Photomemory Effect Research Articles

Gate-tunable non-volatile photomemory effect in MoS2 transistors

Non-volatile memory devices have been limited to flash architectures that are complex devices. Here, we present a unique photomemory effect in transistors. The photomemory is based on a photodoping effect—a controlled way of manipulating the density of free charges in monolayer using a combination of laser exposure and gate voltage application. The photodoping promotes changes on the conductance of leading to photomemory states with high memory on/off ratio. Such memory states are non-volatile with an expectation of retaining up to 50% of the information for tens of years. Furthermore, we show that the photodoping is gate-tunable, enabling control of the recorded memory states. Finally, we propose a model to explain the photodoping, and we provide experimental evidence supporting such a phenomenon. In summary, our work includes the phototransistors in the non-volatile memory devices and expands the possibilities of memory application beyond conventional memory architectures.

Behavioral Features of MIS Memristors with a Si3N4 Nanolayer Fabricated on a Conductive Si Substrate

The effect of the material of the metal plates (Au, Ta, W) and exposure to a high-power blue laser on the memristive characteristics of metal–insulator–semiconductor (MIS) capacitors with a Si3N4 film 6 nm thick fabricated on the basis of n+-Si is studied. It is shown that bipolar switching by the current appears only in capacitors with Au. The causes of the absence of bipolar switching in capacitors with Ta and W are explained. The switching of capacitors with Ta by the current and light and the photomemory effect are detected. It is shown that, despite the high doping level of the semiconductor substrate, it decreases the MIS memristor response rate due to a high density of surface states localized at the Si3N4/n+-Si interface. However, illumination allows a significant increase in the response rate due to a decrease in the semiconductor resistivity. The surface state densities are determined. To improve the frequency characteristics of MIS memristors, it is necessary to achieve a low surface state density.

Traps induced memory effect in rubrene single crystal phototransistor

In this report, phototransistors based on rubrene single crystals have been fabricated using octyltrichlorosilane (OTS) treated SiO2 as a substrate and memory effect has been observed and studied. Memory writing realized by the combined stimulation of applied gate voltage and light illumination was observed to be strongly dependent on the applied gate voltage. When the applied gate voltage, Vg = 100 V, only 500 ms writing time was found to be sufficient to achieve the memory window of 25 V. Long retention time of over 10 000 s as well as stable writing-reading-erasing-circle were also observed in the rubrene single crystal based phototransistor device. Even at high temperature of 100 °C, the device demonstrated stable memory effect. Thus we attributed the excellent memory effect to the deep electron traps. To clarify further the origin of persistent photocurrent, strongly hydrophobic fluorinated polyimide (FPI) was used as a dielectric layer to exclude the hydroxyl groups at the semiconductor/insulator interface. Compared to the OTS treated SiO2 based device, the photocurrent was saturated in a shorter time in FPI based counterpart, regardless of the light intensity and persistent photoconductivity was also observed. X-ray photoelectron spectroscopy analysis of rubrene single crystal revealed the existence of characteristic oxidation states, both in the high resolution C 1s and O 1s spectra, which behave as electron traps. In conclusion, we attribute the photo memory effect in rubrene single crystal based device to the oxygen related defects as well as to the hydroxyl groups at the dielectric/single crystal interface.

Особенности поведения МДП мемристоров с нанослоем Si-=SUB=-3-=/SUB=-N-=SUB=-4-=/SUB=-, изготовленных на основе проводящей подложки Si

AbstractThe effect of the material of the metal plates (Au, Ta, W) and exposure to a high-power blue laser on the memristive characteristics of metal–insulator–semiconductor (MIS) capacitors with a Si_3N_4 film 6 nm thick fabricated on the basis of n ^+-Si is studied. It is shown that bipolar switching by the current appears only in capacitors with Au. The causes of the absence of bipolar switching in capacitors with Ta and W are explained. The switching of capacitors with Ta by the current and light and the photomemory effect are detected. It is shown that, despite the high doping level of the semiconductor substrate, it decreases the MIS memristor response rate due to a high density of surface states localized at the Si_3N_4/ n ^+-Si interface. However, illumination allows a significant increase in the response rate due to a decrease in the semiconductor resistivity. The surface state densities are determined. To improve the frequency characteristics of MIS memristors, it is necessary to achieve a low surface state density.

