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Harnessing energy from the environment promotes the rapid development of micro-power generators and relevant power management modules of alternating current (AC) line-filtering to obtain a stabilized direct current (DC) output for storage and use. Micro-supercapacitors (MSCs) with miniaturized volume and high-frequency response are regarded as a critical component in filtering circuits for microscale power conversion. Here, we reported the fabrication of the wafer-sized planar MSCs (M-MSCs) based on 2D Ti3C2Tx MXene using a photolithography technique. The M-MSCs exhibited an areal capacitance of 153 μF cm−2 and a frequency characteristic (f0) of 5.6 kHz in aqueous electrolyte. Moreover, by employing suitable ionic liquid as electrolyte, the voltage window was expanded to 2 V and the f0 could be pushed to 6.6 kHz relying on the electrical double-layer mechanism and lower adsorption energy while maintaining quasi-rectangular cyclic voltammogram curves at 5000 V s−1. Furthermore, the integrated MSCs pack was constructed and exhibited excellent rectifying ability by filtering various high-frequency 5000 Hz AC signals with different waveforms into stable DC outputs. Such ultrahigh-rate and high-voltage M-MSCs module for kHz AC line-filtering would be potentially integrated with customizable electronics to realize on-chip rectifiers in high-density integrated circuit.

This article presents an ultracompact bandpass filter (BPF) realized by slow wave substrate integrated groove gap waveguide (SW-SIGGW). The SW-SIGGW is composed of two layers of the dielectric substrate, in which periodic mushroom-type electromagnetic band-gap (EBG) unit cells are employed as packaging structures. The gap layer is realized by the upper substrate, and the via-patch mushrooms are designed on the lower substrate. Due to the slow wave structure in the form of periodical metallic via-holes designed on the lower substrate, the guided wavelength is reduced by about 52.8% compared with normal SIGGW. A dual-band resonator and a cascaded second-order BPF are designed based on SW-SIGGW. Compared with the conventional second-order SIGGW BPF, the proposed SW-SIGGW BPF achieves a 62.6% reduction in the area. By adopting vertical stacking technology, the area of the SW-SIGGW BPF is further miniaturized. The final area of the stacked SW-SIGGW BPF is only 18.7% of the conventional filter based on normal SIGGW without slow wave and stacked structure, which is very competitive for the room-limited applications. A prototype of the stacked SW-SIGGW BPF with 5.4% and 7.4% fractional bandwidths at 11.8 and 18 GHz is fabricated and measured. A good agreement between the measured and simulated results verifies the validity of the miniaturized design of SW-SIGGW BPF.

A GaN complementary field-effect transistor (FET) inverter monolithically integrated with power gate-injection high-electron-mobility transistors (HEMTs) was realized on a Si substrate. The GaN p-channel and n-channel logic devices and power devices were fabricated based on a p-GaN/AlGaN/GaN epi-structure. Through optimization of epi-layer thickness and doping, excellent low-level noise margin (NM $_{L}$ ) of 1.47 V and high-level noise margin (NM $_{H}$ ) of 0.98 V were achieved at a supply voltage $V_{DD}$ of 3 V at room temperature. A maximum current density ( $I_{D,max}$ ) of 0.36 mA/mm/220 mA/mm at $V_{DS}$ of -3 V/3 V and a threshold voltage $V_{TH}$ of -2.0 V/+2.3 V were achieved in the p-channel and n-channel FETs, respectively. A propagation delay of an inverter stage $τ_{pd}$ in a ring oscillator was measured to be 1.67 μs. The power gate-injection HEMT has an on-resistance $R_{{on}}$ of 18.7 Ω ·mm and a breakdown voltage (BV) of 900 V. These results show the great potential of the developed GaN complementary FET technology in the applications of GaN power modules.

Nowadays, high-quality metal oxide thin film transistors grown by solution process have the most potential to replace the traditional a-Si TFT as the next generation of transparent electronics for various applications. However, the low intrinsic carrier concentration and poor charge carrier mobility of metal oxide thin film hinder its development. In order to solve these problems, the heterojunction structure was proposed. In this study, the Indium Oxide/Indium Gallium Oxide (In2O3/IGO) heterojunction was systematically investigated, and the existence of a two-dimensional electron gas was found. There is a large accumulation of carriers at the In2O3/IGO heterojunction interface, and the Hall tests show that the In2O3/IGO heterojunction has the highest carrier concentration of 7.82 × 1012 cm−2 and a carrier mobility of 10.22 cm2V−1s−1. This research can provide a theoretical guidance for promoting the development of oxide thin film transistor technology.

In this work, the performance of AlGaN/gallium nitride (GaN) high-electron mobility transistors (HEMTs) with different Fe doping tails was systematically investigated and compared. It is illustrated that the combination of the unintentionally doped (UID) GaN layer and a thinner Fe doping buffer layer would result in a faster slope rate of Fe concentration in the UID GaN layer. The devices with the fastest slope rate of Fe concentration in the UID GaN layer exhibited excellent large signal performance, including the saturated power density ( $P_{sat}$ ) of 9 W/mm and the power-added efficiency (PAE) of 65.6%. In addition, the $P_{sat}$ and the PAE of the device with the fastest slope rate of Fe concentration in UID GaN layer are 27.7% and 14.7%, which are higher than that of the device with the slowest slope rate of Fe concentration under the class AB operation conditions. Pulse I-V measurement results demonstrated that the buffer-related current collapse was more effectively suppressed in the 0.5-μm Fe doping buffer layer because of faster slope rate of Fe concentration in UID GaN layer. Moreover, the frequency-dependent capacitance and conductance measurement results indicated that the current collapse was relevant to deep traps in the UID GaN layer introduced by Fe doping. By reducing the concentration of the deep traps caused by Fe doping, the device showed excellent characteristics of dc and RF. Furthermore, controlling the Fe doping tail was important for designing the GaN-based power amplifier with high $P_{sat}$ and PAE.

