# O-Band and C/L-Band III-V Quantum Dot Lasers Monolithically Grown on Ge and Si Substrate
## 3 InAs QD Microcavity Lasers on (111)-Faceted Hollow Si (001) Substrate
### Optically-Pumped QD Micropillar Laser on Si Substrate  
Optically-pumped InAs/GaAs quantum-dot micropillar laser on an exact Si (001) by a (111)-faceted Si hollow structure has been achieved through the standard fabrication process, including photolithography and dry etch. By calculation, the distributed Bragg reflectors (DBRs) and an active layer with specific thicknesses have been grown on an ultra-flat GaAs/Si (001) substrate. The cross-sectional SEM image of the whole structure is shown in Figure 6a. The DBRs consist of 33.5 bottom and 15 top pairs of alternating quarter-wavelength thick GaAs/AlAs layers, which are 94.2 nm GaAs and 111.1 nm AlAs, respectively. They were grown at an optimum temperature of 610 \({}^{\circ}\)C and 560 \({}^{\circ}\)C. The active layer in the center of one wavelength-thick GaAs cavity is sandwiched between the top and bottom DBRs. The active layer contains five periods of InAs/GaAs dot-in-a-well (DWELLs) structures, each of which consists of a 3.1 monolayer InAs QD layer sandwiched by a 2 nm In\({}_{0.143}\)Ga\({}_{0.857}\)As wetting layer and 6 nm In\({}_{0.143}\)Al\({}_{0.857}\)As capping layer. With only 250 nm GaAs buffer layer grown on (111)-faceted sawtooth hollow Si (001) substrate, subsequent DFLs can be deposited and followed by micropillar laser structures consisting of DBRs and an active layer. The QD micropillar laser structures on Si(001) were fabricated with diameters ranging from 15 to 250 \(\upmu\)m, as shown in Figure 6b. Figure 6c shows the tilted SEM view of the micropillar laser, indicating high quality of the sidewall.  
Figure 5: Room temperature photoluminescence spectra of (**a**) InAs/GaAs QDs grown on GaAs and Si (001) substrates for O-band emission and (**b**) InAs/InGaAs QDs grown on Si (001) substrates for C/L-band emission. Insets: 1 \(\upmu\)m \(\times\) 1 \(\upmu\)m AFM image of (**a**) InAs/GaAs QDs on Si and (**b**) InAs/InGaAs QDs on Si.  
A micro-PL system with a continuous wave (cw) pump laser at 532 nm was used to characterize the laser operation of InAs QD micropillar cavities on Si (001). The laser characteristics (L-L curves) of InAs QD micropillar laser on Si substrate with a mesa diameter of 15 \(\upmu\)m is shown in Figure 7a. By linear fitting the L-L curve, the laser threshold pump power is approximately calculated to be 20 \(\upmu\)W. Figure 7b shows the plot of integrated PL intensity of InAs QDs micropillar with increasing pump power at different operating temperatures ranging from 20 to 100 \({}^{\circ}\)C. During the experiment, the red-shift of laser emission wavelength is observed with increasing operation temperature by approximately 0.165 nm/\({}^{\circ}\)C. The results indicate the great temperature stability of InAs/GaAs QD microcavity lasers on Si (001) hollow structure as a potential platform for III-V optoelectronic devices on standard Si (001) substrates. With reduced density of InAs QDs, such a structure can also be implemented as a silicon-based single photon source for quantum information applications.  
Figure 6: **(a)** The cross-sectional SEM image of InAs/GaAs micropillar laser structure on (111)-faceted Si (001) hollow substrate; InAs/GaAs QDs embedded in one \(\lambda\)-cavity with 15 (33.5) pairs of top (bottom) DBRs; **(b)** top-view SEM image of micropillar lasers with different diameters; **(c)** tilted SEM image of InAs/GaAs QD micropillar laser on Si (001) with 15 \(\upmu\)m diameter.  
Figure 7: **(a)** Output intensity as a function of pump power (L-L curve) of InAs/GaAs QD micropillar laser on Si at room temperature. Inset: spectral plot of micropillar laser at the pump power of 6 mW. **(b)** Integrated PL intensity of InAs QD micropillar on Si (001) as a function of pump power of temperature ranging from 20 to 100 \({}^{\circ}\)C.