Influence of Si doping on size of GaN quantum dots grown by molecular beam epitaxy under Ga-rich conditions

The size control of Si-doped GaN/AlN quantum dots (QDs) was studied by using molecular beam epitaxy under Ga-rich conditions that were widely used for high-quality thin-film growth. The formation of GaN QDs was affected by Si-doping in contrast with that of the QDs under N-rich condition. Atomic force microscopy images of Si-doped GaN QDs and undoped GaN QDs were clearly different. Diameters of Si-doped GaN QDs decreased with increase in Si concentration within 1 x 10(17)-10(20) cm(-3), whereas heights were almost constant. Micro-Raman spectroscopy showed that the LO phonon frequency shifted toward lower wavenumbers with increase in Si concentration. These results suggest that Si doping may affect the length of Ga-N bonds related with the elastic strain and, as a result, influence the aspect ratio of QDs. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.