Parasitic Al_xO_yN_z surface defects on high-temperature annealed AlN and their role in hillock formation

High quality AlN buffer layers on sapphire wafers are a prerequisite for further improving UV LEDs. In addition, AlN templates with low screw-dislocation density might be interesting for future power electronic devices. High-temperature annealing (HTA) has proven to be a viable route to improve the crystallinity of sputtered or thin metalorganic vapor-phase epitaxy (MOVPE) AlN layers. In this work, the influence of two different pretreatment conditions prior to the MOVPE regrowth on HTA AlN templates was analyzed. AFM studies found a hillock density of roughly 10(6) cm(-2) in regrown AlN, whereby such hillocks could no longer be observed after introducing harsher bake conditions. The origin of the observed hillock defects was clarified by using different TEM-related measurement techniques. Based on the TEM and AFM findings, a double-spiral enhanced growth mode that emits concentric surface steps on top of c-AlON islands is suggested as a underlying mechanism for hillock formation. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license