Direct exchange between silicon nanocrystals and tunnel oxide traps under illumination on single electron photodetector

In this paper we present the trapping of photogenerated charge carriers for 300 s resulted by their direct exchange under illumination between a few silicon nanocrystals (ncs-Si) embedded in an oxide tunnel layer (SiOx = 1.5) and the tunnel oxide traps levels for a single electron photodetector (photo-SET or nanopixel). At first place, the presence of a photocurrent limited in the inversion zone under illumination in the I–V curves confirms the creation of a pair electron/hole (e–h) at high energy. This photogenerated charge carriers can be trapped in the oxide. Using the capacitance-voltage under illumination (the photo-CV measurements) we show a hysteresis chargement limited in the inversion area, indicating that the photo-generated charge carriers are stored at traps levels at the interface and within ncs-Si. The direct exchange of the photogenerated charge carriers between the interface traps levels and the ncs-Si contributed on the photomemory effect for 300 s for our nanopixel at room temperature.

Long-term potentiation of magnonic synapses by photocontrolled spin current mimicked in reentrant spin-glass garnet ferrite Lu3Fe5−2xCoxSixO12 thin films

(Co,Si)-cosubstituted Lu3Fe5O12 (Lu3Fe5−2xCoxSixO12; 0.00 ≤ x ≤ 1.00) thin films were grown on Y3Al5O12(001) substrates by pulsed laser deposition. Reentrant spin-glass behavior was observed and its robustness against external magnetic fields was improved by increasing the Co–Si content. In contrast, the spectral linewidth of ferromagnetic resonance was broadened by increasing the Co–Si content, which indicates that the Lu3Fe4.8Co0.1Si0.1O12 thin film is an optimal spin-glass spin-wave conductor. The spin pumping voltage of Lu3Fe4.8Co0.1Si0.1O12 exhibited short-term plasticity with photoinduced magnetic anisotropy and long-term potentiation with the photomemory effect, which mimicked the pre- and postsynaptic potentials of biological systems.

Photomemory effect in pyrolytic cadmium sulfide films doped with alkali metals

Photomemory effect in pyrolytic cadmium sulfide films doped with alkali metals

Optical properties of GaAs1−x N x alloys grown by molecular beam epitaxy

Optical properties of GaAs1−x N x alloys grown by molecular beam epitaxy using GaAs (001) as the substrate have been studied. These include photoluminescence (PL), cathodoluminescence (CL), photocurrent and photomemory effects. The low-temperature (77 K) PL characteristics were measured on samples with 0–0.105% N content. The wide emission band indicates the defective nature of the materials. The widening of the band for materials with increasing nitrogen concentration also suggested that the concentration of defect states in these materials dramatically increased with increasing nitrogen content. The PL and CL spectra for GaAs1−x N x layer 1854 did not show identical characteristics. Some layers showed a very sharp fall in photocurrent at low temperatures, indicating a very sharp photoquenching and an interaction between antisite, interstitial and vacancy defects. The photomemory effect, which causes photoquenching and the transition from the EL2 to the EL2* metastable state, was strongly influenced by the optical exposure and thermal history of the sample.

