Increasing Substrate Temperature Research Articles

Properties of Iodine-Doped CdTe Layers on (211) Si Grown at High Substrate Temperatures by MOVPE

The properties of iodine-doped (211) CdTe layers grown on (211) Si substrates by metalorganic vapor-phase epitaxy at high substrate temperatures from 325°C to 450°C were studied. The growth rate of the doped layer increased with increasing substrate temperature before reaching a maximum value of 2.6 μm/h at 425°C, after which it decreased slightly. On the other hand, the room-temperature electron density showed a strong dependence on the Te/Cd precursor flow-rate ratios, where the electron density increased with a decreasing Te/Cd ratio. The highest electron density of 2.5×1018 cm−3 was obtained by growing the epilayer at a substrate temperature of 400°C and Te/Cd ratio of 0.05. This was considered to be due to decreased donor compensation at a small Te/Cd ratio. Good correspondence was observed between the results obtained from Hall measurements and photoluminescence measurements.

Effects of substrate temperature on physical properties of microrod-type multiferroic composite thin films fabricated by metal organic chemical vapor deposition

Microrod-type CoFe2O4(CFO)/Bi3.25Nd0.65Eu0.10Ti3O12(00ℓ) (BNEuT) composite thin films were fabricated by a combination of high-temperature sputtering, reactive ion etching, and metal organic chemical vapor deposition (MOCVD) on Pt(100)/MgO(100) substrates. The substrate temperature for MOCVD was varied from 450 °C to 600 °C to examine its effect on the structural, magnetic, and ferroelectric properties. The substrate temperature affects the compressive stress at the interface between the CFO and BNEuT. The surface morphology changed drastically above 550 °C. The room temperature magnetization–magnetic field hysteresis loops for the films showed clear ferromagnetic hysteresis loop and magnetic shape anisotropy. The room temperature polarization–electric field (P−E) hysteresis loops for the films showed a clear ferroelectric hysteresis loop, and slightly leaky P−E hysteresis loop. The coercive field increased slightly with increasing substrate temperature. Judging from the structural, ferromagnetic, and ferroelectric properties, the film deposited at 550 °C has potential as an excellent multiferroic material.

Improved fire resistance of boron nitride/epoxy intumescent coating upon minor addition of nano-alumina

This study presents the fire resistance results of incorporating nano-sized alumina in boron nitride reinforced epoxy-based intumescent fire-retardant coating. Structural steel substrates were coated with the developed coating and exposed at 800 °C for 2 h for furnace fire test to examine the char expansion and morphology. The fire-resistance of the coating was tested by heating the coated substrates using a Bunsen burner for 1 h. The coated substrates were tested for water absorption followed by a fire-resistance test. The furnace fire test showed that boron nitride-alumina (BNA-1) reinforced with 0.1 wt% of nano-sized alumina resulted in 45% higher char compared to boron nitride-alumina reinforced with 0.4 wt% (BNA-4) and boron nitride-alumina reinforced with 0.5 wt% (BNA-5). The increased amount of alumina improved the mass of the char. The lowest substrate temperature of 137 °C was recorded by BNA-5 with a maximum char mass of 43.89 wt%. This was considered due to formation of aluminum oxide and aluminum phosphate on the char surface, reduced char pore size, and increased amount of alumina in the gas emission. X-ray Diffraction (XRD) analysis found boron phosphate, boron nitride, and phosphoric nitride compounds were reliable in protecting the substrate at high temperature. The functional groups of char compounds were observed by FTIR. FESEM micrographs showed the presence of nano-sized alumina. XPS results also suggest that nano-alumina may react with boron nitride and ammonium polyphosphate additives, producing aluminium nitride, boron oxide, and aluminium phosphate that are beneficial to the intumescent process and fire-resistant performance. Pyrolysis GC-MS results showed reduced emission of gaseous product in BNA-5. This concluded that the addition of 0.5 wt% alumina in BNA improved char morphology and increased char mass. No changes in the microstructure and hardness of the substrate were observed after the fire test. The fire resistance of the water-immersed samples showed a small increase in substrate temperature which was within the acceptable range for structural safety.

