UV Detector Applications Research Articles

Characterisation of Sn-Cl co-doped β-Ga2O3 thin films deposited via spray pyrolysis and their application in UV detector devices

Ga2O3, an ultrawide bandgap semiconducting oxide, is currently emerging as a promising candidate for various applications, such as power devices, solar-blind UV detectors, high temperature oxygen sensors and biomedical imaging. One significant limitation hindering the application of Ga2O3 as a wide-bandgap semiconductor is its poor conductivity. In this work, we investigate whether doping with tin and chlorine can mitigate this condition. Sn-Cl co-doped β-Ga2O3 thin films are deposited on glass substrates using spray pyrolysis technique. The deposited films are subjected to comprehensive analysis, including structural, optical and morphological measurements using techniques like X-ray diffraction, UV-Vis-NIR spectroscopy, X-ray photoelectron spectroscopy and EDX studies. Electrical properties are assessed using the four-probe method and Hall measurements. The best conductivity of 8.86 Ω−1m−1 is observed when 8.68 at% of Sn and 3.37 at% of Cl were co-doped into Ga2O3 (S(3)) and its optical band gap is calculated to be 4.65 eV. This is about five orders of improvement in conductivity as compared to that of pure Ga2O3 thin film deposited by the same method. Furthermore, we have constructed a deep UV detector utilizing doped β-Ga2O3 thin films as the semiconducting absorbing layer. The detector demonstrated the highest responsivity of 2.54 × 10−4 A/W at 260 nm and the corresponding specific detectivity is 1.4 × 109 Jones. The current research validates the potential of Sn-Cl co-doped β-Ga2O3 thin film as an excellent choice for UV detector application.

Structural, magnetic, and optoelectronic properties of rock salt MgO co-doped with Eu-TM (TM = Cu, Ag, and Au) for spintronic and UV detector applications: SP-DFT investigations

This study analyzes how adding europium and transition metals (Cu, Ag, and Au) at a 12.5% concentration to magnesium oxide (MgO) affects its physical characteristics and potential uses. To do so, the full potential linearized augmented plane wave (FP-LAPW) method, based on spin-polarized density functional theory (SP-DFT), is used to derive the results. Wu and Cohen’s generalized gradient approximation (GGA-WC) described the exchange-correlation potential. The modified Becke-Johnson exchange potential (TB-mBJ) was also used to improve the findings of optoelectronic properties. When Eu and TM (Cu, Ag, and Au) impurities are co-doped into the nonmagnetic (NM) semiconductor MgO, the structural optimization results show that the lattice constants increase, and the bulk modulus decreases with increasing the atomic number of transition metals. The resulting dilute magnetic oxides (DMOs) are stable in the spin-polarized ferromagnetic (FM) phase, and the formation energy values confirm their stability in the [Formula: see text] cubic structure, with the lowest value belonging to Eu[Formula: see text]TM[Formula: see text]Mg[Formula: see text]O. Similarly, calculations of electronic properties using the WC-mBJ functional demonstrate that all compounds have an indirect half-metallic bandgap at L-[Formula: see text] equal to 2.53, 2.49, and 1.39 eV for Eu[Formula: see text]Cu[Formula: see text]Mg[Formula: see text]O, Eu[Formula: see text]Ag[Formula: see text]Mg[Formula: see text]O, and Eu[Formula: see text]Au[Formula: see text]Mg[Formula: see text]O, respectively. They have an integer magnetic moment of 6 [Formula: see text]. The density of states shows that at the Fermi level, the 4f-Eu, d-TM, and p-O states give rise to new energy levels. This indicates that the f–p–d hybridization provides this system with its FM properties. Also, these compounds’ dielectric function and absorption spectra are calculated and analyzed to learn more about their optical properties. The results provide insight into the optical behavior of the materials. It is observed that the co-doped compounds exhibit greater optical absorbance than their un-doped MgO counterparts do. This theoretical investigation opens the way to preparing high magnetic moment DMOs using TM and rare earth as dopants suitable for spintronic and UV devices.

