Semiconductor Space Charge Region Research Articles

Pt/GaN Schottky Barrier Height Lowering by Incorporated Hydrogen

Changes in the hydrogen-induced Schottky barrier height (Φ B) of Pt/GaN rectifiers fabricated on free-standing GaN substrates were investigated using current–voltage, capacitance–voltage, impedance spectroscopy, and current–time measurements. Ambient hydrogen lowered the Φ B and reduced the resistance of the semiconductor space–charge region while only weakly affecting the ideality factor, carrier concentration, and capacitance of the semiconductor space–charge region. The changes in the Φ B were reversible; specifically, the decrease in Φ B upon hydrogen exposure occurred quickly, but the recovery was slow. The results also showed that exposure to dry air and/or the application of a reverse bias to the Schottky electrodes accelerated the reversion compared with the case without the applied bias. The former case resulted in fast reversion because of the catalytic effect of Pt. The latter case, by contrast, suggested that hydrogen was incorporated into the Pt/GaN interface oxides as positive mobile charges. Moreover, both exposure to dry air and the application of a reverse bias increased the Φ B of an as-loaded sample from 0.91 to 1.07 eV, revealing that the Φ B of Pt/GaN rectifiers was kept lower as a result of hydrogen incorporation that likely occurred during device processing and/or storage.

Impedance Analysis of Semiconductor Electrodes Biased in the Accumulation Regime for Fuels Evolution

This work explores the theory and experimental use of impedance analyses of semiconductor electrodes in the accumulation regime of semiconductor electrodes under bias. It contrasts with the established practice of measuring capacitance of the semiconductor-electrolyte biased in the depletion region to obtain semiconductor doping densities and flatband potentials (Ufb). The goal is to establish Ufb and the solution Helmholtz capacitance for an electrode in the working bias region where research is done on semiconductor electrodes for CO2 reduction and H2 evolution.The technique of measuring the capacitance of semiconductor electrodes when polarized in the depletion region was introduced by DeWald1 and is based upon the work of Garrett and Brattain2 where mathematical expressions were derived for the electric field of a semiconductor space charge region. A significant assumption in that work was that a Boltzmann expression could be used to determine the population of the majority charge carriers in the bands created through ionization of dopant. Research in this area is extensive and has been summarized.3 However, for degenerate semiconductors or for bias potentials of the semiconductor where the fermi level at the electrode surface equals the energy of the band edges, a full fermi function must be employed to describe population statistics in the solid. This is the condition commonly found in systems for fuels production at semiconductor electrodes. The solid state physics theory for this situation is known4 and describes the electric field in a semiconductor space charge region. However, it was put aside during the development of impedance evaluations in semiconductor electrochemistry because its mathematical complexity was too tedious to evaluate at that time. Only limits and simplifications were explored.5 With modern computational software, this theory has become straightforward to calculate and it becomes possible to apply it to experimental systems in a description of behavior over the entire range of doping and polarization. The nature of this full theoretical description will be discussed and illustrated through experimental measurements of Si and InP semiconductor electrodes.

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.

A Description of the Faradaic Current in Cyclic Voltammetry of Adsorbed Redox Species on Semiconductor Electrodes.

A framework for interpreting the cyclic voltammetric responses from adsorbed redox monolayers on semiconductor electrodes has been developed. Expressions that describe quantitatively how the rates of the forward and back charge-transfer reactions impact the faradaic current density are presented. The primary insight is an explicit connection between the potential drops across the semiconductor space charge, surface, and electrolyte diffuse layers and the potential dependence of the reaction kinetics. Specifically, the evolution of the voltammetric shapes with experimental variables such as scan rate, standard potential of the redox adsorbate, and semiconductor surface energetics can now be interpreted for information on the operative charge-transfer rate constant and reaction energetics. This model is used to understand the complex dependence of the cathodic and anodic wave shapes for the first redox transition of an asymmetric viologen species adsorbed on n-Si(111). This system exhibited a heterogeneous rate constant of 0.24 s-1 and exhibited features consistent with an overwhelming majority of the applied potential dropping within the semiconductor space charge region. In total, experimentalists now have a visual key on how to interpret the faradaic current in voltammetric data for information on heterogeneous charge-transfer reactions between semiconductor electrodes and molecular adsorbates. The presented approach fills a long-standing knowledge gap in electrochemistry and aids practitioners interested in advancing photoelectrochemical energy conversion/storage strategies.

