Decrease In Barrier Height Research Articles

Low-Power and Controllable Memory Window in Pt/Pr<SUB>0.7</SUB>Ca<SUB>0.3</SUB>MnO<SUB>3</SUB>/Yttria-Stabilized Zirconia/W Resistive Random-Access Memory Devices

Yttria-stabilized zirconia (YSZ) layers of various thicknesses were designed and introduced before Pr0.7Ca0.3MnO3 (PCMO) film was deposited on W bottom electrodes with a submicron via-hole structure. By changing the thickness of the YSZ barrier layer (3, 5, 9, and 13 nm), a tunable memory window can be realized while low power consumption (P(max) < 4 microW) is maintained. Resistive switching (RS) in a Pt/PCMO/YSZ/W stack with a thin YSZ layer can be ascribed to an oxidation/reduction reaction caused by a ring-type PCMO/W contact, while RS with a thick YSZ layer may be related to oxygen migration across the YSZ layer between the PCMO film and the W bottom electrode and the increase (decrease) of the effective tunnel barrier height of the YSZ layer. Excellent RS behavior characteristics, such as a large R(HRS)/R(LRS) ratio (> 10(3)), die-to-die uniformity, sweeping endurance, and a retention time of more than 10(3) s, can be obtained by optimizing the thickness of YSZ layer.

Schottky Barrier Parameters and Interfacial Reactions of Rapidly Annealed Au/Cu Bilayer Metal Scheme on N-type InP

The influence of rapid thermal annealing effect on the electrical and structural properties of Au/Cu Schottky contacts on n-InP has been investigated by the current-voltage (I-V), capacitance-voltage (C-V), auger electron spectroscopy (AES) and the X-ray diffraction (XRD) techniques. As-deposited sample has a barrier height of 0.64 eV (I- V), 0.76 eV (C-V) which increases to 0.82 eV (I-V), 1.04 eV (C-V) after annealing at 400°C for 1min in nitrogen ambient. However, the barrier height decreases to 0.75 eV (I-V), 0.88 eV (C-V) after annealing at 600°C for 1min. Norde method is also employed to calculate the barrier heights of Au/Cu Schottky rectifiers and the values are 0.66 eV for as-deposited, 0.83 eV for 400°C and 0.76 eV for 600°C annealed contacts. These values are in good agreement with the values obtained from I-V method. From the above observations, it is clear that the Schottky barrier height increases with annealing temperatures up to 400°C. Thus, the optimum annealing temperature for the Au/Cu Schottky contact is 400 o C. Based on the AES and XRD results, the formation of indium phases at the Au/Cu/n-InP interface may be responsible for the increase in the barrier height for the contact annealed at 400°C and a corresponding decrease in leakage current. The decrease in the barrier height after annealing at 500 o C may be due to the formation of Cu-P and Au-P interfacial compounds at the interface. The AFM results showed that the surface morphology of Au/Cu Schottky contact is fairly smooth even after annealing at 500°C.

Temperature-dependent characteristics of 4H—SiC junction barrier Schottky diodes

The current—voltage characteristics of 4H—SiC junction barrier Schottky (JBS) diodes terminated by an offset field plate have been measured in the temperature range of 25–300 °C. An experimental barrier height value of about 0.5 eV is obtained for the Ti/4H—SiC JBS diodes at room temperature. A decrease in the experimental barrier height and an increase in the ideality factor with decreasing temperature are shown. Reverse recovery testing also shows the temperature dependence of the peak recovery current density and the reverse recovery time. Finally, a discussion of reducing the reverse recovery time is presented.

Evaluation of parameters of the potential barrier at the metal/polymer interface during recovery of the structure of nanocrystalline nickel

The influence of nanostructured nickel on the parameters of the potential barrier for conduction electrons at the metal/polymer interface has been investigated. It has been shown that conductivity in the multilayer nickel-polymer-vanadium system changes during annealing of nanocrystalline nickel at temperatures of the onset of the recovery of the structure. It has been established that the formation of the structure with a grain size of 100 nm in nickel leads to a noticeable decrease in the potential barrier height at the metal/polymer interface.

