Room Temperature Photoluminescence Research Articles

Investigation of Sn-doped WO3 thin films: One-step deposition by hydrothermal technique, characterization, and photoluminescence study

Thin film technology is significant in technological progress and modern research because it allows for the production of optoelectronic devices with improved characteristics. Because of its superior chromatic efficiency, tungsten oxide (WO3) is one of the best candidates for energy-saving applications. In this study, undoped and tin (Sn)-doped WO3 films were grown on top of WO3 seed layers directly by a facile hydrothermal route at a temperature as low as 110∘C for 24[Formula: see text]h. The seed layers were also deposited on top of glass substrates using spray pyrolysis. The results of tin doping on the structural, optical, and morphological characteristics of the WO3:Sn films were studied. X-ray diffraction patterns show that peak intensities increase significantly by adding Sn and the films’ crystallinity was improved by rising Sn content. In the visible region, the average optical transmittance is around 13% and the optical bandgap changes from 2.61[Formula: see text]eV to 2.81[Formula: see text]eV, by increasing the dopant amount. Finally, the room temperature photoluminescence of samples shows intense green light emissions. The results of this research can be beneficial for the fabrication and performance optimization of electrical and optical devices such as gas sensors, electrochromic devices, and photosensors.

Temperature Dependent Photoluminescence Spectra of Nanocrystalline Zinc Oxide: Effect of processing condition on the excitonic and defect mediated emissions

Nanocrystalline zinc oxide (ZnO) with crystallite size in the range 85 -89 nm are prepared by the thermal decomposition of carbonate precursor under three different atmospheres, viz., in air ambiance, under nitrogen flow, and in vacuum. O 1s X-ray photoelectron spectra indicate that the atomic percentage of oxygen vacancies is more in the sample prepared under vacuum while adsorbed oxygen is more in the sample prepared in air ambience. Optical band gaps for the samples are in the range 3.17–3.20 eV. Room temperature photoluminescence spectra of the samples reveal band edge emission in the UV range (⁓3.18 eV) and broad defect mediated visible emission (⁓1.60–2.70 eV). Emission profile of excitonic emission at 80 K can be resolved into two free excitonic peaks at 3.42 eV (FX-A) and 3.46 eV (FX-B), donor bound excitonic peaks (D0X), peak due to transition of free electrons to acceptor levels (FA) donor-acceptor pair (DAP) emission and phonon replicas. D0X peak at ⁓3.35 eV has contribution from oxygen vacancies (Vo) and Zn interstitials (Zni). The most intense peak in the case of all the three samples is the FA peak at ⁓ 3.31 eV which has contribution from zinc vacancies (VZn). Temperature dependent variation of the dominant D0X and FA peaks in the range 80–400 K are analyzed using modified Varshni model which considers contributions from electron-phonon scattering and lattice thermal expansion. Defect dependent emission intensity is maximum at 80 K due to freeze-out of phonons and decreases with increase in temperature. The evolution of the colour of luminescence with temperature is studied using CIE plot method.

Solution-processable mixed-anion cluster chalcohalide Rb6Re6S8I8 in a light-emitting diode.

Rhenium chalcohalide cluster compounds are a photoluminescent family of mixed-anion chalcohalide cluster materials. Here we report the new material Rb6Re6S8I8, which crystallizes in the cubic space group Fm[Formula: see text]m and contains isolated [Re6S8I6]4- clusters. Rb6Re6S8I8 has a band gap of 2.06(5) eV and an ionization energy of 5.51(3) eV, and exhibits broad photoluminescence (PL) ranging from 1.01 eV to 2.12 eV. The room-temperature PL exhibits a PL quantum yield of 42.7% and a PL lifetime of 77 μs (99 μs at 77 K). Rb6Re6S8I8 is found to be soluble in multiple polar solvents including N,N-dimethylformamide, which enables solution processing of the material into films with thickness under 150 nm. Light-emitting diodes based on films of Rb6Re6S8I8 were fabricated, demonstrating the potential for this family of materials in optoelectronic devices.

