7. Fabrication of Ordered Quantum Rings by Molecular Beam Epitaxy

Quantum rings have attracted a lot of attention due to their unique properties and have been under extensive theoretical and experimental investigations. For example, Aharonov-Bohm effect has been observed in quantum rings which shows potential to realize quantum computational devices. In addition, quantum rings have found application in optoelectronics. Due to the ring-shaped morphology altered from dots, the vertical confinement in nanorings is stronger than in quantum dots. Laser and infrared photodetectors have recently been demonstrated by using quantum rings. To meet the urgent demands for quantum rings, various effects have been devoted to quantum ring fabrication techniques. There are two of the most used bottom-up fabrication methods of self-assembled rings using molecular beam epitaxy (MBE). Semiconductor quantum rings can be created by conventional molecular beam epitaxy and Droplet Epitaxy technique. Despite great efforts devoted to quantum ring fabrication using these techniques, alignment of quantum rings is not well documented. Fabrication of ordered quantum rings is of high priority for theoretical as well as practical investigations, such as persistent current and photodetectors. Recently, both vertically and laterally ordered quantum rings have been demonstrated. In this chapter, the growth mechanisms and fabrication techniques for aligned quantum rings grown are reviewed.