Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to ultraviolet (UV) photodetectors, and more specifically, relates to a photoconductive ultraviolet photodetector device based on antimony-doped cadmium sulfide thin films and method of fabrication.

BACKGROUND
[0002] Photodetectors (PDs) are integral components of modern optical and electronic systems, with widespread applications in optical communication, security systems, flame detection, transparent electronics, night vision, astronomical research, and medical diagnostics. These devices function by converting incident photons into electrical signals, making them crucial for light-based sensing applications. Their integration into Internet of Things (IoT)-based devices has expanded their relevance into areas such as biological diagnostics, environmental monitoring, and intelligent automation systems. Photodetectors are engineered to operate across the ultraviolet, visible, and infrared regions of the electromagnetic spectrum, with UV detection being particularly significant for industrial, scientific, and medical use cases. UV light spans wavelengths from 400 nm to 10 nm and is categorized into UV-A, UV-B, UV-C, and far-UV regions. While naturally emitted by the Sun, UV radiation is also produced by artificial sources such as UV LEDs, phototherapy lamps, plasma torches, welding arcs, and xenon-mercury arc lamps. Controlled UV radiation plays a key role in sterilization, microbial elimination, environmental sensing, and photonic technologies.
[0003] Despite these benefits, excessive exposure to UV light poses health risks, including skin cancer and eye damage, and can also deteriorate agricultural output and infrastructure. As UV radiation is invisible to the human eye, high-performance UV photodetectors are essential for safe and effective monitoring and harnessing of UV light. An ideal UV photodetector must exhibit high sensitivity, responsivity, signal-to-noise ratio, fast response time, and long-term stability.
[0004] While various dopants have been explored to improve CdS-based photodetectors mostly targeting visible light applications limited research exists on optimizing CdS thin films for UV detection. Furthermore, conventional CdS photodetectors often exhibit suboptimal sensitivity and slower response times in the UV region, particularly under low-intensity or noisy environmental conditions. Additionally, the long-term operational stability and robustness of existing devices remain inadequate for harsh environments or extended use, such as in flame detection, sterilization monitoring, or high-temperature sensing systems. Although metal chalcogenides offer an excellent platform for thin-film photodetectors, achieving high responsivity and stability in the UV range using simple, scalable deposition methods remains a technical challenge. Moreover, the effects of antimony (Sb) doping, a promising dopant with a compatible ionic radius for Cd²⁺ substitution on the optoelectronic performance of CdS films for UV detection, have not been thoroughly investigated in the prior art.
[0005] Therefore, it is desired to overcome the drawbacks, shortcomings, and limitations associated with existing solutions and develop a UV photodetector device comprising Sb-doped CdS thin films that offer enhanced sensitivity, stability, and efficiency for long-term and high-performance UV sensing applications.

OBJECTS OF THE PRESENT DISCLOSURE
[0006] An object of the present disclosure is to provide a device for fabricating high-performance ultraviolet photodetectors using Sb-doped CdS thin films with enhanced light absorption properties.
[0007] Another object of the present disclosure is to provide a device that incorporates 1–2% Sb into the CdS lattice to reduce microstrain and structural defects, thereby improving charge carrier mobility.
[0008] Another object of the present disclosure is to provide a device that utilizes nebulizer spray pyrolysis as a simple and reproducible deposition method for large-area photodetector fabrication.
[0009] Another object of the present disclosure is to provide a device capable of generating higher photocurrent and enhanced responsivity under low-intensity UV illumination.
[0010] Another object of the present disclosure is to provide a device with optimized doping concentration to avoid excess recombination centers and maintain low dark current levels.
[0011] Another object of the present disclosure is to provide a device that maintains consistent performance and operational reliability over extended durations for deployment in critical applications.
[0012] Yet another object of the present disclosure is to provide a device that demonstrates improved photodetection capability over a broad range of incident power densities with fast photoresponse and recovery characteristics.

