Photoluminescence and photoconductivity properties of copper-doped Cd1-xZnxS nanoribbons

Copper-doped Cd1-xZnxS (x similar to 0.16) nanoribbons were prepared by controlled thermal evaporation of CdS, ZnS, and CuS powders onto Au-coated silicon substrates. The nanoribbons had a hexagonal wurtzite structure, and lengths of several tens to hundreds of micrometres, widths of 0.6-15 mu m, and thicknesses of 30-60 nm. Cu doping and incorporation into the CdZnS lattice were identified and characterized by low-temperature photoluminescence (PL) and photoconductivity measurements. Temperature-dependent PL measurement showed that the PL spectra of both Cu-doped and undoped CdZnS nanoribbons have two emission peaks at 2.571 and 2.09 eV, which are assigned to band edge emission and deep trap levels, respectively. In addition, the Cu-doped nanoribbons present two extra peaks at 2.448 and 2.41 eV, which are attributed to delocalized and localized donor and acceptor states in the band gap of CdZnS resulting from Cu incorporation. Photoconductivity results showed the nanoribbons can be reversibly switched between low and high conductivity under pulsed illumination. The Cu-doped CdZnS nanoribbons showed four orders of magnitude larger photocurrent than the undoped ones. The current jumped from similar to 2 x 10(-12) to similar to 5.7 x 10(-7) A upon white light illumination with a power density of similar to 9 mW cm(-2). The present CdZnS: Cu nanoribbons may find applications in opto-electronic devices, such as solar cells, photoconductors, and chemical sensors.