Characterization of spray pyrolytically deposited high mobility praseodymium doped CdO thin films

Praseodymium (Pr) doped CdO thin films with high transparency and high mobility were deposited, using a homemade spray pyrolysis setup, on micro-slide glass substrates preheated at 300 °C. Polycrystalline nature and Cd-O bond vibration of deposited films were confirmed by X-ray diffraction, micro-Raman and Fourier transform infrared spectroscopy analyses. The oxidation state of Cd²⁺, O²⁻, and Pr³⁺ was confirmed by X-ray photoelectron spectroscopy analysis. The highest average particle size (92 nm-FESEM) and high RMS (13.48 nm-AFM) values are obtained for 0.50 wt% Pr doped CdO thin film. The optical band gap is varied between 2.38 eV and 2.52 eV, depending on the Pr doping concentration. Photoluminescence spectra revealed that Pr doped CdO thin film exhibits strong green emission at 582 nm. High mobility (82 cm²/V s), high charge carrier concentration (2.19×10²⁰ cm⁻³) and high transmittance (83%) were observed for 0.50 wt% Pr doped CdO film. A high figure of merit (9.79×10⁻³ Ω⁻¹) was obtained for 0.50 wt% Pr doped CdO thin films. The mechanism behind the above results is discussed in detail in this paper.     

Spray pressure variation effect on the properties of CdS thin films for photodetector applications

Herein, we report the photosensing property of CdS thin films. CdS thin films were coated onto glass substrates via a spray pyrolysis method using different spray pressures. Prepared films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical and photoluminescence spectroscopy. XRD analysis demonstrated the growth of crystalline CdS films with crystallite sizes varying from 26 to 29 nm depending on the pressure. The SEM and EDAX analyses revealed nearly-stoichiometric CdS films with smooth surfaces and slight variation in grain morphology due to pressure changes. Optical measurements showed a direct bandgap varying from 2.37 eV to 2.42 eV due to pressure changes. A photodetector was also fabricated using the grown CdS films; the fabricated photodetector exhibited good performance depending on the spray pressure. A spray pressure of 1.5 GPa resulted in high photoresponsivity and external quantum efficiency.     

A comprehensive study on the effects of alternative sulphur precursor on the material properties of chemical bath deposited CdS thin films

Chemical bath deposition (CBD) method was used to deposit CdS thin films on soda-lime glass substrates by using n-methylthiourea (NTU) as an alternative sulphur source and were compared to typical thiourea (TU) precursor. The sulphur source concentration was varied from 0.01 M to 0.1 M and the impact on the microstructural, surface morphology, optical and electrical properties of the grown films were studied. Increasing n-methylthiourea concentration in the precursor yielded thinner films that are less than 100 nm thickness, surface morphology with average surface roughness of 6.4 nm, larger granular structure, wider band gap at 2.3 eV–2.6 eV range. Raman spectroscopy revealed Raman peak at 303 cm-1. In contrast, an increase in thiourea concentration resulted in thinner amorphous films, less distinct granular structure, narrower energy band gap from 2.3 eV to 2.4 eV and a resonance Raman peak at 302 cm-1. CdS thin film deposited from n-methylthiourea precursor at higher precursor concentration of 0.1 M showed better electrical properties such as lower resistivity and higher carrier mobility compared to the thin film deposited from typical thiourea precursor.     

Structural,electrical and optical properties of molybdenum-doped TiO2 thin films

Molybdenum doped TiO₂ (MTO) thin films were prepared by radio frequency (RF) magnetron sputtering at room temperature and followed by a heat treatment in a reductive atmosphere containing 90% N₂ and 10% H₂. XRD and FESEM were employed to evaluate the microstructure of the MTO films, revealing that the addition of molybdenum enhances the crystallization and increases the grain size of TiO₂ films. The optimal electrical properties of the MTO films were obtained with 3 wt% Mo doping, producing a resistivity of 1.1×10^?3 Ω cm, a carrier density of 9.7×10²⁰ cm^?3 and a mobility of 5.9 cm²/Vs. The refractive index and extinction coefficient of MTO films were also measured as a function of film porosity. The optical band gap of the MTO films ranged from 3.28 to 3.36 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.14 eV was attributed to the Burstein–Moss effect.     

