Thickness Of ZnO Layer Research Articles

Redox reaction at buried ZnO/Ti thin film interface as seen by hard x-ray photoemission and thermal desorption spectroscopy

In the context of low-emissivity glazing, the redox reaction at a buried ZnO/Ti interface is studied in model nanometer-thick film stacks synthesized by magnetron sputtering deposition. For a given amount of Ti, the roles of annealing temperature up to 550 °C, of ZnO layer thickness, and of its crystalline quality are explored. The main originality of the approach is the use of hard x-ray photoemission spectroscopy to probe in situ chemical reactions at a buried interface in a non-destructive way. The detailed analysis of relevant core levels reveals the formation of a ZnxTiyOz ternary compound and the nearly complete oxidation of Ti into TiO2. Thanks to complementary measurements of thermal desorption spectroscopy and electron probe microanalysis, unexpected diffusion of the Zn redox reaction by-product through the upper part of the stack and its desorption in vacuum are clearly evidenced. The reaction and mass transport pathways are rationalized through thermodynamic simulations.

Optimizing optoelectronics performance: theoretical and experimental study on ZnO thin film for Al/ZnO/p-Si photodiode

Abstract In this paper, a ZnO photodiode in a p-n heterojunction configuration is fabricated on a p-type Si substrate focusing specifically on ZnO/p-Si heterojunction photosensitive devices and photodiodes (PDs) using Al contacts. Through an experimental and theoretical analysis approach aims to evaluate the effects of important parameters, including ZnO layer thickness, defect density, and contact materials, on PD’s efficiency. Numerical analysis simulations comparatively examine the experimentally fabricated device performance at a 5 nm ZnO layer thickness by balancing photon absorption and carrier formation while minimizing carrier transport limitations. Experimentally process, an Atomic Layer Deposition (ALD) system was used to grow ZnO interlayers on one side of the polished Si wafer. Then, Al metallic contacts were created on the ZnO layers using a hole array mask. The PDs were then subjected to electrical characterization using I-V and I-t measurements under various illumination densities. Al/ZnO/p-Si PD’s device with active performance has been produced and analyzed with electrical parameters such as barrier height, photocurrent, spectral response, ideality factor and EQE were derived, analyzed and studied. In conclusion, this work provides a comprehensive understanding of the performance of Al/ZnO/p-Si PD at varying illumination intensities and offering a detailed analysis of key parameters influencing device efficiency for future optoelectronics applications.

Sensitivity of ZnO Film-Based X-ray Sensors: A Comprehensive Study on the Effect of Thickness of ZnO Layer.

For all types of photosensors, efficient absorption of photons of particular interest is very essential. We report the effect of thickness of the ZnO layer in ZnO film-based X-ray sensors. A set of five samples Z1, Z2, Z3, Z4, and Z5 is developed by varying the thickness of the ZnO layer between 10 and 73 μm. The dark I-V characteristics of the sensors show a "pseudorectifying" type nature. A quantitative analysis of the dark currents reveals that the dark I-V characteristics are affected by space charge limited current (SCLC) due to intrinsic defects present in the ZnO films. The effect of the SCLC is prominent in the thicker films in comparison to the thinner ones. The sensors show high signal-to-noise (S/N) ratio below 5.0 V bias voltage. The S/N ratio is found to increase with the thickness of the ZnO layer due to efficient absorption of X-ray photons. The photoresponse characteristics of the sensors against dose rate are sublinear between 0.015 and 0.234 Gy/s. The photoresponse time of the sensors are found to be nearly 1 s. The sensitivities of Z1, Z2, Z3, Z4, and Z5 sensors at 4.5 V bias voltage for 0.234 Gy/s dose rate are estimated to be 55.51, 337.08, 312.01, 152.81, and 103.52 μC/Gy cm3, respectively. The sensitivity of the device is found to increase with increase in thickness of the ZnO layer and reaches an optimum level for the thickness of about 19-26 μm. Beyond this range, the sensitivity is found to decrease due to the Schubweg effect.

