Hydrogen desorption kinetics and Ge₂H₆ reactive sticking probabilities on Ge-adsorbed Si(0 1 1)

Modeling of Si_1-xGe_x(0 1 1) gas-source epitaxy from hydride precursors requires knowledge of reactive sticking probabilities and hydrogen desorption kinetics. We use D₂ temperature programmed desorption (TPD), reflection high energy electron diffraction (RHEED), Auger electron spectroscopy (AES), and kinetic modeling to determine hydrogen desorption kinetics from, and Ge₂H₆ reactive sticking probabilities at, Si and Ge sites on Ge-adsorbed Si(0 1 1) samples with Ge surface coverages θ_Ge between 0 and 1 ML. Following Ge adsorption, the samples were exposed to atomic D until saturation coverage at 250 °C. TPD spectra consist of five second-order peaks due to D₂ desorption from, in order of decreasing temperature, Si rest-atom and adatom monodeuterides, Si dideuteride, and Ge rest-atom and adatom monodeuteride phases. The maximum temperatures of all five peaks shift to lower values with increasing θ_Ge. We attribute this, as in the case of Ge-adsorbed Si(0 0 1), to a decrease in Si-D and Ge-D binding energies due to long-range electronic interactions. Ge/Si(0 1 1) surface reconstructions, determined by RHEED, are "16 × 2" with θ_Ge < 0.4 ML and "2 × 8" at higher coverages. Quantitative θ_Ge values were obtained by fitting the D₂ TPD spectra and validated using in situ AES. Based upon θ_Ge vs Ge₂H₆ exposure data and modeling of the adsorption kinetics, we obtain zero-coverage Ge₂H₆ reactive sticking probabilities of 1.9 × 10^-2 and 4.8 × 10^-3 at Si and Ge sites, respectively.