Showing papers on "Schottky barrier published in 2007"

Band gap and Schottky barrier heights of multiferroic BiFeO3

Abstract: BiFeO3 is an interesting multiferroic oxide and a potentially important Pb-free ferroelectric. However, its applications can be limited by large leakage currents. Its band gap is calculated by the density-functional based screened exchange method to be 2.8eV, similar to experiment. The Schottky barrier height on Pt or SrRuO3 is calculated in the metal induced gap state model to be over 0.9eV. Thus, its leakage is not intrinsic.

Quantitative Analysis of Current–Voltage Characteristics of Semiconducting Nanowires: Decoupling of Contact Effects

Abstract: A metal-semiconductor-metal (M-S-M) model for quantitative analysis of current–voltage (I–V) characteristics of semiconducting nanowires is described and applied to fit experimental I–V curves of Bi2S3 nanowire transistors. The I–V characteristics of semiconducting nanowires are found to depend sensitively on the contacts, in particular on the Schottky barrier height and contact area, and the M-S-M model is shown to be able to reproduce all experimentally observed I–V characteristics using only few fitting variables. A procedure for decoupling contact effects from that of the intrinsic parameters of the semiconducting nanowires, such as conductivity, carrier mobility and doping concentration is proposed, demonstrated using experimental I–V curves obtained from Bi2S3 nanowires and compared with the field-effect based method.

TiO2 based metal-semiconductor-metal ultraviolet photodetectors

Abstract: Nanocrystalline TiO2 thin films were prepared by sol-gel method and were then used to fabricate metal-semiconductor-metal ultraviolet photodetectors with Au Schottky contact. It was found that dark current of the fabricated devices was only 1.9nA at 5V applied bias. High responsivity of 199A∕W was achieved when it was irradiated by the ultraviolet light (λ=260nm). The low dark current and high responsivity maybe attributed to the effect of Schottky barrier in company with neutral semiconductor owing to the wide finger gap of 20μm. The devices show a slow time response with a rise time of 6s and a decay time of 15s. The authors deduced that the slow time response was caused by defect traps which were widely distributed in nanocrysal.

Barrier inhomogeneity and electrical properties of Pt∕GaN Schottky contacts

Abstract: The temperature dependence of the electrical properties of Pt∕GaN Schottky barrier was studied. In particular, a Schottky barrier height of 0.96eV and an ideality factor of 1.16 were found after a postdeposition annealing at 400°C. Nanoscale electrical characterization was carried out by the conductive biased tip of an atomic force microscope both on the bare GaN surface and on the Pt∕GaN contacts. The presence of a lateral inhomogeneity of the Schottky barrier, with a Gaussian distribution of the barrier height values, was demonstrated. Moreover, GaN surface defects were demonstrated to act as local preferential paths for the current conduction. The temperature dependent electrical characteristics of the diodes were discussed in terms of the existing models on inhomogeneous barriers and correlated to the nanoscale electrical characterization of the barrier. In this way, the anomalous electrical behavior of the ideality factor and of the Schottky barrier and the low experimental value of the Richardson’s ...

Enhancing the electrical and optoelectronic performance of nanobelt devices by molecular surface functionalization.

Abstract: By functionalizing the surfaces of ZnO nanobelts (NBs) with a thin self-assembled molecular layer, the electrical and optoelectronic performances of a single NB-based device are drastically improved. For a single NB-based device, due to energy band tuning and surface modification, the conductance was enhanced by 6 orders of magnitude upon functionalization; a coating molecule layer has changed a Schottky contact into an Ohmic contact without sophisticated deposition of multilayered metals. A functionalized NB showed negative differential resistance and exhibited huge improved photoconductivity and gas sensing response. The functionalized molecular layer also greatly reduced the etching rate of the ZnO NBs by buffer solution, largely extending their life time for biomedical applications. Our study demonstrates a new approach for improving the physical properties of oxide NBs and nanowires for device applications.

