Photoelectric detector and preparation method and application thereof

Abstract

The invention relates to the technical field of photoelectric materials, and discloses a photoelectric detector and a preparation method and application thereof. The photoelectric detector comprises a substrate, a first electrode layer, a photoelectric conversion layer, a CdS buffer layer, an ITO window layer and a second electrode layer which are sequentially stacked. Wherein an intrinsic zinc oxide (i-ZnO) layer is arranged between the CdS buffer layer and the ITO window layer. The i-ZnO layer can effectively optimize an interface energy band structure, passivate interface defects and remarkably reduce dark current and noise of a device. The optimized photoelectric detector has the self-driven working capability, the specific detection rate, the response speed and the ultra-weak light detection capability of the photoelectric detector are remarkably improved, and meanwhile, the photoelectric detector has wide spectral response and good environmental stability. The optical sensor comprising the detector is suitable for the fields of non-invasive blood glucose monitoring based on Raman spectroscopy and the like with extremely high sensitivity requirements, and a core device solution is provided for realizing low-power-consumption and high-precision continuous health monitoring.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic materials technology, and in particular to a photodetector, its preparation method, and its application. Background Technology

[0002] In the field of wearable health monitoring, continuous, non-invasive, and real-time monitoring of key physiological parameters such as blood glucose is of great significance. Optical non-invasive blood glucose detection technology has become a research hotspot due to its non-invasive nature. Its principle lies in detecting the weak optical signal changes caused by the characteristic absorption or scattering of light at specific wavelengths by glucose molecules. The practical application of this technology highly depends on the performance of its core photoelectric detection component—the photodetector. An ideal photodetector for non-invasive blood glucose detection should possess the following characteristics: extremely high sensitivity and detectivity (for extracting physiological signals at the microvolt level or even weaker), a wide spectral response range (to cover the near-infrared "bio-optical window" and multiple characteristic wavelengths, facilitating multispectral analysis to suppress interference), effective operation under ultra-low light conditions (to reduce overall system power consumption), and excellent stability.

[0003] However, the commercial photodetectors commonly used in portable devices (such as silicon-based photodiodes) cannot meet the above stringent requirements. Specifically, they have the following characteristics: 1. They have high intrinsic noise and low detectivity, making it difficult to reliably extract weak blood glucose-related signals from strong background noise; 2. The absorption edge of silicon materials limits their ability to effectively respond to near-infrared light with longer wavelengths, thus limiting the choice of technical path; 3. To compensate for insufficient sensitivity, existing solutions often use multiple detectors and high-power light sources, resulting in high power consumption, large size, and high cost, making it difficult to achieve true wearability and continuous monitoring.

[0004] Numerous studies have been conducted in this field to address the performance bottlenecks of existing devices. Among them, copper-zinc-tin-sulfur-based materials are considered highly promising photoelectric absorption layer materials due to their high light absorption coefficient, tunable direct bandgap, and high elemental abundance. Self-driven photodetectors based on these materials have demonstrated high specific detectivity and nanosecond-level fast response characteristics in biosensing applications such as heart rate monitoring. However, when attempting to apply these detectors to the more demanding scenario of non-invasive blood glucose detection, their performance remains insufficient. Non-invasive blood glucose detection relies on extracting extremely weak light signals modulated by human tissue, the intensity of which is typically several orders of magnitude lower than the pulse wave light signals used in heart rate detection. Therefore, the detector must possess an extremely high signal-to-noise ratio and an ultra-low detection limit.

[0005] One of the key factors limiting its performance breakthrough lies in the contradiction between the material properties of the transparent conductive window layer and the interface requirements in traditional devices. While indium tin oxide (ITO), a widely used transparent conductive window layer material, possesses high conductivity, its inherently high carrier concentration, required to achieve low resistance, can easily lead to suboptimal band alignment at the interface with the underlying buffer layer (CdS), potentially introducing a barrier that hinders efficient carrier extraction. More importantly, the deposition process of ITO thin films (such as sputtering) can cause micro-damage to the heterojunction sensitive junction interface formed by the ITO window layer and the CdS buffer layer. Furthermore, this interface can become an active region for carrier tunneling and non-radiative recombination during subsequent device operation. These factors collectively make the ITO / CdS interface a significant source of dark current and 1 / f noise in the device. When detecting extremely weak blood glucose-related signals, this inherent interface noise will severely overwhelm the effective signal, causing the detector's signal-to-noise ratio and detection limit to fail to meet the requirements of high-precision non-invasive blood glucose monitoring.

