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In recent years, pulsed discharges at atmospheric pressure have attracted extensive attention due to their remarkable discharge advantages. In this article, a fluid model is applied to investigate a new type of pulsed dielectric barrier discharge (DBD), characterized by a sharp rising phase and slow falling phase but without a plateau phase, which could be realized by using a circuit composed of a device called silicon diode for alternating current (SIDAC). Based on the computational data, the influences of voltage waveform on the plasma density and electric field are carefully discussed. The simulation results show that only one significant discharge event occurs during the voltage rising phase, which produces a large electron density with high electron temperature, but the secondary discharge current cannot be observed due to the slow voltage falling phase. We also qualitatively investigate the effects of discharge parameters on the plasma dynamics, such as the relative permittivity, barrier thickness, and repetitive frequency from simulation data, which agree well with the experimental observation. Based on the simulation results, the optimization of this pulsed discharges to enhance the electron density and improve the electron temperature is discussed, thus promoting the wide applications of the pulsed discharges.

InGaN epitaxial layers were grown on c-plane sapphire substrates using the metalorganic vapour phase epitaxy (MOVPE) system at 760 °C. By varying the total flow rate of group-III sources (TMI+TEG) with a fixed molar ratio of group-III sources [TMI/(TMI+TEG)], the influence of V/III ratio were investigated from 4500 to 20000. The grown N-polar InGaN layers were investigated by atomic force microscopy and it is found that the surface roughness decreases with increasing the V/III ratios. High resolution X-ray diffraction analyses show that the phase separation decreases with increasing the V/III ratios. Photoluminescence measurements reveal that the peak position of the band-edge emission shifted toward the shorter wavelength with increasing the V/III ratios. Reciprocal space mapping (RSM) analyses were carried out on InGaN films. At low V/III ratio, the phase separation can be detected in InGaN films.

A supercapacitor electrode featured with a voltage self-stabilizing capability is demonstrated by growing indium tin oxide (ITO) nanowires on Ni foam. The ITO nanowires with a single crystal structure are prepared by using magnetron sputtering technique, and they can act as an active electrode material. Charging–discharging experiments are performed under different current densities, demonstrating a good rate capability. Using properly designing top and bottom double connection circuits, part of the electrode can be used as a resistance switch. An electrode that can function as a supercapacitor and a resistance switch is fabricated. Detailed characteristics confirm that the device not only exhibits high performance as a supercapacitor but also has good characteristics of resistance switching (RS). The specific capacitance is 956 F/g at the scanning rate of 10 mV/s, and the switching ratio as a bipolar resistance switch is as high as 102. The stabilization time of discharging voltage is nearly doubled longer than that without any RS function, revealing the potential application of our devices, which can be used as a supercapacitor with voltage self-stabilizing.

In this work, a near-ultraviolet (380 nm) double Al0.2Ga0.8N/GaN distributed Bragg reflectors (DBRs) stack mirror was designed and fabricated. The double DBRs stack mirror consists of a 30-pair Al0.2Ga0.8N/GaN DBRs centered at 375 nm and a 20-pair Al0.2Ga0.8N/GaN DBRs centered at 385 nm. Our simulation results show that the method of double DBRs stack mirror design can broaden the stopband width greatly and increase the reflected angle efficiently, compared with the single Al0.2Ga0.8N/GaN DBRs mirror. In experiment, the double Al0.2Ga0.8N/GaN DBRs stack mirror and the reference Al0.2Ga0.8N/GaN DBRs mirror were grown on sapphire substrate by metalorganic chemical vapor deposition. The measured stopband width of the double DBRs stack mirror (~ 25 nm) is more than two times that of the reference DBRs mirror (~ 11 nm), which consists well with our simulation results. It is reasonable to believe that this work could provide a valuable information to obtain AlGaN/GaN DBRs with wide stopband width that can be used in the fabrication of GaN-based resonant cavity light-emitting diodes and vertical cavity surface emitting lasers.

In this work, GaN-based vertically conducting near ultraviolet light-emitting diodes (LEDs) were grown on n-SiC substrates by metal-organic chemical vapor deposition. 10 pairs or 20 pairs of Si-doped n-Al0.2Ga0.8N/n-GaN distributed Bragg reflectors (DBRs) were used to improve the performance of the LEDs. The central reflected wavelength of the DBRs structures agreed well with the emission wavelength of the LEDs. A 389 nm near ultraviolet electroluminescence (EL) emission peak could be clearly observed in all the LED samples in our study. The EL intensity of LEDs was obviously enhanced because of the application of DBRs. Angle-dependent EL spectra were measured as well. For all the measurement angle region, the near ultraviolet EL emission intensity of the LEDs with DBRs were higher than that of the LED without DBRs.