Ambient-hydrogen-induced changes in the characteristics of Pt/GaN Schottky diodes fabricated on bulk GaN substrates

Hydrogen-induced changes in the characteristics of Pt/GaN rectifiers fabricated on bulk GaN were studied using current–voltage (I–V), capacitance–voltage (C–V), and impedance spectroscopy measurements. The results were similar to those for Pt/GaN rectifiers fabricated on sapphire substrates [Y. Irokawa, Jpn. J. Appl. Phys. 59, 120901 (2020)]. That is, an ambient H2 atmosphere reduced the Schottky barrier height and the resistance of the semiconductor space-charge region but did not affect the ideality factor, carrier concentration, or capacitance of the semiconductor space-charge region, suggesting that the quality of the GaN layers was not the origin of the observed H2-induced changes.

Direct Imaging of Space Charges Around the Interface between Solid Electrolyte and Electrode of Solid-State Batteries

Solid-state batteries (SSBs) are a major focus for next-generation energy storage that is safe and has high energy density. In recent years, ion conductivity of solid-state electrolytes (SSEs) has developed to a level comparable to liquid electrolytes. However, great challenges are encountered at SSE/electrode interfaces when integrating the SSE into SSB cells. In addition to stability of the interface, which has been discussed extensively in the literature, a space-charge region around the electrode/SSE interface should exist and it can significantly affect Li-ion transport cross the interface [1]. Fermi-level alignment requires an ion charge transfer across the interface between the ion conductors that build an electric field around the interface. This space-charge region has been proposed theoretically,1 but direct measurement of the electric field or electrical potential has not been reported. On the other hand, the electric field in the semiconductor space-charge region has been studied extensively and directly measured and imaged; furthermore, the charge depletion and extension of the electric field into the semiconductor bulk have all been well documented. In fact, operations of many semiconductor micro-devices rely on the non-Ohmic current-voltage (I-V) characteristic across the space-charge region. And this makes the fundamental study and engineering of the semiconductor space charge among the farthestIn this contribution, we report on direct quantitative imaging of electrical potential on the space-charge region around the interface between Li6PS5Cl (LPSC) SSE and a NiMnCoO (NMC) cathode (Fig. 1a). We achieved this nm-scale, two-dimensional measurement by Kelvin probe force microscopy[2] (KPFM) imaging on the cross-section of a LPSC/NMC half-cell. KPFM is based on the non-contact mode of an atomic force microscope (AFM) setup in an Ar glove box. It maps the electrical potential of a sample surface in ~30-nm spatial resolution and ~10-mV voltage sensitivity. In our in-house KPFM setup, we used the second resonant oscillation of the cantilever to enhance the voltage sensitivity. To image the space charges, a well-defined SSE/electrode interface is needed. However, the sideview of the as-made LPSC/NMC half-cell by cold-pressing does not show a well-defined interface, and the surface of the sideview is rough for KPFM imaging. We polished the cross-section by ion-milling and via air-free sample transfer and polishing, and we obtained a well-defined interface exposed on the flat cross-sectional surface.The KPFM results show that the potential increased from the SSE side to the NMC side across the interface (Fig. 1b); this increase is due to the Li cation transferred from the SSE to NMC sides as well as the anion leveraged on the SSE side. This charge transfer is driven by the electrochemical potential difference of the Li ion in the two materials—in contrast to semiconductors, where the electronic charge transfer is driven by both the electronic band misalignment and charge-carrier concentrations at both sides of the interface. The potential is nonuniformly distributed, with 300‒500-mV variations in amplitude and 1‒2-μm variations in distance (Fig. 1c), indicating the nonuniformly distributed Li cations and anions. The nonuniform charge distribution can be caused by local chemical and structural defects and disorders such as grain boundaries, extended plane and line defects, and more. A simple estimate of the charge density is D=εε0V/d=2.3x10-9 C/cm2=1.5x108/cm2, with the assumptions that the potential is increased simply by an electrical double layer, the potential V = 400 mV, the dielectric constant ε=10, and the inter-distance of the double layer d=1.5 μm . This charge density corresponds to 3.3 charges per million (106) unit cells with a unit cell size of 1.5×1.5 nm2.This electrical potential of 300‒500 mV can significantly impede Li-ion transport from the SSE to the cathode during charging, and it should be mitigated. Dividing the potential difference between the two end-materials by engineering the interface (such as inserting a gradient layer) can be a promising approach, and it can also prevent interfacial chemical degradations. Interfacial engineering can effectively facilitate charge transport across the back contact of photovoltaic devices [3]. Further potential imaging on the engineered interfaces and degraded interfaces by cycling could lead to better understanding the interfacial electrical behavior. Our direct nm-scale potential imaging opens up a novel characterization technique for developing next-generation solid-state batteries. References Haruyama, K. Sodeyama, L. Han, K. Takeda, and Y. Tateyama, Chem. Mater. 26, 4248 (2014).C-S. Jiang et al., Nature Communications 6, 8397 (2015).Song, A. Moore, and J.R. Sites, IEEE J. Photovoltaics 8 , 293 (2018). Figure 1