[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a photodetector, its preparation method and application, which aims to solve the problems of high dark current, high noise and insufficient signal-to-noise ratio under ultra-weak light conditions caused by the imperfect CdS / ITO interface characteristics of existing photodetectors.

[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a photodetector comprising a substrate, a first electrode layer, a photoelectric conversion layer, a CdS buffer layer, an ITO window layer, and a second electrode layer stacked sequentially. An intrinsic zinc oxide (i-ZnO) layer is provided between the CdS buffer layer and the ITO window layer.

[0009] Optionally, the thickness of the CdS buffer layer is 50-100 nm; the thickness of the intrinsic zinc oxide layer is 20-500 nm; and the thickness of the ITO window layer is 300-800 nm.

[0010] Optionally, the material of the photoelectric conversion layer includes copper-based chalcogenides.

[0011] Optionally, the copper-based chalcogenide is copper zinc cadmium tin selenide (CZCTSe).

[0012] Optionally, the material of the first electrode includes Mo; the material of the second electrode includes Ag.

[0013] A second aspect of the present invention provides a method for fabricating the photodetector described above, the method comprising the following steps: Provide a base; A first electrode layer, a photoelectric conversion layer, and a CdS buffer layer are sequentially formed on the surface of the substrate. An intrinsic zinc oxide layer is formed on the surface of the CdS buffer layer; An ITO window layer is formed on the surface of the intrinsic zinc oxide layer; A second electrode layer is formed on the surface of the ITO window layer.

[0014] Optionally, the step of forming an intrinsic zinc oxide layer on the surface of the CdS buffer layer specifically includes: Intrinsic zinc oxide layers were prepared using magnetron sputtering under preset vacuum conditions.

[0015] Optionally, the process parameters of the magnetron sputtering technology include: sputtering power of 50-100 W, time of 5-25 min, and substrate temperature of room temperature to 300°C.

[0016] Optionally, the preset vacuum condition includes: a background vacuum of 7 × 10⁻⁶. -4 -1×10 -3 Pa, with a working vacuum degree of 0.1-1 Pa.

[0017] A third aspect of the present invention provides the application of the photodetector of the present invention as described above in blood glucose monitoring.

[0018] In a fourth aspect, the present invention provides an optical sensor for non-invasive blood glucose monitoring, the optical sensor comprising the photodetector described above and integrated into a portable Raman spectrometer system.

[0019] Optionally, the portable Raman spectrometer system includes the aforementioned photodetector, low-power laser excitation module, and high-efficiency optical collection and dispersion system.

[0020] The present invention has the following beneficial effects: This invention proposes a photodetector, its fabrication method, and its application. Compared with existing technologies, the photodetector with an i-ZnO layer provided by this invention has the following significant advantages: 1. Achieving ultra-low noise and ultra-high detection sensitivity: By introducing an intrinsic zinc oxide (i-ZnO) layer between the CdS buffer layer and the ITO window layer, the interface band structure is effectively optimized, significantly suppressing non-radiative recombination and tunneling effects of carriers at the interface, thereby greatly reducing the device's dark current and critical 1 / f noise. This enables the device to possess extremely high specific detectivity (D*) and nanosecond-level fast response characteristics in zero-bias (self-driven) operating mode, effectively extracting microvolt-level and even weaker light signals, fundamentally meeting the stringent requirements of non-invasive blood glucose monitoring for ultra-high signal-to-noise ratio and ultra-low detection limit. 2. Excellent environmental stability: The optimized i-ZnO layer enhances the structural integrity of the device, enabling it to maintain stable performance over a wide temperature range and after long-term storage, ensuring the long-term reliability and consistency of monitoring data under complex operating environments. 3. Meets the low power consumption and miniaturization requirements of wearable devices: The detector of this invention is based on a self-driven (zero bias) operating mode, requiring no external power supply to provide bias voltage, which greatly reduces the power consumption of the detection system itself. This helps to achieve miniaturization and lightweight design of monitoring devices, extend the device's battery life, and provides a key device foundation for developing truly portable, wearable, continuous non-invasive blood glucose monitoring devices. 4. Provides a device-level solution for high-end biosensing: This invention combines a photodetector with the principle of optical non-invasive blood glucose detection, solving the core problem of weak physiological light signal extraction through targeted interface engineering. This provides a practical and innovative device-level solution with significant practical application prospects for overcoming the bottleneck of signal detection in current non-invasive blood glucose monitoring technology. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the layered structure of a photodetector provided in an embodiment of the present invention; Figure 2 Noise characteristic curves of the photodetector prepared in Example 1 (with I-ZnO layer): a is the noise measurement curve, b is the logarithmic curve of photocurrent and theoretical minimum detection power; Figure 3 This is a schematic diagram of the photodetector prepared in Example 1 for extremely weak light detection; Figure 4 This is a schematic diagram illustrating the application of the photodetector from Example 1 in Raman spectroscopy for blood glucose detection. Detailed Implementation

