Search Results (81)

In this study, a thin film of silicon carbide (SiC) was deposited on a porous silicon (P-Si) substrate using pulsed laser deposition (PLD). The photo–electrochemical etching method with an Nd: YAG laser at 1064 nm wavelength and 900 mJ pulse energy and at a vacuum of 10⁻² mbar P-Si was utilized to create a sufficiently high amount of surface area for SiC film deposition to achieve efficient SiC film growth on the P-Si substrate. X-ray diffraction (XRD) analysis was performed on the crystalline structure of SiC and showed high-intensity peaks at the (111) and (220) planes, indicating that the substrate–film interaction is substantial. Surface roughness particle topography was examined via atomic force microscopy (AFM), and a mean diameter equal to 72.83 nm was found. Field emission scanning electron microscopy (FESEM) was used to analyze surface morphology, and the pictures show spherical nanoparticles and a mud-sponge-like shape demonstrating significant nanoscale features. Photoluminescence and UV-Vis spectroscopy were utilized to investigate the optical properties, and two emission peaks were observed for the SiC and P-Si substrates, at 590 nm and 780 nm. The SiC/P-Si heterojunction photodetector exhibited rectification behavior in its dark I–V characteristics, indicating high junction quality. The spectral responsivity of the SiC/P-Si observed a peak responsivity of 0.0096 A/W at 365 nm with detectivity of 24.5 A/W Jones, and external quantum efficiency reached 340%. The response time indicates a rise time of 0.48 s and a fall time of 0.26 s. Repeatability was assured by the tight clustering of the data points, indicating the good reproducibility and stability of the SiC/P-Si deposition process. Linearity at low light levels verifies efficient photocarrier generation and separation, whereas a reverse saturation current at high intensities points to the maximum carrier generation capability of the device. Moreover, Raman spectroscopy and energy dispersive spectroscopy (EDS) analysis confirmed the structural quality and elemental composition of the SiC/P-Si film, further attesting to the uniformity and quality of the material produced. This hybrid material’s improved optoelectronic properties, achieved by combining the stability of SiC with the quantum confinement effects of P-Si, make it useful in advanced optoelectronic applications such as UV-Vis photodetectors. Full article

Recent advancements in metal/perovskite photodetectors have leveraged plasmonic effects to enhance the efficiency of photogenerated carrier separation. In this work, we present an innovative approach to designing heterostructure photodetectors that involved integrating a perovskite film with a plasmonic metasurface. Using finite-difference time-domain (FDTD) simulations, we investigated the formation of hybrid photonic–plasmonic modes and examined their quality factors in relation to loss mechanisms. Our results demonstrate that these hybrid modes facilitated strong light confinement within the perovskite layer, with significant intensity enhancement at the metal–perovskite interface—an ideal condition for efficient charge carrier generation. We also propose the use of low-bandgap perovskites for direct infrared passive detection and explore the potential of highly Stokes-shifted perovskites for active detection applications, including ultraviolet and X-ray radiation. Full article

We studied specially designed InAs/GaSb/AlSb/GaSb M-structures, a type-II superlattice (T2SL), that can serve as active materials for short-wavelength infrared (SWIR) applications. To obtain the dispersion relation of the investigated M-structures, k·p perturbation theory based on the eight-band model implemented in the nextnano++ v1.18.1 (nextnano GmbH, Munich, Germany) software was used. Numerical band-gap engineering and dispersion calculations for the investigated M-structures (composed of 6/1/5/1 monolayers, with InSb interfaces included) revealed the presence of an additional energy level within the energy gap. This energy level originates from the InSb-like interfaces and does not appear in structures with different layer or interface thicknesses. Its properties strongly depend on interface thickness, temperature, and strain. Numerical calculations of the probability density function ${|\Psi |}^2$, absorption coefficients, and optical absorption spectra at varying temperatures demonstrate that, under specific conditions, such as an optimised interface thickness and temperature, optical absorption increases significantly. These theoretical results are based on structures fabricated using molecular-beam epitaxy (MBE) technology. High-resolution X-ray diffraction (HRXRD) measurements confirm the high crystallographic quality of these M-structures. Full article

