Ab Initio Study of H₂ Associative Desorption on Ad-Dimer Reconstructed Si(001) and Ge(001)-(2×1) Surfaces

We investigate the pathways of hydrogen migration and associative desorption of H₂ on the Si(001) and Ge(001)-(2×1) reconstructed surfaces with adsorbed ad-dimers, using density functional theory methods. Although the trends obtained with common semilocal exchange–correlation functionals such as the generalized gradient approximation are correct, we show that the use of exact short-range Fock exchange in the calculations (by means of hybrid functionals) strongly affects the magnitude of the desorption barriers, especially for Ge surfaces, leading to a better estimate of the desorption temperatures. Our results for H₂ desorption kinetic barriers are well-supported experimentally and can therefore help to elucidate the mechanisms driving atomic layer epitaxy growth processes.