Group iii-nitride based self-assembled quantum dots and single quantum dots in nanostructures for quantum photonics

Abstract

Group III-nitride wide bandgap semiconductor quantum dots are attractive structures for practical quantum photonic devices. They have a direct bandgap with a broad spectrum range from UV to IR, and their large exciton binding energy, slow surface recombination velocity, and large band offset enable high temperature operation of nitride based quantum structures. In addition, it is possible to engineer the electronic band structure and increase the quantum efficiency by using low dimensional quantum system. However, group III-nitrides also have lots of difficulties in growth and fabrication due to the absence of homosubstrates and their strong chemical/mechanical stability compared to the mature low bandgap semiconductors such as GaAs and InP. Therefore, despite of their strong possibility of achieving a highly efficient photonic structure, the fabrication of high quality quantum system is a challengeable task. Here, we studied the self-assembled GaN quantum dots with high crystal quality, and single InGaN quantum dots coupled with obelisk-shaped vertical nanostructures. The self-assembled quantum dots show broad, bright emission and distinctive optical properties compared to other semiconductor quantum dots. The existence of large built-in electric fields results in large spectrum shift and long radiative recombination time. However, the GaN quantum dots show unusual high quantum efficiency at room temperature due to the strong carrier localization effect. We also studied the role of the capping layer in the GaN quantum dots and the surface recombination property of the surface quantum dots. Although the self-assembled quantum dot ensemble shows high quantum efficiency at high temperature, there are many obstacles in studying the intrinsic property of single quantum dots due to the large density, random distribution in a film and limited light extraction. To overcome these limitations of conventional self-assembled quantum dots and investigate single quantum do...