Dependence Of Barrier Height Research Articles

The effect of interface states, excess capacitance and series resistance in the Al/SiO 2/p-Si Schottky diodes

The current–voltage ( I– V) characteristics of Al/SiO 2/p-Si metal–insulator–semiconductor (MIS) Schottky diodes were measured at room temperature. In addition the capacitance–voltage ( C– V) and conductance–voltage ( G– V) measurements are studied at frequency range of 10 kHz–1 MHz. The higher value of ideality factor of 3.25 was attributed to the presence of an interfacial insulator layer between metal and semiconductor and the high density of interface states localized at Si/SiO 2 interface. The density of interface states ( N ss) 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) at room temperature for the Schottky diode on the order of ≅4 × 10 13 eV −1 cm −2 . These high values of N ss were responsible for the non-ideal behaviour of I– V and C– V characteristics. Frequency dispersion in C– V and G– V can be interpreted only in terms of interface states. The N ss can follow the ac signal especially at low frequencies and yield an excess capacitance. Experimental results show that the I– V, C– V and G– V characteristics of SD are affected not only in N ss but also in series resistance ( R s), and the location of N ss and R s has a significant on electrical characteristics of Schottky diodes.

Comparison of electrical parameters of Zn/p-Si and Sn/p-Si Schottky barrier diodes

In this study, current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of metal–semiconductor (MS) Zn/p-Si and Sn/p-Si Schottky diodes, with high resistivity silicon structures, are investigated. The parameters of series resistance ( R S), the ideality factor ( n) and the barrier height ( Φ b) are determined by performing different plots from the forward bias current–voltage ( I– V) and reverse bias capacitance–voltage ( C– V) characteristics. Thus, the barrier heights ( Φ b) for the Si Schottky diodes obtained between 0.725 and 1.051 eV, the ideality factor ( n) between 1.043 and 1.309, and the series resistance ( R S) between 12.594 and 12.950 kΩ. The energy distribution of interface states density was determined from the forward bias I– V characteristics by taking into account the bias dependence of the effective barrier height. It was concluded that the density of interface states in the considered energy range are in close agreement with each other values obtained for Zn/p-Si and Sn/p-Si Schottky diodes.

Current transport mechanism in Al/Si 3N 4/p-Si (MIS) Schottky barrier diodes at low temperatures

The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of metal–insulator–semiconductor (Al/Si 3N 4/p-Si) Schottky barrier diodes (SBDs) were measured in the temperature range of 80–300 K. By using the thermionic emission (TE) theory, the zero-bias barrier height Φ B0 calculated from I– V characteristics was found to increase with increasing temperature. Such temperature dependence is an obvious disagreement with the negative temperature coefficient of the barrier height calculated from C– V characteristics. Also, the ideality factor decreases with increasing temperature, and especially the activation energy plot is nonlinear at low temperatures. Such behaviour is attributed to Schottky barrier inhomogeneties by assuming a Gaussian distribution of barrier heights (BHs) at interface. We attempted to draw a Φ B0 versus q/2 kT plot to obtain evidence of a Gaussian distribution of the BHs, and the values of Φ Bo = 0.826 eV and α o = 0.091 V for the mean barrier height and standard deviation at zero-bias, respectively, have been obtained from this plot. Thus, a modified ln( I o/ T 2) − q 2 σ o 2/2( kT) 2 versus q/ kT plot gives Φ B0 and Richardson constant A * as 0.820 eV and 30.273 A/cm 2 K 2, respectively, without using the temperature coefficient of the barrier height. This value of the Richardson constant 30.273 A/cm 2 K 2 is very close to the theoretical value of 32 A/cm 2 K 2 for p-type Si. Hence, it has been concluded that the temperature dependence of the forward I– V characteristics of the Al/Si 3N 4/p-Si Schottky barrier diodes can be successfully explained on the basis of TE mechanism with a Gaussian distribution of the barrier heights. In addition, the temperature dependence of energy distribution of interface state density ( N SS) profiles was determined from the forward I– V measurements by taking into account the bias dependence of the effective barrier height and ideality factor.

On the Current-Voltage Characteristic of an Ideal Metal-Semiconductor Schottky-Barrier Contact

The model of an ideal (without an intermediate layer and electron surface states) metal-semiconductor Schottky-barrier contact is numerically analyzed with allowance for the effect of image-force barrier-height lowering. It is shown that the nonlinear dependence of barrier height on the bias voltage inherent in this contact causes not only the deviation of the current-voltage (I-V) characteristic from an ideal one but also the so-called “low-temperature anomaly” — an increase in the I-V-characteristic ideality factor n and a decrease in the barrier height ϕbm measured from the saturation current as the temperature is decreased. A more exact equation for the I-V characteristic of the ideal contact is theoretically substantiated using parameters n and ϕbm in a wide temperature range.

