Mean Barrier Height Research Articles

Carrier transport across PtSe2/n-type GaN heterojunction

We fabricated PtSe2/n-type GaN heterojunction diode by transferring a large-scale grown two-dimensional (2D) PtSe2 layered film onto a 3D GaN substrate. The PtSe2 film transferred onto GaN was ∼5.84-nm thick and had 11 layers with interlayer spacing of 0.52 nm. An exploration of the temperature-dependence of the current–voltage (I–V) characteristics of the PtSe2/n-type GaN heterojunction in the range 125–400 K revealed a strong dependency of the ideality factor and barrier height on measurement temperature. This indicates a presence of low- and high-barrier-height patches resembling barrier inhomogeneities along the interface. A barrier inhomogeneity analysis with a consideration for the Gaussian barrier heights distribution demonstrated the existence of a double Gaussian barrier distribution having a mean barrier height of 0.97 and 1.41 eV in low- and high-temperature regimes, respectively. An examination of the temperature-dependency of reverse leakage current indicated the dominance of variable-range hopping conduction in lower temperature region (<225 K) and Poole–Frenkel emission mechanism in higher temperature region (>250 K). The interface state density Nss of the PtSe2/n-type GaN heterojunction determined from the capacitance method was lesser than that attained from the forward I–V characteristics that can be accredited to the inhomogeneous spreading of the Nss.

Annealing temperature effect on structural, electronic features and current transport process of Au/CoPc/undoped-InP MPS-type Schottky structure

The influence of annealing on structural, electronic features and the current transport process of the Au/CoPc/undoped-InP (MPS)-type structure is explored. Raman measurements of as-deposited CoPc thin films reveal significant vibrational bands at 593 cm−1, 682 cm−1 and 1537 cm−1 assigned to C-C and C-N band stretching, showing the structural confirmation of CoPc films. The surface topology of CoPc is assessed by AFM at various annealing temperatures. The roughness of CoPc films falls with rising annealing temperature up to 200 °C and then slightly rises after annealing at 300 °C and 400 °C. The electrical features of the MPS structure are explored by the I-V method and observed good rectification nature regardless of annealing temperatures. The mean barrier heights are estimated to be 0.76 eV, 0.89 eV, 0.91 eV, 0.86 eV and 0.85 eV for as-deposited, 100 °C, 200 °C, 300 °C and 400 °C by statistical distribution analysis. Results showed that the BHs increase as annealing rises to 200 °C and decrease after annealing at 300 °C and 400 °C. The derived series resistance of the MPS structure reduces with rising annealing up to 200 °C and then rises after annealing at 300 °C and 400 °C. The acquired density of states (NSS) of the MPS structure varied with annealing temperature may be the reduction in the recombination center and the prevalence of an interfacial layer between the CoPc and InP layers. Findings suggest that the PFE governs reverse current in the lower bias region, while, the SE ruled reverse current in the higher bias region of the MPS structure irrespective of annealing temperatures.

Systematics of Coulomb barriers deduced from experimental capture cross sections and then used to predict the capture cross sections

The experimental data of capture cross sections for 220 light, medium and heavy reaction systems for formation 45≤Z≤102 compound nucleus have been analyzed using a simple formula, this formula is derived by assuming the Gaussian shape of the barrier distribution function. For each reaction, the empirical values of the barrier height, barrier radius and width of the barrier distribution were determined by fitting the experimental data. The obtained mean values of the barrier height have been used for determination of the parameters of the analytical expression in the barrier heights. One finds that the mean barrier heights calculated with analytical expression are reproduced with an accuracy of about 2 MeV. However, other frequently used potentials are systematically overestimated the empirical values, especially for heavy systems. Using analytical expression in the barrier heights can predict nicely the capture cross sections for formation superheavy nuclei at above as well as below barrier energies.