The wake of an Ahmed body may be divided into high- and low-drag regimes where the rear slant angle (φ) is in the ranges of 12.5°–30° and larger than 30°, respectively. This work aims to gain a relatively thorough understanding of unsteady predominant coherent structures around an Ahmed body of φ = 35° in the low-drag regime. Extensive hot-wire, wall pressure, flow visualization and particle image velocimetry measurements have been conducted at Reynolds number based on αS is a constant 0.20, irrespective of the value of φ. A corner vortex rolling upstream is observed near the lower end of the slanted surface, whose formation mechanism and dynamical role are discussed. The Reynolds-number effect on the flow is also documented. Based on the present and previously reported data, a conceptual flow structure model is proposed for a low-drag Ahmed body, including both steady and unsteady coherent structures around the body.

Understanding the role of TiO2 in glass structure is the key to the development of new functional glass materials. In this work, the changes in the structural units of SiO2-TiO2-ZrO2-RO-Al2O3 (R=Ca, Sr, Ba) multicomponent glass were characterized by X-ray photoelectron spectroscopy, magic angular spinning nuclear magnetic resonance and Raman spectra. It is determined that with increasing TiO2/SiO2 molar ratio, the amount of [TiO4] and [TiO6] increase at the expense of [TiO5] and the coordination of Al3+ changes little. Si4+is mainly linked in the Q3 and its proportion is related to the change of TiO2 content, which infers that the nonbridging oxygen number, the proportion of Si-O-Ti, Ti-O-Ti and Si-O-Si also varies accordingly. The changes in structure also affect the performance of the glass. The results indicate that the substitution of TiO2 increases the density and dielectric constant of the glass, makes the glass thermal stability decrease slightly. This work provides a basis for the performance tailoring of high dielectric glass fiber.

The luminescence characteristics of InGaN ultra-thin films with and without GaN cap layer are investigated by temperature-dependent photoluminescence (TDPL) measurements. It is experimentally observed that, during the TDPL measurements at some fixed temperatures, the PL spectra of bare InGaN film show anomalous attenuation and redshift with time passing. This may be attributable to the enhancement of quantum-confined Stark effect in InGaN layer due to the desorption of the negatively charged particles on the surface of bare InGaN film, because the adsorbed negative charges on InGaN surface partially counteract the piezoelectric field in the ultra-thin InGaN film. However, for the GaN-capped InGaN ultra-thin film, those anomalous spectral variations with time vanish, as the adsorption and desorption process on the InGaN surface are screened by the GaN cap layer.

In this paper, near-ultraviolet AlGaN/GaN distributed Bragg reflectors (DBRs) are designed by the optimization of refractive index contrast (△n/n) and prepared by metalorganic vapor phase epitaxy. The relationship between refractive index contrast and Bragg wavelength for Al0.2Ga0.8N/GaN DBRs are analyzed theoretically. Through the calculation, it is found that the refractive index contrast, the reflectivity and the stopband of DBRs are the function of Bragg wavelength. According to the calculation results, Al0.2Ga0.8N/GaN DBRs with Bragg wavelength ranging from 375 nm to 387 nm show a high reflectivity and a wide stopband. To confirm the results above, crack-free Al0.2Ga0.8N/GaN DBRs with different Bragg wavelength and different pairs are prepared. The relationship between the reflectivity and the Bragg wavelength for the prepared DBRs is agreed with the calculation results. Especially, a high peak reflectivity of 95% and wide stopband of about 15 nm are achieved for the 50-pair crack-free Al0.2Ga0.8N/GaN DBRs with Bragg wavelength at 385 nm. It is reasonable believe the that the AlGaN/GaN structured DBRs in this paper can be applied to improve luminous efficieny of near ultraviolet light emitting diodes.

