Pulsed Laser Deposition of Zinc Sulfide Thin Films on Silicon: The influence of substrate orientation and preparation on thin film morphology and texture
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The effect of orientation and preparation of silicon substrates on the growth morphology and crystalline structure of ZnS thin films deposited by pulsed laser deposition (PLD) has been investigated through scanning electron microscopy (SEM) and grazing incidence x-ray diffraction (GIXRD). ZnS thin films were grown on silicon (100) and (111), on HF-treated and untreated silicon (100) as well as substrates coated with Al, Ge and Au. The ZnS films showed entirely different morphologies for ZnS films grown on silicon (100) and (111) substrates, but a preferred orientation largely independent of substrate orientation, preparation or coating. The films are either wurtzite (W) or a mixture of wurtzite or zinc blende (ZB). The preferred orientation is suggested to be related to the lower surface energies of the W(001) surface, and the ZB(111) surface in a Zn-poor environment. A technique for in-situ removal of native oxide from silicon by laser ablation of a ZnS target was tested and found to remove a significant amount of the surface of the substrates. The reoxidation in air of silicon (100) surfaces was monitored by ellipsometry, and HF-treated substrates were examined by RHEED. The results revealed that HF-treated Si(100) showed signs of rapid reoxidation in air, but this had no visible effect on ZnS film growth compared to untreated substrates.