Photoluminescence study of InGaN/GaN multiple-quantum-well with Si-doped InGaN electron-emitting Layer

InGaN/GaN multiple-quantum-well (MQW) structure with Si-doped InGaN electron-emitting layer (EEL) was grown by metal–organic chemical vapor deposition and their characteristics were evaluated by photoluminescence (PL) measurements. In a typical structure, a low indium composition and wide potential well was used to be an EEL, and a six-fold MQW was used to be an active layer where the injected carriers recombine. By comparing the PL spectral characteristics of the MQW samples, the PL intensity of MQW with EEL is about 10 times higher than that of typical MQW. Experimental results indicate that the high electron capture rate of the MQW active region can be achieved by employing EEL.     

Carrier transport effects on the photocurrent spectra of an intrinsic GaAs/AlGaAs multiple quantum well with highly doped AlGaAs contact layers

In this study, we demonstrate how electroreflectance (ER) measurements as a function of bias, and of angle of incidence (θ₀), together with bias dependent photocurrent (PC) measurements, can be used to provide understanding of the complex electric field profile and carrier transport effects in a GaAs/Al_0.3Ga_0.7As multiple quantum well (MQW), grown inside n⁺ contact layers. The PC measurements exhibit split excitonic features, the components of which change in strength with the applied bias. The effect is explained by absorption in the front of the MQW stack, with the back of the stack acting as detector. We examine the θ₀-dependence of the ER lineshape, to determine the depth of the layers responsible for each feature. The ER and PC lineshapes and their bias dependence are explained by the unusual electric field profile across the stack. The field profile appears to be determined by tunnelling of the dark current.     

A simple model for optimization design of high performance In1−x−y Ga y Al x As strained MQW DFB lasers

It is well known that complex rate equations and the couple wave equation have to be solved by the method of iteration in the simulation of multi-quantum well (MQW) distributed feedback Bragg (DFB) lasers, and a long CPU time is needed. In this paper, from the oscillation condition of lasers, we propose a simple and fast model for optimization of In_1–x–y Ga _y Al _x As strained MQW DFB lasers. The well number and the cavity length of 1.55 m wavelength In_1–x–y Ga _y Al _x As MQW DFB lasers are optimized using the model. As a result, the simple model gives almost the same results as the complex one, but 90% CPU time can be saved. In addition, a low threshold, high maximum operating temperature of 550–560 K, and high relaxation oscillation frequency of over 30 GHz MQW DFB laser is presented.     

In组分渐变提高InGaN/GaN多量子阱发光二极管发光性能

利用金属有机物化学气相沉积系统在蓝宝石衬底上通过有源层的变温生长,得到In组分渐变的量子阱结构,从而获得具有三角形能带结构的InGaN/GaN多量子阱发光二极管(LED)(简称三角形量子阱结构LED).变温光致发光谱结果表明,相对于传统具有方形能带结构的量子阱LED(简称方形量子阱结构LED),三角形量子阱结构有效提高了量子阱中电子和空穴波函数的空间交叠,从而增加了LED的内量子效率;电致发光谱结果表明,三角形量子阱结构LED器件与传统结构LED器件相比,明显改善了发光峰值波长随着电流的蓝移现象.通过以上     

First principle theory for cavity solitons in semiconductor microresonators

Cavity solitons are similar to spatial solitons, appearing as localized bright dots in the transverse intensity profile of the electromagnetic field, but they arise in dissipative systems. In this paper we consider a broad-area vertical-cavity semiconductor microresonator, driven by an external coherent field, at room temperature. The active material is constituted by a Multiple Quantum Well GaAs/AlGaAs structure (MQW). We present a set of nonlinear dynamical equations for the electric field and the carrier density valid for both a passive and an active (i.e. with population inversion) configuration. The complex nonlinear susceptibility is derived on the basis of a full many-body theory, with the Coulomb enhancement treated in the Padé approximation. The linear stability analysis of the homogeneous steady states is performed with a generalised approach, and numerical simulations demonstrating the existence of spatial patterns and cavity solitons in experimentally achievable parameter regions are given for the two configurations. Received 18 January 2001     

Efficiency droop suppression in GaN-based light-emitting diodes by chirped multiple quantum well structure at high current injection

