Light Emission by Semiconductor Nanostructures in Dielectric Medium or Close to Plane Interface

P. Lavallard Groupe de Physique des Solides, CNRS URA 17, Universités Paris VI et VII, Tour 23, 2 place Jussieu, 75251 Paris Cedex 05, France

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We review several situations in which the emission rate of a nanostructure is modified by its environment. We first consider small objects embedded in media with different refractive indices. The local electromagnetic field and the rate of spontaneous emission of the nanostructure are enhanced or inhibited by the induced dipole charges on the interface. In quantum wells or nanocrystals embedded in a low dielectric constant medium, the binding energy of excitons is increased. In anisotropic microcrystals, the local field is anisotropic and emission of light is polarized. We consider especially the case of p+-doped porous silicon in which nanocrystals are elongated. Another interesting situation occurs when a dipole is in the vicinity of a dielectric interface. The local field acting on the dipole results from the interferences of incident and reflected beams. Contributions from evanescent waves are important when the dipole is located in the medium of low refractive index, very close to the surface. The intensity of emission and its pattern are modified by the vicinity of the dielectric interface. Close to the interface semiconductor/air, the exciton binding energy is increased. In the vicinity of a metallic surface, a nonradiative transfer to the metal occurs for small distances of the nano-object or quantum well to the surface and the quantum efficiency varies with the distance to the metallic surface. The exciton binding energy of a quantum well is decreased close to a metallic surface.

DOI: 10.12693/APhysPolA.90.645 PACS numbers: 78.20.Bh, 78.55.Cr, 78.55.Et