Dependence Of Barrier Height Research Articles

Clustering of Gold on 6H-SiC and Local Nanoscale Electrical Properties

In this work, a methodology, based on a self-organization process, to form gold nanoclusters on the 6H-SiC surface, is illustrated. By scanning electron microscopy and atomic force microscopy the gold self-organization induced by annealing processes was studied and modelled by classical limited surface diffusion ripening theories. These studies allowed us to fabricate Au nanoclusres/SiC nanostructured materials with tunable structural properties. The local electrical properties of such a nanostructured material were probed, by conductive atomic force microscopy collecting high statistics of I-V curves. The main observed result was the Schottky barrier height (SBH) dependence on the cluster size. This behaviour is interpreted considering the physics of few electron quantum dots merged with the ballistic transport. A quite satisfying agreement between the theoretical forecast behaviour and the experimental data has been found.

An intercepted feedback mode for light sensitive spectroscopic measurements in atomic force microscopy

In most atomic force microscopes (AFMs), the motion of the tip is detected by the deflection of a laser beam shining onto the cantilever. AFM applications such as scanning capacitance spectroscopy or photocurrent spectroscopy, however, are severely disturbed by the intense stray light of the AFM laser. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. The versatility of this feedback method is demonstrated by measuring tip-force dependent Schottky barrier heights on GaAs samples.

The barrier height distribution in identically prepared Al/p-Si Schottky diodes with the native interfacial insulator layer (SiO 2)

The Al/p-Si Schottky diodes (33 dots) with the native interfacial insulator layer (SiO 2) were fabricated on the same quarter Si wafer. The Schottky barrier height (SBH), ideality factor ( n), interface state densities ( N ss) and series resistance ( R s) of these diodes have been calculated from their experimental forward bias current–voltage ( I– V), reverse bias capacitance–voltage ( C– V) and conductance–voltage ( G/ ω– V) measurements. Even though they are identically performed on the same quarter Si wafer, the calculated values of SBH have ranged from 0.680 to 0.736 eV, and ideality factor n from 1.62 to 2.87, and interface state densities N ss from 0.395×10 13 to 1.2×10 13 eV −1 cm −2 and series resistance R s from 623 to 4900 Ω. It was found that the values of barrier height Φ B obtained from C– V characteristics is larger than that of the value from I– V characteristics. The energy distribution of surface state density profiles for the selected six samples Al/p-Si Schottky diodes was determined from forward bias I– V characteristics by taking the bias dependence of the effective barrier height into account at room temperature. The experimental values of SBHs distributions obtained from the I– V and C −2– V characteristics have been fitted by a Gaussian function, and their mean values of SBHs have been calculated to be 0.708 and 0.810 eV, respectively. Experimental results show that the interface states at a native insulator layer between metal and semiconductor play an important role in the value of the SBH, ideality factor, series resistance and the other main electrical parameters of Schottky diodes.

Analysis of interface states and series resistance of MIS Schottky diodes using the current–voltage ( I– V) characteristics

The purpose of this paper is to analyze interface states in Al/SiO 2/p-Si (MIS) Schottky diodes and determine the effect of SiO 2 surface preparation on the interface state energy distribution. The current–voltage ( I– V) characteristics of MIS Schottky diodes were measured at room temperature. From the I– V characteristics of the MIS Schottky diode, ideality factor ( n) and barrier height (Φ B) values of 1.537 and 0.763 eV, respectively, were obtained from a forward bias I– V plot. In addition, the density of interface states ( N ss) as a function of ( E ss– E v) was extracted from the forward bias I– V measurements by taking into account both the bias dependence of the effective barrier height (Φ e), n and R s for the MIS Schottky diode. The diode shows non-ideal I– V behaviour with ideality factor greater than unity. In addition, the values of series resistance ( R s) were determined using Cheung’s method. The I– V characteristics confirmed that the distribution of N ss, R s and interfacial insulator layer are important parameters that influence the electrical characteristics of MIS Schottky diodes.