Top Contact Pentacene Based Organic Thin Film Transistor With Bi-layer TiO2Electrodes

We fabricated a Top contact Pentacene based Organic thin-film transistor (OTFTs) with bi-layer TiO2/Au electrodes. The performance of the devices after inserting TiO2 layer between organic layer and Au electrode is highly improved. On comparing with pentacene based transistor with only Au electrode, the hole injection was largely enhanced and the highest field-effect mobility is increased from 0.37 cm2/ (Vs) to 0.63 cm2/ (Vs) in the device with bilayer TiO2/Au electrodes. We also measured the temperature dependence characteristics and surface morphology of both the devices. Both the devices showed strong temperature dependence. We observed that the barrier height is tremendously decreased after inserting a thin layer of TiO2 between the organic layer and Au electrodes. The improved device performance was due to the decreased barrier height and decrease in the surface roughness of pentacene after inserting a suitable metal oxide layer between the pentacene and the Au electrodes. Our experimental results clearly show that the insertion of metal oxide between Au electrode and pentacene layer is an effective way to improve the performance of the pentacene based organic thin-film transistor (OTFTs).

Barrier height inhomogeneities in Cu-nMoSe2Schottky diode

The current-voltage characteristics of Cu- n MoSe 2 Schottky diodes measured over a wide temperature range 50 T Φ b 0 and an increase in the ideality factor n with a decrease in temperature have been explained on the basis of barrier height inhomogeneities at the metal-semiconductor interface. It is proven that the presence of a distribution of barrier heights is responsible for the apparent decrease of the zero-bias barrier height. The voltage dependence of the standard deviation causes the increase of ideality factor at low temperatures. The mean barrier height Φ b 0 = 1.05 eV and the Richardson constant A * = 89.7 A cm −2 k −2 have been calculated by means of the modified Richardson plot. The value of the Richardson constant found is much closer than that obtained without considering the inhomogeneous barrier heights with that of the theoretical value.

The nature of electrical interaction of Schottky contacts

Electrical interaction between metal-semiconductor contacts combined in a diode matrix with a Schottky barrier manifests itself in an appreciable variation in their surface potentials and static current-volt-characteristics. The necessary condition for appearance of electrical interaction between such contacts consists in the presence of a peripheral electric field (a halo) around them; this field propagates to a fairly large distances (<30 μm). The sufficient condition is the presence of regions where the above halos overlap. It has been shown that variation in the surface potential and the current-voltage characteristics of contacts occurs under the effect of the intrinsic electric field of the contact’s periphery and also under the effect of an electric field at matrix periphery; the latter field is formed as a result of superposition of electric fields of halos which form its contacts. The degree of the corresponding effect is governed by the distance between contacts and by the total charge of the space charge regions for all contacts of the matrix: their number, sizes (diameter Di, j), concentration of doping impurities in the semiconductor ND, and physical nature of a metal-semiconductor system with a Schottky barrier (with the barrier height φb). It is established that bringing the contacts closer leads to a relative decrease in the threshold value of the “dead” zone in the forward current-voltage characteristics, an increase in the effective height of the barrier, and an insignificant increase in the nonideality factor. An increase in the total area of contacts (a total electric charge in the space charge region) in the matrix brings about an increase in the threshold value of the “dead” zone, a relative decrease in the effective barrier height, and an insignificant increase in the ideality factor.

Improved device performance in nonpolar a ‐plane GaN LEDs using a Ni/Al/Ni/Au n‐type ohmic contact

AbstractThe authors report upon the increased light‐output power (Pout) via a reduction in the forward voltage (Vf) for nonpolar a ‐plane GaN LEDs using Ni/Al/Ni/Au n‐type ohmic contacts. The specific contact resistivity of the Ni/Al/Ni/Au contact is found to be as low as 5.6 × 10–5 whereas that of a typical Ti/Al/Ni/Au contact is 6.8 × 10–4 Ω cm2, after annealing at 700 °C. The X‐ray photoelectron spectroscopy results show that the upward surface band bending is less pronounced for the Ni/Al contact compared to the Ti/Al contact, leading to a decrease in the effective Schottky barrier height (SBH). The Vf of the nonpolar LEDs decreases by 10% and Pout increases by 15% when the Ni/Al/Ni/Au scheme is used instead of the typical Ti/Al/Ni/Au metal scheme. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Effect of photovoltage on current flow in metal-semiconductor schottky-barrier contacts

