Gaussian Distribution Of Barrier Heights Research Articles

Single Gaussian distribution of barrier height in Al/PS–ZnPc/p-Si type Schottky barrier diode in temperature range of 120–320 K

Possible current-transport mechanism in aluminum/polystrene–zincphthalocyanine/ptype silicon Schotky barrier diode (Al/PS–ZnPc/p-Si; SBD), for the forward bias current–voltage (I–V) characteristics were carried out in the temperature range of 120–320 K. The high value of ideality factor (n), especially at low temperatures, was attributed to the existence of PS layer, barrier in-homogeneities and particular density distribution of surface states between metal and semiconductor. An abnormal decrease in the zero-bias barrier height (BH) and increase in n with decreasing temperature which leads to non-linearity in the Richardson plot, have been observed. Linear relationship between BH and n was also observed. BH was plotted as a function of q/2kT to obtain evidence of Gaussian distribution (GD) of the BHs. The mean BH and its standard deviation (σ) were obtained as 1.03 eV and 0.117 V from the slope and intercept of this plot, respectively. Thus, the modified ln(Io/T2) − q2σo2/2k2T2 versus q/kT plot gives mean BH and the modified Richardson constant \({\text{A}}_{\bmod }^{*}\) as 1.043 eV and 29.824 A cm−2 K−2, respectively. This value of the Richardson constant is very close to the theoretical value of 32 A cm−2 K−2 for p-type Si. Therefore, non-ideal behavior of forward-bias I–V characteristics in Al/PS–ZnPc/p-Si might be successfully explained in terms of the thermionic emission mechanism with single GD of BHs.

Carrier transport mechanism of Ni/Ag Schottky contacts to n-type GaN grown on Si(111) substrate

We fabricated Ni/Ag Schottky contacts to n-GaN grown on Si substrate and investigated its electrical properties using current–voltage characteristics measured in the temperature range of 200–400 K. The barrier height and ideality factor of Ag/Ni/n-GaN Schottky diode showed strong temperature dependence. The barrier height decreased and ideality factor increased, with decrease in temperature indicating a deviation from ideal thermionic emission. A barrier height of 1.00 eV was obtained for unity ideality factor from the linear relation between the obtained barrier heights and ideality factor. The lateral inhomogeneity of the Schottky barrier at the interface between Ni/Ag and n-GaN could be the main cause of temperature dependence of barrier and ideality factor and has been explained on the basis of thermionic emission with a Gaussian distribution of barrier heights. The electric field dependence of reverse current revealed that the Poole–Frenkel emission mechanism dominates the current transport in the reverse bias.

Gaussian distribution of inhomogeneous barrier height in Au/n-Si (111) Schottky barrier diodes at low temperatures

Forward bias current–voltage (I–V) characteristics of Au/n-Si (111) Schottky barrier diode (SBD) were investigated in the temperature range of 80–290K. Analysis of temperature dependent I–V data in terms of thermionic emission (TE) theory revealed an abnormal increase in zero-bias barrier height (ΦBo) and decrease in ideality factor (n) with increasing temperature. Such behavior of ΦBo and n was attributed to barrier inhomogeneities by assuming a Gaussian distribution (GD) of barrier height. Therefore, mean barrier height and effective Richardson constant (A⁎) values were extracted from the modified Richardson plot, and extracted A⁎ was found close to the theoretical value for n-type Si. Hence, it has been concluded that temperature dependent I–V characteristics of the SBD can be successfully explained on the basis of TE theory with GD of barrier height. In addition, series resistance and energy profile of density of interface traps in the SBD were also investigated.

Electrical characterization of Ni/n-ZnO/p-Si/Al heterostructure fabricated by pulsed laser deposition technique

The ZnO thin films are grown on the p-Si for the heterojunction fabrication by pulsed laser deposition method. X-ray diffraction study showed that the texture of the film is hexagonal with a strong (002) plane as preferred direction. High purity vacuum evaporated nickel and aluminum metals were used to make contacts to the n-ZnO and p-Si, respectively. The current–voltage characteristics of Ni/n-ZnO/p-Si(100)/Al hetero structure measured over the temperature range 80–300K have been studied on the basis of thermionic emission diffusion mechanism. The equivalent Schottky barrier height and diode ideality factor are determined by fitting of measured current–voltage data in to thermionic diffusion equation. It is observed that the barrier height decreases and the ideality factor increases with decrease of temperature and the activation energy plot exhibit non-linear behavior. These characteristics are attributed to the Gaussian distribution of barrier heights. The capacitance–voltage characteristics of Ni/n-ZnO/p-Si(100)/Al heterojunction diode are also studied over wide temperature range. From the measured capacitance–voltage data the built in voltage and impurity concentration in n-type ZnO is estimated.

