The researchers designed subwavelength micro-disk lasers (MDLs) as small as 1μm in diameter on exact (001) silicon, using colloidal lithography (dispersing silica colloidal beads as hard masks before etching the prepared QD material layers). The disk region encapsulates five layers of InAs/InGaAs dot-in-a-well (DWELL) structure. The micro-cavity gain medium was grown on a high crystalline quality GaAs-on-V-grooved-Si template with no absorptive intermediate buffers. Under continuous-wave optical pumping (from an external diode laser operating at 532nm), the micro-disk structure lased in the 1.2μm wavelength range, with low thresholds down to 35μW at 10K (cryogenic temperature).
The researchers note that compared to the quantum dot lasers demonstrated on offcut silicon using Ge buffers, or direct nucleation of GaAs, the use of on-axis (001) silicon offers better compatibility with conventional Si CMOS processes, suggesting that such MDLs could be easily integrated with passive optical components on a silicon-on-insulator (SOI) platform. Next on their agenda is the development of electrically-pumped micro-disk lasers using integrated CMOS drivers.
The research was carried out at the Hong Kong University of Science and Technology; the University of California; Sandia National Laboratories and Harvard University.