Properties of Schottky barrier diodes on heteroeptixial α-Ga2O3 thin films

Schottky barrier diodes on α−Ga2O3:Sn heteroepitaxial thin films grown by pulsed laser deposition on m-plane sapphire substrates are reported. Sets of co-planar diodes were fabricated with different metals and different deposition methods. The current rectification and effective Schottky barrier height of oxidized contacts realized by reactive sputtering significantly exceed the values of non-oxidized contacts realized by thermal evaporation or sputtering in an inert argon atmosphere. The best values obtained are rectification of about eight orders of magnitude (±2 V) and 1.3 eV effective barrier height. The current-voltage characteristics of selected non-oxidized and oxidized platinum diodes have been studied as a function of measurement temperature. The temperature dependence of the effective barrier height and the ideality factor of the diodes were fitted taking into account the lateral potential fluctuations of the barrier potential. The determined mean barrier heights and standard deviations are in the range of 1.76–2.53 and 0.2–0.33 eV, respectively, and are classified with respect to the literature and fulfill a well-established empirical correlation (Lajn’s rule) for a variety of Schottky barrier diodes on different semiconducting materials.

Electrical Behavior of Vertical Pt/Au Schottky Diodes on GaN Homoepitaxy

Schottky barrier diodes on GaN on GaN substrates are fabricated for the purpose of material and technology characterization. The epitaxial layers are grown by MOCVD. I–V measurements as a function of the temperature in the range 80–480 K show ideality factor (n) and barrier height (ϕB) variations not following a thermionic (TE) model. Consequently, barrier height fluctuations are considered. In the temperature range 280–480 K, an average barrier height of 1.31 eV with a relatively large standard deviation (σ) of 0.15 eV is extracted using this model. The n(T) variation is also analyzed in order to extract the field sensibility of 1) the mean barrier height variation (ρ2 = −0.1) and 2) the barrier height standard deviation (ρ3 = −15 mV). The corrected Richardson plot using ϕB and σ values is linear and gives a Richardson constant of 31.5 A cm−2 K−2 close to the theoretical value of 26.4 A cm−2 K−2. For a deeper understanding of ϕB fluctuation origins, micro‐Raman mapping of the epitaxial layers and deep‐level transient spectroscopy (DLTS) are used. μ‐RS mappings show compressive strain for diodes having suffered electrical breakdown. DLTS analysis shows the presence of nine levels whose signatures are extracted and nature discussed.

Electronic Properties of FLG/InP Schottky Contacts

Graphene (Gr) is of great interest in the development of new electronic, photonic, and composite materials. The physical properties of Gr can vary depending on the number of layers, and this unique property makes it a potential material for different electronic applications. In this study, few-layer graphene (FLG) film was spin-coated onto the InP semiconductor surface and the FLG/n-InP Schottky contact was produced. The properties and quality of the FLG nano-film were determined by using Raman spectroscopy. Parameters such as ideality factor, barrier height, and series resistance of Schottky contacts were calculated using current-voltage (I-V) curves. With the Gaussian distribution, the mean ideality factor of the Gr/InP contacts was found to be =1,47, and the mean barrier height values were found to be =0.68 eV. The standard deviation values were calculated as σ=0.32 for the ideality factor and σ=0.06 eV for the barrier height. In addition, the series resistance values were calculated from the Cheung functions and were found to be in agreement with the literature. Finally, the current conduction mechanisms of the Gr/n-InP structure were revealed by examining the logarithmic I-V characteristics.

The Double Gaussian Distribution of Inhomogeneous Barrier Heights in Au/NAMA/n-Si Schottky Diodes

In this work, we report the results of temperature dependent barrier properties of Au/NAMA/n-Si Schottky diode in the low temperature range of 80–330 K. The analysis results of according to thermionic emission theory showed that the barrier height decreases, and the ideality factor increases towards low temperatures, depend on the barrier height inhomogeneities. The obtained results show the presence of a double Gaussian distributions with standard deviations (σ 0) of 0.073 V and 0.18 V and mean barrier height () values of 0.595 and 1.427 eV in the change of 80–140 K and 160–330 K, respectively. Moreover, evaluation of the modified Richardson curve, the values of Richardson constant (A*) of 321.805 and 110.935 A K−2 cm−2, and mean barrier height of 0.606 and 1.422 eV were found for the low- and high-temperature regions, respectively. The A* value of 110.935 A K−2 cm−2 is close to the theoretical value of 112 A K−2 cm−2 for n-Si. These results proved that there is barrier inhomogeneity.

