Effective Barrier Height Research Articles

Au-MoS2 contacts: Quantum transport simulations using a continuum description

We present a novel method of modeling the contact between a metal and a two-dimensional semiconductor. Using Au on MoS2 as an example, we self-consistently solve the Schrödinger and Poisson equations and obtain the charge density in the contact. We consider open boundary conditions using the quantum transmitting boundary method and model the electron current through the contact region. We then investigate the effect of effective Schottky barrier height, electrostatic doping, and length of the overlap region on the contact resistance in a top contact geometry. By using data from experiments or from ab initio calculations for the fitting of parameters, such as the effective Schottky barrier height, the model can be used to efficiently obtain the contact resistance and, therefore, the quality of the contact. Furthermore, we investigate the effect of sampling of the Brillouin zone in the transverse direction on the numerical calculation of key quantities, such as contact resistance and free charge density. Additionally, we show that the boundary conditions applied to the Poisson equation during the calculation of the free charge density have a significant impact on the calculated contact resistance and that the impact is more pronounced in heterostructures with a larger Schottky barrier. We found that the contact resistance may be significantly underestimated, by up to one order of magnitude, when the height of the simulation domain is not large enough.

Carrier transport mechanism of Mg/Pt/Au Ohmic contact on p-GaN/AlGaN/GaN platform with ultra-low resistivity

In this work, the carrier transport mechanism of Mg/Pt/Au Ohmic contact on p-GaN/AlGaN/GaN with a very low specific contact resistivity of 1.98 × 10−5 Ω cm2 is investigated. Secondary ion mass spectroscopy measurement results show that the Mg concentration near the p-GaN surface increases form 8 × 1019 to 7 × 1020/cm3 for Mg/Pt/Au contact after annealing. It indicates that Mg atoms from the Mg/Pt/Au metal stack diffuse into the p-GaN during annealing, forming a heavily Mg doped p++-GaN layer with a depth of about 3 nm. The sheet resistance Rsh depends on temperature for Mg/Pt/Au contacts on p-GaN/GaN, indicating that the influence of 2DHG on carrier transport mechanisms at the metal/p-GaN interface was eliminated. For Mg/Pt/Au contacts at ≥360 K, specific contact resistivity reasonably follows T−1, which indicates that the band conduction of Schottky theory dominates the carrier transport. For Mg/Pt/Au contacts at 200–360 K, the electrical resistivity reasonably follows T−1/4, indicating variable-range hopping (VRH) conduction through Mg-related deep-level defects (DLD). Based on the VRH conduction model, the effective barrier height (qφ) of the Mg-related DLD band is extracted as 0.265 eV, which well matches the excellent Ohmic contact.

Resonant Tunneling Effects on the Double‐Barrier Electron Blocking Layer of a Nitride Deep‐UV Light‐Emitting Diode

The multi‐quantum‐barrier electron blocking layer (EBL) is reported to significantly improve efficiency by nearly 3 times over a single barrier in deep‐UV AlGaN light‐emitting diodes to deal with electron leakage. The improvement is usually attributed to the enhanced effective barrier height, and this article aims to explore the benefits of the tunneling effect by calculating the tunneling currents of electrons and holes through an Al0.6Ga0.4N/AlyGa1−yN double‐barrier EBL under external bias from opposite directions. The results show that the tunneling current for holes Jh is several orders of magnitude higher than that of the electrons Je as the barriers are with Al mole fraction y greater than 0.75 and thickness larger than 2 nm, which promises effective hole injection by tunneling without much electron leakage. Tunneling mechanism works better in EBL with higher and thicker barriers because the tunneling coefficients of light hole drop much slower than electrons due to its small effective mass. A proper distance between the barriers is needed to avoid electron leakage while holes tunnel through the EBL. Built‐in electric fields tilt the band to enlarge the peak‐to‐valley ratio. This work indicates that the tunneling effect substantially facilitates a multibarrier EBL to enhance carrier‐injection efficiency.

