Ultrathin MoO₃ semiconductor nanostructures have garnered significant interest as a promising nanomaterial for transparent nano- and optoelectronics, owing to their exceptional reactivity. Due to the shortage of knowledge about the electronic and optoelectronic properties of MoO₃/n-Si via an ALD system of few nanometers, we utilized the preparation of an ultrathin MoO₃ film at temperatures of 100, 150, 200, and 250 °C. The effect of the depositing temperatures on using bis(tbutylimido)bis(dimethylamino)molybdenum (VI) as a molybdenum source for highly stable UV photodetectors were reported. The ON–OFF and the photodetector dynamic behaviors of these samples under different applied voltages of 0, 0.5, 1, 2, 3, 4, and 5 V were collected. This study shows that the ultrasmooth and homogenous films of less than a 0.30 nm roughness deposited at 200 °C were used efficiently for high-performance UV photodetector behaviors with a high sheet carrier concentration of 7.6 × 10¹⁰ cm⁻² and external quantum efficiency of 1.72 × 10¹¹. The electronic parameters were analyzed based on thermionic emission theory, where Cheung and Nord’s methods were utilized to determine the photodetector electronic parameters, such as the ideality factor (n), barrier height (Φ₀), and series resistance (R_s). The n-factor values were higher in the low voltage region of the I–V diagram, potentially due to series resistance causing a voltage drop across the interfacial thin film and charge accumulation at the interface states between the MoO₃ and Si surfaces.

Photonic crystal (PhC) has been studied for their potential to improve the efficiency of Cu₂ZnSnS₄ solar cells by increasing the generated photocurrent by integrating it as a back reflector with almost zero transmission through the absorption active zone of the solar cell. It was found that the thickness of PhC layers greatly affects the width of the photonic bandgap and that increasing the thickness of VO₂ causes it to shift to a higher wavelength range. The PhC layers were added at the back side of the solar cell in two different configurations: (Monoclinic (M) VO₂/TiO₂) and (Tetragonal (T) VO₂/TiO₂) via SCAPS model. The study found that the (M VO₂/TiO₂) configuration led to an enhancement of the device's efficiency from 11.02 to 12.79%, while the (T VO₂/TiO₂) reaches 16.88%. The study concluded that the PhC layers enhance the light-matter coupling and photonic coupling and improvement in the device's performance.

Nanostructures of ultrathin 2D MoO₃ semiconductors have gained significant attention in the field of transparent optoelectronics and nanophotonics due to their exceptional responsiveness. In this study, we investigate self-powered α-MoO₃/Ir/α-MoO₃ photodetectors, focusing on the influence of induced hot electrons in ultrathin α-MoO₃ when combined with an ultrathin Ir plasmonic layer. Our results reveal the presence of both positive and negative photoconductivity at a 0 V bias voltage. Notably, by integrating a 2 nm Ir layer between post-annealed α-MoO₃ films, we achieve remarkable performance metrics, including a high I_ON/I_OFF ratio of 3.8 × 10⁶, external quantum efficiency of 132, and detectivity of 3.4 × 10¹¹ Jones at 0 V bias. Furthermore, the response time is impressively short, with only 0.2 ms, supported by an exceptionally low MoO₃ surface roughness of 0.1 nm. The observed negative photoresponse is attributed to O₂ desorption from the MoO₃ surface, resulting in increased carrier density and reduced mobility in the Ir layer due to Coulomb trapping and oxygen vacancy deep levels. Consequently, this leads to a decreased carrier mobility and diminished current in the heterostructure. Our findings underscore the enormous potential of ultrathin MoO₃ semiconductors for high-performance negative conductivity optoelectronics and photonic applications.

