Variation Of Barrier Height Research Articles

Thermal Desorption of Deuterium from GaN(0001)

AbstractThe recombinative desorption of deuterium from GaN(0001) has been investigated using temperature programmed desorption (TPD) with variable heating rates. With a heating rate of 1°C/s, molecular deuterium desorption peaks at 410 C in agreement with related previous work. However, the shape of the curve indicates a secondary peak at around 280°C which is merged into the lower temperature shoulder of the dominant peak. By changing linear heating rate from 0.05 C/s to 8°C/s desorption peak temperatures from 380°C to 570°C were observed. Fitting to a pseudo-first-order desorption model results in a hydrogen desorption barrier, Ed, from surfaceof 1.1eV and a pre exponential factor, n, of 2 x 106s-1. Both are below expected values and are assumed to be due to a variation of desorption barrier heights. If a typical pre-exponential factor of 1 x 1013s-1is assumed, reanalysis of the desorption data produce a desorption barrier of 2.0 eV, in agreement with the existence of the surface adsorption barrier at room temperature.

Hydrogen sensing properties of SnO 2 varistors loaded with SiO 2 by surface chemical modification with diethoxydimethylsilane

Effects of chemical surface modification with diethoxydimethylsilane (DEMS) on the H 2 sensing properties of pure SnO 2 and Pd/SnO 2 as a varistor-type sensor have been investigated. The DEMS treatment resulted in an increase in the breakdown voltage, especially in air, and in an improvement in H 2 sensitivity for both SnO 2 and Pd/SnO 2 varistors. A.C. impedance measurement has revealed that variations in potential barrier height per grain boundary, V gb, with H 2 concentration are well coincident with the breakdown voltage shift induced by the presence of H 2. Thus, it was confirmed that the improved H 2 sensitivity arose from the increased V gb in air induced by the SiO 2 thin film coating by the DEMS treatment. The limitation of neck growth between SnO 2 particles by the SiO 2 thin film coating is anticipated to be responsible for the increased V gb.

Schottky barrier studies on single crystal ZnTe and determination of interface index

Detailed studies on metal-(111) p-ZnTe Schottky barriers have been carried out using In, Ag, Al, and Cu as barrier metals. Weak dependence of barrier height on metal work function was observed. The highest and lowest barrier heights of 0.99 and 0.80 eV were found for In and Cu respectively which had lowest and highest work functions. The ideality factor n was found to vary between 1.84 for In and 2.13 for Al contacts. The Fermi level was found to be pinned effectively by interface states, the density of which was calculated to be 4.7×1013 states/cm2/eV. From the current–voltage characteristics measured between 250 and 350 K, the effective Richardson constant A** was determined to be 72±6 A/cm2/K2. This agrees very well with the theoretically calculated value of A** for a hole effective mass mh*=0.6m0. The temperature variation of barrier height was also determined from the capacitance–voltage characteristics. The interface index a parameter used to describe the pinning strength of semiconductors was found to be 0.34 for ZnTe.

Thermally induced variation in barrier height and ideality factor of Ni/Au contacts to p-GaN

In this paper, we describe the change in barrier heights (ϕB) and ideality factors (n) of Ni/Au contacts to p-GaN determined from current-voltage measurements as a result of (a) rapid thermal annealing between 400–700°C under flowing nitrogen, and (b) testing at temperatures of 20–300°C. The lowest barrier height and ideality factor values were obtained from samples annealed at 500–600°C. These results provide supporting evidence that thermal processing helps to remove contaminants at the contact-GaN interface, thus decreasing effective barrier height and consequently, contact resistance.

Temperature dependence of current—voltage characteristics of Au/n-GaAs epitaxial Schottky diode

The influence of temperature on current-voltage (I-V) characteristics of Au/n-GaAs Schottky diode formed on n-GaAs epitaxial layer grown by metal organic chemical vapour deposition technique has been investigated. The dopant concentration in the epitaxial layer is 1 X 1016 cm-3. The change in various parameters of the diode like Schottky barrier height (SBH), ideality factor and reverse breakdown voltage as a function of temperature in the range 80–300 K is presented. The variation of apparent Schottky barrier height and ideality factor with temperature has been explained considering lateral inhomogeneities in the Schottky barrier height in nanometer scale lengths at the metal-semiconductor interface

Tunneling barrier height at defect sites on Si(001)

Tunneling barrier height (BH) has been measured at two types of surface defects on Si(001), the type-C defect and the split-off-dimer defect. Contrary to previous experiments, we find no evidence of large BH reduction at these defect sites. For both defects, the measured BH contour shows a good agreement with the STM topographic contour. The spatial variation in BH is thus dominated by the topographic contribution at these dimer defects, as well as at normal dimers. Our experimental results suggest that a large defect-induced dipole is quite unlikely at type-C and split-off-dimer defects.

