Evaluation of the valence band discontinuity of Si/Si1-xGex/Si heterostructures by application of admittance spectroscopy to MOS capacitors

In this study, admittance spectroscopy is applied for the first time to MOS capacitors fabricated on Si/Si_1-xGe_x/Si double-heterostructures, in order to evaluate the valence band discontinuity ΔE_v at the Si/Si_1-xGe_x interface. The principle of the measurement is presented and verified by the experimental results. A new feature of admittance spectroscopy applied to MOS capacitors is the ability to select the interface whose barrier is measured, by controlling the gate voltage. This fact is confirmed by the measurement of MOS capacitors, which include a SiGe well with different Ge contents at the front and the back interfaces. It is found from this measurement that, while ΔE_v at the back interface of the double-heterostructure is measured under slight depletion conditions for MOS capacitors, ΔE_v averaged between the front and the back interfaces is measured under accumulation conditions. The Ge_x content dependence of the measured ΔE_v is found to be in fairly good agreement with the theoretical values