Gallium nitride(Ga N) based light-emitting diodes(LEDs) with chirped multiple quantum well(MQW) structures have been investigated experimentally and numerically in this paper. Compared to conventional LEDs with uniform quantum wells(QWs), LEDs with chirped MQW structures have better internal quantum efficiency(IQE) and carrier injection efficiency. The droop ratios of LEDs with chirped MQW structures show a remarkable improvement at 600 m A/mm2,reduced down from 28.6%(conventional uniform LEDs) to 23.7%(chirped MQWs-a) and 18.6%(chirped MQWs-b),respectively. Meanwhile, the peak IQE increases from 76.9%(uniform LEDs) to 83.7%(chirped MQWs-a) and 88.6%(chirped MQWs-b). The reservoir effect of chirped MQW structures is the significant reason as it could increase hole injection efficiency and radiative recombination. The leakage current and Auger recombination of chirped MQW structures can also be suppressed. Furthermore, the chirped MQWs-b structure with lower potential barriers can enhance the reservoir effect and obtain further improvement of the carrier injection efficiency and radiative recombination, as well as further suppressing efficiency droop.     

Active antireflection coating electrooptic modulator

A new type of multiple quantum well (MQW) reflection modulator, based on the multilayer active antireflection coating (A-ARC) is proposed and compared theoretically with the conventional MQW modulator based on the asymmetric Fabry-Perot etalon (AFP). It is shown that both a large on-off ratio and a low operating voltage can be achieved. It will be demonstrated that the A-ARC device matches the performance of the recently reported asymmetric Fabry-Perot modulator while requiring smaller device thickness. It will also be shown that A-ARC MQW modulators exhibit superior tolerance to the unavoidable thickness variations, thus allowing fabrication of large-area uniform arrays of modulators.     

Solar energy harvesting scheme using syringe-like ZnO nanorod arrays for InGaN/GaN multiple quantum well solar cells

Syringe-like ZnO nanorod arrays (NRAs) synthesized by a hydrothermal method were applied as the light-harvesting layer on InGaN-based multiple quantum well (MQW) solar cells. Theoretical calculations show that the NRAs with an abrupt shrinkage of tip diameter can further suppress surface reflectance in comparison with the flat NRAs. InGaN-based MQW solar cells with the syringe-like NRAs exhibit greatly improved conversion efficiencies by 36%. These results are attributed to the improved flatness of the refractive index profile at the air/device interface, which results in enhanced light trapping effect on the device surface.     

硅衬底生长的InGaN/GaN多层量子阱中δ型硅掺杂n-GaN层对载流子复合过程的调节作用

为了解决在单晶硅衬底上生长的InGaN/GaN多层量子阱发光二极管器件发光效率显著降低的问题,使用周期性δ型Si掺杂的GaN取代Si均匀掺杂的GaN作为n型层释放多层界面间的张应力。采用稳态荧光谱及时间分辨荧光谱测量,提取并分析了使用该方案前后的多层量子阱中辐射/非辐射复合速率随温度（10~300 K）的变化规律。实验结果表明引入δ-Si掺杂的n-GaN层后,非辐射复合平均激活能由（18±3）meV升高到（38±10）meV,对应非辐射复合速率随温度升高而上升的趋势变缓,室温下非辐射复合速率下降,体系中与阱宽涨落有关的浅能级复合中心浓度减小,PL峰位由531 nm左右红移至579 nm左右,样品PL效率随温度的衰减受到抑制。使用周期性δ型Si掺杂的GaN取代Si均匀掺杂的GaN作为生长在Si衬底上的InGaN/GaN多层量子阱LED器件n型层,由于应力释放,降低了多层量子阱与n-GaN界面、InGaN/GaN界面的缺陷密度,使得器件性能得到了改善。     

InGaN/GaN多量子阱结构发光二极管发光机理转变的低频电流噪声表征

本文对InGaN/GaN多量子阱结构发光二极管开启后的电流噪声进行了测试, 结合低频电流噪声的特点和载流子之间的复合机理, 研究了低频电流噪声功率谱密度与发光二极管发光转变机理之间的关系. 结论表明, 当电流从0.1 mA到10 mA逐渐增大的过程中, InGaN/GaN发光二极管的电流噪声行为从产生-复合噪声逐渐接近于低频1/f噪声, 载流子的复合机理从非辐射复合过渡为电子与空穴之间载流子数的辐射复合, 并具有标准1/f噪声的趋势, 此时多量子阱中的电子和空穴之间的复合趋向于稳定. 本文的结论提供了一种表征InGaN/GaN多量子阱发光二极管发光机理转变的有效方法, 为进一步研究发光二极管中载流子的复合机理、优化和设计发光二极管、提高其发光量子效率提供理论依据.     