Temperature dependent electrical transport studies of self-aligned ZnO nanorods/Si heterostructures deposited by sputtering

Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 1010 cm−2, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120–300 K and it shows a rectifying behavior. Barrier height (ϕB) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A*) was evaluated using Richardson plot of ln(Io/T2) versus q/kT plot by linear fitting in two temperature range 120–180 K and 210–300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic equation gives mean barrier heights of 0.55 ± 0.01 eV and 0.86 ± 0.02 eV for two different temperature regions 120–180 K and 210–300 K, respectively. Modified Richardson plot provided two values of Richardson constant for two temperature regions. However, for higher temperature range (210–300 K), the calculated value of Richardson constant ∼123 A cm−2 K−2 was close to the ideal Richardson constant for n-Si.

Electrical properties and the double Gaussian distribution of inhomogeneous barrier heights in Se/n-GaN Schottky barrier diode

The temperature dependent electrical characteristics of Se/n-GaN Schottky barrier diode have been investigated in the temperature range of 130–400K in the steps of 30K. The estimated barrier height (ϕbo) and ideality factor n are found to be 0.46eV and 3.83 at 130K, 0.92eV and 1.29 at 400K. The ϕbo and n are found to be strongly temperature dependent and while the ϕbo decreases and the n increase with decreasing temperature. Such behavior of ϕbo and n is attributed to Schottky barrier inhomogeneities, explained by the assumption of Gaussian distribution of barrier heights at the metal/semiconductor interface. Experimental results revealed the existence of a double Gaussian distribution with mean barrier height values of 1.33 and 0.90eV and standard deviations (σo) of 0.0289 and 0.010V, respectively. The modified ln(Io/T2)−(q2σo2/2k2T2) versus 103/T plot gives ϕbo and Richardson constant (A∗) values as 1.30 and 0.88eV, 23.6 and 19.2 A/cm2 K2 at 400 and 130K, respectively without using the temperature coefficient of the barrier height. Further, the barrier height obtained from C–V method decreases with an increase in temperature. It is also noted that the barrier height value estimated from the C–V method is higher than that estimated from the I–V method at various temperatures. Possible explanations for this discrepancy are presented. The interface state density (Nss) is found to be decreased with an increasing temperature. The reverse-bias leakage current mechanism of Se/n-GaN Schottky diode is investigated. Both Poole–Frenkel and Schottky emissions are described and discussed.

Determination of the mean and the homogeneous barrier height of Cu Schottky contacts on heteroepitaxial β‐Ga2O3 thin films grown by pulsed laser deposition

AbstractWe have investigated the electrical properties of Cu Schottky contacts (SCs) on ()‐oriented β‐Ga2O3 thin films, which have been grown by pulsed laser deposition (PLD). The I–V characteristics of two different sample structures exhibit rectification ratios at ±2 V up to 7 orders of magnitude. The dominant current transport mechanism is thermionic emission. By fitting the I–V characteristics, we obtained the ideality factor n and the effective barrier height at temperatures between 50 and 320 K. Considering a Gaussian barrier height distribution, we determined a mean barrier height of 1.32 eV. The contacts are stable at high temperatures up to at least 550 K. At this temperature a homogeneous barrier height of 1.32 eV is found, consistent with the determined mean barrier height. The ideality factor for this temperature is 1.03 and barrier inhomogeneities do not influence current transport, making the contact close to ideal. Schematic band diagram of a Cu/β‐Ga2O3 Schottky contact at a temperature of 550 K. The inset shows a photographic image of the sample.

Double barrier heights in 5,6,11,12-tetraphenylnaphthacene (rubrene) based organic Schottky diode

5,6,11,12-Tetraphenylnaphthacene (rubrene) was grown on p type Si (100) substrate using spin coating technique. We have fabricated an Al/rubrene/p-Si Schottky device and measured the current–voltage (I–V) characteristics in the temperature range from 75 to 300K by steps of 25K. An abnormal decrease in the experimental barrier height ΦB and an increase in the ideality factor n with a decrease in temperature have been observed. The I–V characteristics of Al/rubrene/p-Si Schottky diode are analyzed on the basis of thermionic emission (TE) theory and the assumption of double Gaussian distribution of barrier heights due to barrier inhomogeneities. The modified Richardson plots of ln(I0/T2)−(1/2)(qσs0(i)/kT)2 versus 1000/T gives Φ¯B0(i) and AR(i) values as 1.186 and 0.571eV, and 33.85 and 84.63Acm−2K−2, respectively. The modified Richardson constant value of AR(2)=33.85 A cm−2 K−2 for high temperature range (175–300K) is very close to the theoretical value of 32Acm−2K−2 for p-Si.

