CN115084315A - Preparation method of homojunction ultraviolet photoelectric detector based on zinc oxide quantum dots - Google Patents

Abstract

A preparation method of a zinc oxide quantum dot-based homojunction ultraviolet photodetector aims to solve the problem that current carrier transmission of a photodetector is blocked due to lattice mismatch between ZnO and other substances in an existing zinc oxide heterojunction photodetector. The preparation method comprises the following steps: adding a potassium hydroxide solution into a zinc acetate solution, stirring for reaction, and dispersing the obtained ZnO quantum dots into a mixed solution of chloroform and methanol to obtain a ZnO quantum dot dispersion solution; secondly, depositing a ZnO film on the substrate; and thirdly, coating ZnO quantum dot dispersion liquid on the substrate with the ZnO film, forming homojunctions by the quantum dot layer and the deposition layer, and finally annealing. The invention is based on ZnO quantum dot/magnetron sputtering ZnO homojunction, the ZnO quantum dot layer with excess oxygen adsorption-desorption sites ensures high yield of photoinduced carriers, and the magnetron sputtering ZnO layer with preferential orientation crystallinity is suitable for accelerating carrier transmission.

Description

Preparation method of homojunction ultraviolet photodetector based on ZnO quantum dots

technical field

The invention relates to a method for preparing a homojunction ultraviolet photodetector based on zinc oxide quantum dots.

Background technique

Ultraviolet (UV) detection technology provides a powerful method for identifying short-wave electromagnetic radiation below 400 nm and has been used in a wide variety of applications such as space communications, oil leak detection, flame detection, missile plume detection, and more. Photoactive wide-bandgap materials, such as ZnO, TiO ₂ , Ga ₂ O ₃ , GaN and ZnS, prepared by plasma-enhanced chemical vapor deposition, hydrothermal method, sol-gel, etc. Signal conversion to detect current. Among them, ZnO is generally regarded as a popular choice for fabricating high-performance optoelectronic devices due to its excellent chemical stability, non-toxicity, abundant earth storage, large direct band gap (~3.37 eV) and exciton binding energy (~60 meV) choose. In the absence of light, the exposed surface defects of ZnO films will spontaneously adsorb oxygen, thereby forming a depletion layer, while the light-induced unilateral depletion of electron-hole pairs and the spontaneous combination of holes and adsorbed oxygen produce abundant carrier. Therefore, low-dimensional ZnO nanostructures (i.e., nanoparticles, nanorods, and nanowires) have great potential to further improve the optoelectronic performance of photodetectors by enhancing light absorption due to their high surface-to-volume ratio. Meanwhile, solution-processed ZnO quantum dots (QDs) readily form continuous thin films with convenient integration and facile synthesis, which are more favorable for carrier transport than the unavoidable discrete morphology in other nanostructures. The electrical properties of the photoelectric layer also play an important role in the performance of ZnO quantum dots UV photodetectors, and the use of exotic p-type materials to construct heterostructures is considered an effective method to accelerate the photogenerated current-carrying within the device through a built-in electric field Separation and transmission of children. To date, various self-powered ZnO heterojunction photodetectors with excellent optoelectronic properties have been successfully fabricated, such as p-type conducting polyaniline polymer/ZnO core-shell microfilaments, ZnO/NiO nanofibers, ZnO–Ga _{2 O3} core-shell microfilaments, p-Se/n-ZnO hybrid structures, graphene nanodot arrays/ZnO nanostructures, p-type Ag-doped ZnO/n-type ZnO nanostructures, etc. However, the additional stress caused by the lattice mismatch between ZnO and other species may lead to the formation of defects inside the heterojunction, which in turn hinders the carrier transport of the photodetector.

SUMMARY OF THE INVENTION

The present invention is to solve the problem of hindering the carrier transport of the photodetector due to lattice mismatch between ZnO and other substances in the existing zinc oxide heterojunction photodetector, and provides a zinc oxide quantum dot-based photoelectric detector. Preparation method of homojunction ultraviolet photodetector.

The preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots of the present invention is realized according to the following steps:

1. Dissolving zinc acetate in methanol to obtain zinc acetate solution; dissolving potassium hydroxide in methanol to obtain potassium hydroxide solution; then adding potassium hydroxide solution to zinc acetate solution at 50℃～70℃, stirring After the reaction, suction filtration to obtain ZnO quantum dots, which are then washed and dispersed into a mixed solution of chloroform and methanol to obtain a ZnO quantum dot dispersion;

2. Using the magnetron sputtering method to deposit a ZnO film on the substrate to obtain a substrate with a ZnO film;

3. Coating ZnO quantum dot dispersion on the substrate with ZnO thin film, the quantum dot layer and the deposition layer form a homojunction, and after annealing treatment, a homojunction ultraviolet photodetector based on ZnO quantum dots is obtained.

The performance of the photodetector is determined by both the generation and transport of photoinduced charge carriers, thus, due to the irreconcilable contradiction between high crystallinity and additional adsorption-desorption sites, ultrasensitive ZnO quantum dots based UV optoelectronics The fabrication of detectors faces enormous challenges. By changing the thickness ratio between two ZnO layers (quantum dot layer and deposition layer), the present invention prepares a zinc oxide quantum dot/magnetron sputtering ZnO homojunction photodetector with excellent performance. Due to the increased surface defects, ZnO QDs have a good equilibrium ratio, providing additional adsorption-desorption sites, and the effect of accelerating the carrier transport is simultaneously achieved by the highly crystalline magnetron-sputtered ZnO layer. Therefore, the responsivity and external quantum efficiency of the ZnO homojunction photodetector fabricated at 250 °C sharply increased to ~551 mA/W and 195.4% under 350 nm illumination (8.58 mW cm ⁻² ) and 10 V bias. And optimized the annealing temperature, even at the same ratio (ZnO QDs/magnetron sputtered ZnO thickness ratio), the responsivity of ZnO homojunction photodetectors at 450 °C annealing temperature can be improved due to the increase in crystallinity. A further improvement to 1.3 A/W paves the way for overcoming the hurdle of ultrasensitive UV photodetection.

The present invention proposes a ZnO quantum dot/magnetron sputtering ZnO homojunction for fabricating high-performance ultraviolet photodetectors. The ZnO quantum dot layer with excess oxygen adsorption-desorption sites can ensure high yield of photoinduced carriers, while the magnetron sputtered ZnO layer with preferential orientation crystallinity is suitable for accelerating carrier transport. The optimal responsivity and external quantum efficiency (EQE) of the ZnO homojunction photodetector prepared at 250 °C under 350 nm illumination (8.58 mW cm ^-2 ) and 10 V bias, respectively, are about 55 times higher than the initial detectors To 551 mA/W and 195.4%, the responsivity of the device prepared at the same ratio at 450 °C is further improved to 1.3 A/W, which provides a facile and effective way to break through the barrier of high-performance UV detectors. method.

Description of drawings

Fig. 1 is the process flow diagram of the homojunction ultraviolet photodetector based on zinc oxide quantum dots of the present invention;

Fig. 2 is the selected area electron diffraction (SAED) figure of the zinc oxide quantum dots synthesized in the embodiment;

3 is an X-ray diffraction (XRD) spectrum of samples with different thickness ratios (h _MS : h _QD ) in Examples;

Fig. 4 is the absorption spectra of samples with different thickness ratios (h _MS : h _QD ) in the embodiment, which are S6, S5, S4, S3, S2 and S1 in sequence along the arrow direction;

Figure 5 is the room temperature photoluminescence (PL) spectra of samples with different thickness ratios (h _MS : h _QD ) in the examples, wherein 1 represents S1, 2 represents S2, 3 represents S3, 4 represents S4, 5 represents S5, 6 stands for S6;

Fig. 6 is the IV curve diagram of samples with different thickness ratios (h _MS : h _QD ) under dark conditions (I _dark ) in the embodiment, which are S1, S2, S3, S4, S5 and S6 in sequence along the arrow direction;

Fig. 7 is the IV curve diagram of samples with different thickness ratios (h _MS : h _QD ) under 350 nm ultraviolet light illumination (I _light , 8.58 mW/cm ² ) in the embodiment, which are S6, S1, S2, S3, S5 and S4;

