A carbonyl-decorated two-dimensional polymer as a charge-trapping layer for non-volatile memory storage devices with a high endurance and wide memory window.

The charge-trapping mechanism in conjugated polymers is a performance obstacle in many optoelectronic devices harnessed for non-volatile memory applications. Herein, a carbonyl-decorated organic 2D-polymer (TpDb)-based charge-trapping memory device has been developed with a wide memory window (3.2 V) with low programming and erasing voltages of +3/-2 and -3/+2. The TpDb was synthesized by a potentially scalable solid-state aldol condensation reaction. The inherent structural defects and the semi-conjugated nature of the enone network in TpDb offer effective charge-trapping through the localization of charges in specific functional groups (CO). The interlayer hydrogen bonding enhances the packing density of the 2D-polymer layers thereby improving the memory storage properties of the material. Furthermore, the TpDb exhibits excellent features for non-volatile memory applications including over 10 000 cycles of write/read endurance and a prolonged retention performance of 104 seconds at high temperatures (100 °C).

Nano-scale charge trapping memory based on two-dimensional conjugated microporous polymer.

There is a growing interest in new semiconductor nanostructures for future high-density high-performance flexible electronic devices. Two-dimensional conjugated microporous polymers (2D-CMPs) are promising candidates because of their inherent optoelectronic properties. Here, we are reporting a novel donor-acceptor type 2D-CMP based on Pyrene and Isoindigo (PI) for a potential nano-scale charge-trapping memory application. We exfoliated the PI polymer into ~ 2.5 nm thick nanoparticles (NPs) and fabricated a Metal-Insulator-Semiconductor (MIS) device with PI-NPs embedded in the insulator. Conductive AFM (cAFM) is used to examine the confinement mechanism as well as the local charge injection process, where ultrathin high-κ alumina supplied the energy barrier for confining the charge carrier transport. We have achieved a reproducible on-and-off state and a wide memory window (ΔV) of 1.5 V at a relatively small reading current. The device displays a low operation voltage (V < 1 V), with good retention (104 s), and endurance (103 cycles). Furthermore, a theoretical analysis is developed to affirm the measured charge carriers' transport and entrapment mechanisms through and within the fabricated MIS structures. The PI-NPs act as a nanoscale floating gate in the MIS-based memory with deep trapping sites for the charged carriers. Moreover, our results demonstrate that the synthesized 2D-CMP can be promising for future low-power high-density memory applications.

A Rational Design of Isoindigo-Based Conjugated Microporous n-Type Semiconductors for High Electron Mobility and Conductivity.

The development of n-type organic semiconductors has evolved significantly slower in comparison to that of p-type organic semiconductors mainly due to the lack of electron-deficient building blocks with stability and processability. However, to realize a variety of organic optoelectronic devices, high-performance n-type polymer semiconductors are essential. Herein, conjugated microporous polymers (CMPs) comprising isoindigo acceptor units linked to benzene or pyrene donor units (BI and PI) showing n-type semiconducting behavior are reported. In addition, considering the challenges of deposition of a continuous and homogeneous thin film of CMPs for accurate Hall measurements, a plasma-assisted fabrication technique is developed to yield uniform thin films. The fully conjugated 2D networks in PI- and BI-CMP films display high electron mobility of 6.6 and 3.5 cm2 V-1 s-1 , respectively. The higher carrier concentration in PI results in high conductivity (5.3 mS cm-1 ). Both experimental and computational studies are adequately combined to investigate structure-property relations for this intriguing class of materials in the context of organic electronics.

Artificial visual perception neural system using a solution-processable MoS2-based in-memory light sensor.

