Description:TECHNICAL FIELD
[0001] The present disclosure relates, in general, to photodetector technology, and more specifically, relates to thin-film ultraviolet (UV) photodetectors fabricated using earth-abundant, non-toxic semiconducting materials through a cost-effective nebulizer spray pyrolysis technique.

BACKGROUND
[0002] Photodetectors are widely used in a range of fields including biomedical imaging, pollution monitoring, telecommunications, flame detection, smoke alarms, and wearable electronics. To meet modern application demands, photodetectors must possess high sensitivity, fast response time, broad spectral coverage (UV to IR), low toxicity, and compatibility with large-area fabrication techniques. Currently, the majority of commercially used photodetector materials, such as Indium Antimonide (InSb), Gallium Nitride (GaN), Silicon Carbide (SiC), Lead Sulfide (PbS), Mercury Cadmium Telluride (HgCdTe), and Indium Gallium Arsenide (InGaAs), although effective, suffer from numerous limitations:
• Use of toxic heavy-metal elements,
• High production costs due to complex growth methods (e.g., molecular beam epitaxy, MOCVD),
• Requirement of UV filters for short-bandgap materials like silicon,
• Limited scalability and environmental hazards.
[0003] While nanostructured Bi₂S₃ (e.g., nanowires, nanosheets) has shown promise in enhancing photodetector performance, its synthesis often involves costly and complicated fabrication processes, thereby restricting practical large-scale application. Furthermore, existing Bi₂S₃-based photodetectors are underdeveloped in terms of UV-specific responsivity, speed, and environmental adaptability.
[0004] Therefore, it is desired to overcome the drawbacks, shortcomings, and limitations associated with existing solutions, and develop a non-toxic, cost-effective, scalable, and high-performance photodetector structure optimized for ultraviolet light sensing through nebulizer spray pyrolysis-based fabrication.

OBJECTS OF THE PRESENT DISCLOSURE
[0005] An object of the present disclosure is to provide a device for UV light detection comprising Sb-doped Bi₂S₃ thin films with enhanced optoelectronic properties for efficient and stable photodetection.
[0006] Another object of the present disclosure is to provide a device fabricated using nebulizer spray pyrolysis to enable simplified, scalable, and uniform thin-film deposition without complex vacuum or epitaxial methods.
[0007] Another object of the present disclosure is to provide a device in which antimony doping effectively alters the structural, optical, and electrical properties of Bi₂S₃ thin films to optimize their performance as photodetectors in the UV region.
[0008] Another object of the present disclosure is to provide a device with fast response and recovery times, high sensitivity, and improved external quantum efficiency for advanced UV photodetection applications.
[0009] Yet another object of the present disclosure is to provide a device that is low-cost, environmentally benign, and suitable for mass production, enabling widespread deployment in industrial, medical, and consumer electronic applications.

SUMMARY
[0010] The present disclosure relates in general, to photodetector technology, and more specifically, relates to a thin-film ultraviolet (UV) photodetectors fabricated using earth-abundant, non-toxic semiconducting materials through a cost-effective nebulizer spray pyrolysis technique. The main objective of the present disclosure is to overcome the drawback, limitations, and shortcomings of the existing device and solution, by providing a photoconductive-type ultraviolet (UV) photodetector device that includes a substrate over which a thin film layer of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) is deposited using a nebulizer spray pyrolysis technique. The Sb dopant concentration in the Bi₂S₃ thin film ranges from 1 weight percent to 3 weight percent. A pair of metal electrodes is deposited on the surface of the Sb-doped Bi₂S₃ thin film and is spaced apart to define an active region for photoconduction. A power supply is configured to apply a bias voltage in the range of 1 volt to 10 volts across the metal electrodes, thereby enabling drift-driven transport of photogenerated charge carriers within the active region. A UV light source is positioned to irradiate the Sb-doped Bi₂S₃ thin film with light at approximately 365 nanometers wavelength. The device exhibits enhanced photosensitivity under UV illumination in wavelength range of 200 to 400 nm, with a narrowed optical bandgap in the range of 2.08 electron volts to 2.19 electron volts. At 2 weight percent Sb doping, the device demonstrates a photo-to-dark current ratio (PDCR) of at least 13 times higher than the undoped counterpart. The Sb-doped Bi₂S₃ thin film includes a compact grain structure with improved crystallinity and reduced microstrain, leading to increased charge carrier mobility and efficient photogenerated current response.
[0011] The thin film is formed by spraying a solution containing bismuth nitrate, thiourea, and antimony nitrate onto a heated substrate at approximately 350 degrees Celsius. The precursor solution used for nebulization includes 0.02 molar bismuth nitrate and 0.03 molar thiourea dissolved in deionized water, with an appropriate amount of antimony nitrate added to achieve the desired doping concentration. The Sb-doped Bi₂S₃ thin film exhibits a strong UV absorbance peak around 325 nanometers and shows improved responsivity compared to undoped Bi₂S₃ films. When doped with 2 weight percent Sb and operated at 5 volts bias, the device generates a maximum photocurrent of approximately 5.48 microamperes, with a response time of about 0.29 seconds and a recovery time of about 0.89 seconds under UV light. The Sb-doped Bi₂S₃ film possesses an orthorhombic crystal structure, and the grain and crystallite sizes increase with Sb doping up to 2 weight percent. The metal electrodes may be formed of gold, silver, or aluminum, and are preferably deposited using thermal evaporation. The substrate may be made of glass, quartz, or fluorine-doped tin oxide-coated glass. Additionally, the electrodes are operatively connected to a current sensing module configured to monitor photosensing performance parameters such as responsivity, detectivity, external quantum efficiency, and temporal response characteristics.
[0012] 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
[0013] 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.
[0014] FIG. 1 illustrates a schematic representation of the fabricated Sb-doped Bi₂S₃-based UV photodetector along with its associated photosensing characteristics, in accordance with an embodiment of the present disclosure.
[0015] FIG. 2 illustrates an exemplary flow chart of a method for operating a photoconductive-type ultraviolet (UV) photodetector device, in accordance with an embodiment.
[0016] FIG 3A illustrates the X-ray diffraction (XRD) patterns of pristine bismuth sulfide (Bi₂S₃) thin films and Sb-doped Bi₂S₃ thin films at doping concentrations of 1 wt%, 2 wt%, and 3 wt%, in accordance with an embodiment of the present disclosure.
