量子限制受主的光致发光研究

对一系列δ掺杂浅受主铍（Be）原子的GaAs/AlAs多量子阱和均匀掺杂Be受主的GaAs体材料中Be原子的能级间跃迁进行了光致发光（PL）研究.实验中所用的样品是通过分子束外延技术生长的均匀掺杂Be受主的GaAs外延单层样品和一系列GaAs/AlAs多量子阱样品,并在每量子阱中央进行了Be原子的δ掺杂,量子阱宽度为30 到200 ?.在4.2 K温度下测量了上述系列样品的光致发光谱,清楚地观察到了束缚激子的受主从基态1s_3/2（Γ₆）到第一激发态 关键词： 量子限制受主 光致发光 多量子阱 δ掺杂     

Photoionization of a charged exciton in a GaAs/GaAlAs corrugated quantum well

Binding energies of a charged exciton as a function of well width of a GaAs/GaAlAs corrugated quantum well are investigated. The calculations have been performed by the variational method based on a two parametric trial wave function within a single band effective mass approximation. We have also included the effect of nonparabolicity of the conduction band of GaAs. We study the spectral dependence of the charged exciton in a GaAs/GaAlAs corrugated quantum well as a function of well width. The photoionization cross section for the charged exciton placed at the center of the quantum well is computed as a function of normalized photon energy. The cross-section behavior as a function of incident energy is entirely different in the two cases of radiation being x-direction (along the growth direction) or z-direction. The interband emission energy as a function of well width is calculated and the dependence of the photoionization cross section on photon energy is carried out for the charged excitons. The resulting spectra are brought out for light polarized along and perpendicular to the growth direction. The results show that the charged exciton binding energy, interband emission energy and the photoionization cross section depend strongly on the well width. Our results are compared with the other existing literature available.     

氮化物抛物量子阱中类氢杂质态能量

采用变分方法研究氮化物抛物量子阱(GaN/Al_xGa_1-xN)材料中类氢杂质态的能级,给出基态能量、第一激发态能量、结合能和跃迁能量等物理量随抛物量子阱宽度变化的函数关系.研究结果表明,基态能量、第一激发态能量、基态结合能和1s→2p±跃迁能量随着阱宽L的增大而减小,最后接近于GaN中3D值.GaN/Al_0.3Ga_0.7N抛物量子阱对杂质态的束缚程度比GaAs/Al_0.3Ga_0.7As抛物量子阱强,因此,在GaN/Al_0.3-Ga_0.7N抛物量子阱中束缚于杂质中心处的电子比在GaAs/Al_0.3Ga_0.7As抛物量子阱中束缚于杂质中心处的电子稳定.     

The eigenstates and tunnelling time in an interdiffused AlGaAs/GaAs quantum well by the transfer matrix method

A matrix method has been used for the determination of the confined eigenstates and their corresponding tunnelling times in an interdiffused AlGaAs/GaAs single quantum well structure. The nonlinear confinement potential profile of the disordered quantum well is due to the interdiffusion of the constituent Al and Ga atoms and is modeled here by an error function. The results indicate that the interdiffusion, as well as the applied electric field, affect the tunnelling times and the energy linewidths of the corresponding states. The results are compared with those for an AlGaAs/GaAs as-grown single square quantum well without any interdiffusion.     

MBE GaAs1-xSbx/GaAs应变层量子阱的光调制反射光谱

本文采用光调制反射光谱技术研究了MBE GaAs_1-xSb_x/GaAs应变层量子阱。通过实验分析和理论上对受应力作用后能带结构的估算,确认在这一系统中流体静压力作用引起的能带结构变化主要出现在导带上,同时也证实了GaAs_1-xSb_x/GaAs应变层量子阱属于第Ⅱ型量子阱结构。实验结果与理论估算符合很好。 关键词：     

Observation of biexcitonic quantum beat in strain-induced GaAs quantum dots

Four-wave mixing in strain-induced GaAs quantum dots formed in a GaAs quantum well is studied using a highly sensitive heterodyne technique. A clear oscillation with a period of 1 ps is observed, recognized as a biexcitonic quantum beat based on its polarization dependence. The period of the beat is about 1.5 times shorter than that from the quantum well in the same sample. The beat represents direct evidence of an increase in the biexciton binding energy in the dots due to lateral confinement potential originating from the stressors.     

