Showing papers on "Schottky barrier published in 1992"

Electron transport at metal-semiconductor interfaces : general theory

Abstract: A dipole-layer approach is presented, which leads to analytic solutions to the potential and the electronic transport at metal-semiconductor interfaces with arbitrary Schottky-barrier-height profiles. The presence of inhomogeneities in the Schottky-barrier height is shown to lead to a coherent explanation of many anomalies in the experimental results. These results suggest that the formation mechanism of the Schottky barrier is locally nonuniform at common, polycrystalline, metal-semiconductor interfaces.

Optoelectronic measurement of semiconductor surfaces and interfaces with femtosecond optics

Abstract: The basic concepts and preliminary applications of optically induced electromagnetic radiation from semiconductor surfaces and interfaces by using femtosecond optics are discussed. This submillimeter‐wave radiation provides a novel optoelectronic technique to study semiconductor electronic surface and interface properties with a contactless approach. The amplitude and phase of the electromagnetic radiation from the semiconductor surfaces depend on carrier mobility, impurity doping concentration, and strength and polarity of the static internal field. A large selection of bulk, epitaxial layer and superlattice samples from III‐V, II‐VI and group‐IV semiconductors has been tested. The orientation and strength of the static built‐in fields of a wide range of semiconductor surfaces, such as surface depletion, metal/semiconductor Schottky, p‐n junction and strain‐induced piezoelectric fields, can be determined and estimated.

Effects of low work function metals on the barrier height of sulfide‐treated n‐type GaAs(100)

Abstract: A comparative study of the Schottky barrier height variation on sulfide‐treated GaAs(100) surfaces with low work function metal contacts was made using current‐voltage and capacitance‐voltage measurements. Five different wet chemical sulfide treatments were found to cause little variation in the Sm (0.72 eV) and Mg (0.59 eV) Schottky barrier heights, but caused significant variation in the Al (0.58–0.75 eV) barrier heights when compared to the untreated control diodes. A low temperature (160 °C) anneal was found to cause variation in all of these, uniformly raising the barrier heights of the Sm (+0.07 eV) and Al (+0.04 eV) contacts, and degrading the Mg contacts. These results demonstrate the critical importance of both the reaction specifics and the stability of the interface on the Schottky barrier height.

Empirical fit to band discontinuities and barrier heights in III–V alloy systems

Abstract: We present a figure summarizing the variation of conduction band discontinuity, valence band discontinuity, and gold Schottky barrier height for binary and ternary III–V semiconductors. This figure, which applies to unstrained material, makes use of the property of transitivity in band alignments, and the observed experimental correlation between barrier heights and band gap discontinuities, to consolidate a wide range of data. The figure should be very useful in the design of novel heterostructure electronic and optical devices.

Metal Schottky barrier contacts to alpha 6H:SiC

Abstract: Formation of Schottky barrier contacts to n‐type 6H‐SiC for a number of metals chosen to include a variety of physical and chemical properties has been investigated. The metals (Pd, Au, Ag, Tb, Er, Mn, Al, and Mg) were deposited onto room temperature surfaces terminated with a submonolayer coverage of oxygen. The metal/6H‐SiC interface chemistry and Schottky barrier height φB during contact formation were obtained with x‐ray photoemission spectroscopy; the electrical properties of subsequently formed thick contacts were characterized by current‐voltage and capacitance‐voltage techniques. The o/B values for these metals extend over a wide 1.3 eV range. To a varying degree φB depends on the 6H‐SiC crystal face (Si vs C). Mg and Al (Si face of latter) have φB=0.3 eV, a value which is suitable for nonalloyed ohmic contacts.

Silicon-carbide high-voltage (400 V) Schottky barrier diodes

Abstract: The authors describe the fabrication and characteristics of the first high-voltage (400-V) silicon-carbide (6H-SiC) Schottky barrier diodes. Measurements of the forward I-V characteristics of these diodes demonstrate a low forward voltage drop of approximately 1.1 V at an on-state current density of 100 A/cm/sup 2/ for a temperature range of 25 to 200 degrees C. The reverse I-V characteristics of these devices exhibit a sharp breakdown, with breakdown voltages exceeding 400 V at 25 degrees C. In addition, these diodes are shown to have superior reverse recovery characteristics when compared with high-speed silicon P-i-N rectifiers. >

Parameter extraction from non-ideal C−V characteristics of a Schottky diode with and without interfacial layer

Abstract: In this study, we have attempted to interpret experimentally observed non-ideal AlpSi Schottky diode I-V and C−2−V characteristics which are due to an interface layer, interface states and fixed surface charge. A value of 0.68 eV for the barrier height qΦBo for AlpSi diodes without interface layer and fixed surface charge has been obtained from C−2−V characteristics and a value of 0.20 eV for the neutral level of the surface states has been found. Furthermore, the value of the barrier height qΦBp without fixed surface charge and the effective barrier height qΦBp,o are separately obtained from C−2-V characteristics. In addition, values of interface state density Dit have been calculated.

