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

Modeling of Si1−xGex(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 θGe 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 θGe. 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 θGe<0.4 ML and “2×8” at higher coverages. Quantitative θGe values were obtained by fitting the D2 TPD spectra and validated using in situ AES. Based upon θGe 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.