Photomodulated reflectance of tensilely strained InGaAs/InGaAsP quantum well structures

Abstract

Room-temperature photomodulated reflectance (PR) has been performed on a series of tensilely strained undoped multiple quantum well (QW) structures with barriers, which were lattice matched to an InP substrate. The nominal QW Ga composition varied from x = 0.467 to 0.684 corresponding to tensile strains between zero and 1.5%, respectively. In this range of strain, the QW heavy-hole (HH) and light-hole (LH) ground-state zone-centre excitonic transitions increase in energy, with the HH varying more rapidly, with the result that it moves from energies below that of the LH, in the unstrained wells, to above the LH, at the highest strain. The variation in the LH and HH energies with strain is measured using PR which is able to resolve these two transitions even when they are almost degenerate, which occurs at % tensile strain. The results from the PR measurements are also compared with room-temperature photoluminescence and photovoltage measurements on samples from the same wafers. The experimental results are shown to compare well with theoretical QW calculations based on an effective mass formalism.