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GaInAsP surfaces with various treatments were analyzed by contact-angle measurement for wafer direct bonding between GaInAsP and garnet crystals. The contact angle of a water droplet was measured to estimate the hydrophilicity of the wafer surfaces. The most hydrophilic surface was obtained after an O2 plasma activation process. Direct bonding was successfully achieved between GaInAsP activated by O2 plasma and garnet crystals.

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An integrated optical isolator employing a nonreciprocal phase shift is very attractive because it does not need phase matching. We have investigated a novel configuration of the integrated optical isolator, employing the nonreciprocal phase shift, in which the magnetooptic waveguide has a magnetic garnet/GaInAsP/InP structure. The wafer direct bonding technique is necessary to realize this structure. The direct bonding between quaternary III–V compound semiconductors and garnet crystals was experimentally studied. The bonding was achieved by chemical treatment and subsequent heat treatment at temperatures ranging from 110 to 330°C. Cross-sectional scanning electron microscope (SEM) images indicated that there were no gaps between the two wafers in contact.