极化诱导的内建电场对Mn δ掺杂的GaN/AlGaN量子阱居里温度的调制

采用传输矩阵方法分析极化诱导的内建电场对Mn δ掺杂的GaN/Al_xGa_1-xN量子阱居里温度(T_C)的调制作用.通过解薛定谔方程计算出在不同的内建电场条件下半导体量子阱局域态内的基态空穴能级和波函数分布情况，并在此基础上确定量子阱内Mn δ掺杂情况下T_C随内建电场的变化趋势，分析了不同量子阱结构引起的内建电场分布变化及其对T_C的影响.在耦合双量子阱中通过调节左右阱的不对称性可以得到T_C近3倍的增长. 关键词： GaN 量子阱 内建电场 居里温度     

外电场下应变量子阱中电子与空穴的本征态

考虑自发与压电极化引起的内建电场,自由电子-空穴气屏蔽效应和外加电场,基于常微分数值计算,自洽求解电子与空穴的薛定谔方程和泊松方程以获得基态能级。以典型的GaN/A lxGa1-xN纤锌矿氮化物应变量子阱为例,通过数值求解,得到电子与空穴的本征基态能和相应本征波函数。计算结果表明:沿量子阱生长方向所施加的外加电场将抵消阱中内建电场的作用,阱结构的弯曲程度略显平缓,使电子(空穴)本征波函数逆(顺)着外电场方向移动,且均向阱中心移动,波峰峰值增加,隧穿几率减小;在固定外电场情况下,电子与空穴基态能级随阱宽的增加而减小,随掺杂组分的增加而增加,表明外加电场对内建电场有所削弱以及量子限制作用对电子(空穴)基态能有显著的影响。     

Nano-LED半极性面InGaN/GaN单量子阱结构极化和光谱仿真分析

通过有限元分析,利用COMSOL软件模拟计算了Nano-LED半极性面InGaN/GaN单量子阱距离边缘不同位置的应变和压电极化分布,并结合模拟得到的量子阱极化电场,采用Silvaco软件计算得到了Nano-LED InGaN/GaN单量子阱距离边缘不同位置的发光光谱.应变和压电极化分布结果表明,其在距离半极性面量子阱...     

纤锌矿In_(0.19)Ga_(0.81)N/GaN量子阱中光学声子和内建电场对束缚极化子结合能的影响

用改进的Lee-Low-Pines变分方法研究纤锌矿In0.19Ga0.81N/GaN量子阱结构中束缚极化子能量和结合能等问题,给出基态结合能、不同支长波光学声子对能量和结合能的贡献随阱宽和杂质中心位置变化的数值结果.在数值计算中包括了该体系中声子频率的各向异性和内建电场对能量和结合能的影响、以及电子和杂质中心与长波光学声子的相互作用.研究结果表明,In0.19Ga0.81N/GaN量子阱材料中光学声子和内建电场对束缚极化子能量和结合能的贡献很大,它们都引起能量和结合能降低.结合能随着阱宽的增大而单调减小,窄阱中减小的速度快,而宽阱中减小的速度慢.不同支声子对能量和结合能的贡献随着阱宽的变化规律不同.没有内建电场时,窄阱中,定域声子贡献小于界面和半空间声子贡献,而宽阱中,定域声子贡献大于界面和半空间声子贡献.有内建电场时,定域声子贡献变小,而界面和半空间声子贡献变大,声子总贡献也有明显变化.在In0.19Ga0.81N/GaN量子阱中,光学声子对束缚极化子能量和结合能的贡献比GaAs/Al0.19Ga0.81As量子阱中的相应贡献(约3.2—1.8和1.6—0.3 meV)约大一个数量级.阱宽(d=8 nm)不变时,在In0.19Ga0.81N/GaN量子阱中结合能随着杂质中心位置Z0的变大而减小,并减小的速度变快.随着Z0的增大,界面和半空间光学声子对结合能的贡献缓慢减小,而定域光学声子的贡献缓慢增大.     

