Showing papers on "Schottky barrier published in 2001"

Grain Boundary Blocking Effect in Zirconia: A Schottky Barrier Analysis

Abstract: The grain boundary electrical properties of high purity ZrO 2 ceramic materials doped with 2, 3, and 8 mol % Y 2 O 3 , and 8 mol % Y 2 O 3 co-doped with 0.4 mol % Al 2 O 3 were studied in the temperature range of 200 to 500°C by electrochemical techniques and were theoretically analyzed. Although the presence of a siliceous phase is shown to be a major cause for the grain boundary blocking effect, the grain boundary properties appear to he significantly influenced by space charges, particularly in materials of high purity. The oxygen vacancy distribution and the grain boundary resistivity were calculated for 8 mol % Y 2 O 3 doped ZrO 2 by assuming double Schottky barriers, and the results were compared with the experiment. It is shown that reasonable space charge potentials lead to grain boundary effects which are consistent with the experimental features. In contrary to the bulk in which defect associates prevail (at temperatures <560°C), in the boundary regions, association effects can be assumed to be much less pronounced due to the vacancy depletion.

Formation of an electric dipole at metal-semiconductor interfaces

Abstract: The insensitivity of experimentally observed Schottky barrier height (SBH) to the metal work function, a phenomenon known as Fermi level pinning, has traditionally been attributed to the presence of interface states in the band gap of the semiconductor. A recent theory showed that the polarization of the chemical bonds at metal semiconductor interfaces could quantitatively account for the experimentally observed strength of Fermi level pinning on different semiconductors, without regard to the actual distribution of gap states. This bond polarization theory thus provides a coherent explanation of the Fermi level pinning effect, on the one hand, and the experimentally observed dependence of the SBH on interface structure, on the other hand. The method used in this theory, the electrochemical potential equalization method hitherto employed only in molecular physics, and its limitations are here discussed in detail, especially in the context of application to solid interfaces. Similarities and differences between this theory and the metal induced gap state theory are also discussed.

Gain mechanism in GaN Schottky ultraviolet detectors

Abstract: Schottky barrier GaN ultraviolet detectors, both in vertical and in lateral configuration, as well as in a metal–semiconductor–metal geometry were implemented. All devices exhibit a high gain at both reverse and forward bias. The photoresponse in the forward bias is in the positive current direction. We attribute the gain to trapping of minority carriers at the semiconductor–metal interface. The excellent agreement between the calculated responsivity and the experiment indicates that the model is valid for all device structures under study, and represents a unified description of gain mechanism in GaN Schottky detectors.

Trench DMOS transistor with embedded trench schottky rectifier

Abstract: An integrated circuit having a plurality of trench Schottky barrier rectifiers within one or more rectifier regions and a plurality of trench DMOS transistors within one or more transistor regions. The integrated circuit comprises: (a) a substrate of a first conductivity type; (b) an epitaxial layer of the first conductivity type over the substrate, wherein the epitaxial layer has a lower doping level than the substrate; (c) a plurality of body regions of a second conductivity type within the epitaxial layer in the transistor regions; (d) a plurality of trenches within the epitaxial layer in both the transistor regions and the rectifier regions; (e) a first insulating layer that lines the trenches; (f) a polysilicon conductor within the trenches and overlying the first insulating layer; (g) a plurality of source regions of the first conductivity type within the body regions at a location adjacent to the trenches; (h) a second insulating layer over the doped polysilicon layer in the transistor regions; and (i) an electrode layer over both the transistor regions and the rectifier regions.

Electrical transport characteristics of Au/n-GaAs Schottky diodes on n-Ge at low temperatures

Abstract: The currenti?½voltage characteristics of Au/n-GaAs Schottky diodes grown by metal-organic vapor-phase epitaxy on Ge substrates were determined in the temperature range 80i?½300 K. The zero-bias barrier height for current transport decreases and the ideality factor increases at low temperatures. The ideality factor was found to show the T0 effect and a higher characteristic energy. The excellent matching between the homogeneous barrier height and the effective barrier height was observed and infer good quality of the GaAs film. No generationi?½recombination current due to deep levels arising during the GaAs/Ge heteroepitaxy was observed in this study. The value of the Richardson constant was found to be 7.04 A K?2 cm?2, which is close to the value used for the determination of the zero-bias barrier height.