Influence of Annealing Duration on the Structural, Optical and Electrical Properties of ZnO Layers Deposited Using the Dip-Coating Method

Zinc sol deposited via dip coating on Fluorine-doped Tin Oxide (FTO) coated glasses were annealed at 450 °C in normal ambient to form ZnO layers. The effect of annealing durations, i.e. 30, 60, 90, and 120 min on their surface morphology, crystallinity, optical, electrical and Dye-Sensitized Solar Cells (DSSCs) performance were studied. The XRD analyses indicated the formation of wurtzite ZnO after 60 min of annealing. It is noted that the ZnO layers annealed at 60-120 min showed good crystal quality attributed to its sharp, narrow and strong diffraction peaks. Generally, ZnO layers with uniform thickness have been deposited on the FTO coated glasses. The thickness of ZnO layers decreased from 0.88, 0.78, 0.76, and 0.73 mm when the annealing duration increased from 30 to 120 min due to removal of hydrocarbons from the zinc sol. The O at. % increased with annealing duration, indicating that more oxygen reacted with zinc to form ZnO. The ZnO thin film annealed at 60 min had relatively low sheet resistance (9.6 W) with optical bandgap of 3.04 eV. This suggests that ZnO layers annealed at 60 min have the largest amount of oxygen vacancies that contributed electrons for charges transportation in the layers. Besides, the Room Temperature Photoluminescence (RTPL) analyses showed that the ZnO thin film annealed for 60 min showed IUV/IVis ratio = 0.89, suggesting better crystal quality compared to shorter annealing duration.

ZnO Matrices as a Platform for Tunable Localized Surface Plasmon Resonances of Silver Nanoparticles

In this study, the localized surface plasmon resonances (LSPRs) of Ag nanoparticles (NPs) embedded in ZnO dielectric matrices were studied. Initially, continuous Ag thin films were deposited on Corning glass substrates via magnetron sputtering, followed by post annealing, resulting in the formation of self-assembled nanoparticles. In some cases, a heated substrate holder was employed to induce NP formation during the deposition. The morphology of nanoparticles was studied using atomic force microscopy (AFM). Ultraviolet–visible spectroscopy (UV-Vis) probed the LSPRs. Subsequently, a 70 nm thick ZnO layer was deposited on top of the Ag thin films. For the Ag films, LSPR characteristics were found to depend on the initial film thickness. The ZnO capping layer induced an intense red shift, suggesting its potential as a mechanism for tailoring LSPRs. Lastly, theoretical calculations with the rigorous coupled-wave analysis (RCWA) method were carried out for comparison with the experimental results.

Research of photovoltaic properties of cogeneration cylindrical photovoltaic module for hybrid solar panels

Solar energy is the most efficient and cleanest source of energy, as well as a cheap and eternal source of renewable energy. Improving the energy efficiency of solar panels will optimize their energy characteristics and operating modes, taking into account the load and solar radiation energy. The work is aimed at studying photosensitive structures based on porous Si and ZnO that are promising for solar energy. To increase the efficiency of solar panels, hybrid panels based on cogeneration photovoltaic modules of cylindrical shape cooled by liquid have been developed. This will open up the possibility of creating hybrid solar photovoltaic panels for simultaneous the generation of electricity and heat. A scheme for a hybrid solar panel device using a cooled cogeneration cylindrical photomodule based on ZnO/porous-Si/Si heterostructures is proposed. Using the PC1D program, the light characteristics of the manufactured structure (no-load voltage VOC, short-circuit current ISC, fill factor FF, and efficiency η) were calculated and the volt-ampere characteristics were plotted. The influence of porous-Si and ZnO layer thickness, texture, and doping level of the ZnO layer, as well as the effect of temperature on the performance of a ZnO/porous-Si/Si heterojunction solar cell was investigated in order to obtain a device with good conversion efficiency. It has been established that the energy conversion efficiency of a cogeneration cylindrical photomodule based on ZnO/porous-Si/Si heterostructures can reach 23.9 %.

