A diamond immersion detector

Abstract

This invention relates to the field of photoelectric detection technology, specifically to a diamond immersion detector. The invention utilizes ultra-wide bandgap boron-doped p-type diamond single crystal (PDSC) as the photoelectrode to construct a vacuum ultraviolet immersion photodetector with a PDSC-ultrapure water-Pt structure. The PDSC immersion photodetector prepared by this invention exhibits a responsivity as high as 87.8 mA / W under zero bias and 193 nm excitation wavelength conditions, which is close to the photoresponsivity shown by standard commercial Si detectors; furthermore, under low optical power excitation, the responsivity of the PDSC immersion detector can reach as high as 670 mA / W. The immersion detector of this invention is a low-cost, self-powered, and highly sensitive vacuum ultraviolet photodetector with good stability, showing promising application prospects for 193 nm power monitoring in deep ultraviolet light source lithography machines.

Description

Technical Field

[0001] This invention relates to the field of photoelectric detection technology, and specifically to a diamond immersion detector. Background Technology

[0002] High-performance, high-sensitivity vacuum ultraviolet (VUV, 10-200nm) light detection is of great significance for space science (space exploration, astrophysics, etc.), radiation monitoring (synchrotron radiation, free-electron lasers, etc.), the electronics industry (semiconductor lithography, surface technology, etc.), and basic science (analytical instruments, spectroscopic physics, etc.). In particular, the mainstream deep ultraviolet lithography system currently employs immersion projection lithography based on 193nm vacuum ultraviolet light. This technique uses a water immersion method between the bottom lens element and the photoresist to effectively reduce the 193nm wavelength to 134nm, thereby achieving 10-45nm-level lithography on a photoresist-coated silicon wafer. During this process, monitoring and calibrating the 193nm light power is crucial for a stable lithography process and contributes to the development of deep ultraviolet lithography technology.

[0003] Constructing self-powered devices that can operate independently, wirelessly, and sustainably without an external power source has become an important research topic for next-generation electronic systems. Self-powered photodetectors, as a key component of energy-efficient photoelectric sensing systems, have received widespread attention in recent years. Among them, photoelectrochemical detectors (PEC-PDs) possess advantages such as simple fabrication, low cost, good responsiveness, and fast light response, and are therefore widely studied for constructing efficient self-powered photodetectors. However, previous research on photoelectrochemical photodetectors has mainly focused on the visible and long-wavelength ultraviolet (UV) spectral ranges, while research on vacuum ultraviolet detection remains a blank. Therefore, exploring research on photochemical detectors with shorter wavelengths is undoubtedly of great significance for expanding the application scenarios of photochemical detectors.

[0004] In practical applications, Si-based solid-state semiconductor detectors are currently the most mature technology for VUV band detection. However, due to Si's narrow bandgap of only 1.1 eV, the detector exhibits a broad-spectrum optical response and cannot be effectively used for extended periods in harsh environments such as those subjected to radiation. In practical applications, additional filters are required to achieve VUV selective response; however, the use of additional optical components such as filters not only increases device cost but also reduces VUV light transmittance. Therefore, finding semiconductors with larger bandgap capabilities is a prerequisite for realizing highly efficient and selective vacuum ultraviolet photodetectors.

[0005] Diamond is the ideal material for manufacturing electronic and optical devices, possessing excellent properties such as ultra-high thermal conductivity, ultra-high carrier mobility, and ultra-wide bandgap. Furthermore, diamond-based devices have been proven to withstand high temperatures, high ionization currents, and strong X-ray and VUV irradiation, and exhibit good DUV / VUV selective response. Therefore, diamond holds great promise in the field of deep ultraviolet and vacuum ultraviolet photodetector research. With the maturation of two synthetic diamond synthesis methods in recent years—high-temperature high-pressure method and chemical vapor deposition—the acquisition of large-size and high-quality diamond single crystals has become increasingly easier, leading to significant development in diamond-based optoelectronic devices. Against this research background, there is a need to develop diamond-based photoelectrochemical vacuum ultraviolet photodetectors. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention aims to provide a diamond immersion detector. This detector uses ultra-wide bandgap boron-doped p-type diamond (PDSC) as the photoelectrode to construct a vacuum ultraviolet immersion photodetector with a PDSC-ultrapure water-Pt structure. This immersion detector is a low-cost, self-powered, and highly sensitive vacuum ultraviolet photodetector with good stability, and it shows promising application prospects in power monitoring at 193nm in deep ultraviolet light source lithography machines.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] This invention provides a diamond immersion detector, which is an immersion photodetector based on ultra-wide bandgap boron-doped p-type diamond. The detector adopts a two-electrode system with a boron-doped p-type diamond wafer-ultrapure water-Pt structure.