Ohmic contact formation mechanism of Ni on n-type 4H–SiC

Abstract: Ohmic contact formation mechanism of Ni on n-type 4H–SiC is proposed by comparing the electrical properties with microstructural change. The ohmic behavior was observed at temperatures higher than 900 °C, but Ni2Si phase, as formerly reported to be responsible for ohmic contact, was formed after annealing at 600 °C. The higher work function of Ni2Si than Ni and the observation of graphite phase on the surface of Ni silicide after annealing at 950 °C support that a number of carbon vacancies were produced below the contact, playing a key role in forming an ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons.

Controlled creation of a carbon nanotube diode by a scanned gate

Abstract: We use scanning gate microscopy to precisely locate the gating response in field-effect transistors (FETs) made from semiconducting single-wall carbon nanotubes. A dramatic increase in transport current occurs when the device is electrostatically doped with holes near the positively biased electrode. We ascribe this behavior to the turn-on of a reverse biased Schottky barrier at the interface between the p-doped nanotube and the electrode. By positioning the gate near one of the contacts, we convert the nanotube FET into a rectifying nanotube diode. These experiments both clarify a longstanding debate over the gating mechanism for nanotube FETs and indicate a strategy for diode fabrication based on controlled placement of acceptor impurities near a contact.

Surface potential measurements on GaN and AlGaN/GaN heterostructures by scanning Kelvin probe microscopy

Abstract: Surface potentials on GaN epilayers and Al0.35Ga0.65N/GaN heterostructures have been studied by scanning Kelvin probe microscopy (SKPM) in conjunction with noncontact atomic force microscopy. The dependence of the surface potential on doping in GaN films, as well as the variation of surface potential with Al0.35Ga0.65N barrier layer thickness has been investigated. The bare surface barrier height (BSBH), as measured by SKPM, is observed to decrease from ∼1. 40±0.1 eV to ∼0.60±0.1 eV with increasing doping in the GaN epilayers. Schottky barrier height calculated from the measurements of BSBH on n-GaN agrees very well with results from previous studies. We have also estimated the surface state density for GaN based on the measured values of BSBH. The semiconductor “work function” at the Al0.35Ga0.65N surface (in heterostructure samples) is observed to decrease by ∼0.60 eV with increase in barrier layer thickness from ∼50 to ∼440 A. A simple model considering the presence of a uniform density of charged acce...

Nanometer-scale test of the Tung model of Schottky-barrier height inhomogeneity

Abstract: Tung has shown [Phys. Rev. B 45, 13 509 (1992)] that a range of ``nonideal'' behaviors observed in metal/semiconductor (MS) Schottky diodes could be quantitatively explained by assuming that specific microscopic distributions of nanometer-sized ``patches'' of reduced barrier height exist at the MS interface. Here we report a simultaneous microscopic and macroscopic test of this model as applied to $\mathrm{metal}/6H\ensuremath{-}\mathrm{SiC}$ Schottky diodes, by (1) measuring the nm-scale barrier-height distribution (BHD) of particular Schottky diodes using ultrahigh vacuum (UHV) ballistic electron emission microscopy (BEEM), (2) extending the Tung model to calculate the expected nm-scale BHD for particular parameter values, and (3) quantitatively relating the measured nm-scale BHD of a particular Schottky diode to its macroscopic $I\ensuremath{-}V$ characteristic. Our studies indicate that (1) for relatively ideal diodes, both the microscopic and macroscopic behaviors are explained well by the Tung model with a large coverage (g5%) of shallow patches, (2) the measured BHDs are nearly identical for relatively ideal and highly nonideal diodes, and (3) a simple Tung model can account for highly nonideal behavior only by assuming an unphysical patch distribution in which the excess current is dominated by a few patches in the extreme tail of the patch distribution. Our measurements instead suggest that all the diodes contain a broad ``intrinsic'' distribution of shallow patches, while the large excess current in highly nonideal diodes is due to a few large defects of extrinsic origin. This last conclusion is consistent with a recent study by Skromme and co-workers [J. Electron. Mater. 29, 376 (2000)].

