Knee Voltage Research Articles

InAlN/GaN HEMT With n+GaN Contact Ledge Structure for Millimeter-Wave Low Voltage Applications

In this work, high performance InAlN/GaN HEMT based on the n+GaN regrown ohmic contact with n+GaN contact ledge structure is proposed. The regrown ohmic contact of InAlN/GaN HEMT is formed by MBE n+GaN regrowth and selfstopping etching, which makes the total ohmic contact resistance between the 2DEG channel and the ohmic metal decrease to 0.12 Ωmm and forms n+GaN contact ledge structure. Owing to the n+GaN contact ledge on the InAlN barrier, with the increasing of drain-source voltage (VDS), an additional current path comes into being between the n+GaN contact ledge on the InAlN barrier and the 2DEG channel, which can “shorten” the device effective drainsource distance, thus further reducing the parasitic resistance. Compared with regrown InAlN/GaN HEMT without n+GaN contact ledge structure, the peak transconductance (Gm.max) of regrown InAlN/GaN HEMT with n+GaN contact ledge structure increases from 747 mS/mm to 874 mS/mm, and the saturation current density (ID.max) increases from 2.6 A/mm to 2.9 A/mm. Besides, the self-stopping etching on the access region does not induce extra defects, and negligible current collapse is obtained. As the results of low parasitic resistance, high output current density, low knee voltage and negligible current collapse, poweradded-efficiency (PAE) of 44% together with output power density (Pout) of 2.5 W/mm is achieved at 30 GHz and VDS of 10 V, which indicates regrown InAlN/GaN HEMT with n+GaN contact ledge structure has great potential for millimeter-wave low voltage applications. Additionally, the transfer and schottky gate characteristics show negligible degradation after OFF/ON-state electrical stress tests.

Synthesis of Self-Assembled Single Atomic Layer Gold Crystals-Goldene.

We report, for the first time, a technique to synthesize free-standing, one-atom thick 2D gold crystals (namely, goldene) and self-assembled 2D periodic arrays of goldene. High-resolution transmission electron microscopy (HRTEM) imaging of goldene revealed herringbone and honeycomb lattices, which are primarily gold surface features due to its reconstruction. Imaging of these surface-only features by a nonsurface characterization technique such as HRTEM is an unequivocal proof of the absence of three-dimensionality in goldene. Atomic force microscopy confirmed 1-2 Å thickness of goldene. High-resolution X-ray photoelectron spectroscopy (HR-XPS), selective area electron diffraction, and energy-dispersive X-ray spectroscopy confirmed the chemical identity of goldene. We discovered the phenomenon of electric field-induced self-assembly of goldene supracrystals with a herringbone structure and developed an electric field printing (e-print) technique for goldene arrays. Goldene showed a semiconductor response with a knee voltage of ∼3.2 V, and I/V spectroscopy revealed periodic room temperature Coulomb blockade oscillations. These observations are consistent with the theoretical calculations reported in the literature predicting enhanced Coulombic interactions between gold valence electrons and the nucleus in stable 2D gold. Goldene exhibited multiple, intense, and well-resolved optical absorption peaks and several fine bands across the UV-vis region, and we calculated its optical band gap to be 3.59 eV. Magnetic force microscopy measurements of goldene periodic arrays showed a ∼5 mV peak amplitude confirming its ferromagnetism. Optical and magnetic properties of goldene are consistent with those reported in the literature for 2D planar gold clusters with less than 12 atoms.

