Effect of oxygen flow ratio on the performance of RF magnetron sputtered Sn-doped Ga2O3 films and ultraviolet photodetector

This work explored the properties of RF magnetron sputtered Sn-doped Ga₂O₃ films grown on sapphire substrates at different oxygen flow ratios from 0.0 to 2.5%. The in situ optical emission spectroscopy was conducted to monitor the plasma radicals generated during the films’ deposition. All the films deposited at room temperature show amorphous structures with some nanoparticles. The deposition rate decreased monotonically with increasing oxygen flow ratio. The proposed conductive mechanism of the films can be mainly attributed to the changes in the ratio of substitutional Sn (Sn⁴⁺ valance state) atoms replacing lattice Ga sites (Ga³⁺ valance state) and the SnO₂ phase in the films. Metal–semiconductor–metal solar-blind photodetectors were developed and analyzed to illustrate the effect of oxygen flow ratio. A high performance photodetector with a low dark current of 1.14 pA, high on/off ratio of 812 and short rise/decay time of 0.05 s/0.12 s was realized at an optimization growth condition. The elaboration of the conductive mechanism and effect of oxygen flow ratio on the performance of Sn-doped Ga₂O₃ films and their photodetectors is crucial for the preparation of high-quality Sn-doped Ga₂O₃ films and its application in optoelectronic devices.     

Characterization of non-stoichiometric Ga2O3-x thin films grown by radio-frequency powder sputtering

We report the synthesis and characterization of non-stoichiometric Ga₂O_3-x thin films deposited on sapphire (0001) substrates by radio-frequency powder sputtering. The chemical and electronic states of the non-stoichiometric Ga₂O_3-x thin films were investigated. By sputtering in an Ar atmosphere, the as-grown thin films become non-stoichiometric Ga₂O_2.7, due to the difference in sputtering yield between Ga and O species of the Ga₂O₃ target. The electronic states of the thin films consist of ~85% Ga³⁺ and ~15% Ga¹⁺, corresponding to Ga₂O₃ and Ga₂O, respectively. The films have the electrical characteristics of a semiconductor, with electrical conductivity of approximately 5.0 × 10^-4 S cm^-1 and a carrier concentration of 4.5 × 10¹⁴ cm^-3 at 300 K.     

Ultraviolet photodetectors based on ZnO nanorods-seed layer effect and metal oxide modifying layer effect

Pt/ZnO nanorod (NR) and Pt/modified ZnO NR Schottky barrier ultraviolet (UV) photodetectors (PDs) were prepared with different seed layers and metal oxide modifying layer materials. In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively. For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (D _λ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism. Also the ratio of D ₂₅₄* to D ₅₄₆* was calculated above 8 × 10² for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.     

Self-powered broadband α-MoO3/Si photodetector based on photo-induced thermoelectric effect

As a two-dimensional crystal, molybdenum trioxides (α-MoO₃) has been considered as a typical candidate for next-generation photodetectors (PDs) but with limited photodetection applications in the ultraviolet region. Here, a photo-induced thermoelectric (PTE) effect in α-MoO₃ is proposed as a practical approach to realize the broadband photodetection of α-MoO₃/Si heterojunction PDs. High-quality α-MoO₃ films are grown on Si by using an e-beam evaporation method. By modulating the photo-induced thermoelectric potential along the c-axis on the transport properties, the α-MoO₃/Si PDs can be operated as a self-powered device, showing broadband photoresponse beyond the bandgap limitation in the wavelength range of 405–1550 nm. The manipulation of the PTE effect in the heterojunction is investigated carefully, clarifying the corresponding physical mechanisms of the unique photoresponse behaviors. Furthermore, the fabricated device exhibits competitive photodetection performance with a high photoresponsivity of 63.3 mA/W, a high optical detectivity of 3.1 × 10¹¹ cm Hz^1/2W^?1, fast response speeds with the rise/fall times of 0.47/0.76 ms, as well as high durability and environmental stability under 980-nm infrared illumination. These results not only provide a novel strategy to develop novel PDs with high performance, but also supply a deeply understanding of the PTE effect in α-MoO₃/Si heterojunctions.     

