Temperature and Source Flux Dependence of Light Emission, In Incorporation and Quantum Confinement in Self-Formed Core–Shell InGaN Nanowires

We report our recent observations of the growth temperature and source flux dependence of the light emission, In incorporation and quantum confinement of core–shell InGaN nanowires (NWs), self-formed in the growth temperature regime of In desorption by plasma-assisted molecular beam epitaxy on Si(111). For elevated active N flux and for relatively low growth temperatures, the photoluminescence peak wavelength and the In incorporation as a function of growth temperature exhibit an unexpected maximum. With increasing In/Ga flux ratio, this maximum shifts to lower temperature. Together, the overall In content increases, the photoluminescence shifts to longer wavelengths, the In distribution becomes more uniform and the quantum confinement of electrons and holes in the In-rich nanowire core reduces. A model based on the interplay of thermally activated In desorption with thermally activated In surface diffusion on the nanowire sidewalls accounts for the experimental results for the realization of core–shell InGaN nanowires with emission wavelengths tuned to the visible red and green and the near-infrared telecom O-band.

Scheme of the growth process of core−shell InGaN Nanowires by the interplay of In surface desorption and diffusion on the m-plane NW sidewalls and c-plane NW top. In incorporation of the core−shell InGaN Nanowires first increases and further decreases with the increasing growth temperature but the temperature of maximum In incorporation shifts toward lower values for increasing In/Ga flux ratio.