Method and device for testing optically excited semiconductor gas sensors

Abstract

This invention belongs to the field of electronic device technology, specifically relating to a testing method and apparatus for photo-excited semiconductor gas sensors to improve sensitivity and reduce detection limits at room temperature. The invention places the semiconductor gas sensor in a chamber filled with the target gas, periodically turns the excitation light source on and off using a timer, and employs pulsed light modulation testing. The pulsed light (periodically) cleans the surface of the semiconductor sensitive material, generating surface-active oxygen and activating the gas-sensitive response. The resistance (Rt) of the sensor in the carrier gas and the target gas is connected at the end of the light pulse shutdown phase. a_off R g_off ), to obtain the response under optical modulation test (n-type semiconductor to oxidizing gas: R g_off / R a_off ), at the optimal light-on time t on‑ov Optical shutdown time t off‑ov Optical power density P ov Under these conditions, the sensor can achieve the highest gas response. This method overcomes the side effects of existing continuous illumination and fully unleashes the gas-sensing potential of semiconductor materials.

Description

Technical Field

[0001] This invention relates to the field of electronic device technology, specifically to a testing device for a photoexcited semiconductor gas sensor, and a testing method for significantly improving the response sensitivity of the semiconductor gas sensor to target gas molecules and reducing its detection limit at room temperature. Background Technology

[0002] Semiconductor gas sensors are ideal components for building IoT gas sensors due to their advantages such as material stability, small size, low cost, silicon process compatibility, and ease of networking. Semiconductor gas sensors typically require heating to activate the electrical response of the target gas and to regulate its response and recovery (rate). Therefore, semiconductor gas sensors usually require integrated (micro)heaters. Integrated (micro)heaters have the following disadvantages: firstly, they significantly increase the complexity of device fabrication; secondly, they greatly increase sensor power consumption; and thirdly, they limit the use of many flexible substrates (with poor heat resistance).

[0003] Sensors that can operate at room temperature (without the need for an integrated heater) have always attracted much attention. Photoexcitation is one of the most commonly used methods (operating at room temperature) to activate and modulate the response of the analyte gas, and it has been reported in articles since 2000 (Lightenhanced gas sensing properties of indium oxide and tin dioxide sensors, Sensors and Actuators B: Chemical 65 (2000) 260). Photoexcitation with photon energy greater than the semiconductor bandgap (such as ultraviolet light) can, on the one hand, desorb molecules (air and water) adsorbed on the material surface—exposing active sites, and on the other hand, induce the generation of reactive oxygen species (superoxide ions, hydroxyl radicals, etc.) on the semiconductor surface, thereby activating and modulating the response of the analyte gas molecules.

[0004] Conventional photoexcitation testing (using three ventilation stages: background air, target gas, and background air) employs continuous illumination. For a specific sensor and target gas, there exists an optimal light power density—corresponding to a relatively high response and fast response and recovery rates. However, continuous (ultraviolet) illumination also leads to: ① desorption of target gas molecules; ② a decrease in sensor baseline resistance, thus weakening the sensor's response, especially for trace gas molecules at the ppb level (the number of molecules adsorbed on the sensor surface is already small, and ultraviolet illumination significantly enhances the desorption of target molecules, preventing the target gas from exchanging charge with the semiconductor sensor). Therefore, continuous photoexcitation has both promoting and hindering effects on semiconductor gas sensors. In conventional testing, these two effects are coupled, failing to fully utilize the response potential of the semiconductor sensor, resulting in a much lower response of the sensitive material under photoexcitation compared to its response under thermal excitation. Response and detection limit are crucial parameters for evaluating gas sensor performance. The low response sensitivity of continuously photoexcited sensors to trace (ppb-level) gases limits their application in numerous fields (such as indoor and outdoor air quality monitoring and pollutant emission monitoring in chemical industrial parks). Summary of the Invention

[0005] One objective of this invention is to provide a testing method for pulsed light-excited semiconductor gas sensors, addressing the problem of both promoting and inhibiting effects of existing (continuous) light excitation on semiconductor gas sensors. This method utilizes light pulses to periodically "clean" the surface of the semiconductor sensor, inducing the generation of surface-active oxygen species, thereby activating the sensor's surface-active sites. Periodically turning off the light pulses promotes the adsorption of the target gas while simultaneously consuming photogenerated electron-hole pairs, increasing the sensor's baseline resistance, and thus increasing the adsorption probability of the target gas molecules. This fully releases the gas-sensing potential of the sensitive material and enhances the sensor's response sensitivity.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a testing method for a photoexcited semiconductor gas sensor, specifically comprising the following steps:

[0007] S1. Place the semiconductor gas sensor in a sealed cavity. At room temperature, periodically and sequentially introduce a carrier gas and a target gas into the sealed cavity. The introduction time t of one carrier gas is... CG The introduction time t of a target gas TG One ventilation cycle;