The submicrometer gate HEMT is fabricated with an ultrathin-barrier (UTB) AlGaN/gallium nitride (GaN) combined with in situ SiN passivation. The sheet resistance of the UTB Al0.2Ga0.8N (4 nm)/GaN heterostructure is effectively reduced by the SiNx passivation layer grown by metal organic chemical vapor deposition (MOCVD), from 6500 to $312~ \Omega $ /⬜. With the 20-nm stress-engineered in situ SiN, the device not only provides a large output current of 1.05 A/mm but also demonstrates promising potential on the RF applications, which gives AlGaN material two records high cutoff frequency ${f} _{\text {T}}/{f} _{\text {max}}$ of 157 GHz/334 GHz for 100-nm gated device and 211 GHz/379 GHz for 70-nm gated device. During the continuous wave (CW) power measurement at 30 GHz, the 70-nm devices exhibit a large output power of 4.6 W/mm associated with a peak power-added efficiency (PAE) of 48.1% and a gain of 11.6 dB ( ${V} _{\text {ds}} =20$ V), and a high PAE of 53.8% with an output power density of 1.9 W/mm and a gain of 10.8 dB ( ${V} _{\text {ds}} =10$ V), respectively. The huge potential of the UTB-AlGaN/GaN is demonstrated for high-frequency and large-output power applications when it is combined with the in situ SiN, which is necessary for future communication systems.

The semiconductor, β-Ga2O3 is attractive for applications in high power electronic devices with low conduction loss due to its ultra-wide bandgap (∼4.9 eV) and large Baliga's figure of merit. However, the thermal conductivity of β-Ga2O3 is much lower than that of other wide/ultra-wide bandgap semiconductors, such as SiC and GaN, which results in the deterioration of β-Ga2O3-based device performance and reliability due to self-heating. To overcome this problem, a scalable thermal management strategy was proposed by heterogeneously integrating wafer-scale single-crystalline β-Ga2O3 thin films on a highly thermally conductive SiC substrate. Characterization of the transferred β-Ga2O3 thin film indicated a uniform thickness to within ±2.01%, a smooth surface with a roughness of 0.2 nm, and good crystalline quality with an X-ray rocking curves (XRC) full width at half maximum of 80 arcsec. Transient thermoreflectance measurements were employed to investigate the thermal properties. The thermal performance of the fabricated β-Ga2O3/SiC heterostructure was effectively improved in comparison with that of the β-Ga2O3 bulk wafer, and the effective thermal boundary resistance could be further reduced to 7.5 m2K/GW by a post-annealing process. Schottky barrier diodes (SBDs) were fabricated on both a β-Ga2O3/SiC heterostructured material and a β-Ga2O3 bulk wafer. Infrared thermal imaging revealed the temperature increase of the SBDs on β-Ga2O3/SiC to be one quarter that on the β-Ga2O3 bulk wafer with the same applied power, which suggests that the combination of the β-Ga2O3 thin film and SiC substrate with high thermal conductivity promotes heat dissipation in β-Ga2O3-based devices.

A physical transient memristor synapse with self-rectifying and analogue switching behaviors based on Mo/MgO/AZO (Al2O3 2 wt %, ZnO 98 wt %)/W is presented. By modulating thickness of MgO layer, the device with 5 nm MgO insulator layer shows stable resistive switching memory with a rectification ratio up to 102, and precise tuning synaptic functions. Meanwhile, the formation of Schottky barrier and oxygen vacancy conductive filament is proposed to further explain self-rectifying and analogue switching behaviors. Additionally, the electrical characteristics of the Mo/MgO/AZO/W devices degraded after being immersed in deionized water (DI) for 3 min, which demonstrated the physically transient features successfully. The physical transient self-rectifying memristors have great potential for applications in secure neuromorphic computing systems, and bio-integrated electronics.

The lead contamination and long-term stability are the two important problems limiting the commercialization of organic-inorganic lead halide perovskites. In this study, through an innovative multi-scale simulation strategy based on the first-principle calculations coupling with drift-diffusion model and Monte Carlo method, a new discovery is shed on the vacancy-ordered double perovskite Cs2TiI6, a potential nontoxic and stable perovskite material for high-performance solar cell and α-particle detection. The excellent photon absorption character and ultrahigh carrier mobility (μn = 2.26×104 cm2/Vs, μp = 7.38×103 cm2/Vs) of Cs2TiI6 induce ultrahigh power conversion efficiency (PCE) for both single-junction solar cell (22.70%) and monolithic all-perovskite tandem solar cell (26.87%). Moreover, the outstanding device performance can be remained even in high energy charge particle detection (α-particle) with excellent charge collection efficiency (CCE = 99.2%) and mobility-lifetime product (μτh = 1×10−3 cm2/V). Furthermore, to our surprise, the solar cell and α-particle detector based on Cs2TiI6 material are able to withstand ultrahigh fluence proton beam up to 1013 and 1015 p/cm2 respectively, which strongly suggests that semiconductor devices based on Cs2TiI6 material are able to apply in the astrospace. The multi-scale simulation connecting from material to device reveals that Cs2TiI6 perovskite has the great potential for photovoltaic cells, α-particle detection and even their space application.

GaN-based light-emitting diodes (LEDs) grown on the insulating sapphire substrate suffer from a severe current crowding effect. To alleviate the current crowding effect, we demonstrate a current spreading structure for 365-nm ultraviolet LED using Fe doping in n-GaN layer. The surface morphology was studied by atomic force microscope, and the crystal quality was evaluated by high-resolution X-ray diffraction, which shows that a thin insertion layer doped with Fe has less influence on the crystalline quality. Additionally, inserting a Fe-doped layer with appropriate doping concentration enables to induce a barrier in the n-type layer, which contributes to the uniform current distribution. As a result, compared with conventional LED, the light output power obtains a 170.6% enhancement at 100 mA. Furthermore, the uniform optical emission distribution is also achieved by inserting a Fe-doped layer. Finally, the conduction band structures and horizontal hole concentration distributions are calculated by Advanced Physical Models of Semiconductor Devices, which illustrates the mechanism of current spreading.