Adequate UV photoemission from Ga2O3/ZnO/Ga2O3 thin film epistructures

Epistructures of Ga2O3/ZnO/Ga2O3 were grown on c-Al2O3 substrate using pulsed laser deposition route. Thickness of ZnO layer varied to form these epistructures were investigated structurally, micro-structurally and optically using respective techniques. The modification made with the epistructures are observed to change the peak position of longitudinal optical phonon plasmon (LPP) i.e. A1(LO) mode of the wurtzite ZnO. The specific mode position observed suggests the presence of optical phonon confinement, defects and impurities present at the interface of the layer with others. However the photoluminescence spectra recorded on these epistructures showed quenching of unwanted visible emissions generally observed in device quality of ZnO and gallium oxide films/crystals is interesting. Further the temperature dependent PL investigations performed on selected specimens confirmed that the donor and acceptor excitonic emissions observed are purely governed by either the electron phonon interactions or due to the lattice dilation and the electron phonon interactions both, depending on the thickness of a sandwiched layer i.e. ZnO. The results observed herewith are encouraging considering use epistructures in thin film form to fabricate UV detectors where cost, repeatability and ease of manufacturing are one of the prerequisites.

High sensitivity and stability probe-type refractive index sensor based on an optical fiber metasurface

A specific probe-type sensor based on an optical fiber metasurface was proposed and simulated for refractive index (RI) sensing. In this work, a metasurface has been integrated with an optical fiber platform, which has huge potential applications in imaging, sensing, and communications. The designed RI sensor consists of stacking layers of Au and ZnO in a 2D structure deposited on the end face of commercial multimode optical fiber. The parameters and performance of the sensor structure are designed and simulated. The results show that the designed sensor structure can generate mode resonance and realize RI sensing. Numerical simulations reveal that when the pair of Au/ZnO layers is 4, the width of the nanopillars is 300 nm, the thickness of the Au layer is 45 nm, the thickness of ZnO layer is 40 nm, and the RI sensitivity of the designed sensor reaches 1415 nm/RIU. In addition, the high RI of Au/ZnO, along with its compatibility with the fiber core (SiO2), makes it a perfect candidate to realize a multifunctional device. It also is a the biocompatible material that can be functionalized easily and used to realize biosensing.

Sensitization of ZnO Photoconductivity in the Visible Range by Colloidal Cesium Lead Halide Nanocrystals

In this work, colloidal perovskite nanocrystals (PNCs) are used to sensitize the photoconductivity of nanocrystalline ZnO films in the visible range. Nanocrystalline ZnO with a crystallite size of 12-16 nm was synthesized by precipitation of a zinc basic carbonate from an aqueous solution, followed by annealing at 300 °C. Perovskite oleic acid- and oleylamine-capped CsPbBr3, CsPb(Cl/Br)3 and CsPb(Br/I)3 PNCs with a size of 6-13 nm were synthesized by a hot injection method at 170 °C in 1-octadecene. Photoconductive nanocomposites were prepared by applying a hexane sol of PNCs to a thick (100 μm) polycrystalline conductive ZnO layer. The spectral dependence of the photoconductivity, the dependence of the photoconductivity on irradiation, and the relaxation of the photoconductivity of the obtained nanocomposites have been studied. Sensitization of ZnO by CsPbBr3 and CsPb(Cl/Br)3 PNCs leads to enhanced photoconductivity in the visible range, the maximum of which is observed at 460 and 500 nm, respectively; close to the absorption maximum of PNCs. Nanocomposites ZnO/CsPb(Br/I)3 turned out to be practically not photosensitive when irradiated with light in the visible range. The data obtained are discussed in terms of the position of the energy levels of ZnO and PNCs and the probable PNCs photodegradation. The structure, morphology, composition, and optical properties of the synthesized nanocrystals have also been studied by XRD, TEM, and XPS. The results can be applied to the creation of artificial neuromorphic systems in the visible optical range.

