Growth of CuCl thin films by magnetron sputtering for ultraviolet optoelectronic applications

Copper (I) chloride (CuCl) is a potential candidate for ultraviolet (UV) optoelectronics due to its close lattice match with Si (mismatch less than 0.4%) and a high UV excitonic emission at room temperature. CuCl thin films were deposited using radio frequency magnetron sputtering technique. The influence of target to substrate distance $(dts)$ and sputtering pressure on the composition, microstructure, and UV emission properties of the films were analyzed. The films deposited with shorter target to substrate spacing $(dts=3cm)$ were found to be nonstoichiometric, and the film stoichiometry improves when the substrate is moved away from the target (⁠$dts=4.5$ and $6cm$⁠). A further increase in the spacing results in poor crystalline quality. The grain interface area increases when the sputtering pressure is increased from $1.1×10−3to1×10−2mbar$ at $dts=6cm$⁠. Room temperature cathodoluminescence spectrum shows an intense and sharp UV exciton $(Z3)$ emission at $∼385nm$ with a full width at half maximum of $16nm$ for the films deposited at the optimum $dts$ of $6cm$ and a pressure of $1.1×10−3mbar$⁠. A broad deep level emission in the green region $(∼515nm)$ is also observed. The relative intensity of the UV to green emission peaks decreased when the sputtering pressure was increased, consistent with an increase in grain boundary area. The variation in the stoichiometry and the crystallinity are attributed to the change in the intensity and energy of the flux of materials from the target due to the interaction with the background gas molecules.