Hysteretic behavior of magnetic particles with dipole interaction

Energy barrier height and coercivity variation of a pair of interacting particles has been studied as a function of the bonding angle β for 0°⩽β⩽π/2 and applied field using the fixed step Monte Carlo simulation approach supplemented by the perturbation method. Coercivity Hc(β) of the system has local maxima at β=0 and π/2, and a global minimum at β≃65°, and remains depressed compared to the noninteracting case for β⩽30° at any temperature. The barrier height behaves similarly. Due to the random nature of distribution dipole interaction, on average, leads naturally to a reduction in coercivity and energy barrier height in comparison with the noninteracting case.

Anomalous current transport in Au/low-doped n-GaAs Schottky barrier diodes at low temperatures

The current-voltage characteristics of Au/low-doped n-GaAs Schottky diodes were determined at various temperatures in the range of 77-300 K, The estimated zero-bias barrier height and the ideality factor assuming thermionic emission (TE) show a temperature dependence of these parameters. While the ideality factor was found to show the $T_o$ effect, the zero-bias barrier height was found to exhibit two different trends in the temperature ranges of 77-160 K and 160-300 K, The variation in the Bat-band barrier height with temperature was found to be - (4.7 +/- 0.2) $210^4$ $eVK^1$, approximately equal to that of the energy band gap, The value of the Richardson constant, A**, was found to be $0.27 A cm^-^2 K^-^2$ after considering the temperature dependence of the barrier height. The estimated value of this constant suggested the possibility of an interfacial oxide between the metal and the semiconductor. Investigations suggested the possibility of a thermionic field- emission-dominated current transport with a higher characteristic energy than that predicted by the theory, The observed variation in the zero-bias barrier height and the ideality factor could be explained in terms of barrier height inhomogenities in the Schottky diode.

Simulation of Electrical Properties of Recrystallized SiC.

The height of the potential barrier originating at the grain boundaries of recrystallized SiC was experimentally controlled by varying the nitrogen pressure during sintering. The variation in electrical properties with respect to the variation of the potential barrier height was simulated using a computer. There are two conduction mechanisms for recrystallized SiC. One is thermal excitation conduction over the potential barrier and the other is tunnel conduction through the potential barrier. The WKB (Wentzel, Kramers, Brillouin) approximation was applied to calculate the number of carriers that pass through the potential barrier by the tunnel effect. The variation of electrical properties was calculated by varying the height of the potential barriers, and the result corresponded fairly well with the experimentally determined variation of these properties. This simulation method will be useful in designing the electrical properties of recrystallized SiC.

Correlation between barrier height and band offsets in metal/Si1−xGex/Si heterostructures

The variation of barrier height with the band gap in the metal/heterojunction systems is related to how the Fermi level position varies with respect to band edges. If the Fermi level is pinned by the interface states its movement will also correspond to the movement of the neutrality level at the interface. Metal/Si1−xGex/Si heterostructures (0⩽x⩽0.24) for both n- and p-type substrates were studied to understand the relation between Schottky barrier, Fermi level movement, and the band gap variations. It was shown that a correlation exists between Schottky barrier height variation and band-offset values ΔEc and ΔEv. For n-type substrate, measured barrier height differences are almost the same as the band offsets in the conduction band ΔEc. For p-type substrates they were found to be slightly smaller than ΔEv. This shows that Fermi level position relative to the conduction band edge does not change with band gap variation.

