Manipulation of carrier densities at the single electron level is inevitable in modern silicon based transistors to ensure reliable circuit operation with sufficiently low threshold-voltage variations. However, previous methods required statistical analysis to identify devices which exhibit random telegraph signals (RTSs), caused by trapping and de-trapping of a single electron. Here, we show that we can deliberately introduce an RTS in a silicon nanowire transistor, with its probability distribution perfectly controlled by a triple gate. A quantum dot (QD) was electrically defined in a silicon nanowire transistor with a triple gate, and an RTS was observed when two barrier gates were negatively biased to form potential barriers, while the entire nanowire channel was weakly inverted by the top gate. We could successfully derive the energy levels in the QD from the quantum mechanical probability distributions and the average lifetimes of RTSs. This study reveals that we can manipulate individual electrons electrically, even at room temperature, and paves the way to use a charged state for quantum technologies in the future.
Symmetries of waveguides determine fundamental properties of photons such as mode profiles, polarisation, and effective refractive indexes as well as practical properties affecting the propagation loss. Here, we review our recent progress on manipulating symmetries of silicon (Si) photonic waveguides. Starting from the strategic choice of Si-On-Insulator (SOI) wafer specifications, we established the process technologies to fabricate Si wire and slot waveguides with atomically-flat interfaces, defined by Si (111) planes. These waveguides have relatively low propagation loss (∼ 1 dB/cm), even though they were fabricated in a university line. By combining patterning and re-growth of deposited amorphous Si, we also fabricated an Si slot waveguide with a nano-meter-scale vertical oxide layer, which is useful for optical modulators and various sensing applications. We also fabricated a horizontal slot waveguide using our manually bonded double-SOI substrate. The self-limited alkali-wet-etching allowed us to pattern the bottom SOI layer on top of the top SOI layer, by properly designing the mask to align along the mirror asymmetric Si (110) surface, allowing to access to top and bottom SOI layers individually through connected multiple-fin arrays. The patterning technique can be readily applicable to the other platform such as Si/LiNbO 3 -hybrid wafers, and we discuss our design of electro-optic (EO) modulator towards zero-power consumptions. We also investigate photonic crystal waveguides with broken mirror symmetries. By manipulating the mismatch between adjacent photonic crystals across the waveguide made of line defects, we could continuously control the band gap of the photonic crystals. Moreover, the phase profiles of modes exhibited photonic graphene and poly-acetylene shapes, made of optical vortices with optical orbital angular momentum (OAM). This shows that the most energetically favourable configuration of a photonic material under the triangular lattice is topologically equivalent to an organic material. We discuss the potential for the photonic organic chemistry and possible applications in quantum technologies.
A new LiNbO3/Si-hybrid electro-optic modulator that utilizes a doped-Si slot waveguide is proposed. An excellent performance, i.e., an improvement of two orders of magnitude in VπL, is demonstrated via simulations when compared with the performance of the conventional LiNbO3 modulators.
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