Improvement of radiative recombination rate in deep ultraviolet laser diodes with step-like quantum barrier and aluminum-content graded electron blocking layer

The design of the active region structures,including the modifications of structures of the quantum barrier(QB)and electron blocking layer(EBL),in the deep ultraviolet(DUV)Al Ga N laser diode(LD)is investigated numerically with the Crosslight software.The analyses focus on electron and hole injection efficiency,electron leakage,hole diffusion,and radiative recombination rate.Compared with the reference QB structure,the step-like QB structure provides high radiative recombination and maximum output power.Subsequently,a comparative study is conducted on the performance characteristics with four different EBLs.For the EBL with different Al mole fraction layers,the higher Al-content Al Ga N EBL layer is located closely to the active region,leading the electron current leakage to lower,the carrier injection efficiency to increase,and the radiative recombination rate to improve.

A GaN AlGaN InGaN last quantum barrier in an InGaN/GaN multiple-quantum-well blue LED

The advantages of a GaN-AlGaN-InGaN last quantum barrier （LQB） in an InGaN-based blue light-emitting diode are analyzed via numerical simulation. We found an improved light output power, lower current leakage, higher recombi- nation rate, and less efficiency droop compared with conventional GaN LQBs. These improvements in the electrical and optical characteristics are attributed mainly to the specially designed GaN-AlGaN-InGaN LQB, which enhances electron confinement and improves hole injection efficiency.

Efficiency enhancement of an InGaN light-emitting diode with a p-AlGaN/GaN superlattice last quantum barrier

In this study, the efficiency droop of an InGaN light-emitting diode （LED） is reduced slgnlncanUy oy using a p-AlGaN/GaN superlattice last quantum barrier. The reduction in efficiency droop is mainly caused by the decrease of electron current leakage and the increase of hole injection efficiency, which is revealed by investigating the light currents, internal quantum efficiencies, energy band diagrams, carrier concentrations, carrier current densities, and radiative recombination efficiencies of three LED structures with the advanced physical model of semiconductor device （APSYS）.

The effect of multi-quantum barrier structure on light-emitting diodes performance by a non-isothermal model

A multi-quantum barrier structure is employed as the electron blocking layer of light-emitting diodes to enhance their performance.Using the non-isothermal multi-physics-field coupling model,the internal quantum efficiency,internal heat source characteristics,spectrum characteristics,and photoelectric conversion efficiency of light-emitting diodes are analyzed systematically.The simulation results show that:introducing multi-quantum barrier electron blocking layer structure significantly increases the internal quantum efficiency and photoelectric conversion efficiency of light-emitting diodes and the intensity of spectrum,and strongly ensures the thermal and light output stability of light-emitting diodes.These results are attributed to the modified energy band diagrams of the electron blocking layer which are responsible for the decreased electron leakage and enhanced carrier concentration in the active region.

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells

The structural and optical properties of InGaN/GaN multiple quantum wells （MQWs） with different barrier thick-nesses are studied by means of high resolution X-ray diffraction （HRXRD）, a cross-sectional transmission electron mi-croscope （TEM）, and temperature-dependent photoluminescence （PL） measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodic- ity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization po- tentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence, and the corresponding activation energy （or the localization potential） increases with the increase of the barrier thickness. The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers, i.e., clusters with lower In contents aggregate into clusters with higher In contents.

Quantum Mechanical Tunneling of Dislocations: Quantization and Depinning from Peierls Barrier

Theories of Mott and Weertmann pertaining to quantum mechanical tunneling of dislocations from Peierls barrier in cubic crystals are revisited. Their mathematical calculations about logarithmic creep rate and lattice vibrations as a manifestation of Debye temperature for quantized thermal energy are found correct but they can not ascertain to choose the mass of phonon or “quanta” of lattice vibrations. The quantum mechanical yielding in metals at relatively low temperatures, where Debye temperatures operate, is resolved and the mathematical formulas are presented. The crystal plasticity is studied with stress relaxation curves instead of logarithmic creep rate. With creep rate formulas of Mott and Weertmann, a new formula based on logarithmic profile of stress relaxation curves is proposed which suggests simultaneous quantization of dislocations with their stress, i.e., and depinning of dislocations, i.e., , where is quantum action, σ is the stress, N is the number of dislocations, A is the area and t is the time. The two different interpretations of “quantum length of Peierls barrier”, one based on curvature of space, i.e., yields quantization of Burgers vector and the other based on the curvature of time, i.e., yields depinning of dislocations from Peierls barrier in cubic crystals, are presented. , i.e., the unitary operator on shear modulus yields the variations in the curvature of time due to which simultaneous quantization, and depinning of dislocations occur from Peierls barrier in cubic crystals.