The narrow bandgap InN material, with exceptional physical properties, has recently gained considerable attention, encouraging many scientists/engineers to design infrared photodetectors, light-emitting diodes, laser diodes, solar cells, and high-power electronic devices. The InN/Sapphire samples of different film thicknesses that we have used in our methodical experimental and theoretical studies are grown by plasma-assisted molecular-beam epitaxy. Hall effect measurements on these samples have revealed high-electron-charge carrier concentration, η. The preparation of InN epifilms is quite sensitive to the growth temperature T, plasma power, N/In ratio, and pressure, P. Due to the reduced distance between N atoms at a higher P, one expects the N-flow kinetics, diffusion, surface components, and scattering rates to change in the growth chamber which might impact the quality of InN films. We believe that the ionized N, rather than molecular, or neutral species are responsible for controlling the growth of InN/Sapphire epifilms. Temperature- and power-dependent photoluminescence measurements are performed, validating the bandgap variation (~0.60–0.80 eV) of all the samples. High-resolution X-ray diffraction studies have indicated that the increase in growth temperature caused the perceived narrow peaks in the X-ray-rocking curves, leading to better-quality films with well-ordered crystalline structures. Careful simulations of the infrared reflectivity spectra provided values of η and mobility μ, in good accordance with the Hall measurements. Our first-order Raman scattering spectroscopy study has not only identified the accurate phonon values of InN samples but also revealed the low-frequency longitudinal optical phonon plasmon-coupled mode in excellent agreement with theoretical calculations. Full article

Artificial heterostructures are typically created by layering distinct materials, thereby giving rise to unique characteristics different from their individual components. Herein, two-dimensional α-MnSe nanosheets with a non-layered structure were fabricated on Ga_0.6Fe_1.4O₃ (GFO) films. The superior crystalline properties of MnSe/GFO heterostructures were confirmed through structural and morphological analyses. The remanent polarization is around 1.5 μC/cm² and the leakage current density can reach 2 × 10⁻³ A/cm² under 4 V. In addition, the piezo-response force microscopy amplitude and phase images further supported the ferroelectric property. The significant improvement of coercive field and saturated magnetization, along with the antiparallel signals of Mn and Fe ions observed through synchrotron X-ray analyses, suggest the presence of magnetic interaction within the MnSe/GFO heterostructure. Finally, the excellent photodetector with a photo detectivity of 6.3 × 10⁸ Jones and a photoresponsivity of 2.8 × 10⁻³ A·W⁻¹ was obtained under 532 nm in the MnSe/GFO heterostructure. The characteristics of this heterostructure, which include multiferroic, magnetic exchange bias effect, and photodetection capabilities, are highly beneficial for multifunctional devices. Full article

This study employed atomic layer deposition (ALD) to fabricate an Al₂O₃ passivation layer to optimize the performance of ultraviolet (UV) photodetectors with a TiO₂-nanorod-(NR)-containing active layer and a solid–liquid heterojunction (SLHJ). To reduce the processing time and enhance light absorption, a hydrothermal method was used to grow a relatively thick TiO₂-NR-containng working electrode. Subsequently, a 5-nm-thick Al₂O₃ passivation layer was deposited on the TiO₂ NRs through ALD, which has excellent step coverage, to reduce the surface defects in the TiO₂ NRs and improve the carrier transport efficiency. X-ray photoelectron spectroscopy revealed that the aforementioned layer reduced the defects in the TiO₂ NRs. Moreover, high-resolution transmission electron microscopy indicated that following the annealing treatment, Al, Ti, and O atoms diffused across the interface between the Al₂O₃ passivation layer and TiO₂ NRs, resulting in the binding of these atoms to form Al–Ti–O bonds. This process effectively filled the oxygen vacancies in TiO₂. Examination of the photodetector device revealed that the photocurrent-to-dark current ratio exhibited a difference of four orders of magnitude (10⁻⁴ to 10⁻⁸ A), with the switch-on and switch-off times being 0.46 and 3.84 s, respectively. These results indicate that the Al₂O₃ passivation layer deposited through ALD can enhance the photodetection performance of SLHJ UV photodetectors with a TiO₂ active layer. Full article

