Influence of DX centers on the performance of unipolar semiconductor lasers based on GaAs-AlxGa1-xAs

Optical and electrical characteristics of quantum cascade lasers, made in t he GaAs-AlxGa1-xAs material system, show persistent changes at low temperat ures, when devices are illuminated with an external white light. The magnit ude of the effect is a function of the exposure time and finally saturates. The induced variation on the threshold current density of the lasers is mo re than 30%. This effect is related to the presence of deep donors (DX cent ers) in the high aluminum content AlGaAs cladding layers, which under illum ination release electrons, thus increasing waveguide losses. By analyzing t he light induced variations of the optical characteristics we were able to deduce the waveguide losses of our devices.