Near-band Edge Emission Research Articles

Effect of magnesium doping on the structure, optical properties and photocatalytic efficiency of ZnO nanostructures deposited by atmospheric pressure MOCVD

ZnO nanostructures doped by magnesium impurity were grown on Si substrates by atmospheric pressure MOCVD deposition using Zn and Mg acetylacetonates as initial precursors. XRD patterns confirm the successful incorporation of Mg ions into ZnO lattice. Room-temperature photoluminescence spectra of Mg-doped ZnO nanostructures demonstrate near-band edge emission and visible deep-level emission with ratios 2.9, 1.3 and 0.3 correspondingly for 1, 2.4 and 5.7 at. % of Mg in ZnO nanostructures. Raman measurements showed decreasing in intensity for ZnO modes with increasing Mg content. The best photodegradation rate constant was observed for ZnO NS with 2.4 at. % of Mg.

Crystal Structure, Optical, Photoluminescence, Raman, and Magnetic properties for Sm-doped Cr-Mg-Bi Ferrites using sensor

The current work,A series of rare earth Sm3+ ion substituted Cr-Mg-Bi ferrites Cr0.7Mg0.2Bi0.1SmxFe2-xO4 (x = 0.00, 0.02, 0.04, and 0.06) have beensynthesized by thesol-gel auto-combustion method. The XRD, FESEM, HRTEM,UV-Vis, FTIR, Raman spectroscopy, Photo Luminesce and Magnetic Properties analysis have been used to investigate structural, morphological, optical, Raman spectroscopy, Photo Luminesce and Magnetic Properties. Every sample contains a single-phase spinel structure, as confirmed by XRD.The substitution of Sm3+ ions is found to increase the lattice parameter from 8.258–8.248Å.A monotone diffraction peak (311) is visible near small angles of degrees (35.33 to 35.13). The Debye-Scherrer equation, the nanoparticles' crystallite size ranges from 35.357–54.778 nm.FE-SEMs reveal a spherical grain that groups and has a porous form, with particles 38.13 to 53.28 nmin size.HR-TEM micrographs illustrate spherical morphology and their average particle size decreases from 55.32 to 65.42 nm. The selected area electron diffraction (SAED) pattern confirms the crystal planes which were revealed from XRD calculations.The spinel structure was confirmed by FTIR spectroscopy, which found 414 cm-1 and 516 cm-1 vibrational band at the octahedral and tetrahedral sites.As the concentration of Sm3+ rises, the direct and indirect band gap energy values determined from UV-Vis show an increase and decrease.The generated NPs' semiconducting nature is confirmed by the strong correlation between the g-value and particle size change.Photoluminescence (PL) investigation shows that all processed samples have four bands.(i) peak centered at 412 nm, which is near-band edge emission and corresponds to the ultraviolet (UV) band,(ii) The violet band has a high-intensity peak at 434 nm,(iii) The blue band is related to a low-intensity, sharp peak located at 466 nm, and (iv) A broad peak at 502 nm with a very low intensity distinguishes the green band.The Raman spectroscopy investigation revealed that the CMBSF nanoparticles had a mixed spinel structure. The magnetic investigation shows that when the Sm content of ferrites increases, saturation magnetization drops from 39.86 to 33.16 emu/g.The sample's coercivity (Hc) increases from 16.06 to 21.90 KOe with Sm substitution.

Switching of major nonradiative recombination centers (NRCs) from carbon impurities to intrinsic NRCs in GaN crystals

The external quantum efficiency (EQE) and internal quantum efficiency (IQE) of radiation are quantified by omnidirectional photoluminescence measurements using an integrating sphere for two types of GaN crystals with different carbon concentrations ([C] = 1×1014 cm−3, 2×1015 cm−3). In the sample with lower [C], when the excitation density is 140 W cm−2, the EQE and IQE for near-band-edge (NBE) emission are 0.787% and 21.7%, respectively. The relationship between [C] and the IQE for NBE emission indicates that carbon impurities work as effective nonradiative recombination centers (NRCs) in n-type GaN, and major NRCs switch from carbon impurities to intrinsic NRCs, such as vacancies, when [C] falls below 3.5×1014 cm−3.

