Search

Abstract: Ferroelectric field effect transistors (FeFETs), characterized by their low power consumption and polarization effect, can be employed in photodetectors based on 2D materials. In this paper, a MoS2 phototransistor with epitaxial ferroelectric (Hf0.5Zr0.5)O2 (HZO) is reported as a gate dielectric layer. Gate‐dielectric‐polarization‐dependent ambipolar behavior is observed in the FET, and relatively low power consumption and hysteresis‐free loop are achieved in the FeFET. The anomalous negative photoconductivity (NPC) is observed as well. Possible reasons for such phenomenon are clarified including the photogating effect originating from the interface traps and the polarization‐dependent electric‐field control through ferroelectric gating. The high responsivity of −8.44 × 103 A W−1 in the negative photoconductivity as well as the response time of 500 ms are reported. The demonstrated Molybdenum disulfide (MoS2) FeFET photodetectors show great potential in the on‐chip complementary metal‐oxide semiconductor (CMOS)‐compatible circuits for multifunctional devices.

PbTe-based compounds are excellent candidates for the different types of optical detector applications from near to far IR ranges. In the present work, a technology has been developed for the fabrication of Pb 1 − x Sn x Te compositions, doped with In, on a thin amorphous substrate (polyimide). The film preparation was performed by the electron gun evaporation method. The systematic study of structure and transport properties (Hall coefficient and electric conductivity) in the entire temperature range of 10–300 K for Pb 1 − x Sn x Te:In films (x = 0 , 0.1, 0.2) was investigated. It was studied that the photoconductivity of the films in the telecom wavelength range, including kinetics, sensitivity, and noise equivalent power, has been conducted and it discovered persistent photoconductivity for all compositions at the temperature T < 21 K. The results of the work have promising potential to use poly(nano) crystalline Pb 1 − x Sn x Te:In films on an amorphous substrate both for photodetection in the telecom wavelength range and for the creation of all-optical neuromorphic systems, cooled memory, and logic elements operating at the low energy of laser pulses. [ABSTRACT FROM AUTHOR]

Three sets of heteroepitaxial diamond crystals grown under nominally identical process conditions on Ir/YSZ/Si(001) substrates have been studied with respect to structural defects, chemical purity, and x-ray induced photoconductivity (PC). The dislocation density that varied systematically between 10 7 and 10 9 cm − 2 had a minor influence on dark conductivity and photoconductive gain G. In contrast, the substitutional nitrogen (N N ) and substitutional boron (N B ) defects, which are both present at very low concentrations (≤ 1 ppb), turned out to be the crucial factors controlling the electrical behavior. Small differences between both resulted in variations of the photocurrents by up to 5 orders of magnitude. The maximum in G of 0.75 × 10 4 was measured in the sample with highest dark conductivity. It could be explained conclusively within our model calculations on gain formation by N N ≤ N B . For low gain samples, we found N N > --> N B . However, the measured G values were far from theoretical predictions. This indicates a dominating role of additional traps. After x-ray switch-off, persistent photoconductivity (PPC) was observed in high gain samples. It was attributed to an energetic barrier hampering the recharging of nitrogen atoms by hole capture. As a possible source, strain fields generated by dislocations are suggested. [ABSTRACT FROM AUTHOR]

This research investigates the effects of barium (Ba) doping the photoelectric properties of zinc oxide (ZnO) nanoparticles (NPs) to explore their potential applications in optoelectronic devices.Photocurrent experiments reveal intriguing negative photoconductivity (NPC) behavior in Ba:ZnO based UV photodetectors (PDs).Moreover, the exploration of UV PD performance reveals rise and fall times of approximately 8.26s and 8.72s, respectively, under a -1V external bias.Our fabricated device shows higher detectivity about 1.33 × 10 16 Jones and external quantum efficiency exceeding 100 %, compared to other PD. The analysis of transient currentsuggests the existence of two kinds of defects contributing to NPC. Through an investigation of the noise density, exponents γ ranging between −2.048 and −1.76 were determined, substantiating the hypothesis that the observed noise originates from a distribution of defects. Overall, these results underscore the potential of Ba:ZnO NPs for high-performance devices compared to conventional ZnO-based PDs. [ABSTRACT FROM AUTHOR]