氮化物半导体耦合量子阱中非线性光整流特性:压电效应与自发极化效应

考虑了由于压电与自发极化引起的强内电场效应,基于密度矩阵与久期处理方法,理论考察了纤锌矿氮化物半导体耦合量子阱体系的非线性光整流特性。根据已经成功建立的耦合量子阱的内建电场模型,精确求解了体系的电子本征态。以典型的GaN/InxGa1-xN纤锌矿氮化物耦合量子阱为例进行了数值计算,结果发现共振光整流系数达到了10-6m/V的量级(体系的偶极矩阵元大小超过了2nm),这比同样尺寸的单氮化物量子阱的相应值高一个数量级。而且,计算还发现光整流系数对耦合量子阱的结构与掺杂组分呈现非单调的依赖关系,这一特性被归结为体系的强内建电场与量子尺寸效应对载流子受限特性的强烈竞争。计算结果还表明,通过选择小尺寸阱宽与垒宽的耦合量子阱,适当降低掺杂组分,可在氮化物耦合量子阱中获得较强的光整流效应。     

纤锌矿氮化镓基阶梯量子阱中界面声子的色散谱与散射率

本文理论分析了纤锌矿GaN-基阶梯量子阱中的电子-界面光学声子散射性质。阶梯量子阱中的解析的界面声子态及Frhlich电子-声子相互作用哈密顿被导出了。在考虑强内建电场效应及能带的非抛物性特性的情况下,阶梯量子阱结构精确解析的电子本征态也被给出了。以一个四层纤锌矿AlN-基阶梯量子阱为例进行了数值计算。结果发现,系统中存在四支界面光学声子模,这一观察明显不同于对称的GaN/AlN单量子阱与双量子阱的情况。这一差异被归结为阶梯量子结构的非对称性。GaN-基阶梯量子阱中的子带内散射率与子带间散射率比GaAs-基阶梯量子阱的结果大一个数量级,这被归因于GaN-基晶体大的电子-声子耦合常数。GaN-基阶梯量子阱的子带内散射率表现出与GaAs-基体系类似的结构参数依赖关系,但两类体系的子带间散射率对阶梯量子阱结构参数依赖则明显不同,这被归结为GaN-基阶梯量子阱结构中强的内建电场效应及带的非抛物性。结果还表明,高频界面声子模相对于低频界面声子模,对散射率的贡献更大。     

非对称耦合量子阱的吸收非线性增强

基于V 形三能级模型运用密度矩阵方程推导了非对称耦合量子阱三阶光学非线性极化率. 具体分析了三阶吸收非线性效率（三阶光学非线性极化率与线性吸收系数之比）随阱间电子相干振荡频率的变化规律. 理论结果表明：三阶吸收非线性效率对阱间电子相干振荡频率相当敏感，当阱间电子相干振荡频率增大时三阶吸收非线性效率显著增强，而当阱间电子相干振荡频率为零时，这种非线性效率类似于单量子阱情况. 与单量子阱相比，对于已设计好的非对称耦合量子阱结构其突出特征表现在，其非线性吸收与色散特性可经由沿材料生长方向偏压进行控制. 据此，我们预期利用这种非对称耦合量子阱结构能设计成光通信中的光限幅器和可控克尔光开关.     

高In组分InxGa1－xN/GaN多量子阱材料电致荧光谱的研究

研究了高In组分In_xGa_1-xN/GaN（x≈30%）多量子阱（MQWs）结构 发光二极管样品在不同注入电流下的电致荧光（EL）谱及反常的双峰现象.结果表明：有源区 内建电场在外界电流注入条件下逐渐受屏蔽，这一效应在高In组分In_xGa_{1 -x}N/GaN MQWs材料的发光复合机理中占有重要地位. 关键词： xGa_1-xN/GaN多量子阱')" href="#">In_xGa_1-xN/GaN多量子阱 电致荧光谱 内建电场     

分子束外延生长亚稳态ZnCdSe/MgSe低维量子阱结构及其光学性质

采用分子束外延技术在(001)取向的InP衬底上外延生长了亚稳态的ZnxCd1-xSe/MgSe低维量子阱结构,并通过光致发光和子带吸收方法,分析其能带结构。在单量子阱样品制备过程中,高能电子衍射强度振荡表明MgSe可以实现二维生长模式,衍射图样证明其为亚稳态闪锌矿结构。通过引入厚的ZnxCd1-xSe空间层,抑制了MgSe垒层的相变,并能进一步提高样品的结晶质量,得到高结晶质量的多量子阱结构。通过计算不同阱宽的能带与光致发光实验比较,证明了ZnxCd1-xSe/MgSe的导带带阶为1.2 eV,价带带阶为0.27 eV。为了进一步验证其能带结构,制备了电子掺杂的ZnxCd1-xSe/MgSe的多量子阱,观测到半高宽很窄的中红外吸收。利用发光谱确定的带阶计算了量子阱中子带的吸收波长,和实验结果非常吻合。设计了一种双量子阱结构,计算结果显示,通过利用量子阱中的耦合效应,可以实现1.55μm光通信波段的吸收。     