Improved the electrochemical performance between ZnO@Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte and lithium metal electrode for all-solid-state lithium-ion batteries

Spherical Li1.3Al0.3Ti1.7(PO4)3 (LATP) solid electrolyte powders are first successfully synthesized by spray-drying and O2 pressure-controlled calcination processes, and then the targeted ZnO@LATP composite solid electrolytes are gained by coating 2 μm thickness of ZnO layer on the surface of the LATP powders, in which the ZnO layer effectively not only isolates the direct contact between LATP electrolyte sheet and lithium metal electrode, but also regulates the lithium deposition reaction on the surface of the electrolytes, thereby restraining the overgrowth of lithium dendrites to prolong the life span of the assembled coin cell. Specifically, the Li/ZnO@LATP@ZnO/Li symmetric cell enhances the cycle stability without obvious increment of the overpotential compared to the Li/LATP/Li cell at 0.4 mA cm−2 for 500 h, and the assembled LiCoO2/ZnO@LATP/Li coin cell can deliver excellent rate and cycling performance, in which the discharge specific capacity is still retained at 118.5 mAh g−1 after 100 cycles at 0.1 C and quickly recovers to 121.2 mAh g−1 when the current is set back to 0.1 C after cycles. Furthermore, the ZnO@LATP solid electrolyte powders after being cycled present integrally spherical shape without any remarkable crack compared with the LATP solid electrolyte powders. Therefore, the investigations may provide an effective strategy to significantly lower the probability of side reactions between LATP electrolyte and lithium metal electrode to promote the electrochemical properties of LATP-based all-solid-state lithium-ion batteries.

Photoresponse improvement of a MAPbI3 p-i-n heterojunction photodetector by modifying with a PCBM layer and optimizing ZnO layer thickness

In this manuscript, a series of Spiro-OMeTAD/CH3NH3(MA)PbI3/ZnO p-i-n heterojunction PDs are prepared and the photoresponses are well studied by modifying the MAPbI3/ZnO interface with a PCBM layer and modulating the ZnO film thickness ranging from 20 to 95 nm. The PD shows an excellent self-powered capability due to the suitable band alignment. After introducing the PCBM layer, both the photoresponse and stability are greatly improved, which can be attributed to its suitable band level and outstanding properties of contact passivation and interfacial modification. Besides, it is indicated that the photoresponse is strongly dependent on the thickness of the ZnO layer. The PD with a 65 nm-thick ZnO layer achieves the best performances in a broadband spectral range of ∼350 to ∼800 nm with the maximum responsivity (R) of 0.443 A/W and response times of 0.25/0.14 s. This work provides an essential insight for designing high-performance ZnO electron-transport layer-based perovskite heterojunction PDs.

Plasmonic induced 5D3–5D4 cross-relaxation of Tb3+ in CaF2 thin films

Au nanoparticles (NPs) interleaved between ZnO films were prepared on Si substrates and CaF2:Tb3+ thin films were then spin coated on top. The Au NPs were ∼43 nm in diameter and exhibited a plasmonic absorption band at ∼544 nm, which red-shifted with increasing ZnO layer thickness. Photoluminescence (PL) of the Si/ZnO/Au/ZnO/CaF2:Tb3+ structure exhibited characteristic Tb3+ emissions at 450 nm (5D3 – 7F3) and 489, 543, 585, 621 nm (5D4 – 7FJ, J = 3, 4, 5, 6). For the sample with no ZnO spacer layer, the PL intensity associated with the 5D4 transitions increased in the presence of the Au NPs, while that of the 5D3 transition decreased. The emission intensity showed similar trends for the sample with ∼25 nm ZnO spacer layers although the enhancement was less. The PL intensity for the sample with thicker ZnO spacer layers (∼50 nm) exhibited overall reduction of the emission intensity. Lifetime measurement indicated that the lifetime of the sample with no ZnO spacer layer slightly increased compared to their reference samples without Au NPs, but remained almost unchanged for the samples with ZnO spacer layers. These results suggest that the Au NPs enhanced cross-relaxation energy transfer between Tb3+ ions.