Nature of the photographic diamond surface phenomenon on boron-doped diamond

We have recently reported the photo-memory effect on boron-doped semiconducting diamond surfaces, which involves the photoelectrochemical pretreatment and subsequent sensitized deposition of copper and which we have referred to as the ‘photographic diamond surface phenomenon’ [S. Yoshihara, K. Shinozaki, T. Shirakashi, K. Hashimoto, D.A. Tryk, A. Fujishima, Electrochim. Acta 44 (1999) 2711]. In the present work, the origin of this phenomenon was investigated by AC impedance and contact angle methods. After polarization at −0.25 V versus SCE in aqueous H 2SO 4 solution under UV illumination, the surface exhibited the photographic effect. The polarized surface showed higher surface conductivity and increased hydrophilicity. Also, surface analysis suggested that the polarized surface has a higher surface coverage of hydrogen. These results strongly suggest that this phenomenon is related to changes of the surfacial functional groups induced by photoelectrochemical hydrogen evolution.

Surface electron properties of 6H and 15R modifications of silicon carbide

The temperature dependences of the surface potential on the (0001)Si and (0001)C surfaces of 6H- and 15R-SiC have been studied by the surface photovoltage method. It is found that the depletion layer is at all surfaces and and values are determined by the physical-chemical conditions of the surfaces. For the (0001)Si surfaces of 6H- and 15R-SiC oxidized electrolytically and etched in HF the dependences have an N-like behaviour; for the (0001)C surfaces they have a V-like behaviour. Following from the Hall effect data and dependences we have carried out calculations of temperature dependences of the charge in the surface electron states (SES) and the Fermi level position at surfaces. It is shown that the dependence with decreasing temperature is determined by charging SES with electrons and reconstruction of the SES system. We have found and studied the photomemory effect of the surface potential related to the capture of non-equilibrium holes by surface traps under illumination. The maximum trap concentration of is observed at the (0001)C surface of 15R-SiC and the minimum, at , is at the (0001)Si surface of 6H-SiC etched in HF.

Light-Controlled Transport in Doped Diluted Magnetic Semiconductors near Localization Boundary

In the studies of the metal-insulator transition (MIT) the control of a certain parameter, such as electron concentration n, or external conditions, such as magnetic field B, are of great importance. Unusual properties of diluted magnetic semiconductors (DMS), particularly the giant negative magnetoresistance, have made it possible to tune MIT by the magnetic field [1], and thus to examine quantitatively the behavior of transport phenomena in the vicinity of MIT critical point. The obtained results referred to the case of the high magnetic fields, in which electrons resided in one spin subband and Mn spins were spin polarized. With no doubt, the exploration of the critical region in DMS in the absence of the external magnetic field, as well as the study of 3D (B, n, σ) diagram of MIT would be equally important. Such an opportunity is offered by the recently discovered photomemory effect in some doped n-type II-VI semiconductors [3-5, 9]. This photomemory effect can serve as a tuning mechanism of the transition, as was demonstrated for GaAlAs [2]. Previous transport [3, 4] far infrared (FIR) absorption [4] and SQUID magnetization experiments [5] performed for In and Ga doped Cd1-xMnxΤe and Cd1xMn xTe1ySe y crystals on insulator side of MIT showed persistent increase in the concentration of shallow donors after illumination of the sample at low temperature. In the FIR experiment strong persistent increase in absorption due to impurity and optical hopping transitions, as well as the appearance of the electric-dipole

Magnetization of bound magnetic polarons: Direct determination via photomemory effect.

Light-induced persistent change in the concentration of occupied shallow donors (photomemory effect) in ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$${\mathrm{Te}}_{1\mathrm{\ensuremath{-}}\mathit{y}}$${\mathrm{Se}}_{\mathit{y}}$:In has been used for determining the contribution of donor-bound magnetic polarons to the total magnetization of the crystal. This contribution must be taken into account in any precise description of low temperature properties of diluted magnetic semiconductors containing shallow donors. The observed agreement between experimental data and the theory of bound magnetic polarons provides additional support for the negative-U model of DX-like centers in II-VI semiconductors.

Novel Photo-Memory Effect in Photoconductivity of Conducting Polymer Containing Photochromic Dye

Abstract Photoconduction of a conducting polymer, poly(9,9-dihexadecylfluorene) containing a photochromic dye, cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene, is suppressed upon photoisomerization of the dye from ring-open form to ring-closed form but recovered by the reverse photoisomerization. The reversible memory effect in the photoconduction has been discussed on the basis of the energy states of the dye and those trapping effects on the photo-carriers in the conducting polymer.