Impact of substrate temperature on the properties of yttrium oxide thin films prepared by nebulizer spray pyrolysis technique

In this study, the yttrium oxide (Y2O3) thin films were prepared at different substrate temperatures (Tsub) 300 °C, 350 °C, 400 °C, 450 °C, and 500 °C by nebulizer spray pyrolysis technique. Structural studies confirm the formation of Y2O3 in the cubic phase. The trap rock structure was obtained from the SEM micrograph. It was observed that the yttrium oxide thin films show better particle growth at higher substrate temperatures. XRD results reveal that the crystalline nature of the Y2O3 thin films increased with the increasing of substrate temperatures, and the SEM morphology grain size will decrease in higher temperatures, which is good agreement with the XRD results. The optical bandgap varied from 2.58 to 3.6 eV among an increased substrate temperature from 350 °C to 500 °C. The recorded photoluminance spectra of Y2O3 thin films exhibit a sharp and broad emission at 310 nm and 466 nm.

A theoretical framework for comprehensive modeling of steadily fed evaporating droplets and the validity of common assumptions

A theoretical framework is established to model the evaporation from continuously fed droplets, promising tools in the thermal management of high heat flux electronics. Using the framework, a comprehensive model is developed for a hemispherical water droplet resting on a heated flat substrate incorporating all of the relevant transport mechanisms: buoyant and thermocapillary convection inside the droplet and diffusive and convective transport of vapor in the gas domain. At the interface, mass, momentum, and thermal coupling of the phases are also made accounting for all pertinent physical aspects including several rarely considered interfacial phenomena such as Stefan flow of gas and the radiative heat transfer from interface to the surroundings. The model developed utilizes temperature dependent properties in both phases including the density and accounts for all relevant physics including Marangoni flow, which makes the model unprecedented. Moreover, utilizing this comprehensive model, a nonmonotonic interfacial temperature distribution with double temperature dips is discovered for a hemispherical droplet having internal convection due to buoyancy in the case of high substrate temperature. Proposed framework is also employed to construct several simplified models adopting common assumptions of droplet evaporation and the computational performance of these models, thereby the validity of commonly applied simplifying assumptions, are assessed. Benchmark simulations reveal that omission of gas flow, i.e. neglecting convective transport in gas phase, results in the underestimation of evaporation rates by 23–54%. When gas flow is considered but the effect of buoyancy is modeled using Boussinesq approximation instead of assigning temperature dependent density throughout the gas domain, evaporation rate can be underestimated by up to 16%. Deviation of simplified models tends to increase with increasing substrate temperature. Moreover, presence of Marangoni flow leads to larger errors in the evaporation rate prediction of simplified models.

Co-Evaporated p-i-n Perovskite Solar Cells beyond 20% Efficiency: Impact of Substrate Temperature and Hole-Transport Layer.

For methylammonium lead iodide perovskite solar cells prepared by co-evaporation, power conversion efficiencies of over 20% have been already demonstrated, however, so far, only in n-i-p configuration. Currently, the overall major challenges are the complex evaporation characteristics of organic precursors that strongly depend on the underlying charge selective contacts and the insufficient reproducibility of the co-evaporation process. To ensure a reliable co-evaporation process, it is important to identify the impact of different parameters in order to develop a more detailed understanding. In this work, we study the influence of the substrate temperature, underlying hole-transport layer (polymer PTAA versus self-assembling monolayer molecule MeO-2PACz), and perovskite precursor ratio on the morphology, composition, and performance of co-evaporated p-i-n perovskite solar cells. We first analyze the evaporation of pure precursor materials and show that the adhesion of methylammonium iodide (MAI) is significantly reduced with increased substrate temperature, while it remains almost unaffected for lead iodide (PbI2). This substrate temperature-dependent evaporation behavior of MAI is also transferred to the co-evaporation process and can directly influence the perovskite composition. We demonstrate that the optimal substrate temperature window for perovskite deposition is close to room temperature. At high temperature, not enough MAI for precise stoichiometry is incorporated even with very high MAI rates. While, at temperatures below -25 °C, the conversion of MAI with PbI2 is inhibited, and an amorphous yet unreacted film is formed. We observe that perovskite composition and morphology vary widely between the organic hole-transport layers (HTLs) PTAA and MeO-2PACz. For all substrate temperatures, MeO-2PACz enables higher solar cell PCEs than PTAA. Through the combination of vapor-deposited perovskites and a self-assembled monolayer, we achieve a stabilized power conversion efficiency of 20.6%, which is the first reported PCE above 20% for evaporated perovskite solar cells in p-i-n architecture.