[0017] FIG. 3B illustrates the field emission scanning electron microscopy (FESEM) images of pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films at Sb doping concentrations, in accordance with an embodiment of the present disclosure.
[0018] FIG. 3C illustrates the energy-dispersive X-ray (EDX) spectroscopy, in accordance with an embodiment of the present disclosure.
[0019] FIG. 3D illustrates the PL emission spectra of the pristine and Sb-doped Bi₂S₃ thin films with doping concentrations ranging from 1 wt% to 3 wt%, recorded over the wavelength range of 500 nm to 800 nm using a 325 nm excitation wavelength, in accordance with an embodiment of the present disclosure.
[0020] FIG. 4A illustrates the ultraviolet-visible (UV-Vis) absorption spectra, in accordance with an embodiment.
[0021] FIG. 4B depicts the corresponding Tauc plots used to estimate the optical bandgap energies of pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films at doping concentrations of 1 wt%, 2 wt%, and 3 wt%, in accordance with an embodiment.
[0022] FIG. 5 illustrates the current–voltage (I–V) characteristics of photodetectors (PDs) fabricated using pristine and 1–3 wt% Sb-doped Bi₂S₃ thin films, in accordance with an embodiment.
[0023] FIG. 6 illustrates the time-dependent photoresponse characteristics of pristine and Sb-doped (1 wt%, 2 wt%, and 3 wt%) Bi₂S₃ thin film photodetectors (PDs), in accordance with an embodiment.
[0024] FIG. 7 illustrates the response and recovery time estimation curves for pristine and Sb-doped (1 wt%, 2 wt%, and 3 wt%) Bi₂S₃ thin film photodetectors (PDs), in accordance with an embodiment.

DETAILED DESCRIPTION
[0025] 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.
[0026] 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.
[0027] The present disclosure relates to a photoconductive-type ultraviolet (UV) photodetector device that includes a substrate over which a thin film layer of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) is deposited using a nebulizer spray pyrolysis technique. The Sb dopant concentration in the Bi₂S₃ thin film ranges from 1 weight percent to 3 weight percent. A pair of metal electrodes is deposited on the surface of the Sb-doped Bi₂S₃ thin film and is spaced apart to define an active region for photoconduction. A power supply is configured to apply a bias voltage in the range of 1 volt to 10 volts across the metal electrodes, thereby enabling drift-driven transport of photogenerated charge carriers within the active region. A UV light source is positioned to irradiate the Sb-doped Bi₂S₃ thin film with light at approximately 365 nanometers wavelength. The device exhibits enhanced photosensitivity under UV illumination, with a narrowed optical bandgap in the range of 2.08 electron volts to 2.19 electron volts. At 2 weight percent Sb doping, the device demonstrates a photo-to-dark current ratio (PDCR) of at least 13 times higher than the undoped counterpart. The Sb-doped Bi₂S₃ thin film includes a compact grain structure with improved crystallinity and reduced microstrain, leading to increased charge carrier mobility and efficient photogenerated current response.
[0028] The thin film is formed by spraying a solution containing bismuth nitrate, thiourea, and antimony nitrate onto a heated substrate at approximately 350 degrees Celsius. The precursor solution used for nebulization includes 0.02 molar bismuth nitrate and 0.03 molar thiourea dissolved in deionized water, with an appropriate amount of antimony nitrate added to achieve the desired doping concentration. The Sb-doped Bi₂S₃ thin film exhibits a strong UV absorbance peak around 325 nanometers and shows improved responsivity compared to undoped Bi₂S₃ films. When doped with 2 weight percent Sb and operated at 5 volts bias, the device generates a maximum photocurrent of approximately 5.48 microamperes, with a response time of about 0.29 seconds and a recovery time of about 0.89 seconds under UV light. The Sb-doped Bi₂S₃ film possesses an orthorhombic crystal structure, and the grain and crystallite sizes increase with Sb doping up to 2 weight percent. The metal electrodes may be formed of gold, silver, or aluminum, and are preferably deposited using thermal evaporation. The substrate may be made of glass, quartz, or fluorine-doped tin oxide-coated glass. Additionally, the electrodes are operatively connected to a current sensing module configured to monitor photosensing performance parameters such as responsivity, detectivity, external quantum efficiency, and temporal response characteristics. The present disclosure can be described in enabling detail in the following examples, which may represent more than one embodiment of the present disclosure.
[0029] The advantages achieved by the device of the present disclosure can be clear from the embodiments provided herein. The photodetector device for ultraviolet (UV) light detection, comprising a thin film of antimony (Sb)-doped bismuth sulfide (Bi₂S₃), wherein the thin film is fabricated using earth-abundant, non-toxic, and environmentally benign materials, thereby eliminating reliance on hazardous or high-cost heavy-metal-based semiconductors. The device employs a nebulizer spray pyrolysis (NSP) technique for large-area, uniform thin-film deposition under ambient atmospheric conditions, without requiring high-vacuum or high-temperature processing environments. In one embodiment, the incorporation of 2 wt% antimony dopant into the Bi₂S₃ lattice enhances optical absorption and reduces the optical bandgap, thereby improving UV light sensitivity. The photodetector demonstrates high performance through increased photoresponsivity, detectivity, and external quantum efficiency (EQE), as well as fast response and recovery times, ensuring reliable and efficient detection of ultraviolet radiation. Furthermore, the fabrication process supports cost-effective, scalable manufacturing, enabling potential integration of the device into diverse optoelectronic platforms, such as wearable electronics, environmental sensing modules, and UV safety detection systems. 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.
[0030] FIG. 1 illustrates a schematic representation of the fabricated Sb-doped Bi₂S₃-based UV photodetector along with its associated photosensing characteristics, in accordance with an embodiment of the present disclosure.
[0031] Referring to FIG. 1, photodetector device 100 (also referred to as device 100, herein) based on pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films. The photodetector device 100 can be ultraviolet (UV) photodetectors that are low-cost, environmentally friendly, and scalable, fabricated using nebulizer spray pyrolysis (NSP), configured to operate over ultraviolet (UV), visible, and near-infrared (NIR) spectral regions. The present disclosure provides an efficient solution for light detection applications by utilizing earth-abundant, non-toxic semiconducting materials with enhanced optoelectronic properties achieved through controlled Sb doping.
