Takahiro Shinada

Array of bright silicon-vacancy centers in diamond fabricated by low-energy focused ion beam implantation

Among promising color centers for single-photon sources in diamond, the negatively charged silicon-vacancy (SiV−) has 70% of its emission to the zero-phonon line (ZPL), in contrast to the negatively charged nitrogen vacancy (NV−), which has a broad spectrum. Fabricating single centers of useful defect complexes with high yield and excellent grown-in defect properties by ion implantation has proven to be challenging. We have fabricated bright single SiV− centers by 60-keV focused ion beam implantation and subsequent annealing at 1000 °C with high positioning accuracy and a high yield of 15%.

Band transport across a chain of dopant sites in silicon over micron distances and high temperatures.

Macroscopic manifestations of quantum mechanics are among the most spectacular effects of physics. In most of them, novel collective properties emerge from the quantum mechanical behaviour of their microscopic constituents. Others, like superconductivity, extend a property typical of the atomic scale to macroscopic length scale. Similarly, features of quantum transport in Hubbard systems which are only observed at nanometric distances in natural and artificial atoms embedded in quantum devices, could be in principle extended to macroscopic distances in microelectronic devices. By employing an atomic chain consists of an array of 20 atoms implanted along the channel of a silicon transistor with length of 1 μm, we extend to such unprecedented distance both the single electron quantum transport via sequential tunneling, and to room temperature the features of the Hubbard bands. Their observation provides a new example of scaling of quantum mechanical properties, previously observed only at the nanoscale, up to lengths typical of microelectronics, by opening new perspectives towards passage of quantum states and band engineering in silicon devices.

In situ modification of cell-culture scaffolds by photocatalytic decomposition of organosilane monolayers

We demonstrate a novel application of TiO2 photocatalysis for modifying the cell affinity of a scaffold surface in a cell-culture environment. An as-deposited octadecyltrichlorosilane self-assembled monolayer (OTS SAM) on TiO2 was found to be hydrophobic and stably adsorbed serum albumins that blocked subsequent adsorption of other proteins and cells. Upon irradiation of ultraviolet (UV) light, OTS molecules were decomposed and became permissive to the adhesion of PC12 cells via adsorption of an extracellular matrix protein, collagen. Optimal UV dose was 200 J cm(-2) for OTS SAM on TiO2. The amount of collagen adsorption decreased when excessive UV light was irradiated, most likely due to the surface being too hydrophilic to support its adsorption. This UV-induced modification required TiO2 to be present under the SAM and hence is a result of TiO2 photocatalysis. The UV irradiation for surface modification can be performed before cell plating or during cell culture. We also demonstrate that poly(ethylene glycol) SAM can also be patterned with this method, indicating that it is applicable to both hydrophobic and hydrophilic SAMs. This method provides a unique tool for fabricating cell microarrays and studying dynamical properties of living cells.

Comparison of self-heating effect (SHE) in short-channel bulk and ultra-thin BOX SOI MOSFETs: Impacts of doped well, ambient temperature, and SOI/BOX thicknesses on SHE

Self-heating effects (SHEs) of bulk and SOI FETs including 6-nm ultra-thin (UT) BOX devices are systematically investigated and compared using the four-terminal gate resistance technique. For bulk FETs, it has been verified for the first time that the SHE is not negligible in nanoscale devices mainly owing to a decrease in the thermal conductivity of the more heavily doped well. Furthermore, it has been demonstrated that the magnitude of the SHE strongly depends on the chip (ambient) temperature (Tchip). For SOI FETs, the impacts of BOX/SOI thinning are evaluated and explained in terms of the thermal conductivities of materials within heat dissipation paths. It has been demonstrated that the device temperature of 6-nm UT BOX SOI FETs is close to that of bulk FETs at Tchip under operating conditions. A thermal-aware device design of the UT Body and BOX (UTBB) structure is proposed on the basis of the evaluated BOX/SOI thickness dependences of the SHE. The SHE of UTBB FETs with a raised source/drain and/or shorter contact pitch could be comparable to that of bulk FETs in deeply scaled nodes. In addition, the doping concentration under the BOX should be optimized in order to achieve low and Tchip-independent SHE.

Investigation of the silicon vacancy color center for quantum key distribution.

