Novel semiconductors with controlled both single-atom number and position

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Doping of impurity atoms into semiconductors is essential to achieving the proper function of semiconductor devices. So far the semiconductor has been assumed to be homogeneously doped in the active channel region. In the nano-scale semiconductor devices, however, the channel region will contain few dopant atoms and the assumption of uniform dopant distribution is no longer feasible. In this situation, the statistical fluctuation in dopant atom number due to random Poisson distribution will elicit deleterious effects on the device's functioning. We have been developing a single-ion implantation(SII) method that enables us to implant dopant ions one-by-one into semiconductors until the desired number is reached In this study, we have improved the beam diameter approximately 10nm by modifying the focused ion beam optics for the SII and achieved the single-ion detection efficiency 100% by detecting the change in drain-current induced by single-ion incidence. We have then fabricated semico … More nductor devices with ordered dopant arrays by the SII. Electrical measurements of the resulting transistors revealed that there are fewer device-to-device fluctuations in the threshold voltage (V_<th> ; the turn-on voltage of the device) of the devices with ordered dopant arrays than of those with conventional randomly doped distribution. We also found that the average value of V_<th> for the devices with ordered dopants is two times lower than that of the devices with a random distribution of dopants. We explain this pronounced difference in threshold voltage as follows : the uniformity of electrostatic potential lowers the voltage required to open the channel from source to drain, which allows for early turn-on in those parts of the channel that correspond to the positioning of the implanted ions and results in the lower threshold voltage. It must be noted that current technology, which is based on random distribution of ions, cannot control either the number or the positioning of the ions, while our method can control both the number and the positioning of the ions and that this control is essential for future nanoscale semiconductor devices. Less