Ultrawide bandgap vertical β-(AlxGa1−x)2O3 Schottky barrier diodes on free-standing β-Ga2O3 substrates

Ultrawide bandgap β-(AlxGa1−x)2O3 vertical Schottky barrier diodes on (010) β-Ga2O3 substrates are demonstrated. The β-(AlxGa1−x)2O3 epilayer has an Al composition of 21% and a nominal Si doping of 2 × 1017 cm−3 grown by molecular beam epitaxy. Pt/Ti/Au has been employed as the top Schottky contact, whereas Ti/Au has been utilized as the bottom Ohmic contact. The fabricated devices show excellent rectification with a high on/off ratio of ∼109, a turn-on voltage of 1.5 V, and an on-resistance of 3.4 mΩ cm2. Temperature-dependent forward current-voltage characteristics show effective Schottky barrier height varied from 0.91 to 1.18 eV while the ideality factor from 1.8 to 1.1 with increasing temperatures, which is ascribed to the inhomogeneity of the metal/semiconductor interface. The Schottky barrier height was considered a Gaussian distribution of potential, where the extracted mean barrier height and a standard deviation at zero bias were 1.81 and 0.18 eV, respectively. A comprehensive analysis of the device leakage was performed to identify possible leakage mechanisms by studying temperature-dependent reverse current-voltage characteristics. At reverse bias, due to the large Schottky barrier height, the contributions from thermionic emission and thermionic field emission are negligible. By fitting reverse leakage currents at different temperatures, it was identified that Poole–Frenkel emission and trap-assisted tunneling are the main leakage mechanisms at high- and low-temperature regimes, respectively. Electrons can tunnel through the Schottky barrier assisted by traps at low temperatures, while they can escape these traps at high temperatures and be transported under high electric fields. This work can serve as an important reference for the future development of ultrawide bandgap β-(AlxGa1−x)2O3 power electronics, RF electronics, and ultraviolet photonics.

The effect of temperature on the electrical characteristics of Ti/n-GaAs Schottky diodes

Schottky diodes still attract researchers as they are used in various device applications. This study provides I–V characteristics of Ti/n-GaAs (80–300 K). Higher barrier height (ΦB0) values were obtained for higher temperatures, whereas the ideality factor exhibited the opposite behavior. This was associated with a barrier inhomogeneity at the Ti/GaAs interface, which has a Gaussian distribution (GD). The mean barrier height values calculated from the modified Richardson and ΦB0 - q/2 kT plots were found to be 0.584 eV and 0.575 eV in the temperature range of 80–160 K. They were found as 1.041 eV and 1.033 eV between 180 K and 300 K, respectively. The modified Richardson constant value, on the other hand, was calculated as 22.06 A cm−2 K−2 (80–160 K) and 13.167 A cm−2 K−2 (180–300 K). These values are higher than the theoretical value for n-GaAs, which is 8.16 A cm−2 K−2. This difference may stem from intense inhomogeneity at the Ti/n-GaAs interface.

The Barrier's Heights and Its Inhomogeneities on Diamond Silicon Interfaces.

In this work, the electrical parameters of the polycrystalline diamonds’ p-PCD/n-Si heterojunction were investigated using temperature-dependent current–voltage (I-V) characteristics. In the temperature range of 80–280 K, the ideality factor () and energy barrier height (φb) were found to be strongly temperature dependent. The φb increases with temperature rise, while the n value decreases. The observed dependencies are due to imperfections at the interface region of a heterojunction and the non-homogeneous distribution of the potential barrier heights. Values of the φb were calculated from I-V characteristics using the thermionic emission theory (TE). The plot of φb versus 1/2 kT revealed two distinct linear regions with different slopes in temperature regions of 80–170 K and 170–280 K. This indicates the existence of a double Gaussian distribution (DGD) in heterojunctions. Parameters such as mean barrier heights and standard deviations σ were obtained from the plots linearization and read out from intercepts and slopes. They take values = 1.06 eV, σ = 0.43 eV, respectively. The modified Richardson plot is drawn to show the linear behavior in these two temperature ranges, disclosing different values of the effective Richardson constants (A*).