Solution Processed Trilayer Structure for High-Performance Perovskite Photodetector

Due to their outstanding performance, low cost, ease of fabrication, diverse photonic, and optoelectronic applications, metal halides perovskite have attracted extensive interest in photodetector applications. Currently, devices made by metal oxides, metal sulfides, and 2D materials had achieved good responsivity, but suffered from high dark current, slow response speed, small on-off ratio, and poor stability. Whole performances of these photodetectors are not satisfactory. Here, a lateral perovskite (CH₃NH₃PbBr₃)/Ethanolamine/TiO₂ (in ethanol) trilayer photodetector is designed for achieving high performance. EA treatment enhances electron extraction and reduces undesired recombination. This trilayer device shows good performances with low dark current of 1.5?×?10^?11 A, high on-off ratio of 2700, high photodetectivity of 1.51?×?10¹² Jones, high responsivity of 0.13 A W^?1, and high stability, comparative to conventional single layer devices. This work provides the way to improve the performance of metal halide perovskite photodetectors.     

Resistive random access memory based on gallium oxide thin films for self-powered pressure sensor systems

The resistive switching (RS) behavior of a gallium oxide (Ga₂O₃) thin film for use in resistive random access memory (RRAM) was investigated. Ta/Ga₂O₃/Pt memory devices exhibited favorable RS behavior, such as a small distribution of switching parameters and switching cycles of more than 3 × 10⁶. X-ray photoelectron spectroscopy and the current transport mechanism indicated that that the RS behavior was attributed to the local variation on the Schottky barrier near the Pt electrode interface due to oxygen vacancies. A hybrid system for self-powered data storage and deletion was built by combining the RRAM device with a commercial Pb(Zr_1-xTi_x)O₃ piezoelectric ceramic as a pressure sensor/power generator. The excellent anti-interference and reuse performance of the system indicated promising potential for the application of this memory device.     

Flower-like Sc2Mo3O12 nanosheet clusters: Synthesis,thermal expansion and photocatalytic properties

In this work, Sc₂Mo₃O₁₂ has been synthesized via one-pot hydrothermal reaction. The effects of process conditions on the crystal structure, morphology, photocatalytic activity and negative thermal expansion (NTE) behaviors of flower-like Sc₂Mo₃O₁₂ were systematically investigated. Results indicate that orthorhombic flower-like Sc₂Mo₃O₁₂ assembled by nano-size flaky crystal grains can be synthesized by one-pot hydrothermal reaction at a temperature as low as 120 °C for 2 h. The hydrothermal reaction temperature and time have no obvious effects on the crystal structure and morphology. However, the photocatalytic property of synthesized Sc₂Mo₃O₁₂ is sensitive to the above parameters. The sample synthesized at 200 °C for 2 h shows the best photocatalytic degradation of methyl orange, and the degradation rate is 73.32% in 2 h ¹The coefficient of thermal expansion (CTE) of Sc₂Mo₃O₁₂ is ?1.99 × 10^?6 °C^?1 in 50–500 °C tested using TMA. The high-temperature XRD analysis reveals that Sc₂Mo₃O₁₂ exhibits anisotropic NTE and the intrinsic CTE is measured to be ?2.09 × 10^?6 °C^?1 in 25–800 °C.     

Depolarization electric field and poling voltage-modulated Pb,La(Zr,Ti)O3-based self-powered ultraviolet photodetectors

Traditional self-powered ultraviolet photodetectors, which are usually designed based on p-n junction interfacial effects, exhibit low responsivity and specific detectivity because the photogenerated electrons and holes cannot be separated effectively. Unlike wide band-gap semiconductor materials, ferroelectrics have large remnant polarization and thus high depolarization electric field throughout the whole bulk region, which can cause effective separation of photogenerated electrons and holes. Based on this, in this study, we prepare Pb_0.93La_0.07(Zr_1-xTi_x)_0.9825O₃ (PLZT) ferroelectric thin films with large remnant polarization and self-powered ultraviolet photodetectors with Au/PLZT/FTO structure. The results indicate that the photoelectric response performances of the detectors improve as the remnant polarization of the PLZT thin film and positive poling voltage increase. By adjusting the Ti content, due to large remnant polarization of 47.4 μC/cm² in the PLZT thin films with 80 mol% Ti, the corresponding photodetector exhibits the best self-powered ultraviolet photoelectric response with the high photo/dark current ratio of 2600, responsivity of 2.05 mA/W, specific detectivity of 5.45 × 10¹⁰ Jones, and fast response speed (rise time of 18 ms). These values are superior to those of recently reported self-powered ultraviolet photodetectors.     

