Barrier Height Inhomogeneities Research Articles

Double Gaussian distribution of barrier heights and self-powered infrared photoresponse of InN/AlN/Si (111) heterostructure

InN epilayer has been grown by plasma-assisted molecular beam epitaxy on the AlN/n-Si (111) substrate. The self-powered photodetection has been carried out with an infra-red (IR) laser (λ=1550nm, power density ∼106.2mA/cm2), where a photoresponsivity was observed to be 3.36 μA/W with response times in milliseconds from the InN/AlN/n-Si (111)-based semiconductor–insulator–semiconductor (SIS) interface. Furthermore, to elucidate the vertical electrical transport properties of the SIS interface, low-temperature electrical behavior has been investigated over a range of 100–400 K. Experimental studies revealed an abnormal increase in the barrier height and a decrease in the ideality factor with increasing temperature, suggesting inhomogeneous barrier heights across the heterojunctions. Such inhomogeneity behaviors have been successfully explained on the basis of thermionic emission theory, assuming the existence of a double Gaussian distribution of barrier heights at the heterostructure interface. Moreover, the SIS device structure exhibits mean barrier heights (φ¯b0) of 1.11 and 0.63 eV, respectively, in two temperature regimes, indicating the presence of defect states and inhomogeneity at the interface, which is supported by the nonlinear behavior of the photocurrent with the power density.

Analysis on the temperature dependent electrical properties of graphene/Al–ZnO Schottky contact

The electrical characteristics of the graphene/Al–ZnO schottky contact with the temperature of 180 K–300 K have been discussed in detail. Based on the TE model, the barrier height increased and the ideal factor decreased with the increasing of temperature from 180 K to 300 K, which can be interpreted by the lateral inhomogeneities of schottky barrier height. Combined with the single gauss distribution function of barrier height, the lateral inhomogeneities distribution of barrier height at the interface was confirmed. By DLTS measurement, one electron trap centers were observed at the interface.

Determination of current transport characteristics in Au-Cu/CuO/n-Si Schottky diodes

In this study, the material properties of CuO thin films fabricated by sputtering technique and electrical properties of CuO/n-Si structure were reported. Temperature-dependent current-voltage (I-V) measurement was carried out to determine the detail electrical characteristics of this structure. The anomaly in thermionic emission (TE) model related to barrier height inhomogeneity at the interface was obtained from the forward bias I-V analysis. The current transport mechanism at the junction was determined under the assumption of TE with Gaussian distribution of barrier height. In this analysis, standard deviation and mean zero bias barrier height were evaluated as 0.176 and 1.48 eV, respectively. Depending on the change in the diode parameters with temperature, Richardson constant was recalculated as 110.20 Acm−2K−2 with the help of modified Richardson plot. In addition, density of states at the interface were determined by using the forward bias I-V results.

Gaussian distribution of inhomogeneous barrier height in nanocrystalline graphite (NCG)/p-Si Schottky diodes

Schottky characteristics of nanocrystalline graphite/p-Si junction were investigated using current–voltage measurements at various temperatures between 298 and 473 K. Using the thermionic emission theory, the extracted ideality factor reduces by 77% while Schottky barrier height increases by 46% with increasing temperature. The initial obtained value of Richardson constant, A* from this device was 7.92 × 10−10 A cm−2 K−2. This value is far smaller than the theoretical value of 32 A cm−2 K−2 for p-Si which indicates inhomogeneity of a barrier height at the device interface. The Gaussian distribution plot was employed to explain the barrier height inhomogeneity, which gives the mean barrier height and standard deviation of 1.23 eV and 0.19 eV, respectively. By including the Gaussian distribution, the analysis of a modified Richardson plot gives a mean barrier height of 1.25 eV and a Richardson constant of 31.09 A cm−2 K−2, which are close to the theoretical values.

Structural and electrical properties of heteroepitaxial (111)Fe3O4/(0001)GaN Schottky junction

We investigated the structural and electrical properties of the half-metallic oxide Fe3O4 film grown on an n-type semiconducting gallium nitride GaN. X-ray diffraction and transmission electron microscopy analyses confirmed the heteroepitaxial growth of the (111) Fe3O4 film on (0001) GaN with a clear interface. The current–voltage measurement for the Fe3O4/GaN heterojunction indicated a strong temperature dependence of the Schottky diode behavior. At room temperature, the Fe3O4/GaN heterojunction exhibited a weak diode-like behavior for the bias-voltage sweep. However, as the temperature decreased from room temperature to 30 K, the current in negative-bias voltages decreased significantly, but its change in the positive bias regions was small. Thus, the rectification ratio increased by ∼104 times, while the barrier height decreased and the ideality factor increased. The barrier height inhomogeneities at the interface could be an origin for such distinctive temperature dependences of barrier height and ideality factor.

