Characterization of Electronic Charged States of Si-based Quantum Dots for Multi-valued MOS Memories

We have found that, for Si dots individually charged with a few electrons or holes, characteristic potential profiles with a dimple around the center of the charged Si dot are observed and can be interpreted in terms of the Coulomb repulsion among the charges retained in the dot. By an introduction of Ge core in Si dots, holes can be well-confined in the Ge core while electrons are stored in the Si clad because of the energy band discontinuity at the interface between the Si clad and the Ge core. The influence of ionized impurity doping to Si-QDs on their electron charging and discharging characteristics has also been studied. For metal-oxide-semiconductor (MOS) capacitors and n-channel MOS field-effect-transistors (n-MOSFETs) with Si-QDs floating gates, distinct multiple-step charging to (or discharging from) the Si-QDs floating gate have been confirmed at room temperature, which are regulated presumably by redistribution of injected electrons in the Si-QDs floating gate for further electron injection (or emission)