Population inversion in narrow-gap heterostructures due to the interband tunneling

The process of interband tunneling in a heterostructure with a wide-gap barrier between two layers of narrow-gap doped semiconductors is investigated. The tunneling probability, intraband and interband current components, and non-equilibrium carrier concentration are calculated using the transfer matrix method and a Dirac-like model for lead chalcogenide-type heterostructures. It is shown that the generation of electron-hole pairs due to interband tunneling may produce a population inversion and laser generation in the near-barrier region.     

Optical spin resonances due to structure and bulk inversion asymmetry in heterostructures

Optical spin–flip excitations in the conduction band of III–V semiconductor heterostructures are considered theoretically taking into account structure inversion asymmetry (SIA) and bulk inversion asymmetry (BIA) of such systems. Possible spin transitions both in the absence of a magnetic field (B=0) as well as in the presence of a magnetic field B parallel to the growth direction [0 0 1] are investigated. The theory is based on the three-level model of the narrow-gap band structure including the BIA [Phys. Rev. 100 (1955) 580] and SIA [J. Phys. C. 17 (1984) 6039] contributions. We show in particular that the SIA mechanism not only results in the Bychkov–Rashba spin splitting at B=0 but it also gives rise to the possibility of optical transitions between the two spin-split energy branches.     

Giant population inversion of hot electrons in GaAs/AlAs type heterostructures with quantum wells

The heating of electrons in an Al_xGa_1−x As/GaAs (x>0.42) heterostructure in a lateral (directed along the heterointerfaces) electric field is studied. Population inversion on the size-quantization subbands of the Γ valley of GaAs and a giant population inversion between the X-valley states of Al_xGa_1−x As and Γ-valley states of GaAs are predicted. The possibility of using these inversions for achieving stimulated IR emission is discussed. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 73–77 (10 July 1998)     

Effects of inversion asymmetry on electron-nuclear spin coupling in semiconductor heterostructures: possible role of spin-orbit interactions

We show that electron-nuclear spin coupling in semiconductor heterostructures is strongly modified by their potential inversion asymmetry. This is demonstrated in a GaAs quantum well, where we observe that the current-induced nuclear spin polarization at Landau-level filling factor nu=2/3 is completely suppressed when the quantum well is made largely asymmetric with gate voltages. Furthermore, we find that the nuclear spin relaxation rate is also modified by the potential asymmetry. These findings strongly suggest that even a very weak Rashba spin-orbit interaction can play a dominant role in determining the electron-nuclear spin coupling.     

Interfaces in perovskite heterostructures

Recent advances in film synthesis have made it possible to investigate the properties of well-controlled interfaces in perovskite metal-oxides. A review of published experimental data and computational results indicate that so far most interfaces that have been analyzed in ferroelectric materials—while necessary to impose large lattice strain on the polar material—contribute little to the ferroelectricity and may instead be detrimental to the desired properties. In contrast, a very different situation arises at interfaces that show changes in the electronic configuration as a consequence of a compositional discontinuity. Data is shown for LaMnO₃/SrTiO₃ superlattices as an example of electronic effects that produce enhanced properties, further illustrating the richness of interfacial properties that can be obtained at interfaces (as shown in numerous published results for different but related interfaces).     

尖端放电中的极性效应

基于气体击穿的汤森德理论和流注理论定性地分析了一个尖端放电演示实验中极板的极性对放电过程的影响．指出了尖端接电源的阳极时击穿电压比接阴极时低的原因．     

Size distribution in quantum-dot heterostructures

The size distribution functions for nanoclusters in quantum-dot heterostructures are calculated within the LSW theory. The most common numerical characteristics are calculated for these distributions. The corresponding size distribution functions are selected by means of comparison of the calculated dispersion and mean square deviation with the experimental values obtained for real quantum-dot heterostructures. The regularities of variations of certain numerical characteristics as a function of growth mechanism are shown for different distributions, from the well-known modified Wagner and Lifshitz-Slezov distributions to the distributions proposed in this work. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 59–66, April, 2006.     

Topological transitions in size-quantized heterostructures

An exact solution is obtained to the problem of the spectrum of holes, described by the Luttinger Hamiltonian, in a quantum well of finite depth under arbitrary uniaxial stresses in the well and the barrier. Conditions for the topological transitions accompanied by the variation in the connectivity of the isoenergetic surface are found. It is shown that, for certain values of model parameters, the effective mass of holes in the ground-state subband of size quantization becomes negative.     

