuum‐cleaved interfaces are independent of donor concentration within an experimental uncertainty of about ±0.05 eV for 1014 cm−3≤ND≤1019 cm−3. Within the same uncertainty and over the same doping range, barrier heights determined from capacitance using the standard formula are equal to those determined from photoemission thresholds. A theory for deducing barrier heights from photoemission thresholds that includes the effects of tunneling and image force is presented. The results are interpreted in terms of a simple model for the interface, which is characterized by the thickness d and dielectric constant κ′ of the interfacial film and the density nss of interface states. The insensitivity of the barrier height to the quantity of space charge leads to the following limit on the interfacial parameters: (k′/d)+1.8×10−6nss≥3.8×108 cm−1 for d in cm, and nss in cm−2 eV−1.

Dynamic performance of Schottky-barrier field-effect transistors

Abstract: The dynamic performance of Schottky-barrier field-effect transistors is discussed, with the aim of finding in a most simple way the physical parameters on which the dynamic properties of a FET depend, how strong they influence the dynamic qualities of FET'S, and what recommendations can be given as to proper choice of material or structure for FET'S with good high-frequency performance.

High-speed gallium-arsenide Schottky-barrier field-effect transistors

Abstract: The letter shows that gallium arsenide is a well suited material for high-frequency field-effect transistors. From preliminary measurements on realised transistors, it is shown that the frequency limit for power amplification is considerably higher than for other known transistors. The processes involved are briefly described.

Fabrication of insulated gate field-effect transistors involving ion implantation

Abstract: An insulated gate field-effect transistor is made which utilizes both Schottky barrier connections and ion-implanted zones. The resultant structure incorporates source and drain zones, which are formed by ion implantation and whose spacing is fixed by the gate electrode, and source and drain electrodes which make ohmic connection to the implanted source and drain zones and rectifying connections to unimplanted material.

Minority carrier storage and oscillation efficiency in read diodes

Abstract: Computer simulations indicate that the oscillation efficiency of a Read diode is appreciably reduced from Read's prediction of 30 per cent because of a minority-carrier storage effect. A space-charge-neutral end region stores minority carriers which back-diffuse from the adjacent avalanche region and releases them at the critical moment to flood the space-charge region. This deteriorates the phase relation between current and voltage. A theoretical efficiency of only 12.7 per cent was possible with a 10 GHz Si p+nvn+ unit studied. The effect can be avoided by a careful profiling of the field distribution between the avalanche region and the neutral region. However, a simpler solution is to utilize a Schottky barrier in place of the p-n junction. The metal which replaces the neutral region does not store back-diffused carriers.

Electrical and Photovoltaic Properties of CdS-Si Junctions

Abstract: CdS-pSi and CdS-nSi junctions are prepared by vacuum evaporation of CdS on Si crystals, and their electrical and photovoltaic properties are studied. The junction prepared on hot Si substrate (substrate temperature; 150°–250°C) has properties of hetero-junction, while the one on cold substrate (50°–80°C) shows properties resembling those of Schottky barrier. CdS-pSi junctions are generally superior to CdS–nSi junctions in rectifying properties. CdS–pSi cell on cold substrate shows excellent photovoltaic effect which is comparable to that of Si solar cell. The maximum solar conversion efficiency of CdS-pSi cells is about 5.5%. Here, the CdS layer is supposed to act as a semi-transparent electrode.

The metal-semiconductor contact: an old device with a new future

Abstract: Advances in process technology are making possible the fabrication of Schottky barriers with reliable, ideal electrical characteristics. With these advances, one can anticipate a rapid increase in the utilization of Schottky barriers, not only as discrete devices but also as a new component in integrated circuits. This article presents a unified picture that quantitatively characterizes both the Schottky barrier and ohmic contacts on silicon. Fabrication techniques and various applications are also discussed.

Use of a double diffused guard ring to obtain near ideal I V characteristics in Schottky barrier diodes

Abstract: This paper reports the use of a unique double-diffused guard ring Schottky barrier diode. The electrical characteristics of the conventional Schottky barrier diode are compared with the single and double guard ring devices. It is shown that both guard ring devices give near ideal I–V characteristics by eliminating the edge effects inherent with metal-semiconductor contacts. It is also shown that the double guard ring structure maintains the fast recovery time of the Schottky diode to higher current levels than the single ring structure by suppression of minority carrier injection.

Contact Properties of Metal-Silicon Schottky Barriers

Abstract: Barrier heights of Schottky diodes prepared by vacuum depositions of metals onto chemically etched silicon surfaces were investigated by measuring the current-voltage and capacitance-voltage characteristics. The barrier height varied remarkably with the work function of metal and the sum of the barrier heights measured on n-type and p-type silicon was nearly equal to the energy gap of silicon. The results were well explained by applying the theory of Cowley and Sze, leading to the conclusion that the Fermi level is not always pinned at the semiconductor surface.