SUMMARY
[0013] The present disclosure relates to ultraviolet (UV) photodetectors, and more specifically, relates to UV photodetectors comprising antimony (Sb)-doped cadmium sulfide (CdS) thin films fabricated using a nebulizer spray pyrolysis method. The main objective of the present disclosure is to overcome the drawbacks, limitations, and shortcomings of the existing system and solution, by fabricating ultraviolet (UV) photodetector devices comprising antimony (Sb)-doped cadmium sulfide (CdS) thin films deposited on glass substrates using a nebulizer spray pyrolysis (NSP) technique. The fabricated thin films exhibit a hexagonal crystal structure, as confirmed by X-ray diffraction (XRD) analysis, wherein the film doped with 2 wt% Sb demonstrates the highest crystallinity among the samples tested. Field Emission Scanning Electron Microscopy (FESEM) analysis reveals that Sb doping promotes the formation of enlarged, densely packed grains in the 2 wt% doped CdS thin film, thereby enhancing the charge transport characteristics of the material. Optical absorption studies indicate improved light-harvesting capability upon Sb incorporation, which contributes to enhanced UV photodetection performance. The photoresponse of the thin film photodetector is characterized through current-voltage (I-V) measurements, with the 2 wt% Sb-doped CdS film exhibiting a responsivity (R) of 1.84 A/W, a detectivity (D*) of 1.45 × 10¹¹ Jones, and an external quantum efficiency (EQE) of 626%. The device further demonstrates a fast temporal response, with rise and fall times measured at 1.02 s and 0.56 s, respectively. Additionally, the photodetector device maintains consistent and stable operational performance over multiple cycles, thereby indicating reliability and suitability for long-term UV sensing applications. The results collectively highlight the effectiveness of Sb-doped CdS thin films as promising candidates for high-performance, durable UV photodetectors.
[0014] The present disclosure provides a photoconductive-type ultraviolet (UV) photodetector device includes a substrate; a thin film layer of antimony (Sb)-doped cadmium sulfide (CdS) deposited over the substrate using a nebulizer spray pyrolysis (NSP) technique, wherein the Sb dopant concentration ranges from 1 wt% to 3 wt%; a pair of metal electrodes deposited on the surface of the Sb-doped CdS thin film, the pair of electrodes spaced apart to define an active region for photoconduction. A power supply configured to apply a bias voltage in the range of 1 V to 10 V across the pair of metal electrodes, enabling drift-driven transport of photogenerated charge carriers and a UV light source positioned to irradiate the active region of the Sb-doped CdS thin film, wherein the device exhibits enhanced photosensitivity under UV illumination in wavelength range of 300 nm to 400 nm, a narrowed optical bandgap in the range of 2.30 eV to 2.38 eV, and a peak photocurrent of approximately 92.1 μA at 2 wt% Sb doping, and wherein the Sb-doped CdS thin film includes enhanced crystallinity, compact surface morphology, and reduced trap density, enabling increased charge carrier mobility and improved device performance. The Sb-doped CdS thin film is deposited at a substrate temperature of approximately 350°C using the nebulizer spray pyrolysis technique with a flow rate of 1 mL/min and a compressed air pressure of 1.5 kg/cm². The precursor solution used in the NSP process includes 0.02 M cadmium acetate and 0.03 M thiourea dissolved in deionized water, and antimony nitrate added in quantities calculated to achieve the desired Sb doping concentration. The Sb-doped CdS thin film exhibits a redshift in absorption edge and an increased UV absorbance peak around 500 nm, with maximum absorbance observed at 2 wt% doping. The photodetector device exhibits enhanced photosensing parameters, including a responsivity of approximately 1.84 A/W, a detectivity of approximately 1.45 × 10¹¹ Jones, and an external quantum efficiency of approximately 626% at 2 wt% Sb doping. The device exhibits a response time of approximately 1.02 seconds and a recovery time of approximately 0.56 seconds under 365 nm UV illumination. The CdS thin film has a hexagonal crystal structure with a crystallite size of approximately 23–25 nm and a grain size of approximately 222 nm at 2 wt% Sb doping. The pair of metal electrodes is selected from a group including silver, gold, or aluminum, and is deposited by thermal evaporation or sputtering. The device maintains stable photocurrent performance over a period of 50 days under continuous 365 nm UV illumination, and exhibits consistent current response over repeated light–dark cycles, indicating durable, reliable, and environmentally stable photosensing performance suitable for long-term applications.
[0015] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.
[0017] FIG. 1 illustrates a schematic diagram depicting the Sb-doped cadmium sulfide (CdS) thin film photodetector and its associated photosensing characteristics, in accordance with an embodiment of the present disclosure.
[0018] FIG. 2 illustrates an exemplary flow chart of a method for fabricating a photoconductive-type ultraviolet (UV) photodetector device, in accordance with an embodiment.
[0019] FIG. 3 illustrates X-ray diffraction (XRD) patterns of undoped cadmium sulfide (CdS) thin films and Sb-doped CdS thin films with 1 wt%, 2 wt%, and 3 wt% Sb doping concentrations, in accordance with an embodiment of the present disclosure.
[0020] FIG. 4 illustrates the surface morphology of undoped and 1 wt%, 2 wt%, and 3 wt% Sb-doped cadmium sulfide (CdS) thin films, along with the corresponding particle size distribution histograms, in accordance with an embodiment of the present disclosure.
[0021] FIG. 5A illustrates the UV–Visible optical absorption spectra of pristine (undoped) and Sb-doped CdS thin films with 1 wt%, 2 wt%, and 3 wt% Sb concentrations, in accordance with an embodiment of the present disclosure.
[0022] FIG. 5B depicts the corresponding Tauc plots used to estimate the optical band gap of the aforementioned thin films, in accordance with an embodiment.
[0023] FIG. 6 illustrates the photoluminescence (PL) emission spectra of pristine (undoped) and Sb-doped cadmium sulfide (CdS) thin films with 1 wt%, 2 wt%, and 3 wt% Sb doping concentrations, recorded using a 365 nm excitation source, in accordance with an embodiment of the present disclosure.
[0024] FIG. 7 illustrates current–voltage (I-V) curves of pristine and Sb-doped CdS thin films measured in dark and illumination conditions, in accordance with an embodiment.
[0025] FIG. 8 illustrates time-dependent photoresponse (current versus time) curves of (a) undoped and (b–d) 1–3 at% Sb-doped CdS thin-film photodetectors, recorded under ultraviolet (UV) illumination at varying power densities ranging from 1 mW/cm² to 5 mW/cm², in accordance with an embodiment.
[0026] FIG. 9 illustrates the response and recovery time characteristics of pristine and 1–3 at% Sb-doped CdS thin film photodetectors, recorded under UV illumination conditions, in accordance with an embodiment.
[0027] FIG. 10 illustrates a graphical representation of the long-term stability of undoped and Sb-doped CdS thin film photodetectors by showing the variation in photocurrent response over a period of 50 days under continuous UV illumination at an intensity of 5 mW/cm², in accordance with an embodiment.