Aluminum doped Zinc oxide anode film for performance enhancement of trilayer fluorescence organic light emitting diode

The industrialization of fluorescence organic light-emitting diodes (OLEDs) has seriously been impacted by high fabrications cost and a short device lifespan. Particularly for transparent conductive anodes (TCA) in an OLED, which benefit manufacturing the simplest configuration with an abundant platform, more flexibility, potentially low cost-effective, and wide-ranging light flux. The goal of this effort has been to look into the possibility of aluminum-doped zinc oxide (AZO) as TCA, typically AZO/SpiroOMeTAD/Alq3: Ir(ppy)3/Bphen/LiF/Al structure is remarkably thought-out by drift–diffusion model. In addition, maximizing the light flux and minimizing the knee voltage necessitates a well-organized trilayer bandgap alignment towards exciton confinement and steadiness charge carrier transport. To enhances the hysteresis of the recombination prefactor through the higher hopping mechanism, the organic layers are staked in between AZO anode and bilayer cathode (LiF/Al) units. Moreover, optimization of the device structure is intended to eliminate the influence on OLED performances under the better thickness adjustment of consecutive layers. The maximum light flux of 1.7095 × 102 Wm−2 has been attained for 70 nm thickness of SpiroOMeTAD as hole conducting layer (HCL), 10 nm thickness of Alq3 as an organic emissive layer (OEL) with Ir(ppy)3 emitter, and 80 nm thickness of Bphen as electron conducting layer (ECL). The exposed different optoelectronic appearance curve signifies the maximum charge carrier density and current density of 1.18 × 1024 m−3, and 1.035 × 106 Am−2 for knee voltages of 2.64 V. The highest recombination prefactor of 1.174 × 10-21 m-6s−1 is achieved at 300 K for different opto-electrical considerations. Hence, future studies may be an alternative strategy for enlightening the efficiency of AZO anode-based OLEDs.

Study of Electrochemical Properties of Compared Indigo for Metal–Semiconductor–Metal Diode

Indigo blue was discovered as a semiconductor material because of its organic semiconductor properties. This paper shows a primary study of the electrochemical properties of Sakon Nakhon-indigo strain used in the metal–semiconductor–metal (MSM) diode. The fermentation and extraction of our local indigo plant are explained. Indian indigo in the MSM diode is compared in the same conditions of preparation. The electrochemical properties, including the current–voltage (I–V) characteristic, static resistance, and rectification ratio, are discussed. The results show that the electron and hole characteristics and band gap energy of the indigo blue affects the electrochemical properties of the device. Our local MSM diode has a suitable operation between −1 and +3 VMSM with a knee voltage of 1.0 VMSM. Especially, it can produce the highest forward-bias current of about 3.19 mA at linear operation between +2 and +3 VMSM, whereas the review MSM diode is about 2–3 hundred times lower. This shows that this strain has more conductive properties because of its effective electron and hole characteristics obtained by an indigo yield concentration. Therefore, the MSM diode based on Sakon Nakhon-indigo strain is an important role in an electronic semiconductor device for low voltage consumption and high sensitivity. In the future, the molecular characteristics of local indigo may be deeply analyzed to be further developed into a thin-film form used as an organic semiconductor material in several electronic devices.

Study of the influence of gate etching and passivation on current dispersion, trapping and reliability in RF 0.15 μm AlGaN/GaN HEMTs

In this paper we examine the effect of passivation and gate etching processes on the current dispersion and reliability of AlGaN/GaN HEMTs for RF applications. We compared the performance of HEMTs with a standard gate etching and passivation processes (reference wafer) with the performances of HEMTs with improved etching process (etching variant wafer) and improved passivation process (passivation variant wafer). In order to study the trapping behavior, we performed dispersion measurements in off-state conditions and drain current transients (DCT) and we found that:1)The use of improved passivation process determines a decrease of current dispersion, in particular at the knee voltage, where current collapse depends on both threshold voltage and on-resistance variation,2)The trapping process linked to surface states is influenced by the gate etching and passivation processes; the use of improved passivation slows down the trapping/de-trapping kinetics, resulting in a lower impact on dynamic performance.The study of reliability is based on high-temperature reverse bias (HTRB) stresses. The gate-drain diodes are biased in the same voltage stress conditions (VGS,Stress = -7 V, VDS,Stress = 50 V) at high temperatures (175 °C) for 24 h. We demonstrated that the improved passivation limits the increase of gate leakage current during HTRB stress and prevents the belly shape effect linked to the presence of donor traps in the surface between SiN and GaN cap.We performed gate step stress increasing the negative voltage applied to the Schottky contact. The electroluminescence images performed during the stress show spots along the gate finger that are the responsible of the failure of the devices. The results presented in the paper provide information on the optimization of GaN HEMTs for RF applications.