Faster photoswitching and amplified NBE emission from mg doped sol-gel derived ZnO thin films

ABSTRACT Photoconductivity and photoluminescence of highly transparent predominantly c-axis oriented hexagonal wurtzite nanocrystalline Mg doped zinc oxide thin films are reported here. These films prepared by sol-gel spin coating are useful for switching and UV detector applications. The increase in dopant concentration tunes the optical band-gap from 3.15 to 3.41 eV. Amplified NBE emission with low defect emission is obtained in appropriately doped sample along with high suitability for switching applications since the photocurrent sharply falls to a very low value as the illumination is put off and the rise and decay pattern is reproducible for several consecutive cycles. The films have crystallite size less than 16 nm and rod-like structures of diameter 50 to 100 nm are seen to grow out of spherical granular background. Doping reduces the size of grains and rods as well as the surface roughness.

Laser induced hydrothermal growth of ZnO rods for UV detector application

Laser induced hydrothermal growth of ZnO rods for UV detector application

Investigation of conduction mechanism and UV light response of vertically grown ZnO nanorods on an interdigitated electrode substrate.

Vertically aligned zinc oxide nanorod (ZnO-NR) growth was achieved through a wet chemical route over a comb-shaped working area of an interdigitated Ag-Pd alloy signal electrode. Field-emission scanning electron microscopy images confirmed the formation of homogeneous ZnO-NRs grown uniformly over the working area. X-ray diffraction revealed single-phase formation of ZnO-NRs, further confirmed by energy-dispersive X-ray spectroscopy analysis. Temperature-dependent impedance and modulus formalisms showed semiconductor-type behavior of ZnO-NRs. Two electro-active regions i.e., grain and grain boundary, were investigated which have activation energy ∼0.11 eV and ∼0.17 eV, respectively. The conduction mechanism was investigated in both regions using temperature-dependent AC conductivity analysis. In the low-frequency dispersion region, the dominant conduction is due to small polarons, which is attributed to the grain boundary response. At the same time, the correlated barrier hopping mechanism is a possible conduction mechanism in the high dispersion region attributed to the bulk/grain response. Moreover, substantial photoconductivity under UV light illumination was achieved which can be attributed to the high surface-to-volume ratio of zinc oxide nanorods as they provide high density of trap states which causes an increase in the carrier injection and movement leading to persistent photoconductivity. This photoconductivity was also facilitated by the frequency sweep applied to the sample which suggests the investigated ZnO nanorods based IDE devices can be useful for the application of efficient UV detectors. Experimental values of field lowering coefficient (βexp) matched well with the theoretical value of βS which suggests that the possible operating conduction mechanism in ZnO nanorods is Schottky type. I-V characteristics showed that the significantly high photoconductivity of ZnO-NRs as a result of UV light illumination is owing to the increase in number of free charge carriers as a result of generation of electron-hole pairs by absorption of UV light photons.

Spin-Coating and Aerosol Spray Pyrolysis Processed Zn1-xMgxO Films for UV Detector Applications.

A series of Zn1−xMgxO thin films with x ranging from 0 to 0.8 were prepared by spin coating and aerosol spray pyrolysis deposition on Si and quartz substrates. The morphology, composition, nano-crystalline structure, and optical and vibration properties of the prepared films were studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and optical and Raman scattering spectroscopy. The optimum conditions of the thermal treatment of samples prepared by spin coating were determined from the point of view of film crystallinity. The content of crystalline phases in films and values of the optical band gap of these phases were determined as a function of the chemical composition. We developed heterostructure photodetectors based on the prepared films and demonstrated their operation in the injection photodiode mode at forward biases. A device design based on two Zn1−xMgxO thin films with different x values was proposed for extending the operational forward bias range and improving its responsivity, detectivity, and selectivity to UV radiation.