Electrical properties of poly(vinyl alcohol) (PVA) based on LiFePO<Subscript>4</Subscript> complex polymer electrolyte films

Li ion conducting polymer electrolyte films were prepared based on poly(vinyl alcohol) (PVA) with 5, 10, 15, 20, 25 and 30 wt% lithium iron phosphate (LiFePO₄) salt using a solution-casting technique. X-ray diffraction (XRD) was used to determine the complexation of the polymer with LiFePO₄ salt. Differential scanning (DSC) calorimetry was used to determine the melting temperatures of the pure PVA and complexed films. The maximum ionic conductivity was found to be 1.18 × 10⁻⁵ S cm⁻¹ for (PVA:LiFePO₄) (75:25) film, which increased to 3.12 × 10⁻⁵ S cm⁻¹ upon the addition of propylene carbonate (PC) plasticizer at ambient temperature. The Li⁺ ion transport number was found to be 0.40 for (PVA: LiFePO₄) (75:25) film using AC impedance and DC polarization methods. Dielectric studies were performed for these polymer electrolyte films in the frequency range of 10 Hz to 10 MHz at different temperatures. The activation energies of the complexed films were calculated from the dielectric loss tangent spectra and were found to be 0.35, 0.30, 0.27 and 0.28 eV. The cyclic voltammogram (CV) curves of (PVA: LiFePO₄) (75:25)+PC film exhibited higher specific capacities than those for other films.     

Enhancing the ultraviolet photosensing properties of nickel oxide thin films by Zn–La co-doping

In this work, co-doping effects of transition (Zn) and rare-earth (La) elements on the crystalline structure, surface morphology, photoluminescence, optical and photosensing properties of NiO thin films are studied. NiO, NiO:Zn(1%), NiO:La(1%), and NiO:Zn(1%):La(1%) thin films are fabricated using the nebulizer spray pyrolysis (NSP) method. X-ray diffraction study revealed the cubic NiO structure of all the films. Photoluminescence (PL) spectra of thin films exhibit various emission peaks centered at the wavelengths of 387, 414, 437, 451, 477, and 521 nm. The optical bandgap energy (E_g) values are found to be 3.46, 3.43, 3.39 and 3.33 eV for NiO, NiO:Zn(1%), NiO:La(1%) and NiO:Zn(1%):La(1%) thin films, respectively. The fabricated (Zn, La) co-doped NiO i.e., NiO:Zn(1%):La(1%) photo-detector exhibits highest responsivity (R), external quantum efficiency (EQE) and detectivity (D*) values of 0.50AW^-1, 169% and 14.5 × 10⁹ Jones, respectively as compared to NiO, NiO:Zn(1%) and NiO:La(1%) photo-detectors. The present study revealed that the transition and rare-earth elements co-doping can be an effective approach for tuning the various physical properties of semiconducting oxide films.     

Solution Synthesis of BiFeO3 Thin Films onto Silicon Substrates with Ferroelectric,Magnetic, and Optical Functionalities

Single‐BiFeO₃ perovskite films onto Pt‐coated silicon substrates have been fabricated by chemical solution deposition using a synthesis strategy based on the use of nonhazardous reagents. Different routes were tested to obtain precursors for the deposition of the films, inferring that bismuth (III) nitrate and iron (III) 2,4‐pentanedionate dissolved in acetic acid and 1,3‐propendiol led to the best solution. Ferroelectric, magnetic, and optical functionalities were demonstrated in these films, obtaining a high ferroelectric polarization at room temperature, ~67 μC × cm^?2, a dependence of the magnetization with the film thickness, 0.60 and 2.50 emu × g^?1 for the ~215 and ~42‐nm‐thick films, and a direct band gap in the visible range, E_g ~2.82 eV. These results support the interest of solution methods for the fabrication of BiFeO₃ thin films onto the silicon substrates required in microelectronic devices.     