Preparation of Hybrid Junction Light Emitting Device from Cadmium Sulphite Quantum dot/ poly-TPD Junction

Stratums of ITO/TPD:PMMA/CdS/Alq3/Al were used to make the hybrid nanoparticles light emitting diode (NPs-LED), which were created using the phase segregation method and the spin coating procedure. Light-generating NPs-LED hybrid device is composed of 3 stratums stacked in a certain order on an Indium tin oxide(ITO) substrate made of transparent conducting oxide. The first stratum was (N, N'-bis (3-methylphenyl)-N, N'-bis (phenyl) benzidine) (TPD) polymer, and polymethyl methacrylate (PMMA) polymer. Cadmium Sulphite (CdS) is the second stratum, while Tris (8-hydroxyquinolinato) aluminum (Alq3) is the last stratum, which is one of the materials used as electron injector stratums.
 Various bias voltages (28, 30, and 32V) were used to examine the electroluminescence (EL) of NPs-LEDs at room temperature, depending on the CIE 1931 color spaces, `light was created at 32V, whereas blue light was generated at 28V. The transmission between sub levels in the energy gap of CdS NPs (surface state). Voltages are controlling the current change, and the knee voltage is 6.6 V, as seen by the current – voltage (I-V) distinctive. EL spectrum demonstrates a broadband emission spanning 300 nm to 700 nm. Finally, it is discovered that the correlated color temperature (CCT) is about (7450 to 11820k).

2+δ-Dimensional Materials via Atomistic Z-Welding.

Pivotal to functional van der Waals stacked flexible electronic/excitonic/spintronic/thermoelectric chips is the synergy amongst constituent layers. However; the current techniques viz. sequential chemical vapor deposition, micromechanical/wet-chemical transfer are mostly limited due to diffused interfaces, and metallic remnants/bubbles at the interface. Inter-layer-coupled 2+δ-dimensional materials, as a new class of materials can be significantly suitable for out-of-plane carrier transport and hence prompt response in prospective devices. Here, the discovery of the use of exotic electric field ≈106 Vcm- 1 (at microwave hot-spot) and 2 thermomechanical conditions i.e. pressure ≈1MPa, T≈ 200°C (during solvothermal reaction) to realize 2+δ-dimensional materials is reported. It is found that Pz Pz chemical bonds form between the component layers, e.g., CB and CN in G-BN, MoN and MoB in MoS2 -BN hybrid systems as revealed by X-ray photoelectron spectroscopy. New vibrational peaks in Raman spectra (BC ≈1320cm-1 for the G-BN system and MoB ≈365cm-1 for the MoS2 -BN system) are recorded. Tunable mid-gap formation, along with diodic behavior (knee voltage ≈0.7V, breakdown voltage ≈1.8V) in the reduced graphene oxide-reduced BN oxide (RGO-RBNO) hybrid system is also observed. Band-gap tuning in MoS2 -BN system is observed. Simulations reveal stacking-dependent interfacial charge/potential drops, hinting at the feasibility of next-generation functional devices/sensors.

Monolithic Reverse Blocking 1.2 kV 4H-SiC Power Transistor: A Novel, Single-Chip, Three-Terminal Device for Current Source Inverter Applications

Current sourceinverters (CSIs) require power switches with first quadrant current conduction and gate-controlled output characteristics as well as reverse blocking capability. Experimental demonstration of a SiC monolithic reverse blocking transistor (MRBT) suitable for CSI applications is described in this letter. The proposed device is based on the integration of a SiC JBS diode with a SiC power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> on the same chip. The cathode of the SiC JBS diode is connected to the drain of the SiC power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> by their common N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> substrate. The proposed device structure creates a novel SiC-based unipolar single-chip three-terminal transistor with reverse blocking capability. The measured characteristics of a 1.2 kV 4H-SiC MRBT, fabricated in a commercial six-inch wafer foundry, are reported in this letter. The devices show a diode-like <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state characteristic with a low knee voltage of 1.3 V and an <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state voltage drop of 2.8 V at 5 A. The measured reverse transfer capacitance and output capacitance for the MRBT at a drain bias of 2 and 1000 V are a factor of ∼3x and ∼1.6x smaller than the measured values for the internal <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> device. Switching measurements show a 12% reduction in the gate-drain charge for the MRBT compared with the internal <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> which is favorable for reducing switching losses.