[0032] In accordance with an embodiment, photoconductive-type ultraviolet (UV) photodetectors (PDs) were fabricated using as-deposited pristine Bi₂S₃ thin films and Sb-doped Bi₂S₃ thin films with doping concentrations of 1 wt%, 2 wt%, and 3 wt%, respectively, to evaluate their photosensing performance. FIG. 1 illustrates a schematic representation of the fabricated Sb-doped Bi₂S₃-based UV photodetector along with its associated photosensing characteristics. A laser light source with a wavelength of 365 nm can be employed for photoexcitation. However, other light sources of varying wavelengths within the UV spectral range may also be utilized. Additionally, silver (Ag) contacts are thermally evaporated onto the film to establish electrical connectivity for device operation and measurement, although alternative electrically conductive metals or metal alloys may be employed without deviating from the scope of the invention.
[0033] The device 100 includes a substrate 102 that can be placed directly on a heater/hot plate, which is part of the NSP system setup and maintained at a controlled temperature typically 300–400°C during deposition. A nebulizer unit, containing precursor solutions of Bi₂S₃ and Sb in varying concentrations (1, 2, 3 wt%), generates a fine aerosol that is directed toward the heated substrate surface. During deposition, the Sb-doped Bi₂S₃ thin films 104 are formed on the surface of the substrate 102 through thermal decomposition. Post-deposition, a pair of metal electrodes 106 are applied onto the surface of the thin films 104 to define the active region and enable electrical biasing. A power supply 108 can be connected to the metal contacts 106 to apply a known bias voltage, typically 5V, during testing. A UV light source 110, aligned perpendicular to the film surface, is used to irradiate the film to measure its photoresponse. The generated photocurrent is measured using a current sensing module 112, such as an ammeter or digital oscilloscope, connected in series with the power supply 108 and electrodes 106.
[0034] The present disclosure relates to a photoconductive-type ultraviolet (UV) photodetector device 100 including the substrate 102, over which a thin film layer 104 of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) is deposited using a nebulizer spray pyrolysis (NSP) technique. The Sb dopant concentration in the Bi₂S₃ thin film ranges from 1 wt% to 3 wt%. The pair of metal electrodes 106 is deposited on the surface of the Sb-doped Bi₂S₃ thin film 104 and is spaced apart to define an active region for photoconduction. The power supply 108 is configured to apply a bias voltage in the range of 1 V to 10 V across the pair of metal electrodes 106, thereby enabling drift-driven transport of photogenerated charge carriers within the active region. The UV light source 110 is positioned to irradiate the Sb-doped Bi₂S₃ thin film 104 in the active region with light of approximately 365 nm wavelength. The device 100 exhibits enhanced photosensitivity under 365 nm UV illumination and demonstrates a narrowed optical bandgap in the range of 2.08 eV to 2.19 eV. At an Sb doping concentration of 2 wt%, the device shows a photo-to-dark current ratio (PDCR) of at least 13 times greater than undoped films. The Sb-doped Bi₂S₃ thin film 104 includes a compact grain structure with increased crystallinity and reduced microstrain, which collectively improve charge carrier mobility and facilitate an efficient photogenerated current response.
[0035] The thin film 104 is formed by spraying a solution containing bismuth nitrate [Bi(NO₃)₃·5H₂O], thiourea [CS(NH₂)₂], and antimony nitrate [Sb(NO₃)₃] onto the substrate 102 maintained at a temperature of approximately 350 °C. The thin film of Sb-doped Bi₂S fabricated using a nebulizer spray pyrolysis process. In the fabrication method, a precursor solution is atomized at a controlled flow rate of approximately 1 milliliter per minute using compressed air at a pressure of approximately 1.5 kilograms per square centimeter, enabling uniform deposition of the thin film. The precursor solution comprises 0.02 molar bismuth nitrate pentahydrate and 0.03 molar thiourea dissolved in 10 milliliters of deionized water, with antimony nitrate added in appropriate quantities to achieve antimony doping concentrations ranging from 1 to 3 weight percent, thereby ensuring uniform film deposition and controlled elemental incorporation. The resulting antimony-doped bismuth sulfide thin film exhibits a maximum optical absorbance peak around 325 nanometers in the ultraviolet spectrum, demonstrating enhanced ultraviolet responsivity relative to undoped films. The device exhibits distinct current–voltage and current–time characteristics under a bias voltage of 5 volts, allowing estimation of photosensing parameters including photocurrent, response time, recovery time, photoresponsivity, specific detectivity, and external quantum efficiency. In particular, when doped with 2 weight percent antimony, the thin film demonstrates a maximum photocurrent of approximately 5.48 microamperes, a response time of approximately 0.29 seconds, and a recovery time of approximately 0.89 seconds under 365-nanometer ultraviolet illumination. Furthermore, the device achieves enhanced photodetection performance, exhibiting a photoresponsivity of approximately 0.109 amperes per watt, a specific detectivity of approximately 9.42 × 10⁹ Jones, and an external quantum efficiency of approximately 37.1 percent. Structurally, the Sb-doped Bi₂S crystallizes in an orthorhombic phase with improved grain size and a crystallite dimension of approximately 22 nanometers at 2 weight percent antimony doping. The device further includes a pair of metal electrodes deposited via thermal evaporation, wherein the metal is selected from the group consisting of gold, silver, or aluminum. The electrodes define an active photodetection region of approximately 1 centimeter by 1 centimeter, facilitating efficient charge transport and accurate measurement of photodetection metrics. The substrate for the thin film is selected from the group consisting of plain glass, quartz, or fluorine-doped tin oxide-coated glass, thereby offering compatibility with transparent and conductive device platforms.
[0036] In an embodiment, the substrate 102 acts as a foundational support for the deposition of Bi₂S₃ thin films 104. Suitable materials include glass, quartz, or FTO-coated glass, chosen for their transparency and thermal stability. The substrate 102 facilitates uniform heat distribution and acts as an optical window for incoming UV radiation. The Bi₂S₃ thin film layer 104 is the photosensitive active region. Bi₂S₃ is a non-toxic, n-type semiconducting material with an orthorhombic crystal structure, high optical absorption (~10⁵ cm⁻¹), and moderate bandgap (1.3–2.3 eV), making it suitable for UV to NIR photodetection. Sb doping is introduced to alter the band structure, reduce the optical bandgap, and improve light absorption and charge carrier mobility. NSP is the deposition technique used for film fabrication. It includes an ultrasonic nebulizer to convert precursor solution into fine aerosol droplets. A carrier gas flow controller to direct aerosol toward the heated substrate. A temperature-controlled heater platform to promote pyrolytic decomposition and thin film growth. The NSP enables large-area, uniform deposition of thin films in an open-air environment, reducing the need for vacuum systems or complex epitaxial processes.