Electrical, optical and nonlinear optical process in spray pyrolyzed Zn:CuO nanostructures for optoelectronic device applications

Nanostructured pure and Zn doped CuO thin films were deposited on a glass substrate at 400 °C using the chemical spray pyrolysis method. The fabricated thin films were characterized to study the compositional, structural, morphological, optical and electrical properties. X-ray diffraction spectra show the polycrystalline nature of the sample and confirm the monoclinic phase of copper oxide. Raman analysis further confirms the absence of cuprous oxide phases and impurities. High absorbance in the visible region was observed for the films with bandgap values ranging from 1.7–2.0 eV. A near-band edge emission peak in the red region is recorded in the photoluminescence spectra. Uniformly distributed nanoparticles are observed in SEM images. Hall effect measurements indicate p-type conductivity and 5% Zn doped copper oxide showed the highest conductivity and carrier concentration. The non-linear absorption coefficient (β eff) of the samples was obtained with the help of z-scan method with a Helium-Neon laser under the CW regime. Zn doping results in an increase in nonlinear absorption, supporting the use of Zn:CuO for optoelectronic devices.

Improved midgap recombination lifetimes in GaN crystals grown by the low-pressure acidic ammonothermal method

To investigate the carrier recombination processes in GaN crystals grown by the low-pressure acidic ammonothermal (LPAAT) method, the photoluminescence (PL) spectra and PL lifetimes of LPAAT GaN crystals grown on acidic ammonothermal (AAT) GaN seed crystals were correlated with the growth polarity and species/concentration of point defects. The PL spectra of LPAAT GaN grown toward the (0001¯) direction (−c region), which provided the highest growth rate, exhibited a predominant near-band edge (NBE) emission. Neither bandgap narrowing nor Burstein–Moss shifts due to high concentration residual impurities were observed in the NBE emissions, indicating higher purity than the previously reported AAT GaN crystals. In addition, strain-induced energy shift or energy broadening of excitonic emission peaks was not observed, indicating excellent crystal coherency. Because of the reduced concentration of midgap recombination centers, a record-long room-temperature PL lifetime for the NBE emission of ammonothermal GaN (40 ps) was obtained from the −c region. Meanwhile, the PL spectra also exhibited the yellow and blue luminescence bands originating from particular deep-state radiative recombination centers. The major vacancy-type defects acting as midgap recombination centers are identified as vacancy complexes comprising a Ga vacancy (VGa) and a few N vacancies (VN), namely, VGa(VN)n buried by H and/or O, where n is an integer. Further reduction of such defect complexes will allow less compensated stable carrier concentration in the LPAAT GaN crystals.

Improvements of multifunctional spintronic and optoelectronic applications of nanostructured Eu-doped ZnS thin films through magnetic and linear, nonlinear optical investigations

