Droplet epitaxy for advanced optoelectronic materials and devices

Droplet epitaxy was proposed to fabricate quantum dots in the early 1990s. Even though many research efforts have been devoted to droplet epitaxy since then, it is only until recently that droplet epitaxy has received worldwide attention. Compared with the well-known Stranski-Krastanow (S-K) growth mode, droplet epitaxy consists of the formation and crystallization of droplets, which enables fabrication of three-dimensional nanostructures in both lattice-mismatched and lattice-matched material systems. The flexibility of the droplet epitaxy growth method has brought to light the great potential of droplet epitaxy in optoelectronic applications. However, most works on droplet epitaxy focus on fabrication, optical properties and understanding the growth mechanisms of various nanostructures. In terms of device applications, droplet epitaxy has fallen behind conventional nanostructure self-assembly using the S-K mode. One of the major reasons is the relative low optical quality of the nanostructures obtained at low growth temperatures, and so careful attention has to be given to growth conditions to create device-grade materials. Through the developments in droplet epitaxy in the last decade, the issues can be overcome and more importantly a rich spectrum of nanostructures can be obtained, which enables the development of novel devices. This review focuses on recent developments in droplet epitaxy and presents the challenge and promise of its application in the optoelectronic field.