Preparation method of zinc tin nitride homojunction

Abstract

The invention discloses a ZnSnN2 homojunction and a preparation method thereof, and the method comprises the steps: depositing a zinc-tin alloy target in which the ratio of Zn to Sn is 3: 1 on a substrate through a radio frequency sputtering method in a flowing nitrogen and argon atmosphere at 50 DEG C to obtain a ZnSnN2 film. And in the flowing nitrogen and argon atmosphere, Ag doping is carried out on the ZnSnN2 thin film in the room temperature environment, and the ZnSnN2: Ag thin film is obtained. And depositing a Pt target on the ZnSnN2: Ag film through a direct current sputtering method in a flowing argon atmosphere to obtain the ZnSnN2 homojunction. The problem that the ZnSnN2 homojunction prepared by the existing method is poor in rectification characteristic and has no photovoltaic effect is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor thin film materials technology, and in particular to a method for preparing a zinc tin nitride homojunction. Background Technology

[0002] Zinc tin nitride (ZnSnN2) thin films, as an emerging ternary semiconductor material, are composed of zinc (Zn), tin (Sn), and nitrogen (N), elements extremely abundant in the Earth's crust. Due to their numerous advantages, including non-toxicity, high elemental abundance, low preparation cost, high optical absorption coefficient, and tunable bandgap, they meet the requirements of thin-film solar cells, making them a relatively ideal material for such cells. However, despite the superior performance of ZnSnN2 thin films, their electron concentration is limited to around 10⁻⁶. 16 ~10 21 cm -3 The ZnSnN2 exhibits degeneracy within a certain range, which researchers have found is primarily due to the very low enthalpy of formation of ZnSnN2 under thermodynamic equilibrium conditions. This leads to the formation of secondary phases such as Sn and Zn, and the coexistence of Zn and Sn metallic phases results in a high electron concentration, limiting the application of ZnSnN2 in devices. P-type doping of ZnSnN2 can be achieved through co-doping with metals Ag, Zn, and Sn, and this doping is non-degenerate. Ag provides good electrical contact and, unlike Cu, does not compromise the integrity of the bulk material. Furthermore, Ag is mostly monovalent, making it an effective acceptor in doping. Platinum (Pt) was chosen as the electrode because it hardly oxidizes in air, maintains its metallic state even at high temperatures, and has a work function of 5.65 eV, enabling it to form ohmic contacts with Ag-doped ZnSnN2 thin films (ZnSnN2:Ag, a P-type semiconductor). Studying the p-type doping of Ag and ZnSnN2 thin films and the photovoltaic performance of ZnSnN2 homojunctions (ITO / ZnSnN2 / ZnSnN2:Ag / Pt) is of great value. Currently, there is limited research on p-type doping of ZnSnN2:Ag and its homojunctions.

[0003] Therefore, there is an urgent need for a simple and effective method to prepare a P-type doped ZnSnN2:Ag ZnSnN2 homojunction with photovoltaic effect, so as to enhance its application value in photovoltaics. Summary of the Invention

[0004] In view of the above-mentioned problems, the purpose of this invention is to provide a method for preparing a ZnSnN2 homojunction with good rectification effect and photovoltaic effect, aiming to expand the application of ZnSnN2 material in solar cells.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing a ZnSnN2 homojunction, comprising the following steps:

[0007] In a nitrogen and argon atmosphere, a zinc-tin alloy target is deposited on indium tin oxide (ITO) glass by radio frequency sputtering to obtain ITO / ZnSnN2.

[0008] In a nitrogen and argon atmosphere, a zinc-tin alloy target is deposited on ITO by radio frequency sputtering and a silver (Ag) target is deposited on ITO by DC sputtering to obtain ITO / ZnSnN2 / ZnSnN2:Ag.

[0009] In an argon atmosphere, metallic Pt is deposited on a ZnSnN2:Ag thin film by DC sputtering to obtain an ITO / ZnSnN2 / ZnSnN2:Ag / Pt homojunction.

[0010] The method for preparing the ZnSnN2 homojunction includes the following steps:

[0011] First, fix the zinc-tin alloy target on the radio frequency target position, evacuate the sputtering system, then continuously introduce nitrogen and argon gas and keep the gas pressure stable. Then, zinc and tin are deposited on the ITO glass simultaneously by radio frequency sputtering to obtain ITO / ZnSnN2.

[0012] ITO / ZnSnN2 was placed in the sputtering chamber, and after being evacuated to the required vacuum level, a mixture of nitrogen and argon was continuously introduced to maintain a stable working pressure. Then, in a mode combining RF sputtering and DC sputtering, a zinc-tin alloy target and an Ag target were simultaneously sputtered, depositing a ZnSnN2:Ag layer on the ITO / ZnSnN2 surface, thus obtaining ITO / ZnSnN2 / ZnSnN2:Ag.

