Electrooptic modulation in an InGaAs/GaAs strained layer multiple quantum well structure

GaAs/AlGaAs multiple quantum well structures have been studied extensively for applications in electrooptic modulation. 1 One drawback of the GaAs/AlGaAs material system is the opacity of the GaAs substrate at the exciton absorption wavelength. This problem can be avoided with the InGaAs/GaAs material system because the exciton absorption energy is less than the GaAs band gap. Unlike AlGaAs, InGaAs is not lattice-matched to GaAs, but thin layers of InGaAs can be grown on GaAs with the lattice mismatch accommodated by strain rather than misfit dislocations. A device consisting of ten periods of 100-Å thick In 0.13 Ga 0.87 As quantum wells and 150-Å thick GaAs barriers was fabricated. The quantum wells are in the intrinsic region of a PIN diode so that a large, nearly uniform electric field can be applied. With zero applied bias there is a single sharp absorption peak at a wavelength of 950 nm. With increasing reverse bias the absorption peak rapidly collapses while shifting slightly to lower energy. With only 2 V applied to ten quantum wells, 6.4% intensity modulation is obtained at the peak wavelength. This rate of modulation per well is comparable with that reported for GaAs/AlGaAs quantum wells. 1