A near-edge X-ray absorption fine structure study of atomic layer epitaxy: the chemistry of the growth of CdS layers on ZnSe(100)

Atomic layer epitaxy (ALE) using a binary reaction sequence of the precursors dimethylcadmium (DMCd) and hydrogen sulfide (H2S) is shown to produce epitaxial layers of CdS on a ZnSe(100) substrate. Near-edge X-ray adsorption fine structure (NEXAFS) spectra taken at the carbon K-edge and sulfur L-edge are consistent with a growth model based on self-limiting surface reactions and support a mechanism based on sequential surface ligand displacement. This evidence, combined with a TPD study, shows the presence of alternating methyl- and hydride-terminated surfaces, which are passivated to further uptake of Cd or S, respectively. Layer-by-layer growth of good quality CdS was confirmed by comparison of NEXAFS spectra of bulk CdS with our grown films.