This study focused on investigating the optoelectronic properties of molybdenum trioxide (α-MoO₃) thin films using the atomic layer deposition (ALD) technique through different cycle numbers and theoretical investigation. Initial band gap calculations using standard DFT with GGA-PBE resulted in a value of 1.19 eV, which deviated significantly from experimental measurements. The GGA + U method with Hubbard U corrections was applied for the first time to improve the accuracy. This refinement led to a more precise band gap value of 3.09 eV, closely matching previously reported experimental data. The electronic parameters of the α-MoO₃ photodetector, such as ideality factor (n), barrier height (Φ₀), and series resistance (R_s), were analyzed using the thermionic emission theory and confirmed by Cheung and Nord's methods. The results demonstrated that the sample deposited with 100 pulses exhibited higher photodetector performance under UV illumination, despite having a lower R_s.

Self-powered UV sensing has enormous potential in military and civilian applications. However, achieving high responsivity and fast response/recovery time presents significant challenges. Self-powered photodetectors (PDs) have several advantages over traditional PDs, including higher sensitivity, lower power consumption, and simpler design. This study introduces a breakthrough self-powered PD that uses a Schottky junction of 2D α-MoO₃/iridium (Ir)/Si ultrathin film to detect 365 nm light at 0 V bias through using atomic layer deposition (ALD) and sputtering systems. The PD response is enhanced by plasmonic Ir-induced hot carriers, enabling detection in a mere 0.1 ms. Incorporating a 4 nm Ir layer boosts the responsivity from 0 to 34 A W⁻¹, and the external quantum efficiency is elevated from 0 to 7E11 under 365 nm light illumination. It also has a high I_ON/I_OFF ratio of 11.22E4 at 0 V. These results make the MoO₃/4 nm Ir/Si structure an interesting option for self-powered PDs with high efficiency, and the use of a simple ALD system for large-scale fabrication of 2D α-MoO₃ on hot carrier Ir plasmonic layer. The findings of this research hold tremendous promise in the field of UV sensing and can lead to exciting developments in military and civilian technology.

The efficiency of ultraviolet (UV) illumination in gas adsorption/desorption is remarkable due to its capacity to activate and energize CO₂ molecules, rendering them more reactive and prone to surface interactions. A heterojunction device for room-temperature optoelectronic gas sensing has been fabricated. This was achieved through the deposition of an orthorhombic vanadium pentoxide (V₂O₅) thin film onto a wafer scale 2D p-type tungsten disulfide (WS₂)/silicon (Si). The incorporation of the V₂O₅ layer brings about alterations in WS₂'s electronic properties, resulting in increased energy states for photo-generated carriers and a promising approach to enhance the intensity of exciton and trion peaks. Specifically, the WS₂ film exhibits a carrier concentration of 3.67 × 10¹⁸ cm⁻³, while incorporating the V₂O₅ layer significantly raises this concentration to 1.20 × 10²⁰ cm⁻³. The experiments reveal a rapid response time of 0.4 s and a recovery time of 0.2 s, respectively, demonstrating the swift desorption capability of the device in a CO₂ environment. Remarkably, this device exhibits high optoelectronic performances, boasting a detectivity of 1.22 × 10¹³ Jones and a responsivity of 177.21 A/W. These findings have the potential to advance the development of improved gas-sensing devices, offering heightened sensitivity and selectivity in diverse optoelectronic applications.

The aim of this research is to analyze the influence of various factors on the photo-ionization cross-section in (Al, Ga)N/AlN double triangular quantum wells. Using the finite difference method, the effects of the electric field, hydrostatic pressure, temperature, and Ga concentration were investigated within the effective mass and parabolic approximations. Our findings show that the photo-ionization cross-section (PICS) is highly dependent on all the variables under consideration. The optical spectra were blue-shifted with increasing electric field and pressure and red-shifted with increasing temperature and impurity displacement far from the center of the structure. Furthermore, it was found that changes in gallium content and impurity position can increase the PICS amplitude. A comparison of the obtained results with the existing literature as a limiting case of the reported problem is also provided, and excellent agreement is found.