Ag@CoFe2O4/Fe2O3 nanorod arrays on carbon fiber cloth as SERS substrate and photo-Fenton catalyst for detection and degradation of R6G

In this study, Ag nanoparticles loaded CoFe₂O₄/Fe₂O₃ nanorod arrays on carbon fiber cloth have been successfully fabricated by a hydrothermal route followed by a calcination treatment and photochemical reduction process. The as-prepared composite has been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The obtained Ag@CoFe₂O₄/Fe₂O₃ nanorod arrays show excellent SERS performance, which provides enhancement factors (EF) as high as about 1.2 × 10⁸ for Rhodamine 6G (R6G). The SERS signals collected over a 20?µm × 20?µm area show relative standard deviation lower than 12%, suggesting good SERS signal uniformity. In addition, the Ag@CoFe₂O₄/Fe₂O₃ nanorod arrays can be used as an effective photo-Fenton catalyst photocatalytical degradation of R6G. It was found that 99.15% of R6G can be degraded in an hour. This bifunctional composite that can act both as SERS substrates and as photo-Fenton catalyst would facilitate the cleaning and recycling of SERS substrates for reusing through a photocatalytic process, as well as facilitate the integration of rapid detection and effective degradation of organic pollutants.     

Phase evolution,structure, and electrochemical performance of Al-, Ga- and Ta- substituted Li7La3Zr2O12 ceramic electrolytes by a modified wet chemical route

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is one of the most promising solid-state electrolytes (SSEs) for advanced solid-state lithium batteries (SSLBs). In this work, Li_6.25Al_0.25La₃Zr₂O₁₂, Li_6.4Ga_0.2La₃Zr₂O₁₂, and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ ceramics are prepared by a modified wet chemical route. The composition of the black mixtures derived from the precursors is ascertained. The phase evolution and structural properties from the ceramic mother powders to the final ceramic electrolytes are discussed in detail. The characteristic of cubic LLZO with the space group I-43d arises in the Li_6.4Ga_0.2La₃Zr₂O₁₂ ceramic electrolyte pellet after the secondary higher-temperature (1200 °C) sintering. The Rietveld refinement reveals the roles of Al³⁺ substitution at the Li⁺ sites and Ta⁵⁺ substitution at the Zr⁴⁺ sites to adjust crystal structure. In addition, the electrochemical performance of the ceramic pellets is also investigated. Remarkably, the Li_6.4La₃Zr_1.4Ta_0.6O₁₂ ceramic electrolyte has the most outstanding electrochemical performance, showing the high ionic conductivity of 6.88 × 10^?4 S cm^?1 (25 °C), the low activation energy of 0.42 eV and an extremely low electronic conductivity of 1.77 × 10^?8 S cm^?1 (25 °C). Overall, it is supposed that this work may help to achieve high-quality modified LLZO ceramic electrolytes, especially using the wet chemical strategy.     

Triple-doping of (Ga1/2Nb1/2)xTi1-xO2 ceramics with Al3+ for enhanced giant dielectric response with simultaneous decrease in dielectric loss