A monolithic bidirectional switch based on anti-paralleled two reverse blocking p-GaN HEMTs has been proposed and demonstrated in this work. The recessed Schottky drain technique is utilized to effectively reduce the on-state voltage and thus lowering the power loss of bidirectional switches. A significant reduction in parasitic elements and switch area is obtained by monolithic integration. The fabricated bidirectional switch exhibits a threshold voltage of ~1.85 V, on-state voltage of ~0.63 V, and the forward and reverse off-state breakdown voltages of ~650 V at ${I}_{{\text {S1}-\text {S2}}} = 1\,\,\mu \text{A}$ /mm. In addition, the function of proposed bidirectional switch as an AC power chopper has been successfully verified.

In this article, the Au-free complementary metal oxide semiconductor (CMOS) transistor compatible AlGaN-channel high-electron-mobility transistors (HEMTs) on silicon substrate with 2-kV forward and reverse blocking voltages have been reported. Due to the designed AlGaN epitaxial layers, breakdown voltages (BVs) of the conventional AlGaN-channel HEMTs with $L_{GD} =5$ /10/15/ 20/ $25~\mu \text{m}$ are 420/1070/1590/1920/2000 V respectively, and the values are increased to 760/1420/1980/1990/2000 V by using Schottky-drain technique. The reverse-blocking HEMTs demonstrate reverse blocking voltages of −790/−1300/−1810/−2000 V for ${L}_{GD}=5$ /10/15/ $20~\mu \text{m}$ . Meanwhile, the conventional HEMT power figure-of-merit (FOM) of 397 MW/cm2 is the highest FOM for AlGaN-channel HEMTs on silicon, and the Schottky-drain HEMT forward FOM of 384 MW/cm2 and reverse FOM of 321 MW/cm2 are the highest FOM values for all GaN-based reverse-blocking HEMTs on silicon.

A novel slow wave (SW) substrate-integrated waveguide (SIW) with enhanced SW factor (SWF) and broadened bandwidth is proposed by simultaneously increasing the effective permeability and permittivity. The effective permittivity is increased by the enhanced capacitance between the top plane of the waveguide and the loaded patches which are shorted to the SIW bottom plane by the blind via-holes. The effective permeability is increased by lengthening the current path by adding patches on the blind via-holes. The proposed SW-SIW with simultaneous increased effective permeability and permittivity has two obvious advantages over the reported SW-SIW with only effective permeability or permittivity increased: 1) smaller longitudinal and lateral dimensions resulted from higher SWF and lower cutoff frequency, respectively, and 2) wider bandwidth due to stable wave impedance along the periodical SW structure. The lateral dimension of the proposed SW-SIW is decreased by 53% compared with the normal SIW with the same cutoff frequency. The phase velocity is decreased by 73%, which means the longitudinal length is reduced by 73% consequently. The operation band is 7.0–18.8 GHz (91.5% fractional bandwidth) covering ${X}$ - and Ku -bands. A prototype of the proposed SW-SIW is manufactured and measured, and the measured results agree well with the simulations.

High-mobility Ge nMOSFETs with ZrO2 gate dielectric are demonstrated and compared against transistors with different interfacial properties of ozone (O3) treatment, O3 post-treatment and without O3 treatment. It is found that with O3 treatment, the Ge nMOSFETs with ZrO2 dielectric having a EOT of 0.83 nm obtain a peak effective electron mobility (μeff) of 682 cm2/Vs, which is higher than that of the Si universal mobility at the medium inversion charge density (Qinv). On the other hand, the O3 post-treatment with Al2O3 interfacial layer can provide dramatically enhanced-μeff, achieving about 50% μeff improvement as compared to the Si universal mobility at medium Qinv of 5 × 1012 cm−2. These results indicate the potential utilization of ZrO2 dielectric in high-performance Ge nMOSFETs.

InGaN/GaN multiple quantum-well (MQW) structures with a wavelength range of green were successfully grown on a c-plane GaN template with SiO2 stripe patterns along the [11-20] and [1-100] directions as a mask. The surface morphologies of both samples were investigated using scanning electron microscopy and demonstrated anisotropic growth characteristics of GaN. The optical characteristics were investigated using Raman spectra and photoluminescence (PL). The InGaN/GaN MQW structure grown on the GaN template with SiO2 stripes along the [1-100] orientation exhibited less stress and higher PL intensity. Transmission electron microscopy results indicated that portions of MQWs were grown on an inclined semipolar plane, and air voids occurred only when the direction of the mask stripe was along the [1-100] orientation. The enhancement of the optical characteristic was due to the air-void structure and inclined semipolar quantum-well sidewalls.

In this article, we have systematically investigated the effect of annealing of fabricated GaN Schottky barrier diodes (SBDs) and anode metals with various work-functions on the performance of AlGaN/GaN SBDs. It is found that after annealing of fabricated GaN SBDs, the interface states between the metal and GaN etching surface are suppressed, the device stability is enhanced, and the turn-on voltage ( ${\mathrm {V}}_{ \mathrm{\scriptscriptstyle ON}}$ ) shows negligible degradation. Meanwhile, high-performance AlGaN/GaN SBDs with various work-function metals as anode have been achieved by adapting the annealing treatment. The calculated Schottky barrier heights of the fabricated SBDs with Cr, W, and Ni anode is 0.27, 0.68, and 0.98 eV, respectively, which are almost the same as those estimated from XPS measurements. A low turn-on voltage of 0.42 V and low leakage current of $0.3~\mu \text{A}$ /mm are obtained by using the low work-function metal W (4.6 eV) as anode. Furthermore, the SBDs fabricated with the high work-function metal Ni (5.1 eV) shows an extremely low-leakage current of 6 nA/mm and exhibit a current ON/OFF ratio of $10^{{9}}$ while also showing great characteristics at high temperature.

Gallium Oxide (Ga2O3) for solar‐blind photodetectors (PDs) has drawing increasing research interest in recent years because of its natural wide bandgap. However, the traditional material growth methods are always complicated and the corresponding PD performance is also not good enough. In this work, amorphous Ga2O3 (a‐Ga2O3) thin film grown by mist chemical deposition applied as solar blind deep ultraviolet phototransistors (PTs) is investigated for the first time, to solve the problem of high cost and time‐consuming by traditional methods. Bottom‐gate a‐Ga2O3 three terminal thin film transistors (TFTs) are fabricated to boost their ultraviolet (UV) photodetection properties. Under the 254 nm UV illumination, the a‐Ga2O3 PTs demonstrates a very high responsivity of 2300 AW−1, external quantum efficiency of 1.12 × 106% and detectivity of 1.87 × 1014 Jones. Such field‐effect PTs with the ultrahigh performance address a significant step toward the feasibility and practicability of Ga2O3 PDs in the future applications.

