Dependence Of Barrier Height Research Articles

Theory of grain boundary recombination and carrier transport in polycrystalline silicon under optical illumination

The physics controlling the recombination of minority carriers at grain boundaries in polycrystalline silicon under optical illumination is described theoretically, and a model for the grain boundary space-charge potential barrier height is presented. The model is based on the assumption of a Gaussian energy distribution of grain boundary interface states. Attention is also focused on the electrical conduction in this material under illumination. The dependence of space-charge potential barrier height and the effective recombination velocity on the illumination level, the grain size, and the bulk diffusion length of minority carriers (L/sub b/) is investigated. Computations show that if the illumination level is high, the sensitivity of effective recombination velocity to grain size (d) in the intermediate grain size range (i.e. d approximately=L/sub b/) is much higher than that in the small and large grain size ranges. It is found that the resistivity of polysilicon decreases on increasing illumination level. The dependence of polysilicon resistivity on grain size under optical illumination is found to be much higher than that under dark conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Temperature dependence of Schottky barrier height on Si: Experimental evidence for Fermi energy pinning relative to either valence or conduction band

We investigated the temperature dependence of Schottky barrier heights in epitaxial silicide/silicon diodes, using internal photoemission techniques. Temperature variation of the Fermi level position in the Si band gap shows that the Fermi level at the interface is pinnedeither relative to the Si conduction bandor to the Si valence band. The contribution of the semiconductor to the interface states is restricted to the semiconductor band nearest in energy. We then discuss the effect of the metal on the interface states and propose different models of Schottky barrier formation which may account for these results.

High-barrier height metal-insulator-semiconductor diodes on n-InP

Metal-insulator-semiconductor diodes were fabricated using Pd, Ni, and Au contacts on n-InP covered by a 40-Å chemically grown oxide. The oxide had a refractive index of 1.4–1.6 with a composition of mainly In2O3+some InPO3 near the surface and mixed oxide+InP near the interface. Pd devices gave the highest-barrier height of 0.80 eV and the lowest reverse saturation current density of 3×10−8 A/cm2. Current-voltage-temperature and capacitance-voltage-temperature data gave temperature dependence of barrier height and revealed an interface state recombination current mechanism with surface states 0.4 eV above the valence-band level. Richardson plots gave good straight lines when empirically corrected using barrier height divided by ideality factor.

Dependence of apparent barrier height on barrier thickness for perpendicular transport in AlAs/GaAs single-barrier structures grown by molecular beam epitaxy

Current-voltage characteristics of single-barrier AlAs/GaAs heterostructures measured over a wide temperature range are used to elucidate the mechanisms governing electron transport through these barriers. Five barriers, ranging in thickness from 14.2 to 150 Å, are examined. The results clearly illustrate Γ-band, elastic-tunneling-dominated transport for the thinnest barrier (14.2 Å) devices and thermionic emission characteristics for the thickest barrier (150 Å) devices. However, devices with an intermediate barrier thickness exhibited tunneling-like currents larger than calculated low-temperature elastic tunneling currents. This effect is apparently due to inelastic tunneling from the GaAs Γ band through the AlAs X-point barrier.

Pressure dependence of Schottky barrier height at the Pt/GaAs interface

The Schottky barrier height at the Pt/GaAs interface has been measured as a function of pressure using a diamond anvil cell. The Schottky barrier height was found to shift to higher energy with a linear pressure coefficient of 11 meV/kbar, which is equal to the pressure coefficient of the fundamental gap of GaAs and with a nonlinear coefficient of −0.26 meV/kbar2. These results are discussed in terms of defect models which have been proposed to explain the Fermi level pinning in Schottky barriers.

Increased dependence of Schottky barrier height on metal work functions due to a thin-oxide layer

Ultraviolet illumination has been used to form a few monolayers of GaAs oxide in dry oxygen on both p-type and n-type GaAs(100) surfaces. Some of the oxides have been annealed to form Ga-rich oxide surfaces. Six metals with a wide range of work functions and different reactivity with the oxide layer have been used to form Schottky contacts on clean GaAs and on the thin-oxide layers. Large variations from the Schottky barrier height on clean GaAs have been observed for both doping types due to the photo-oxidation of the GaAs surfaces. The trend in Schottky barrier change is toward the ideal Schottky limit where the metal work function determines the barrier height. The GaAs Fermi level is shown to move in a much wider region of the band gap for the oxidized surfaces than for clean surfaces, however, it is still confined to a midgap region.

