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 model of their optical properties is described. The bandstructure of the heterostructure is calculated using a k.p envelope function method. The first conduction band and the three lowest valence bands (heavy hole, light hole and spin split-off) of the bulk materials are included in the calculation, with all other bands treated as a perturbation. The method adopted to solve for the electronic states is to break the active region into a finite number of thin layers where the electrostatic potential due to the applied electric field can be taken as spatially constant and equal to the local average value. The allowed bulk states are calculated for each layer and matched at each layer interface, and at the hetero-interfaces using Burt-Foreman boundary conditions. Absorption spectra have been calculated for an InP:110 Å In_0.55Ga_0.45As/25 Å InP/65 Å In_0.55Ga_0.45As/InP structure for a range of electric fields and compared to experimental data. Absorption spectra have also been calculated for a second structure which consists of InP/60 Å In_0.53Ga_0.47As/20 Å InP/100 Å In_0.53Ga_0.47As/InP, and these results are examined in terms of light intensity modulation at a wavelength of 1.55 μm. The calculated absorption spectra show encouraging agreement with the experimentally measured photocurrent spectra for the first structure. The calculated absorption coefficient at 1.55 μm for the second structure is predicted to increase with moderate applied bias by approximately an order of magnitude, suggesting that it could form the basis of a room temperature modulator for light at that wavelength