Ultraviolet photo-response properties of bush-like ZnO nanorods deposited by chemical bath deposition

“Bush-like zinc oxide nanorods (ZnO NRs) has been deposited on soda-lime glass substrate via two step deposition process: seed layer deposition through Atmospheric chemical vapor deposition (APCVD) followed by chemical bath deposition (CBD) for growing NRs. Depositional parameters were carefully optimized so as to obtain a porous bush-like aggregation of ZnO NRs. X-ray Diffraction confirmed the formation of ZnO and scanning electron microscope showed bush-like aggregation of ZnO NRs. Transmission Electron Microscopy revealed that mostly non-polar {101¯0} and {112¯0} surfaces were exposed to the ambience. Room temperature Photoluminescence spectroscopy indicated the presence of mostly oxygen vacancy (VO) related defect states centered at 2.32 and 2.0 eV. Ultraviolet (UV) photo-response of the specimen was measured in air and nitrogen ambience. Higher photosensitivity (3166 % in nitrogen; 2233 % in air) but slower photo-response were observed under nitrogen ambience. It was found that UV photo-response properties of ZnO NRs were mostly a surface phenomenon dominated by adsorption-desorption mechanism of ambient oxygen molecules on the ZnO surface, mediated by surface defects related to VO, such as singly ionized state of VO. Bush-like aggregation of the ZnO NRs might have aided adsorption-desorption mechanism.”

Preparation and characterization of SbSeI thin films

Metal chalcohalides are promising candidates for next-generation technologies that include energy conversion, information storage, and quantum computing. Among them, antimony selenoiodide (SbSeI) has received rising interest for different optoelectronic devices, including photovoltaics, due to its bandgap energy, strong optical absorption, stability, and earth abundant, low-cost, and low toxicity constituents. In this work, SbSeI thin films were prepared through a two-step process. At first, antimony selenide (Sb2Se3) thin films were deposited at 300 °C (Sb2Se3-300) and at room temperature (Sb2Se3-RT) onto molybdenum covered soda-lime glass substrates by a magnetron sputtering method. The formation of SbSeI thin films was performed by isothermally annealing the as-deposited Sb2Se3 thin films in sealed quartz ampoules in the atmosphere of antimony iodide (SbI3) with the presence of 100 Torr of argon pressure. The influence of the annealing temperature and time during the iodization of different types of substrates on the morphology and composition of SbSeI thin films was investigated. The well-oriented and dense single-phase SbSeI thin films with stoichiometric composition and single-crystal micro-columnar structures were achieved by annealing Sb2Se3-RT in SbI3 atmosphere at 250 °C for 5 min under 100 Torr of Ar pressure. The room temperature photoluminescence (RT-PL) of SbSeI exhibited a broad asymmetric PL band with a maximum at 1.67 eV. The low-temperature (T = 8 K) PL study of SbSeI showed a broad and asymmetric PL band at 1.4 eV, being quite distant from the bandgap. This PL band at 1.4 eV with obtained small thermal quenching activation energy of 12.7 meV is proposed to originate from the deep donor-deep acceptor pair (DD-DA) recombination.

Epitaxial growth of high-quality Ge layers on Si with Ge2H6 under UHV-CVD conditions

Epitaxial growth of Ge films on Si(100) substrates has been studied under ultra-high vacuum chemical vapor deposition (CVD) conditions by using digermane (Ge2H6) as the precursor. It was found out that high quality layers with thicknesses beyond 500 nm could be produced at complementary metal–oxide–semiconductor compatible conditions, demonstrating low defect density, sharp and narrow x-ray diffraction peaks, as well as room temperature photoluminescence around 1550 nm. The surface roughness values are comparable to prior reduced pressure CVD results at similar growth temperatures. By employing higher growth temperatures, growth rates are significantly enhanced, resulting in much thicker layers beyond 2000 nm. Smoother sample surface could also be obtained, yielding a state-of-the-art surface root-mean-square roughness value of 0.34 nm for the as-grown sample. At the same time, after being annealed at 750 °C for 20 min, the full width at half maximum (FWHM) of x-ray diffraction 004 rocking curve spectrum of the Ge layer is as low as 88 arcseconds, which stands the best among all Ge/Si samples. The current work has provided important reference for Ge/Si growth with Ge2H6 in low pressure regime and solidified material grounding for Ge-based optoelectronics and Si photonics.