It is shown that changes in device characteristics and an increase in the light-to-electrical energy conversion efficiency in metal-semiconductor Schottky barrier contacts are associated with a peripheral electric field built into the contact. For contacts with longer perimeters, variations in device characteristics and the light-to-electrical energy conversion efficiency are significantly larger. Since the photovoltage and peripheral electric fields in the contact region are codirected with the intrinsic electric field of the space-charge region, contact illumination results in a larger increase in the “dead” zone in forward portions of current-voltage characteristics, a larger decrease in the effective Schottky barrier height, and an increase in the field electron emission. An increase in the reverse field emission under photovoltage leads to an increase in the recombination current in the space-charge region, which provides dc photocurrent flow in the circuit.

AC ageing characteristics of Y2O3-doped ZnO varistors with high voltage gradient

In this paper, AC ageing characteristics of high voltage gradient ZnO varistors doped with different Y 2 O 3 concentration were investigated. The voltage gradient of these samples is markedly improved by increasing Y 2 O 3 content, however, the nonlinear coefficient decreases and the leakage current increases at the same time. Y 2 O 3-doped ZnO samples exhibit lower stability under accelerated AC ageing stress of 0.85 V 1mA/135 °C/168 h, compared with samples without Y 2 O 3. Double-Schottky barrier(DSB) parameters before and after ageing tests indicate that the decrease of barrier height for traditional sample is less than that for high voltage gradient sample, which should be ascribed to its slight variation in the interface state density.

Tunnelling current in Schottky diodes containing InAs quantum dots

Current transport mechanism in Schottky diode containing InAs quantum dots (QDs) is investigated using temperature-varying current–voltage characteristics. We found that the tunnelling emission has obvious effects on the I–V characteristics. The I–V–T measurements revealed clear effects of QDs on the overall current flow. Field emission (FE, pure tunnelling effect) was observed at low temperature and low voltages bias region. The zero-bias barrier height decreases and the ideality factor increases with decreasing temperature, and the ideality factor was found to follow the T0-effect. When the reverse bias is varied, the ideality factors of Schottky barriers exhibit oscillations due to the tunnelling of electrons through discrete levels in quantum dots. The traps distributed within InAlAs layer can also act as a transition step for reverse bias defect-assisted tunnelling current which can phenomenologically explain the decrease of the effective barrier height with measurement temperature.

Electrical transport characteristics of Ni/Pd/n-GaN Schottky barrier diodes as a function of temperature

The electrical transport properties of Ni/Pd/n-GaN Schottky barrier diodes (SBDs) have been investigated in the wide temperature range of 100–425K. An abnormal decrease in the experimental barrier height (ϕb) and an increase in the ideality factor (n) with a decrease in the temperature have been observed. The observed variation in ϕbo and n is attributed to the spatial barrier inhomogeneities in Schottky barrier height by assuming a Gaussian distribution (GD) of barrier heights (BHs) at 100–175K and 175–425K. The temperature-dependent current–voltage characteristics of the SBDs has shown a double Gaussian distribution giving mean barrier heights of 0.65eV and 1.21eV and standard deviations of 0.085 and 0.159V, respectively. A modified ln (Io/T2)–q2σo2/2k2T2 versus 103/T plot for the two temperature regions gives ϕbo¯ and A⁎ as 0.713eV and 13.56Acm−2K−2, and 1.34eV and 28.645Acm−2K−2 respectively. Such temperature dependence of modified Richardson plot and electrical parameters of Ni/Pd/n-GaN SBD can be explained based on the thermionic emission theory with double GD of BHs due to the barrier height inhomogeneities at the metal/semiconductor interface. The themionic field emission is considered as the phenomena responsible for the excess currents observed in both forward and reverse direction of Schottky barriers.

