Investigation of the Non-Square InGaAsP/InP Quantum Wells in the Electric Field by Photoreflectance

Non-square quantum wells in electric field have been investigated by photoreflectance and photoluminescence spectroscopies. The structures have been obtained by a post-growth modification (rapid thermal annealing) of standard 1.55μm InGaAsP-based laser structures that were grown by gas source molecular beam epitaxy. During rapid thermal annealing a migration of semiconductor atoms across quantum well interfaces changes the quantum well profile from a square well to a rounded well. The modification of the profile changes energy levels in the quantum well and in consequence a blue shift of the quantum well emission peak is observed in photoluminescence. In this paper the blue shift of the ground state transition of post-growth modified quantum well structures has been investigated by both photoluminescence and photoreflectance techniques. Also a blue shift of excited state transitions has been observed in photoreflectance spectra. Generally, a stronger blue shift for the ground state transition than for excited state transitions has been observed. Additionally, oscillator strengths for all quantum well transitions have been determined from photoreflectance spectra. It has been found that the oscillator strength is constant for all quantum well transitions despite of modification of the quantum well profile.