Intraband spectroscopy of self-organized GaN/AlN quantum dots

GaN/AlN quantum dots grown by molecular beam epitaxy either on silicon (1 1 1), sapphire or 6H–SiC (0 0 0 1) substrate have been investigated using photoluminescence, cathodoluminescence, Fourier transform infrared spectroscopy and attenuated total reflection spectroscopy. In-plane polarized intraband absorption is observed at energies of ∼150 and View the MathML source in GaN dots with 22 and View the MathML source base diameter, respectively. For bigger dots, we observe three interlevel absorptions with a polarization component along the c-axis at energies ranging from 0.52 to View the MathML source. Based on a simple 2D modelling of the confinement energies we show that the resonant absorptions involve conduction-band interlevel transitions between the electron ground state and states with one or two nodes along the c-axis and that in large dots, the internal field governs the transition energies.