An AlGaN/GaN Lateral Bidirectional Current-Regulating Diode with Two Symmetrical Hybrid Ohmic-Schottky Structures.

Bidirectional current-regulating ability is needed for AC light emitting diode (LED) drivers. In previous studies, various rectifier circuits have been used to provide constant bidirectional current. However, the usage of multiple electronic components can lead to additional costs and power consumption. In this work, a novel AlGaN/GaN lateral bidirectional current-regulating diode (B-CRD) featuring two symmetrical hybrid-trench electrodes is proposed and demonstrated by TCAD Sentaurus (California USA) from Synopsys corporation. Through shortly connecting the Ohmic contact and trench Schottky contact, the unidirectional invariant current can be obtained even with the applied voltage spanning a large range of 0–200 V. Furthermore, with the combination of two symmetrical hybrid-trench electrodes at each side of the device, the proposed B-CRD can deliver an excellent steady current in different directions. Through the TCAD simulation results, it was found that the device’s critical characteristics (namely knee voltage and current density) can be flexibly modulated by tailoring the depth and length of the trench Schottky contact. Meanwhile, it was also demonstrated through the device/circuit mixed-mode simulation that the proposed B-CRD can respond to the change in voltage in a few nanoseconds. Such a new functionality combined with excellent performance may make the proposed B-CRD attractive in some special fields where the bidirectional current-limiting function is needed.

Fast Unveiling of T max in GaN HEMT Devices via the Electrical Measurement-Assisted Two-Heat Source Model

Gallium nitride (GaN) high-electron-mobility transistor (HEMT) devices, which have wide application potential from power amplifiers to satellite, need to be thoroughly examined in terms of reliability in order to benefit the superior intrinsic properties of the device. The most critical parameter in the device reliability is the hotspot, or <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> , which occurs somewhere on the subsurface and along the channel of the GaN HEMT, which is optically inaccessible due to optical path disability. Therefore, the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> value is underestimated in optical measurements, such as the thermographic IR and Raman methods. With 3-D electrothermal simulations, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> is obtained close to reality, but it requires a huge computation load and the complex modeling of semiconductor device physics. In 2-D or 3-D thermal simulations that do not use electrothermal simulations, since the self-heating is mostly modeled with a single heat source, neither the correct <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> value is obtained nor the effect of bias conditions is considered. To address the aforementioned shortcomings, a hybrid method is demonstrated, which exploits the electrical measurements of GaN HEMT, which RF and reliability engineers often and easily do. It is demonstrated that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${T}_{\text {max}}$ </tex-math></inline-formula> can be determined quickly and close to the electrothermal simulations in a GaN HEMT device with a two-heat source method and finite element analysis (FEA) hybrid interaction with respect to various bias conditions. Moreover, the impact of the knee voltage is investigated with different knee-detection techniques. The proposed method provides GaN HEMT reliability engineers with an easy-to-implement alternative to reveal the hotspot location and the value.

