Crystal structure and optical properties of a high-density InGaN nanoumbrella array as a white light source without phosphors

We demonstrated the fabrication of a peculiar GaN/InGaN-based high-density nanocrystal array on a nitrogen polarity GaN layer using a simple self-assembly process for the first time. The nanocrystals consist of bending InGaN nanoplates and supporting GaN nanocolumns. The nanocrystals are umbrella shaped with diameters of ∼200–700 nm; therefore, they are referred to as InGaN nanoumbrellas. Transmission electron microscopy revealed the crystal structures of the nanoumbrellas and provided information about their growth mechanism. The photoluminescence (PL) properties of the InGaN nanoumbrellas were also characterized, and an extremely wide range of optical emission wavelengths (∼360–800 nm) was obtained from a small excitation diameter of ∼10 μm. Multiple sharp peaks resembling lasing actions were also observed in the PL spectrum; the resonant mode was likely caused by the whispering gallery mode. These results indicate that the high-density GaN/InGaN-based nanoumbrella array can be used as a source of white light without phosphors. NPG Asia Materials (2016) 8, e289; doi:10.1038/am.2016.99; published online 22 July 2016