Magnetic polarons in semimagnetic-semiconductor-based heterostructures

Specific features in the behavior of localized magnetic polarons formed under optical excitation in heterostructures based on semimagnetic semiconductors are considered. These features are due to the strong anisotropy of the hole g factor in low-dimensional systems based on zincblende crystals. The anisotropy is due to the strong spin-orbit coupling in the valence band which, in quantum confinement conditions, results in quadrupole splitting of the hole spin levels. The g factor anisotropy manifests itself in a strong anisotropy of the magnetic and magneto-optical characteristics of localized magnetic polarons. Fiz. Tverd. Tela (St. Petersburg) 40, 800–802 (May 1998)     

钙钛矿氧化物异质结的光电特性研究进展

光与物质相互作用可以产生各种光学现象,其中光电效应是非常重要的现象之一.文中集中回顾了文章作者在钙钛矿氧化物异质结的光电效应研究中的进展.在钙钛矿氧化物异质结中,分别观测到了传统的纵向光电效应和反常的横向光电效应,并通过对含时的漂移-扩散方程的自洽求解,从理论上分别揭示了钙钛矿氧化物异质结纵向和横向光电效应的动态过程.文章首先介绍了钙钛矿氧化物异质结纵向光电效应的研究进展,接着概述了钙钛矿氧化物异质结横向光电效应研究的进展.最后对氧化物异质结的纵向和横向光电效应的潜在应用前景进行展望.     

钙钛矿氧化物异质结的光电特性研究进展

光与物质相互作用可以产生各种光学现象,其中光电效应是非常重要的现象之一.文中集中回顾了文章作者在钙钛矿氧化物异质结的光电效应研究中的进展.在钙钛矿氧化物异质结中,分别观测到了传统的纵向光电效应和反常的横向光电效应,并通过对含时的漂移-扩散方程的自洽求解,从理论上分别揭示了钙钛矿氧化物异质结纵向和横向光电效应的动态过程.文章首先介绍了钙钛矿氧化物异质结纵向光电效应的研究进展,接着概述了钙钛矿氧化物异质结横向光电效应研究的进展.最后对氧化物异质结的纵向和横向光电效应的潜在应用前景进行展望.     

Charge-carrier separation in rolled heterostructures

The strains in rolled InAs/GaAs heterostructures of nanometer sizes are calculated. It is shown that the strain distributions in nanotubes (structures with coherently bounded rolls) and nanoscrolls are essentially different, resulting in different energy spectra of the charge carriers. Photogenerated electrons and holes in nanotubes can be spatially separated across the wall width.     

Gain saturation in quantum-well heterostructures

The effect of radiation gain saturation in quantum-well heretostructures was investigated in the system GaAs—AlGaAs with regard to the spectral line broadening and the type of radiation polarization. Belarusian State University, 4, F. Skorina Ave., Minsk, 220050, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 797–800, November–December, 1997.     

Quantum pumping in helimagnet heterostructures

Spin-dependent diffraction occurs in helimagnet-related transport processes. In this work, we investigated quantum pumping properties in the normal-metal/helimagnet/normal-metal heterostructure driven by two out of phase time-dependent gate potentials. At the condition when one of the diffracted beams goes out of the horizon the pumped charge and spin currents demonstrate sharp dips and rises as a function of the helimagnet spiral wave vector q. At small and large q?s, the transmission and pumping properties approach the behaviors of a ferromagnet and an insulating barrier, respectively. For different helimagnet spiral periods, the diffracted angles are different. As a result, the pumped charge and spin currents demonstrate multiple maximal and minimal peaks as a function of q, hence, sensitively depend on the helimagnet spin configuration. All the pumping properties can be interpreted by the quantum gate-switching mechanisms.     

Graphene based heterostructures

The two dimensional charge carriers in monolayer and bilayer graphene are described by massless and massive chiral Dirac Hamiltonians, respectively. These two-dimensional materials are predicted to exhibit a wide range of behavior, etc. However, graphene devices on a typical three-dimensional insulating substrates such as SiO₂ are highly disordered, exhibiting characteristics that are far inferior to the expected intrinsic properties of graphene. We have developed a novel technique for substrate engineering of graphene devices using layered dielectric materials to build graphene based vertical heterostructures. We employ hBN, an insulating isomorph of graphite, as a substrate and gate dielectric for graphene electronics. In this review, we describe the fabrication and characterization of high-quality exfoliated mono- and bilayer graphene devices on single-crystal hBN substrates, using a mechanical transfer process. Graphene devices on hBN substrates have mobilities and carrier inhomogeneities that are almost an order of magnitude better than devices on SiO₂. We use the enhanced mobility of electrons in hBN supported graphene to investigate the effects of electronic interactions. We find that interactions drive spontaneous breaking of the emergent SU(4) symmetry of the graphene Landau levels, leading to a variety of non-trivial integer and fractional quantum Hall states. The ability to assemble crystalline layered materials in a controlled way permits the fabrication of graphene devices on other promising dielectrics and allows for the realization of more complex graphene heterostructures.     

Electron-interface-phonon interaction in wurtzite multilayer heterostructures

Within the framework of the dielectric-continuum model and Loudon's uniaxial crystal model, the equation of motion for the p-polarization field in a wurtzite quasi-two-dimensional multilayer heterostructure is solved exactly for the interface optical-phonon modes. The eigenvector, the dispersion relation and the electron-interface-phonon interaction Fröhlich-like Hamiltonian are derived using the transfer-matrix method. The analytical formulas are universal and can be applied to single heterojunctions, single/multiple quantum wells and superlattices.