Gate Bias Voltage Research Articles

Carcinogenic Heavy Metals Detection Based on ZnO Nanoribbons

The theoretical investigation of zigzag ZnONRs for the detection of carcinogenic heavy metal atoms is reported in the current manuscript. The sensing characteristics of the ZnONRs towards toxic heavy metal atoms are examined by deploying the density functional theory (DFT) calculations together with non-equilibrium Green’s function (NEGF). The variation in the structural, electronic, and transport properties of the ZnONRs post passivation with heavy metal atoms at the edges are considered for the detection. Pristine ZnONR is a semiconductor with an energy bandgap of 0.49 eV and the ZnONRs become metallic after exposure to heavy metal atoms. The quantum transport calculations reveal the enhanced current conductivity in the heavy metal atom exposed ZnONR devices relative to the pristine ZnONR due to the induced metallicity. The local device density of states (LDOS) calculations reveal the major transmission of the carriers occurs through the edges. The ZnONR devices are highly sensitive to Sb and As as compared to the Pb atom. The ZnONR exhibit the highest sensitivity towards the Sb atoms with the sensor response around 3.57 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,{10}^{{7}}$ </tex-math></inline-formula> %. The sensor sensitivity towards the As and Pb is slightly lower with the sensor responses measured to be 3.52 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{{7}}$ </tex-math></inline-formula> % and 2.86 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{{7}}$ </tex-math></inline-formula> %, respectively. Further, FET devices exhibit high sensitivity at zero gate bias voltage of the order of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{10}}$ </tex-math></inline-formula> for Sb-ZnO-Sb, As-ZnO-As, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{{9}}$ </tex-math></inline-formula> for Pb-ZnO-Pb devices. The obtained findings suggest that ZnONRs can effectively be used for the detection of carcinogenic heavy metal atoms.

A 4H-SiC trench IGBT with controllable hole-extracting path for low loss

A novel 4H-SiC trench insulated gate bipolar transistor (IGBT) with a controllable hole-extracting (CHE) path is proposed and investigated in this paper. The CHE path is controlled by metal semiconductor gate (MES gate) and metal oxide semiconductor gate (MOS gate) in the p-shield region. The grounded p-shield region can significantly suppress the high electric field around gate oxide in SiC devices, but it weakens the conductivity modulation in the SiC trench IGBT by rapidly sweeping out holes. This effect can be eliminated by introducing the CHE path. The CHE path is pinched off by the high gate bias voltage at on-state to maintain high conductivity modulation and obtain a comparatively low on-state voltage (V ON). During the turn-off transient, the CHE path is formed, which contributes to a decreased turn-off loss (E OFF). Based on numerical simulation, the E OFF of the proposed IGBT is reduced by 89% compared with the conventional IGBT at the same V ON and the V ON of the proposed IGBT is reduced by 50% compared to the grounded p-shield IGBT at the same E OFF. In addition, the average power reduction for the proposed device can be 51.0% to 81.7% and 58.2% to 72.1% with its counterparts at a wide frequency range of 500 Hz to 10 kHz, revealing a great improvement of frequency characteristics.

Reverse gate leakage mechanism of AlGaN/GaN HEMTs with Au-free gate

The reverse gate leakage mechanism of W-gate and TiN-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with N2 plasma surface treatment is investigated using current–voltage (I–V) and capacitance–voltage (C–V) characteristics and theoretical calculation analysis. It is found that the main reverse gate leakage mechanism of both devices is the trap-assisted tunneling (TAT) mechanism in the entire reverse bias region (–30 V to 0 V). It is also found that the reverse gate leakage current of the W-gate AlGaN/GaN HEMTs is smaller than that of the TiN gate at high reverse gate bias voltage. Moreover, the activation energies of the extracted W-gate and TiN-gate AlGaN/GaN HEMTs are 0.0551 eV–0.127 eV and 0.112 eV–0.201 eV, respectively.

Effective integration of a MOSFET phototransistor to a GaN LED for UV sensing.