Effect of substrate temperature on the properties of spray deposited Ga2O3 thin films, for solar blind UV detector applications

In this work, Ga2O3 thin films were deposited on glass substrates by chemical spray pyrolysis technique at three different substrate temperatures 350 °C, 400 °C, and 450 °C. The structural, optical, morphological and electrical characteristics of the deposited sample thin films were investigated. From the studies, it is understood that by tuning substrate temperature, we can extensively change the properties of the film. Optimum temperature for coating Ga2O3 thin films was understood and the work was extended to demonstrate a simple deep UV detector, working in photoconductive mode. The fabricated device exhibit medium response to UV light at 254 nm. The present work report the fabrication of solar blind UV detector based on Ga2O3 thin film, grown using low cost, easily scalable spray deposition technique.

Lithium activated enhancement in UV-photo response of europium doped ZnO thin film

The advancement in material functionality is an important tool to enhance the sensitivity of ZnO-based UV detectors. The ZnO-based UV detector with different morphology has shown interesting results but the improvement is limited. The incorporation of dopant not only gives the characteristic property of dopant but also tunes electron, hole, and defect concentrations. This work has shown significant improvement in the performance of ZnO-based UV detector with the incorporation of Eu1% and Li1% as the dopants. Sol-gel derived ZnO and Eu 1% doped ZnO (Eu1) and Eu1% Li1% doped ZnO thin film (Eu1Li1) have been investigated for UV detector application. The HRXRD and AFM confirm the high crystalline quality with granular structure in all deposited thin films. The enhanced UV absorption in doped thin film confirms the potentiality of Eu1Li1 thin film as a UV detector. The observed photocurrent value increases twice in Eu1%Li1% doped ZnO thin film (6.75 μA) as compared to pure ZnO (3.14 μA) at 4.0 V bias voltage under UV irradiation of wavelength 325 nm. The responsivity of the Eu1Li1 UV detector is twice as compared to pure ZnO. The enhanced photocurrent is due to an increase of favorable oxygen defect concentration arising with Eu1% and Li1% substitution.

The influence of TMGa pre-flow time and amount as surfactant on the structural and optical properties of AlN epilayer

AIN is used as a template layer for deep UV (DUV) emitter and detector applications, because of its wide bandgap and high thermal conductivity. In this study, trimethylgallium (TMGa) source is used as surfactant to improve crystal quality and decrease dislocation density (DD) of AlN layers grown on sapphire (Al2O3) substrate surfaces by Metal Organic Vapor Phase Epitaxy (MOVPE) system. TMGa pre-flow time and pre-flow amount that TMGa pre-flow to the nucleation stage are the subjects of two distinct optimization studies. The structural and optical properties of grown AIN are examined by a high resolution X-ray diffractometer (HR-XRD), Raman spectroscopy, and UV–Vis–NIR spectrophotometer, respectively. TMGa pre-flow time and TMGa pre-flow amount determined to obtain high crystal quality AlN epilayers are 2 s and 0.446 × 10−5 mol/min, respectively. HR-XRD investigation of these growths yields FWHM values of 159/2718 arcsec and 201/1550 arcsec for the ω (002) and ω (102) scans, respectively.

Flexible ultraviolet detector with robust ZnO nanoparticle nanoassemblies on catechol‐functionalized polysiloxane nanofilms

AbstractAs a result of the vast Young's moduli difference between an inorganic semiconducting channel and flexible substrates, flexible optoelectronic devices readily lose their functionality through material delamination and local fracturing, which lead to short‐circuiting of devices. For this study, we synthesized a catechol‐containing polysiloxane (CFPS) adhesive and applied it to ZnO nanoparticle (NP) assembly on plastic substrates for flexible UV detector applications. The 30 nm thick CFPS adhesive can anchor 70 nm thick ZnO NPs strongly through a coordination bond, thereby forming an ultra‐stable ZnO NP channel layer. A peeling test of ZnO NP layer was conducted using transparent tape (Scotch®; 3 M Inc.). The ZnO NPs were firmly immobilized, reflecting the outstanding mechanical stability of CFPS adhesives. A UV detector also exhibited stable photo‐response performance even after a thousand iterations of bending with 3 mm curvature radii. The result indicates the polycyclosiloxane‐based flexible device as promising for wearable detector applications.

