Optical characterisation of high Q silicon rich silicon nitride µ-disks in the visible range

One of the main drawbacks that explain why Si photonics is still not dominant with respect to compound semiconductors and Si microelectronics lies on the difficulties associated with making Si a host material for efficient light emission. Among the several alternatives to obtain highly efficient Si-based emitting materials, dielectric matrices with Silicon in excess have been probably the most investigated, since they can even provide optical gain in the visible region. An interesting strategy has been to combine the light emission properties of those materials and the optical properties of circular microcavities (such as disks or rings). In the present work, we report an experimental characterisation of the optical properties of active Si rich Si₃N₄ μ-disk cavities in the visible range. In particular, we have studied the correlation between the quality factor (Q) of the cavities and the active material deposition parameters. Micro-photoluminescence (μ-PL) measurements have revealed subangstrom whispering galley modes (WGM) resonances and maximum Q of 10⁴ around 760 nm. These values improve the best results reported so far for Si based light emitting circular resonators in the visible range. We have also quantified the on-plane emitted powers (hundreds of nW) and power efficiencies (10^-6-10^-5). In contrast to what reported on substoichiometric SiO₂ based microcavities, we demonstrate the absence of a spectral widening at high pump fluxes associated to carrier absorption (CA) mechanisms, which allows high emitted power without degrading the quality factor of the cavity.