Quantum-confined Stark shift in electroreflectance of a cylindrical GaN quantum dot

The electroreflectance (ER) spectra in the presence of the modulated electric field have been employed to study the fine structure of a cylindrical GaN quantum dot (QD), including the light hole and heavy hole interband transitions, and the ER spectra exhibit Franz-Keldysh oscillation characteristics with abscissa of energy (E−E_g). The quantum-confined Stark shift (QCSS) happened when the electric field intensity increased and the light and heavy holes dependent characteristics have been shown. The three-dimensional Schrödinger equation of QD has been calculated within the framework of effective-mass approximation, and the ER indices have been obtained from modulation absorption coefficients using the Seraphin coefficients and the Kramer-Kroning relation.     

Quantum-confined Stark effects in semiconductor quantum disks

Quantum-confined Stark effects (QCSE's) on excitons in semiconductor quantum disks with finite-potential barriers have been calculated as a function of disk size parameters by a variational calculation in an effort to examine possible application to optical devices. The calculations agree with experimental data reported so far. Although the exciton binding energy, E_b, for smaller diameters is large at zero bias, it decreases more with increasing electric field, which is contrary to the E_b behavior in a spherical quantum dot and quantum well. This larger decrease results in a smaller red Stark shift. Both the red Stark shift and the oscillator strength can be controlled by changing disk diameter and height. The analysis shows that favorable QCSE characteristics, i.e., a large red Stark shift at a small electric field with large oscillator strength, can be obtained     

Quantum-confined stark effect and localization of charge carriers in Al0.3Ga0.7N/Al0.4Ga0.6N quantum wells with different morphologies

The electric fields in Al_0.3Ga_0.7N/Al_0.4Ga_0.6N quantum wells are estimated. The quantum wells are grown by plasma-assisted molecular-beam epitaxy with plasma activation of nitrogen. The three-dimensional and planar modes of buffer layer growth are used. The transition to the three-dimensional mode of growth yields a substantial increase in the photoluminescence intensity of the quantum wells and a shift of the photoluminescence line to shorter wavelengths. These effects are attributed to the fact that, because of the extra three-dimensional localization of charge carriers in the quantum-well layer, the quantum-confined Stark effect relaxes. The effect of localization is supposedly due to spontaneous composition fluctuations formed in the AlGaN alloy and enhanced by the three-dimensional growth.     

Broad-area InAs/GaAs quantum dot lasers incorporating intermixed passive waveguide

InAs/GaAs quantum dot lasers incorporating passive waveguide created by post-growth intermixing processing have been studied. Emission wavelength of the passive section shows relative blueshift as high as 135 nm with respect to the emission wavelength of the active section. Intrinsic losses in the section formed by the intermixing are very small. Broad-area lasers with 100 mum stripe width incorporating intermixed section have demonstrated improvements in far-field pattern under both pulsed and continuous wave pumping current     

量子点及量子点器件

量子点是纳米科学与技术研究重要的组成部分,量子点器件又是纳米器件的发展方向之一.详细介绍了量子点的分类、量子点的主要制备方式、量子点特性的传统研究和微波类比仿真研究方法,系统论述了量子点器件的分类应用及噪声抑制.     

Observation of the quantum confined stark effect in ZnSe/ZnCdSe single quantum well systems

We report the observation of the quantum-confined Stark effect (QCSE) in ZnSe/ ZnCdSe single quantum wells grown by molecular beam epitaxy, using photoluminescence. In our experiments the electric field was applied via a reverse-biased Schottky barrier contact. To our knowledge, this is the first observation of the QCSE in any wide gap II-VI semiconductor heterostructure. Significant red shifts, typically 10–15 meV, are detected before quenching. An associated reduction in the transition intensity, consistent with the QCSE. is clearly observed. The dependence of these results will be discussed as a function of quantum well depth and thickness. Complete quenching of the luminescence is observed with applied voltages as low as 5 V. In addition, at lowest voltages, we also detect small blue shifts (up to 4 meV), which we attribute to the interaction between the externally applied electric field and the built-in field of the structure.     

Wannier-stark effect in Ge/Si quantum dot superlattices

Deep level transient spectroscopy (DLTS) measurements were performed to study electron emission from quantum states in a 20-layer Ge quantum-dot superlattice (QDSL) in a Ge/Si p-n heterostructure. It was established that the changes in the DLTS spectra depend heavily on the magnitude of the applied reverse bias U _r . Three regions of the reverse bias U _r were identified, corresponding to the manifestation of the three modes of the Wannier-Stark effect: Wannier-Stark ladder mode, Wannier-Stark localization, and nonresonant Zener tunneling mode. Furthermore, it was found that the appearance of DLTS peaks for all three modes is associated with electron emission from deep-level defects via Wannier-Stark localized states arising as a result of the splitting of the electron miniband of the Ge/Si QDSL.     

1.43 /spl mu/m InAs bilayer quantum dot lasers on GaAs substrate

An edge emitting quantum dot (QD) laser at 1430 nm is demonstrated with a structure grown by molecular beam epitaxy on GaAs substrate. The active region is based on three InAs bilayer QDs embedded in a conventional AlGaAs/GaAs waveguide. The threshold current density is 134 A/cm/sup 2/. Output power of 23 mW per facet is achieved.     

