Schottky Contact Model Research Articles

Large‐Area Self‐Assembled Hexagonal Boron Nitride Nanosheet Films for Ultralow Dark Current Vacuum‐Ultraviolet Photodetectors

AbstractHexagonal boron nitride (hBN) is one of the most promising candidates for vacuum‐ultraviolet photodetectors (VUV PDs). However, the efficient and low‐cost fabrication of large‐area hBN‐PDs still encounters challenges. Herein, a cost‐effective route is proposed for fast and scalable fabrication of high‐performance VUV PDs via hBN nanosheet (BNNS) films. BNNSs are peeled from bulk hBN and self‐assembled into large‐area ordered films. In such PDs, junction barriers are present at the contact interfaces of BNNSs and give the PDs a “light‐induced reduction of junction barrier height” working mechanism. The number of junction barriers are qualitatively adjusted by designing the size of BNNSs to optimize the performance of the devices. The performance of ultralow dark current (0.27 pA@80 V), high detectivity (3.42 × 1011 Jones), and fast response speed (20.97/17.69 ms) for 185 nm VUV light is achieved by a fabricated PD. Analysis based on the Schottky contact model proves that the large photoresponse is mainly attributed to the reduction of the barriers and series resistance on illumination. Meanwhile, a physical model is established to describe the working process of such PDs, of which conductivity is dominated by the junction barriers. Besides, a flexible PD is also fabricated, depicting excellent stability, and robustness.

The Impact of Non-Ideal Ohmic Contacts on the Performance of High-Voltage SiC MPS Diodes

The wide band gap of SiC semiconductor devices constitutes a serious challenge to build good Ohmic contacts on the surface of the p-type material. This is reflected in the numerical analysis of ”realistic” devices, where we have to cope with serious problems, such as a shifting threshold voltage, reduced forward conductivity, and no noticeable conductivity modulation by minority carrier injection from p+-emitters, in matching measured data with simulation results, as a consequence of the significant impact of non-ideal poor Ohmic contacts. In this work, we used a Schottky contact model together with a barrier tunneling model, instead of common ideal Ohmic contact model, to simulate the non-ideal Ohmic contact on SiC MPS diodes. Based on this approach, the I-V characteristics of real Ohmic contacts can be reproduced in high-fidelity simulations, providing us physical insight of the observed operational behavior.

Utilizing Modelling, Experiments, and Statistics for the Analysis of Water-Splitting Photoelectrodes

Photoelectrochemical (PEC) water-splitting is a promising route for the direct conversion of solar energy into chemical energy[1]. The PEC synthesis of hydrogen uses catalytically active light-capturing semiconductors in contact with an electrolyte forming the semiconductor-electrolyte interface. The semiconductor-electrolyte interface is at the core of photoelectrochemical water splitting devices performance and therefore requires special focus and investigation[2]. Charge transfer at semiconductor-electrolyte interface is often discussed in terms of the Marcus-Gerischer model which refers to ideal, direct charge transfer[3]. Nevertheless, deviations from the ideal charge transfer are observed in the presence of interface states which were considered in this work. We developed a multi-physics 1D model of a planar water-splitting photoelectrode accounting for electromagnetic wave propagation within the electrolyte and the semiconductor, charge transport and conservation within the semiconductor, and charge transfer across the semiconductor-electrolyte interface[4]. Interface states at the semiconductor-electrolyte interface influence the potential barrier and were considered developing an extended Schottky contact model[4]. The photoelectrode model was validated with current-voltage measurements using a n-type GaN photoelectrode immerged in 1M H2SO4 utilizing additional experimental measurements (impedance spectroscopy and cyclic voltammetry) to determine missing material parameters of GaN, namely flatband potentials, surface lifetimes, surface transfer kinetic velocities and hydrogen evolution reaction exchange current density. The validated multi-physics model was then used to predict the performance of other semiconductor materials with different semiconductor-electrolyte interface properties through variation of parameter such as electron and hole mobilities, surface lifetimes, flatband potential, permittivity, doping concentration, bulk Shockley-Read-Hall recombination, and hole and electron interface kinetics. The large number of relevant material and interface characteristics renders the identification of the most significant parameters challenging and we used statistical tools, i.e. fractional factorial design (FFD), as an approach for solving this challenge. The statistically identified significant parameters were further investigated and theoretically optimized in a detailed parameter study. Key factors based on our model system GaN were identified using FFD at two different potentials: 0.3V vs RHE and 1.23V vs RHE. Hole and electron surface lifetimes and doping concentration appeared to be the most significant factors at 1.23V vs RHE. At 0.3V vs RHE, hole and electron surface lifetimes and flatband potential were the most significant factors. The parametric analysis of hole and electron lifetimes and doping concentration for varying potential further showed that the photocurrent resulted from a complex combined influence of the numerical values of all three parameters. The photocurrent, being a minority current, was generally more influenced by the hole surface lifetime in n-type GaN at 1.23V vs RHE. Especially at large hole surface lifetimes, the influence of electron surface lifetime became negligible. The insensitivity of the photocurrent on electron surface recombination lifetime at high doping concentrations resulted from the dominating terms in the recombination, namely the electron concentration and hole surface lifetime. Nevertheless, under low doping and short hole surface lifetimes, the electron surface lifetime showed to still have an impact on the photocurrent at 1.23V vs RHE. This counterintuitive but numerically proven result might be particularly important when explaining measurements of surface-treated photoelectrodes[5]. These three parameters must be simultaneously considered when optimizing the photocurrent for varying operating potential. For example at an operating potential of 0.3V vs RHE, the photocurrent density increases by 0.25mA/cm2 or 69% only by increasing the doping concentration from 1014cm-3 to 1016cm-3. The developed methodology uses an experimentally-validated numerical model and statistical analysis to provide understanding of the performance of water-splitting photoelectrodes and to identify most significant material parameters and interface properties. Subsequent in-depth parametric analysis of the most significant parameters allows for the quantification of their effect and subsequent optimization of the device for maximum performance. The presented methodology provides a general approach to identify and quantify main material challenges and design considerations in working PEC devices. The predictive character of the validated model can be further exploited with confidence to approach and investigate morphologically complex electrodes and material classes for which research-related questions are not yet answered.

