C incorporation and segregation during Si 1y C y =Si(0 0 1) gas-source molecular beam epitaxy from Si 2 H 6 and CH 3 SiH 3 Y.L. Foo, K.A. Bratland, B. Cho, J.A.N.T. Soares, P. Desjardins, J.E. Greene * Frederick Seitz Materials Research Laboratory and the Materials Science Department, University of Illinois, 104 S Goodwin Avenue, Urbana, IL 61801, USA Received 12 December 2001; accepted for publication 23 April 2002 Abstract We have used in situ D 2 temperature-programmed desorption (TPD) to probe C incorporation and surface segre- gation kinetics, as well as hydrogen desorption pathways, during Si 1y C y (0 0 1) gas-source molecular beam epitaxy from Si 2 H 6 /CH 3 SiH 3 mixtures at temperatures T s between 500 and 650 °C. Parallel D 2 TPD results from C-adsorbed Si(0 0 1) wafers exposed to varying CH 3 SiH 3 doses serve as reference data. Si 1y C y (0 0 1) layer spectra consist of three peaks: first-order b 1 at 515 °C and second-order b 2 at 405 °C, due to D 2 desorption from Si monodeuteride and dideuteride phases, as well as a new second-order C-induced c 1 peak at 480 °C. C-adsorbed Si(0 0 1) samples with very high CH 3 SiH 3 exposures yielded a higher-temperature TPD feature, corresponding to D 2 desorption from surface C atoms, which was never observed in Si 1y C y (0 0 1) layer spectra. The Si 1y C y (0 0 1) c 1 peak arises due to desorption from Si monodeuteride species with C backbonds. c 1 occurs at a lower temperature than b 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 ðb 1 þ c 1 Þ 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 Si 1y C y (0 0 1) growth. Si  coverages increase with y at constant T s and with T s at constant y. The positive T s -dependence shows that C segregation is kinetically limited at T s 6 650 °C. D 2 desorption activation energies from b 1 , c 1 and b 2 sites are 2.52, 2.22 and 1.88 eV. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Thermal desorption spectroscopy; Epitaxy; Surface segregation; Silicon; Carbon; Alloys 1. Introduction C-containing group-IV semiconductor alloys are of intense technological and scientific interest due to the potential they offer for both bandgap and strain-state engineering of layers used in mi- croelectronic and optoelectronic devices compati- ble with Si integrated circuit technology. Adding C to Si 1x Ge x alloy layers pseudomorphically grown on Si(0 0 1) rapidly reduces the compressive strain and leads to increased critical thicknesses for nucleation of misfit dislocations. The addition of C has also been shown to inhibit B diffusion in npn bipolar heterojunction transistors [1], while pseudomorphic Si 1y C y /Si(0 0 1) structures provide Surface Science 513 (2002) 475–484 www.elsevier.com/locate/susc * Corresponding author. Tel.: +1-217-3331370; fax: +1-217- 2442278. E-mail address: greene@mrlxp2.mrl.uiuc.edu (J.E. Greene). 0039-6028/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0039-6028(02)01821-6