Dominant effect of near-interface native point defects on ZnO Schottky barriers

Abstract: The authors used depth-resolved cathodoluminescence spectroscopy and current-voltage measurements to probe metal-ZnO diodes as a function of native defect concentration, oxygen plasma processing, and metallization. The results show that resident native defects in ZnO single crystals and native defects created by the metallization process dominate metal-ZnO Schottky barrier heights and ideality factors. Results for ZnO(0001¯) faces processed with room temperature remote oxygen plasmas to remove surface adsorbates and reduce subsurface native defects demonstrate the pivotal importance of crystal growth quality and metal-ZnO reactivity in forming near-interface states that control Schottky barrier properties.

Electrical characterization of Al/MEH-PPV/p-Si Schottky diode by current-voltage and capacitance-voltage methods

Abstract: The electrical characterization of the Al/poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/p-Si structure has been investigated by current–voltage and capacitance–voltage methods. The Al/MEH-PPV/p-Si Schottky diode with the ideality factor value of 1.88 obeys a metal–interfacial layer–semiconductor (MIS) configuration rather than an ideal Schottky diode due to the existence of an insulating layer on the organic semiconductor. The barrier height ( Φ b , o = 0.80 eV ) obtained from the I–V characteristic is lower than the barrier height ( Φ b , o = 1.19 eV ) obtained from the C–V characteristic. The discrepancy between Φ b , o ( I – V ) and Φ b , o ( C – V ) can be due to the existence of the interfacial native oxide and the organic MEH-PPV layers between the semiconductor and Schottky contact metal. The barrier height value for the Al/MEH-PPV film/p-Si/Al contact obtained at the room temperature that is significantly larger than that for the conventional Al/p-Si Schottky diode. The density distribution curves of the interface states is in the range (0.32-Ev) to (0.68-Ev)eV. The interface state density Nss ranges from 3.84×1014 cm−2 eV−1 in (0.32-Ev)eV to 1×1014 cm−2 eV−1 in (0.68-Ev)eV, of the Al/MEH-PPV/p-Si. The interface state density has an exponential rise with bias from the midgap towards the top of the valence band of the p-Si.

Schottky barriers to colloidal quantum dot films

Abstract: We elucidate experimentally a quantitative physical picture of the Schottky barrier formed at the junction between a metallic contact and a semiconducting colloidal quantum dot film. We used a combination of capacitance-voltage and temperature-dependent current-voltage measurements to extract the key parameters of the junction. Three differently processed Al∕PbS colloidal quantum dot junction devices provide rectification ratios of 104, ideality factors of 1.3, and minimal leakage currents at room temperature. The Schottky barrier height is 0.4eV and the built-in potential 0.3V. The depletion width ranges from 90to150nm and the acceptor density ranges from 2×1016to7×1016cm−3.

High-performance nano-Schottky diodes and nano-MESFETs made on single CdS nanobelts.

Abstract: Nano-Schottky diodes and nanometal-semiconductor field-effect transistors (MESFETs) on single CdS nanobelts (NBs) have been fabricated and studied. The Au/CdS NB Schottky diodes have very low reverse current density ( approximately 3.0 x 10-5 A.cm-2 at -10 V reverse bias) and the highest on/off current ratio (approximately 108) reported so far for nano-Schottky diodes. The single CdS NB MESFETs exhibit n-channel normally on (depletion) mode, low threshold voltage (approximately -1.56 V), high transconductance ( approximately 3.5 microS), low subthreshold swing ( approximately 45 mV/dec), and the highest on/off current ratio (approximately 2 x 108) reported so far for nanofield-effect transistors. We also show that the absolute value of threshold voltage for a metal-insulator-semiconductor field-effect transistor made on a single CdS NB can be reduced from approximately 12.5 to approximately 0.4 V and its transconductance can be increased from approximately 0.2 to approximately 3.2 microS by adding an extra Au Schottky contact on the CdS NB, the mechanism of which is discussed.

Imaging of the Schottky barriers and charge depletion in carbon nanotube transistors.

