Spatial and time-resolved properties of emission enhancement in polar/semi-polar InGaN/GaN by surface plasmon resonance.

Light-emitting diodes (LEDs) are widely used as next-generation light sources because of their various advantages. However, their luminous efficiency is remarkably low at the green-emission wavelength. The luminous efficiencies of InGaN/GaN quantum wells (QWs) significantly decrease with increasing indium content in the green wavelength region, mainly owing to the quantum-confined Stark effect (QCSE). This green gap problem can be solved using QWs grown on semi-polar GaN substrates, such as the {11-22} planes, to reduce the QCSE. We propose that the use of surface plasmons (SPs) is a promising way to improve the light emission efficiency of light-emitting materials such as InGaN/GaN QWs. SP resonance increases the spontaneous emission rates of the excited states, causes a relative reduction in non-radiative relaxation, and ultimately increases the internal quantum efficiencies. In this study, the light emissions of InGaN/GaN QWs grown on polar and semi-polar GaN were investigated using micro-photoluminescence (PL). We successfully enhanced the light emission of semi-polar GaN via SP resonance. The PL peak intensities and wavelengths were mapped and compared to determine the underlying mechanisms. We also measured the emission lifetimes by time-resolved PL and interpreted the detailed mechanism of SP-enhanced emissions. It was found that SP resonances can control not only the emission efficiency but also the exciton dynamics, such as exciton localization effects, QCSE screening, and defect level saturation. We conclude that the green gap problem can be solved by SP-enhanced light emission in semipolar InGaN/GaN.