[0037] Antimony ions (Sb³⁺) are introduced into the Bi₂S₃ lattice to form Sb-doped Bi₂S₃ films 104. Sb has a smaller ionic radius than Bi³⁺, enabling it to substitute bismuth sites and modify the electronic structure. The concentrations tested include 1 wt%, 2 wt%, and 3 wt%, with 2 wt% showing optimal performance in terms of crystallinity, grain size, and optical bandgap (reduced from 2.33 eV to 2.08 eV). This component provides the necessary thermal energy to decompose aerosol droplets and form the thin film through chemical reaction at the substrate surface. The controlled temperature ensures uniform grain growth and crystallization of the Bi₂S₃ phase.
[0038] The present disclosure relates to the preparation of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films using a nebulizer spray pyrolysis technique. High-purity precursor chemicals having a purity level of 99.99%, namely bismuth nitrate (Bi(NO₃)₃·5H₂O), thiourea (CS(NH₂)₂), and antimony nitrate (Sb(NO₃)₃), were employed. A spraying solution can be formulated by dissolving 0.02 M of Bi(NO₃)₃ and 0.03 M of thiourea in 10 milliliters of deionized (DI) water, followed by magnetic stirring for a duration of one hour to ensure homogeneity. To obtain Sb-doped Bi₂S₃ thin films, a calculated amount of Sb(NO₃)₃ can be introduced into the aforementioned spraying solution, with continuous stirring, to achieve desired doping concentrations ranging from 1 wt% to 3 wt%. During film deposition, air at a pressure of 1.5 kg/cm² can be utilized as a carrier gas to atomize the solution into fine aerosol droplets. The spray flow rate can be maintained at a constant 1 ml/min. The deposition can be carried out onto glass substrates within a chamber held at a temperature of 350 °C, while maintaining a fixed nozzle-to-substrate distance of 5 cm. Following deposition, the thin film samples were allowed to cool naturally to room temperature and were subsequently stored in a desiccator for further analysis.
[0039] Photoconductive-type photodetectors having an active area of 1 cm × 1 cm were fabricated by thermally evaporating silver (Ag) electrodes onto the prepared thin films. Structural characterization of the films was conducted using X-ray diffraction (XRD) in the 2θ range of 10° to 90°, utilizing a PANalytical X’Pert Pro diffractometer equipped with a CuKα radiation source (λ = 1.5405 Å), to determine the crystalline structure and phase composition. Surface morphology and elemental analysis of the thin films were carried out using a field emission scanning electron microscope (FESEM, Aspreo S) and energy-dispersive X-ray spectroscopy (EDS, Oxford Instruments, 50 mm² detector), respectively. The optical absorbance spectra of the thin films were recorded in the wavelength range of 300 nm to 900 nm using a UV–VIS–NIR spectrometer (Lambda 35, PerkinElmer). Photoluminescence (PL) spectra were obtained using a fluorescence spectrometer (PerkinElmer LS-55). The photosensing behavior of the fabricated photodetectors was evaluated using laser illumination at a wavelength of 365 nm and a Keithley 2450 source meter.
[0040] In another embodiment, metal electrodes 106 e.g., gold, silver, or aluminum are deposited on top of the Bi₂S₃ thin films 104 to form the photodetector device 100. These contacts facilitate external bias application and charge extraction during illumination. The power supply unit 108 provides a bias voltage typically 5 V is applied across the electrodes 106 to create an electric field within the film, enabling the separation and collection of photogenerated carriers i.e., electrons and holes. The UV light source 110 is a monochromatic or broadband UV lamp e.g., 365 nm wavelength is used to irradiate the device. The absorbed photons excite electrons across the bandgap, generating a measurable photocurrent. The current sensing module 112 includes a current amplifier or oscilloscope, which measures the output current as a function of time (I-t curves) and voltage (I-V curves) to determine device parameters like Responsivity (R) in AW⁻¹, Detectivity (D*) in Jones, External Quantum Efficiency (EQE) and Response and Recovery Times.
[0041] FIG. 2 illustrates an exemplary flow chart of a method for operating a photoconductive-type ultraviolet (UV) photodetector device, in accordance with an embodiment. The method 200 for operating a photoconductive-type ultraviolet (UV) photodetector device is provided. The method includes at block 202, providing a substrate 102, optionally selected from glass, quartz, or fluorine-doped tin oxide (FTO)-coated glass, suitable for supporting thin-film deposition, depositing a thin film layer 104 of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) over the substrate (102) using a nebulizer spray pyrolysis (NSP) technique, wherein the Sb dopant concentration in the Bi₂S₃ thin film is in the range of 1 wt% to 3 wt%.
[0042] At block 204 forming a pair of metal electrodes 106 on the surface of the Sb-doped Bi₂S₃ thin film (104), wherein the electrodes are spaced apart to define an active region for photoconduction, and are optionally selected from gold (Au), silver (Ag), or aluminum (Al). At block 206 connecting a power supply 108 across the pair of metal electrodes 106 and applying a bias voltage in the range of 1 V to 10 V to enable drift-driven transport of photogenerated charge carriers through the active region of the Sb-doped Bi₂S₃ thin film 104.
[0043] At block 208, irradiating the active region of the Sb-doped Bi₂S₃ thin film (104) with a UV light source (110) that emits light at a wavelength of approximately 365 nm. At block 210 enabling the device to exhibit enhanced photosensitivity under 365 nm UV illumination, wherein the Sb-doped Bi₂S₃ thin film (104) demonstrates a narrowed optical bandgap in the range of 2.08 eV to 2.19 eV, a photo-to-dark current ratio (PDCR) of at least 13 when the Sb doping concentration is 2 wt%, and a compact grain structure with increased crystallinity and reduced microstrain, thereby facilitating enhanced charge carrier mobility and efficient photogenerated current response.
