C incorporation and segregation during Si1−yCy/Si(0 0 1) gas-source molecular beam epitaxy from Si2H6 and CH3SiH3

We have used in situ D2 temperature-programmed desorption (TPD) to probe C incorporation and surface segregation kinetics, as well as hydrogen desorption pathways, during Si1−yCy(0 0 1) gas-source molecular beam epitaxy from Si2H6/CH3SiH3 mixtures at temperatures Ts between 500 and 650 °C. Parallel D2 TPD results from C-adsorbed Si(0 0 1) wafers exposed to varying CH3SiH3 doses serve as reference data. Si1−yCy(0 0 1) layer spectra consist of three peaks: first-order β1 at 515 °C and second-order β2 at 405 °C, due to D2 desorption from Si monodeuteride and dideuteride phases, as well as a new second-order C-induced γ1 peak at 480 °C. C-adsorbed Si(0 0 1) samples with very high CH3SiH3 exposures yielded a higher-temperature TPD feature, corresponding to D2 desorption from surface C atoms, which was never observed in Si1−yCy(0 0 1) layer spectra. The Si1−yCy(0 0 1) γ1 peak arises due to desorption from Si monodeuteride species with C backbonds. γ1 occurs at a lower temperature than β1 reflecting the lower D–Si* bond strength, where Si* represents surface Si atoms bonded to second-layer C atoms, as a result of charge transfer from dangling bonds. The total integrated monohydride (β1+γ1) intensity, and hence the dangling bond density, remains constant with y indicating that C does not deactivate surface dangling bonds as it segregates to the second-layer during Si1−yCy(0 0 1) growth. Si* coverages increase with y at constant Ts and with Ts at constant y. The positive Ts-dependence shows that C segregation is kinetically limited at Ts⩽650 °C. D2 desorption activation energies from β1, γ1 and β2 sites are 2.52, 2.22 and 1.88 eV.