Air stable plasma passivation of GaAs at room temperature

GaAs surfaces require electrical and chemical passivation for semiconductor devices, but in order to have air stable passivation, high temperatures have been previously required in the passivation step. Here, we demonstrate air-stable, ex situ plasma passivation of GaAs using consecutive hydrogen and nitrogen plasmas at room temperature. No pre-clean using deoxidizing wet chemistry or other means is required. The hydrogen plasma step removes surface oxides and As, which leaves a Ga-rich layer that the nitrogen plasma then turns to GaN. The formed GaN layer efficiently passivates the surface. The plasma-passivated GaAs shows upto 5× room-temperature photoluminescence after 1 year, and room-temperature time-resolved photoluminescence demonstrates robust passivation even after 3 years, both comparisons to similarly aged unpassivated GaAs. Atomic force microscopy was used to confirm that the passivated surfaces can be made smooth enough for microelectronic applications. Grazing incidence x-ray diffraction indicated that the nitride films are amorphous, and energy-dispersive x-ray spectroscopy was used to estimate the nitrogen content. We used a common inductively coupled plasma reactive ion etching system for plasma passivation, thus enabling the rapid adoption of this technique.

Deposition and photoluminescence of zinc gallium oxide thin films with varied stoichiometry made by reactive magnetron co-sputtering

This paper reports on the deposition and photoluminescence of amorphous and crystalline thin films of zinc gallium oxide with Ga:Zn atomic ratio varied between 0.3 and 5.7. The films are prepared by reactive direct current magnetron co-sputtering from liquid/solid gallium/zinc targets onto fused quartz substrates; the temperature of the substrate is varied from room temperature (RT) to 800 °C. The sputtering process is effectively controlled by fixing the sputtering power of one of the targets and controlling the power of the other target by plasma optical emission spectroscopy. The method, in conjunction with oxygen flow adjustment, enables the production of near-stoichiometric films at any temperature used. The composition analysis suggests a few at% oxygen deficiency in the films. The resulting deposition rate is at least an order of magnitude higher compared to the commonly used radio-frequency sputtering from a ceramic ZnO:Ga2O3 target. Deposited onto unheated substrates, the films with Ga:Zn ≈ 2 are X-ray amorphous. Well-defined X-ray diffraction peaks of spinel ZnGa2O4 start to appear at a substrate temperature of 300 °C. The surface of the as-deposited films is dense and exhibits a fine-featured structure observed in electron microscopy images. Increasing the deposition temperature from RT to 800 °C eliminates defects and improves crystallinity, which for the films with Ga:Zn ratio close to 2 results in an increase in the optical band gap from 4.6 eV to 5.1 eV. Room temperature photoluminescence established the main peak at 3.1 eV (400 nm); a similar peak in Ga2O3 is ascribed to oxygen-vacancy related transitions. A prominent feature around 2.9 eV (428 nm) is attributed to self-activation center of the octahedral Ga-O groups in the spinel lattice of ZnGa2O4. It was found that photoluminescence from ZnGa2O4 depends significantly on the stoichiometric ratio between Ga and Zn and the deposition/annealing temperature.

