Substrate Temperature Tsub Research Articles

Combined effect of substrate temperature and laser energy density on laser ablated BiFeO3 thin films

Bismuth ferrite (BiFeO3) thin films were prepared on Pt(111)/Ti/SiO2/Si substrates by laser ablation deposition at various substrate temperature (Tsub) and laser energy density (DL). The combined effect of Tsub and DL on crystalline phase, preferential orientation and surface morphology of the films were investigated. The microstructure and morphology of the films showed a strong dependence on Tsub and DL simultaneously. BiFeO3 thin films with single phase could be prepared at Tsub-DL of 893 K−1 J/cm2, 943 K−2 J/cm2 and 963 K−3 J/cm2, respectively. Film deposited at Tsub = 963 K and DL = 3 J/cm2 exhibited better ferroelectric property due to the combination of high (111) preferential orientation, dense surface morphology and less Fe2+ content.

Effect of Ga content and growth temperature on Cu(In,Ga)Se2 thin film deposited on heat‐resistant glass substrates

AbstractCu(In,Ga)Se2 (CIGS) thin films were deposited on the Mo/heat‐resistant glasses (SS‐8, Nippon Electric Glass) by the three‐stage evaporation process. The coefficient of thermal expansion (CTE) of SS‐8 is 8.4×10–6/K, strain point of SS‐8 is 582 °C. SS‐8 has the CTE similar to that of SLG but higher thermal tolerance. Substrate temperature (Tsub) during deposition and Ga/(In+Ga) atomic ratio of CIGS thin films were controlled to 550∼600 °C and 0∼0.7, respectively. The effect of Tsub and Ga/(In+Ga) atomic ratios of CIGS films have been characterized by electron backscatter diffraction (EBSD) measurements. Grain size and ∑3 grain boundary ratio increased at higher Tsub. ∑3 grain boundary ratio was calculated from the fraction of the length of ∑3 grain boundary by the length of the total grain boundaries on EBSD image. There was the correlation among Ga contents, Tsub, grain size and efficiency. It is difficult to distinguish between effect of grain size and effect of grain boundary to efficiency. However, it is found that high Ga content up to 0.7 results in both high efficiency and ∑3 grain boundary ratio. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structural, optical and electrical properties of RuS2 ± x films, prepared by reactive magnetron sputtering

Thin layers of ruthenium sulfide (RuS2±x, laurite) were deposited on a heated substrate by reactive magnetron sputtering using a metallic ruthenium target and H2S as reactive gas. The balanced magnetron plasmas were excited by a direct-current (DC) or a radio-frequency (RF, 27MHz) power supply, respectively. To comprehensively study the influence of substrate temperature, H2S partial pressure and total pressure of Ar–H2S mixtures of different ratio on film composition, density, film structure, morphology and optical as well as electrical properties series of layers were deposited on different substrates such as titanium foil, glassy carbon and oxidized silicon wafers. Highest density of 5.5 to 5.6gcm−3 in films of 600nm thickness deposited on glassy carbon was found using a total sputtering pressure in the sputter chamber of 0.5–1.5Pa, a DC sputter power of 100W and an Ar:H2S ratio=3:1 at a substrate temperature Tsub=360°C.Layers deposited on glassy carbon at a pressure>1Pa were sulfur rich with a S-to-Ru ratio of 2.1. To elucidate phase formation during film growth in-situ energy dispersive X-ray diffraction experiments were performed employing Ti foil and thermally oxidized Si wafers as substrates. In both cases ruthenium rich (S:Ru=1.7) seed layers were formed prior to the growth of nearly stoichiometric laurite crystallites. Evaluating the width of the diffraction peaks 111 and 200 a growth of laurite grains from 20 to 40nm was inferred when increasing the substrate temperature from 150 to 450°C. The formation of larger grains is correlated with an increase in resistivity. Absorption spectra obtained from laurite layers deposited under RF sputter conditions at substrate temperatures of 360 and 430°C indicate a direct band gap of 1.8eV and a high number of defect states in the band gap.