Fig. 8 is the electric field distribution diagram in the ZnO thin film in the samples with different thickness ratios (h _MS : h _QD ) in the embodiment;

9 is a wavelength-dependent R contour plot of samples with different thickness ratios (h _MS : h _QD ) in the Examples;

Figure 10 is a cross-sectional SEM image of a sputtered ZnO/ZnO quantum dot (S7) sample in Examples;

Figure 11 is a cross-sectional SEM image of a ZnO quantum dot/sputtered ZnO(S8) sample in Examples;

Figure 12 is a simulation diagram of the density of states (DOS) of the ZnO thin film with oxygen vacancies in the example, wherein a represents DOS, b represents oxygen, and c represents zinc;

Figure 13 is a simulation diagram of the density of states (DOS) of the ZnO thin films without oxygen vacancies in the Examples, wherein a represents DOS, b represents oxygen, and c represents zinc;

Figure 14 is the absorption spectrum of the sample at different annealing temperatures (h _MS : h _QD = 210: 140) in the embodiment, which are S9, S10, S11, S12 and S13 in sequence along the arrow direction;

Fig. 15 is the Tauc curve diagram of the samples at different annealing temperatures (h _MS : h _QD = 210: 140) in the embodiment, which are S9, S10, S11, S12 and S13 in sequence along the arrow direction;

Figure 16 is the room temperature PL spectra of samples at different annealing temperatures (h _MS : h _QD = 210: 140) in the embodiment, which are S9, S10, S11, S12 and S13 in sequence along the arrow direction;

Figure 17 is a graph of the IV curves of the sample under dark conditions (I _dark ) at different annealing temperatures between -10 and 10 V in the Examples, followed by S9, S10, S11, S12 and S13 along the direction of the arrows;

FIG. 18 is the I-V curve diagram of the sample under 350 nm ultraviolet light illumination at different annealing temperatures between -10 and 10 V in the example, S9, S10, S11, S12 and S13 in sequence along the arrow direction.

Detailed ways

Embodiment 1: The preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots in this embodiment is implemented according to the following steps:

1. Dissolving zinc acetate in methanol to obtain zinc acetate solution; dissolving potassium hydroxide in methanol to obtain potassium hydroxide solution; then adding potassium hydroxide solution to zinc acetate solution at 50℃～70℃, stirring After the reaction, suction filtration to obtain ZnO quantum dots, which are then washed and dispersed into a mixed solution of chloroform and methanol to obtain a ZnO quantum dot dispersion;

2. Using the magnetron sputtering method to deposit a ZnO film on the substrate to obtain a substrate with a ZnO film;

3. Coating ZnO quantum dot dispersion on the substrate with ZnO thin film, the quantum dot layer and the deposition layer form a homojunction, and after annealing treatment, a homojunction ultraviolet photodetector based on ZnO quantum dots is obtained.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that in step 1, the concentration of the zinc acetate solution is 40-60 mmol/L, and the concentration of the potassium hydroxide solution is 120-180 mmol/L.

Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that the potassium hydroxide solution is added to the zinc acetate solution at 60° C. in step 1.

Embodiment 4: The difference between this embodiment and one of Embodiments 1 to 3 is that the molar ratio of zinc acetate to potassium hydroxide in step 1 is 1:(1.2-2).

Specific embodiment 5: The difference between this embodiment and one of specific embodiments 1 to 4 is that the stirring reaction time in step 1 is 1.5-3 h.

Embodiment 6: The difference between this embodiment and one of Embodiments 1 to 5 is that the volume ratio of chloroform and methanol in the mixed solution of chloroform and methanol in step 1 is 2:1.

Embodiment 7: The difference between this embodiment and one of Embodiments 1 to 6 is that a ZnO target is used in step 2, and a ZnO film is deposited at a rate of 0.1-0.3 nm/s under a pressure of 3×10 ^-4 Pa.

Embodiment 8: The difference between this embodiment and one of Embodiments 1 to 7 is that the total thickness of the homojunction in step 3 is 330 nm to 400 nm.