Herein, physically transient diode based on W/ZnO/MgO/W device with ultrathin MgO tunneling layer as selector for bipolar one diode-one resistor (1D1R) memory was demonstrated. By modulating thickness of MgO tunneling layer, the diode of ultrathin MgO (3 nm) tunneling layer exhibits stable rectifying behaviors, good endurance, high uniformity and a suitable reverse current. Meanwhile, the self-rectifying resistance switching functions of bipolar 1D1R memory that utilize reverse current of diode as compliance current are successfully obtained, which can suppress the sneak current of crossbar network. Importantly, the electrical feature of the transient 1D1R memory degraded after being immersed in deionized water (DI) for 1 min and completely triggered failure after 2 min. These results reveal that the transient 1D1R memory is promising for secure memory, neuromorphic computing and novel bio-integrated electronics systems.

A novel low-loss suspended-line gap waveguide (SLGW) supporting transverse electromagnetic (TEM) propagation is presented for millimeter-wave applications for the first time. The suspended line is composed of two parallel strips connected by metal via holes. Periodic stacked-mushroom electromagnetic band gap (SM-EBG) structures are used to package the suspended line by creating a stopband for all parallel-plate modes. According to the different packaging requirements of the circuit, the SM-EBG unit cell can be composed of several stacked mushrooms and metal covers. The air gaps’ thickness between face-to-face patches of the adjacent mushrooms is near zero, confining more power in the air-filled guiding region of the SLGW. Furthermore, the SM-EBG structures with near-zero thick air gaps can provide more stable mechanical support for the multilayer structure. Therefore, SLGW has a lower loss and more robust gap stability compared with the conventional air-filled printed versions of GWs, such as printed ridge gap waveguide (PRGW) and inverted microstrip gap waveguide (IMGW). On the other hand, compared with the self-packaged double-sided interconnected strip line (DSISL), the proposed SLGW packaged with SM-EBG structures has the advantage of no electrical contact, avoiding the power leakages in the gap between plates at discontinuities and simplifying the assembly. The design and analysis of the SM-EBG structure, the design of SLGW, and the microstrip-to-SLGW transition design are given in this article. A prototype of the proposed SLGW with back-to-back transition is fabricated packaged with SM-EBG structures to prove the concept.

This study used density functional theory and the quantum transport method to investigate the interfacial coupling and spin transport of transition metals (TMs) with a Fe, Co, and Ni/2H-VSe2 hybrid nanostructure. Because the indirect coupling of TM-Se-V led to an obvious reduction of the magnetic moment and the disappearance of the half-metal characteristics of 2H-VSe2, the expected spin-filtering effect of individual TMs and 2H-VSe2 deteriorated at the contact region. Nevertheless, all the TM/2H-VSe2-based dual-probe devices exhibited an interesting bias-dependent spin-injection efficiency with a maximum output spin-polarized current of 666 mA mm−1 in Co/2H-VSe2. The proposed TM/2H-VSe2-based spin-field-effect transistor demonstrated outstanding performance. The Ni/2H-VSe2-based transistor achieved a maximum output spin-polarized current of 3117 mA mm−1 and demonstrated a good switching characteristic of 106 mV dec−1. Importantly, all transistors achieved a widely tunable scale of spin extraction efficiency ranging consistently between 96% and −92% with gate bias. These results indicate a promising candidate for use in high-performance spintronic devices.

Multiple-channel GaN heterostructures have been used to improve the device performance of high electron mobility transistors (HEMTs). The object is to achieve highly linear transconductance, low ON-resistance, and large output current. However, the complicated situation of the multiple channels made it difficult to model multiple-channel HEMTs. We report an analytical model of the electron population and the energy band diagram of multiple-channel GaN heterostructures. It is established based on the continuity of electric displacement vector at various interfaces and the electric neutrality of the whole heterostructure. The double-channel, triple-channel, four-channel, and ten-channel heterostructures have been investigated, and the calculation results are compared with the numerical self-consistent Schrodinger–Poisson solution to show the feasibility of the model.

A ferroelectric based electrostatic doping (Fe-ED) technique is proposed, as the alternative to chemical doping, providing non-volatile and programmable free electrons and holes for nanoscale devices. We show that Fe-ED achieves non-volatility and reconfigurability via the ferroelectric film inserted into the polarity gate, producing the reconfigurable nanosheet FETs (NSFETs) without the requirement of a constant bias. Thanks to the naturally formed lightly doped drain structures and the extremely high doping concentration over $1\times 10^{21}$ cm−3 in source/drain (S/D) regions, Fe-ED NSFETs exhibit the promising potential benefits for device scaling including the improved subthreshold swing, the suppressed drain-induced barrier lowering, and the ultralow S/D region resistance. Our study suggests a promising doping strategy of Fe-ED for versatile reconfigurable nanoscale transistors and highly integrated circuits.

As an important part of wireless communication systems, the technology of RF devices and circuits has been progressing rapidly. For high-frequency and high-power applications, vacuum electronic devices (e.g., traveling wave tubes) have been widely used, although the vacuum tube is large in size and hard to integrate.

In this article, the AlGaN barrier fully removed recessed-gate normally off AlGaN/GaN high electron mobility transistors (HEMTs) with N2O plasma treatment are fabricated. The low speed and low damage etching is used in recessed-gate etching, the etching depth is about 26 nm with 0.4 nm remaining, and then, the remaining barrier layer is oxidized by N2O plasma treatment. In the terms of devices’ characteristics, the threshold voltage of the recessed-gate HEMT is +1.5 V, and the channel current of recessed-gate HEMTs at $V_{\mathrm {GS}} - V_{\mathrm {TH}} = 1.5$ V is about 110 mA/mm. Moreover, 14 mV/V of drain-induced barrier lowering (DIBL) and 70 mV/decade of subthreshold slope (SS) are achieved. More importantly, the fully recessed-gate HEMT shows the average breakdown electric field at $V_{G}= 0$ V of about 0.64 MV/cm, which is a very high value in the fully normally off recessed-gate HEMTs without metal insulator semiconductor (MIS) structure, which will be beneficial to the application of this device in the low power supply topology circuit.

