Exploring the structural, optical, and optoelectrical characteristics of p-type CuNiBiS₃ thin films prepared by the chemical deposition method

Abstract

The authors use chemical bath deposition to synthesize novel copper-nickel bismuth sulfide (CuNiBiS₃) thin films on glass slides. The X-ray diffraction measurements detected the crystal structure of the CuNiBiS₃ layers, which display orthorhombic structures for these films. The structural indices of the CuNiBiS₃ layers were determined by the Williamson–Hall relationship. Furthermore, the Energy dispersive spectroscopy of the CuNiBiS₃ layers refers to these layers having a stoichiometric composition. On the other side, the linear optical indices of the CuNiBiS₃ layers were determined depending on the transmittance and reflectance data. The energy gap analysis indicates that the CuNiBiS₃ layers have a direct optical transition. The energy gap values of the CuNiBiS₃ layers were reduced from 1.43 to 1.31 eV by enlarging the thickness of these layers. These layers’ nonlinear, optoelectrical, and dispersion indices, like the static high-frequency dielectric constant, optical conductivity, dispersion energy, nonlinear refractive index, and optical carrier concentration, were improved by boosting the layer thickness. Moreover, the hot probe test revealed that CuNiBiS₃ layers tended to acquire p-type characteristics.

1 Introduction

Most scientists are now concentrating on developing efficient materials for solar energy. Despite silicon technology’s commercial dominance, thin films like CdTe and Cu (In, Ga) Se₂ may present practical alternatives (Wang et al. 2021, 2022). The severe toxicity of cadmium and the scarcity of indium material present problems, though low-cost and earth-abundant materials are essential to meet the demands of researchers. The discovery has therefore prompted a renewed interest in metal sulfide compounds (Gao and Zhao 2022; Li et al. 2022).

Metal sulfides have received extensive study due to their applications in various devices, including lithium-ion batteries, solar cells, optical sensors, light-emitting diodes, nonvolatile memory devices, fuel cells, and thermoelectric devices. Metal sulfides are a significant group of materials that provide n-type and p-type semiconductors for research due to their various structural types since they are typically found in various forms as binary, ternary, and quaternary metal sulfides (Kajana et al. 2022; Vakalopoulou et al. 2022a; Verma et al. 2022).

Binary metal sulfide (BMS) is a great and inexpensive material that can be used in solar cells as n-type and p-type semiconductor materials. BMS such as copper sulfide (CuS), pyrite (FeS₂), zinc sulfide (ZnS), cadmium sulfide (CdS), bismuth sulfide (Bi₂S₃), and indium sulfide (In₂S₃) are abundant and inexpensive (Karsandık et al. 2022; Vakalopoulou et al. 2022b). Zinc sulfide (ZnS) is a vital metal sulfide with n-type conductivity, high transmittance, high refractive index, good chemical stability, and a wide direct bandgap. So, it can be used to create electroluminescent phosphors, sensors, photocatalysis, and light-emitting diodes (Hathot et al. 2022; Jrad et al. 2022). Copper sulfide (CuS) compound is one of the essential materials used in various applications like hydrogen storage, optoelectronic devices, photocatalysis, and photovoltaic absorbers because it has a low energy gap, p-type conductivity, and a high absorption coefficient. Further, indium sulfide (In₂S₃) drew particular attention among various chalcogenides due to its abundance on earth, nontoxicity, wider optical absorption, and narrow bandgap (Habiboglu et al. 2022; Vinotha et al. 2022).

On the other hand, ternary metal sulfide (TMS) is a significant semiconductor material that can be utilized in a variety of applications because it displays exceptional physical and chemical characteristics that make them suited for a variety of uses, such as solar panels, IR sensors, IR lasers, window coatings, energy systems, and optical fiber and light-emitting diodes (LEDs). TMS like CuInS₂, CuSbSe₂, CuBiS₂, CuSbS₂, and CuInSe₂ are important absorbers with narrow band gaps, p-type conductivity, and an absorption coefficient of more than 10^–4 cm⁻¹ (Chalapathi et al. 2022; Surucu et al. 2022).

