Epitaxial metastable Ge1-yCy (y <= 0.02) alloys grown on Ge(001) from hyperthermal beams: C incorporation and lattice sites

Epitaxial metastable Ge1-yCy alloy layers with y less than or equal to 0.02 were grown on Ge(001) at temperatures T-s=200-550 degrees C using hyperthe rmal Ge and C beams with average energies of 16 and 24 eV, respectively, in order to investigate C incorporation pathways in the Ge lattice. High-reso lution reciprocal lattice maps show that all as-deposited alloy layers are fully coherent with the substrate. Layers grown at T(s)less than or equal t o 350 degrees C are in compression due to higher C concentrations in inters titial than in substitutional sites. The compressive strain decreases (i.e. , the substitutional C concentration increases) with increasing T-s within this temperature range. At higher growth temperatures, as-deposited alloys are nearly strain free since the majority of the incorporated C is trapped at extended defects. Annealing the Ge1-yCy layers at T-a=450 and 550 degree s C leads to a significant increase, proportional to the strain in the as-d eposited films, in compressive strain. Further annealing at T-a=650 degrees C results in the formation of dislocation loops which act as sinks for int erstitial and substitutional C atoms and thus relieves residual macroscopic strain. Finally, we show that the large compressive strain associated with interstitial C atoms must be accounted for in order to determine the total incorporated C fraction from diffraction analyses. (C) 2000 American Insti tute of Physics. [S0021-8979(00)03513-1].