Intra-cavity contacted VCSELs with polarization control

Top-emitting intra-cavity VCSELs have been fabricated by reactive-ion etching of a double mesa and applying p and n contact metallizations at the bottom of both mesas, respectively, where highly doped layers are inserted into the cavity on either side of the active region. The VCSELs are designed to emit around 980 nm, and use two strained InGaAs quantum wells and AlAs/GaAs DBR mirrors. Efficient lateral current constriction is realized by selective oxidation of two AlAs layers in the second mesa. A sealing method has been developed to prevent simultaneous oxidation of the top-DBR. A novel asymmetric contacting scheme is introduced in order to avoid current crowding at the inner edges of the oxidized AlAs layers and to stabilize the polarization. Devices with various mesa shapes and either symmetric or asymmetric contacts have been fabricated on the same wafer. Experimental analysis of these VCSELs demonstrates polarization control by asymmetric current injection, where the polarization perpendicular to the current path is favored due to anisotropy of both gain and optical losses. The strength of this effect relative to others (anisotropic loss in rectangular mesas, crystal anisotropy) and its use in electrically controlled polarization switching is explored.