Cu2ZnSnSe4 thin film solar cells based on a single-step co-evaporation process

Cu2ZnSnSe4 (CZTSe) thin films were deposited on Mo-coated soda–lime glass substrates by single-stage co-evaporation process and the effect of substrate temperature (Tsub) was investigated on the CZTSe thin film growth during the process. The film thickness decreased and the grain size increased with increasing Tsub. The optimum substrate temperature to obtain CZTSe films was found to be 593K. The film grown at Tsub of 773K seems to have the phase decomposition into CuxSe and ZnSe, probably because of Sn loss during the process. The best cell fabricated with a CZTSe absorber layer grown at Tsub of 593K produced 2.88% of conversion efficiency.

Structural, optical and electrical properties of low-temperature deposition Cu(InxGa1−x)Se2 thin films

In this paper, we study the structural, optical and electrical properties of polycrystalline Cu(In, Ga)Se2 (CIGS) thin films fabricated by the three-stage co-evaporation process on glass substrate at low substrate temperature (TSub). The structural, optical and electrical properties of the as-grown CIGS films have been investigated by X-ray diffraction spectra, transmittance and reflectance spectra, scanning electron microscope and temperature dependent Hall Effect measurement. The results reveal that the properties of the CIGS film deposited at low temperature strongly depend on the chemical composition. A CIGS solar cell with competitive conversion efficiency of 13.2% without anti-reflection layer using low-temperature process at TSub of 450°C has been demonstrated. Our results suggest that the CIGS absorber for high efficiency solar cells via the low TSub process has a relatively narrow compositional ratio compared to the high TSub process.

12% efficient CdTe/CdS thin film solar cells deposited by low-temperature close space sublimation

We report 12% efficient CdS/CdTe thin film solar cells prepared by low temperature close space sublimation (CSS). Both semiconductor films, CdS and CdTe, were deposited by high vacuum CSS in superstrate configuration on glass substrates with fluorine doped tin oxide (FTO) front contact. The CdTe deposition was carried out at a substrate temperature (Tsub) of ≤340 ∘C, which is much lower than that used in conventional processes (>500 ∘C). The CdTe films were treated with the usual CdCl2 activation process. Different optimal annealing times and temperatures were found for low-temperature cells (Tsub≤ 340 ∘C) compared to high-temperature cells (Tsub = 520 ∘C). The influence of the activation step on the morphology of high-temperature and low-temperature CdTe is determined by XRD, AFM, SEM top views, and SEM cross-sections. Grain growth, strong recrystallization, and a reduction of planar defects during the activation step are observed, especially for low-temperature CdTe. Further, the influence of CdS deposition parameters on the solar cell performance is investigated by using three different sets of parameters with different deposition rates and substrate temperatures for the CdS preparation. Efficiencies about 10.9% with a copper-free back contact and 12.0% with a copper-containing back contact were achieved using the low temperature CdTe process.

Influence of substrate temperature and bias voltage on properties of chromium nitride thin films deposited by cylindrical cathodic arc deposition

Chromium nitride (CrN) thin films have been deposited on high speed steel (HSS) substrates using rotating cylindrical cathodic arc deposition technique and the influence of substrate temperature (TSub) and bias voltage (VSub) on the physical/mechanical and corrosion resistance properties of the films comprehensively investigated. An increase in TSub was found to significantly influence the phase composition of films, which changed from a mixture of Cr + CrxN + CrN to predominantly CrN. This was also accompanied by an increase in droplet formation and columnar grain size. With increase in TSub over the range investigated (230 °C to 500 °C), an increase in adhesion strength by nearly 30% was observed. In contrast, change in VSub from −50 to −150 V resulted in the growth of highly dense (111) oriented CrN thin films but with relatively little change in phase constitution, adhesion strength or microdroplet formation. A change in TSub from 230 °C to 500 °C was accompanied by a nearly 50% fall in corrosion resistance, plausibly due to the concomitant decrease in pure Cr phase content and increase in macroscopic defect concentration with increase in TSub. In view of the above, CrN thin films deposited using cylindrical cathodic arc deposition technique yield better corrosion resistance and mechanical properties when grown at low TSub.

