Charge Conveyance and Nonlinear Acoustoelectric Phenomena for Intense Surface Acoustic Waves on a Semiconductor Quantum Well

Abstract

The combination of semiconductor quantum well structures and strongly piezoelectric crystals leads to a system in which surface acoustic waves with very large amplitudes can interact with charge carriers in the well. The surface acoustic wave induces a dynamic lateral superlattice potential in the plane of the quantum well which is strong enough to spatially break up a two-dimensional electron system into moving wires of trapped charge. This transition is manifested in an increase of the electron transport velocity with sound amplitude, eventually reaching the sound velocity. The sound absorption by the electron system then becomes governed by nonlinearities and is strongly reduced. We study the transition from the linear towards the strongly nonlinear regime of interaction and present a theoretical description of such phenomena in a 2D system. [S0031-9007(99)08621-4] PACS numbers: 73.50. Rb, 72.50. + b, 73.50.Fq Electron transport in semiconductor quantum well structures is usually governed by drift or diffusive current flow. Also ballistic carrier motion can be observed, provided that the size of the system is smaller than the mean-free path, ranging up to some hundred microns in very pure semiconductor material. Conceptually different from those mechanisms are transport phenomena based on momentum transfer from externally propagating entities to the electron system. Such "dragging" experiments have been studied in great detail in double electron layer systems [1], where internal "Coulomb friction" between the two layers causes the dragging force. "Photon drag" induced transport was observed for intersubband transitions of a quasi-two-dimensional electron system (2DES) [2]. Nagamune et al. [3] observed the effect of a dc current on the drift of optically generated carriers in a quantum well. Acoustic charge transport (ACT) has been investigated on a variety of different systems in view of possible device applications [4]. Using surface acoustic waves (SAW), Rocke et al. [5] showed that photogenerated electron-hole pairs in a semiconductor quantum well can be efficiently trapped in the moving lateral potential of the sound wave and then be reassembled into photonic signals. Recently, SAW have been combined with Coulomb blockade to drive single electrons through a quantum point contact [6]. In addition, the interaction between SAW and mobile charges in semiconductor layered structures has become an important method to study the dynamic conductivity of low-dimensional systems in quantum wells. These studies include the integer quantum Hall effect [7], the fractional quantum Hall effect [8], Fermi surfaces of composite Fermions around a half-filled Landau level [9], and commensurability effects caused by the lateral superlattice induced by a SAW [10]. These studies, however, were restricted to the small signal limit, i.e., to a regime where the presence of the lateral potential of a piezoelectric wave does not significantly modulate the carrier density in the quantum well.Here, we would like to report on experim...

Surface-acoustic-wave-induced carrier transport in quantum wires

“…6͑c͒ indicates that not all photogenerated carriers are transported within a single cycle of the SAW. A similar spreading of the detection time was observed recently by Rotter et al 17 during the unipolar transport of electrons by SAW's in two-dimensional electron gases for low SAW amplitudes. In the case of ambipolar transport investigated here, the presence of several pulses is attributed to the partial screening of the piezoelectric field by photogenerated carriers.…”

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

“…If one takes the liberal view of charge carriers in semiconductors as a fluid, or, more appropriately, as a gas (Hohenberg et al, 1964), the manipulation and transport of these charge carriers can represent an extension of what is presented in this review. Simple SAW can be used to transport charge carriers in semiconductor quantum well structures fabricated in thin-film GaAs=InGaAs atop LN (Rotter et al, 1999) to even form moving quantum dots as reported by Fletcher et al (2003), naturally leading to the use of such quantum dots in quantum computing by Furuta et al (2004) and even SAW-induced luminescence (Gell et al, 2006) in the quest to obtain a single-photon source. Aside from quantum applications, the ability to transport charge within semiconductors offers interesting applications in UV detectors using epitaxial ZnO thin films (Emanetoglu et al, 2004) and ZnO nanoparticles (Chivukula et al, 2010), and even solar cells (Yakovenko et al, 2009).…”

Radio frequency occupancy state control of a single nanowire quantum dot

“…For axial NW based QDs key experiments including ultra-bright single photon emission [9], quasi-static charge state control [10] and optical initialization of spin states [11] clearly underpinned the large potential of these systems. Radio frequency surface acoustic waves (SAWs) represent a particularly attractive and powerful tool to probe and dynamically control charge excitations in semiconductor heterostructure including Quantum Hall systems [12,13,14], charge transport in oneand two-dimensional electron channels [15,16], transport of charges [17,18,19], spins [20] or dipolar excitons [21] and precisely timed carrier injection into QDs for low-jitter single photon emission [22,23,24,25]. Recently, these concepts have been transferred to intrinsic nanowires (NWs) [26] and nanotubes [27] and NWs containing complex radial and axial heterostructures [28,29,30].…”