Copper antimony selenide CuSbSe₂ is a vital absorber layer characterized by a low energy gap, abundance on earth, and p-type conductivity (Abouabassi et al. 2022; Vázquez-Barragán et al. 2022). The CuSbSe₂ display good photovoltaic performance in different devices. Further, high-quality p-type CuSbSe₂ thin films were successfully created by Elradaf et al. These films helped fabricate ITO/CdS/CuSbSe₂/Au solar cells that produce solar conversion efficiency of about 1.66% (El-Bana and El Radaf 2022). Also, tin-antimony sulfide (SnSb₂S₄) is a vital ternary chalcogenide with good optical and electrical properties. El Radaf et al. success in fabricating SnSb₂S₄ by spray pyrolysis procedure. This compound displays good absorption coefficients, optical conductivity, refractive index, nonlinear optical parameters, and small bandgap energy (El Radaf 2020a).

On the other side, researchers have recently concentrated on creating novel quaternary metal sulfide (QMS) thin films due to their intriguing optoelectronic, electrical, and optical characteristics. The development of QMS thin films into a new type of material has led to applications in photovoltaics, phase change materials, thin film solar cells (TFSC), optical fibers, holography, inorganic photoresists, reversible optical recording, and infrared devices (Akcay et al. 2022; Liu et al. 2022).

The Ag₂ZnSnS₄, Cu₂ZnSnS_4, and Cu₂ZnGeS₄ compositions are important QMS that exhibit interesting optical and electrical features. In prior literature, it was reported that these films exhibited good photoelectric properties as significant absorption layers. They are also inexpensive to manufacture, stable, non-toxic, and abundant on Earth (El Radaf 2020b; El Radaf and Al-Zahrani 2020; Tian et al. 2014). According to previous studies, Ag₂ZnSnS₄ films have good optical conductivity, suitable nonlinear optical parameters, and a high absorption coefficient. So, Ag₂ZnSnS₄ films make an excellent absorber layer (Das and Mahanandia 2022).

On the other hand, Cu₂ZnSnS₄ (CZTS₄) is important QMS material and displays good optical and electrical performance. CZTS₄ thin films make an excellent absorber layer, according to prior research. The Mo/CZTS₄/CdS/ZnO/Al-doped ZnO/Al/LiF₂ solar cell has an efficiency of 11%, according to Chang et al. (Yan et al. 2018). On the other hand, Fouad et al. (2018) successfully created high-quality CZTS₄ films with good optical conductivity, nonlinear optical characteristics, and an increased absorption coefficient. The Al/n-Si/CZTS₄/Au heterojunction they created also had a solar efficiency of 3.37% (Fouad et al. 2018). Cu₂ZnSnSe₄ thin films are also adequate absorber layers for the Mo/Cu₂ZnSnSe₄/CdS/ZnO/Al-doped ZnO/Ni/Al/MgF₂ solar cells, which display an efficiency of 12.5% (Yin et al. 2022). Previous studies have focused on various quaternary metals sulfides like Ag₂ZnSnS_4, Cu₂ZnSnS_4, Cu₂FeSnS_4, and Cu₂MnSnS₄ thin films, but no research has been done on the physical characteristics of CuNiBiS₃ thin films. So, in the current study, the novel CuNiBiS₃ thin films are being created using the chemical bath deposition process. Also, the authors investigated the impact of layer thickness on the optoelectrical and optical characteristics and linear and nonlinear parameters.