This study describes the spintronic and optoelectronic improvements upon Eu substitution in Zn atomic site of the nanostructure ZnS thin films. The electron beam deposition technique has been used to deposit a series of Zn1-xEuxS thin films on a glass substrate with different Eu dopants (x = 0, 0.01, 0.03, 0.05, and 0.08). The nanostructure nature of the Eu-doped ZnS thin film has been confirmed from structural and morphology studies performed by the X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. XRD investigations further show a hexagonal-type structure with no detectable extra phases with the lattice parameter c increasing, while a decrease linearly with increasing Eu-dopant in the ZnS hosted lattice. The microstructures analysis reveals a reduction in the mean crystallite size and increasing in the lattice strain of the films with rising Eu doping. The Fourier transform infrared spectra display the existence of chemical bonds in the thin films whereas photoluminescence reveals near-band edge emission. The linear optical parameters were obtained from the analysis of the transmission data measured by the spectrophotometer technique. The results reveal that the band gap energy (EgOpt) reduces by raising ohe Eu doping ratio, which is ascribed to the structural deformation (strain and/or defects) confirmed from structural analysis, density of localized states and PL measurements. The index of refraction n was calculated using the Swanepoel method. The values were found to increase as the level of Eu doping grows, which is associated with the rise in polarizability. Wemple and DiDomenico's (WDD) model was utilized to compute the dispersive and oscillator energies (Eo, and Ed), the nonlinear absorption coefficient βc, nonlinear refractive index n2, and nonlinear optical susceptibility χ3. The results demonstrate that the adjustability of EgOpt , Eo, and Ed of ZnS: Eu films is conducted to improve the nonlinear optical characteristics, providing it well-suited for optoelectronic device implementations. On the other hand, ZnS doped with Eu film displays inherent ferromagnetic properties at room temperature, as evidenced by the results of the magnetic investigation. This finding could be attributed to the presence of sulphur defects (vacancies), as supported by photoluminescence (PL) measurements, which lead to the creation of the bound magnetic polaron. These discoveries indicate the potential of utilizing Eu-doped ZnS film in the effective development of spintronic devices.

The effects of nontoxic bio-based substances (egg white) on the performance and passivation of ZnO nanorods arrays-based light emitting devices

An innovative approach is proposed to passivate the existing defects from metal oxide semiconductors by functionalizing nontoxic bio-based substances. As a demonstration, we synthesized zinc oxide nanorods (ZnO NRs) using a hydrothermal method and incorporated chicken egg white (albumen) as a passivator to the defects. X-ray diffraction analysis of ZnO NRs shows enhanced quality and crystallinity features after incorporating albumen. XPS measurements were performed not only to introduce the chemical bonding between the albumen and the bare ZnO NRs but also specifically provide evidence of successful capping and defect passivation to the surface layer of ZnO NRs. It was observed that when the albumen was annealed, it formed sulfhydryl groups and disulfide bonds (which created disulfide bridges) from the chemical reaction in irreversible thermal denaturation. Steady-state photoluminescence of ZnO NRs showed two emission bands, i.e. near band-edge emission (NBE) and deep-level emission (DL). The NBE is significantly improved as compared to DL emission after capping and annealing the albumen, while the quenching of DL emission confirmed the reduced defects arising from the surface of ZnO NRs. The advantages and enhanced characteristics of the albumen-capped ZnO NRs led to fabricating a stable and highly efficient light-emitting device. This work opens the great potential of utilizing nontoxic and low-cost biomaterials in passivating the defects of metal oxide nanomaterials for the development of bio-inspired and stable optoelectronic devices.

Effect of aspect ratio on the nonlinear optical properties of ZnO nanorods

In this work, we synthesized ZnO nanorods with two different aspect ratios using the solution method. Morphological and crystalline structures were investigated using TEM and XRD analysis. Also investigated the effect of aspect ratio on the optical properties of ZnO nanorods. With an increasing aspect ratio of the nanorods, the absorption peak is red-shifted and near-band edge emission is suppressed. The nonlinear absorption is enhanced with the increasing aspect ratio of ZnO nanorods.

The impact of silver incorporation on the structural, morphological, and optical properties of spray-pyrolyzed cubic SnS thin films

Cubic/π-SnS phase has a strong optical absorption onset and larger dielectric constant, which is favorable for solar energy conversion. Hence, these cubic SnS phase films are gaining intense interest in the research community. However, the physical properties and thus its practical application heavily depends on the synthesis condition. We present here the effects of incorporation of silver (Ag) on the physical characteristics of cubic-SnS thin films synthesized by spray pyrolysis. Ag was incorporated at different atomic concentrations of 5, 10, 15, and 20% on cubic SnS thin films. A variety of methods were used to characterize and analyze Ag-incorporated thin films. Structural and vibrational properties were analyzed using x-ray diffraction (XRD) and Raman Spectroscopy, which shows that 5 at% Ag incorporated cubic-SnS have most desirable properties. However, on higher incorporation of Ag, the deterioration of cubic SnS and formation of secondary phases (SnS2 and Sn2S3) is evident. The existence of Sn, S, and Ag ions in the necessary oxidation state has been confirmed by XPS analysis. A direct bandgap was observed in the region of 1.79 and 1.59 eV for the SnS and Ag: SnS thin films, respectively with the aid of Ultraviolet-Visible Spectroscopy (UV–vis Spectroscopy). The Photoluminescence Spectroscopy (PL) showed the near-band edge emission peak for all the samples. The needle shape morphology was observed in Scanning Electron Microscopy (SEM) images and roughness variation is estimated using optical profilometer.