GaAsN/GaAs量子阱在1 MeV电子束辐照下的退化规律

为研究GaAsN/GaAs量子阱在电子束辐照下的退化规律与机制,对GaAsN/GaAs量子阱进行了不同注量(1×1015,1×1016 e/cm2)1 MeV电子束辐照和辐照后不同温度退火(650,750,850℃)试验,并结合Mulassis仿真和GaAs能带模型图对其分析讨论。结果表明,随着电子注量的增加,GaAsN/GaAs量子阱光学性能急剧降低,注量为1×1015 e/cm2和1×1016 e/cm2的电子束辐照后,GaAsN/GaAs量子阱PL强度分别衰减为初始值的85%和29%。GaAsN/GaAs量子阱电子辐照后650℃退火5 min,样品PL强度恢复到初始值,材料带隙没有发生变化。GaAsN/GaAs量子阱辐照后750℃和850℃各退火5 min后,样品PL强度随退火温度的升高不断减小,同时N原子外扩散使得样品带隙发生约4 nm蓝移。退火温度升高没有造成带隙更大的蓝移,这是由于进一步的温度升高产生了新的N—As间隙缺陷,抑制了N原子外扩散,同时导致GaAsN/GaAs量子阱光学性能退化。     

Electronic states in a step quantum well in a magnetic field

The quantum states and energy spectrum of an electron in a rectangular step quantum well in a magnetic field parallel to the plane of two-dimensional electronic gas are investigated. It is shown that the joint effect of a magnetic field and confining potential of quantum well results in radical change of the electron energy spectrum. The energy dependencies on the parameters of the quantum well and magnetic field induction are investigated. Numerical calculations are carried out for an AlAs/ GaAlAs/ GaAs/ AlAs step quantum well.     

Influence of the cap layer thickness on photoluminescence properties in strained InGaAs/GaAs single quantum wells

The influence of the GaAs cap layer thickness on the luminescence properties in strained In_0.20Ga_0.80As/GaAs single quantum well (SQW) structures has been investigated using temperature-dependent photoluminescence (PL) spectroscopy. The luminescence peak is shifted to lower energy as the GaAs cap layer thickness decreases, which demonstrates the effect of the GaAs cap layer thickness on the strain of InGaAs/GaAs single quantum wells (SQW). We find the PL quenching mechanism is the thermal activation of electron hole pairs from the wells into the GaAs cap layer for the samples with thicker GaAs cap layer, while in sample with thinner GaAs cap layer exciton trapping on misfit dislocations is dominated.     

The isotropic-to-nematic transition in a two-dimensional fluid of hard needles: a finite-size scaling study

Laser dependence of binding energy on exciton in a GaAs quantum well wire embedded on an AlGaAs wire within the single band effective mass approximation is investigated. Laser dressed donor binding energy is calculated as a function of wire radius with the renormalization of the semiconductor gap and conduction valence effective masses. We take into account the laser dressing effects on both the impurity Coulomb potential and the confinement potential. The valence-band anisotropy is included in our theoretical model by using different hole masses in different spatial directions. The spatial dielectric function and the polaronic effects have been employed in a GaAs/AlGaAs quantum wire. The numerical calculations reveal that the binding energy is found to increase with decrease with the wire radius, and decrease with increase with the value of laser field amplitude, the polaronic effect enhances the binding energy considerably and the binding energy of the impurity for the narrow well wire is more sensitive to the laser field amplitude.     

Polaron Energy and Effective Mass in Parabolic Quantum Wells

The energy and effective mass of a polaron in a parabolic quantum well are studied theoretically by using LLP-like transformations and a variational approach. Numerical results are presented for the polaron energy and effective mass in the GaAs/Al0.3Ga0.7As parabolic quantum well. The results show that the energy and the effective mass of the polaron both have their maxima in the finite parabolic quantum well but decrease monotonously in the infinite parabolic quantum well with the increasing well width. It is verified that the bulk longitudinal optical phonon mode approximation is an adequate formulation for the electron-phonon coupling in parabolic quantum well structures.     

Effect of conduction band parabolicity on the spectrum and binding energy of a hydrogenic impurity in GaAs spherical quantum dots

The energy levels and binding energies of a hydrogenic impurity in GaAs spherical quantum dots with radius R are calculated by the finite difference method. The system is assumed to have an infinite confining potential well with radius R, which can be viewed as a hard wall boundary condition. The parabolicity of the conduction band profile for GaAs material can be viewed as a parabolic potential well. The energy levels and binding energies are depended dramatically on the radius of the quantum dot and the parabolic potential well. The results show that parabolic potential can remarkably alter the energy level ordering and binding energy level ordering of hydrogenic impurity states for the quantum dot with a smaller radius R.     

