Monosulfide Thin Films Research Articles

Role of triethanolamine complexing agent in chemical bath deposition of tin sulfide thin films: Microstructural and optical properties

This paper reports the experimental results studying the structure, optical and dielectric properties of tin monosulfide thin films. Tin monosulfide (SnS) films were deposited on glass substrate by chemical bath deposition to study the role of triethanolamine (TEA: complexing agent) concentration on the film properties. X-ray diffraction spectra reveal that the films exhibit mainly cubic phase which remain stable over the range of TEA concentration (3.0 M − 5.0 M). FTIR spectra indicate the S-Sn bond stretching in all films. Raman spectroscopy analysis shows the presence of minor trace of secondary SnS2 phase (along with main cubic π-SnS phase) in all films. SEM micrographs show cauliflower-like surface morphology of all films. Optical results reveal that the films possess high value of absorption coefficient (≥105 cm−1) in the visible region. Direct optical transition behavior is observed in all films. From Tauc plots, the calculated optical band gap (Eg) varies from 1.79 eV to 1.91 eV with the variation in TEA concentration. The dielectric constant, refractive index and an extinction coefficient are also calculated and observed to decrease with increasing TEA concentration. Experimental results suggest that an appropriate concentration of a complexing agent (TEA) can be chosen to obtain crystalline films without deterioration of crystalline structure and phase, not effecting Eg significantly.

Synthesis of submillimeter-scale laterally-grown germanium monosulfide thin films and their electro-optic applications

Submillimeter-scale laterally-grown germanium monosulfide thin films and gate voltage-dependent hysteresis response of fabricated GeS field-effect transistor arrays.

Phase control in solution deposited tin monosulfide thin films: the role of Pb2+ cations

A “single pot” solution deposition methodology was employed to fabricate phase controlled lead-doped tin monosulfide thin films.

Influence of S/Sn ratio on microstructural, morphological and optical properties of tin monosulfide thin films

Tin monosulfide (SnS) is promising candidate as a photovoltaic material due to its large tuneable physical properties, which can be achieved by altering the synthesis conditions. Synthesis of pure phase SnS with high crystallinity is really a challenging issue for researchers. The present work mainly focuses on synthesis SnS nanoparticles using a direct reaction approach and manipulate their properties by altering S content. The formation of orthorhombic α-SnS nanoparticles with preferential orientations along the (400) direction has been confirmed by X-ray Diffraction (XRD). Energy Dispersive X-ray analysis (EDX) is used to investigate the elemental composition of all synthesised SnS nanoparticles. SnS nanoparticles of different compositions are deposited on glass substrate using thermal evaporation. The crystal structures of deposited SnS thin films are analysed by XRD. Fourier Transform Infrared (FTIR) spectra indicate the Sn–S bond stretching around 580 - 950 cm−1 including a broad peak around 950 - 1450 cm−1. The Raman spectrum of all SnS thin films shows peaks at 136 ± 2, 190 ± 2, and 231 ± 2 cm−1 assigned as Ag mode of SnS. The presence of excess sulphur impacts on the surface morphology of the SnS thin film and is noticeable in FESEM images. UV–Vis–NIR absorbance spectrum revealed that the visible-light absorption of the SnS thin film was significantly high (α ∼105 cm−1). The calculated direct bandgaps of SnS thin films are found to increase (1.63–2.43 eV) with increasing sulphur ratio.

Sulfurization temperature dependent properties of tin mono-sulfide thin films

Tin mono-sulfide thin films were prepared using a two-step process consisting of DC sputtered deposition of Sn precursors over glass substrate held at 150 oC, followed by sulfurization for 1 hour at different temperatures ranging from 250 oC to400 oC. The influence of the sulfurization temperature on resultant films was studied in terms of its structure, morphology and opto-electronic properties. X-ray diffraction study revealed that the films sulfurized at lower temperature (~250 oC) had prominent SnS2 phase in addition to SnS. A single-phase tin mono-sulfide planes corresponding to orthorhombic structure has been observed at 300 oC and found to be highly crystalline at 350 oC. Further, three distinct Raman modes observed at 95, 190 and 218 cm-1 for Sn precursors sulfurized at 350 oC, strongly supporting the formation of single phase SnS. The optimized SnS film showed a direct band gap of 1.35 eV with an absorption coefficient of 5 x 104 cm-1. The valence states of Sn (+2) and S (-2) determined from X-ray photoelectron spectroscopy analysis for Sn precursors sulfurized at 350 oC, indicating the existence of SnS. These films had stoichiometric atomic ratio of Sn/S ~ 1 with surface roughness of 20 nm. All the films have shown p-type conductivity and the Sn precursors sulfurized at 350 oC exhibited relatively high conductivity of 0.947 x 10-2 (Ω cm)-1. The optoelectronic properties of SnS films reported in the present work would be highly suitable for device fabrication and promising as an alternative absorber for thin film solar cells. Copyright © 2017 VBRI Press.

