Abstract
The realisation of photonic devices for different energy ranges demands materials with different bandgaps, sometimes even within the same device. The optimal solution in terms of integration, device performance and device economics would be a simple material system with widely tunable bandgap and compatible with the mainstream silicon technology. Here, we show that gallium arsenide nanowires grown epitaxially on silicon substrates exhibit a sizeable reduction of their bandgap by up to 40% when overgrown with lattice-mismatched indium gallium arsenide or indium aluminium arsenide shells. Specifically, we demonstrate that the gallium arsenide core sustains unusually large tensile strain with hydrostatic character and its magnitude can be engineered via the composition and the thickness of the shell. The resulted bandgap reduction renders gallium arsenide nanowires suitable for photonic devices across the near-infrared range, including telecom photonics at 1.3 and potentially 1.55 μm, with the additional possibility of monolithic integration in silicon-CMOS chips.
Highlights
The realisation of photonic devices for different energy ranges demands materials with different bandgaps, sometimes even within the same device
GaAs by up to 40% (≈600 meV) in a continuous manner, which renders GaAs nanowires a versatile material system for various photonic devices in the near-infrared range, including the 1.3 μm and potentially the 1.55 μm telecom windows, monolithically integrated on the same Si chip
Vertical GaAs/InxGa1 −xAs and GaAs/InxAl1−xAs core/shell nanowires were grown on Si(111) substrates by molecular beam epitaxy (MBE)
Summary
The realisation of photonic devices for different energy ranges demands materials with different bandgaps, sometimes even within the same device. III–V semiconductors in the form of freestanding nanowires have shown new potentials for a wide range of future applications in nanotechnology, e.g., photovoltaic cells with enhanced light absorption[7], lasers with sub-wavelength size[8], tunnel field-effect transistors as energy-efficient electronic switches[9], and entangled photon-pair sources for quantum information technology[10]. Owing to their small footprint, nanowires can be grown epitaxially without dislocations on lattice-mismatched substrates, enabling the monolithic integration of dissimilar materials with complementary properties, such as III–V semiconductors and Si11–14 or graphene[15,16]. Quantum confinement in thin nanowires[33] or post-growth external stress[34,35], which is less practical though for device applications, have been suggested for tuning the GaAs bandgap
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