Effect of film thickness of ZnO as the electron transport layer on the performance of organic photodetectors

Organic photodetectors with bulk heterojunctions were constructed with a structure of ITO/ZnO/P3HT:PC61BM/MoO3/Al. The effect of the thickness of the ZnO layer on the properties of the device were investigated by fabricating photodetectors with different ZnO layer thicknesses: 20, 40, 50, 60, and 80 nm. The 40 nm-thick ZnO electron transport layer provided the device with a low dark current density (1.7 × 10−9 A/cm2), high specific detectivity (2.7 × 1013 Jones), wide linear dynamic range (78.9 dB), and fast response speed (τr/τf = 0.61/0.75 μs). The results show that an optimal thickness of the ZnO electron transport layer can effectively block hole injection into the active layer, which is a promising strategy to improve the performance of organic photodetectors.

Structural Engineering Effects on Hump Characteristics of ZnO/InSnO Heterojunction Thin-Film Transistors.

Transparent conductive oxides (TCO) have been extensively investigated as channel materials for thin-film transistors (TFTs). In this study, highly transparent and conductive InSnO (ITO) and ZnO films were deposited, and their material properties were studied in detail. Meanwhile, we fabricated ZnO/ITO heterojunction TFTs, and explored the effects of channel structures on the hump characteristics of ZnO/ITO TFTs. We found that Vhump–VON was negatively correlated with the thickness of the bottom ZnO layer (10, 20, 30, and 40 nm), while it was positively correlated with the thickness of the top ITO layer (3, 5, 7, and 9 nm), where Vhump is the gate voltage corresponding to the occurrence of the hump and VON is the turn-on voltage. The results demonstrated that carrier transport forms dual current paths through both the ZnO and ITO layers, synthetically determining the hump characteristics of the ZnO/ITO TFTs. Notably, the hump was effectively eliminated by reducing the ITO thickness to no more than 5 nm. Furthermore, the hump characteristics of the ZnO/ITO TFTs under positive gate-bias stress (PBS) were examined. This work broadens the practical application of TCO and provides a promising method for solving the hump phenomenon of oxide TFTs.

Trials to achieve high-quality c-axis-oriented LiNbO3 thin films: Sputter-deposition on a-SiO2, ZnO/SiO2, quartz(0001), and SrTiO3(111) substrates

The crystallographic orientation, crystallinity, and surface morphology of LiNbO3 (LN) thin films sputter-deposited on less investigated a-SiO2, ZnO-covered a-SiO2 (ZnO/SiO2), quartz(0001), and SrTiO3(111) substrates were studied with X-ray diffraction and atomic force microscopy. Under precise control of the deposition temperature and O2 flow rate, c-axis-oriented LN films were obtained on a-SiO2. The same condition was applied to deposition on quartz(0001) substrate that has similar a-axis parameter of LN. Preferentially c-axis-oriented LN films, but not epitaxial, were obtained on quartz(0001). Although Solid-phase crystallization on quartz(0001) improved the c-axis orientation compared with crystallization during deposition, out-grown grains on the LN base layer roughened the surface morphology. The atomically not smooth quartz(0001) surface may hinder close lattice matching with LN crystal. While c-axis oriented ZnO layer on a-SiO2 plays a role of lattice-matched template substrate, the morphology of the ZnO is the key factor controlling crystallinity; sufficiently thick and smooth ZnO layer was effective to obtain highly c-axis-oriented epitaxial-like LN film. Chemical interaction is another factor affecting crystal growth. Only epitaxial LiNb3O8 layer could be obtained on SrTiO3(111) substrate with loss of Li at deposition temperatures between 350 and 550 °C. Migrating Li atoms reacted with SrTiO3 resulting in a substantial loss of Li from the LN film.