In this work, GaN films were grown on SiC substrates by metal-organic chemical vapor deposition. The influence of the growth temperature, thickness, and growth rate of graded AlGaN buffer on the stress state in the GaN films were investigated. We find that the in-plane tensile stress in the GaN film can be reduced from ∼0.58 to ∼0.16 GPa by the optimization of the growth parameters of the graded AlGaN buffer. Under the optimized growth parameters, the GaN film also possess the best crystalline quality, for which the full width at half maximum (FWHM) of (0002) and ( 10 1 ¯ 2 ) X-ray diffraction (XRD) rocking curves are 240 and 288 arcsec, respectively. Based on the optimized growth parameters of the graded AlGaN buffer, the SiNx interlayer with a deposition time of 180 s was employed in the growth processes of the GaN film. As a result, the in-plane tensile stress in the GaN film is reduced to a much smaller value, which is about 0.04 GPa, and the crystalline quality of the GaN are further improved, for which the FWHM of (0002) and ( 10 1 ¯ 2 ) XRD rocking curves are 98 and 128 arcsec, respectively.

In this paper, near-ultraviolet AlGaN/GaN distributed Bragg reflectors (DBRs) were prepared on GaN/sapphire templates by metal organic chemical vapor deposition. A single low-temperature AlN interlayer was adopted to prevent the formation of cracks in DBRs. Moreover, different pairs of DBRs with AlN interlayer were grown to investigate the stress distribution through the epilayer, the surface morphology evolution and the variation of reflectivity spectra. The in-situ stress monitoring shows a compressive-to-tensile stress transition with the increase of DBRs pairs. The optical microscope and atomic force microscope images show that the AlN interlayer induces the appearance of trenches on the surface of DBRs and the trenches gradually coalesce when DBRs grow. Meanwhile, the experimental reflectivity spectra get closer to the simulated results. Finally, we obtain a smooth-surface 25-pair Al.32Ga.68N/GaN DBRs with a reflectance of 94% at 390 nm and a 16 nm stopband bandwidth. The preparation of high-quality DBRs lays the foundation for the future development of high efficiency resonant cavity UV LEDs.

In InGaN/GaN multi-quantum wells (MQWs), a low temperature cap (LT-cap) layer is grown between the InGaN well layer and low temperature GaN barrier layer. During the growth, a temperature ramp-up and ramp-down process is added between LT-cap and barrier layer growth. The effect of temperature ramp-up time duration on structural and optical properties of quantum wells is studied. It is found that as the ramp-up time increases, the Indium floating layer on the top of the well layer can be diminished effectively, leading to a better interface quality between well and barrier layers, and the carrier localization effect is enhanced, thereby the internal quantum efficiency (IQE) of QWs increases surprisingly. However, if the ramp-up time is too long, the carrier localization effect is weaker, which may increase the probabilities of carriers to meet with nonradiative recombination centers. Meanwhile, more nonradiative recombination centers will be introduced into well layers due to the indium evaporation. Both of them will lead to a reduction of internal quantum efficiency (IQE) of MQWs.

In this paper, GaN-based yellow light-emitting diodes (LEDs) were homoepitaxially grown on free-standing (0001) GaN substrates by metal-organic chemical vapor deposition. X-ray diffraction (XRD), photoluminescence (PL), and electroluminescence (EL) measurements were conducted to investigate the structural, optical, and electrical properties of the yellow LED. The XRD measurement results showed that the InGaN/GaN multiple quantum wells (MQWs) in the LED structure have good periodicity because the distinct MQWs related higher order satellite peaks can be clearly observed from the profile of 2θ-ω XRD scan. The low temperature (10 K) and room temperature PL measurement results yield an internal quantum efficiency of 16% for the yellow LED. The EL spectra of the yellow LED present well Gaussian distribution with relatively low linewidth (47–55 nm), indicating the homogeneous In-content in the InGaN quantum well layers in the yellow LED structure. It is believed that this work will aid in the future development of GaN on GaN LEDs with long emission wavelength.

N-polar GaN-based blue-green light-emitting diodes (LEDs) with p-AlGaN electron blocking layer (EBL) were numerically investigated by simulation and experimentally grown on vicinal C-face SiC substrates by metal–organic chemical vapor deposition. By numerical simulation, we can find that p-AlGaN EBL in N-polar LEDs is able to play a more important role in blocking electron overflow than that in Ga-polar LEDs due to the reversed polarization, which leads to a high output power and internal quantum efficiency. Besides, the holes injection efficiency is enhanced in N-polar LED, resulting in a lower turn-on voltage. In experimental studies, N-polar LEDs based on different numbers of quantum wells were grown on vicinal C-face n-SiC substrates. When a forward bias is applied to the epitaxial N-polar LED with two quantum wells, a strong blue-green emission located at 480 nm can be observed. This work indicates that N-polar group-III nitrides have great potential in the application of optoelectronic devices.

