| At high B doping concentrations in GS-MBE Si(001):B films, ordered B subunits in the second layer weaken surface Si-H bonds while deactivating Si dimer dangling bonds during film growth. TPD was used to obtain the B segregation enthalpy DeltaHs as -0.53 eV. RSi increases with increasing CB ≥ 2 x 1019 cm -3 at Ts ≤ 550°C, where steady state H coverages are high, due to B-enhanced H desorption rates. At Ts ≥ 600°C, corresponding to much lower steady state thetaH values, R Si decreases due to B-induced deactivation of Si dangling bonds. For B-doped Ge(001) layers, similar results to B-doped Si have been found. The TPD results were used to determine the B segregation enthalphy, -0.64 eV. At Ts = 600°C, RGe decreases by up to 40% with increasing CB ≥ 1020 cm-3 due primarily to the deactivation of surface dangling bonds.; From TPD measurements, it was shown that hydrogen desorption from Si 1-xGex(001) occurs directly from Si sites rather than Ge sites. However, the H desorption activation energy at Si sites decreases rapidly with increasing Ge concentration both in the surface layer and in the underlayer due to bond weakening resulting from long range electronic interactions. The Ge segregation enthalpy varies from -0.28 eV at T s ≥ 700°C where thetaH → 0 to -0.1 eV at Ts ≤ 450°C where thetaH → 1 ML. Film growth rates RSiGe decreases with increasing Ge concentration in the flux-limited regime due to a corresponding decrease in Si2H 6 and Ge2H6 reactive sticking probabilities. At lower growth temperatures, in the surface-reaction-limited regime, R SiGe increases rapidly with increasing Ge concentration since the higher steady-state dangling bond coverages more than compensate for the loss in reactive sticking probabilities. RSiGe curves calculated using a simple transition-state model together with measured kinetic parameters SSiGe2H6, SGeSi2H6, qGe, and thetaH, were found to exhibit good agreement with experimental data.; Based on all the above results, the growth kinetics of B doped Si 1-xGex(001) GS-MBE were modeled. Film deposition rates RSiGe decrease by ≈50% with increasing CB ≥ 5 x 1019 cm-3 at Ts = 500°C. The TPD results were used to determine the B segregation enthalpy, -0.4 eV, significantly lower than the value for Si(001):B, -0.53 eV. |