[0009] Figure 1 Figures a and b illustrate the basic working principle of a DUV immersion lithography machine. The 193nm immersion lithography technology effectively reduces the 193nm wavelength to 134nm by immersing the bottom lens element and photoresist in ultrapure water, opening up space for improved resolution and depth of focus. Monitoring the 193nm laser power is crucial in this process. To effectively monitor deep ultraviolet 193nm light, a detector based on an ultra-wide bandgap semiconductor is required. Here, considering diamond's ultra-wide bandgap (Eg = 5.5 eV), ultra-high carrier mobility, and absolute advantage in DUV / VUV selective response, this invention proposes constructing a diamond-based immersion solution photodetector for detecting 193nm light.

[0010] For currently mature high-temperature and high-pressure diamond growth (such as...) Figure 1As shown in Figure c), boron doping of diamond is relatively easy. Electrodes made of boron-doped diamond (BDD) exhibit wide potential windows, low background current, and high corrosion resistance in electrochemical analysis. Furthermore, boron-containing diamond possesses excellent oxidation resistance, thermal conductivity, and thermal stability. In addition, boron, as a shallow acceptor impurity in diamond, contributes to its p-type conductivity. Therefore, based on this idea, this invention uses boron-doped p-type HPHT diamond single crystal (PDSC) as the working electrode to attempt to construct a diamond-based immersion photodetector for monitoring 193nm deep ultraviolet light. A schematic diagram is shown below. Figure 1 As shown in d, when 193nm light irradiates the working electrode of the PDSC, the PDSC will generate photogenerated electron-hole pairs, and the electrons will flow from the Pt electrode along the external circuit to the working electrode of the PDSC.

[0011] Preferably, the diamond immersion detector is prepared by using a boron-doped p-type diamond wafer and a platinum electrode as the working electrode and counter electrode, respectively, connected by ultrapure water, to obtain the diamond immersion detector.

[0012] Preferably, the boron-doped p-type diamond wafer is synthesized under high temperature and high pressure conditions using a temperature gradient method.

[0013] More preferably, the solvent alloy used in the method for synthesizing boron-doped p-type diamond wafers is a nickel-based alloy, the carbon source is high-purity graphite, and amorphous boron is added to the carbon source for diamond growth.

[0014] More preferably, the boron-doped p-type diamond wafer is synthesized by growing at a high temperature of 1300–1400°C and a high pressure of 5.0–6.0 GPa for 22–52 hours using a temperature gradient method.

[0015] The diamond immersion detector provided by this invention is applied to vacuum ultraviolet light detection.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention utilizes ultrawide-bandgap boron-doped p-type diamond (PDSC) as the photoelectrode to construct a vacuum ultraviolet immersion photodetector with a PDSC-ultrapure water-Pt structure. The diamond used in this invention is synthesized under high temperature and high pressure (HPHT) conditions via a temperature gradient method, resulting in wafers with excellent crystal quality. The PDSC immersion photodetector prepared in this invention exhibits a responsivity as high as 87.8 mA / W under zero bias and 193 nm excitation wavelength conditions, approaching the photoresponsivity shown by standard commercial Si detectors. Furthermore, under low optical power excitation, the responsivity of the PDSC immersion photodetector can reach as high as 670 mA / W. This immersion detector is a low-cost, self-powered, and highly sensitive vacuum ultraviolet photodetector with good stability, showing promising application prospects for power monitoring at 193 nm in deep ultraviolet light source lithography machines. Attached Figure Description

[0018] Figure 1 Photodetection of a 193nm immersion lithography machine using a PDSC immersion detector, including (a) the principle of 193nm immersion lithography; (b) the principle of 193nm immersion lithography; (c) from left to right: the internal structure of a high-temperature and high-pressure autoclave; boron-doped blue diamond synthesized by the high-temperature and high-pressure method; diamond single crystal wafers sliced ​​out; and (d) the working principle of the PDSC immersion detector.