[0022] This invention provides a photodetector, its fabrication method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0023] Currently, the photodetectors commonly used in wearable medical devices have significant limitations: insufficient sensitivity and detectivity result in low signal-to-noise ratios; limited spectral response range makes it difficult to fully utilize the near-infrared "bio-optical window"; and performance degrades sharply in low-light conditions such as indoor environments or after transmission through biological tissues. To compensate for these shortcomings, existing solutions often resort to using multiple detectors in parallel and equipped with high-power light sources. This not only significantly increases the overall power consumption of the system and shortens the device's battery life, but also makes the hardware design complex and the manufacturing cost high. In addition, the response speed and long-term environmental stability (such as sensitivity to temperature fluctuations and continuous use) of such detectors need to be improved, making it difficult to meet the reliability requirements of continuous medical-grade monitoring.

[0024] Based on this, embodiments of the present invention provide a photodetector, the photodetector comprising a substrate, a first electrode layer, a photoelectric conversion layer, a CdS buffer layer, an ITO window layer and a second electrode layer stacked sequentially; An intrinsic zinc oxide (i-ZnO) layer is provided between the CdS buffer layer and the ITO window layer.

[0025] The photodetector provided in this invention has the following core performance advantages: it can achieve self-driven operation without external bias voltage, and simultaneously possesses ultra-high specific detectivity, nanosecond-level fast response, ultra-wide spectral response from visible light to near-infrared, and excellent ultra-weak light detection capability. This superior comprehensive performance allows it to operate stably under extremely low incident light intensity in applications such as non-invasive blood glucose monitoring without relying on high-power excitation sources, thereby fundamentally reducing the power consumption of the entire detection system. Furthermore, the introduction of the i-ZnO layer enhances the structural stability, giving the device good environmental tolerance and ensuring the reliability of long-term, continuous monitoring. Therefore, this detector is an ideal core sensing element for building a new generation of high-precision, low-power, long-endurance wearable non-invasive health monitoring devices.

[0026] The aforementioned superior performance is fundamentally due to the successful manipulation of the CdS / ITO heterointerface by the i-ZnO layer. The high resistivity and high transmittance of the i-ZnO film enable electrical reconstruction and physical manipulation of the interface, specifically through the following two synergistic mechanisms: 1. Interface bandgap manipulation and tunneling suppression mechanism: i-ZnO possesses a moderate work function between CdS and ITO, and an extremely low free carrier concentration. Its insertion between CdS and highly doped ITO forms a controllable stepped bandgap transition region. This structure optimizes band alignment at the interface, particularly smoothing or eliminating potential conduction band spikes, thereby effectively suppressing dark currents dominated by direct carrier tunneling or trap-assisted tunneling under zero or small bias voltages. The significant reduction in dark current is a decisive factor in improving the detector's specific detectivity (D*) and reducing background noise. 2. Interface defect passivation and recombination suppression mechanism: The i-ZnO layer physically acts as a protective barrier. In the subsequent fabrication of the ITO window layer, a sputtering process with high-energy particles is typically employed. The presence of the i-ZnO layer effectively blocks or attenuates the bombardment damage of these high-energy particles to the underlying sensitive CdS layer and, more critically, the CdS / CZCTSe main junction interface, avoiding the introduction of numerous interface defect states and impurity scattering centers. This essentially passivates interface defects, significantly reduces the density of non-radiative recombination centers, thereby further suppressing noise generated by carrier recombination (especially the critical 1 / f noise) and improving the collection efficiency of photogenerated carriers.

[0027] In summary, this invention, by introducing an i-ZnO layer, achieves precise optimization of the electrical properties of the heterojunction interface through the synergistic effect of bandgap engineering and interface passivation at two core physical levels, without significantly sacrificing the device's optical transmittance and lateral conductivity. This optimization ultimately aims to fundamentally reduce the detector's dark current and various types of noise (especially low-frequency 1 / f noise), and significantly improve its specific detectivity and signal-to-noise ratio under ultra-weak light conditions. This enables the photodetector to meet the extremely demanding requirements of biomedical sensing applications such as non-invasive blood glucose monitoring for core photoelectric sensing elements, providing an effective device-level solution to the bottleneck problem of weak physiological signal extraction.

