In general, the invention relates to a unit that includes a semiconductor and a plasmonic material disposed on the semiconductor, where a potential barrier is formed between the plasmonic material and the semiconductor. The unit further includes an insulator disposed on the semiconductor and adjacent to the plasmonic material and a transparent conductor disposed on the plasmonic material, where, upon illumination, the plasmonic material is excited resulting the excitation of an electron with sufficient energy to overcome the potential barrier.