Effects of substrate temperature and film thickness on properties of CuIn3Te5 thin films and solar cells

The effects of substrate temperature (Tsub) and film thickness (dCIT) on the properties of CuIn3Te5 thin films and solar cells were investigated. CuIn3Te5 thin films (dCIT = 1.8–4.0 μm) were grown on both bare and Mo-coated soda-lime glass substrates at Tsub of 250–400 °C by single-step co-evaporation using a molecular beam epitaxy system. The microstructural properties were examined using scanning electron microscopy and x-ray diffraction. Well-developed (112)-oriented CuIn3Te5 grains were obtained by increasing the dCIT for Tsub of 250 °C. Cathodoluminescence analysis and temperature-dependent Hall measurements indicate the formation of shallow defect levels in the CuIn3Te5 films grown at higher Tsub. An optimum solar cell fabricated using CuIn3Te5 thin films (Tsub = 250 °C, and dCIT = 4.0 μm) yielded a total area (0.504 cm2) efficiency of 6.28%. Recombination mechanisms in the CdS/CuIn3Te5 thin-film solar cells are discussed on the basis of the temperature-dependent electrical properties of the films and solar cells.

Low-temperature synthesis of microcrystalline 3C-SiC film by high-pressure hydrogen-plasma-enhanced chemical transport

The synthesis of microcrystalline 3C-SiC films on glass substrates at relatively low temperatures (⩽600 °C) by the plasma-enhanced chemical transport method was carried out using a high-pressure pure hydrogen glow discharge. This method used the chemical erosion products of graphite and silicon in the hydrogen plasma as the deposition source. The temperature dependence of the etching rate of graphite and the generated volatile C-species were investigated by exposing sintered graphite to a pure hydrogen plasma at 100 Torr. Infrared absorption gas analysis indicated that the C-related film precursor generated from the graphite was mainly CH4. The etch rate of graphite reached a maximum at a sample temperature of 200 °C. The deposition rate of the SiC film prepared at a hydrogen pressure of 200 Torr increased monotonically from 14 to 29 nm min−1 with an increase in substrate temperature (Tsub) from 100 to 600 °C. The Si/C composition ratio in the films was independent of Tsub and all the film compositions were nearly stoichiometric. The prepared SiC films were microcrystalline 3C-SiC. Raman spectroscopy indicated that the film quality significantly depends on Tsub. The electrical conductivity of the films at room temperature was found to increase exponentially from 3 × 10−4 to 1.7 S cm−1 with Tsub.

Growth behavior of CuPc films by physical vapor deposition

AbstractVarious Cu‐phthalocyanine (CuPc) films were grown from physical vapor deposition on top of indium‐tin‐oxide glass substrates by controlling substrate temperature (Tsub), source temperature (Tsou), and growth time. From side‐view SEM pictures, the growth rates for these CuPc films are estimated and can be categorized into three regions. From the Arrhenius plot of growth rate versus 1/Tsub, the activation energy EA can be obtained. As Tsou = 390 °C, for region (A) with Tsub < 140 °C, the growth of CuPc films is dominated by the adhesion process with EA = 810 meV. For region (B) with 140 °C < Tsub < 320 °C, the growth is then limited by the steric character associated with the organic molecular solids with EA = 740 meV. For region (C) with Tsub > 320 °C, the re‐evaporation of the CuPc adhered molecules from the interface becomes dominant. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells

The change of morphology in mixed layers due to different substrate temperature Tsub of organic solar cells containing C60 and zinc phthalocyanine (ZnPc) is studied. Heating the substrate during deposition of the bulk heterojunction C60:ZnPc leads to a significant improvement of solar cell performance, mainly due to an increase in photocurrent and fill factor (FF). This is attributed to improved charge carrier percolation pathways within the C60:ZnPc blend. Using atomic force microscopy, scanning electron microscopy, transmission electron microscopy, organic field effect transistor, X-ray diffraction, and absorption measurements, we observe aggregation, cluster-like, and polycrystalline growth of the heated bulk layer. This provides better transport percolation paths by inducing a phase separation of the molecules. Heated blend layer with thickness of 60nm shows high performance without loss in FF. When heating the substrate to the optimum temperature of 110°C, a power conversion efficiency of 3.0% is achieved, compared to 1.4% for an identical device prepared on a substrate held at room temperature.

Preparation of Ca–Si–O films by chemical vapor deposition

Ca–Si–O films were prepared by chemical vapor deposition using calcium dipivaloylmethanates (Ca(dpm)2) and tetraethyl orthosilicate (TEOS). The effects of the Si to Ca precursor molar ratio (RSi/Ca) and the substrate temperature (Tsub) on the crystal phase, microstructure and deposition rate of Ca–Si–O films were investigated. Three main phases, i.e., CaSiO3, Ca2SiO4 and Ca3SiO5, were obtained along with the CaO and amorphous phases. At Tsub=923 to 1023K and RSi/Ca=49, Ca2SiO4 film in a single phase was obtained. The microstructure was granular and changed from a cauliflower-like to a granular type with increasing RSi/Ca. The maximum deposition rate was 240μmh−1 at Tsub=1323K and RSi/Ca=29.