[0028] In some embodiments, the thickness of the CdS buffer layer is 50-100 nm; the thickness of the intrinsic zinc oxide layer is 20-500 nm; and the thickness of the ITO window layer is 300-800 nm.

[0029] In some preferred embodiments, the thickness of the intrinsic zinc oxide layer is 60 nm.

[0030] The specific thickness range of the I-ZnO layer in this embodiment of the invention is based on its mechanism of achieving the best balance between interface bandgap modulation, efficient carrier transport, and suppression of optical loss. The specific principles are as follows: 1. Interface modulation efficiency and carrier tunneling suppression principle: When the I-ZnO layer thickness is approximately 60 nm, it is sufficient to form an intrinsic semiconductor spacer layer with sufficient modulation capability between CdS and ITO. This thickness ensures the establishment of a sufficient built-in electric field, effectively blocking excessive dark current caused by direct carrier tunneling at the CdS / ITO interface, achieving effective extension and optimization of the intrinsic junction electric field; it also avoids the significant series resistance effect on the longitudinal transport of photogenerated carriers caused by excessive thickness, ensuring low-loss operation of the device at high response speeds. 2. Optical transmittance and interface defect passivation principle: I-ZnO has extremely high intrinsic optical transmittance. A thickness of approximately 60 nm is sufficient to physically isolate the underlying CdS sensitive surface from the bombardment of high-energy particles during subsequent ITO layer deposition, thereby maximizing the material quality of the heterojunction main junction interface and the CdS bulk phase, and passivating interface defects introduced by process damage. Simultaneously, this thickness introduces negligible optical interference losses in the near-infrared band, ensuring efficient delivery of incident light to the absorption layer and enabling the effective detection of extremely weak reflected or transmitted light signals modulated by biological indicators such as blood glucose levels.

[0031] Using an approximately 60 nm thickness for processing, compared to excessively thin or thick I-ZnO layers, yields the following synergistic technical effects: 1. Optimal dark current suppression and noise reduction: At this optimized thickness, the I-ZnO layer can most effectively suppress interface tunneling current and recombination current, minimizing dark current in self-driven mode. This directly translates to a significant reduction in detector noise floor and a substantial improvement in specific detectivity (D*), providing a foundation for detecting picowatt-level optical signals. 2. Formation of a highly efficient photoelectric conversion and carrier collection interface: This thickness ensures that photogenerated carriers can recombine within the I-ZnO layer with an extremely low probability and be efficiently extracted to the electrodes, while maintaining the device's extremely high external quantum efficiency. This allows the detector to output high signal-to-noise ratio electrical signals even under ultra-weak light conditions. 3. Guaranteed process compatibility and device performance reproducibility: The 60 nm thickness window is highly compatible with standard magnetron sputtering process parameters, facilitating the deposition of uniform, dense, high-quality thin films. This endows the processing method with excellent process robustness and reproducibility in large-scale fabrication, laying the technological foundation for obtaining high-end detector products with consistent and reliable performance.

[0032] In some embodiments, the material of the photoelectric conversion layer includes copper-based chalcogenides.

[0033] In some embodiments, the copper-based chalcogenide is copper zinc cadmium tin selenide (CZCTSe).

[0034] Based on the CZCTSe absorption layer, the photodetector has a wide spectral response range, covering multiple near-infrared characteristic bands related to blood glucose detection.

[0035] In some embodiments, the material of the first electrode includes Mo; the material of the second electrode includes Ag.

[0036] This invention provides a method for fabricating a photodetector, the method comprising the following steps: Provide a base; A first electrode layer, a photoelectric conversion layer, and a CdS buffer layer are sequentially formed on the surface of the substrate. An intrinsic zinc oxide layer is formed on the surface of the CdS buffer layer; An ITO window layer is formed on the surface of the intrinsic zinc oxide layer; A second electrode layer is formed on the surface of the ITO window layer.

[0037] In some embodiments, the step of forming an intrinsic zinc oxide layer on the surface of the CdS buffer layer specifically includes: Intrinsic zinc oxide layers were prepared using magnetron sputtering under preset vacuum conditions.

[0038] In some embodiments, the process parameters of the magnetron sputtering technology include: sputtering power of 50-100 W, time of 5-25 min, and substrate temperature of room temperature to 300°C.