[0008] S2. Under the ventilation conditions of step S1, the optical power density P of the excitation light source is selected to be 0.01–5 mW / cm². 2 Values ​​within the range, light-on time t on The values ​​are in the range of 1–50 s, and the light-off time t is... offThe values ​​are in the range of 1–150 s. One light-on time and one light-off time constitute one light modulation cycle. The light power density P and the light-on time t of the light modulation cycle are kept constant. on Keeping the optical modulation period unchanged, adjust the optical off time t. off t off-1 t off-2 t off-3 ...t off-m Where m is an integer 3 ≤ m ≤ 10, t CG ≥3(t off +t on ), t TG ≥3(t off +t on The transient resistance signal of the semiconductor gas sensor to the target gas was collected under different optical modulation periods. The resistance value at the end of the optical off time period in each optical modulation period was connected to obtain the optical modulation response curve, i.e., the upper envelope curve. The optical off time t was then extracted. off The resistivity change rate of the upper and lower envelope curves is used to plot the optical modulation response as a function of the optical shutdown time. The optical shutdown time corresponding to the maximum point of the optical modulation response in the curve, or the optical shutdown time closest to the maximum point, is the optimal optical shutdown time t. off-ov ;

[0009] S3. Under the ventilation conditions of step S1, select an excitation light source with an optical power density P of 0.01–5 mW / cm². 2 The values ​​are within the range, and the light-off time is t. off-ov Light-on time t on The values ​​are in the range of 1–50 s. One optical on time and one optical off time constitute one optical modulation period. The optical off time, which maintains the optical power density P and the optical modulation period, is t. off-ov Keep it unchanged, adjust the light-on time t on t on-1 t on-2 t on-3 ...t on-n Where n is an integer 3 ≤ n ≤ 10, t CG ≥3(t off +t on ), t TG ≥3(t off +t on The transient resistance signal of the semiconductor gas sensor to the target gas was collected under different optical modulation periods. The resistance value at the end of the optical off time period in each optical modulation period was connected to obtain the optical modulation response curve, i.e., the upper envelope curve. The optical on time t was then extracted. onThe resistivity change rate of the upper and lower envelope curves is used to plot the optical modulation response as a function of the on-time. The on-time corresponding to the maximum point of the optical modulation response in the curve, or the on-time closest to the maximum point, is the optimal on-time t. on-ov ;

[0010] S4. Under the ventilation conditions of step S1, select a light-off time of t. off-ov The light-on time is t on-ov The optical power density P of the excitation light source is 0.01–5 mW / cm². 2 Within the range of values, one optical on time and one optical off time constitute one optical modulation cycle, and the optical off time for each optical modulation cycle is t. off-ov The light-on time is t on-ov Keeping the optical power density P constant, adjust the optical power density P of each optical modulation period to P1, P2, P3...Pz, where z is an integer 3 ≤ z ≤ 10, and t... CG ≥3(t off +t on ), t TG ≥3(t off +t on The transient resistance signals of the semiconductor gas sensor to the target gas under different optical modulation cycles were collected. The resistance values ​​at the end of the optical off period in each optical modulation cycle were connected to obtain the optical modulation response curve, i.e., the upper envelope curve. The resistance change rate of the upper envelope curve under different optical power densities P was extracted, and the optical modulation response as a function of optical power density P was plotted. The optical power density P corresponding to the maximum point of the optical modulation response in the curve, or the optical power density P closest to the maximum point, is the optimal optical power density P. ov ;

[0011] S5. Under the ventilation conditions of step S1, select a light-off time of t. off-ov The light-on time is t on-ov The light power density of the excitation light source is P ov The optical modulation response of target gases at different concentrations was tested, and the optical modulation response versus target gas concentration curve was obtained.

[0012] Further improvements to the testing method for photoexcited semiconductor gas sensors:

[0013] Preferably, in step S1, the flow rates of both the carrier gas and the target gas are 100–1000 sccm, the carrier gas inlet time is 300–1000 s, the target gas inlet time is 300–1000 s, and the target gas concentration is 1 ppb–100 ppm.

[0014] Preferably, the carrier gas is air, and the target gas is one of NO2, O3, H2S, and NH3.

[0015] Preferably, the excitation light source is ultraviolet-visible light with a wavelength of 250-650 nm, and the optical power density P of the excitation light source is 0.5–5 mW / cm². 2 .

[0016] Preferably, the sensitive material in the semiconductor gas sensor is one of ZnO, SnO2, TiO2, and MoS2.

[0017] Preferably, the light-on time in the light modulation cycle is 5–15s and the light-off time is 50–100s.

[0018] The second objective of this invention is to provide a testing device for a photoexcited semiconductor gas sensor, used for the testing method of the photoexcited semiconductor gas sensor described in any one of the above-mentioned methods. The testing device includes a semiconductor gas sensor, an excitation light unit, and a gas-sensitive testing unit.

