Epitaxial growth of InP to bury directly bonded thin active layer on SiO2/Si substrate for fabricating distributed feedback lasers on silicon

The authors have developed a new heterogeneous-integration method for fabricating semiconductor lasers with high modulation efficiency on Si substrates. The method employs the direct bonding of an InP-based active layer to the SiO₂ layer of a thermally oxidised Si substrate (SiO₂/Si substrate), followed by the epitaxial growth of InP to form a buried heterostructure (BH). By using the InP membrane, the authors realise epitaxial growth of an InP on the InP membrane directly bonded to Si without crystal quality degradation. Both a theoretical estimation and photoluminescence measurements revealed that the total laser thickness must be less than the critical thickness determined by the applied thermal strain. The authors confirmed that the crystal quality of the BH is comparable to that fabricated on an InP substrate when using a 250-nm-thick InP-based membrane. A distributed feedback laser fabricated on a SiO₂/Si substrate exhibited continuous-wave operation up to 100°C and was directly modulated by a 40 Gbit/s non-return-to-zero signal with a bias current of 15 mA. These results indicate that epitaxial growth using a directly bonded InP-based active layer on a SiO₂/Si substrate allows us to achieve lasers with high modulation efficiency and to use a large-scale Si wafer as a fabrication platform, resulting in low-cost fabrication.