B incorporation in Ge(001) grown by gas-source molecular-beam epitaxy from Ge2H6 and B2H6

Secondary-ion-mass spectrometry (SIMS) was used to determine the concentration and depth distribution of B incorporated into Ge(001)2×1 films grown on Ge(001) substrates by gas-source molecular-beam epitaxy using Ge2H6 and B2H6. B concentrations CB (3×1016–4×1019 cm−3) were found to increase linearly with increasing flux ratio JB2H6/JGe2H6 (8.2×10−3–1.7) at constant film growth temperature Ts (300–400 °C) and to increase exponentially with 1/Ts at constant JB2H6/JGe2H6 ratio. The difference in the overall activation energies for B and Ge incorporation over this growth temperature range is ≂0.22 eV while B2H6 reactive sticking probabilities ranged from 8×10−4 at 300 °C to 2×10−5 at 400 °C. SIMS depth profiles from B modulation-doped samples and two-dimensional δ -doped samples grown at Ts<350 °C were abrupt to within instrumental resolution with no indication of surface segregation. Structural analysis by in situ reflection high-energy electron diffraction combined with postdeposition high-resolution plan-view and cross-sectional transmission electron microscopy showed that all films were high-quality single crystals with no evidence of dislocations or other extended defects. B doping had no measurable affect on Ge deposition rates.