Inducing a direct-to-pseudodirect bandgap transition in wurtzite GaAs nanowires with uniaxial stress

Abstract

Many efficient light-emitting devices and photodetectors are based on semiconductors with, respectively, a direct or indirect bandgap configuration. The less known pseudodirect bandgap configuration can be found in wurtzite (WZ) semiconductors: here electron and hole wave-functions overlap strongly but optical transitions between these states are impaired by symmetry. Switching between bandgap configurations would enable novel photonic applications but large anisotropic strain is normally needed to induce such band structure transitions. Here we show that the luminescence of WZ GaAs nanowires can be switched on and off, by inducing a reversible direct-to-pseudodirect band structure transition, under the influence of a small uniaxial stress. For the first time, we clarify the band structure of WZ GaAs, providing a conclusive picture of the energy and symmetry of the electronic states. We envisage a new generation of devices that can simultaneously serve as efficient light emitters and photodetectors by leveraging the strain degree of freedom.

Strain-engineered direct-indirect band gap transition and its mechanism in two-dimensional phosphorene

“…This detailed analysis on the direct-indirect band gap transition is crucial for optical applications of phosphorene. For example, Peng and Copple at Arizona State University predicted a similar direct-indirect band gap transition in GaAs nanowires with uniaxial strains [28,29] and the gap transition was observed in a recent experiment [30] in which the luminescence of GaAs nanowires can be switched on and off under the influence of a uniaxial stress.…”

Zinc-blende and wurtzite GaAs quantum dots in nanowires studied using hydrostatic pressure

“…For instance, the bright conduction band was claimed to be the lowest conduction band by some theoretical calculations and experimental measurements, [10][11][12] giving rise to a direct bandgap transition. However, other researchers argued for a pseudodirect bandgap, where the dark conduction band is the lowest conduction band.…”

“…[6][7][8][9] In WZ GaAs, the ( ) band is a bright (dark) conduction band, corresponding to the ( ) band in the ZB GaAs phase. 10 The hexagonal crystal field significantly reduces the energy difference between and conduction bands in bulk WZ phase, 11,12 leading to a debate regarding whether the bright or dark band is the lowest conduction band.…”

Probing inhomogeneous composition in core/shell nanowires by Raman spectroscopy

“…32 Raman spectroscopy has also recently been used for the characterization of crystal phase and chemical composition of III-V nanowires. 30,[33][34][35] Due to the one-dimensional geometry of the nanowire and the dielectric mismatch with the surrounding medium, the bulk Raman selection rules are slightly modified leading to a strong dependence on the polarization angle between the incident electric field and the nanowire axis. 36 In particular, the intensity of the scattered mode is higher for incident and scattered light with polarization parallel to the nanowire axis.…”