Current transport in Zn/p-Si(1 0 0) Schottky barrier diodes at high temperatures

In this study, we have performed behavior of the non-ideal forward bias current–voltage ( I–V) and the reverse bias capacitance–voltage ( C–V) characteristics of Zn/p-Si (metal–semiconductor) Schottky barrier diode (SBDs) with thin interfacial insulator layer. The forward bias I–V and reverse bias C–V characteristics of SBDs have been studied at the temperatures range of 300–400 K. SBD parameters such as ideality factor n, the series resistance ( R S) determined Cheung's functions and Schottky barrier height, Φ b , are investigated as functions of temperature. The ideality factor n and R S were strongly temperature dependent and changed linearly with temperature and inverse temperature, respectively. The zero-bias barrier heights Φ b 0 ( I – V ) calculated from I–V measurements show an unusual behavior that it was found to increase linearly with the increasing temperature. However, the barrier height Φ b ( C – V ) calculated from C–V measurements at 500 kHz frequency decreased linearly with the increasing temperature. The correlation between Φ b 0 ( I – V ) and Φ b ( C – V ) barrier heights have been explained by taking into account ideality factors n and the tunneling factor ( α χ 1 / 2 δ ) in the current transport mechanism. Also, the temperature dependence of energy distribution of interface state density ( N SS ) was determined from the forward I–V measurements by taking into account the bias dependence of the effective barrier height. The higher values of n and R S were attributed to the presence of a native insulator on Si surface and to high density of interface states localized at semiconductor–native oxide layer (Si/SiO 2) interface.

Composition Dependence of the Energy Barrier for Lithium Diffusion in Amorphous WO[sub 3

Lithium insertion into amorphous films prepared by the electron beam evaporation technique was investigated by measurements of voltage-composition curve and chemical diffusion coefficient. The extraction of equilibrium and kinetic parameters allows the determination of the jump diffusion coefficient dependence on composition. In addition, first-principles calculations combining a pseudopotential plane wave scheme have been performed with the aim of providing a better understanding of the dependence of the potential barrier height for the hopping pathway with the insertion level for crystalline compounds. Our results predict a lowering of the barrier height for less doped systems and both experiments and simulations exhibit a relation of the type for the composition range .

The energy distribution of the interface state density of SnO 2/p-Si (1 1 1) heterojunctions prepared at different substrate temperatures by spray deposition method

We have fabricated the Al/SnO 2/p-Si (1 1 1) Schottky diodes having the SnO 2/p-Si heterojunction prepared using the spray deposition process at various Si substrate temperatures and report the first investigation of the energy distribution of the interface state density of these diodes. The barrier height Φ B estimated from the I– V and C– V measurements agrees with each other and increased with increasing substrate temperature. The energy distribution of interface state density N ss was determined from the forward bias I– V characteristics by taking into account the bias dependence of the effective barrier height. The interface state density N ss of the diodes has an exponential growth with bias from the midgap towards the top of the valance band for each diode; for example, from 1.46 × 10 12 eV −1 cm −2 in (0.46 − E v) eV to 1.29 × 10 12 eV −1 cm −2 in (0.53 − E v) eV for SD3 sample.

Photoemission study of energy-band alignment for RuOx∕HfO2∕Si system

Conductive oxides RuOx as alternative electrode on high-κ HfO2 gate dielectric have been fabricated by ultrahigh-vacuum sputtering and subsequently oxidized using oxygen plasma. The energy-band alignment for the RuOx∕HfO2∕Si system and the oxidation-state dependence of barrier height for RuOx contacting to HfO2 dielectrics has been analyzed by x-ray photoemission spectroscopy. The valence- and conduction-band offsets of HfO2∕Si are determined to be 3.05±0.1 and 1.48±0.1eV, respectively. The barrier heights for the RuOx contacting to HfO2 are oxidation-state dependent, in the range of 1.95–2.73eV.