InGaAs/InAlAs多量子阱结构的量子限制Stark效应研究

通过吸收光电流谱的测量.观察到用国产MBE设备生长的与InP衬底晶格匹配的In-GaAs/InAlAs多量子阱结构的量子限制Stark效应及其与光偏振方向有关的各向异性电吸收特性.报道了可用于波导型调制器制作的MQW样品材料的X射线双晶衍射结果,并用计算机模拟出与实测十分相似的曲线,得到了可靠的量子阱结构参数,证明样品材料具有优良的外延质量.利用等效无限深阱模型进行的理论计算表明,应考虑样品p-i-n结内建电场的影响,才能使算出的吸收边红移与实验值符合. 关键词：     

光抽运实验中的微波-射频多量子跃迁(续)

我们观察了不同射频功率下的微波-射频多量子跃迁的光检测谱线,还观察到了射频频率等于共振频率一半时的微波-射频多量子跃迁。 关键词：     

Multi-quantum photoconductivity in Cdln2S4

A study has been made of photoconductivity in Cdln₂S₄ induced by 1.17 eV photons from a Q-switched neodymium laser. Both three-photon absorption, and two-photon absorption involving the emission of a phonon, have been investigated. The experimental data are in satisfactory agreement with the theory of multi-quantum transitions which takes into account the peculiarities of crystal zone structure.The investigation of competing multi-quantum transitions is a new method which permits one to obtain information on the fundamental optical constants of solids.     

Synchronized double rotation 2D NMR

Analytical expressions for multi-quantum signal generation of quadrupole nuclei have been derived. Combined with numerical simulation of the double rotor motion, a strategy is suggested for partial sideband suppression in multi-quantum NMR spectra. Synchronization of multi-quantum excitation and selective flip pulses with outer rotor motion increase outer rotor speed effectively two times. This is also demonstrated experimentally by triple–single quantum correlation spectra of ²³Na and ⁶⁷Rb.     

Butt-joint regrowth method by MOCVD for integration of evanescent wave coupled photodetector and multi-quantum well semiconductor optical amplifier

We have realized integration of evanescent wave coupled photodetector (ECPD) and multi-quantum well (MQW) semiconductor optical amplifier (SOA) on MOCVD platform by investigating butt-joint regrowth method of thick InP/InGaAsP waveguides to deep etched SOA mesas. The combination of inductively coupled plasma etching and wet chemical etching technique has been studied to define the final mesa shape before regrowth. By comparing the etching profiles of different non-selective etchants, we have obtained a controllable non-reentrant mesa shape with smooth sidewall by applying one step 2HBr:2H₃PO₄:K₂Cr₂O₇ wet etching. A high growth temperature of 680 ℃ is found helpful to enhance planar regrowth. By comparing the growth morphologies and simulating optical transmission along different directions, we determined that waveguides should travel across the regrowth interface along the [110] direction. The relation between growth rate and mask design has been extensively studied and the result can provide an important guidance for future mask design and vertical alignment between the active and passive cores. ECPD-SOA integrated device has been successfully achieved by this method without further regrowth steps and provided a responsivity of 7.8 A/W. The butt-joint interface insertion loss is estimated to be 1.05 dB/interface.     

A new multi-quantum version of the HBHA(CBCACO)NH experiment with enhanced sensitivity for partially deuterated samples

A new multi-quantum version of the HBHA(CBCACO)NH experiment for partially deuterated protein samples is presented. The method is based on the significant reduction of the proton and carbon relaxation rates due to multi-quantum delays in highly deuterated proteins recently published by our group. The introduction of a multi-quantum period in the coherence transfer pathway of the HBHA(CBCACO)NH experiment yields a dramatic increase of sensitivity-on average 46% with a 75% deuterated sample of the homodimeric 31 kDa E. coli IIAMan domain. Additional resolution in the proton dimension can be achieved by a double time shared approach keeping the 1H single-quantum period at a minimum.     

