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In this paper, a magnon-bandgap controllable artificial domain wall waveguide is proposed by means of micromagnetic simulation. By the investigation of the propagation behavior and dispersion relationship of spin waves in artificial domain wall waveguides, it is found that the nonreciprocal propagation of spin waves in the artificial domain walls is mainly affected by the local effective exchange field, and the magnon bandgap can be controlled by changing the maximum value of the effective exchange field. In addition, it is observed that the artificial domain wall waveguides are structurally more stable than the natural domain wall waveguides under the same spin wave injection conditions, and the magnon bandgap of the artificial domain wall waveguides can be adjusted by its width and magnetic anisotropy parameters. The bandgap controllable artificial domain wall scheme is beneficial to the miniaturization and integration of magnon devices and can be applied to future magnonic technology as a high-pass filter with adjustable cutoff frequency. [ABSTRACT FROM AUTHOR]

A three-dimensional breakdown behavior of the magnetic Bloch-point domain wall (BP-DW) propagation was investigated in a ferromagnetic nanowire with the variation of the external magnetic field by means of micromagnetic simulation. As magnetic field strength increases up to a threshold value, the BP-DW velocity approaches a critical phase velocity of the spontaneously emitting spin wave (SW), where a Cherenkov-type DW breakdown phenomenon is observed originating from an interaction between the spontaneously emitting SW and the BP-DW. It is found that the velocity of the BP-DW approaches a maximum value (∼2000 m/s) due to the intrinsic reversal time of a BP spin texture. This suggests that although cylindrical ferromagnetic nanowires might be free from the two-dimensional Walker breakdown phenomenon, there exists a Cherenkov-type three-dimensional breakdown behavior. [ABSTRACT FROM AUTHOR]

The impact of the nanochannel geometry on the thermal performance of AlGaN/GaN Fin-HEMTs was investigated. Structures with a larger nanochannel space (Sfin) or a smaller nanochannel width (Wfin) show the suppressed self-heating effect, which was confirmed by the smaller dispersion between DC and pulsed measurements together with the reduced high temperature degradation of the drain current. A closed-form expression based on the heat flow theory was used to illustrate the coupling effect of Wfin and Sfin, and the channel temperature was mapped considering the different nanochannel geometries. As Wfin and Sfin scale down simultaneously, the nanochannel structure would present a much lower channel temperature, demonstrating that the heat generation dominated by Wfin has a greater impact on the self-heating in Fin-HEMTs. [ABSTRACT FROM AUTHOR]

The impact of embedded microfluidic cooling on the performance of Ku-band gallium nitride (GaN) microwave monolithic integrated circuit (MMIC) power amplifiers (PAs) has been studied in this work. The research demonstrates that embedded cooling can substantially lower junction temperatures, mitigate the self-heating effect, and thereby improve the electrical performance of GaN MMIC PAs. Using merely 10.4 mW of pumping power (Ppump), the technology reduces the maximum junction temperature (Tj,max) from 216.7 to 147.8 °C. Furthermore, the system enhances the saturation current by 13.8%, increases output power (Pout) and gain (Gain) by 1.8 dB, elevates the power added efficiency (PAE) by 5.9%, and improves the heat flux of last gate (Qgate) to 37.3 kW/mm2 and the heat flux of MMIC (QMMIC) over 2.6 W/mm2, while reducing the thermal resistance (Rj-c) from 2.13 to 1.26 °C/W. Additionally, there is a notable improvement of the small signal gain (S21) by 2.5 dB. Therefore, the achievements in this work indicate that embedded cooling offers a powerful technique to suppress the thermal effects on GaN MMIC PAs, consequently improving their electrical performance. [ABSTRACT FROM AUTHOR]

In this work, the effects of proton-induced trap evolution on the electrical performances of AlGaN/GaN metal–insulator–semiconductor (MIS) high-electron-mobility-transistors (HEMTs) have been investigated in detail. Contrary to observed proton-induced degradation in sheet electron density (ns), carrier mobility (μn), and sheet resistance (RSH), a significant improvement in gate leakage current (IG) and off-state drain–source breakdown voltage (BVDS) is found in irradiated devices. The low-frequency noise (LFN) results show that the density of traps in the AlGaN layer and AlGaN/GaN interface increases after irradiation, which leads to a degradation in ns, μn, and RSH and an improvement in BVDS due to enhanced electron trapping and depletion. Furthermore, the measurement results obtained from the frequency-dependent conductance technique show that irradiated devices exhibit decreased trap density (DT) at the insulator/semiconductor interface with hardly changed trap energy level (ET), which confirms the observed proton-induced decrease in IG. An increase in DT at the AlGaN/GaN interface is also found after irradiation, which is consistent with LFN results. These traps with deeper ET induce a serious Coulomb scattering effect. This work provides valuable information for the systematic understanding of the proton irradiation effect of AlGaN/GaN MIS-HEMTs. [ABSTRACT FROM AUTHOR]