Hole trap, leakage current and barrier inhomogeneity in (Pt/Au)[sbnd]Al0.2Ga0.8N/GaN heterostructures

In this work, we report on the electrical characteristics of Pt/Au Schottky contacts to Al0.2Ga0.8N/GaN heterostructures. Indeed, we have realized gate current-voltage I(V) and deep level transient spectroscopy (DLTS) measurements. The behavior study of series resistance RS, ideality factor n, the effective barrier height Фb and leakage current with the temperature have emphasize barrier height inhomogeneity and extended defect in the (Pt/Au)Al0.2Ga0.8N/GaN system. The abnormal behavior of all these parameters can be attributed to the presence of traps thermally activated. Using the DLTS technique, we have detected one hole trap having an activation energy of 0.28eV and a capture cross-section of 1.9 × 10−19cm2. This trap should be a threading dislocation extending from the GaN layer to the surface.

<italic>In Situ</italic> Study of Radiation Stability and Associated Conduction Mechanisms of Nb-Doped TiO2/p-Si Heterojunction Diode Under Swift Heavy Ion Irradiation

In situ current–voltage characteristics of Nb-doped TiO2/p-Si-based heterojunction diode have been studied under dense electronic excitations of 84-MeV Si6+ ions. The diode parameters such as ideality factor ( $\eta $ ), barrier height ( $\phi _{B}$ ), reverse saturation current ( ${J}_{s}$ ), and series resistance ( ${R}_{s}$ ) are found to be a strong function of ion irradiation fluence. The observed anomalies of fluence dependence of barrier height and ideality factor are explained in terms of irradiation-induced created defects complexes, modification of interface states and structural properties of Nb-doped TiO2 (NTO) layer. Several mechanisms such as barrier height inhomogeneity, donor defects-induced enchantment in n-NTO layer conductivity, and various current conduction mechanisms involved at different voltage ranges are discussed as a function of fluence with the help of constructed energy band diagram. Such in situ studies on n-NTO/p-Si heterojunction diode under radiation harsh environment are very appropriate for the better understanding of heterojunction interface properties and make it suitable for use in aerospace industry and nuclear reactors.

Temperature dependence of electrical properties in $$\hbox {In/Cu}_{{2}}\hbox {ZnSnTe}_{{4}}\hbox {/Si/Ag diodes}$$ In/Cu 2 ZnSnTe 4 /Si/Ag diodes

\(\hbox {Cu}_{{2}}\hbox {ZnSnTe}_{4}\) (CZTTe) thin films with In metal contact were deposited by thermal evaporation on monocrystalline n-type Si wafers with Ag ohmic contact to investigate the device characteristics of an In/CZTTe/Si/Ag diode. The variation in electrical characteristics of the diode was analysed by carrying out current–voltage (I–V) measurements in the temperature range of 220–360 K. The forward bias I–V behaviour was modelled according to the thermionic emission (TE) theory to obtain main diode parameters. In addition, the experimental data were detailed by taking into account the presence of an interfacial layer and possible dominant current transport mechanisms were studied under analysis of ideality factor, n. Strong effects of temperature were observed on zero-bias barrier height \((\Phi _{\mathrm{B}0} )\) and n values due to barrier height inhomogeneity at the interface. The anomaly observed in the analysis of TE was modelled by Gaussian distribution (GD) of barrier heights with 0.844 eV mean barrier height and 0.132 V standard deviation. According to the Tung’s theoretical approach, a linear correlation between \(\Phi _{\mathrm{B}0} \) and n cannot be satisfied, and thus the modified Richardson plot was used to determine Richardson constant \((A^{*})\). As a result, \(A^{*}\) was calculated approximately as \(120.6\hbox { A cm}^{-2}~\hbox {K}^{-2}\) very close to the theoretical value for n-Si. In addition, the effects of series resistance \((R_{\mathrm{s}} )\) by estimating from Cheng’s function and density of surface states \((N_{\mathrm{ss}} )\) by taking the bias dependence of effective barrier height, were discussed.