Al0.2Ga0.8N/Al0.45Ga0.55N multiple quantum wells (MQWs) were grown on SiC substrates by metal–organic chemical vapor deposition. We studied the influence of well width and barrier width on the structural and optical properties of AlGaN MQWs in details. The MQWs structures prepared in this work all exhibited good periodicity and abrupt interfaces. When the barrier width was fixed, the thinner well was benefit to increase the integrated photoluminescence (PL) intensity of the MQWs and obtain a shorter ultraviolet wavelength. And the thicker barrier was also contributed to improve the optical properties while the well width remained the same. Compared with the effect of the well width, the emission wavelength of MQWs was less dependent on the barrier width. A 318-nm room-temperature PL emission was achieved when the well width and barrier width were 2.5 and 11 nm, respectively.

Low temperature grown p-AlGaN layer with a small resistivity is crucial to improve the performance of the GaN-based laser diodes (LDs). In this study, growth temperature of the p-AlxGa1-xN (0.08 ≤ x ≤ 0.104) layers are controlled to be relatively low, and the influence of hydrogen impurity on the resistivity is investigated in detail. According to the dependence of hole concentration and resistivity on hydrogen impurity concentration, it is found that when Mg doping concentration is unchanged, reducing hydrogen impurity concentration in p-AlxGa1-xN (0.08 ≤ x ≤ 0.104) layers could reduce the resistivity effectively, which is attributed to weaken the compensation or passivation effect of hydrogen impurities on Mg acceptors. A p-Al0.09Ga0.91N layer with a low resistivity of 4.6 Ω cm has been achieved.

In atmospheric radio-frequency (RF) discharges, two discharge modes, namely $\alpha $ and $\gamma $ modes, have been deeply discussed by experimental measurements and computational data, and another mode, known as $\Omega $ mode, has also been reported in the electronegative gas. In this paper, we present a fluid model to investigate the formation and dynamics of $\Omega $ mode in atmospheric RF discharges but controlled by dielectric barriers with pure helium as working gas. The simulation results show that the $\Omega $ mode can be observed right after the breakdown event, and only sustained in a very narrow voltage range; then, the discharge will enter into the $\alpha $ mode as the applied voltage is further increased. Compared with the $\alpha $ mode, the numerical data reveal that in the $\Omega $ mode, a relatively larger electric fields are sustained in the bulk plasma to ensure the continuity of discharge current due to the lower electron density, consequently the Ohmic heating and ionization processes mainly take place in the central region of discharge gap.

Under the pressures of the current global pandemic, researchers have been working hard to find a reliable way to suppress infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent the spread of COVID-19. Studies have shown that the recognition and binding of human angiotensin-converting enzyme 2 by the receptor-binding domain (RBD) of the spike protein on the surface of SARS-CoV-2 is a crucial step in viral invasion of human receptor cells, and blocking this process could inhibit the virus from invading normal human cells. Plasma treatment can disrupt the structure of the RBD and effectively block the binding process. However, the mechanism by which plasma blocks recognition and binding is not clear. In this study, the reaction between reactive oxygen species (ROS) in plasma and a molecular model of the RBD was simulated using a reactive molecular dynamics method. The results showed that the destruction of the RBD by ROS was triggered by hydrogen abstraction reactions: O and OH abstracted H atoms from the RBD, while the H atoms of H2O2 and HO2 were abstracted by the RBD. This hydrogen abstraction resulted in the breakage of C–H, N–H, O–H and C=O bonds and the formation of C=C and C=N bonds. The addition reaction of OH increased the number of O–H bonds and caused the formation of C–O, N–O and O–H bonds. The dissociation of N–H bonds led to the destruction of the original peptide bond structure and amino acid residues, changed the type of amino acid residues and caused the conversion of N–C and N=C and C=O and C–O. The simulation partially elucidated the microscopic mechanism of the interaction between ROS in plasma and the capsid protein of SARS-CoV-2, providing theoretical support for the control of SARS-CoV-2 infection by plasma, a contribution to overcoming the global pandemic.