Studying the Structural, Morphological, Optical, and Electrical Properties of CdS/PbS Thin Films for Photovoltaic Applications

The cadmium sulfide (CdS) and lead sulfide (PbS) materials have been chosen in order to boost solar energy conversion from ultraviolet region to the near-infrared (NIR) spectral region. These materials belonging to the II–VI group have suitable direct band gaps and in solar energy conversion. CdS and PbS layers are used as window and absorber materials, respectively, in solar cells. This paper presents structural, morphological, and optical properties of PbS and CdS thin films prepared by chemical spray pyrolysis at different temperatures as well as its photovoltaic performance. The X-ray diffraction results show the PbS films have cubic structure and CdS films have hexagonal structure. FESEM measurements reveal the films have homogeneous surfaces with spherical particles. Optical analyses exhibit the optical band gap redshifts as the substrate temperature increases. Illumination current density–voltage test of ITO/CdS/PbS/Au heterojunction with different thicknesses of PbS layer has been evaluated. The optimal results are obtained in ITO/CdS/PbS/Au solar cell where thickness of PbS layer is of 0.9 μm with maximum short circuit current, open circuit voltage, and fill factor as well as highest efficiency.

Effect of temperature and deposition rate on the surface morphology of thin Al metal films on glass substrate: Application in Solar Cell

Thin Al films with thickness around 300nm are grown on glass substrate by thermal evaporation technique. The temperature of the substrate has varied in between 2500C - 3000C and the deposition rates are varied in the range of 0.5nm/s to 3nm/s. During the evaporation process, the vacuum level as lower as 10-5 Pa is maintained. The surface morphology/roughness of the thin films are studied using Scanning Electron Microscopy (SEM) technique. SEM images have shown that the surface roughness increases with the increasing deposition rate. The mean grain size of the metallic films on glass substrate increases from 25nm to 60nm (approx.) with the increasing deposition rate. In addition to that, the study reveals increasing substrate temperature will increase the average surface roughness.

Influence of high dielectric HfO2 thin films on the electrical properties of Al/HfO2/n-Si (MIS) structured Schottky barrier diodes

The presence of high dielectric material between the metal and semiconductor interface played a significant role in many electronic device applications. In this work, we have fabricated Al/n-Si Schottky barrier diode by introducing nanostructured HfO2 films as a middle layer with different substrate temperatures via JNSP technique. XRD analysis revealed significant phase change from amorphous to monoclinic phase while increasing substrate temperature. Through FESEM images, a porous structure and irregular sphere-like grains were observed. The optical energy band gap of the HfO2 films has found to vary from 3.41 to 3.73 eV respectively. From I–V characterization, the obtained diode ideality factor was found to be decreasing and their corresponding barrier height increased with respect to substrate temperature. Particularly, the diode fabricated at 600 °C exhibited better ideality factor value (n = 3.4). We observed that the presence of highly dielectric films strongly improved the diode parameters, especially at high substrate temperature.

