Transfer matrix formalism applied to above barrier energy states in strained multiple quantum wells

We have used the effective mass approximation in a transfer matrix formalism to describe both confined and unconfined (above barrier) states in strained InGaAs/GaAs multiple quantum well (MQW) structures. We deduce the transfer matrices for a pseudomorphic MQW structure from the envelope wavefunction boundary conditions, modified to account for the discontinuities in the lattice constant. In the calculations we also take into account the finite width of the cap-layer, and the finite height of the vacuum potential. The potential profiles of the InGaAs/GaAs MQWs are derived using the calculated positions of the band-edges, taken from the model-solid theory. Photoluminescence excitation (PLE) spectroscopy has been performed on a series of InGaAs/GaAs MQWs (4-6 periods) at 11K. We observed excitonic peaks at energies both below and above the GaAs free exciton. The values of the calculated transition energies are in good agreement with the experimental peaks.