[0019] Figure 2 The XRD diffraction pattern of boron-doped diamond;

[0020] Figure 3 The Raman diffraction pattern of boron-doped diamond;

[0021] Figure 4 The infrared spectrum of boron-doped diamond;

[0022] Figure 5 Test results of boron-doped diamond UPS

[0023] Figure 6The detection performance of the PDSC immersion detector is shown in the following figures: (a) the response gate function of the PDSC-based immersion detector at an external potential of 0–0.1 V (temperature T = 21 °C), with an inset showing a schematic diagram of the PDSC-based immersion detector; (b) the IV curves of the PDSC immersion detector at an external potential of 0–0.1 V under illumination and darkness; (c) the response gate function of the PDSC-based immersion detector at 0 V under different light power intensities; (d) the relationship between photocurrent density and responsivity at 0 V and power intensity; (e) the UV-Vis absorption spectrum of the PDSC and the responsivity of the PDSC-based immersion detector in ultrapure water under different wavelengths (193, 257, 325, 450, 532, 785 nm) excitation at 0 V; and a comparison of the responsivity and detection wavelength of different photoelectrochemical detectors.

[0024] Figure 7 The test results show the response performance of a PDSC immersion detector and a Si standard detector to 193 nm excitation light, with (a) test results of the PDSC immersion detector; (b) test results of the PDSC immersion detector to 193 nm; (c) test results of the Si standard detector; and (d) test results of the Si standard detector to 193 nm.

[0025] Figure 8 The detection mechanisms of the PDSC immersion detector are shown in (a) a schematic diagram of the multi-molecule catalytic photoelectrochemical detection mechanism; (b) a schematic diagram of the photocurrent multiplication photoelectrochemical detection mechanism; (c) the charge transfer process of the PDSC-ultrapure water-Pt system under illumination; and (d) the charge transfer process of the PDSC-ultrapure water-Pt system in the dark.

[0026] Figure 9 The photoelectrochemical microscopic mechanism is illustrated in the following diagrams: (a) Short-circuit measurement results connected to the source electrode, where the high-potential end of the source electrode is connected to the Pt counter electrode and the low-potential end is connected to the diamond working electrode; (b) Schematic diagram of the short-circuit recovery process after laser shutdown; (c) Device voltage output signal after the 193nm laser is shut off under different measurement conditions, recorded at different time points; (d) Evolution of the background signal. Results were measured under open-circuit conditions using an oscilloscope, with the positive terminal of the oscilloscope connected to the diamond working electrode and the negative terminal grounded to the Pt counter electrode; (e) Mechanism of the background signal recovery process in the open-circuit state after laser shutdown; (f) Change of device photoresponse voltage output signal generated by the 193nm pulse over time, recorded by the oscilloscope; (g) Decay time of the voltage output signal generated by the 193nm pulse over time; (h) Mechanism of the voltage output signal decay process under the 193nm pulse.

[0027] Figure 10The temperature-dependent response of the PDSC immersion detector is shown in the following figures: (a) I-wave curves under illumination measured at different temperatures (4°C, 25°C, and 50°C); (b) It curves at different temperatures and excitation powers (1278 nW, 1015 nW, 640 nW, 404 nW, 321 nW, 128 nW, and 65 nW from left to right) at zero bias; (c) response gate functions at different temperatures with a laser power of 1278 nW at zero bias; (d) comparison of responsivity at different temperatures with laser powers of 65 nW and 404 nW at zero bias; (e) change of responsivity at different temperatures with laser power at zero bias; and (f) comparison of response gate functions and responsivity at different temperatures with a laser power of 65 nW. Detailed Implementation

[0028] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0030] Example 1: Fabrication of a PDSC Immersion Detector

[0031] 1. Fabrication of PDSC immersion detector

[0032] S1. Preparation of high temperature and high pressure single crystal diamond: The high temperature and high pressure synthesis experiment was carried out on an SPD 6×1400 six-sided top press. The (100) face of the diamond seed crystal was used as the initial growth crystal face. High purity graphite column (99.999%) was used as carbon source, FeNiCo™ alloy was used as solvent alloy, and high purity boron powder (99.999%) was used as boron source. 0.5 at% boron powder was added to the carbon source for diamond growth. The HPHT temperature gradient method was used for synthesis. The growth pressure and temperature were 5.5 GPa and 1450℃, respectively. Ti was added as nitrogen agent and the growth time was 22-52 hours, preferably 40 hours. After the experiment, the sample was taken out and placed in a beaker containing dilute nitric acid to remove the metal catalyst wrapped around the synthesized diamond. Then, a mixed acid solution of sulfuric acid and nitric acid (volume ratio 3:1) was poured in to remove the metal and graphite residues on the surface and obtain ultra-wide bandgap boron-doped p-type diamond single crystal (PDSC).

[0033] S2. Cut the PDSC prepared in S1 into pieces with dimensions of 5.0 × 5.0 × 0.5 mm. 3A boron-doped p-type diamond wafer was used as the working electrode, secured by a J110 platinum sheet electrode clamp, with dimensions of 15×15×0.1mm. 3 A platinum electrode is used as the counter electrode, and ultrapure water is used to connect the two electrodes to form a photoelectrochemical immersion detector.

