Methods of forming isolation structures are disclosed. A method of forming isolation structures for an image sensor array of one aspect may include forming a dielectric layer over a semiconductor substrate. Narrow, tall dielectric isolation structures may be formed from the dielectric layer. The narrow, tall dielectric isolation structures may have a width that is no more than 0.3 micrometers and a height that is at least 1.5 micrometers. A semiconductor material may be epitaxially grown around the narrow, tall dielectric isolation structures. Other methods and apparatus are also disclosed.