[0039] In some embodiments, the specified vacuum condition includes: a background vacuum of 7 × 10⁻⁶. -4 -1×10 -3 Pa, with a working vacuum degree of 0.1-1 Pa.

[0040] In some preferred embodiments, the sputtering power is 50 W, the sputtering time is 10 min, the working vacuum is 0.3 Pa, and the substrate temperature is room temperature.

[0041] Compared to high-temperature growth or certain chemical deposition processes, the room-temperature magnetron sputtering process employed in this embodiment of the invention achieves low-temperature, low-damage epitaxial growth of I-ZnO films on the surface of a CdS buffer layer by precisely controlling plasma energy and deposition time. This gentle physical vapor deposition method ensures the formation of a high-purity, high-density intrinsic zinc oxide layer while minimizing thermal damage and chemical erosion to the underlying CdS buffer layer and the sensitive interface of the heterojunction. Furthermore, the resulting I-ZnO layer exhibits natural vacuum compatibility and interface affinity with the subsequent sputtering deposition process of the ITO window layer, guaranteeing smooth integration and stability throughout the entire process.

[0042] The sputtering power and time parameter combination selected in this embodiment of the invention is based on its precise control mechanism for film growth kinetics, interface microstructure, and electrical properties: 1. Power-controlled film growth quality and stress regulation mechanism: Setting the sputtering power to 50 W is based on the balance between the kinetic energy of deposited particles and the film quality. This power provides sufficient sputtering yield for the ZnO target, ensuring a stable deposition rate and giving the particles reaching the substrate appropriate energy. It ensures that the deposited I-ZnO film has good crystal orientation (such as c-axis preferred growth) and high density to achieve effective interface control; it also avoids excessive bombardment of the CdS surface by high-energy particles due to excessive power, which could cause lattice damage or introduce compressive stress, thus achieving an optimal balance between film quality and interface integrity. 2. Time-controlled film thickness accuracy and functional realization mechanism: Setting the sputtering time to 10 minutes is based on the precise matching of the target film thickness (approximately 60 nm) and interface functional requirements. This duration is key to achieving the aforementioned optimal thickness window. This process exhibits excellent controllability and repeatability: with fixed power and gas pressure, the film thickness exhibits a linear relationship with time. Therefore, this time window is sufficient to grow a uniform and fully functional I-ZnO interface layer, while avoiding film discontinuities and uneven coverage due to excessively short time, or unnecessary deposition time and potential stress accumulation due to excessively long time, thus achieving a balance between interface optimization and fabrication efficiency. 3. Mechanism for film purity and uniformity ensured by a low-pressure environment: A working gas pressure of 0.3 Pa is used to maintain a pure sputtering environment with a suitable mean free path. The lower gas pressure reduces the scattering of sputtering gas molecules on the deposited particles, allowing them to deposit onto the substrate in a more perpendicular direction, which is beneficial for forming a uniform and dense film and reducing the incorporation of gaseous impurities in the film layer. This ensures the high intrinsic resistivity and high optical transmittance of the I-ZnO layer, essentially guaranteeing the realization of its interface control function and process reproducibility.

[0043] Using the optimized parameter combination of 50 W power, 10 minutes time, and 0.3 Pa pressure, synergistic and significant technical effects were achieved: 1. High-quality, low-damage interface layer preparation: Under these parameters, a high-quality intrinsic ZnO film with good crystallinity and tight bonding with the substrate can be formed on the CdS surface. This film, as an ideal interface layer, effectively blocks potential damage from subsequent ITO deposition without introducing microstructural problems such as pinholes and excessively high defect density caused by improper processing. This is the direct technological basis for fundamentally suppressing the device's dark current. 2. Optimized interface band structure and electrical properties: This parameter combination contributes to the ideal intrinsic electrical properties (high resistivity, moderate work function) and excellent film quality of the I-ZnO layer. The low-defect-density heterojunction formed with CdS optimizes band transition and significantly suppresses interfacial tunneling and recombination of charge carriers, thereby jointly leading to a significant reduction in device noise and a substantial improvement in specific detectivity. 3. Ensuring high process controllability and industrialization potential: Based on this preferred feature, the embodiments of the present invention provide a broad and stable process window. This parameter combination is easily implemented and repeated on standard magnetron sputtering equipment, demonstrating excellent process controllability, consistency, and high production capacity potential, laying a solid process foundation for the large-scale fabrication of high-performance detectors.