The total thickness of the homojunction in this embodiment is optimized to be 350 nm.

Embodiment 9: This embodiment differs from Embodiment 8 in that the thickness ratio of the quantum dot layer and the deposition layer in step 3 is (130-150): (200-220).

Embodiment 10: The difference between this embodiment and one of Embodiments 1 to 9 is that in step 3, the annealing treatment is performed at 250° C. to 450° C. for 1 to 2 hours.

The annealing temperature in this embodiment is preferably 450°C.

Embodiment 11: The difference between this embodiment and Embodiments 1 to 11 is that in step 3, electrodes are also deposited on both sides of the quantum dot layer.

The electrode material of this embodiment is preferably a gold electrode.

Embodiment: The preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots in this embodiment is implemented according to the following steps:

1. Synthesis of ZnO quantum dots:

Dissolve 4.46 mmol of zinc acetate dihydrate (Zn(CH ₃ COO) ₂ ) in 84 mL of methanol to obtain a zinc acetate solution; dissolve 7.22 mmol of potassium hydroxide (KOH) in 46 mL of methanol to obtain a potassium hydroxide solution; then The potassium hydroxide solution was gradually added dropwise to the zinc acetate solution at 60°C, and the reaction was stirred at 60°C for 2 hours, followed by suction filtration to obtain ZnO quantum dots, which were washed with methanol and dispersed into a mixed solution of chloroform and methanol (V _chloroform : V _ethanol ). =2:1), obtain ZnO quantum dots (QD) dispersion;

2. Preparation of ZnO thin film on glass substrate:

The glass substrates were ultrasonically cleaned with deionized water, ethanol, and acetone in turn for 20 minutes, respectively, in a radio frequency magnetron sputtering chamber at a rate of 0.1-0.3 nm/s under a pressure of 3 × 10 ^-4 Pa. A ZnO film is deposited on a glass substrate to obtain a substrate with a ZnO film;

3. Device manufacturing:

The ZnO quantum dot dispersion was spin-coated on the substrate with ZnO thin film at a speed of 2000 rpm, the quantum dot layer and the deposition layer formed a homojunction, annealed at 250 °C for 2 hours, and finally on both sides of the quantum dot layer. Gold electrodes with a spacing of 200 μm were deposited by magnetron sputtering to obtain a homojunction UV photodetector based on ZnO quantum dots.

In this example, in order to study the influence of the thickness ratio of the quantum dot layer and the deposition layer on the performance of the device, six devices with different thickness ratios were fabricated. The total thickness of ZnO homojunction of each device is 350 nm, and the thickness ratio of ZnO thin film (h _MS ) and QD (h _QD ) is different: S1 (0:350), S2 (70:280), S3 (140:210 ), S4 (210:140), S5 (280:70), and S6 (350:0).

In this example, in order to study the configuration effect, the sample ZnO film/quantum dots (S7) and ZnO quantum dots/film (S8) were prepared with a thickness ratio of 210:140 (h _MS :h _QD ).

In this example, in order to study the temperature effect, the thickness ratio of 210:140 (h _MS :h _QD ) was adopted, and the temperature was adjusted at room temperature (S9), 150°C (S10), 250°C (S11), 350°C (S12), and 450°C, respectively. (S13) Five devices were fabricated at different annealing temperatures.

The manufacturing process of the ZnO quantum dot/magnetron sputtering ZnO homojunction photodetector in this embodiment is shown in FIG. 1 . The lattice spacing of the colloidal ZnO quantum dots synthesized in this example is 0.26 nm, which is consistent with the (002) crystal plane of the wurtzite structure ZnO. The wurtzite structure of ZnO was confirmed by the six diffraction rings in the selected area electron diffraction (SAED) pattern of FIG. 2 . The surface morphology of ZnO QDs/magnetron sputtered ZnO homojunctions develops gradually with the ratio of h _MS (thickness of sputtered ZnO seed layer) to h _QD (thickness of ZnO quantum dots), which is due to magnetron sputtering The presence of the ZnO layer relieves the distortional stress within the homojunction, thereby improving the uniformity and grain size of the film.