In this paper, we performed a one-dimensional fluid model to study the mechanism and optimization of pulse-modulated Radio-Frequency (RF) discharges at atmospheric pressure assisted by short pulse voltages. The evolution of discharge current density, helium metastable ( He*) density, and total electron density from the simulation demonstrates that the ignition of RF discharge could be effectively enhanced by the short pulsed discharge, and a large Peak Current in the First Period (PCFP) can be produced, which agrees well with the experimental measurements. Due to the assistance of pulsed voltage, a strong electric field could be formed near the anode with the same polarity of that near the cathode, which can reaccelerate the electrons near the anode to generate a large PCFP. Based on the simulation results, reducing the time interval and increasing the pulse rise rate are very helpful to enhance the ignition of subsequent RF discharge by strengthening the electric field near the anode. It is shown that by choosing the appropriate time interval and pulse rise rate, the pulse-modulated RF discharge assisted by the pulsed discharge can be effectively modulated and optimized for applications.

A kinetic insight into microwave plasma oxidation on 4H-SiC is of great importance to improve the quality of SiO2 dielectric and SiO2/SiC interface in SiC MOSFETs. In this work, quantitative study on SiC plasma oxidation has been performed for a wide range of oxidation conditions by using Massoud’s empirical relation. In this relation, an additional exponential term related to the diffusion coefficient, the oxidation coefficient and the emission ratio of Si and C is introduced to describe the deviation of oxidation behavior relative to the Deal-Grove model. In plasma oxidation, the exponential term is dominant, especially in the growth-rate enhancement stage. Moreover, the contribution of the exponent increases with increasing temperature. Finally, a plausible kinetic model is proposed by considering exchange in the surface region, diffusion in oxide and reaction at the SiO2/SiC interface.

In this work, AlGaN/GaN superlattices (SLs) structures were grown on SiC substrates by metal-organic chemical vapor deposition (MOCVD). The influence of AlGaN/GaN period numbers, the ratio of AlGaN thickness to GaN thickness ( t A l G a N / t G a N ), and the Al content on the strain state of AlGaN/GaN SLs are investigated. Moreover, the strain relaxation mechanism of the SLs is analysed. Our results show that the surface roughening, the formation of misfit dislocations and the generation of cracks are all contribute to the strain relaxation of the SLs. Moreover, the main reason cause the formation of cracks in the SLs is the large lattice mismatch between the SLs and the template rather than the large lattice mismatch between the GaN and AlGaN in the SLs. It is worth noting that understanding the strain relaxation mechanism is crucial for the design and fabrication of high-quality optoelectronic devices based on AlGaN/GaN SLs by MOCVD.

In recent years, cold atmospheric plasma (CAP) has been found to induce apoptosis selectively in cancer cells and has become a research hotspot, but the underlying mechanisms remain unclear. Aquaporins (AQPs) on the cell membranes of cancer cells are believed to be related to the selective therapeutic mechanism of CAP. In this study, the reactive oxygen species (ROS) generated by CAP, which are believed to play an important role in the apoptosis of cancer cells, crossed the membrane through aquaporin-1 (AQP1). The process of membrane penetration, the distribution of ROS on the membrane, and the free energy barrier of AQP1 on ROS are determined by the molecular dynamics simulation based on the GROMOS 53A6 force field. The ROS distribution shows that the presence of AQP1 results in a deeper distribution of hydrophilic ROS in cell membranes. The free energy barrier for the movement of hydrophilic ROS through AQP1 is significantly lower than that for their movement through the lipid bilayer. Therefore, AQP1 on the cell membrane can improve the efficiency of the entry of hydrophilic ROS into cancer cells. These results illustrate that AQP1 can improve the transmembrane efficiency of ROS and provide insights into the mechanism underlying the selectivity of CAP at the atomic level.

In this paper, we investigated the optimization of pulse-modulated radio frequency (rf) discharges in the range of very high frequency from 50 to 800 MHz by a fluid model. A very strong Peak Current in the First Period (PCFP) during the power-on phase can be observed only when the excitation frequency is large enough, usually larger than 50 MHz, and the reversal electric field near the anode due to the accumulation of electrons contributes greatly to the formation of this peak current from the simulation data. The highest electron temperature is achieved in the first period, while the largest electron density is usually obtained in the last period during the power-on phase. By increasing the duty cycle, the value of PCFP increases initially, then it reaches the peak value at a duty cycle of approximately 70%, and later it drops to the normal value generated in a continuous rf discharge, and the maximum electron temperature also shows the similar evolution. However, as the duty cycle is increased, the electron density is always enhanced during the power-on phase. According to the simulation results, the duty cycle and modulation frequency can be effectively applied to modulate and optimize the electron density and electron temperature for applications.