[0044] Currently, the core bottleneck in achieving high-precision non-invasive physiological indicator (such as blood glucose) monitoring lies in how to stably extract weak, specific signals originating from subcutaneous blood vessels or tissue fluid from complex surface optical signals. The strong scattering and absorption of light by the superficial layers of the skin constitutes the main background noise, severely limiting the signal-to-noise ratio and reliability of the detection.

[0045] This invention provides the application of the above-described photodetector in blood glucose monitoring.

[0046] This invention provides an optical sensor for non-invasive blood glucose monitoring, the optical sensor including the photodetector described above and integrated into a portable Raman spectrometer system.

[0047] In some embodiments, the portable Raman spectrometer system includes the aforementioned photodetector as the core sensing unit, combined with optional 905 nm, 1064 nm, and 1310 nm low-power laser excitation modules and a high-efficiency optical collection and dispersive system, to construct a complete spectral analysis device suitable for body surface detection. This system utilizes Raman spectroscopy, irradiating the palm (thenar eminence) with a laser and collecting the resulting Raman scattered light. The skin of the palm is relatively thin, with a rich subcutaneous capillary network, and is easy to locate and stably measure, making it an ideal detection site for obtaining spectral information related to blood components.

[0048] In this application scenario, the photodetector provided by this invention plays a crucial role. The specific principles and effects are as follows: 1. Broad spectral response and signal capture capability: The photodetector possesses a broad spectral response covering the visible to near-infrared range (e.g., 300 nm to 1700 nm). This characteristic enables it to effectively capture Stokes or anti-Stokes scattering signals generated by biomolecules such as glucose at specific Raman shifts after stimulation. The detector's spectral response range completely covers the important wavebands associated with glucose characteristic peaks.

[0049] 2. Enhanced Sensitivity and Signal-to-Noise Ratio: The photodetector, with its extremely high specific detectivity and picowatt-level ultra-weak light detection capability, can reliably extract extremely weak glucose characteristic Raman peak signals from strong background interference (such as skin autofluorescence and tissue elastic scattering). This directly translates into high signal-to-noise ratio in the acquired raw spectral data, laying a solid foundation for subsequent accurate analysis. 3. Low Power Consumption and System Integration Advantages: The photodetector can operate in self-driven mode without an external bias voltage, significantly reducing power consumption as the sensing front end. Combined with its high sensitivity allowing the use of low-power excitation sources, the overall power consumption of the portable spectrometer system is greatly reduced. This not only facilitates miniaturization and lightweight design of the device but also directly extends the battery life after a single charge, meeting the stringent power consumption requirements of wearable devices.

[0050] The complete workflow and final function of the system: By deeply integrating the high-performance photodetector with portable Raman spectroscopy technology, the optical sensor system of this invention enables rapid, non-invasive monitoring of blood glucose concentration trends, for example, on the user's palm. During system operation, a low-power laser safely irradiates the skin, and the detector collects the resulting Raman scattered light and converts it into a high signal-to-noise ratio electrical signal. The collected high-quality Raman spectral data can be further transmitted to a processing unit for analysis using chemometric algorithms (e.g., partial least squares) to establish a quantitative calibration model between spectral features (such as the intensity, shift, or shape of specific Raman peaks) and blood glucose concentration, ultimately achieving non-invasive detection and trend analysis of blood glucose concentration.

[0051] Fundamental Analysis of the Advantages of the Solution: The aforementioned advantages achieved by this technical solution are fundamentally rooted in the superior physical performance of the photodetector itself. Specifically: 1. Detector Performance Foundation: The self-driven photodetector based on copper-based chalcogenide thin films such as copper-zinc-tin-sulfur-selenium achieves extremely high specific detectivity, ultra-wide spectral response range, and picowatt-level ultra-weak light detection capability through i-ZnO interface optimization. These core performance indicators are the physical basis for its excellent performance in applications. 2. Signal Extraction Mechanism: These characteristics enable the photodetector to capture extremely weak light intensity changes modulated by subcutaneous biological tissue with exceptional sensitivity. In applications, the sensor system utilizes a low-intensity light source and, through optimized optical design, allows the detector to primarily receive light signals carrying blood glucose information from the subcutaneous target depth (such as the dermis). 3. System-Level Benefits: Because the core detector possesses high sensitivity even in ultra-weak light, the entire system does not require high-power light sources or multi-source arrays designed to compensate for insufficient sensitivity. This not only significantly reduces the overall power consumption, hardware complexity, and manufacturing cost of the system, but also enables end-consumer devices that integrate this solution to have longer battery life and a better user experience, truly meeting the expectations of personal health management for portable, non-invasive continuous monitoring devices.