The Properties of Cd1−xZnxTe Films Prepared by RF Magnetron Sputtering

Cd1−xZnxTe films were prepared on borosilicate glass substrate using RF magnetron sputtering in this work. The effects of sputtering power, sputtering pressure and substrate temperature on the properties of the films were investigated in detail. The films were annealed in CdCl2 atmosphere for 2 h at 200 °C, 300 °C, and 400 °C, respectively. The effects of annealing treatment on the properties of the films were also investigated. The properties of the films were investigated by x-ray diffraction, atomic force microscopy, and current–voltage (I–V) characterization. The results indicate that crystalline quality and the average grain size of the films increases with the increases of sputtering power. The grain size of the films becomes larger as the substrate temperature increases. The Zn concentration of the films rises as the sputtering pressure increases. After annealing, the grain size of the films becomes larger, furthermore, the resistivity decreases.

Phase evolution, morphological, optical and electrical properties of femtosecond pulsed laser deposited TiO2 thin films

In this paper, we report anatase and rutile titanium oxide (TiO2) nanoparticulate thin films fabricated on silica and Indium Tin Oxide (ITO) substrates using femtosecond pulsed laser deposition (fs-PLD). Depositions were carried-out at substrate temperatures of 25 °C, 400 °C and 600 °C from anatase and rutile phase target materials. Effect of substrate temperature on the surface morphology, microstructural, optical, and electrical properties of these films were systematically investigated by using various range of measurements such as scanning electron microscopy, (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Ultraviolet–visible-near infrared (UV–Vis–NIR) spectroscopy, and Hall Effect measurements. It is observed that the TiO2 thin films surface are predominated with nanoparticulates of diameter less 35 nm, which constitute about ~ 70%; while the optical bandgaps and electrical resistivity decrease with increasing substrate temperature. A mixed-phase (anatase/rutile) TiO2 thin film was produced at a substrate temperature of 400 °C when samples are fabricated with anatase and rutile target materials. The results of this study indicate that the structural and crystallinity, optical, and electrical properties can be controlled by varying fs-PLD process parameters to prepare TiO2 thin films, which are suitable for applications in photovoltaics, solar cells, and photo-catalysis.

Formation and suppression of hydrogen blisters in tunnelling oxide passivating contact for crystalline silicon solar cells

The formation of hydrogen blisters in the fabrication of tunnelling oxide passivating contact (TOPCon) solar cells critically degrades passivation. In this study, we investigated the formation mechanism of blisters during the fabrication of TOPCons for crystalline silicon solar cells and the suppression of such blisters. We tested the effects of annealing temperature and duration, surface roughness, and deposition temperature on the blister formation, which was suppressed in two ways. First, TOPCon fabrication on a rough surface enhanced adhesion force, resulting in reduced blister formation after thermal annealing. Second, deposition or annealing at higher temperatures resulted in the reduction of hydrogen in the film. A sample fabricated through low-pressure chemical vapor deposition at 580 °C was free from silicon–hydrogen bonds and blisters after the TOPCon structure was annealed. Remarkably, samples after plasma-enhanced chemical vapor deposition at 300, 370, and 450 °C were already blistered in the as-deposited state, despite low hydrogen contents. Analysis of the hydrogen incorporation, microstructure, and deposition mechanism indicate that in plasma-enhanced chemical vapor deposition (PECVD) deposition, although the increase of substrate temperature reduces the hydrogen content, it risks the increase of porosity and molecular-hydrogen trapping, resulting in even more severe blistering.

Characteristics of polymer semiconductor film prepared by evaporative spray deposition using ultra-dilute solution (ESDUS): application to polymer photovoltaic cells

Organic photovoltaics (OPV) with junction controlled structure are prepared by the evaporative spray deposition using ultra-diluted solution (ESDUS) method with different donor polymer(p) and acceptor fullerene(n) ratio solution. In order to demonstrate the ideal junction, we fabricate the polymer solar cells with single junction(p/n), pin-layered junction (pin) or bulk-heterojunction (BHJ) active layer. The photovoltaic performance is dramatically varied with its junction. And the pin junction has best performance under the sunlight due to its good carrier generation and transport. And also we investigated the temperature dependence of the active layer morphologies at each substrate temperature 60 − 160 °C during its spray-depositing. The domain of active layer became smaller with increasing substrate temperature. The pin-layered cell sprayed at 120 °C gives best photovoltaic performance. Thus, ESDUS enables us to control the junction and morphologies of active layer.

