# O-Band and C/L-Band III-V Quantum Dot Lasers Monolithically Grown on Ge and Si Substrate
## 2 O-Band and C/L-Band III-V Quantum Dot Devices via III-V/IV Hybrid Growth
### O-Band and C/L-Band InAs/GaAs Quantum Dots on (111)-Faceted Si Hollow Substrate
Inset: High resolution TEM image of a trapezoidal InAs/InGaAs QD. In order to verify the influence of (111)-faceted-sawtooth Si (001) hollow structure on defect suppression at the GaAs/Si interface, surface SEM images of identical GaAs structures directly grown on a (111)-faceted Si and standard Si are compared here, as shown in Figure 4a,b, respectively. The images of the atomic force microscope (AFM) with the scanning area of 2 \(\upmu\)m \(\times\) 2 \(\upmu\)m are shown in Figure 4c,d. It is clear that a high quality GaAs buffer layer with a root-mean-square (RMS) roughness of approximately 0.4 nm can be obtained on (111)-faceted-sawtooth hollow Si (001) substrates, comparing with the rough surface for the InAs QDs structure on a standard Si (001) substrate. The great surface flatness and low defect density are contributed to by the designed (111)-faceted Si hollow structure. The Si (111) facets can effectively annihilate the APDs generated at the GaAs/Si interface by simply changing the propagating direction of Ga-Ga and As-As APDs from a vertical direction to 54.74 \({}^{\circ}\)C. Therefore, the generated APDs can join and annihilate within 30 nm from the interface, which effectively reduce the propagating defects into the upper structures. By applying this technique, a high quality GaAs surface can be created as shown in Figure 4, that leads to an essential platform for the hybridization of a III-V photonic structure on Si substrates. Photoluminescence (PL) measurements were carried out for O-band InAs/GaAs and C-band InAs/InGaAs QDs on (111)-faceted-hollow Si (001) substrates, as shown in Figure 5. InAs/GaAs QDs on GaAs substrate were grown as a reference sample to compare with that grown on the Si substrate. A high quality QDs on Si substrate was confirmed by the FWHM of 36 meV in PL emission for InAs/GaAs QDs on Si (001). It is shown in Figure 5a that PL peak intensity is approximately 25% higher for InAs/GaAs QDs on Si than that on the GaAs substrate. This is due to the enhanced pump power from the grating-like (111)-faceted Si substrate. The experimental result is verified by measuring the surface reflectivity of the grating structure at the wavelength of 1300 nm, which gives a value of approximately 55%. In comparison, the GaAs on the offcut Si substrate exhibits a surface reflection of only 33%. Therefore, it can be concluded that the enhanced PL peak intensity is induced from the increased reflection from Si grating structures. This further confirms a high-quality GaAs layer on Si (001). As shown in Figure 5b, the PL intensity of the C/L-band InAs/InGaAs QDs is  
Figure 4: Top-view SEM images of GaAs grown on (**a**) (111)-faceted sawtooth-structured Si (001) and (**b**) standard Si (001) substrates, and 2 \(\upmu\)m \(\times\) 2 \(\upmu\)m atomic force microscope (AFM) images of GaAs film on (**c**) (111)-faceted Si (001) hollow structure and (**d**) GaAs/Si substrate. approximately one order of magnitude lower than that of O-band InAs/GaAs QDs. This is because the carrier confinement of the InAs/InGaAs structure is weaker than that of the standard InAs/GaAs QD structure. Similar photoluminescence intensity to that on the GaAs substrate is observed. Moreover, a metamorphic InGaAs buffer layer is utilized to extend the emission wavelength of InAs QDs to the C/L band on GaAs/Si (001) substrates. Strong 1550 nm light emission is realized in the absence of an intermediate layer or any InP-based material systems. With such a technique, highly efficient and integrated O-band and C/L-band InAs/(In)GaAs QD lasers on the Si (001) substrate are expected in the near future.