Progress in efficient doping of Al-rich AlGaN

The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wavelength of 275 nm,there is still a huge gap in comparison with GaN-based visible light-emitting diodes(LEDs),mainly attributed to the inefficient doping of AlGaN with increase of the Al composition.First,p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency.Although p-GaN cladding layers are widely adopted as a compromise,the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected.While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%,resulting in a low electrical efficiency in sub-250 nm UV-LEDs.This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN,meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.

Lithiophilicity: The key to efficient lithium metal anodes for lithium batteries

Lithium metal anode of lithium batteries,including lithium-ion batteries,has been considered the anode for next-generation batteries with desired high energy densities due to its high theoretical specific capacity(3860 mA h g^(-1))and low standards electrode potential(-3.04 V vs.SHE).However,the highly reactive nature of metallic lithium and its direct contact with the electrolyte could lead to severe chemical reactions,leading to the continuous consumption of the electrolyte and a reduction in the cycle life and Coulombic efficiency.In addition,the solid electrolyte interface formed during battery cycling is mainly inorganic,which is too fragile to withstand the extreme volume change during the plating and stripping of lithium.The uneven flux of lithium ions could lead to excessive lithium deposition at local points,resulting in needle-like lithium dendrites,which could pierce the separator and cause short circuits,battery failure,and safety issues.In the last five years,tremendous efforts have been dedicated to addressing these issues,and the most successful improvements have been related to lithiophilicity optimizations.Thus,this paper comprehensively reviewed the lithiophilicity regulation in lithium metal anode modifications and highlighted the vital effect of lithiophilicity.The remaining challenges faced by the lithiophilicity optimization for lithium metal anodes are discussed with the proposed research directions for overcoming the technical challenges in this subject.

β-Ga_2O_3 thin film grown on sapphire substrate by plasmaassisted molecular beam epitaxy

Monoclinic gallium oxide(Ga_2O_3) has been grown on(0001) sapphire(Al_2O_3) substrate by plasma-assisted molecular beam epitaxy(PA-MBE). The epitaxial relationship has been confirmed to be [010]( 2ˉ01) β-Ga_2O_3||[ 011ˉ0](0001)Al_2O_3 via in-situ reflection high energy electron diffraction(RHEED) monitoring and ex-situ X-ray diffraction(XRD) measurement. Crystalline quality is improved and surface becomes flatter with increasing growth temperature, with a best full width at half maximum(FWHM) of XRD ω-rocking curve of( 2ˉ01) plane and root mean square(RMS) roughness of 0.68° and 2.04 nm for the sample grown at 730 °C,respectively. Room temperature cathodoluminescence measurement shows an emission at ～417 nm, which is most likely originated from recombination of donor–acceptor pair(DAP).

Comprehensive Design of the High-Sulfur-Loading Li–S Battery Based on MXene Nanosheets

The lithium-sulfur battery is the subject of much recent attention due to the high theoretical energy density,but practical applications are challenged by fast decay owing to polysulfide shuttle and electrode architecture degradation.A comprehensive study of the sulfur host microstructure design and the cell architecture construction based on the MXene phase(Ti3C2Tx nanosheets) is performed,aiming at realize stable cycling performance of Li-S battery with high sulfur areal loading.The interwoven KB@Ti3C2Tx composite formed by self-assembly of MXene and Ktej en black,not only provides superior conductivity and maintains the electrode integrality bearing the volume expansion/shrinkage when used as the sulfur host,but also functions as an interlayer on separator to further retard the polysulfide cross-diffusion that possibly escaped from the cathode.The KB@Ti3C2Tx interlayer is only 0.28 mg cm-2 in areal loading and 3 μm in thickness,which accounts a little contribution to the thick sulfur electrode;thus,the impacts on the energy density is minimal.By coupling the robust KB@Ti3C2Tx cathode and the effective KB@Ti3C2Tx modified separator,a stable Li-S battery with high sulfur areal loading(5.6 mg cm-2) and high areal capacity(6.4 mAh cm-2) at relatively lean electrolyte is achieved.