Temperature dependence of electrical characteristics and interface state densities of Au/n-type Si structures with SnS doped PVC interface

In this study, the electrical properties of Au/(SnS doped PVC)/n–Si structures were investigated in detail using current/voltage (IV) data in wide temperature range (80–340 K by 20 K steps). Some of the basic electrical parameters such as ideality factor (n), saturation current (I 0), and barrier height (Φ bo ) were obtained. When these parameters were extracted using thermionic emission (TE) theory, it was found that the value of n decreases whereas Φ bo increases with increasing temperature. This result can be explained by the barrier height (BH) inhomogeneity. The observed two linear regions in the plots of Φ bo –n, Φ bo –(1/2kT)1 and (n −1–1)–(1/2kT) in temperature regions of 80–160 K and 80–340 K form an evidence to the presence of Double Gaussian distribution (DGD). Using the plot of Φ bo –(1/2kT), the values of mean BH () and standard deviation (σ S) were found as 0.486 eV and 66 mV for first region, and 0.984 eV and 139 mV for second region, respectively. Thus, the effective Richardson constant (A*) was obtained using the interception point of the modified Richardson plot for these regions as 7.013 × 10−6 A.K−2cm−2 and 88.12 A.K−2cm−2, respectively. It is clear that A* value for second region is closer to theoretical value (=112 A.K−2cm−2 for n–Si). Finally, the energy dependent profile of the surface-states (Nss) was extracted using Card-Rhoderick method and Nss was found to range from ∼1012 (at 80 K) to 1013 eV−1 cm−2 (at 340 K).

Improved barrier homogeneity in Pt/Al0.75Ga0.25N Schottky barrier diodes by graphene interlayer

Pt/Al0.75Ga0.25N Schottky barrier diodes (SBDs) with graphene (w/Gr) and without graphene (w/o Gr) interlayer between metal and semiconductor were fabricated to determine the effects of Gr interlayer on the device electrical characteristics. The temperature dependent current–voltage (I–V) and capacitance–voltage (C–V) characteristics were systematically measured and comparably analyzed for both structures. The ideality factor (n) and Schottky barrier height (SBH) were determined by the thermionic emission model and barrier inhomogeneity model. The results reveal that the values of ideality factor varied from 4.25 to 2.5 for w/Gr SBDs and 6.61 to 3.19 for w/o Gr SBDs with a temperature range from 293 to 433 K. The mean barrier height and standard deviation values are 2.355 and 0.266 eV for w/Gr SBDs, while 2.128 and 0.272 eV for w/o Gr SBDs, respectively. The C–V data also shows the enhancement of the SBH for w/Gr SBDs. The results indicate a higher SBH and more barrier uniform distribution for w/Gr SBDs compared to w/o Gr SBDs, contributing to a quality improvement of Schottky contact. The insights granted by this research may pave a new pathway for improving the performance of AlGaN SBDs through Gr engineering.

Analysis of temperature dependent current-voltage characteristics of Sn/p-GaTe/In Schottky diode

In present study, Sn/p-GaTe/In Schottky diode is fabricated using thermal evaporation method. The current–voltage (I–V) measurements of Sn/p-GaTe/In diode are carried out in the temperature range of 40–300 K with the steps of 10 K under dark conditions. While the ideality factor takes values between 1.03 and 1.24 at 300–180 K temperature range, it has values between 1.30 and 5.18 at 170–40 K temperature range. It is observed that the values of ideality factor and series resistance (RS) decrease with increasing temperature. The barrier height increases due to barrier inhomogeneity with increasing temperature since the current prefers to flow through the lowest barrier height with decreasing temperature. The temperature dependence of the inhomogeneous barrier height exhibites a double-Gaussian distribution. The mean barrier height and standard deviation values calculated from the barrier height versus 1/2 kT curve are 0.68 eV and 88.9 meV for the distribution-1 (D1) and 0.36 eV and 42.2 meV for the distribution-2 (D2), respectively. The Richardson constant (A*) value is calculated to be 41.7 for D1 and 55.0 A/K2cm2 for D2 from modified Richardson plot, respectively. These values are very close to the theoretical value of 55.8 A/K2cm2 for the p-GaTe semiconductor.