Effect of Sulfurization Time on the Physical Properties of Tin (II) Monosulfide Thin Films

Tin (II) monosulfide (SnS) films were prepared via sulfurization using sputtered Sn precursors of the tin metal layers in the presence of elemental sulfur vapor as a function of sulfurization time (ts) in the range of 30–180 min while keeping other parameters constant. The properties of these sulfurized layers were examined through suitable characterization techniques. The diffraction patterns exhibited various planes with the orientations (110), (120), (021), (101), (111), (211), (131), (210), (141), (002), (112), (122), and (042) corresponding to orthorhombic SnS at ts ≤ 90 min. However, for ts ≥ 120 min, the diffraction patterns showed a single (111) plane and enhanced the intensity of the peak with the increase of ts up to 150 min; with further increase of time, the peak intensity was found to decrease. The Raman spectra of films sulfurized at various ts showed modes at 95, 162, 189, 219, and 284 cm−1 for times were lower than 120 min and 95, 189, and 219 cm−1 for ts ≥ 120 min, related to SnS. In the transmittance spectra of the sulfurized films, it is clear that the film grown at ts = 30 min had higher transmittance, and with the increase of ts to 120 min, transmittance was decreased. For further extension of ts to 150 min, a sharp falling of the absorption edge was observed.

Effect of source temperature on the electrical transport, microstructural and optical properties of tin monosulfide thin films prepared by close spaced sublimation method

Tin monosulfide (SnS) thin films were prepared by close spaced sublimation method at three different source temperatures of 550, 575 and 600°C. Structural, textural and compositional features were investigated by XRD, SEM, EDS and Raman spectroscopy. From absorption spectra, direct band gap increased from 1.18 to 1.23 eV with increasing source temperature. Electrical resistivity, Hall constant, carrier concentration and mobility values of the films prepared at source temperature of 600°C were 0.54 Ω.cm, 40.76 cm3/C, 1.537#x00D7;1017 and 75.48 cm2/(V.s), respectively. The temperature-dependent conductivity was performed in the temperature range of 50-300 K. It was shown that three types of conduction mechanisms can be expected: thermionic emission passing through grain boundary at high temperature range (240-300 K), the Mott variable-range hopping (Mott-VRH) at low temperature range (135-235 K) and the Efros-Shklovskii variable-range hopping (ES-VRH) at very low temperature range (80-130 K).

Facile strategy for the formation of tin monosulfide thin films by rapid thermal annealing

A simple but facile way to form phase-pure tin monosulfide (SnS) thin films is proposed using a rapid thermal annealing (RTA) process. SnS powder and substrate were loaded into a vacuum-sealed quartz ampoule and treated by RTA at 500°C for 10min. This allowed the formation of single-phase SnS films. The densely packed morphology and phase purity of the films were confirmed by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. A preliminary thin-film solar cell was fabricated that demonstrated the efficiency of 0.42%.

Grain size, texture, and crystallinity in lanthanum monosulfide thin films grown by pulsed laser deposition

We report a detailed investigation of the growth of lanthanum monosulfide (LaS) thin films by pulsed laser deposition on (001) magnesium oxide (MgO) substrates in a background of H2S for the purpose of optimizing their crystallinity, texture, and grain size. A variety of films were grown while varying the laser repetition rate, the temperature of the substrate, and the partial pressure of H2S. The thin films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy, and high resolution transmission electron microscopy. Films grown at 500°C with a H2S background pressure of 3.4×10−4Pa and a laser repetition rate of 8Hz produced the LaS film with the largest grains whose size averaged 293nm. The XRD pattern of these films revealed that their orientation was predominantly (200). AFM images of the surface of these films showed large plate-like grains. This contrasts with the fine grain structure observed in LaS films grown at a lower substrate temperature and lower H2S pressure.