Schottky Barrier Parameters of Pd/Ti Contacts on N-Type InP Revealed from I-V-T And C-V-T Measurements

We report on the current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the Pd/Ti/n-InP Schottky barrier diodes (SBDs) in the temperature range 160-400 K in steps of 40 K. The barrier heights and ideality factors of Schottky contact are found in the range 0.35 eV (I-V), 0.73 eV (C-V) at 160 K and 0.63 eV (I-V), 0.61 eV (C-V) at 400 K, respectively. It is observed that the zero-bias barrier height decreases and ideality factor n increase with a decrease in temperature, this behaviour is attributed to barrier inhomogeneities by assuming Gaussian distribution at the interface. The calculated value of series resistance (Rs) from the forward I-V characteristics is decreased with an increase in temperature. The homogeneous barrier height value of approximately 0.71 eV for the Pd/Ti Schottky diode has been obtained from the linear relationship between the temperature-dependent experimentally effective barrier heights and ideality factors. The zero-bias barrier height ( ) versus 1/2kT plot has been drawn to obtain evidence of a Gaussian distribution of the barrier heights and values of = 0.80 eV and = 114 mV for the mean barrier height and standard deviation have been obtained from the plot, respectively. The modified Richardson ln(I0/T2)- ( ) versus 1000/T plot has a good linearity over the investigated temperature range and gives the mean barrier height ( ) and Richardson constant (A*) values as 0.796 eV and 6.16 Acm-2K-2 respectively. The discrepancy between Schottky barrier heights obtained from I-V and C-V measurements is also interpreted.

Controlling of electronic parameters of GaAs Schottky diode by poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic interlayer

The electronic properties of metal–organic semiconductor–inorganic semiconductor structure between GaAs and poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol) organic film have been investigated via current–voltage and capacitance–voltage methods. The Au/PEDOT/ n-GaAs contact exhibits a rectification behavior with the barrier height of 0.69 eV and ideality factor value of 3.94. The barrier height of the studied diode (0.67 eV) is lower than that of Ni/ n-GaAs/In (0.85 eV) and Au/ n-GaAs/In Schottky diodes. The decrease in barrier height of Au/ n-GaAs/In Schottky diode is likely to be due to the variation in the space charge region in the GaAs. The obtained results indicate that control of the interfacial potential barrier for metal/ n-GaAs diode was achieved using thin interlayer of the poly(3,4-ethylenedioxithiophene)-block-poly(ethylene glycol).

Electrical and structural properties of double metal structure Ni/V Schottky contacts on n-InP after rapid thermal process

The electrical, structural, and surface morphological properties of Ni/V Schottky contacts have been investigated as a function of annealing. The Schottky barrier height value from I–V and C–V measurements for as-deposited Ni/V/n-InP diode is 0.61 eV (I–V) and 0.91 eV (C–V), respectively. It has been observed that the Schottky barrier height decreases with increasing annealing temperature as compared to the as-deposited contact. For the contact annealed at 200 °C, the obtained barrier height decreased to 0.52 eV (I–V) and 0.78 eV (C–V). Further, the annealing temperature increased to 300 and 400 °C, the barrier height slightly increased to 0.58 eV (I–V), 0.82 eV (C–V) and 0.59 eV (I–V), 0.88 eV (C–V). However, after annealing at 500 °C, results then decrease in barrier height to 0.51 eV (I–V) and 0.76 eV (C–V), which is lower than the value obtained for the sample annealed at 200 °C. The Norde method is also employed to extract the barrier height of Ni/V/InP Schottky diode, and the values are 0.68 eV for the as-deposited and 0.56 eV for the contact annealed at 500 °C, which are in good agreement with those obtained by I–V technique. Based on the results of AES and XRD studies, it is concluded that the formation of indium phases at the Ni/V/n-InP interface may be the reason for the increase in the barrier height for the as-deposited contact. The decrease in the barrier height upon annealing at 500 °C may be due to the formation of phosphide phases at the interface. The AFM results showed that there is no significant degradation in the surface morphology (RMS roughness of 0.61 nm) of the contact even after annealing at 500 °C.