Structural, microstructure, optical, and dielectric properties of Sr1.99M0.01SnO4 (M: La, Nd, Eu) Ruddlesden–Popper oxide

This manuscript deals with the structural and optical properties of Sr1.99M0.01SnO4 (M: La, Nd, Eu). The single phase of the compositions is prepared by a conventional ceramic route followed by calcination at 1000 °C for 8 h. The lattice parameters determined from Rietveld refinement indicate that it gradually increases with doping of La to Eu. Microstructural analysis of the samples has been analyzed using scanning electron microscopy (SEM) and found that Nd3+ and Eu3+ act as grain growth promoters and La3+ as grain growth inhibitor. However, energy-dispersive X-ray (EDX) analysis shows the compositional homogeneity of the surface of samples. The absorption spectrum of the samples suggests that it is optically active in the UV region but transparent from the visible to IR region. The direct and indirect bandgap values of the samples are follow similar trend as lattice parameters because of the lower ionic radii of dopant. Urbach energy of the samples has been calculated from absorption data, which gradually increases with the dopant concentration except for Nd3+. The dielectric constant and dissipation factor of the samples are found to be in the range of 167–240 and 0.01–0.68, respectively. By utilizing these optical states as a metastable state, it can be used in UV detector, semiconductor devices, and optoelectronic device applications. The dielectric properties of samples make it a promising candidate for high frequency-based devices and dielectric capacitor application.

Synthesis and UV detection characteristics of TiO2 thin film prepared through sol gel route

In this work, TiO2 thin films were synthesized by sol-gel route initiating titanium isopropoxide and ethanol mixture as a precursor solution. Crystallization and Phase transitions of thin films were studied by X-ray diffraction (XRD). The XRD spectrum shows polycrystalline anatase phase without any considerable impurity phase. UV-VIS spectroscopy of the films shows 70-80% of transmission in the visible region. Optical band gap was calculated from the Tauc’s plot and was found to be around 3.3 eV. Scanning electron microscope was used to study the morphological characteristics of TiO2 thin films. The AFM images indicate that the surface morphology of the film is found to be uniform. Above the film, the aluminum interdigitated electrodes were deposited by thermal evaporation technique. The photo response of the film was measured at different incident powers. The film showed a good photo response with linear behavior for the incident light intensity and applied bias. The better performance of the presented TiO2 detector suggests that it will have promising potential for UV detector applications.

Optical and electrical properties of E-Beam deposited TiO2/Si thin films

In this paper, optical and electrical properties of E-Beam deposited TiO2/Si thin films have been studied and investigated extensively. The films were deposited on p-type (100) silicon wafer by using electron beam evaporation technique. The thickness of the thin films was measured by a spectroscopic reflectometer, which is about 216 nm. The fabricated titanium oxide (TiO2) thin films were annealed at 800 °C for 1 h under N2 ambient. X-ray diffraction measurements were performed to study the structure and phase identification of the fabricated TiO2 thin films. For the optical properties, reflection, transmittance, refractive index and absorption coefficient were obtained and analyzed. The photocurrent and dark current of the fabricated films were measured by I–V measurements. The measurement of the current–voltage (I–V) characteristics possesses good ohmic contact. The electrical characterizations of the films were performed in the range of the low frequencies (50 and 100 kHz) and high frequencies (750 kHz and 1 MHz) by the capacitance–voltage and conductance–voltage measurements at room temperature. The capacitance of the fabricated TiO2 MOS capacitor at both high and low frequencies increases with the decrease in frequencies. The obtained conductance curves (peaks) increase with the decreasing in the frequencies. This can be due to the interface state density, series resistance and interfacial dielectric of the fabricated MOS capacitors. The variation in the characteristics of the fabricated film shows that TiO2 is a promising candidate to be used in the optoelectronic and future UV detector applications as a switch, such as an optical amplifier, emitter, and UV light detectors.

