Internal quantum efficiency drop induced by the heat generation inside of light emitting diodes (LEDs)

The reasons for low output power of AlGalnP Light Emitting Diodes （LEDs） have been analysed. LEDs with AlGaInP material have high internal but low external quantum efficiency and much heat generated inside especially at a large injected current which would reduce both the internal and external quantum efficiencies. Two kinds of LEDs with the same active region but different window layers have been fabricated. The new window layer composed of textured 0.5 μm GaP and thin Indium-Tin-Oxide film has shown that low external quantum efficiency （EQE） has serious impaction on the internal quantum efficiency （IQE）, because the carrier distribution will change with the body temperature increasing due to the heat inside, and the test results have shown the evidence of LEDs with lower output power and bigger wavelength red shift.

Experimental Study on Vortex-Induced Vibration of Marine Riser Model with Coupling Interference Effect Under Combined Internal and External Flow

A partition model of interference efficiency was constructed to study the coupling interference effect under combined internal and external flow.The concept of“internal flow efficiency”,“velocity ratio”and“interference efficiency”were introduced to quantify the effect of internal flow and interference,and reveal the coupling mechanism among internal flow,external flow and interference effect.The results showed that the dynamic response of risers under variable angles was significantly different after considering the effect of internal flow.When the external flow velocity was smaller than 0.25 m/s,the vibration of risers was promoted by the internal flow.With the increase of external flow velocity,the effect of internal flow was weakened and the dynamic response of riser mainly depended on the external flow and interference effect.Under the effect of different internal flow,the interference efficiency had similar change trend.The interference effect amplified the complex secondary flow effect inside the riser,making the dynamic response of riser complex and random.In this paper,the overlap area and subdivision criterion of interference effect were constructed within the range of experimental velocity ratio,and the change curve of interference efficiency was obtained with an average meaning,which may have important practical meaning.

Potassium accumulation and translocation a mongrice genotypes in relation to internal potassium use efficiency(IKUE)

Abiotie stresses including potassium deficiency are limitingfactors for increasing rice yield.Nine rice genotypes(Oryza Sativa L.,indica)differing in sensitivity to low Kstress selected from 200 volume-solution screening wereused in this study to examine accumulation and transloca-tion ofK.The powdery-muddy paddy soil tested contained 30.6mg·kgavailable K(1 N NHAcO extracted),1.92%

Improved efficiency droop characteristics in an InGaN/GaN light-emitting diode with a novel designed last barrier structure

In this study, the characteristics of nitride-based light-emitting diodes with different last barrier structures are analysed numerically. The energy band diagrams, electrostatic field near the last quantum barrier, carrier concentration in the quantum well, internal quantum efficiency, and light output power are systematically investigated. The simulation results show that the efficiency droop is markedly improved and the output power is greatly enhanced when the conventional GaN last barrier is replaced by an AlGaN barrier with Al composition graded linearly from 0 to 15% in the growth direction. These improvements are attributed to enhanced efficiencies of electron confinement and hole injection caused by the lower polarization effect at the last-barrier/electron blocking layer interface when the graded Al composition last barrier is used.

Peanut yield,nutrient uptake and nutrient requirements in different regions of China

Nutrient balance is essential for attaining high yield and improving profits in agricultural farming systems,and crop nutrient uptake ratio and stoichiometry can indicate crop nutrient limitations in the field.We collected a large amount of field data to study the variations in yield,nutrient uptake and nutrient stoichiometry of peanut(Arachis hypogaea L.)in Southeast China(SEC),North-central China(NCC),and Northeast China(NEC),during 1993 to 2018.Peanut pod yield gradually increased from 1993 to 2018,with average yields of 4148,5138,and 4635 kg ha–1 in SEC,NCC,and NEC,respectively.The nitrogen(N)internal efficiency(NIE,yield to N uptake ratio)was similar among the three regions,but phosphorus(P)IE(PIE,yield to P uptake ratio)changed from low to high among regions:NCC<SEC<NEC,while potassium(K)IE(KIE,yield to K uptake ratio)portrayed a different pattern of SEC<NCC<NEC.Based on the nutrient IE,to produce 1 Mg of pod yield,the average N,P,and K requirements of the above-ground parts of peanut were roughly 47.2,5.1,and 25.5 kg in SEC,44.8,5.7,and 20.6 kg in NCC,and 44.6,4.4,and 14.7 kg in NEC,respectively.The N/P ratio changed in the sequence NCC<SEC<NEC,and the N/K ratio was similar in NEC and NCC,but lower in SEC.The N harvest index(HI)and KHI declined with increasing nutrient uptake across all regions under high nutrient uptake.The low PIE and N/P ratios in NCC could be explained by the high P accumulation in stover,and high KIE and N/K ratios in NEC may be attributed to the low soil K supply.The frontier analysis approach provides a practical framework and allows documentation of a decline in nutrient HI as nutrient uptake increases.Lastly,this study reveals the limitation and surplus of nutrients of peanut in different regions of China.