Modification of contact properties in Pt/n-GaN Schottky junctions with ZnO and TiO2/ZnO interlayers

In this study, ZnO (10 nm) and TiO2 (2 nm) were grown on a GaN substrate via atomic layer deposition, and the modified properties of Pt/GaN Schottky diodes with ZnO and ZnO/TiO2 interlayers (ILs) were electrically investigated. The barrier height increased with the ZnO and ZnO/TiO2 ILs; however, the ideality factor increased with the ZnO/TiO2 IL. The reverse-current–voltage characteristics were associated with the Poole–Frenkel emission for all the three junctions. Compared with the Pt/GaN junction, the density of the surface states decreased for the Pt/ZnO/GaN junction but increased for the Pt/ZnO/TiO2/GaN junction. An increase in the ideality factor and a decrease in the barrier height with decreasing temperature were observed at the Pt/GaN and Pt/ZnO/TiO2/GaN junctions. In general, the diode characteristics of the Pt/GaN junction improved owing to the ZnO IL, whereas it degraded owing to the ZnO/TiO2 IL. However, both ZnO and ZnO/TiO2 ILs demonstrate worse diode characteristics at higher temperatures. A thicker ZnO layer (>10 nm) is suggested for improved thermal stability.

Электронные состояния зоны проводимости ультратонких пленок тиофен-фенилен со-олигомера и замещенного бифенила на поверхности послойно выращенного ZnO

The results of studying the electronic states of the conduction band and interface potential barrier during the formation of ultrathin films of thiophene-phenylene co-oligomer CH3-phenylene-thiophene-thiophene-phenylene-CH3 (CH3-PTTP-CH3) on the surface of ZnO and films of biphenyl tetracarboxylic dianhydride (BPDA) on the ZnO surface are presented. A 100 nm thick ZnO layer was prepared by atomic layer deposition (ALD). Organic CH3-PTTP-CH3 films and BPDA films up to 8 nm thick were formed by thermal vacuum deposition. During film deposition, the electronic characteristics of the surface were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF. In this energy range, the structure of the maxima of the unoccupied electronic states of CH3-PTTP-CH3 and BPDA films was determined. As a result of the CH3-PTTP-CH3 film deposition, a decrease in the work function to 4.0 eV was found, compared with the value of the work function of 4.2 eV measured from the ALD ZnO substrate. This corresponds to the transfer of a negative charge from the СH3-PTTP-CH3 film to the substrate. The charge transfer at the interface between the BPDA film and the ALD ZnO substrate occurs in the opposite direction, since a 4.7 eV increase of the work function was registered during the formation of this interface. The СH3-PTTP-СH3 and BPDA films studied and the layer-by-layer grown ZnO film represent a continuous coating on sufficiently large surface areas of the order of 10 micrometers x 10 micrometers. The roughness of the ZnO surface does not exceed 4 nm, and the surface roughness of CH3-PTTP-CH3 and BPDA films was 10–15 nm.

Conduction band electronic states of ultrathin thiophene-phenylene co-oligomer and substituted biphenyl films on the surface of layer-by-layer grown ZnO