Evidence for Fermi level shift in GaInAs/GaAs quantum wells upon nitrogen incorporation

GaInAs/GaAs and GaInNAs/GaAs quantum well (QW) structures grown by metalorganic vapor phase epitaxy have been studied by contactless electroreflectance spectroscopy. In addition to the N-related redshift of QW transitions, an increase in the electric field in the GaAs cap layer has been observed after the incorporation of nitrogen atoms into the GaInAs QW. This observation is associated with the tendency of the Fermi level shift to a given energy in the GaInNAs QW region due to N-related defects.     

N-Composition and Pressure Dependence of the Inter Band Transitions of Ga(N,As)/GaAs Quantum Wells

A series of GaN x As 1 m x /GaAs quantum well structures with well widths of about 20 nm and x varying between 1% and 3.5% has been grown by metal-organic vapour phase epitaxy. We have studied the evolution of the quantum well states under hydrostatic pressure up to 20 kbar at 300 K by photomodulated reflectance (PR) spectroscopy. The energy positions of the quantum well transitions have been obtained by fitting the PR spectra. The pressure dependence of the allowed heavy-hole transitions e n hh n decreases with increasing n . This directly reflects the strong non-parabolic dispersion of the conduction band originating from the interaction of the N-impurity level with the bands of the GaAs host. The fitted energy positions and their pressure dependence can be well described by a 10 band k.p model. The observed splitting between the lowest light-hole and heavy-hole transitions are in agreement with a type I band alignment.     

关于RHEED振荡技术优化GaAs(110)量子阱生长的研究

在GaAs(110)衬底上生长的半导体材料有诸多优良性能，使得在非极性GaAs(110)衬底上获得高质量各类异质结材料，成为近年来分子束外延生长关注的课题.考虑GaAs(110)表面是Ga和As共面，最佳生长温度窗口很小；反射式高能电子衍射的(1×1)再构图案对生长温度和V/Ⅲ束流比不敏感，难于通过观察再构图案的变化，准确地找到最佳生长条件.作者在制备GaAs(110)量子阱过程中，观察到反射式高能电子衍射强度振荡呈现出的单双周期变化.这意味着不同工艺条件下，在 GaAs(110)衬底上量子阱有单层和双层两种生长模式.透射电子显微镜和室温光致荧光光谱测量结果表明：在双层生长模式下量子阱样品光学性能较差，而在单层生长模式下量子阱光学性能较好，但是界面会变粗糙.利用这一特点，我们采用反射式高能电子衍射强度振荡技术，找到了一种在GaAs(110)衬底上生长高质量量子阱的可行方法. 关键词： 反射高能电子衍射 量子阱 分子束外延     

Discrete electroluminescence lines in sub-micron p-i-n resonant tunnelling diodes

We have fabricated GaAs/AlAs p-i-n double barrier resonant tunnelling diodes with active lateral dimensions down to 0.25μn² using optical lithography and wet etching. Many devices have been investigated and systematic variations in the quantum well emission have been observed as the device size is decreased. We observe a red shift of the quantum well recombination lines. In addition a new line is observed at lower energy in the spectra of the smallest devices. The quantum well luminescence efficiency is found to be constant down to the smallest device size.     

Observation of Overhauser shift in a self-assembled InAlAs quantum dot

We report the polarization-dependent energy shift of excitonic emission in a self-assembled InAlAs/AlGaAs quantum dot (QD). The energy shift is well known as Overhauser shift and was observed in a naturally formed GaAs QD using monolayer fluctuation of a quantum well. However, there has been no observation so far in a self-assembled QD, which is suitable for formation of vertically coupled QDs. We demonstrate that the magnitude of the Overhauser shift is enhanced by the photo-injection of the highly polarized electron and is controllable by the polarization of the excitation light in a self-assembled InAlAs QD.     

电场下GaAs/Ga1-xAlxAs量子阱中的子带和激子

本文利用有限势垒模型,研究电场对GaAs/Ga_1-xAl_xAs量子阱中子带和激子的影响。对阱宽为105?的GaAs/Ga_0.66Al_0.34As量子阱,电场由0—1.2×10⁵V/cm,我们计算了电子和空穴的子带以及激子的结合能。基于上述计算结果,所得电子-空穴重叠函数和激子峰的能量移动与实验测量符合得较好。 关键词：     

Small-signal modulation characteristics for 1.5 μm lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers

The small-signal modulation characteristics of 1.5 m lattice-matched InGaNAs/GaAs and InGaAs/InP quantum well lasers and their temperature dependence have been calculated. It is found that the maximum bandwidth of the InGaNAs/GaAs quantum well lasers is about 2.3 times larger than that of the InGaAs/InP quantum well lasers due to the high differential gain which results from the large electron effective mass in the dilute nitride system. The slope efficiency for the 3 dB bandwidth as a function of optical density is twice as large for InGaNAs/GaAs as for InGaAs/InP quantum well lasers.     

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.