[0013] ITO / ZnSnN2 / ZnSnN2:Ag is placed in a sputtering system, a Pt metal target is fixed on a DC target position, the vacuum chamber is evacuated, and argon gas is continuously introduced and the gas pressure is kept stable. Then, Pt is deposited on ITO / ZnSnN2 / ZnSnN2:Ag by DC sputtering, thus obtaining the ITO / ZnSnN2 / ZnSnN2:Ag / Pt structure, i.e., ZnSnN2 homojunction.

[0014] In the method for preparing the ZnSnN2 thin film, the nitrogen gas is 99.999% high-purity nitrogen gas, and the argon gas is 99.995% high-purity argon gas.

[0015] In the method for preparing the ZnSnN2 thin film, the flow rate of nitrogen is 5 sccm and the flow rate of argon is 8 sccm.

[0016] The method for preparing the ZnSnN2 thin film, wherein the radio frequency sputtering power is 35W.

[0017] The method for preparing the ZnSnN2 thin film, wherein the radio frequency sputtering pressure is 5 Pa.

[0018] In the method for preparing the ZnSnN2 thin film, the substrate needs to be heated to 50°C before thin film deposition.

[0019] The method for preparing the ZnSnN2:Ag thin film, wherein the nitrogen gas is 99.999% high-purity nitrogen gas and the argon gas is 99.995% high-purity argon gas.

[0020] In the method for preparing the ZnSnN2:Ag thin film, the flow rate of nitrogen is 5 sccm and the flow rate of argon is 8 sccm.

[0021] The method for preparing the ZnSnN2:Ag thin film, wherein the radio frequency sputtering power is 35W and the DC sputtering power is 3W.

[0022] The method for preparing the ZnSnN2:Ag thin film, wherein the radio frequency sputtering pressure is 5 Pa.

[0023] The method for preparing the Pt electrode, wherein the argon gas is 99.995% high-purity argon gas.

[0024] In the method for preparing the Pt electrode, the flow rate of the argon gas is 30 sccm.

[0025] In the method for preparing the Pt electrode, the pressure of the DC sputtering is 1 Pa.

[0026] In the method for preparing the Pt electrode, the power of the DC sputtering is 20W.

[0027] A ZnSnN2 homojunction, characterized in that it is prepared by the method described above.

[0028] Beneficial effects: This invention prepares ITO / ZnSnN2 by sputtering a zinc-tin alloy target on an ITO substrate in a flowing nitrogen and argon atmosphere using radio frequency sputtering. Then, ZnSnN2:Ag is deposited on the ITO / ZnSnN2 using a dual-target co-sputtering method, with the zinc-tin alloy target still using radio frequency sputtering and the Ag target using DC sputtering, to obtain an ITO / ZnSnN2 / ZnSnN2:Ag structure. A Pt layer is then sputtered on this structure to form a ZnSnN2 homojunction. The prepared homojunction has good rectification characteristics and exhibits photovoltaic effects. Attached Figure Description

[0029] Figure 1The image shows the dark-state IV test pattern of the zinc tin nitride homojunction with a sputtering time of 2 hours provided by this invention.

[0030] Figure 2 The image shows the dark-state IV test pattern of the zinc tin nitride homojunction with a sputtering time of 3 hours provided by this invention.

[0031] Figure 3 The image shows the dark-state IV test pattern of the zinc tin nitride homojunction with a sputtering time of 4 hours provided by this invention.

[0032] Figure 4 The image shows the illumination state IV test pattern of the zinc tin nitride homojunction with a sputtering time of 2 hours provided by this invention.

[0033] Figure 5 The image shows the illumination state IV test pattern of the zinc tin nitride homojunction with a sputtering time of 3 hours provided by this invention.

[0034] Figure 6 The image shows the illumination state IV test pattern of the zinc tin nitride homojunction with a sputtering time of 4 hours provided by this invention. Detailed Implementation

[0035] This invention provides a method for preparing a ZnSnN2 homojunction. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are only for explaining this invention and are not intended to limit this invention.

[0036] The method for preparing a ZnSnN2 homojunction according to the present invention includes the following steps:

[0037] In a flowing nitrogen and argon atmosphere, a zinc-tin alloy target is deposited on a substrate by radio frequency sputtering to obtain a ZnSnN2 thin film.