In this Letter, we report an effective monolithic integration of a metal oxide semiconductor field effect (MOSFET) phototransistor (PT) and a light-emitting diode (LED) on a GaN-on-Si LED epitaxial (epi) wafer. Avoiding additional growth or Si diffusion, the PT was directly fabricated on the LED epi layer, providing a cost-effective and facile method. As a driver, the PT could modulate both peak value of the light intensity and output current of the integrated LED. As an ultraviolet (UV) detector, our PT showed sufficient responsivity. It was found that the gate-voltage-dependent photocurrent-response of the device had a shorter response time, and a higher responsivity was obtained at a higher gate-voltage bias. The device demonstrated a switching effect that the photoinduced current from the PT drove the LED when the UV lamp was turned on, whereas the photoinduced current stopped driving upon powering off the UV lamp. The experiment proved that the integrated device working as a UV detector exhibited a fast response time and a longstanding stability. We anticipate that such an approach could have potential applications for UV light detection and visible light communication (VLC).

(Invited) Recent Advances in the Research of Graphene Plasmonic Terahertz Laser Transistors

Electrons and holes in graphene behave as relativistic charged massless Dirac fermions due to the graphene unique gapless electronic band structure with a linear dispersion law. Dirac plasmons - the quanta of the plasma oscillation of the Dirac electrons - can dramatically enhance the interaction of terahertz (THz) photons with graphene. We have proposed an original current-injection graphene THz laser transistor, demonstrated single-mode THz laser oscillation at low temperatures [1-3], and discovered and demonstrated the THz giant gain enhancement effect by the graphene Dirac plasmons [4-8]. However, further breakthroughs are needed to realize room-temperature high-intensity THz lasing and ultrafast modulation operation for the next generation wireless 6G and 7G communications. In this paper, we will present new ideas on the operating principle and device structures of the THz graphene plasmonic laser transistors with a high radiation intensity and ultrafast modulation capability operating at room temperature.To dramatically improve the quantum efficiency and gain, we utilize the Coulomb drag effect in lateral n+ - i – n - n+ graphene diode/transistor structures with the ballistic injection of the graphene Dirac fermions [9-11]. Such injection strongly modifies the current-voltage characteristics producing “plasmonic gain” in the THz frequency range applicable for THz oscillations and amplifications. This phenomenon is associated with the specifics of the ballistic electron scattering on quasi-equilibrium electrons in graphene. Depending on the device structural parameters (in particular, the gated region length and its electron Fermi energy), the graphene diode/transistor structures can exhibit either S-shaped or monotonic current-voltage characteristics [9]. In the former case, the resulting hysteresis and current filamentation effects can be used for the implementation of the voltage-switching devices. The feedback between the amplified dragged electrons current and the injected ballistic electrons current can lead to the negative THz dynamic conductivity. The self-excitation of the THz plasma oscillations in the gated region enables the realization of the graphene transistor-based sources of THz radiation [11].To realize ultrafast modulation of lasing intensity/phase, we introduce actively controlling the parity and time-reversal (PT) symmetry [12] of the graphene Dirac plasmons (GDPs) in the dual-grating-gate graphene-channel field effect transistor (DGG-GFET) nanostructures for the ultrafast modulation of the lasing intensity and phase. [13]. The PT symmetry is expressed by a pair of complementary gain and loss elements. This gain–loss balance leads to the exceptional points at the real frequency axis in the exact PT-phase resulting in the extraordinary frequency response of “unidirectionality” [14]. The DGG-GDP metasurface, which consists of a unit cell comprising a pair of gain and loss regions and its periodical arrangement, promotes the GDP instability. The PT symmetry can be controlled (to be held or broken) by altering the gate or drain bias voltages. Our numerical simulations showed that the laser cavity Q values can be dynamically controllable in a DGG-GDP transistor structure [6] demonstrating 100-Gbit/s-class ultrafast modulation capabilities [13].The authors thank A.A. Dubinov, D. Yadav, T. Watanabe, T. Suemitsu, W. Knap, V. Kachorovskii, and V.V. Popov for their contributions. This work was supported by JSPS-KAKENHI No. 21H04546, and No. 20K20349, Japan. V. Ryzhii, M. Ryzhii, and T. Otsuji, J. Appl. Phys. 101, 083114 (2007).T. Otsuji et al., IEEE J. Sel. Top. Quantum Electron. 19, 8400209 (2013).D. Yadav et al., Nanophoton. 7, 741-752 (2018).A.A. Duvinov el al., J. Phys.: Cond. Matters 23, 145302 (2011).T. Watanabe et al., New J. Phys. 15, 075003 (2013).Y. Koseki et al., Phys. Rev. B 93, 245408 (2016).S. Boubanga-Tombet et al., Phys. Rev. X 10, 031004 (2020).S. Boubanga-Tombet et al., Front. Phys. 9, 726806 (2021).V. Ryzhii et al., Phys. Rev. Appl. 16, 014001 (2021).V. Ryzhii et al., Appl. Phys. Lett. 119, 093501 (2021).V. Ryzhii et al., Physica Status Solidi A 218, 2100535 (2021).M.-A. Miri and A. Alu, Science 363, eaar7709 (2019).T. Otsuji et al., Nanophoton. under review.H. Ramezani and T. Kottos, Phys. Rev. A 82, 04383 (2010). Figure 1