Doping dependence of the barrier height and ideality factor of Au/n-GaAs schottky diodes at low temperatures

Abstract: The barrier height and ideality factor of Au/n-GaAs Schottky diodes grown by metal-organic vapor-phase epitaxy (MOVPE) on undoped and Si-doped n-GaAs substrates were determined in the doping range of 2.5 � 10 15 – 1 � 10 18 cm � 3 at low temperatures. The thermionic-emission zero-bias barrier height for current transport decreases rapidly at concentrations greater than 1 � 10 18 cm � 3 . The ideality factor also increases very rapidly at higher concentration and at lower temperature. The results agree quite well with thermionic field emission (TFE) theory. The doping dependence of the barrier height and the ideality factor were obtained in the concentration range of 2.5 � 10 15 – 1.0 � 10 18 cm � 3 and the results are well described using TFE theory. An excellent match between the homogeneous barrier height and the effective barrier height was observed which supports the good quality of the GaAs film. The observed variation in the zero-bias barrier height and the ideality factor can also be explained in terms of barrier height inhomogeneities in the Schottky diode. r 2001 Elsevier Science B.V. All rights reserved.

Semiconductor device with schottky electrode having high schottky barrier

Abstract: A carrier travel layer is formed on the substrate of a semiconductor device with a buffer layer interposed, and a spacer layer and carrier supply layer are then formed on this carrier travel layer. On the carrier supply layer are provided a source electrode and a drain electrode, and a gate electrode is provided on an interposed Schottky layer. The carrier supply layer is composed of AlGaN and has tensile strain. The Schottky layer is composed of InGaN and has compressive strain. A negative piezoelectric charge is induced on the carrier supply layer side of the Schottky layer, and a positive piezoelectric charge is induced on the opposite side of the Schottky layer, whereby a sufficient Schottky barrier height is obtained and leakage current is suppressed.

Comparison of GaN p-i-n and Schottky rectifier performance

Abstract: The performance of GaN p-i-n and Schottky rectifiers fabricated on the same wafer was investigated as a function of device size and operating temperature. There was a significant difference in reverse breakdown voltage (490 V for p-i-n diodes; 347 V for the Schottky diodes) and forward turn-on voltage (/spl sim/5 V for the p-i-n diodes; /spl sim/3.5 V for the Schottky diodes). Both types of device showed a negative temperature coefficient for reverse breakdown, with value -0.34/spl plusmn/0.05 V/spl middot/K/sup -1/.

GaN and InGaN Metal-Semiconductor-Metal Photodetectors with Different Schottky Contact Metals

Abstract: The characterizations of n-type doped GaN, p-type doped GaN and n-type doped In0.2Ga0.8N Schottky metal-semiconductor-metal (MSM) photodetectors were reported. The epilayers were grown on sapphire by metalorganic chemical vapor deposition (MOVCD). Schottky contacts were fabricated using Au, Ti, Ni and Pt metals. The dark and illuminated current–voltage characteristics of GaN and InGaN MSM photodetectors with different Schottky metals were studied. The n-GaN MSM photodetectors with Au Schottky contacts showed better responsivity than those with other metals and they were also better than Au/p-GaN and Ti/n-In0.2Ga0.8N MSMs. The effects of the pitch width between the interdigitate fingers and the thickness of Schottky metals on the characteristics of photocurrents were also studied.

Deep centers in a free-standing GaN layer

Abstract: Schottky barrier diodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy (HVPE) on Al2O3 followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy (DLTS) measurements. From a 1/C2 vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap B′ with activation energy ET=0.53 eV was found in the Ga-face sample. Also, trap E1 (ET=0.18 eV), believed to be related to the N vacancy, was found in the N-face sample, and trap C (ET=0.35 eV) was in the Ga-face sample. Trap C may have arisen from reactive-ion-etching damage.

Injection- and space charge limited-currents in doped conducting organic materials

Abstract: Most conducting organic materials have a background p-type doping varying in the range 1015–1017 cm−3. We report results of a theoretical and experimental study of carrier transport in p-doped organic Schottky diodes. The theory given in this article shows that in a doped organic material with ohmic contacts the current is ohmic at low voltages. If the ohmic contact at the cathode is replaced by an Al Schottky contact the current varies exponentially with the applied voltage V. The current changes to space charge limited current (SCLC) at high voltages. The voltage at which the change takes place depends on the doping concentrations. In the SCLC regime the current varies according to the well-known V2 law if there are no traps and the mobility is independent of the electric field. If either trapping or effect of field on mobility is important, the current varies as Vm, where m>2. We have investigated experimentally the I–V characteristics of Schottky diodes fabricated using the PPV-based oligomer 2,5-di-n...