DETAILED DESCRIPTION
[0028] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. If the specification states a component or feature “may”, “can”, “could”, or “might” be included or have a characteristic, that particular component or feature is not required to be included or have the characteristic.
[0029] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0030] The present disclosure demonstrates the successful fabrication of antimony (Sb)-doped cadmium sulfide (CdS) thin films utilizing a nebulizer spray pyrolysis (NSP) technique and their enhanced performance in ultraviolet (UV) photodetection applications. Structural, morphological, and optical characterizations confirm that doping CdS thin films with 2 wt% Sb results in improved crystallinity, increased grain size, and enhanced optical absorption characteristics. The 2 wt% Sb-doped CdS photodetector exhibits superior optoelectronic performance, including a high responsivity of 1.84 A/W, a detectivity of 1.45 × 10¹¹ Jones, and an external quantum efficiency (EQE) of 626%. Furthermore, the device demonstrates rapid photoresponse dynamics and maintains a stable current output over repeated illumination cycles, indicating high durability and operational reliability. These results substantiate the efficacy of Sb-doped CdS thin films as promising materials for high-sensitivity and efficient UV photodetectors, thereby advancing the development of durable, high-performance optoelectronic devices for long-term practical applications. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0031] The advantages achieved by the device of the present disclosure can be clear from the embodiments provided herein. The present disclosure provides a device for fabricating photoconductive-type ultraviolet (UV) photodetectors using antimony (Sb)-doped cadmium sulfide (CdS) thin films that exhibit enhanced optical absorption and a reduced bandgap, thereby improving light harvesting efficiency. The device incorporates approximately 2% Sb into the CdS lattice, which significantly enhances the crystallinity, particle size, and charge carrier transport properties of the thin film, resulting in substantially higher photocurrent generation. The device achieves improved responsivity and detectivity compared to undoped CdS and previously reported doped CdS photodetectors. Additionally, the Sb-doped CdS photodetector demonstrates superior photoconductive gain and quantum efficiency, with external quantum efficiency (EQE) values reaching up to 626%. The device enables rapid and reproducible response and recovery times, making it suitable for real-time UV light detection applications. Furthermore, the photodetector fabricated using this device offers excellent long-term environmental stability, as evidenced by minimal variation in photocurrent over a period of 50 days under continuous UV illumination. The device is fabricated using a cost-effective and scalable nebulizer spray pyrolysis technique, thereby making it viable for commercial-scale production of high-performance UV photodetectors. The description of terms and features related to the present disclosure shall be clear from the embodiments that are illustrated and described; however, the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents of the embodiments are possible within the scope of the present disclosure. Additionally, the invention can include other embodiments that are within the scope of the claims but are not described in detail with respect to the following description.
[0032] FIG. 1 illustrates a schematic diagram depicting the Sb-doped cadmium sulfide (CdS) thin film photodetector and its associated photosensing characteristics, in accordance with an embodiment of the present disclosure.
[0033] Referring to FIG. 1, a photodetector device 100 (also referred to as device 100, herein) is based on antimony (Sb)-doped cadmium sulfide (CdS) thin films. The photodetector device 100 is configured as an ultraviolet (UV) photodetector that is low-cost, environmentally friendly, and scalable. The thin films are fabricated using a nebulizer spray pyrolysis (NSP) technique, and the device is operable across a broad spectral range, including the ultraviolet (UV), visible, and near-infrared (NIR) regions. The present disclosure provides an efficient solution for light detection applications by employing semiconducting materials with enhanced optoelectronic properties, achieved through controlled Sb doping of the CdS thin films.
[0034] The device 100 includes a substrate 102, a thin film layer 104 of antimony (Sb)-doped cadmium sulfide (CdS) deposited over the substrate 102 using a nebulizer spray pyrolysis (NSP) technique, wherein the Sb dopant concentration ranges from 1 wt% to 3 wt%. A pair of metal electrodes 106 deposited on the surface of the Sb-doped CdS thin film 104, the pair of electrodes 106 spaced apart to define an active region for photoconduction. A power supply 108 configured to apply a bias voltage in the range of 1 V to 10 V across the pair of metal electrodes 106, enabling drift-driven transport of photogenerated charge carriers and a UV light source 110 positioned to irradiate the active region of the Sb-doped CdS thin film 104, wherein the device 100 exhibits enhanced photosensitivity under 365 nm UV illumination, a narrowed optical bandgap in the range of 2.30 eV to 2.38 eV, and a peak photocurrent of approximately 92.1 μA at 2 wt% Sb doping, and wherein the Sb-doped CdS thin film 104 includes enhanced crystallinity, compact surface morphology, and reduced trap density, enabling increased charge carrier mobility and improved device performance.
[0035] The device 100 further includes a current sensing module 112 configured to measure the photocurrent generated in the Sb-doped CdS thin film 104 upon exposure to ultraviolet (UV) illumination. The current sensing module 112 is connected in series with the power supply 108 and the pair of metal electrodes 106, forming a closed electrical circuit for current measurement during bias operation. In one embodiment, the current sensing module 112 includes an ammeter, a digital multimeter, or a digital oscilloscope capable of capturing both steady-state and transient photocurrent responses with high temporal resolution.
[0036] The Sb-doped CdS thin film 104 is deposited at a substrate temperature of approximately 350°C using the nebulizer spray pyrolysis technique with a flow rate of 1 mL/min and a compressed air pressure of 1.5 kg/cm². The precursor solution used in the NSP process includes 0.02 M cadmium acetate Cd (CH₃COO)₂·2H₂O and 0.03 M thiourea CS(NH₂)₂ dissolved in deionized water, and antimony nitrate Sb(NO₃)₃ added in quantities calculated to achieve the desired Sb doping concentration. The Sb-doped CdS thin film 104 exhibits a redshift in absorption edge and an increased UV absorbance peak around 500 nm, with maximum absorbance observed at 2 wt% doping. The photodetector device 100 exhibits enhanced photosensing parameters, including a responsivity (R) of approximately 1.84 A/W, a detectivity (D*) of approximately 1.45 × 10¹¹ Jones, and an external quantum efficiency (EQE) of approximately 626% at 2 wt% Sb doping. The device 100 exhibits a response time of approximately 1.02 seconds and a recovery time of approximately 0.56 seconds under 365 nm UV illumination. The CdS thin film 104 has a hexagonal crystal structure with a crystallite size of approximately 23–25 nm and a grain size of approximately 222 nm at 2 wt% Sb doping. The pair of metal electrodes 106 is selected from a group including silver (Ag), gold (Au), or aluminum (Al), and is deposited by thermal evaporation or sputtering. The device 100 maintains stable photocurrent performance over a period of 50 days under continuous 365 nm UV illumination, indicating long-term environmental stability.
[0037] In accordance with an embodiment of the present disclosure, photoconductive-type ultraviolet (UV) photodetectors 100 were fabricated using as-deposited undoped and antimony (Sb)-doped cadmium sulfide (CdS) thin films to evaluate their photosensing performance. As illustrated in FIG. 1, a schematic representation of the Sb-doped CdS thin film photodetector and its photosensing characteristics is provided. In an exemplary embodiment, the laser source 110 with a wavelength of 365 nm can be employed as the optical excitation source, and silver (Ag) electrodes were thermally evaporated onto the film surface to establish electrical contacts.
[0038] In one embodiment, undoped and antimony (Sb)-doped cadmium sulfide (CdS) thin films were deposited on glass substrates maintained at a temperature of approximately 350 °C using a nebulizer spray pyrolysis (NSP) technique. The NSP technique facilitates the formation of uniform, high-quality thin films that are critical for enhancing photodetector performance. For the precursor solution preparation, high-purity (99.99%) cadmium chloride (CdCl₂), thiourea (NH₂CSNH₂), and antimony nitrate (N₃O₉Sb) were employed. The Sb doping concentrations were varied at 0 wt%, 1 wt%, 2 wt%, and 3 wt%. A mixture of 0.03 M thiourea and 0.02 M cadmium chloride can be dissolved in 10 mL of deionized water to form the spray solution. The solution can be magnetically stirred for a duration of approximately one hour to ensure complete homogeneity. During the deposition process, compressed air at a pressure of approximately 1.5 kg/cm² can be utilized to generate fine aerosol droplets, enabling uniform and consistent film formation on the heated substrate. The deposition conditions included a maintained substrate temperature of 350 °C, a spray rate of 1 mL/min, a total deposition time of 10 minutes, and a nozzle-to-substrate distance of approximately 5 cm.
[0039] The present disclosure demonstrates the successful fabrication of antimony (Sb)-doped cadmium sulfide (CdS) thin films using a nebulizer spray pyrolysis (NSP) technique, and their enhanced performance in ultraviolet (UV) photodetection applications. Structural, morphological, and optical characterizations confirm that a doping concentration of approximately 2 wt% Sb results in improved crystallinity, increased grain size, and enhanced optical absorption, thereby contributing to superior photodetector performance. The Sb-doped CdS photodetector device incorporating 2 wt% Sb demonstrates a high responsivity of approximately 1.84 A/W, a detectivity of approximately 1.45 × 10¹¹ Jones, and an external quantum efficiency (EQE) of approximately 626%, under 365 nm UV illumination. The device further exhibits fast response and recovery times, indicating efficient photocarrier dynamics. Moreover, the photodetector maintains a stable photocurrent response over repeated light–dark cycles, validating its durability and operational reliability for long-term UV sensing applications. These findings substantiate the potential of Sb-doped CdS thin films as high-performance, environmentally friendly semiconductor materials for the development of next-generation, high-sensitivity optoelectronic and UV photodetector devices.
[0040] FIG. 2 illustrates an exemplary flow chart of a method for fabricating a photoconductive-type ultraviolet (UV) photodetector device, in accordance with an embodiment.
[0041] The method 200 includes at block 202, providing a substrate 102 selected from a group comprising glass, quartz, or fluorine-doped tin oxide (FTO)-coated glass. At block 204, depositing a thin film layer 104 of antimony (Sb)-doped cadmium sulfide (CdS) over the substrate 102 using a nebulizer spray pyrolysis (NSP) technique, wherein the Sb dopant concentration ranges from 1 wt% to 3 wt%, and wherein the NSP process comprises atomizing a precursor solution containing cadmium acetate [Cd(CH₃COO)₂·2H₂O], thiourea [CS(NH₂)₂], and antimony nitrate [Sb(NO₃)₃], dissolved in deionized water and sprayed at a flow rate of approximately 1 mL/min and a compressed air pressure of 1.5 kg/cm².
[0042] At block 206, forming a pair of metal electrodes 106 on the surface of the Sb-doped CdS thin film (104), the pair of electrodes 106 being spaced apart to define an active region for photoconduction. At block 208, applying a bias voltage in the range of 1 V to 10 V across the pair of metal electrodes 106 using a power supply 108, enabling drift-driven transport of photogenerated charge carriers through the active region. At block 210, irradiating the active region of the Sb-doped CdS thin film 104 with a UV light source 110 emitting radiation at a wavelength of approximately 365 nm, enabling the photodetector device to generate enhanced photocurrent, wherein at 2 wt% Sb doping, the device exhibits a narrowed optical bandgap of approximately 2.30 eV, a photocurrent of approximately 92.1 μA, and enhanced responsivity, detectivity, and external quantum efficiency (EQE), thereby confirming suitability for ultraviolet photodetection applications.