AlGaN is attractive for fabricating deep ultraviolet (DUV) optoelectronic and electronic devices of light-emitting diodes (LEDs), photodetectors, high-electron-mobility field-effect transistors (HEMTs), etc. We investigated the quality and optical properties of Al_xGa_1−xN films with high Al fractions (60–87%) grown on sapphire substrates, including AlN nucleation and buffer layers, by metal–organic chemical vapor deposition (MOCVD). They were initially investigated by high-resolution X-ray diffraction (HR-XRD) and Raman scattering (RS). A set of formulas was deduced to precisely determine x(Al) from HR-XRD data. Screw dislocation densities in AlGaN and AlN layers were deduced. DUV (266 nm) excitation RS clearly exhibits AlGaN Raman features far superior to visible RS. The simulation on the AlGaN longitudinal optical (LO) phonon modes determined the carrier concentrations in the AlGaN layers. The spatial correlation model (SCM) analyses on E₂(high) modes examined the AlGaN and AlN layer properties. These high-x(Al) Al_xGa_1−xN films possess large energy gaps E_g in the range of 5.0–5.6 eV and are excited by a DUV 213 nm (5.8 eV) laser for room temperature (RT) photoluminescence (PL) and temperature-dependent photoluminescence (TDPL) studies. The obtained RTPL bands were deconvoluted with two Gaussian bands, indicating cross-bandgap emission, phonon replicas, and variation with x(Al). TDPL spectra at 20–300 K of Al_0.87Ga_0.13N exhibit the T-dependences of the band-edge luminescence near 5.6 eV and the phonon replicas. According to the Arrhenius fitting diagram of the TDPL spectra, the activation energy (19.6 meV) associated with the luminescence process is acquired. In addition, the combined PL and time-resolved photoluminescence (TRPL) spectroscopic system with DUV 213 nm pulse excitation was applied to measure a typical AlGaN multiple-quantum well (MQW). The RT TRPL decay spectra were obtained at four wavelengths and fitted by two exponentials with fast and slow decay times of ~0.2 ns and 1–2 ns, respectively. Comprehensive studies on these Al-rich AlGaN epi-films and a typical AlGaN MQW are achieved with unique and significant results, which are useful to researchers in the field. Full article

We investigate the effects of incorporating single-walled carbon nanotubes (CNTs) into sol–gel-derived ZnO thin films to enhance their optoelectronic properties for photodetector applications. ZnO thin films were fabricated on c-plane sapphire substrates with varying CNT concentrations ranging from 0 to 2.0 wt%. Characterization techniques, including high-resolution X-ray diffraction, photoluminescence, and atomic force microscopy, demonstrated the preferential growth of the ZnO (002) facet and improved optical properties with the increase in the CNT content. Electrical measurements revealed that the optimal CNT concentration of 1.5 wt% resulted in a significant increase in the dark current (from 0.34 mA to 1.7 mA) and peak photocurrent (502.9 µA), along with enhanced photoresponsivity. The rising and falling times of the photocurrent were notably reduced at this concentration, indicating improved charge dynamics due to the formation of a p-CNT/n-ZnO heterojunction. The findings suggest that the incorporation of CNTs not only modifies the structural and optical characteristics of ZnO thin films but also significantly enhances their electrical performance, positioning CNT-ZnO composites as promising candidates for advanced photodetector technologies in optoelectronic applications. Full article

