Optimisation and fabrication of ultra violet emitting CuC1 thin films by RF sputtering
Natarajan, Gomathi (2007) Optimisation and fabrication of ultra violet emitting CuC1 thin films by RF sputtering. PhD thesis, Dublin City University.
Full text available as:
Wide direct band gap CuCl is a promlslng candidate for the next generation Si based optoelectronics, thanks to its excellent properties such as high excltonic binding energy (190 meV) and a close lattice matching with Si.
In this thesis, growth of CuCl using RF magnetron sputtering is investigated in detail. Stoichiometry and microstructure are the two major deciding factors for the UV emission from the film. We have successfully controlled both these properties by varying the sputtering parameters. Chemical stoichiometry was mainly controlled by the spacing between the target and substrate. An optimum spacing of 6 cm was found to yield films with Cu/Cl ratio almost close to stoichiometry (Cu/Cl = 0.94). A more fine control was achieved providing a suitable bias to the substrate and high quality stoichiometric CuCl films were obtained.
Microstructural evaluation revealed that the grain interface area of the film increases on increasing the sputtering pressure. UV emission properties were found to be influenced by the existence of meso- and nanostructural interfaces within the thin film. Cathodoluminescence studies showed a strong UV exciton emission and a green emission from deep levels in a non-stoichiometric and lower crystalline quality samples. CuCl films deposited with optimum sputtering parameters showed good optical quality with an intense and sharp UV emission at room temperature without any deep level emission.
Excitonic line transitions of sputtered CuCl films were investigated using temperature dependant PL spectroscopy. The thermal activation energy was calculated to be 112 meV. Our results show that the sputtered CuCl films have relative higher optical quality compared to the other UV emitting materials such as epitaxially grown GaN and ZnO, demonstrating the potential for Si based UV photonic devices.
Preliminary electrical studies were carried out to identify the conduction mechanism associated with the sputtered CuCl thin films. Field dependant DC conduction studies on CuCl/Si structure indicates that ohmic conduction prevails in the lower field region and an electrode limited Schottky emission process was found to dominate the mechanism of charge carrier transport through these structures at higher fields.
Archive Staff Only: edit this record