High power, high frequency metal-semiconductor field-effect transistor formed in silicon carbide

Abstract: A high power, high frequency, metal-semiconductor field-effect transistor comprises a bulk single crystal silicon carbide substrate, an optional first epitaxial layer of p-type conductivity silicon carbide formed upon the substrate, and a second epitaxial layer of n-type conductivity silicon carbide formed upon the first epitaxial layer. The second epitaxial layer has two separate well regions therein that are respectively defined by higher carrier concentrations of n-type dopant ions than are present in the remainder of the second epitaxial layer. Ohmic contacts are positioned upon the wells for respectively defining one of the well regions as the source and the other as the drain. A Schottky metal contact is positioned upon a portion of the second epitaxial layer that is between the ohmic contacts and thereby between the source and drain for forming an active channel in the second epitaxial layer when a bias is applied to the Schottky contact.

GaAs Schottky diodes for THz mixing applications

Abstract: The operation of GaAs Schottky barrier diodes, the critical mixer element used in heterodyne receivers for a variety of scientific applications in the terahertz frequency range, is reviewed. The constraints that the receiver system places on the diodes are considered, and the fundamental guidelines for device optimization are presented. The status of ongoing research, both experimental and theoretical, is examined. Emphasis is placed on investigations of the various effects that can limit diode performance at these high frequencies. Investigations of planar diode technology are summarized, and the potential replacement of whisker-contacted devices with planar structures is considered. >

Photovoltaic output limitation of n‐FeS2 (pyrite) Schottky barriers: A temperature‐dependent characterization

Abstract: Metal/n‐pyrite (metal=Pt, Au, Nb) Schottky barrier type diodes were fabricated on electrochemically reduced either synthetic or natural (100) and (111) surfaces of single crystalline n‐FeS2. The temperature dependence of I‐V curves in darkness were analyzed in the range of 200–350 K on the basis of thermionic emission and recombination models. The calculated effective barrier height was ∼0.60 eV and the activation energy for recombination ∼0.50 eV for all investigated n‐FeS2/Pt samples. The doping density and the extrapolated potential (pseudo flatband situation) from the Mott–Schottky plot, obtained from capacities deduced from potentiostatic complex impedance measurements, were 2.0×1016 cm−3 and 0.25 eV vs Pt for the synthetic n‐pyrite crystal, respectively. From the donor density and barrier height a band bending of 0.5 eV was deduced. Photovoltaic parameters like open‐circuit photovoltage and short‐circuit photocurrent were studied down to temperatures of 200 K. The main phenomenon preventing the gene...

Schottky barrier height and negative electron affinity of titanium on (111) diamond

Abstract: Titanium was deposited on a natural type IIb diamond surface with a (111) orientation. The titanium‐diamond interface was studied with ultraviolet photoemission spectroscopy, using 21.2 eV light. Prior to deposition, the diamond was chemically cleaned, and a sharp (0.5 eV full width at half‐maximum) peak was observed at the position of the conduction band, indicating a negative electron affinity surface. After a subsequent argon plasma clean this peak disappeared, while the spectrum shifted 0.5 eV towards higher energies. Upon submonolayer titanium deposition the spectrum shifted 0.5 eV down, while the negative electron affinity peak reappeared. Further titanium depositions caused this titanium induced negative electron affinity peak to be attenuated, indicating that the emission originated from the interface. By determining the relative positions of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond (111) was measured and found to be 1.0±0.2 eV....

On the inhomogeneity of Schottky barriers

Abstract: It is shown that the wide diversity of behavior observed from common Schottky barriers is difficult to reconcile with the traditional view of a homogeneous barrier height which is determined by Fermi level pinning, but is consistent with the presence of inhomogeneities in the barrier height. The demonstrated inhomogeneity in Schottky barriers, which is shown to have a dominant effect on electron transport, is suggestive of a dependence on the barrier height on the interface structure. Experimental and theoretical results obtained from high-quality epitaxial Schottky junctions are also discussed to show the correlation between the interface structure and the barrier height.

Interfacial reactions and Schottky barriers of Pt and Pd on epitaxial Si1-xGex alloys

Abstract: The evolution of interfacial reactions during the deposition of Pt and Pd on epitaxial Si1−xGex alloys was studied using x‐ray photoelectron spectroscopy (XPS) for metal coverage up to 10 A. Auger electron depth profiling was performed on a thicker metal overlayer before and after in vacuo annealing to study the redistribution of composition in the reactions. We have found that Pt and Pd react mainly with Si to form silicides at 350 °C, leaving some Ge to segregate at the surface. These results were correlated with Schottky barrier height measurements. We found that the Schottky barrier heights of Pt/n‐Si0.8Ge0.2 and Pd/n‐Si0.8Ge0.2 are about the same, pinned at 0.68 eV, which is much smaller than those of n‐Si. These barrier heights are quite stable up to 550 °C.

