Low-temperature epitaxial growth of CaF, on (NH 4)2S .-treated GaAs( 100) surface

We have investigated the method of forming a high-quality CaF, film onto a GaAs(100) surface. We used X-ray diffractometry and Rutherford backscattering spectrometry to characterize the film quality. We demonstrate that pretreatment of GaAs wafer surfaces by (NH,),S, solution leads to the epitaxial growth of CaF, on the GaAs(100) surface at a substrate temperature of around 200°C. We suggest that both oxide removal by (NH&S, etching and sulfur passivation of the surface are crucial to the low-temperature epitaxial growth of CaF,. At a substrate temperature of 3OO”C, the epitaxy quality of CaF, is deteriorated.