Evaluation of the valence band discontinuity of Si/Si/sub 1-x/Ge/sub x//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/sub 1-x/Ge/sub x//Si double-heterostructures, in order to evaluate the valence band discontinuity /spl Delta/E/sub v/ at the Si/Si/sub 1-x/Ge/sub 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 /spl Delta/E/sub v/ at the back interface of the double-heterostructure is measured under slight depletion conditions for MOS capacitors, /spl Delta/E/sub v/ averaged between the front and the back interfaces is measured under accumulation conditions. The Ge/sub x/ content dependence of the measured /spl Delta/E/sub v/ is found to be in fairly good agreement with the theoretical values.