Impurity compensation and band-gap renormalization in double-quantum-wires

We investigate the band-gap renormalization due to electron-electron interaction in the n-type doped GaAs-based double-quantum-wire systems. Electron self-energy is calculated using the leading-order perturbation theory (GW) within the full random-phase-approximation (RPA). We include the impurity effects through Mermin expression and show that decreasing the spacing in double-wire system can compensate partly the undesirable effect of impurities on the band-gap renormalization. Therefore, it is possible to offset the effect of impurity in related devices and to adjust the band-gap. We also, apply a constant electric field to one of the wires. It is shown that the change of the band-gap renormalization in the other wire will be insignificant if the drift velocity does not exceed Fermi velocity.     

Simplified calculations of band-gap renormalization in quantum-wells

Non-linear optical properties of photoexcited semiconductor quantum-wells are of interest because of their opto-electronic device application possibilities. Many-body interactions of the optically created electrons and holes lead to the band-gap renormalization which in turn determines the absorption spectra of such systems. We employ a simplified approach to calculate the band-gap renormalization in quantum-well systems by considering the interaction of a single electron-hole pair with the collective excitations (plasmons). This method neglects the exchange-correlation effects but fully accounts for the Coulomb-hole term in the single-particle self-energy. We demonstrate that the density, temperature, and well-width dependence of the band-gap renormalization for GaAs quantum-wells within our model is in good agreement with the experimental results.     

A survey of band-gap renormalization in quantum well structures

The band-gap renormalization at finite temperatures in quantum wells is calculated from the dynamical self energy. Sublevel formfactors and non-diagonal screening are taken into account. In order to compare with these calculations, the chemical potential and the carrier density in the active layer of a quantum-well laser diode are determined experimentally based on a novel non-spectroscopic method.     

GaAs中带填充效应与带隙重整化效应的竞争

采用时间分辨线偏振光抽运-探测光谱研究常温下本征GaAs中载流子弛豫动力学,观察到饱和吸收和吸收增强现象.发现载流子浓度为2×10¹⁷ cm^-3, 探测光子能量小于1.549 eV时,饱和吸收现象比较明显,反之,有明显的吸收增强现象出现.载流子浓度大于7×10¹⁶ cm^-3的范围内,吸收增强信号随时间增大没有减弱的趋势,反而有继续增强的趋势.理论上,考虑带填充效应和带隙重整化效应的竞争,模拟得到与实验谱线相符合的结果. 关键词： 飞秒抽运-探测光谱 带填充效应 带隙重整化效应 载流子寿命     

The renormalization group and the ϵ expansion

The modern formulation of the renormalization group is explained for both critical phenomena in classical statistical mechanics and quantum field theory. The expansion in ? = 4?d is explained [d is the dimension of space (statistical mechanics) or space-time (quantum field theory)]. The emphasis is on principles, not particular applications. Sections 1–8 provide a self-contained introduction at a fairly elementary level to the statistical mechanical theory. No background is required except for some prior experience with diagrams. In particular, a diagrammatic approximation to an exact renormalization group equation is presented in sections 4 and 5; sections 6–8 include the approximate renormalization group recursion formula and the Feyman graph method for calculating exponents. Sections 10–13 go deeper into renormalization group theory (section 9 presents a calculation of anomalous dimensions). The equivalence of quantum field theory and classical statistical mechanics near the critical point is established in section 10; sections 11–13 concern problems common to both subjects. Specific field theoretic references assume some background in quantum field theory. An exact renormalization group equation is presented in section 11; sections 12 and 13 concern fundamental topological questions.     

Operator product expansion in the Weinberg renormalization scheme and factorization

The operator product expansion (OPE) is derived in the framework of the Weinberg renormalization 3cheme [1]. The coefficient functions of the OPE are explicitly expressed in terms of certain Green functions. The OPE provides factorization, i.e. separation of large and small distances.     