Indium-Silicon Co-Doping of High-Aluminum-Content AlGaN for Solar Blind Photodetectors

Abstract: We report on an indium–silicon co-doping approach for high-Al-content AlGaN layers. Using this approach, very smooth crack-free n-type AlGaN films as thick as 0.5 μm with Al mole fraction up to 40% were grown over sapphire substrates. The maximum electron concentration in the layers, as determined by Hall measurements, was as high as 8×1017 cm−3 and the Hall mobility was up to 40 cm2/Vs. We used this doping technique to demonstrate solar-blind transparent Schottky barrier photodetectors with the cut-off wavelength of 278 nm.

Trenched schottky rectifiers

Abstract: Inner trenches (11) of a trenched Schottky rectifier (1a; 1b; 1c; 1d) bound a plurality of rectifier areas (43a) where the Schottky electrode (3) forms a Schottky barrier 43 with a drift region (4). A perimeter trench (18) extends around the outer perimeter of the plurality of rectifier areas (43a). These trenches (11, 18) accommodate respective inner field-electrodes (31) and a perimeter field-electrode (38) that are connected to the Schottky electrode (3). The inner field-electrodes (11) are capacitively coupled to the drift region (4) via dielectric material (21) that lines the inner trenches (11). The perimeter field-electrode (38) is capacitively coupled across dielectric material (28) on the inside wall (18a) of the perimeter trench 18, without acting on any outside wall (18b). Furthermore, the inner and perimeter trenches (11, 18) are closely spaced and the intermediate areas (4a, 4b) of the drift region (4) are lowly doped. The spacing is so close and the doping is so low that the depletion layer (40) formed in the drift region (4), from the Schottky barrier (43) and from the field-relief regions (31,21; 38,28) in the blocking state of the rectifier, may deplete the whole of the intermediate areas (4a, 4b) between the trenches (11, 18) at a blocking voltage just below the breakdown voltage. This arrangement reduces the risk of premature breakdown that can occur at high field points in the depletion layer (40), especially at the perimeter of the array of rectifier areas (43a).

Crystal-polarity dependence of Ti/Al contacts to freestanding n-GaN substrate

Abstract: The effect of crystal polarity on the electrical properties of Ti/Al contacts to n-GaN substrate has been investigated. The Ti/Al contacts prepared on Ga-face n-GaN substrate became ohmic with a contact resistivity of 2×10−5 Ω cm2 after annealing at temperatures higher than 600 °C for 30 s. On the contrary, the contacts on N-face n-GaN substrate exhibited nonlinear current–voltage curve and high Schottky barrier heights over 1 eV were measured at the same annealing conditions. These results could be explained by opposite piezoelectric-field at GaN/AlN heterostructure resulted from different polarity of the GaN substrate.

Design rules for field plate edge termination in SiC Schottky diodes

Abstract: Practical design of silicon carbide (SiC) Schottky diodes incorporating a field plate necessitates an understanding of how the addition of the field plate affects the performance parameters and the relationship between the diode structure and diode performance. In this paper, design rules are presented for SiC Schottky diodes that incorporate field plate edge termination. The use of an appropriate field plate edge termination can improve the reverse breakdown voltage of a SiC Schottky diode by a factor of two. Reverse breakdown voltage values can be obtained that are up to 88% of the theoretical maximums.

Hydrogen induced tunnel emission in Pt/(BaxSr1−x)Ti1+yO3+z/Pt thin film capacitors

Abstract: The leakage current density–applied field (J−EA) characteristics of (BaxSr1−x)Ti1+yO3+z (BSTO) thin film capacitors with Pt electrodes that have been annealed in forming gas (95% Ar 5% H2 or D2) were investigated over the temperature range from −60 to +60 °C. Forming gas annealing significantly increased the leakage current density. The J–EA characteristics exhibited features that could not be fully explained by either a simple thermionic emission or tunneling (Fowler–Nordeim) formalism. Using the general charge transport theory of Murphy and Good, we show that the J–EA characteristics can be successfully interpreted in terms of tunneling of electrons through the interfacial Schottky barrier with the peak in energy distribution of the incident carriers strongly dependent on applied field. At high applied fields the energy distribution of incident carriers is peaked near the Fermi level in the electron injecting metal electrode at all temperatures considered in this study, leading to almost temperature ind...