Quantum compact model for thin-body double-gate Schottky barrier MOSFETs

Nanoscale Schottky barrier metal oxide semiconductor field-effect transistors （MOSFETs） are explored by using quantum mechanism effects for thin-body devices. The results suggest that for small nonnegative Schottky barrier heights, even for zero barrier height, the tunnelling current also plays a role in the total on-state current. Owing to the thin body of device, quantum confinement raises the electron energy levels in the silicon, and the tradeoff takes place between the quantum confinement energy and Schottky barrier lowering （SBL）. It is concluded that the inclusion of the quantum mechanism effect in this model, which considers an infinite rectangular well with a first-order perturbation in the channel, can lead to the good agreement with numerical result for thin silicon film. The error increases with silicon thickness increasing.

Wave-vector filtering effect of the electric-magnetic barrier in HgTe quantum wells

Because of the helicity of electrons in HgTe quantum wells（QWs） with inverted band structures,the electrons cannot be confined by electric barriers since electrons can tunnel the barriers perfectly without backscattering in the HgTe QWs.This behavior is similar to Dirac electrons in graphene.In this paper,we propose a scheme to confine carriers in HgTe QWs using an electric-magnetic barrier.We calculate the transmission of carriers in 2-dimensional HgTe QWs and find that the wave-vector filtering effect of local magnetic fields can confine the carriers.The confining effect will have a potential application in nanodevices based on HgTe QWs.

A Novel Investigation on Using Strain in Barriers of 1.3 μm AlGaInAs-InP Uncooled Multiple Quantum Well Lasers

In this study we investigate strain effect in barriers of 1.3 μm AlGaInAs-InP uncooled multiple quantum welllasers.Single effective mass and Kohn-Luttinger Hamiltonian equations have been solved to obtain quantum states andenvelope wave functions in the structure.In the case of unstrained barriers,our simulations results have good agreementwith a real device fabricated and presented in one of the references.Our main work is proposal of 0.2% compressivestrain in the structure Barriers that causes significant reduction in Leakage current density and Auger current densitycharacteristics in 85℃.20% improvement in mode gain-current density characteristic is also obtained in 85℃.

Quantum Supercurrent Transistors in Silicon Quantum Wells Confined by Superconductor Barriers

We present the findings of spin-dependent single-hole and pair-hole transport in plane and across the p-type high mobility silicon quantum wells (Si-QW), 2 nm, confined by the superconductor δ-barriers on the n-type Si (100) surface. The oscillations of the conductance in normal state and the zero-resistance supercurrent in superconductor state as a function of the top gate voltage are found to be correlated by on- and off-resonance tuning the two-dimensional levels of holes in Si-QW with the Fermi energy in the superconductor δ-barriers. The SIMS and STM studies have shown that the δ-barriers heavily doped with boron, 5 × 1021 cm–3, represent really alternating arrays of silicon empty and doped dots, with dimensions restricted to 2 nm. This concentration of boron seems to indicate that each doped dot located between empty dots contains two impurity atoms of boron. The EPR studies show that these boron pairs are the trigonal dipole centres, B+ - B–, that contain the pairs of holes, which result from the negative -U reconstruction of the shallow boron acceptors, 2B0 => B+ - B–. The electrical resistivity, magnetic susceptibility and specific heat measurements demonstrate that the high density of holes in the Si-QW (> 1011 cm–2) gives rise to the high temperature superconductor properties for the δ-barriers. The value of the superconductor energy gap obtained is in a good agreement with the data derived from the oscillations of the conductance in normal state and of the zero-resistance supercurrent in superconductor state as a function of the bias voltage. These oscillations appear to be correlated by on- and off-resonance tuning the two-dimensional subbands of holes with the Fermi energy in the superconductor δ-barriers. Finally, the proximity effect in the S-Si-QW-S structure is revealed by the findings of the quantization of the supercurrent and the multiple Andreev reflection (MAR) observed both across and along the Si-QW plane thereby identifying the spin transistor effect.