Tin Monosulfide Thin Films Grown by Atomic Layer Deposition Using Tin 2,4-Pentanedionate and Hydrogen Sulfide

Tin monosulfide (SnS) was grown by atomic layer deposition (ALD) using sequential exposures of tin(II) 2,4-pentanedionate (Sn(acac) 2 ) and hydrogen sulfide (H 2 S). In situ quartz crystal microbalance (QCM) studies showed that the SnS ALD mass gain per cycle was 11-12 ng/cm 2 at 175 °C on a gold-covered QCM sensor. Using a film density of 5.07 g/cm 3 determined by X-ray reflectivity measurements, these mass gains are equivalent to SnS ALD growth rates of 0.22-0.24 A/cycle. The ratio of the mass loss and mass gain (|Δm 2 / Δm 1 |) from the H 2 S and Sn(acac) 2 reactions was |Am 2 /Δm 1 | ~ 0.32 at 175 °C. This measured ratio is close to the predicted ratio from the proposed surface chemistry for SnS ALD. The SnS ALD was self-limiting versus the Sn(acac) 2 and H 2 S exposures. The SnS ALD growth rate was also independent of substrate temperature from 125 to 225 °C. The SnS ALD growth on Al 2 O 3 ALD substrates displayed nucleation problems and smaller growth rates. These differences may be caused by site blocking by the Al(acac)* surface species. X-ray fluorescence studies confirmed a Sn/S atomic ratio of ~1.0 for the SnS ALD films. X-ray photoelectron spectroscopy measurements revealed that the SnS ALD films contained oxygen impurities at 15-20 atom % after air exposure. These oxygen-containing SnS ALD films displayed a band gap of ~ 1.87 eV that is higher than the SnS bulk value of ~1.3 eV. In addition, these SnS ALD films produced very weak photoluminescence at room temperature. SnS ALD may be useful to fabricate photovoltaic or solar conversion devices.

Field emission from lanthanum monosulfide thin films grown on the (100) magnesium oxide substrates

Lanthanum monosulfide (LaS) films were grown by pulsed laser deposition on the (100) magnesium oxide (MgO) substrates at an elevated substrate temperature and in a background gas of H2S. The thin films have been characterized by x-ray diffraction (XRD), atomic force microscopy (AFM), and high resolution transmission electron microscopy. The film surface is composed of grainlike features with an average size of approximately 34nm. The root-mean-square variation of the film surface roughness measured over a 2×2μm2 area by AFM was found to be approximately 1.5nm. XRD data indicate that the average size of the nanocrystalline grains in the film is about 26nm, which is about twice the size of the grains found in LaS thin films deposited at room temperature on Si. The field emission (FE) properties of the films have been characterized by scanning anode field emission microscopy and are interpreted in terms of a recently developed patchwork FE model. The FE data indicate that there is roughly a seven times increase in emission area due to the (100) patch areas outcropping the surface for LaS∕MgO compared to LaS∕Si thin films.

Chemistry of delta-SnS: New Tin Monosulfide Polymorph Thin Films from Galvanostatic Electrodeposition

Galvanostatic deposition of tin monosulfide thin films (d-SnS phase) on transparent conductive glass was studied. Uniform films were deposited in aqueous baths with tartaric acid. Cyclic voltammetry suggested tin-tartrate complexes were crucial to film electrodeposition, suppressing tin metal reduction in favor of sulfur species reduction. X-ray diffraction showed primitive orthorhombic symmetry for d-SnS (a = 11.380 Aå, b= 4.029 Aå, c = 4.837 Aå). d-SnS was converted to a-SnS (a = 11.172 Aå, b = 3.994 Aå c = 4.311 Aå) following annealing at ~ 270 {degree sign}C in Ar(g). Characterization of the as-deposited films confirmed 1:1 Sn/S. The d-SnS structure was consistent over a range of deposition temperatures (50, 70, and 90 {degree sign}C). UV/Vis spectrometry confirmed increased disorder in films deposited at 50 {degree sign}C. A direct allowed optical band gap transition of lower energy for the d-SnS phase (1.05 eV) was obtained compared to that for a-SnS (direct, 1.2 eV).