Synthesis and optical characterization of nanocrystalline CdTe thin films

From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10 −6 Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400–2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index ( n) and extinction coefficient ( k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size.

Potential and flux landscapes quantify the stability and robustness of budding yeast cell cycle network

Studying the cell cycle process is crucial for understanding cell growth, proliferation, development, and death. We uncovered some key factors in determining the global robustness and function of the budding yeast cell cycle by exploring the underlying landscape and flux of this nonequilibrium network. The dynamics of the system is determined by both the landscape which attracts the system down to the oscillation orbit and the curl flux which drives the periodic motion on the ring. This global structure of landscape is crucial for the coherent cell cycle dynamics and function. The topography of the underlying landscape, specifically the barrier height separating basins of attractions, characterizes the capability of changing from one part of the system to another. This quantifies the stability and robustness of the system. We studied how barrier height is influenced by environmental fluctuations and perturbations on specific wirings of the cell cycle network. When the fluctuations increase, the barrier height decreases and the period and amplitude of cell cycle oscillation is more dispersed and less coherent. The corresponding dissipation of the system quantitatively measured by the entropy production rate increases. This implies that the system is less stable under fluctuations. We identified some key structural elements for wirings of the cell cycle network responsible for the change of the barrier height and therefore the global stability of the system through the sensitivity analysis. The results are in agreement with recent experiments and also provide new predictions.

Fabrication of ZnO/α-NPD:F 4-TCNQ based inorganic–organic hybrid junction: Effect of doping of organic layer on the diode like characteristics

In the present work, we report fabrication and current–voltage characteristics of ZnO/α-NPD:F 4-TCNQ based inorganic–organic hybrid junction. Current–voltage characteristics of hybrid junctions show diode like behavior. The effect of organic layer doping on the diode like characteristics of the junction has been investigated. The diode parameters viz. barrier height, ideality factor and rectification ratio have been calculated from the current–voltage semi-log plots. The improvement of diode parameters i.e. increase in rectification ratio and decrease in barrier height as well as improvement in ideality factor has been observed with doping. The improvement of the diode parameters has been attributed to the modification at ZnO/α-NPD interface. The current is also found to increase with the increase in doping concentration which has been attributed to the increased conductivity of α-NPD and interface barrier lowering after doping of α-NPD with F 4-TCNQ.

Low threshold field emission from nitrogen-incorporated carbon nanowalls

Field emission performance of nitrogen-incorporated vertically-aligned graphene layers, so called “carbon nanowalls (CNWs)”, is found to depend upon their electrical conduction properties. The CNW samples with n-type conduction exhibit near-ideal Ohmic contacts with various metals such as Cu, Ti, and Au, regardless of the work function of the metals. The high resistivity CNWs for lower deposition temperatures ( T D ) show semiconducting behavior in the Arrhenius plots, while the low resistivity CNWs for higher T D show semi-metallic behavior. The emission turn-on field versus T D has a very similar trend to the bulk resistivity versus T D , and is reduced down to about 3 V/μm when the resistivity reaches a minimum (3.0 × 10 − 3 Ω cm). The lower turn-on field for semi-metallic CNWs is attributed to an upward shift of the emission level, which is responsible for a decrease in the surface potential barrier height for emission.

Schottky Barrier Height of Nickel Silicide Contacts Formed on $\hbox{Si}_{1 - x}\hbox{C}_{x}$ Epitaxial Layers

Embedded Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> C <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> source/drain junctions are currently considered to achieve electron mobility enhancement in nMOSFETs by inducing uniaxial tensile strain in the channel region. To utilize the mobility advantage of this technology, it is imperative to form low-resistivity contacts to Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> C <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> alloys. In this letter, the electron and hole barrier heights at the NiSi/Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 -</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> C <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</i> interface were measured up to a carbon concentration of 1.2%. The results indicate that the NiSi Fermi level moves away from the valence-band edge with increasing carbon concentration such that the hole barrier height increases by 68 meV in spite of the upward movement of the valence band. Within the same carbon concentration range, the electron barrier height decreases by as much as 170 meV, which is significant considering the exponential dependence of contact resistivity on barrier height.