Temperature dependence of electrical behaviour of inhomogeneous Ni/Au/4H–SiC Schottky diodes

Temperature dependence of electrical parameters of Ni/Au/4H–SiC Schottky diodes in a small temperature interval has been studied. Current–voltage characteristics were measured between 35 and 80 °C. I–V curves have not a linear part in semi-logarithmic plot which indicates barrier height inhomogeneity. We analyzed forward part of the I–V curves assuming Gaussian barrier height distribution and parallel connection of diode patches with different barrier heights. Using the least squares method we determined mean barrier height, standard deviation of the barrier height distribution and finally series resistance of the diode as a function of temperature. The extracted barrier height and standard deviation of the distribution decrease with increasing temperature. In contrary the series resistance of the diode increases with increasing temperature. As an interesting feature and a consequence of the series resistance increase with temperature a crossing of the I–V curves in practically the one point of the I–V curve has been observed. At this cross-point the current flowing through the diode is independent of the temperature.

General electrical characterisation of Ag/TiO2/n-InP/Au Schottky Diode

In this study Ag/TiO2/n-InP/Au structures are formed on 500 μm thick, (100) oriented n-InP semiconductor having 3.13x1018 cm-3 carrier density, by using sputtering method. TiO2 is grown as an interface with thickness of 60 Å. Some parameters of this structure are investigated in temperature range of 120- 360 K. It is noticed that there are two linear regions in forward bias current-voltage (I-V) plot. These two regions are called as LBR (low bias region) and MBR(middle bias region). Richardson coefficient is determined and mean barrier height is calculated with double Gaussian distribution.

Realization of highly rectifying Schottky barrier diodes and pn heterojunctions on κ-Ga2O3 by overcoming the conductivity anisotropy

Novel devices based on orthorhombic κ-Ga2O3 could enable solar blind infrared detection or high-electron mobility transistors with large two-dimensional electron gas densities. Here, we report on the current transport parallel to the growth direction of κ-Ga2O3 layers grown by pulsed-laser deposition on highly conductive Al-doped ZnO back contact layers. Besides ohmic Ti/Al/Au contact layer stacks, vertical Pt/PtOx/κ-Ga2O3 and Pd/PdOx/κ-Ga2O3 Schottky barrier diodes and NiO/κ-Ga2O3 and ZnCo2O4/κ-Ga2O3 pn-heterodiodes are investigated by current–voltage measurements. While a lateral current transport is severely suppressed to less than 10−9Acm−2 due to rotational domains, we record a significant current flow through the ohmic contacts in the vertical direction of &amp;gt;0.1Acm−2. The Schottky barrier diodes and the pn-heterojunctions exhibit rectification ratios of up to seven orders of magnitude. Room temperature current–voltage characteristics of diode ensembles as well as temperature-dependent measurements for selected Pt-based diodes reveal a mean barrier height of ϕBm≈2.1eV and ideality factors down to η≈1.3.

The structural and optical properties of GO: Temperature-dependent analysis of the electrical properties of Al/GO/p-type Si semiconductor structures

A spin-coating process has been used to generate graphene oxide (GO) thin films on p-type silicon. The temperature-dependent basic electrical characteristics of Al/GO/p-type Si metal–semiconductor structures have been examined through current–voltage (I–V) measurements in the temperature range 80–420 K by increments of 20 K based on thermionic emission (TE) theory. At each temperature, the main electrical parameters, such as ideality factor (n), rectification ratio (RR), saturation current (I0), barrier height (Φbo), and series resistance (RS), were determined. With increasing temperature, the values of n, I0, RR, and RS decreased, whereas the value of Φbo increased. These unusual temperature fluctuations in Φbo and n may be rationalized in terms of twofold Gaussian distributions at 80–200 K and 220–420 K. For the high- and low-temperature regions, evaluation of these two Gaussian distributions of the I–V curves for the Al/GO/p-type Si structure yielded mean barrier heights of 1.676 and 0.555 eV with standard deviations (σ0) of 166 mV and 76 mV, respectively. Modified ln(I0/T2)−(q2σs2)/(2k2T2) vs. q/(kT) plots, which correspond to these two separate temperature regions, further corroborated these barrier height values. The value of the Richardson constant (A*), 3.567 × 10−6 A K−2 cm−2, is substantially lower than the known value for p-Si. However, for the distribution in the 220–420 K region, the Richardson constant of 48.069 A K−2 cm−2 is near to the known theoretical value of 32 A K−2 cm−2 for p-type Si.

