GaN/Al 0.5 Ga 0.5 N quantum dots and quantum dashes

GaN/Al 0.5 Ga 0.5 N nanostructures grown on c ‐plane sapphire by molecular beam epitaxy using ammonia as N source have been studied. Depending on the ammonia pressure during the two dimensional – three dimensional transition of the GaN layer, the shape of the islands is strongly modified: elongated or isotropic islands are observed, leading to the formation of quantum dashes or quantum dots, respectively. This shape transition is seen as a consequence of a change in surface energy. The change of morphology of the GaN layer is clearly evidenced by photoluminescence measurements, and a large redshift in the emission peak is observed for quantum dashes as compared to quantum dots. An electric field ∼3 MV/cm is estimated from the measurements at an excitation power ∼20 mW/cm 2 . Weak photoluminescence quenching between low and room temperature for both QDs and QDashes structures is observed, indicating a strong confinement of carriers into the nanostructures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)