GaAs/GaAsPBi core–shell nanowires grown by molecular beam epitaxy

Abstract

We report on the growth, structural, and optical properties of GaAs/GaAsPBi core–shell nanowires (NWs) synthesized by molecular beam epitaxy (MBE). The structure presents advantageous optical properties, in particular, for near- and mid-infrared optical applications. Scanning electron microscopy shows that although the stems of GaAs/GaAsP and GaAs/GaAsBi core–shell NWs preserve the hexagonal prism shape, the GaAs/GaAsPBi core–shell NWs develop a quasi-three-fold orientational symmetry affected by the hexagonal prismatic core. Detailed structural analyses of a GaAs/GaAsPBi core–shell stem show that it crystallized with zincblende structure with a nominal shell composition of GaAs0.617P0.362Bi0.021. Photoluminescence of GaAs/GaAsPBi core–shell NWs shows the luminescent peak at 1.02 eV with high internal quantum efficiency at room temperature (IQERT ∼ 6%) superior to those of MBE-grown GaAs core NWs and GaAsPBi multiple quantum wells earlier reported. Energy-dispersive x-ray spectroscopy performed on the GaAs/GaAsPBi core–shell NWs yields an estimated bandgap different from the optically measured value. We attribute this discrepancy to the NW compositional fluctuations that also may explain the high IQERT.

High verticality vapor–liquid–solid growth of GaAs0.99Bi0.01 nanowires using Ga–Bi assisted catalytic droplets

“…To further understand, we compare the result with other Bi-containing structures: bulk, 44 multiple quantum wells, 44 and nanowires. 34 By the same criteria, I 80 / I 20 values for Bi containing bulk, multiple-quantum wells, and nanowires are 0.05, 0.15, and 0.8, respectively. Theoretically, the NW should possess two-dimensional confinement behavior.…”

“…Droplets of NW5 were crystallized, and the GaAsBi cores were surrounded by thin GaP shells. Passivation with a higher band gap material facilitates luminescence studies 34,42,43 since the GaAs surface has high surface recombination velocity 35,36 and acts as a non-radiative recombination center.…”

“…Droplets of NW5 were crystallized, and the GaAsBi cores were surrounded by thin GaP shells. Passivation with a higher band gap material facilitates luminescence studies 34,42,43 since the GaAs surface has high surface recombination velocity 35,36 and acts as a non-radiative recombination center. shows the photoluminescence spectra for NW5 measured at 30 K. Luminescence spectra 'A' and 'B' arise from the as-grown and the NW-scraped-out areas, respectively.…”

“… 31 The shell compositional inhomogeneity and metamorphic structure exist even though the strain-balanced GaAs/GaAsPBi core–shell concept is applied. 34 To obtain homogeneous GaAsBi NWs, one might need to incorporate Bi atoms through a vapor–liquid–solid (VLS) mechanism – the main focus of this work.…”

The roles of Bi in InAs and InAsBi nanostructure growth

“…[1][2][3][4][5][6][7][8][9][10] Among the various combinations of III-V alloy nanostructures, bismuth (Bi) containing alloys have drawn significant attention for the strong bandgap bowing and large spin-orbit splitting effects. [11][12][13][14][15][16][17] For example, Bi incorporation in InAs was reported to reduce the bandgap up to 55 meV per Bi% 18 and shift its photo-response beyond 3.5 mm, making InAsBi alloy suitable for mid-infrared to longwave infrared applications. As a heavy element, alloying with Bi enlarges the splitting of the valence band between the heavy hole band and causes an increase in spin-orbit energy.…”