The phenomenon of hot carriers, which are generated through the nonradiative decay of surface plasmons in ultrathin metallic films, offers an intriguing opportunity for subbandgap photodetection even at room temperature. These hot carriers possess sufficient energy to inject into the conduction band of a semiconductor material. The groundbreaking use of iridium (Ir) ultrathin film as an ultraviolet (UV) plasmonic material on silicon (Si) for high-performance photodetectors (PHDs) has been successfully demonstrated. Elevating the thickness of the sputtered Ir film to 4 nm yields a notable surge in photocurrent, registering an impressive 600 μA under 365 nm UV illumination with electron mobility of 1.37E3 cm² V⁻¹ s. This PHD exhibits excellent OFF-ON photoresponses at various applied voltages ranging from 0 to 5 V, maintaining a stable photocurrent. Under UV illumination, it displays exceptional performance, achieving a high detectivity of 1.25E14 Jones and a responsivity of 1.28 A W⁻¹. These outstanding results underscore the significant advantages of increasing the thickness of the Ir film in PHDs, leading to improvements in conductivity, detectivity, external quantum efficiency, responsivity, as well as superior sensitivity for light detection.

The application of the photonic superlattice in advanced photonics has become a demanding field, especially for two-dimensional and strongly correlated oxides. Because it experiences an abrupt metal-insulator transition near ambient temperature, where the electrical resistivity varies by orders of magnitude, vanadium oxide (VO2) shows potential as a building block for infrared switching and sensing devices. We reported a first principle study of superlattice structures of VO2 as a strongly correlated phase transition material and tungsten diselenide (WSe2) as a two-dimensional transition metal dichalcogenide layer. Based on first-principles calculations, we exploit the effect of semiconductor monoclinic and metallic tetragonal state of VO2 with WSe2 in a photonic superlattices structure through the near and mid-infrared (NIR-MIR) thermochromic phase transition regions. By increasing the thickness of the VO2 layer, the photonic bandgap (PhB) gets red-shifted. We observed linear dependence of the PhB width on the VO2 thickness. For the monoclinic case of VO2, the number of the forbidden bands increase with the number of layers of WSe2. New forbidden gaps are preferred to appear at a slight angle of incidence, and the wider one can predominate at larger angles. We presented an efficient way to control the flow of the NIR-MIR in both summer and winter environments for phase transition and photonic thermochromic applications. This study's findings may help understand vanadium oxide's role in tunable photonic superlattice for infrared switchable devices and optical filters.

Vanadium oxide (VO₂) is considered a Peierls–Mott insulator with a metal–insulator transition (MIT) at T_c = 68^◦ C. The tuning of MIT parameters is a crucial point to use VO₂ within thermoelectric, electrochromic, or thermochromic applications. In this study, the effect of oxygen deficiencies, strain engineering, and metal tungsten doping are combined to tune the MIT with a low phase transition of 20^◦C in the air without capsulation. Narrow hysteresis phase transition devices based on multilayer VO₂, WO₃, Mo_0.2W_0.8O_3, and/or MoO₃ oxide thin films deposited through a high vacuum sputtering are investigated. The deposited films are structurally, chemically, electrically, and optically characterized. Different conductivity behaviour was observed, with the highest value towards VO_1.75/WO_2.94 and the lowest VO_1.75 on FTO glass. VO_1.75/WO_2.94 showed a narrow hysteresis curve with a single-phase transition. Thanks to the role of oxygen vacancies, the MIT temperature decreased to 35^◦C, while the lowest value (T_c = 20^◦C) was reached with Mo_0.2W_0.8O₃/VO₂/MoO₃ structure. In this former sample, Mo_0.2W_0.8O₃ was used for the first time as an anti-reflective and anti-oxidative layer. The results showed that the MoO₃ bottom layer is more suitable than WO₃ to enhance the electrical properties of VO₂ thin films. This work is applied to fast phase transition devices.

