Investigations of optical properties of active regions in vertical cavity surface emitting lasers grown by MBE

Abstract

The design of the vertical cavity surface emitting lasers (VCSELs) needs proper tuning of many different optical parameters of those structures. So, the optimisation of the VCSELs requires deep understanding of optical processes occurring in the active regions of such lasers. In a series of MBE processes, active regions of VCSELs as well as the whole VCSELs were grown. The active regions of the VCSEL structures were designed for λ=1000 nm and 980 nm emission. They consisted of a pair of distributed Bragg reflectors (DBRs) composed of AlAs and GaAs quarter wavelength layers and a cavity made of GaAs. The cavities contained one or several quantum wells (QWs) made of In 0.2Ga 0.8As. To optimise the optical characteristics of the active regions, several experimental methods have been applied. The Bragg reflectors and the whole microcavities were investigated by optical reflectivity. For selective excitation of a QW in a cavity active layer, a Ti–sapphire tuneable laser has been used. The fine tuning between the QW emission and the cavity Fabry–Pérot resonance has been investigated by photoluminescence at varying temperatures of the sample. For monitoring the temporal evolution of the luminescence from the active region of the laser, time-resolved spectroscopy has been employed. The combination of many methods of optical investigations enabled a comprehensive characterisation and as a result an optimisation of the whole laser structure.