An optical device includes a first electrode of a first conductivity type, and a second electrode of a second conductivity type. A nanowire is positioned between the first and second electrodes. The nanowire has at least two segments and a junction region formed between the at least two segments. One of the segments is the first conductivity type and the other of the segments is the second conductivity type. At least one of the at least two segments has a predetermined characteristic that affects optical behavior of the junction region.