Transient processes in the photoconductivity of TiS3 single crystals exposed to rectangular light pulses in the wavelength range of λ = 405–940 nm are investigated. It is established that the decay in the photoconductivity after switching the light off at temperatures from 78 to 180 K is described by a logarithmic law in the range from 10–3 to 102 s (i.e., when time changes by five orders of magnitude). This means that the relaxation process is characterized by times ranging, at least, from several tens of microseconds to several tens of minutes. It is shown that the relaxation is basically successive: the recombination barrier increases while the conductivity approaches the equilibrium value. [ABSTRACT FROM AUTHOR]

In this work, the photoconductivity (PC) spectrum of thin CdSe films was studied. In the course of studies on glass substrates, thin films of cadmium and selenium with a thickness of h = 200 nm and h = 400 nm were selected. The thickness of the samples obtained by chemical deposition was determined by the gravimetric method. Since CdSe crystal is a light-sensitive semiconductor material, the photoconductivity of thin films has been studied. The spectra obtained during studies carried out at a wavelength λ = 600-1100 nm were analyzed. It has been established that the spectrum is chaotic, since in the h = 200 nm layers the phase is not completely formed. In the layers h = 400 nm, a maximum centered at the wavelength λ = 710 nm was recorded. [ABSTRACT FROM AUTHOR]

This study describes the fabrication of hybrid two-dimensional (2D)-quantum dot (QD) MoS2–AgInS2 photoconductive devices through the mechanical pressing of a MoS2 flake onto an AgInS2 QD film. The devices exhibit an enhanced photoresponse at both continuous and modulated optical excitations, compared with the bare MoS2 or AgInS2 layer, due to the formation of a built-in electric field near the MoS2/AgInS2 interface. The continuous wave photoresponse is significantly higher due to the effective photoconductive gain when electrons flow freely through the MoS2 flake, whereas holes are effectively trapped in AgInS2 QDs. The study highlights the potential of hybrid 2D-QD MoS2–AgInS2 devices for photovoltaic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this study, undoped hydrogenated amorphous silicon (a-Si:H) thin films deposited under moderate dilution ratios of silane by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) have been investigated using steady-state photoconductivity and improved dual beam photoconductivity (DBP) methods to identify changes in multiple gap states in annealed and light-soaked states. Four different gap states were identified in annealed state named as A, B, C, and X states. The peak energy positions of these Gaussian distributions are consistent with those recently identified by Fourier transform photocurrent spectroscopy (FTPS). After in situ light soaking, their density increases with different rates as peak energy positions and half-widths remain unaffected. The electron-occupied A and B states located below the dark Fermi level and their density and ratios in the annealed and light-soaked states correlate well with those defects detected by time-domain pulsed electron paramagnetic resonance (EPR) experiments. The A, B, and X states located closer to the middle of the bandgap anneal out at room temperature in dark and define the "fast" states. However, the C states show no sign of room temperature annealing such that they must define the "slow" states in undoped a-Si:H. The results found in this study indicate that the anisotropic disordered network is a more appropriate model than previously proposed defect models based on the continuous random network to define the nanostructure of undoped a-Si:H, where multiple defects, D0 and non-D0 defects, can be identified by using the improved DBP method. [ABSTRACT FROM AUTHOR]

Semi‐organic materials consisting of organic and inorganic semiconductors, exhibit the characteristic properties like strong optical nonlinearity and thermal stability. Lithium Fumarate (LF) is grown as a semi‐organic single crystal using lithium hydroxide and fumaric acid employing a slow evaporation method with de‐ionized water as the solvent. Classical NucleationTheory (CNT) is used to calculate the speed of LF nucleation. By altering the temperature, the thermogravimetric (TG) models, namely Coats–Redfern and Piloyan–Novikova equations are used to calculate the kinetic parameters such as enthalpy, Gibbs free energy, real heat power, and entropy of activation values. The width of the metastable zone in the LF crystal is determined by evaluating the relationship between supersaturation and temperature and it is found to exhibit a linear dependence on temperature and possess positive solubility. Lithium Fumarate's (LF) photoconductivity test shows that the grown crystal has positive photoconductivity. Photoluminescence studies conclude that Correlated Colour Temperature (CCT) values and color purity of LF crystal are suited to the green light emitting devices and flat panel displays. [ABSTRACT FROM AUTHOR]

