Green luminescence of InGaN nanowires grown on silicon substrates by molecular beam epitaxy

Indium gallium nitride nanowires show promise as being prime candidates for optical devices since they can be grown with band gaps spanning the visible spectra, while at the same time can be composed of stress free material. The goal of the work presented here was to obtain InGaN nanowires producing green emission at room temperature. Two growth recipes were found to yield InGaN nanowire growth on silicon substrates using plasma-assisted molecular beam epitaxy. At room temperature the photoluminescence (PL) of wire ensembles indeed peaked at 530 nm but, in addition, it was discovered that at low temperatures the emission often covered a broader (360–700 nm) spectrum. This broad optical range indicated indium content fluctuations in individual wires, wire-to-wire fluctuations, or a combination of the two. EDX measurements performed on single wires confirmed this hypothesis and correlated well with PL data. Low temperature PL studies of InGaN individual wires also revealed interwire and intrawire inhomogeneity of emission spectra stemming from a nonuniform indium distribution. The emission quantum yield for bright single wires was extracted to be more than 50% at 4 K. The findings suggest that the wire surfaces do not efficiently quench optical emission at low temperatures. These defect-free wires offer not only a potential path for green emitters, but also as integrated phosphors for broad spectral emission.