This paper investigates the optoelectronic properties of CsPbBr₃, a lead-based perovskite, and Cs₂AgBiBr₆, a lead-free double perovskite, in composite thick films synthesized using mechanochemical and hot press methods, with poly(butyl methacrylate) as the matrix. Comprehensive characterization was conducted, including X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV–visible spectroscopy (UV–Vis), and photoluminescence (PL). Results indicate that the polymer matrix does not significantly impact the crystalline structure of the perovskites but has a direct impact on the grain size and surface area, enhancing the interfacial charge transfer of the composites. Optical characterization indicates minimal changes in bandgap energies across all different phases, with CsPbBr₃ exhibiting higher photocurrent than Cs₂AgBiBr₆. This is attributed to the CsPbBr₃ superior charge carrier mobility. Both composites showed photoconductive behavior, with Cs₂AgBiBr₆ also demonstrating higher-energy (X-ray) photon detection. These findings highlight the potential of both materials for advanced photodetector applications, with Cs₂AgBiBr₆ offering an environmentally Pb-free alternative. Full article

The long-term afterglow of scintillators is an important aspect, especially when the light signal from a scintillator is evaluated in the current mode. Scintillators used for radiation detection exhibit an afterglow, which usually comes from multiple components that have different decay times. A high level of afterglow usually has a negative influence on the detection parameters for the energy resolution in spectrometry measurements or X-ray and neutron imaging. The paper deals with the long-term afterglow of some types of scintillators, which is more significant for integral measurement when the current is measured in a photodetector. The range of decay times studied was in the order of tens of seconds to days. Seven types of scintillators were examined: BGO, CaF₂(Eu), CdWO₄, CsI(Tl), LiI(Eu), NaI(Tl), and plastic scintillator. The scintillators were excited by gamma-ray radiation. After irradiation, the detection unit, along with the scintillator, was moved to a laboratory where the anode current of the photomultiplier tube was measured using a picoammeter for at least a day. The measurements showed that CdWO₄ and plastic scintillators have relatively low long-term afterglow signals in comparison to the other scintillators studied. Full article

Ga₂O₃ has received increasing interest for its potential in various applications relating to solar-blind photodetectors. However, attaining a balanced performance with Ga₂O₃-based photodetectors presents a challenge due to the intrinsic conductive mechanism of Ga₂O₃ films. In this work, we fabricated amorphous Ga₂O₃ (a-Ga₂O₃) metal–semiconductor–metal photodetectors through capacitive coupled plasma assisted magnetron sputtering at room temperature. Substantial enhancement in the responsivity is attained by regulating the capacitance-coupled plasma power during the deposition of a-Ga₂O₃. The proposed plasma energy generated by capacitive coupled plasma (CCP) effectively improved the disorder of amorphous Ga₂O₃ films. The results of X-ray photoelectron spectroscopy (XPS) and current-voltage tests demonstrate that the additional plasma introduced during the sputtering effectively adjust the concentration of oxygen vacancy effectively, exhibiting a trade-off effect on the performance of a-Ga₂O₃ photodetectors. The best overall performance of a-Ga₂O₃ photodetectors exhibits a high responsivity of 30.59 A/W, a low dark current of 4.18 × 10⁻¹¹, and a decay time of 0.12 s. Our results demonstrate that the introduction of capacitive coupled plasma during deposition could be a potential approach for modifying the performance of photodetectors. Full article

