High quality crystalline ZnS films grown on sapphire and silicon using pulsed laser deposition

Abstract

Crystalline Zinc sulphide (ZnS) is widely applied in electroluminescent devices, blue or ultraviolet light emitting diodes, laser diodes and tuneable mid-infrared lasers and second harmonic generation devices. Crystalline ZnS has two crystallographic phases, zinc blende (cubic) and wurtzite (hexagonal): wurtzite has strong nonlinear optical effects and it transforms to the zinc blende structure at 1020 C. Problems arise however from lattice, polarity and thermal parameter matches in using commonly available substrates Si, GaAs, sapphire, GaP and Ge for epi-growth of crystalline ZnS.
Crystalline ZnS thin films can be prepared by conventional deposition techniques such as liquid or vapour phase epitaxy. Due to low growth temperature and low kinetic energy of the transporting molecules in conventional epitaxy, crystalline ZnS grown on various substrates is normally of zinc blende structure and poor crystalline quality. Pulsed laser deposition (PLD) on the other hand is a carbon-free and physical transport process. The ablative target material has very high kinetic energy and forms a high flux plasma plume. This is particularly helpful for the vapour phase epitaxial growth of stoichiometric ZnS films.

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ORCID for R.W. Eason: orcid.org/0000-0001-9704-2204

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