[0044] In an embodiment, a method 200 is disclosed for fabricating ultraviolet (UV) light photodetectors, comprising the steps of depositing pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films onto glass substrates using a nebulizer spray pyrolysis technique, wherein the Sb doping concentration is selected from 1 wt%, 2 wt%, and 3 wt%. X-ray diffraction (XRD) analysis reveals that a 2 wt% Sb doping level enhances crystallinity and reduces microstrain in the Bi₂S₃ thin films. Field emission scanning electron microscopy (FESEM) confirms that the 2 wt% Sb-doped Bi₂S₃ films exhibit a more compact surface morphology with enlarged grain size relative to other doping concentrations. At 3 wt% doping, deterioration in crystallinity, grain size, and surface uniformity is observed. Optical characterizations demonstrate a reduction in the optical bandgap and an increase in optical absorption with Sb doping up to 2 wt%. Photoluminescence measurements identify defect states associated with Sb doping in the Bi₂S₃ matrix. Photoconductive-type photodetectors are fabricated using the doped thin films, and performance is evaluated based on current-voltage (I–V) characteristics and time-dependent photoresponse analysis.
[0045] The 2 wt% Sb-doped Bi₂S₃-based photodetector exhibits an improved response time of approximately 0.29 seconds, while the 1 wt% Sb-doped film shows a minimal recovery time of approximately 0.27 seconds. Among all tested devices, the 2 wt% Sb-doped Bi₂S₃ film demonstrates superior performance metrics, including a photoresponsivity of 1.09 × 10⁻¹ A/W, a detectivity of 9.42 × 10⁹ Jones, and an external quantum efficiency (EQE) of 37.1%. Accordingly, the Sb-doped Bi₂S₃ thin film system, particularly at 2 wt% doping concentration, provides a low-cost, environmentally benign, and structurally optimized material platform suitable for ultraviolet photodetector applications and optoelectronic device integration.

EXPERIMENTAL ANALYSIS
[0046] In accordance with an embodiment, FIG. 3A illustrates the X-ray diffraction (XRD) patterns 300 of pristine bismuth sulfide (Bi₂S₃) thin films and Sb-doped Bi₂S₃ thin films at doping concentrations of 1 wt%, 2 wt%, and 3 wt%. The observed diffraction patterns exhibit prominent peaks corresponding to the (130) and (221) planes, along with several other reflections attributable to an orthorhombic crystal structure of Bi₂S₃, consistent with JCPDS Card No. 43-1471. As the Sb doping concentration increases up to 2 wt%, the intensity of the dominant (130) diffraction peak is enhanced, indicating improved crystallinity of the Sb-doped Bi₂S₃ thin films. Beyond this concentration (i.e., at 3 wt% Sb), a deterioration in crystallinity is observed. The average crystallite size (D) of the films was calculated using the Scherrer equation, expressed as:
[0047] D = Kλ / βcosθ (1) where β denotes the full width at half maximum (FWHM) of the diffraction peak, θ is the Bragg angle of the corresponding diffraction peak, λ represents the wavelength of the incident X-ray (1.5405 Å for CuKα radiation), and K is a dimensionless shape factor, which is set at 0.9. Microstrain (ε) developed in the films was estimated using the following relation: ε = β / 4tanθ (2)
[0048] Crystallite size, microstrain, lattice parameters, and unit cell volumes for both pristine and Sb-doped Bi₂S₃ thin films were calculated and are presented in Table 1. The data indicates that the average crystallite size increases with increasing Sb doping up to 2 wt%, whereas crystallinity degrades at 3 wt% doping. Furthermore, the lowest microstrain is observed for the film doped with 2 wt% Sb, suggesting optimal structural ordering at this concentration. The substitution of Sb³⁺ ions into the Bi₂S₃ lattice is believed to contribute to the observed increase in crystallite size, particularly at low doping levels. Given that Sb³⁺ possesses a smaller ionic radius (0.076 nm) compared to Bi³⁺ (0.103 nm), these dopant ions can more readily occupy Bi lattice sites, thereby facilitating the formation of additional nucleation centers and promoting more uniform crystallite growth during the deposition process. At a doping concentration of 3 wt%, the observed reduction in crystallite size may be attributed to the saturation limit of Sb incorporation. Beyond this threshold, excess Sb³⁺ ions may either integrate into interstitial lattice sites or segregate at grain boundaries, causing disruptions in lattice order and inhibiting grain growth. The reduction in microstrain at 2 wt% doping corresponds with enhanced long-range atomic ordering within the crystalline domains, supporting the conclusion that this concentration provides a favorable doping environment for defect minimization and crystal quality. A comparable enhancement in crystallinity and reduction in microstrain has been previously reported for Al-doped Bi₂S₃ thin films. The lattice parameters (a, b, c) and unit cell volume (V) of the orthorhombic Bi₂S₃ structure were determined using the following relationships:
1/d² = (h²/a² + k²/b² + l²/c²) (3)
V = abc (4) where h, k, l are the Miller indices and d is the interplanar spacing derived from XRD data. For pristine Bi₂S₃ thin films, the calculated lattice constants exhibit close agreement with previously reported values in the literature. Table 1 shows that a marginal variation in lattice parameters is observed with Sb doping, accompanied by a general decrease in unit cell volume. This reduction in volume is consistent with the substitution of smaller Sb³⁺ ions in place of larger Bi³⁺ ions, leading to a contraction in interplanar distances.
Samples Crystallite size (nm) Strain
× 10-3 Lattice constant Cell
Volume (Å3)
a (Å) b(Å) c(Å)
Bi2S3 18 8.59 11.12 11.17 3.95 491.70
Bi2S3:Sb 1 wt% 20 7.90 11.14 11.14 3.95 490.84
Bi2S3: Sb 2 wt% 22 7.15 11.14 11.14 3.94 488.65
Bi2S3: Sb 3 wt% 21 7.50 11.09 11.13 3.94 487.52
Table 1: Structural parameters of pristine and Sb-doped Bi2S3 thin films obtained by XRD data
[0049] In accordance with an embodiment, FIG. 3B illustrates the field emission scanning electron microscopy (FESEM) images of pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films at Sb doping concentrations of 1 wt%, 2 wt%, and 3 wt%. The surface morphology of the pristine Bi₂S₃ thin film is characterized by densely packed grains of relatively smaller size, distributed non-uniformly across the substrate surface. Additionally, sporadic agglomerated large particles are observed on the film surface, although no visible cracks or voids are present in any of the films, regardless of Sb concentration. As the Sb doping concentration increases from 1 wt% to 2 wt%, a corresponding increase in grain size is observed. However, at 3 wt% Sb doping, a decrease in grain size is noted, suggesting a non-linear dependence of grain morphology on dopant concentration. Among the examined films, the 2 wt% Sb-doped Bi₂S₃ film demonstrates a more compact and uniform surface morphology, characterized by relatively larger grains and the absence of agglomerated or poorly crystalline features between the grains, which are otherwise visible in the pristine and 1 wt% doped films.