2 Experimental details

A low-cost chemical bath deposition approach was utilized in this study to create the CuNiBiS₃ thin films. We initially carried out a substrate cleaning technique to produce CuNiBiS₃ thin films of higher quality. For cleaning, the glass sheets were submerged in pure acetone (CH₃COCH₃) in an ultrasonic bath for 15 min. Following that, the glass slides were immersed in isopropanol for 15 min. After being thoroughly cleaned with deionized water, the glass slides were air dry. Four solutions interacted with one another to form the CuNiBiS₃ solution: 20 ml of deionized water was dissolved in 0.06 M copper chloride (CuCl₂) to make the first solution. In order to make the second solution, 0.06 M nickel acetate (Ni(OCOCH₃)₂) was also dissolved in 20 ml of deionized water. To make the third solution, 0.06 M of bismuth nitrate (Bi(NO₃)₃) was dissolved in 10 ml of deionized water. In order to prepare the fourth solution, 0.18 M thiourea (SC(NH₂)₂ was dissolved in 60 ml of deionized water. All used chemicals are Sigma Aldrich-99.99%). The final solution’s pH was raised to 11 by adding a few drops of an ammonium hydroxide solution. The glass substrates were cleaned and placed vertically inside the glass beaker at room temperature. After the chemical reaction had taken place for 3, 5, 7, and 9 h, the slides were removed from the beaker, cleaned with deionized water, and dried in the air. A Philips-X’Pert X-ray diffractometer extensively inspected the structural features of the CuNiBiS₃ layers. Further, the field emission scanning electron microscope (Quanta-FeG-250 USA) was utilized to study the morphology and composition of the CuNiBiS₃ films. On the other hand, a Shimadzu spectrophotometer (type UV-3600 Plus UV–VIS–NIR) was utilized to list the optical data in the wavelength range of 400–2500 nm.

3 Results and discussions

3.1 Morphological and XRD studies

The FESEM equipment has been used to analyse the CuNiBiS₃ surface morphology. Figure 1a, b, c, and d depicted the morphological characteristics of CuNiBiS₃ films 1 µm.

Fig. 1

SEM of the CuNiBiS₃ layer of thickness: a 165 nm, b 232 nm, c 349 and d 437 nm

According to these FESEM micrographs, the surface of these layers is nearly homogeneous and uniform. Moreover, boosting the layer thickness enhanced the surface uniformity of the investigated layers due to the space between film grains getting less as they get bigger.

On the other hand, the chemical composition of the CuNiBiS₃ layers has been explored using energy-dispersive X-ray spectroscopy as presented in Fig. 2a and b. According to the reported data, the respect ratio utilized to create the CuNiBiS₃ samples was nearly identical to 1:1:1:3.

Fig. 2

EDAX spectra of the a CuNiBiS₃ layer of thickness 165 nm, b CuNiBiS₃ layer of thickness 437 nm

Figure 3 displays the XRD results of the CuNiBiS₃ layers deposited at different thicknesses. These illustrations show that these layers are polycrystalline, and the standard JCPDS file no. 46–1319. The displayed peaks belonged to a single CuNiBiS₃ phase with an orthorhombic structure.

Fig. 3

XRD charts for the CuNiBiS₃ layers

The average crystallite sizes (D_W–H) and the microstrain ($\varepsilon$) of the CuNiBiS₃ layers were assessed using the Williamson–Hall (W–H) relationship (Akl et al. 2021; Akl and Hassanien 2014):

$$\beta\, \mathrm{cos}\,\theta =\frac{k\lambda }{D}+4\,\varepsilon \mathrm{sin}\,\theta$$

(1)

where β refers to the experimental full width at half maximum intensity.

Using the integral breadth of the sample and the gaussian distribution function, the values of β were evaluated. Figure 4 shows the Williamson–Hall plots for the CuNiBiS₃ layers. According to this plot, the data points were fit to a straight line, where the slope gives the microstrain of the CuNiBiS₃ layers, and the inverse of the y-intercept gives the grain size of the CuNiBiS₃ layers. In Table 1, the D_W–H and $\varepsilon$ values of the CuNiBiS₃ layers were recorded. This table shows how the crystallite size of the CuNiBiS₃ layers rose when the layer’s thickness was boosted. On the other hand, as the thickness was boosted, the values of $\varepsilon$ decreased.