Performance evaluation of bottom gate ZnO based thin film transistors with different W/L ratios for UV sensing

In this paper, we report the simulation, fabrication and characterisation of UV photo-detectors with bottom gate ZnO Thin Film Transistors (TFTs), grown on silicon at room temperature using RF magnetron sputtering process. The static performance of these detectors have been explored by varying the channel lengths (6 μm and 12 μm). The fabricated devices show low leakage currents with threshold voltages of 1.18 & 2.33 V, sub-threshold swings of 13.5 & 12.8 V/dec for channel lengths of 6 μm and 12 μm TFT, respectively. They also exhibit superior electrical characteristics with an ON-OFF ratio of the order of 3. The detector was also tested for device stability, with the transfer characteristics of the TFTs, which got deteriorated mainly by the negative bias-stress. The TFTs were further tested for UV detector applications and found to exhibit good photo-response.

Faster photoresponse, enhanced photosensitivity and photoluminescence in nanocrystalline ZnO films suitably doped by Cd

Abstract Faster photoresponse, enhanced photosensitivity and photoluminescence are obtained in Cd doped nanocrystalline ZnO films obtained by sol-gel method. The rise and decay times decrease for 0.56 at% Cd doping and the photosensitivity increases by approximately 20% rendering the sample very useful for switching and UV detector applications. Comparatively larger surface to volume ratio occurs for this sample. Consistent switching behavior is obtained throughout. The films are optically transparent with crystallite size less than 22 nm. Optical band-gap is tuned between 3.22 and 3.15 eV by increasing the Cd doping slightly which compares favorably well with earlier reports. The NBE emission in the ultraviolet at 386 nm, from 0.51 at% Cd doped sample, is remarkably good with suppressed defect-emissions and six-fold higher intensity as compared to that from undoped sample. The surface roughness decreases with increase in dopant concentration.

High-Performance Self-powered Photodetectors Based on ZnO/ZnS Core-Shell Nanorod Arrays.

In recent years, there is an urgent demand for high-performance ultraviolet photodetectors with high photosensitivity, fast responsivity, and excellent spectral selectivity. In this letter, we report a self-powered photoelectrochemical cell-type UV detector using the ZnO/ZnS core-shell nanorod array as the active photoanode and deionized water as the electrolyte. This photodetector demonstrates an excellent spectral selectivity and a rapid photoresponse time of about 0.04 s. And the maximum responsivity is more than 0.056 (A/W) at 340 nm, which shows an improvement of 180 % compared to detectors based on the bare ZnO nanorods. This improved photoresponsivity can be understood from the step-like band energy alignment of the ZnO/ZnS interface, which will accelerate the separation of photoexcited electron-hole pairs and improve the efficiency of the photodetector. Considering its uncomplicated low-cost fabrication process, and environment-friendly feature, this self-powered device is a promising candidate for UV detector application.

Excellent photocatalytic performance of Zn(1 − x)MgxO/rGO nanocomposites under natural sunlight irradiation and their photovoltaic and UV detector applications

Photocatalytic activity, photovoltaic, and UV detector applications of Zn(1−x)MgxO (x=0.02, 0.04, and 0.06) nanoparticles (NPs) and Zn(1−x)MgxO/graphene nanocomposites were investigated. Graphene oxide (GO) sheets with a few layers were utilized as a graphene source, and the Zn(1−x)MgxO nanoparticles were synthesized and decorated on graphene oxide sheets by a simple sol-gel method. Transmission electron microscope (TEM) images and X-ray diffraction (XRD) patterns indicated that the Zn(1−x)MgxO NPs/GO nanocomposites had significantly smaller diameter and crystallite size compared to the Zn(1−x)MgxO NPs. Several techniques, including XRD, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, and Raman spectroscopy demonstrated that graphene oxide (GO) sheets reduced and changed into reduced graphene oxide (rGO) during the synthesis process. It was observed that the absorption peak of the Zn(1−x)MgxO/rGO nanocomposites was blue-shifted in comparison with the Zn(1−x)MgxO NPs. It was discovered that the Zn(1−x)MgxO/rGO nanocomposites showed an excellent performance to remove methylene blue (MB) dye under natural sunlight illumination compared to the Zn(1−x)MgxO NPs. Finally photodetector application of the samples under UV source illumination and photovoltaic performance of the samples were also investigated. It was observed a superior solar cell applications for the Zn(1−x)MgxO/rGO nanocomposites in comparison to the Zn(1−x)MgxO NPs.