Patchwork field emission properties of lanthanum monosulfide thin films

The field emission properties of lanthanum monosulfide (LaS) films, deposited on Si substrates by pulsed laser deposition, have been thoroughly analyzed via the scanning anode field emission microscopy technique. Using the conventional Fowler-Nordheim relation, the work function of LaS thin films has been extracted from the slope of the plot ln(J∕F2) vs 1∕F, where J is the field emission current density and F is the local applied electric field. The threshold for an emission current density of 1mA∕cm2 occurs around a 230V∕μm electric field applied across the vacuum gap. This leads to an outstanding, reproducible effective work function value of ∼1eV across a 1cm2 sample area.

Physical properties of lanthanum monosulfide thin films grown on (100) silicon substrates

Thin films of lanthanum monosulfide (LaS) have been deposited on Si (100) substrates by pulsed laser deposition. The films are golden yellow in appearance with a mirrorlike surface morphology and a sheet resistance around 0.1Ω∕◻, as measured using a four-probe measurement technique. The thin films are characterized by atomic force microscopy (AFM), x-ray diffraction (XRD) analysis, high resolution transmission electron microscopy (HRTEM), ellipsometry, and Raman spectroscopy. The root-mean-square variation of (1μm thick) film surface roughness measured over a 1μm2 area by AFM was found to be 1.74nm. XRD analysis of fairly thick films (micrometer size) reveals the growth of the cubic rocksalt structure with a lattice constant of 5.863(7)Å, which is close to the bulk LaS value. HRTEM images reveal that the films are comprised of nanocrystals separated by regions of amorphous material. Two beam bright field TEM images show that there is a strain contrast in the Si substrate right under the interface with the LaS film and penetrating into the Si substrate. This suggests that there is an initial epitaxial-like growth of the LaS film on the Si substrate that introduces a strain as a result of the 8% lattice mismatch between the film and substrate. Ellipsometry measurements of the LaS films are well characterized by a Drude-Lorentz model from which an electron concentration of about 2.52×1022cm−3 and a mobility around 8.5cm2∕Vs are derived. Typical crystalline LaS features were evident in Raman spectra of the films, but the spectra also revealed their disordered (polycrystalline) nature.

Pulsed laser deposition of lanthanum monosulfide thin films on silicon substrates

Thin films of lanthanum monosulfide (LaS) have been successfully deposited on Si substrates by pulsed laser deposition. The values of deposition parameters (chamber pressure, substrate temperature, substrate-to-target separation, laser energy, repetition rate, and spot size on the target) leading to a successful growth of films in their cubic rocksalt structure are identified. The films are golden yellow in appearance with a mirror-like surface morphology and possess a sheet resistance around 0.1Ω∕square. X-ray diffraction analysis of thick films (several microns) leads to a lattice constant of 5.863(7)Å, which is close to the bulk LaS value. High-resolution transmission electron microscopy reveals the films to be comprised of nanocrystalline regions separated by amorphous ones. The root-mean-square variation of film surface roughness measured over a 1μm×1μm area is found to be 1.74nm by atomic force microscopy. These films have potential for semiconductor, vacuum microelectronics, and optoelectronics applications.

Growth of samarium monosulfide thin films by co-sputtering deposition

Thin films of SmS, either the semiconductor phase (S-SmS) or the metal one (M-SmS) stable at atmospheric pressure, were grown for the first time by co-sputtering of a Sm 2S 3 compound target and a Sm metal target in Ar discharge. The reactive species (sulfur) was self-provided in a controllable way from the dissociation of Sm 2S 3 during sputtering, thus minimizing the conventional use of toxic H 2S or contaminative solid sources. X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and spectrophotometry were employed in film characterization. Stoichiometric S-SmS films were formed by optimizing the power ratio applied to the two targets, and M-SmS films were directly obtained by slightly enriching the film with Sm. The films were dense with little impurity. The S-SmS and M-SmS films differ substantially in optical properties from the visible region to the IR.