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1.
Spacer layer thickness fluctuation scattering in a modulation-doped AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well
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We theoretically study the influence of spacer layer thickness fluctuation(SLTF) on the mobility of a twodimensional electron gas(2DEG) in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer. 相似文献
2.
The effect of hydrogen on donors and interface defects in silicon modulation doped AlxGa1−xAs/InyGa1−yAs/GaAs heterostructures has been investigated by photoluminescence (PL). Hydrogenation was carried out on two sets of samples, one set consists of high quality pseudomorphic heterostructures and another set having partially lattice relaxed structures prone to the defects. On exposure of high quality pseudomorphic structures to hydrogen plasma above 150 °C, a significant blue shift in the PL peak positions as well as bandwidth narrowing is observed. This indicates, the reduction in two-dimensional electron gas in the InyGa1−yAs quantum well due to hydrogen passivation of silicon donors in the AlxGa1−xAs supply layer. The reactivation of the donors is observed upon annealing the hydrogenated sample for 1 h at 250 °C under hydrogen ambient. Another interesting feature is a significant improvement in the PL of lattice-relaxed structures upon hydrogenation of the samples above 250 °C, which is attributed to the hydrogen passivation of interface defects due to the misfit dislocations. 相似文献
3.
《Superlattices and Microstructures》1995,18(3):209
In this paper, we explore theoretically the possibility of applying AlGaAs/GaAs-based quantum wire systems as a terahertz (THz) ultrasonic generator. For structures such as AlxGa1-xAs/GaAs-based low-dimensional semiconductor systems and semiconductor nanostructures, electrons are confined within the nanometer distance scale so that energies (e.g. electronic subband energy, electron kinetic energy, Fermi energy, etc.) are in the meV scale, which consequently results in the acoustic-phonons generated by heated electrons from these novel systems to be around the THz frequency range. Our theoretical results indicate that: (i) AlxGa-xAs/GaAs-based quantum wires are suitable for generating THz acoustic-phonon signals; (ii) both longitudinal and transverse acoustic-phonon modes contribute to the detected phonon signals; (iii) the THz ultrasound wave can be generated through both intra- and inter-subband scattering processes; and (iv) the strong dependence of the acoustic-phonon emission from a quantum wire on phonon frequency and phonon emission angle can be observed. 相似文献
4.
《Superlattices and Microstructures》1995,17(4):397-400
Energy levels of electrons in nonabrupt GaAs/AlxGa1-xAs single quantum wells are calculated with and beyond the constant interfacial effective mass approximation (CIEMA), and compared with those of abrupt GaAs/AlxGa1-xAs quantum wells. For a given interface width, the energy levels calculated with the CIEMA are higher than those calculated beyond it, but both are higher than those of the abrupt semiconductor quantum well. The shifts of the energy levels increase with the interfacial width of the nonabrupt quantum well, as well as with the degree of interfacial asymmetry. 相似文献
5.
详细讨论了GaAs/AlxGa1-xAs球形量子点内的单电子束缚能级随量子点半径、Al组分以及外电场的变化规律,并计算了考虑量子点内外电子有效质量不同后对电子能级的修正. 另外,用解析和平面波展开两种方法对球形量子点内的电子能级进行了计算,并对计算结果做了比较,发现它们符合的很好. 结论和方法为量子点的研究和应用提供了有益的信息和指导.
关键词:
球形量子点
解析方法
平面波展开方法
有效质量 相似文献
6.
M.-E. Pistol S. Nilsson P. Silverberg L. Samuelson M. Rask G. Landgren 《Superlattices and Microstructures》1986,2(6)
We report optical characterization of high quality quantum well (QW) structures grown by metal-organic vapour-phase epitaxy (MOVPE). Thin QW layers of GaAs of thicknesses between 20 Å and 80 Å inserted between Al0.36Ga0.64 As confining layers as well as nominally 20 Å QW's in AlxGa1−xAs with varying x have been studied. Exciton confinement energies exceeding 250 meV and a FWHM of 6 meV for the thinnest QW have been observed. The photoluminescence (PL) data allows the observation of monolayer fluctuations in the QW widths and indicates an interface abruptness of about one atomic layer. Photoluminescence excitation spectroscopy allows electronic excited states to be seen. 相似文献
7.