Greenish-yellow emitting CdS: Sm3+ nanoparticles: Structural and optical analysis

Different concentrations of trivalent samarium (Sm³⁺) ions doped cadmium sulphide (CdS) nanoparticles were fabricated by one-step solid-state method at low temperature using C₁₀H₆(SO₃Na)₂ as surfactant for optoelectronic and solar cell applications. They were characterized through powder X-ray diffraction, Fourier transform infrared, Raman, scanning electron microscopy, transmission electron microscopy, UV–Vis absorption and photoluminescence studies. These nanoparticles establish cubic structure without any foreign phase and it was confirmed by Raman studies. The Raman spectrum of CdS nanoparticles shows first three longitudinal optical phonon orders. The adjacent lattice fringes were spaced about 0.30 nm. The direct band gap energy was found slightly higher than the bulk crystallites. The photoluminescence spectra of CdS: Sm³⁺ exhibits a broad peak at 563 nm with a shoulder at around 607 nm corresponding to Sm³⁺: ⁴G_5/2 → ⁶H_7/2 transition at 402 nm excitation. A luminescence quenching was noticed at higher Sm³⁺ ions concentration due to transfer of energy among the excited Sm³⁺ ions. The CdS: Sm³⁺ particles were fabricated with a size of the order of nanoscale and they can be used for efficient energy conversion. The studied CdS: Sm³⁺ nanoparticles are suitable for optoelectronic and solar cell applications.     

Preparation and characteristics study of self-powered and fast response p-NiO/n-Si heterojunction photodetector

The growth of crack-free nanostructured NiO films with good crystalline quality is of high importance for photodetectors to avoid performance failure. In this work, physical properties of spin coated NiO films were controlled by changing diethanolamine (DEA) to nickel acetate (NiAc) molar ratio (0:1–1:1) and post annealing temperature (300–650 °C). NiO film coated at DEA:NiAc molar ratio of 0:1 suffered from severe cracks and poor crystallinity, and by increasing the molar ratio to 1:1 a crack-free NiO with enhanced grain growth was obtained. With the increase of annealing temperature from 300 C to 600 °C, the crystallite size increased from 12.79 to 37.31 nm, and the bandgap decreased from 3.81 to 3.42 eV, indicating an enhancement in NiO film quality. A self-powered photodetector based on p-NiO/n-Si heterojunction showed broadband (UV-NIR) photodetection owing to synergistic photoelectric effect from both NiO film and Si substrate. The responsivity, detectivity, and external quantum efficiency were measured as 13.08, 46.02, 44.49, mA/W, 1.03 × 10¹¹, 3.65 × 10¹¹, 3.53 × 10¹¹, Jones, and 4.43%, 8.62%, 6.47% upon illumination with UV (365 nm), red (660 nm), and NIR (850 nm) lights, respectively. The photodetector showed high on/off current ratio of 1.210 × 10³ and fast response (less than 85 ms). These findings introduce p-NiO/n-Si heterojunction as a promising candidate for next generation optoelectronics.     

Straightening of chemically deposited CdS nanowires through annealing towards improved PV device performance

Cadmium sulfide (CdS) thin film consisting of nanowires over a flat CdS thin film were synthesized by depositing cadmium hydroxide [Cd(OH)₂] nanowires (NW) bundles, followed by conversion to sulfide phase by using ion exchange route at room temperature (300 K) based on negative free energy of formation. The influence of post annealing treatment on as-deposited CdS NW films has been studied in the temperature range 423–523 K through the observation of nanowires alignments. The annealing effect on the intrinsic properties have been studied in relation with the crystallites sizes, micro strain, dislocation density and optical band gap of the deposited films. Furthermore, the behavior of inter- and intramolecular hydroxide ion (OH⁻) has been investigated from FTIR analysis. Additionally, the effects of post annealing on photovoltaic device performance has been scrutinized and the obtained results were correlated with structural and optical properties.     

