Waveguide modulator structures with soft optical confinement grown by the epitaxial shadow mask (ESM) MBE-technique

Abstract

Abstract Excellent selective n- and p-contacts to highly doped and closely adjacent layers in n-i-p-i doping superlattices can be fabricated using the epitaxial shadow mask molecular beam epitaxy (ESM-MBE). With this method the growth within the window of a GaAs AlGaAs mask obtained by selective wet chemical etching is controlled by the geometrical aspect of the effusion cells relative to the substrate. We demonstrate first results of using ESM-MBE for the in-situ fabrication of waveguide structures, including waveguide modulators. This double hetero p-i-n modulator exhibits a modulation contrast of more than 30 dB (for a 900 μm long device) for a voltage swing of 6.5 V. Propagation losses in the waveguide structure are less than 11 dB/cm and mainly due to free carrier absorption in the waveguide region.