Low temperature wafer direct bonding between GaInAsP etch stop layer and Gd3Ga5O12

Wafer direct bonding is an attractive technique for the integration of different materials without any adhesives. The authors have applied this technique to bonding of a III-V compound semiconductor and a garnet crystal for the aim of integrating a laser diode and an optical isolator. In a previous study, we demonstrated the bonding between InP and several kinds of garnets [1], the latter of which are essential to an optical isolator. Figure 1 shows a laser diode integrated with an optical isolator by wafer direct bonding. A GaInAsP etch stop layer of the laser diode is prepared for vertical alignment between an active layer of the laser diode and a guiding layer of the optical isolator. The vertical alignment can be achieved by adjusting the thickness of cladding layers. The lateral alignment of a waveguide with the laser stripe can be accomplished by conventional lithography and etching techniques. In this paper, we report the direct bonding between GaInAsP and Gd3Ga5O12 (GGG). GGG is used as a substrate for epitaxial growth of magnetic garnets.