Evaporation of sessile ethanol-water droplets on a critically inclined heated surface

The evaporation of a binary sessile ethanol-water droplet on an inclined substrate is studied experimentally just below the critical sliding angles for different substrate temperatures. A customized goniometer equipped with a CMOS camera and an infrared (IR) camera is used. The droplet is observed to remain pinned in the advancing side during the evaporation process, while the receding side contracts. The asymmetry in the advancing and receding contact angles of the droplet on inclined substrate results in complex thermo-solutal Marangoni convection that is captured through IR images. The droplet exhibits two distinct oscillatory water-rich cold regions around the advancing contact line during the early stage of evaporation, while the more volatile and lighter ethanol creates a hotter and rapidly evaporating cell near the receding side. As ethanol evaporates away, the ethanol rich cells collapse producing thermal pulsations along the incline. Subsequently, the thermal patterns become similar to that of the pure-water droplet. It is also observed that the thermo-solutal driven oscillatory convection increases with increasing substrate temperature. Despite the complexity in convection dynamics, the evaporation rate exhibits a universal behavior in the normalized time at different substrate temperatures which can be represented by piecewise linear fits at the early and late stages of evaporation.

Characteristic studies on the ZrCuAlSi multi-component thin-film metallic glasses fabricated by pulsed laser deposition

(Zr47Cu44Al9)100−xSix (x = 0, 0.5, 1.5 and 2.5 at%) thin-film metallic glasses (TFMGs) were deposited at glass substrate by pulsed laser deposition. The influence of Si content and substrate temperature on the microstructure, optical and electrical properties was investigated. After adding Si in the Zr47Cu44Al9 system, the transmittance of the films enhances obviously, especially in the near-infrared region. The resistivity increases and becomes more sensitive to the temperature due to Si addition. With increasing substrate temperatures from room temperature to 430 °C, (Zr47Cu44Al9)98.5Si1.5 films display fully amorphous structure. Appropriate substrate temperature drastically decreases the resistivity of films without degrading the transmittance. (Zr47Cu44Al9)98.5Si1.5 TFMG deposited at 330 °C exhibits the visible transmittance of 49.38%, the infrared transmittance of 80.27% and the resistivity of 7.62 mΩ cm, which are useful properties for their potential applications in infrared technology with the high requirement of radiation resistance and corrosion resistance.

Iron silicides formation on Si (100) and (111) surfaces through theoretical modeling of sputtering and annealing

The iron silicides formation during epitaxial film grown process on the (100) and (111) silicon surfaces were investigated using molecular dynamics (MD). The iron and silicon atom deposition rate and silicon substrate temperature influence on the formed iron silicide structure and stoichiometric composition were studied in detail. During the growth of iron silicide crystal structure significant diffusion of the substrate atoms into the forming BCC core occurs, this intensifies with the substrate temperature increase, and the ratio of substrate atoms inside the Fe3Si phase reaches nearly 12%. The BCC structure formation is less active on the (100) surface, and at the temperatures as low as 26 °C and 300 °C the iron silicide crystal phase does not form at all. However, with the temperature increase or the deposition rate decrease, the crystal structure formation processes occur more actively in both cases of (100) and (111) surfaces. Thus, the effect of the deposition rate decrease is identical to the temperature growth. It was shown that the formation of the structured B2 phase of iron silicide in buffer layer between the film and the substrate leads to the inhibition of the mutual diffusion of iron and silicon atoms.

