Innovative concave SiGe/Ge microdisk directly on Si substrates

Microdisks/microrings have been of great interest for the exploration of comprehensive cavity quantum electrodynamics and innovative optoelectronic devices. Here, unique concave microdisks on silicon substrates are designed and fabricated via epitaxial growth of SiGe/Ge on concave Si micropillars, followed by selective etching of Si in a KOH solution. The photoluminescence spectra exhibit distinguished peaks that agree with the whispering gallery modes (WGMs) of concave microdisks based on the finite-difference time-domain simulations. Moreover, the simulated spectra and light field distributions demonstrate that the concave microdisk can be regarded as a promising architecture of top-microring on base-microdisk with dominant WGMs analogous to those of a suspended microring. Our results pave the way for the suspended-microring-like cavity. Given the microring-like cavity properties, the capability of carrier injection and heat dissipation, and the compatibility with Si technology, the concave SiGe microdisk may have great potential for applications in Si-based monolithic optical-electronic integrated circuits.