A vertical optimization method for a simultaneous extraction of the five parameters characterizing the barrier height in the Mo/4H–SiC Schottky contact

The temperature dependence of the parameters related to the barrier height inhomogeneities for Mo/4H–SiC Schottky diode in 298–498 K temperature range has been investigated. Due to the barrier height inhomogeneities that prevail at the interface of the Schottky diode, a Gaussian distribution of the barrier height is assumed. We have extracted simultaneously, for every temperature, all the parameters characterizing the barrier height such as the mean barrier height $$ \bar{\phi }_{{{\text{B}}0}} $$ , the coefficients ρ2, ρ3 quantifying the deformation of the barrier height, the corresponding temperature T0 modeling the divergence of the ideality factor n from the unity, the standard deviation of the Gaussian distribution of the barrier σs and also the series resistance Rs using a vertical optimization process on the current without any graphical extraction about ρ2, ρ3, $$ \bar{\phi }_{{{\text{B}}0}} $$ , σs and Rs. The extracted parameters like ( $$ \bar{\phi }_{{{\text{B}}0}} $$ , ρ2, ρ3, σs, Rs) were found to be a temperature dependent. Moreover, an excellent agreement was obtained between the I–V–T plots calculated with the extracted parameters using a vertical optimization process with the experimental one.

Oxidized Metal Schottky Contacts on (010) <inline-formula> <tex-math notation="LaTeX">$\beta$ </tex-math> </inline-formula>-Ga2O3

Oxidized Ir, Pd, Pt, Ag and Au Schottky contacts (SCs) were fabricated on (010) β-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> single crystal substrates via reactive RF sputtering using an O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> : Ar plasma. The use of in situ oxidizing conditions resulted in SCs with very high rectifying barriers in excess of 2.0 eV for all the metals investigated, representing an increase of 0.4-0.9 eV compared with the corresponding plain metal versions. Both the plain and oxidized metal SCs showed evidence of Fermi level pinning with their laterally homogeneous barrier heights lying in narrow ranges of ~1.3-1.5 eV and ~2.2-2.4 eV, respectively, with little correlation with metal work function. This was attributed to the influence of metal-induced oxygen vacancies and gap states at the SC interface, respectively. The very high barriers of the oxidized SCs resulted in excellent high-temperature performance with ~10 orders of magnitude of rectification at 180 °C, indicating the potential of this technique for the fabrication of high-temperature unipolar devices.

Direct comparison of plain and oxidized metal Schottky contacts on β-Ga2O3

High quality Ru, Ir, Pd, Pt, Ag, and Au Schottky contacts (SCs) were fabricated on 2¯01 β-Ga2O3 single crystal substrates via rf sputtering under inert and oxidizing plasma conditions. The oxidized SCs exhibited significantly higher rectifying barriers and, with the exception of gold oxide, significantly improved high temperature performance, with more than 12 orders of magnitude of stable rectification at 180 °C. With the exception of Ag, the image-force-corrected laterally homogeneous barrier heights of the plain metal SCs were pinned close to 1.3 eV, irrespective of the metal work function, with the Fermi level at the SC interface close to the predicted VO (2+/0) transition level of fourfold coordinated oxygen vacancies. The equivalent barrier heights of the oxidized SCs were consistently 0.5–0.8 eV higher than their plain metal counterparts, lying in the range of 1.8–2.5 eV, with the increase attributed to the passivation of interfacial oxygen vacancies and a significant increase in the work function of the oxidized metals. The highest Schottky barriers for both the plain and oxidized metal SCs involved Ag, which may be linked to the relative ease of its unintentional and intentional oxidation, respectively. The very high rectifying barriers and the thermal stability of oxidized Schottky contacts to β-Ga2O3 indicate their potential for high temperature device applications.

Analysis of current transport mechanisms in sol-gel grown Si/ZnO heterojunction diodes in high temperature environment

This paper analyzes the electrical parameters of Si/ZnO heterojunction diodes in the wide temperature range, i.e. from room temperature (298 K) to 573 K to study the electrical performance of the diode in very high temperature environment. In this work, sol-gel derived nanostructured ZnO thin film was deposited directly on p-Si substrate using spin coating technique. Electrical parameters, such as rectification ratio, reverse saturation current, ideality factor, barrier height, series resistance and activation energy are derived from current-voltage characteristics of the device, measured using semiconductor parameter analyzer in the temperature range of 298 K–573 K for bias voltage of ±5 V. The ideality factor, barrier height and series resistance is derived as 2.66, 0.789 eV and 3554 Ω respectively at 298 K, whereas at 573 K these are modified as 1.58, 1.15 eV and 801 Ω respectively. The above-mentioned results indicate the presence of spatial barrier height inhomogeneities (BHI) in high temperature environment. Hence, we have included the Gaussian distribution of spatial BHI in our analysis to calculate the effective Richardson constant (RC). Before inclusion of spatial BHI, RC was 4.026 × 10−6 Acm−2K−2. However, after inclusion of spatial BHI, RC is modified to 29.14 Acm−2K−2, which is nearer to the theoretical value (32 Acm−2K−2). Therefore, this study indicates that our as-fabricated Si/ZnO heterojunction diodes can sustain their electrical behaviour in very high temperature environment also and they are suitable for high temperature electronic and optoelectronic application.

