Free-Standing ZnSe-Based Microdisk Resonators: Influence of Edge Roughness on the Optical Quality and Reducing Degradation with Supported Geometry

Microdisk resonators offer a small mode volume and are therefore commonly investigated for their suitability as platforms for low-threshold lasing. In addition, the inherent strong confinement of light not only renders such structures promising candidates for efficient single-photon sources, but even motivates a key role for integrated photonic circuitry. Herein, ZnSe-based microdisks with ZnCdSe quantum well (QW) structures in ZnMgSe barriers are analyzed. In microphotoluminescence (mu PL), stimulated emission into whispering gallery modes (WGMs) is demonstrated. Scanning electron microscopy (SEM) is used to determine the edge roughness of a multitude of resonators using a fitting routine, revealing a correlation between the edge roughness and overall optical quality of the resonators. These results are confirmed by calculations based on the boundary element method using the measured roughness as input parameter. To avoid the common problem of degradation under excitation in ZnSe-based structures, an alternative fabrication technique is introduced, which is new to this material system. It yields supported disks in direct contact with an Al2O3 layer on the substrate, which enhances the mechanical and thermal stability of the resonator. The occurrence of WGMs in supported ZnSe:Cl resonators is demonstrated in mu PL experiments and confirmed by theoretical calculations.