The thermal expansion of GaP below room temperature

The thermal expansion of GaP is estimated theoretically as a function of temperature using the experimental pressure dependence of elastic stiffness constants and phonon frequencies. The numerical values of the linear expansion coefficient and the Grüneisen constant do not become negative at low temperatures, contrary to other tetrahedrally bonded covalent solids. This positive thermal expansion of GaP at low temperatures is closely connected with the small values of the transverse acoustical mode Grüneisen parameter and with the large value of the metallic phase transition pressure from the linear correlation obtained by Weinstein.     

Non-diffractive Pomeron renormalization,multiplicities, and the topological expansion

The renormalization of the Pomeron due to nondiffractive K$\text{K}$, B$\text{B}$ production thresholds is considered within a simple generalization of the Chew-Rosenzweig multiperipheral realization of Veneziano's topological expansion. The results are consistent with the existence of both the “low-energy” bare Pomeron with intercept $\text{α=0.85}$ and Gribov bare Pomeron with intercept above one. The vacuum exchange part of 2σ_KN?σ_πN basically rises with energy. Qualitatively correct features of shrinkage and breaks of $\text{d}\text{σ}\text{d}\text{t}$ emerge. The multiplicity of product clusters (n) increases with energy faster than 1ns and agrees with experiment for an average number of particles per cluster of 3–4. Independently of our model the Harari-Freund multiperipheral realization of the topological expansion is shown to be in serious difficulty with multiplicities, requiring around 20 particles per cluster.     

Plasma expansion into a vacuum

The charge separation effects in the collisionless plasma expansion into a vacuum are studied in great detail. Accurate results are obtained concerning the structure of the ion front, the resultant ion energy spectrum, and more specifically the maximum ion energy. These are of crucial importance for the interpretation of recent experiments, where high-energy ion jets were produced from short pulse interaction with solid targets.     

Plasma acceleration by area expansion

As the area of a plasma increases, the plasma can accelerate smoothly from subsonic to supersonic velocity. The singularity which ordinarily occurs at the sonic velocity is resolved not by charge separation, as is the case for a sheath, but rather by a zero in the numerator at the same spatial position as the zero in the denominator, the sonic point. That is, at the sonic point, the acceleration due to expansion just cancels out the deceleration due to ion and electron neutral collisions. It turns out that, in this configuration, the plasma can accelerate to about three times the ion sound speed. The electron temperature is determined by the geometry, gas species, and, mostly, by the gas pressure. Applications to the production of a stream of neutrals for etching, and to space plasma propulsion are discussed     

Electrophysical characteristics of MIS structures based on graded band-gap MBE HgCdTe with grown in situ CdTe as a dielectric

Capacitance-voltage characteristics of MIS structures based on graded band-gap heteroepitaxial HgCdTe (x = 0.22–0.23 and 0.32–0.36) with grown in situ CdTe as a passivating coating are examined. The average surface-state densities as well as mobile- and fixed-charge densities are determined for the HgCdTe/CdTe, HgCdTe/CdTe–SiO₂–Si₃N₄, and HgCdTe/CdTe–ZnTe systems. It is shown that grown in situ CdTe forms a fairly qualitative interface, and deposition of additional SiO₂–Si₃N₄ and ZnTe layers makes it possible to control the electric strength and charges in the dielectric used.     

Electrostatic model of band-gap renormalization and the photoluminescence line shape in a GaAs/AlGaAs two-dimensional layer at a high excitation level

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 Al_xGa_1?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.     

Three-dimensional massive scalar field theory and the derivative expansion of the renormalization group

We show that non-perturbative fixed points of the exact renormalization group, their perturbations and corresponding massive field theories can all be determined directly in the continuum — without using bare actions or any tuning procedure. As an example, we estimate the universal couplings of the non-perturbative three-dimensional one-component massive scalar field theory in the Ising model universality class, by using a derivative expansion (and no other approximation). These are compared to the recent results from other methods. At order derivative-squared approximation, the four-point coupling at zero momentum is better determined by other methods, but factoring this out appropriately, all our other results are in very close agreement with the most powerful of these methods. In addition we provide for the first time, estimates of the n-point couplings at zero momentum, with n = 12, 14, and the order momentum-squared parts with n = 2,…, 10.