Improvement of gas-sensing properties of SnO 2 by surface chemical modification with diethoxydimethylsilane

SnO 2 powder was subjected to repeated surface chemical modification with diethoxydimethylsilane (DMES) through condensation reaction with hydroxyl groups on the surface Sn 4+ sites, followed by calcination at 600°C, in order to investigate the effects of the incorporation of the SiO 2 component on the gas-sensing properties of a partially sintered SnO 2 sensor. Secondary ion mass spectroscopy and elemental analysis confirmed the incorporation of the SiO 2 component on the SnO 2 surface. The amount of the Si atoms introduced with a single time modification was about 25% of the surface Sn 4+ sites. Temperature programmed desorption peaks of oxygen adsorbates and surface hydroxyl groups on the SnO 2 surface apparently disappeared with the repeated modification, but it was suggested that the surface was not completely covered with a monolayer of SiO 2, suggesting that the SiO 2 component aggregated to some extent into fine particles. Gas sensitivity to H 2 was found to be markedly enhanced by the surface chemical modification, though the recovery rate became very slow. In contrast, sensitivity to CH 4 and C 3H 8 increased up to two cycles of modification. The variations in the gas-sensing properties are discussed in terms of the variations in the potential barrier height at the grain boundaries or necks.

Barrier-Height Imaging of Si(001) 2 × n

We have carried out barrier-height imaging on clean Si(001) 2 ×1 and Ni-contaminated 2 ×n surfaces and investigated the local barrier-height variation at and around Ni-related dimer-vacancy (DV) defects which are referred to as (1+2)-DVs. The barrier-height images show atomic contrast which conforms nicely with corresponding constant-current scanning-tunneling-microscopy (STM) topographs. No strong defect-induced modification was observed in the local barrier height at (1+2)-DV. Our direct barrier-height measurements thus provide a negative result on the barrier-height reduction at (1+2)-DV, which was predicted by Ukraintsev et al. [Surf. Sci. 388 (1997) 132)].

Electron transfer through interfacial water layer studied by scanning tunneling microscopy

The effective barrier height for electron tunneling is measured across the aqueous capacitor junction composed of a scanning tunneling microscopy (STM) tip and a surface. At a junction distance of a water monolayer, the barrier height strongly varies with the polarity and the magnitude of the applied junction voltage. This monolayer barrier height increases with an increasing positive value of the sample bias, while it does not for the negative bias. Such asymmetric variation of the tunneling barrier height manifests the influence of water molecular geometry on electron tunneling.

Electron tunneling across an interfacial water layer inside an STM junction: tunneling distance, barrier height and water polarization effect

surfaces in air. The electron tunneling distance ranges from 7–20 A when the junction resistance is of the order of 108 Ω. We suggest that the unusually low value of the barrier height (<1.5 eV) originates from the three-dimensional nature of the electron tunneling through the interfacial water layer present inside the junction. An asymmetric variation in barrier height is observed with respect to the applied bias voltage at a junction distance of water monolayer thickness, which reflects the polarization of the water layer on the surface.

Features of InGaAlAs/InP heterostructures

InGaAlAs epilayers lattice matched to an InP substrate are grown by molecular beam epitaxy with band gap energies varying in the range 0.8–1.42 eV. The I–V/C–V characteristics of the Schottky diodes fabricated on InGaAlAs/InP heterostructures are investigated in the temperature range 80–300 K to study the variation of barrier heights with the Al mole fraction in the alloy. It is noted that at room temperature due to the dominance of thermionic emission the Schottky characteristics are not observable on low Al fraction structures, primarily because of the low metal–semiconductor barrier and low heterostructure barrier potentials. However, at 80 K the potentials are high enough to provide measurable characteristics. For an Al mole fraction of 0.23, the band lineup of the InGaAlAs/InP heterostructure changes from type I to staggered type II. Also, for the band gap engineered InGaAlAs alloys, the variations of mobility and doping concentration in the temperature range 80–400 K are presented as a function of the Al mole fraction in the alloy.

Schottky Barrier Modification Of Low Energy Ar-Ion Bombarded GaAs And Si

AbstractEpitaxially grown GaAs (p- and n-type) and n-Si were bombarded with low energy Ar-ions. Current voltage measurements on Schottky barrier diodes fabricated on the sputtered p-GaAs (Sc) and n-Si (Pd) showed that the series resistance and ideality factor were increased as the Arion dose was increased. The respective increase and decrease in barrier heights of Sc/p-GaAs and Pd/n-Si diodes were attributed to the presence of donor-type surface states in the bombarded material. The barrier heights of Au Schottky diodes made on n-GaAs changed nonmonotonically with Ar-ion sputter voltage. Variations of barrier height in the 0-1 kV range were explained by the introduction of donor-type defects. We demonstrated that the introduction of high concentrations of continuous level defects above 1 kV resulted in Fermi level pinning to become the dominant mechanism for controlling the effective barrier of current transport. Our results have shown that Schottky barrier properties could be changed by controlled amounts by varying the bombarding ion dose or sputter voltage.

