Résumé
The development of semiconductor lasers in the deep ultra-violet (UV) spectral range is attracting a strong interest, related to their multiple applications for optical storage, biochemistry or optical interconnects. UV-emitting ridge lasers usually embed nitride heterostructures grown on complex buffer layers or expensive substrates – an approach that cannot be extended to nano-photonics and microlasers. We demonstrate here the first deep UV microlaser by combining binary GaN/AlN thin quantum wells (QWs) grown on a silicon substrate and high quality factor microdisk resonators. Those microdisk lasers operate at 275nm at room temperature under optical pumping.The nitride heterostructures grown on silicon present a strong interest for nanophotonic devices emitting in the blue and UV range. The etching selectivity of the silicon substrate allows to realize free membrane photonic structures with high quality factors (Q) [1-3]. In the present microdisk resonators, the electromagnetic modes, the so-called Whispering-Gallery Modes (WGMs), present a low modal volume and Q factors of 6000 [4]. The difficulty in extending their lasing operation in the UV range mainly lies in the control of the active layer. Low defect density quantum wells grown on thick buffer layers or nitride substrates are usually employed for ridge lasers. Here we show that binary GaN/AlN ultra-thin quantum wells directly grown on a silicon substrate can maintain a large emission efficiency and lead to lasing at room temperature (Figure 1). This active layer can form free-standing membranes and is further compatible with future developments of nitride nanophotonic platforms on silicon.