Two color, low intensity photocurrent feedback for local photocurrent spectroscopy

In this work, we introduce a two color, low intensity photocurrent feedback method for photocurrent spectroscopy utilizing an atomic force microscope (AFM). In most applications, measurements with weak optical excitations are not feasible with an AFM because the powerful AFM feedback laser severely disturbs the measurements. Therefore, we have developed a feedback system based on the pressure dependent Schottky barrier height at the tip-sample interface. The versatility of the new feedback system is demonstrated by recording high resolution photocurrent spectra on GaAsInAs heterostructures.

On the difference in the apparent barrier height of inhomogeneous Schottky diodes with a Gaussian distribution

The differences in the calculated apparent Schottky barrier heights as obtained from different approaches assuming a Gaussian distribution model of barrier potential are discussed. A modified theoretical expression for the saturation current and consequently a new expression for the apparent barrier height, evaluated numerically, are proposed. The current–voltage (I–V) expression obtained is subsequently used to generate I–V curves. An adequate genetic algorithm has been used to extract diode parameters. While the previous approaches used may lead to an unphysical negative apparent barrier height at low temperatures, or may suggest the existence of a lowest critical temperature up to which the apparent barrier height can be calculated, our approach presented here yields results for the apparent barrier height in good agreement with the extracted values at different temperatures. Therefore, it is concluded that the temperature dependence of the apparent Schottky barrier height can be successfully explained with the presently proposed approach, the detailed aspects of which are presented in this contribution.

Theoretical analysis of effect of tip atomic species on apparent barrier height on Al(1 0 0) surface

We have analyzed the effect of the tip atomic species on the tip–sample separation and the bias-voltage dependence of apparent barrier height (ABH) on an Al(1 0 0) surface using the boundary-matching scattering-state density functional method, which can be used to calculate electron states under applied bias voltages self-consistently within the density functional theory. We found that, from the dependence of the tip–sample separation, the difference between measurements with the two tip atomic species is larger in the ABH than in the maximum barrier height evaluated from the calculated potential profile. Furthermore, we found that the bias-polarity dependence of the ABH measured with the Na tip shows behavior opposite to that shown by the ABH measured with the Al tip. These results can be understood from the difference in the degree of lateral confinement of tunneling electrons in the tunneling barrier region between the two atomic species.

Electrical transport characteristics of Sn/p-Si schottky contacts revealed from I– V– T and C– V– T measurements

The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of metal–semiconductor (Sn/p-Si) Schottky contacts were measured in the temperature range 150–400 K. The effect of the temperature on the series resistances R S, ideality factors n, the barrier height Φ b and interface state density N SS obtained from the I– V and C– V characteristics were investigated. The n, Φ b, R S, and N SS values were seen to be strongly temperature dependent. The ideality factors, series resistances and interface state densities decreased with increasing temperature for all diodes and the values of n, R S, and N SS obtained from I– V and C– V measurements were found in the ranges of 2.024–1.108, 2.083–1.121; 79.508–33.397 Ω; and 2.14×10 13–0.216×10 13 cm 2 eV −1, 2.277×10 13–0.254×10 13 cm 2 eV −1, respectively. The temperature dependence of energy distribution of interface state density ( N SS) profiles has been determined from I– V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.

The effect of series resistance and oxide layer formed by thermal oxidation on some electrical parameters of Al/SiO 2/p-Si Schottky diodes

Two types of Schottky diodes with and without thermal-growth oxide layer, were fabricated to investigate whether or not the thermal-growth oxide layer is effective on some electrical parameters such as ideality factor n, barrier height Φ B, series resistance R s and interface state density N ss. The current–voltage ( I– V) characteristics were measured for these two diodes at 150 K and room temperature (300 K). Electrical parameters of these two diodes were calculated and compared at two temperatures. At the temperatures of 150 and 300 K, Φ B, n, and R s for diode without oxide layer ranged from 0.50 to 0.81 eV, 4.12 to 1.54, and 481 to 156 Ω respectively. The Φ B, n, and R s for diode with thermal-growth oxide layer have ranged from 0.54 to 0.87 eV, 6.83 to 1.66, and 503 to 281 Ω, respectively. For two diodes, the temperature dependence energy density distribution profiles of interface state were obtained from forward bias I– V measurements by taking into account the bias dependence of effective barrier height Φ e and R s of the devices and the value of N ss in diode without oxide layer is almost one order of magnitude larger than the diode with oxide layer.

