Reproducible reflection high energy electron diffraction signatures for improvement of AlN using in situ growth regime characterization

Recently published methods that answer the previously unresolved critical issue of in situ growth regime determination during molecular beam epitaxy of AlN are used to address issues of material quality and intergrowth nonuniformity for improved repeatability using a modulated flux technique. A shutter modulation growth technique, defined as metal modulation epitaxy (MME), using the previously published reflection high-energy electron diffraction (RHEED) signatures was developed with the goal of obtaining materials with the properties of droplet regime materials, without the adverse effect of droplets. The films grown using MME were compared to films grown with no shutter modulation, and the surface roughness determined by atomic force microscopy was improved. For an unmodulated sample without droplets, the rms surface roughness was 6.9nm, while a sample with droplets had a rms surface roughness of 1.2nm. For the same Al flux that resulted in droplets with the unmodulated sample, the MME sample had no droplets and had a surface roughness of 3.3nm. Furthermore, while a nearly 20% increase in the Al flux still did not result in droplets for MME, a nearly 50% increase in the al flux did finally result in droplets. Therefore, by using MME, a wider range of Al flux is allowed for Al-rich growths without droplets. The results from the recently published RHEED transient characterization provide a powerful new tool that can be used as repeatable growth indicators that can possibly be used to standardize growths with techniques such as MME presented herein.