Papers by Author: Michiharu Tabe

Abstract: Further development of dopant-atom-based transistors requires investigation of the effects of discrete dopant distribution on device operation. Hence, it is important to monitor dopants’ arrangement inside transistor channels. We used Kelvin Probe Force Microscope (KPFM) to measure surface potential profiles of field-effect transistor (FET) channels doped with different concentrations of phosphorus atoms. We observed three basic configurations of dopants: solitary donors, “clusters” of a few coupled donors, and “clusters” of many donors. Our systematic observation provides information about the formation of quantum dots consisting of a single donor or a number of coupled donors.

Abstract: In silicon nanoscale transistors, dopant (impurity) atoms can significantly affect transport characteristics, in particular at low temperatures. Coupling of neighboring dopants in such devices is essential in defining the properties for transport. In this work, we briefly present a comparison of different regimes of inter-dopant coupling, controlled by doping concentration and, to some extent, by selective, local doping. Tunneling-transport spectroscopy can reveal the energy spectrum of isolated dopants and of strongly-coupled dopant atoms. Interactions of multiple-dopants quantum dots (QDs) and satellite individual dopant-traps, as observed in some devices, can provide further information to bridge such inter-dopant coupling regimes for more advanced applications.

Abstract: We have recently proposed and demonstrated a new device concept, “Si-based single-dopant atom device”, consisting of only one or a few dopant atoms in the channel of Si field-effect transistors. The device characteristics are determined by a dopant, which is mediating electron or hole transport between source and drain electrodes. In this paper, our recent results on electronic and photonic applications are introduced. Furthermore, single-dopant images obtained by a scanning probe microscope are also presented.

Abstract: Transistors have been significantly downsized over the past decades, reaching channel dimensions of around 100 nm. In nanoscale, quantum effects start to play a key role in device operation, allowing the development of applications based on new physics. In silicon nanodevices, for instance, the device downsizing is associated with a reduction of the number of impurities (dopants) incorporated in the channel. Dopants can play an active role in device operation, mediating the electron transport between source and drain. Here, we present a new device concept of a memory based on the interaction between dopants in nanoscale field-effect transistors. As a basis for memory operation, we show experimental results of single-electron charging in individual dopants monitored by a single-electron current flowing through a dopant array.

Abstract: Kelvin Probe Force Microscopy is an attractive technique for characterizing the surface potential of various samples. The main advantage of this technique is its high spatial resolution together with high sensitivity. However as in any nanoscale measurements also in case of KFM it is extremly difficult to describe the uncertainty of the measurement. Moreover, a wide variety of measuring conditions, together with the complicated operation principle cause situation, where no standard calibration methods are available. In the paper we propose the model of the KFM microscope and analyze the uncertainty of the KFM measurement.

Abstract: Low temperature Kelvin Probe Force Microscopy (LT-KFM) can be used to monitor the electronic potential of individual dopants under an electric field. This capability is demonstrated for silicon-on-insulator field-effect-transistors (SOI-FETs) with a phosphorus-doped channel. We show results of the detection of individual dopants in Si by LT-KFM. Furthermore, we also observe single-electron charging in individual dopants located in the Si channel region.

Abstract: An individual dopant atom may become the active unit of future electronic devices by mediating single-electron transport in nanoscale field-effect transistors. Single dopants can be accessed electrically even in a dopant-rich environment, offering the opportunity to develop applications based on arrays of dopants. Here, we focus on single-electron turnstile operation in arrays of dopant-induced quantum dots realized in highly-doped nanoscale transistors. We show that dopant-based single-electron turnstile can be achieved and tuned with a combination of two gates and we indicate guidelines for further optimization.