A 365 nm AlxGa1-xN-based ultraviolet light-emitting diodes (LEDs) with double Al composition gradient last quantum barrier and hole supply layer structure has been studied. Experimental results show that the proposed structure enhances the carrier injection efficiency and suppresses the overflow of electrons. The introduction of three-dimensional hole gas further enhances the hole injection efficiency. As a result, the wall plug efficiency and electroluminescence intensity are significantly improved. In addition, the carrier concentration and the radiative recombination rate in the active region of the quantum well increases. Looking at the energy band diagram, one sees that the double Al composition gradient structure leads to higher electron blocking and alleviates the hole blocking effect. Overall, we conclude that the double Al composition gradient structure provides a pathway to achieve high-efficiency ultraviolet LEDs.

Reducing the toxic Pb component in perovskites is an important step to realize environment-friendly perovskite optoelectronic devices. Herein, the structural, electronic, and optical properties of Zn and Mn codoped CsPbBr3 have been investigated based on first-principle calculations and experimental verifications. Although the Zn dopant could reduce the optical band gap and exciton binding energy and enhance the optical absorption and defect tolerance for CsPbBr3, the maximum reduction of the toxic Pb component was just about 12.5% in the experiment because the Zn dopant enlarges the formation energy of CsPb1-xZnxBr3. For the stable CsPb1-x-yMnxZnyBr3 perovskite, the largest y and corresponding (x + y) could reach up to 25% and 83% respectively, since the Mn dopant could reduce the structural disorder. Especially when (x + y) < 50%, CsPb1-x-yMnxZnyBr3 exhibits a comparable carrier lifetime and exciton binding energy with a lower band gap to those of the CsPbBr3, since the Zn dopant supplies a charge to CsPbBr3 to counteract the variation of Pb-Br bonds induced by the Mn dopant. Meanwhile, the d orbitals of the dopant increase the optical absorption. These suggest that a 50% reduction of toxic Pb could be realized for stable CsPb1-x-yMnxZnyBr3 with negligibly deteriorated optoelectronic properties. This work provides an alternative approach to achieve a Pb-less perovskite with a high performance.

Perovskite film modification is one of the most effective methods to improve the performance of perovskite solar cells. The modification should follow its characters of an asymmetric structure and the corresponding charge transportation and extraction. In this work, it is shown that synchronous interface modification and bulk passivation for highly efficient PSCs can be achieved by a one-step cesium bromide (CsBr) diffusion process because it is more suitable for an asymmetric structure. The synchronous interface modification and bulk asymmetric passivation can be better applied to the asymmetric PSC structure and can boost the power conversion efficiency apparently from 19.5 to 22.1%. It is shown that the perovskite crystallization is improved and the charge extraction is also enhanced obviously due to the better band alignment matching. The diffusion of CsBr into the perovskite bulk could form a gradient distribution, which is more applicable to the asymmetric charge transport and extraction. Thus, the CsBr at the interface between the electronic transport layer (ETL) and perovskite, as well as in the perovskite bulk, could suppress charge recombination. All of these factors can improve the JSC and VOC as well as the power conversion efficiency (PCE) of the PSCs. The results point out that the studied method is a simple and efficient way to fabricate high-performance PSCs by interface modification and bulk asymmetric passivation in a single step.

The effect of gamma ( $\gamma $ )-irradiation on AlGaN-based light-emitting diodes (LEDs) in the short-wavelength ultraviolet (UVC, 210–280 nm) spectral range under electrical stress is characterized by electroluminescence and current–voltage measurement. Different from previous reports that $\gamma $ -irradiation can hardly damage nitride devices, we observe that the optical power decreases and leakage current increases obviously after electrical stress under $\gamma $ -irradiation. To delve into the nature of degradation, variation of defects is studied using temperature-dependent low-frequency noise measurement. After stress, the ~0.78-eV defects attributed to N antisite are generated and lead to device degradation, which is accompanied by a reduction of the intrinsic Ga vacancy with an energy level of ~0.38 eV. The variation of defects after stress in $\gamma $ -irradiated environment is more evident than that in nonirradiated environment, which is well corresponding to the performance degradation behavior. In conclusion, $\gamma $ -irradiation is found to accelerate degradation induced by electrical stress, and the study can help improve irradiation resistance in AlGaN-based UVC LEDs.

The lower luminous efficiency is a critical issue for ultraviolet light-emitting diodes (UV-LEDs) owing to the poor carrier injection efficiency and high dislocation density. Here, we can improve the luminous efficiency in two avenues by adjusting the Al composition of the InGaN/AlxGa1-xN pre-well superlattice. First, due to the strain-induced piezoelectric and intrinsic spontaneous polarization, a large number of electrons gather at the InGaN/AlxGa1-xN interface, which improves the electron concentration of the pre-well superlattice and lowers the conduction band energy of the first quantum barrier layer (FQB), thus enhancing the electron injection efficiency. Second, the pre-well superlattice can act as a hole blocking layer to prevent holes from leaking into the n-type layer and confine them in the quantum well layer. As the Al composition increases, the hole blocking effect of the pre-well superlattice is strengthened. However, higher Al composition decreases the lattice quality, which makes it possible for carrier loss through defect-related non-radiative recombination. Finally, the output power of the samples with 5% Al composition in the pre-well superlattice is 5.9% and 102.5% higher than that of the samples with 3% and 7% Al composition, respectively.

