Carrier spin dynamics in GaAs/AlGaAs quantum wells with a laterally localizing electric potential

The spin orientation dynamics in a GaAs quantum well with a laterally nonuniform electric potential generated by a mosaic electrode deposited on the surface of the sample has been investigated using the photoinduced magneto-optical Kerr effect. It has been found that the application of a negative potential higher than 1 V to the electrode leads to more than a hundredfold increase in the spin polarization lifetime in the sample under study. It is concluded that so strong slowing down of the relaxation is caused by a combined action of two effects, namely, the spatial separation of electron and hole, which reduces the radiative recombination rate of electron-hole pair, and the localization of electron, which is accompanied by the suppression of spin relaxation processes caused by electron motion.     

Thermal interdiffusion in InGaAs/GaAs and GaAsSb/GaAs strained quantum wells as a function of doping density

We studied the thermal stability and interdiffusion of InGaAs/GaAs and GaAsSb/GaAs single quantum wells as a function of temperature for both Be and Si doping at various doping concentrations. The interdiffusion was monitored using the photoluminescence from the ground states of the valence- and conduction-band quantum wells. Using a Green's function method to solve the diffusion equation, assuming Fick's law behaviour, the evolution of the well shape during annealing was determined, and Schrödinger's equation was solved for this well shape to provide the ground-state energy levels of the system using the diffusion constant as the only fitting parameter. The validity of this model as applied to both systems is discussed.Strained Layer Structures Research Group.     

GaAs/AlGaAs多量子阱中载流子动力学的实验研究

利用瞬态光栅激光光谱技术测量了(110)方向生长的本征GaAs/AlGaAs多量子阱的双极扩散系数.室温下,光激发的载流子浓度n_ex=3.4×10¹⁰/cm²时,测得双极扩散系数D_a=13.0 cm²/s,载流子的寿命τ_R=1.9 ns.改变光激发的载流子浓度(n_{ex关键词： 瞬态光栅 量子阱 空穴输运}     

Carrier diffusion in InGaAs/GaAs quantum wells grown on vicinal GaAs(0 0 1) substrates

We have investigated the influence of vicinal GaAs substrates on the optical and electronic properties of InGaAs/GaAs quantum wells (QWs). A single In_0.10Ga_0.90As QW was grown by molecular-beam epitaxy on a vicinal GaAs(0 0 1) substrate with a miscut angle of 0° (nominal), 2°, 4° and 6° towards [1 1 0]. The carrier diffusion was obtained by a micro-photoluminescence scan technique that permits to observe the effective diffusion length characterized by the lateral spread of carriers in the QW followed by radiative recombination. The carrier diffusion length was obtained parallel (L_||) and perpendicular (L) to the atomic steps. The diffusion length decreases as the temperature increases up to 100 K. Above this temperature we found different behaviours that depend on the sample miscut angle.     

Optical gain modeling of InP based InGaAs(N)/GaAsSb type-II quantum wells laser for mid-infrared emission

Optical gain performance of InP based “W” structure with InGaAs(N)/GaAsSb type-II quantum wells are investigated theoretically. The band structure was calculated by using k.p model, taking into account the conduction band mixing with N resonant band, valence band mixing, as well as strain effect. Our studies show that these type-II quantum wells are suitable for mid-infrared (2–4 μm) operation at room temperature.     

High-frequency magneto-oscillations in GaAs/AlGaAs quantum wells

We have observed very high-frequency, highly reproducible magneto-oscillations in modulation doped GaAs/AlGaAs quantum well structures. The oscillations are periodic in an inverse magnetic field (1/B) and their amplitude increases with temperature up to T approximately 700 mK. Being initially most pronounced around the filling factor nu=1/2, they move towards lower nu with increasing T. Front and back-gating data imply that these oscillations require a coupling to a parallel conducting layer. A comparison with existing oscillation models renders no explanation.     

Design of strain compensated InGaAs/GaAsSb type-II quantum well structures for mid-infrared photodiodes

In this paper, the transition wavelength and wave function overlap of type-II In_xGa_1-xAs/GaAs_1-ySb_y quantum wells are numerically calculated using a 4-band k · p Hamiltonian model. The simulation results indicate that absorption wavelength from 2 to 4?μm can be achieved with a strain compensated quantum well structure. The transition wavelength and wave function overlap can be optimized by properly selecting the thicknesses and composition of the quantum well layers.     