EXPERIMENTAL ANALYSIS
[0043] In accordance with one embodiment of the present disclosure, antimony (Sb)-doped cadmium sulfide (CdS) thin films are fabricated and evaluated for their UV photodetection performance. The Sb-doped CdS thin films are deposited onto glass substrates using a nebulizer spray pyrolysis (NSP) technique, ensuring uniform coverage and controlled doping concentrations.
[0044] Structural analysis using X-ray diffraction (XRD) confirms the formation of a hexagonal crystal structure across all thin film samples. Notably, the CdS thin film doped with 2 wt% Sb exhibits the highest degree of crystallinity among the tested compositions. Field emission scanning electron microscopy (FESEM) reveals that Sb doping results in the formation of larger and more densely packed grains in the 2 wt% doped thin film, which contributes to enhanced charge transport properties.
[0045] Optical characterization demonstrates improved light absorption with increasing Sb content, particularly in the 2 wt% Sb-doped CdS film, indicating enhanced suitability for UV photodetection applications. Electrical performance is assessed through current–voltage (I–V) measurements, wherein the 2 wt% Sb-doped CdS photodetector device achieves a responsivity (R) of approximately 1.84 A/W, a detectivity (D*) of approximately 1.45 × 10¹¹ Jones, and an external quantum efficiency (EQE) of approximately 626%.
[0046] Additionally, the photodetector exhibits fast temporal characteristics, with a response time of approximately 1.02 seconds and a recovery time of approximately 0.56 seconds. The device further demonstrates stable and repeatable performance over extended light–dark cycles, underscoring its durability and reliability for long-term UV sensing applications. These findings substantiate the efficacy of Sb-doped CdS thin films as high-sensitivity, robust materials for advanced UV photodetector devices.
[0047] FIG. 3 illustrates X-ray diffraction (XRD) patterns of undoped cadmium sulfide (CdS) thin films and Sb-doped CdS thin films with 1 wt%, 2 wt%, and 3 wt% Sb doping concentrations, in accordance with an embodiment of the present disclosure.
[0048] X-ray diffraction (XRD) analysis can be performed to investigate the structural characteristics of both undoped and antimony (Sb)-doped cadmium sulfide (CdS) thin films. The XRD patterns were recorded over a 2θ range of 10° to 80°, as illustrated in FIG. 3. The observed diffraction patterns for all films exhibited a prominent peak corresponding to the (002) crystallographic plane, along with minor peaks that align well with the standard hexagonal phase of CdS, as referenced by JCPDS card No. 65-3414.
[0049] No additional diffraction peaks corresponding to secondary or impurity phases were detected in any of the samples, indicating the phase purity of the deposited films. The crystallinity of the CdS thin films can be found to be strongly influenced by the Sb doping concentration. An enhancement in the intensity of the (002) diffraction peak can be observed for films doped with 1 wt% and 2 wt% Sb, suggesting improved crystallinity at these concentrations. However, a reduction in peak intensity can be noted in the 3 wt% Sb-doped CdS thin film, indicating possible degradation in crystallinity at higher doping levels. To further evaluate the influence of Sb doping on the microstructural properties of the CdS thin films, several structural parameters including average crystallite size (D_avg), microstrain (ε), lattice parameters (a and c), and unit cell volume (V) were calculated from the XRD data using standard analytical equations.
[0050]
[0051] where β indicates the corrected full width at half maximum (FWHM) of the diffraction peaks, and θ represents the Bragg angle. The shape factor (K) was set to 0.9.
[0052]
[0053]
[0054] where h, k, l denotes the Miller indices, and d represents the interplanar spacing and a, c are lattice parameters.
[0055] V=
[0056] In accordance with an embodiment of the present disclosure, the crystallite size of cadmium sulfide (CdS) thin films was observed to increase with increasing antimony (Sb) doping concentration, with the highest crystallinity obtained at 2 wt% Sb doping. The structural parameters, including average crystallite size, microstrain, lattice constants, and unit cell volume, are presented in Table 1. The CdS thin film doped with 2 wt% Sb exhibited the lowest microstrain value of 2.06 × 10⁻³, indicative of reduced lattice defects and improved long-range atomic ordering. The calculated lattice parameters (a and c) and unit cell volume (V) were found to be slightly lower than those of bulk CdS as reported in the standard JCPDS data, with the 'a' parameter exhibiting a gradual increase and the 'c' parameter showing a steady decrease up to 2 wt% Sb doping.
[0057] An overall increase in unit cell volume was observed as the Sb doping concentration increased from 1 wt% to 3 wt%, suggesting effective incorporation of Sb³⁺ ions into the CdS lattice. Given that the ionic radius of Sb³⁺ (0.78 Å) is smaller than that of Cd²⁺ (0.95 Å), the substitution of Cd²⁺ by Sb³⁺ is structurally favorable and results in local lattice strain, contributing to the observed expansion in unit cell volume.
[0058] The enhancement in crystallite size and crystallinity for 1–2 wt% Sb doping is attributed to the substitutional incorporation of Sb³⁺ at regular Cd²⁺ lattice sites, which likely promotes the formation of additional nucleation centers and supports more ordered crystal growth during film formation. In contrast, at higher doping levels (e.g., 3 wt%), excess Sb may occupy interstitial sites or segregate at grain boundaries, increasing lattice strain, introducing structural disorder, and impeding atomic diffusion, thereby resulting in reduced crystallinity.
[0059] The calculated values for each parameter corresponding to different doping levels are presented in Table 1.
Samples Crystallite size
(nm) Strain
×10-3 Lattice constant Cell
Volume
(Å3)
a (Å)
c(Å)