Metallic phase W_(0.9)Mo_(0.1)S_(2)for high-performance anode of sodium ion batteries through suppressing the dissolution of polysulfides

WS_(2)with layered graphite-like structure as anode for sodium ion batteries has high specific capacity.However,the poor cycling performance and rate capability of WS_(2)caused by the low electronic conductivity and structure changes during cycles inhibit its practical application.Herein,metallic phase(1T)W_(x)Mo_(1−x)S2(x=1,0.9,0.8 and 0.6)with high electronic conductivity and expanded interlayer spacing of 0.95 nm was directly prepared via a simple hydrothermal method.Specially,1T W_(0.9)Mo_(0.1)S_(2)as anode for sodium ion batteries displays high capacities of 411 mAh g^(-1)at 0.1 A g^(-1)after 180 cycles and 262 mAh g^(-1)at 1 A g^(-1)after 280 cycles and excellent rate capability(245 mAh g^(-1)at 5 A g^(-1)).The full cell based on Na_(3)V_(2)(PO_(4))_(2)O_(2)F/C cathode and 1T W_(0.9)Mo_(0.1)S_(2)anode also exhibits high capacity and good cycling performance.The irreversible electrochemical reaction of 1T W_(0.9)Mo_(0.1)S_(2)with Na ions during first few cycles results in the main products of W-Mo alloy and S.The strong adsorption of W-Mo alloy with polysulfides can effectively suppress the dissolution and shuttle effect of polysulfides,which ensures the excellent cycling performance of 1T W_(0.9)Mo_(0.1)S_(2).

Effect of Transverse Abdominis Plane Block on Chronic Post-Operative Pain—A Review

Chronic post-operative pain is a recognized adverse consequence of surgery;managing and preventing it are always a better choice. Proper choice of Anesthetic technique, use of combined anesthesia and pre-emptive analgesia may prevent and decrease the incidence of chronic post-operative pain. Transverse abdominis plane block (TAP Block) is a regional anesthesia technique following abdominal surgeries which involve injection of a large amount of local anesthetics in TAP, an anatomical space between the internal oblique and transverse abdominis muscle. The aim of this review is to show the effect and uses of TAP block as a combined anesthesia and multimodal analgesia in preventing chronic post-operative pain.

Structure and defect dual-engineering of cobalt oxides for lowtemperature Zn-air batteries

The exploration of bifunctional electrocatalysts with high catalytic activity and long-term durability for low-temperature Zn-air batteries(ZABs)is an ongoing challenge.Here,quintet-shelled hollow spheres,P-doped multi-layer Co_(3)O_(4)(PM-Co_(3)O_(4)),with enriched oxygen vacancies are prepared by thermally induced mass relocation and a simple phosphating process.Various advanced characterizations reveal P anion-induced effects on internal electronic structure and local coordination environment.The finite element method elucidates that the complex multi-layer spherical nanostructure is conducive to the transport and diffusion of OH-and O_(2).Benefiting from its unique structural features and abundant oxygen vacancies,the well-designed PM-Co_(3)O_(4) presents small reversible oxygen overpotential for catalyzing oxygen reduction/evolution reactions.Accordingly,the fabricated low-temperature ZABs based on PM-Co_(3)O_(4) as air-cathode exhibit high power density(20.8 mW·cm^(-2))and long-term stability(over 600 cycles)at the ultra-low temperature of-40℃,outperforming state-of-art Pt/C+IrO_(2)-based ZABs.Furthermore,the dynamic evolution mechanism of cobalt oxide catalysts during ZAB operation is elucidated.This work provides a guideline to design efficient electrocatalysts with regulated electronic configurations and exquisite nano-/microstructures for ZABs under extreme working conditions.

High-pressure MOCVD growth of InGaN thick films toward the photovoltaic applications

The highly efficient photovoltaic cells require the In-rich InGaN film with a thickness more than 300 nm to achieve the effective photo-electricity energy conversion.However,the InGaN thick films suffer from poor crystalline quality and phase separations by using the conventional low-pressure metal organic chemical vapor deposition(MOCVD).We report on the growth of 0.3-1μm-thick InGaN films with a specially designed vertical-type high-pressure MOCVD at the pressure up to 2.5 atms.The In incorporation is found to be greatly enhanced at the elevated pressures although the growth temperatures are the same.The phase separations are inhibited when the growth pressure is higher than atmospheric pressure,leading to the improved crystalline quality and better surface morphologies especially for the In-rich InGaN.The In 0.4 Ga 0.6 N with the thickness of 300 nm is further demonstrated as the active region of solar cells,and the widest photoresponse range from ultraviolet to more than 750 nm is achieved.