Voltage-margin limiting mechanisms of AlScN-based HEMTs

In this work, the off-state characteristics of AlScN/GaN high electron mobility transistors (HEMTs) grown by metalorganic chemical vapor deposition (MOCVD) were studied and directly compared to an AlGaN- and an AlN-HEMT grown in the same MOCVD. Pinch-off instability and leaky capacitive measurements were observed for AlScN-based HEMTs, which was correlated with a higher ideality factor and lower effective potential barrier height than the AlGaN and AlN-HEMTs. However, the reverse bias characteristics exhibited a sudden drain-current increase without a significant increase in gate-leakage current. The drain-leakage current is assumed to be related to a parasitic channel across the AlScN-barrier as a result of trap-assisted carrier transport with a Poole–Frenkel characteristic. The demonstrated pinch-off instability led to significant gain expansion in load-pull measurements and early soft-breakdown, which, in turn, limits the achievable voltage-margin. The results demonstrate a key issue to reveal the full potential of AlScN-based HEMTs for mm-wave applications.

Effect of CuO doping on the performance of LaB6 interlayer films in Al/CuO:LaB6/p-Si/Al diodes

This study investigates the fabrication and performance analysis of Al/CuO:LaB6/p-Si/Al diodes with CuO-doped LaB6 interlayer films of varying concentrations (1%, 5%, and 10%). Experimental evidence demonstrates the limitations of 0% CuO doping, as pure LaB6 lacks a significant barrier height, resulting in ohmic behavior unsuitable for intended applications. Through comprehensive analyses under varying illuminations (20–100 mW/cm2) and frequencies (10 kHz–1 MHz), the study reveals that controlling CuO doping in LaB6 significantly enhances the effective barrier height at the LaB6:CuO heterojunction, improving rectification properties. This enhancement enables the diode to be well-suited for high-speed photonic devices utilizing one-step photoemission. The findings contribute to the development of high-performance LaB6-based devices, advancing photonic technologies by emphasizing the advantages of CuO doping.

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.

Effects of active noise on transition-path dynamics

We propose an extension of the existing model describing a biomolecular reaction such as protein folding or ligand binding which is usually visualised as the barrier crossing of a diffusing particle in a double-well potential. In addition to the thermal noise, an active noise modelled in terms of an Ornstein–Uhlenbeck process is introduced to the dynamics. Within this framework, we investigate the transition-path properties of an underdamped particle surmounting an energy barrier, and we show explicitly how these properties are affected by the activity and persistence of the particle. Our theoretical study suggests that an active particle can cross the barrier at comparatively shorter timescales by lowering the (effective) barrier height. In particular, we study how the persistence time of the active force alters the transition-path time (TPT) at different friction limits. Interestingly, in one of our models we find a nonmonotonic behaviour of the TPT which is absent in the overdamped limit. The framework presented here can be useful in designing a reaction in a non-equilibrium environment, particularly inside a living biological cell in which active fluctuations keep the system out of equilibrium.

Collision of two interacting electrons on a mesoscopic beam splitter: Exact solution in the classical limit

Experiments on collisions of isolated electrons guided along the edges in quantum Hall setups can mimic mixing of photons with the important distinction that electrons are charged fermions. In the so-called electronic Hong-Ou-Mandel (HOM) setup uncorrelated pairs of electrons are injected towards a beamsplitter. If the two electron wave packets were identical, Fermi statistics would force the electrons to scatter to different detectors, yet this quantum antibunching may be confounded by Coulomb repulsion. Here we model an electronic HOM experiment using a quadratic 2D saddle point potential for the beamsplitter and unscreened Coulomb interaction between the two injected electrons subjected to a strong out-of-plane magnetic field. We show that classical equations of motion for the drift dynamics of electrons' guiding centers take on the form of Hamilton equations for canonically conjugated variables subject to the saddle point potential and the Coulomb potential where the dynamics of the center-of-mass coordinate and the relative coordinate separate. We use these equations to determine collision outcomes in terms of a few experimentally tuneable parameters: the initial energies of the uncorrelated electrons, relative time delay of injection and the shape of the saddle point potential. A universal phase diagram of deterministic bunching and antibunching scattering outcomes is presented with a single energy scale characterizing the increase of the effective barrier height due to interaction of coincident electrons. We suggest clear-cut experimental strategies to detect the predicted effects and give analytical estimates of conditions when the classical dynamics is expected to dominate over quantum effects.