CdS 62 2.43 4.104 6.696 97.70
CdS:Sb1% 70 2.15 4.109 6.691 97.84
CdS: Sb2% 73 2.06 4.115 6.684 98.05
CdS : Sb3% 55 2.72 4.122 6.688 98.43
Table 1. Structural parameters of pristine and Sb-doped Bi2S3 thin films obtained by XRD data
[0060] FIG. 4 illustrates the surface morphology of undoped and 1 wt%, 2 wt%, and 3 wt% Sb-doped cadmium sulfide (CdS) thin films, along with the corresponding particle size distribution histograms, in accordance with an embodiment of the present disclosure. In accordance with an embodiment of the present disclosure, the surface morphology of undoped and Sb-doped cadmium sulfide (CdS) thin films can be examined using Field Emission Scanning Electron Microscopy (FESEM), and the corresponding particle size distributions were analyzed using histograms fitted with Gaussian functions, as shown in FIG. 4. The undoped CdS thin film exhibited a compact granular structure with densely packed particles averaging approximately 84 nm in size, and a relatively narrow particle size distribution, indicating uniform nucleation and growth. Upon Sb doping at 1 wt% and 2 wt%, the average grain size increased to approximately 136 nm and 222 nm, respectively, accompanied by a notable reduction in surface pinholes. This increase in grain size is attributed to the substitutional incorporation of Sb³⁺ ions into the CdS lattice, which likely reduces the density of nucleation sites and promotes the formation of fewer but larger grains through enhanced grain growth dynamics. The CdS thin film doped with 3 wt% Sb displayed an average particle size of approximately 112 nm and a broader size distribution, suggesting non-uniform growth and particle aggregation. The presence of excess Sb dopants may lead to segregation at grain boundaries or occupation of interstitial lattice sites, which can act as growth inhibitors and introduce strain or defects, thereby impeding uniform grain development.
[0061] These observations confirm that Sb doping is an effective method for tuning the grain growth behavior of CdS thin films. The 2 wt% Sb-doped sample exhibited the largest grain size and the most uniform morphology, which correlates with improved crystallinity and reduced surface defects. Larger grain sizes contribute to reduced grain boundary density, minimized carrier scattering at interfaces, and enhanced charge carrier mobility characteristics that are advantageous for optoelectronic and photodetector applications.\
[0062] FIG. 5A illustrates the UV–Visible optical absorption spectra of pristine (undoped) and Sb-doped CdS thin films with 1 wt%, 2 wt%, and 3 wt% Sb concentrations, in accordance with an embodiment of the present disclosure. In accordance with an embodiment of the present disclosure, the UV–Visible optical absorption characteristics of undoped and antimony (Sb)-doped cadmium sulfide (CdS) thin films were investigated in the wavelength range of 350 nm to 900 nm, as illustrated in FIG. 5A. All the examined thin films exhibited strong optical absorption in the UV-visible region, with a distinct absorption edge near 500 nm, which is a characteristic spectral feature of CdS. The incorporation of Sb was observed to significantly influence the optical behavior of the CdS films. An enhancement in optical absorbance was recorded with Sb doping concentrations of 1 wt% and 2 wt%, with the 2 wt% Sb-doped CdS film demonstrating the highest absorbance intensity. However, a notable decrease in absorbance was observed in the film doped with 3 wt% Sb. The absorption edge of the films exhibited a red shift (i.e., shift toward longer wavelengths) with increasing Sb content, indicating a reduction in optical bandgap energy (bandgap narrowing).
[0063] FIG. 5B depicts the corresponding Tauc plots used to estimate the optical band gap of the aforementioned thin films, in accordance with an embodiment. The enhanced optical absorption observed in the 1–2 wt% Sb-doped CdS films is attributed to the introduction of impurity-induced localized states within the bandgap, which arise from Sb incorporation. These midgap defect states facilitate additional electronic transitions, thereby broadening the absorption range beyond the intrinsic bandgap of CdS and enabling the absorption of lower-energy (longer wavelength) photons. Furthermore, improved film crystallinity and reduced defect density contribute to the observed optical behavior. The energy bandgap (Eg) of the deposited films can be determined using Tauc's relation, based on the absorption coefficient derived from the optical absorbance data, as shown in Figure 5B. These optical characteristics confirm that Sb doping at optimal levels enhances the light-harvesting efficiency of CdS thin films, rendering them highly suitable for ultraviolet and visible light sensing applications.
[0064] The Tauc’s relation mentioned below was used to determine the energy bandgap (Eg) of the deposited films based on optical absorbance data.
[0065]
[0066] where α represents the absorption coefficient, A is a proportionality constant, and n is ½ for direct allowed transitions and 2 for indirect allowed transitions. The direct optical bandgap of the films is determined using the (αhν)² versus photon energy (eV) plot, as shown in FIG. 4B. By extending the linear portion of the plot to the x-axis, the optical bandgap is obtained. The estimated direct bandgap of 2.38 eV for the undoped CdS thin film closely aligns with previously reported values for CdS films fabricated using the spray pyrolysis technique. The estimated bandgap values of 1, 2 and 3 % Sb-doped CdS films decreased to 2.37 eV, 2.35 eV and 2.30 eV respectively. A similar bandgap narrowing effect is observed earlier in Fe, Sm, Gd and Al-doped CdS thin films. The dopant atoms create localized energy levels within the bandgap by forming band tail states near the conduction band. This results in a decrease in the optical bandgap as more states become available for the excitation of electrons by absorbing lower energy photons. Narrowing of bandgap and the enhanced optical absorbance observed in 2 % Sb-doped CdS practically advantageous for PD application. The reduction in the optical bandgap allows the material to absorb lower energy photons and may extend the sensitivity over a broader wavelength range. Higher optical absorption also results in enhanced quantum efficiency, larger photocurrent and better responsivity.
[0067] FIG. 6 illustrates the photoluminescence (PL) emission spectra of pristine (undoped) and Sb-doped cadmium sulfide (CdS) thin films with 1 wt%, 2 wt%, and 3 wt% Sb doping concentrations, recorded using a 365 nm excitation source, in accordance with an embodiment of the present disclosure. In accordance with an embodiment of the present disclosure, photoluminescence (PL) emission spectra of undoped and Sb-doped cadmium sulfide (CdS) thin films were recorded in the wavelength range of 500 nm to 750 nm using a 325 nm laser excitation source, as illustrated in FIG. 6. The PL spectra revealed two prominent emission peaks around 525 nm and 680 nm, attributed to near band edge (NBE) excitonic recombination and deep-level defect-related emissions, respectively. An increase in PL intensity was observed with increasing Sb doping concentration, reaching a maximum at 2 wt% Sb, followed by a decrease at 3 wt%, indicating the onset of nonradiative recombination due to defect-induced quenching. The NBE emission at 525 nm corresponds to excitonic transitions, while the broad peak at 680 nm is associated with recombination from cadmium vacancies and interstitial defects. The enhancement in PL intensity for the 2 wt% Sb-doped CdS thin film is attributed to substitutional incorporation of Sb³⁺ ions, which introduce radiative defect states, improve crystallinity, and increase free carrier concentration, collectively promoting stronger radiative recombination of photo-generated electron-hole pairs. In contrast, the reduction in PL intensity for 3 wt% doping is attributed to increased nonradiative recombination pathways. The observed PL characteristics, particularly the intense NBE peak at approximately 525 nm (2.36 eV), confirm efficient light absorption and minimal defect-related losses, which are critical for enhancing the sensitivity, quantum efficiency, and responsivity of CdS-based ultraviolet photodetectors.
[0068] FIG. 7 illustrates current–voltage (I-V) curves of pristine and Sb-doped CdS thin films measured in dark and illumination conditions, in accordance with an embodiment. In accordance with one embodiment of the present disclosure, the current–voltage (I–V) characteristics of undoped and antimony (Sb)-doped cadmium sulfide (CdS) thin-film photodetectors were measured under both dark and ultraviolet (UV) illuminated conditions at room temperature using a light source having a wavelength of 365 nm and an intensity of 5 mW/cm², and an applied bias voltage ranging from −5 V to +5 V. The I–V characteristics exhibited linear behavior in both conditions, indicating the presence of ohmic contacts at the metal–semiconductor interface, thereby enabling efficient carrier transport and reduced contact resistance.
[0069] The photocurrent can be calculated using the expression:
where Id and Ii denote the current measured in dark and illumination conditions, respectively.
where represents the current measured under illumination and represents the current measured in the dark. Based on this relation, the calculated photocurrent values were approximately 1.81 μA, 17.7 μA, 92.1 μA, and 24.1 μA for the undoped, 1 wt%, 2 wt%, and 3 wt% Sb-doped CdS thin-film devices, respectively. The 2 wt% Sb-doped CdS photodetector demonstrated a peak photocurrent of 92.1 μA under a 5 V bias, which is substantially higher than those of the other samples and exceeds previously reported photocurrent values for similarly processed CdS-based photodetectors. The observed enhancement in photocurrent performance is attributed to increased crystallinity, enlarged grain size, reduced defect states, enhanced ultraviolet absorption, and improved charge carrier mobility resulting from optimal Sb³⁺ incorporation into the CdS lattice. The measured dark currents were approximately 0.36 μA, 0.41 μA, 0.50 μA, and 0.24 μA for the undoped, 1 wt%, 2 wt%, and 3 wt% Sb-doped films, respectively, confirming that Sb doping effectively suppresses thermally generated carriers and non-radiative recombination by minimizing trap states and structural defects. The results indicate that the 2 wt% Sb-doped CdS thin film achieves a favorable trade-off between photocurrent gain and dark current suppression, rendering it suitable for high-performance UV photodetector applications.
[0070] FIG. 8 illustrates time-dependent photoresponse (current versus time) curves of (a) undoped and (b–d) 1–3 at% Sb-doped CdS thin-film photodetectors, recorded under ultraviolet (UV) illumination at varying power densities ranging from 1 mW/cm² to 5 mW/cm², in accordance with an embodiment. In accordance with one embodiment, FIG. 8 illustrates the time-dependent photoresponse characteristics of undoped and 1–3 at% Sb-doped CdS thin-film photodetectors measured under varying ultraviolet (UV) power densities ranging from 1 mW/cm² to 5 mW/cm² at a constant bias voltage of 5 V. Upon UV illumination, the photocurrent exhibits a rapid increase and subsequently decreases when the light is turned off, confirming reversible and repeatable switching behavior under periodic ON/OFF cycles, thereby demonstrating the stability and reliability of the photodetectors. Sb doping resulted in enhanced photosensitivity, with the 2 at% Sb-doped CdS photodetector exhibiting a maximum photocurrent of approximately 92 μA at 5 mW/cm² power density. In contrast, the 3 at% Sb-doped CdS device exhibited reduced photocurrent response, attributed to excess dopant-induced recombination centers, increased structural defects, and deteriorated crystallinity. Furthermore, the photocurrent of all tested devices increased proportionally with incident power density, indicating a linear power-dependent behavior. This linearity confirms efficient photogeneration, separation, and transport of charge carriers in the fabricated CdS-based photodetectors.
[0071] FIG. 9 illustrates the response and recovery time characteristics of pristine and 1–3 at% Sb-doped CdS thin film photodetectors, recorded under UV illumination conditions, in accordance with an embodiment. In accordance with an embodiment, the response time (τr) and recovery time (τf) of undoped and Sb-doped CdS thin film photodetectors were evaluated, wherein τr refers to the time taken for photocurrent to rise to 90% of its peak value upon illumination, and τf refers to the time taken to decay to 10% after the light is turned OFF. The undoped CdS thin film exhibited a fast response time of approximately 0.30 s and a relatively longer recovery time of 1.16 s, while the 2 at% Sb-doped CdS film demonstrated a balanced response time of 1.02 s and a reduced recovery time of 0.56 s. The reduced response and recovery times in the 2% Sb-doped CdS thin film are attributed to enhanced crystallinity, minimized grain boundary scattering, and reduced defect states, resulting in higher charge carrier mobility and faster electron-hole recombination dynamics. Conversely, increased defect states and recombination centers at 3% Sb doping degraded the temporal response performance.
[0072] The key photosensing parameters- responsivity (R), detectivity (D*) and external quantum efficiency (EQE) of the fabricated PDs are calculated using the following



