Large Anisotropy of Electron Mobilities in Laterally Modulated Two-Dimensional Systems Grown on the (775)B-Oriented GaAs Substrates by Molecular Beam Epitaxy

Abstract

We have investigated the transport properties of electron gas in a GaAs/(GaAs)4(AlAs)2 quantum well with a regularly corrugated upper interface formed on (775)B-oriented GaAs substrates by molecular beam epitaxy (MBE). The electron mobility perpendicular to the corrugation (µ⊥) was suppressed to 1/70th of that parallel to the corrugation (µ∥) for a quantum well with a well width of L w=5 nm at a temperature of 10 K, and µ⊥ with a thin L w of 5 nm monotonically increased with increasing temperature (10–300 K). These results suggest that the lateral potential induced by the thickness modulation is so strong in the nominally 5-nm-thick quantum well that the electron gas has a quasi-one-dimensional nature.

Pseudo-Band-Structure in a Disordered Quantum Wire Array

“…4,5) The mobility in the quantum wire direction is 30 -70 times larger than that in the perpendicular direction. An opening-up of a band gap at the zone boundary due to a periodic potential 6) was suggested as the origin.…”

“…[1][2][3][4] This was achieved by the growth of a corrugated GaAs quantum well with a zigzag shape on top of a flat AlAs surface and covered by an AlAs barrier layer. Actually, zigzag corrugations have some fluctuations.…”

“…An opening-up of a band gap at the zone boundary due to a periodic potential 6) was suggested as the origin. 4) However, a self-consistent calculation of electronic states showed that the gap is not so appreciable and the Fermi wave number does not touch the zone boundary, giving almost circularly symmetric dispersion. 7) As a result, the band structure effects like anisotropic effective masses cannot explain the observed behavior.…”

Pseudo-Band-Structure of Disordered Lateral Superlattice in Magnetic Field

“…[1][2][3][4] Because the well width of a GaAs layer changes periodically, it was expected that this superlattice forms an extremely high density quantum-wire array. Actually, zigzag corrugations have some fluctuations 1,2) and the Bragg peak spreads in the wave-vector space.…”

“…4,7) Band-gap opening at the zone boundary due to periodic potential 8) was suggested as the origin of this anisotropy. 4) However, a self-consistent calculation of electronic states showed that the gap is not so appreciable and the Fermi wave-number does not reach the zone boundary, giving almost circularly symmetric dispersion. 9) As a result, the band structure cannot be the origin of the observed huge anisotropy.…”