Record &amp;gt;10 MV/cm mesa breakdown fields in Al0.85Ga0.15N/Al0.6Ga0.4N high electron mobility transistors on native AlN substrates

The ultra-wide bandgap of Al-rich AlGaN is expected to support a significantly larger breakdown field compared to GaN, but the reported performance thus far has been limited by the use of foreign substrates. In this Letter, the material and electrical properties of Al0.85Ga0.15N/Al0.6Ga0.4N high electron mobility transistors (HEMT) grown on a 2-in. single crystal AlN substrate are investigated, and it is demonstrated that native AlN substrates unlock the potential for Al-rich AlGaN to sustain large fields in such devices. We further study how Ohmic contacts made directly to a Si-doped channel layer reduce the knee voltage and increase the output current density. High-quality AlGaN growth is confirmed via scanning transmission electron microscopy, which also reveals the absence of metal penetration at the Ohmic contact interface and is in contrast to established GaN HEMT technology. Two-terminal mesa breakdown characteristics with 1.3 μm separation possess a record-high breakdown field strength of ∼11.5 MV/cm for an undoped Al0.6Ga0.4N-channel layer. The breakdown voltages for three-terminal devices measured with gate-drain distances of 4 and 9 μm are 850 and 1500 V, respectively.

Effect of Substrate Temperature on the Properties of RF Magnetron Sputtered p-CuInOx Thin Films for Transparent Heterojunction Devices

Copper indium oxide (CuInOx) thin films were deposited by the RF magnetron sputtering technique using a Cu2O:In2O3 target at varying substrate temperatures up to 400 °C. Mutually exclusive requirements of having a p-type thin film along with increased conductivity and high transparency were achieved by controlling the migration of indium oxide phases during the sputtering process, as verified by the XPS studies. A morphological study performed using SEM further confirmed the crystallization and the grain growth (95–135 nm) with increasing substrate temperatures, resulting in superior conductivity and an enhanced transparency of more than 70% in the 400–700 nm range. This is due to the controlled replacement of copper sites with indium while maintaining the p-type characteristic of the thin film. Optical studies carried out on the films indicated a bandgap change in the range of 2.46–2.99 eV as a function of substrate heating. A p-CuInOx/n-Si heterojunction was fabricated with a measured knee voltage of 0.85 V. The photovoltaic behavior of the device was investigated and initial solar cell parameters are reported.

High performance millimeter-wave InAlN/GaN HEMT for low voltage RF applications via regrown Ohmic contact with contact ledge structure

Benefitting from regrown Ohmic contact with a contact ledge structure, high performance millimeter-wave InAlN/GaN HEMT is fabricated to satisfy low voltage RF applications. Different from the commonly seen fabrication process for regrown Ohmic contact, the scheme proposed in this work features MBE regrowth of n+ GaN on the whole wafer after formation of regrowth well without masks and partial removal of n+ GaN grown on the access region by self-stopping etching. The remaining n+ GaN on the barrier, serving as contact ledges, provides an additional current path to achieve the reduced equivalent source-drain distance and, thus, improved output current, and more current contribution is made by contact ledge as the actual source-drain distance shrinks. With the assistance of contact ledge, the fabricated device demonstrates output current density of 2.8 A/mm, a peak extrinsic transconductance of 823 mS/mm, a knee voltage of 1.6 V, and an on-resistance of 0.47 Ω·mm. Although self-stopping etching is performed on the access region, the device exhibits ignorable current collapse. At 30 GHz and VDS of 6 V, decent power-added-efficiency of 52% together with output power density of 1.2 W/mm is achieved, revealing the great potential of the proposed regrown Ohmic contact with contact ledge structure for low voltage RF applications.

8.7 W/mm output power density and 42% power-added-efficiency at 30 GHz for AlGaN/GaN HEMTs using Si-rich SiN passivation interlayer

In this work, high-performance millimeter-wave AlGaN/GaN structures for high-electron-mobility transistors (HEMTs) are presented using a Si-rich SiN passivation layer. The analysis of transient and x-ray photoelectron spectroscopy measurements revealed that the presence of the Si-rich SiN layer leads to a decrease in the deep-level surface traps by mitigating the formation of Ga–O bonds. This results in a suppressed current collapse from 11% to 5% as well as a decreased knee voltage (Vknee). The current gain cutoff frequency and the maximum oscillation frequency of the devices with the Si-rich SiN layer exhibit the values of 74 and 140 GHz, respectively. Moreover, load-pull measurements at 30 GHz show that the devices containing the Si-rich SiN deliver excellent output power density of 8.7 W/mm at Vds = 28 V and high power-added efficiency up to 48% at Vds = 10 V. The enhanced power performance of HEMTs using Si-rich SiN interlayer passivation is attributed to the reduced Vknee, the suppressed current collapse, and the improved drain current.