[0073] The photoresponsivity (R) and specific detectivity (D*) of the fabricated photodetectors (PDs) were determined using the parameters: photocurrent (Iₚ), dark current (I_d), incident power (P_in), detector area (A), and incident light wavelength (λ), measured under a fixed bias of 5 V and incident light power density of 5 mW/cm². The 2% Sb-doped CdS PD demonstrated a peak responsivity of 1.84 A/W and a peak detectivity of 1.45 × 10¹¹ Jones. The photodetector with 3% Sb doping exhibited a reduction in both parameters, indicating an optimum doping concentration at 2%. The responsivity and detectivity values of the 2% Sb-doped CdS PD exceed those reported in prior art for Fe-, Eu-, and Tb-doped CdS devices. Additionally, the external quantum efficiency (EQE) increased from 12% in the undoped device to 626% in the 2% Sb-doped device, with a subsequent decrease to 171% at 3% doping due to recombination from excess defect states. The enhanced photodetector performance observed in the 2% Sb-doped CdS film is attributed to improved optical absorption, reduced recombination losses, efficient carrier generation and transport, and the formation of good ohmic contacts facilitating enhanced charge extraction. These features collectively improve photocurrent, responsivity, and EQE, confirming the suitability of Sb doping for performance-optimized CdS-based UV photodetectors.
Samples Responsivity
(AW−1) Detectivity
(Jones) × 1010 (EQE)
(%) Rise
time (s) Fall
time (s)
CdS 0.036 0.34 12 0.30 1.16
CdS:Sb1% 0.354 3.10 120 1.43 0.61
CdS:Sb2% 1.84 14.5 626 1.02 0.56
CdS:Sb3% 0.504 5.46 171 2.80 0.88
Table 2. The photosensing parameters of the undoped and Sb-doped CdS thin film photodetectors.
Sl. No Sample Responsivity (AW−1) Detectivity (Jones) EQE (%) Response time (s) Recovery time (s) Reference
1 CdS:Pr 2.71 6.94×1011 629 0.09 0.17 [25]

