Epitaxial growth of InP to bury directly bonded thin active layer on SiO ₂ /Si substrate for fabricating distributed feedback lasers on silicon

Abstract

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 SiO 2 layer of a thermally oxidised Si substrate (SiO 2 /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 SiO 2 /Si substrate exhibited continuous-wave operation up to 100°C and was directly modulated by a 40 Gbit/s non-return-tozero signal with a bias current of 15 mA. These results indicate that epitaxial growth using a directly bonded InP-based active layer on a SiO 2 /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.

λ-Scale Embedded Active Region Photonic Crystal (LEAP) Lasers for Optical Interconnects

“…However, the different thermal coefficients of Si and InP remain a problem [20][21][22], as it will degrade the crystal quality. In our device configuration, the critical thickness was estimated to be 450 nm [19]. Thus, the use of a lateral current injection structure is quite important.…”

“…Finally, we fabricated p-and n-doping regions and air holes by using the same fabrication method as described in Figure 3 (Figure 7f). The key factor in achieving epitaxial growth on a thin InP template is the total thickness of the III-V layers, which should be thinner than the critical thickness [18,19]. This fabrication procedure does not require epitaxial growth under lattice-mismatch conditions.…”

Membrane InGaAsP Mach–Zehnder Modulator Integrated With Optical Amplifier on Si Platform

“…4(i)]. Thanks to the membrane structure, the InGaAsP and InP bulk layer were regrown on the SOI wafer without any of the cracks typically caused by thermal expansion during the epitaxial growth process [19]. This is beneficial for wafer-level integration of various III-V devices on Si.…”

“…In addition, such III-V layer thickness is much smaller than the critical thickness. Here, the critical thickness (∼430 nm) is determined by the difference in the thermal expansion coefficients between the III-V layer and Si substrate, as discussed in our previous work [19]. So, materials with various bandgaps can be integrated on Si waveguide circuits by using epitaxial regrowth.…”

Comparison of processing-induced deformations of InP bonded to Si determined by e-beam metrology: Direct vs. adhesive bonding

“…After substrate removal, the temperature limit of the critical stress values in III-V directly bonded to Si depends on the III-V layer thickness. An InP layer of 250 nm is able to withstand temperatures encountered during the epitaxial growth without exceeding the critical stress values and generation of dislocations [9]. BCB bonding is generally not suitable for processing where prolonged high temperature exposure is required or certain chemical resistance limitations apply, as after curing the glass transition occurs above 350 • C temperature [10].…”