Fabrication and Characterization of Multiquantum Shell Light-Emitting Diodes with Tunnel Junction

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.