We report the growth of GaAs/GaNAs/GaAs core-multishell nanowires having N compositions exceeding 2%. The structures were grown by plasma-assisted molecular beam epitaxy using constituent Ga-induced vapor-liquid-solid growth on Si(111) substrates. The GaNAs shell nominally contains 0%, 2%, and 3% nitrogen. The axial cross-sectional scanning transmission electron microscopy measurements confirm the existence of core-multishell structure. The room temperature micro-photoluminescence measurements reveal a red-shift of the detected emission with increasing N content in the nanowires, consistent with the expected changes in the GaNAs bandgap energy due to the bowing effect.
A coherent photon source emitting at near-infrared (NIR) wavelengths is at the heart of a wide variety of applications ranging from telecommunications and optical gas sensing to biological imaging and metrology. NIR-emitting semiconductor nanowires (NWs), acting both as a miniaturized optical resonator and as a photonic gain medium, are among the best-suited nanomaterials to achieve such goals. In this study, we demonstrate the NIR lasing at 1 μm from GaAs/GaNAs/GaAs core/shell/cap dilute nitride nanowires with only 2.5% nitrogen. The achieved lasing is characterized by an S-shape pump-power dependence and narrowing of the emission line width. Through examining the lasing performance from a set of different single NWs, a threshold gain, g th, of 4100–4800 cm–1, was derived with a spontaneous emission coupling factor, β, up to 0.8, which demonstrates the great potential of such nanophotonic material. The lasing mode was found to arise from the fundamental HE11a mode of the Fabry–Perot cavity from a single NW, exhibiting optical polarization along the NW axis. Based on temperature dependence of the lasing emission, a high characteristic temperature, T 0, of 160 (±10) K is estimated. Our results, therefore, demonstrate a promising alternative route to achieve room-temperature NIR NW lasers thanks to the excellent alloy tunability and superior optical performance of such dilute nitride materials.
We report the growth of dilute nitride GaNAs and GaInNAs core-multishell nanowires by plasma-assisted molecular beam epitaxy. Using constituent Ga-induced vapor-liquid-solid growth, these nanowires were grown on Si(111) and silicon on insulator (SOI) substrates. The GaNAs shell nominally contains 0%, 2%, and 3% nitrogen. We also report the growth of GaAs/GaInNAs/GaAs core-multishell nanowires nominally containing 30% In and 2% N. Axial cross-sectional scanning transmission electron microscopy measurements and energydispersive X-ray spectrometry confirm the formation of the core-multishell nanowire structure. We obtained high-quality GaNAs nanowires with nitrogen compositions up to 2%. On the other hand, GaNAs containing 3% nitrogen, and GaInNAs nanowires, show distorted structure; moreover, the optical emissions seem to be related to defects. Further optimisations of the growth conditions will improve these properties, promising future applications in nanoscale optoelectronics.
We report on optimization of growth conditions of GaAs/GaNAs/GaAs core/shell/shell nanowire (NW) structures emitting at ∼1 μm, aiming to increase their light emitting efficiency. A slight change in growth temperature is found to critically affect optical quality of the active GaNAs shell and is shown to result from suppressed formation of non-radiative recombination (NRR) centers under the optimum growth temperature. By employing the optically detected magnetic resonance spectroscopy, we identify gallium vacancies and gallium interstitials as being among the dominant NRR defects. The radiative efficiency of the NWs can be further improved by post-growth annealing at 680 °C, which removes the gallium interstitials.
Core/shell nanowire (NW) heterostructures based on III-V semiconductors and related alloys are attractive for optoelectronic and photonic applications owing to the ability to modify their electronic structure via bandgap and strain engineering. Post-growth thermal annealing of such NWs is often involved during device fabrication and can also be used to improve their optical and transport properties. However, effects of such annealing on alloy disorder and strain in core/shell NWs are not fully understood. In this work we investigate these effects in novel core/shell/shell GaAs/GaNAs/GaAs NWs grown by molecular beam epitaxy on (111) Si substrates. By employing polarization-resolved photoluminescence measurements, we show that annealing (i) improves overall alloy uniformity due to suppressed long-range fluctuations in the N composition; (ii) reduces local strain within N clusters acting as quantum dot emitters; and (iii) leads to partial relaxation of the global strain caused by the lattice mismatch between GaNAs and GaAs. Our results, therefore, underline applicability of such treatment for improving optical quality of NWs from highly-mismatched alloys. They also call for caution when using ex-situ annealing in strain-engineered NW heterostructures.
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