Electron-Irradiation-Induced Degradation of Transfer Characteristics in Super-Junction VDMOSFET

High electric-field stress is an effective solution to the recovery of irradiated devices. In this paper, the dependence of the recovery level on the magnitude of gate voltage and duration is investigated. Compared with the scheme of high gate-bias voltage with a short stress time, the transfer characteristics are significantly recovered by applying a low electric field with a long duration. When the electric field and stress time are up to a certain value, the threshold voltage almost approaches the limitation, which is less than that before irradiation. Meanwhile, the effect of temperature on the recovery of the irradiated devices is also demonstrated. The result indicates that a high temperature of 175 °C used for the irradiated devices’ annealing does not play a role in promoting the recovery of transfer characteristics. In addition, to obtain a deep-level understanding of threshold degradation, the first-principles calculations of three Si/SiO2 interfaces are performed. It is found that new electronic states can be clearly observed in the conduction bans and valence bands after the Si-H/-OH bonds are broken by electron irradiation. However, their distribution depends on the selection of the passivation scheme. Ultimately, it can be observed that the threshold voltage linearly decreases with the increase in interface charge density. These results can provide helpful guidance in the deep interpretation of threshold degradation and the recovery of the irradiated super-junction devices.

Competition between heating and cooling during dynamic self-heating degradation of amorphous InGaZnO thin-film transistors

The dynamic self-heating (SH) instability of a-InGaZnO (a-IGZO) thin-film transistors (TFTs) was systematically investigated under static drain bias and pulsed gate voltage. The a-IGZO TFTs exhibited three distinct degradation stages, including a slightly positive shift of threshold voltage (ΔVth), then a gradually negative ΔVth, and finally an accelerated negative shift leading to normally-on characteristics. The underlying mechanisms were clarified to be SH-enhanced positive bias stress (PBS) instability, SH-generated donor defects, and the donor-populated central channel, respectively. By changing the duty ratio, frequency, peak, and base periods of gate pulses. The competition between heating and cooling periods was found to dominate the behavior and degree of dynamic SH degradations, suggesting a feasible instability-relieving method by sophisticatedly adjusting the dynamic operating conditions.

Orbital Hall effect in bilayer transition metal dichalcogenides: From the intra-atomic approximation to the Bloch states orbital magnetic moment approach

Using an effective Dirac model, we study the orbital Hall effect (OHE) in bilayers of transition metal dichalcogenides with 2H stacking (2H-TMD). We use first-order perturbation theory in the interlayer coupling of the bilayer system to obtain analytical expressions for the orbital Hall conductivity in the linear response regime. We use two distinct descriptions of the orbital angular momentum (OAM) operator. The first one is the intra-atomic approximation that considers only the intrasite contribution to the OAM [Cysne et al., Phys. Rev. Lett. 126, 056601 (2021)]. The second one uses the Berry phase formula of the orbital (valley) magnetic moment to describe the OAM operator [Bhowal and Vignale, Phys. Rev. B 103, 195309 (2021)]. This approach includes both intersite and intrasite contributions to the OAM. Our results suggest that the two approaches agree qualitatively in describing the OHE in bilayers of 2H-TMDs, although they present some quantitative differences. We also show that interlayer coupling plays an essential role in understanding the OHE in the unbiased bilayer of 2H-TMD. This coupling causes the Bloch states to become bonding (antibonding) combinations of states of individual layers, demanding the consideration of the non-Abelian structure of the orbital magnetic moment to the occurrence of OHE. As we discuss throughout the work, the emerging picture of transport of OAM in the unbiased bilayer of 2H-TMDs based on OHE is very different from the usual picture based on the valley Hall effect, shedding new light on previous experimental results. We also discuss the effect of the inclusion of a gate-voltage bias in the bilayer system. Our work gives support to recent theoretical predictions on OHE in two-dimensional materials.

