Crystallization (set) time is a key bottleneck to achieve high-speed programming in phase change memory (PCM). Overcoming this limitation requires a deeper understanding of the solidification processes within nanoscale device configuration. This study explores crystallization dynamics in Ge₂Sb₂Te₅ by measuring the transient resistance and power during the set process in confined PCM cells with nanosecond resolution. The transient resistance probes the phase, while the power can be used to evaluate temperature, thus uncovering details of the phase change dynamics. Our findings reveal a notable trend indicating that solidification from the melt results in faster crystallization compared with annealing the glassy state. Moreover, we observed notable differences in the solidification dynamics during set (crystallization) and reset (amorphization) pulses. Our nanosecond transient measurement methodology proves valuable in revealing crucial aspects of PCM crystallization dynamics, holding the potential to enable higher-speed programming.

Transition metal oxides (TMOs) exhibit a broad spectrum of functional electronic, magnetic, and optical properties, making them attractive for various technological applications. The scale and impact of surface defects and inhomogeneity can extend many unit cells below the surface. Overlooking this aspect of TMO surfaces can result in an incorrect interpretation of their physics and inhibit their maturation into device technology. Soft x-ray absorption spectroscopy (XAS) is a common technique for TMO studies, and different XAS acquisition modes can be used to measure different depth regimes in the sample. Here, we demonstrate a substantial disparity between the near-surface region and the “bulk” of the prototypical TMO SrVO₃. By driving the system across two scenarios of orbital polarization, we illustrate how a common XAS surface-sensitive acquisition technique fails to detect the intrinsic orbital polarization. By stark contrast, a “bulk”-sensitive technique successfully captures this effect, elucidating the expected orbital occupation inversion. These results not only underscore the impact of the near-surface region on the correct interpretation of TMO fundamental physics, but further highlight the scale of surface inhomogeneity, a critical aspect of nanoscale functional devices.

Hysteresis in organic electrochemical transistors (OECT) is a basic effect in which the measured current depends on the voltage sweep direction and velocity. This phenomenon has an important impact on different aspects of the application of OECT, such as the switching time and the synaptic properties for neuromorphic applications. Here we address the combined ionic and electronic kinetic effects that cause the dominant hysteresis effects. We use a combination of tools consisting on basic analytical models, advanced 2D drift-diffusion simulation, and the experimental measurement of a Poly(3-hexylthiophene) (P3HT) OECT, working in an accumulation mode. We develop a general transmission line model considering drift electronic transport and ionic injection and diffusion from the electrolyte. We provide a basic classification of the transient response to a voltage pulse, according to the dominant ionic or electronic relaxation time, and the correspondent hysteresis effects of the transfer curves according to the general categories of inductive and capacitive hysteresis. These are basically related to the main control phenomenon, either the vertical diffusion of ions during doping and dedoping, or the equilibration of electronic current along the channel length.

Although p-type organic mixed ionic electronic conductors (OMIECs) are susceptible to oxidation, it has not yet been considered as to whether oxygen could behave as an uncontrolled p-dopant. Here, oxygen dissolved in solvents is shown to be behave as a p-dopant, that fills traps to enable more effective electrochemical doping in OMIECs and organic electrochemical transistors (OECTs). Yet the presence of oxygen also jeopardizes OECT stability. A two-step strategy is introduced to solve this contradictory problem, where first the solvent is degassed, and second the OMIEC is doped in a controlled manner using a chemical p-dopant. This strategy has a remarkable impact on OECT stability in air and water, while simultaneously increasing on-off ratio, tuning the threshold voltage, and enhancing the transconductance, mobility and the µC* product. This simple solution-processing technique is easily implemented, low-cost, highly effective in air and water, and effective in materials systems with different polymers, solvent and dopants. Overall, the data herein suggests that combining chemical doping with solvent degassing could be a broadly applicable technique to improve essential criteria needed to realize organic bioelectronics and more complex OMIEC circuitry.

We have successfully demonstrated the first CMOS-compatible monolithic epitaxial integration of GaN-based infrared (IR) detectors on Si. The device is a GaN/AlGaN quantum cascade detector (QCD) grown selectively in windows on a 4-in Si (111) substrate using plasma-assisted molecular beam epitaxy. The CMOS compatibility of the QCD growth method was verified by applying it to Si circuitry fabricated on (100) surface of a double hetero-oriented silicon on insulator (SOI) substrate. The photo signal, centered at a wavelength of 4.6 $\mu \text{m}$ , was measured at 110 K. The zero-bias responsivity of 81 $\mu \text{A}$ /W at 18 K and detectivity of $1.2\times 10^{{7}}$ Jones were recorded.