Gate leakage mechanisms of the AlGaN/GaN HEMT with fluorinated graphene passivation

The AlGaN/GaN high-electron-mobility transistor (HEMT) passivated by fluorinated graphene (FG) has been investigated. The performances of the HEMTs without passivation before and after F plasma treatment, with FG, Silicon nitride (SiNx), FG/SiNx passivation were contrasted. Compared with the HEMT without F plasma treatment and passivation, the gate leakage current decreases one and a half orders of magnitude after F plasma treatment and SiNx passivated, and four orders of magnitude after FG and FG/SiNx passivated. To study the leakage mechanisms, the temperature dependences of gate leakages have been tested at 323 K–473 K. Through analysis and fitting, the leakages are composed of three components, which are thermionic emission (TE) current, two-dimensional variable range hopping (2D-VRH) current, and Fowler–Nordheim tunneling (FNT) current. TE dominates in the high forward bias region. 2D-VRH dominates in low forward bias. And the chief leakage mechanisms at reverse bias are 2D-VRH and FNT. At 473 K, Schottky barrier height of the HEMT with FG passivation is 1.21 eV. The activation energy and the effective barrier height on the HEMT with FG passivation are 0.64 eV and 0.33 eV respectively. Furthermore, the reasons for the decrement of the gate leakage on the HEMT with FG and FG/SiNx passivation are the enhancement of Schottky barrier heights and augmentation of activation energy. And the improvement in gate leakages for the HEMT passivated by FG/SiNx mainly results from the effect of FG.

Barrier Modification by Methyl Violet Organic Dye Molecules of Ag/P-Inp Structures

Abstract This work includes fabrication and electrical characterization of Metal/Interlayer/Semiconductor (MIS) structures with methyl violet organic film on p-InP wafer. Metal(Ag)/ Interlayer (methyl violet =MV)/Semiconductor(p-InP) MIS structure presents a rectifying contact behavior. The values of ideality factor (n) and barrier height (BH) for the Ag/MV/p-InP MIS diode by using the current-voltage (I-V) measurement have been extracted as 1.21 and 0.84 eV, respectively. It was seen that the BH value of 0.84 eV calculated for the Ag/MV/p-InP MIS structure was significantly higher than the value of 0.64 eV of Ag/p-InP control contact. This situation was ascribed to the fact that the MV organic interlayer increased the effective barrier height by influencing the space charge region of inorganic semiconductor. The values of diffusion potential and barrier height for the Ag/MV/p-InP MIS diode by using the capacitance-voltage (C-V) measurement have been extracted as 1.21 V and 0.84 eV, respectively. The interface-state density of the Ag/MV/p-InP structure was seen to change from 2.57×1013 eV-1cm-2 to 2.19×1012 eV-1cm-2.

Extremely high frequency Schottky diodes based on single GaN nanowires

Gallium nitride (GaN) is one of the most promising materials for high-frequency devices owing to its prominent material properties. We report on the fabrication and study of a series of Schottky diodes in the ground-signal-ground topology based on individual GaN nanowires. The electrical characterization of I–V curves demonstrated relatively high ideality factor value (about 6–9) in comparison to the planar Au/GaN diodes that can be attributed to the nanowire geometry. The effective barrier height in the studied structures was defined in the range of 0.25–0.4 eV. The small-signal frequency analysis was employed to study the dependency of the scattering parameters in the broad range from 0.1 to 40 GHz. The approximation fitting of the experimental data indicated the record high cutoff frequency of about 165.8 GHz.

Interfacial properties of In-plane monolayer 2H-MoTe2/1T'-WTe2 heterostructures

One of the most appealing aspects of the two-dimensional transition-metal dichalcogenides (2D-TMDs) is that they have a variety of crystal types, which can exist in three different atomic lattices, 2H, 1 T and 1 T', and can therefore exhibit diverse electronic properties. In addition, 2D-TMD heterostructures with distinctive features can be generated by combining two monolayers either vertically or laterally (in-plane). In this work, we used first-principles calculations to explore the structural and electronic properties of the H-phase MoTe2 monolayer, the T'-phase WTe2 monolayer, and their in-plane heterostructures (H-MoTe2/T'-WTe2). The H-phase MoTe2 monolayer has a band structure with a direct band gap, whereas the 1 T'-WTe2 monolayer is projected to be a Weyl semimetal based on our findings. We constructed a series of five relatively stable in-plane H-MoTe2/T'-WTe2 heterostructures with metal–semiconductor and studied their electronic properties. The band structures of these in-plane heterostructures were shown to be strongly related to the relative orientations of the monolayers at the interface. In particular, the band gaps of the heterostructures joined along the armchair direction were found to be smaller than 0.1 eV. By sewing the MoTe2 and WTe2 monolayers along the zigzag direction, two relatively stable structures were created, with according to the band structure analysis, exhibited metallic characteristics. Surprisingly, band inversion appeared near the Fermi level due to boundary effects. Therefore, topological properties may be present in such in-plane heterostructures. Moreover, some of these in-plane H-MoTe2/T'-WTe2 heterostructures have effective Schottky barrier heights smaller than 0.25 eV for holes, and could thus be used to construct field effect transistors (FETs). We also found that the effective Schottky barrier height was largely determined by the interfacial bonding environment, the external electric field, and uniaxial strains. Our findings enrich the diversity of the 2D-TMDs heterostructures and point to a viable approach for the design of high-performance electronic and optoelectronic devices.