Geometry optimization of interdigitated Schottky-barrier metal–semiconductor–metal photodiode structures

Abstract: The optimum geometry of an interdigitated Schottky-barrier metal–semiconductor–metal photodetector (MSM-PD) is discussed. From the calculated MSM-PD capacitance and transit time of optically generated carriers, the response time and quantum efficiency are evaluated and analysed. We propose a simple scaling rule to achieve the best high-speed response of the MSM detector. The optimum interelectrode spacing for interdigitated MSM-PD has been established. The potential of different semiconductor materials for high-speed MSM detectors is examined.

Method concerning a junction barrier Schottky diode, such a diode and use thereof

Abstract: A method for controlling the temperature dependence of a junction barrier Schottky diode of a semiconductor material having an energy gap between the valence band and the conduction band exceeding 2 eV provides for doing this when producing the diode by adjusting the on-state resistance of the grid portion of the diode during the production for obtaining a temperature dependence of the operation of the diode adapted to the intended use thereof.

Case study of an InAs quantum dot memory: Optical storing and deletion of charge

Abstract: We have studied self-assembled InAs quantum dots embedded in an InP matrix using photocapacitance and photocurrent spectroscopy. These dots are potentially promising for memories due to the large confinement energy for holes. In this work we have realized simple quantum dot memory by placing the dots in the space–charge region of a Schottky junction. Our measurements reveal that a maximum of about one hole can be stored per dot. We also find that illumination for an extended period deletes the stored charge. We show that these limitations do not reflect the intrinsic properties of the dots, but rather the sample structure in combination with deep traps present in the sample.

Epitaxial edge termination for silicon carbide Schottky devices and methods of fabricating silicon carbide devices incorporating same

Abstract: Edge termination for a silicon carbide Schottky rectifier is provided by including a silicon carbide epitaxial region on a voltage blocking layer of the Schottky rectifier and adjacent a Schottky contact of the silicon carbide Schottky rectifier. The silicon carbide epitaxial layer may have a thickness and a doping level so as to provide a charge in the silicon carbide epitaxial region based on the surface doping of the blocking layer. The silicon carbide epitaxial region may form a non-ohmic contact with the Schottky contact. The silicon carbide epitaxial region may have a width of from about 1.5 to about 5 times the thickness of the blocking layer. Schottky rectifiers with such edge termination and methods of fabricating such edge termination and such rectifiers are also provided. Such methods may also advantageously improve the performance of the resulting devices and may simplify the fabrication process.

Pd- and Pt-SiC Schottky diodes for detection of H2 and CH4 at high temperature

Abstract: Hydrogen- and methane-sensing characteristics of Pt- and Pd-SiC Schottky diodes, fabricated on the same SiC substrate, have been compared and analyzed as a function of hydrogen partial pressure and temperature by I – V and Δ I – t methods under steady-state and transient conditions at high temperature. The effects of the gas adsorption on the parameters such as barrier height, initial rate of gas adsorption, and gas reaction kinetics are investigated. Analysis of steady-state reaction kinetics using I – V method confirmed that the atomistic hydrogen adsorption process is responsible for the barrier height change in the diodes.

Low-frequency noise in Al0.4Ga0.6N-based Schottky barrier photodetectors

Abstract: The low-frequency generation recombination and the 1/f noise in AlGaN Schottky barrier photodetectors with high (40%) Al fraction has been investigated under forward and reverse bias conditions. The activation energy of local level contributing to noise was found to be Ea≈1 eV. Depending on the forward current level, the noise from Schottky barrier or from the series resistance (contacts and/or base) predominates. The upper bound of the Hooge parameter in Al0.4Ga0.6N was estimated as α⩽10.

Effect of donor and acceptor dopants on Schottky barrier heights and vacancy concentrations in barium strontium titanate

Abstract: This paper discusses the effect of donors and acceptors on the electronic band structure and defect properties of Ba 0.7 Sr 0.3 TiO 3 film (BST). Based on X-Ray Photoelectron Spectroscopy (XPS) data and an extension of previous work by Robertson and Chen (Robertson, J. and Chen, C. W., Schottky barrier heights of tantalum oxide, barium strontium titanate, lead titanate, and strontium bismuth tantalate. Appl. Phys. Lett., 1999, 74 , 1168–1170), Schottky barrier heights are calculated for BST films in which La and Mn dopants have been added (0.7%). The barrier height expression of Cowley and Sze (Cowley, A. M. and Sze, S. M., Journal of Applied Physics, 1965, 36, 3212) is discussed with attention to the term neglected in their original paper. The effect of dopants on the oxygen vacancy concentration is also discussed.