Influence of top contact noble metals on leakage current properties of epitaxial BaTiO3 film capacitors

Dielectric properties, ferroelectric hysteresis loops, and leakage current characteristics of an epitaxial BaTiO3 (BTO) film were investigated with La0.5Sr0.5CoO3 as bottom electrode and the different noble metal as top electrodes (Au, Ag and Pt, which were deposited on the same surface of a BTO film). The dielectric constants, dielectric loss, leakage currents and ferroelectric loops all exhibited the top-electrode-dependent behavior, which can be attributed to the different interface state. The J–V characteristics were analyzed with various transportation mechanisms in detail. Regardless of the top electrode materials, the leakage current characteristics were described by a modified Schottky contact model for all BTO film capacitors. It was proved that large space charge densities were the main contribution to the slim hysteresis loops. The potential of these interface charge dominated BTO film heterostructures in the application of high energy density storage capacitors was also demonstrated.

Thickness-dependent ferroelectric behavior of predominantly (117)-oriented Bi3.15Nd0.85Ti3O12 thin-film capacitors

Ferroelectric hysteresis loops, remanent polarization, coercive field, and leakage current characteristics were investigated by increasing the film thickness (from 103 nm to 401 nm) of predominantly (117)-oriented Bi3.15Nd0.85Ti3O12 films. The thickness dependence of the coercive fields shows log coercive field vs. log thickness with a slope of approximately −0.65, which is characteristics of the Kay–Dunn scaling law. The films exhibited very low leakage current on the order of 10−7A/cm2 at an applied electric field of 100 kV/cm. Without a discernible thickness-dependence behavior, the leakage current characteristics, including both Schottky emission and space-charge-limited conduction, were well described by a modified Schottky contact model.

Space-charge dominated epitaxial BaTiO3 heterostructures

Epitaxial BaTiO3 thin films (∼300nm thick) with various conductive oxide bottom electrodes including (La0.5Sr0.5)CoO3, SrRuO3 and LaNiO3 were prepared on single-crystalline SrTiO3 substrates using a radiofrequency magnetron sputtering technique in an oxygen-rich atmosphere and at a deposition temperature of 700°C. The charge transport phenomena of these films were systematically investigated. Comparison of leakage current levels with respect to different BaTiO3–bottom electrode interfaces gave a direct proof of the p-type semiconducting behavior in the BaTiO3 films, whose I–V characteristics were well described by a modified Schottky contact model up to an applied field of ∼60MVm−1. By adapting this model, we obtained interface potential barriers, space-charge and free charge carrier densities, as well as depletion layer width and interface layer thickness for the epitaxial BaTiO3 films. The dominance of space-charges (∼1020cm−3) over intrinsic polarizations in these films well explained the apparent reduction in remnant polarization and tilting of the P–V hysteresis loops, as well as an enhanced dielectric strength. Further increase of the applied electric field will result in complete depletion of the BTO films. Consequently, charge transport in these films will become bulk-controlled. This prediction was validated by experimental J–V curves acquired for a broad range of applied electric field, where ionic conduction and Pool–Frenkel emission currents consecutively dominated in the high field (60–220MVm−1) and ultrahigh field (220–300MVm−1) regions. Finally, the potential of these lead-free heterostructures as high-energy density dielectric capacitors was demonstrated.

