Fabrication of Single-Photon Sources by Use of Pyramidal Quantum-Dot Microcavities
In recent years the interest in single-photon emitters for quantum-optical applications is strongly increasing. For this purpose, we have investigated In(Ga)As quantum-dots (QDs) embedded in reversed pyramidal GaAs microcavities (Fig. 52.1a). Even though it has been shown recently, that such cavities can act as high-Q optical resonators , our focus has been on the directional radiation of the QD emission due to reflection at the facets of the reversed pyramids. With QDs embedded close to the vertex of the four facets and a base angle adaptable between 35° and 55° the pyramids can be perceived as a kind of retroreflector. Since the QD layer is inserted near the tip of the predicted reversed pyramid during molecular-beam epitaxial (MBE) growth, the average number of QDs inside the cavity can be reduced to one, depending on the size of the pyramid and density of QDs. The pyramidal cavities are shaped after MBE growth by a wet-chemical etching process with a solution of H3PO4, H2O2 and H2O [2, 3].
In order to analyze the radiation characteristics for continuous optical excitation, a Hanbury-Brown and Twiss setup has been used. The measured correlation function reveals a g(2)(0) of 0.26 which is sufficient to prove the single-photon character of the emitted light (Fig. 52.1c).