The results of studying the electronic states of the conduction band and interface potential barrier during the formation of ultrathin films of thiophene-phenylene co-oligomer CH3-phenylene-thiophene-thiophene-phenylene -CH3(CH3-PTTP-CH3) on the surface of ZnO and films of biphenyl tetracarboxylic dianhydride (BPDA) on the ZnO surface are presented. A 100 nm thick ZnO layer was prepared by atomic layer deposition (ALD). Organic CH3-PTTP-CH3 films and BPDA films up to 8 nm thick were formed by thermal vacuum deposition. During film deposition, the electronic characteristics of the surface were studied using total current spectroscopy (TCS) in the energy range from 5 eV to 20 eV above EF. In this energy range, the structure of the maxima of the unoccupied electronic states of CH3-PTTP-CH3 and BPDA films was determined. As a result of the CH3-PTTP-CH3 film deposition, a decrease in the work function to 4.0 eV was found, compared with the value of the work function of 4.2 eV measured from the ALD ZnO-substrate. This corresponds to the transfer of a negative charge from the CH3-PTTP-CH3 film to the substrate. The charge transfer at the interface between the BPDA film and the ALD ZnO-substrate occurs in the opposite direction, since a 4.7 eV increase of the work function was registered during the formation of this interface. The CH3-PTTP-CH3 and BPDA films studied and the layer-by-layer grown ZnO film represent a continuous coating on sufficiently large surface areas of the order of 10 μmx10 μm. The roughness of the ZnO surface does not exceed 4 nm, and the surface roughness of CH3-PTTP-CH3 and BPDA films was 10-15 nm. Keywords: thiophene-phenylene co-oligomers, biphenyl tetracarboxylic dianhydride, ultrathin films, ZnO, atomic layer deposition method, electronic properties, low-energy electron spectroscopy, interface potential barrier.

Flexible in-plane thermoelectric modules based on nanostructured layers ZnO and ZnO:In

In this study, with the aim of developing flexible in-plane thermoelectric module we deposited via SILAR method 0.3–1.4 thick nanostructured layers of undoped and indium doped zinc oxide on Kapton polyimide (PI) substrates and thus prepared ZnO:In/PI and ZnO/PI samples. We analyzed surface morphology, crystal structure, chemical composition, optical, electrical and thermoelectric properties of ZnO and ZnO:In thin films grown via SILAR on PI substrates. It was shown that ZnO:In/PI samples are consisted of flower-like ZnO:In microstructures with rod petals having pencil-like ends. ZnO/PI samples have lily flower-like ZnO microstructures with rounded petals. Despite the fact that crystal structure and optical properties of the nanostructured ZnO:In and ZnO films were almost the same, their morphology determined the electrical and thermoelectric properties. More compact 1.4 µm thick ZnO layer in sample ZnO/PI provided the best thermoelectric power factor ≈ 8 µW/(m·K2) due to its lower resistivity at near-room ≈ 0.15 Ω cm. Among four samples of the prepared flexible in-plane thermoelectric modules with single legs in the form of PI strips 3 cm long and 0.5 cm wide, covered with the semiconductor film ZnO or ZnO:In and having thin-film Al ohmic contacts at the edges, the TE module based on ZnO/PI showed the best output characteristics. At the temperature difference 50 К, its output power density reaches 10 µW/cm2, which is commensurate with the up-to-date values for solid miniature and flexible TEGs.

Structural, optical and electrochemical transient photoresponse properties of ZnO/Ga2O3 nanocomposites prepared by two-step CVD method

The influence of ZnO layer thickness on the structural, optical and electrochemical transient photoresponse properties of Ga2O3/ZnO heterostructured nanocomposites is evaluated. The increasing thickness of ZnO layer from 0 to 7.868 μm on the nanocomposites show an increase in the concentration of photogenerated electron-hole pairs, improve carrier separation and transportation to the electrolyte. This results to an enhanced photocurrent density from 164 to 833 μA/cm2 at 1 V vs Ag/AgCl electrode. The unhybridized β-Ga2O3 film and the ZnO/Ga2O3 nanocomposites exhibit nanoblock-like and nanoplate-like morphologies, respectively. Structural studies reveal hexagonal ZnO and β-Ga2O3 crystalline phases for the nanocomposites. Optical bandgap of the reference β-Ga2O3 film is found to be 4.79 eV whereas, the nanocomposites exhibit two bandgaps: 3.30–3.25 eV belonging to the crystalline hexagonal ZnO phase, and 4.87–4.83 eV traced to the β-Ga2O3 phase. Photoluminescence spectroscopy exhibits blue-green emissions for the unhybridized film and ultraviolet-green emissions for the nanocomposites.