Studying the mechanical properties mismatching of SnSe₂/ZrS₂ 2D materials with Voigt-Reuss-Hill (VRH) schemes promise a novel structure for sensing applications. For the first time, we studied the effect of mechanical mismatching properties of SnSe₂/ZrS₂ multilayers with VRH schemes on the acoustic wave's propagation through acoustic superlattice (AS). We proposed [(SnSe₂/ZrS₂)⁴] superlattice with VRH schemes as a new THz multichannel sensor for acetonitrile sensing. The [(SnSe₂/ZrS₂)⁴] with Voigt scheme introduced several resonant peaks for acetonitrile inside the superlattice bandgap compared to Hill and Reuss schemes. The appropriate relation between resonance frequency shift and resonance bandwidth is the key to improving the multichannel sensor's sensitivity to liquid characteristics. Further, we studied the effect of low and high temperatures on our multichannel sensor. Furthermore, the highest sensitivity and resonance frequency were recorded by our AS with the Voigt scheme towards acetonitrile having values of 0.287 (GHz/(kg/m³)) and 0.237 THz at 0 °C. The results show a novel sensitivity of acetonitrile for low-temperature environments.

Gold (Au) nanoparticles trapped within Cu₂SnS₃ (CTS) thin films were effectively deposited on a low-cost glass substrate using a simple pulsed laser deposition of 15 mJ for 5 ns at a 10 Hz repetition rate. The film's structural, morphological, topography, optical, and optoelectronic properties were investigated. Highly crystalline ternary chalcogenide CTS with tetragonal symmetry and 17 nm grain size is prepared. The 110 Ω resistivity of the thin film increases up to 125 Ω indicating a negative photoresponse under visible light excitation. The decrease in the photocurrent is also observed with Cu₂SnS₃/Au/Cu₂SnS₃ sandwich ternary chalcogenide structure at resistivities values from 31 to 35 Ω and a Joule effect influence the presence of plasmonic Au nanoparticle interlayers involved a lower phonon disorder given a higher photoresponse effect as predicted from Urbach energy.

This study was on the optoelectronic properties of multilayered two-dimensional MoS₂ and WS₂ materials on a silicon substrate using sputtering physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques. For the first time, we report ultraviolet (UV) photoresponses under air, CO₂, and O₂ environments at different flow rates. The electrical Hall effect measurement showed the existence of MoS₂ (n-type)/Si (p-type) and WS₂ (P-type)/Si (p-type) heterojunctions with a higher sheet carrier concentration of 5.50 × 10⁵ cm⁻² for WS₂ thin film. The IV electrical results revealed that WS₂ is more reactive than MoS₂ film under different gas stimuli. WS₂ film showed high stability under different bias voltages, even at zero bias voltage, due to the noticeably good carrier mobility of 29.8 × 10² cm²/V. WS₂ film indicated a fast rise/decay time of 0.23/0.21 s under air while a faster response of 0.190/0.10 s under a CO₂ environment was observed. Additionally, the external quantum efficiency of WS₂ revealed a remarkable enhancement in the CO₂ environment of 1.62 × 10⁸ compared to MoS₂ film with 6.74 × 10⁶. According to our findings, the presence of CO₂ on the surface of WS₂ improves such optoelectronic properties as photocurrent gain, photoresponsivity, external quantum efficiency, and detectivity. These results indicate potential applications of WS₂ as a photodetector under gas stimuli for future optoelectronic applications.