Trench field-effect transistors integrated in a microfluidic channel and design considerations for charge detection.

Field-effect transistors (FETs) combined with a microfluidic system allow for the electrical detection of charged materials moving in a microfluidic channel. Here, we demonstrate trench-shaped silicon FETs with the combination of a microfluidic channel that can be used for simultaneous electrical and optical detection of charged fluorescent beads. The n-channel silicon trench FETs have a maximum transconductance of 1.83 × 10-5 S at near-zero gate bias voltage, which is beneficial for the high sensitivity of electrical detection. The optical transparency and physical robustness of the integrated microfluidic channel are achieved by a polydimethylsiloxane (PDMS)/glass hybrid cover combining the good sealing characteristics of PDMS, and the thin and flat properties of glass. Device evaluation methodologies and measurement approaches are also presented demonstrating a synchronized time-lapse imaging and electronic detection of bead transport. The proposed device and design consideration could advance the promise of electronic sensing to measure potential differences induced by charged analytes.

Highly Sensitive Photodetectors Based on Monolayer MoS2 Field-Effect Transistors.

Molybdenum disulfide (MoS2) is a promising candidate for the development of high-performance photodetectors, due to its excellent electric and optoelectronic properties. However, most of the reported MoS2 phototransistors have adopted a back-gate field-effect transistor (FET) structure, requiring applied gate bias voltages as high as 70 V, which made it impossible to modulate each detecting device in the fabricated array. In this paper, buried-gate FETs based on CVD-grown monolayer MoS2 were fabricated and their electric and photoelectric properties were also systematically investigated. A photoresponsivity of around 6.86 A/W was obtained at 395 nm, under the conditions of zero gate bias voltage and a light power intensity of 2.57 mW/cm2. By application of a buried-gate voltage of 8 V, the photoresponsivity increased by nearly 10 times. Furthermore, the response speed of the buried-gate MoS2 FET phototransistors is measured to be around 350 ms. These results pave the way for MoS2 photodetectors in practical applications.

1T and 2H heterophase MoS2 for enhanced sensitivity of GaN transistor-based mercury ions sensor

We report significantly enhanced sensitivity of AlGaN/GaN-based high electron mobility transistor (HEMT) sensor by the targeted synthesis of IT and 2H coexisting phase MoS2 and applying the gate bias voltage. The HEMT structures on Si (111) substrates were used for the detection of Hg2+ ions. The optimum sensitive regime in terms of V GS and V DS of the sensor was investigated by keeping the drain source voltage V DS constant at 2 V and by only varying the gate bias voltage V GS from 0 to 3 V. The strongest sensing response obtained from the device was around 0.547 mA ppb−1 at V GS = 3 V, which is 63.7% higher in comparison to the response achieved at 0 V which shows a sensing response of around 0.334 mA ppb−1. The current response depicts that the fabricated device is very sensitive and selective towards Hg2+ ions. Moreover, the detection limit of our sensor at 3 V was calculated around 6.21 ppt, which attributes to the strong field created between the gate electrode and the HEMT channel due to the presence of 1T metallic phase in synthesized MoS2, indicating that the lower detection limits are achievable in adequate strong fields.

