Local probe techniques for luminescence studies of low-dimensional semiconductor structures

With the rapid development of technologies for the fabrication of, as well as applications of low-dimensional structures, the demands on characterization techniques increase. Spatial resolution is especially crucial, where techniques for probing the properties of very small volumes, in the extreme case quantum structures, are essential. In this article we review the state-of-the-art in local probe techniques for studying the properties of nanostructures, concentrating on methods involving monitoring the properties related to photon emission. These techniques are sensitive enough to reveal the electronic structure of low-dimensional semiconductor structures and are, therefore, able to give detailed information about the geometrical structure, including fabrication-related inhomogeneities within an ensemble of structures. The local luminescence probe techniques discussed in this review article can be divided into four categories according to the excitation source: (i) spatially localized microphotoluminescence spectroscopy using either strong focusing or masking; (ii) near-field optical microscopy to reach below the diffraction limitation of far-field optics, by either exciting, detecting, or both exciting and detecting in the near field; (iii) cathodoluminescence using focused energetic electrons in an electron microscope; and (iv) scanning tunneling luminescence, using low-energy electrons injected or extracted from the tip of a scanning tunneling microscope.