Cd@ZnS microspheres with diameters of ~ 4 μm and a shell thickness of about ~ 1 μm have been successfully fabricated via green, ecofriendly solvothermal approach. These microspheres are tailored using chelating agent ethylenediamine tetra acetic acid, non-ionic surfactant poly ethylene glycol (PEG) and precursor thioacetamide. The structural information such as phase, size and morphology of prepared microspheres is characterised using X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) while the optical properties are studied using optical absorption of as prepared products. It is found that cubic phase of prepared products formed with tiny constituent as crystallites are about ~ 15 nm in size, as indicated by TEM observation. Temporal-dependent photoconductive response characteristics are quantitatively analysed thoroughly. The results clearly demonstrate that the fabrication of Cd@ZnS microspheres-based photoconductive devices will have potential applications in the future optoelectronics as optical switching and visible-light photodetectors. [ABSTRACT FROM AUTHOR]

We report a detailed study of the bipolar persistent photoconductivity in an HgTe/CdHgTe double quantum well (DQW), which can be a perspective for studying topological states in these structures. Photoconductivity spectra measurements in the range of 1.1–3.1 eV as well as transport measurements under different illumination conditions were performed at T = 4.2 K. Based on the results, the processes occurring in the structure under illumination and leading to a change in the carrier concentration in the DQW have been established. They include interband generation in the CdTe cap layer and in the CdHgTe barrier layer and electron transitions from the spin-split band in the CdHgTe barrier layer to the conduction band in the CdTe cap layer. The presence of the CdTe cap layer and the appropriate cadmium fraction in the CdHgTe barrier layers have been shown to be the main factors determining the key features of the spectra. Finally, we suggest an effective method of controlling the conductivity type of HgTe/CdHgTe structures using light with different wavelengths. [ABSTRACT FROM AUTHOR]

In this work, we consider the results of studying the spectral distribution, the temperature dependence of photoconductivity, and the dependence of the spectral distribution of photoconductivity on the applied electric field of doped with rare earth elements GaTe single crystals in the temperature range of 30–300 K. As the temperature decreases to 30 K, the impurity peaks disappear, and the intense maximum shifts to the short wavelength region. The increase in impurity photoconductivity with increasing temperature is due to the thermooptical filling of acceptor levels with electrons and their further transition to the conduction band under the action of illumination. Such a temperature dependence of the photoconductivity is explained by the presence of acceptor levels in the band gap. [ABSTRACT FROM AUTHOR]

Engineering transition metal dichalcogenides-based semiconducting two-dimensional (2D) layered materials for photo(electro)chemical (PEC) hydrogen evolution reaction (HER) by water splitting is an enduring challenge. Here, alloy-assisted photoconductivity and photoresponse from CVD-grown MoS2(1-x)Se2x (MSSE) 2D ternary atomic layered alloy-based photodetector device is presented for the realization of PEC HER. The explicit role of ‘S–Se’ and ‘Se2’ atomic alloy sites including chalcogen-induced vacancy defects on the photoconductivity/photoresponse and PEC HER performance of MSSE 2D alloy is investigated. Alloy formation, atomic site-by-site ‘Se’ composition and atomic structure are characterized using Raman/Photoluminescence (PL) spectroscopy, high-angle annular dark field (HAADF)- scanning transmission electron microscopy (STEM) extensively and supported with Auger Electron Spectroscopy (AES) mapping. Further, the local density and concentration of S–Se, Se2 atomic sites and defects were quantitatively estimated using HAADF-STEM image analysis in correlation with AES and it is found between the range of ∼15–20 % in MSSE alloy. A 10-fold high photoresponsivity in the case of MSSE concerning as-grown MS having fast photocurrent growth time and the prolonged decay time originates from the ‘Se’ and this alloy assisted states to enhance the PEC performance of MSSE alloy. The enhanced PEC HER activity of MSSE alloy was identified in terms of overpotential and current density. In addition, increased density of states as a function of ‘Se’ alloying, shifts in a p-band centre and lowers ΔGH* according to density functional theory calculations, which makes MSSE alloy an efficient HER activity. Further, the PEC stability and presence of the ‘S–Se’ and ‘Se2’ alloying and their role towards HER have been correlated by the spectral line shape analysis of PL and Raman spectra from post-PEC HER catalysts. These experimental and theoretical findings establish the role of chalcogen, and transition metal-based 2D alloy, leading to the design of new PECs of engineered 2D atomic layer interfaces.