Effect of hydrogen on Pt/GaN Schottky diodes

The effect of hydrogen on Pt/GaN Schottky diodes was studied using current–voltage (I–V), capacitance–voltage (C–V), and impedance spectroscopy measurements. The results showed that hydrogen exposure reduced the Schottky barrier height and the resistance of the semiconductor space-charge region but did not affect the ideality factor, carrier concentration, or capacitance of the semiconductor space-charge region. Exposure to dry air restored the I–V curves, 1/C2–V curves, and Nyquist plots to the original values more rapidly than exposure to pure N2, suggesting that Pt functioned as a catalyst. Hydrogen-induced changes in the properties of the Pt/GaN interface oxide may be related to these phenomena.

Effect of Sb, Tb3+ Doping on Optical and Electrical Performances of SnO2 and Si Based Schottky Diodes

(Sb, Tb3+)-doped SnO2 thin films were deposited on monocrystalline silicon (Si) and on porous silicon (PS) layer from sol-gel spin coating method. The photoluminescence spectrum shows that Tb3+ ions presents higher emission with the PS layer. The fabricated junctions are treated as a metal-semiconductor (MS) Schottky diodes. The current–voltage (I-V) characteristics of SnO2:Sb/p-Si (D1), SnO2:Sb:Tb3+/p-Si (D2) and SnO2:Sb:Tb3+/PS (p) (D3) were measured for these diodes at room temperature. Electronic parameters such as ideality factor, barrier height and series resistance were calculated and compared for the main junctions. Based on the thermoionic emission model, it appears that the contacts presents non-ideal I-V behaviour with a relatively high values of ideality factor (n = 12 for Si based diode, and n = 24 for PS based diode) and a relatively large values of series resistance RS (RS = 2 103 Ω for D3). After the incorporation of Tb3+, the junction characteristics show that the formed diode exhibits high forward current density and a decrease in the series resistance RS (RS = 600 Ω for D2). The non-ideality character of the elaborated MS junctions seems to be principally due to the effects of the interface. The relatively high values of the ideality factor was attributed to the sharing of the applied voltage V by a diffusion potential (VD) across the semiconductor space charge region and a potential (Vi) devoted to the interfacial layer formed between the silicon and the tin oxide. The trapped-limited current was found to dominate the current transport mechanisms through the fabricated junctions. The above results highlight the role of the interfacial layer and interface states in the determination of the electrical performance of Sb-doped SnO2/p-Si, (Sb, Tb3+) co-doped SnO2/p-Si and (Sb, Tb3+) co-doped SnO2/PS(p). They show that the simultaneous presence of Tb3+ ions and porous silicon layer allows an obvious enhancement of both optical and electrical properties of the main junction increasing then the applicability of SnO2/silicon based devices.