In situ formation of ionically conductive nanointerphase on Si particles for stable battery anode

Silicon(Si)is a promising anode candidate for next-generation lithium-ion batteries(LIBs)due to its high theoretical capacity.Solar Si photovoltaic waste possesses good purity and high output.Using it as the raw material for battery anodes can synchronously solve the problem of solid waste pollution and enable high energy density LIBs.A critical issue impeding the practical application of Si is the undesirable side reactions at the electrolyte-particle interface and the resulting increase in impedance during cycling.Herein,a Si-P core shell structure with chemical bonding at the Si-P interface is fabricated through a simple mechanical alloying reaction between red P and solar Si photovoltaic waste.The P nanoshell with thickness within 15 nm converts to Li3P during the initial lithiation process and maintains its phase on cycling.The as-formed Li3P nanolayer functions as a stable,ionically conductive protective layer that reduces the direct contact between Si and electrolytes,and thus suppresses undesired side reactions.The Si-P nanocomposite exhibits stable electrochemical cycling with a high reversible capacity of 1,178 mAh g^(−1)after 500 cycles at 1,200 mA g^(−1),as well as excellent rate capability(912 mAh g^(−1)at 2 C).With 15 wt%addition to graphite,a graphite/Si-P hybrid electrode shows a high overall reversible specific capacity of 447 mAh g^(−1)and 88.3%capacity retention after 100 cycles at high areal capacity of 2.64 mAh cm^(−2) at 100 mA g^(−1),indicating its promise as a drop-in anode in practical LIBs.

Sub-nanometer ultrathin epitaxy of AlGaN and its application in efficient doping

Solving the doping asymmetry issue in wide gap semiconductors is a key dificulty and long-standing challenge for device applications.Here,a desorption-tailoring strategy is proposed to juggle the carrier concentration and transport.Specific to the p-doping issue in Al-rich AlGaN,self-assembled p-AlGaN superlattices with an average Al composition of over 50%are prepared by adopting this approach.The hole concentration as high as 8.1×10^(18)cm^(-3)is thus realized at room temperature,which is attributed to the signifcant reduction of effective Mg activation energy to 17.5 meV through modulating the activating path,as well as the highlighted Mg surface-incorporation by an intentional interruption for desorption.More importantly,benefting from the constant ultrathin barrier thickness of only three monolayers via this approach,vertical miniband transport of holes is verifed in the p-AlGaN superlattices,greatly satisfying the demand of hole injection in device application.280 nm deep-ultraviolet light emitting diodes are then fabricated as a demo with the desorption-tailored Al-rich p-AlGaN superlattices,which exhibit a great improvement of the carrier injection efficiency and light extraction efficiency,thus leading to a 55.7%increase of the light output power.This study provides a solution for p-type doping of Al-rich AlGaN,and also sheds light on solving the doping asymmetry issue in general for wide-gap semiconductors.

A review on the GaN-on-Si power electronic devices

The past decades have witnessed a tremendous development of GaN-based power electronic devices grown on Si substrate.This article provides a concise introduction,review,and outlook of the research developments of GaN-on-Si power device technology.The comprehensive review has discussed the crucial issues in the state-of-the-art device technology based on both GaN materials epitaxy including stress control and point defects study,and device fabrication including normally offsolutions like Cascode,trench MIS-gate,and p-GaN gate.Device reliability and other common fabrication issues in GaN high electron mobility transistors(HEMTs)are also discussed.Lastly,we give an outlook on the GaN-on-Si power devices from two aspects,namely high frequency,and high power GaN ICs,and GaN vertical power devices.

