Increase In Barrier Height Research Articles

Temperature sensor using thermally stable TiN anode GaN Schottky barrier diode for high power device application

The characteristics of GaN Schottky barrier diodes fabricated with TiN and Ni anodes were evaluated in the temperature range from 25 to 175 °C. The Schottky barrier height (ideality factor) increases (decreases) with increasing temperature for both kinds of diodes owing to the barrier height being nonhomogeneous. The GaN diode with TiN anode presents better interface quality and thermal stability is adopted for temperature sensing application. It demonstrated that the sensitivity of the TiN diode is approximately 1 mV/K and varies only slightly for all current levels.

For high-precision bosonic Josephson junctions, many-body effects matter

Typical treatments of superconducting or superfluid Josephson junctions rely on mean-field or two-mode models; we explore many-body dynamics of an isolated, ultracold, Bose-gas long Josephson junction using time-evolving block decimation simulations. We demonstrate that with increasing repulsive interaction strength, localized dynamics emerge that influence macroscopic condensate behavior and can lead to the formation of solitons that directly oppose the symmetry of the junction. Initial state population and phase yield insight into dynamic tunneling regimes of a quasi one-dimensional double well potential, from Josephson oscillations to macroscopic-self-trapping. Population imbalance simulations reveal substantial deviation of many-body dynamics from mean-field Gross–Pitaevskii predictions, particularly as the barrier height and interaction strength increase. In addition, the sudden approximation supports localized particle–hole formation after a diabatic quench, and correlation measures unveil a new dynamic regime: the Fock flashlight.

Improvement of breakdown field and dielectric properties of CaCu3Ti4O12 ceramics by Bi and Al co-doping

Bi and Al co-doped CaCu3Ti4O12 (CCTO) ceramics with different doping concentration were fabricated by the solid-state sintering method. Great enhancements in dielectric and varistor properties of CCTO ceramic were achieved by co-doping at the concentration of 1 mol%. It is found that grain size distribution of co-doped sample is more uniform and the grain alignment is more compact. The improved morphologies could facilitate the macroscopic properties. Additionally, a relaxation peak, of activation energy at 0.39 eV, at relatively low frequency was characterized. It is likely to be originated from Cu-rich phase related defect in the grain boundary. This defect may be concomitantly aggravated by Bi and Al co-doping. The frequency dependence of the conductivity was interpreted with the Jonscher's law, indicating that the dc conduction loss at low frequency can be suppressed by additives. Comparing with the pure CCTO, the breakdown field Eb of co-doped sample at the concentration of 1 mol% was greatly enhanced from 2088 V/cm to 7839 V/cm due to the increase of Schottky barrier height (from 0.56 eV to 0.72 eV).

Formation of ZnO nanopowders by the simple ultrasound-assisted method: Exploring the dielectric and electric properties of the Au/(ZnO-PVA)/n-Si structure

ZnO nanopowders have been prepared by a simple ultrasound-assisted method, and the prepared nanopowders have been utilized for fabrication of Au/(ZnO-PVA)/n-Si structures. Size and morphology of ZnO have been studied by X-ray diffraction and scanning electron microscopy (SEM) techniques. The average nanocrystallite size of ZnO nanopowders was estimated less than 50 nm and the XRD pattern are shown in a hexagonal lattice. Its band gap was obtained from Uv–Visible absorption spectrum as 3.15 eV. Electric and dielectric parameters of MPS structures were analyzed by impedance spectroscopy technique. The measured capacitance and conductance have a strong function of frequency and voltage in depletion and accumulation regions because of the presence of interface states (Nss), series resistance (Rs), interfacial (ZnO-PVA) layer and polarization processes particularly at low frequencies. This is because the Nss and dipoles have enough time to follow external ac signal and can be turned around at low frequencies. The barrier height (ΦB) and depletion layer wides (Wd) increase linearly with increasing frequency. The voltage-dependent profile of Nss extracted from the low-high frequency capacitance process and it has two distinctive peaks due to a particular distribution of interface charges at (ZnO-PVA)/n-Si in the forbidden band-gap of Si. The dielectric constants (ε′) and dielectric loss (ε′′) values increase with decreasing frequency, however the tangent loss (tanδ), real and imaginary components of the electric modulus (M′, M′′) and electrical conductivity (σ) increase with increasing frequency. The increase of σac with increasing frequency was attributed to the increase eddies current that leads to the increase in the energy tanδ. Interestingly, the high value of ε′ (≈30) even at 1 kHz shows that the prepared ZnO-PVA nanocomposite interlayer can capability to the storage more and more charges or energy and so it can be used instead of traditional interfacial insulator layers.

