HIGH-SPEED AND HIGH CONTRAST ELECTROOPTICAL MODULATORS BASED ON N-I-P-I DOPING SUPERLATTICES

We report on electro-optical modulators with high contrast ratio. The on/off ratio of a homogenous GaAs n-i-p-i structure only 3.9μm thick is larger than 6:1, without additional cavity effects for a voltage swing of only 7V. This change of the reflection corresponds to an absorption change of more than 2000 cm-1, averaged over the whole sample thickness. The modulation ratio exceeds 3 within a wavelength range of more than 20nm and remains constant up to an optical power of about 50 mW. The structure is grown with a novel shadow mask regrowth technique, which allows in situ fabrication of excellent selective n- and p-type contacts to doping superlattices with typical dimensions of several μm. In agreement with calculations a 45×45 μm2 device with a 60pF capacitance reveals a 3dB frequency of 40MHz. By further reducing the device dimension to 3×3 μm2 a 3dB frequency of 4GHz is expected. © 1993 Academic Press. All rights reserved.