Effects of parabolic barrier design for multiple GaAsBi/AlGaAs quantum well structures

The results of a comparative study on how the design of multiple quantum structures containing a parabolic barrier profile affects optical properties are presented. All quantum well (QW) structures were grown by molecular beam epitaxy (MBE) on semi-insulating GaAs substrates. The investigated samples consisted of (i) double parabolic quantum wells (type A) or (ii) multiple (two or three) rectangular quantum wells surrounded by parabolic barriers (type B). The optical quality of samples was characterized performing room-temperature (RT-PL) and temperaturedependent photoluminescence (TD-PL) measurements. The investigation aimed at the optimization of a multiple quantum well (MQW) structure design for application in the gain region of near infrared (NIR) laser diodes (LDs) revealed benefits of both double parabolic quantum wells and a mixed design (rectangular MQW with parabolic barriers). The PL band position for all samples was registered in the vicinity around 1.19 eV, which corresponds to the Bi content in QW of ~4.4%. It was shown that all structures of type A exhibit an intense emission, while the intensity of photoluminescence measured for the samples of type B depends on the number of QWs. The weaker intensity of the PL signal from two QWs inserted between parabolic barriers was explained by a larger point defect density at low temperature grown inner GaAs barriers. The room-temperature PL intensity of the structure with three GaAsBi QWs embedded in one parabolic AlGaAs barrier was the highest one. The shift of PL peak position to lower energies (1.16 eV) was attributed to the slightly higher bismuth concentration, 4.9%.

Near UV-photons excited highly pure and thermally stable Ca2B2O5: Sm3+ phosphor for filling the amber gap

Un-doped and a series of Sm3+ ion-doped orange-red emitting Ca2(1-x)B2O5:2xSm3+ (x = 0.005–0.025 mol) phosphors were synthesized and explored for their potential to fill the amber gap. Structural, thermal, spectral, luminescence, and temperature-dependent luminescence studies of the obtained phosphors were carried out to investigate the synthesized phosphors. The powder X-ray diffraction and Rietveld refinement results confirmed the formation of the monoclinic phase of Ca2B2O5. The room temperature photoluminescence study revealed that under 405 nm excitation, the prepared phosphor shows four characteristic emissions due to the 4f-4f transitions i.e.4G5/2 → 6H5/2 (568 nm), 6H7/2 (607 nm), 6H9/2 (650 nm) and 6H11/2 (712 nm). The color purity of the prepared phosphors was determined to be 97.7 % with the Commission International de l'Eclairage coordinates of (0.60, 0.40) that correspond to a strong orange-red emission located in the amber gap. Moreover, temperature-dependent luminescence studies depicted that the phosphor is highly stable, at 150 ℃ retaining 89 % of its luminescence intensity compared to room temperature. The thermal stability was further verified by thermogravimetric analysis of the phosphors which revealed high thermal stability with no weight loss upto 900 ℃. The quantum yield was determined on prepared samples and found to be 84.25 %. Thus, the promising experimental result suggests that the extremely stable orange-red emitting Ca2B2O5:Sm3+ phosphor can be a potential choice to fill the amber gap in light-emitting diodes.

Graphene nanoplatelets anchored into Ag doped spinel CoFe2O4 nanohybrid: Synthesis, structural, electrical, superior dielectric and room temperature induced ferromagnetism performance for high frequency device application

Graphene (GnPs) incorporated Ag-CoFe2O4 nanocomposite was synthesized using a simple solvothermal method using green synthesis method by okra plant extract. The prepared materials were micro-analyzed by X-ray diffraction (XRD) measurements, Fourier transform-infrared (FT-IR) spectra, Field emission scanning electron microscope (FESEM) and transmission electron microscopy (TEM) microanalysis. The average particle size obtained from XRD data was calculated to be 32.6 nm for Ag- CFO nanoparticles and 24 nm for GnPs doped Ag- CFO nanocomposite which was in good agreement with the particle size (in nm) estimated from the FESEM and TEM micrographs. The effective charge carriers transfer from the from Ag- CFO nanoferrites to graphene pallets and in case of GnPs incorporated Ag- CFO nanocomposite and the long-drawn-out recombination of electron–hole pairs were evidently shown by means of room temperature PL measurements. The photocurrent values well support the PL measurements signifying transfer of the electron-hole pairs. Light dependent Electrochemical Impedance Spectroscopy indicates the incidence of a light dependent dielectric relaxation phenomenon. Massive dielectric values with low loss suggest the GnPs doped nanohybrid to be well suited for high frequency device application. Interestingly, incorporation of GnPs alters the electronic configuration of the nanocomposites inducing ferromagnetic interaction.