Engineering the Palladium–WSe2 Interface Chemistry for Field Effect Transistors with High-Performance Hole Contacts

Palladium has been widely employed as a hole contact to WSe2 and has enabled, at times, the highest WSe2 transistor performance. However, there are orders of magnitude variation across the literature in Pd–WSe2 contact resistance and ION/IOFF ratios with no true understanding of how to consistently achieve high-performance contacts. In this work, WSe2 transistors with impressive ION/IOFF ratios of 106 and Pd–WSe2 Schottky diodes with near-zero variability are demonstrated utilizing Ohmic-like Pd contacts through deliberate control of the interface chemistry. The increased concentration of a PdSex intermetallic is correlated with an Ohmic band alignment and concomitant defect passivation, which further reduces the contact resistance, variability, and barrier height inhomogeneity. The lowest contact resistance occurs when a 60 min post-metallization anneal at 400 °C in forming gas (FG) is performed. X-ray photoelectron spectroscopy indicates this FG anneal produces 3× the concentration of PdSex and an Ohmic...

Analysis of temperature dependent electrical performance of Al/CuO/ITO Schottky barrier diode and explanation of inhomogeneous barrier heights by double Gaussian distribution

Here temperature dependent electrical properties of two differently synthesized CuO nanoparticles (hydrothermal (CuO (H)) and reflux (CuO (R))) based Schottky barrier diodes (SBDs) have been investigated. Both the materials based devices show an abnormal decrease in the ideality factor (η) and an increase in the barrier height (BH) with the increase in temperature. Experimentally obtained Richardson constant (A*) for both materials based devices show much lower values than the theoretical values. This discrepancy in A* due to the presence of inhomogeneities at the barrier height (BH) of metal-semiconductor (MS) interface has been analyzed by assuming double Gaussian distribution (GD) of the BHs.The mean BH values (ϕb0¯) for CuO (H) based devices obtained as 1.18eV and 1.07eV with standard deviation 0.18V and 0.15 V respectively which are less than the values of its counterpart. The obtained values of A* from the modified plot for both SBDs are in close agreement with the theoretical values. This study portrays a successful explanation of temperature dependent current-voltage characteristics of these two SBDs assuming double GD of the BHs.

Inhomogeneous barrier heights at dipole-controlled SrRuO3/Nb:SrTiO3 Schottky junctions

It has recently been shown that the Schottky barrier height (SBH) formed at metal-semiconductor perovskite oxide heterojunctions can be dramatically tuned by the insertion of atomic-scale dipole layers at the interface. However, in idealized form, this would only allow for specific values of the SBH, discretized by the dipole layer thickness. Here, we examine the effect of fractional unit cell LaAlO3 dipoles inserted between SrRuO3 and Nb:SrTiO3 in (001) Schottky junctions, as a function of their in-plane lateral distribution. When the LaAlO3 dipoles are finely dispersed, we observe uniformly rectifying junctions, with SBHs reflecting the fractional LaAlO3 coverage. For larger length-scale distributions, the junction characteristics reflect the inhomogeneous combination of regions with and without the interface dipole. The characteristic length scale dividing the two regimes corresponds to the semiconductor depletion width scaled by the dipole potential, determining the effective scale for which the SBH can be continuously tuned.

Mixed-Phase (2H and 1T) MoS2 Catalyst for a Highly Efficient and Stable Si Photocathode

We describe the direct formation of mixed-phase (1T and 2H) MoS2 layers on Si as a photocathode via atomic layer deposition (ALD) for application in the photoelectrochemical (PEC) reduction of water to hydrogen. Without typical series-metal interfaces between Si and MoS2, our p-Si/SiOx/MoS2 photocathode showed efficient and stable operation in hydrogen evolution reactions (HERs). The resulting performance could be explained by spatially genuine device architectures in three dimensions (i.e., laterally homo and vertically heterojunction structures). The ALD-grown MoS2 overlayer with the mixed-phase 1T and 2H homojunction passivates light absorber and surface states and functions as a monolithic structure for effective charge transport within MoS2. It is also beneficial in the operation of p-i-n heterojunctions with inhomogeneous barrier heights due to the presence of mixed-phase cocatalysts. The effective barrier heights reached up to 0.8 eV with optimized MoS2 thicknesses, leading to a 670 mV photovoltage enhancement without employing buried Si p-n junctions. The fast-transient behaviors via light illumination show that the mixed-phase layered chalcogenides can serve as efficient cocatalysts by depinning the Fermi levels at the interfaces. A long-term operation of ~70 h was also demonstrated in a 0.5 M H2SO4 solution.

