We propose a procedure to grow GaN quantum dots (QDs) on AlN by using the Ga surfactant effect in plasma-assisted molecular beam epitaxy. Self-formed GaN islands were spontaneously generated under vacuum, after evaporation of the Ga bilayer stabilizing the two-dimensional GaN layer grown under Ga-rich conditions. Island characteristics (size and density) are studied as a function of the nominal amount of GaN deposited. We demonstrate that the QD density can be controlled in the ${\text{3×10}}^{10}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}{\text{–2×10}}^{11}\hspace{0.17em}{\mathrm{cm}}^{\text{−2}}$ range. It is shown that beyond a given amount of GaN nominally deposited, there is a coexistence between elastic and plastic relaxation, with GaN islands being formed on a partially relaxed two-dimensional GaN layer thicker than two monolayers.

In this article, the surfactant capability of In for AlGaN growth by plasma-assisted molecular beam epitaxy has been assessed. We have determined the range of substrate temperatures and In fluxes to form a self-regulated 1×1 In adlayer on AlxGa1−xN(0001). The presence of this In film favors two-dimensional growth of AlGaN under stoichiometric conditions. The formation of metal droplets on the surface is inhibited. In incorporation, if any, is lower than 0.01%. The structural quality of the layers is verified by high-resolution x-ray diffraction, both in symmetric and asymmetric reflections.

We have studied the surface kinetics of N-face GaN during molecular-beam epitaxial growth by investigating the Ga wetting and the surface morphology. In the case of N-face GaN, it is not possible to establish the self-regulated Ga bilayer that is used as a surfactant for molecular-beam-epitaxy growth of Ga-face GaN. Indeed, to prevent the accumulation of Ga droplets, growth of the N-face GaN must be performed with less than one monolayer of excess Ga on the growing surface. Optimum surface morphology is achieved when growth is performed at the Ga accumulation limit.

Hybrid heterostructures based on bulk GaN and two-dimensional (2D) materials offer novel paths toward nanoelectronic devices with engineered features. Here, we study the electronic properties of a mixed-dimensional heterostructure composed of intrinsic $n$-doped $\mathrm{Mo}{\mathrm{S}}_2$ flakes transferred on $p$-doped GaN(0001) layers. Based on angle-resolved photoemission spectroscopy (ARPES) and high resolution x-ray photoemission spectroscopy (HR-XPS), we investigate the electronic structure modification induced by the interlayer interactions in $\mathrm{Mo}{\mathrm{S}}_2/\mathrm{GaN}$ heterostructure. In particular, a shift of the valence band with respect to the Fermi level for $\mathrm{Mo}{\mathrm{S}}_2/\mathrm{GaN}$ heterostructure is observed, which is the signature of a charge transfer from the 2D monolayer $\mathrm{Mo}{\mathrm{S}}_2$ to GaN. The ARPES and HR-XPS revealed an interface dipole associated with local charge transfer from the GaN layer to the $\mathrm{Mo}{\mathrm{S}}_2$ monolayer. Valence and conduction band offsets between $\mathrm{Mo}{\mathrm{S}}_2$ and GaN are determined to be 0.77 and $-0.51\mathrm{eV}$, respectively. Based on the measured work functions and band bendings, we establish the formation of an interface dipole between GaN and $\mathrm{Mo}{\mathrm{S}}_2$ of 0.2 eV.