III-nitride on silicon microdisks: electrical injection and bus waveguide side-coupling (Conference Presentation)

Group-III-nitride nanophotonics on silicon is a booming field, from the near-IR to the UV spectral range. The main interest of III-nitride nanophotonic circuits is the integration of active structures and laser sources. Laser sources with a small footprint can be obtained with microresonators formed by photonic crystals or microdisks, exhibiting quality factors up to a few thousand down to the UV-C. So far, single microdisk laser devices have been demonstrated, mostly under optical pumping. Combining microdisk lasers under electrical injection with passive devices represents a major challenge in realizing a viable III-nitride nanophotonic platform on silicon. As a first step to realize this goal, we have separately demonstrated electroluminescence from microdisks and side-coupling of microdisks to bus waveguides with outcoupling gratings in the blue spectral range. We have developed the fabrication of electrically injected microdisks with a circular p-contact on top of the disk that is connected to a larger pad via a mechanically stable metal microbridge. Blue electroluminescence is observed under current injection at room temperature. We also demonstrated high Q factor (Q > 2000) WGMs in the blue spectral range from microdisks side-coupled to bus waveguides, as measured from the luminescence of embedded InGaN quantum wells. The WGM resonances are clearly observed through outcoupling gratings following propagation in partially etched waveguides to remove quantum well absorption. Small gaps between microdisks and bus waveguides of around 100 nm are necessary for efficient coupling in the blue spectral range, which represents a major fabrication challenge. We will discuss the progress brought by these building blocks to generate future III-nitride photonic circuits.