Characterisation of the influence of multi-quantum barrier reflectors within GaInP/AlGaInP quantum well lasers using near-field imaging techniques

Using a near-field scanning optical microscope, near-field photocurrent and topographic imaging has measured the effect on intrinsic electric fields and photocurrent propagation resulting from inserting multi-quantum barrier (MQB) super-lattices into quantum well lasers. Measurements on devices at two different excitation wavelengths have highlighted the sensitivity of the near-field optical technique. Strong correlations were seen in the photocurrent response of the multi-quantum barrier regions when compared with simulations made on the electric field generated within the structure. As a result, photocurrent attenuation was attributed to carrier confinement in these barrier regions when compared to a control sample. The measurements illustrate the effectiveness of the MQB, in addition to the sensitivity and power of the near-field photocurrent technique.     

2H T2rho relaxation dynamics and double-quantum filtered NMR studies

In this study 2H T2rho DQF NMR spectra of water in MCM-41 were measured. The T2rho double-quantum filtered (DQF) NMR signal is generated by applying a radio frequency (RF) field for various durations and then observed after a monitor RF pulse. It was found that the transfer between different quantum coherences by the couplings during long-duration RF fields (i.e., soft pulses) and that residual quadrupolar interaction dominates the signal decay. Knowledge of coherence transfer during long-RF pulses has special significance for the development of sophisticated multi-quantum NMR experiments especially multi-quantum MRI applications.     

Polarity control and residual strain in ZnO epilayers grown by molecular beam epitaxy on (0001) GaN/sapphire

We report on the polarity control of ZnO grown by plasma assisted molecular beam epitaxy on Ga polar (0001) GaN/sapphire templates simply via the oxygen‐to‐Zn (VI/II) ratio during the growth of a thin nucleation layer at 300 °C. Following Zn pre‐exposure, the ZnO layers nucleated with low VI/II ratios (<1.5) exhibited Zn‐polarity. Those nucleated with VI/II ratios above 1.5, exhibited O‐polarity. Supported by scanning transmission electron microscopic imaging, we have unequivocally demonstrated that polarity inversion takes place without formation of any vertical inversion domains and within one monolayer of presumably non‐stoichiometric GaO_x formed at the ZnO/GaN interface. A direct correlation between polarity and strain sign of ZnO layers has been found. The Zn‐polar ZnO layers were under tensile biaxial strain, whereas the O‐polar material exhibited compressive strain. Moreover, the amount of residual strain varied linearly with VI/II ratio used during the low‐temperature nucleation layer growth. Strain control with VI/II ratio has been explained by the potential formation of Zn interstitials.     

Recent advances in MOCVD process technology for the growth of compound semiconductor devices

This paper gives an overview of the current state of the technology of metal-organic vapor phase epitaxy (MOVPE), which has established itself as the method of choice for the mass production of (opto)electronic semiconductor devices. The use of in situ reflectometry and emissivity corrected surface temperature measurement for the improvement of process yield is covered as well as recent advances in the growth on larger wafers. Employing novel methods of ex situ characterization to assess the bow of the sapphire wafer during growth, we achieved blue-emitting multi-quantum well (MQW) structures on 4 inch substrates with 1.3 nm standard deviation of the wavelength. It is shown that the thickness of the substrate as well as the off-cut of the sapphire surface must be taken into account and correctly matched. PACS 81.05.Ea; 81.07.Sz; 81.15.Kk; 85.35.Be; 85.60.-q     

Temperature dependence of the cyclotron mass in ZnCdSe/ZnSe multi-QWs

The temperature dependence of the cyclotron resonance mass (CRM) of the magnetopolaron in ZnCdSe/ZnSe multi-quantum wells with strong magnetic field is investigated theoretically using the Lee-Low-Pines variational method. The contributions to the CRM due to the nonparabolicity of the conduction band and the coupling of electron with both confined longitudinal optical and interface optical phonons are considered. Results of our calculations are compared with the experimental data, and a qualitative agreement is found over a large temperature range. We show that these three contributions complement each other to determine the cyclotron mass as a function of the temperature.