SiGe/Si multiquantum well structure for light modulation

The study of a light modulator (λ=1.3 μm) integrated on a silicon-on-insulator substrate (SOI) is presented. The device is based on electrorefractive effect in SiGe strained on Si: holes, originating from Si-p delta-doped layers, are confined in SiGe multi-quantum wells. The active structure is embedded in a PN diode, so that it can be depleted by a reverse bias. The device operation is simulated by numerical calculations of the hole distributions coupled with the optical guided mode profile. The mode effective index variation versus applied bias can then be obtained. Influences of parameters, such as doping and thickness of the delta-doped layers and number of wells, on the mode effective index and on the depletion bias are investigated with a design of experiment method. This optimisation gives an effective index variation in the region of 10−5 V−1. The structure has first been epitaxially grown by UHV-CVD on a N-type Si substrate. Reverse leakage current as low as 10−3 mA cm−2 and breakdown bias larger than 10 V are measured by current–voltage characteristics. The depletion is evaluated from capacitance–voltage measurements.