Semiconductor photodetectors can work only in specific material-dependent light wavelength ranges, connected with the bandgaps and absorption capabilities of the utilized semiconductors. This limitation has driven the development of hybrid devices that exceed the capabilities of individual materials. In this study, for the first time, a hybrid heterojunction photodetector based on methylammonium lead bromide (MAPbBr₃) polycrystalline film deposited on gallium arsenide (GaAs) was presented, along with comprehensive morphological, structural, optical, and photoelectrical investigations. The MAPbBr₃/GaAs heterojunction photodetector exhibited wide spectral responsivity, from 540 to 900 nm. The fabrication steps of the prototype device, including a new preparation recipe for the MAPbBr₃ solution and spinning, will be disclosed and discussed. It will be shown that extending the soaking time and refining the precursor solution’s stoichiometry may enhance surface coverage, adhesion to the GaAs, and film uniformity, as well as provide a new way to integrate MAPbBr₃ on GaAs. Compared to the pristine MAPbBr₃, the enhanced structural purity of the perovskite on GaAs was confirmed by X-ray Diffraction (XRD) upon optimization compared to the conventional glass substrate. Scanning Electron Microscopy (SEM) revealed the formation of microcube-like structures on the top of an otherwise continuous MAPbBr₃ polycrystalline film, with increased grain size and reduced grain boundary effects pointed by Energy-Dispersive Spectroscopy (EDS) and cathodoluminescence (CL). Enhanced absorption was demonstrated in the visible range and broadened photoluminescence (PL) emission at room temperature, with traces of reduction in the orthorhombic tilting revealed by temperature-dependent PL. A reduced average carrier lifetime was reduced to 13.8 ns, revealed by time-resolved PL (TRPL). The dark current was typically around 8.8 × 10⁻⁸ A. Broad photoresponsivity between 540 and 875 nm reached a maximum of 3 mA/W and 16 mA/W, corresponding to a detectivity of 6 × 10¹⁰ and 1 × 10¹¹ Jones at −1 V and 50 V, respectively. In case of on/off measurements, the rise and fall times were 0.40 s and 0.61 s or 0.62 s and 0.89 s for illumination, with 500 nm or 875 nm photons, respectively. A long-term stability test at room temperature in air confirmed the optical and structural stability of the proposed hybrid structure. This work provides insights into the physical mechanisms of new hybrid junctions for high-performance photodetectors. Full article

Ga₂O₃, with its large band gap, is a promising material suitable for utilization in solar-blind photodetection. Sapphire with a higher lattice match with Ga₂O₃ was used as the substrate for epitaxial growth of Ga₂O₃. Here, the epitaxial layers of Ga₂O₃ were deposited by MOCVD on patterned sapphire substrates. The structure of epitaxial Ga₂O₃ layers on patterned substrates has been identified by X-ray diffractometry. To investigate the influence of the patterned substrates on the formation of epitaxial layers, thin Ga₂O₃ layers were grown on a flat sapphire substrate under the same conditions. Both types of samples were β-phase. However, no improvement in the layers’ crystalline quality was discovered when utilizing patterned sapphire substrates. In addition, the performance of the obtained two types of Ga₂O₃ photodetectors was compared. The photoelectric properties, such as responsivity, response speed, and detection capability, were different in the case of flat samples. Full article

The single crystals of CsI-Yb²⁺ were grown, and their spectroscopic studies were conducted. The observed luminescence in CsI-Yb²⁺ is due to 5d–4f transitions in Yb²⁺ ions. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were found. The excitation spectra of Yb²⁺ luminescence bands were obtained in the range of 3–45 eV. The mechanism of charge compensation of Yb²⁺ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity–vacancy complexes in two different positions. The charge compensation of Yb²⁺ occurs via cation vacancies in the nearest-neighbor and next-nearest-neighbor positions.The Yb²⁺ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors. Full article

Visible light photodetectors are extensively researched with transparent metal oxide holes/electron layers for various applications. Among the metal oxide transporting layers, nickel oxide (NiO) and zinc oxide (ZnO) are commonly adopted due to their wide band gap and high transparency. The objective of this study was to improve the visible light detection of NiO/ZnO photodiodes by introducing an additional quantum dot (QD) layer between the NiO and ZnO layers. Utilizing the unique property of QDs, we could select different sizes of QDs and responsive light wavelength ranges. The resulting red QDs utilized device that could detect light starting at 635 nm to UV (Ultra-violet) light wavelength and exhibited a photoresponsivity and external quantum efficiency (EQE) of 14.99 mA/W and 2.92% under 635 nm wavelength light illumination, respectively. Additionally, the green QDs, which utilized a device that could detect light starting at 520 nm, demonstrated photoresponsivity values of 8.34 mA/W and an EQE of 1.99% under 520 nm wavelength light illumination, respectively. In addition, we used X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) to investigate the origin of the photocurrents and the enhancement of the device’s performance. This study suggests that incorporating QDs with metal oxide semiconductors is an effective approach for detecting visible light wavelengths in transparent optoelectronic devices. Full article