Leveraging plasmonic hot electrons to quench defect emission in metal-semiconductor nanostructured hybrids.

Modeling light-matter interactions in hybrid plasmonic materials is vital to their widening relevance from optoelectronics to photocatalysis. Here, we explore photoluminescence (PL) from ZnO nanorods (ZNRs) embedded with gold nanoparticles (Au NPs). A progressive increase in Au NP concentration introduces significant structural disorder and defects in ZNRs, which paradoxically quenches defect related visible PL while intensifying the near band edge (NBE) emission. Under UV excitation, the simulated semi-classical model realizes PL from ZnO with sub-bandgap defect states, eliciting visible emissions that are absorbed by Au NPs to generate a non-equilibrium hot carrier distribution. The photo-stimulated hot carriers, transferred to ZnO, substantially modify its steady-state luminescence, reducing NBE emission lifetime and altering the abundance of ionized defect states, finally reducing visible emission. The simulations show that the change in the interfacial band bending at the Au-ZnO interface under optical illumination facilitates charge transfer between the components. This work provides a general foundation to observe and model the hot carrier dynamics and strong light-matter interactions in hybrid plasmonic systems.

Enhancing the optoelectronic performance of CZTS thin films through cobalt doping via nebulizer-assisted spray pyrolysis technique

In the current investigation, the influence of cobalt doping on the optoelectronic performance of Copper Zinc Tin Sulfide (CZTS) thin films is analyzed. An economic route of synthesis is achieved by employing nebulizer-assisted spray pyrolysis technique. The cobalt concentration is varied from 1 to 5 wt%. The structural, morphological, optical and electrical studies were also made to understand the underlying mechanism that supports the enhancement of photo detecting-capability of these films. It is observed from the XRD studies that initially the doped cobalt replaces zinc in the CZTS lattice. When the concentration of Co was increased beyond 3 wt%, in addition to CZTS we could observe the phase of Copper Cobalt Tin Sulfide (CCTS). At higher concentration the samples exhibit the presence of two phases simultaneously with CCTS as dominant phase. Morphological images from SEM show larger distinct particles for 3% Co doped CZTS. A better absorption in the visible region is witnessed for all the films. The band gap was found to increase with the increase in the concentration of the dopant atom upto 3 wt%. The photoluminescence analysis supports a near-band edge emission around 735 nm. The photocurrent was found to be maximum for 3% Co doped CZTS sample. The rise time and fall time of Co-doped samples becomes halved when compared with the pristine sample. Our research demonstrates the potential applications of CZTS:Co thin films in the realm of photodetectors.

Rational construction of hollow ZnO@SnS2 core-shell nanorods: A way to boost catalytic removal of Cr (VI) ions, antibiotic and industrial dyes

Herein, the novel hollow ZnO@SnS2 core-shell nanorods with variable shell thickness have been synthesized by a chemical synthesis approach. The transmission electron microscopy (TEM) images signified the creation of a hollow core-shell nanostructure. The SnS2 layer coating on ZnO nanorods broadens visible light absorption and suppresses near-band edge emission of ZnO nanorods. Interestingly, the band gap (optical) of the developed ZnO nanorods decreased from 3.3 eV to 2.1 eV after the coating of SnS2 shell. Consequently, the coated hollow ZnO@SnS2 core-shell nanorods displayed a significant enhancement in catalytic activity for the decomposition of toxic industrial dyes, pharmaceutical pollutant tetracycline, and Cr(VI) ion in comparison to hollow ZnO NRs. The photon-induced charge carrier generation and separation were confirmed by the three-electrode electrochemical amperometric analysis and impedance analysis under illumination of simulated solar light (AM 1.5, One Sun). Moreover, an exceptionally higher photocurrent generation (∼10 times higher than ZnO nanorod). The improved ZnO@SnS2 core shell NRs catalytic activity was attributed to its core-shell structure, proper band structure, and effective charge carrier transfer across the core shell interface. This work offers new insights for the design and growth of visible light-active core shell nanorods for resolving environmental pollution and photocurrent generation.