An InGaN/GaN Superlattice to Enhance the Performance of Green LEDs: Exploring the Role of V-Pits.

Despite the fact that an InGaN/GaN superlattice (SL) is useful for enhancing the performance of a GaN-based light-emitting diode (LED), its role in improving the efficiency of green LEDs remains an open question. Here, we investigate the influence of a V-pits-embedded InGaN/GaN SL on optical and electrical properties of GaN-based green LEDs. We recorded a sequence of light emission properties of InGaN/GaN multiple quantum wells (MQWs) grown on a 0- and 24-pair InGaN/GaN SL by using scanning electron microscopy (SEM) in combination with a room temperature cathodoluminescence (CL) measurement, which demonstrated the presence of a potential barrier formed by the V-pits around threading dislocations (TDs). We find that an increase in V-pit diameter would lead to the increase of V-pit potential barrier height. Our experimental data suggest that a V-pits-embedded, 24-pair InGaN/GaN SL can effectively suppress the lateral diffusion of carriers into non-recombination centers. As a result, the external quantum efficiency (EQE) of green LEDs is improved by 29.6% at an injection current of 20 mA after implementing the V-pits-embedded InGaN/GaN SL layer. In addition, a lower reverse leakage current was achieved with larger V-pits.

Enhanced Performance of Ge Photodiodes via Monolithic Antireflection Texturing and α-Ge Self-Passivation by Inverse Metal-Assisted Chemical Etching.

Surface antireflection micro and nanostructures, normally formed by conventional reactive ion etching, offer advantages in photovoltaic and optoelectronic applications, including wider spectral wavelength ranges and acceptance angles. One challenge in incorporating these structures into devices is that optimal optical properties do not always translate into electrical performance due to surface damage, which significantly increases surface recombination. Here, we present a simple approach for fabricating antireflection structures, with self-passivated amorphous Ge (α-Ge) surfaces, on single crystalline Ge (c-Ge) surface using the inverse metal-assisted chemical etching technology (I-MacEtch). Vertical Schottky Ge photodiodes fabricated with surface structures involving arrays of pyramids or periodic nano-indentations show clear improvements not only in responsivity, due to enhanced optical absorption, but also in dark current. The dark current reduction is attributed to the Schottky barrier height increase and self-passivation effect of the i-MacEtch induced α-Ge layer formed on top of the c-Ge surface. The results demonstrated in this work show that MacEtch can be a viable technology for advanced light trapping and surface engineering in Ge and other semiconductor based optoelectronic devices.

Interfacial Properties of Atomic Layer Deposited Al2O3/AlN Bilayer on GaN

An Al2O3/AlN bilayer deposited on GaN by atomic layer deposition (ALD) is employed to prepare Al2O3/AlN/GaN metal-insulator-semiconductor (MIS) diodes, and their interfacial properties are investigated using X-ray photoelectron spectroscopy (XPS) with sputter etch treatment and current-voltage (I-V) measurements. XPS analyses reveal that the native oxides on the GaN surface are reduced significantly during the early ALD stage, indicating that AlN deposition effectively clelans up the GaN surface. In addition, the suppression of Al-OH bonds is observed through the ALD process. This result may be related to the improved device performance because Al-OH bonds act as interface defects. Finally, temperature dependent I-V analyses show that the barrier height increases and the ideality factor decreases with an increase in temperature, which is associated with the barrier inhomogeneity. A Modified Richardson plot produces the Richardson constant of A** as 30.45 Acm−2K−2, which is similar to the theoretical value of 26.4 Acm−2K−2 for n-GaN. This indicates that the barrier inhomogeneity appropriately explains the forward current transport across the Au/Al2O3/AlN/GaN interface.

Effects of fluorine incorporation into β-Ga2O3

β-Ga2O3 rectifiers fabricated on lightly doped epitaxial layers on bulk substrates were exposed to CF4 plasmas. This produced a significant decrease in Schottky barrier height relative to unexposed control diodes (0.68 eV compared to 1.22 eV) and degradation in ideality factor (2.95 versus 1.01 for the control diodes). High levels of F (>1022 cm−3) were detected in the near-surface region by Secondary Ion Mass Spectrometry. The diffusion of fluorine into the Ga2O3 was thermally activated with an activation energy of 1.24 eV. Subsequent annealing in the range 350–400 °C brought recovery of the diode characteristics and an increase in barrier height to a value larger than in the unexposed control diodes (1.36 eV). Approximately 70% of the initial F was removed from the Ga2O3 by 400 °C, with the surface outgas rate also being thermally activated with an activation energy of 1.23 eV. Very good fits to the experimental data were obtained by integrating physics of the outdiffusion mechanisms into the Florida Object Oriented Process Simulator code and assuming that the outgas rate from the surface was mediated through fluorine molecule formation. The fluorine molecule forward reaction rate had an activation energy of 1.24 eV, while the reversal rate of this reaction had an activation energy of 0.34 eV. The net carrier density in the drift region of the rectifiers decreased after CF4 exposure and annealing at 400 °C. The data are consistent with a model in which near-surface plasma-induced damage creates degraded Schottky barrier characteristics, but as the samples are annealed, this damage is removed, leaving the compensation effect of Si donors by F− ions. The barrier lowering and then enhancement are due to the interplay between surface defects and the chemical effects of the fluorine.

