Acoustically Driven Storage of Light in a Quantum Well

Abstract

The strong piezoelectric fields accompanying a surface acoustic wave on a semiconductor quantum well structure are employed to dissociate optically generated excitons and efficiently trap the created electron hole pairs in the moving lateral potential superlattice of the sound wave. The resulting spatial separation of the photogenerated ambipolar charges leads to an increase of the radiative lifetime by orders of magnitude as compared to the unperturbed excitons. External and deliberate screening of the lateral piezoelectric fields triggers radiative recombination after very long storage times at a remote location on the sample. [S0031-9007(97)03194-3] PACS numbers: 73.50. Rb, 77.65.Dq, 78.20.Hp, 78.55.Cr The dynamics of photogenerated carriers in semiconductor structures with reduced dimensionality has been the subject of intensive investigations in recent years [1,2]. State-of-the-art band-gap engineering technologies enable us to tailor low-dimensional semiconductor systems with desirable optoelectronic properties and study the fundamental aspects of carrier dynamics. This has increased tremendously our fundamental understanding of the dynamic properties of artificial semiconductor structures and has also resulted in a wide range of novel devices such as quantum well lasers, modulators, and detectors, as well as all-optical switches. Nevertheless, the bulk band structure of semiconductors seems to dominate optoelectronic properties since the strength of interband transitions is largely governed by the atomiclike Bloch parts of the wave function [3]. Thus it appears at first glance unavoidable that strong interband optical transitions are linked to direct band-gap semiconductors with short radiative lifetimes such as GaAs, whereas long radiative lifetimes of photogenerated carriers imply utilization of semiconductors with indirect band gaps such as Si and correspondingly reduced interband absorption. Initial attempts to employ band-gap engineering in order to combine strong interband absorption with long radiative lifetimes have focused on so-called doping superlattices [4]. There, alternate n and p doping along the growth direction is utilized to combine a direct gap in momentum space with an indirect gap in real space which causes a spatial separation of photogenerated electron-hole ͑e-h͒ pairs and hence considerably prolonged lifetimes.Here, we introduce a new way of band-gap engineering in which we expose a semiconductor quantum well of a direct gap material to a moving potential superlattice modulated in the plane of the well. We show that the confinement of photogenerated e-h pairs to two dimensions, together with the moving lateral superlattice, allows reversible charge separation [5]. We demonstrate that the combination of both the advantages of strong interband absorption and extremely long lifetimes of the optical excitations is achieved without affecting the superior optical quality of the quantum well material.The spatial separation of the electron-hole pairs is achieved via the piezoelectric pot...

Surface acoustic wave-driven planar light-emitting device

“…Two different regimes can be observed: an increase in EL intensity up to P RF ∼ −5 dBm followed by an abrupt suppression of the emission. The latter regime can be linked to the spatial separation between electrons and holes induced by the SAW electric field [15,16], which is also observed in the PL measurements [18] (filled triangles in Fig 3(a)). Remarkably, the increase in intensity observed for P RF < −5 dBm is unique to the EL measurements as it was not observed in the PL data.…”

Focusing of surface-acoustic-wave fields on (100) GaAs surfaces

“…4,5 There has been renewed interest in SAWs since the demonstration that they can be applied to dynamically modulate the electronic properties of GaAs-based low-dimensional semiconductor structures like photonic crystals, 6 microresonators, 7,8 quantum wells, 9-11 quantum wires, 12 and quantum dots. 13 The traveling SAW fields in these structures have been used to transport electron-hole pairs 9,12,14 and spin excitation. 15 Many of the applications mentioned above require a strong SAW beam concentrated on a small area of the sample surface.…”

Pressure-driven flow in open fluidic channels

“…In principle, the geometry of the 'reaction' chamber could be adjusted such that the mixing occurs even more homogeneously as in the experiment shown here. used in the recent past to study the interaction between SAWs and mobile electrons and holes in semiconductor layered systems (14) to acoustically move those charges along the plane of a semiconductor quantum well (15). For our microfluidic processor, direct acoustoelectric coupling can also be exploited for charged or polarizable media.…”