Epitaxial ZnS films grown on GaAs (001) and (111) by pulsed-laser ablation

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Abstract
Pulsed KrF (248 nm) laser ablation of a polycrystalline ZnS target has been used to grow very smooth and carbon-free, epitaxial ZnS thin films on GaAs (001) and (111). Films were grown at temperatures of 150–450 °C, using a rotating substrate heater and deposition geometry that produces highly uniform film thickness, without nucleation or surface-roughening problems. X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) show that the ZnS films are fully epitaxial (in-plane aligned). Films grown at the optimum temperature of 325 °C have x-ray rocking curve widths that are indistinguishable from molecular-beam-epitaxy-grown ZnS/GaAs films of the same thickness. Rutherford backscattering spectrometry and HRTEM show that in films ∼275 nm thick, the ∼150 nm nearest the GaAs-ZnS interface is highly faulted, due to the ∼4.1% lattice mismatch and/or the low ZnS stacking fault energy, but the upper ∼125 nm is much less defective. The anisotropy of the ZnS epitaxial growth rate between the GaAs (001) and GaAs (111) surfaces was found to be slightly temperature dependent.