Optoelectronic devices are advantageous in in-memory light sensing for visual information processing, recognition, and storage in an energy-efficient manner. Recently, in-memory light sensors have been proposed to improve the energy, area, and time efficiencies of neuromorphic computing systems. This study is primarily focused on the development of a single sensing-storage-processing node based on a two-terminal solution-processable MoS2 metal-oxide-semiconductor (MOS) charge-trapping memory structure-the basic structure for charge-coupled devices (CCD)-and showing its suitability for in-memory light sensing and artificial visual perception. The memory window of the device increased from 2.8 V to more than 6 V when the device was irradiated with optical lights of different wavelengths during the program operation. Furthermore, the charge retention capability of the device at a high temperature (100 °C) was enhanced from 36 to 64% when exposed to a light wavelength of 400 nm. The larger shift in the threshold voltage with an increasing operating voltage confirmed that more charges were trapped at the Al2O3/MoS2 interface and in the MoS2 layer. A small convolutional neural network was proposed to measure the optical sensing and electrical programming abilities of the device. The array simulation received optical images transmitted using a blue light wavelength and performed inference computation to process and recognize the images with 91% accuracy. This study is a significant step toward the development of optoelectronic MOS memory devices for neuromorphic visual perception, adaptive parallel processing networks for in-memory light sensing, and smart CCD cameras with artificial visual perception capabilities.

Mechanical characterization and optical microscopy of homemade slime and the effect of some common household products.

In this work, we demonstrate the synthesis of homemade slime and investigate how adding different household chemicals such as shaving cream and clay affects the chemical properties and hence the mechanical behavior. The purpose of this study is to instill scientific curiosity in young learners by establishing a relationship between a material's chemical structure and its mechanical properties. Eight types of slime were studied: basic slime (borax with glue), slime with the addition of: (a) shaving cream, (b) clay, (c) shaving cream and clay together, (d) baking soda, (e) cornstarch, (f) hand soap, and (g) toothpaste. It was found that basic slime has a Young's Modulus of 93 MPa while adding shaving cream and clay increased the modulus of elasticity to 194 and 224 MPa respectively. Adding thickening agents such as baking soda and corn starch increased the modulus to 118 and 110 MPa respectively while the incorporation of foaming agents, for example, hand soap and toothpaste rendered the sample very gelatinous. The Young's modulus of samples C and D was the highest recorded and this is attributed to the presence of clay, which is relatively the stiffest material from the choice of additives used in this study. The results were supported by FT-IR spectroscopy which showcased the formation of different chemical structures of the slime with the added chemical agents.

Utilizing trapped charge at bilayer 2D MoS2/SiO2interface for memory applications.

In this work we use conductive atomic force microscopy (cAFM) to study the charge injection process from a nanoscale tip to a single isolated bilayer 2D MoS2flake. The MoS2is exfoliated and bonded to ultra-thin SiO2/Si substrate. Local current-voltage (IV) measurements conducted by cAFM provides insight in charge trapping/de-trapping mechanisms at the MoS2/SiO2interface. The MoS2nano-flake provides an adjustable potential barrier for embedded trap sites where the charge is injected from AFM tip is confined at the interface. A window of (ΔV∼ 1.8 V) is obtain at a reading current of 2 nA between two consecutiveIVsweeps. This is a sufficient window to differentiate between the two states indicating memory behavior. Furthermore, the physics behind the charge entrapment and its contribution to the tunneling mechanisms is discussed.

Author Correction: Photodetection Characteristics of Gold Coated AFM Tips and n-Silicon Substrate nano-Schottky Interfaces.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Time dependence of electrical characteristics during the charge decay from a single gold nanoparticle on silicon.

In this work, we investigate the time dependence of trapped charge in isolated gold nanoparticles (Au-NPS) dispersed on n-Si substrates, based on the electrical characteristics of nano metal-semiconductor junctions. The current-voltage (I-V) characteristics have been analysed on a single Au-NP at different time intervals, using conductive mode atomic force microscopy (AFM). The Au-NPs have been characterized for their morphology and optical properties using transmission electron microscopy (TEM), ultraviolet visible (UV-vis) spectroscopy and scanning electron microscopy (SEM). The tunneling current is found to be a direct function of the trapped charge in the NP, due to the charge screening effect of the electric field at the NP/n-Si interface. The evolution of the I-V curves is observed at different time intervals until all the trapped charge dissipates. Moreover, the time needed for nanoparticles to restore their initial state is verified and the dependence of the trapped charge on the applied voltage sweep is investigated.

Improved figures of merit of nano-Schottky diode by embedding and characterizing individual gold nanoparticles on n-Si substrates.