Degradation in super-junction MOSFET under successive exposure of heavy ion strike and gamma ray irradiation

The degradation of 200 V super-junction MOSFET under successive exposure of heavy ion strike and gamma ray irradiation is investigated for the first time in this paper. Compared with the device purely irradiated with gamma ray, the MOSFET subjected to superimposed irradiation stress, e.g. irradiated with heavy ion strike first and then irradiated with gamma ray, exhibits more serious deterioration in static characteristics, such as threshold voltage and transconductance. Moreover, the devices under superimposed irradiation stress exhibits very different dynamic characteristics, such as more obviously increased gate charges and improved reverse recovery. In addition, the degradation mentioned above caused by the extra oxide traps and interface strain bonds generated by heavy ion strike can be attenuated with applying negative gate voltage bias during the whole experiments, which provides a solution to avoid this potential threat in aerospace application.

Light-enhanced gating effect at the interface of oxide heterostructure

In semiconducting materials, electrostatic gating and light illumination are widely used stimuli to tune the electronic properties of the system. Here, we show a significant enhancement of photoresponse at the conducting interface of LaVO3–SrTiO3 under the simultaneous application of light and negative gate bias voltage, in comparison to their individual application. On the other hand, the illuminated LaVO3-SrTiO3 interface does not show any enhancement, when a positive gate bias voltage is applied. Our x-ray diffractometer, Raman spectroscopy and photoemission measurements show that unlike the LaAlO3–SrTiO3 interface, migration of oxygen vacancies may not be the prime mechanism for the enhanced photoresponse. Rather, we suggest that the photoresponse of our system is intrinsic and this intrinsic mechanism is a complex interplay between band filling, electric field at the interface and modification of conducting channel width.

A Micro Broadband Photodetector Based on Single Wall Carbon Nanotubes-Graphene Heterojunction

A room-temperature broadband (visible to near infrared spectrum) photodetector based on single wall carbon nanotubes (SWCNTs) and graphene heterojunction was fabricated in this work, by drop-casting the SWCNTs suspension onto the graphene field-effect transistor with the buried-gate electrode. A high photoresponsivity of 109 A/W and a fast photoresponse speed of 2.9 ms were obtained within the visible region based on the photogating effect. This high gain mechanism leads to a high photoconductive gain (9.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ). In addition, the photodetector exhibits a photoresponsivity of 51.5 A/W at 940 nm, indicating a wide spectrum detection capability. Moreover, a higher photoresponsivity can be obtained by tuning the source-drain and gate bias voltages. This approach provides an easy and feasible way to achieve broadband heterojunction photodetectors with high-performance.

Electrical Properties in Ta2NiSe5 Film and van der Waals Heterojunction

Ternary Ta2NiSe5 is a novel electronic material having the property of an excitonic insulator at room temperature. The electrical properties of Ta2NiSe5 have not been elucidated in detail. We discuss the electronic properties in Ta2NiSe5 films and the formation of heterojunctions. Hall effect measurements showed p-type conductivity. The activation energies estimated from the temperature dependence of the carrier concentration were seen to be 0.17 eV and 0.12 eV, at approximately 300 and 400 K, respectively. It was observed that carrier generation behavior changes at the critical temperature of the excitonic insulator state (328 K). The temperature dependence of the Hall mobility below the critical temperature nearly follows the bell-shaped curves for conventional semiconductor materials. A MoS2/Ta2NiSe5 van der Waals heterojunction was fabricated using the transfer method. Rectification characteristics, which depend on the gate bias voltage, were obtained. The barrier height at the MoS2/Ta2NiSe5 heterointerface and the on/off ratio could be modulated by applying a gate bias voltage, suggesting that the carrier transport was exhibited in band-to-band flow. Our demonstration suggests that the knowledge of Ta2NiSe5 increased as an electronic material, and diode performance was successfully achieved for the electronic device applications.

Microwave response of an Andreev bound state

We develop a theory for the dynamics of an Andreev bound state hosted by a weak link of finite length for which charging effects are important. We derive the linear response of both the current through the link and charge accumulated in it with respect to the phase and gate voltage biases. The resulting matrix encapsulates the spectroscopic properties of a weak link embedded in a microwave resonator. In the low-frequency limit, we obtain the response functions analytically using an effective low-energy Hamiltonian, which we derive. This Hamiltonian minimally accounts for Coulomb interaction and is suitable for a phenomenological description of a weak link having a finite length.