基于量子阱结构的高效磷光有机电致发光器件

采用多重量子阱结构制作了高效红色磷光有机电致发光器件。以4,4'-bis(N-carbazolyl)-1,10-biphenyl (CBP)掺杂bis(1-phenyl-isoquinoline)(Acetylacetonato) iridium(Ⅲ) (Ir(piq)₂(acac))为发光层,4,4'-bis(N-carbazolyl)-1,10-biphenyl(Bphen)为电荷控制层,形成了Ⅱ型双量子阱结构,器件的最大亮度为15 000 cd/m²,最大电流效率为7.4 cd/A,相对于参考器件提高了21%。研究结果表明:以Bphen为电荷控制层形成的Ⅱ型多重量子阱结构能有效地将载流子和激子限制在势阱中,并且使空穴和电子的注入更加平衡,从而提高了载流子复合的几率和器件的效率。     

The effects of quantum wells number and the built-in polarization on the performance of quaternary AlInGaN UV laser diode

The performance of quaternary Al_0.08In_0.08Ga_0.84N multi-quantum well (MQW) laser diodes (LDs) using the simulation program of Integrated System Engineering Technical Computer Aided design (ISE TCAD) was studied. The simulation results show that the low threshold current, high output power and slope efficiency can be obtained when the quantum wells number is 4. Although, the fourth quantum well which placed in the right side (n-side) of the active region has a negative value of optical gain this means that the optical gain does not occur in this quantum well of laser structure. However, high external differential quantum efficiency (DQE) inside the active region was also observed. Optical gain and intensity were increased when the numbers of quantum wells increase reached 4. The built-in electric field effect inside the quantum well leads to the reduction of the overlap integral between the electrons and holes by separating their wave function was included. As well as, Al_0.25In_0.08Ga_0.67N electron blocking layer (EBL) employed to enhance the performance of Al_0.08In_0.08Ga_0.84N MQW LDs by increasing the optical confinement factor (OCF) inside the quantum wells.     

Lateral carrier confinement and threshold current reduction in InGaN QW lasers with deeply etched mesa

Shallow etch depths may contribute to a reduction in the optical gain of multiple quantum well (MQW) lasers through the lateral diffusion of carriers away from the region of greatest optical intensity. Deeply etched mesas can prevent this lateral diffusion, but this practice may itself contribute to a degradation of optical gain if the sidewalls are not effectively passivated. Simulation results considering the effects of surface recombination velocity (SRV) at the edge of etched active layers indicate that SRV must be reduced below approximately 10⁵cm/s in order for deep etch designs to provide benefit. Very few experimental studies quantify the efficiency of GaN surface passivation in terms of SRV. Further experimental studies are required to better assess the viability of deep etch MQW laser designs.     

Electro-optic low-voltage InGaAs/GaAs multiple quantum well modulator with organic–inorganic distributed Bragg reflector

We have realized a reflection-type electro-optic InGaAs/GaAs multiple quantum well (MQW) modulator using an organic–inorganic distributed Bragg reflector (DBR). The MQW active layer is embedded in the intrinsic region of a p-i-n diode. The DBR consists of few pairs of CF_x/TiO_xlayers, fabricated by room-temperature ion beam sputtering on the rear side of the device. The reflectivity of the mirror approaches 98% in the infrared spectral region and is centered at then = 1 exciton resonance of the MQW. ON–OFF driving reverse voltages of 0.5 and 1.8 V are measured at room temperature. In this range the static response of the device is linear so that it can be used for analog electro-optic modulation.     