Single photon sources (SPS) are crucial for quantum key distribution. Here we demonstrate a stable triggered SPS at 738 nm with linewidth less than 5 nm at room temperature based on a negatively charged single silicon vacancy color center. Thanks to the short photon duration of about 1.3-1.7 ns, by using high repetition pulsed excitation at 30 MHz, the triggered single photon source generates 16.6 kcounts/s. And we discuss the feasibility of this triggered SPS in the application of quantum key distribution.

Direct Evaluation of Self-Heating Effects in Bulk and Ultra-Thin BOX SOI MOSFETs Using Four-Terminal Gate Resistance Technique

We demonstrate clear self-heating effects (SHEs) of bulk and silicon-on-insulator (SOI) MOSFETs for various SOI/buried oxide (BOX) thicknesses including ultra-thin 6 nm BOX, which was not detected by the ac conductance method, using the four-terminal gate resistance technique. We clarify that the SHE in bulk MOSFETs originates from the degradation of thermal conductivity in a heavily doped well region. The strong chip-temperature dependence of the SHE was observed only in bulk MOSFETs. As results of the chip temperature-dependent SHE of bulk devices and the SHE suppression by BOX thinning, the device temperature of ultra-thin BOX SOI MOSFETs is close to that of bulk MOSFETs at an elevated chip temperature, which suggests the thermal advantage of extremely thin BOX structures.

Atomic scale devices: Advancements and directions

We review the theoretical and experimental advances in nanometric-scale devices and single atom systems. Few electron devices are currently obtained either by fabricating nanometric-scale semiconductor FinFETs and quantum dots, or by doping them with few impurity atoms. Devices of such size, originally realized by employing either pre-industrial or laboratory processes, are now being fabricated in commercial 14 nm node architecture. They have lead, starting from the 90s, to the observation of classical non-linear effects, to spin- and orbital-related quantum effects, manipulation of few qubits and to many-body quantum effects. As scaling of devices continues, the natural question is whether single atom and few electron devices will represent the ultimate scaled technology. We highlight high points and major constraints and limitations to state-of-the-art fabrication based on lithography and doping, and their possible integration with different methods such as self-assembly, inspired by biology and natural systems. “At the atomic level, we have new kinds of forces and new kinds of possibilities, new kinds of effects. The problems of manufacture and reproduction of materials will be quite different. I am, as I said, inspired by the biological phenomena in which chemical forces are used in repetitious fashion to produce all kinds of weird effects (one of which is the author). R. Feynman, 1957”.

Fluorescence Polarization Switching from a Single Silicon Vacancy Colour Centre in Diamond.

Single-photon emitters with stable and uniform photoluminescence properties are important for quantum technology. However, in many cases, colour centres in diamond exhibit spectral diffusion and photoluminescence intensity fluctuation. It is therefore essential to investigate the dynamics of colour centres at the single defect level in order to enable the on-demand manipulation and improved applications in quantum technology. Here we report the polarization switching, intensity jumps and spectral shifting observed on a negatively charged single silicon-vacancy colour centre in diamond. The observed phenomena elucidate the single emitter dynamics induced by photoionization of nearby electron donors in the diamond.

Revisiting room-temperature 1.54 μιη photoluminescence of ErO x centers in silicon at extremely low concentration

Luminescence of erbium in silicon has been intensively explored in the past in the high power emission regime, but its employment for manufacturability of active components for silicon photonics proved unfeasible. We explore the room-temperature photoluminescence (PL) at the telecomm wavelength of very low implantation doses of ErOx in Si for accessing few photon regime towards single photon emission. We achieve countable photon regime and we assess the lower-bound number of detectable emission centers by micron scale implanted dots, whose emission is collected by an inverted confocal microscope.

Atom probe study of erbium and oxygen co-implanted silicon

It has been reported that erbium (Er) is a source of optical emission at λ=1.54 pm due to ⁴I<inf>13/2</inf> →⁴I<inf>15/2</inf> transition of Er³⁺. A method of oxygen (O) codoping with Er has attracted attention as a candidate for obtaining more efficient optical gain by forming Er:O complex. Although several simulations predict the equilibrium structure of Er:O complex, it is difficult to understand experimentally how related between these implanted ions followed by annealing for optical activation. In this workshop, we reported the preliminary results on three-dimensional distributions of Er and O co-implanted into Si investigated by atom probe tomography.