Self-aligned gate field effect transistor with schottky barrier drain and source

Abstract: A LOW PARASITIC CAPACITANCE FIELD EFFECT TRANSISTOR IS FABRICATED BY THE UTILIZATION OF A SELF-ALIGNING GATE TECHNIQUE. A METAL GATE IS FORMED AND THEN, EMPLOYING THE GATE AS A MASK, LOW TEMPERATURE SCHOTTKY BARRIER SOURCE AND DRAIN JUNCTIONS ARE FORMED. THE TECHNIQUE IS PARTICULARLY USEFUL IN THE FABRICATION OF THE FIELD EFFECT TRNASISTOR AS AN ELEMENT OF A LARGE INTEGRATED CIRCUIT WHERE MANY SUCH ALIGNMENTS MUST BE MADE SIMULTANTEOUSLY. D R A W I N G

Low thermal impedance field effect transistor

Abstract: This disclosure is directed to a Schottky Barrier field effect transistor (FET) having a low thermal impedance and to a process of producing it.

Metallization processes in fabrication of Schottky-barrier FET's

Abstract: The metallization processes necessary for the production of microwave Schottky-barrier field-effect transistors are described. Since the gate contact is only 1 micrometer wide, the holes and the metallization of the source, drain and gate contacts are produced simultaneously. Then in a subsequent process,the source and drain contacts are converted to ohmic contacts by the evaporation of Au-Sb onto these contacts. Mask alignment is not a problem because the Au-Sb spreads across the surface after suitable heat treatment.

A hot carrier pn-diode

Abstract: Disclosed is a Schottky barrier or hot carrier diode and process for making same wherein a diffused PN junction and a Schottky barrier junction are both formed in a body of semiconductor material. The diffused PN junction is formed by first diffusing an impurity through an opening in a diffusion mask and into one surface of the semiconductor body to form PN junction. Next, a large central portion of the region formed by the above diffusion is removed by etching or cutting, leaving unaffected by the etchant only that portion of the diffused region underlying and adjacent to the diffusion mask on the surface of the semiconductor body. The latter portion of the diffused region forms a relatively small area diffused PN junction. Finally, a Schottky barrier junction is formed in the etched out area of the semiconductor body, and the diode including the diffused and Schottky barrier junctions has a near-ideal current-voltage characteristic and still maintains its fast recovery time.

GaAs Schottky-barrier avalanche diodes

Abstract: Efficient microwave power generation in a mesa type GaAs Schottky-barrier avalanche diode is reported An output power of 600 mW (cw) at 82 GHz with an efficiency over 10 per cent was obtained when the diodes were mounted with the metal-semiconductor interface adjacent to the heat sink The diodes were fabricated using nickel on n -type epitaxial GaAs substrate It is observed that for the same doping profile, the diodes performed similarly to (zinc) diffused abrupt p + - n junction avalanche diodes, and the initial result indicates that GaAs Schottky-barrier avalanche diodes are comparable to ordinary p - n junction avalanche diodes in their microwave performance

Schottky barrier diodes as impedance elements and method of making same

Abstract: The reverse characteristic of Schottky barrier diodes provides easily fabricated, small area, high impedance elements for micropower circuits. Advantageously, the diodes are fabricated within semiconductive integrated circuit arrays by forming rhodium silicide on relatively high resistivity P-type silicon. Such diodes are particularly useful in the loads of flip-flops used as cells of a semiconductor memory.

The measurement of doping profiles in thick epitaxial layers of GaP using Schottky barrier C-V data

Abstract: Using a Schottky diode technique investigations have been made of the variation in carrier concentration through epitaxial layers of GaP grown by liquid epitaxy and vapour transport methods using tellurium, sulphur and zinc as principal dopants. In all cases it is found that the carrier concentration alters significantly over the thickness of the grown layer and in some cases by as much as two orders of magnitude. The measured values of Hall concentration in the layers are weighted towards the higher levels of doping and are often not indicative of surface carrier concentration. This creates difficulties in trying to predict the electrical properties of epitaxial p - n junction diodes from Hall measurements alone.

Characteristics of pulse excited electroluminescence from ZnS films containing rare earth fluroide

Abstract: The transient behavior of the electrical and the optical properties under pulse excitation has been studied and analyzed in detail on the electroluminescent devices made of Au-ZnS: NdF 3 - Ta 2 O 5 -Ta composite films. The ZnS-Ta 2 O 5 interface is capable of accommodating a large number of trapped electrons, up to 1013cm-2, with the majority of the interfacial states located at a fixed energy below the conduction band of ZnS. Carrier injection is achieved by electrons tunneling through the Au-ZnS Schottky barrier at a field of 2.6×106V/cm. The threshold field of impact excitation for 1 percent NdF 3 in ZnS was found to be 1.5×106V/cm; while the coefficient of impact excitation at 2.6×106V/cm was estimated to be 1750 cm-1. In addition, the emission time constants of several rare earth fluorides were also studied.