Interdiffused strained InGaAs/InP single quantum wells with different rates of diffusion on Group III and Group V sublattices.

Abstract

In this thesis, an account is given of a theoretical study of intermixed InGaAs/InP quantum well structures. These structures are important in photonic applications because of their response in the optically important 1.3 µm to 1.55 µm region. Quantum well intermixing may occur on both Group III and Group V sublattices, and results are presented for the case where the interdiffusion rates for cations and anions are different. An error function distribution is used to model the compositional profile after interdiffusion. The as-grown quantum well is unstrained, but the intermixing induces a spatially-dependent strain in the structure, which in tum affects the carrier confinement profile. The subband structure of the interdiffused quantum well is calculated, and hence the polarization dependent absorption spectrum is obtained. From the results exhibited, it is observed that when the rate of interdiffusion on the Group V sublattice is greater than that on the Group III sublattice, the effective handgap increases. This increase leads to a blue shift in the fundamental absorption edge of the QW structure. Furthermore, the light hole ground state can be shifted above the heavy hole ground state. The results presented also show that it is possible to obtain a polarization insensitive response from an intermixed quantum well device. This is achieved by tailoring the interdiffusion process so as to merge the heavy hole and light hole ground state transition energies, taking into account excitonic effects. As a result the electroabsorption near the fundamental absorption edge becomes polarization independent. Furthermore, it is shown that this polarization independence persists with the application of an electric field, which is of interest in waveguide modulators.