Numerical study of aluminum doped zinc oxide anode based fluorescent bilayer organic light-emitting diode

The simulation study is carried out to investigate the performance of organic light-emitting diode (OLED), AZO/NPB/Alq3: Ir(ppy)3/LiF/Al configuration. To minimize the turn-on (knee) voltage, the LiF layer is staked with the organic emissive layer's (OEL's) and cathode. This interface enhances hysteresis of recombination prefactor due to the higher hopping effect of OEL with bilayer cathode unit (LiF/Al). To counteract such improvements, an electron injecting layer (EIL) free OLED is considered to nullify the impact under the thickness optimization of OEL. The maximum light flux of 9.5 × 106 Wm−2 has been achieved for 20 nm thickness of electron emission layer/electron transport layer (EML/ETL) and 10 nm thickness of hole transport layer (HTL). Thus, portrayed different characteristics curve implies the charge density and mean current density is 3 × 1024 m−3, and 1.2 × 106 Am−2 at 1.75 V turn-on (knee) voltages, respectively. The maximum recombination prefactor of 4 × 10−17 m−6 s−1 is found at 300 K for different optoelectronic parameters. This study also offers an alternative way to optimize further the efficiency of the Aluminium doped zinc oxide (AZO) anode contact OLED devices.

Channel Design Optimization for 1.2-kV 4H-SiC MOSFET Achieving Inherent Unipolar Diode 3rd Quadrant Operation

1.2 kV 4H-SiC MOSFETs operating with a low knee voltage and forward voltage drop under third quadrant mode are proposed and experimentally demonstrated by using optimized accumulation mode channels to eliminate external SiC SBDs in power converter applications. By removing epitaxial regrowth process step, the overall fabrication process for the proposed MOSFET is more concise and manageable. Channel design parameters, such as channel doping concentration, channel length, and different gate oxides were investigated to achieve low knee voltage and forward voltage drop under third quadrant operation mode ensuring high breakdown voltages. To understand the impact of channel potential (barrier) on the current conduction behavior as well as leakage current during the blocking mode, 2D simulations were conducted. In addition, the reverse recovery characteristics and switching characteristics are discussed. Based on the optimized channel design, the promising devices for high density power electronics are proposed.

NiO/AlGaN interface reconstruction and transport manipulation of p-NiO gated AlGaN/GaN HEMTs

Normally off AlGaN/GaN high electron mobility transistors with a p-type gate are promising for power switching applications, with advantages of low energy consumption and safe operation. In this work, p-NiO is employed as a gate stack, and the interfacial reconstruction and band structure modification at the p-NiO/AlGaN interface have been demonstrated to manipulate channel transport of AlGaN/GaN high electron mobility transistors by post-annealing. In addition to achieving a positive threshold voltage of 0.6 V and a large saturation output current of 520 mA/mm, we found that the gate leakage and On/Off drain current ratio can be improved significantly by more than 104 due to the p-NiO/AlGaN interfacial reconstruction. However, high annealing temperature also results in an increasing ON-resistance and a dramatically increased knee voltage (VK), which can be attributed to the formation of an ultra-thin γ-Al2O3 layer and the substitution of O on N site as a shallow donor at the p-NiO/AlGaN interface confirmed by experimental analyses. Theoretical calculations indicate that such interface reconstruction facilitates an additional potential well at the p-NiO/AlGaN interface to which electrons are spilled out from a two-dimensional electron gas channel under high forward gate voltage, resulting in the increased VK. Finally, an optimized annealing condition was confirmed that can eliminate this increased VK phenomenon and simultaneously remain these significantly improved device performances. These findings provide deep understanding of the performance manipulation of AlGaN high electron mobility transistors, which is very important for engineering the p-NiO/AlGaN interface toward high-performance and stable devices.