Nonradiative (surface and bulk) polaritons in a semiconductor structure composed of two heterojunctions GaAs/AlxGa1?x As are investigated under the integer quantum Hall effect (IQHE) conditions. The dispersive, polarization, and energy characteristics of these polaritons are determined including energy dissipation in the two-dimensional electron semiconductor layers. The phase and group velocities of surface and bulk polaritons are shown to be quantized under the IQHE conditions. It is found that resonance coupling of two surface polariton modes may occur in double GaAs/AlxGa1?x As heterojunctions. Possible experimental observation of nonradiative polaritons is discussed. 相似文献
8.
《Superlattices and Microstructures》2005,38(3):161-167
We have calculated the spectral regime of subband transitions in AlxGa1−xN/GaN and AlxGa1−xN/InN single quantum wells. We used a simplified model to account for the internal electric fields, which modify the shape of the quantum well. Some of the parameters for these materials have not yet been firmly established. Therefore, we carried out the analysis for the extremes of the reported values of conduction band discontinuities and band gaps (in the case of InN). This analysis shows that the spectral regime of interband transitions for 1–4 nm thick wells has wavelengths above 0.5 μm for AlGaN/InN and above 0.8 μm for AlGaN/GaN and both heterostructures cover several μm wavelengths. The spectral variation with alloy composition is less pronounced in the AlxGa1−xN/InN single quantum wells due to the higher electric field present across the InN quantum well as compared to GaN. The results of these calculations are in good agreement with more rigorous theoretical approaches and available experimental values for AlxGa1−xN/GaN. 相似文献
9.
Interest in the study of the behavior of shallow impurity centers in superlattices and quantum well structures is fairly recent. This paper reviews briefly both the theoretical and experimental work done in this field in the last few years. Several recent calculations of the energy levels of hydrogenic impurity states in quantum well structures, such as Ga1?xAlxAsGaAsGa1?xAlxAs, are reviewed. The behavior of these levels as a function of the quantum well size is discussed. Recent experimental data concerning the variations of the binding energies of shallow donors and acceptors as a function of the GaAs quantum well size are reviewed. A comparison between these experimental measurements and the results of recent calculations is presented. 相似文献
10.
An electrostatic model for calculating the band-gap renormalization in a two-dimensional (2D) semiconductor layer (quantum well) due to the Coulomb interaction between nonequilibrium charge carriers has been proposed. Consideration is given only to the first quantum-well energy levels for electrons and heavy holes. The exchange and correlation energies are calculated for the first time taking into account the charge-carrier potential energyfluctuations created by electrons and holes along the 2D layer. A relationship for the screened Coulomb potential along the 2D layer is derived, which, within the extremely narrow quantum-well approximation, transforms into the known expression. The band-gap renormalization and the photoluminescence line shape for the GaAs 2D layer in an AlxGa1?x As matrix are computed depending on the concentration of nonequilibrium electrons and holes. The calculated band-gap renormalization is in agreement with the available experimental data at a high photoexcitation of the quantum well when the electrons and holes form the 2D plasma. 相似文献
11.
The influence of exciton energy on intersubband transition was simulated for a chirped supperlattice quantum cascade laser of GaAs/AlxGa1-xAs. Exciton energy was modelled as a function of QW width for alloys of various percentages of constituent elements. The results showed that the exciton energy decreased proportionally with increasing QW width. Models were also generated to study exciton energy as a function of the percent alloy contents of AlxGa1-xAs barriers for QWs of various widths. Exciton energy showed characteristics of higher discrete energy when QW width was narrower. Transition energy was also simulated from e1 and e2 to the 1s exciton state as functions of applied electric field at various QW widths. Our simulation results showed that the transition energy from e2 to the 1s exciton state increased proportionally to the increasing strength of the electric field. This transition energy was indicative of THz range radiation. 相似文献
12.
Binding energies of the ground state and of four excited states of a hydrogenic impurity in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1?xAlxAs are calculated using a variational approach. The ground-state binding energy is calculated as a function of the barrier potential for a given size of the GaAs quantum well and is found to be linearly dependent on the inverse of the square root of the barrier potential except for very small potentials. The variation of the binding energies of all five states as a function of the size of the GaAs quantum well are also calculated and their behavior is discussed. 相似文献
13.