Epitaxial growth of SrTiO3 films on Pt electrodes and their electrical properties

Abstract: Heteroepitaxial SrTiO3 films of perovskite structure with thicknesses of 46 to 184 nm were prepared by rf magnetron sputtering, holding substrate temperature at 400°C, on Pt films which were also epitaxially grown on a MgO(100) substrate in advance. The relative dielectric constant was estimated to be more than 300, and the leakage current density was less than 10-8 A/cm2. The analysis of the leakage current suggests Schottky barrier formation at the interface between SrTiO3 and Pt films, with a barrier height of about 1 V.

A novel Schottky/2-DEG diode for millimeter- and submillimeter-wave multiplier applications

Abstract: A high-frequency diode is proposed for use as a frequency multiplier element in the millimeter- and submillimeter-wavelength regions. The Schottky/2-DEG diode utilizes a Schottky contact along the edge of a two-dimensional electron gas (2-DEG) structure. This geometry allows one to combine a very low series resistance due to the excellent transport properties of the 2-DEG with a high breakdown voltage caused by the 2-D electric field spreading in the depletion region (compared to a 1-D field variation in the conventional Schottky diode). The higher Fermi velocity of the 2-DEG leads to a less severe transit-time limitation of the frequency response. >

Vacuum‐deposited metal/polyaniline Schottky device

Abstract: All vacuum‐deposited metal/semiconducting polyaniline hetrojunction Schottky devices using vacuum‐evaporated polyaniline films of a thickness of the order of 0.1 μm have been prepared. Schottky junctions have been formed using the following metals, Al, Sn, In, Pb, Sb, and Ag. Electrical characterization has been carried out and electronic parameters, including the barrier height and ideality factor, have been determined. Infrared optical absorption spectroscopy of the vacuum‐deposited polyaniline films were used to determine the structure, energy band gap, and effect of various ambients on the vacuum‐deposited polyaniline films.

Luminescent Properties of Doped Organic EL Diodes Using Naphtalimide Derivative

Abstract: An organic dye was doped into the naphtalimide (NA) emission layers of some organic thin-film electroluminescent (EL) diodes to evaluate those layers EL emission intensity distribution and to understand their general emission properties. After a certain point, the nearer the doped layer was to the cathode, the weaker was its EL emission intensity; a steep drop-off began at approximately 25 nm. This phenomenon may result from exciton dissociation, due to the presence of a Schottky barrier, at the emission layer/cathode interface

Electrically programmable antifuse using metal penetration of a junction

Abstract: An improved antifuse uses metal penetration of either a P-N PN junction or a Schottky diode. The P-N junction or Schottky diode (11), is contacted by a diffusion barrier (14) such as TiN, W, Ti-W alloy, or layers of Ti and Cr, with a layer (15) of a metal such as Al, Al-Cu alloy, Cu, Au, or Ag on top of the diffusion barrier. The junction (11) is surrounded by an electrical isolation structure (13) which also serves to thermally isolate the said junction. When this junction is stressed with voltage pulse producing a high current density, severe joule heating occurs resulting in metal penetration of the diffusion barrier and the junction to form a metal contact (15'). The voltage drop across the junction decreases by about a factor of ten after the current stress and is stable thereafter. Alternatively, a shallow P-N junction in a silicon substrate is contacted by a layer of metal that forms a silicide, such as Ti, Cr, W, Mo, or Ta. Stressing the junction with a voltage pulse to produce a high current density results in the metal penetrating the junction and reacting with the substrate to form a silicide.

Schottky barrier height enhancement on n‐In0.53Ga0.47As

Abstract: Schottky barrier height enhancement on n‐InGaAs is studied on structures with thin surface layers of different compositions. Counter‐doped p+‐InGaAs layers, as well as layers of n‐ and p‐InP, n‐GaAs, and n‐InGaP of different thicknesses and dopant densities, respectively, were used to enhance the barrier. Titanium was used as a barrier metal to prepare Schottky diodes of different areas and the barrier height is analyzed by current‐voltage measurements. It is observed that the barrier height enhancement by p+‐InGaAs layers increases with the layer thickness and dopant density, respectively, and effective barrier heights up to 0.63–0.68 eV, i.e., higher values than previously reported, have been measured. The barrier height enhancement by counter‐doped p+‐InGaAs layers on n‐InGaAs can be described by the two‐carrier model. Schottky diodes with extremely low reverse current densities have been prepared, JR(1 V) =4.5×10−6 A/cm2. It is shown that lattice‐matched InP surface layers can be used as an alternativ...