Phase transition induced double-Gaussian barrier height distribution in Schottky diode

The charge transport mechanisms of Hg contact on n-type silicon crystal having 〈100〉 orientation were investigated in the temperature range of 160–293K by the thermionic emission theory. The temperature variation of barrier height and ideality factor illustrates an inhomogeneous interface with a Gaussian barrier height distribution. The plots of temperature dependent zero-bias barrier height, ideality factor, series resistance and reverse leakage current show a discontinuity below 240K. The experimental barrier height and ideality factor versus 1/T plot gives two slopes, one in the 160–220K region and the other in the 240–293K region, thereby revealing a double Gaussian distribution of barrier heights. The observed discontinuity in the diode parameters and the existence of double Gaussian barrier heights are interpreted on the basis of phase transition of mercury from its liquid state to solid form.

Systematic study of interface trap and barrier inhomogeneities using I-V-T characteristics of Au/ZnO nanorods Schottky diode

This paper presents in-depth analysis of I-V-T characteristics of Au/ZnO nanorods Schottky diodes. The temperature dependence I-V parameters such as the ideality factor and the barrier heights have been explained on the basis of inhomogeneity. Detailed and systematic analysis was performed to extract information about the interface trap states. The ideality factor decreases, while the barrier height increases with increase of temperature. These observations have been ascribed to barrier inhomogeneities at the Au/ZnO nanorods interface. The inhomogeneities can be described by the Gaussian distribution of barrier heights. The effect of tunneling, Fermi level pinning, and image force lowering has contribution in the barrier height lowering. The recombination-tunneling mechanism is used to explain the conduction process in Au/ZnO nanorods Schottky diodes. The ionization of interface states has been considered for explaining the inhomogeneities.

Temperature-dependent current–voltage characteristics of Se Schottky contact to n-type Ge

We fabricated Se Schottky contacts to n-type Ge and demonstrated their electrical properties using temperature-dependent current–voltage measurements in the temperature range of 200–300K. As the temperature decreased, the barrier height decreased and the ideality factor increased. These anomalies could be associated with the barrier height inhomogeneities prevailing at the metal–semiconductor contact. On the assumption of the Gaussian distribution of barrier height, the mean value and standard deviation of barrier height, extracted from the plot of barrier height as a function of q/2kT, were found to be 0.70 and 0.089eV, respectively. The electric field dependence of the reverse current revealed that the Schottky emission mechanism dominates the current conduction in the reverse bias.

Electrical properties of Au/perylene-monoimide/p-Si Schottky diode

Abstract In this work, we have fabricated an Au/perylene-monoimide (PMI)/p-Si Schottky barrier diode. We have investigated how electrical and interface characteristics like current–voltage characteristics (I–V), ideality factor (n), barrier height (ΦB) and series resistance (Rs) of diode change with temperature over a wide range of 100–300 K. Detailed analysis on the electrical properties of structure is performed by assuming the standard thermionic emission (TE) model. Possible mechanisms such as image force lowering, generation–recombination processes and interface states which cause deviations of n values from the unity have been discussed. Cheung–Cheung method is also employed to analysis the current–voltage characteristics and a good agreement is observed between the results. It is shown that the electronic properties of Schottky diode are very sensitive to the modification of perylene-monoimide (PMI) interlayer organic material and also to the temperature. The ideality factor was found to decrease and the barrier height to increase with increasing temperature. The temperature dependence of barrier height shows that the Schottky barrier height is inhomogeneous in nature at the interface. Such inhomogeneous behavior was explained on the basis of thermionic emission mechanism by assuming the existence of a Gaussian distribution of barrier heights.

