Effects of passivation and ambient gases on the photoluminescence of ZnSe nanowires

The effects of photoadsorbed H-2, N-2, O-2 and Ar on the photoluminescence (PL) of ZnSe nanowires are studied. The nanowires were grown by metalorganic chemical vapour deposition. Passivation and cleaning by photodesorption in vacuum serve to sensitize the surface of the nanowires to adsorbed gases. The PL intensity of the near band edge emissions is enhanced after each sensitizing step. When different gases are photoadsorbed, different responses in the intensity are observed; it increases for H-2 while it decreases for N-2, O-2 and Ar. While the effects of other gases can be reversed by photodesorption, that Of O-2 cannot. Once oxidized, the nanowires are no longer sensitive to the ambient gases. Only above band gap photons are found to induce the adsorption, desorption and oxidation, below band gap photons are found to be ineffective. The results are understood from a picture of surface states and band bending and may form the basis of using nanowires to fabricate re-useable, multi-gas sensors.