Schottky barrier height at the Au/porous silicon interface

The Schottky barrier height at the Au/porous silicon interface has been studied with ballistic electron emission microscopy (BEEM). The porous silicon thin films were prepared by laser ablation. The barrier height was found to display considerable variation across the interface. We suggest that this barrier height variation is a reflection of the local bonding differences at the Au/porous Si interface.

Variations of interface potential barrier height and leakage current of (Ba, Sr)TiO3 thin films deposited by sputtering process

Variations of the leakage current behaviors and interface potential barrier height (ΦB) of rf-sputter deposited (Ba, Sr)TiO3 (BST) thin films with thicknesses ranging from 20 nm to 150 nm are investigated as a function of the thickness and bias voltages. The top and bottom electrodes are dc-sputter-deposited Pt films. ΦB critically depends on the BST film deposition temperature, postannealing atmosphere and time after the annealing. The postannealing under N2 atmosphere results in a high interface potential barrier height and low leakage current. Maintaining the BST capacitor in air for a long time reduces the ΦB from about 2.4 eV to 1.6 eV due to the oxidation. ΦB is not so dependent on the film thickness in this experimental range. The leakage conduction mechanism is very dependent on the BST film thickness; the 20 nm thick film shows tunneling current, 30 and 40 nm thick films show Schottky emission current.

Time dependence of etch-induced damage generated by an electron cyclotron resonance source

The effects of etch time on the damage induced during dry etching have been studied. GaAs- and InP-based materials were etched for different times in an electron cyclotron resonance source and the electrical and optical characteristics were measured. Variations in Schottky diode ideality factor (n) and barrier height (φb) were used to measure dry-etch-induced electrical damage at the surface of GaAs after different etch times. The contact resistance of In0.53Ga0.47As, extracted from transmission line measurements, was also investigated for different etch times and compared to the etch time dependence of GaAs. Capacitance–voltage (C–V) measurements from Schottky diodes and photoluminescence (PL) intensity from GaAs/Al0.30Ga0.70As multiple quantum well (MQW) structures were used to investigate the time dependence of the etch damage farther below the surface. The damage in GaAs as shown by n and φb shows marked deterioration after 10 s of etching but improves after longer etching. The contact resistance of In0.53Ga0.47As was found to increase fastest in the first 10 s, but the electrical characteristics did not improve with etch time as the GaAs did. There was no etch time dependence in the C–V measurements from the diodes or the PL spectra from the MQWs, indicating that variations in dry-etch-induced damage with etch time are mostly confined to the surface. Using wet chemical etching, the damage profile was investigated and the most damage was found within ∼15 nm from the surface for GaAs while In0.53Ga0.47As did not return to the original value after removing 20 nm of the surface. This indicates that the damage generation, removal, diffusion, and channeling mechanisms or rates may be different for the two materials. By changing the temperature of the stage during etching from −130 to 350 °C, the etch time dependence of the n and φb of GaAs was affected, indicating that diffusion of defects may be mainly responsible for the variations in electrical characteristics with etch time.

Collective excitation inGaAs−AlxGa1−xAs quantum wires: Multisubband model

The effects of the potential barrier height on the collective excitations of an electron gas confined in a GaAs-Al${}_{x}$Ga${}_{1\ensuremath{-}x}$As quantum wire of rectangular cross section are investigated theoretically by using the self-consistent field approximation theory proposed by Singwi, Tosi, Land, and Sj\"olander (STLS) [Phys. Rev. 176, 589 (1968)]. For several potential barrier heights, we calculated the effective potential, plasmon energy, structure factor, and pair-correlation function, considering a three-subband model with only the lowest subband populated by electrons. We verified that the intersubband plasmon is more sensitive to the potential barrier height variation than the intrasubband plasmon. We also observed that the confining potential effect decreases with the increasing of the wire width. The random-phase approximation results are also presented by comparison with the STLS results and significant differences were found.