有源区掺杂的AlGaN基深紫外激光二极管性能优化

为了改善深紫外激光二极管的性能,本文提出了有源区量子势垒n掺杂、p掺杂和n-p掺杂三种结构.利用Crosslight软件,对原始结构和有源区掺杂的三种结构进行仿真研究,比较四种结构的P-I特性曲线、V-I特性曲线、载流子浓度、辐射复合速率和能带图.仿真结果表明,有源区量子势垒n-p掺杂结构的性能更优,其阈值电压和阈值电流分别为4.40V和23.8mA;辐射复合速率达到1.64×10^(28)cm^(-3)/s;同一注入电流下电光转换效率达到42.1%,比原始结构增加了3.9%;改善了深紫外激光二极管的工作性能.

通过诱导载流子的V坑传输提升GaN基绿光LED的空穴注入效率

为了提升GaN基多量子阱LED的空穴注入效率,设计了具有不同最后势垒层结构的GaN基多量子阱外延结构,并将其制备为绿光mini-LED发光芯片,利用低温电致发光光谱、电流电压特性测试对其载流子传输机制进行了研究。结果表明,在采用AlGaN或GaN/AlN最后势垒层的样品中,有更多载流子可以传输到深层量子阱,空穴注入效率获得提升。本文对这一现象中的载流子运输机制以及V坑缺陷在其中所起的作用进行了研究,发现这种提升主要来自空穴V坑注入比例的增大。实验还发现,过大的V坑注入比例也会造成非辐射复合率上升,从而抑制了AlGaN最后势垒层样品的电光转换效率。

一维三方势垒量子隧穿特性的研究

本文通过严格求解定态薛定谔方程,研究了一维对称三方势垒的量子隧穿特性,解析地给出透射系数的精确表达式,并且数值模拟了势垒高度、势垒间距以及粒子入射能量对透射系数的影响.结果表明:当取不同的势垒宽度,或者不同的粒子入射能量时,透射系数随着势垒间距的增加而呈现出明显的周期式振荡.将一维对称双方势垒和三方势垒进行比较,透射系数随着势垒间距的增大,均呈现周期性振荡,并且振荡周期相同,但三方势垒振荡更剧烈,振幅越大,并且三方对称势垒是双峰曲线,而双方对称势垒是单峰曲线.该特性为设计新型纳米器件以及共振隧穿量子器件等提供理论指导.

Explanation of Unusual Photoluminescence Behavior from InAs Quantum Dots with InAlAs Capping

The effect of different kinds of cap layers on optical property of InAs quantum dots （QDs） on GaAs （100） substrate was studied. Temperature dependent photoluminescence （PL） indicates that the PL integrated intensity from the ground state of InAs QDs capped with an intermediate InAIAs layer drops very little as compared to QDs capped with a thin InGaAs or GaAs cap layer from 15 K up to room temperature. PL integrated intensity ratio of the first excited to ground states for InAs QDs capped with an intermediate InAIAs layer is unexpectedly decreased with increasing temperature, which are attributed to phonon bottleneck effect. A virtual barrier is proposed to describe this physics process and shows good agreement with experimental results when fitting the curve with the value of the virtual barrier 30 meV.

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.

熔融共混一步法制备具有优异水氧阻隔性能的苯乙烯-甲基丙烯酸甲酯共聚物量子点扩散板

为了同时增强苯乙烯-甲基丙烯酸甲酯共聚物(SMMA)的光扩散性能和水氧阻隔性能,首次将阻隔性能优异的乙烯-乙烯醇共聚物(EVOH)作为光扩散粒子,通过简单的熔融共混法制备了不同EVOH含量的SMMA/EVOH复合材料。采用扫描电子显微镜、透光率雾度仪、气体渗透仪、水蒸气透过率测试仪等详细研究了复合材料的微观结构、光扩散性能、水氧阻隔性能、力学性能以及量子点荧光强度的变化。研究结果表明,EVOH与SMMA不完全相容,质量分数40%以下的EVOH在SMMA体系中以球形分散相形式存在,可将雾度从纯SMMA的0.3%提高至80%以上,起到光散射粒子的作用,透光率依然保持在60%以上;随着EVOH含量增加,复合材料的拉伸力学性能呈现先增加后降低的趋势,但水氧阻隔性能逐渐提高。将量子点加入阻隔扩散板中,能够有效延长量子点的荧光寿命,具有较强的应用价值。