Abstract: The photovoltage produced by local illumination at the Schottky contacts of carbon nanotube field-effect transistors varies substantially with gate voltage. This is particularly pronounced in ambipolar nanotube transistors where the photovoltage switches sign as the device changes from p-type to n-type. The detailed transition through the insulating state can be recorded by mapping the open-circuit photovoltage as a function of excitation position. These photovoltage images show that the band-bending length can grow to many microns when the device is depleted. In our palladium-contacted devices, the Schottky barrier for electrons is much higher than that for holes, explaining the higher p-type current in the transistor. The depletion width is 1.5 mum near the n-type threshold and smaller than our resolution of 400 nm near the p-type threshold. Internal photoemission from the metal contact to the carbon nanotube and thermally assisted tunneling through the Schottky barrier are observed in addition to the photocurrent that is generated inside the carbon nanotube.

Responsivity and Noise Measurements of Zero-Bias Schottky Diode Detectors

Abstract: Schottky barrier diodes can be used as direct detectors throughout the millimeterand submillimeterwave bands. When the diodes are optimized to have a low forward turn-on voltage, the detectors can achieve excellent frequency response and bandwidth, even with zero-bias. This paper reports on the characterization of VDI’s zerobias Schottky detectors. Responsivity typically ranges from 4,000 V/W at 100 GHz to 400 V/W at 900 GHz and each detector achieves good responsivity across the entire singlemoded bandwidth of the input rectangular waveguide. Under low power operation the detectors achieve a measured noise-equivalent-power (NEP) of about 1.5x10 W/√Hz, even without signal modulation. Such high sensitivity is expected for any zero-bias diode detector with high responsivity when there is no incident RF power; since only thermal noise can be generated under this condition. However, as the input power is increased, excess noise is generated. This noise typically has a 1/f power spectrum and is commonly known as flicker noise. Flicker noise becomes increasingly important as the input power is increased and signal modulation is generally required to achieve maximum sensitivity. The signal-to-noise of the VDI zero-bias detectors has been carefully measured as a function of input power and modulation rate. This data allows the user to understand the sensitivity of the detector under real operating conditions, and is therefore far more useful than the simple measurement of detector NEP with zero RF power, which is commonly quoted in the literature for new diode detector designs. Index Terms — Terahertz detectors, zero-bias detectors, noise-equivalent power, flicker noise.

Leakage current analysis of diamond Schottky barrier diode

Abstract: The current-voltage characteristics of non-punch-through-type diamond Schottky barrier diodes (SBDs) are analyzed by using thermionic and thermionic-field emission (TFE) models. Diamond SBD with defects such as nonepitaxial crystallites (NCs) shows shunt path conductance both under forward and reverse bias conditions. However, SBD without NCs shows a low reverse leakage current density of less than 1×10−11A∕cm2, which is more than 12 orders of magnitude smaller than the forward current density. From the fitting of the reverse leakage current of SBD without NCs, TFE current dominates when the reverse electric field is larger than 1.2MV∕cm and its current density value reaches 10−6A∕cm2 even at 1.6MV∕cm, which is lower than the avalanche limit.

Schottky contact on a ZnO (0001) single crystal with conducting polymer

Abstract: High quality Schottky junctions were fabricated on a ZnO (0001) bulk single crystal by spin coating a commercial conducting polymer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), as the metal electrodes. The junctions exhibited excellent rectifying behavior with a typical ideality factor of 1.2. Such parameters as Schottky barrier height (ϕb) and built-in potential (Vbi) show negligible variation among junctions. The electron affinity of ZnO derived from ϕb and qVbi values show a slight deviation (∼0.2eV), suggesting the existence of spontaneously formed interfacial dipole layer between ZnO (0001) polar surface and anionic PSS molecules.

Photoswitchable Semiconductor Bismuth Sulfide (Bi2S3) Nanowires and Their Self-Supported Nanowire Arrays

Abstract: Self-supported Bi2S3 nanowire arrays with sizes up to several millimeters were prepared by a facile hydrothermal method. In our work, the oriented nanowire arrays were supported on a self-generated nanowire networked substrate. The as-prepared Bi2S3 nanowire exhibited nonlinear current−voltage (I−V) characteristics and excellent photoresponse. It is suggested that the rectifying behavior comes from the Schottky contact between the Bi2S3 nanowire and the Au electrodes. As the light source was switched on and off, the nanowire could be reversibly switched between low and high conductivity, indicating its potential applications in optoelectronic nanodevices.