An acceptor-donor co-doped (Ga_1/2Nb_1/2)_0.1Ti_0.9O₂ ceramic is triple-doped with Al³⁺, followed by sintering at 1450 °C for 5 h to obtain (Al_xGa_1/2-xNb_1/2)_0.1Ti_0.9O₂ ceramics with improved giant dielectric properties. Homogeneous dispersion of all dopants inside the grains, along with the partially segregated dispersion of the Ga³⁺ dopant along the grain boundaries, is observed. The (Al_xGa_1/2-xNb_1/2)_0.1Ti_0.9O₂ ceramics exhibit high dielectric permittivities (ε′～4.2–5.1 × 10⁴) and low loss tangents (tanδ～0.007–0.010), as well as a low-temperature coefficients (<±15%) between ? 60 and 200 °C. At 1 kHz, tanδ is significantly reduced by ～4.4 times, while ε′ is increased by ～3.5 times, which is attributed to the higher Al³⁺/Ga³⁺ ratio. The value of tanδ at 200 °C is as low as 0.04. The significantly improved dielectric properties are explained based on internal and surface barrier-layer capacitor effects, which are primarily produced by the Ga³⁺ and Al³⁺ dopants, respectively, whereas the semiconducting grains are attributed to Nb⁵⁺ doping ions.     

Synthesis of Ga-doped Li7La3Zr2O12 solid electrolyte with high Li+ ion conductivity

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) Li⁺ ion solid electrolyte is a promising candidate for next generation high-safety solid-state batteries. Ga-doped LLZO exhibits excellent Li⁺ ion conductivity, higher than 1 × 10^?3 S cm^?1. In this research, the doping amount of Ga, the calcination temperature of Ga-LLZO primary powders, the sintering conditions and the evolution of grains are explored to demonstrate the optimum parameters to obtain a highly conductive ceramics reproducibly via conventional solid-state reaction methods under ambient air sintering atmosphere. Cubic LLZO phase is obtained for Li_6.4Ga_0.2La₃Zr₂O₁₂ powder calcined at low temperature 850 °C. In addition, ceramic pellets sintered at 1100 °C for 320 min using this powder have relative densities higher than 94% and conductivities higher than 1.2 × 10^?3 S cm^?1 at 25 °C.     

Improved photodetection capabilities of Ag@CeO2 Nanorod composite array using GLAD technique

This work reports the growth of an Ag@CeO₂ nanorod (NR) composite array using the glancing angle deposition (GLAD) technique for UV photodetector application. It showed improvement in performance by decorating plasmonic nanoparticles (NPs) on the semiconductor surface. The interaction between the plasmonic NPs and the semiconductor under the influence of light manifested a localised surface plasmon resonance (LSPR) effect. This allowed for strong absorption, scattering and inducement of an intense electric field, which resulted in the enhancement of photocurrent and, consequently, the device performance. The use of the GLAD technique also allowed the growth of vertically oriented NR composite structures, which assisted in increased absorption. It was found that the fabricated structure exhibited an increase in the responsivity at 370 nm with a value of 18.74 AW^-1 as compared to the previous work of only 4.51 AW^-1. A comparably high detectivity of 3.94 × 10¹² Jones and a low NEP value of 10.67 fW at ?6 V were also exhibited by the device on account of low dark current and enhanced photocurrent. The maximum internal gain obtained for the device was 62.92. The presence of Ag NPs all around the semiconductor NR structure had led to a substantial increase in the photoresponse with a rise time and fall time of 65 ms and 58 ms respectively. These results are believed to offer new ways of harnessing light to boost the functioning of 1D nanostructure-based UV photodetectors.     

Synthesis of polycrystalline gallium oxide solar-blind ultraviolet photodetector by Aerosol Deposition

An aerosol deposition method was used to fabricate a solar-blind photodetector (for UV-C) using thin films of β-Ga₂O₃, which is a wide-bandgap oxide material. The Ga₂O₃ films deposited at room temperature presented a polycrystalline structure and a thickness of approximately 4 µm and showed a high transmittance of approximately 70–80 % in the visible region; the transmittance was approximately 60–80 % even after heat treatment up to a 800 °C. The Ga₂O₃ films that were post-annealed at a temperature of 800 °C showed an I_photo/I_dark ratio of approximately 40,000 in the solar-blind region with a light source of 254 nm, together with very good light detection characteristics (initial rising and decay times of 0.45 s and 0.13 s, respectively). Because of the good performances observed for the Ga₂O₃ thin films even at extreme conditions, they exhibit a high potential for use as photodetectors in several applications.     

