The coming of the big-data era brought a need for power-efficient computing that cannot be realized in the Von Neumann architecture. Neuromorphic computing which is motivated by the human brain can greatly reduce power consumption through matrix multiplication, and a device that mimics a human synapse plays an important role. However, many synaptic devices suffer from limited linearity and symmetry without using incremental step pulse programming (ISPP). In this work, we demonstrated a charge-trap flash (CTF)-based synaptic transistor using trap-level engineered Al 2 O 3 /Ta 2 O 5 /Al 2 O 3 gate stack for successful neuromorphic computing. This novel gate stack provided precise control of the conductance with more than 6 bits. We chose the appropriate bias for highly linear and symmetric modulation of conductance and realized it with very short (25 ns) identical pulses at low voltage, resulting in low power consumption and high reliability. Finally, we achieved high learning accuracy in the training of 60000 MNIST images.

Interfacial bubbles are unintentionally created during the transfer of atomically thin 2D layers, a required process in the fabrication of van der Waals heterostructures. By encapsulating a WSe2 monolayer in hBN, we study the differing photoluminescence (PL) properties of the structure resulting from bubble formation. Based on the differentiated absorption probabilities at the bubbles compared to the pristine areas, we demonstrate that the visibility of the bubbles in PL mapping is enhanced when the photoexcitation wavelength lies between the n = 1 and n = 2 resonances of the A-exciton. An appropriate choice of detection window, which includes localized exciton emission but excludes free exciton emission, further improves bubble imaging capability. The interfacial position dependence of the bubbles, whether they are located above or below the WSe2 monolayer, gives rise to measurable consequences in the PL shape.

The spatially isolated environment reduces the trion binding energy and limits the Fermi energy, which increases the spectral weight of neutral excitons at a high excitation density.

For decades, group‐III‐nitride‐based light‐emitting diodes (LEDs) have been regarded as a light emitting source for future displays by virtue of their novel properties such as high efficiency, brightness, and stability. Nevertheless, realization of high pixel density displays is still challenging due to limitations of pixelation methods. Here, a maskless and etching‐free micro‐LED (µLED) pixelation method is developed via tailored He focused ion beam (FIB) irradiation technique, and electrically driven sub‐micrometer‐scale µLED pixel arrays are demonstrated. It is confirmed that optical quenching and electrical isolation effects are simultaneously induced at a certain ion dose (≈1014 ions cm−2) without surface damage. Furthermore, highly efficient µLED pixel arrays at sub‐micrometer scale (square pixel, 0.5 µm side length) are fabricated. Their pixelation and brightness are verified by various optical measurements such as cathodo‐, photo‐, and electroluminescence. It is expected that the FIB‐induced optical quenching and electrical isolation method can pioneer a new defect engineering technology not only for µLED fabrication, but also for sub‐micrometer‐scale optoelectronic devices.

a self-assembled growth process on a 2D planar structure. [10,11] Because the size, shape, and position of SK QDs cannot be determined during growth, they are not appropriate for various applications. [10,11] To overcome these limitations, alternative methods for controlling the size and location of the QDs have been proposed. [12][13][14] Growing geometrical QDs at the apex region of nonplanar (e.g., upright or inverted pyramidal) substrates is a representative method for fabricating sitecontrolled QDs. [12][13][14] For controlling the size and shape of the geometrical QDs during the growth, it is beneficial to adopt the self-limited epitaxial growth mechanism, which is based on the equilibrium between surface flux caused by the chemical potential gradient and the growth rate anisotropy between the adjacent facets. [15,16] When the growth rates between the planar plane and the vertical growth rate of sidewall facets coincide, self-limiting growth maintains the surface profile and hence creates a small plateau with a lateral width of less than tens of nm at the apex region of the pyramidal structures, on which size-and shape-controlled single QD can be formed on these plateaus.To form the geometrical QDs, we first prepared nonplanar array patterns with high uniformity, which is typically fabricated by using the top-down etching process and/or the bottom-up selective-area growth (SAG) technique. Most results are based on triangular-shaped inverted pyramids with recess patterns of the group III-arsenide system to make self-limited growth of highly uniform and geometrical QDs. Due to its threefold symmetry, highly symmetric QD can be stably formed on the bottom of recess patterns without deformation or elongation of the triangular shape, resulting in quite uniform emission properties with small inhomogeneous broadening. [12][13][14][17][18][19] Single photon emitters based on group III-nitride QDs have attracted considerable attention because of their wide tunable range from ultraviolet to near-infrared and the possibility of room-temperature operation caused by the strong carrier confinement between constituent materials and the large exciton binding energy. [20,21] In general, bottom-up growth with a SAG pattern has been used to form hexagonal-shaped upright pyramids in the nitride system due to the difficulty of the fabrication Controlling the site, size, and shape of group III-nitride quantum dots (QDs) is critical for the development of mass-producible single-photon sources for scalable quantum technologies operable at room temperature. Herein, a methodology is proposed for fabricating high-purity single QD emitters by controlling site-controlled GaN micro-pyramid structures with a high degree of uniformity and symmetry. To achieve a uniformly grown, hexagonally symmetric micro-pyramid array, the H 2 /N 2 carrier gas ratio, growth temperature, and V/III ratio are controlled to attain self-limited growth regime and selflimited width at the GaN pyramid apex. A thin InGaN layer is consecutively grown on a pyramid ...