Experimental determination of wave function spread in Si inversion layers

We have experimentally determined the extent of wave function spread T QM in Si inversion layers on (100)-oriented surface in metal-oxide-semiconductor field-effect transistors (MOSFETs) using the back gate bias sensitivity of front gate threshold voltage of planar fully depleted silicon-on-insulator (SOI) MOSFETs. We show that the sum of TQM for large positive and negative F is an electrically determined value of the SOI thickness TSI. We find that the electric field dependence of T QM for electrons and holes is given by TQM ∼ F -0.4 and F-0.6, respectively, at high electric fields with TQM being larger for holes at a given F. Larger TQM for holes can be explained by the fact that holes have a smaller effective mass along the confinement direction than electrons in (100) Si. The field dependences of TQM are, however, not consistent with the results of variational calculations that assume single-subband occupancy and predict TQM ∼ F -1/3. The discrepancy likely indicates that the effects of multiple-subband occupation are significant at room temperature, especially for holes. © 2010 American Institute of Physics.