Characterization of Si/Si1−xGex/Si quantum wells by space-charge spectroscopy

Results are presented concerning the electrical characterization of p-Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$/Si quantum well (QW) structures by admittance spectroscopy, capacitance measurements, and deep-level transient spectroscopy (DLTS). The capture and emission processes of holes in QW structures are theoretically analyzed for equilibrium and nonequilibrium conditions taking into account external electric fields as well as local electric fields induced by confined charge carriers. The temperature dependence of potential barriers at the QW and of the Fermi level determines the activation energy ${\mathit{E}}_{\mathit{a}}$ of the conductance across the QW. Admittance spectroscopy data of QW’s with x=0.25 and thicknesses in the range from 1 to 5 nm are in fair agreement with the proposed theoretical model. Hole emission from the QW region was studied by DLTS investigations on ${\mathit{n}}^{+}$p mesa diodes for QW’s with x=0.17.