A multi-quantum-shell (MQS) grown on a GaN nanowire is a promising three-dimensional active region and it is expected to show excellent performance, compared with conventional nitride-based LEDs. However, there are no suitable simulators for calculating optical properties of MQS-LEDs, because of their complex structure. In this study, a hybrid simulation, which is composed of the finite-difference time-domain method, the rigorous coupled wave analysis method, and the ray tracing method, is developed. Applying this useful tool to the calculation of the light extraction efficiency (LEE) of MQS-LEDs, we have found considerable light absorption loss by the large refractive index steps between the active layer, ITO layer and air in the commonly used MQS-LED structure with the ITO electrode. Thus, to eliminate the large refractive index steps, the MQS-LED buried with the n-GaN current diffusion layer, which has a high LEE, was proposed.

A GaInN/GaN multiquantum shell (MQS) structure grown over GaN nanowires can be utilized as active regions in optoelectronic devices because of its advantages such as high crystalline quality and the absence of internal polarization. To improve the current injection toward the sidewall of the MQS active regions, a tunnel junction (TJ) and n‐GaN‐embedded cap layer are adopted without using an indium‐tin‐oxide film. A light‐emitting diode (LED) composed of n‐GaN nanowires, MQS active regions, TJs, and an n‐GaN‐embedded cap layer is demonstrated for the first time. Without the activation process of Mg acceptors, the MQS LED exhibits a linear increase in the light output with current injection and a high operating voltage. After removing the upper part of the n‐GaN‐embedded cap layer, thermal annealing is confirmed to activate Mg acceptors in p‐GaN and p+‐GaN, and the reduction of the operating voltage is observed, despite the lack of current spreading in the n‐GaN‐embedded cap layer by Mg diffusion.