Application of Photomemory Effect in Cd1-xMnxTe1-ySey:In for Direct Measurements of Magnetization of Bound Magnetic Polarons

Application of Photomemory Effect in Cd_1-xMn_xTe_1-ySe_y:In for Direct Measurements of Magnetization of Bound Magnetic Polarons

Mechanical properties of anthracene crystals under illumination: Photoplastic effect

The mechanical properties of the photoplastic effect (PPE) in anthracene crystals were extensively studied. Detailed results of its dependence on strain rates ε̇, strain-rate sensitivity, temperature, and wavelength of exciting light have been obtained, and also the photomemory effect of PPE has been observed. Temperature dependence of PPE showed that the formation energy of physical dimers (photoinduced products) was estimated to be about 0.2 eV. Moreover, the strain-rate dependence of PPE indicated that the change in stress Δτs decreased with increasing strain rates, namely, the strain-rate sensitivity m=Δτs/Δ ln ε̇<0. In addition, the photomemory effect shows that physical dimers were stable at dislocation cores with a long life.

Long lifetime photoconductivity in semi-insulating bulk GaAs

We report a new photomemory effect in semi-insulating bulk GaAs. Persistent illumination with 1.15 eV photons induces a photosensitivity state in GaAs, which is characterized by a slow decay of the photoconductivity, after the light is switched-off. The most relevant phenomenological aspects of this effect are summarized in this communication.

Optically enhanced defect reactions in semi-insulating bulk GaAs

We investigate in this paper a photomemory effect in the photocurrent of semi-insulating GaAs when it is illuminated with photons ranging from 1 to 1.35 eV. We observe a strong enhancement of the photocurrent after long excitation with those photons, which is thermally quenched between 123 and 135 K. We explain this phenomenon by a defect reaction, dealing with the association of two or more complex defects, as a result of the electrostatic interaction between the original defects when their charge state is changed by means of the illumination. The formation of this complex drives the sample into a high-sensitivity state, which we have called ‘‘on-state.’’ The dissociation of the photogenerated complex defect, due to thermal emission of electrons to the conduction band, restores the crystal into its normal photosensitivity state, which we have called ‘‘off-state.’’

Investigation of deep levels in PbI2 by photoinduced current transient spectroscopy

Deep levels in PbI2 have been investigated by photoinduced current transient spectroscopy for the first time. By separating the signal processing from the data acquisition it was possible to analyze the transient using different methods, in particular a four-gate treatment which allows to clear the detrapping current of uncontrolled changes of the recombination lifetime of thermally released carriers. Three hole traps located at 0.30, 0.47, and 0.66 eV have been detected and the corresponding thermal capture cross sections evaluated. In addition a photomemory effect has been evidenced. The main features of the excited state of the crystal are increased photosensitivity, neutralization of hole traps, and residual conductivity. It is believed that macroscopic recombination barriers acting as minority carrier traps under optical excitation are responsible for this phenomenon. The presence of these extended defects is probably related to the layered structure of PbI2. An energy model is proposed on the basis of which the observed logarithmic time dependence of the photosensitization at room temperature can be predicted. The model allows also to give a plausible interpretation for all the characteristic features of the photomemory effect and for various results previously reported by other authors.

EPR investigation of the photomemory effect of Cu2O

EPR investigation of the photomemory effect of Cu2O

Photorefractive effect in strontium barium niobate: The internal field in the inhomogenous ferroelectric crystal

The photorefractive effect is observed in strongly unipolar SBN crystals in the absence of the external bias field. The formation of a photorefractive space-charge field Esc is due to the existence of the internal inhomogenous field in the bulk of the crystals. Simultaneously the photomemory effect is observed which is characteristic of the inhomogenous photoconductors.