Enhanced optoelectronic properties of Ti-doped ZnO nanorods for photodetector applications

We report the effect of Ti-doping on structural, morphological, photoluminescence, optical and photoconductive properties of ZnO thin films. Pure and Ti(1, 3 and 5%)-doped ZnO thin films are deposited by the successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction analysis revealed the single-phase hexagonal wurtzite ZnO structure of all the films. Scanning electron microscope images suggest the formation of rod shaped particles in Ti-doped ZnO thin films. Photoluminescence spectra of all the films show emission peaks centered at 398 nm, 413 nm, 438 nm, 477 nm and 522 nm wavelengths. Optical properties support the semiconducting nature of all the films. The optical bandgap values are estimated to be 3.29 eV, 3.26 eV, 3.19 eV and 3.23 eV for ZnO, ZnO:Ti(1%), ZnO:Ti(3%) and ZnO:Ti(5%) thin films, respectively. Photoconductivity study indicates that ZnO:Ti(3%) thin film exhibits high responsivity, external quantum efficiency and detectivity of 0.30 AW^-1, 97% and 5.49 × 10¹⁰ Jones, respectively, among all the films. The enhanced photoconductivity of Ti-doped ZnO thin films make them useful for optoelectronic applications.     

Indium-free large area Nb-doped SnO2 thin film as an alternative transparent conducting electrode

Niobium doped tin oxide (NTO) thin film deposited via facile chemical spray pyrolysis technique on to a large area (10 × 10 cm²) glass substrate exhibits better optical and electrical properties. The structural, surface, optical and electrical properties were analyzed by means of XRD, XPS, AFM, SEM-EDS, Hall Effect, and four-point probe techniques. The deposited NTO thin film was found to possess a maximum average transmittance value around 75% due to enhanced optical bandgap (3.77 eV) by Nb-dopant effect. The variation of sheet resistance of the large area (10 × 10 cm²) coated thin film over the entire region was studied at every 1 × 1 cm² area. The film doped with 1.5 wt% of Nb content showed improved carrier concentration (9.33 × 10¹⁹ cm^-3), higher free carrier mobility (39.4 cm²/V·s), improved electrical resistivity (1.69 × 10^-3 Ω cm) and low sheet resistance (26.5 Ω/□). The temperature dependent electrical measurement was carried out from 200 to 450 °C in steps of 50 °C to understand the resistance stability of the film. In addition to these studies, we report the surface work function of NTO thin film to identify its suitability in optoelectronic devices. The estimated electrical properties confirm the substitution of Nb⁵⁺ in Sn site of SnO₂ lattice. Our results indicate the optimized NTO thin film to possess promising optical and electrical transport properties to serve as a better indium-free alternate transparent conducting electrode in various optoelectronic devices.     

Dielectric and electrical properties of La@NiO SNPs for high-performance optoelectronic applications

A successful flash combustion synthesis of NiO spherical nanoparticles with various contents of lanthanum (La) doping (La@NiO SNPs) with remarkably enhanced dielectric and electrical properties are reported. Single phase has been confirmed through X-ray diffraction and FT-Raman spectroscopic analysis. Increasing La content in NiO reduced the crystallite size by 341% to 6.65 nm from 22.70 nm. The composition of elements in the final product was assessed via EDX analysis. Moreover, monophasic La@NiO SNPs synthesis with size reduction was observed using field emission scanning electron microscopy (FESEM). A red shift in optical energy gaps (3.52–3.26 eV) was observed with increasing La contents from pure to 10 wt%. Capacitance (109–964 PF), impedance (9.41 × 10⁴–1.67 × 10⁴ kΩ), dielectric constant (100–967), dielectric loss (335–10666), and electrical conductivity (4–5 S/m) values were remarkably improved with La doping. The current (I)–voltage (V) characteristics of pure and La@NiO NPs were performed under the biased voltage of ±20 V. Current was noticed in the range of (3.81 × 10^?4–9.91 × 10^?3 amp) at pure, 1.0, 3.0, 5.0, and 10 wt% of La@NiO NPs. Enhancements in the dielectric and electrical properties of as-synthesized NPs make them suitable for optoelectronics uses.     