Xenon gas and mercury vapor based broad spectrum light sources have wide application, however, are hard to compact. On the contrary, LEDs are easy for compaction, but are hard to emit a broad spectrum. In this work, we demonstrate a simple phosphor free LED structure of ZnO/MgO/ITO, of which the spectrum covers the range from 300 to 650 nm. The device was fabricated on commercially available ITO substrate, and the ZnO/MgO structure was successively grown by MOCVD method, of which the morphology, crystallinity and optical quality were characterized. A thin MgZnO layer with graded composition is believed to form through the miscibility of MgO and ZnO during the initial growth stage of ZnO. The active region of the device includes the thin MgZnO layer and part of the subsequent grown ZnO layer. The light with wavelength shorter than ~360 nm is attributed to the near band edge emission of the MgZnO layer. And the near band edge emission and deep level emissions of ZnO contribute to the spectrum from ~360 to 650 nm. The working mechanism of the device is discussed mainly based on the energy band diagram.

The indium (In) incorporation induced morphological evolution and strain relaxation of high In content InGaN epilayers grown by metal–organic chemical vapor deposition (MOCVD) were investigated. With the decrease of growth temperature from 753 to 627 °C, In incorporation increases from 0.10 to 0.42, and the surface morphology evolves from initially mound-like three-dimensional surface roughness to progressive smoothness. Such morphology evolution mechanism can be well accounted for by a self-regulating model of islands’ proportions considering both strain relaxation and In surfactant effect comprehensively. Additionally, the strain relaxation and microstructural defects of such InGaN epilayers were investigated by X-ray diffraction reciprocal space mapping and cross-sectional transmission electron microscopy, respectively. It is found that, with the increase of In content, plastic relaxation via generating random stacking faults along with the surface sawtooth roughening becomes a more important strain re...

β-Ga2O3 films were grown on c-plane sapphire substrates at different substrate temperatures by metal-organic chemical vapor deposition. The effects of substrate temperature on transparence, optical band gap and photoluminescence of the films were studied systematically. With increasing the substrate temperature, the films structure was changed from amorphous to single orientation β-Ga2O3. The β-Ga2O3 films exhibited excellent optical transparency in the ultraviolet and visible regions. The ultraviolet-blue photoluminescence was observed at room temperature. The temperature-dependent photoluminescence was also carried out and the relative intensity of the blue emission with respect to the ultraviolet emission decreased with increasing the measured temperature. The origin of luminescence was discussed.

We utilized in-situ grown SiNx insertion mask to improve the quality of N-polar GaN films on sapphire substrates by metal-organic chemical vapor deposition. The influences of deposition time and position of SiNx insertion mask were studied. Under the optimal SiNx mask growth conditions, the full width at half maximum values of (0002) and (10 1 ¯ 2) XRD rocking curves of N-polar GaN films are decreased to 88″ and 172″, respectively. Simultaneously, Raman spectroscopy measurements reveal that SiNx mask can also reduce the tensile residual stress of N-polar GaN films. In addition, the electrical and optical properties of N-polar GaN films with and without SiNx insertion mask were investigated by temperature dependent Hall and photoluminescence measurements. It is found that N-polar GaN film with SiNx insertion mask has lower background carrier concentration, higher mobility and lower nonradiative recombination rate.

We presented the epitaxial growth of n-GaN films on n-SiC substrates with n-Al0.3Ga0.7N buffer and SiNx interlayer by metal organic vapor phase epitaxy. In order to optimize the properties of n-GaN films, a comparative investigation was performed by modifying SiNx deposition time and its insert location. Under the optimal growth parameters of SiNx, the full width at half maximum values of GaN $$(0002)$$ and $$(10\bar{1}2)$$ diffraction peaks effectively reduced to 208 and 226 arcsec, respectively. Simultaneously, molten NaOH based wet etchings were used to verify the reduction of the dislocation densities in GaN films. Good vertical conducting characteristics in n-GaN/n-SiC homo-type heterojunction were achieved by inserting SiNx into n-GaN film. Additionally, Raman and low-temperature photoluminescence measurements were employed to determine the stress state in GaN film.