A novel magnetic NiFe2O4-Ag-ZnO hybrid nanocomposite for the escalated photocatalytic dye degradation and antibacterial activities

The eco-friendly and cost-effective NiFe2O4-Ag-ZnO (nickel ferrite-silver-zinc oxide) (NFAZnO) nanocomposite was made using an easy straightforward chemical co-precipitation method and subsequent thermal treatment process. The increased UV light-driven photocatalytic performance and enhanced antibacterial activity of the nanocomposite were reported. The structural, morphological, magnetic, and catalytic characteristics of the nanocomposite were characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR), photoluminescence (PL), Raman, vibrating-sample magnetometry (VSM), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis. The results from XRD revealed that NFAZnO has a crystalline structure and EDAX elemental mapping confirmed the uniform distributed of all the elements in the matrix. Investigations into the microstructure found ultrafine grained structure of NFAZnO nanocomposite with an average crystallite size of 27.95 ± 0.38 nm as calculated from Scherrer’s formula. NFAZnO nanocomposite has a specific surface area of 13.56 m2/g, which is significantly more than ZnO (6.89 m2/g) as calculated from BET. At normal temperature, the magnetic characteristics showed the superparamagnetic behavior of the nanocomposite with saturation magnetization (Ms) value of 6.59 emu/g, remnant magnetization (Mr) value of 0.75 emu/g, and coercive field (Hc) value of 170 Oe. The Ag doping and addition of NiFe2O4 induces depletion in near-band edge emission, which lowers the rate of electron-hole recombination, according to the PL observations. Methylene Blue (MB) dye was subjected to photocatalytic degradation under the exposure to UV light, and according to the findings, NFAZnO nanocomposite exhibited the highest levels of photocatalytic activity with 98% degradation in just 60 min. The NFAZnO nanocomposite also showed enhanced antibacterial activity against Escherichia coli (E. coli) having zone of inhibition (ZOI) of about 28.9 ± 0.28 mm showing 123.5% activity as compared to control ampicillin having ZOI of 23.4 ± 0.13 mm, proving its applicability for both biomedical and environmental applications.

Sm doped ZnO-SnO2 nanocomposites with improved photo-degradation strength and antibacterial properties

In this work, we devoted our effort to synthesize rare-earth (Sm3+) doped ZnO-SnO2 nanocomposites by sol-gel method to address issues like wastewater treatment and minimization of bacterial infection. Successful formation of multi-phase nanocomposites of hexagonal ZnO and tetragonal SnO2 has been confirmed by x-ray diffraction (XRD) analysis. The effect of Sm doping is understood from the enhancement in ZnO grain growth and shift in diffraction peaks. The morphology study by FESEM reveals the variation in sample morphology with Sm doping with energy-dispersive analysis of x-ray (EDAX) study providing the confirmation on the existence of Sm ions in the crystal lattice of ZnO-SnO2 heterostructure. Transmission electron microscopic (TEM) study manifests the formation of two distinct types of particles (hexagonal & spherical) corresponding to ZnO and SnO2 which has been further clarified from the measurement of lattice spacing from the high-resolution TEM images and indexing of selected area electron diffraction (SAED) pattern. The near band edge emission (NBE) of ZnO is blue shifted along with the evolution of oxygen vacancy defects which induced new bands at 488 nm and 613 nm upon Sm doping. Further, intra-4f transitions of Sm3+ ions have also been observed at 560 nm, 590 nm and 638 nm linked to 4G5/2– 6HJ (J = 5/2, 7/2, 9/2) transitions. The Zn, Sn, O, and Sm elements are confirmed to exist in the nanocomposite according to the X-ray photoelectron spectroscopy (XPS) investigation which provided information on the chemical composition and electronic states of the material. Photocatalytic degradation study of toxic environmental dyes like methylene blue (MB), Congo red (CR) and methyl orange (MO) shows that Sm3+ ions in ZnO/SnO2 helps to enhance the degradation efficiency by the formation of Z-scheme heterojunctions between ZnO and SnO2. This allows the delay in recombination rate of the photoinduced electron/hole pairs. The antibacterial behavior of the prepared nanocomposites against E. Coli and S. Aureus has also been studied in detail which demonstrates improved antibacterial efficiency of the samples.