Au–Ag binary alloys on n-GaAs substrates and effect of work functions on Schottky barrier height

In this study, I investigated the effect of work function (ϕm) of AuxAg1−x (x = 0, 0.22, 0.37, 0.71 and 1) on the Au–Ag/n-GaAs Schottky diode (SD) parameters. Ag, Au metals and three alloys with different compositions deposited on n-GaAs substrates by the thermal evaporation method. Surface morphologies of the samples were investigated by an atomic force microscope (AFM). Elemental compositions of Schottky contact metals were conducted by energy dispersive X-ray spectroscopy (EDX). Current–voltage (I–V) and capacitance–voltage (C–V) measurements were performed at room temperature. SD parameters such as barrier height (Φb0), ideality factor (n), series resistance (Rs), and interface state density (Dit) of the SD’s were calculated from the obtained I–V and C–V data. Experimental results showed that all calculated SD parameters depend on the alloy composition. The lowest mean barrier height value was found as 0.789 ± 0.022 eV for Au/n-GaAs SDs and the highest value was determined 0.847 ± 0.008 eV for Au0.71Ag0.29/n-GaAs SDs from I–V measurements. Weak dependencies of barrier height to ϕm existed and gap state parameter (S) determined as 0.0526. The S value was close to the Bardeen limit (S = 0) and indicates that the Fermi level was strongly pinned in Au–Ag/n-GaAs SDs. Also, main SD parameters like series resistance (Rs), ideality factor (n), reverse bias barrier height (ΦbRB), doping density (Nd) and density of interface states (Dit) were calculated via using different methods from I–V and C–V measurement results. Also, to determine the leakage current mechanism Poole–Frenkel emission (PFE) and Schottky emission (SE) models applied on reverse bias I–V data.

Temperature-dependent interface barrier behavior in MoS2/n-GaN 2D/3D heterojunction

We fabricated MoS2/n-type GaN 2D/3D heterojunction diode, investigated its structural properties and temperature-dependent current–voltage (I–V) characteristics. The MoS2 2D film on GaN is 5.2-nm-thick with ~ 0.64 nm interlayer distance. The Barrier height and ideality factor of the MoS2/n-type GaN heterojunction increase and decrease, respectively with rising temperature, associated with the barrier height inhomogeneities. The barrier height inhomogeneity evaluation considering the Gaussian distribution of barrier heights indicate the presence of double Gaussian barrier distribution with mean barrier heights of 0.95 and 1.44 eV and standard deviations of 0.11 and 0.18 eV in the temperature range of 125–225 and 225–400 K, respectively. Reverse current showed an electric field dependence with the carrier transport dominated by Poole-Frenkel emission irrespective of the temperature.

Effect of Temperature on the Electrical and Current Transport Properties of Au/Nd2O3/n-GaN Metal/Interlayer/Semiconductor (MIS) Junction

The Au/Nd2O3/n-type GaN metal/interlayer/semiconductor (MIS) junctions were fabricated with high-k rare-earth oxide interlayer and explored its electrical properties in the wide temperature range of 150–400 K. An anomalous decrease in barrier height and an increase in the ideality factor with a decrease in the temperature were observed. The anomalous barrier height and ideality factor are ascribed to a role of barrier inhomogeneities at the interface of MIS junction assuming a double Gaussian distribution of barrier heights in the temperature ranges of 150–225 K and 225–400 K. Double Gaussian distribution giving mean barrier heights of 0.84 eV and 1.23 eV and standard deviations of 0.0085 V and 0.0187 V for the two temperature regions. A modified conventional energy plot gives mean barrier height $$\left( {\overline{\Phi }_{bo} } \right)$$ and Richardson constant (A*) as 0. eV and 13.44 Acm−2 K−2 (150–225 K) and 1.23 eV and 22.85 Acm−2 K−2 (250–400 K), respectively. The estimated A* value in the temperature range of 250–400 K was closely matched with the theoretical value of n-type GaN. Moreover, results express that the obtained interface state density of the MIS junction decreases with increasing temperature. Results explained that the reverse current conduction governed by Poole–Frenkel emission at the temperature range of 150–225 K and Schottky emission at 250–400 K, respectively.