[0050] The compact grain structure observed in the 2 wt% Sb-doped Bi₂S₃ thin film is anticipated to result in a reduced density of grain boundaries, thereby enhancing the electrical transport properties, such as charge carrier conductivity and mobility, due to the minimization of grain boundary scattering phenomena. In the case of substitutional doping, Sb³⁺ ions—having a smaller ionic radius compared to Bi³⁺ ions—replace Bi³⁺ ions in the Bi₂S₃ lattice. This ionic mismatch introduces point defects within the crystal lattice, which may act as nucleation centers during thin film growth and promote grain enlargement. However, when the dopant concentration exceeds an optimal threshold (e.g., above 2 wt%), excess Sb³⁺ ions may occupy interstitial lattice positions or segregate at grain boundaries, leading to disruptions in grain growth and the formation of less ordered or smaller crystalline domains. This mechanism is proposed to account for the observed surface morphology variations in Sb-doped Bi₂S₃ thin films across the 1–3 wt% doping range.
[0051] In accordance with an embodiment, energy-dispersive X-ray (EDX) spectroscopy can be employed to analyze the elemental composition of the Sb-doped Bi₂S₃ thin films. A representative EDX spectrum corresponding to the 2 wt% Sb-doped Bi₂S₃ thin film is illustrated in FIG. 3C. The spectrum exhibits characteristic X-ray emission peaks associated with bismuth (Bi), sulfur (S), and antimony (Sb), thereby confirming the elemental purity of the film as well as the successful incorporation of Sb dopant within the Bi₂S₃ matrix. The quantitative elemental analysis reveals the atomic concentrations of the constituent elements in the thin film as follows: bismuth (Bi) – 32.24%, sulfur (S) – 65.83%, and antimony (Sb) – 1.93%. These results corroborate the targeted doping concentration and indicate uniform dopant distribution in the thin film.
[0052] In accordance with an embodiment, photoluminescence (PL) spectroscopy can be employed to investigate the defect states and radiative recombination behavior in pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films. FIG. 3D illustrates the PL emission spectra of the pristine and Sb-doped Bi₂S₃ thin films with doping concentrations ranging from 1 wt% to 3 wt%, recorded over the wavelength range of 500 nm to 800 nm using a 325 nm excitation wavelength. The PL spectra exhibit two dominant emission peaks centered at approximately 525 nm and 620 nm, along with several low-intensity peaks appearing in the range of 550 nm to 600 nm. The PL emission intensity is observed to be strongly influenced by the level of Sb doping. As the doping concentration increases, the PL intensity of the Bi₂S₃ films increases, reaching a maximum at 2 wt% Sb doping, beyond which a decline in intensity is noted at 3 wt% doping.
[0053] The increase in PL intensity up to the 2 wt% Sb doping level is attributed to enhanced crystallinity and reduced defect density, which collectively promote more efficient radiative recombination of electron-hole pairs. Conversely, further increase in dopant concentration beyond the optimal level introduces trap states that facilitate non-radiative recombination processes, thereby quenching the luminescence properties of the thin films. The emission peak at approximately 525 nm is assigned to oxygen-mediated defect levels associated with sulfur vacancies (S_vac), which are introduced as a result of substitutional doping of Sb³⁺ ions into the Bi₂S₃ lattice. Due to their low formation energy, S_vac defects are likely to form as intrinsic defects in Bi₂S₃ and exhibit a strong tendency to adsorb oxygen species, given their low adsorption energies for both molecular oxygen (O₂) and atomic oxygen (O). These oxygen species can trap free electrons via the mechanism O₂ + e⁻ → O₂⁻, thereby creating mid-gap states within the energy bandgap. The sulfur vacancies and oxygen-mediated defects significantly influence the optoelectronic properties of Bi₂S₃-based photodetectors (PDs), wherein S_vac-enriched PDs demonstrated higher responsivity and detectivity, while oxygen-passivated detectors exhibited improved response speeds. The passivation of S_vac sites was also found to result in the removal of donor-level states from within the bandgap. Further, the emission peak at approximately 620 nm is ascribed to bismuth (Bi) site vacancies. The intensity of this peak is observed to increase with Sb doping levels of 1 wt% and 2 wt%, indicating that the presence of Sb dopant promotes the formation of Bi site vacancies to some extent. The above observations support the conclusion that substitutional Sb doping modulates both sulfur and bismuth vacancy-related defect states, which in turn influence the PL behavior and optoelectronic performance of the Bi₂S₃ thin films.
[0054] FIG. 4A illustrates the ultraviolet-visible (UV-Vis) absorption spectra 400, and FIG. 4B depicts the corresponding Tauc plots used to estimate the optical bandgap energies of pristine and antimony (Sb)-doped bismuth sulfide (Bi₂S₃) thin films at doping concentrations of 1 wt%, 2 wt%, and 3 wt%, in accordance with an embodiment. In accordance with an embodiment, ultraviolet-visible (UV-Vis) absorption spectroscopy and Tauc plot analysis confirm that Sb doping in Bi₂S₃ thin films significantly modifies the optical properties, including absorption behavior and bandgap energy. The 2 wt% Sb-doped Bi₂S₃ thin film exhibits the highest optical absorbance around 325 nm and demonstrates a narrowed direct bandgap of approximately 2.08 eV, compared to 2.33 eV for the pristine film. This enhancement is attributed to improved crystallinity, formation of impurity states, and sulfur vacancy-induced defect levels within the bandgap, which collectively facilitate sub-bandgap photon absorption and electronic transitions. At 3 wt% doping, a slight increase in bandgap and decrease in absorbance are observed due to crystallinity deterioration. The optical results indicate that 2 wt% Sb doping optimally enhances light absorption and bandgap narrowing, rendering the film particularly suitable for ultraviolet photodetector applications.