Preparation and properties of AZO/PS/AZO tri-layer transparent conductive film with a light-trapping structure

The light-trapping structure is an effective method to increase solar light capture efficiency in the solar cells. In this study, Al-doped ZnO (AZO)/polystyrene (PS)/AZO tri-layer transparent conductive film with light-trapping structure was fabricated by magnetron sputtering and liquid phase methods. The structural, optical and electrical properties of the AZO films could be controlled by different growth conditions. When the sputtering pressure of the under-layer AZO film was 0.2 Pa, the discharge voltage was around 80 V, which was within the optimal process window for obtaining AZO film with high crystallinity. The optimal under-layer AZO film had a large surface roughness and a very low static water contact angle of 75.71°, promoting the relatively uniform distribution of PS spheres. Under this sputtering condition, the prepared AZO/PS/AZO tri-layer film had the highest crystallinity and least point defects. The highest carrier concentration and Hall mobility are 3.0 × 10²¹ cm^-3and 5.39 cm² V^-1 s^-1, respectively. Additionally, a transparent conductive film with the lowest resistivity value (3.88 × 10^-4 Ω cm) and the highest average haze value (26.5%) was obtained by optimizing the process parameters. These properties were comparable to or exceed the reported values of surface-textured SnO₂-based as well as ZnO-based TCOs films, making our films suitable for transparent electrode applications, especially in thin-film solar cells.     

Structure,electrical and optical properties of (PVA/LiAsF6) polymer composite electrolyte films

In this work, Li⁺ ion conducting polymer composite electrolyte films (PECs) were prepared based on poly (vinyl alcohol) (PVA), lithium hexafluoro arsenate (LiAsF₆), and ceramic filler TiO₂ using solution cast technique. The XRD and FTIR spectra were used to determine the complexation of the PVA polymer with LiAsF₆ salt. The ionic conductivities of the (PVA + LiAsF₆) and (PVA + LiAsF₆ + TiO₂) films have been determined by the A.C. impedance measurements in the temperature range 320–440 K. The maximum conductivity was found to be 5.10 × 10^?4 S cm^?1 for PVA:LiAsF₆ (75:25) + 5 wt% TiO₂ polymer composite film at 320 K. The calculation of Li⁺ ion transference number was carried out by the combination of A.C. impedance and D.C. polarization methods and is found to be 0.52 for PVA:LiAsF₆ (75:25) + 5 wt% TiO₂ film. Optical properties such as direct energy gap, indirect energy gap, and optical absorption edge values were investigated in pure PVA and salt complexed PVA films from their optical absorption spectra in the wavelength range of 200–600 nm. The absorption edge was found at 5.76 eV for undoped film, while it is observed at 4.87 and 4.70 eV for 20 and 25 wt% LiAsF₆ doped films, respectively. The direct band gaps for these undoped and salt doped PVA films were found to be 5.40, 5.12, and 4.87 eV, respectively, whereas the indirect band gaps were determined as 4.75, 4.45, and 4.30 eV. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Preparation and characterization of nanoporous films derived from alicyclic copolyimides having pendent poly(propyleneglycol) groups

Nanoporous films were prepared with alicyclic copolyimides (coPIs) having polypropylene glycol (PPG) side chains by way of spontaneous phase separation in the film forming process and the subsequent thermal degradation of PPG moieties. PIs having various content (6.5, 11.9, 26.3, 52.7 wt%) and different length (M_w = 1.2 × 10³ and 2.4 × 10³) of PPG side chains were examined in order to clarify the relationship between chemical structure and pore characteristics. Nanopores were formed by heating the coPI films at 200 °C for 9 h under slightly reduced pressure. The size and the number of the pores observed by SEM varied depending on the content and molecular weight of PPG moieties. In many cases, the pore size was larger than those of the reported values for related aromatic copolyimide films. The dielectric constant of the nanoporous films ranged from 2.52 to 3.38.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Effects of ammonia concentration on the formation of CdS fabricated via microwave‐assisted chemical bath deposition

