Strain-Induced Spectral Red-Shifting from Nanoscale Frustum Arrays Fabricated over InGaN/GaN Quantum Wells for Light-Emitting Applications

While spectral blue-shifting caused by nanostructuring of InGaN/GaN quantum wells has been widely reported for altering the emission color of light-emitting diodes, the same cannot be said for spectral red-shifting. It is well-known that nanostructuring of the quantum wells gives rise to relaxation of the strain incurred in the quantum wells, reducing the quantum confined stark effect with a consequence of spectral shifting to shorter wavelengths. In this report, we demonstrate a nanostructure configuration that produces the opposite effect, spectral red-shifting, by increasing the strain in the quantum wells through the formation of an inverted nanoconical-frustum array over the quantum wells, without allowing the nanostructures to penetrate through the quantum wells. Under such conditions, spectral red-shifting of the photoluminescence spectrum can be observed, consistent with the prediction of strain induction in the quantum wells by molecular dynamics simulations. Experimentally, spectral red-shift of the photoluminescence spectrum by up to 7.6 nm has been observed, when the proposed nanostructures are fabricated on InGaN/GaN quantum wells grown on a c-plane sapphire substrate with a nominal emission wavelength of ∼560 nm.