Determination of band gap energy (Eg) of Cu2ZnSnSe4 thin films: On the discrepancies of reported band gap values

We demonstrate experimental data to elucidate the reason for the discrepancies of reported band gap energy (Eg) of Cu2ZnSnSe4 (CZTSe) thin films, i.e., 1.0 or 1.5 eV. Eg of the coevaporated CZTSe film synthesized at substrate temperature (Tsub) of 370 °C, which was apparently phase pure CZTSe confirmed by x-ray diffraction (XRD) and Raman spectroscopy, is found to be around 1 eV regardless of the measurement techniques. However, depth profile of the same sample reveals the formation of ZnSe at CZTSe/Mo interface. On the other hand, Eg of the coevaporated films increases with Tsub due to the ZnSe formation, from which we suggest that the existence of ZnSe, which is hardly distinguishable from CZTSe by XRD, is the possible reason for the overestimation of overall Eg.

Structural, electrical, and optical properties of reactively sputtered SnO2 thin films

SnO2 thin films prepared by reactive rf magnetron sputtering have been investigated to examine the effect of deposition parameters on its crystallinity and electrical and optical properties. Of particular interest was whether the nonequilibrium nature of sputtering could create large departures from the bulk defect properties, especially in amorphous films. Two deposition parameters were examined: substrate temperature (Tsub) and oxygen content. The films were characterized by X-ray diffraction (XRD), optical transmission, four point probe electrical conductivity, and Hall effect measurements. The crystallinity was found to be enhanced by the incease in each of the three processing variables. Below a substrate temperature of 300 °C a large processing window for depositing amorphous SnO2 was found.

Characterization of microcrystalline Si films deposited at low temperatures with high rates by atmospheric‐pressure plasma CVD

AbstractLow‐temperature and high‐rate depositions of hydrogenated microcrystalline silicon (μc ‐Si:H) films are investigated using stable plasma excited at atmospheric pressure (AP) by supplying 150‐MHz very high‐frequency (VHF) power. VHF power density, H2/SiH4 ratio and plasma gap are varied as parameters under a fixed substrate temperature (Tsub) of 220 ΩC. Increasing VHF power density and H2/SiH4 ratio is primarily important for the sufficient decomposition of source gas molecules, improving both deposition rate and film property. In addition, the plasma gap is found to be another crucial parameter in the deposition process using AP‐VHF plasma. Numerical analyses on the temperature distribution around the plasma region have revealed that the steady‐state surface temperature of the glass substrate becomes approximately 100 ΩC higher than the back surface temperature (Tsub), which is caused by the moderate surface heating effect of the AP‐VHF plasma. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Investigation of structural properties of high‐rate deposited SiNx films prepared at low temperatures (100–300 °C) by atmospheric‐pressure plasma CVD

AbstractWe have investigated the structural properties of silicon nitride (SiNx) films deposited at low temperatures (100–300 °C with very high rates (>50 nm/s) in atmospheric‐pressure He/H2/SiH4/NH3 plasma excited by a 150 MHz very high‐frequency (VHF) power using a cylindrical rotary electrode. For this purpose, SiNx films are prepared on Si(001) wafers varying NH3/SiH4 ratio, H2 concentration in the plasma and substrate temperature (Tsub). Infrared absorption spectroscopy is used to analyze the bonding configurations of Si, N and H atoms in the films. It is shown that by decreasing NH3/SiH4 ratio or increasing H2 concentration, Si–N and Si–H bond densities increase, while N–H bond density decreases. A reasonably good‐quality film showing a BHF etching rate of 28 nm/min and a refractive index of 1.81 is obtained at Tsub = 300 °C despite the very high deposition rate of 166 nm/s. However, it is found that the decrease in Tsub causes the deterioration of film quality. Further surface excitation by increasing VHF power and/or H2 concentration together with the optimization of other deposition parameters will be needed to form high‐quality SiNx films with high rates at lower temperatures (Tsub ≤ 100 °C). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation of Functionally Graded Bio-Ceramic Film by MOCVD