Improving Schottky diode characteristics in semiconducting devices is essential for better functionality in electronic and optoelectronic devices at nanoscale. In this paper, we investigate the electric transport characteristics of a gold (Au)-tip/n-Si-based nano-Schottky diode by using a conductive-mode atomic force microscope (CAFM). First, 10 nm average diameter Au nanoparticles (NPs) are monodispersed on the highly cleaned n-type Si substrate using an optimized spin-coating technique. The controlled and well dispersed NPs are confirmed by using the AC imaging mode of the AFM. The electrical characteristics are established by using an Au-coated AFM tip, by either soft engaging at the surface of the n-Si substrate or at the top of an individual Au NP. Landing of the AFM tip on the NP or n-Si substrate is validated by the force curves of the AFM. From the localized CAFM electrical characteristics, we observed the improvement in the figures of merit (FOM) that characterize the rectification performance including the (1-V) asymmetry (f ASYM), and the turn-on voltage due to placing the Au NP between the AFM tip and n-Si substrate. These improved FOM of the nanoscale diodes are explained based on the increase in the tunneling current at the nanoscale Au-NP/n-Si interface. Moreover, the nanoscale control of interface structure is extremely important to improve the characteristics of nano-Schottky diodes.

Photodetection Characteristics of Gold Coated AFM Tips and n-Silicon Substrate nano-Schottky Interfaces.

Silicon (Si)-based photodetectors are appealing candidates due to their low cost and compatibility with the complementary metal oxide semiconductor (CMOS) technology. The nanoscale devices based on Si can contribute efficiently in the field of photodetectors. In this report, we investigate the photodetection capability of nano-Schottky junctions using gold (Au) coated conductive atomic force microscope (C-AFM) tips, and highly cleaned n-Si substrate interface. The Au nanotip/n-Si interface forms the proposed structure of a nano Schottky diode based photodetector. The electrical characteristics measured at the nanoscale junction with different Au nanotip radii show that the tunneling current increases with decreasing the tip radius. Moreover, the tunneling process and photodetection effects are discussed in terms of barrier width/height decrease at the tip-semiconductor interface due to the applied electric field as well as the generation of plasmon-induced hot-electron at the nanoparticle (i.e. C-AFM tip)/n-Si interface. Furthermore, the photodetection sensitivity is investigated and it is found to be higher for C-AFM tips with smaller radii. Moreover, this research will open a new path for the miniaturization of photodetectors with high sensitivity based on nano-Schottky interfaces.

Hexagonal germanium formation at room temperature using controlled penetration depth nano-indentation.

Thin Ge films directly grown on Si substrate using two-step low temperature growth technique are subjected to low load nano-indentation at room temperature. The nano-indentation is carried out using a Berkovich diamond tip (R ~ 20 nm). The residual impressions are studied using ex-situ Raman Micro-Spectroscopy, Atomic Force Microscopy combined system, and Transmission Electron Microscopy. The analysis of residual indentation impressions and displacement-load curves show evidence of deformation by phase transformation at room temperature under a critical pressure ranging from 4.9GPa-8.1GPa. Furthermore, the formation of additional Ge phases such as r8-Ge, hd-Ge, and amorphous Ge as a function of indentation depth have been realized. The inelastic deformation mechanism is found to depend critically on the indentation penetration depth. The non-uniform spatial distribution of the shear stress depends on the indentation depth and plays a crucial role in determining which phase is formed. Similarly, nano-indentation fracture response depends on indentation penetration depth. This opens the potential of tuning the contact response of Ge and other semiconductors thin films by varying indentation depth and indenter geometry. Furthermore, this observed effect can be reliably used to induce phase transformation in Ge-on-Si with technological interest as a narrow band gap material for mid-wavelength infrared detection.

Interface engineering of graphene-silicon Schottky junction solar cells with an Al2O3 interfacial layer grown by atomic layer deposition.