Ultra-sensitive greenhouse gas sensors for CO₂, N₂O, and CH₄ gases based on Fano resonance modes have been observed through periodic and quasi-periodic phononic crystal structures. We introduced a novel composite based on metal/2D transition metal dichalcogenides (TMDs), namely; platinum/platinum disulfide (Pt/PtS₂) composite materials. Our gas sensors were built based on the periodic and quasi-periodic phononic crystal structures of simple Fibonacci (F(5)) and generalized Fibonacci (FC(7, 1)) quasi-periodic phononic crystal structures. The FC(7, 1) structure represented the highest sensitivity for CO₂, N₂O, and CH₄ gases compared to periodic and F(5) phononic crystal structures. Moreover, very sharp Fano resonance modes were observed for the first time in the investigated gas sensor structures, resulting in high Fano resonance frequency, novel sensitivity, quality factor, and figure of merit values for all gases. The FC(7, 1) quasi-periodic structure introduced the best layer sequences for ultra-sensitive phononic crystal greenhouse gas sensors. The highest sensitivity was introduced by FC(7, 1) quasiperiodic structure for the CH₄ with a value of 2.059 (GHz/m.s⁻¹). Further, the temperature effect on the position of Fano resonance modes introduced by FC(7, 1) quasi-periodic PhC gas sensor towards CH₄ gas has been introduced in detail. The results show the highest sensitivity at 70 °C with a value of 13.3 (GHz/°C). Moreover, the highest Q and FOM recorded towards CH₄ have values of 7809 and 78.1 (m.s⁻¹)⁻¹ respectively at 100 °C.

Artificial periodic structures drew a lot of attention because of their ability to be built with novel acoustic features. A novel nanostructured phononic superlattice (NPhS) based two-dimensional multilayer structure as a high-sensitive multichannel liquid sensor that provided bright multichannel band gap windows has been introduced. Theoretically, the designed structure is composed of [(MoS₂/PtSe₂)⁴] NPhS with a cavity filled with different concentrations of Ethylene Glycol at room temperature toward acoustic bandgap engineering multichannel sensor. We examined the interaction of acoustic waves with nano and bulk phononic superlattice (PhS) structures. In addition, we studied the effect of using different analyte layer thicknesses on the resonance peaks that appeared inside the band gaps. Many sharp resonance peaks appeared in multi-band gaps, which introduced high sensitivity, Q-factor, and figure of merit (FOM) values for each concentration of Ethylene Glycol. Furthermore, the effect of resonance peaks' full width at half maximum (FWHM) on the Q-factor of the NPhS multichannel sensor has been studied. From our results, the relation between the sensitivity of our multichannel sensor and the resonance frequency of each concentration shows a linear behavior. The highest sensitivity was obtained for a 1.00 m% concentration of 0.21 (GHz/(kg/m³)) at a resonance frequency value of 0.21 THz. In addition, the NPhS multichannel sensor recorded the highest Q-factor for 0.8069 m% with a value of 1744 and the highest FOM for 0.3819 m% with a value of 0.05988 (m³/kg). Moreover, we studied the effect of temperature on the sensitivity of the NPhS multichannel sensor. We showed the highest sensitivity value of 1.79 (GHz/^o C) at 10 °C towards Ethylene Glycol. Further, the dispersion relation of an acoustic wave propagating inside perfect and defected nano and bulk PhS structures has been introduced. Our proposed multichannel liquid sensor can introduce a novel sensitivity at Terahertz frequency ranges.