In this paper, N-polar GaN films were grown on vicinal C-face SiC substrates by metal–organic chemical vapor deposition. In situ porous SiNx interlayers with different deposition times of 0 s to 120 s were adopted in the growth processes of N-polar GaN films. We find that the crystalline quality, such as surface morphology and structural characteristics, of N-polar GaN films can be controlled by changing the deposition time of the SiNx interlayers. The N-polar GaN film with a SiNx deposition time of 60 s exhibits the best crystallinity. Based on the observed porous feature of the SiNx interlayer from the phase image obtained using an atomic force microscope, we propose a model to illustrate the epitaxial growth mechanism of N-polar GaN films grown on the top of the porous SiNx interlayer. In this model, we reveal that the SiNx deposition time determines the SiNx coverage and the nucleated island density of overgrown GaN, which markedly affects the structural characteristics of the N-polar GaN films. This model can also be used to analyze the influence of SiNx deposition times on the stress states in N-polar GaN films. Additionally, the threading dislocation propagation behaviors were observed experimentally from the cross-sectional transmission electron microscopy image of N-polar GaN with a SiNx interlayer, which demonstrates the reasonability of this model. It is reasonably believed that this work provide a valuable information to obtain high-quality GaN films that can be used to the fabrication of N-polar GaN-based optoelectronic devices.

Perovskite light-emitting diodes (PeLEDs), because of its fundamental scientific importance and practical applications in the fields of low-cost light source or display applications, have drawn worldwide attention in recent years. However, PeLEDs available today suffer from a compromise in their emission efficiency and operation stability. In this study, we designed and fabricated a stacking all-inorganic multilayer structure by using inorganic perovskite CsPbBr3 quantum dots (QDs) as the emissive layer and inorganic n-type MgZnO and p-type MgNiO as the carrier injectors, respectively. Through energy band engineering of carrier injectors by Mg incorporation and their thickness optimization, PeLEDs with maximum luminance of 3809 cd/m2, luminous efficiency of 2.25 cd/A, and external quantum efficiency of 2.39% have been realized, which are much better than most PeLEDs from CH3NH3PbBr3 films, and comparable with the highest results reported on CsPbBr3 QDs LEDs. More importantly, the unencapsulated PeLEDs in ...

In this work, blue-green InGaN/GaN multiple quantum wells (MQWs) were grown on SiC substrates by metal-organic chemical vapor deposition. The influence of growth pressure on the structural and optical properties and surface morphology of the MQWs was studied. The photoluminescence measurement results indicate that the indium content in the MQWs nearly doubles when the growth pressure increases from 100 to 400 mbar, and the MQWs grown at different pressures exhibit distinct temperature-dependent optical behaviors. Meanwhile, the growth pressure also influences the structural characteristics of the MQWs significantly. Besides, with changing the growth pressure, the surface root-mean-square roughness, V-shaped pits density, V-shaped pits size, and localization state density of the MQWs were changed accordingly.

Increasing concern with regard to food safety in the presence of pesticide residues (PRs) on the surface of agricultural products has resulted in the rapid development of practical degrading technologies for corresponding PRs. In this paper, an unconventional method of degrading pesticides, non-thermal atmospheric plasma (NTAP), was proposed to degrade the avermectin (AVM) in aqueous solution. Optical emission spectroscopy shows that NTAP, consisting of filamentary streamers, contains a variety of reactive oxygen species (ROS) that may interact with AVM. The high-performance liquid chromatography (HPLC)-MS/MS results indicate that the efficiency of AVM degradation seriously depends on multiple operation parameters of the NTAP, including the applied voltage, treatment time and gas flow rate. The maximum degradation rate of AVM was observed to be 97.47% after 240 s exposure under NTAP with an applied voltage of 18 kV and gas flow rate of 1 l min−1. Molecular dynamics simulation based on a reactive force field for the interaction between O (ground state atomic oxygen) and AVM was performed to analyze the underpinning mechanisms. The simulation result shows the possible pathways of the NTAP-generated O degrading AVM by destroying the glycosyl group or fracturing the ester group.

High quality N-polar n-type GaN films were deposited on vicinal C-face n-SiC substrates by metal organic chemical vapor deposition for vertical conducting devices. We employed the SiNx interlayer to N-polar GaN growth and studied the effect of SiNx interlayer on the properties of N-polar GaN. We found that the properties of N-polar films were greatly improved by using SiNx interlayer as characterized by X-ray diffraction, photoluminescence, and I-V measurements. N-polar n-type GaN films with SiNx interlayer exhibited a full width at half maximum of 422 arcsec for (0002) omega scan and 335 arcsec for ( 10 1 ¯ 2 ) omega scan, respectively. Integrated intensity ratio of near-band-edge emission and yellow-luminescence was increased by a factor of 4 by using SiNx interlayer. Besides, the resistance of the vertical structure with SiNx interlayer was reduced by 25% in comparison with that without SiNx interlayer.