Dual-Stimulus-Driven Dynamically Controllable [3]Rotaxane with Tunable Organic Room-Temperature Phosphorescence.

A dual-stimulus-driven stiff-stilbene-based dynamic [3]rotaxane has been facilely developed using the threading-stoppering strategy and exhibits reversible shuttling motions and bidirectional rotations upon encountering acid-base and distinct light stimulations, respectively. Herein, the two dibenzo-24-crown-8 macrocycles can undergo reversible switching motion between two different stations along the axle suffered from acid-base stimulation, and simultaneously, the two rotaxanes can also perform cis-trans rotations upon irradiation with distinct light. In other words, the constructed rotaxanes can conduct two modes of regular motions without interference. Interestingly, reciprocating switching motion of the rings along the axle enabled the rotaxanes to exhibit controllable and reversible photoisomerization speed, conversion yield, and quantum yield. Crucially, these rotaxanes also manifest adjustable solid-state organic room-temperature phosphorescence (RTP) and photoluminescence stimulated by dual factors (acid-base and diverse light), which are further applied in information encryption and anticounterfeiting. The presented study provides an instructive way for precisely boosting photoisomerization performances and the fabrication of dual-stimuli-induced molecular machines with functions of two-mode mechanical motions and controllable pure organic RTP switches.

Two dysprosium complexes based on TEMPO radical derivative: synthesis, structures, magnetic and fluorescent properties

A new TEMPO derivative was synthesized and two Dy-radical complexes, [Dy(hfac)3(H2O)hmb-TEMPO] (1) and [Dy(hfac)3(hmb-TEMPO)2] (2, hmb-TEMPO = 4-((2-hydroxy-3-methoxybenzylidene)amino)-2,2,6,6-tetramethyl; hfac = hexafluoroacetylacetonate), were synthesized through reacting hmb-TEMPO radical and Dy(hfac)3 with 1:1 and 1:2 ratio, respectively. The structures of 1 and 2 were elucidated by single-crystal X-ray structural analysis. Both 1 and 2 feature mononuclear structures. Nonzero out-of-phase signals were observed for both Dy derivatives, indicating single-molecule magnet behavior. The room-temperature photoluminescence spectra of 1 and 2 exhibit strong emissions in the visible region.

Development of Highest Value of the Measured Efficiency of Mesoporous Petal Shaped Europium (III) Doped Cobalt Tetroxide@Cupric Oxide Hybrid Nanomaterials for Enhanced Room Temperature Photoluminescence and Fluorescence Decay Properties.

In our work, a novel series of europium (III) (Eu3+) (5, 10 and 15 wt %) doped cobalt tetroxide@cupric oxide (Co3O4@CuO) nanomaterials (NMs) were synthesized by facile coprecipitation method. The synthesized NMs were characterized by XRD (X-ray diffraction), FT-IR (Fourier transform infrared), UV (ultraviolet)-visible absorption spectra, XPS (X-ray photoelectron), BET (Brunauer-Emmett-Teller) analytical methods. Crystal structure studies revealed the formation of polycrystalline nature with monoclinic and cubic phase. The morphology studies of Eu3+x:Co3O4@CuO (x = 5, 10 and 15 wt %) showed petal shape nanoparticles (NPs) with agglomeration. Redshift in optical absorption spectra appeared with a significant impact on the optical band gap as Eu3+ concentration increases on Co3O4@CuO bimetallic oxide NMs. The chemical composition and valence state of the elements confirmed from XPS studies detected the presence of Eu, Cu, Co, O and C elements. An increase in the pore size and surface area resulted as the Eu3+ concentration increased on Co3O4@CuO NMs. However, room temperature photoluminescence (RTPL) spectra of Co3O4@CuO bimetallic oxide NMs at two different excitations (λ excitation = 280nm, 320nm) showed sharp, strong emission intensities located at near ultraviolet (NUV) region and weak emissions detected at far ultraviolet (FUV) regions of the RTPL spectrum. Further, visible range emission intensities were displayed by Eu3+:Co3O4@CuO (5, 10 and 15 wt %) NMs when exited at 280nm. The characteristic white light emission peaks in the visible range of the RTPL spectra showed intense blue, green and orange colours. Emission intensity increases with an increase in Eu3+ concentration on Co3O4@CuO bimetallic oxide NMs. The fluorescence (FL) decay spectra of Eu3+ 10wt% and 15 wt%: Co3O4@CuO NMs showed a decay lifetime of 2.54 and 2.31ns (ns) attributed to the dynamic, ultrafast excitation energy transfer between Eu3+ (dopant) and Co3O4@CuO (host) NMs. It is proposed that enhanced RTPL emission intensity and FL decay behavior of Eu3+x:Co3O4@CuO NMs closely related to the change in the optical band gap, variation in the crystallite size, formation of more number of oxygen vacancies in the crystal structure of hybrid nanomaterials.

