Fig. 1. Schematic of the epilayer structure. Inset, AFM morphology of the uncapped dots.

Fig. 2. (a) Schematic illustration and (b) tilted SEM image of one fabricated microring laser; (c) top view of the probed microring under infrared imaging.

Fig. 3. Measured L-I-V curve of a microring laser with intrinsic active region. The device features an outer ring radius of 15 μm and a ring waveguide width of 4 μm. Inset, zoomed-in view of the L-I curve in the low-injection region.

Fig. 4. Emission spectra for the same device in Fig. 3 at various injection currents under CW operation at room temperature. Inset, emission spectrum around lasing threshold.

Fig. 5. Measured L-I curves as a function of the heat sink temperature for two microring lasers with (a) an intrinsic active region and (b) a modulation p-doped active region. Both devices have an outer ring radius of 15 μm and a ring waveguide width of 4 μm. (c) Temperature-dependent threshold current versus heat sink temperature for the two microring lasers, where the dashed lines represent the linear fit to the experimental data.

Fig. 6. Threshold currents as a function of outer ring radius for microring lasers (a) with an intrinsic active region and a modulation p-doped active region on the GaP/Si, and (b) on GaP/Si substrate and native GaAs substrate with an intrinsic active region.

Fig. 7. Small-signal modulation responses of the QD ring laser biased from 21 to 86 mA. The fitting curves are drawn using a three-pole fitting function H(f). Inset, L-I-V characteristics from the same device.

Fig. 8. 3 dB bandwidth f3 dB and relaxation oscillation frequency fr versus square root of the bias current above threshold. Inset, damping rate γ versus squared relaxation oscillation frequency fr. The maximum 3 dB bandwidth limited by K-factor f3 dB,max is 9.7 GHz.

Fig. 9. (a) Impedance measurement of QD microring laser on Si; (b) equivalent circuit model used for the fitting. Measured and fitted curves of reflection S11 characteristics for reverse (−3  V) and forward (50 mA) biased condition from 0.14 to 5 GHz.