Effect of aging on microstructural and optical properties of sol-gel dip coated BaTiO3 thin films

This paper reports the effect of aging, thickness, and annealing temperature on microstructural and optical properties of sol-gel dip-coated BaTiO3 (BTO) thin films. The absence of any sharp peaks in the XRD pattern confirmed the amorphous nature of thin films regardless of the aging time of the solution and the thickness. Annealed BTO thin films showed the polycrystalline structure of films, which indicated the formation of a single-phase compound, and increased the intensity with respect to the annealing temperature from 550 to 650 °C. The crystallite size of annealed films increased from 19.44 nm to 23.6 nm, while the lattice strain and dislocation density decreased from 6.63 × 10−3 to 5.65 × 10−3 and 2.65 × 1011 to 1.79 × 1011 cm−2 as the annealing temperature increased from 550 to 650 °C, respectively. The bandgap of as-deposited (solution aged from 48 - 96 h) films decreased from 3.90 to 3.87 eV, while the bandgap of annealed films increased from 3.19 to 3.86 eV as the annealing temperature increased from 550 to 650 °C owing to releasing the defects of films. The near band edge emission (NBE) of all annealed samples was observed to be 361 nm which is in close agreement with the estimated bandgap. The variation of aging, thickness, and annealing temperature of BTO thin films can significantly improve the physical properties of optoelectronic applications.

Encapsulated Co-ZnO nanospheres as degradation tool for organic pollutants: Synthesis, morphology, adsorption and photo luminescent investigations

Zinc oxide (ZnO) nanostructures, both undoped and Co-doped, were synthesized through the solution combustion process. The diffraction patterns from powder XRD revealed that the materials were crystalline. The morphology of the spherically formed nanoparticles was visualized in SEM micrographs. FTIR spectra verified the existence of a defect-associated peak in Co-encapsulated ZnO (Zn0.98Co0.02O) NPs. Photoluminescence studies are undertaken. Malachite Green (MG) dye is used as a representative organic pollutant to study the adsorptive degradation of Co-doped ZnO nanomaterial. Moreover, the adsorption properties, including isotherm and kinetics, are investigated by analyzing the degradation of MG dye. Experimental parameters, such as the concentration of the MG dye, dosage and pH, were varied to ascertain favorable conditions for the degradation study. The results indicate that the MG dye is 70% degraded. After Co-doping, near-band edge emission in undoped ZnO changed into intense red defect emission and was directly correlated with changes in PL emission.

Influence of deposition temperature on structure and optical properties of spray pyrolyzed Zn0.97Nd0.03O thin films

The addition of a suitable dopant to the host matrix can alter the structure and optical characteristics of the nanostructures. Here, we studied the influence of deposition temperature on the structural and optical properties of Zn0.97Nd0.03O thin film prepared on a glass substrate using the spray pyrolysis method. The structural study revealed that XRD peak intensity decreased as deposition temperature increased, and the prominent peak intensity shifted from the (101) plane to the (002) at higher temperatures. With increasing temperature, the estimated crystallite size reduced from 16.34 to 12.12 nm. The bandgap value decreased (3.24–3.07 eV) with an increase in the deposition temperature. The photoluminescence spectra contained the peaks corresponding to Deep Level Emissions (DLE) along with Near Bandedge Emission (NBE). Thus, our findings emphasize the important role of deposition temperature in controlling and adjusting the structural and optical features of ZnO nanostructures.