Synergism of spray-pyrolyzed aliovalent Ga (iii) ions and ZnO nanostructures for selective sensing of hazardous CO gas towards low ppm levels

Ga-doped ZnO (GZO) nanostructures deposited via low-cost spray pyrolysis process are employed in this study to identify low quantities of carbon monoxide gas. XRD studies reveal the single-phase wurtzite structure of ZnO thin films, thereby confirming the structural stability post-Ga doping. Raman examination discloses the vibrational characteristics and provides some early insights into the existence of defects in the films. The nanograins having well-defined grain boundaries noticed from the inspection of SEM images participate in the gas sensing performance as the site for the active adsorption of CO molecules. The defects, mainly oxygen vacancies responsible for the enhancement in the CO sensing characteristics were confirmed from room temperature photoluminescence (RTPL) spectra and XPS analysis. The CO sensing measurements reveal that 15 wt% GZO exhibited the highest sensing performance of 0.08 towards 1 ppm and 0.41 towards 5 ppm. GZO thin films had response and recovery times that were both extraordinarily quick under 40 s

Germylenes Exhibiting Solid-State Emissions that Extend to NIR.

Low-valent main group compounds that fluoresce in the solid-state were previously unknown. To address this, we investigated room-temperature photoluminescence from a series of crystals of germylenes 3-8 in this article; they exhibited emissions nearly reaching the NIR. Germylene carboxylates (3-8) were synthesized by reacting dipyrromethene stabilized germylene pyrrolide (2) with carboxylic acids such as acetic acid, trifluoroacetic acid, benzoic acid, p-cyanobenzoic acid, p-nitrobenzoic acid, and acetylsalicylic acid.

Study on the stable and efficient white-emitting Bi/Tb/Eu tridoped single-phase borate Sr3YB3O9 phosphors

Several series of novel broad band white light emitting Bi/Tb/Eu tridoped in multiple lattice sites of single-phase Sr3YB3O9 (SYBO) borate phosphors, which covered almost all visible range through mixing the separate blue, green and red emissions from dopants of Bi, Tb and Eu, respectively, were successfully obtained by using the facile and conventional solid-state reaction method under air condition. Rietveld refinements based on XRD data together with the combination match of charge and ion radius for dopants of Bi, Tb, Eu and lattice cations of Sr, Y and B show that Bi is more inclined to replace the Sr site while Tb/Eu are more likely to enter the Y site, respectively. Through spectrum analysis of photoluminescence excitation (PLE), PL and decay lifetime, the efficient energy transfer (ET) from the Bi to both Tb and Eu, and from Tb to Eu are all testified via the dipole-dipole interactions, indicating that the non-rare-earth activator Bi is acting both as the blue luminescence center and ET sensitizer, while the Tb contributes both as ET bridge and green luminescence center to better connect the Bi and Eu. The optimal tridoped white emission SYBO phosphor appears good thermal stability, which could continue to have its PL intensity above 75% at 150 °C as compared with the original room temperature PL intensity. Altogether, the single-component SYBO:Bi/Tb/Eu phosphor could be well served as potential white light phosphor for n-UV pumped wLED devices.