Junction properties analysis of silicon back-to-back Schottky diode with reduced graphene oxide Schottky electrodes

Reduced graphene oxide (rGO)/silicon (Si) Schottky junction possesses promising attributes for various applications such as chemical sensor and photodetector. In this paper, a fabrication of simple back-to-back rGO/Si Schottky junction structure is presented. The device was fabricated via wet processes such as vacuum filtration, patterning by delamination, wet transfer and chemical reduction by ascorbic acid. From the current-voltage measurement, series resistance, barrier height and ideality factor were investigated at different temperature. Barrier height increases and ideality factor decreases with the increase of temperature indicating the inhomogeneity of the junction interface. By considering the Gaussian distribution of barrier height, the fabricated Schottky junction was shown to possess the mean barrier height of 1.24 eV with standard deviation value of 0.16 eV. The obtained mean barrier height was larger than the bandgap of Si, indicating the presence of thin insulation layer at the interface.

Computational study of graphene‐gated graphene‐Si thin film Schottky junction field‐effect solar cell by finite difference method

AbstractModeling and simulation approaches are developed to investigate our proposed graphene‐gated graphene‐Si thin film Schottky junction field‐effect solar cell. Algorithm based on finite difference method is developed to solve the Poisson equation, drift‐diffusion equations, and current continuity equations. Charge transfer effect in the proposed solar cell is not significant due to light doping in the Si thin film. The open‐circuit voltage and short‐circuit current can be tuned by gate bias. As the magnitude of negative bias increases, both the open‐circuit voltage and short‐circuit current increase due to the increase of Schottky barrier height and depletion width. Thin oxide thickness leads to high modulation efficiency. Optimization of the solar cell is achieved by introducing back field layer to increase carrier collection efficiency.

Schottky junction interfacial properties at high temperature: A case of AgNWs embedded metal oxide/p-Si

Studying the performance limiting parameters of the Schottky device is an urgent issue, which are addressed herein by thermally stable silver nanowire (AgNW) embedded metal oxide/p-Si Schottky device. Temperature and bias dependent junction interfacial properties of AgNW-ITO/Si Schottky photoelectric device are reported. The current−voltage−temperature (I−V−T), capacitance-voltage-temperature (C−V−T) and impedance analysis have been carried out in the high-temperature region. The ideality factor and barrier height of Schottky junction are assessed using I−V−T characteristics and thermionic emission, to reveal the decrease of ideality factor and increase of barrier height by the increasing of temperature. The extracted values of laterally homogeneous Schottky (ϕb) and ideality factor (n) are approximately 0.73 eV and 1.58, respectively. Series resistance (Rs) assessed using Cheung's method and found that it decreases with the increase of temperature. A linear response of Rs of AgNW-ITO/Si Schottky junction is observed with respect to change in forward bias, i.e. dRS/dV from 0 to 0.7 V is in the range of 36.12–36.43 Ω with a rate of 1.44 Ω/V. Impedance spectroscopy is used to study the effect of bias voltage and temperature on intrinsic Schottky properties which are responsible for photoconversion efficiency. These systematic analyses are useful for the AgNWs-embedding Si solar cells or photoelectrochemical cells.

Resonant tunneling properties of inverted Morse double quantum barrier

We study resonant tunneling characteristics of inverted Morse double quantum barrier structures. The effect of electric bias and structure parameters is calculated by using non-equilibrium Green's function method. Results for the transmission coefficients are compared with the structure parameters. Our results show that the widths of the wells and heights of barriers have a significant effect on the transmission properties. We found that the resonant peak of the transmission coefficient decreases with increasing electric field bias. Moreover, resonant energy level increases with increasing barrier height and increasing width parameters.

