Provided is a nanowire array, in which a plurality of nanowires are densely packed and in contact with each other via side walls to form a three-dimensional, compact layer structure, wherein the plurality of nanowires are formed from InGaN-based material. Also provided is an optoelectronic device comprising the nanowire array which is epitaxially grown on a surface of a substrate (12). Further provided are methods for preparing the nanowire array and the optoelectronic device.