Flexible aluminium nitride (AlN) films can enable the future preparation of carbon-based nitride devices. We report a novel diffusion–adsorption regulation growth method in the epitaxy of AlN on graphene for high-quality and transferable large-size AlN films. Then, the growth mode of AlN on graphene is summarized in turn as diffusion-dominated, combined-effect, adsorption-dominated and decomposition-dominated. A high-quality and transferable AlN epitaxial layer was obtained by regulating the combination of graphene and AlN. Finally, a flexible 3 × 3 cm2 AlN film with an RMS of 0.748 nm was achieved. The proposed growth mechanism fills the gap in the study of the growth mechanism of AlN on graphene, and will help to explore new methods for the preparation of carbon-based nitride devices based on van der Waals epitaxy-transfer printing, realize substrate selection that does not rely on epitaxial relationships, and provide a revolutionary technology for the development of high-efficiency flexible devices.

In this work, low voltage RF power capability on AlGaN/GaN and InAlN/GaN HEMTs is analyzed from the perspective of DC and pulse characteristics, for terminal applications whose operating voltage is usually in the range of 3 to 15 V. Device fabrication is performed on mature AlGaN/GaN heterojunction as well as strongly polarized InAlN/GaN heterojunction, to make a comparison of low voltage RF power capability between two devices. Although it suffers from relatively severe RF dispersion, InAlN/GaN HEMT delivers higher output power density (Pout) than its opponent, benefiting from the lower parasitic resistance and knee voltage as well as higher output current density. At 8 GHz, Pout of 1.62 W/mm and 1.10 W/mm are achieved for InAlN/GaN and AlGaN/GaN HEMT, respectively, both of which are biased at class AB operation and Vds of 9 V. However, the tremendous degradation of power added efficiency (PAE) occurs as the higher drain voltage is applied on InAlN/GaN HEMT, as the result of the severe gate leakage. What is more, a higher PAE is more necessary than Pout for terminal applications. Either InAlN/GaN HEMT or AlGaN/GaN HEMT has its own specific voltage range to deliver higher PAE. Concretely, InAlN/GaN HEMT is more suitable to applications with operating voltage not exceeding 6 V, and AlGaN/GaN HEMT is preferred for ones with relatively higher voltage, accompanied by the decent PAE as high as 62% to 66% and moderate Pout to meet the demand of various low voltage terminal applications.

This article presents a terahertz integrated cavity bandpass filter based on cyclic etched silicon carbon (SiC) via-holes. Solutions are discussed in detail, including design, fabrication, and optimization. The fabrication procedures of the integrated filters are specially optimized, which are fully compatible with that of the common terahertz monolithic integrated circuit. The cyclic via-hole etching technique based on inductively coupled plasma (ICP) is proposed, which achieves via-holes with a controllable inclination on SiC substrate. Measurements show that the insertion loss of the cavity integrated filter is only 1.55 dB at 185 GHz, with a relative bandwidth of 9.7%. Two transmission zeros are introduced by the over-moded technique, achieving the out-of-band suppression of the filter higher than 40 dB. Compared with the traditional terahertz cavity filters, the integrated cavity on SiC substrate provides similar electric performances and better integration but with the one-thousandth of the volume.

We experimentally demonstrate ferroelectric-like non-volatile field-effect transistor (NVFET) with the amorphous Al2O3 gate insulator for artificial synapse applications. The switchable polarization (P) is attributed to the voltage modulation of mobile ions in the gate insulator. The ferroelectric-like NVFETs integrated with 3 nm and 6 nm-thick Al2O3 dielectrics demonstrate the capability to mimic various synaptic behaviors including long-term potentiation (LTP), long-term depression (LTD), and spike-timing-dependent plasticity (STDP), under different types of electrical stimuli to the gate electrode. To verify the application of the ferroelectric-like transistors in the Spike Neural Network (SNN), the online training has been carried out based on the synaptic characteristics of the devices, and a decent accuracy (>80%) is achieved for fixed-amplitude ±3 V/100 ns potentiation/depression pulses.

This work provides insight into the design principles and the reasonable construction of Ga2O3 heterojunction diode. We chose TiO2 grown by atomic layer deposition (ALD) as a suitable insulator with a small conduction band offset of TiO $_{2} \boldsymbol / \beta $ -Ga2O3 heterojunction and a large dielectric constant. The type-I band alignment of the TiO $_{2} \boldsymbol / \beta $ -Ga2O3 heterojunction was obtained using X-ray photoelectron spectroscopy (XPS). We demonstrated a high-performance vertical metal/TiO $_{2} \boldsymbol / \beta $ -Ga2O3 dielectric heterojunction diode with reverse blocking voltage of 1010 V and differential ON-resistance of 3.3 $\text{m}\Omega \cdot $ cm2. The proposed design principles of dielectric heterojunction diode and the insulator selection can also provide a simple, effective, and feasible technology for other wideband and ultrawideband semiconductors in which bipolar doping is challenging to achieve high power device performance.

In this letter, we demonstrate a high performance lateral $\beta $ -Ga2O3 solar-blind Schottky barrier photodiode (SBPD) with record detectivity (D*) and ultrahigh gain via carrier multiplication process. Due to the strong electric field, the carriers generated under the 254 nm light illumination undergo acceleration and impact ionization, contributing to the internal carrier multiplication process. Therefore, the photodetector (PD) is equipped with record D* of $2\times 10 ^{{16}}$ Jones and ultrahigh gain of $1.7\times 10^{{4}}$ , combining with a high photo-to-dark-current ratio of more than 105, a responsivity of $1.2\times 10 ^{{5}}$ A/W and a large external quantum efficiency of $5.6\times 10 ^{{5}}$ %. Without the requirement of complex device structure like other avalanche PDs, our SBPD can be used as a low-cost and easy-to-integrate technology to prepare high performance solar-blind PDs.

The performance of perovskite solar cells (PSCs), especially for the parameters of open-circuit voltage (Voc) and fill factor, is seriously restricted by the unavoidable interfacial charge recombination. In this study, an ultrawide band gap semiconductor material of Ga2O3 is introduced between fluorine-doped tin oxide and SnO2 to regulate the interfacial charge dynamics by forming the Ga2O3/SnO2 electron-transporting bilayer. Ga2O3 has an appropriate conduction band minimum which benefits the electron transport, and at the same time, it has a very deep valence band maximum which could be regarded as an effective blocking layer. Such an innovative structure triggers the advantages of a lower work function and a smoother surface of the electron-transporting bilayer which leads to a high-quality perovskite film. Furthermore, superior hole-blocking properties of the introduced Ga2O3 layer could effectively reduce the interfacial recombination. All the properties could help to improve the extracting and transporting ability of charge carriers synergistically. Finally, the efficiency and stability of PSCs are greatly enhanced. All results suggest that the performance of PSCs could be improved effectively by introducing the ultrawide band gap oxide semiconductor of Ga2O3.