The recent progress in graphene (Gr)/silicon (Si) Schottky barrier solar cells (SBSC) has shown the potential to produce low cost and high efficiency solar cells. Among the different approaches to improve the performance of Gr/Si SBSC is engineering the interface with an interfacial layer to reduce the high recombination at the graphene (Gr)/silicon (Si) interface and facilitate the transport of photo-generated carriers. Herein, we demonstrate improved performance of Gr/Si SBSC by engineering the interface with an aluminum oxide (Al2O3) layer grown by atomic layer deposition (ALD). With the introduction of an Al2O3 interfacial layer, the Schottky barrier height is increased from 0.843 V to 0.912 V which contributed to an increase in the open circuit voltage from 0.45 V to 0.48 V. The power conversion efficiency improved from 7.2% to 8.7% with the Al2O3 interfacial layer. The stability of the Gr/Al2O3/Si devices was further investigated and the results have shown a stable performance after four weeks of operation. The findings of this work underpin the potential of using an Al2O3 interfacial layer to enhance the performance and stability of Gr/Si SBSC.

Metal-germanium-metal photodetector grown on silicon using low temperature RF-PECVD.

In this paper, germanium metal-semiconductor-metal photodetectors (MSM PDs) are fabricated on Si using a low-temperature two-step deposition technique by RF-PECVD. The photodetectors are optimized to effectively suppress the dark current through the insertion of n-type a-Si:H interlayer between the metal/Ge interface. Tuning the Schottky Barrier Height (SBH) by inserting different thickness of the interlayer is investigated. Results revealed that SBH for electrons and holes can effectively be enhanced by 0.3eV and 0.54eV, respectively. Furthermore, the dark-current (IDark) is suppressed significantly by more than four orders of magnitude. The measured IDark is ∼76 nA for an applied reverse bias of 1.0 V. Additionally, the Ge MSMs structure exhibited a photo responsivity of 0.8A/W at that bias. The proposed low-temperature (<550°C) Ge-on-Si MSM PD demonstrates a great potential for high-performance Ge-based photodetectors in monolithically integrated CMOS platform.

Cubic-phase zirconia nano-island growth using atomic layer deposition and application in low-power charge-trapping nonvolatile-memory devices.

The manipulation of matter at the nanoscale enables the generation of properties in a material that would otherwise be challenging or impossible to realize in the bulk state. Here, we demonstrate growth of zirconia nano-islands using atomic layer deposition on different substrate terminations. Transmission electron microscopy and Raman measurements indicate that the nano-islands consist of nano-crystallites of the cubic-crystalline phase, which results in a higher dielectric constant (κ âˆ¼ 35) than the amorphous phase case (κ âˆ¼ 20). X-ray photoelectron spectroscopy measurements show that a deep quantum well is formed in the Al2O3/ZrO2/Al2O3 system, which is substantially different to that in the bulk state of zirconia and is more favorable for memory application. Finally, a memory device with a ZrO2 nano-island charge-trapping layer is fabricated, and a wide memory window of 4.5 V is obtained at a low programming voltage of 5 V due to the large dielectric constant of the islands in addition to excellent endurance and retention characteristics.

~3-nm ZnO Nanoislands Deposition and Application in Charge Trapping Memory Grown by Single ALD Step.

Low-dimensional semiconductor nanostructures are of great interest in high performance electronic and photonic devices. ZnO is considered to be a multifunctional material due to its unique properties with potential in various applications. In this work, 3-nm ZnO nanoislands are deposited by Atomic Layer Deposition (ALD) and the electronic properties are characterized by UV-Vis-NIR Spectrophotometer and X-ray Photoelectron Spectroscopy. The results show that the nanostructures show quantum confinement effects in 1D. Moreover, Metal-Oxide-Semiconductor Capacitor (MOSCAP) charge trapping memory devices with ZnO nanoislands charge storage layer are fabricated by a single ALD step and their performances are analyzed. The devices showed a large memory window at low operating voltages with excellent retention and endurance characteristics due to the additional oxygen vacancies in the nanoislands and the deep barrier for the trapped holes due to the reduction in ZnO electron affinity. The results show that the ZnO nanoislands are promising in future low power memory applications.

1D versus 3D quantum confinement in 1-5 nm ZnO nanoparticle agglomerations for application in charge-trapping memory devices.