Fig. 4

The plot of 4sin(θ) against βcos (θ) for the CuNiBiS₃ layers

Table 1 Structural indices for the CuNiBiS₃ layers

Additionally, the following relationships were utilized to estimate the number of crystallites (${N}_{C}$), and the dislocation density ($\delta$) of the CuNiBiS₃ layers (Hassanien et al. 2021; Hathot et al. 2022):

$$N_{C} = \frac{t}{{D^{3} }}$$

(2)

$$\delta = \frac{1}{{D^{2} }}$$

(3)

Moreover, crystallite sizes (D_S) of the CuNiBiS₃ layers can be evaluated using Scherer relationships (Akl et al. 2020; Akl and Hassanien 2021; Das et al. 2023; Hassanien and El Radaf 2020; Priyadarshini et al. 2021; El Radaf 2023):

$$D_{S} = \frac{0.9 \lambda }{{\beta \cos \theta }}$$

(4)

Table 1 shows the $\delta$, D_S, D_W–H, N_C, and ε for the CuNiBiS₃ layers, displaying that as the film thickness of the CuNiBiS₃ samples increased, the D_S, and D_W–H values were expanded while the $\delta$, N_C, and ε values were reduced. According to this table the evaluated values of the D_S, and D_W–H of the CuNiBiS₃ layers are near to each other.

3.2 Linear optical studies

In the current work, the optical transmittance (T) and reflectance (R) of the CuNiBiS₃ films were obtained using a double-beam spectrophotometer. Using the T and R, the linear optical parameters of the CuNiBiS₃ have been computed. The T and R spectra of the novel CuNiBiS₃ layers in the 400–2500 nm wavelength range are shown in Fig. 5a and b. This graph shows that the CuNiBiS₃ layers have high optical transmittance of up to 86% and that the T of the CuNiBiS₃ layers is reduced by boosting the layer thickness. This trend was related to increasing the thickness of the samples increasing the absorbance value in the films, which decreased the transmittance value in the films (Behera et al. 2020; Naik et al. 2013; Naik and Ganesan 2014). Further, the R of the CuNiBiS₃ films improved by enlarging the layer thickness.

Fig. 5

a The spectral alterations of T as functions of λ for the CuNiBiS₃ samples, b the spectral variations of R as functions of λ for the CuNiBiS₃ films

The absorption coefficient of the studied films is a very relevant factor that illustrates how deep into the substance can travel the light when absorbed. In this report, the absorption coefficient of the CuNiBiS₃ films was computed using the below formula (El Radaf and Al-Zahrani 2022):

$$\alpha =\frac{1}{d}ln\left[\frac{{\left(1-R\right)}^{2}}{2T}+{\left(\frac{{\left(1-R\right)}^{4}}{{4T}^{2}}+{R}^{2}\right)}^{1/2}\right]$$

(5)

where d refers to the thickness of the sprayed CuNiBiS₃ films.

Figure 6a shows the reliance of $\alpha$ on the in λ for the novel CuNiBiS₃ films. It is revealed that the CuNiBiS₃ layers have large values of the $\alpha$. By raising the layer thickness of the CuNiBiS₃ layers, the values of $\alpha$ were boosted.

Fig. 6

a The absorption coefficient $\alpha$ of the novel CuNiBiS₃ layers versus $\lambda$, b the (αhν)² against hν for the CuNiBiS₃ samples, c the alteration of ln (α) with the $h\nu$ for the CuNiBiS₃ samples

On the other side, the energy gap (E_g) of the sprayed CuNiBiS₃ films was obtained by Tauc’s relationship (Mohamed et al. 2019b; Qasem et al. 2020; Tauc et al. 1966):

$$\alpha h\nu =R{\left(h\nu -{E}_{g}\right)}^{g}$$

(6)

Here, R is Tauc parameter, and f designates the optical transition kind, either direct allowed (g = 0.5) or indirect allowed (g = 2).

