Low-voltage high-contrast n-i-p-i-based waveguide modulators with alloyed selective contacts

We investigated an electroabsorptive n-i-p-i waveguide modulator based on the Franz-Keldysh effect (FKE), which is especially designed to operate with very low voltage swings over a broad wavelength range. In order to contact the n-i-p-i structure, the layer sequence and annealing conditions of Au-Zn-Au and Ni-Ge-Au contacts were optimized with respect to good selectivity and low contact resistance. The transmission measurements yield a contrast ratio of 30 dB, achieved with a voltage swing less than 1.5 V at a wavelength of 910 μm with a 900-μm-long waveguide modulator. Contrast ratios of /spl ges/20 dB have been obtained within the whole spectral range from 910 nm to 940 mm with a voltage swing less than 2 V. The absorption loss due to the FKE is below 3 dB.