Epitaxial SiP growth is done by CVD process that utilizes Dichlorosilane (DCS) as the Silicon source and Phosphine (PH3) as the phosphorus source. We further add HCl gas precursor that selectively etches away any non-crystalline material (typically deposited on the side walls). This helps improve the selectivity of the epi process and ensures that we only get a high-quality mono-crystalline epi film at the very bottom of the trench .