The microwave‐assisted chemical bath deposition (MACBD) process was successfully developed in this study for the preparation of cadmium sulfide (CdS) films as the buffer layers in Cu(In,Ga)Se₂ solar cells. The MACBD process reduces the reaction time to just 8 min. During the MACBD process, increasing the concentration of NH₄OH in the solution effectively reduced the thickness of the films as well as the particle sizes of in CdS films. At high NH₄OH concentrations, the heterogeneous nucleation of CdS dominated, and the formation of films was controlled via the ion‐by‐ion growth mechanism. Increasing the concentration of NH₄OH from 1 to 2.5 M significantly increased the conversion efficiency of the fabricated CIGS solar cells from 7.15% to 9.12%. The increase in the efficiency was attributed to an increase in the absorption of incident light and the enhancement of the carrier collection due to a reduction in the thickness of the prepared CdS films. According to diode analysis, the improvement in the diode ideality factor and leakage current was owing to the uniform coverage of CdS films and a reduction in series resistance associated with a decrease in the thickness of CdS films. When the concentration of ammonia was further increased to 3 M, incomplete coverage of CdS films on CIGS layers resulted in the formation of shunt paths and degraded the cell performance. This study demonstrated that CdS films prepared using the MACBD process with the optimum concentration of ammonia effectively improved the photovoltaic performance of Cu(In,Ga)Se₂ solar cells.     

Concentration dependence of physical properties of low temperature processed ZnO quantum dots thin films on polyethylene terephthalate as potential electron transport material for perovskite solar cell

Colloidal Zinc oxide quantum dots (ZnO QDs) prepared with varying concentrations through precipitation method were deposited on flexible ITO/PET substrates using spin-coating technique. Various characterization tools were utilized to investigate the morphological, structural, electrical and optical properties of the films. The crystallinity of the films was found to improve with increasing ZnO QD concentration (ZQ_C) as evident from the X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) studies. Crystallographic and optical parameters were evaluated and explained in depth. The average nanograin size and bandgap were increased and decreased respectively, from ～5 nm to ～8 nm and 3.29 eV–3.24 eV with an increase in ZQ_C from 10 mg/mL to 70 mg/mL. Columnar structure growth of the films is revealed by AFM results. The films showed decent optical transparency up to 81%. All the ZnO films exhibited n-type semiconducting property as indicated by the electrical measurements with carrier mobility and low resistivity of 12.21–26.63 cm²/Vs and 11.84 × 10^?3 to 13.16 × 10^?3 Ω cm respectively. Based on the experimental findings, ZnO QD nanostructure film grown at 50 mg/mL is envisaged to be a potential candidate for flexible perovskite photovoltaic application.     

Properties of solution-processed MgInZnO semiconductor thin films and photodetectors fabricated at a low temperature using UV-assisted thermal annealing

Ultraviolet (UV) irradiation-assisted thermal annealing is used for the fabrication of Mg doped InZnO (MIZO) semiconductor thin films and metal-semiconductor-metal (MSM) type photodetectors on alkali-free glasses at a low temperature of 300 °C. In this study, the effects of UV irradiation time on the structural features and the optical and electrical properties of sol-gel derived MIZO thin films were investigated, and the photoresponse properties of MIZO photodetectors fabricated using UV-assisted thermal annealing (UV-TA) and conventional thermal annealing (CTA) were compared. The molar ratio of In:Zn was fixed at 3:2, and the Mg content was maintained at 20 at% ([Mg]/[In+Zn]) in the precursor solution. After a spin-coating and drying procedure was performed twice, the dried sol-gel films were heated on a hotplate at 300 °C and exposed to UV irradiation in ambient air. The UV irradiation time was adjusted to 1, 2, 3, and 4 h. All annealed MIZO thin films had a dense microstructure, uniform film thickness, and flat surface and exhibited good optical transmittance (> 86.0%). The mean resistivity decreased with increasing irradiation time, and the samples irradiated for 4 h exhibited the lowest mean resistivity of 4.4×10² Ω-cm. Current-voltage (I-V) characteristics showed that the MIZO photodetectors operated in the photoconductive mode. Under illumination with UVC light, the MIZO photodetectors exhibited an I_light-to-I_dark ratio of 7.7 × 10² and had a photoresponsivity of 5.0 A/W at a bias of 5 V.