Size-dependent Schottky Barrier Height in self-assembled gold nanoparticles

(Au nanocluster)/6H-SiC Schottky contacts were electrically characterized by conductive atomic force microscopy, collecting a high number of current-voltage (I-V) curves. The main observed result is the Schottky barrier height (SBH) dependence on the cluster size. The SBH increases from 1.35±0.01to1.77±0.01eV when the cluster size increases from 1.5to6.8nm and it tends, asymptotically, to the theoretical SBH of the macroscopic contact Au∕SiC (∼1.9eV). This behavior is interpreted considering the thermoionic transport theory through the Au cluster/SiC barrier coupled with the concept of ballistic transport within few electron quantum dots.

60Co γ irradiation effects on the current–voltage ( I– V) characteristics of Al/SiO 2/p-Si (MIS) Schottky diodes

It is well known that the exposure of any semiconductor surfaces to the 60Co γ-ray irradiation causes electrically active defects. To investigate the effect of γ-ray irradiation dose on the electrical characteristics of metal–insulator–semiconductor (MIS) Schottky diodes, the fabricated devices were exposed to γ radiation at a dose of 2.12 kGy/h. The total dose range was from 0 to 450 kGy at room temperature. The density of interface states N ss as a function of E ss− E v, the values of series resistance R s and the bias dependence of the effective barrier height Φ e for each dose were obtained from the forward bias I– V characteristics. Experimental results show that the γ-irradiation gives rise to an increase in the zero bias barrier height Φ BO, as the ideality factor n, R s and N ss decreases with increasing radiation dose.

Characteristics of Ni/SiC Schottky diodes grown by ICP-CVD

A Ni/SiC Schottky diode was fabricated with an α-SiC thin film grown by the inductively coupled plasma chemical vapor deposition, ICP-CVD method on a (111) Si wafer. The α-SiC film was grown on a carbonized Si layer that the Si surface had been chemically converted to a very thin SiC layer by the ICP-CVD method at 700°C. To reduce defects between the Si and α-SiC, the surface of the Si wafer is slightly carbonized. The film characteristics of α-SiC were investigated by employing TEM and FT-IR. A sputtered Ni thin film was used for the anode metal. The boundary status of the Ni/SiC contact was investigated by AES as a function of annealing temperature. It is shown that the ohmic contact could be acquired below 1000°C annealing temperature. The forward voltage drop of the Ni/α-SiC Schottky diode is 1.0V at 100A/cm2. The breakdown voltage is 545V which is five times larger than the ideal breakdown voltage of a silicon device. Also, the dependence of barrier height on temperature was observed.

The determination of electronic and interface state density distributions of Au/n-type GaAs Schottky barrier diodes

The electronic and interface state density distribution properties obtained from current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of Au/n-type GaAs Schottky barrier diode (SBD) at room temperature was investigated. SBD parameters such as ideality factor ( n), series resistance ( R S) and barrier height ( Φ IV ) were obtained from I– V and C– V measurements using Cheung's method. The diode parameters such as ideality factor, series resistance and barrier heights were found as 1.51–1.78, 7.597–8.167 Ω and 0.88–1.14 eV, respectively. The diode shows non-ideal I– V behaviour with an ideality factor greater than unity. Furthermore, the energy distribution of interface state density was determined from the forward bias I– V characteristics by taking into account the bias dependence of the effective barrier height. The results show the presence of thin interfacial layer between the metal and semiconductor.