[0052] In summary, the optical sensor provided by the embodiments of the present invention, by systematically integrating a high-performance photodetector with portable Raman spectroscopy technology, offers an effective technical solution to address key issues in non-invasive blood glucose monitoring such as weak signals, high power consumption, and difficulty in portability, demonstrating its enormous application potential in the field of personal health management.

[0053] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0054] The following detailed description uses specific examples.

[0055] Example 1: Fabrication of a photodetector The photodetector comprises, in sequence, a soda-lime glass substrate, a Mo back electrode layer, a copper zinc cadmium tin selenide (CZCTSe) photoelectric absorption layer, a CdS buffer layer, an intrinsic zinc oxide (I-ZnO) layer, an ITO window layer, and an Ag top electrode layer. The soda-lime glass substrate is 2 mm thick, the Mo layer is 700 nm thick, the CZCTSe film is 1.2 μm thick, the CdS buffer layer is 100 nm thick, the I-ZnO layer is 100 nm thick, the ITO window layer is 450 nm thick, and the Ag top electrode layer is 500 nm thick. A schematic diagram of its structure is shown below. Figure 1 .

[0056] The fabrication of a photodetector includes the following steps: 1. Provide and fabricate back electrode: Provide a soda-lime glass substrate and deposit a Mo layer with a thickness of 700 nm on the substrate as the back electrode using DC magnetron sputtering.

[0057] 2. Preparation of copper-zinc-cadmium-tin-selenium (CZCTSe) absorber layer: Cuprous chloride (CuCl, 1.326 g), zinc acetate (Zn(CH3COO)2·2H2O, 1.647 g), tin tetrachloride (SnCl4·5H2O, 2.922 g), cadmium chloride pentahydrate (CdCl2·2.5H2O, 0.366 g), and thiourea (CS(NH2)2, 4.872 g) were used as reaction sources and dissolved together in 20 mL of ethylene glycol monomethyl ether solvent. The solution was magnetically stirred until completely dissolved and clear, forming a precursor solution. The molar ratio of each metal source was controlled as Cu / (Zn+Cd+Sn) ≈ 0.8, (Zn+Cd) / Sn ≈ 1.2, where Cd / (Zn+Cd) ≈ 0.2.

[0058] The substrate coated with the Mo layer is placed on a heating stage, and the precursor solution is coated onto it by spin coating to form a preform.

[0059] The obtained sample was placed in a tube furnace and selenized in a selenium-containing atmosphere to finally obtain a copper zinc cadmium tin selenide (CZCTSe) absorber layer with a thickness of about 1.2 μm.

[0060] 3. Preparation of a CdS buffer layer using a chemical bath deposition method: Cadmium sulfate, thiourea, and ammonia were dissolved in deionized water to form a reaction solution. The concentration of cadmium sulfate in the reaction solution was 0.015 mol / L, the concentration of thiourea was 0.75 mol / L, the mass fraction of ammonia was 28%, and the mass ratio of ammonia to deionized water was 1:7. The sample with the deposited CZCTSe absorber layer was immersed in the above reaction solution at 80°C and reacted for 9 minutes. After the reaction, the sample was removed, thoroughly rinsed with deionized water to terminate the reaction and remove residues, and finally dried with nitrogen or at low temperature to obtain a uniform CdS buffer layer with a thickness of approximately 60 nm on the surface of the absorber layer. 4. Preparation of the I-ZnO layer: The above sample was transferred to a magnetron sputtering apparatus. Using a high-purity ZnO ceramic target, an I-ZnO layer was deposited under a pure argon atmosphere. The process parameters were: sputtering power of 50 W, working pressure of 0.3 Pa, deposition time of 10 minutes, and substrate maintained at room temperature. This low-temperature, low-damage process yielded an intrinsic zinc oxide thin film with a thickness of approximately 100 nm, high resistivity, and high transmittance.

[0061] 5. Preparation of the ITO window layer: On the I-ZnO layer, an ITO layer was deposited using magnetron sputtering. The process parameters were: sputtering power of 100 W and working pressure of 0.35 Pa, resulting in an ITO film with a thickness of approximately 450 nm.

[0062] 6. Fabrication of the top electrode: An Ag electrode with a thickness of approximately 500 nm was deposited on the ITO window layer using a thermal evaporation method through a mask.

