A method of forming an array of nanostructures includes forming a plurality of seed points on a surface of a substrate, and growing masks from the seed points to create masked regions of the substrate underlying the masks. A remainder of the substrate comprises an unmasked region. Each mask and masked region increase in size with growth time while the unmasked region of the substrate decreases in size. During the growing, the unmasked region is etched to remove material from the substrate in a depth direction, and, simultaneously, unetched structures are formed from the masked regions of the substrate underlying the masks. Each of the unetched structures has a lateral size that increases with depth.