Single electron states in lateral surface superlattice

Solid-State Electronics, 1996

We report on the motion of two-dimensional electrons in a magnetic field which is periodic on the scale of a few hundred nanometres. Such a system exhibits novel magnetoresistance oscillations that we unambiguously identify as due to a commensurability effect between the period of the magnetic field and the diameter of the cyclotron orbit. We find that a semiclassical picture of electron motion can quantitatively describe all of the observed experimental features. We also propose methods of optimizing the effects of the magnetic modulation in hybrid semiconductor-superconductor devices.

Physical Review B, 1990

A terminated Kronig-Penney-like model is proposed for studying electronic surface states in compositional {potential-modulation) and in effective-mass {mass-modulation) superlattices. The existence of surface states in the minigaps of both types of superlattices is shown explicitly and their properties are discussed.

Physical Review Letters, 2004

We report on magnetotransport of a two-dimensional electron system (2DES), located 32 nm below the surface, with a surface superlattice gate structure of periodicity 39 nm imposing a periodic modulation of its potential. For low Landau level fillings ν, the diagonal resistivity displays a rich pattern of fluctuations, even though the disorder dominates over the periodic modulation. Theoretical arguments based on the combined effects of the long-wavelength, strong disorder and the short-wavelength, weak periodic modulation present in the 2DES qualitatively explain the data.

Physical Review B (Condensed Matter and Materials Physics), 2014

We found that the transitions between delocalized electronic states in quantum-dot superlattices with smaller size dispersion can account for higher electron mobility. In particular, we solved for the quantum states of a twodimensional quantum-dot (QD) superlattice using a one-electron approximation. Electron transport properties were studied by considering hopping transitions among coupled delocalized electronic states. Molecular dynamics simulations were employed to introduce disorders in superlattice configurations as a function of QD size and size dispersion for calculation of electron mobility. The interparticle spacing, size, and temperature dependence of the electron mobility can be well explained within the framework of our analysis.

Surface Science, 1996

A laterally modulated gate electrode was evaporated on high-mobility two-dimensional electron systems embedded in ~G a A s h e t e r o ~. At mmafl lateral potential modulation of square geometry, as induced by a suitable gate voltage commensurabKity oscillations dominate the low-field magnetoresistanc¢, in~cating the oscillating width of the Landau bands. For increasing potential modulation the width of the Landau bands increases, the band contributions to the conductivity are suppressed, and scattering conductivity dominates. ~ reflects progress in the resolution of the internal structure of a Landau band.

Physics Letters A, 2000

A one-dimensional model of electron diffusion in a superlattice is examined here. The analytical dependence of the diffusion coefficient on the applied electric field is determined. We show that the applied field suppresses diffusion and that diffusion is absent at the electric field strengths corresponding to electrophonon resonances. q 2000 Elsevier Science B.V. All rights reserved. ) Corresponding author. Tel.: q1 201 216 5651; fax: q1 201 216 5638. Ž .

Physical Review B, 1994

We have calculated the piezoelectric coupling between a two-dimensional electron gas and the stress field due to a lateral surface superlattice, a periodic striped gate. The stress is assumed to arise from differential contraction between the metal gate and semiconductor. The piezoelectric potential is several times larger than the deformation potential and generally gives the dominant coupling. It depends on the orientation of the device and vanishes on a (100) surface if current flows parallel to a crystallographic axis. Most devices, however, are fabricated parallel to {011} cleavage planes and in this case the piezoelectric potential is at a maximum. We also discuss different elastic models for the gate and sources of screening, which include the partlyoccupied donors in a typical GaAs-AlGaAs heterostructure.

Journal of Applied Physics, 2003

A dispersion relation for an electron in a two-layer ͑and also multilayer͒ quantum well ͑QW͒ is formed as a result of a certain combination of initial dispersion relations for each of the forming layers. Such a combination can be used to engineer new dispersion relations with desirable properties. The same relates to a two-dimensional electron gas ͑2DEG͒ induced in a multilayer medium. In this study, we consider first such a 2DEG in a specific two-layer structure where a superlattice ͑SL͒ plays the role of the second half-infinite layer, and electrons with large wave numbers along the SL vector spread from the first ordinary QW layer to this SL. As a result of such a quantum ͑dynamic͒ real-space transfer, electrons become heavier, and the dispersion relation achieves an additional negative effective mass ͑NEM͒ section. Such NEM dispersion relations were studied for several different material systems, including the two most interesting three-material systems: ͑1͒ an isomorphic Al 0.15 Ga 0.85 As//GaAs/Al 0.5 Ga 0.5 As structure and ͑2͒ a strained In 0.53 Ga 0.47 As//In x Ga 1Ϫx As/In y Al 1Ϫy As structure (xϾ0.53, yϽ0.52) with a strain-balanced In x Ga 1Ϫx As/In y Al 1Ϫy As SL. Most of the results were verified using a simplified 1D model, but some of them were verified by more complicated 2D-model calculations.

Surface Science Reports, 2002

The existence and properties of localised electronic states are described in binary (two layers per period) and polytype (multiple layers per period) semiconductor superlattices. Special attention is paid to surface effects, due to the superlattice potential termination by a clad layer, and the resulting Tamm-like surface states localised at the superlattice/clad-layer interface. The effect of the Bragg con®nement of electrons in coupled superlattices, particularly the formation of above-barrier bound states at the junction of superlattices or the spacer layer embedded in a superlattice, is also discussed. Based on peculiar properties of localised superlattices states, with respect to extended miniband states, their importance for both the fundamental research and various device applications is stressed out. The most frequently used Kronig±Penney-like approaches within the framework of effective-mass and envelope-function approximation, namely, the direct-matching procedure and the transfermatrix technique, are described for bulk-and surface-electronic-structure calculations of terminated binary and polytype superlattices, as well as for coupled superlattices. Comparison of the results with experimental data and/ or more advanced computations indicates that these simple models are versatile and accurate (within their domain of validity), when applied to AlGaAs-based heterostructures. Two Green-function techniques, one based on the combined factorisation and Wronskian methods, and the other on the interface-response theory, are presented for the purpose of density-of-states analysis. For terminated binary GaAs/AlGaAs superlattices, an appropriate choice of the superlattice and clad-layer parameters, as well as the surface location within the superlattice period, enables a surface state with desired energy position inside the minigap, and required extension into the superlattice bulk, to be achieved. Introduction of additional layers into the superlattice sequence, resulting in a polytype superlattice, offers a further means of in¯uencing the energies and localisation properties of surface states, but, more importantly, creates an opportunity for surface states to occur under classical Shockley conditions, which is not possible in binary superlattices, where only Tamm-like surface states can exist. The Surface Science Reports 47 (2002) 93±196

2012

In the present thesis we implement a simple numerical method to solve a onedimensional time-independent Schrödinger equation in any arbitrary periodic potential. We apply this method to study the energy band structure, the Bloch wavefunctions and the 1D-density of states of a simple 1D-superlattice model. The results obtained for this model exhibit nontrivial features of real hetero-crystalline superlattices. Several of these features can be understood in terms of a one-band effective mass model which is one of the simplest electronic-structure approaches for superlattices. This approach is then applied to obtain the energies of the conduction electrons in a model for a perfect GaAs/Ga 0.8 Al 0.2 As superlattice and its 3D-density of states.