Electrically and Optically Controllable p-n Junction Memtransistor Based on an Al2 O3 Encapsulated 2D Te/ReS2 van der Waals Heterostructure.

The exploration of memtransistors as a combination of a memristor and a transistor has recently attracted intensive attention because it offers a promising candidate for next-generation multilevel nonvolatile memories and synaptic devices. However, the present state-of-the-art memtransistors, which are based on a single material, such as MoS2 or perovskite, exhibit a relatively low switching ratio, require extremely high electric fields to modulate bistable resistance states and do not perform multifunctional operations. Here, the realization of an electrically and optically controllable p-n junction memtransistor using an Al2 O3 encapsulated 2D Te/ReS2 van der Waals heterostructure is reported. The hybrid memtransistor shows a reversible bipolar resistance switching behavior between a low resistance state and a high resistance state with a high switching ratio up to 106 at a low operating voltage (<10V), high cycling endurance, and long retention time. Moreover, multiple resistance states are achieved by applying different bias voltages, gate voltages, or light powers. In addition, logical operations, including the inverter and AND/OR gates, and synaptic activities are performed by controlling the optical and electrical inputs. The work offers a novel strategy for the reliable fabrication of p-n junction memtransistors for multifunctional devices and neuromorphic applications.

Envelope-function-based analysis of the dependence of shot noise on the gate voltage in disordered graphene samples

We perform simulations, by means of an envelope-function-based approach, of shot noise in disordered monolayer graphene devices, as a function of the gate bias voltage. In order to approach the experimental conditions, large graphene samples with characteristic sizes of the order of hundreds of nanometers or microns have been considered. We investigate different device geometries, including back-gated graphene samples with different aspect ratios and a graphene constriction biased by two side gates. We compare our results with available experimental data that were collected by a few authors in an attempt to validate an interesting prediction made by Tworzyd\l{}o et al. [Phys. Rev. Lett. 96, 246802 (2006)] on the shot noise dependence on carrier density in samples with a large aspect ratio. On the basis of the comparison of our results with the experimental data, we conclude that the effect predicted by Tworzyd\l{}o et al. (resulting from the distribution of the transmission eigenvalues associated with propagation via evanescent modes) has not been observed yet. Finally, we provide some guidelines for the design of experiments aimed at the verification of such an effect.

Investigating the Impact of Self-Heating Effects on some Thermal and Electrical Characteristics of Dielectric Pocket Gate-all-around (DPGAA) MOSFETs

The dielectric pocket gate-all-around (DPGAA) MOSFET is being considered the best suited candidate for ULSI electronic chips because of excellent electrostatic control over the channel. However, the phenomena of self-heating and hot carrier injection (HCI) severely affect the performance of the device, and make the behaviour of the DPGAA FET very unpredictable. In the present article, a comprehensive investigation under the influence of self-heating effects has been done for the variation in the lattice and carrier temperature against spacer length, ambient temperature, device length, and thermal contact resistance including ON and Off currents with gate bias voltage (VGS). In order to analyse the SHEs, the hydrodynamic (HD) and thermodynamic (TD) transport models have been used for three-dimensional (3D) electrothermal (ET) simulation. The Lucky (hot carrier injection) model has been used to study the HCI degradation in DPGAA MOSFET using Sentaurus 3D TCAD simulator.

Gate-Induced Threshold Voltage Instabilities in p-Gate GaN HEMTs

In this study, we investigate the threshold voltage ( V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> th</sub> ) instability of p-gate GaN HEMTs induced by gate bias. Experimental results are acquired by a custom pulse setup for two commercially available devices with an ohmic gate and a Schottky gate. A transient drain current change is observed, which corresponds to a shift of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> th</sub> . A negative V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> th</sub> instability is identified for the ohmic gate, a mostly positive for the Schottky gate that can also become negative depending on the gate bias voltage and duration. The impact of the gate-bias-induced V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> th</sub> instability on the Schottky-gate device is significantly higher compared to the ohmic-gate device, but clearly noticeable at the nominal rated ON-state gate voltage for both devices. Electron depletion and trapping as well as hole accumulation and trapping are identified to cause this transient V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> th</sub> instability.