An optoelectronic device includes a semiconductor substrate with a first set of epitaxial layers formed on an area of the substrate defining a lower distributed Bragg-reflector (DBR) stack. A second set of epitaxial layers formed over the first set defines a quantum well structure, and a third set of epitaxial layers, formed over the second set, defines an upper DBR stack. At least the third set of epitaxial layers is contained in a mesa having sides that are perpendicular to the epitaxial layers. A dielectric coating extends over the sides of at least a part of the mesa that contains the third set of epitaxial layers. Electrodes are coupled to the epitaxial layers so as to apply an excitation current to the quantum well structure.