Energy-selective charging of type-II GaSb/GaAs quantum dots

The hole confinement in type-II self-organized GaSb/GaAs quantum dots (QDs) was investigated by combining optical excitation and time-resolved capacitance spectroscopy. The experimental results indicate energy-selective charging even for type-II QDs. With increasing excitation energy the apparent hole activation energy decreases, which is attributed to light absorption in sub-ensembles of QDs with decreasing hole localization. The large localization energy of about 450 meV and the possibility of optical-multiplexing makes type-II GaSb/GaAs QDs a potential material system for QD memory concepts.     

Excitons in GaAs quantum wells

This paper attempts to summarize some of the salient properties of excitons in GaAs quantum wells and in doing so it will emphasize work at AT&T Bell Labs with which the authors have been associated. Although the text relies heavily on published material, an effort has been made to stress new material, and where feasible, unpublished aspects, e.g., figures, related to earlier work. Topics discussed on the quasi-2D excitons in GaAs quantum well include: their inherent tendency for intrinsic free-exciton emission, exciton binding energies, bound and localized excitons including biexcitons and excitons bound to neutral impurities, effects of n- and p-type modulation and antimodulation doping, and the developments leading to a proposed set of quantum well parameters that results in acceptable fits to the observed exciton transitions for GaAs quantum wells with both square and parabolic potential profiles.     

Optical properties of type-II InGaN/GaAsN/GaN quantum wells

Optical properties of type-II InGaN/GaNAs QW light-emitting diodes are investigated by using the multiband effective mass theory. These results are compared with those of conventional InGaN/GaN QW structures. The type-II InGaN/GaNAs/GaN QW structure shows much larger spontaneous emission and optical gain than that of a conventional QW structure. This can be explained by the fact that, in the case of the type-II QW structure, the effective well width is greatly reduced. A type-II QW structure shows that the peak position at a high carrier density is similar to that (530 nm) at a low carrier density. On the other hand, in the case of a conventional QW structure, the peak position is largely blueshifted at a high carrier density.     

Magneto-optical studies of GaAs/AlAs quantum wells

We present a magnetoreflectivity study of three GaAs/AlAs multiple quantum wells with widths 75, 100 and 150 Å. At T = 5K, the reflectivity spectra exhibit features associated with the excitons as well as interband Landau transitions. The slopes of these transitions imply that the electrons are confined in the GaAs layers. In addition, experimental values for the exciton binding energies are determined from the zero field intercepts of the Landau transitions.     

Photoreflectance measurements in GaAs/AlGaAs asymmetric quantum wells

In this work we investigated the optical control of the bidimensional electron gas density in a single asymmetric quantum well using, for the first time, photoreflectance. We performed our measurements at 80 and 300 K as a function of the power density of the pump beam. Under strong illumination, the bidimensional electron gas density is washed out of the quantum well and under a dark condition, it reaches its maximum value. The variation of the optical transitions observed in our photoreflectance spectra was related to the induced changes of the band profile in between these two limiting cases.     

Photoluminescence saturation in InGaAs/GaAs single quantum wells

Saturation of the photoluminescence associated with the 11H transition in the InGaAs single quantum wells is observed under high intensity optical excitation. At the onset of saturation, a spill-over of the photoluminescence occurs into the GaAs cladding layers as the excitation intensity is increased. The measurements are used to determine a limiting value of the quantum efficiency of the quantum-well associated photoluminescence.     

Time-resolved studies of electron and hole spin dynamics in modulation-doped GaAs/AlGaAs quantum wells

Spin dynamics in semiconductors have gained much interest in the past years due to the emerging field of semiconductor spintronics. This review is focussed on the observation and control of electron and hole spin dynamics in modulation-doped heterostructures based on the GaAs/AlGaAs material system. Modulation doping allows for the creation of two-dimensional electron and hole systems with high carrier mobility. By confining carriers to a two-dimensional sheet, the spin–orbit interaction is modified significantly. In addition to this, it can be further modified by changing the symmetry of the system, for example by externally applied or built-in electric fields along the growth direction. Our recent experimental results on spin dynamics in two dimensions are reviewed and discussed in connection with theoretical considerations. A brief overview of the current research challenges in this field is given.