Effect of perylenetetracarboxylic dianhydride on the main electrical properties and interface states of Al/p-Si structures

In this our study, we were examined role on the electrical characteristics and interface state densities of Al/p-type Si metal semiconductor (MS) structures of perylenetetracarboxylic dianhydride (PTCDA) used at the interface as a thin film layer. The PTCDA thin film layer was coated on p-type Si by Spin Coating method. The main electrical characteristics such as ideality factors (n), barrier height (Φbo), series resistances (RS), and interface states of Al/p-type Si and Al/PTCDA/p-type Si devices were calculated using current–voltage (I–V) and capacitance–voltage (C–V) characteristics at the room temperature. The values of n, Φbo, RS which basic electrical parameters were calculated and compared with each other using different calculation methods such as Cheung and Norde methods. Additionally, the interface state densities (NSS) as a function of energy distributions (ESS-EV) were calculated from the I–V measurements by accounting for the bias dependence of the effective barrier heights (Φe) and ideality factor n(V). The experimental results showed that while the evaluated values of NSS has increased exponentially from 1.56x1015 cm−2eV−1 in (0.730- EV) eV to 3.09x1015 cm−2eV−1 in (0.501- EV) eV for Al/p-Si Structure, the NSS has increased exponentially with bias from of 2.05x1015 cm−2eV−1 to 6.50x1015 cm−2eV−1 for Al/PTCDA/p-Si structure in the same interval. As conclusions, we can say that PTCDA thin film layer play important roles on the electrical characteristics and interface state densities of metal semiconductor (MS) structures such as Al/p-type Si.

Vertical Nonvolatile Schottky‐Barrier‐Field‐Effect Transistor with Self‐Gating Semimetal Contact

AbstractEmerging 2D nonvolatile Schottky‐barrier‐field‐effect transistors (NSBFETs) are envisaged to build a promising reconfigurable in‐memory architecture to mimic the brain. Herein, a vertically stacked multilayered graphene (MGr)‐molybdenum disufide (MoS2)‐tungsten ditelluride (WTe2) NSBFET is reported. The semimetal WTe2 with the charge‐trapping effect enables the simultaneous integration of the electrode and the self‐gating function. The effective Schottky barrier height offset ΔΦB is programed from ΔΦB‐p = 132.6 meV to ΔΦB‐n = 109.4 meV, inducing the reversed built‐in electric field to make the NSBFET, so as to provide one with a multifunctional platform to integrate the nonvolatility and the reconfigurable self‐powered photo response. The reversible open‐circuit voltages of NSBFET synapse are programmed from −0.1 to 0.25 V and the self‐powered responsivity with reversed signs is tuned from 290 to −50 mA W−1, which enables the representation of a signed weight in a single device to enrich multiple optical sensing and computing capabilities.

Theoretical analysis of tunneling current in 4H-SiC Schottky barrier diodes under reverse-biased conditions based on the complex band structure

The tunneling current in heavily doped 4H-SiC Schottky barrier diodes under reverse-biased conditions is calculated based on the complex band structure by the empirical pseudopotential method. When the experimental values for effective mass and barrier height are assumed, the calculation result by the approximation assuming a parabolic complex band significantly underestimates the experimental tunneling current. In contrast, the calculation using the non-parabolic complex band by the empirical pseudopotential method we propose in this study reproduces the experimental result with better accuracy. These results imply that it is important to consider the non-parabolicity of the complex bands when calculating the tunneling current.