Numerical Study of SiC MOSFET With Integrated n-/n-Type Poly-Si/SiC Heterojunction Freewheeling Diode

It is highly desirable to monolithically integrate a high-performance freewheeling diode (FWD) in both Si and SiC power MOSFETs for power electronic applications. This is especially true for a SiC MOSFET since its inherent body diode has a very large turn-on knee voltage (~2.7 V). The purpose of this numerical study is to investigate a new 1200 V SiC MOSFET structure with an integrated heterojunction diode formed between n-type polysilicon and n-type SiC (termed HJD-MOSFET). The proposed HJD-MOSFET uses a mesa structure to accommodate the heterojunction FWD without sacrificing any active area while leaving the split-gate planar MOSFET cells in the trench. A p-shield region surrounding the heterojunction, along with the p-base of the MOS cells, shields high electric fields and maintains a high breakdown voltage. Three key HJD-MOSFET device parameters are identified and optimized in this article. The HJD-MOSFET offers a turn-on knee voltage of 0.5 V, roughly five times lower than the intrinsic SiC body diode or two times lower than a typical SiC Schottky barrier diode due to the low barrier height of the n/n heterojunction (~0.68 eV). Finally, the gate charge of HJD-MOSFET is reduced by 42% compared with conventional MOSFET since the poly-Si gate electrode is significantly reduced to accommodate the heterojunction FWD.

Gate-on-Drain Overlapped L-Shaped Channel Tunnel FET as Label-Free Biosensor

In this work gate-on-drain L-shaped channel Tunnel FET is proposed to detect various biomolecules through label-free bio-sensing detection technique. Biomolecules can be detected in the proposed structure through modulation of ambipolar current between channel and drain. Modulation of ambipolar current is performed by extending gate over drain in order to create a gate to drain overlap (cavity) by etching the specific portion of the gate. Trapped biomolecules within cavity gets immobilized. Immobilized biomolecules change the drain to channel tunneling width, thus changing the ambiploar leakage current. Drain doping and cavity length was fine-tuned to achieve better sensitivity in terms of ambipolar current and ambipolar knee voltage shift with and without presence of biomolecules. A maximum sensitivity of 3.8 × 107 is achieved for drain doping of 5 × 1019 donors/cm3 and cavity length of 60 nm. A high value of sensitivity is achieved for each biomolecules when drain doping ranged from 1019 donors/cm3 to 5 × 1019 donors/cm3 and cavity length ranged between 40 nm to 50 nm. Effect of differently charged biomolecules on sensitivity has also be structured.

Epitaxial Molybdenum Disulfide/Gallium Nitride Junctions: Low-Knee-Voltage Schottky-Diode Behavior at Optimized Interfaces.

Low turn-on (knee) voltage (∼0.3 V) Schottky-diode behavior of a four-layer (4L) MoS2/GaN junction is achieved by optimizing the in situ interface preparation of the GaN substrate prior to MoS2 overlayer growth in a vacuum system using metallic molybdenum and hydrogen sulfide gas as precursors. The process leads to a clean nitrogen-terminated GaN surface that bonds well to the MoS2 film revealing a 2 × 2 reconstruction at the interface observed in low-energy electron diffraction (LEED). Atomic force microscopy and X-ray photoelectron spectroscopy provide clear images of the GaN terraces through the MoS2 overlayer confirming close adhesion and absence of oxygen and other contaminants. Density functional theory calculations predict the formation of the 2 × 2 superstructure at a clean interface. Transport measurements show diode behavior at an on/off ratio of ∼105 for ±1 V with a forward direction for the positive voltage applied to the MoS2 layer. Combining transport and photoelectron spectroscopy measurements with theory, we deduce a Fermi-level position in the MoS2 gap consistent with interface charge transfer from MoS2 to the substrate. The high performance of the MoS2/Gan diode highlights the technological potential of devices based on GaN/MoS2 interfaces.