[0034] 2. Characterization of PDSC

[0035] The basic material characterization of boron-doped HPHT diamond used in this experiment, among which... Figure 2 The results of X-ray diffraction (XRD) are shown. The sharp diffraction peaks indicate that the wafer has good crystal quality. The diffraction characteristic peaks correspond to the (220) and (111) crystal planes of the diamond phase, respectively, indicating that there are two growth orientations of diamond grains. Figure 3 The results of the Raman test are shown, with a wavelength of ~1331 cm⁻¹. -1 The appearance of vibration peaks indicates the presence of the diamond phase (sp) inside the sample. 3 The high C content indicates good phase formation quality of the sample, and the sharp scattering peaks also show good crystallization quality of the wafers. Figure 4 The infrared test results are then displayed, with 2453 cm⁻¹ showing the result. -1 and 2789cm -1 The peaks at these locations are characteristic peaks related to uncompensated boron, corresponding to the transitions of electrons from the ground state to the first excited state and to the second excited state of the uncompensated boron atom, respectively. This indicates that the wafer contains a small amount of boron. Figure 5 The results of the study on the band structure of PDSC using ultraviolet photoelectron spectroscopy (UPS) are shown in the image. The experimental results show that the Fermi level is located 0.25 eV above the top of the valence band, indicating that the sample has p-type conductivity. The work function value obtained from the experiment is 4.33 eV, and the vacuum level of the electron is located below the bottom of the conduction band.

[0036] Example 1: Characterization and Feasibility Study of PDSC Immersion Detector

[0037] The following tests were performed using a Keythley 2636B source meter for It and IV tests. The low-potential terminal of the source meter was connected to a diamond working electrode, and the high-potential terminal was connected to a Pt electrode. A square quartz beaker (60×60×60mm) was used. 3The laser beam (JGS1) transmits 193nm light; this 193nm light is generated by an EX5 / 250-478ArF excimer pulse laser (GAM Laser, Inc.), with a laser frequency of 250Hz and an operating voltage of 11kV. In the optical path, a UV-fused silica right-angle prism is added to disperse the short-wavelength stray light, and a quartz lens is added for focusing to obtain a higher laser power density. Using 193nm irradiation, the focused spot size incident on the diamond wafer is approximately 4cm. 2 .

[0038] 1. Detection performance of PDSC immersion detectors

[0039] Figure 6 The response performance of a PDSC-based immersion detector under 193 nm light excitation is shown, where Figure 6 An illustration shows the setup for the experimental measurements. The response gate function of the PDSC-based immersion detector at an external potential of 0–0.1 V is shown below. Figure 6 As shown in Figure a, in order to measure the cyclic stability of the PDSC immersion detector under different bias potentials from 0 to 0.1V, the incident light was alternately switched on and off under the conditions of a temperature of 21℃ and a power intensity of 1278nW. The time interval between the switching states of the photodetector was 30 seconds, showing highly repeatable switching behavior. Figure 6 b shows the linear sweep voltammetry curves of the PDSC photoelectrode in ultrapure water, under illumination, and in darkness. When the bias voltage increases from 0 to 0.1 V, the photocurrent of the fabricated PDSC electrode increases almost linearly, indicating that the photocurrent response is related to the bias voltage. According to existing research, this relationship is reasonable because an external potential can effectively induce electron-hole acceleration, separation, and transport, thereby generating a higher photocurrent in the circuit. In addition, without any external bias potential, the PDSC immersion detector exhibits a significant photoresponse to 193 nm illumination, revealing the possibility of the PDSC immersion detector as a self-powered device.

[0040] Besides the bias potential, the incident light intensity also has a significant impact on the photoresponse of the PDSC immersion detector, which warrants further investigation. Figure 6 c plots the changes in the response gate function of the PDSC immersion detector under zero bias at different laser powers (65, 128, 321, 404, 640, 1015, 1278 nW). The response gate function increases with increasing laser power. Figure 6 The photocurrent density at different laser powers was extracted. It can be seen that as the laser power increases, the photocurrent density decreases from 10.93 nA / cm². 2 Increased to 27.94 nA / cm 2Furthermore, to evaluate the sensing performance of photocurrent as a function of light intensity, a responsivity (R) is introduced, which describes the photocurrent generated by unit power incident light in the effective region. The responsivity R is obtained by the following formula:

[0041]

[0042] Where is I light Photocurrent, I dark Here, is the dark current, p is the laser power density, and S is the effective illumination area. The responsivity calculation results under different incident light intensities are as follows: Figure 6 As shown in d, the PDSC immersion detector has a high photoresponse rate. In the range of 1278nW to 65nW, the photoresponse rate of the PDSC immersion detector is approximately 87.4 to 670 mA / W. Figure 6 This paper summarizes and compares the response performance of PDSC immersion detectors with currently reported photoelectrochemical detectors (including common GaN-based photodetectors). It can be seen that PDSC immersion detectors are currently the electrochemical-based detectors with the shortest detection wavelength (193 nm for vacuum ultraviolet light). They have the highest reported photoresponsivity of 670 mA / W (@65 nW), showing great application potential.