[0019] The testing device includes a semiconductor gas sensor, an excitation light unit, and a gas-sensitive testing unit;

[0020] The semiconductor gas sensor includes an insulating substrate and two interdigitated electrodes with toothed structures disposed opposite each other on the upper surface of the insulating substrate. The toothed structures of the two interdigitated electrodes are opposite to each other and staggered to form a serpentine channel. The interdigitated electrodes are made of noble metals or tin-doped indium oxide (ITO). The interdigitated electrodes and the upper surface of the insulating substrate on which the interdigitated electrodes are located are provided with a sensitive material.

[0021] The excitation unit includes an excitation light source, a timer for controlling the periodic switching of the excitation light source, and an optical attenuator for adjusting the light power density of the excitation light source. The light power density of the excitation light source is 0.5–5 mW / cm². 2 ;

[0022] The gas-sensitive testing unit includes a sealed cavity for housing a semiconductor gas sensor. A transmission window is provided on the cavity. The excitation light source passes through an optical attenuator and the transmission window in sequence before irradiating the sensitive material. A gas path system is provided outside the cavity to control the flow rate of the carrier gas and the target gas inside the cavity. A resistance testing system is also provided outside the cavity and connected to two interdigitated electrodes to collect and record changes in the sensor resistance.

[0023] Further improvements were made to the testing device for the photoexcited semiconductor gas sensor:

[0024] Preferably, the insulating substrate is one of insulating glass, alumina substrate, silicon substrate with SiO2 oxide layer, and polymer substrate (PET, PI, PET);

[0025] The interdigitated electrodes are made of one of Pt, Au, or ITO.

[0026] The sensitive material is a semiconductor micron or nano-sensitive material, specifically one or more of the following: metal oxide semiconductor, metal sulfide, selenide, telluride, and carbon-based materials (graphene, graphene oxide, carbon nanotubes, etc.).

[0027] The material of the transmission window is quartz glass.

[0028] Preferably, the transmittance of the optical attenuator is 0.1%-90%, and the optical attenuator is an ultraviolet filter with a transmittance wavelength of 250-400nm or a visible light filter with a transmittance wavelength of 400-650nm.

[0029] Preferably, the resistance testing system can measure the sensor resistance from 100Ω to 10GΩ, and the frequency for testing the sensor resistance is 0.5–50Hz.

[0030] Preferably, the excitation light source is ultraviolet-visible monochromatic light or polychromatic light with a wavelength of 250–650 nm; the device emitting the excitation light source is a semiconductor light-emitting diode (LED).

[0031] Preferably, the timer can periodically turn the excitation light source on and off to periodically excite the sensor using light modulation, and the on and off time periods of the timer can be controlled independently.

[0032] Preferably, the photon energy of the excitation light source is greater than the band gap of the sensitive material, so as to effectively activate the room temperature gas-sensitive response performance of the semiconductor sensitive material.

[0033] The advantages of this invention compared to the prior art are as follows:

[0034] 1) This invention discloses a testing method for a photoexcited semiconductor gas sensor. The semiconductor gas sensor is placed in a chamber filled with the target gas. A timer periodically turns the excitation light source on and off, and pulsed light modulation is used for testing. The periodic light pulses "clean" the surface of the semiconductor sensor, generating surface-active oxygen—activating the sensor's surface active sites. Periodically turning off the light pulses promotes the adsorption of the target gas—increasing the adsorption probability of the gas molecules—and also consumes photogenerated electron-hole pairs, increasing the sensor's baseline resistance—improving the sensor's response sensitivity. This method overcomes the side effects of continuous illumination in existing methods and fully releases the gas-sensing potential of the semiconductor material.

[0035] 2) Taking a semiconductor gas sensor with ZnO as the sensitive material as an example, under ultraviolet pulsed light modulation, the sensor's response to 20ppb NO2 is 200, while the same sensor's response under the optimal ultraviolet UV light intensity and continuous illumination test mode is only 2. The response is amplified by nearly two orders of magnitude, and the theoretical detection limit is reduced from 5ppb to 0.2ppb. Under pulsed light modulation, the sensor's response to ppb-level O3, H2S, and trimethylamine is improved by 1-2 orders of magnitude compared to the control.

[0036] Taking a semiconductor gas sensor with MoSe2 as the sensitive material as an example, the response of NO2 under ultraviolet pulse light modulation is 3 times that of the comparative test mode (optimal UV light intensity, continuous illumination).