[0055] FIG. 5 illustrates the current–voltage (I–V) characteristics 500 of photodetectors (PDs) fabricated using pristine and 1–3 wt% Sb-doped Bi₂S₃ thin films, measured under both dark and illuminated conditions using a 365 nm laser source at a fixed power density of 5 mW/cm² and an applied bias voltage sweep of ±5 V. The linear increase in dark current with applied voltage indicates the formation of excellent ohmic contacts between the Ag electrodes and the Bi₂S₃ thin films, which facilitates efficient transport of photogenerated charge carriers. At a +5 V bias, the measured dark current values are 0.13 μA, 0.29 μA, 0.42 μA, and 0.22 μA for the 0 wt%, 1 wt%, 2 wt%, and 3 wt% Sb-doped films, respectively. The highest dark current observed at 2 wt% Sb doping is attributed to enhanced crystallinity and reduced grain boundary density, which improve charge carrier mobility and reduce resistive losses. Conversely, lower dark current values at 0 wt%, 1 wt%, and 3 wt% doping levels result from suboptimal microstructure with increased grain boundary scattering, which impedes charge transport.
[0056] In accordance with an embodiment, photodetectors (PDs) fabricated using Sb-doped Bi₂S₃ thin films exhibit enhanced photocurrent under UV illumination compared to their dark current, demonstrating high UV sensitivity. Among all samples, the 2 wt% Sb-doped Bi₂S₃ PD exhibits the highest photocurrent of 5.48 μA and a maximum photo-to-dark current ratio (PDCR) of 13 at 5 V bias, attributed to improved crystallinity, reduced defects, and enhanced grain size that collectively promote efficient charge carrier generation, separation, and transport. Sub-optimal doping levels result in lower photocurrent and PDCR due to increased structural defects or excessive doping-induced lattice distortions that degrade optoelectronic performance.
[0057] Referring to FIG. 6, which illustrates the time-dependent photoresponse characteristics 600 of pristine and Sb-doped (1 wt%, 2 wt%, and 3 wt%) Bi₂S₃ thin film photodetectors (PDs) under varying UV light power densities ranging from 1 mW/cm² to 5 mW/cm² at a constant bias voltage of 5 V, the photocurrent increases rapidly upon UV light illumination and returns to baseline when the light is turned off, demonstrating stable and repeatable switching behavior. In accordance with an embodiment, the Sb-doped Bi₂S₃ PD with 2 wt% Sb concentration exhibits the highest photocurrent of approximately 6 μA under a light power density of 5 mW/cm², indicating optimal photogeneration efficiency. The generated photocurrent is linearly proportional to the incident power density across all devices, confirming their stability and linear light response behavior. Further, the photodetectors were characterized by their response time (τr) and recovery time (τf) as key indicators of their speed. The response time decreased after Sb doping, reaching a minimum of 0.29 s for the 2 wt% Sb-doped sample, while the fastest recovery time of 0.27 s was recorded for the 1 wt% Sb-doped sample. The 2 wt% Sb-doped film, while exhibiting improved crystallinity and enhanced charge carrier mobility, demonstrated a relatively slower recovery time attributed to the presence of substitutional defects acting as electron traps, leading to persistent photoconductivity and delayed current decay post-illumination. The results indicate that moderate Sb doping (specifically at 2 wt%) enhances photodetector performance by balancing improved crystallinity and optical response with defect-controlled carrier dynamics, thereby offering an optimal combination of high sensitivity and fast switching speed for UV photodetector applications.
Samples Responsivity
(AW−1) Detectivity
(Jones) (EQE)
(%) Response
time
(s) Recovery
time
(s)
Bi2S3 1.22 × 10-2 1.90× 109 4.1 0.59 0.54
Bi2S3:Sb 1 wt% 4.07× 10-2 4.26× 109 13.8 0.52 0.27
Bi2S3: Sb 2 wt% 1.09× 10-1 9.42× 109 37.1 0.29 0.89
Bi2S3: Sb 3 wt% 5.04× 10-2 6.02× 109 17.1 0.72 0.50
Table 2. Photo sensing parameters of pristine and Sb-doped Bi2S3 thin film PDs.
[0058] Referring to FIG. 7, which illustrates the response and recovery time estimation curves 700 for pristine and Sb-doped (1 wt%, 2 wt%, and 3 wt%) Bi₂S₃ thin film photodetectors (PDs), the time-resolved photoresponse measurements were conducted to determine key photodetector performance metrics under UV illumination. In accordance with an embodiment, the responsivity (R), specific detectivity (D*), and external quantum efficiency (EQE) of the fabricated photodetectors were calculated using the following relations:



[0059] The results demonstrate that the 2 wt% Sb-doped Bi₂S₃ thin film PD exhibits the highest responsivity of 1.09 × 10⁻¹ A/W, a significantly enhanced value compared to the pristine sample, and comparable to previously reported metal-doped Bi₂S₃ PDs. This improvement is attributed to enhanced crystallinity, reduced defects, and improved optical absorption that facilitate effective photocarrier generation and separation.
Sl. No Sample Responsivity (AW−1) Detectivity (Jones) EQE (%) Response time (s) Recovery time (s) Reference
1 Bi2S3:Fe 2 wt % 0.096 1.34 × 1010 22.4 0.3 0.4 [50]

2 Bi2S3:Eu 3 wt% 0.388 1.82 × 1010 125 0.3 0.4 [39]

3 Bi2S3:Sn 2 wt% 0.124 1.83 × 1010 40 0.6 0.2 [34]

4 Bi2S3:Nd 3 wt% 0.136 3.05 × 1010 43 0.1 0.2 [37]

5 Bi2S3:Al 3 wt% 0.402 3.36 × 1010 130 0.38 0.6 [36]

6 Bi2S3:Ce 4 wt% 1.87 5.73 × 1010 435 5 2.6 [38]

7 Bi2S3:Sm 2 wt% 0.957 1.97 × 1011 309 1.6 1.8 [40]

8 Bi2S3 (Ts =350 °C) 0.158 9.75×109 50.8 0.3 0.4 [22]

9 Bi2S3:Sb 2 wt% 0.109 9.42×109 37.1 0.29 0.89 This work
Table 3. Comparison of the photosensor parameters of present work with Bi2S3-based PDs reported in literature.