Characterization of current–voltage ( I– V) and capacitance–voltage–frequency ( C– V– f) features of Al/SiO 2/p-Si (MIS) Schottky diodes

The current–voltage ( I– V) characteristics of metal–insulator–semiconductor Al/SiO 2/p-Si (MIS) Schottky diodes were measured at room temperature (300 K). In addition, capacitance–voltage–frequency ( C– V– f) characteristics are investigated by considering the interface states ( N ss) at frequency range 100 kHz to 1 MHz. The MIS Schottky diode having interfacial insulator layer thickness of 33 Å, calculated from the measurement of the insulator capacitance in the strong accumulation region. At each frequency, the measured capacitance decreases with increasing frequency due to a continuous distribution of the interface states. From the I– V characteristics of the MIS Schottky diode, ideality factor ( n) and barrier height ( Φ b) values of 1.766 and 0.786 eV, respectively, were obtained from a forward bias I– V plot. In addition, the interface states distribution profile as a function of ( E ss − E v) was extracted from the forward bias I– V measurements by taking into account the bias dependence of the effective barrier height ( Φ e) for the Schottky diode. The diode shows non-ideal I– V behaviour with ideality factor greater than unity. This behaviour is attributed to the interfacial insulator layer, the interface states and barrier inhomogeneity of the device. As expected, the C– V curves gave a barrier height value higher than those obtained from I– V measurements. This discrepancy is due to the different nature of the I– V and C– V measurement techniques.

Schottky barrier heights of metal contacts to n-type gallium nitride with low-temperature-grown cap layer

The Schottky barrier heights of metal contacts, including WSi0.8, Cr, Ti, Pt, and Ni, on n-type gallium nitride (GaN) with a GaN cap layer grown at low-temperature (LTG) were studied. Higher barriers can be formed by introducing LTG GaN on top of the conventional structures. The higher Schottky barrier observed in samples with the LTG GaN cap layer may be due to the facts that the high-resistivity LTG GaN layer may passivate the surface defects (pits) formed from threading dislocations or it may cause the Fermi-level pinning effect at the metal/semiconductor interface, revealing a weak dependence of Schottky barrier height on the metal work function. The measured barrier heights of the LTG GaN-capped samples were 1.02–1.13eV.

Dependence of local electronic structure in p-type GaN on crystal polarity and presence of inversion domain boundaries

Scanning probe techniques including scanning capacitance microscopy, scanning capacitance spectroscopy, scanning Kelvin probe force microscopy, and atomic force microscopy have been used to assess structure and local electronic properties of Ga-face and N-face p-type GaN and of inversion domain boundaries in p-type GaN. Epitaxial layers of p-type GaN were grown by molecular-beam epitaxy, and by adjustment of the Ga:N flux ratio samples containing both Ga-face and N-face material were obtained. Under identical growth conditions, net incorporation of electrically active Mg acceptors was found to be more efficient for material with Ga-face polarity. Only a very small dependence of surface potential on polarity was observed, in contrast to results reported for n-type GaN, in which a substantial dependence of Schottky barrier height on polarity has been found. In addition, elevated net concentrations of ionized Mg acceptors were observed in Ga-face regions in the immediate vicinity of some, but not all, inversion domain boundaries, consistent with theoretical suggestions that incorporation of high concentrations of Mg within an inversion domain boundary can lead to increased concentrations of Mg acceptors near the inversion domain boundary.

The role of the interface insulator layer and interface states on the current-transport mechanism of Schottky diodes in wide temperature range

In order to interpret in detail the experimentally observed current–voltage–temperature ( I– V– T) and capacitance–voltage–temperature ( C– V– T) results of Al/p-Si metal–semiconductor Schottky barrier diodes (SBDs) we have been examined the samples in the temperature range of 150–375 K. In the calculation method, to confirm the relationship between the I– V– T and C– V– T results, we have reported a modification which includes the ideality factor, n, and tunnelling parameter δχ 1/2 in the forward bias current characteristics. In the intermediate bias voltage region (0.1 < V < 0.6 V), the semi-logarithmic plots of the forward I– V– T curves were found to be linear. From the reverse saturation currents I 0 obtained by extrapolating the linear region of curves to zero applied voltage, the values of zero bias barrier heights ϕ B0 were calculated at each temperature. The values of ideality factor calculated from the slope of each curves were plotted as a function of temperature. The values of n are 3.41–1.40 indicating that the Al/p-Si diode does obey the thermionic field emission (TFE) mechanism rather than the other transport mechanism, particularly at low temperature. The high value of ideality factors is attributed to high density of interface states in the SBDs. The temperature dependence energy density distribution profile of interface state was obtained from the forward bias I– V– T measurements by taking into account the bias dependence of the effective barrier height and ideality factor. The interface states density N ss decreasing with increasing temperature was interpreted by the result of atomic restructuring and reordering at the metal–semiconductor interface. After the modification was made to the forward current expression, we obtained a good agreement between the values of barrier height obtained from both methods over a wide temperature.