Ultrasensitive Strain Sensor Based on a Tunnel Junction with an AlN/GaN Core-Shell Nanowire

Piezotronic transistor operating in the quantum tunneling regime has recently roused wide interest for developing ultrasensitive strain sensing with applications in wearable electronics and human-machine interfaces. However, the lack of a strict theoretical demonstration from a quantum perspective renders the development of such an emerging area particularly slow due to their complex fabrication process and vulnerable experimental interference. Here, by combining third-dimensional self-consistent calculation with a nonequilibrium Green's function framework, we study the intrinsic device properties of piezotronic tunneling transistor (PTT) based on $\mathrm{Al}\mathrm{N}/\mathrm{Ga}\mathrm{N}$ core-shell nanowire. The results show that strain-induced piezoelectric polarization can remarkably tune tunneling barrier height and width, both of which are increased by tensile strain and decreased by compressive strain. At a moderate strain amplitude of 1.0% and bias of 2.0 V, the strain-induced change in effective barrier height and width can reach as high as 0.5 eV and 4.0 nm, respectively. This remarkable tunability in the barrier allows for an ultrahigh on/off current ratio ${10}^{17}$, and giant gauge factor 1.2 \ifmmode\times\else\texttimes\fi{} ${10}^{8}$ in current and 1.1 \ifmmode\times\else\texttimes\fi{} ${10}^{13}$ in resistance. The performance can be further optimized by properly tailoring device architectures, including insulator thickness, nanowire length, or core-shell size. Our demonstration of the PTT with combined quantum tunneling and piezotronic effect opens a window for designing highly sensitive, large on/off ratio and low-power strain sensing.

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.

All-epitaxial Al/AlGaN/GaN low-barrier Schottky diodes

All-epitaxial Al/AlxGa1−xN/GaN low-barrier Schottky diodes with different x compositions were fabricated in the single process of molecular-beam epitaxy. A decrease in the effective barrier height is achieved by polarization-induced δ-doping of the AlxGa1−xN/GaN heterojunction. At zero bias, the diodes have high values of ampere-watt sensitivity (7 A/W) with a low specific value of differential resistance (5 × 10−4 Ω⋅cm2) and retain non-linear properties when the resistance decreases to 10−4 Ω⋅cm2. The fundamental importance of the absence of impurities, oxides, and structural defects at the metal–semiconductor interface for effective control of the transport properties of diodes is demonstrated.

Schottky barrier contact on In0.53Ga0.47As with short-wave infrared transparent conductive oxide

In this study, we fabricate and investigate Schottky barrier contact on n- and p-type In0.53Ga0.47As with transparent conductive oxide (TCO) that transmits light from the visible to short-wave infrared (SWIR) region. The TCO/p-In0.53Ga0.47As contact exhibits explicit rectifying behavior in current–voltage measurement, with an effective Schottky barrier height of 0.587 eV (I–V) and 0.567 eV (C–V). Conversely, the TCO/n-In0.53Ga0.47As exhibits the Ohmic behavior. From high-resolution transmission electron microscopy observations, we identified two types of interfacial layers between TCO and InGaAs: an In/Ga-rich InGaAs oxide layer and an In/Ga-deficient InGaAs layer. These interfacial layers may have a significant impact on the performance of the Schottky barrier contact. An ultra-thin Ni-layer insertion at the TCO/n+-InGaAs interface reduces the contact resistivity by more than an order of magnitude while maintaining high transparency. The TCO/p-InGaAs Schottky barrier contact also performs broadband light detection from the visible to SWIR region in a front-side illumination manner, which is highly promising for detecting wavelengths covering the optical communication band.

Effective Schottky barrier height and interface trap density reduction engineering using 2-dimensional reduced graphene oxide interlayer for metal-interlayer-semiconductor contact structure

The contact resistance at the metal-semiconductor (MS) interface has become the foremost challenge to ensuring high performance in nanoelectronics as devices are scaled down. A metal-interlayer-semiconductor (MIS) contact structure is a promising technique for Fermi-level unpinning to overcome the issue of fundamental contact resistance. Herein, an MIS contact structure with a 2-dimensional reduced graphene oxide (rGO) interlayer is proposed as an effective source/drain contact structure. The demonstration of a metal-rGO-semiconductor MIS (rGO MIS) contact structure with different interlayer thicknesses indicated that the rGO interlayer with a thickness of a few nanometers significantly enhanced the reverse current density (JR) by ∼2.0 × 103 times compared to that of the MS contact. In addition, the effective Schottky barrier height was reduced from 0.576 to 0.205 eV. This drastic improvement is attributed to the unique properties of rGO, such as its wide band gap, electrical conductivity, and Van der Waals interface leading to a metal-induced gap state reduction, tunneling resistance lowering, and passivation effect when it is adopted as an interlayer of the MIS contact. This result demonstrates the promising potential of using rGO as an MIS interlayer, which will pave the way toward high-performance emerging nanoelectronic devices.