The Synthesis of the Fe3O4 Nanoparticles and the Analysis of the Current–Voltage Measurements on Au/Fe3O4/p-Si Schottky Contacts in a Wide Temperature Range

The iron oxide (Fe3O4) magnetic nanoparticles were synthesized via the organic solution phase method and used for the fabrication of the Au/Fe3O4/p-Si rectifying device. The variation in electrical characteristics of the Au/Fe3O4/p-Si Schottky contacts was investigated as a function of temperature using current–voltage (I–V) measurements in the temperature range of 40 K to 370 K (−233 °C to 97 °C). The I–V characteristics of the contacts indicated extremely strong temperature dependence. The double distribution of barrier heights was found in the Fe3O4/p-Si Schottky diodes from the I–V-T measurements. The Schottky barrier height (Φb) increases with the increasing temperature, while the ideality factor n decreases. The nonlinearity in the activation energy plot was observed, which is attributed to barrier inhomogeneities by assuming a Gaussian distribution of barrier heights at the Fe3O4/p-Si interface. The Richardson constant measured from the temperature-dependent I–V characteristics is 2.99 A/K2 cm2, which is lower than the ideal value.

Temperature-Dependent Current–Voltage (I–V) and Capacitance–Voltage (C–V) Characteristics of Ni/Cu/n-InP Schottky Barrier Diodes

The current-voltage (I–V) and capacitance-voltage (C–V) characteristics of Ni/Cu/n-InP Schottky barrier diodes are studied over a wide temperature range, from 210 K to 420 K. The I–V characteristics display anomalous thermal behavior. The apparent barrier height decays, and the ideality factor grows at low temperatures, and the series resistances resulting from Cheung’s and Norde’s procedures are markedly temperature dependent. The nonlinearity of the Richardson plot and the strong temperature dependence of the Schottky-barrier parameters indicate that the interface is spatially inhomogeneous. Plots of the zero-bias barrier height as a function of 1/(2kT) points to a Gaussian distribution of barrier heights with 0.90 eV mean height and 0.014 eV standard deviation. When this distribution is accounted for, a Richardson of 6.5 A/(cm K)2 results, relatively close to the 9.4/(cm K)2 predicted by theory. We conclude that, combined with a Gaussian distribution of barrier heights, the thermionic-emission mechanism explains the temperature-dependent I–V and C–V characteristics of the studied Schottky-barrier diodes.

Comparative study of transparent rectifying contacts on semiconducting oxide single crystals and amorphous thin films

We demonstrate fully transparent, highly rectifying contacts (TRC) on amorphous GaInZnO and compare them to TRC fabricated on single crystalline bulk ZnO and heteroepitaxial ZnO thin films. The contacts’ transparency in the visible spectral range exceeds 70%. From numerical simulations, we conclude that thermionic emission is the dominating transport mechanism, however, for several samples with low net doping density diffusion theory must be applied. The detailed investigation of the rectification properties of the TRC using temperature-dependent current-voltage and capacitance-voltage measurements reveals that barrier inhomogeneities govern the IV-characteristics of all diodes irrespective of the sample crystallinity. Assuming a Gaussian barrier height distribution, the extracted mean barrier heights typically range between 1.1 and 1.3 V. The width of the barrier distribution correlates with the mean barrier height and ranges from 110 to 130 mV. By compiling literature data, we found that this correlation holds also true for Schottky diodes on elemental and III-V semiconductors.

Investigation of the inhomogeneous barrier height of an Au/Bi4Ti3O12/n-Si structure through Gaussian distribution of barrier height

A Au/Bi4Ti3O12/n-Si structure is fabricated in order to investigate its current—voltage (I–V) characteristics in a temperature range of 300 K–400 K. Obtained I–V data are evaluated by the thermionic emission (TE) theory. Zero-bias barrier height (ΦB0) and ideality factor (n) calculated from I–V characteristics, are found to be temperature-dependent such that ΦB0 increases with temperature increasing, whereas n decreases. The obtained temperature dependence of ΦB0 and linearity in ΦB0 versus the n plot, together with a lower barrier height and Richardson constant values obtained from the Richardson plot, indicate that the barrier height of the structure is inhomogeneous in nature. Therefore, I–V characteristics are explained on the basis of Gaussian distribution of barrier height.

Barrier height distribution and dipolar relaxation in metal-insulator-semiconductor junctions with molecular insulator: Ageing effects