Unpinned Schottky barrier formation at metal–GaAs interfaces

We have used soft x-ray photoemission spectroscopy measurements to demonstrate that metal–GaAs interfaces can exhibit relatively unpinned Fermi level (Ef) movements. For clean GaAs (100) surfaces obtained by molecular-beam epitaxy (MBE) growth and thermal decapping of a protective As overlayer, the metals Au, Al, Cu, and In produce a 0.6–0.7-eV range of Ef stabilization. For a given metal, this stabilization occurs at the same energies for n-type and p-type GaAs. Furthermore, Ef movements are metal-dependent and can evolve over multimonolayer coverages. These results are examined with respect to pronounced differences in semiconductor quality between MBE versus melt-grown GaAs and in the context of previous GaAs Ef measurements. A self-consistent analysis of the junction electrostatics accounts for the functional dependence of barrier height on metal work function. The results highlight the importance of bulk quality as well as interface specific phenomena in controlling the Schottky barrier formation at metal/III–V compound semiconductor interfaces.

Characterization of Schottky barrier diodes by means of modulation technique

On the basis of the ac modulation technique a novel method is developed, which permits the extraction of the key parameters of Schottky diodes, i.e., the ideality factor, the barrier height, and the series resistance. These properties can be derived at any forward bias voltage from the current-voltage characteristic and its first and second derivative. Limitations to the method arise mainly from the voltage dependence of the effective barrier height, as can be shown by a model calculation. Applicability and exactness are demonstrated by experimental investigations of Ti/n-Si diodes with high series resistance, Yb/n-Si junctions, and Ti contacts on n-type InP, In0.73Ga0.27As0.64P0.36, and In0.53Ga0.47As.

Control of the barrier height of triangular-barrier diodes by doping their intrinsic layers

An analytic model for the control of the barrier height of a triangular-barrier diode (TBD) is proposed. It is shown that an extra (p- or n-type) doping given to the two intrinsic layers of a TBD changes its barrier height over a wide range (over all 40%). A simple closed-form expression is derived to give the dependence of barrier height on the extra dopings. It is seen that the ideality of the diode is not affected in spite of a wide range of changes obtained in the barrier height. Furthermore, the differential resistance of the device is shown to exponentially decrease with the extra n-type doping given to the structure. Such a strong dependence leads to an improvement in the forward-bias cut-off frequency of the device.

Experimental investigation of the dependence of barrier height on metal work function for metalSiO 2pSi (MIS) Schottky-barrier diodes in the presence of inversion

The dependence of barrier height on the metal work function of metal-SiO 2- p-Si Schottky barrier diodes was investigated and nonlinearity was found. This is explained by the theoretical model proposed recently by Chattopadhyay and Daw. The values of interface trap density and fixed charge density of the insulating layer of the diodes were calculated using this model and found to be appreciably different from those estimated by the usual method.

High Barrier Height MIS Diodes on n-InP Using Pd, Ni and Au on a Chemical Oxide

ABSTRACTMIS diodes were fabricated using Pd, Ni and Au- contacts on n-InP covered by a 40 Å chemically-grown oxide. The oxide had a refractive index of 1.4–1.6 with a composition of mainly In2O3 + some InPO3 near the surface and mixed oxide + InP near the interface. Pd-devices gave the highest barrigr height of 0.80 eV and lowest reverse saturation current density of 3×10−8A/cm2. I-V-T and C-V-T data gave temperature dependence of barrier height and revealed an interface state recombination current mechanism. Richardson plots gave good straight lines when empirically corrected using øB/n instead of just øB.

Electrical properties of ZnxCd1-xSe

The variation in bandgap energy with composition was determined for single crystals of ZnxCd1-xSe at 300 and 90 K. Au-ZnxCd1-xSe (x<0.45) diodes were fabricated and used to determine the dependence of barrier height and uncompensated donor density on composition. Deep levels were also investigated in these diodes using photocapacitance, which revealed the presence of two dominant levels with activation energies of 0.55–0.6 and 1.14–1.16 eV (referred to the valence band edge) that were independent of the composition.

The Resistance of Grain Boundaries in BaTiO&amp;lt;inf&amp;gt;3&amp;lt;/inf&amp;gt;-Based Ceramic

Evidence for grain boundary (GB) resistance in BaTiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> based capacitor ceramic exists in superohmic current voltage characteristics, in voltage-dependent activation energies, in high-voltage ohmic behavior, and in a conductivity peak at the Curie temperature. These phenomena are reviewed. Impedance-frequency measurements are reported for GB-controlled varistors and for BaTiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> -based capacitor ceramic under increasing voltage bias. The impedance plots are discussed in terms of grain and GB contributions. No contribution from contacts is evident. The resistance attributed to GB decreases faster with voltage bias than that due to grains. Schö11's model for dependence of GB barrier height on grain curvature for polycrystalline silicon is adapted to high-K ceramic. It is seen that grain curvature, along with carrier depletion in the grains, can result in significant reductions in GB barrier height and hence resistance. Variation in grain size in a given ceramic can result in GB resistance variations throughout the material.

