Can we always control the thickness layer in the MBE method with atomic precision? Analysis of the problem on the MQWs GaN/AlN example

The GaN/AlN multiple-quantum-wells (MQWs) structures were studied using high resolution scanning transmission electron microscopy simulations (HR STEM) and the experimental data from HR STEM measurements. GaN/AlN MQWs were synthesized by plasma-assisted molecular beam epitaxy (PAMBE). The electron microscopy methods were used to examine both interfaces. It was shown that AlN /GaN interfaces are sharp while the GaN/AlN are diffuse over two atomic layers. The latter diffusional disorder is not related to the basic limitation of the PAMBE method, but to the chemical growth properties of GaN. The three cases were investigated: sharp interface, diffuse single monolayer (ML) and diffusive two MLs.