2 CdS: Eu 0.61 1.38 × 1012 43 0.079 0.159 [26]

3 CdS:Sm 1.10 2.21 × 1012 257 0.157 0.166 [24]

4 CdS:Mg 1.40 4.05× 1011 327 0.78 0.88 [14]

5 CdS:Al 2.13 5.23× 1011 497 0.75 0.85 [14]

6 CdS:Fe 0.55 9.05 × 1010 180 0.1 0.2 [27]

7 CdS 0.37 2.68×1010 120 0.92 0.28 [23]

8 CdS:Sb 1.84 1.45× 1011 626 1.02 0.56 Present work
Table 3. Comparison of photosensing parameters of Sb-doped CdS with previously reported CdS-based photodetectors.
[0074] In accordance with an embodiment, the comparative evaluation of photosensing parameters of antimony-doped cadmium sulfide (CdS:Sb) photodetectors (PDs) with previously reported CdS-based PDs demonstrates that 2 wt% Sb doping significantly enhances photodetector performance. The responsivity (R) of CdS:Sb exceeds that of CdS PDs doped with rare-earth and transition metals such as samarium (Sm), magnesium (Mg), europium (Eu), aluminum (Al), and iron (Fe), indicating superior photon-to-electron conversion efficiency. The specific detectivity (D*) of the Sb-doped CdS PD is substantially higher than that of the undoped CdS PD, thereby confirming the enhanced ability of the device to detect weak optical signals under low-light conditions. Although the response and recovery times of CdS:Sb are not the fastest among doped CdS-based devices, they remain within an acceptable operational range for UV photodetection applications. Furthermore, the developed CdS:Sb PDs provide a performance advantage by combining high responsivity, improved detectivity, and a simplified, cost-effective fabrication process using nebulizer spray pyrolysis. The integration of these features establishes Sb-doped CdS as a promising material system for ultraviolet photodetector applications where high quantum efficiency and robust responsivity are prioritized over ultrafast temporal response characteristics.
[0075] FIG. 10 illustrates a graphical representation of the long-term stability of undoped and Sb-doped CdS thin film photodetectors. The present disclosure provides a stability assessment of the undoped and Sb-doped CdS thin film photodetectors, wherein the photodetectors were subjected to a UV light intensity of 5 mW/cm² and the corresponding light current was measured immediately after fabrication and at regular intervals of ten days over a period of 50 days. The measured time-dependent photoresponse, as illustrated in FIG. 10, exhibited minimal variation in photocurrent, thereby indicating excellent long-term stability, durability, and consistent operational performance of the photodetectors. Such stability confirms the photodetectors' suitability for prolonged use in real-world applications including, but not limited to, healthcare, environmental monitoring, and aerospace systems, where sustained efficiency, sensitivity, and response speed are essential
[0076] Thus, the present invention overcomes the drawbacks, shortcomings, and limitations associated with existing solutions, and provides a device for fabricating photoconductive-type ultraviolet (UV) photodetectors using antimony (Sb)-doped cadmium sulfide (CdS) thin films that exhibit enhanced optical absorption and a reduced bandgap, thereby improving light harvesting efficiency. The device incorporates approximately 2% Sb into the CdS lattice, which significantly enhances the crystallinity, particle size, and charge carrier transport properties of the thin film, resulting in substantially higher photocurrent generation. The device achieves improved responsivity and detectivity compared to undoped CdS and previously reported doped CdS photodetectors. Additionally, the Sb-doped CdS photodetector demonstrates superior photoconductive gain and quantum efficiency, with external quantum efficiency (EQE) values reaching up to 626%. The device enables rapid and reproducible response and recovery times, making it suitable for real-time UV light detection applications. Furthermore, the photodetector fabricated using this device offers excellent long-term environmental stability, as evidenced by minimal variation in photocurrent over a period of 50 days under continuous UV illumination. The device is fabricated using a cost-effective and scalable nebulizer spray pyrolysis technique, thereby making it viable for commercial-scale production of high-performance UV photodetectors
[0077] It will be apparent to those skilled in the art that the device 100 of the disclosure may be provided using some or all of the mentioned features and components without departing from the scope of the present disclosure. While various embodiments of the present disclosure have been illustrated and described herein, it will be clear that the disclosure is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the disclosure, as described in the claims.