Theoretical analysis of the bias-voltage dependence of the apparent barrier height

We have analyzed the bias voltage dependence of the apparent barrier height (ABH), using a self-consistent calculation within the density functional theory. We have found that the ABH shows the bias polarity dependence in both of the two $\mathrm{Al}(100)$ surfaces, the one without reconstruction and the one containing the vacancy cluster in the layer next to the surface. We have also found that the surfaces have opposite bias polarity dependences of the ABH. These results cannot be understood in the light of the formation of the surface dipole layer, but can be understood from two factors: the reduction in the effective potential and the change in the surface electron states by the applied bias voltage.

Reliability of High-K Dielectrics and Its Dependence on Gate Electrode and Interfacial / High-K Bi-Layer Structure

In this work, we present the reliability of HfO 2 and how it depends on the barrier height and the nature of the bi-layer structure. We will also discuss how these factors lead to different charge fluence, charge-to-breakdown, and breakdown characteristics. It is found that the lower Weibull slope of high-k dielectrics is partially attributed to high charge fluence by the lower barrier height of high-k dielectrics, and a different nature of bi-layer structure. In addition, it has been found that there is distinct bi-modal defect generation rate for high-k/SiO 2 stack. A two-step breakdown process was clearly observed. Soft breakdown characteristics were dependent on the barrier heights. It is attributed to different charge fluence by different barrier heights. Charge-to-breakdown shows strong barrier height dependence.

Distinguishing the dependence of the apparent local barrier height on measurement conditions

AbstractWe have investigated a method for finding the dependency of the apparent local barrier height (LBH) on measurement parameters (tunnelling current, bias voltage and tip–sample separation). The validity of the method is demonstrated by measuring the LBH on an Au(111) surface. This method enables comparison of LBH values on various surfaces. Copyright © 2004 John Wiley & Sons, Ltd.

Current transport properties of Pd/3C–SiC Schottky junctions with planar and vertical structures

Palladium Schottky contacts were fabricated on 3C–SiC heteroepitaxial layers (grown on Si substrates) and characterized by current–voltage measurements. The effects of epitaxial layer thickness and the device configuration on the diode parameters were investigated and analyzed in terms of the interfacial defect density. The influence of operating temperature on the I–V characteristics of the Schottky junctions were studied and the apparent anomalies in temperature dependence of barrier height and ideality factor were explained with the model of localized inhomogeneities of barrier height over the Schottky contact region.

On the Origin of Higher Rotational Barriers in Thioamides than in Amides. Remote Substituent Effects on the Conformational Stability of the Thioamide Group in Thioacetanilides

The variations of barrier heights for rotation around the amide C−N bond in para-substituted thioacetanilides was studied in a comparative context with data for a series of acetanilides by applying density functional theory at the B3LYP/6-31G(d,p) level. The shifts of the energy barriers induced by remote substituents in the para position of the aromatic ring are interpreted in terms of changes of the bond lengths and electric-charge parameters for the equilibrium configurations, as well as in terms of charge fluctuations that accompany the internal rotation. A satisfactory explanation for the distinctly greater shifts of rotational barriers in the thioacetanilide series upon substitution in the aromatic ring, as compared with data for the respective acetanilides, is obtained by analyzing the dependences of barriers heights on the charge shifts upon substitution in the aromatic ring and upon rotation. Several linear relationships are established linking the barrier heights with structural and electronic parameters that characterize the amide and thioamide groupings. A common linear equation quantifying the dependence of barrier heights on the shifts of natural bond orbital partial charges at the amide S and O atoms upon substitution in the aromatic ring in the two series is found. The relationship is confirmed by data from a Mulliken population analysis. The results obtained are consistent with the views for a classical amide resonance as being the origin of higher rotational barriers in thioamides than in amides.

Bias voltage dependence of apparent local barrier height at constant tip–sample separation

The bias voltage dependence of the apparent local barrier height (LBH) corresponding to the “work function” on a nanometer-scale was measured by scanning tunneling microscopy on an Au (111) surface with an Au tip. There have been reports of the bias voltage dependence of the LBH under constant current (CC) conditions. However, under CC, a change in the bias voltage causes a change in the tip–sample separation. In this situation, the measured results contain both effects (the bias voltage and the separation). Therefore, to accurately measure the effect of the bias voltage on the LBH, the separation effects must be eliminated. We measured the bias voltage dependence of the LBH at a constant separation (CS) using the current on the current–voltage (I–V) curve and compared the results with CC. For CS measurements, in the ohmic range (the I–V curve is linear), the LBH does not depend on the bias voltage within the experimental error. Beyond the ohmic range, the LBH decreases with increased bias voltage. In contrast, CC measurement results are clearly affected by both effects. In the region where the separation effect can be neglected, the CC result corresponds to the CS result.