Influence of Co concentration on the structural, optical, morphological and photo-diode properties of cerium oxide thin films

Highly uniform and well-dispersed ring shaped particles of CDC (Cobalt doped cerium oxide) films are successfully deposited by Nebulizer Spray Pyrolysis (NSP) technique. The structural, morphological, optical and photo-diode properties of the films are investigated. Cubic fluorite crystallites are detected by X-ray diffraction pattern with preferred orientation along (111) direction. Co concentrations distress the crystallinity and structural parameters. The transmittance decreases with increasing Co concentration due to the presence of covalent bonds between cerium and oxygen. PL spectra revealed that three consistent sharp and broad peaks observed at 369 (3.31eV), 394 (3.14eV) and 425nm (2.91eV) correspond to near-band-edge emission (NBE) in UV region, deep level emission (DLE) in violet and blue of the visible region respectively. The deep level emissions result from the recombination of electrons with holes trapped in singly ionized oxygen vacancies (Vo+). Large agglomerated ring, button and spherical crystallites are obtained with the typical size in the range 83–207nm. XPS analysis exhibits the presence of Ce, Co, O, C and Na in the films that indicates the non-stoichiometric behavior. I-V characteristics show the rectifying nature with a typical forward to reverse current ratio of ~7 in the range −4 to +4V. The turn-on voltage of the hetero-junction is found to be ~1.7V. The transient photocurrent behavior indicates that the device has a good stability and quick response to suggests that the prepared heterojunction device can be used as a white light photodetector and UV detector applications.

Visible blind ultraviolet photodetector based on CH3NH3PbCl3 thin film.

We report a prototypical device of CH3NH3PbCl3 film ultraviolet photodetectors that were fabricated with a coplanar metal-semiconductor-metal Au interdigital electrode configuration. Pure phase CH3NH3PbCl3 films with a good crystallinity were formed by a hybrid sequential deposition process featured with inter-diffusion of PbCl2 and CH3NH3Cl upon annealing. The CH3NH3PbCl3 film photodetector exhibits a high responsivity of 7.56 A /W at 360 nm, a ultraviolet/visible rejection ratio (R360 nm/R500 nm) was about two orders of magnitude and fast response speed with a rising time of 170 μs and a decay time of 220 μs. All the above results demonstrate CH3NH3PbCl3 film photodetector as a competitive candidate in the application of visible blind UV detectors.

Effect of Post Deposition Annealing Treatments on Properties of AZO Thin Films for Schottky Diode Applications.

High-quality aluminum (Al) doped ZnO (AZO) thin films were deposited on silicon substrates by RF sputtering at room temperature. The deposited films were annealed from the temperatures 350 °C to 650 °C in pure nitrogen (N₂) ambient. The effects of annealing on the microstructural, optical and electrical properties of the AZO films were investigated. A detailed analysis by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Four Probe and Hall measurements was performed to study the properties of these AZO thin films. It was observed that all of the as-deposited and annealed AZO films have homogenous surfaces and hexagonal wurtzite structures with good crystalline quality. The study also suggested that there was an intermediate post annealing temperature (450 °C) at which the deposited ZnO film exhibit best surface characteristics. Pd/AZO Schottky devices were fabricated with 450 °C annealed AZO thin films and the parameters of Schottky devices were extracted from I-V characteristics. These results indicated that the Pd/AZO films were very much suitable for various optoelectronics applications particularly for metal semiconductor metal based UV detector application.