ADVANTAGES OF THE PRESENT INVENTION
[0078] The present disclosure provides a device for fabricating photoconductive-type UV photodetectors using Sb-doped CdS thin films that demonstrate enhanced optical absorption and reduced bandgap for improved light harvesting.
[0079] The present disclosure provides a device wherein the incorporation of 2% Sb into the CdS lattice significantly enhances crystallinity, particle size, and charge transport, resulting in higher photocurrent generation.
[0080] The present disclosure provides a device that achieves improved responsivity and detectivity compared to undoped and previously reported doped CdS photodetectors.
[0081] The present disclosure provides a device wherein the Sb-doped CdS photodetector exhibits superior photoconductive gain and quantum efficiency, with external quantum efficiency (EQE) reaching up to 626%.
[0082] The present disclosure provides a device capable of delivering rapid and reproducible response and recovery times suitable for real-time UV light detection applications.
[0083] The present disclosure provides a device that offers long-term environmental stability, with minimal variation in photocurrent over a 50-day period under constant UV illumination.
The present disclosure provides a device fabricated using a cost-effective and scalable nebulizer spray pyrolysis technique, making it suitable for commercial production of high-performance UV photodetectors.
, Claims:1. A photoconductive-type ultraviolet (UV) photodetector device (100) comprising:
a substrate (102);
a thin film layer (104) of antimony (Sb)-doped cadmium sulfide (CdS) deposited over the substrate using a nebulizer spray pyrolysis (NSP), wherein the Sb dopant concentration ranges from 1 wt% to 3 wt%;
a pair of metal electrodes (106) deposited on surface of the Sb-doped CdS thin film, the pair of electrodes (106) spaced apart to define an active region for photoconduction;
a power supply (108) configured to apply a bias voltage in a range of 1 V to 10 V across the pair of metal electrodes (106), enabling drift-driven transport of photogenerated charge carriers; and
a ultraviolet (UV) light source (110) coupled to the power supply (108), positioned to irradiate an active region of the Sb-doped CdS thin film (104), wherein the device exhibits enhanced photosensitivity under UV illumination in wavelength range of 300 nm to 400 nm, a narrowed optical bandgap in range of 2.30 eV to 2.38 eV, a peak photocurrent of approximately 92.1 μA at 2 wt% Sb doping, and wherein the Sb-doped CdS thin film (104) comprises enhanced crystallinity, compact surface morphology, and reduced trap density, enabling increase charge carrier mobility and device performance.
2. The photodetector device as claimed in claim 1, wherein the Sb-doped CdS thin film (104) is deposited at a substrate temperature of approximately 350°C using the NSP that comprises atomizing a precursor solution at a flow rate of 1 mL/min and compressed air pressure of 1.5 kg/cm².
3. The photodetector device as claimed in claim 2, wherein the precursor solution used in the NSP comprises 0.02 M cadmium acetate [Cd(CH₃COO)₂·2H₂O] and 0.03 M thiourea [CS(NH₂)₂] dissolved in deionized water, and Sb(NO₃)₃ added in amounts calculated to obtain desired Sb doping concentrations.
4. The photodetector device as claimed in claim 1, wherein the Sb-doped CdS thin film (104) exhibits a redshift in absorption edge and an increased UV absorbance peak around 500 nm with maximum absorbance at 2 wt% doping.
5. The photodetector device as claimed in claim 1, wherein the device exhibits current–voltage (I–V) and current–time (I–t) characteristics under the bias voltage of 5 V, enabling estimation of photosensing parameters, the photosensing parameters measured comprises a responsivity (R) of approximately 1.84 A/W, detectivity (D*) of approximately 1.45 × 10¹¹ Jones, and an external quantum efficiency (EQE) of approximately 626% at 2 wt% Sb doping.
6. The photodetector device as claimed in claim 1, wherein the device (100) exhibits a response time of approximately 1.02 seconds and a recovery time of approximately 0.56 seconds under 365 nm illumination.
7. The photodetector device as claimed in claim 1, wherein the CdS thin film (104) has a hexagonal crystal structure with a crystallite size of approximately 23–25 nm at 2 wt% Sb doping and grain size of approximately 222 nm.
8. The photodetector device as claimed in claim 1, wherein the pair of metal electrodes (106) is selected from a group comprising silver (Ag), gold (Au), or aluminum (Al), and deposited by thermal evaporation or sputtering.
9. The photodetector device as claimed in claim 1, wherein the device maintains stable photocurrent performance over 50 days under continuous 365 nm UV illumination, and exhibits consistent current response over repeated light–dark cycles, indicating durable, reliable, and environmentally stable photosensing performance for long-term applications.
10. A method (200) for operating a photoconductive-type ultraviolet (UV) photodetector device (100), the method comprising:
providing (202) a substrate (102);
depositing (204) a thin film layer (104) of antimony (Sb)-doped cadmium sulfide (CdS) over the substrate using a nebulizer spray pyrolysis (NSP), wherein the Sb dopant concentration ranges from 1 wt% to 3 wt%;
forming (206) a pair of metal electrodes (106) on the surface of the Sb-doped CdS thin film, the pair spaced apart to define an active region;
applying (208) a bias voltage in the range of 1 V to 10 V across the metal electrodes using a power supply (108);
irradiating (210), by a ultraviolet (UV) light source (110), the active region of the Sb-doped CdS thin film (104), wherein the device exhibits enhanced photosensitivity under UV illumination in wavelength range of 300 nm to 400 nm, a narrowed optical bandgap in range of 2.30 eV to 2.38 eV, a peak photocurrent of approximately 92.1 μA at 2 wt% Sb doping, and wherein the Sb-doped CdS thin film (104) comprises enhanced crystallinity, compact surface morphology, and reduced trap density, enabling increase charge carrier mobility and device performance.