Admittance spectroscopy studies of boron δ-doped Si quantum wells

The admittance spectroscopy technique has been used to study the hole confinement in boron δ-doped Si quantum wells. Based on the carrier thermal emission model, the activation energies of holes confined in the quantum wells are obtained from the measured conductance spectra. For different well widths, i.e., different boron doping amounts, the well depths and the subband positions are different. We observe the shifts of the conductance peaks in the spectra for δ-doped samples with the peak doping concentration of 2×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and doped thicknesses of 1.2, 3.0, and 5.0 nm. The activation energies derived from the measurements are 0.11, 0.30, and 0.34 eV, respectively. A self-consistent calculation of the subbands in the quantum wells verifies that these activation processes correspond to the hole emissions from the hole ground states in the δ-doped quantum wells to the Si valence band.