[0043] 2. Response performance of PDSC immersion detector and Si standard detector to 193nm excitation light

[0044] The experiment used a commercially available AXUV100G standard Si detector manufactured by An ITW Company, with a responsivity of 83.7 mA / W at a wavelength of 193 nm. In the experiment, a lens was used to focus the 193 nm laser beam, reducing its size so that it was entirely incident on the effective area of ​​the standard Si detector for detection. A Keythley 2636B source meter was used for IT testing. Figure 7 a and c are test working diagrams for the PDSC immersion detector and the Si standard detector, respectively. Figure 7 Figures b and d compare the response performance of the PDSC immersion detector and the standard Si detector at 193 nm. During this process, lens focusing ensured that the laser power incident on both detectors was equal. It can be seen that, under zero bias and the same power excitation conditions at 193 nm, the fabricated immersion photodetector exhibits a high responsivity of 87.8 mA / W, close to the 83.7 mA / W shown by the standard commercial Si detector, demonstrating its significant detection potential. Furthermore, the PDSC immersion detector operates in pure water, thus holding promise for applications in deep ultraviolet lithography for detecting 193 nm light. These results indicate that the PDSC immersion detector exhibits highly stable response performance due to its simple detector structure and the high stability of the diamond material.

[0045] 3. Detection mechanism of PDSC immersion detector

[0046] According to the formula for calculating external quantum efficiency At 193 nm excitation and EQE of 100%, the detector's limiting photoresponsivity is 155 mA / W. However, according to... Figure 6 The results show that, under low light conditions, the responsivity of the PDSC immersion detector (670 mA / W (@65 nW)) can be 3 to 4 times the theoretical maximum responsivity. This result can be understood based on the theoretical article by V. Sukhovatkin et al. (Science 324, 1542-1544, 2009), in which, in the case discussed, after a photon excites an exciton, the recombination of that exciton leads to the hyperexcitation of a carrier associated with another exciton within its band, i.e., effective Auger recombination. In photoelectrochemistry, this invention considers the possibility of a photon exciting an electron-hole pair, thereby electrolyzing multiple water molecules; this is defined here as a multimolecular catalytic effect, as illustrated in the diagram. Figure 8 As shown in Figure a, in the photoelectrochemical system composed of PDSC-water-Pt, when the PDSC is excited by 193nm (6.42eV) light, photogenerated electrons with an energy of at least 5.5eV will be generated. Note that if thermal relaxation of charge carriers is not considered, the energy of the photoelectrons is the same as that of deep ultraviolet photons, meaning that the photogenerated electrons participate in the photoelectrochemical reaction before thermally relaxing to the bottom of the conduction band. However, as mentioned earlier, theoretically, water electrolysis requires 1.23eV of energy. Considering polarization, the actual energy required for water electrolysis, even for a 1mol / L acid or alkali solution, is only 1.7eV. In other words, the energy of the photogenerated electrons in the PDSC is actually enough to decompose 3-4 water molecules. Otherwise, the probability of dissipating excess energy through lattice thermal vibration pathways such as phonons is low (note that the maximum phonon energy in diamond is only 165meV). Therefore, the external quantum efficiency of over 100% exhibited by PDSC immersion detectors is reasonable from an energy perspective.

[0047] Furthermore, this invention also requires the observation that the weaker the intensity of the excitation light, the higher the photoresponsivity of the PDSC detector. This phenomenon is reasonable because photodetection itself is a process in which electrons in the photosensitive material absorb photon energy and break free from atomic bonds. The number of electrons produced is proportional to the number of incident photons. However, the number of electrons in the outer shell of the atoms of the photodetector is finite, and the number of electrons that can be provided per unit time is also finite. Therefore, when the optical power is low, the photocurrent I is proportional to the optical power P. When the optical power increases to a certain amount, I no longer increases with the optical power P, but reaches saturation. Therefore, if P continues to increase, the ratio of I to P, i.e., the photoresponsivity, becomes smaller and smaller.