The Analysis of Inhomogeneous Barrier Height in In/SnTe/Si/Ag Diode

SnTe thin film layer was fabricated by magnetron sputtering technique on n-Si substrate, and the electrical properties of the In/SnTe/Si/Ag diode structure was investigated by using temperature dependent forward bias current-voltage (I-V) measurements. The main diode parameters were calculated according to the thermionic emission (TE) model and they were found in an abnormal behavior with change in temperate in which zero-bias barrier height ( Φ B 0 ) increases and ideality factor ( n ) decreases with increasing temperature. Therefore, the total current flow though the junction was expressed by the Gaussian distribution (GD) of barrier height. The plot of Φ B 0 vs q 2 kT showed the existence of inhomogeneous barrier formation and evidence for the application of Gaussian function to identify the distribution of low barrier height patches. The mean barrier height was found as 1.274 with the 0.166 eV standard deviation. From the modified Richardson plot, Richardson constant was calculated as 119.5A/cm 2 K 2 in very close agreement with the reported values. Additionally, the effects of the series resistance ( R S ) were analyzed by using Cheung’s function. Distribution of the interface states ( D it ) were extracted from the I-V characteristics and found in increasing behavior with decreasing temperature.

Piezotronic Tuning of Potential Barriers in ZnO Bicrystals.

Coupling of magnetic, ferroelectric, or piezoelectric properties with charge transport at oxide interfaces provides the option to revolutionize classical electronics. Here, the modulation of electrostatic potential barriers at tailored ZnO bicrystal interfaces by stress-induced piezoelectric polarization is reported. Specimen design by epitaxial solid-state transformation allows for both optimal polarization vector alignment and tailoring of defect states at a semiconductor-semiconductor interface. Both quantities are probed by transmission electron microscopy. Consequently, uniaxial compressive stress affords a complete reduction of the potential barrier height at interfaces with head-to-head orientation of the piezoelectric polarization vectors and an increase in potential barrier height at interfaces with tail-to-tail orientation. The magnitude of this coupling between mechanical input and electrical transport opens pathways to the design of multifunctional electronic devices like strain triggered transistors, diodes, and stress sensors with feasible applications for human-computer interfacing.

Gaussian Distribution of Inhomogeneous Barrier Height of Al/ZnS/ITO Schottky Barrier Diodes

The current–voltage (I–V) measurements on Al/ZnS Schottky barrier diodes in the temperature range 303 –423 K by the step of 15 K were carried out. The forward I–V characteristics were analyzed on the basis of the thermionic emission theory. The temperature dependence I-V parameters such as ideality factor (n) and barrier height (ϕb0) have been explained on the basis of inhomogeneity. An abnormal increase of apparent barrier height and decrease of ideality factor with increasing temperature have been explained due to the barrier height inhomogeneities on the basis of the thermionic emission theory with Gaussian distribution. Experimental results reveal the existence of a single Gaussian distribution with apparent barrier height value (ϕb0‾) of 1.091 eV and standard deviations (σs) of 0.18 V. Richardson constant (A*) was obtained as 8.49 x 10-2 A.m-2K-2 from the ln(I0/T2) vs. q/kT plot, which is far from the calculated value of 5.6 x 105 A.m-2K-2. The modified Richardson plotof ln(I0/T2) – (q2σs2/2k2T2) gives ϕb0‾ and A* values as 1.093 eV and 6.07 x 105 A.m-2K-2, without using the temperature coefficient of the barrier height. This obtained value of A* is extremely close to the previously calculated value. So, the temperature dependence of the forward bias I-V characteristics of the Schottky device can be successfully explained on the basis of the thermionic emission mechanism with a single Gaussian distribution of the barrier heights.

Electronic transport in armchair graphene nanoribbon under double magnetic barrier modulation

We present a theoretical investigation of the transport properties and the magnetoresistance effect in armchair graphene nanoribbons (AGNRs) under modulation by two magnetic barriers. The energy levels are found to be degenerate for a metallic AGNR but are not degenerate for a semiconducting AGNR. However, the conductance characteristics show quantized plateaus in both the metallic and semiconducting cases. When the magnetization directions of the barriers change from parallel to antiparallel, the conductance plateau in the metallic AGNR shows a degenerate feature due to matching between the transport modes in different regions. As the barrier height increases, the conductance shows more oscillatory behavior with sharp peaks and troughs. Specifically, the initial position of nonzero conductance for the metallic AGNR system moves towards a higher energy regime, which indicates that an energy gap has been opened. In addition, the magnetoresistance ratio also shows plateau structures in certain specific energy regions. These results may be useful in the design of electron devices based on AGNR nanostructures.

Effect of an Interfacial Layer on Electron Tunneling through Atomically Thin Al2O3 Tunnel Barriers.