Sulfur‐coordinated coordination polymers (S−CPs) have unique optoelectrical properties that originate from infinite M−S bond networks. In this study, we synthesized and characterized two polymorphs of a two–dimensional (2D) Pb(II) S−CP with a formula of [Pb(tzdt)(OAc)] (Htzdt=1,3‐thiazolidine‐2‐thione, OAc=acetate). Our findings revealed that the thermodynamic product (KGF‐26) possesses quasi‐2D (−Pb−S−)n layers with weak nonbonded Pb−S bonds, whereas the kinetic product (KGF‐27) has intrinsic 2D (−Pb−S−)n layers with Pb−S bonds. The results of time‐resolved microwave conductivity measurements and first–principles calculations confirmed that KGF‐27 exhibits higher photoconductivity than KGF‐26, which establishes that the inorganic (−Pb−S−)n networks with Pb−S bonds are crucial for achieving high photoconductivity. This is the first experimental demonstration of the impact of the (−M−S−)n networks in S−CPs on photoconductivity through the comparison of crystal polymorphisms. [ABSTRACT FROM AUTHOR]

The temperature dependence of photoconductivity in p-GaSe crystals with different initial (having at 77 K) dark resistivities (ρ77 = 2·103 ÷ 7·106 Ω·cm) was experimentally studied in the temperature range of 77 ÷ 300 K. It has been established that in crystals with ρ77 < 104 Ω cm, only the value of the photocurrent changes depending on temperature. At T ≤ 250 K, in the higher-resistivity crystal, the spectral distribution, lux-ampere characteristic, as well as photoconductivity kinetics also change noticeably with a change in temperature. The obtained experimental results are explained on the basis of a model of crystalline semiconductor with random macroscopic defects. [ABSTRACT FROM AUTHOR]

In this work, the photoconductivity (PC) spectrum of thin CdSe films was studied. In the course of studies on glass substrates, thin films of cadmium and selenium with a thickness of h = 200 nm and h = 400 nm were selected. The thickness of the samples obtained by chemical deposition was determined by the gravimetric method. Since CdSe crystal is a light-sensitive semiconductor material, the photoconductivity of thin films has been studied. The spectra obtained during studies carried out at a wavelength λ = 600-1100 nm were analyzed. It has been established that the spectrum is chaotic, since in the h = 200 nm layers the phase is not completely formed. In the layers h = 400 nm, a maximum centered at the wavelength λ = 710 nm was recorded.

The manifestation of giant persistent photoconductivity (GPPC) is demonstrated with a fs (femtosecond) Ti:sapphire laser pulse that has a duration of 40 fs and a central wavelength of 400 nm. The femtosecond laser pulse was irradiated on a two-terminal VO2 device fabricated on a corning glass substrate. Under the applied voltages of 9–12 V, the GPPC takes place within 8.6–15 μs after the laser irradiation. The photocurrent from the GPPC in the VO2 device remains stable with the current decreasing slope of ∼0.003%/minute. With one-dimensional thermal model, the temperature (TIR) of the irradiated area is estimated as a function of time, indicating that TIR is above the insulation-to-metal transition temperature of VO2 thin film prior to the onset of GPPC. The ultrafast onset of GPPC of VO2 device can be utilized for ultrafast optoelectronic switch and memory device. [ABSTRACT FROM AUTHOR]

Abstract Developing devices with a wide-temperature range persistent photoconductivity (PPC) and ultra-low power consumption remains a significant challenge for optical synaptic devices used in neuromorphic computing. By harnessing the PPC properties in materials, it can achieve optical storage and neuromorphic computing, surpassing the von Neuman architecture-based systems. However, previous research implemented PPC required additional gate voltages and low temperatures, which need additional energy consumption and PPC cannot be achieved across a wide temperature range. Here, we fabricated a simple heterojunctions using zinc(II)-meso-tetraphenyl porphyrin (ZnTPP) and single-walled carbon nanotubes (SWCNTs). By leveraging the strong binding energy at the heterojunction interface and the unique band structure, the heterojunction achieved PPC over an exceptionally wide temperature range (77 K-400 K). Remarkably, it demonstrated nonvolatile storage for up to 2×104 s, without additional gate voltage. The minimum energy consumption for each synaptic event is as low as 6.5 aJ. Furthermore, we successfully demonstrate the feasibility to manufacture a flexible wafer-scale array utilizing this heterojunction. We applied it to autonomous driving under extreme temperatures and achieved as a high impressive accuracy rate as 94.5%. This tunable and stable wide-temperature PPC capability holds promise for ultra-low-power neuromorphic computing.