B-doped fully strained Si1−xGex layers grown on Si(001) by gas-source molecular beam epitaxy from Si2H6, Ge2H6, and B2H6: Charge transport properties

Abstract

B-doped Si1−xGex layers with Ge fractions, determined by Rutherford backscattering spectroscopy, ranging from 0 to 0.28 and B concentrations, from quantitative secondary-ion spectroscopy measurements, between 5×1016 and 4×1019 cm−3 were grown on Si(001) at temperatures Ts=475–575 °C by gas-source molecular beam epitaxy from Si2H6, Ge2H6, and B2H6. Film thicknesses ranged from 200 nm for alloys with x=0.28 to 800 nm with x=0.05 to 1.4 μm for Si. Structural analyses by high-resolution x-ray diffraction and reciprocal lattice mapping combined with transmission electron microscopy showed that all films were fully strained, with measured relaxations of only ≂4×10−5, and exhibited no evidence of dislocations or other extended defects. The hole conductivity mobility μc,h in these layers increased continuously with increasing Ge concentrations, whereas the Hall mobility decreased yielding a Hall scattering factor that ranged from 0.75 for Si to 0.26 for Si0.72Ge0.28 but was not strongly affected by B concentration. μc,h, with CB=2×1018 cm−3, varied from 110 cm2 V−1 s−1 for Si0.95Ge0.05 to 158 cm2 V−1 s−1 for Si0.72Ge0.28, compared to 86 cm2 V−1 s−1 for Si, in good agreement with Boltzmann transport model calculations accounting for changes in the valence-band structure due to the effects of both alloying and biaxial in-plane compressional strain.