Combined effects of carrier scattering and Coulomb screening on photoluminescence in InGaN/GaN quantum well structure with high In content

Photoluminescence(PL) spectra of two different green InGaN/GaN multiple quantum well(MQW) samples S1 and S2,respectively with a higher growth temperature and a lower growth temperature of InGaN well layers are analyzed over a wide temperature range of 6 K-3 30 K and an excitation power range of 0.001 mW-75 mW.The excitation power-dependent PL peak energy and linewidth at 6 K show that in an initial excitation power range,the emission process of the MQW is dominated simultaneously by the combined effects of the carrier scattering and Coulomb screening for both the samples,and both the carrier scattering effect and the Coulomb screening effect are stronger for S2 than those for S1;in the highest excitation power range,the emission process of the MQWs is dominated by the filling effect of the high-energy localized states for S1,and by the Coulomb screening effect for S2.The behaviors can be attributed to the fact that sample S2 should have a higher amount of In content in the InGaN well layers than S1 because of the lower growth temperature,and this results in a stronger component fluctuation-induced potential fluctuation and a stronger well/barrier lattice mismatchinduced quantum-confined Stark effect.This explanation is also supported by other relevant measurements of the samples,such as temperature-dependent peak energy and excitation-power-dependent internal quantum efficiency.

Optical polarization characteristics for AlGaN-based light-emitting diodes with AlGaN multilayer structure as well layer

The optical properties of AlGaN-based quantum well(QW)structure with two coupled thin well layers are investigated by the six-by-six K-P method.Compared with the conventional structure,the new structure,especially the one with lower Al-content in the barrier layer,can enhance the TE-/TM-polarized total spontaneous emission rate due to the strong quantum confinement and wide recombination region.For the conventional QW structure,the reduction of well thickness can lead the degree of polarization(DOP)to decrease and the internal quantum efficiency(IQE)to increase.By using the coupled thin well layers,the DOP for the structure with high Al-content in the barrier layer can be improved,while the DOP will further decrease with low Al-content in the barrier layer.It can be attributed to the band adjustment induced by the combination of barrier height and well layer coupling.The IQE can also be further enhanced to 14.8%-20.5%for various Al-content of barrier layer at J=100 A/cm^(2).In addition,the efficiency droop effect can be expected to be suppressed compared with the conventional structure.

Performance improvement of InGaN blue light-emitting diodes with several kinds of electron-blocking layers

The performance of InGaN blue light-emitting diodes（LEDs） with different kinds of electron-blocking layers is investigated numerically.We compare the simulated emission spectra,electron and hole concentrations,energy band diagrams,electrostatic fields,and internal quantum efficiencies of the LEDs.The LED using AlGaN with gradually increasing Al content from 0% to 20% as the electron-blocking layer（EBL） has a strong spectrum intensity,mitigates efficiency droop,and possesses higher output power compared with the LEDs with the other three types of EBLs.These advantages could be because of the lower electron leakage current and more effective hole injection.The optical performance of the specifically designed LED is also improved in the case of large injection current.

Sources of Nitrogen in Combination with Systems of Irrigation Influence the Productivity of Modern Rice(Oryza sativa L.)Cultivars during Dry Season in Sub-Tropical Environment

In irrigated agricultural systems,nitrogen(N)and water are the vital resources for sustainability of the crop production in the modern era of climate change.The current study aimed to assess the impact of water and N management on the productivity of irrigated rice cultivars.In the context,a field observation was done at the research farm of Bangladesh Agricultural University,Mymensingh,during dry seasons in consecutive two years(2018–2019 and 2019–2020).The experiments were set up following split-plot design assigning water management in the main plots,nitrogen management in the sub-plots,and the cultivars were approved in the split-split plot with three replications.After two years observation,it was revealed that rice cultivar Binadhan-8 gave the maximum value of leaf area index,number effective tillers hill-1 and grains panicle-1 which lead to the higher grain yield(GY).Substantial relationships were observed among the concentration of N,growth,total dry matter(TDM)and N content,N uptake,N utilization effectiveness,and GY.However,with little exception,the Combined effect of water and N,cultivars and water management were varied significantly for all parameters.Finally,the results of the current study concluded that application of irrigation at 8 days after the disappearance of ponded water and source of 105 kg N ha-1 from PU+Poultry manure are the best management approach for the excellent performance of rice cultivar Binadhan-8.

Fabrication and optimization of 1.55-μm InGaAsP/InP high-power semiconductor diode laser

A comprehensive design optimization of 1.55-#m high power InGaAsP/InP board area lasers is performed aiming at increasing the internal quantum efficiency （ηi） while maintaining the low internal loss （αi） of the device, thereby achieving high power operation. Four different waveguide structures of broad area lasers were fabricated and characterized in depth. Through theoretical analysis and experiment verifications, we show that laser structures with stepped waveguide and thin upper separate confinement layer will result in high αi and overall slope efficiency. A continuous wave （CW） single side output power of 160 mW was obtained for an uncoated laser with a 50μm active area width and 1 mm cavity length.

Organic Light-Emitting Diodes Based on an Iron(III) Complex with Doublet Emission

Because iron is the richest transition-metal element in the earth’s crust,if iron complexes could be used as the emitters in organic light-emitting diodes(OLEDs),the cost of OLEDs would be reduced dramatically.Luminescent iron(III)complexes with low-spin d5 electronic structure theoretically possess spin-allowed doublet metal-to-ligand charge transfer(^(2)MLCT)emission,but little attention has been paid to their application in OLEDs.