A good match has been identified for g = 2, indicating the allowed direct transition state. Figure 6b depicts the relationship between (hv)² against hv for the novel CuNiBiS₃ layers. The E_g values of the novel CuNiBiS₃ layers are listed in Table 2. The k selection rule and the disorder-induced spatial correlation of optical transitions between the valence and conduction bands are both reflected in the constant R, which also contains information about the convolution of the valence and conduction band states and the matrix element of optical transitions. Not only that, but R is extremely bond type dependant. When compared to the intense absorption in the band gap region, the loss due to reflection was relatively little (Ghosh et al. 2023). It is obvious that the E_g values decreased from 1.43 to 1.31 eV as the layer thickness was raised. This tendency results in the film energy gap narrowing, which may be explained by the correlation between the increasing layer thickness and the rise in localized states inside the gap (Dughaish and Mohamed 2013; Hassanien et al. 2016; Mohamed et al. 2010). Typically, film thickness increases concurrently with the creation of defects in the layer that result in localized states along the valence band and conduction band boundaries.

Table 2 The optical and dispersion constants of the CuNiBiS₃ samples

Additionally, we compute the Urbach energy (E_u) of the novel CuNiBiS₃ films using the Urbach relation (Qasem et al. 2022):

$$\mathrm{\alpha }={\mathrm{\alpha }}_{\mathrm{o}}\mathrm{exp}\left(\mathrm{h\upsilon }/{\mathrm{E}}_{\mathrm{u}}\right)$$

(7)

A plot of the ln (α) of the innovative CuNiBiS₃ films against hv is provided in Fig. 6c. This graph indicates how the values of E_u for CuNiBiS₃ films can be obtained using the slope of a straight line. Likewise, Table 2 lists the E_u of the novel CuNiBiS₃ films. It is apparent from the table that the E_u values increased as the film thickness. This trend was related to increasing the annealing the number of defect states in the confined region and the degree of disorder, both of which lead to a smaller band gap, as reported by this and other studies (Naik et al. 2009; Sahoo et al. 2020).

Furthermore, the extinction coefficient of the novel CuNiBiS₃ layers (k) was computed by the below formula (Hassanien et al. 2020b):

$$k = \frac{\alpha \lambda }{{4\pi }}$$

(8)

Figure 7a implies the alteration of k of the CuNiBiS₃ layers with $\lambda$. It was evident that when thickness rose, the values of the extinction coefficient, k, were also boosted. This trend may be attributed to enlarging these samples’ absorption coefficient by boosting the thickness (Mohamed et al. 2019a).

Fig. 7

a The relationship between the k and λ of the CuNiBiS₃ layers, b The variance of the n with λ of the CuNiBiS₃ layers

On the other side, the refractive index (n) of the novel CuNiBiS₃ layers was estimated according to the Kramer-Kroning relationship (El Radaf et al. 2020):

$$n = \frac{1 + R}{{1 - R }} + \left( {\frac{4R}{{\left( {1 - R} \right)^{2} }} - k^{2} } \right)^{1/2}$$

(9)

The variation in the n of the CuNiBiS₃ layers with λ is established in Fig. 7b. It is noted that the $n$ was boosted as the layer thickness enlarged. This behavior might be ascribed to enlarging of these samples’ reflectance by boosting the thickness (Naik et al. 2020).

Likewise, the Wemple–DiDomenico relations was employed to determine the dispersion parameters of the novel CuNiBiS₃ films (Wemple 1973; Wemple and DiDomenico 1971):

$$n^{2} = 1 + \frac{{E_{o} E_{d} }}{{E_{o}^{2} - \left( {h\upsilon } \right)^{2} }}$$

(10)

where E_d refers to the dispersion energy of the CuNiBiS₃ layers, and E_o stands for the oscillator energy of the CuNiBiS₃ layers.