Effect of electrode material on the resistance switching of Cu2O film

Abstract: The effect of the bottom electrode material on the resistance switching characteristics was evaluated on the structure of Pt∕Cu2O/bottom electrode). It was confirmed that Ohmic or low Schottky contact is needed to induce the effective electric field for resistance switching across the Cu2O film. Pt, TiN, TaN, and strontium-ruthenium oxide belong to this group. For high Schottky contact, the resistance switching characteristics could not be observed due to a large voltage drop at the rectifying interface with insufficient electric field in the Cu2O film. Also, it was confirmed that interlayer formation from the reaction at the electrode-oxide interface increased the barrier height and brought about the switching failure in the case of Ru. The resistance switching properties depend on the barrier height and the reactivity between metal and Cu2O film.

Schottky-Barrier Height Tuning by Means of Ion Implantation Into Preformed Silicide Films Followed by Drive-In Anneal

Abstract: An experimental study on Schottky-barrier height (SBH) tuning using ion implantation followed by drive-in anneal of As, B, In, and P in preformed NiSi and PtSi films is presented. Measured on B-implanted NiSi and PtSi Schottky diodes, the effective SBH on n-type Si is altered to ~1.0 eV. For As- and P-implanted diodes, the SBH on p-type Si can be tuned to around 0.9 eV. The process window for the most pronounced SBH modification is dopant dependent.

Gate Current Degradation Mechanisms of GaN High Electron Mobility Transistors

Abstract: In spite of their extraordinary performance, GaN HEMTs still lack solid reliability. Gate current degradation during RF power device operation is a great concern because it impacts PAE, gain, and output power. In this paper, we have experimentally studied gate current degradation under high forward and reverse bias conditions on the gate. We find that strong reverse bias on the gate produces defects that become paths for excess IG. On the other hand, strong forward bias on the gate degrades Schottky junction probably due to thermal effects.

Electrical properties of individual tin oxide nanowires contacted to platinum electrodes

Abstract: A simple and useful experimental alternative to field-effect transistors for measuring electrical properties free electron concentration nd, electrical mobility , and conductivity in individual nanowires has been developed. A combined model involving thermionic emission and tunneling through interface states is proposed to describe the electrical conduction through the platinum-nanowire contacts, fabricated by focused ion beam techniques. Current-voltage I-V plots of single nanowires measured in both two- and four-probe configurations revealed high contact resistances and rectifying characteristics. The observed electrical behavior was modeled using an equivalent circuit constituted by a resistance placed between two back-to-back Schottky barriers, arising from the metal-semiconductor-metal M-S-M junctions. Temperature-dependent I-V measurements revealed effective Schottky barrier heights up to BE=0.4 eV.

Temperature dependence of characteristic parameters of the Au/SnO2/n-Si (MIS) Schottky diodes

Abstract: The variation in electrical characteristics of Au/SnO2/n-Si (MIS) Schottky diodes have been systematically investigated as a function of temperature by using forward bias current–voltage (I–V) measurements The main diode parameters, ideality factor n and zero-bias barrier height ΦB0, were found strongly temperature dependent and while the zero-bias barrier height ΦB0(I–V) increases, the n decreases with increasing temperature This behavior has been interpreted by the assumption of a Gaussian distribution of barrier heights due to barrier inhomogenities that prevail at the metal–semiconductor interface The zero-bias barrier height ΦB0 vs q/(2kT) plot has been drawn to obtain evidence of a Gaussian distribution of the barrier heights, and values of Φ ¯ B 0 = 1101 eV and σ0 = 0158 V for the mean barrier height and zero-bias standard deviation have been obtained from this plot, respectively Thus a modified ln(I0/T2) − ( q 2 σ 0 2 ) /2k2T2 vs q/(kT) plot has given mean barrier height Φ ¯ B 0 and Richardson constant (A*) as 1116 eV and 12786 A cm−2 K−2, respectively The A* value 12786 A cm−2 K−2 obtained from this plot is in very close agreement with the theoretical value of 120 A cm−2 K−2for n-type Si Hence, it has been concluded that the temperature dependence of the forward bias I–V characteristics of the Au/SnO2/n-Si (MIS) Schottky diode can be successfully explained on the basis of a thermionic emission (TE) mechanism with a Gaussian distribution of the Schottky barrier heights (SBHs) In addition, we have reported a modification by the inclusion of both n and αχ05δ in the expression of I0 to explain the positive temperature dependence of ΦB0 against that of energy band-gap of Si Thus, the values of temperature coefficient of the effective barrier height ΦBef(−364 × 10−4 eV/K) is very close agreement with the temperature coefficient of Si band-gap (−473 × 10−4 eV/K)

