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The impact of dopant atoms in transistor functionality has significantly changed over the past few decades. In downscaled transistors, discrete dopants with uncontrolled positions and number induce fluctuations in device operation. On the other hand, by gaining access to tunneling through individual dopants, a new type of devices is developed: dopant-atom-based transistors. So far, most studies report transport through dopants randomly located in the channel. However, for practical applications, it is critical to control the location of the donors with simple techniques. Here, we fabricate silicon transistors with selectively nanoscale-doped channels using nano-lithography and thermal-diffusion doping processes. Coupled phosphorus donors form a quantum dot with the ground state split into a number of levels practically equal to the number of coupled donors, when the number of donors is small. Tunneling-transport spectroscopy reveals fine features which can be correlated with the different numbers of donors inside the quantum dot, as also suggested by first-principles simulation results. [ABSTRACT FROM AUTHOR]

We study interaction of single-electron current and incident photons in nanometer-scale phosphorus-doped silicon-on-insulator field-effect transistors. Trapping events of a photoexcited-electron by a trap donor are observed as random telegraph signals in single-electron-tunneling current flowing through a current-path donor. Trapping causes a potential change at the current-path donor, inducing a current change. An opposite current change is caused by electron detrapping from the trap donor to the current-path donor. This indicates that only a few donors (two donors in this study) work in the interaction between single-electron transport and photoexcited-electron trapping, even in the presence of many donors. [ABSTRACT FROM AUTHOR]

The authors have detected the ionization of single-acceptors in the underlying p on p+ substrate of a silicon-on-insulator (SOI) wafer using a single-hole-tunneling (SHT) transistor fabricated in the top Si layer of the SOI at low temperatures. It was found that freeze-out boron atoms in the substrate are sequentially ionized from near the buried SiO2/p-Si substrate interface to deeper positions by application of a vertical electric field, creating steplike features in the time-dependent SHT current. [ABSTRACT FROM AUTHOR]

Single-hole transport in a two-dimensional Si multidot-channel field-effect transistor is studied. It is found that the single-hole-tunneling current fluctuates in the particular ranges of drain voltage and gate voltage. Such a phenomenon can be explained by a model that the hole transport through the percolation path is sensitively influenced and fluctuates with the time due to charging–discharging and polarity-switching of the dots adjacent to the percolation path. A Monte Carlo simulation using a parallel-double-dot circuit shows good agreement with the experimental characteristics. [ABSTRACT FROM AUTHOR]