# In-Plane Monolithic Integration of Scaled III-V Photonic Devices
## 3 Hybrid III-V/Si Photonic Crystal Cavity Lasers
### Characterization of Hybrid III-V/Si PhC Cavities
Figure 5c emphasizes this behavior by considering only the lasing threshold, which we extract from the LL curves at the \(x\)-axis intersection of the linear slope. A higher temperature leads to a larger threshold, as marked by the different colors. Additionally, the threshold increases with the fraction of InP rods to Si rods in the cavity. The absorption of light in the PhC mirror part of the cavity evidently plays an important role and the threshold is lower since Si is less absorptive than InP, even though it does not contribute to the gain. Thus, we benefit from being able to place the gain material only in the part of the cavity with a large overlap to the desired resonant mode, and which can be efficiently pumped. We show these results for three different temperatures, but cannot achieve lasing in the InP-based devices above a temperature of 150 K. Going to room temperature operation,  
Figure 5: (**a**) Absorption coefficient of Si, InP, and InGaAs [44]. At 900 nm, the absorption coefficient of InP is two orders of magnitude larger than for Si. (**b**) Light in-light out curves for hybrid InP/Si cavities measured at different temperatures (line color) and for different numbers of Si rods in the PhC mirror (color intensity). The inset shows the far-field emission pattern above threshold. (**c**) Lasing threshold of typical devices with increasing ratio of III-V/Si rods, where 0 corresponds to all Si and 1 to all InP; in all cases, the total number of rods is 41. The threshold increases with the temperature and III-V/Si ratio. a different material with emission above the Si band edge is necessary to eliminate the contribution of absorption losses in the mirrors. A natural choice is In\({}_{0.5}\)Ga\({}_{0.5}\)As as it is lattice matched to InP. The InGaAs of course will also absorb, but we only keep it in the cavity center where it can be efficiently pumped. Indeed, we already saw this effect on devices with InGaAs as a gain material in Figure 4c, as these measurements were performed at room temperature, for which the spectra of similar InP devices did not show any cavity modes. A direct comparison between the devices with different gain material is not possible because of their different design and different emission wavelength, for which also the pump laser wavelength was adjusted. The lack of absorption from the mirrors might not fully explain the gain in performance. The InGaAs-based devices do not contain a uniform In\({}_{0.5}\)Ga\({}_{0.5}\)As profile, but it is sandwiched between two InP regions which possess a larger bandgap energy. Together with the in situ \(p\)- and \(n\)-type doping of the two InP regions, respectively, a wide potential-well like structure is formed which might improve the carrier confinement. Additionally, a \(p\)-type doped InGaAs is added to the \(p\)-type InP to reduce the contact resistance in future design, but this should not impact the performance of the present devices. Whereas the PhC structures are currently based on optical pumping, we are investigating a path towards electrical actuation. For this, the aforementioned \(n\)-In\(P\)/\(i\)-InGaAs/\(p\)-InP/\(p\)-InGaAs nanorods already contain an appropriate materials profile.