Electron mobility related to scattering caused by the strain variation of AlGaN barrier layer in strained AlGaN∕GaN heterostructures

Abstract: Using the measured capacitance- voltage curves of Ni Schottky contacts with different areas on strained AlGaN/ GaN heterostructures and the current- voltage characteristics for the AlGaN/ GaN heterostructure field- effect transistors at low drain- source voltage, we found that the two- dimensional electron gas (2DEG) electron mobility increased as the Ni Schottky contact area increased. When the gate bias increased from negative to positive, the 2DEG electron mobility for the samples increased monotonically except for the sample with the largest Ni Schottky contact area. A new scattering mechanism is proposed, which is based on the polarization Coulomb field scattering related to the strain variation of the AlGaN barrier layer. (C) 2007 American Institute of Physics.

Differences in the reaction kinetics and contact formation mechanisms of annealed Ti∕Al∕Mo∕Au Ohmic contacts on n-GaN and AlGaN∕GaN epilayers

Abstract: Ti∕Al-based multilayer metallizations are usually used interchangeably for n-GaN and AlGaN∕GaN epilayers. Our investigations show that, although excellent Ohmic performances were obtained on both cases, the reaction pathways/kinetics and Ohmic contact formation mechanisms of Ti∕Al∕Mo∕Au metallization on n-GaN and AlGaN∕GaN are different. In the case of n-GaN, the reaction proceeds by the formation of continuous TiN layer at the metal/GaN interface. Low-barrier Schottky contact or tunneling contact is the possible contact formation mechanisms. On AlGaN∕GaN heterostructures, the existence of the AlGaN layer significantly modifies the reaction pathway, where discrete TiN protrusions form nonuniformly along threading dislocations. The TiN protrusions penetrate through the AlGaN layer and form direct electrical link between the two-dimensional electron gas and the metal contacts which would otherwise be separated by the AlGaN barrier layer. A contact formation mechanism, similar to the “spike mechanism,” which...

HPHA effect on reversible resistive switching of Pt/Nb-doped SrTiO3 Schottky junction for nonvolatile memory application

Abstract: We investigated the effect of high-pressure hydrogen annealing (HPHA) on a Pt/Nb-doped SrTiO 3 Schottky junction for nonvolatile memory applications. Hysteretic current-voltage (I-V) characteristic curves reveal that the HPHA-treated Schottky junction interface has a higher resistance ratio than the control sample in dc bias sweep. The HPHA sample also exhibits switching behavior by pulsed voltage stress with excellent electrical characteristics including voltage pulse duration as short as 1 μs, endurance cycles of up to 10 6 times, and retention time as long as 10 5 s. These indicate that HPHA improved resistance switching characteristics of the Schottky junction.

Field-programmable rectification in rutile TiO2 crystals

Abstract: The authors report “field-programmable rectification” in crystals of rutile TiO2. A “programming” voltage is applied between two Pt electrodes on the surface of a crystal. Afterwards, current can pass in the direction of the programming voltage, but not in the reverse direction. The polarity of the rectification can be reversed by applying a programming voltage of opposite sign. The effect was observed on the (110) and (100) surfaces, but not the (001) surface. The proposed mechanism is field-induced motion of oxygen vacancies, which pile up under the negative terminal, eliminating a Schottky barrier, but leaving one at the positive terminal intact.