Bipolar resistive switching in metal-insulator-semiconductor nanostructures based on silicon nitride and silicon oxide

Bipolar resistive switching in metal-insulator-semiconductor (MIS) capacitor-like structures with an inert Au top electrode and a Si3N4 insulator nanolayer (6 nm thick) has been observed. The effect of a highly doped n+-Si substrate and a SiO2 interlayer (2 nm) is revealed in the changes in the semiconductor space charge region and small-signal parameters of parallel and serial equivalent circuit models measured in the high- and low-resistive capacitor states, as well as under laser illumination. The increase in conductivity of the semiconductor capacitor plate significantly reduces the charging and discharging times of capacitor-like structures.

Role of highly doped Si substrate in bipolar resistive switching of silicon nitride MIS-capacitors

Bipolar resistive switching of the metal-insulator-semiconductor (MIS) capacitor-like structures with the inert Au top electrode and Si3N4 dielectric nanolayer (6nm thick) has been investigated. The effect of highly doped n+-Si substrate is revealed related to the changes in semiconductor space charge region on the small-signal parameters of parallel and serial equivalent circuit models measured in the high- and low-resistive capacitor states, as well as under laser illumination. The increase in conductivity of semiconductor capacitor plate significantly reduces the charging and discharging times of capacitor-like structures.

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

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.

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

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.

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

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.

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

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.

Insulator charging limits direct current across tunneling metal-insulator-semiconductor junctions

Molecular electronics studies how the molecular nature affects the probability of charge carriers to tunnel through the molecules. Nevertheless, transport is also critically affected by the contacts to the molecules, an aspect that is often overlooked. Specifically, the limited ability of non-metallic contacts to maintain the required charge balance across the fairly insulating molecule often have dramatic effects. This paper shows that in the case of lead/organic monolayer-silicon junctions, a charge balance is responsible for an unusual current scaling, with the junction diameter (perimeter), rather than its area. This is attributed to the balance between the 2D charging at the metal/insulator interface and the 3D charging of the semiconductor space-charge region. A derivative method is developed to quantify transport across tunneling metal-insulator-semiconductor junctions; this enables separating the tunneling barrier from the space-charge barrier for a given current-voltage curve, without complementary measurements. The paper provides practical tools to analyze specific molecular junctions compatible with existing silicon technology, and demonstrates the importance of contacts' physics in modeling charge transport across molecular junctions.

Exact 3D simulation of Scanning Electron Microscopy images of semiconductor devices in the presence of electric and magnetic fields

Simulations of Scanning Electron Microscopy images of semiconductor devices in the presence of electric fields are usually too simplistic, since they just rely on approximated solutions of the Poisson equation. In this paper, the 3D Poisson equation is solved in a TCAD environment, which accounts for realistic boundary conditions, as well as for complex physical effects like the formation of space charge regions in semiconductors and the polarization of dielectrics. The calculated solution is then passed to a Monte Carlo code that implements a new electron tracking engine optimized for speed, stability, and accuracy. After introducing the new tracking engine, three simulation examples are presented dealing with the presence of an extraction field, self-charging of the irradiated sample, and potential contrast in a biased silicon junction.