Investigation of inhomogeneous barrier height for Au/n-type 6H-SiC Schottky diodes in a wide temperature range

Curent-Voltage (I-V) properties of Au/6H-SiC/Au Schottky diodes are investigated and results are analised dependent on temperature at 80–400 K range. Fundamental parameters such as ideality factors (n), barrier heights (Φb0), saturation currents (I0) are calculated for this diode. Also, series resistance (Rs) is calculated with different methods. Richardson curves are plotted for this structure and Richardson constant (A∗) is calculated. Results are compared with literature. Gaussian distribution is examined by using barrier inhomogeneity. Parameters belonging to Gaussian disribution are calculated and results are compared with previous studies done by different authors.

Temperature- and doping-dependent nanoscale Schottky barrier height at the Au/Nb:SrTiO3 interface

We use ballistic electron emission microscopy to investigate prototypical Au/Nb-doped SrTiO3 (NSTO) Schottky barrier diodes for different temperatures and doping levels. To this end, ultrathin Au overlayers are thermally evaporated onto TiO2-terminated NSTO single crystal substrates. We show that at room temperature, regardless of the nominal doping, rectification is controlled by a spatially inhomogeneous Schottky barrier height (SBH), which varies on a length scale of tens of nanometers according to a Gaussian distribution with a mean value of 1.29–1.34 eV and the standard deviation in the range of 80–100 meV. At lower temperatures, however, doping effects become relevant. In particular, junctions with a low Nb content of 0.01 and 0.05 wt. % show an ∼300 meV decrease in the mean SBH from room temperature to 80 K, which can be explained by an electrostatic analysis assuming a temperature-dependent dielectric permittivity for NSTO. In contrast, this model fails to predict the weaker temperature dependence of SBH for junctions based on 0.5 wt. % NSTO. Our nanoscale investigation demands to reassess conventional models for the NSTO polarizability in high-intensity electric fields. Furthermore, it contributes to the comprehension and prediction of transport in metal/SrTiO3 junctions and devices.

Current Transport and 1/f Noise Characteristics in Ferromagnetic Permalloy/n-type Ge Schottky Contacts

The current transport mechanism in permalloy/n-type Ge Schottky diodes was studied over the temperature range from 200 to 400 K. At temperatures above 250 K, the forward current-voltage (I-V) characteristics of the diode were ideal and obeyed the thermionic emission theory. Below 250 K, however, the recombination process was found to contribute to current transport. Similarly, in reverse bias, the thermionic emission mechanism appeared to dominate current transport at temperatures above 250 K, and the carrier generation mechanism dominated the reverse current below 250 K. A temperature-driven change in the current conduction mechanism from conduction dominated by low-barrier-height patches to conduction dominated by high-barrier-height regions suggests inhomogeneity in the Schottky barrier height. The barrier height inhomogeneity led to deviations in the Richardson constant from its theoretical value at lower temperatures. The room-temperature low-frequency noise measurements taken at different forward biases for the permalloy/n-type Ge Schottky diodes showed a 1/fγ dependence with a tight variation of γ between 1.20 and 1.31. The current dependence of the noise power spectral density exhibited a 1/f noise behavior, indicating the operation of the permalloy/n-type Ge Schottky diodes in the thermionic emission mode.

Analysis of barrier inhomogeneities in AuGe/n-Ge Schottky diode

The barrier inhomogeneities in AuGe/n-Ge Schottky diode have been analyzed by using current–voltage (I–V) measurements over a wide temperature range of 200 to 400 K. The electrical parameters such as ideality factor (n), zero-bias barrier height (ΦBo), and series resistance (Rs) of the diode were found to be strongly temperature dependent. The abnormal increase of the barrier height with temperature was attributed to the existence of barrier height inhomogeneities at the metal/semiconductor interface. Therefore, the conventional and modified Richardson plots were drawn to explain Gaussian distribution (GD) of barrier heights. The modified Richardson plot shows a good linearity over the temperature range. The modified Richardson constant (A*) was found to be 141.49 A cm−2 K−2, which is close to the theoretical value of 140 A cm−2 K−2 for n-Ge. Moreover, the barrier height values obtained from I–V and Norde methods are found to be in good agreement with each other.