We have measured the cathodoluminescence of individual GaN quantum discs embedded in GaN/AlGaN nanowires. The measured sizes of the individual QDiscs, which could be as small as 1 nm (4 monolayers) were correlated one to one to their emission wavelengths, showing a marked Quantum confined Starck effect and a clear effect of the local strain on the optical properties of QDiscs. The results just appeared in (L. F. Zagonel et al., Nano Letters (2011)). A video of a recent seminar by L. F. Zagonel has been recently released.
We report the spectral imaging in the UV to visible range with nanometer scale resolution of closely packed GaN/AlN quantum disks in individual nanowires using an improved custom-made cathodoluminescence system. We demonstrate the possibility to measure full spectral features of individual quantum emitters as small as 1 nm and separated from each other by only a few nanometers and the ability to correlate their optical properties to their size, measured with atomic resolution. The direct correlation between the quantum disk size and emission wavelength provides evidence of the quantum confined Stark effect leading to an emission below the bulk GaN band gap for disks thicker than 2.6 nm. With the help of simulations, we show that the internal electric field in the studied quantum disks is smaller than what is expected in the quantum well case. We show evidence of a clear dispersion of the emission wavelengths of different quantum disks of identical size but different positions along the wire. This dispersion is systematically correlated to a change of the diameter of the AlN shell coating the wire and is thus attributed to the related strain variations along the wire. The present work opens the way both to fundamental studies of quantum confinement in closely packed quantum emitters and to characterizations of optoelectronic devices presenting carrier localization on the nanometer scale.