Defect reduction by epitaxial lateral overgrowth of nanorods in ZnO/(0001) sapphire films

Abstract

It is shown that epitaxial ZnO/(0001) sapphire films grown by pulsed laser deposition have defect-free Zn-polar nanorods protruding from a continuous O-polar underlayer containing high densities of threading dislocations (TDs). By continuing the ZnO growth hydrothermally, the nanorods grew laterally over the O-polar layer. TDs in the underlayer were thereby blocked and only formed in the overlayer when nanorods coalesced. This epitaxial lateral overgrowth produced continuous Zn-polar films with TD densities reduced to 1×109∕cm2 from 7×1010∕cm2 in the underlayer. It is noted that the same growth mode can be achieved in GaN/(0001) sapphire films.