[0063] The performance of the photodetector prepared in Example 1 was tested, and the results are shown in [Figure 1]. Figure 2 and Figure 3 ,in, Figure 2 In the graph, 'a' represents the noise measurement plot, and 'b' represents the logarithmic curve of the photocurrent and the theoretical minimum detection power. Photoelectric response and detection capability: Under weak light illumination in the near-infrared band, the detector exhibits a significant photoelectric response. Its specific detectivity (D*) has been greatly improved after optimization, and the lower limit of stable detectable light intensity is extremely low, indicating that it has excellent weak light detection capability.

[0064] Dark current and noise characteristics: When tested in zero bias (self-driven) mode, its dark current is significantly reduced compared to the comparison device without the introduction of I-ZnO layer, and the corresponding noise is effectively suppressed, resulting in a significant improvement in signal-to-noise ratio.

[0065] Environmental stability: After being placed in high-temperature and low-temperature environments for 1 hour each, the detector showed minimal performance degradation; after being stored indoors for a long time, the main photoelectric parameters remained stable, demonstrating excellent reliability.

[0066] Example 2: Fabrication of a photodetector The method in this embodiment is basically the same as that in embodiment 1, except that the deposition parameters of the I-ZnO interface optimization layer are adjusted in step 4: the sputtering power is adjusted to 60 W and the deposition time is adjusted to 15 minutes to verify the breadth of the process window and its impact on performance.

[0067] Application example: Demonstration of non-invasive blood glucose trend monitoring The photodetector prepared in Example 1 was integrated into a prototype portable Raman spectroscopy detection module for demonstration of non-invasive blood glucose-related signal detection. (See schematic diagram below.) Figure 4 .

[0068] Validation of the potential for blood glucose-related signal detection: The sensing module constructed based on the detector of Embodiment 1 of this invention exhibits excellent performance in blood glucose testing based on Raman spectroscopy under simulated physiological conditions. Test results show that the module can clearly distinguish weak optical signal changes caused by the target glucose concentration gradient, and the output signal shows a high correlation with the concentration change. The detector's superior ultra-weak light detection capability and high signal-to-noise ratio characteristics are the physical basis for achieving this high-sensitivity detection, validating its great potential as a core sensing element for next-generation non-invasive, continuous blood glucose monitoring devices.

[0069] In summary, this invention provides a photodetector, its fabrication method, and its applications. The core of this invention lies in the effective electrical reconstruction and defect passivation of key heterojunctions by introducing an intrinsic zinc oxide layer into the device structure. After this optimization, the detector achieves fundamentally improved overall performance, including significantly enhanced specific detectivity, rapid response speed, and superior detection capability for ultra-weak light signals. Simultaneously, the device also exhibits excellent environmental stability and reliability.

[0070] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A photodetector, characterized in that, The photodetector comprises a substrate, a first electrode layer, a photoelectric conversion layer, a CdS buffer layer, an ITO window layer, and a second electrode layer, which are stacked sequentially. An intrinsic zinc oxide layer is provided between the CdS buffer layer and the ITO window layer.

2. The photodetector according to claim 1, characterized in that, The thickness of the intrinsic zinc oxide layer is 20-500 nm.

3. The photodetector according to claim 1, characterized in that, The material of the photoelectric conversion layer includes copper-based chalcogenides.

4. The photodetector according to claim 3, characterized in that, The copper-based chalcogenide is copper-zinc-cadmium-tin-selenium.

5. The photodetector according to claim 1, characterized in that, The material of the first electrode includes Mo; the material of the second electrode includes Ag.

6. A method for fabricating a photodetector according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: Provide a base; A first electrode layer, a photoelectric conversion layer, and a CdS buffer layer are sequentially formed on the surface of the substrate. An intrinsic zinc oxide layer is formed on the surface of the CdS buffer layer; An ITO window layer is formed on the surface of the intrinsic zinc oxide layer; A second electrode layer is formed on the surface of the ITO window layer.

7. The method for fabricating a photodetector according to claim 6, characterized in that, The step of forming an intrinsic zinc oxide layer on the surface of the CdS buffer layer specifically includes: Intrinsic zinc oxide layers were prepared using magnetron sputtering under preset vacuum conditions.

8. The method for fabricating a photodetector according to claim 7, characterized in that, The process parameters of the magnetron sputtering technology include: sputtering power of 50-100 W, time of 5-25 min, and substrate temperature of room temperature to 300℃.

9. The application of the photodetector according to any one of claims 1-5 in blood glucose monitoring.

10. An optical sensor for non-invasive blood glucose monitoring, characterized in that, The optical sensor includes the photodetector as described in any one of claims 1-5 and is integrated into a portable Raman spectrometer system.

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