Optical mode competition in tensile-strained Ge microdisks fabricated by laser-induced liquid-phase crystallization

Abstract The lack of CMOS-compatible on-chip light sources remains a major bottleneck for silicon photonics. We report high-crystallinity, tensile-strained Ge microdisk resonators fabricated by laser-induced liquid-phase crystallization. Photoluminescence measurements show that radial modes dominate the emission spectra, in contrast to the whispering-gallery modes (WGMs) typically observed in microdisks. Position-controlled excitation reveals that edge excitation activates additional WGM-like subsets, yet the spectra remain primarily governed by radial families. To understand this behavior, we perform electromagnetic simulations examining two loss scenarios. A uniform absorption model fails to reproduce the experimental results, whereas an edge-localized loss model yields spectra dominated by radial modes, consistent with measurements. These findings indicate that edge-related scattering and absorption preferentially suppress WGMs, explaining their infrequent observation. This work elucidates the mode-competition mechanism in Ge microdisks and highlights the role of edge-induced losses in shaping their optical behavior, offering useful insights for future WGM-favored cavity designs on CMOS-compatible platforms.