GaAs photodetectors integrated with lithium niobate waveguides

The authors report on the application of an epitaxial lift-off to achieve the integration of a semiconductor device with an LiNbO/sub 3/ optical waveguide and on the optical interaction between the two. The semiconductor device is a GaAs metal-semiconductor-metal photodetector that was processed entirely after the epitaxial lift-off. Because of the high index of refraction difference between the two materials, light evanescently couples readily from the low-index waveguide into the high-index GaAs photodetector. HeNe laser light ( lambda =633 nm) was prism coupled into the waveguide. Light was totally extinguished within approximately 1 mm from the edge of the GaAs film. The photocurrent of the first detector, which was about 150 mu m behind the leading edge of the GaAs, was 6 mu A with 0.5-mW incident laser power. The second detector, 100 mu m behind the first, gave 4 mu A of photocurrent. These photocurrents correspond to a waveguide-detector absorption coefficient of 40 cm/sup -1/.