The role of interface states and series resistance on the I– V and C– V characteristics in Al/SnO 2/p-Si Schottky diodes

In order to good interpret the experimentally observed non-ideal Al/SnO 2/p-Si (MIS) Schottky diode parameters such as the barrier height Φ B, series resistance R s and density of interface states N ss, a calculation method has been reported by taking into account interfacial oxide layer and ideality factor n in the current transport mechanism. The current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics of MIS diodes are studied over a wide temperature range of 80–350 K. The effects of R s, interfacial layer and N ss on I– V and C– V characteristics are investigated. The values of n were strongly temperature dependent and decreased with increasing temperature. The energy distribution of N ss was determined from the forward bias I– V characteristics by taking into account the bias dependence of the effective barrier height. The mean N ss estimated from I– V and C– V measurements decreased with increasing temperature. The R s estimated from Cheung’s functions was strongly temperature dependent and decreased with increasing temperature. The I– V characteristics confirmed that the distribution of N ss, R s and interfacial layer are important parameters that influence the electrical characteristics of MIS devices.

Measurement of bias voltage dependence of local barrier height at constant tip-sample separation

We measured the bias voltage dependence of the apparent local barrier height (LBH) by STM on an Au (1 1 1) surface with an Au tip. The results under two different conditions, a constant tip-sample separation and a constant current, were compared in the low bias voltage range (−30 to −5 mV). Under constant separation, the LBH does not change with the bias voltage, indicating that the LBH is independent of the bias voltage. Under constant current, the LBH increases with increasing absolute value of the bias voltage due to the increase of the tip-sample separation with increasing absolute bias voltage. We found that the LBH depends only on the separation in the low bias voltage range.

Direct and trap-assisted elastic tunneling through ultrathin gate oxides

The direct and assisted-by-trap elastic tunnel current in metal–oxide–semiconductor capacitors with ultrathin gate oxide (1.5–3.6 nm) has been studied. Bardeen’s method has been adapted to obtain the assisted tunnel current, in addition to the direct tunnel current. The dependence of the assisted current on the trap distribution in energy has also been analyzed. This allows us to obtain the trap distribution in energy from experimental current curves. Finally, we have analyzed the role of the image force, the inclusion of which can avoid a barrier height dependence on the oxide thickness.

On the Nature of the “Low-Temperature Anomaly” in Metal–Semiconductor Schottky-Barrier Contacts

It is shown that the “low-temperature anomaly” of the I-V characteristics of homogeneous metal–semiconductor Schottky-barrier contacts (an increase in the ideality factor n and a decrease in the barrier height ϕbm, measured using the saturation current, with decreasing temperature, as well as the fact that their product ϕbn≡ nϕbm coincides very closely with the actual barrier height ϕb(V)) is a consequence of two factors: (1) the nonlinear dependence of the actual barrier height on the bias, resulting in an increase in the ideality factor with increasing bias voltage (current) and (2) measurement of the parameters n and ϕbm for the same current for all temperatures. A new expression for the flat-band barrier height ϕbf is derived.

Ａｕ（１１１）再構成表面での局所ポテンシャル障壁高さ測定

The bias voltage dependence of the apparent local barrier height (LBH) corresponding to “work function” at nanometer-scale has been measured by scanning tunnel microscope (STM) on the reconstructed Au (111) surface with Pt-Ir and Au tips at a low bias voltage from ± 50 to ±400 mV. The LBH value measured under a constant-current condition increases with increasing absolute bias voltage. Under a constant current condition, increase of the absolute bias voltage causes increase of the tip-sample separation. Therefore, the result is due to the separation effects rather than bias voltage effects.

Characterization of metal/GaN Schottky interfaces based on I– V– T characteristics

Interface properties of metal/n- and p-GaN Schottky diodes are studied by I– V– T and C– V– T measurements, and simulation of their characteristics. On the basis of the previously proposed “surface patch” model, the gross behavior of I– V– T characteristics, which includes Richardson plots together with temperature dependence of the effective Schottky barrier heights (SBHs) and n-values, can be well reproduced. Furthermore, the dependence of the true SBH on the metal work function was also deduced from high-temperature I– V curves, giving S-values of 0.28 and 0.20 for n- and p-GaN samples, respectively, and the interface Fermi level tends to be pinned at a characteristic energy of about two-third of the bandgap.