A study of GaInP/GaAs interfaces: metallurgical coupling of successive quantum wells

We present a study of GaInP/GaAs interfaces by means of photoluminescence (PL) of multi quantum wells (MQW), embedded in GaInP, or asymmetric structures having an AlGaAs barrier GaInP/GaAs/AlGaAs. The PL energies of quantum wells were compared with calculations based on the transfer matrix envelope function approximation, well suited for asymmetric structures. GaInP/GaAs/AlGaAs MQW structures (GaInP grown first) are in reasonably good agreement with calculations. Reverse ones, AlGaAs/GaAs/GaInP, present a lower PL energy than calculated. But the agreement with theory is recovered on single quantum well samples, or in MQW when the GaInP thickness is increased up to 100 nm. We interpret this phenomenon as a diffusion of arsenic atoms from the next GaAs well through the GaInP barrier. Arsenic atoms exchange with phosphorus atoms at the GaInP-on-GaAs interface of the former well, leading to a small gap strained InGaAs region responsible for the lowering of PL energies.     

High quality above 3-μm mid-infrared InGaAsSb/AlGaInAsSb multiple-quantum well grown by molecular beam epitaxy

The GaSb-based laser shows its superiority in the 3–4 μm wavelength range. However, for a quantum well(QW) laser structure of InGaAsSb/AlGaInAsSb multiple-quantum well(MQW) grown on GaSb, uniform content and high compressive strain in InGaAsSb/AlGaInAsSb are not easy to control. In this paper, the influences of the growth temperature and compressive strain on the photoluminescence(PL) property of a 3.0-μm InGaAsSb/AlGaInAsSb MQW sample are analyzed to optimize the growth parameters. Comparisons among the PL spectra of the samples indicate that the In0.485GaAs0.184Sb/Al0.3Ga0.45In0.25As0.22Sb0.78MQW with 1.72% compressive strain grown at 460 C posseses the optimum optical property. Moreover, the wavelength range of the MQW structure is extended to 3.83 μm by optimizing the parameters.     

Velocity–vorticity–helicity formulation and a solver for the Navier–Stokes equations

For the three-dimensional incompressible Navier–Stokes equations, we present a formulation featuring velocity, vorticity and helical density as independent variables. We find the helical density can be observed as a Lagrange multiplier corresponding to the divergence-free constraint on the vorticity variable, similar to the pressure in the case of the incompressibility condition for velocity. As one possible practical application of this new formulation, we consider a time-splitting numerical scheme based on an alternating procedure between vorticity–helical density and velocity–Bernoulli pressure systems of equations. Results of numerical experiments include a comparison with some well-known schemes based on pressure–velocity formulation and illustrate the competitiveness on the new scheme as well as the soundness of the new formulation.     

用直接模拟法分析量子阱半导体激光器瞬态响应

根据光增益与载流子密度的对数关系 ,通过适应于多量子阱激光器的速率方程的直接模拟分析 ,得到了注入电流、阱数和腔长对多量子阱激光器的激射阈值、开关延迟时间、弛豫振荡频率和光输出等参量之间的依赖关系 .运用相图确立了在瞬态过程中 ,载流子数密度和光子数密度之间的转化过程 .从而为改善量子阱激光器的高频调制特性以及优化设计器件结构参数提供了理论依据     

用直接模拟法分析量子阱半导体激光器瞬态响应

根据光增益与载流子密度的对数关系,通过适应于多量子阱激光器的速率方程的直接模拟分析,得到了注入电流、阱数和腔长对多量子阱激光器的激射阈值、开关延迟时间、弛豫振荡频率和光输出等参量之间的依赖关系.运用相图确立了在瞬态过程中,载流子数密度和光子数密度之间的转化过程.从而为改善量子阱激光器的高频调制特性以及优化设计器件结构参数提供了理论依据.     

Light propagation characteristics in quantum well structures of photonic crystals

Two-dimensional （2D） closed-cavity single quantum well （SQW） and multiple quantum well （MQW） structures are proposed based on the traditional 2D open-cavity SQW structures of photonic crystals. The numerical calculation results show that the proposed structures can greatly improve the optical characteristics compared with the traditional structures. It is found that the barrier thickness has a great impact on the optical characteristics of the closed-cavity MQW structures： when the barrier thickness is narrower, each resonant peak which appears in the SQW would split, the number of split times is just equal to the number of wells, and each well in the MQW structures is a travelling-wave-well, similar to the well in the open-cavity SQW structures; when the barrier thickness is wider, there is no effect of spectral splitting, and each well in the MQW structures is a standing-wave-well, just like the well in the closed-cavity SQW. The physical origin of different field distributions and the effect of the spectral splitting are provided.