Mechanism of converting n-type to p-type conductivity in ZnO nanorods array films co-implanted with nitrogen and lithium ions

Here, we report a stable p-type conductivity in aqueous chemically grown ZnO nanorods array films co-implanted with N and Li ions. We have successfully achieved p-type conductivity, attaining a hole concentration as high as 8.97 × 1018 cm−3 and a mobility of 0.92 cm2.V−1.s−1 by co-implanting N and Li ions at a fluence of 5 × 1014 ions/cm2 for each ion. X-ray photoelectron spectroscopy analysis reveals the formation of NO, LiZn acceptors, and Lii-NO complexes. Furthermore, room temperature photoluminescence and SRIM simulation results confirm the presence of VZn. The formation of Lii-NO complex helps LiZn, VZn, and NO acceptors to actively participate in p-type conduction process. A detailed photoluminescence and Raman spectroscopy analyses together with simulation results reveal that, as the co-implantation fluence increases, excess Lii and implantation-induced structural disorders are produced, resulting in a decrease in the hole concentration. Our study showcases the potential benefits of developing a stable p-type component in ZnO-based electronic devices.

The microstructural evolution of sputtered ZnO epitaxial films to stress-relaxed nanorods

Epitaxial ZnO thin films and nanorods were grown on c-sapphire substrate by reactive sputtering of Zn in Ar-O2 atmosphere at substrate temperatures ranging from near room temperature to 700 °C. Scanning electron microscopy showed that with increase in substrate temperature, the morphology transformed from columnar films to vertically aligned ZnO nanorods. High resolution x-ray diffraction revealed improvement in crystalline and epitaxial quality with increase in substrate temperature, along with the decrease of edge dislocation density from 5 × 1012 cm−2 to 8 × 1010 cm−2. The films grown near room temperature showed large hydrostatic strain (∼6 × 10−3) and compressive intrinsic biaxial stress (-0.8 GPa), which decreased substantially with increase in substrate temperature, due to the desorption of excess oxygen and reduction in edge dislocation density. Above the substrate temperature of 500 °C, the intrinsic biaxial stress reversed from compressive to mildly tensile in the case of nanorods, due to the intrinsic tensile stress, originating from crystallite coalescence. Raman measurements correlate well with the changes in biaxial stress and confirm the improvements in crystallinity and epitaxial quality of nanorods grown at higher temperatures. Room temperature photoluminescence of the ZnO films showed weak near-band-edge emission, which enhanced drastically in the case of nanorods due to their superior microstructure and epitaxial quality.

Effect of Post-thermal Annealing on the Structural, Morphological, and Optical Properties of RF-sputtered In2S3 Thin Films

Indium sulfide films were deposited by radio frequency magnetron sputtering technique on soda lime glass substrate. The deposition was conducted at the temperature of 150 °C and prepared films were then thermally annealed under argon atmosphere at 350 °C and 450 °C for 30 min. The impact of post-thermal annealing treatment on the properties of the films was investigated. From X-ray diffraction analysis, the formation of the stable tetragonal β-In2S3 crystal structure was substantiated and revealed that the thermal annealing treatment at 450 °C improved the crystallization of the films. The change in surface topographies and morphologies of the films depending on the post-thermal annealing process were examined by atomic force microscopy and scanning electron microscopy techniques, respectively. The stoichiometric ratio of constituent elements in the films was obtained by elemental analysis and it was seen that the films had slightly sulfur (S) deficit composition. It was found that the concentration of S slightly increased with the thermal annealing process. The room temperature photoluminescence spectra revealed that the films included vacancies of sulfur (VS: donor) and indium (In) (VIn: acceptor), indium interstitial (Ini: donor) and oxygen (O) in vacancy of sulfur (OVs: acceptor) defects with strong and broad emission bands at around 1.70, 2.20, and 2.71 eV.