(GaAl)P optical-waveguide modulators fabricated by liquid-phase epitaxy

Single- and double-heterojunction structures of (GaAl)P have been grown by liquid-phase epitaxy using a rotary multiple-bin jig of alumina. A purity corresponding to net donor concentrations as low as 2 × 1016 cm−3 has been reached, and flat plane-parallel layers as thin as 1.5 μm have been made. p-n junctions were produced by doping with Mg during growth or by diffusion of Zn. These structures have been used as waveguides for 0.6328-μm light. The application of a reverse voltage produces an electro-optic modulation with retardations of about 90°, which corresponds to 70% intensity modulation. The measurements were done with edge-on coupling through flat faces cleaved perpendicularly to the guide plane. A special technique is used to eliminate the unguided background light from the result. The magnitude of the measured modulations agrees fairly well with simple theory. There is also good agreement with respect to the dependence of the modulation on geometry and, to a lesser degree, on voltage.