[0037] 3) This invention discloses a testing device for a photoexcited semiconductor gas sensor. The semiconductor gas sensor used in this testing device has a simple structure, requiring only the coating of sensitive material onto an insulating substrate with interdigitated electrodes, followed by a simple aging process. It eliminates the need for integrated heaters, resulting in low-cost mass production. The device operates at room temperature with low power consumption, meeting the requirements of grid-based monitoring applications. This method is compatible with flexible substrates. The method of this invention is simple and can be extended to the high-sensitivity detection of various trace gas molecules using multiple sensitive materials, providing important reference for the future room-temperature high-sensitivity detection of trace gas molecules using semiconductor gas sensors.

[0038] 4) The semiconductor gas sensor designed in this invention is exposed to both the air background and the target gas for a time that is not less than the light modulation period (t). on +t off Three times that of the semiconductor sensing material can achieve a stable optical modulation response. The photon energy of the excitation light source is designed to be greater than the band gap of the semiconductor sensing material, so as to effectively activate the room-temperature gas-sensitive response performance of the semiconductor sensing material during optical modulation (on-off phase), thereby achieving a significant sensitization effect during optical modulation (off-off phase). Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the test device for the optical pulse excited semiconductor gas sensor of the present invention. The meanings of the markings in the figure are as follows:

[0040] Substrate (11), interdigitated electrode (12), sensitive material (13);

[0041] Excitation light source (21), timer (22), optical attenuator (23);

[0042] Cavity (31), transmission window (32), air path system (33), resistance testing system (34).

[0043] Figure 2 (a) is a schematic diagram of the structure of a photoexcited semiconductor gas sensor; Figure 2 (b) is a physical image of a photoexcited semiconductor gas sensor.

[0044] Figure 3 This is a comparison diagram of the test methods for Example 2 and the comparative example, in which... Figure 3 (a) shows the test curve of Example 2 under pulsed light modulation. Figure 3 (b) is the test curve of the comparative example under continuous illumination.

[0045] Figure 4 The images show scanning electron microscope (SEM) images of ZnO (a) and MoSe2 (b), photoexcitation sensitive materials; and X-ray diffraction (XRD) images of ZnO (c) and MoSe2 (d), photoexcitation sensitive materials.

[0046] Figure 5 The response of the ZnO sensor to 20 ppb NO2 under comparative testing mode (continuous illumination, different 365nm UV light power densities): Figure 5 (a) Dynamic response curves of the sensor to NO2 under different light power density illumination (three ventilation cycles); Figure 5 (b) shows the relationship between NO2 response and UV light power density.

[0047] Figure 6 Taking the response of a ZnO sensor to 1 ppm NO2 as an example, the three-step optimization steps of the test method in the embodiment (pulse light modulation) are: (a)-(b) light-off time t off The effect on the optical modulation response, (c)-(d) optical on-time t on The effect on the optical modulation response is shown in (e)-(f), which represent the effect of the excitation light source power density P on the optical modulation response.

[0048] Figure 7 To compare the response characteristics of the ZnO sensor to NO2 under the comparative example (continuous illumination, optimal light power density) and Example 2 (pulsed light modulation, optimal light on, light off, and light power density): (a)-(b) Comparison of the dynamic response curves and response-concentration curves of the sensor to 20-1000 ppb NO2; (c)-(d) Repeatability test of the sensor to 20 ppb NO2.

[0049] Figure 8 The responses of the sensor using ZnO as the sensing material to O3, H2S, and trimethylamine under the test method of Example 2 are shown in Figures (a)-(c).

[0050] Figure 9 The sensor using MoSe2 as the sensitive material responds to NO2 under the test methods of Example 2 and the comparative example. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0052] Example 1

[0053] like Figure 1 The diagram shown is a structural diagram of the test device for the optical pulse excited semiconductor gas sensor of the present invention. Figure 2 (a) is a schematic diagram of the interdigitated electrode structure in a semiconductor gas sensor. Figure 2 (b) is a picture of the semiconductor gas sensor in the test setup.

[0054] like Figure 1 The diagram shown is a structural diagram of the test device for the optical pulse excited semiconductor gas sensor of the present invention. The test device includes a semiconductor gas sensor, an excitation light unit, and a gas-sensitive test unit.

[0055] The semiconductor gas sensor includes an insulating substrate 11 and two interdigitated electrodes 12 with toothed structures disposed opposite each other on the upper surface of the insulating substrate 11. The toothed structures of the interdigitated electrodes 12 are opposite to each other and staggered to form a serpentine channel. The interdigitated electrodes 12 are made of noble metal. The interdigitated electrodes 12 and the upper surface of the insulating substrate 11 on which the interdigitated electrodes 12 are disposed are provided with a sensitive material 13.

[0056] The excitation light unit includes an excitation light source 21 and a timer 22 for setting the irradiation time of the excitation light source, and an optical attenuator 23 for adjusting the light power density of the excitation light source.

