Selective Control of Electrons in Quantum Wires Formed by Highly Uniform Multiatomic Step Arrays on GaAs(331) Substrates

Abstract

Coherently aligned, multiatomic step arrays on GaAs(331) substrates generate a periodic array of conductive quantum wires in a two-dimensional (2D) electron gas. A small number of wires is selected by superimposing a constriction with independent side-gate control. By tuning the gate-voltage window, wires can be selected one by one. The resulting oscillatory current transmission provides a new functionality by switching between spatially separated electron channels. The wires are coupled by a small number of 2D electrons resulting in orders of magnitude reduced conductance perpendicular to the step edges. 73.61.Ey Semiconductor quantum wires (QWRs) with widths #100 nm have been widely investigated because of their unique electrical and optical properties, which have a profound impact on basic physics as well as device applications [1,2]. Novel in situ growth techniques allow for further developments in the fabrication of dense arrays of QWRs and dots with lateral periodicities of several 10 nm [3,4]. One major advantage in implementing these arrays in future device concepts is the increased current for multiple wires acting in parallel and the related averaging over conductance fluctuations due to defects to provide a well defined output signal [5]. In addition, a higher functionality can be achieved by selective electrical access to a distinct single QWR within the array, which allows for adding, subtracting, and coupling of one-dimensional (1D) conducting channels.Previous approaches for the formation of dense arrays of QWRs rely on the accumulation of monolayer high step and terrace arrays on vicinal substrates [4,6,7]. However, the high density of kinks and the meandering of the step edges, which cannot be avoided for monolayer high steps, are to a large extent transferred to the multiatomic step arrays (MSA) resulting in pronounced fluctuations in the height and a large number of step crossings limiting the effective length of the wires. The conductance along the wire array between two macroscopic contacts thus includes frequent transitions of carriers from wire to wire, which reduces the conductance and increases conductance fluctuations.We have recently fabricated highly uniform MSA, which are formed along ͓110͔ on high-index GaAs(331) surfaces by atomic-hydrogen-assisted molecular beam epitaxy [8]. The MSA exhibit a lateral periodicity of 250 nm and are straight over distances .10 mm with minimized height fluctuations. This high structural perfection is related to the microscopic surface structure, which is composed of (110) terraces and (111) steps of similar size, resulting in a higher stability against kink formation during step bunching [9]. The step height can be tuned in a wide range up to 13 nm by the substrate temperature while maintaining the lateral periodicity.We utilize the MSA as a template for the formation of dense arrays of conductive QWRs by transferring the periodic surface corrugation to the interface of Si modulation-doped GaAs͞Al 0.3 Ga 0.7 As heterostructures. The two-dimensional...

Atomic Hydrogen Induced Step Bunching on High-Index GaAs Substrates for Fabrication of Novel Quantum Wire and Quantum Dot Arrays by Molecular Beam Epitaxy

“…A novel functionality in transistor concepts based on lateral switching between individual conducting quantum wires has been demonstrated with the present structure. 15) The surface morphology observed on GaAs (311)A substrates after growth by atomic hydrogen assisted MBE is similar to that obtained by metalorganic vapor phase epitaxy (MOVPE), 16) thus indicating a similar mechanism for promotion of step bunching: 17) In homoepitaxial growth, step bunching occurs when the incorporation probability of adatoms at down-steps is larger than that at up-steps leading to an attractive interaction of step edges. What hinders preferential attachment of adatoms at down-steps are additional energy barriers at step edges (Schwoebel barriers 18) ) reflecting the migrating adatoms back to the terraces.…”

Dynamical nonlinearity in strained InGaAs (311)A sidewall quantum wires

“…[1][2][3] In order to overcome the technological bottleneck associated with the control of the nanostructure geometry not only along the epitaxial growth direction but also along the lateral directions, several growth techniques have been developed providing different kinds of QWRs with different shapes, strain patterns, structural, and electronic properties. 1,4 The disposability of good quality QWR has stimulated studies covering a wide range of physical processes, such as, lasing action, 3 transport processes, 5 strain effects in mismatched structures on the exciton and carrier dynamics, 1,4 kinetics of carrier recombination, 4,[6][7][8] and dot-wire coupling for spintronics. 9,10 In particular, different kinds of nonlinearity are expected in semiconductor QWRs.…”