Pressure dependence of barrier heights of schottky contacts on silicon

physica status solidi (a)Volume 101, Issue 1 p. K29-K32 Short Note Pressure dependence of barrier heights of schottky contacts on silicon N. Balasubramanyam, N. Balasubramanyam Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this authorVikram Kumar, Vikram Kumar Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this author N. Balasubramanyam, N. Balasubramanyam Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this authorVikram Kumar, Vikram Kumar Department of Physics, Indian Institute of Science, Bangalore Search for more papers by this author First published: 16 May 1987 https://doi.org/10.1002/pssa.2211010137Citations: 3 Bangalore 560012, India. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume101, Issue116 May 1987Pages K29-K32 RelatedInformation

Effect of hydrostatic pressure on GaAs-Ga1-xAlxAs microstructures.

Some detailed experimental studies of the effect of hydrostatic pressure on the energy levels of GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As quantum-well heterostructures have been recently published. The heterostructures used are grown by molecular-beam epitaxy and consist of several single GaAs wells with different widths separated by wide ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As barriers. Photoluminescence measurements at low temperature and up to 70 kbar show that all the peaks move to higher energy as the pressure is applied. The pressure coefficients of the heavy- and light-hole excitonic transitions appear to be different. On the other hand these coefficients decrease with decreasing well widths. In this paper we present a theoretical calculation of these pressure coefficients and of their well-width and barrier-height dependence, which quantitatively fits the experimental results.

Metal / Hydrogenated Amorphous Silicon Interfaces

The contact properties between different metals and hydrogenated amorphous silicon, prepared by various deposition techniques in different laboratories, are reviewed. From these studies the appropriate metallizations have been established for the achievement of Schottky diode, quasi-ohmic or ohmic contact to undoped and doped films. The various characteristic parameters describing Schottky barrier interfaces such as ideality factor, current saturation, contact resistance and barrier height are discussed. The dependence of Schottky barrier height upon the metal work function, measuring and annealing temperature, and optical band-gap are also reported. The minority-carrier injection and series resistance effects on the contact properties of a-Si:H diodes are described. All the results are interpreted in terms of a self-consistent model that exhibits an electrode-limited to bulk-limited transition.

Equilibrium properties of thin-oxide metal-oxide-semiconductor diodes

The zero-bias resistance and high frequency capacitance of Al- and Pd-gated thin-oxide metal-oxide-semiconductor diodes have been measured as a function of temperature. The temperature dependence of the semiconductor barrier height is found to be large, primarily due to inversion effects. The relatively low activation energies observed for the zero-bias resistance, as well as actual measurements of spatial variations in device current, strongly suggest the presence of large variations in the semiconductor band bending. These variations may be directly related to thickness nonuniformities which are known to occur in SiO2 films processed at low temperatures.

Barrier height enhancement of triangular barrier diodes

A modified model of a triangular barrier diode has been proposed and analyzed by considering the effect of low to moderate p-type doping in the two intrinsic regions. The presence of such acceptor impurities is shown to increase the effective barrier height. The functional dependence of barrier height, saturation current, and ideality factor on various technological parameters is discussed. A method to determine the barrier height and effective Richardson constant has also been suggested. The high-speed switching behavior of this diode is shown to improve.

On the difference in apparent barrier height as obtained from capacitance-voltage and current-voltage-temperature measurements on Al/ p-InP Schottky barriers

The difference in apparent barrier height as obtained from capacitance-voltage and current-voltage measurements on Al/ p-InP Schottky barriers was explained by introducing a distribution of barrier heights over the contact area and a temperature dependence of the real barrier height. Taking into account this barrier height distribution and the temperature dependence of the barrier height, we were also able to explain the measured values of the effective Richardson constant. As a result a modified expression for the temperature dependence of the current-voltage characteristics was obtained.

On the current transport mechanism in a metal—insulator—semiconductor (MIS) diode

The current transport mechanism in an MIS-tunnel diode has been studied by considering both the process of tunneling and the effect of pinholes in the insulating layer. It has been shown that in order to explain the experimental J- V characteristics of MIS-diodes, presence of a thin interfacial layer of thickness δ p within the pinholes should be considered. From an analysis of the tJ- V and C- V characteristics, a method has been suggested for the estimation of the value of δ p. The values of interface trap density and barrier height for the MOS-part of the diodes are also calculated. The dependence of barrier height on oxide thickness for the diodes is found to obey the barrier height model of Cowley and Sze.