V. N. Mughnetsyan A. A. Kirakosyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2008,43(4):173-176
The effect of interdiffusion of aluminum and indium atoms on the exciton emission energy and binding energy in InxGa1?xAs/AlyGa1?yAs quantum dots is studied. It is shown that the emission energy increases monotonically with increasing diffusion length, while the binding energy has a maximum. 相似文献
14.
The formation of a system of one-dimensional quantum conductors in porous multilayer InxGa1?xAs/GaAs structures with a two-dimensional charge-carrier gas in the InxGa1?xAs layers is discussed. The transition from the single-crystalline to porous matrix is studied with scanning atomic force microcopy. A decrease in the dimensionality of the electron-hole gas in the objects, i.e., a transition from the two-dimensional to a one-dimensional system, is established by analyzing the dependences of the position and width of a spectral line in the photoluminescence spectra on the etching time. Both multilayer periodic superlattices and a structure with a single InxGa1?xAs layer located near the surface of gallium arsenide are studied. The electrophysical characteristics of electrons in the porous superlattices are measured as functions of temperature. They confirm the formation of a new structure and indicate a change in the mechanism of electron scattering in the quasi-one-dimensional transport channels formed in the system. 相似文献
15.
16.
Electronic parameters of a two-dimensional electron gas (2DEG) in modulation-doped highly strained InxGa1−xAs/InyAl1−yAs coupled double quantum wells were investigated by performing Shubnikov-de Haas (S-dH), Van der Pauw Hall-effect, and cyclotron resonance measurements. The S-dH measurements and the fast Fourier transformation results for the S-dH at 1.5 K indicated the electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and satisfied qualitatively the nonparabolicity effects in the quantum wells. The electronic subband structures were calculated by using a self-consistent method. 相似文献
17.
Binding energies of Wannier excitons in a quantum well structure consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1?xAlxAs are calculated using a variational approach. Due to reduction in symmetry along the axis of growth of these quantum well structures and the presence of band discontinuities at the interfaces, the degeneracy of the valence band of GaAs is removed leading to two exciton systems, namely, the heavy hole exciton and the light hole exciton. The variations of the binding energies of these two excitons as a function of the size of the GaAs quantum wells for various values of the heights of the potential barrier are calculated and their behavior is discussed. 相似文献
18.
Sheet density of two-dimensional electron gas at the AlxGa1?xAs heterointerface is calculated self-consistently as a function of doping level in n-AlxGa1?xAs layer by taking into account shallow donor level and the DX centers. The results show a good agreement with the experimental results reported by Ishikawa et al. Dingle's rule of the conduction band discontinuity does not agree with the present results but with 0.62 rule proposed recently by Watanabe et al. 相似文献
19.
In this paper we present analytical site-dependent and composition-dependent spatial dielectric functions for Ga1?xAlxAs involving compositions from x =0.1 to x =0.4 in steps of 0.1. The spatial dielectric functions we present describe the response of the valence electrons of Ga1?xAlxAs to charges Z = ± 1 (in atomic unit) placed on Ga, Al and As sites. To these sites we assign the effective charges (due to the partial ionicity of the bonds) of Z = +0.16, +0.20 and ?0.16 (in atomic unit). 相似文献
20.
Performance comparison of Pt/Au and Ni/Au Schottky contacts on AlxGa1-x N/GaN heterostructures at high temperatures
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In contrast with Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts,this paper systematically investigates the effect of thermal annealing of Au/Pt/Al 0.25 Ga 0.75 N/GaN structures on electrical properties of the two-dimensional electron gas in Al 0.25 Ga 0.75 N/GaN heterostructures by means of temperature-dependent Hall and temperature-dependent current-voltage measurements.The two-dimensional electron gas density of the samples with Pt cap layer increases after annealing in N 2 ambience at 600℃ while the annealing treatment has little effect on the two-dimensional electron gas mobility in comparison with the samples with Ni cap layer.The experimental results indicate that the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts reduce the reverse leakage current density at high annealing temperatures of 400-600℃.As a conclusion,the better thermal stability of the Au/Pt/Al 0.25 Ga 0.75 N/GaN Schottky contacts than the Au/Ni/Al 0.25 Ga 0.75 N/GaN Schottky contacts at high temperatures can be attributed to the inertness of the interface between Pt and AlxGa1-xN. 相似文献