Functionally graded Ca-Ti-O/Ca-P-O films were prepared by MOCVD. The phases, composition and morphology of Ca-Ti-O and Ca-P-O films changed depending on the molar ratio of each precursors, total pressure (Ptot) and substrate temperature (Tsub). CaTiO3 films in a single phase were obtained at Tsub = 973 and 1073 K. CaTiO3 films prepared at 873 K had a dense and smooth surface, whereas that prepared at Tsub = 1073 K had complicated rough surface with a cauliflower-like texture. The graded texture of CaTiO3 films from columnar to fine grains was advantageous to good adherence for metal substrates. -TCP and HAp films in a single phase were obtained at Tsub = 973 and 1073 K. Both -TCP and HAp films had a dense and smooth surface. The maximum deposition rate of Ca-Ti-O and Ca-P-O films were 44 and 20 m/h, respectively, and several 10 times grater than that of sputtering method. Apatite formation rate strongly depended on the surface morphology of film. Apatite formed after 3 days on the CaTiO3 film, 14 days on the -TCP film and 6 hours on the HAp film in a Hanks’ solution.

Characterization of High-Rate Deposited Microcrystalline Si Films Prepared using Atmospheric-Pressure Very High-Frequency Plasma

Using stable plasma excited at atmospheric pressure by supplying 150-MHz very high-frequency (VHF) power, low-temperature and high-rate deposition of hydrogenated microcrystalline silicon (mc-Si:H) films is investigated. H2/SiH4 ratio and substrate temperature (Tsub) are varied as parameters under supplying an optimized VHF power density of 24 W/cm2. It is observed that increasing H2/SiH4 ratio leads to the improvement of both deposition rate and crystalline volume fraction (ICRS). It is worth to note that ICRS of approximately 72% is obtained even at H2/SiH4 = 0. The Tsub dependence of Raman crystallinity of the mc-Si:H films indicates that a highly crystallized mc-Si:H film grows even when Tsub is reduced down to 90 ºC. One of the contributing factors to this low-temperature deposition of mc-Si:H is the moderate heating effect of the growing film surface by the atmospheric-pressure VHF plasma while suppressing ion damage of the surface.

Microcrystalline Si films grown at low temperatures (90–220 °C) with high rates in atmospheric-pressure VHF plasma

This work deals with the structural properties of microcrystalline silicon (μc-Si:H) films grown at low temperatures (90–220 °C) with high rates in atmospheric-pressure He/H2/SiH4 plasma, which is excited by a 150 MHz very high frequency power using a porous carbon electrode. This plasma permits to enhance the chemical reactions both in gas phase and on the film-growing surface, while suppressing ion impingement upon the surface. Raman crystalline volume fractions of the μc-Si:H films are studied in detail as functions of film thickness and substrate temperature (Tsub). The results show that the μc-Si:H film deposited with 50 (SCCM) (SCCM denotes standard cubic centimeters per minute at STP) SiH4 has no amorphous transition layers at the film/substrate interface in spite of the high deposition rate of 6.4 nm/s, which is verified by the cross sectional observations with a transmission electron microscope. In addition, the Tsub dependence of Raman crystallinity of the μc-Si:H films indicates that a highly crystallized μc-Si:H film grows even when Tsub is reduced to 90 °C. Further systematic studies are needed for both device applications and deposition on thermally sensitive plastic materials.

Size and density control of In droplets at near room temperatures

We report on the ability to control the size and density of In droplets on GaAs(100) substrates atnear room temperatures using solid source molecular beam epitaxy. We specifically demonstratethe height, diameter and density control of In droplets as functions of substrate temperature(Tsub) and monolayer (ML) coverage. For a range of density (∼109–1010 cm−2), the growth window is revealed to be between 20 and70 °C. For a fixed ML coverage, the size and density of droplets can be controlled by controlling theTsub. For afixed Tsub, bycontrolling the ML coverage, droplet size and density can be controlled. Even at near room temperatures(20–70 °C), In atoms are extremely sensitive to surface diffusion and this enables the control of thesize and density of droplets. This study provides an aid to understanding theformation of In droplets at near room temperatures and can find applications inthe formation of quantum structures and/or nanostructures based on dropletepitaxy.