Blue-green emitting microdisks using low-temperature-grown ZnO on patterned silicon substrates

Zinc oxide (ZnO) as an extremely bright emitter is an attractive material for photonic devices. However, devices made of epitaxially grown ZnO are difficult to fabricate due to the lack of selective etching processes. Here, we demonstrate that by a low-temperature growth process on pre-patterned silicon dioxide (SiO₂) microdisks (MDs) high quality ZnO resonators are created. The devices exhibit whispering gallery modes (WGMs) over the blue-green part of the visible spectrum with quality factors exceeding Q = 3500, which are among the highest values reported in this material system so far. By deposition of SiO₂ capping layers we find an enhanced coupling of the spontaneous emission from the active medium into the MDs, observed by sharp WGMs up to a radial quantum number of N = 3.