Formation of a compact Ga-doped ZnO layer over vertical free-standing GaP nanowires

We studied the process of deposition of a thin nanocrystalline ZnO layer on vertical free-standing GaP nanowires (NWs). The paper presents the preparation of a new type of composite antireflection coating based on a compact GaP NW/ZnO layer structure. The NWs were prepared using metal organic vapour phase epitaxy. They were grown at Au seeds created from a ∼0.3 nm thick Au layer, which was deposited on GaP substrate by evaporation. RF sputtering was used to cover the NWs and substrate with a ZnO layer with a nominal thickness between 50 and 250 nm. While thinner ZnO layers wrapped the NWs and covered the substrate, thicker ones also filled the volume between the NWs and the ZnO wrapping acquired a shape that resembled that of cotton swabs. A compact and planarized GaP NW/ZnO layer structure was achieved by altering ZnO deposition with ZnO etching by Ar ions. GaP NW/ZnO layer structures, which differed in the degree of ZnO filling, exhibited antireflection behaviour that was superioir to that of GaP substrate with GaP NWs.