Low-temperature epitaxy of transferable high-quality Pd(111)films on hybrid graphene/Cu(111)substrate

The continuous pursuit of miniaturization in the electronics and optoelectronics industry demands all device components with smaller size and higher performance,in which thin metal film is one heart material as conductive electrodes.However,conventional metal filmns are typically polycrystalline with random domain orientations and various grain boundaries,which greatly degrade their mechanical,thermal and electrical properties.Hence,it is highly demanded to produce single-crystal metal films with epitaxy in an appealing route.Traditional epitaxy on non-metal single-crystal substrates has difficulty in exfoliating away due to the formation of chemical bonds.Newly developed epitaxy on single-crystal graphene enables the easy exfoliation of epilayers but the annealing temperature must be high(typical 500-1,000℃ and out of the tolerant range of integrated circuit technology)due to the relative weak intertacial interactions.Here we demonstrate the facile production of 6-inch transferable high-quality Pd(111)filims on single-crystal hybrid graphene/Cu(111)substrate with CMOS-compatible annealing temperature of 150℃ only.The interfacial interaction between Pd and hybrid graphene/Cu(111)substrate is strong enough to enable the low-temperature epitaxy of Pd(111)films and weak enough to facilitate the easy film release from substrate.The obtained Pd(111)films possess superior properties to polyrystalline ones with-0.25 eV higher work function and almost half sheet resistance.This technique is proved to be applicable to other metals,such as Au and Ag.As the single-crystal graphene/Cu(111)substrates are obtained from industrial Cu foils and accessible in meter scale,our work will promote the massive applications of large-area high-quality metal fims in the development of next-generation electronic and optoelectronic devices.

Principle and applications of semiconductor optical amplifiers-based turbo-switches

All-optical effectively increase the semiconductor optical recovery time or the high-speed turbo-switches can switching speed using cascaded amplifiers （SOAs）. The overall bandwidth of turbo-switch was numerically analyzed with time-domain and frequency-domain SOA models. The turbo-switch was explored from the fundamental carrier dynamics in SOAs for the purpose of further increasing its operation speed. An integrated turbo-switch was also been proposed and demonstrated, where a phase adjustable Mach-Zehnder interferometer （MZI） was applied as an optical band-pass filter between SOAs. Wavelength conversion was first demonstrated at 84.8 Gbit/s using the integrated turbo-switch.

Infrared stimulated emission with an ultralow threshold from low-dislocation-density InN films grown on a vicinal GaN substrate

Near-infrared stimulated emission from a high-quality InN layer under optical pumping was observed with a threshold excitation power density of 0.3 and 4 kW cm^(−2) at T=8 and 77 K,respectively.To achieve such a low threshold power density,vicinal GaN substrates were used to reduce the edge-component threading dislocation(ETD)density of the InN film.Cross-sectional transmission electron microscopy images reveal that the annihilation of ETDs can be divided into two steps,and the ETD density can be reduced to approximately 5×10^(8) cm^(−2) near the surface of the 5-μm-thick film.The well-resolved phonon replica of the band-to-band emission in the photoluminescence spectra at 9 K confirm the high quality of the InN film.As a result,the feasibility of InN-based photonic structures and the underlying physics of their growth and emission properties are demonstrated.

Simultaneously enhancing ionic conductivity and interfacial stability by Fe_(2)O_(3) for solid-state sodium metal batteries

NASICON-structured Na_(3)Zr_(2)Si_(2)PO_(12)(NZSP)has been considered as one of the ideal electrolytes for all-solid-state sodium metal batteries(ASSSB).However,the practical application of NZSP-based ASSSB is hindered by the low ionic conductivity and large interfacial resistance caused by the poor contact between NZSP and Na metal.Herein,the introduction of Fe_(2)O_(3) not only improves ionic conductivity and reduces activation energy by the doping of Fe^(3+)in the crystal structure of NZSP,but also reduces the interfacial resistance and enhances interface stability between NZSP and Na metal anode.The synergistic effects significantly enhance the cycling stability,rate capability,and critical current density of the symmetrical solid-state cells.The interfacial reaction mechanism indicates that Fe3+in the interface is reduced Fe2+by Na anode,which effectively even the electric-filed distribution and suppresses the dendrite growth.Consequently,the symmetric solid-state cells exhibit stable cycling performance for 1,500 h at 0.1 mA·cm−1/0.1 mA·h·cm−1 and over 900 h at 0.2 mA·cm−1/0.2 mA·h·cm−1.The Na|NZSP-0.075%Fe_(2)O_(3)|Na_(2)FePO_(4)F solid-state full cells display high capacity retention of 94.2%after 100 cycles at 0.5 C.The stable interface of NZSP/Na and improved ionic conductivity contribute to excellent electrochemical performance,which accelerates the practical application of ASSSB.