An obvious increase in the gate leakage current has been commonly observed in GaN HEMTs, after Plasma-enhanced chemical vapor deposition (PECVD) SiN passivation has been observed to obviously increase. This paper presents an Al/SiN stack layer passivation structure. The high gate leakage current in GaN HEMTs caused by the PECVD SiN passivation is distinctly reduced by 2 to 3 orders of magnitude by introducing a thin Al layer. It is mainly attributed to the Al layer blocking and minimizing the damage for the (Al)GaN surface in the build-up of the luminance process of PECVD SiN and then reducing the surface trap density. TEM mapping and SRIM software simulation reveal that neither damage nor inter-diffusion is demonstrated at the Al/AlGaN interface, where a continuous crystalline region is observed. The moderate current collapse suppression and 32.8% improvement in VBR are achieved in GaN HEMTs with Al/SiN passivation. [ABSTRACT FROM AUTHOR]

This Letter reports two kinds of oxygen-containing plasma treated β-Ga2O3 Schottky barrier diodes (SBDs), including N2O plasma treatment and O2 plasma treatment, and the SBD without plasma is prepared for comparison. I–V characteristics, breakdown characteristics, and trap state characteristics of three devices have been studied. It is found that the turn-on voltage of SBDs with N2O plasma can reduce to 0.6 V, and the better current density of 750 A/cm2 and an on-resistance of 3.5 mΩ cm2 are obtained after the N2O plasma treatment. Moreover, the breakdown voltage of SBDs with N2O plasma is 50.2% higher than the conventional one, whose value reaches 323 V. In addition, the trap states' characteristics of the devices are studied, which show that the oxygen-containing plasma can reduce the deep level trap states density partly in the anode region, which can improve the surface quality effectively. [ABSTRACT FROM AUTHOR]

A β-Ga2O3 Schottky barrier diode (SBD) with a p-type NiOx guard ring was fabricated, and the reverse leakage and subthreshold leakage current reduction was found at high temperatures from temperature-dependent I–V characteristics. The functional mechanisms of NiOx as edge termination on leakage reduction were studied. NiOx can increase the barrier height and passivate the defects at the interface, resulting in the suppression of subthreshold leakage and elimination of current crowding effect confirmed by a thermal emission microscope. From the temperature-dependent x-ray photoelectron spectroscopy characteristics, more holes generated to deplete Ga2O3 at higher temperatures were found. It leads to reduce the reverse leakage current. The small-polaron transportation in NiOx is proposed to argue the implausibility of the leakage conduction in NiOx. This work will offer critical physical insight and a valuable route for developing low-leakage Ga2O3 SBDs. [ABSTRACT FROM AUTHOR]

A 2D ZrI2 monolayer with a high dimensionless figure of merit (ZT) is analyzed in terms of intrinsic carrier concentrations, transport coefficients, and a bipolar effect. The ZrI2 monolayer with a space group of P21/m is fully optimized. The dynamic and thermal stabilities are verified by computing the phonon dispersion in addition to performing ab initio molecular dynamics simulation. The thermal conductivity of the lattice is evaluated by employing the phonon Boltzmann transport theory and the first-principle second and third force constants. The Seebeck coefficients, electronic thermal conductivities, and electric conductivities of the monolayer are determined by solving the relaxation time approximation semiclassical Boltzmann transport equation. To further explore the chance for promoting ZT, we investigate the manipulating effect of the carrier concentrations. The largest ZT with the bipolar effect can reach 7.86 at 700 K, implying that the ZrI2 monolayer has excellent thermoelectric performance. [ABSTRACT FROM AUTHOR]

In this work, a high linearity AlGaN/GaN HEMT integrated dual threshold coupling (DT) technology and Schottky–Ohmic drain (SOD) were fabricated and analyzed. Since the architecture of DT synthesized planar- and recess-HEMT periodically along the gate width, SOD alleviated the peak electric field (E-field) around the gate region and the peak transconductance (Gm-max) of 248 mS/mm with the associated transconductance plateau of ∼4.0 V at Vds = 28 V was obtained, which is evidently flatter than that of HEMT without the SOD structure. Attributed to the improved Gm linearity at high E-field, the DT-SOD HEMT exhibits the predicted linearity figure of merit of 5–13 dB when biased at class AB operation, which is ∼10 dB higher than that of DT-HEMT. Moreover, the fabricated device yields a nearly constant fT/fmax of 47/118 GHz over a wide gate voltage, and load-pull measurements at 30 GHz reveal that these devices deliver output power density (Pout) of 7.8 W/mm with the associated 1-dB compression point (P1dB) of 28.5 dBm at Vds = 28 V. The experimental results indicate that the employment of DT technology and SOD structure is an attractive approach to enhance the linearity at high E-field for millimeter wave devices. [ABSTRACT FROM AUTHOR]

