Strong Enhancement of Light Emission in Core-Shell InGaN/GaN Multi-Quantum-Well Nanowire Light-Emitting Diodes by Incorporating Graphene Quantum Dots

One-dimensional (1D) vertical nitrides are highly attractive for light-emitting diode (LED) applications because they are useful for overcoming the drawbacks of conventional GaN planar structures. However, the internal quantum efficiency (IQE) of GaN multi-quantum-well (MQW) nanowire (NW) LEDs, typical 1D GaN structures, is still too low to replace standard planar LEDs. Here, we report a phenomenon of light amplification from core-shell InGaN/GaN NW LEDs by incorporating graphene quantum dots (GQDs). The photoluminescence (PL) and electroluminescence (EL) intensities are greatly enhanced when GQDs of 5, 10, and 20 nm size are located solely in the MQWs or both in the MQWs and on the p-GaN surface, but much fewer PL and EL increases are observed for 30 and 40 nm GQDs, consistent with the size-dependent optical output power (OOP) and light-extraction efficiency (LEE). The carrier transfer between GQDs and MQWs is strongly affected by the size-dependent band-gap variation and the band profile depending on whether the forward bias is applied on the LED or not. This explains why the PL and EL spectra show different size dependences of the GQDs. The variation of the OOP by the inclusion of GQDs in the LED turns out to be governed by the IQE rather than by the LEE. Our findings highlight remarkable enhancement of light emission from GaN MQW NW LEDs by a simple approach of incorporating GQDs in the MQWs and on the p-GaN surface, also very promising for applications in a wide range of optoelectronic devices.