Crystallite size and intrinsic strain contribution in band gap energy redshift of ultrasonic-sprayed kesterite CZTS nanostructured thin films

The effect of crystallite size and intrinsic strain on the band gap shift of ultrasonically sprayed Cu2ZnSnS4 films has been discussed. The films have been deposited over glass substrates under various temperatures, namely 280, 320, 360, and 400 °C. X-ray diffraction revealed the presence of kesterite single phase with preferential orientation along (112) plan. The band gap energy decreases from 1.84 to 1.51 eV with increasing substrate temperature, where an increase in crystallite size from 5.92 to 21 nm was observed as well as relaxation of intrinsic strain from 6.82 × 10−3 lines−2 m−4 to 2.11 × 10−3 lines−2 m−4. A concurrency behavior between crystallite size and intrinsic strain effect on the band gap shift has been noticed. The intrinsic strain effect is dominant in higher substrate temperature and that of crystallite size in low temperatures owing to the presence of a strong quantum confinement.

Reactive Sputtering Growth of Indium Nitride Thin Films on Flexible Substrate Under Different Substrate Temperatures

Indium nitride (InN) thin films were deposited on kapton polyimide substrate by using reactive gas-timing radio frequency (RF) sputtering technique. An indium target with purity of 99.999% was used. Throughout this work, the RF power and gas ratio of argon and nitrogen were maintained at 60 W and 40:60 (Ar:N2), respectively. The substrate temperature was varied from room temperature to 300°C. The surface morphology, structural and electrical properties of the deposited thin films as a function of the substrate temperature were investigated. All the deposited InN thin films have wurtzite crystal structure with preferred orientation along the (101) direction. The InN (101) peak becomes stronger and sharper as the substrate temperature increases from 100°C to 300°C. In addition, the packing density of the grains increases as the substrate temperature increases. The deposited InN films exhibit n-type conductivity behavior and its Hall mobility increases from 720 cm2/V-s to 2670 cm2/V-s as the substrate temperature increases from room temperature to 300 °C. These results imply that nucleation and crystal growth as well as the crystalline quality were improved at higher substrate temperatures. All the results lead to conclude that the optimal substrate temperature for the deposition of InN was 300 °C.

Highly Selective Dimethylamine Sensing Performance of TiO₂ Thin Films at Room Temperature.

To date, reports on metal oxide semiconductors for selective detection of dimethylamine (DMA) is in scarce. Hence in our study, we report titanium oxide (TiO₂) as a promising candidate for tuned selectivity towards DMA. Highly uniform TiO₂ thin films were successfully deposited on glass substrates using reactive dc magnetron sputtering at various substrate temperatures. Polycrystalline nature of rutile TiO₂ was confirmed by X-ray diffraction technique (XRD). The uniform surface morphology of the sputtered TiO₂ thin films was revealed by Field Emission Scanning Electron Microscopy (FESEM). An upsurge in optical band gap from 3.18 to 3.4 eV was observed with increase in substrate temperature. The sensing studies of the sputtered TiO₂ thin films exhibited a significant sensor response towards the lower concentration of DMA at ambient temperature. It is deemed that this work will provide an insight to develop DMA sensors based on TiO₂ thin films.

Structural, Morphological, and Optical Properties of Iron Doped WO3 Thin Film Prepared by Pulsed Laser Deposition

The iron doped tungsten-oxide (Fe and WO3) thin film with different morphology and crystalline structures were obtained for different substrate temperatures at the oxygen pressure of 14.66 Pa. The Fe-doped WO3 films were deposited by pulsed laser deposition (PLD). The influence of the substrate temperature on the surface and on the crystalline phases of the films was studied. The XRD (X-ray diffraction) analysis indicates the changing in the crystalline phases from γ-monoclinic to a mixture of γ-monoclinic and hexagonal phases dependent on the temperature of annealing and as-grown films. Related to the as-grown and annealing films conditions, the SEM (scanning electron microscopy) shows a change in the image surface from nanoneedles, to nanoporous, and further to long nanowires and broad nanobands. Energy-dispersive X-ray spectroscopy (EDX) shows the elemental composition of the Fe-doped WO3 film as-grown and after annealing treatment. Raman spectroscopy presented the main vibration mode of the Fe-doped WO3 thin film. The optical energy bandgap of the films is decreasing as the substrate temperature increases.