Sulfide precursor concentration and lead source effect on PbS thin films properties
Introduction
Lead sulfide (PbS, galena) is a semiconducting material belonging to IV-VI group with a narrow band gap (0.41 eV) [1], [2] and a large exciton Bohr radius of 18 nm, which permits a strong confinement effects visible, even for larger particles [3]. It has been a subject of considerable research activity due to its technological importance. PbS thin films have been used as a material for temperature and gas sensors, photodetectors in the infrared band (850–3100 nm), photoresistors [4], [5], [6], photovoltaic and photocatalysis applications [7].
Several techniques were used for thin films deposition such as spray pyrolysis (SP) [8], chemical vapor deposition (CVD), vacuum evaporation [9] SILAR [10] and chemical bath deposition (CBD) [2], [11], [12], [13], [14]. Among these techniques, CBD method is attracting, since it does not require sophisticated instrumentation. It is simple and cost-effective, suitable for large area deposition with good quality thin films [15]. Chemical bath deposition technique also offers the advantage of being able to deposit films on different kinds, shapes and sizes of substrates [16].
The correlation between the bath composition and physical properties of resulting film is still an open problem and a subject of investigations. Several authors have reported that small changes in the bath composition can lead to important changes in films properties [13]. In CBD method, the crystallites sizes can be controlled by varying experimental parameters. Most investigations on PbS thin films studied the temperature effect on films properties. Abbas et al. [17], [18] have reported that deposition temperature besides thermal treatment influences strongly the films crystallites structure. However, the deposition time controls the films stochiometry, microstructure and crystallinity [14], [18]. The pH effect has also been investigated and found that it improves the films crystallinity [19]. The bath composition, the concentrations of sulfide and lead precursors, complexing agents and solvents were also studied [20], [21]. While, to our knowledge, few investigations dealing with the lead source nature were carried. Hence, the lack of studies related to the precursor nature motivates the present work.
The main goal of the this paper is the investigation of lead source nature and sulfide precursor concentration effects on structural and optical properties of PbS thin films.
Section snippets
Experiment details
Microscope glass slide (75 × 25 × 2 mm) were used as substrates. First, substrates were washed with distilled water, immersed in methanol and cleaned ultrasonically for 20 min. Then, substrates were cleaned again ultrasonically with distilled water for 20 min and dried, after that, in air.
The films deposition was done in a reactive bath prepared in a 50 mL beaker. Various molar concentrations of thiourea (0.6, 0.8, 1, 1.2 M) and 0.1 M of lead salt (lead nitrate or lead acetate) were used.
Results and discussion
In Fig. 1 we have reported the dependence of the films growth rate as a function of thiourea concentration for both studied precursors. The growth rate varies in the range from 2.1 to 2.5 nm/min. The growth rate is calculated from the ratio of the final thickness to the deposition time. It is well known that the growth rate in CBD technique is not linear, it passes by the incubation step followed by a subsequent linear growth and then the termination step. Hence, the slower step may control the
Cristallinity
Fig. 2, Fig. 3 showed the XRD patterns of PbS thin films deposited with different thiourea concentrations for the two studied Pb precursors. The recorded patterns display different diffraction peaks, they are assigned to (111), (200), (220), (311), (222), (400), (331), (420) and (422) diffraction plans indicating the face cubic PbS rock-salt structure formation. This is confirmed by comparing peaks positions with the standard X-ray data file (card no. 77-0244). The absence of any other
Surface morphology
AFM images shown in Fig. 6 reveal that the deposited films have a continuous and dense surfaces morphology regardless the used lead source. In Table 2, we have reported the values of films surface roughness. As can be seen, films prepared with lead acetate have a smother surface than the film prepared with lead nitrate. This confirms the growth mechanism of films prepared with lead acetate is the ion by ion process while when using lead nitrate, films growth is achieved by the
Transmittance
The transmittance spectra, in the visible and near infrared range wavelength, of PbS films obtained from lead acetate and lead nitrate are shown in Fig. 7 a. and b., respectively. The whole films exhibit a low transmittance in the visible range. The transmittance in the infrared range varies from 25 to 47% in films prepared with lead acetate precursor and from 15 to 74% for films prepared with lead nitrate. This difference can be explained in terms of thickness variation.
Films thicknesses and
Conclusion
PbS thin films were synthesized at low temperature (60 °C) by chemical bath deposition. The effect of the Pb source and the thiourea concentration on films structural and optical properties has been investigated. Films are formed through the ion by ion process when using the acetate lead source and through the complex-decomposition process when using nitrate source. XRD study and AFM images indicate that PbS thin films have a nanocrystalline structure. Lead acetate yields to dense films with
References (41)
- et al.
Appl. Surf. Sci.
(2004) - et al.
J. Alloy. Compd.
(2010) - et al.
Vacuum
(2015) - et al.
Sol. Energy Mater. Sol. Cells
(2015) - et al.
Mater. Sci. Semicond. Process
(2014) - et al.
J. Alloy. Compd.
(2015) - et al.
J. Alloy. Compd.
(2013) - et al.
Thin Solid Films
(2001) - et al.
Mater. Sci. Eng. B
(2001) - et al.
Thin Solid Films
(2003)
Phys. B
Thin Solid films
Curr. Appl. Phys.
Thin Solid Films
Thin Solid Films
Solid State Commun.
Mater. Lett.
Mater. Chem. Phys.
Appl. Surf. Sci.
Mater. Sci. Semicond. Process
Cited by (29)
Flexible infrared photodetector based on polyethylene terephthalate (PET) supported lead sulfide thin film
2023, Physica B: Condensed MatterMicrostructures and optical properties of porous PbSe film prepared by ion exchange process
2022, Materials Science in Semiconductor ProcessingTwo-step chemical bath deposition enhanced mobility of PbS thin films
2021, Materials Science in Semiconductor ProcessingCitation Excerpt :Out of them, CBD is widely adopted for the fabrication of PbS because of its cost-effectiveness, simplicity and scalability. Number of attempts have already been made to fabricate PbS films by CBD using various complexing agents [10,11], precursors [12], bath temperatures [13] and pH of the solution [14]. Out of them, only a few studies have achieved the growth of high-quality and large-grained PbS films with better hole mobility values [15–17].
Study on highly crystallized PbS films synthesized from alkaline chemical bath: Effect of coordinating solvents and molar concentration
2021, Materials Science in Semiconductor ProcessingCitation Excerpt :Lead sulfide (PbS) is a representative group IV–VI compound semiconductor with a direct band gap of 0.41 eV and a large exciton Bohr radius of 18 nm at room temperature [1].
Deposition of p-type Al doped PbS thin films for heterostructure solar cell device using feasible nebulizer spray pyrolysis technique
2019, Physica B: Condensed MatterCitation Excerpt :PbS, one of the attractive semiconducting material in recent years for its wide range of applications in terms of low cost and as easily available material. PbS is a narrow band gap material with ~0.41 eV at room temperature with direct transition in bulk form [4]. Solar cell fabrication technologies have been attracted towards lead sulfide, a group IV–VI semiconductor with low cost and non toxic nature.
Effect of Zn doping concentration on optical band gap of PbS thin films
2019, Journal of Alloys and Compounds