Formation of quantum dots in the contact region of high-mobility Si inversion layers in the metal-insulator transition regime

We have electrically investigated the two dimensional electron gas (2DEG) of Si inversion layers in MOS structures based on silicon on insulator (SOI) substrates. When investigating the metal-to-insulator transition in two dimensions (2D-MIT), we observed strong reproducible fluctuations in the measured signals versus gate voltage. We propose that in the gated transition region from the implanted to non-implanted regions of the hall-bar mesa, the implanted impurity atoms lead to strong fluctuations in the potential landscape. Electrically these potential fluctuations may behave like quantum dots, which will block or allow electron transport totally random as a function of gate voltage and will thus generate the observed fluctuations. Measurements depending on both, gate and contact bias, indeed shows diamond like shapes typical for Coulomb blockade, supporting our interpretation. We discuss how these findings allow us to improve our measurements in the insulating region of the 2D-MIT.