How non-invasive are metal nano-apertures on a semiconductor quantum well?

Summary form only given. Metal apertures, with diameters down to 100 nm, on semiconductor quantum well (QW) samples have extensively been used to obtain subwavelength optical resolution in quantum dot experiments, e.g. When preparing such samples for time-resolved experiments, we have noticed that the optical properties of the semiconductor film underneath the metal aperture do not remain unchanged. Our investigations have shown (a) that this effect is intrinsic for a QW near the surface and (b) that the interplay of optically excited carriers and the built-in electrostatic potential well underneath the aperture leads to characteristic ring structures in luminescence images.