Characterization of Density-of-States in Polymer-based Organic Thin Film Transistors and Implementation into TCAD Simulator

In this work, we report extraction of the density-of-states (DOS) in polymer-based organic thin film transistors through the multi-frequency C-V spectroscopy. Extracted DOS is implemented into a TCAD simulator and obtained a consistent output curves with non-linear characteristics considering the contact resistance effect. We employed a Schottky contact model for the source and drain to fully reproduce a strong nonlinearity with proper physical mechanisms in the output characteristics even under a very small drain biases. For experimental verification of the model and extracted DOS, 2 different OTFTs (P3HT and PQT-12) are employed. By controlling the Schottky contact model parameters in the TCAD simulator, we accurately reproduced the nonlinearity in the output characteristics of OTFT.

Impact of Random Dopant Fluctuation on Size-Dependence of Contact Resistance

Reducing the size of semiconductor devices causes contact in deca-nano size. Substantial fluctuation of contact resistance is anticipated owing to the reduction of impurity atoms in the contact holes. In this study, the impact of the random dopant fluctuation on the contact resistance is revealed by three-dimensional device simulation with a Schottky contact model. The standard deviation of the contact resistance could become 50%, dominated by the number of impurity atoms in the depletion layer formed by the Schottky barrier. The average value of the contact resistance could increase as the impurity concentration decreases because of the reduction of the tunneling path.

Physical Foundation of a Recently Proposed Schottky-Contact Model

The goal of this correspondence is to supplement the Schottky-contact model proposed in “A Generalized Drift-Diffusion Model for Rectifying Schottky Contact Simulation,” IEEE Transactions on Electron Devices, vol. 57, no. 7, July 2010, with a solid physical foundation by rigorously rederiving it from an analytical solution of Boltzmann's equation in the boundary layer.

Improved electrical performance of erbium silicide Schottky diodes formed by Pre-RTA amorphization of Si

Erbium silicide Schottky diodes formed on Si(001) substrate using rapid thermal annealing method show degraded Schottky-barrier height /spl phi//sub Beff/ and ideality factor n due to the presence of silicide-induced microstructural defects which are likely sources of trap states. A method to improve the /spl phi//sub Beff/ and n of the diodes utilizing in situ Ar plasma cleaning to induce a light amorphization of the Si(001) substrate is proposed. Even though the diodes formed in this way are less textured and have a poorer interface, they are free of silicide-induced microstructural defects, leading to an overall improvement in current transport and conduction properties which can be modeled using inhomogenous Schottky contact model.

A unified simulation of Schottky and ohmic contacts

The Schottky contact is an important consideration in the development of semiconductor devices. This paper shows that a practical Schottky contact model is available for a unified device simulation of Schottky and ohmic contacts. The present model includes the thermionic emission at the metal/semiconductor interface and the spatially distributed tunneling calculated at each semiconductor around the interface. Simulation results of rectifying characteristics of Schottky barrier diodes (SBD's) and resistances under high impurity concentration conditions are reasonable, compared with measurements. As examples of application to actual devices, the influence of the contact resistance on salicided MOSFETs with source/drain extension and the immunity of Schottky barrier tunnel transistors (SBTTs) from the short-channel effect (SCE) are demonstrated.

Quantum Transport with Band-Structure and Schottky Contacts

We describe (i) a parametrized single-band model that mimics the full-band Γ-valley non-parabolicity, (ii) a method for calculating the semi-classical and quantum electron charge with the sp3s* band-structure model, and (iii) a Schottky contact model compatible with any localized orbital band-structure model.

New Aspects of (Semi-Insulating) GaP:Cu

buried Schottky contact model for the complex behavior of Cu in GaP. PIXE studies show that Cu can reach very high concentrations in that material. Channeling indicates that a part of the Cu forms precipitates. Hall measurements on sets of samples were made to examine the electrical trans port coefficients. The mobilities of the samples with the most abundant concentration of Cu were found to be dominated by a term ocT0·5 which was identified as a component induced by metallic spikes with non-overlapping depl etion zones. We come to the conclusion that Cu introduces an acceptor like defect as well as precipitates. For high initial carrier concentrations,

A possible scaling limit for enhancement-mode GaAs MESFETs in DCFL circuits

A possible scaling limit for ion-implanted GaAs MESFETs with buried p-layer LDD structure has been numerically investigated. A Schottky-contact model with a thin interfacial layer and interface states was used to simulate the Schottky-barrier height of a scaled-down MESFETs. When enhancement-mode MESFETs in direct-coupled FET logic (DCFL) circuits are scaled down, the gate length can be reduced to 0.21 mu m at an interface-state density of 6.6*10/sup 12/ cm/sup -2/.eV/sup -1/, when the barrier height is greater than 0.6 V, the threshold voltage is less than 0.1 V, and the channel aspect ratio is 8. >