Efficient field emission and optical properties of in-doped cadmium sulphide nanopens and nanopencils

Quasi-aligned indium (In)-doped cadmium sulphide (CdS) nano structures synthesised by the gold (Au) metal-catalysed vapour-liquid-solid growth method on silicon (Si) substrates under different experiment conditions are reported. X-ray diffraction analysis on the as-prepared samples indicated the nanostructures as ´wurtzite-type´ CdS crystal structures. Characterisation of the morphology and structure revealed the growth of two different geometries; nanopens and nanopencils with tip diameters ranging from 50-100 nm which can be varied through experimental conditions. Electron field emission measurements on the indium-doped quasi-aligned nanopencils and nanopens exhibit low turn-on electric fields of 5.5 and 4.5 V/μm (at the current density of 0.01 mA/cm²) for nanopens and nanopencils, respectively. This low turn-on field can be attributed to the sharp tip and higher indium doping level in the nanostrcutures. In addition, the indium doping into the CdS lattice was analysed by low-temperature photoluminescence spectroscopy (LT-PL). Temperature-dependent PL measurements showed that the PL spectra have three emission peaks at 9 K, which can be attributed to band edge free exciton emission and shallow donor levels donor-acceptor pair exciton emission because of doping. The result presents the promising application of these materials in the field of optoelectronics as efficient electron field emitters.