Simulation of the spectroscopic response and electron dynamics in a double quantum dot

We present the results of the numerical simulation of the dependence of the absorption spectrum of a single-electron semiconductor double quantum dot placed in a microcavity on structural parameters and the time dependence of populations of quantum dot states. The investigated physical system can be used for quantum information coding and processing. Initialization and one-qubit operations correspond to the redistribution of populations of localized states of a quantum dot under the action of laser and cavity optical fields.     

Electro-magnetic weak coupling optical polaron and temperature effect in quantum dot

We investigate the influence of the electric field and magnetic fields on the ground state energy of a polaron in a spherical semiconductor quantum dot (QD) using the modified Lee Low Pines (LLP) method.The numerical results show the increase of the ground state energy with the increase of the electric field and the electron-phonon coupling constant, and the decrease with the magnetic field and the longitudinal confinement length.It is also seen that the temperature is an increasing function of the cyclotron frequency and the coupling constant whereas it decreases with the electric field strength.The modulation of the electric field, the magnetic field and the confinement length leads to the control of decoherence in the system.     

Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers

It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.     

Influence of the stark effect on the resonance excitation transfer between quantum dots

The resonance energy transfer between exciton states in a system comprised of two semiconductor quantum dots is studied theoretically. A model Hamiltonian is constructed to describe the influence of the laser pulse, Coulomb interaction, the static Stark effect, and the relaxation of exciton states on the dynamics of the system. Specific calculations of the efficiency of energy transfer under different excitation conditions and different positions of energy levels are exemplified. It is shown that the transfer process can be controlled by shifting the levels in a constant electric field.     

Excitonic dynamics of a quantum dot coupled to a laser-driven semiconductor microcavity

Within the density matrix formalism, we report on the quantum control of the excitonic coherences in quantum dots coupled to a single mode field resonant semiconductor cavity. We use an external classical laser field to drive the dynamical response of the excitonic states. Dissipation mechanisms associated with the cavity field and the excitonic states are explicitly included in the model. Our numerical simulations of the excitonic dynamics are in good agreement with recent experimental reports. Furthermore, we compute and show how to tailor such a dynamics in the presence of the laser field by means of controlling the detuning between the laser and the cavity field frequencies. The results are analyzed with a view to implementing quantum control of local qubit operations.     

Quantum size effect on excitons in zinc-blende GaN/AlN quantum dot

Within the framework of effective-mass approximation, exciton states confined in zinc-blende GaN/AlN quantum dot (QD) are investigated by means of a variational approach, including three-dimensional confinement of the electron and hole in the QD and finite band offsets. Numerical results show that the exciton binding energy and the interband emission energy are both decreased when QD height (or radius) is increased. Our theoretical results are in agreement with the experimental measurements.     

Exciton enhancement effect on the third harmonic generation in ZnS/CdSe quantum dot quantum well

Exciton enhancement effect on the third-order optical nonlinearities of a ZnS/CdSe quantum dot quantum well (QDQW) has been theoretically studied. The wave functions and eigenenergies of excitons in QDQW have been calculated under the effective-mass approximation. By solving a three-dimensional nonlinear Schrödinger equation and by means of compact density matrix method, the third-order nonlinear susceptibilities for third-harmonic generation (THG) have been calculated in a two energy levels model of QDQW. Firstly, we studied the size effect on THG in QDQW. Then we compared the value of THG with the case that only considering electron states. The results show that the THG is greatly enhanced when compared with the condition just considering electron states.     

Rashba效应下量子点中束缚极化子的有效质量

采用线性组合算符、LLP幺正变换和变分方法,研究Rashba效应下量子点中强耦合束缚极化子有效质量的性质。对RbCl量子点数值计算的结果表明：极化子的振动频率、有效质量均随极化子速率、受限强度和库仑束缚势的增大而增大,原因是极化子速率增大电子动能增加,库仑束缚势增大导致电子-声子间相互作用增强,受限强度增大使电子运动的有效范围减小导致电子能量增大,进而使极化子的振动频率和有效质量增大。受Rashba自旋轨道相互作用的影响,极化子的有效质量发生劈裂,劈裂间距随极化子速率的增大而减小。     

PbTe quantum dot doped glasses with absorption edge in the 1.5μm wavelength region

PbTe nanocrystals have been grown in doped glasses. By choosing the appropriate glass matrix and controlling the heat treatment temperatures and times, the quantum confined energy gaps of the PbTe dots can be changed in the wavelength range 1.1-2.0 μm. These glasses are potential materials for applications in optical communication and optoelectronic devices     

The absorption coefficient of low dimensional semiconductor systems: the photoluminescence of InGaN quantum dot

The free carrier absorption coefficient of a low dimensional semiconductor system is formulated, with inclusion of interparticle Coulomb interaction, perturbatively, considering the bubble diagrams summed up to infinite order, which accounts for the multisubband (Q2D or Q1D case) or multilevel (Q0D case) electronic structure for reduced dimensionality. The experimental photoluminescence spectrum of a quantum dot of InGaN is used to estimate indirectly, through the absorption coefficient, the length of the side of the cube, which seems to be the geometry of the dots obtained in recent experiments. The results are consistent with other, independent, measurements.