Figure 8 illustrates the plot of the ($({n}^{2}-1{)}^{-1}$ versus $(h\upsilon {)}^{2}$ for the novel CuNiBiS₃ films. The values of the E_o and the E_d of the novel CuNiBiS₃ films were computed from this plot. Table 2 lists the values of the E_o and the E_d of the novel CuNiBiS₃ films. According to this table, E_d values climbed while E_o values dropped as film thickness grew.

Fig. 8

The alteration of ${\left({n}^{2}-1\right)}^{-1}$ as function of ${\left(h\nu \right)}^{2}$ for the CuNiBiS₃ layers

Additionally, we compute the oscillator parameter of the novel CuNiBiS₃ films (the static high-frequency dielectric constant, ${\varepsilon }_{s}$ refers to the static refractive index, n_o and the oscillator strength, f) by the Wemple-DiDomenico relations (Aly 2010; Hassanien 2016; Mohamed et al. 2019a):

$$f = E_{o} E_{d}$$

(11)

$$n_{o} = \sqrt {1 + \frac{{E_{d} }}{{E_{o} }}}$$

(12)

$$\varepsilon_{s} = n_{o}^{2}$$

(13)

Table 2 shows the magnitudes of the ${\varepsilon }_{s}$, n_o and f of the novel CuNiBiS₃ layers. It can be detected that as the layer thickness of the CuNiBiS₃ layers boosted, the ${\varepsilon }_{s}$, n_o, and f values were enlarged.

3.3 Optoelectrical characterization

The optoelectrical characteristics of the substances under study, such as lattice dielectric constant, optical carrier concentration, optical conductivity, plasma frequency, and electrical conductivity, play a critical role in assessing whether the materials will be employed in optoelectronic devices. In this paper, the below optoelectrical relations were employed in order to evaluate the lattice dielectric constant ${\varepsilon }_{L}$, plasma frequency ${\omega }_{p}$, and the values of charge carrier concentration to effective mass ratio ${N}_{opt}/{m}^{*}$ of the CuNiBiS₃ films (Sharma et al. 2022; Sharma and Katyal 2008):

$$n^{2} = \varepsilon_{L} - \left( {\frac{{e^{2} }}{{4\pi^{2} c^{2} \varepsilon_{0} }}} \right)\left( {\frac{{N_{opt} }}{{m^{*} }}} \right)\lambda^{2}$$

(14)

$$\omega_{p} = \sqrt {\frac{{e^{2} N_{opt} }}{{\varepsilon_{0} \varepsilon_{\infty } m^{*} }}}$$

(15)

where ${\varepsilon }_{0}$ refers to the free space electric permittivity, $c$ stands for the speed of light, $e$ stands for the electronic charge.

The fluctuations of ${n}^{2}$ versus ${\lambda }^{2}$ for the CuNiBiS₃ films can be seen in Fig. 9a. From this plot, we deduce the $\left({N}_{opt}/{m}^{*}\right)$ and ${\varepsilon }_{L}$ values. Table 3 provides the values of the $\left({N}_{opt}/{m}^{*}\right)$ and ${\varepsilon }_{L}$. It has been established that as the film thickness is raised, the $\left({N}_{opt}/{m}^{*}\right)$ enlarged. This performance could possibly be attributed to the rise in lone-pair electrons of sulfur atoms in the layer. On the other hand, as the film thickness is raised, the values of ${\varepsilon }_{L}$ improve. The possibility of ordering CuNiBiS₃ films, which would improve the film’s atom arrangement in comparison to other investigated films, may be the cause of this pattern. The in ${\varepsilon }_{L}$ value of the studied layers enlarged. Moreover, the values of ${\omega }_{p}$ of the CuNiBiS₃ layers reduced by enlarging the layer thickness.

