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EFFECT OF SUBSTRATE TEMPERATURE ON STRUCTURAL AND MORPHOLOGICAL PROPERTIES OF SbxSy THIN FILMS GROWN BY CMBD METHOD
T.M.Razikov -
D.Sc., Prof., head of Lab.; K.M.Kuchkarov -D.Sc., Senior Researcher PTI; D.Z.Isakov, M.P.Pirimmetov master PhD student PTI, R.R.Khurramov
master Senior Researcher PTI,
Q.F. Shakhriev bachelor student NUU. Uzbekistan.
1.Introduction. Currently, a lot of research has been done on the thin film of Sb2S3, which is used as an absorbing in various studies. One of the main reasons for this is its competitive physical properties[1-3]. Today, SbS-based thin films are grown and researched in several methods (VTE, CSS, CBD and etc.) [4-6]. The primary goal of the ongoing research is to optimize the physical properties of Sb2S3 thin films and obtain a solar cell with high efficiency based on them. Therefore, the quality of the obtained films depends on their structural, morphological and optical properties. In this work, for the first time, we managed to grow SbxSy thin films using the CMBD method. We studied its structural and morphological characteristics and the laws of dependence on the substrate temperature.
2. Experiments. The experiment started with cutting soda lime glasses in certain sizes (14x14 mm2). Subsequently, they were chemically cleaned with a soapy solution, and the pads in an ultrasonic bath were washed in solutions of acetic acid, distilled water, and ethanol. Then the substrate glasses were dried in nitrogen (N) gas. Cleaned glass slides were placed in a chemical molecular beam deposition (CMBD) device[7]. The process was carried out inside a cylindrical quartz chamber. The distance between the base and the source is d=10 cm. A molybdenum wire was used to heat the source. The substrates were heated by an external heater. The temperature of the substrate and the source was determined using a thermocouple made of chrome-aluminum wire. A high-quality Sb2S3 compound (purity 99.999%; Chemsavers) was
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Uchinchi renessans yosh olimlari: zamonaviy vazifalar,
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used as a source. substrate temperatures of 300°C, 350°C, 400°C, and 450°C were selected for the experiment.
3. Results and discussion. Figure 1 shows XRD images of Sb2S3 thin films grown at various substrate temperatures. At all substrate temperatures (except 450°C), the XRD analysis revealed distinct peaks corresponding to (020), (120), (130), (211), (221), (301), and (240) planes of Sb2S3, indicating its orthorhombic structure as per JCPDS pdf 00-006-0474.
Sb S 1 i JCPDS 01-085-1322 s 2 «N - - w ¡o S S II =,11,1 -1
450oC : . A A » .
30 40
26, deg
50 100 150 200 250 300 350 400 450 500
Raman shift (cm 1)
Fig 1. XRD patterns of SbxSy thin films Fig. 2. Raman spectra of SbxSy thin at different substrate temperatures films at different substrate
temperatures
10
20
50
60
Additionally, peaks corresponding to Sb were observed at (012), (104), and (110) planes in the Sb2S3 thin films, consistent with JCPDS pdf 01-085-1322, across all substrate temperatures. Notably, at the highest substrate temperature of450°C, the intensity of Sb2S3 peaks notably diminished, particularly (020), (120), (130), (211), (221), and (501), while peaks corresponding to Sb, such as (110) and (202), increased. This observation suggests that excessively high substrate temperatures are unfavorable for Sb2S3 thin film formation. The consistent presence of Sb peaks in all samples indicates a high proportion of Sb within the Sb2S3 thin film composition. For SbxSy thin films, phase analysis was carried out in order to check the bonding of Sb with S. (Fig. 2). Raman spectroscopy analysis showed that intensity peaks at 110cm-1, 150cm-1, 237cm-1, 280cm-1 and 310cm-1 are present in all Sb2S3 thin films. This confirms that the main lattice structure is preserved in the grown samples. It can be seen from the figure that the intensity of the 280cm-1 and 310cm-1 peaks increases with the increase of the base temperature. These peak values correspond to Sb-S vibration phases [8]. The intense peak at 237cm-1 is almost unchanged with the change of the
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base temperature. The band at 237 cm-1 corresponds to symmetric S-Sb-S bending modes [9,10]. Intense peaks at 110cm-1 and 150cm-1 indicate the presence of Sb-Sb phases in thin films [11]. In addition, there are several intense peaks at 80, 189, 372, 252, and 450 cm-1 in SbS thin films, and these peaks correspond to Sb2O3 phases [12]. It can be seen that peaks at 80, 252, 372 and 450 cm-1, which were not observed in the films, appeared at the substrate temperature of 350oC. The intense peak of 72cm-1, corresponding to the Sb2O4 phase, decreased with increasing substrate temperature [13].
Morphological properties of SbxSy thin films grown by CMBD method were studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM micrographs show that SbxSy thin films prepared at substrate temperatures of 300oC and 350oC have a much smoother surface (Fig. 3). SbxSy films consist of nanosheets with a length of 1-2 ^m and a thickness of 100-500 nm. Some of the grains coalesced to form 2-3 ^m large grains. Such associations were also observed in samples obtained by the VTD method [14]. At the substrate temperature of 300oC, the grains were smaller and the spaces between the grains were larger. An increase in the temperature of the substrate led to an increase in the size of the grains and a decrease in the spaces between them. At the substrate temperature of 450oC, the grains reached the largest size (2.5^m). Also, the gaps between them have grown significantly. Figure 4 shows the AFM images of the samples. The measured surface roughness parameters are listed in Table 1. The RMS surface roughness Sq values were found to be between 0.3206 and 0.96675 nm. As the temperature of the substrate increases, the roughness increases.
300oC 350oC 400°C 450oC
Fig. 3. Surface morphology of SbxSy thin films at different substrate
temperatures
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0 5 10 15 20 25 30 35 40 45 50
um
300°C 350°C 400° C 450°C
Fig. 4. 2D topography obtained on an AFM of the surface of SbxSy thin films at different substrate temperatures
Table 1. Surface roughness parameters of SbxSy thin films at different substrate temperatures
Tsub C 300 350 400 450
Average roughness Sa, ^m 0,2526 0,3204 0,727 0,76775
RMS roughness Sq, ^m 0,3206 0,417 0,9062 0,96675
Ssk asymmetry Ssk 0,8554 0,9118 0,7362 0,5165
Ska kurtosis Ska 4,3714 4,8162 3,2544 3,1985
4. Conclusion. The study investigated the effect of substrate temperature on the structural and morphological properties of SbxSy thin films grown by the CMBD method. The XRD analysis revealed an orthorhombic crystal structure for the films grown at different substrate temperatures, with notable changes in peak intensities as the temperature varied. Raman spectroscopy confirmed the preservation of the main lattice structure across all samples, with variations in peak intensities attributed to Sb-S vibration phases and symmetric S-Sb-S bending modes. SEM and AFM analysis provided insights into the morphological properties, revealing changes in grain size and surface roughness with increasing substrate temperature. Overall, these findings contribute to our understanding of the growth parameters influencing the properties of SbxSy thin films and provide valuable insights for optimizing their performance in various applications.
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