An embodiment includes a device comprising: a fin structure including an upper portion and a lower portion, the upper portion having a bottom surface directly contacting an upper surface of the lower portion; wherein (a) the lower portion is included in a trench having an aspect ratio (depth to width) of at least 2:1; (b) the bottom surface has a bottom maximum width and the upper surface has an upper maximum width that is greater the bottom maximum width; (c) the bottom surface covers a middle portion of the upper surface but does not cover lateral portions of the upper surface; and (d) the upper portion includes an upper III-V material and the lower portion includes a lower III-V material different from the upper III-V material. Other embodiments are described herein.