贫PbI_(2)基体的胶体量子点固体用于高效红外太阳能电池

胶体量子点(CQD)具有优异的红外光吸收能力和光谱可调特性,是用于制备高效太阳能电池最有前途的红外光电材料之一。然而,以醋酸铵(AA)为添加剂的液相配体交换会导致CQD固体中产生宽带隙PbI_(2)基质,其将作为电荷传输势垒,在很大程度上影响了CQD太阳能电池(CQDSC)中载流子的提取,从而影响了光伏性能。本文报道利用二甲基碘化铵(DMAI)调节CQD配体交换过程,使载流子在CQD固体中的传输势垒大幅降低。通过对CQD固体进行全面的表征和理论计算,充分揭示了DMAI和CQD之间的相互作用。结果表明,通过DMAI调节CQD配体交换过程,使CQD固体均匀堆积,提高了载流子输运性能,并且陷阱辅助复合受到显著抑制。因此,CQDSC器件中的载流子提取得到了大幅提高,能量转换效率(PCE)比用AA制备的CQDSC器件提高了17.8%。此工作为调控CQD表面化学特性提供了新的研究思路,并为降低CQD固体中载流子输运的势垒提供了可行的方法。

基于GO电子阻挡层的量子点发光二极管优化

量子点发光二极管高性能的关键是实现空穴与电子之间的电荷平衡。本文将氧化石墨烯(Graphene oxide,GO)引入到量子点发光层和电子传输层之间作为电子阻挡层,通过调节GO的厚度,使器件的亮度提高了96.7%,电流效率提高146%。光电性能的改善主要归因于加入电子阻挡层的能带结构,增大了电子传输层与量子点层之间的能级势垒。研究结果表明,引入GO层能够减少电子的注入数目,从而提高器件性能。

电磁波在薄膜界面反射透射的量子力学方法

平面电磁波垂直入射到介质界面时,电磁波满足的亥姆霍兹方程和边界条件与量子力学中粒子入射到势垒时的方程和边界条件具有相同的形式,因此也具有相同形式的解.其本质原因在于电磁波与微观粒子具有相同的波动属性.利用量子力学中势垒隧穿的方法讨论垂直入射的电磁波在薄膜界面上的反射和透射,以及电磁波通过光子势垒的光子隧穿.

应用于液晶显示背光的量子点光转换膜研究进展

胶体量子点由于具有宽吸收、窄发射、可溶液加工等优异光学特性,可以赋能液晶显示技术实现高色域的画质效果而获得越来越多的产业应用,目前应用范围较广的产品为量子点光转换膜。典型的量子点光转换膜为上下阻隔膜加中间量子点树脂的三明治结构:上下阻隔膜起到隔绝水、氧,实现保护量子点中间层的作用;量子点树脂层为实现量子点光转换效果的重要载体,一般包含红色和绿色量子点材料,在背光蓝色LED的激发下发射红光和绿光,并与透过的蓝光一起实现R/G/B的三基色白光,可以实现100%NTSC以上色域覆盖。量子点光转换膜从最开始昂贵的高阻隔(10^(-3)~10^(-4)g·m^(-2)·day^(-1))方案逐渐发展为高性价比的较低阻隔(10^(-1)g·m^(-2)·day^(-1))技术方案,进而使产品应用得到普及。其产品形态也从最开始的大尺寸电视产品1397~2159 mm(55~85 in),逐步渗透到显示器、笔记本、车载、平板、VR以及可穿戴等中小尺寸显示产品等。因其能够大幅提高产品的色彩显现力和产品附加值,从而获得品牌客户和消费者越来越多的认可。本文从量子点光转换膜的结构、功能着手,综述了量子点光转换膜的技术发展过程、最新的研究进展、标准研制情况以及市场发展趋势等。