[0057] The gas-sensitive testing unit includes a cavity 31 for housing a semiconductor gas sensor; a transmission window 32 is provided on the cavity 31, and the excitation light source 21 passes through the optical attenuator 23 and the transmission window 32 in sequence before irradiating the sensitive material 13; an air inlet and an air outlet are provided outside the cavity 31, the air inlet is connected to the target gas and the carrier gas, and a flow meter is provided on the connected pipe, the air inlet, the air outlet, the pipe, the flow meter, the target gas and the carrier gas together form a gas path system 33; a resistance testing system 34 is provided outside the cavity, and the resistance testing system 34 is respectively connected to the two interdigitated electrodes 12 in the semiconductor gas sensor.

[0058] The excitation light source 21 in the excitation light unit irradiates the cavity 31 after passing through the optical attenuator 23. The material of the irradiated area on the cavity 31 is quartz, forming a quartz window. The irradiated area on the cavity 31 corresponds to the surface where the sensitive material 13 in the semiconductor gas sensor is located.

[0059] The sensitive material is a semiconductor micron or nano-sensitive material, specifically one or a composite of several of the following: metal oxide semiconductor, metal sulfide, selenide, telluride, and carbon-based materials (graphene, graphene oxide, carbon nanotubes, etc.).

[0060] The interdigitated electrode material can be one of Pt, Au, or tin-doped indium oxide (ITO).

[0061] The insulating substrate may be one of insulating glass, alumina, silicon with a SiO2 oxide layer, or polymer substrate (PET, PI, PET, etc.).

[0062] Example 2

[0063] This embodiment provides a testing method using the pulsed light modulation testing device in Embodiment 1, including the following steps:

[0064] S1. Under room temperature and continuous light illumination, a constant flow rate of carrier gas (air) and target gas (such as NO2) is sequentially introduced into the gas-sensitive chamber containing the ZnO gas sensor using a gas flow meter. The flow rates of air and target gas are 500 sccm, and the carrier gas introduction time is t. CG The target gas introduction time t is 300s. TG The time limit is 300 seconds, and the target NO2 gas concentration is 1 ppm.

[0065] S2. Under the ventilation conditions of step S1, the optical power density of the excitation light source is fixed at 1.6 mW / cm². 2 Light-on time t on (15s), adjust the light-off time t within the range of 1–150s. off (10s, 30s, 50s, 70s, and 90s respectively), one optical on-time and one optical off-time constitute one optical modulation cycle. The transient resistance signal of the semiconductor gas sensor to the target gas is collected under different optical modulation cycles. The resistance value at the end of the optical off-time in each optical modulation cycle is connected to obtain the optical modulation response curve (upper envelope). The optical off-time t is then extracted. off The optical modulation response of the target gas (the resistivity change rate of the upper envelope curve) is used to plot the optical modulation response versus the optical shutdown time. The optical shutdown time corresponding to the maximum point of the optical modulation response in the curve, or the optical shutdown time closest to the maximum point, is the optimal optical shutdown time. The optimal optical shutdown time t is then obtained. off-ov (70s, Figure 6 a, b);

[0066] S3. Under the ventilation conditions of step S1, the optical power density of the excitation light source is fixed at 1.6 mW / cm². 2 ), Optical shutdown time toff-ov (70s), adjust the light-on time t within the range of 1–50s. on The light modulation cycles were 5s, 15s, 20s, and 40s, respectively. One light-on time and one light-off time constituted one light modulation cycle. The transient resistance signal of the semiconductor gas sensor to the target gas was collected under different light modulation cycles. The resistance value at the end of the light-off time in each light modulation cycle was connected to obtain the light modulation response curve (upper envelope). The light-on time t was then extracted. on The optical modulation response of the target gas (the resistivity change rate of the upper envelope curve) is used to plot the optical modulation response versus the light-on time curve. The light-on time corresponding to the maximum point of the optical modulation response in the curve, or the light-on time closest to the maximum point, is the optimal light-on time. The optimal light-on time t is obtained. on-ov (15s, Figure 6 c, d);

[0067] S4. Under the ventilation conditions of step S1, fix the light-off time t. off-ov (70s), light-on time t on-ov (15s), at 0.01–5mW / cm 2 The optical power density P of the excitation light source was adjusted within the range of 0.003, 0.8, 1.6, 1.8, and 2.7 mW / cm². 2 The transient resistance signals of the target gas obtained by the semiconductor gas sensor under different optical modulation cycles are collected respectively. The resistance value at the end of the optical off period in each optical modulation cycle is connected to obtain the optical modulation response curve (upper envelope). The optical modulation response of the target gas under different optical power densities P (the resistance change rate of the upper envelope curve) is extracted. The curve of optical modulation response versus optical power density P is plotted. The optimal excitation light source power density P is obtained from the optical power density P corresponding to the maximum point of optical modulation response in the curve, or the optical power density closest to the maximum point. ov (1.6mW / cm 2 , Figure 6 e, f);

[0068] S5. Under the same ventilation conditions as in step S1, at the optimal light-off time t off-ov (70s), light-on time t on-ov (15s), excitation light source power P ov (1.6mW / cm 2 The optical modulation response of target gases at different concentrations was tested, and the optical modulation response versus concentration curves were obtained. Figure 7 a, b).

