Sub-nanosecond acousto-electric carrier redistribution dynamics and transport in polytypic GaAs nanowires

Abstract

The authors report on a combined structural, optical and acousto-electric study of polytypic GaAs nanowires. Two types of nanowires with different zincblende and wurtzite crystal phase mixing are identified by transmission electron microscopy and photoluminescence spectroscopy. The nanowires exhibit characteristic recombination channels which are assigned to different types of spatially direct recombination (electron and hole within the same crystal phase segment) and spatially indirect recombination (electron and holes localized in different segments). Contact-free acousto-optoelectric spectroscopy is employed to resolve spatiotemporal charge carrier dynamics between different recombination channels induced by a piezoelectric surface acoustic wave. The observed suppression of the emission and its dynamic temporal modulation shows unambiguous fingerprints of the local bandedge variations induced by the crystal phase mixing. A nanowire, which exhibits a variation from a near-pristine zinc blende crystal structure to a highly mixed crystal phase, shows a clear dependence on the propagation direction of the acoustic wave. In contrast, no pronounced directionality is found for a nanowire with an extended near-pristine zincblende segment. The experimental findings are corroborated by solving the drift and diffusion equations of electrons and holes induced by the surface acoustic wave. The key characteristics observed in our experimental data are well reproduced in the numerical simulations by assuming two general bandedge modulations and realistic parameters for the bandedge discontinuities and transport mobilities of electrons and holes. This evidences that even all relevant physical processes are accounted for in the model.

Sb‐Mediated Tuning of Growth‐ and Exciton Dynamics in Entirely Catalyst‐Free GaAsSb Nanowires

“…Such ZB/WZ/ZB crystal interfaces are well known to be characterized by a staggered band lineup for GaAs‐ and GaSb‐materials alike, [ 60,61 ] which induces a type‐II excitonic transition, as verified comprehensively in refs. [62,63]. As illustrated in Figure c, from a structural point of view, recombination takes, therefore, place essentially between electrons confined in ZB domains with spatially separated holes confined at fixed energy level in adjacent twin defects.…”

“…As illustrated in Figure 6c, from a structural point of view, recombination takes, therefore, place essentially between electrons confined in ZB domains with spatially separated holes confined at fixed energy level in adjacent twin defects. [62,63] For low and intermediate Sb-content, the twin domain segment length is relatively short, ≈3.3 ± 0.11 nm (Sb-BEP = 1 × 10 −7 mbar) and 6.7 ± 0.44 nm (Sb-BEP = 3 × 10 −7 mbar) (cf. Figure 4), and hence electrons localized in the ZB domains are relatively strongly confined.…”

Large Tolerance of Lasing Properties to Impurity Defects in GaAs(Sb)‐AlGaAs Core‐Shell Nanowire Lasers

“…[61] Such twin domains induce type-II interfaces and are well known to cause a slight redshift in the PL emission, regardless of the growth technique and mode used. [32,61,73] To provide an estimate of the intrinsic carrier density of the undoped NW, we fit the emission spectrum at lowest pump fluence to extract an upper bound of the intrinsic n-type carrier density of ≈4(± 1) × 10 17 cm −3 . By increasing the pump fluence above a certain threshold (>3.0 μJ cm −2 ), we observe a sharp peak at 1.50 eV that arises with a significantly higher intensity than the spontaneous emission background.…”

Influence of confined acoustic phonons on the acousto-electric field in doped semiconductor superlattices

“…The optical properties have been investigated in quantum wells and quantum wires [1,2,14], and the acoustic properties have been researched in two-dimensional systems [3,4]. The acousto-electric (AE) effect is based on the electric current generated by a longitudinal acoustic wave and has been taken into account in [5,6,11]. In addition, the effect of the phonon confinement is remarkable and should be taken into consideration for kinetic effect in low-dimensional systems.…”