[0048] The present invention also considers another possible mechanism, specifically as follows: Figure 8 As shown in b. In fact, the quantum efficiency greater than 1 in photoelectrochemical detection has been widely reported in previous studies, such as the reduction of oxygen on p-GaP and p-GaAs, and photoelectrochemical systems based on Si and Ge elemental electrodes. Among these, LM Peter's theoretical work (Chem. Rev. 90, 753-769, 1990) provided a relatively detailed summary and analysis of its mechanism, pointing out in his theoretical article that the phenomenon of quantum yield greater than 1 is called photocurrent multiplication. Specifically, current multiplication involves capturing minority carriers generated by light to form an active intermediate that can inject majority carriers into the semiconductor. Figure 8 b shows an example of the reaction on the p-type electrode. These photocurrent multiplication processes must involve majority carrier hole injection of intermediates during lattice dissolution, i.e., process reaction (3), which is the injection step that contributes to the photocurrent multiplication. It is worth noting here that the injection step (3) must effectively compete with the intermediate minority carrier (here, electron) trapping step (4), otherwise the intermediate (here, electron) will not be able to effectively compete with the intermediate. This will trap a second minority carrier, reducing the overall quantum efficiency to 1. Experimentally, the competition between the two pathways manifests as an intensity-dependent quantum efficiency; in the low-intensity region where minority carrier density is low, the current multiplication pathway dominates. As intensity increases, the minority carrier density becomes so high that the intermediate does not have time to inject carriers before trapping them. Figure 6 The variable power experimental results of d show that under high light intensity, the quantum efficiency of the PDSC immersion detector is less than 1 and tends to saturate; under low light intensity, the quantum efficiency exceeds 1, and the relevant experimental results have also been observed in p-GaP.

[0049] The following sections will discuss the photoelectrochemical mechanism of the PDSC-water-Pt system. For example... Figure 8 As shown in c and d, for the PDSC-water-Pt system, the current changes from negative to positive before and after illumination. The mechanism of this transition will be discussed below. Studies have shown that water decomposition to produce H2 and O2 is a high-energy-barrier reaction, with ΔG > 0 (ΔG = 237 kJ / mol). Theoretically, the potential for water decomposition to produce oxygen is 1.23 V, while the potential for hydrogen generation at the cathode is 0 V. This means that theoretically, a voltage exceeding 1.23 V is sufficient for water decomposition. From an energy conversion perspective, exciting the diamond electrolysis reaction with 193 nm light converts light energy into chemical and electrical energy. For water to decompose and release oxygen and hydrogen, thermodynamics requires that the conduction band potential of the semiconductor material be higher than the standard hydrogen electrode potential E(H2). + The potential of the valence band (O2 / H2O) electrode should be slightly negative, while the potential of the valence band electrode (O2 / H2O) should be slightly positive than that of the oxygen electrode electrode (E(O2 / H2O)).

[0050] like Figure 8 As shown in Figure c, after illumination, photogenerated electrons in the PDSC participate in the hydrogen reduction reaction, and electrons flow from Pt to the PDSC electrode in the external circuit. At this point, a reduction reaction occurs at the PDSC electrode, electrolyzing water to produce hydrogen gas. In this process, light energy is converted into chemical energy and electrical energy. Figure 8 In section c, the electrochemical potential window for water electrolysis was plotted relative to the conduction and valence bands of the PDSC used in this experiment, based on the UPS valence band spectrum results. For the PDSC, its band gap is approximately 5.5 eV, corresponding to a relatively large electrochemical window, where the conduction band potential is higher than the standard hydrogen electrode potential E(H). + The p-type semiconductor has a negative valence band potential (E(O2 / H2O)) and a more negative valence band potential than the standard oxygen electrode potential (E(O2 / H2O)). Therefore, from an electrode potential perspective, it is more likely to produce hydrogen under illumination. Furthermore, for p-type semiconductors, the downward bending of the energy band at the semiconductor-electrolyte interface hinders the movement of photogenerated holes to the interface. Therefore, under illumination, photogenerated electrons are more likely to move to the interface and undergo reduction reactions. Thus, under illumination, in the photoelectrochemical system composed of PDSC-water-Pt, the p-type semiconductor PDSC acts as the photocathode, undergoing the reduction reaction of water electrolysis to produce hydrogen. In this process, photogenerated electrons in the PDSC are continuously consumed, while Pt, acting as an electron ocean, continuously transfers electrons to the PDSC along the wire to maintain charge balance.