This work reports an AlN/GaN/InGaN high electron mobility transistor (HEMT) with a steep subthreshold swing (SS) of sub-60 mV/dec utilizing a coupling-channel architecture. The fabricated transistors show a negligible hysteresis, a SS of 39 mV/dec, a large gate voltage swing of >4.2 V, and achieving an excellent quality factor Q = gm/SS of 6.3 μS-dec/μm-mV. The negative differential resistance effect was found in the subthreshold region in the gate current–voltage (Ig–VGS) curve. The hot carrier transfer mechanism that occurred in the turn-on/pinch-off progress of the CC-HEMT under the dual-directional sweep, proved by the VDS- and Lg-dependent bi-directional transfer I–V characteristics, can be responsible for these excellent device performances. This work is believed to encourage further study of the AlN/GaN platform to power the future group III-nitrides CMOS technology. [ABSTRACT FROM AUTHOR]

A 1.5-μm polycrystalline diamond was deposited on the AlGaN/GaN heterojunction on the SiC substrate with a 20-nm SiN dielectric. A 4.9% increase in 2DEG density after the diamond growth due to the increase in tensile strain of the GaN layer is confirmed by micro-Raman measurements. The interfacial analysis through the transmission electron microscopy and electron energy loss spectroscopy shows a thickness reduction in the SiN layer of ∼1.7 nm, which converts to a thin SiC layer at the diamond/SiN interface, and no carbon diffusion is found in the SiN layer after the diamond growth. Device simulation using the thermal properties extracted by time domain thermoreflectance predicts a temperature drop of 17.1 °C when the diamond only covers the device access region and reveals that the improvement of thermal boundary resistance is much more effective than that of the diamond thermal conductivity for the top-side heat spreading, which is mainly due to the limited thickness of the top diamond film. [ABSTRACT FROM AUTHOR]

In this work, ultrathin barrier (∼6 nm) AlGaN/GaN high-electron-mobility transistors (HEMTs) with in situ SiN gate dielectric and slant-field plate (SFP) T-gates were fabricated and analyzed. Since the proposed scheme of gate dielectric and SFP effectively suppresses the gate leakage and alleviates the peak electric field (E-field) around gate region, the maximum breakdown voltage (VBK) was improved to 92 V, which is 54 V higher than that of the conventional device. The fabricated ultrathin AlGaN/GaN HEMT with 60-nm SFP-T-gate exhibited the peak fT of 177 GHz and peak fmax of 393 GHz, yielding high figure-of-merits of fT · VBK = 16 THz V and fmax·VBK = 36 THz V. Moreover, load-pull measurements at 30 GHz reveal that these devices deliver output power density (Pout) of 4.6 W/mm at Vds = 20 V and high power-added efficiency up to 52.5% at Vds = 10 V. Essentially, the experimental results indicate that the employment of SFP and in situ SiN gate dielectric is an attractive approach to balance the breakdown and speed for millimeter wave devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A low temperature controlled annealing technique was utilized to improve the performance of vertical β-gallium oxide (β-Ga2O3) Schottky barrier diodes (SBDs) in this work. The nickel is diffused into Ga2O3, and NiO was formed at the interface between the anode and semiconductor generating p–n junction after low temperature annealing. Simultaneously, the trap state density of interface Ni/Ga2O3 as well as the carbon bonded with oxygen on the surface was reduced, which was proved by the capacitance and conductance measurements and x-ray photoelectron spectroscopic analysis, respectively. Combined the decreased saturation current density by three orders of magnitude from 1.21 × 10−6 to 9.27 × 10−8 and 5.12 × 10−9 A/cm2 and larger breakdown voltage from 220 to 270 V owing to the optimized interface and the formation of NiO, a low temperature annealing technique makes certain effective improvement for vertical β-Ga2O3 SBDs via interface engineering. [ABSTRACT FROM AUTHOR]

