Investigation of dielectric cap induced intermixing of InxGa1−xAsyP1−y/InP quantum well laser structures by photoreflectance and photoluminescence

The quantum well intermixing (QWI) of 1.55 μm laser structure through thermal treatment, utilising various cap layers, has been investigated by both photoluminescence (PL, emission-like) and photoreflectance (PR, absorption-like) experiments. A blue shift of the QW ground state transition has been observed for post-grown-modified laser structures. The influence of the cap stoichiometry on QWI has been analysed. It has been found that the magnitude of the blue shift strongly depends on the stoichiometry of the dielectric film. In PR, besides the blue shift of the fundamental transition, a blue shift of the excited state transitions has been observed. The blue shift is evidently stronger for the ground state transition than for the higher energy ones. The character of the recombination process at room temperature has been found as free carrier recombination for both as-grown- and post-grown-modified laser structures.