[0051] Here, we attempt to present the photoelectrochemical reaction process of the PDSC-water-Pt system, such as... Figure 8 As shown in Figure c. First, consider the case where a p-type semiconductor is in contact with an electrolyte. As electrons are transported from the electrolyte to the semiconductor to achieve electrochemical equilibrium, the interfacial bands in contact with the solution bend downwards to form a hole barrier, preventing valence band holes from flowing further into the solution. In this case, when exposed to external ultraviolet light, photogenerated electrons are more likely to transfer to the semiconductor / electrolyte interface, which is the opposite of the situation with n-type semiconductors. Second, consider the presence of surface states and the effect of surface recombination on the photoelectrochemical process (the majority carrier injection multiplication reaction is temporarily disregarded here). Since a p-type semiconductor is being treated, surface recombination involves the capture of photogenerated electrons from surface states, followed by the influx of holes. The surface states formed under illumination are a result of light generation from hydrogen atoms diffusing to the semiconductor surface. Then, the recombination reaction involves H+ ions in the lattice capturing electrons, acting as "near-surface" states, followed by the capture of holes by hydrogen atoms. This situation is similar to that of p-GaP. When a minority carrier electron reaches the solid-liquid interface, it may transfer directly from the band gap to a redox species, or it may be captured by a local energy level located in the band gap. The minority carrier capture rate (often called the surface recombination rate) can be expressed as s t =υσ t N tWhere υ is the thermal velocity of the charge carrier, σ t For the capture section, N t This represents the surface number density of redox states. In other words, in the PDSC photoelectrochemical system, hydrogen reduction can occur either through direct charge transfer of conduction band electrons or indirectly through electrons trapped in surface states (surface-mediated charge transfer). Therefore, the following reactions can be considered:

[0052] Photoexcitation: hυ→h + +e - (2a)

[0053] Direct charge transfer: 2H + +2e - →H2(2b)

[0054] Electron surface capture:

[0055] Surface-mediated indirect charge transfer:

[0056] Surface composite:

[0057] Here, (2e) actually represents the dissipation of photogenerated electrons and holes through surface recombination near the surface states. Its reaction rate depends on the hole supply; as the band bending increases (the higher the hole blocking layer), the reaction rate gradually decreases. When reaction (2d) can effectively compete with reaction (2e), effective surface-mediated charge transfer can occur. According to... Figure 2 The gate function shown in c indicates that under 193nm excitation, the PDSC-pure water-Pt system actually undergoes relatively effective charge transfer, while surface recombination between minority and majority carriers is relatively weak, i.e., the (2e) process is weak. This contrasts sharply with the photocurrent transient response of p-GaP in acid. After the lamp is turned on, the photocurrent relaxes exponentially to the steady-state cathode value, then overshoots to the anode transient and decays exponentially to the steady value when the lamp is turned off. These effects are characteristic of surface recombination, which arises from the different relaxation times and opposite signs of electron and hole currents (i.e., the photogenerated minority carrier current captured by the surface state has opposite signs to the majority carrier current that must flow to the surface to participate in surface recombination). This indicates that stronger surface recombination occurs, or that surface recombination makes the relaxation and overshoot in the current response more pronounced.

[0058] like Figure 8As shown in Figure c, the dark current is negative after illumination stops (the sign here is relative to the source surface; at this point, the negative terminal of the source surface is connected to the PDSC, and the positive terminal is connected to the Pt). This conversion between positive and negative currents may be because the photogenerated minority carrier current trapped by the surface states has the opposite sign to the majority carrier current that must flow to the surface to participate in surface recombination. To verify this conclusion, the charge transfer process of the PDSC-water-Pt system in the dark state is as follows: Figure 8 As shown in d.

[0059] 4. Detection mechanism of PDSC immersion detector

[0060] Furthermore, in order to quantitatively evaluate the response speed of the PDSC immersion detector, from Figure 9 The decay time t is derived from one photoresponse cycle under the short-circuit condition shown in diagram a, with a bias potential of 0V. d The time interval during which the response decreases from 90% to 10% is taken, and is calculated using the following formula:

[0061]

[0062] Where A is the scaling constant and τ is the relaxation time constant, the descent time is 3s. Figure 9 b shows a schematic diagram of the system's recovery mechanism under short-circuit conditions after the laser is turned off. Figure 9 The magnified image shows the decay kinetics curve under short-circuit conditions, a relatively fast process corresponding to the recombination of majority carrier holes with electrons trapped at the surface states. However, in pure water, we need to consider the diffusion of ionized ions, leading to a slow decay background. To measure the lifetime of ion diffusion, an oscilloscope was used for testing under open-circuit conditions. Specifically, after 20 minutes of excitation with a 193nm laser pulse, once the system reached stability, the 193nm excitation was stopped, and the recovery process of the background signal was recorded. The results are as follows: Figure 9 As shown in d, where Figure 9 Figure e illustrates the recovery mechanism of the system under open-circuit conditions after the laser is turned off. It can be seen that the ion diffusion process is very slow, taking up to 11 minutes. It is noteworthy that, because electrons cannot conduct through the external circuit in the open-circuit state, the charge balance of the electrodes can only be restored through the slow diffusion of ions in the solution. Figure 9 The decay time recorded by d corresponds to the ion diffusion time, from Figure 9 The comparison of c shows that the recovery process of the system under the open circuit state is a rather slow process because it can only rely on ion diffusion.