ZnO nanoparticles (NPs) have attracted considerable interest from industry and researchers due to their excellent properties with applications in optoelectronic devices, sunscreens, photocatalysts, sensors, biomedical sciences, etc. However, the agglomeration of NPs is considered to be a limiting factor since it can affect the desirable physical and electronic properties of the NPs. In this work, 1-5 nm ZnO NPs deposited by spin- and dip-coating techniques are studied. The electronic and physical properties of the resulting agglomerations of NPs are studied using UV-vis-NIR spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM), and their application in metal-oxide-semiconductor (MOS) memory devices is analyzed. The results show that both dip- and spin-coating techniques lead to agglomerations of the NPs mostly in the horizontal direction. However, the width of the ZnO clusters is larger with dip-coating which leads to 1D quantum confinement, while the smaller ZnO clusters obtained by spin-coating enable 3D quantum confinement in ZnO. The ZnO NPs are used as the charge-trapping layer of a MOS-memory structure and the analysis of the high-frequency C-V measurements allow further understanding of the electronic properties of the ZnO agglomerations. A large memory window is achieved in both devices which confirms that ZnO NPs provide large charge-trapping density. In addition, ZnO confined in 3D allows for a larger memory window at lower operating voltages due to the Poole-Frenkel charge-emission mechanism.

Enhanced non-volatile memory characteristics with quattro-layer graphene nanoplatelets vs. 2.85-nm Si nanoparticles with asymmetric Al2O 3/HfO 2 tunnel oxide.

In this work, we demonstrate a non-volatile metal-oxide semiconductor (MOS) memory with Quattro-layer graphene nanoplatelets as charge storage layer with asymmetric Al2O3/HfO2 tunnel oxide and we compare it to the same memory structure with 2.85-nm Si nanoparticles charge trapping layer. The results show that graphene nanoplatelets with Al2O3/HfO2 tunnel oxide allow for larger memory windows at the same operating voltages, enhanced retention, and endurance characteristics. The measurements are further confirmed by plotting the energy band diagram of the structures, calculating the quantum tunneling probabilities, and analyzing the charge transport mechanism. Also, the required program time of the memory with ultra-thin asymmetric Al2O3/HfO2 tunnel oxide with graphene nanoplatelets storage layer is calculated under Fowler-Nordheim tunneling regime and found to be 4.1 ns making it the fastest fully programmed MOS memory due to the observed pure electrons storage in the graphene nanoplatelets. With Si nanoparticles, however, the program time is larger due to the mixed charge storage. The results confirm that band-engineering of both tunnel oxide and charge trapping layer is required to enhance the current non-volatile memory characteristics.

A complete physical germanium-on-silicon quantum dot self-assembly process.

Achieving quantum dot self-assembly at precise pre-defined locations is of vital interest. In this work, a novel physical method for producing germanium quantum dots on silicon using nanoindentation to pre-define nucleation sites is described. Self-assembly of ordered ~10 nm height germanium quantum dot arrays on silicon substrates is achieved. Due to the inherent simplicity and elegance of the proposed method, the results describe an attractive technique to manufacture semiconductor quantum dot structures for future quantum electronic and photonic applications.

Silicon-Germanium multi-quantum well photodetectors in the near infrared.

Single crystal Silicon-Germanium multi-quantum well layers were epitaxially grown on silicon substrates. Very high quality films were achieved with high level of control utilizing recently developed MHAH epitaxial technique. MHAH growth technique facilitates the monolithic integration of photonic functionality such as modulators and photodetectors with low-cost silicon VLSI technology. Mesa structured p-i-n photodetectors were fabricated with low reverse leakage currents of ~10 mA/cm² and responsivity values exceeding 0.1 A/W. Moreover, the spectral responsivity of fabricated detectors can be tuned by applied voltage.

High-efficiency metal-semiconductor-metal photodetectors on heteroepitaxially grown Ge on Si.

We demonstrate extremely efficient germanium-on-silicon metal-semiconductor-metal photodetectors with responsivities (R) as high as 0.85 A/W at 1.55 microm and 2V reverse bias. Ge was directly grown on Si by using a novel heteroepitaxial growth technique, which uses multisteps of growth and hydrogen annealing to reduce surface roughness and threading dislocations that form due to the 4.2% lattice mismatch. Photodiodes on such layers exhibit reverse dark currents of 100 mA/cm2 and external quantum efficiency up to 68%. This technology is promising to realize monolithically integrated optoelectronics.