Capping of $\mathrm{GaN}$ quantum dots with $\mathrm{AlN}$ has been studied at the monolayer scale by combining atomic force microscopy, high resolution electron microscopy, and grazing incidence x-ray anomalous diffraction. Consistent with the results provided by these three techniques, it has been demonstrated that, following a wetting of the dots by an $\mathrm{AlN}$ layer up to $4\mathrm{ML}$ coverage, subsequent capping is dominated by a preferential $\mathrm{AlN}$ growth in between the dots, eventually resulting in a complete smoothing of $\mathrm{AlN}$. Interdiffusion has been shown to be negligible during this process, which makes the $\mathrm{GaN}∕\mathrm{AlN}$ system unique among semiconductors.

• Received 29 May 2006

DOI:https://doi.org/10.1103/PhysRevB.74.195302