  Low-threshold lasing under pulsed optical pumping is demonstrated at room
temperature for III-nitride microdisks with InGaN/GaN quantum wells on Si in
the blue spectral range. Thresholds in the range of 18 kW/cm2 have been
achieved along with narrow linewidths of 0.07 nm and a large peak to background
dynamic of 300. We compare this threshold range with the one that can be
calculated using a rate equation model. We show that thresholds in the few
kW/cm2 range constitute the best that can be achieved with III-nitride quantum
wells at room temperature. The sensitivity of lasing on the fabrication process
is also discussed.