Fabrication of double-cladding Ho3+/Tm3+ co-doped Bi2O3–GeO2–Ga2O3–BaF2 glass fiber and its performance in a 2.0-μm laser

A novel double-cladding Ho³⁺/Tm³⁺ co-doped Bi₂O₃–GeO₂–Ga₂O₃–BaF₂ glass fiber, which can be applied to a 2.0-μm infrared laser, was fabricated by a rod-tube drawing method. The thermal properties of the glass were studied by differential scanning calorimetry. It showed good thermal stability and matching thermal expansion coefficient for fiber drawing when T_x−T_g > 193°C and the maximum difference of the thermal expansion coefficient is 3.55 × 10⁻⁶/°C or less. The 2.0-μm luminescence characteristics were studied using the central wavelength of 808 nm pump light excitation. The results show that when the concentration ratio of Ho³⁺/Tm³⁺ reaches 0.5 mol%:1.0 mol%, the maximum fluorescence intensity was obtained in the core glass, the emission cross section reached 10.09 × 10⁻²¹ cm², and the maximum phonon energy was 751 cm⁻¹. In this paper, a continuous laser output with a maximum power of 0.986 W and a wavelength of 2030 nm was obtained using an erbium-doped fiber laser as a pump source in a 0.5 m long Ho³⁺/Tm³⁺ co-doped glass fiber. In short, the results show that Ho³⁺/Tm³⁺ co-doped 36Bi₂O₃–30GeO₂–15Ga₂O₃–10BaF₂–9Na₂O glass fiber has excellent laser properties, and it is an ideal mid-infrared fiber material for a 2.0-μm fiber laser with excellent characteristics     

Synthesis and characterization of Ga-doped Ba3MoNbO8.5 electrolytes for intermediate temperature-solid oxide fuel cells

Ba₃MoNb_1-xGa_xO_8.5-δ (BMNG, 0 ≤ x ≤ 0.2) powders are successfully prepared by sol-gel autoignition method. The effects of acceptor-type Ga³⁺ doping on Ba₃MoNbO_8.5 (BMN) are characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscope, Raman spectroscopy, and electrochemical impedance spectroscopy. All BMNG samples crystallize as a single phase in the R-3m space group and show great phase stability at various environments. Doping a small amount of gallium can effectively improve bulk conductivity and sintering density of BMN. The ionic conductivity of Ba₃MoNb_0.9Ga_0.1O_8.5-δ (BMNG10) is the highest, which can reach 2.05 × 10^?2 S cm^?1 at 800 °C. The enhanced ionic conductivity is primarily related to the increase of oxygen vacancy concentration and the number of tetrahedral units within the structure. In addition, through successfully assembling and evaluating a single cell supported by the BMNG10 electrolyte, it is proved that the practical utilization of BMNG10 in intermediate temperature-solid oxide fuel cells (IT-SOFCs) is feasible. In short, hexagonal perovskite derivative BMNG10 is a promising oxide ion conductor for IT-SOFCs.     

Investigation of the Ga-Sb-S chalcogenide glass with low thermo-optic coefficient as an acousto-optic material

In this study, two series of Ga_xSb_40-xS₆₀ (x = 4, 6, 8, 10 mol%) and Ga_ySb₃₆S_64-y (y = 3, 5, 6 mol%) glasses were prepared and the relationship between their compositional and acousto-optic (AO) properties was investigated systematically for the first time. In the Ga_ySb₃₆S_64-y system, the AO figure of merit (M₂) increased as the Ga increased, and the maximum M₂ of the Ga₆Sb₃₆S₅₈ glass was 455.78 × 10^?18 s³/g, which is ～301 times greater than that of fused silica and ～2.5 times greater than that of As₂S₃ chalcogenide (ChG) glass at 1550 nm. However, its thermo-optic coefficients (dn/dT) varied greatly (32.1 × 10^?6 °C^?1–57.2 × 10^?6 °C^?1), and acoustic attenuations (α) at 10 MHz were high, from 5.446 dB/cm to 7.274 dB/cm. In the Ga_xSb_40-xS₆₀ glass system, the M₂ value and α at different ultrasonic frequencies gradually decreased with the improvement of Ga. Compared with the Ga_ySb₃₆S_64-y system, the Ga_xSb_40-xS₆₀ glass system had lower α (at 10 MHz) and dn/dT, which are 5.001 dB/cm–5.563 dB/cm and 17.3 × 10^?6 °C^?1–55.6 × 10^?6 °C^?1, respectively. These results provide a significant reference for the further development of novel ChG glasses and help expand their application fields.     