Electrical transport through molecular monolayers being very sensitive to disorder effects, admittance and current density characteristics of Hg//C12H25 – n Si junctions incorporating covalently bonded n-alkyl molecular layers, were investigated at low temperature (150–300 K), in the as-grafted state and after ageing at the ambient. This comparison reveals local oxidation effects both at the submicron scale in the effective barrier height distribution and at the molecular scale in the dipolar relaxation. In the bias range dominated by thermionic emission and modified by the tunnel barrier (TB) attenuation, exp(−β0dT), where dT is the thickness of the molecular tunnel barrier and β0 is the inverse attenuation length at zero applied bias, some excess current is attributed to a distribution of low barrier height patches. Complementary methods are used to analyze the current density J(V, T) characteristics of metal-insulator-semiconductor tunnel diodes. Assuming a Gaussian distribution of barrier heights centered at qΦB provides an analytical expression of the effective barrier height, qΦEFF(T)=qΦB+(kT)β0dT−(qδΦ)2/2kT; this allows fitting of the distribution standard deviation δΦ and tunnel parameter (β0dT) over a wide temperature range. In a more realistic modeling including the voltage dependence of barrier height and circular patch area, the so-called “pinch-off” effect is described by a distribution of parameter γ=3(ΔPRP2/4)1/3, which combines interface potential modulation and patch area variations. An arbitrary distribution of γ values, fitted to low-temperature J(V) data, is equally well described by Gaussian or exponential functions. Ageing in air also increases the interface oxidation of Si substrate and affects the density of localized states near mid gap, which typically rises to the high 1011 eV−1 cm−2 range, as compared with DS < 1011 eV−1 cm−2 in the as-grafted state. The bias-independent relaxation observed near 1 kHz at low temperature may be attributed either to dipoles in the alkyl chain induced by the strong permanent dipoles of interface silicon oxide or to a local relaxation of water molecules trapped at the OML/silicon interface. The respective roles of SiO2 formation and water physisorption on the decrease of patch barrier height are also discussed.

The double Gaussian distribution of inhomogeneous barrier heights in the organic‐on‐inorganic Schottky devices

AbstractWe have fabricated an Au/perylene–monoimide (PMI)/n‐Si organic‐on‐inorganic Schottky device by spin coating of PMI solution on an n‐Si semiconductor wafer. Current–voltage (I–V) measurements on the device in the temperature range of 75–300 K were carried out. An abnormal decrease in the experimental barrier height ΦB and an increase in the ideality factor n with a decrease in temperature have been observed. This behaviour has been explained on the basis of thermionic emission theory with a double Gaussian distribution of the barrier heights due to the barrier height inhomogeneities.

Current transport in nonpolar a-plane InN/GaN heterostructures Schottky junction

The temperature dependent current transport properties of nonpolar a-plane (112¯0) InN/GaN heterostructure Schottky junction were investigated. The barrier height (ϕb) and ideally factor (η) estimated from the thermionic emission (TE) model were found to be temperature dependent in nature. The conventional Richardson plot of the ln(Is/T2) versus 1/kT has two regions: the first region (150–300 K) and the second region (350–500 K). The values of Richardson constant (A*) obtained from this plot are found to be lower than the theoretical value of n-type GaN. The variation in the barrier heights was explained by a double Gaussian distribution with mean barrier height values (ϕb¯) of 1.17 and 0.69 eV with standard deviation (σs) of 0.17 and 0.098 V, respectively. The modified Richardson plot in the temperature range 350–500 K gives the Richardson constant which is close to the theoretical value of n-type GaN. Hence, the current mechanism is explained by TE by assuming the Gaussian distribution of barrier height. At low temperature 150–300 K, the absence of temperature dependent tunneling parameters indicates the tunneling assisted current transport mechanism.

Study of barrier inhomogeneities in I–V-T and C-V-T characteristics of Al/Al2O3/PVA:n-ZnSe metal–oxide–semiconductor diode

This paper presents detailed analysis of forward and reverse bias I-V and C-V characteristics of Al/Al2O3/PVA:n-ZnSe metal-oxide-semiconductor diode. PVA:n-ZnSe nanocomposites are prepared by chemical bath deposition technique. The alumina layer is deposited on Al substrate by electrolytic anodization method. The temperature dependence I-V parameters such as series resistance (RS), the ideality factor (n), the barrier height (φb), the Richardson constant (A*), mean barrier height, and the leakage current (Ileakage) have been explained on the basis of inhomogeneity. The series resistance obtained from Chenug’s method and Norde’s method shows close agreement with each other. In C-V measurements, in the reverse bias of Al/Al2O3/PVA:n-ZnSe metal-oxide-semiconductor diode has been performed as a function of temperature. The temperature dependence C-V parameters barrier height φ(C−V), the built-in-voltage (Vbi), carrier concentration (ND), Fermi energy (EF), and depletion layer width (W) have been calculated at different temperatures. The discrepancy in barrier height obtained from I-V and C-V measurements and barrier inhomogeneities of Al/Al2O3/PVA:n-ZnSe contact has been explained by assuming Gaussian distribution of barrier heights using potential fluctuation model.