Molybdenum - tungsten oxide (Mo_1-xW_xO₃, x = 1, 0.8, and 0.6) nanostructured thin films-based room temperture (RT) gas sensors are prepared by means of reactive RF magnetron co-sputtering at 400 °C. The structural, morphology, topography, optical, and electrical characterizations of the prepared sensors are carried out by XRD Rietveld structure refinement analyses, SEM, AFM, UV-VIS spectrophotometer, and source meter. By controlling the deposition temperture of 400 °C, a co-existing phase of MoO₃ and MoO₂ in WO₃ matrix is presented with high oxygen vacancies concentration as calculated from the XRD Rietveld Refinement analyses. By increasing the Mo content, the calculated oxygen vacancies concentration increases by factor of 1.36. The optical characterization of Mo_0.2W_0.8O₃ thin film shows a high transparent of 99.6% at 500 nm. The prepared thin films have successfully tested to detect carbon dioxide (CO₂) at RT (20 °C) with high selectivity and repeatability. The Mo_0.4W_0.6O₃ sensor film shows an electrical Schottky contact with fast response and recovery times towards CO₂ under UV light activation. Mo_0.4W_0.6O₃ thin film under dark and UV conditions were able to detect low CO₂ concentration of 2 and 0.5 sccm CO₂ at RT, respectively. Under UV illumination, Mo_0.4W_0.6O₃ film shows a fast response and recovery time of 6.53 and 8.05 s at 0.5 sccm with sensitivity of 29.19%. Under UV photonic activation, higher electron concentration is presented in the oxide surface, which leads to high probability for reaction with CO₂ molecules, and consequently enhanced the chemisorption of CO₂. The enhanced CO₂ gas sensitivity and fast response may refer to the high oxygen vacancies concentration and the active role of the grain boundaries in MoO₂, MoO₃ and WO₃ mixed-valence nanostructured under UV activation.

The distinctive properties of strongly correlated oxides provide a variety of possibilities for modulating the properties of 2D transition metal dichalcogenides semiconductors; which represent a new class of superior optical and optoelectronic interfacing semiconductors. We report a novel approach to scaling-up molybdenum disulfide (MoS₂) by combining the techniques of chemical and physical vapor deposition (CVD and PVD) and interfacing with a thin layer of monoclinic VO₂. MoWO₃/VO₂/MoS₂ photodetectors were manufactured at different sputtering times by depositing molybdenum oxide layers using a PVD technique on p-type silicon substrates followed by a sulphurization process in the CVD chamber. The high quality and the excellent structural and absorption properties of MoWO₃/VO₂/MoS₂/Si with MoS₂ deposited for 60 s enables its use as an efficient UV photodetector. The electronically coupled monoclinic VO₂ layer on MoS₂/Si causes a redshift and intensive MoS₂ Raman peaks. Interestingly, the incorporation of VO₂ dramatically changes the ratio between A-exciton (ground state exciton) and trion photoluminescence intensities of VO₂/(30 s)MoS₂/Si from < 1 to > 1. By increasing the deposition time of MoS₂ from 60 to 180 s, the relative intensity of the B-exciton/A-exciton increases, whereas the lowest ratio at deposition time of 60 s refers to the high quality and low defect densities of the VO₂/(60 s)MoS₂/Si structure. Both the VO₂/(60 s)MoS₂/Si trion and A-exciton peaks have higher intensities compared with (60 s) MoS₂/Si structure. The MoWO₃/VO₂/(60 s)MoS₂/Si photodetector displays the highest photocurrent gain of 1.6, 4.32 × 10⁸ Jones detectivity, and ~ 1.0 × 10¹⁰ quantum efficiency at 365 nm. Moreover, the surface roughness and grains mapping are studied and a low semiconducting-metallic phase transition is observed at ~ 40 °C.

Effect of in-/ex-situ annealing on the structure, optical, photoluminescence, electrical characterization and gas sensing dynamics on CdS thin films are presented. Raman characterizations showed an increase in the peak intensity with increasing the annealing temperature under ex-situ, while a lower peak intensity observed through the in-situ annealing condition. No shift was observed in the Photoluminescence peaks through the yellow band peaks of in-situ annealed samples, however, a slightly blue shift was observed through the ex-situ annealed samples. High conductivity was observed for all samples, while in the case of in-situ RT, in-situ 100 °C, ex-situ 200 °C and ex-situ 300 °C, a CO₂ and O₂ gas sensing activity have been tested. The ex-situ 300 °C sample shows a higher response towards CO₂ compared with the ex-situ 200 °C film. While, both in-situ RT and 100 °C sensors show the same response towards CO₂ with a high gas response. However, the in-situ 100 °C sensor has the highest response compared to in-situ RT film with a high response of 25% at 50 sccm towards O₂.