[0063] To characterize the actual response time of the PDSC immersion detector, the optical response time of the PDSC immersion detector was measured using an oscilloscope, and the results are as follows: Figure 9 As shown in f. Figure 9 The data extracted by g shows a decay time constant in the range of 3.3-3.7 ms, indicating an ultrafast time response. We consider this fast time response to correspond to the electron charge transfer in the photoexcited PDSC participating in the hydrogen evolution reduction reaction, specifically as follows... Figure 9 The illustration is shown in Figure h.

[0064] 5. Device temperature stability of PDSC immersion detectors

[0065] The temperature stability of the PDSC immersion detector was tested. Low temperatures were achieved using an ice-water mixture made from pure water; high temperatures were achieved using a Japanese ASONE NINOS NDK-1K heating stage. During testing, the heating stage was turned off after the temperature had stabilized for a period of time before data acquisition. Results are as follows: Figure 10 As shown, Figure 10 a shows the IV values ​​under illumination at different temperatures (4°C, 25°C, and 50°C) within a bias range of 0-0.1V. Figure 10 b shows the It optical response of the device at these three temperatures under different 193nm laser power pulse excitations. Figure 10 c magnified the gate function attenuation part under 1278W laser power excitation. It can be seen that within a large temperature range, the response of the PDSC immersion detector to 193nm light changes little and is relatively stable, showing that it can operate in a wide operating temperature range. Figure 10 d and Figure 10 e shows the change in the responsivity of the PDSC immersion detector with laser power at different temperatures. It can be seen that within the studied temperature range, the change in detector responsivity with laser power follows a similar pattern, which also reflects the stability of the detector during temperature changes. Figure 10 f shows a comparison of the response gate function and responsivity at different temperatures when the laser power is 65nW. At higher temperatures (>50℃), the responsivity of the PDSC immersion detector decreases, and the current value in the dark state tends to be more positive. This is reasonable because as the temperature increases, the dissolved oxygen concentration in the water decreases, the photomultiplication effect weakens, and the increase in temperature increases the thermal motion of electrons, intensifying electron collisions, which is not conducive to the water electrolysis process.

[0066] In summary, this invention utilizes ultra-wide bandgap boron-doped p-type diamond (PDSC) as the photoelectrode to construct a vacuum ultraviolet immersion photodetector with a PDSC-ultrapure water-Pt structure. Electron-hole pairs are generated by photoexcitation of the PDSC working electrode, and electrons flow from the Pt electrode along the external circuit to the diamond working electrode. The PDSC immersion photodetector prepared by this invention exhibits a responsivity as high as 87.8 mA / W under zero bias and 193 nm excitation wavelength conditions; furthermore, under low optical power excitation, the responsivity of the PDSC immersion detector can reach as high as 670 mA / W. This immersion detector is a low-cost, self-powered, and highly sensitive vacuum ultraviolet photodetector with good stability, showing promising application prospects for 193 nm power monitoring in deep ultraviolet light source lithography machines.

[0067] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A diamond immersion detector, characterized in that, The detector is an immersion photodetector based on ultra-wide bandgap boron-doped p-type diamond, and the detector adopts a two-electrode system with a boron-doped p-type diamond wafer-ultrapure water-Pt structure. The boron-doped p-type diamond wafers were synthesized by growing at a high temperature of 1300-1400℃ and a high pressure of 5.0-6.0 GPa for 22-52 hours using a temperature gradient method. The solvent alloy used in the method for synthesizing boron-doped p-type diamond wafers is a nickel-based alloy, the carbon source is high-purity graphite, and amorphous boron is added to the carbon source for diamond growth.

2. The diamond immersion detector according to claim 1, characterized in that, The diamond immersion detector is prepared by using a boron-doped p-type diamond wafer and a platinum electrode as the working electrode and counter electrode, respectively, connected by ultrapure water to obtain the diamond immersion detector.

3. The application of the diamond immersion detector according to claim 1 or 2 in 193 nm photolithography vacuum ultraviolet light detection.

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