[0069] Comparative Example

[0070] The comparative test used continuous illumination (365nm ultraviolet light). Figure 5 The response characteristics of the same ZnO sensor to 20 ppb NO2 under comparative testing show that, even with optimization of the excitation light source power density, the optimal continuous light excitation power (0.8 mW / cm²) is achieved. 2 The sensor's response to 20 ppb is only 7.1, while in the embodiment, the same sensor can respond to the same concentration of target gas as high as 220.

[0071] The embodiment (photomodulation response) overcomes the problem of the comparative example (conventional continuous illumination excitation) being unable to simultaneously promote gas adsorption and increase the sensor baseline resistance. It can more efficiently utilize the advantages of photoexcitation and avoid its disadvantages. Therefore, the embodiment is much higher than the conventional continuous illumination (even at the optimal excitation light power density, compared to the comparative example). Figure 7 , Figure 8 , Figure 9 This allows for the full exploitation of the potential of gas-sensitive materials.

[0072] Figure 3 This is a comparison diagram of the test methods for Example 2 and the comparative example. Figure 3 (a) is the specific test method for Example 2 (pulse light modulation), which involves periodically switching on the excitation light source (period t). on ), shutdown (period t) off The ventilation and resistance acquisition tests are the same as in the comparative example. Because the photon energy of the excitation light source is greater than the band gap of the semiconductor sensitive material used, when the excitation light source is turned on, a large number of electron-hole pairs are generated inside the sensitive layer, and the sensor resistance gradually decreases. Conversely, when the excitation light source is turned off, the sensor resistance gradually increases as the photo-excited electron-hole pairs are consumed. Therefore, the sensor resistance (gray dot) will fluctuate and oscillate with the periodic on and off of the excitation light source (including in background air and target gas atmospheres). Connecting the resistance value at the end of each light-on cycle yields a response curve and response (R0) similar to the comparative example. g-on / R a-on By connecting the resistance value at the end of each optical shutdown cycle, the optical modulation response (R) under optical shutdown is obtained. g-off / R a-off (This is abbreviated as optical modulation response). Figure 3 (b) As a comparative example, the test curve under continuous illumination shows that the resistance testing system can record the transient resistance (gray dots) of the sensor under background air, target gas, and background air conditions. Based on the sensor's resistance value R under an air background... a Resistance R in the target gas g The sensor response R under comparative testing can be obtained. g / R a Example 2 (optical modulation response) is much higher than that of the comparative example under conventional continuous illumination (even under optimal excitation light power density).

[0073] Figure 4 The images show scanning electron microscope (SEM) images of the photoexcitation-sensitive materials ZnO(a) and MoSe2(b); and X-ray diffraction (XRD) images of the photoexcitation-sensitive materials ZnO(c) and MoSe2(d). The SEM images confirm that both sensitive materials exhibit a sheet-like nanostructure and are free of impurities.

[0074] Figure 5 The response of the ZnO sensor to 20 ppb NO2 under comparative testing mode (continuous illumination, different 365nm UV light power densities): Figure 5 (a) Dynamic response curves of the sensor to NO2 under different light power densities (three ventilation cycles); the sensor is difficult to recover after being exposed to NO2 in the dark; as the excitation UV light power density increases, the sensor baseline resistance gradually decreases, and the response rate and response first increase and then decrease. Figure 5 (b) shows the relationship between the NO2 response and UV light power density, at the optimal photoexcitation power (~0.8 mW / cm²). 2 Under these conditions, the sensor's optimal (parabolic maximum) response (R) g / R a It is only 7.1.

[0075] Figure 6 Taking the response of a ZnO sensor to 1 ppm NO2 as an example, the three-step optimization steps of the test method in Example 2 (pulse light modulation) are as follows: (a)-(b) are the light-off time t. off The sensor resistance fluctuates with the UV light switching on and off, affecting the optical modulation response. Connecting the resistance values ​​at the end of each UV-off state forms the upper envelope of the optical modulation response. The upper envelope (UV-off) response value (R) g_off / R a_off The response value was significantly higher than the lower envelope response value (R). g_on / R a_on As the optical off time increases, the optical modulation response first increases and then decreases, with 70s being the optimal value. off The response to 1 ppm NO2 reaches a peak value of 10¹⁸ t; (c)-(d) show the effect of light-on time on the optical modulation response. As the light-on time increases, the optical modulation response increases rapidly and then saturates, with 15 s being the optimal t. on The response to 1 ppm NO2 reached a peak value of 10¹⁸ over time; (e)-(f) show the effect of excitation light source power density on the optical modulation response. As the excitation light source power density increases, the optical modulation response first increases and then decreases, reaching ~1.6 mW / cm². 2 For optimal optical power density, the response to 20 ppb NO2 reaches a peak value of 131.