To further evaluate the effect of _hMS :h _QD ratio, this example analyzes the evolution of the structure and optical properties of ZnO quantum dots/magnetron sputtered ZnO homojunctions. The zinc and oxygen distributions are uniform in sample S4 (h _MS :h _QD =210:140), indicating the high uniformity of the resulting films. X-ray photoelectron spectroscopy (XPS) of O1s features on samples S1 (h _MS :h _QD = 0:350), S4 (h _MS : h _QD = 210:140) and S6 (h _MS : h _QD = 350:0) ) in the spectrum can be decomposed into two peaks located at 530.1 eV and 531.4 eV, indicating oxygen lattices and oxygen vacancies. As the proportion of the magnetron sputtered ZnO layer increases, the proportion of the oxygen vacancy peak area in the entire region of the O1s signal decreases from 52.5% to 38.0%, which indicates that the ZnO QD layer has more inherent defects. Figure 3 shows the X-ray diffraction (XRD) spectra of samples with different _hMS :h _QD ratios. The (100) and (101) peaks of the pristine ZnO QD sample (S1) have relatively low intensities, and the (002) peak gradually dominates as the _hMS : _hQD ratio increases, indicating that along the perpendicular to the c-axis Orientation prioritizes growth. By introducing a magnetron sputtered ZnO layer, it can be strongly demonstrated that the crystallinity of the ZnO homojunction is improved. As shown in Fig. 4, the absorption peak gradually increases with the increase of the ratio of the magnetron sputtered ZnO layer, which is consistent with the improved surface topography with reduced surface defects. Meanwhile, after the Tauc test, there is a gradual blue-shift from 3.27 eV to 3.35 eV with the increase of the ZnO quantum dot layer ratio due to the quantum confinement effect. Correspondingly, the near-gap edge luminescence peak (NBE) of the ZnO homojunction is broadened, which is attributed to the superposition of the two luminescence peaks between the ZnO quantum dots and the magnetron sputtered layer.

Figures 6 and 7 show the optoelectronic properties of ZnO quantum dots/magnetron sputtered ZnO homojunction photodetectors as a function of h _MS : h _QD ratio: S1 (0:350), S2 (70:280), S3 (140:210), S4 (210:140), S5 (280:70) and S6 (350:0). At each bias, the dark current (I _dark ) increases slowly with increasing ratio of magnetron sputtered ZnO films due to the reduction of defects, as shown in Fig. 6 . As shown in Fig. 7, the pristine ZnO quantum dot (S1) photodetector exhibits significantly enhanced photocurrent (I _light ) at each bias compared with the magnetron sputtered ZnO thin film device, and the I _light It initially increases with the ratio of magnetron sputtered ZnO layers until the ratio reaches 210:140 (S4). Intrinsic defects existing in the ZnO lattice can serve as adsorption sites for oxygen, thereby deriving photoinduced charge carriers from the desorption process, which is considered a classic model for the photodetection mechanism of ZnO. ZnO QD layers with more defects tend to provide more adsorption sites for photo-induced carrier generation, and magnetron-sputtered ZnO layers with high crystallinity are favorable for carrier transport by properly balancing h The _MS :h _QD ratio provides a way to improve device performance. After testing, the I _light of device S4 is _70.83 times higher than that of S6, reaching about 37.9 μA. Compared with the pristine ZnO QD photodetector (S1), the homojunction photodetector (S4) exhibits slightly improved stability over several cycles. Therefore, for the ZnO homojunction photodetector with reduced exposure adsorption sites, the response time can be prolonged when the ratio of h _MS : h _QDs is higher. With the increase of optical power, the photocurrent of the device shows an increasing trend. The relationship between optical power and photocurrent can be described by the following equation:

I=CP ^θ (1)

where C is the wavelength-dependent fitting constant, θ is the power fitting exponent, and P is the incident light intensity. As the ratio of magnetron sputtered ZnO layers increases, θ continuously decreases from 0.978 to 0.289, which indicates that at relatively high optical powers, the photo-induced charge carriers tend to be saturated due to the limited adsorption-desorption process described above. To understand the photoresponse mechanism, the electromagnetic field (EM) distributions of ZnO homojunctions with different _hMS :h _QD ratios were simulated according to the refractive index (n) and extinction (k) coefficients of the materials. As shown in Fig. 8, the electromagnetic field distributed in the ZnO QD layer is gradually enhanced with increasing ratio, reaching 140:210 (S3), followed by a significant damping according to the thickness of the magnetron-sputtered ZnO layer. The responsivity (R) is given by the following formula:

where P and A represent the incident light intensity (8.58 mW/cm ² ) and the illumination area between the two electrodes, respectively. Under 10 V/350 nm illumination, the responsivity of device ^S4 increased by about 55 times compared with that of device S1 from 10.1 mA W, indicating that the performance of the photodetector is comprehensively determined by the combination of photoexcitation and carrier transport. Accordingly, the responsivity R of each device similarly increases with increasing bias voltage. The normalized detection rate (D*) is expressed by the following equation:

where q represents the charge of a single electron.

The External Quantum Efficiency (EQE) can be derived from the following formula:

where h, c, and λ are Planck's constant, the speed of light in vacuum, and the wavelength of the incident light. According to the thickness ratio, the EQE increases significantly from 3.6% to 195.4% under 350 nm illumination. With the change of light wavelength, under 350nm illumination, each photodetector can obtain the highest I _light at different bias voltages. As shown in Fig. 9, the enhancement of R can be similarly viewed as a function of the thickness ratio, with a contour plot of the spectral responsivity, and the device exhibits a broadband wavelength up to 500 nm due to the enhancement of I _light over a wide range.

To verify the configuration effect, as shown in Figures 10 and 11, a ZnO homojunction photodetector was fabricated with the same thickness of 350 nm by changing the position of the ZnO quantum dot layer. For the sample sputtered ZnO film/ZnO quantum dots (S7), the (002) peak mainly appears in the XRD spectrum, while the (100) and (101) peaks of the sample ZnO quantum dot/sputtered ZnO (S8) film are observed. The _Idark of device S7 is better than that of device _S8 , which indicates that the carrier transport is improved by sputtering the ZnO layer. The effect of defects (oxygen vacancies) on ZnO electron orbital transitions was investigated using density functional theory (DFT). The density of states (DOS) simulations of the ZnO films with and without oxygen vacancies are shown in Figure 12 and Figure 13. In the presence of oxygen vacancies, the forbidden band width of ZnO is smaller than that in the absence of defects. The calculated band gap of intrinsic ZnO is 0.64 eV, which is much smaller than the experimental result. This can be attributed to a disadvantage that standard DFT calculations inevitably underestimate the band gap of ZnO. However, this does not affect the analysis of its properties. The band gap of ZnO QD films containing more defects is larger than that of magnetron-sputtered ZnO, suggesting that quantum confinement effect plays an important role in band gap tuning. As shown in Fig. 13, the steep peak at 0.34 eV indicates that under the same conditions, electrons in the valence band are more easily transported to the conduction band, which will increase the carrier concentration in the conduction band, explaining the dark current of the intrinsic ZnO higher than the dark current of defective ZnO. The simulated phenomenon is consistent with the conclusion in Fig. 6.

Furthermore, in this example, the effect of temperature on the surface morphology evolution of a ZnO homojunction with a _hMS :h _QD thickness ratio of 210:140 was investigated in the range between room temperature and 450 °C. Due to the enhanced aggregation, the grains gradually expanded from 27.9 nm to 46.5 nm with the change of annealing temperature. The full width at half maximum (FWHM) of the (002) peak is determined by the Scheler equation:

BLcosθ=Kλ (5)

where B, L, θ, K, and λ are the full width at half maximum, grain size, diffraction peak position, shape-dependent factor, and X-ray wavelength, respectively. Therefore, the FWHM slowly drops from 0.5 degrees to 0.3 degrees. As the grain size increases, the peak strength also increases correspondingly, depending on the annealing temperature, and the preferential grain growth within the homojunction is enhanced. The absorption of the ZnO homojunction increases slightly with increasing temperature, and the bandgap redshifts from 3.32 eV to 3.27 eV due to the additional stress introduced by the grain growth in the film, as shown in Fig. 15. Correspondingly, the PL intensity increases with temperature due to the improvement in crystallinity as shown in FIG. 16 . Figures 17 and 18 show the photoelectric properties associated with different annealing temperatures for ZnO homojunctions. As shown in Figures 17 and 18, both I _dark and I _light increased depending on the annealing temperature, which was due to the enhanced carrier transport brought about by the increased crystallinity. Therefore, I _dark increases from 0.2 nA to 1.2 μA and I _light also increases from 0.83 to 89.5 μA at a bias of 10 V over the entire temperature range. After testing, R reaches 1297.8mA/W at 450℃, and the best D* of 384.3×10 ⁹ Jones is obtained at 250℃. As the annealing temperature was changed, the EQE increased dramatically, resulting in a significant improvement of about 106-fold to 456%.

In conclusion, the present invention systematically analyzes the effects of h _MS : h _QD ratio and annealing temperature on the surface morphology evolution and photodetection performance of ZnO quantum dots/magnetron sputtered ZnO homojunctions. The presence of additional surface defects on the ZnO QD layer exacerbates the oxygen adsorption-desorption process, and the relatively high crystallinity magnetron sputtering correspondingly accelerates the carrier transport. The I _dark of the ZnO homojunction photodetector under 350 nm UV light irradiation (8.58 mW/cm ² ) gradually increased with the increase of h _MS : h _QD ratio. An optimal I _light of about 37.9 μA was obtained at a ratio of _MS :h _QD = 210:140, resulting in a significant increase in EQE from 3.6% to 195.4%. Depending on the annealing temperature, the responsivity and EQE were optimized to 1.3 A/W and 456% at 450 °C, respectively, which successfully resolved the additional adsorption-desorption sites required for high crystallinity and high performance ZnO UV photodetectors irreconcilable contradictions.

Claims (10)

1. the preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots is characterized in that this preparation method is realized according to the following steps: 1. Dissolving zinc acetate in methanol to obtain zinc acetate solution; dissolving potassium hydroxide in methanol to obtain potassium hydroxide solution; then adding potassium hydroxide solution to zinc acetate solution at 50℃～70℃, stirring After the reaction, suction filtration to obtain ZnO quantum dots, which are then washed and dispersed into a mixed solution of chloroform and methanol to obtain a ZnO quantum dot dispersion; 2. Using the magnetron sputtering method to deposit a ZnO film on the substrate to obtain a substrate with a ZnO film; 3. Coating ZnO quantum dot dispersion on the substrate with ZnO thin film, the quantum dot layer and the deposition layer form a homojunction, and after annealing treatment, a homojunction ultraviolet photodetector based on ZnO quantum dots is obtained. 2. the preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1, is characterized in that the concentration of zinc acetate solution in step 1 is 40～60mmol/L, the concentration of potassium hydroxide solution It is 120～180mmol/L. 3. The preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1, is characterized in that in step 1, the molar ratio of zinc acetate and potassium hydroxide is 1:(1.2～2). 4 . The method for preparing a homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1 , wherein the stirring reaction time in step 1 is 1.5-3 h. 5 . 5. the preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1, is characterized in that the volume ratio of chloroform and methanol in the mixed solution of chloroform and methanol in step 1 is 2:1. 6 . The method for preparing a homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1 , wherein in step 2, a ZnO target is used, and under a pressure of 3×10 ⁻⁴ Pa, the concentration of 0.1～ ZnO films were deposited at a rate of 0.3 nm/s. 7 . The method for preparing a homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1 , wherein the total thickness of the homojunction in step 3 is 330 nm to 400 nm. 8 . 8. the preparation method of the homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 7, is characterized in that in step 3, the thickness ratio of quantum dot layer and deposition layer is (130～150): (200 ~220). 9 . The method for preparing a homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1 , wherein in step 3, annealing is performed at 250° C.˜450° C. for 1˜2 hours. 10 . 10 . The method for preparing a homojunction ultraviolet photodetector based on zinc oxide quantum dots according to claim 1 , wherein electrodes are also deposited on both sides of the quantum dot layer in step 3. 11 .

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