Annealing-induced phase conversion on spray pyrolyzed cubic-SnS thin films

The cubic-tin sulfide (SnS) compound material is optimal for the absorber layer in photovoltaic technology. In this study, the role of annealing temperature on the physical properties of cubic-SnS thin film has been determined. The spray pyrolyzed SnS thin films were post-annealed, using the chemical vapor deposition system, at the temperature range between 350 and 500 °C The annealed films have been analyzed using a comprehensive range of characterization techniques i.e., X-ray diffraction (XRD), Raman spectroscopy, UV–Vis spectroscopy, Photoluminescence spectroscopy (PL), Field-emission scanning electron microscopy (FESEM), Energy dispersive spectroscopy (EDS) and Hall measurements. The XRD results discovered the phase deterioration of cubic-SnS at higher annealing temperatures i.e., > 350 °C. Further, the Raman analysis confirmed the cubic-SnS phase deterioration, along with the formation of SnS2 and Sn2S3 secondary phases, at higher annealing temperatures. Besides that, a band gap in the range of 1.63–1.68 eV has been obtained for the SnS thin films. The films exhibit the near-band edge emission peak in the PL spectra. Moreover, the SEM micrographs show the needle-shaped grains, and their size and distribution were increased with respect to the enhancement in annealing temperature. A considerable amount of sulfur inclusion was observed in EDS analysis and the films annealed at 450° exhibit the near stoichiometric composition ratio of Sn/S = 1.01. The hall measurement studies showed resistivity, carrier concentration, and mobility of 29.4–376.5 Ω cm, 4.2 × 1014–3.0 × 1016 cm−3 and 13.1–66.1 cm2/Vs, respectively.

Positive impurity size effect in degenerate Sn-doped GaN prepared by pulsed sputtering

This study reports on the epitaxial growth of heavily Sn-doped GaN films by pulsed sputtering deposition (PSD) and their basic characteristics, which include electrical, optical, and structural properties. Heavily Sn-doped GaN yielded a maximum electron concentration of 2.0 × 1020 cm−3 while keeping an atomically flat surface. The high electron concentration was confirmed by Raman spectroscopy measurements. X-ray diffraction analysis revealed that the Sn dopants exhibited a positive-size effect coefficient, which is opposite to conventional n-type dopants, such as Si and Ge. Furthermore, the shifts toward higher energy of optical bandgap energies and near-band edge emission peaks clearly indicated the highly degenerated nature of the PSD-grown Sn-doped GaN. These results indicate that the introduction of Sn atoms is quite promising for stress control in n-type GaN.

Tuning the diameter and optical properties of ZnO nanorods grown onto flexible substrates at different temperatures

In this study, ZnO nanorods (NRs) have been successfully grown onto polytetrafluoroethylene (PTFE) substrates at low temperatures (85, 90, 95, 100 °C) by chemical bath deposition. Growth temperature for the prepared ZnO NRs was controlled by using electrical oven equipped with digital heat control. It is found that at 95 °C, well vertically aligned ZnO NRs are obtained with enhanced structural and optical properties. The crystallite size, lattice strain, and near-band edge emission of ZnO NRs band gap energy have been significantly improved as confirmed by X-ray diffraction and photoluminescence measurements. The crystallite size increases significantly from 52 to 94 nm as the growth temperature is raised by 10 °C only, i.e., from 85 to 95 °C. Besides, the near band edge emission to deep level emission ratio has been also enhanced, from 1.328 to 4.474 for 85 to 95 °C, respectively. The obtained results highlight that the properties of ZnO NRs can be tuned and controlled through the growth temperature. Besides, this study introduced a facile cost-effective method to produce ZnO NRs for flexible based-electronic applications.