The droop behaviors of two InGaN/GaN multiple-quantum-well blue-green light-emitting diodes grown on c-plane sapphires with different In content are investigated. The higher-In-content sample exhibits a lower efficiency, followed by a more significant droop as current increases in comparison with the lower-In-content diode. However, it is found that for both samples their efficiency reduction trend with increasing carrier density is nearly the same. Combining with the recombination rate equations, an analysis reveals that at the same injection current level, the carrier density in the higher-In-content quantum wells which have stronger polarization effect is larger due to the smaller bimolecular recombination coefficient, resulting in a more significant droop with current. Therefore, a study on the dependence of efficiency on carrier density can provide a clear elucidation to the physical mechanism of the efficiency droop behavior.

In this study, 4.5 μm thick GaN films with graded AlxGa1−xN/AlN buffer and SiNx interlayer were prepared on 6H–SiC substrates by metal–organic chemical vapor deposition. To determine the effects of SiNx interlayer on epitaxial quality and stress state of GaN films, a series of comparative experiments were carried out by changing the deposition time and the insert location of SiNx interlayer. By optimizing growth conditions of SiNx interlayer, the full width at half maximum values of $$ (0002) $$ and $$ (10\bar{1}2) $$ rocking curves of GaN films were improved to 142 and 170 arcsec, respectively. A crack-free GaN film with a small root-mean-squared roughness of 0.21 ± 0.02 nm was achieved. Simultaneously, the reduction in threading dislocation density of GaN films was confirmed by using wet etching method. In addition, stress values in GaN films were investigated by Raman and low-temperature photoluminescence spectra, which indicated that the lower tensile stress in GaN film, the higher the film’s crystallinity.

The crystal quality and stress state of Al0.5Ga0.5N epitaxial layers on 6H-SiC wafers by introducing an in-situ deposited SiNx nanomask layer grown by metal-organic chemical vapor deposition (MOCVD) were investigated. A SiNx interlayer with various growth times was inserted to the Al0.5Ga0.5N epilayers. The full width at half maximum (FWHM) of X-ray diffraction peaks and the density of etch pits decreased dramatically by the SiNx interlayer, indicating an improved crystalline quality. Also, it was found that the crack density and biaxial tensile stress in the Al0.5Ga0.5N film was significantly reduced by in situ SiNx interlayer from optical microscopy, photoluminescence spectra and Raman spectra. Finally, a crack-free 1.8 μm thick Al0.5Ga0.5N epilayer grown on 6H-SiC substrate using the optimized SiNx interlayer growth time was obtained.

KOH based wet etchings were performed on both undoped and Mg-doped N-polar GaN films grown by metal-organic chemical vapor deposition. It is found that the etching rate for Mg-doped N-polar GaN gets slow obviously compared with undoped N-polar GaN. X-ray photoelectron spectroscopy analysis proved that Mg oxide formed on N-polar GaN surface is insoluble in KOH solution so that kinetic-limited etching occurs as the etching process goes on. The etching process model of Mg-doped N-polar GaN in KOH solution is tentatively purposed using a simplified ideal atomic configuration. Raman spectroscopy analysis reveals that Mg doping can induce tensile strain in N-polar GaN films. Meanwhile, p-type N-polar GaN film with a hole concentration of 2.4 y 10 17 cm ⿿3 was obtained by optimizing bis-cyclopentadienyl magnesium flow rates.

β gallium oxide (β-Ga2O3) homoepitaxy films were grown on ( 2 ‾ 01) β-Ga2O3 substrates by metal organic chemical vapor deposition (MOCVD). The effect of growth temperature on the crystalline quality was measured and systematically analyzed. The results showed the growth temperature played an important role in crystalline quality of β-Ga2O3. The optimized single crystalline β-Ga2O3 film was grown at 750 °C, and the full width at half maximum (FWHM) of X-ray diffraction (XRD) rocking curve was 21.6 arcsec, smaller than that of the β-Ga2O3 substrate (26.3 arcsec). The film exhibited a greatly smooth surface and the root-mean-square (RMS) roughness was 0.68 nm. And the arrangement of atoms inside the film was in good accordance with lattice constants of β-Ga2O3. In addition, the effect of the band structure on the luminescent properties of β-Ga2O3 was discussed.