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Abstract.We have used electrochemical anodic oxidation to form gate oxides on strained n-channel Si:SiGe quantum wells. The oxides are characterized by current-voltage and capacitance-voltage measurements. Comparison of measured and calculated electron sheet densities in the quantum well, indicates that the oxide growth does not cause degradation of the Si:SiGe material. This is confirmed by low-temperature measurements of the electron mobility and sheet density in the quantum well.

DC transfer characteristic measurements have been carried out on one n-channel Si/SiGe MODFETs with a MOS gate at three different substrate biases. For our layer structure, electrons are supplied into the strained Si quantum well (QW) from the top heavily doped layer and below the QW is non-intentionally doped (setback). Here, we numerically studied the setback layer, for which the doping can be systematically designed to reduce the influence of the substrate bias on the threshold voltage (VTH) shift. By inserting and positioning a layer of 15 nm-thick heavily doped n+ (2.10" cm") into the 700nm-thick setback layer, we found that, when we positioned the n+ layer 635 nm below the QW, the VTH shifted by only 37 mV and only a slight change of the subthreshold slope occurred, 3.12 mV/dec, for -2 V applied to the substrate IntroductionImprovements in the frequency response of silicon-based circuits can be achieved through the use of Si/SiGe modulation-doped field-effect transistors (MODFETs) which exhibit higher camer mobilities for both n-and p-channels than their Si MOSFET counterparts [1]- [2]. The possibility of achieving highmobility p-channels also makes these new devices very attractive for integrated CMOS circuits [3].