The sintering behavior,microstructure, and electrical properties of gallium-doped zinc oxide ceramic targets

The properties of sputtering targets have recently been found to affect the performances of sputtered films and the sputtering process. To develop high-quality GZO ceramic targets, the influences of Ga₂O₃ content and sintering temperature on the sintering behavior, microstructure, and electrical properties of GZO ceramic targets were studied.The results showed that the increase in Ga₂O₃ content from 3 wt% (GZO-3Ga) and 5 wt% (GZO-5Ga) not only inhibited the densification but retarded grain growth. During sintering, ZnGa₂O₄ phase formed before 800 °C, and Zn₉Ga₂O₁₂ phase was found after sintering at 1000 °C. Moreover, after sintering at 1200 °C, the number of Zn₉Ga₂O₁₂ precipitates increased at the expense of ZnGa₂O₄ and ZnGa₂O₄ disappearing completely. The relative density, grain size, and resistivity of GZO-3Ga sintered at 1400 °C in air were 99.3%, 3.3 μm, and 2.8 × 10⁻³ Ω cm, respectively. These properties of GZO ceramics are comparable to properties reported in the literature for AZO sintered in air.     

High pyroelectric performance in Pb0.99Nb0.02[(Zr0.57Sn0.43)0.94Ti0.06]0.98O3/Al2O3 composites by design

High pyroelectric performance around human body temperature is essential for ultra-sensitive infrared detectors of medical systems. Herein, toward human health monitoring, composite ceramics (1-x)Pb_0.99Nb_0.02[(Zr_0.57Sn_0.43)_0.94Ti_0.06]_0.98O₃/xAl₂O₃ (x = 0, 0.1, and 0.2) were designed. A metastable ferroelectric (FE) phase was induced in the anti-FE matrix by the Al₂O₃ component-induced internal stress, and in turn FE-anti-FE phase boundary was constructed. The ceramics at x = 0.2 exhibit high pyroelectric coefficient with p = 10.9 × 10⁻⁴ C·m⁻²·K⁻¹ and figures of merit with current responsivity F_i = 6.23 × 10⁻¹⁰ m·V⁻¹, voltage responsivity F_v = 12.71 × 10⁻² m²·C⁻¹, and detectivity F_d = 7.03 × 10⁻⁵ Pa^−1/2 around human body temperature. Moreover, the enhanced pyroelectric coefficients exist in a broad operation temperature range with a large full width at half maximums of 18.5°C and peak value of 29.2 × 10⁻⁴ C·m⁻²·K⁻¹ at 48.2°C. The designed composite ceramic is a promising candidate for infrared thermal imaging technology of noncontact human health monitoring system.     

Spinel Mg(Al,Ga)2O4 Solid Solution as High‐Performance Microwave Dielectric Ceramics

Spinel Mg(Al_1?xGa_x)₂O₄ (x = 0–1) solid solutions were synthesized via solid‐state method. Replacement of Al³⁺ by Ga³⁺ in MgAl₂O₄ gave rise to the expansion of the lattice, as well as blueshifts of FT‐IR and Raman peaks. The homogeneous solid solutions, high relative densities, large grain sizes, and compact microstructures resulted in excellent microwave dielectric properties for spinel Mg(Al_1?xGa_x)₂O₄ (x = 0.6) ceramics sintered at 1485°C: that is, ε_r = 8.87, Q × f = 107 000 GHz (at 14.8 GHz), and τ_f = ?16 ppm/°C. Spinel‐structured Mg(Al_1?xGa_x)₂O₄ (x = 0–1) solid solutions possessed low sintering temperatures, wide temperature regions (~100°C), and small negative τ_f values. These outstanding performance make Mg(Al, Ga)₂O₄ a promising candidate material for millimeter‐wave devices.