Polaron binding energy and effective mass in nitride single semiconductor heterostructures

Polaronic corrections in the conduction band of III–V nitride-based single heterostructures (SHS) are calculated within second-order Rayleigh–Schrödinger perturbation theory, using the dielectric continuum model for the interface and half-space polar optical phonon modes. The particular case of the AlN/GaN system is considered for illustration. The formation of a polarization-induced sheet density charge at the interface between both materials allows to study the single-electron states with the use of an approximate analytical expression for the potential energy function. The band-bending profile is then described in a way that includes many-body effects through a one-dimensional Hartree potential. Comparison of the calculated polaron effective mass in this material with recent experimental results in nitride SHS shows that higher perturbative orders in the interaction should be included in order to obtain better agreement.     

Energy and effective mass of a polaron in asymmetric semiconductor quantum well structures

In this paper, the correct electron extended states wave functions and the density of states in asymmetric single quantum wells (QWs) are given for the first time, we put right mistakes from some previous papers of some other authors. Within the framework of the secondorder perturbation theory, the ground-state polaron binding energy and effective mass correction in asymmetric single QWs are studied including the full energy specturm, i.e., the discrete energy levels in the well and the continuum energy spectrum above the barrier, and all possible optical-phonon modes. The effects of the finite electronic confinement potential and the subband nonparabolicity are considered. The relative importance of the different phonon modes is investigated. Our results show that the polaron energy and effective mass are sensitive to the asymmetry of the structure and have a close relation to the interface phonon dispersion. When well width and one side barrier height of asymmetric QWs are fixed and identical with those of symmetric QW, the polaron binding energy and effective mass in asymmetric QWs are always less than those in symmetric QW. It is necessary to include the continuum energy spectrum as intermediate states in the study of polaron effects in QWs in order to obtain the correct results. The subband non-parabolicity has little influence on the polaron effects. The polaron energies given in this paper are excellent agreement with our variational results.     

Field-induced energy band and effective mass anisotropy in coupled double quantum wells

The effects of the field-induced conduction band anisotropy on the electron effective mass and electrical transport properties of coupled double quantum well structures are discussed. This anisotropy is due to the formation of a partial energy gap in the dispersion curves of coupled double quantum wells by an in-plane magnetic field. The reported data show that the magnitude of this gap is mainly dependent on the interwell coupling, although it also depends on the magnitude of the applied magnetic field. A field-induced anisotropy of the electron effective mass and the in-plane electrical transport properties, due to the formation of a saddle point at the lower edge of this gap, is predicted. Further, a simple model to estimate the critical field at which a saddle point appears is also discussed.     

Optimization of semiconductor quantum devices by evolutionary search

A novel simulation strategy is proposed for searching for semiconductor quantum devices that are optimized with respect to required performances. Based on evolutionary programming, a technique that implements the paradigm of genetic algorithms in more-complex data structures than strings of bits, the proposed algorithm is able to deal with quantum devices with preset nontrivial constraints (e.g., transition energies, geometric requirements). Therefore our approach allows for automatic design, thus avoiding costly by-hand optimizations. We demonstrate the advantages of the proposed algorithm through a relevant and nontrivial application, the optimization of a second-harmonic-generation device working in resonance conditions.     

Coulomb effects in semiconductor quantum dots

This paper presents a new model for the Internet graph (AS graph) based on the concept of heuristic trade-off optimization, introduced by Fabrikant, Koutsoupias and Papadimitriou in [5] to grow a random tree with a heavily tailed degree distribution. We propose here a generalization of this approach to generate a general graph, as a candidate for modeling the Internet. We present the results of our simulations and an analysis of the standard parameters measured in our model, compared with measurements from the physical Internet graph.Received: 9 February 2004, Published online: 14 May 2004PACS: 89.75.-k Complex systems - 89.75.Hc Networks and genealogical trees - 89.75.Da Systems obeying scaling laws - 89.75.Fb Structures and organization in complex systems - 89.65.Gh Economics; econophysics, financial markets, business and managementLRI: http: //www.lri.fr/~ihameli; CNRS, LIP, ENS Lyon : http: //www.ens-lyon.fr/~nschaban     

Spin polarization dependence of carrier effective mass in semiconductor structures: spintronic effective mass

We introduce the concept of a spintronic effective mass for spin-polarized carriers in semiconductor structures, which arises from the strong spin-polarization dependence of the renormalized effective mass in an interacting spin-polarized electron system. The majority-spin many-body effective mass renormalization differs by more than a factor of 2 at r(s) = 5 between the unpolarized and the fully polarized two-dimensional system, whereas the polarization dependence (approximately 15%) is more modest in three dimensions around metallic densities (r(s) approximately 5). The spin-polarization dependence of the carrier effective mass is of significance in various spintronic applications.     