Defect behaviors in the degradation of AlGaN-based UV-C light emitting diodes (LEDs) under constant current stress have been intensively investigated in this work. It is found that both the reduction of the optical power and the increase in the leakage current are derived from the newly generated Ga vacancy (VGa) along dislocation, based on the evidence of a strong "yellow" emission peak at 515 nm in the photoluminescence spectra and an energy level of 0.25–0.38 eV. More importantly, the defect evolution behind it was determined through the deep level transient spectroscopy, secondary ion mass spectrometry measurements, and density functional theory. VGa is found to be generated by the departure of the unintentionally doped Mg from MgGa along dislocation in the Si-doped region. The high activity of the unintentionally doped Mg under electrical stress can be an essential factor in the degradation of UV-C LEDs. This study not only provides an in-depth insight into the electrical stress-induced degradation in UV-C LEDs but also sheds light on the way for fabricating AlGaN-based devices with high reliability. [ABSTRACT FROM AUTHOR]

In the present work, single-phase Ba4Sm2Fe0.5Ti3Nb6.5O30 ceramics with a tetragonal tungsten bronze structure (TTB) were synthesized. Pinched polarization–electric field (P–E) hysteresis loops are observed below the Curie temperature (Tc) in the as-synthesized ceramics. The origin of the loops was thoroughly studied using in situ TEM and XRD. The in situ selected area electron diffraction (SAED) patterns showed that the pinched loops originated from the coexistence of polar commensurate and nonpolar incommensurate superlattice reflections. In situ XRD results revealed increasing tetragonality with rising temperature, implying that the enhancement in octahedral tilting was closely related to the commensurate-incommensurate structural modulation. [ABSTRACT FROM AUTHOR]

This letter studies the effect of the thickness of the top electrode on the performance of a SiNx resistive switching layer. We fabricated six devices with Ta electrodes of different thickness values (8 nm, 10 nm, 15 nm, 30 nm, 40 nm, and 50 nm) in a Ta/SiNx/Pt structure and then systematically investigated their performance. The high electrode thickness devices show stable and self-compliant bipolar resistive switching characteristics. In contrast, low electrode thickness devices display unstable RS behavior and have a high set voltage. In the low resistance state region, the Ta/SiNx/Pt devices obey Ohmic conduction, while in the high resistance state region, the conduction mechanism is Schottky emission. To explain the different RS behavior in the two device types, a nitrogen-ion-based model has been presented. According to this model, the device with a thicker top electrode has a stronger nitrogen accommodation ability, while the migration of nitrogen ions and silicon dangling bonds dominates conductive behavior. [ABSTRACT FROM AUTHOR]

In this study, an Ag-Cu alloy was chosen as the electrode in conductive bridging random access memory (CBRAM), with results indicating a significant decrease in forming voltage. In addition, resistive switching characteristics as well as a retention test indicated better stability and a resistive switching window of at least an order. The switching time of the Ag-Cu alloy CBRAM is shorter than that of both Ag and Cu electrode CBRAMs under fast current-voltage (fast I-V). The experimental result indicated that the mechanism was dominated by the galvanic effect. Active atoms (Ag) captured electrons of inactive atoms (Cu) and generated metallic ions (Cu ions) in the alloy electrode. Cu ions drifted into the insulator and generated a conductive path when applying voltage bias. The use of this alloy as an electrode in CBRAM can significantly decrease forming voltage and enhance CBRAM characteristics. [ABSTRACT FROM AUTHOR]

This paper provides a systematic study on the bulk traps and interface states in a typical AlGaN/GaN Schottky structure under proton irradiation. After 3 MeV proton irradiation with a dose of 5 × 1014 H+/cm2, a positive flat band voltage shift of 0.3 V is observed according to the capacitance-voltage (C-V) measurements. Based on this, the distribution of electrons across AlGaN and GaN layers is extracted. Associated with the numerical calculation, direct experimental evidences demonstrate that the bulk traps within the AlGaN layer dominate the carrier removal effect under proton irradiation. Furthermore, the effects of proton irradiation on AlGaN/GaN interface states were investigated by utilizing the frequency dependent conductance technique. The time constants are extracted, which increase from 1.10–2.53 μs to 3.46–37 μs after irradiation. Meanwhile, it shows that the density of interface states increases from 9.45 × 1011–1.70 × 1013 cm−2·eV−1 to 1.8 × 1012–1.8 × 1013 cm−2·eV−1 with an increase in trap activation energy from 0.34 eV–0.32 eV to 0.41 eV–0.35 eV after irradiation. The Coulomb scattering effect of electron trapping at interface states with deeper energy levels is utilized to explain the mobility degradation in this paper. [ABSTRACT FROM AUTHOR]