Barrier height enhancement of metal/semiconductor contact by an enzyme biofilm interlayer

A metal/interlayer/semiconductor (Al/enzyme/p-Si) MIS device was fabricated using α-amylase enzyme as a thin biofilm interlayer. It was observed that the device showed an excellent rectifying behavior and the barrier height value of 0.78 eV for Al/α-amylase/p-Si was meaningfully larger than the one of 0.58 eV for conventional Al/p-Si metal/semiconductor (MS) contact. Enhancement of the interfacial potential barrier of Al/p-Si MS diode was realized using enzyme interlayer by influencing the space charge region of Si semiconductor. The electrical properties of the structure were executed by the help of current–voltage and capacitance–voltage measurements. The photovoltaic properties of the structure were executed under a solar simulator with AM1.5 global filter between 40 and 100 mW/cm2 illumination conditions. It was also reported that the α-amylase enzyme produced from Bacillus licheniformis had a 3.65 eV band gap value obtained from optical method.

Effect of a Nanodimensional Polyethylenimine Layer on Current–Voltage Characteristics of Hybrid Structures Based on Single-Crystal Silicon

In this paper the study of the tunneling current–voltage (I–V) characteristics of silicon surfaces with n- and p-type conductivity as a function of roughness in the presence of an adsorbed insulating layer of polyethylenimine (PEI) is presented. A new approach is proposed for analysis of the tunnel current–voltage characteristics of a metal–insulator–semiconductor structure based on the combination of two models (Simmons and Schottky). Such joint analysis demonstrates the effect of surface states and evaluates changes in the band bending and electron affinity after the deposition of the polyelectrolyte layer on the semiconductor surface. As a result, we are able to differentiate between the equilibrium tunnel barrier (qφ 0) and the barrier height (qφ B). It is shown that the deposition of the polymer leads to an increase of the equilibrium tunnel barrier by more than 250 meV, irrespective of the roughness and the conductivity type of the silicon substrate. The PEI deposition also leads to changes in the barrier height (less than 25 meV) that are smaller than the equilibrium tunnel barrier changes, indicating pinning of the Fermi level by the electron surface states that are energetically close to it. These surface states can trap charge carriers, a process leading to the formation of a depletion region and band bending on the semiconductor surface. Moreover, the change in the barrier height qΔφ B depends on the conductivity type of the semiconductor, being positive for n-type and negative for p-type, in contrast to qΔφ 0, which is positive for all substrates. The change is explained by capture of electrons preferably from the semiconductor space-charge region in the presence of a cationic polyelectrolyte, e.g., PEI.

Electronic effects at self-assembled 4,4′-thio-bis-benzenethiolate protected Au nanoparticles on p-GaAs (1 0 0) electrodes

The effects of the self-assembled 4,4′-thio-bis-benzenethiolate protected gold nanoclusters onto a p-GaAs (100) electrode were examined by AFM, XPS, SHG and EIS investigations. The AFM and XPS results revealed a well-ordered overlayer exhibiting a bi-modal highly correlated fractal behavior which, however, cannot fully protect the semiconducting surface against the oxidation in air. The EIS data pointed out the influence exerted by the gold-monolayer protected clusters (Au-MPCs) over the charging/discharging processes observed at p-GaAs (100) electrode. Although the applied potential is varied linearly, the potential drop within the semiconductor space charge region as well as that across the Au-MPCs layer undergoes stepped changes supposed to result in the discrete charging of the Au-MPCs. These effects point to an electronic equilibrium between the Au-MPCs and the semiconducting substrate. Fermi level pinning and enhancement of the SHG response in the potential range where the surface/interface states in the semiconductor band gap become electrically active bring further proof in this respect.

Implanted bottom gate for epitaxial graphene on silicon carbide

We present a technique to tune the charge density of epitaxial graphene via an electrostatic gate that is buried in the silicon carbide substrate. The result is a device in which graphene remains accessible for further manipulation or investigation. Via nitrogen or phosphor implantation into a silicon carbide wafer and subsequent graphene growth, devices can routinely be fabricated using standard semiconductor technology. We have optimized samples for room temperature as well as for cryogenic temperature operation. Depending on implantation dose and temperature we operate in two gating regimes. In the first, the gating mechanism is similar to a MOSFET, the second is based on a tuned space charge region of the silicon carbide semiconductor. We present a detailed model that describes the two gating regimes and the transition in between.