Ideal Schottky diodes on passivated silicon

Abstract: Because of the complicated electronic and metallurgical properties of the metal-semiconductor interface, there is much controversy about the theoretical interpretation of experimental results on Schottky barrier heights. We present a new approch of barrier height measurements on a prototypical clean, abrupt and noninteracting system consisting of mercury contacts to hydrogen-passivated silicon surfaces. The resulting barrier to p-silicon is 0.9 V, totally at variance with all results presented for silicon Schottky barriers fabricated by standard metal deposition techniques. We believe this to be the first report in the limit of noninteracting metal contacts to silicon.

Properties of the planar poly(3‐octylthiophene)/aluminum Schottky barrier diode

Abstract: Formation and characterization of planar polymer Schottky barrier diodes are presented. Electrical characteristics of planar aluminium‐poly(3‐octylthiophene) Schottky barrier diodes are studied with emphasis on the current transport mechanisms. The device exhibits nearly ideal diode behavior in dark with an ideality factor of n=1.2. Temperature dependence of the current‐voltage characteristics of the diode is studied in the range 170–370 K. Agreement with the diffusion theory of metal‐semiconductor rectification is demonstrated for high temperatures T≳300 K. For temperatures less than room temperatures tunneling is proposed to be the dominant current transport mechanism.

A novel PVD technique for the preparation of SnO2 thin films as C2H5OH sensors

Abstract: A sensor for ethyl alcohol, based on an SnO2 thin film, is described. This film is grown by means of sputtering with a novel technique, called RGTO (rheotaxial growth and thermal oxidation). The RGTO thin film with an ultra-thin layer of Pd shows a good sensitivity to ethyl alcohol in the temperature range 523–773 K and a high selectivity to CO, CH4, C3H8 and C4H10. The maximum value of the sensitivity, defined as the relative variation of conductance ΔG/G, is obtained at 650 K; it is equal to 150 for 1000 ppm of ethyl alcohol in synthetic air. The height of the Schottky barrier between adjacent grains is obtained by electrical measurements of the conductance stimulated by the temperature. The average height of the barrier as a function of the operating temperature shows a maximum at 773 K (eVs = 0.65 eV).

Theoretical Models of Hot Carrier Effects at Metal‐Semiconductor Electrodes

Abstract: The physical and electrochemical properties of hot carriers at metallized semiconductor electrodes in contact with a redox electrolyte are described. Theoretical ballistic mean‐free paths, , for hot carriers in Ag, Cu, Au, Al, Ru, Pd, and Pt, were calculated as a function of excess energy above the Fermi energy. At 0.5 eV hot, was 580 A for Ag, 420 A for Cu and Au, 90 to 130 A for the remaining metals, with Pt having the lowest value. Using the Marcus‐Gerischer model, currents at the equilibrium potential were calculated as a function of built‐in barrier, film thickness, and reorganization energy for Au and Pt. The current for a simple outer sphere electron transfer reaction is predicted to be enhanced when the film thickness becomes . For Au/n‐Si diodes, the enhancement for reorganization energy, , 100 A Au and built‐in barriers of 0.4 to 0.6 eV are predicted to be 60 to 10 times. Larger enhancements are predicted for larger reorganization energies, the maximum effect being predicted for . The stage most likely to limit observation of hot carriers effects is slow vibrational or vibrational‐rotational relaxation of the redox acceptor or donor. By a combination of theoretical calculations and empirical data, we conclude that it is possible to observe hot carrier effects under real conditions. Experimental data that support the theoretical development and the hot carriers concept are presented in the following paper.

On the reverse blocking characteristics of Schottky power diodes

Abstract: An analytical model for the reverse blocking characteristics of Schottky power diodes has been obtained by incorporating the impact ionization multiplication factor into the thermionic-emission reverse leakage current with field-dependent Schottky-barrier lowering. Excellent agreement has been found between calculated curves and measured data. This model allows the accurate calculation of the reverse-leakage current of Schottky diodes at high reverse voltage. >

Electrochemical and electric properties of vacuum-deposited poly(arylene)s: electrochemical activity, diode, and electroluminescence

Abstract: Vacuum-deposited thin films of poly(arylene)s [poly(p-phenylene), poly(thiophene-2,5-diyl) (PTh), poly(pyridine-2,5-diyl), and poly(2,2{prime}-bipyridine-5,5{prime}-diyl)] are electrochemically active, giving rise to doping and undoping peaks at essentially the same positions as those of original poly(arylene)s. Al/vacuum-deposited PTh/Au and Al/vacuum-deposited PTh/ITO electric junctions show rectification of electric current, which is accounted for by assuming the presence of a Schottky barrier between Al and PTh. The Al/vacuum-deposited PTh/ITO junction emits light at an applied voltage of 15 V. 9 refs., 4 figs., 1 tab.