[0060] 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
[0061] The present disclosure provides a device for fabricating UV photodetectors using Sb-doped Bi₂S₃ thin films that are non-toxic, environmentally friendly, and composed of earth-abundant materials, thereby eliminating the need for hazardous and expensive heavy-metal-based semiconductors.
[0062] The present disclosure provides a device that employs a nebulizer spray pyrolysis technique, facilitating large-area, uniform thin-film deposition in an ambient atmosphere without reliance on high-vacuum or high-temperature fabrication processes.
[0063] The present disclosure provides a device wherein doping Bi₂S₃ with 2 wt% antimony significantly improves the optical absorption characteristics and reduces the optical bandgap, leading to enhanced UV light sensitivity.
[0064] The preset disclosure provides a device capable of exhibiting high photoresponsivity, detectivity, and external quantum efficiency along with fast photoresponse and recovery times, thereby enabling reliable and efficient UV light detection.
[0065] The present disclosure provides a device that supports cost-effective and scalable production, making it suitable for integration into a wide range of optoelectronic platforms including wearable electronics, environmental monitoring, and safety detection systems.
, Claims:1. A photoconductive-type ultraviolet (UV) photodetector device (100) comprising:
a substrate (102);
a thin film layer (104) of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) deposited over the substrate through a nebulizer spray pyrolysis (NSP), wherein Sb dopant concentration ranges from 1 wt% to 3 wt%;
a pair of metal electrodes (106) deposited on surface of the Sb-doped Bi₂S₃ thin film, the pair of metal electrodes (106) spaced apart to define an active region for photoconduction;
a power supply (108) configured to apply a bias voltage in 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) positioned to irradiate the active region of the Sb-doped Bi₂S₃ thin film (104), wherein the device exhibits enhanced photosensitivity under UV illumination in wavelength range of 200 to 400 nm, a narrowed optical bandgap in range of 2.08 eV to 2.19 eV, and a photo-to-dark current ratio (PDCR) of at least 13 times more when Sb doping concentration is 2 wt%, and wherein the Sb-doped Bi₂S₃ thin film comprises a compact grain structure with increased crystallinity and reduced microstrain, facilitating enhanced charge carrier mobility and efficient photogenerated current response.
2. The photodetector device as claimed in claim 1, wherein the Sb-doped Bi₂S₃ thin film (104) is formed by spraying a solution comprising bismuth nitrate [Bi(NO₃)₃·5H₂O], thiourea [CS(NH₂)₂], and antimony nitrate [Sb(NO₃)₃] onto the substrate at a substrate temperature of approximately 350 °C.
3. The photodetector device as claimed in claim 1, wherein the Sb-doped Bi₂S₃ thin film (104) is fabricated using the nebulizer spray pyrolysis (NSP), wherein the NSP comprises atomizing a precursor solution at a flow rate of approximately 1 ml/min using compressed air at a pressure of approximately 1.5 kg/cm².
4. The photodetector device as claimed in claim 3, wherein the precursor solution comprises 0.02 M bismuth nitrate [Bi(NO₃)₃·5H₂O] and 0.03 M thiourea [CS(NH₂)₂] dissolved in 10 mL of deionized water, with antimony nitrate [Sb(NO₃)₃] added in calculated amounts to obtain Sb doping concentrations between 1 wt% and 3 wt%, to ensure uniform film deposition and controlled doping.
5. The photodetector device as claimed in claim 1, wherein the Sb-doped Bi₂S₃ thin film exhibits a maximum optical absorbance peak around 325 nm in UV spectrum and shows enhanced UV responsivity compared to undoped Bi₂S₃.
6. 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 pertain to photocurrent, response time, recovery time, photoresponsivity, detectivity, and external quantum efficiency (EQE), wherein the Sb-doped Bi₂S₃ thin film deposited with 2 wt% Sb exhibits:
a maximum photocurrent of approximately 5.48 μA under 5 V bias;
a response time of approximately 0.29 seconds and a recovery time of approximately 0.89 seconds under 365 nm illumination; and
enhanced photodetection performance with the photoresponsivity (R) of approximately 0.109 A/W, the detectivity (D*) of approximately 9.42 × 10⁹ Jones, and the external quantum efficiency (EQE) of approximately 37.1%.
7. The photodetector device as claimed in claim 1, wherein the Sb-doped Bi₂S₃ thin film has an orthorhombic crystal structure with a grain size enhanced due to Sb doping and a crystallite size of approximately 22 nm at 2 wt% doping.
8. The photodetector device as claimed in claim 1, wherein the pair of metal electrodes (106) selected from a group comprising gold (Au), silver (Ag), or aluminum (Al), and deposited via thermal evaporation, wherein the active region defined between the pair of metal electrodes is approximately 1 cm × 1 cm, configured to optimize photocurrent generation and enable accurate estimation of the responsivity (R) and the detectivity (D*).
9. The photodetector device as claimed in claim 1, wherein the substrate (102) is selected from a group comprising glass, quartz, and fluorine-doped tin oxide (FTO)-coated glass.
10. A method (200) for fabricating a photoconductive-type ultraviolet (UV) photodetector device, the method comprising:
depositing (202) a thin film layer of antimony (Sb)-doped bismuth sulfide (Bi₂S₃) over a substrate using a nebulizer spray pyrolysis (NSP), wherein Sb dopant concentration in the Bi₂S₃ thin film is in range of 1 wt% to 3 wt%;
forming (204) a pair of metal electrodes on surface of the Sb-doped Bi₂S₃ thin film, wherein the pair of metal electrodes are spaced apart to define an active region for photoconduction;
connecting (206) a power supply across the pair of metal electrodes, and applying a bias voltage in the range of 1 V to 10 V to enable drift-driven transport of photogenerated charge carriers through the active region;
irradiating (208) the active region of the Sb-doped Bi₂S₃ thin film with a UV light source emitting light at a wavelength of approximately 365 nm;
enabling (210) device to exhibit enhanced photosensitivity under UV illumination in wavelength range of 200 to 400 nm, a narrowed optical bandgap in the range of 2.08 eV to 2.19 eV, a photo-to-dark current ratio (PDCR) of at least 13 times more when the Sb doping concentration is 2 wt%, wherein the Sb-doped Bi₂S₃ thin film exhibits a compact grain structure with increased crystallinity and reduced microstrain, facilitating enhanced charge carrier mobility and efficient photogenerated current response.