Fig. 9

a The variation of ${n}^{2}$ with ${\lambda }^{2}$ for the CuNiBiS₃ layers, b the credence of the ε₂ on ${\lambda }^{3}$ for the CuNiBiS₃ layers

Table 3 The optoelectrical parameters of the CuNiBiS₃ layers

Likewise, the relaxation time τ of the novel CuNiBiS₃ layers was estimated according to the below relationship (Sharma and Hassanien 2020):

$$\varepsilon_{2} = \frac{1}{{4\pi^{3} \varepsilon_{0} }}\left( {\frac{{e^{2} }}{{c^{3} }}} \right)\left( {\frac{{N_{opt} }}{{m^{*} }}} \right)\left( {\frac{1}{\tau }} \right)\lambda^{3 }$$

(16)

Figure 9b implies the alteration of the ε₂ on the λ³ for the CuNiBiS₃ films. It was evident that when thickness rose, the values of τ were reduced.

Furthermore, the following equations were employed to compute the optical resistivity and optical mobility of the CuNiBiS₃ films (El-Denglawey et al. 2022; Hassanien and Sharma 2021):

$$\rho_{opt} = \frac{1}{e}\mu_{opt}$$

(17)

$$\mu_{opt} = \frac{e\tau }{{m^{*} }}$$

(18)

Table 3 lists the magnitudes of the µ_opt and ρ_opt for the CuNiBiS₃ layers. It can be detected that as the film thickness of the CuNiBiS₃ layers enlarged, the µ_opt and ρ_opt values were boosted. These findings exhibit good consistency with the other papers that have already been published (Hassanien et al. 2020a).

Depending on the values of the n and α of the novel CuNiBiS₃ layers, the values of the optical conductivity (σ_opt) and the electrical conductivity (σ_e) can be estimated according to the below relations (El Radaf et al. 2018; El Radaf and Abdelhameed 2018):

$$\sigma_{opt} = \frac{\alpha nc}{{4\pi }}$$

(19)

$$\sigma_{e} = \frac{{2{\uplambda }\sigma_{opt} }}{{\upalpha }}$$

(20)

A plot of the σ_opt versus hv for the CuNiBiS₃ layers can be seen in Fig. 10a. It was evident that as layer thickness expanded, optical conductivity values also steadily enlarged. The improvement of charge carriers was related to this performance. Likewise, when the incident photon energy grew, so did the optical conductivity. Increased photon energy-induced electronic charge excitation is the cause of this pattern (Wassel and El Radaf 2020).

Fig. 10

a The alteration of the ${\sigma }_{opt}$ with the $h\upsilon$ for the CuNiBiS₃ samples, b the ${\sigma }_{e}$ against the $h\upsilon$ for the CuNiBiS₃ samples

The relationship between electrical conductivity and photon energy is seen in Fig. 10b. The graph clearly indicates that the electrical conductivity values of the CuNiBiS₃ films enhance with film thickness while diminishing with incident photon energy.

Additionally, we compute the imaginary and real components of the optical dielectric constant (${\varepsilon }_{1} \mathrm{and} {\varepsilon }_{2} )$ of the novel CuNiBiS₃ layers using the below relations (Ali et al. 2018; El Radaf et al. 2019):

$$\varepsilon_{1} = n^{2} - k^{2}$$

(21)

$$\varepsilon_{2} = 2nk$$

(22)

Figure 11a and b indicate the alteration of the ε₁ and ε₂ of the novel CuNiBiS₃ layers with λ. It can be observed that the ε₁ and ε₂ of the novel CuNiBiS₃ layers were supposedly enhanced by boosting the layer thickness. This performance may be related to enlarging the values of n and k by boosting the film thickness.

