Separation of AlN layers from silicon substrates by KOH etching

In this work, the AlN/Si(111) epitaxial structures grown consistently by plasma assisted molecular beam epitaxy (PA MBE) and hydride vapour phase epitaxy (HVPE) methods were studied. The PA MBE AlN buffer layers were synthesized via coalescence overgrowth of self-catalyzed AlN nanocolumns on Si(111) substrates and were used as templates for further HVPE growth of thick AlN layer. It was shown that described approaches can be used to obtain AlN layers with sufficiently smooth morphology. It was found that HVPE AlN inherited crystallographic polarity of the AlN layer grown by PA MBE. It was demonstrated that the etching of such AlN/Si(111) epitaxial structures results in partial separation of the AlN epilayers from the Si(111) substrate and allows to form suspended structures. Moreover, the avoidance of surface damage and backside overetching was achieved by use thin Cr film as surface protective coating and by increasing the layer thickness accordingly.