Engineering Interface-Dependent Photoconductivity in Ge2Sb2Te5 Nanoscale Devices

Mechanism and Impact of Bipolar Current Voltage Asymmetry in Computational Phase-Change Memory

Nanoscale resistive memory devices are being explored for neuromorphic and in-memory computing. However, non-ideal device characteristics of read noise and resistance drift pose significant challenges to the achievable computational precision. Here, it is shown that there is an additional non-ideality that can impact computational precision, namely the bias-polarity-dependent current flow. Using phase-change memory (PCM) as a model system, it is shown that this "current-voltage" non-ideality arises both from the material and geometrical properties of the devices. Further, we discuss the detrimental effects of such bipolar asymmetry on in-memory matrix-vector multiply (MVM) operations and provide a scheme to compensate for it.

Advances in Emerging Photonic Memristive and Memristive-Like Devices

Possessing the merits of high efficiency, low consumption, and versatility, emerging photonic memristive and memristive-like devices exhibit an attractive future in constructing novel neuromorphic computing and miniaturized bionic electronic system. Recently, the potential of various emerging materials and structures for photonic memristive and memristive-like devices has attracted tremendous research efforts, generating various novel theories, mechanisms, and applications. Limited by the ambiguity of the mechanism and the reliability of the material, the development and commercialization of such devices are still rare and in their infancy. Therefore, a detailed and systematic review of photonic memristive and memristive-like devices is needed to further promote its development. In this review, the resistive switching mechanisms of photonic memristive and memristive-like devices are first elaborated. Then, a systematic investigation of the active materials, which induce a pivotal influence in the overall performance of photonic memristive and memristive-like devices, is highlighted and evaluated in various indicators. Finally, the recent advanced applications are summarized and discussed. In a word, it is believed that this review provides an extensive impact on many fields of photonic memristive and memristive-like devices, and lay a foundation for academic research and commercial applications.

Chalcogenide optomemristors for multi-factor neuromorphic computation

Neuromorphic hardware that emulates biological computations is a key driver of progress in AI. For example, memristive technologies, including chalcogenide-based in-memory computing concepts, have been employed to dramatically accelerate and increase the efficiency of basic neural operations. However, powerful mechanisms such as reinforcement learning and dendritic computation require more advanced device operations involving multiple interacting signals. Here we show that nano-scaled films of chalcogenide semiconductors can perform such multi-factor in-memory computation where their tunable electronic and optical properties are jointly exploited. We demonstrate that ultrathin photoactive cavities of Ge-doped Selenide can emulate synapses with three-factor neo-Hebbian plasticity and dendrites with shunting inhibition. We apply these properties to solve a maze game through on-device reinforcement learning, as well as to provide a single-neuron solution to linearly inseparable XOR implementation.

Some types of machine learning rely on the interaction between multiple signals, which requires new devices for efficient implementation. Here, Sarwat et al demonstrate a memristor that is both optically and electronically active, enabling computational models such as three factor learning.

Chalcogenide-based, all-dielectric, ultrathin metamaterials with perfect, incidence-angle sensitive, mid-infrared absorption: inverse design, analysis, and applications

The demand for miniature, low-cost, utmost efficient optical absorbers triggered ongoing research efforts to minimize the overall design thickness, particularly the photo-active layer, while still maintaining a high optical absorptance. In this study, we present all-dielectric nanophotonic metamaterials of optimized, fabrication compatible and tolerant, architecture for perfect mid-wave infrared absorptance. Overall sub-vacuum-wavelength thick designs are intended to couple and confine light inside an ultrathin 100 nm PbTe photo-absorbing film. Three application-oriented structures, with dimensions inversely designed to provide diverse requirements, are introduced: a two-dimensional metasurface embedded design for unpolarised wide-band absorption and two, one-dimensional metasurface embedded designs for s-polarised wide-band and non-polarised narrow-band absorption. A comprehensive study of the structures' spectral absorptance under normal- and oblique-incidence irradiation is performed. The conical-mounting absorptance analysis elucidates that the high absorption can be continuously spectrally tuned with the azimuthal component of the incidence angle. To the best of our knowledge, this property is discussed for the first time for all-dielectric metamaterials. Also, the ranges of geometrical tuning of the peak absorptance are investigated in detail, and usage of another prospective semiconductor absorber is explored. To unfold the mutual, and essentially different, physical mechanisms that fuel the perfect absorptance, an elaborated analysis is presented. The electromagnetic power transport, portrayed by the Poynting vector, displays three-dimensional singular flows around points, such as vorticity centers, saddles, sinks, and spirals. The potential mid-infrared applications which can benefit from the peculiar properties of the designed structures, such as spectroscopy, sensing, thermal radiation manipulations, and communication, are also discussed.

Stability improvement of Cu(ii)-doped ZnS/ZnO photodetectors prepared with a facile solution-processing method

The solution-processed growth of Cu²⁺ doped ZnS as protective coatings on ZnO nanorods with improved photoresponsivity and stability was presented.

CMOS compatible novel integration solution for broad range tunable photodetection using phase-change material based heterostructures

Heterostructures (HS) have always been in attraction due to their inherited properties and different important applications. Integration of a phase-change material (PCM) with HS can tremendously extend the operating and application range using the "phase-tuning" of PCM for any optoelectronic devices. In the present study, we report a detailed study of electrical and optoelectronic characteristics of a p-p and p-n HS combining Ge₂Sb₂Te₅ (GST) and Si. Reasonable 2 order of resistance switching is achieved by thermal annealing. The changes in optical properties are analysed using Ellipsometry, UV-Vis-NIR and Raman spectroscopy to speculate the optoelectronic behaviour of GST/Si samples. The optical and electrical characterization were analysed with aluminium (Al), platinum (Pt) and Ti/Au contacts. Appreciable rectifications varying from 500 to 1,000 at lower voltages are achieved with different contacts for both phases of GST. The change in rectification amount and current polarity are obtained with different kinds of contacts and at different incident wavelengths indicating different mechanisms of charge separation and collection. Responsivity of more than 9 A/W with < 1,000 photo-current to dark-current ratio is demonstrated in wavelength range of 0.8-2 μm under moderate range of biasing under ~ μW source power illumination. The characteristics obtained were justified with the prediction of band alignment with the help of work-function difference measurement by Kelvin-probe force microscopy and carrier density measurement by Hall experiment. Our results provide understanding to the opto-electrical behaviour of a heterojunction made of stacking PCM (GST) on Si highlighting their future use in photonic/optoelectronic-integrated circuits.

Strong Opto-Structural Coupling in Low Dimensional GeSe3 Films

Chalcogenide glasses as nanoscale thin films have become leading candidates for several optical and photonic technologies, ranging from reflective displays and filters to photonic memories. Current material systems, however, show strong optical absorption which limits their performance efficiencies and complicates device level integration. Herein, we report sputter deposited thin films of GeSe₃, which are low loss and in which the flexible nature of the atomic structure results in thermally activated tunability in the refractive index as well as in the film's physical volume. Such changes, which occur beyond a threshold temperature are observed to be accumulative and directed toward a more equilibrium amorphous state of the film, instead of crystallization. Our results provide insight into a new type of configurability that is based on strong coupling in the material's opto-structural properties. The low optical losses in this material system combined with the tunability in the optical properties in the visible and near-infrared have direct application in higher performing optical coatings and in corrective optics.