EPITAXIAL ZNS FILMS GROWN ON GAAS (001) AND (111) BY PULSED-LASER ABLATION

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-degrees-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-degrees-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 approximately 275 nm thick, the approximately 150 nm nearest the GaAs-ZnS interface is highly faulted, due to the approximately 4.1 % lattice mismatch and/or the low ZnS stacking fault energy, but the upper approximately 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.