Dynamic Changes of Nutrients in Different Growth Stages of Trichosanthes kirilowii in Shishou City

To explore the relationship between soil nutrients,plant nutrients,and the growth and development of Trichosanthes kirilowii,the soil pH,organic matter,available nitrogen,available phosphorus,available potassium content,and leaf total nitrogen,total phosphorus,total potassium,and SPAD in different growth stages of T.kirilowii in the main production area of Shishou City were measured and analyzed.The changes in soil nutrient content and leaf nutrient content at different growth stages of T.kirilowii were compared,and correlation analysis was conducted.The results showed that the average soil pH,organic matter content,alkaline nitrogen content,available phosphorus content,and available potassium content during the entire growth period of T.kirilowii were 7.03,14.01 g/kg,98.79 mg/kg,14.84 mg/kg,and 135.20 mg/kg,respectively;the average total nitrogen content,total phosphorus content,total potassium content,and SPAD of the leaves were 0.55%,0.23%,1.78%,and 77.66,respectively.The nutrient dynamics of T.kirilowii at different growth stages exhibited certain regularity,with most nutrients reaching their maximum values during the flowering and fruiting stages,and then showing a decreasing or stabilizing trend.There was a varying degree of correlation between the nutrient content of leaves and soil,among which the nitrogen,phosphorus,and potassium contents of leaves were significantly or extremely significantly correlated with soil organic matter and alkaline nitrogen content.It can be seen that the nutrient abundance or deficiency level of soil in T.kirilowii field significantly affected the nutrient content of the leaves at different growth stages,thereby restricting its growth and development status.

Direct demonstration of carrier distribution and recombination within step-bunched UV-LEDs

AlGaN-based solid state UV emitters have many advantages over conventional UV sources. However, UV-LEDs still suffer from numerous challenges, including low quantum efficiency compared to their blue LED counterparts. One of the inherent reasons is a lack of carrier localization effect inside fully miscible AlGaN alloys. In the pursuit of phase separation and carrier localization inside the active region of AlGaN UV-LED, utilization of highly misoriented substrates proves to be useful, yet the carrier distribution and recombination mechanism in such structures has seldom been reported. In this paper, a UV-LED with step-bunched surface morphology was designed and fabricated, and the internal mechanism of high internal quantum efficiency was studied in detail. The correlation between microscale current distribution and surface morphology was provided, directly demonstrating that current prefers to flow through the step edges of the epitaxial layers. Experimental results were further supported by numerical simulation. It was found that efficient radiative recombination centers were formed in the inclined quantum well regions. A schematic three-dimensional energy band structure of the multiple quantum wells(MQWs) across the step was proposed and helps in further understanding the luminescence behavior of LEDs grown on misoriented substrates. Finally, a general principle to achieve carrier localization was proposed, which is valid for most ternary Ⅲ-Ⅴ semiconductors exhibiting phase separation.

Revealing the surface electronic structures of AIGaN deep-ultraviolet multiple quantum wells with lateral polarity domains

We report on the carrier dynamic and electronic structure investigations on AlGaN-based deep-ultraviolet multiple quantum wells (MQWs)with lateral polarity domains.The localized potential maximum is predicted near the domain boundaries by first-principle calculation,suggesting carrier localization and efficient radiative recombination.More importantly,lateral band diagrams of the MQWs are proposed based on electron affinities and valance band levels calculated from ultraviolet(UV)photoelectron spectroscopy.The proposed lateral band diagram is further demonstrated by surface potential distribution collected by Kelvin probe microscopy and the density-of-state calculation of energy bands.This work illustrates that lateral polarity structures are playing essential roles in the electronic properties of II nitride photonic devices and may provide novel perspective in the realization of high-efficiency UV emitters.

高质量的AlGaN外延结构和UVC垂直腔面发射激光器的实现

AlGaN基垂直腔面发射激光器(VCSEL)因其优越的材料性质和器件优点吸引了很多关注.然而,由于材料外延生长和器件制备工艺的局限,AlGaN基VCSEL制备很困难.本工作通过侧向外延生长技术制备了高质量的AlGaN多量子阱(MQWs)结构的外延片,并通过X射线衍射(XRD)和光致发光(PL)实验对外延片进行了分析.XRD测量显示,外延片中的AlN模板层几乎是弛豫的,刃位错密度为10^(9)cm^(-2).随后,生长的AlGaN/AlN超晶格(SL)层被用来减少刃位错密度,使得量子阱中的位错密度为10^(8)cm^(-2).根据PL测试结果,MQWs的内量子效率(IQE)为62%,且在室温下的发光以辐射复合为主.通过激光剥离(LLO)和化学机械抛光(CMP)技术,将这些外延片制备成UVC VCSEL.经过这些工艺,MQWs的晶体质量没有受到影响,还在抛光之后的表面观察到了UVC波段的受激辐射.这些AlGaN基UVC VCSEL在275.91,276.28和277.64 nm实现了激射,最小激射阈值为0.79 MW cm^(-2).

Multiband camouflage design with thermal management

Although the effective“stealth”of space vehicles is important,current camouflage designs are inadequate in meeting all application requirements.Here,a multilayer wavelength-selective emitter is demonstrated.It can realize visible light and dual-band mid-infrared camouflage with thermal control management in two application scenarios,with better effect and stronger radiation cooling capability,which can significantly improve the stealth and survivability of space vehicles in different environments.The selective emitter demonstrated in this paper has the advantages of simple structure,scalability,and ease of large-area fabrication,and has made a major breakthrough in driving multiband stealth technology from simulation research to physical verification and even practical application.

Individually resolved luminescence from closely stacked GaN/AlN quantum wells

Investigating closely stacked GaN/AlN multiple quantum wells(MQWs)by means of cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope,we have reached an ultimate spatial resolution ofσCL=1.8 nm.The pseudomorphically grown MQWs with high interface quality emit in the deep ultraviolet spectral range.Demonstrating the capability of resolving the 10.8 nm separated,ultra-thin quantum wells,a cathodoluminescence profile was taken across individual ones.Applying a diffusion model of excitons generated by a Gaussian-broadened electron probe,the spatial resolution of cathodoluminescence down to the free exciton Bohr radius scale has been determined.

Multi-step in situ interface modification method for emission enhancement in semipolar deep-ultraviolet light emitting diodes

SemipolarⅢ-nitrides have attracted increasing attention in applications of optoelectronic devices due to the much reduced polarization field.A high-quality semipolar AlN template is the building block of semipolar AlGaN-based deep-ultraviolet light emitting diodes(DUV LEDs),and thus deserves special attention.In this work,a multi-step in situ interface modification technique is developed for the first time,to our knowledge,to achieve high-quality semipolar AlN templates.The stacking faults were efficiently blocked due to the modification of atomic configurations at the related interfaces.Coherently regrown AlGaN layers were obtained on the in situ treated AlN template,and stacking faults were eliminated in the post-grown AlGaN layers.The strains between AlGaN layers were relaxed through a dislocation glide in the basal plane and misfit dislocations at the heterointerfaces.In contrast,high-temperature ex situ annealing shows great improvement in defect annihilation,yet suffers from severe lattice distortion with strong compressive strain in the AlN template,which is unfavorable to the post-grown AlGaN layers.The strong enhancement of luminous intensity is achieved in in situ treated AlGaN DUV LEDs.The in situ interface modification technique proposed in this work is proven to be an efficient method for the preparation of high-quality semipolar Al N,showing great potential towards the realization of high-efficiency optoelectronic devices.