Quantum confinement of holes in ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$/Si quantum wells studied by admittance spectroscopy

A carrier thermal-emission model is presented to analyze the emission and capture of carriers in the admittance spectroscopy of Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$/Si quantum wells. The experimental activation energy is related to the band offset at the interface of the SiGe well and the Si barrier as well as the confined hole-energy level in the well. The measured band offset for a single quantum well with Ge content of 0.33 is much closer to the theoretical prediction than that derived from the equivalent circuit model. The quantum size effects for both single-quantum-well and multiple-quantum-well samples are clearly revealed by the peak shifts of the conductance spectra. The emissions of holes from the confined heavy-hole subband and the light-hole subband in multiple-quantum-well samples with small well widths appear as a distinct doublet in the conductance spectra.