Dependence of barrier height and effective mass on nitrogen concentration at SiOxNy/Si interface and gate oxide thickness

In this work, we have examined the dependence of barrier height and effective mass onSiO2 thickness and nitrogenconcentration at the SiOxNy/Si interface. From the measurements of the direct tunneling and Fowler–Nordheim (FN)tunneling currents, we have determined both the barrier height and the effective masswithout assuming a value for either the effective mass or the barrier height. It isobserved that with increases of interfacial nitrogen concentration the barrier heightdecreases, and the effective mass increases. On the other hand, the reduction of thegate oxide thickness leads to a decrease in the barrier height but an increase inthe effective mass. These results are explained using the electronic structures ofSiO2 and SiOxNy.

Effects of 60Co γ-ray irradiation on the electrical characteristics of Au/n-GaAs (MS) structures

In order to interpret the effect of 60Co γ-ray radiation dose on the electrical characteristics of metal–semiconductor (Au/n-GaAs) Schottky barrier diodes (SBDs), these devices were stressed with a zero bias during 60Co γ-ray source irradiation with the dose rate 2.12 kGy h −1 and the total dose range was 0–500 kGy at room temperature. Experimental results show that γ-irradiation induces an increase in the barrier height Φ b( C–V) obtained from reverse-bias C–V measurements, whereas barrier height Φ b( I–V) obtained from forward-bias I–V measurements remained essentially constant. This negligible change of Φ b( I–V) is attributed to the low barrier height in regions associated with the surface termination of dislocations. The experimental I–V and C–V characteristics prove that there is a reaction for extra recombination centers in case of SBDs exposed to γ-ray radiation. Also, the ideality factor n and donor concentration decrease with increasing dose rate. Both I–V and C–V characteristics of the Schottky diode indicate that the total dose radiation hardness of GaAs devices may be limited by the susceptibility of the Au–GaAs interface to radiation-induced damage. The density of interface states N SS distribution profiles as a function E CC– E SS for each dose rate was extracted from the forward-bias I–V characteristics taking into account the bias dependence of the effective barrier height Φ e at room temperature. N SS decreases with increasing dose rate and above 250 kGy it remains constant. Such a behavior of N SS is attributed to the existence of the native insulator layer between the metal and semiconductor that passivates the surface of semiconductor, and thus the increase of the N SS.

Electrical transport characteristics of single-layer organic devices from theory and experiment

An electrical model based on drift diffusion is described. We have explored systematically how the shape of the current density-voltage (J-V) curves is determined by the input parameters, information that isessential when deducing values of these parameters by fitting to experimental data for an ITO/PPV/Al organic light-emitting device (OLED), where ITO is shorthand for indium tin oxide and PPV is poly(phenylene vinylene). Our conclusion is that it is often possible to obtain a unique fit even with several parameters to fit. Our results allowing for a tunneling current show remarkable resemblance to experimental data before and after the contacts are conditioned. We have demonstrated our model on single-layer devices with ITO/PFO/Au and ITO/PEDOT/PFO/Au at room temperature and ITO/TPD/Al over temperatures from 130to290K. PFO is shorthand for poly(9,9′-dialkyl-fluorene-2,7-dyl) and TPD is shorthand for N,N′-diphenyl-N,N′-bis(3-methylphenyl)1-1′-biphenyl-4,4′-diamine. Good fits to experimental data have been obtained, but in the case of the TPD device, only if a larger value for the relative permittivity ϵs than would be expected is used. We infer that a layer of dipoles at the ITO/TPD interface could be responsible for the observed J-V characteristics by locally causing changes in ϵs. The strong temperature dependence of the hole barrier height from fitting J-V characteristics to the experimental data may indicate that the temperature dependence of the thermionic emission model is incorrect.