[0076] Figure 7 To compare the response characteristics of the ZnO sensor to NO2 under the comparative example (continuous illumination, optimal optical power density) and Example 2 (pulsed light modulation, optimal light on, light off, and optical power density): (a)-(b) Comparison of the dynamic response curves and response-concentration curves of the sensor to 20-1000 ppb NO2; the response of the same sensor under the example is about two orders of magnitude higher than that under the comparative example, and the response of the sensor to 20 ppb NO2 is as high as 131, and the theoretical detection limit is reduced from 5 ppb to 0.2 ppb; (c)-(d) Repeatability test of the sensor to 20 ppb NO2, it can be seen that the test of the example has better repeatability stability and the response is much higher than that under the comparative example.

[0077] Figure 8 The response of the sensor using ZnO as the sensing material to O3, H2S, and trimethylamine under the test method of Example 2 is shown in Figures (a)-(c); Figure (d) is a bar chart comparing the response under Example 2 and the comparative example test, indicating that the test method described in Example 2 has good universality and can significantly improve the room temperature response performance of the sensor to various trace gas molecules.

[0078] Figure 9 The response of the MoSe2 sensor, using MoSe2 as the sensing material, to NO2 was tested under the methods described in Example 2 and the comparative example. The test results confirm that the test method in Example 2 can significantly improve the response of the MoSe2 sensor to NO2.

[0079] Those skilled in the art should understand that the above descriptions are merely several specific embodiments of the present invention, and not all embodiments. It should be noted that many modifications and improvements can be made by those skilled in the art, and all modifications or improvements not exceeding the scope of the claims should be considered within the protection scope of the present invention.

Claims

1. A testing method for a photoexcited semiconductor gas sensor, characterized in that, Specifically, the steps include the following: S1. Place the semiconductor gas sensor in a sealed cavity. At room temperature, periodically and sequentially introduce a carrier gas and a target gas into the sealed cavity. The introduction time t of one carrier gas is... CG The introduction time t of a target gas TG One ventilation cycle; S2. Under the ventilation conditions of step S1, the optical power density P of the excitation light source is selected to be 0.01–5 mW / cm². 2 Values ​​within the range, light-on time t on The values ​​are in the range of 1–50 s, and the light-off time t is... off The values ​​are in the range of 1–150 s. One optical on time and one optical off time constitute one optical modulation cycle. The optical power density P and the optical on time t of the optical modulation cycle are kept constant. on Keeping the optical modulation period unchanged, adjust the optical off time t. off t off-1 t off-2 t off-3 ...t off-m Where m is an integer 3 ≤ m ≤ 10, t CG ≥3(t off +t on ), t TG ≥3(t off +t on The transient resistance signal of the semiconductor gas sensor to the target gas was collected under different optical modulation periods. The resistance value at the end of the optical off time period in each optical modulation period was connected to obtain the optical modulation response curve, i.e., the upper envelope curve. The optical off time t was then extracted. off The resistivity change rate of the upper and lower envelope curves is used to plot the optical modulation response as a function of the optical shutdown time. The optical shutdown time corresponding to the maximum point of the optical modulation response in the curve, or the optical shutdown time closest to the maximum point, is the optimal optical shutdown time t. off-ov ; S3. Under the ventilation conditions of step S1, select an excitation light source with an optical power density P of 0.01–5 mW / cm². 2 The values ​​are within the range, and the light-off time is t. off-ov Light-on time t on The values ​​are in the range of 1–50 s. One optical on time and one optical off time constitute one optical modulation period. The optical off time, which maintains the optical power density P and the optical modulation period, is t. off-ov Keep the time constant, adjust the light-on time t on t on-1 t on-2 t on-3 ...t on-n Where n is an integer 3 ≤ n ≤ 10, t CG ≥3(t off +t on ), t TG ≥3(t off +t on The transient resistance signal of the semiconductor gas sensor to the target gas was collected under different optical modulation periods. The resistance value at the end of the optical off time period in each optical modulation period was connected to obtain the optical modulation response curve, i.e., the upper envelope curve. The optical on time t was then extracted. on The resistivity change rate of the upper and lower envelope curves is used to plot the optical modulation response as a function of the on-time. The on-time corresponding to the maximum point of the optical modulation response in the curve, or the on-time closest to the maximum point, is the optimal on-time t. on-ov ; S4. Under the ventilation conditions of step S1, select a light-off time of t. off-ov The light-on time is t on-ov The optical power density P of the excitation light source is 0.01–5 mW / cm². 2 Within the range of values, one optical on time and one optical off time constitute one optical modulation cycle, and the optical off time for each optical modulation cycle is t. off-ov The light-on time is t on-ov Keeping the optical power density P constant, adjust the optical power density P of each optical modulation period to P1, P2, P3...Pz, where z is an integer 3 ≤ z ≤ 10, and t... CG ≥3(t off +t on ), t TG ≥3(t off +t on The transient resistance signals of the semiconductor gas sensor to the target gas under different optical modulation cycles were collected. The resistance values ​​at the end of the optical off period in each optical modulation cycle were connected to obtain the optical modulation response curve, i.e., the upper envelope curve. The resistance change rate of the upper envelope curve under different optical power densities P was extracted, and the optical modulation response as a function of optical power density P was plotted. The optical power density P corresponding to the maximum point of the optical modulation response in the curve, or the optical power density P closest to the maximum point, is the optimal optical power density P. ov ; S5. Under the ventilation conditions of step S1, select a light-off time of t. off-ov The light-on time is t on-ov The light power density of the excitation light source is P ov The optical modulation response of target gases with different concentrations was tested, and the optical modulation response versus target gas concentration curve was obtained.