Electron tunneling through high-quality, atomically thin dielectric films can provide a critical enabling technology for future microelectronics, bringing enhanced quantum coherent transport, fast speed, small size, and high energy efficiency. A fundamental challenge is in controlling the interface between the dielectric and device electrodes. An interfacial layer (IL) will contain defects and introduce defects in the dielectric film grown atop, preventing electron tunneling through the formation of shorts. In this work, we present the first systematic investigation of the IL in Al2O3 dielectric films of 1-6 Å's in thickness on an Al electrode. We integrated several advanced approaches: molecular dynamics to simulate IL formation, in situ high vacuum sputtering atomic layer deposition (ALD) to synthesize Al2O3 on Al films, and in situ ultrahigh vacuum scanning tunneling spectroscopy to probe the electron tunneling through the Al2O3. The IL had a profound effect on electron tunneling. We observed a reduced tunnel barrier height and soft-type dielectric breakdown which indicate that defects are present in both the IL and in the Al2O3. The IL forms primarily due to exposure of the Al to trace O2 and/or H2O during the pre-ALD heating step of fabrication. As the IL was systematically reduced, by controlling the pre-ALD sample heating, we observed an increase of the ALD Al2O3 barrier height from 0.9 to 1.5 eV along with a transition from soft to hard dielectric breakdown. This work represents a key step toward the realization of high-quality, atomically thin dielectrics with electron tunneling for the next generation of microelectronics.

Two-well terahertz quantum cascade lasers with suppressed carrier leakage

The mechanisms that limit the temperature performance of diagonal GaAs/Al0.15GaAs0.85-based terahertz quantum cascade lasers (THz-QCLs) have been identified as thermally activated leakage of charge carriers through excited states into the continuum. THz-QCLs with energetically higher-laying excited states supported by sufficiently high barriers aim to eliminate these leakage mechanisms and lead to improved temperature performance. Although suppression of thermally activated carrier leakage was realized in a three-well THz-QCL based on a resonant-phonon scheme, no improvement in the temperature performance was reported thus far. Here, we report a major improvement in the temperature performance of a two-quantum-well direct-phonon THz-QCL structure. We show that the improved laser performance is due to the suppression of the thermally activated carrier leakage into the continuum with the increase in the injection barrier height. Moreover, we demonstrate that high-barrier two-well structures can support a clean three-level laser system at elevated temperatures, which opens the opportunity to achieve temperature performance beyond the state-of-the-art.

Enhancing the barrier height in oxide Schottky junctions using interface dipoles

We demonstrate a 0.37 eV increase in the n-type Schottky barrier height at the Pt/TiO2-terminated SrTiO3 (001) interface by insertion of an ultrathin insulator AgTaO3. While a conventional metal-insulator-semiconductor model predicts a reduction in the barrier height with insulator thickness, the observed increase originates from the two polar surface layers, (AgO)– and (TaO2)+ in AgTaO3 (001), forming an electrostatic dipole directed towards the metal, increasing the barrier height. Based on directly measured optical and dielectric properties of high quality AgTaO3 thin films, we determine the interface energy band diagram including the interface dipole. The capability to exploit the strong ionic charges of oxide surfaces to manipulate interface band alignments beyond bulk values greatly expands the design strategies for tailoring functional oxide interfaces. Up to now, the use of an ultrathin LaAlO3 layer could only decrease the barrier height, but now bidirectional control is possible.

Si heterojunction solar cells employing graphene transparent conductive electrodes co-doped with gold chlorides and silver nanowires

Graphene/Si Schottky junction is highly attractive for its application in solar cells due to the excellence of graphene as a transparent conducting electrode. However, the high sheet resistance of the chemical vapor deposition-grown graphene films, mostly used for the solar cells, is still one of the principal factors limiting the power conversion efficiency of graphene/Si solar cells. Here, we report an approach of co-doping with gold (III) chloride (AuCl3) and silver nanowires (Ag NWs) to reduce the sheet resistance (Rs) of graphene as well as to control its work function (WG) for well-matched graphene/Si wafer junction. The molar concentration (nD) of AuCl3 is varied from 1 to 10 mM while the fraction (nA) of Ag NWs is fixed at 0.1 wt% for the fabrication of the solar cells, based on nA-dependent behaviors of Rs and WG. The co-doped graphene/n-Si Schottky solar cells show a maximum power-conversion efficiency of 7.01% at nD = 7.5 mM, resulting from the increased barrier height at the graphene/Si junction and the reduced sheet resistance/transmittance of graphene by the co-doping, as proved from the nD-dependent behaviors of open-circuit voltage, DC conductivity/optical conductivity ratio, series resistance, and external quantum efficiency.