Herein, we demonstrate an artificial optic-neural synapse based on physically transient memristor. The physically transient optic-neural synapse with structure of W/MgO/ZnO/Mo exhibits remarkable long-term plasticity under light with various wavelengths and intensity including the red, green, and blue lights. In addition, a complete electro-thermal resistive switching model accurately simulates the migration and redistribution of oxygen vacancies in the memristor. Importantly, the long-term plasticity can disappear when the devices were immersed in deionized (DI) water, demonstrating the physically transient nature of the device. Finally, an optical convolutional neural network based on the physically transient optic-neural synapse was successfully simulated. These results show that the transient optical synapse has a great prospect for in-sensor computing and secure electronics.

In this letter, a high-performance GaN quasi-vertical Schottky barrier diode (SBD) is demonstrated via oxygen plasma termination. A specific on-resistance of 0.2 $\text{m}\Omega \cdot $ cm2, turn-on voltage of 0.71 V, and breakdown voltage of 193 V are achieved with a GaN SBD of $1.3~\mu \text{m}$ drift layer. The average breakdown electric field is calculated to be about 1.48 MV/cm, which is much higher than the state-of-art value for GaN vertical SBDs. The temperature-dependent forward and reverse I-V characteristics confirm the high-temperature stability of the oxygen plasma treated SBDs. X-ray spectroscopy and Kelvin Probe Force Microscopy reveal that the surface potential is increased after the oxygen plasma treatment, which results in the suppression of the leakage current and improvement of the breakdown electric field.

In order to further improve the electrical characteristics of AlGaN-buffer devices, we propose a new in situ SiN/AlGaN-sandwich-barrier (SWB)/GaN/Al0.05GaN high-electron mobility transistors (HEMTs). The dc, channel temperature, and RF temperature of the proposed AlGaN-buffer devices have been systematically studied and analyzed. The SWB structure can effectively reduce the peak value of the electric field, thus effectively reducing the self-heating effect and improving the breakdown characteristics. Through the channel temperature extraction method of pulsed IV and TCAD thermal simulation, the channel temperature of devices with different barrier structures is compared and analyzed, which proves that SWB structure can effectively reduce the channel temperature of devices. Due to the more obvious potential modulation effect between gate and drain, the ${f}_{\text {max}}$ of device can improve more effectively with the increase of drain voltage. In addition, load-pull measurement at 10 GHz revealed that a saturated power density increased from 7.3 to 8.4 W/mm and an associated PAE increased from 24.9% to 29.4%.

The emerging micro-nano-processing technologies have propelled significant advances in multifunctional systems that can perform multiple functions within a small volume through integration. Herein, we present an on-chip multifunctional system based on a 1T/2H-MoS2/graphene fishnet tube, where a micro-supercapacitor and a gas sensor are integrated. A hybrid three-dimensional stereo nanostructure, including MoS2 nanosheets and graphene fishnet tubes, provides K+ ions with a short diffusion pathway and more active sites. Owing to the large layer spacing of 1T-MoS2 promoting fast reversible diffusion, the on-chip micro-supercapacitor exhibits excellent electrochemical properties, including an areal capacitance of 0.1 F·cm−2 (1 mV·s−1). The variation in the conductivity of 2H-MoS2 when ammonia molecules are adsorbed as derived from the first-principles calculations proves the Fermi level-changes theory. Driven by a micro-supercapacitor, the responsivity of the gas sensor can reach 55.7% at room temperature (27 °C). The multifunctional system demonstrates the possibility of achieving a two-dimensional integrated system for wearable devices and wireless sensor networks in the future.

Exploring the high-performance non-volatile memories for realizing energy-efficient memory in complementary metal–oxide–semiconductor (CMOS) circuits, memory-in-computing, and the artificial synapse is the key to the rapid growth in data markets. One of the significant aspects is the development of non-volatile field-effect transistor (NVFET), which possesses the advantage of decoupling the “write” and “read” functions using the third terminal. In this work, building on a semiconductor channel integrated with an amorphous Al2O3 gate insulator, we report a ferroelectric-like NVFET memory and analog synapse that differ from those utilizing polycrystalline-doped HfO2 films. Switchable polarization ( ${P}$ ) is demonstrated in TaN/Al2O3/TaN, TaN/Al2O3/Si, and TaN/Al2O3/Ge stacks, which is attributed to the voltage-modulation of the oxygen vacancy and negative charge dipoles in gate insulator. A TaN/Al2O3/Ge capacitor achieves over 1010 cycles endurance of polarization-voltage measurement. A memory window (MW) of 0.85 V is obtained in the NVFET integrated with Al2O3 insulator under ±3 V at 100 ns program/erase (P/E) condition, and the P/E voltage can be reduced to ±1.6 V. A NVFET analog synapse is demonstrated to have a dynamic range above 100 [asymmetry ( $\vert \alpha _{p} - \alpha _{d} \vert $ )< 0.1] with ±2 V/100 ns potentiation/depression pulses. These results can be extended universally to other amorphous oxides and show promise for 3-D (fin-shaped) NVFETs with very small fin pitch.

Non-volatile field-effect transistor (FET) with amorphous Al2O3 dielectric is demonstrated on Si substrate, which is enabled by the voltage modulation of the oxygen vacancy and negative charge dipoles in gate insulator. Ferroelectric-like behavior in TaN/Al2O3/Si0.70Ge0.30 stacks with different thicknesses of Al2O3 is proved by polarization-voltage tests, positive-up and negative-down tests, piezoresponse force microscopy, and electrical measurements. The Al2O3 capacitors attain over 108 cycles’ endurance of polarization versus voltage measurement. A 6.5 nm-thick Al2O3 non-volatile FET achieves a memory window above 0.6 V under ±2 V at 100 ns program/erase (P/E) condition, over 104 cycles P/E endurance, and >105s data retention at room temperature.

