Optical properties of asymmetric InGaAs/InP coupled quantum wells

Asymmetric double quantum well structures with applied transverse electric field are of interest in optical modulator applications. A theoretical mode l of their optical properties is described. The bandstructure of the hetero structure is calculated using a k,p envelope function method. The first con duction band and the three lowest valence bands (heavy hole, light hole and spin split-off) of the bulk materials are included in the calculation, wit h all other bands treated as a perturbation. The method adopted to solve fo r the electronic states is to break the active region into a finite number of thin layers where the electrostatic potential due to the applied electri c field can be taken as spatially constant and equal to the local average v alue. The allowed bulk states are calculated for each layer and matched at each layer interface, and at the hetero-interfaces using Burt-Foreman bound ary conditions. Absorption spectra have been calculated for an InP/110 Angs trom In0.55Ga0.45As/25 Angstrom InP/65 Angstrom In0.55Ga0.45As/InP structur e for a range of electric fields and compared to experimental data. Absorpt ion spectra have also been calculated for a second structure which consists of InP/60 Angstrom In0.53Ga0.47As/20 Angstrom InP/100 Angstrom In0.53Ga0.4 7As/InP, and these results are examined in terms of light intensity modulat ion at a wavelength of 1.55 mu m. The calculated absorption spectra show en couraging agreement with the experimentally measured photocurrent spectra f or the first structure. The calculated absorption coefficient at 1.55 mu m for the second structure is predicted to increase with moderate applied bia s by approximately an order of magnitude, suggesting that it could form the basis of a room temperature modulator for light at that wavelength.