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

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Abstract
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/J Ge2H6 (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/J Ge2H6 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 Tsin 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.