Reduced contact resistance between an individual single-walled carbon nanotube and a metal electrode by a local point annealing

Abstract: The achievement of low-resistance contact is a key requirement for carbon-electrode electronics. In this study, we have obtained contacts with very low resistance between an individual single-walled carbon nanotube (SWNT) and palladium (Pd) electrodes using electric-current-induced Joule heating without destroying the field effect transistor device that these form. The SWNT is deposited onto Pd electrodes prepatterned on a SiO2/Si substrate, through which an electrical pulse is applied for a microsecond duration. As a result, the source?drain current through the SWNT is greatly increased owing to the elimination of tunnelling barriers between the SWNT and the electrodes. In the case of semiconducting SWNTs, the Schottky barrier is estimated to increase slightly after pulse annealing in some cases, resulting in a relatively high resistance and asymmetrical current?voltage characteristics.

Single Schottky-barrier photodiode with interdigitated-finger geometry: Application to diamond

Abstract: The authors propose a single Schottky-barrier photodiode (SPD) with interdigitated Ohmic and Schottky contacts. A homoepitaxial diamond layer with low boron concentration has been utilized as an example for the fabrication of solar-blind deep-ultraviolet detector. This device structure enables the operations in both photoconductive mode with large photocurrent gain and depletion mode with fast response speed. The photosensitivity and spectral response of such kind of device are greatly improved when compared with a conventional SPD with semitransparent dotted Schottky contact. The present device structure can be extended to other semiconductor photodetectors.

Temperature-dependent electrical characteristics of bulk GaN Schottky rectifier

Abstract: The temperature-dependent electrical characteristics of Schottky rectifiers fabricated with a SiO2 field plate on a freestanding n− gallium nitride (GaN) substrate were reported in the temperature range of 298–473K. The Schottky barrier heights evaluated from forward current-voltage measurement revealed an increase of Schottky barrier height and series resistance but a decrease of ideality factor (n) with increasing temperature. However, the Schottky barrier heights evaluated from capacitance-voltage measurement remained almost the same throughout the temperature range measured. The Richardson constant extrapolated from ln(J0∕T2) vs 1∕T plot was found to be 0.029Acm−2K−2. A modified Richardson plot with ln(J0∕T2) vs 1∕nT showed better linearity, and the corresponding effective Richardson constant was 35Acm−2K−2. The device showed a high reverse breakdown voltage of 560V at room temperature. The negative temperature coefficients were found for reverse breakdown voltage, which is indicative of a defect-assi...

Physics of ultrathin-body silicon-on-insulator Schottky-barrier field-effect transistors

Abstract: In this article we give an overview over the physical mechanisms involved in the electronic transport in ultrathin-body SOI Schottky-barrier MOSFETs. A strong impact of the SOI and gate oxide thickness on the transistor characteristics is found and explained using experimental as well as simulated data. We elaborate on the influence of scattering in the channel and show that for a significant barrier the on-state current is insensitive to scattering once the mean free path for scattering is larger than a characteristic length scale. In addition, recent efforts to lower the Schottky barrier at the source/drain channel interfaces are presented. Using dopant segregation during silicidation significantly lower effective Schottky barriers can be realized that allow for high performance SB-MOSFET devices.

Temperature-dependent behavior of Ni/4H-nSiC Schottky contacts

Abstract: The current-voltage (I-V) characteristics of Ni/4H-nSiC Schottky diodes have been measured in the temperature range of 180–300 K with a temperature step of 20 K. An experimental barrier height (BH) Φap value of about 1.32 eV was obtained for the Ni/4H-nSiC Schottky diode at the 300 K. A decrease in the experimental BH Φap and an increase in the ideality factor n with a decrease in temperature have been explained on the basis of a thermionic emission mechanism with Gaussian distribution of the barrier heights due to the BH inhomogeneities at the metal-semiconductor interface. Φ¯b and A* as 1.71 eV, and 156.3 A/cm2 K2, respectively, have been calculated from a modified ln(I0/T2)−q2σs2/2k2T2 vs 1/T plot using the temperature-dependent experimental I-V characteristics of the Ni/4H-nSiC contact. The Richardson constant value of 156.3 A/cm2 K2 is in close agreement with 146 A/cm2 K2 known for 4H-nSiC.