2. The testing method for the photoexcited semiconductor gas sensor according to claim 1, characterized in that, In step S1, the flow rates of both the carrier gas and the target gas are 100–1000 sccm, the carrier gas inlet time is 300–1000 s, the target gas inlet time is 300–1000 s, and the target gas concentration is 1 ppb–100 ppm.

3. The test method for the photoexcited semiconductor gas sensor according to claim 1 or 2, characterized in that, The carrier gas is air, and the target gas is one of NO2, O3, H2S, NH3, trimethylamine, and formaldehyde.

4. The testing method for the photoexcited semiconductor gas sensor according to claim 1, characterized in that, The excitation light source is ultraviolet-visible light with a wavelength of 250–650 nm, and the optical power density P of the excitation light source is 0.5–5 mW / cm². 2 .

5. The testing method for the photoexcited semiconductor gas sensor according to claim 1, characterized in that, The following test apparatus is used, which includes a semiconductor gas sensor, an excitation light unit, and a gas-sensitive test unit; The semiconductor gas sensor includes an insulating substrate (11) and two interdigitated electrodes (12) with toothed structures disposed opposite each other on the upper surface of the insulating substrate (11). The toothed structures of the two interdigitated electrodes (12) are opposite to each other and staggered to form a serpentine channel. The interdigitated electrodes (12) are made of noble metal or tin-doped indium oxide (ITO). The interdigitated electrodes (12) and the upper surface of the insulating substrate (11) on which the interdigitated electrodes (12) are located are provided with a sensitive material (13). The excitation unit includes an excitation light source (21), a timer (22) for controlling the periodic switching of the excitation light source, and an optical attenuator (23) for adjusting the light power density of the excitation light source. The light power density of the excitation light source is 0.5–5 mW / cm². 2 ; The gas-sensitive testing unit includes a sealed cavity (31) for placing a semiconductor gas sensor. A transmission window (32) is provided on the cavity (31). An excitation light source (21) passes through an optical attenuator (23) and the transmission window (32) in sequence before irradiating the sensitive material (13). A gas path system (33) is provided outside the cavity (31) to control the flow rate of the carrier gas and the target gas inside the cavity (31). A resistance testing system (34) is also provided outside the cavity (31) and is connected to two interdigitated electrodes (12) respectively to collect and record the changes in the sensor resistance.

6. The testing method for the photoexcited semiconductor gas sensor according to claim 5, characterized in that, The insulating substrate (11) is one of insulating glass, alumina substrate, silicon substrate with SiO2 oxide layer, and polymer substrate; Alternatively, the interdigitated electrode (12) may be made of one of Pt, Au, or ITO. Alternatively, the sensitive material (13) may be one or more of the following: metal oxide semiconductor, metal sulfide, selenide, telluride, and carbon-based material; Alternatively, the material of the transmission window (32) may be quartz glass.

7. The testing method for the photoexcited semiconductor gas sensor according to claim 5, characterized in that, The transmittance of the optical attenuator (23) is 0.1%-90%, and the optical attenuator is an ultraviolet filter with a transmittance wavelength of 250-400nm or a visible light filter with a transmittance wavelength of 400-650nm.

8. The testing method for the photoexcited semiconductor gas sensor according to claim 5, characterized in that, The resistance testing system (34) has a test range of 1kΩ–10GΩ and a sampling rate of 0.5–50Hz.

9. The testing method for the photoexcited semiconductor gas sensor according to claim 5, characterized in that, The excitation light source (21) is ultraviolet-visible monochromatic light or polychromatic light with a wavelength of 250–650 nm; the device emitting the excitation light source (21) is one of semiconductor light-emitting diode (LED), semiconductor laser, or fiber laser.

10. The testing method for the photoexcited semiconductor gas sensor according to claim 5, characterized in that, The photon energy of the excitation light source (21) is greater than the band gap of the sensitive material (13).

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