C incorporation and segregation during Si1-yCy/Si(001) gas-source molecular beam epitaxy from Si2H6 and CH3SiH3

We have used in situ D-2 temperature-programmed desorption (TPD) to probe C incorporation and surface segregation kinetics, as well as hydrogen desorption pathways, during Si1-yCy(001) gas-source molecular beam epitaxy from Si2H6/CH3SiH3 mixtures at temperatures T-s between 500 and 650degreesC. Parallel D-2 TPD results from C-adsorbed Si(001) wafers exposed to varying CH3SiH3 doses serve as reference data. Si1-yCy(001) layer spectra consist of three peaks: first-order beta(1) at 515degreesC and second-order beta(2) at 405degreesC, due to D-2 desorption from Si monodeuteride and dideuteride phases, as well as a new second-order C-induced gamma(1) peak at 480degreesC. C-adsorbed Si(001) samples with very high CH3SiH3 exposures yielded a higher-temperature TPD feature, corresponding to D-2 desorption from surface C atoms, which was never observed in Si1-yCy(001) layer spectra. The Si1-yCy(001) gamma(1) peak arises due to desorption from Si monodeuteride species with C backbonds gamma(1) occurs at a lower temperature than beta(1) 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 (beta(1) + gamma(1)) intensity, and hence the dangling bond density, remains constant with gamma indicating that C does not deactivate surface dangling bonds as it segregates to the second-layer during Si1-yCy(001) growth. Si-* coverages increase with gamma at constant T-s and with T-s at constant gamma. The positive T-s-dependence shows that C segregation is kinetically limited at T-s less than or equal to 650degreesC. D-2 desorption activation energies from beta(1), gamma(1) and beta(2) sites are 2.52, 2.22 and 1.88 eV. (C) 2002 Elsevier Science B.V. All rights reserved.