Intraband Optical Transitions

Abstract

The photoluminescence measurements are the basic tool that allow for the investigation of discrete energy levels of quantum dots. For this reason this is usually the first step in the studies of quantum dots obtained by various methods (described previously in Chap. 2). The idea of the photoluminescence experiment is presented in Fig. 6.1. A laser beam of appropriate wavelength excites the electrons from the valence band (VB) to the conduction band (CB) and creates electron-hole pairs (γin → e + h). These pairs can be excited directly into the discrete levels in the quantum dot, or above the discrete levels; to the two-dimensional quantum-well continuum or (even higher excitation energy) to the bulk semiconductor continuum. A fraction of the generated particles relax nonradiatively and fall to the ground state or to weakly excited states in quantum dots. The electron-hole pairs confined in the dots recombine, emitting photons, which are then registered (e + h →γOut)