Localized-state band induced by B δ-doping inSi/Si1−xGex/Siquantum wells

The density of states of the two-dimensional hole band in B δ-doped ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{1-x}{\mathrm{Ge}}_x/\mathrm{Si}$ quantum wells was obtained using space-charge spectroscopy. ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{0.75}{\mathrm{Ge}}_{0.25}/\mathrm{S}\mathrm{i}$ structures studied have a $(2\mathrm{}–5)\times {10}^{11}{\mathrm{cm}}^{\mathrm{-}2}$ concentration of B δ doping in the middle of the quantum well. We have observed the effect of localization for small concentrations of confined holes. The activation energy for the hole emission rate increases as the concentration of confined holes decreases. This allows one to estimate the density of states for the tail of the two-dimensional acceptor band.