Fig. 11

a The plot of ε₁ against the λ for the CuNiBiS₃ samples, b the ε₂ versus the λ for the CuNiBiS₃ samples

3.4 Nonlinear optical indices

On the other side, Miller’s relations can also be used to predict the third-order nonlinear susceptibility ${\upchi }^{\left(3\right)}$, the first-order nonlinear susceptibility ${\upchi }^{\left(1\right)}$, and the nonlinear refractive index ${n}_{2}$ of the CuNiBiS₃ layers by (Alzaid et al. 2020; Hassanien 2022; Hassanien et al. 2021; Shaaban et al. 2019):

$$\upchi^{\left( 1 \right)} = \frac{{{\text{n}}^{2} - 1}}{4\uppi }$$

(23)

$$\upchi^{\left( 3 \right)} = B\left[ {\frac{{{\text{n}}^{2} - 1}}{4\uppi }} \right]^{4}$$

(24)

$${\text{n}}_{2} = \frac{{12\uppi \upchi^{\left( 3 \right)} }}{{{\text{n}}_{0} }}$$

(25)

Figure 12a–c indicates how the nonlinear indices of the novel CuNiBiS₃ films rely on the photon energy. These figures indicate that increasing the thickness of the explored layers boosted the values of the ${\upchi }^{(1)}$, ${\upchi }^{\left(3\right)}$, and ${\mathrm{n}}_{2}$. This may be connected to the improvement in film refractive indices, which helps to expand the three-dimensional network of the films. The obtained values for the indices ${\upchi }^{(1)}$, ${\upchi }^{\left(3\right)}$, and ${n}_{2}$ are also roughly higher than those for earlier described semiconductors (Das et al. 2022; Naik et al. 2020; El Radaf 2020c; El Radaf and Al-Zahrani 2021; El Radaf and Wassel 2021; Sahoo et al. 2021a, 2021b). This would suggest that there are additional carriers in the CuNiBiS₃ material under study. The bound electrons’ nonlinear reaction to the light’s electric field in the material is enhanced.

Fig. 12

a–c: The alteration of the ${\upchi }^{(1)}$, ${\upchi }^{\left(3\right)}$, and ${\mathrm{n}}_{2}$ with $h\nu$ for the CuNiBiS₃ samples

3.5 Identifying the majority carriers in the CuNiBiS₃ layers

The hot-probe procedure is crucial for identifying the semiconductor type. The hot-probe technique reveals p-type conductivity in the CuNiBiS₃ layers. During this process, a soldering iron and a sensitive multimeter are used. Figure 13 indicates how to do a hot probe. The heated side of the CuNiBiS₃ film was attached to the positive multimeter terminal, which was attached to the multimeter’s negative terminal. The n-type semiconductor is represented by the positive voltage that was recorded on the multimeter after the experiment, whereas the p-type semiconductor is represented by the negative voltage (Göde 2011; Golan et al. 2006). Our studies have shown that all CuNiBiS₃ films generate a negative voltage when heated. This demonstrates that the films frequently behave as p-type semiconductors.

Fig. 13

The hot-probe experiment applied to the CuNiBiS₃ samples

4 Conclusion

This study presented the fabrication of the CuNiBiS₃ layers of various thicknesses using the chemical bath deposition method. The XRD measurements investigated the structure of the as-deposited CuNiBiS₃ samples to be orthorhombic. The composition of the CuNiBiS₃ layers was confirmed by the EDAX measurements, which show stoichiometric composition. Additionally, the novel CuNiBiS₃ layers show a direct energy gap, and by increasing the layer thickness from 165 to 437 nm, the energy gaps of these layers were reduced from 1.43 to 1.31 eV. The extinction coefficient, refractive index, Urbach energy, and absorption coefficient values also increased as the layer thickness was boosted. Also, increasing the thickness of the investigated layers boosted the optoelectrical indices, such as optical mobility, optical carrier concentration, optical conductivity, relaxation duration, and optical resistivity. The nonlinear optical investigation showed that enlarging the thickness improved the nonlinear optical characteristics. The hot prob method also proved the p-type semiconducting characteristics of our samples.