The increasing interest in realizing the full potential of two-dimensional (2D) layered materials for developing electronic components strongly relies on quantitative understanding of their anisotropic electronic properties. Herein, we use conductive atomic force microscopy to study the anisotropic electrical conductance of multilayer MoS2 by measuring the spreading resistance of circular structures of different radii ranging from 150 to 400 nm. The observed inverse scaling of the spreading resistance with contact radius, with an effective resistivity of ρeff  = 2.89 Ω cm, is compatible with a diffusive transport model. A successive etch of the MoS2 nanofilms was used to directly measure the out-of-plane resistivity, i.e., 29.43 ± 7.78 Ω cm. Based on the scaling theory for conduction in anisotropic materials, the model yields an in-plane resistivity of 0.28 ± 0.07 Ω cm and an anisotropy of ∼100 for the ratio between the in-plane and out-of-plane resistivities. The obtained anisotropy indicates that the probed surface area can extend up to 400 times the metal contact area, whereas the penetration depth is limited to roughly 20% of the contact radius. Hence, for contact radius less than 3 nm, the conduction will be limited to the surface. Our investigation offers important insight into the anisotropic transport behavior of MoS2, a pivotal factor enabling the design optimization of miniaturized devices based on 2D materials.

Phase-change memory (PCM) devices have great potential as multilevel memory cells and artificial synapses for neuromorphic computing hardware. However, their practical use is hampered by resistance drift, a phenomenon commonly attributed to structural relaxation or electronic mechanisms primarily in the context of bulk effects. In this study, we reevaluate the electrical manifestation of resistance drift in sub-100 nm Ge₂Sb₂Te₅ (GST) PCM devices, focusing on the contributions of bulk vs interface effects. We employ a combination of measurement techniques to elucidate the current transport mechanism and the electrical manifestation of resistance drift. Our steady-state temperature-dependent measurements reveal that resistance in these devices is predominantly influenced by their electrical contacts, with conduction occurring through thermionic emission (Schottky) at the contacts. Additionally, temporal current–voltage characterization allows us to link the resistance drift to a time-dependent increase in the Schottky barrier height. These findings provide valuable insights, pinpointing the primary contributor to resistance drift in PCM devices: the Schottky barrier height for hole injection at the interface. This underscores the significance of contacts (interface) in the electrical manifestation of drift in PCM devices.

Electrical doping of semiconductors is a revolutionary development that enabled many electronic and optoelectronic technologies. While doping of many inorganic and organic semiconductors has been well-established, controlled electrical doping of metal halide perovskites is yet to be demonstrated. In this work, we achieve efficient n- and p-type electrical doping of metal halide perovskites by co-evaporating the perovskite precursors alongside organic dopant molecules. We demonstrate that the Fermi level can be shifted by up to 500 meV towards the conduction band and by up to 400 meV towards the valence band by n- and p-doping, respectively, which increases the conductivity of the films. The doped layers were employed in PN and NP diodes, showing opposing trends in rectification. Demonstrating controlled electrical doping by a scalable, industrially relevant deposition method opens the route to developing perovskite devices beyond solar cells, such as thermoelectrics or complementary logic.

Synaptic transistors (STs) with a gate/electrolyte/channel stack, where mobile ions are electrically driven across the solid electrolyte, have been considered as analog weight elements for neuromorphic computing. The current (I_D) between the source and drain in the ST is analogously updated by gate voltage (V_G) pulses, enabling high pattern recognition accuracy in neuromorphic systems; however, the governing physical mechanisms of the ST are not fully understood yet. Our previous physics-based simulation study showed that ion movement in the electrolyte, rather than the electrochemical reactions that occur in the channel, plays an important role in switching. In this study, we experimentally explore the properties of the HfO_x electrolyte and show that by tuning the density of oxygen vacancies, it can assume the dual role of electrolyte and channel. We demonstrate analog synaptic behavior using a novel ST with a two-layer stack of CuO_x/HfO_x, where the CuO_x is the gate and Cu ion reservoir, and the HfO_x is the electrolyte and channel. To improve state retention and linearity, we introduce a Cu ion transport barrier in the form of a dense and stoichiometric Al₂O₃ layer. The CuO_x/Al₂O₃/HfO_x exhibits excellent state retention and improved potentiation and depression response. Energy dispersive spectroscopy mapping following potentiation confirms the role of the Al₂O₃ layer in confining the Cu ions in the HfO_x layer. We also show that a two-step programming scheme can further enhance synaptic response and demonstrate high recognition accuracy on the Fashion-MNIST dataset in simulation.

It is impossible to imagine modern electronic circuitry without a p–n junction—an essential building block for transistors, rectifiers, amplifiers, photovoltaics, etc. Conventional fabrication processes (ion implantation or chemical diffusion) result in an immutable potential configuration depriving reconfigurability. In contrast, the superior electrostatic tunability, dangling bonds- and reconstruction-free interfaces are some of the key features of 2D based heterostructures, making them promising candidates for cutting-edge optoelectronic and memory applications. Herein, the intercoupled 2D ferroelectricity of -In₂Se₃ is utilized to introduce micron-scale, non-volatile electrostatic doping in ambipolar WSe₂, enabling reconfigurable p–n junction. The actuation mechanism is based on the strong polarization field along the edge topology of In₂Se₃. The fabricated device presents stable p–n to n–p switching, a superior rectification ratio of ≈10⁶, and a low leakage current of ≈10⁻¹² A. Furthermore, the switchable short-circuit current response is utilized to demonstrate a novel self-powered, non-volatile memory based on photovoltaic reading. The ferroelectric non-volatility coupled with the ability to control the device operation using optical and electrical signals paves the way for ultrathin energy-efficient, multi-level optoelectronic and in-memory logic devices.