Ion Implantation and Synthesis of Materials - Studium

10.2 Epitaxial Growth of Implanted Amorphous Si 1315400020000depth A°Backscattering yield (counts x 10 -3 )43210 min30 min60 min90 min120 min150 min00.9 1.0 1.1 1.2Energy (MeV)Fig. 10.4. Aligned spectra for 2 MeV He ions incident on Si samples implanted at liquidnitrogen temperature, preannealed at 400°C for 60 min and annealed at 550°C. The depthscale is calculated assuming the bulk density of Si (after Csepregi et al. 1976)Measurements of the growth velocity as a function of temperature indicate thatthe growth process is thermally activated, with an activation energy of about2.7 eV for Si and 2.0 eV for Ge. The Arrhenius plot of regrowth rate versus 1/T(Fig. 10.5) shows that the rate is strongly dependent on the orientation of theunderlying crystal substrate, and that the same activation energy (solid lines)describes the growth for the different orientations. For 〈111〉 oriented Si crystals,the initial growth rate over the first 1,000 Å of regrowth is plotted.Measurements of the growth velocity, v g of the crystal-amorphous interface areshown in Fig. 10.6. The measured velocities extend over nearly ten orders ofmagnitude and can be characterized by a single-activation energy, E A = 2.76 eV,(Olson and Roth 1988) so thatAg = v0 exp⎛ −⎞v⎜⎝E⎟kT ⎠(10.1)where the pre-exponential factor v0= 3.68 × 10 8 cm s −1 . The activation energymeasured for the epitaxial regrowth process is about half the value that is observed