Polaronic correction to the first excited electronic energy level in an anisotropic semiconductor quantum dot

Within the framework of second-order Rayleigh-Schrödinger perturbation theory, the polaronic correction to the first excited state energy of an electron in an quantum dot with anisotropic parabolic confinements is presented. Compared with isotropic confinements, anisotropic confinements will make the degeneracy of the excited states to be totally or partly lifted. On the basis of a three-dimensional Fröhlichs Hamiltonian with anisotropic confinements, the first excited state properties in two-dimensional quantum dots as well as quantum wells and wires can also be easily obtained by taking special limits. Calculations show that the first excited polaronic effect can be considerable in small quantum dots.     

Approximate calculation of electronic energy levels of axially symmetric quantum dot and quantum ring by using energy dependent effective mass

Calculations of electronic structures about the semiconductor quantum dot and the semiconductor quantum ring are presented in this paper. To reduce the calculation costs, for the quantum dot and the quantum ring, their simplified axially symmetric shapes are utilized in our analysis. The energy dependent effective mass is taken into account in solving the Schr?dinger equations in the single band effective mass approximation. The calculated results show that the energy dependent effective mass should be considered only for relatively small volume quantum dots or small quantum rings. For large size quantum materials, both the energy dependent effective mass and the parabolic effective mass can give the same results. The energy states and the effective masses of the quantum dot and the quantum ring as a function of geometric parameters are also discussed in detail.     

Influence of magnetic quantization on the effective mass in semiconductor superlattices

An attempt is made to study the effect of a quantizing magnetic field on the effective electron mass in a semiconductor superlattice at low temperatures. It is found on the basis of the tight-binding approximation, taking GaAs-Ga_1–x Al _x As an example, that the effective mass at the Fermi level depends on the magnetic quantum number due to the cosine dependence of the wave-vector in the superlattice direction. The mass also exhibits oscillatory features in the presence of magnetic quantization because of its dependence on Fermi energy which oscillates with changing magnetic field.     

Determination of electron effective mass from optical transition energy in InGaAs/InAlAs quantum wells

Nonparabolic effective mass of conduction subbands in InGaAs/InAlAs quantum wells (QWs), lattice-matched to InP, was quantitatively obtained by analyzing interband-optical transition spectra. Thickness of InGaAs well was 5.3, 9.4, and . Thickness of InAlAs barrier was about , and each QW was independent. Excellent agreement was obtained between experimental mass and theoretical mass predicted by Kane's three-level band theory on bulk InGaAs, in a wide energy range of from the bandedge. Method of experimental analysis on a relation between eigen energy and effective mass was described.     

半导体器件单粒子效应的加速器模拟实验

着重描述了应用加速器开展半导体器件的单粒子效应实验研究的方法。采用金箔散射法可以降低加速器束流几个量级,从而满足半导体器件单粒子效应实验的要求。研制的弱流质子束流测量系统和建立的质子注量均匀性测量方法解决了质子注量的准确测量问题。实验测得静态随机存取存储器的质子单粒子翻转截面为10-7 cm2·bit-11量级,单粒子翻转重离子LET阈值为4～8MeV·cm2/mg,重离子单粒子翻转饱和截面为10-7 cm2·bit-1量级。     

半导体器件单粒子效应的加速器模拟实验

 着重描述了应用加速器开展半导体器件的单粒子效应实验研究的方法。采用金箔散射法可以降低加速器束流几个量级，从而满足半导体器件单粒子效应实验的要求。研制的弱流质子束流测量系统和建立的质子注量均匀性测量方法解决了质子注量的准确测量问题。实验测得静态随机存取存储器的质子单粒子翻转截面为10^-7 cm²·bit^-11量级，单粒子翻转重离子LET阈值为4～8MeV·cm²/mg，重离子单粒子翻转饱和截面为10^-7 cm²·bit^-1量级。     

Electronic energy levels in semiconductor quantum wells and superlattices

We present the results of the calculations of some electronic properties of semiconductor quantum wells and superlattices. The review includes the superlattice band structure and the quantum well bound energy levels; the virtual bound states of semiconductor quantum wells and their influence on the energy spectrum of separate confinement heterostructures. Finally the perturbation of quantum well bound states and exciton states by a static electric field applied parallel to the growth axis is considered.