In this paper, the hybrid β-Ga2O3Schottky diodes were fabricated with PEDOT:PSS as the anode. The electrical characteristics were investigated when the temperature changes from 298 K to 423 K. The barrier heightϕbincreases, and the ideality factorndecreases as the temperature increases, indicating the presence of barrier height inhomogeneity between the polymer and β-Ga2O3interface. The mean barrier height and the standard deviation are 1.57 eV and 0.212 eV, respectively, after taking the Gaussian barrier height distribution model into account. Moreover, a relatively fast response speed of less than 320 ms, high reponsivity of 0.6 A/W, and rejection ratio ofR254 nm/R400 nmup to 1.26 × 103are obtained, suggesting that the hybrid PEDOT:PSS/β-Ga2O3Schottky barrier diodes can be used as deep ultraviolet (DUV) optical switches or photodetectors.

In this article, we have carried out a comprehensive study on the wireless power transfer (WPT) concept from the rectifier circuit construction and state-of-art GaN Schottky barrier diode (SBD) device technology to the WPT system demonstration. Benefited from the wide bandgap, high mobility, and saturation velocity of the gallium nitride (GaN) two-dimensional electron gas, engineered lateral GaN SBD with low turn- on voltage ( V on) of 0.47 V, on -resistance ( R on) of 4 Ω, breakdown voltage of 170 V, and junction capacitance $(C_{j})$ of 0.32 pF at 0 V bias are achieved, which satisfy the fundamental requirements for microwave power rectification. After incorporating the high-performance GaN SBD into the optimized rectifier circuit, high radio frequency (RF)/dc conversion efficiency of 79% is achieved, and the input power of per single GaN SBD is increased by 10X when compared with that of a commercially available silicon (Si) SBD at the same efficiency of 50% and frequency of 2.45 GHz. Based on the rectifier circuit, a microwave power transfer system is constructed with 400 light emitting diodes lighted up, verifying the great promise of adopting high-power GaN SBD for the wireless high-power transfer as an alternative energy-harvesting technique for future WPT application.

In this article, Si (100) inks’ array is integrated on SiN/AlGaN/GaN substrate to demonstrate a zero deviation and wafer-scale Si–GaN monolithic integration by transfer printing and self-aligned etching technology. During the heterogeneous integration process, it does not depend on any equipment, such as metal–organic chemical vapor deposition (MOCVD) (epitaxial growth) and wafer bonding machine (wafer bonding) which are costly. The transferred Si and SiN/AlGaN/GaN substrates show an excellent interface morphology. Based on this material system, the monolithic integrated E-mode cascode FETs are demonstrated with good uniformity. The ${I}_{GS}$ is below 10−5 mA/mm within a large gate voltage swing of ±18 V. Threshold voltages of a series of cascode FETs are extracted as 2.2 V (±0.2 V). This novel low-cost technology shows great potential in monolithic heterogeneous integration.

Large-area single-crystal graphene (LSG) over half a millimeter were synthesized via chemical vapor deposition, and a flexible ion gel-gated graphene field-effect transistor (FET) was fabricated to explore the electrical properties of the graphene based on the mechanism of electronic double layers. A procedure of cyclical oxidation/hydrogen-annealing processes by chemical vapor deposition (CVD) was proposed and optimized as a new growth method for the large single-crystal graphene, to facilitate the reconstruction of copper foil surface. To form a flexible FET on the polyethylene terephthalate substrate, LSG was utilized as a channel layer, and a spin-coated ion gel film was used as a gate dielectric. The flexible device demonstrates excellent electrical properties and high degree of bendability. When the device was bent by 8.1%, the on/off current ratio exceeded 400 because the deformation of the graphene crystal lattice widened graphene’s bandgap. This work is a fundamental study on the growth mechanism of LSG and the two-dimensional-material-based ion gel-gated transistor for application in flexible electronic devices.

All-inorganic, Cl-based perovskites are promising for visible-blind UV photodetectors (PDs), particularly the self-powered ones. However, the devices are rarely reported until now since the low solubility of raw materials hinders significantly the thickness and electronic quality of solution-processed Cl-based perovskite films. Herein, we demonstrate a simple intermediate phase halide exchange method to prepare desired dual-phase CsPbCl3-Cs4PbCl6 films. It is achieved by spin-coating of a certain dose of CH3NH3Cl/CsCl solution onto a CsI-PbBr2-dimethyl sulfoxide (DMSO) intermediate phase film, followed by thermal annealing. The inclusion of CsCl species in the solution is crucial to a stable dual-phase CsPbCl3-Cs4PbCl6 film, while a high annealing temperature contributes to improving its quality. Therefore, the dual-phase CsPbCl3-Cs4PbCl6 film with an absorption onset of ∼420 nm, microsized grains, a few defects, and a proper work function is obtained by optimizing the annealing temperature. The final self-powered, visible-blind UV PD exhibits the superior performance, including a favored response range of 310-420 nm, a high responsivity (R) peak value of 61.8 mA W-1, an exceptional specific detectivity (D*) maximum of 1.35 × 1012 Jones, and a particularly fast response speed of 2.1/5.3 μs, together with amazing operational stability. This work represents the first demonstration of solution-processed, self-powered, visible-blind UV PDs with all-inorganic, Cl-based perovskite films.

Herein, physically transient Schottky diode with a structure of W/ZnO/MgO/W was proposed. By insert of 5 nm MgO layer between ZnO and W, Schottky barrier diode with rectification ratio of $7.8\times 10^{3}$ at ±1.5 V and a current density of 1780 mA/cm2 is obtained. In addition, the AC rectification frequency exceeds 1 MHz is observed. Meanwhile, stable resistive switching (RS) memory with remarkable performance and typical synapse functions have also been observed by applying a larger forming voltage. Additionally, the dissolution tests of ZnO, MgO and W films in deionized water (DI) demonstrate physically transient nature of the devices. The proposed transient W/ZnO/MgO/W Schottky diode provides the feasibility to control the functional for target use which have great potential for security computing systems, environmental friendly electronics, and biological integrated interfaces application.