Self-Assembly of Semiconductor Quantum Rings by Local Droplet Etching

We give an overview on the self-assembly and optical properties of strain-free semiconductor quantum rings (QRs) generated by the novel technique local droplet etching (LDE). LDE is fully compatible with conventional molecular beam epitaxy equipment and utilizes liquid metallic droplets which perform a spatially limited drilling and form nanovolcanoes in semiconductor surfaces. A nanovolcanoe is build of a nanohole and a wall surrounding the hole opening. Using Ga droplets on AlGaAs, the wall acts a quantum ring. Here, the formation mechanism and structural properties of such GaAs QRs are discussed. Furthermore, data on the optical emission are presented. As an additional interesting point, GaAs quantum dots fabricated by filling of the nanoholes are addressed. This opens the door for studies of the coupling between quantum dot and quantum ring electronic states.