Mechanism of aluminum nitride etching with variation of potassium hydroxide molarity

Abstract AlN has become an essential base layer for AlGaN UV LEDs heterostructure. In an effort to improve the LED performance, which is crucial for large-scale applications, the AlN layer must exhibit low threading dislocation density. This goal can be achieved by introducing patterns structures on the surface of the AlN layer. In the present study, the patterns in the form of hexagonal pits were introduced by electrochemical KOH etching with different KOH molarities, i.e., 2.5M, 5M, 10M and 20M. The obtained results have revealed that the number of hexagonal pits increased with increasing KOH concentration up to 10M. An increase in the KOH concentration resulted in a higher number of OH - components, which enhanced the etching effect. Nonetheless, the number of pits was reduced with 20M KOH etching. Under this condition, excessive OH - components can completely remove a few nanometres layer of the AlN. Additionally, over period of time, Al-O compounds formed on the surface, passivating the AlN layer. This, in turn, restricted the lateral etching, while enhancing the vertical etching, resulting in deeper pits. Further analysis revealed that 10M KOH etching promoted a higher number of hexagonal pits, leading to further XRD-FWHMs reduction and strain relaxation compared to other cases. The results from this study shed light on how KOH molarity can influence the etching mechanism for AlN, paving a way to develop optimal AlN layers in a straightforward manner for AlGaN UV LED.