Si1-xGex(001) layers doped with B concentrations CB between 2 × 1016 and 2 × 1021 cm-3 were grown on Si(001)2×1 at Ts = 500-700°C by gas-so urce molecular-beam epitaxy (GS-MBE) from Si2H6, Ge2H6, and B2H6. Secondary-ion mass spectrometry measurements of modulation-doped structures demonstrate that B doping has no effect on the Ge incorporation probability. Steady-state B and Ge surface coverages (θB and θGe) were determined as a function of CB using in situ isotopically tagged temperature-programmed desorption. Results for Si0.82Ge0.18 layers grown at Ts = 500°C show that θGe, remains constant at 0.63 ML while the bulk B concentration increases linearly up to 4.6×1020cm-3 corresponding to saturation coverage at θB,sal = 0.5ML, with the incident precursor flux ratio ξ=B2H6/(JSi2H6 + JGe2H6). B is incorporated into substitutional electrically active sites over this entire concentration range. At higher B concentrations, CB increases faster than ξ and there is a large decrease in the activated fraction of incorporated B. The B segregation enthalpy during Si0.82Ge0.18(001) growth is -0.42 eV, compared to -0.53 and -0.64 eV during Si(001):B and Ge(001):B GS-MBE, respectively. Measured segregation ratios rB = θB/XB, where XB is the bulk B fraction, range from 15 to 500 with a temperature dependence which is consistent with equilibrium segregation. Film deposition rates R SiGe(CB) decrease by up to a factor of 2 with increasing CB ≥ 5 × 1019 cm-3, due primarily to a B-segregation-induced decrease in the dangling bond density. The above results were used to develop a robust model for predicting the steady-state H coverage θH, θB, θGe, and RSiGe as a function of ξ and Ts.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)