[0038] Unlike previous methods that used radio frequency sputtering of zinc and DC sputtering of tin to simultaneously deposit ZnSnN2 thin films on a substrate using a dual-target co-sputtering method, this invention uses radio frequency sputtering of a zinc-tin alloy target to deposit the ZnSnN2 thin film onto the substrate, thus obtaining a ZnSnN2 thin film with low carrier concentration.

[0039] In the method for preparing the ZnSnN2 thin film described in this invention, a zinc-tin alloy target is first fixed on the radio frequency target, and then the entire sputtering system is evacuated to a pressure of 5.0 × 10⁻⁶. -4To ensure the absence of impurities such as oxygen, nitrogen and argon are continuously introduced while maintaining a stable pressure. In other words, nitrogen and argon are introduced and discharged at a certain rate to ensure that the entire magnetron sputtering system is maintained at a certain pressure environment. Then, zinc and tin are simultaneously deposited on ITO by radio frequency sputtering to obtain a ZnSnN2 thin film.

[0040] Preferably, the substrate is ITO glass, used in the preparation of ZnSnN2 thin films in this invention.

[0041] Preferably, in this invention, the substrate is preheated and kept at 50°C before thin film deposition, because excessively high temperatures can easily lead to impurities, while excessively low temperatures can easily cause the thin film to become amorphous.

[0042] Before depositing the thin film, the alloy target can be pre-sputtered for a period of time (e.g., 5 minutes) to remove oxides and impurities on the target surface, thus avoiding the deposition of these oxides or impurities onto the substrate, which could ultimately lead to contamination or even failure of the ZnSnN2 thin film.

[0043] The zinc-tin alloy target is a zinc-tin alloy target with Zn:Sn = 3:1. The zinc-tin alloy target is subjected to radio frequency sputtering at a power of 35W to deposit it onto the substrate to form a ZnSnN2 thin film.

[0044] In the method for preparing the ZnSnN2 thin film, the nitrogen gas is 99.999% high-purity nitrogen gas and the argon gas is 99.995% high-purity argon gas, so as to minimize the interference of impurity gases on the sputtering reaction and thus improve the quality of the ZnSnN2 thin film.

[0045] Preferably, the flow rate of nitrogen is 5 sccm and the flow rate of argon is 8 sccm. ZnSnN2 thin films prepared under the above-mentioned flow rates of nitrogen and argon have low carrier concentrations and good quality.

[0046] In a flowing nitrogen and argon atmosphere, zinc, tin and silver are co-sputtered onto a ZnSnN2 thin film by radio frequency sputtering of a zinc-tin alloy target and DC sputtering of an Ag target, thus obtaining a ZnSnN2:Ag thin film.

[0047] Unlike previous doping methods, this invention uses argon gas at a certain flow rate to maintain stable gas pressure, thus enabling the preparation of ZnSnN2:Ag thin films with low carrier concentration.

[0048] The preparation of the ZnSnN2:Ag thin film layer described in this invention specifically involves placing the prepared ITO / ZnSnN2 into a sputtering system, and then evacuating the entire sputtering system to a pressure of 5.0 × 10⁻⁶. -4Pa, while controlling the temperature at 22℃~30℃, and continuously introducing nitrogen and argon while maintaining stable gas pressure, that is, introducing nitrogen and argon while venting at a certain rate to ensure that the entire vacuum chamber is maintained at a certain gas pressure environment, and then maintaining it for a period of time, sputtering to prepare ZnSnN2:Ag thin film, to obtain ITO / ZnSnN2 / ZnSnN2:Ag structure.

[0049] Preferably, the ZnSnN2 thin film layer needs to be prepared in advance. ZnSnN2 thin films prepared under other conditions can also be used to prepare ZnSnN2 thin films in this invention.

[0050] In the ZnSnN2:Ag thin film preparation method, the argon gas is 99.995% high-purity argon gas to minimize the interference of impurity gases on doping, thereby improving the quality of ZnSnN2:Ag. At the same time, it ensures that the gas pressure of the entire system is stable at 5 Pa. Under this pressure, the thin film can have better crystallinity, better film compactness, and better P-type doping, resulting in a lower carrier concentration.

[0051] Preferably, the flow rate of nitrogen is 5 sccm and the flow rate of argon is 8 sccm. ZnSnN2:Ag thin films prepared under the above-mentioned flow rates of nitrogen and argon have low carrier concentrations and good quality.

[0052] In a flowing argon atmosphere, under a fixed pressure, a Pt target is deposited on a ZnSnN2:Ag thin film by DC sputtering to obtain a ZnSnN2 homojunction.

[0053] In this invention, argon gas with a certain flow rate is used to maintain stable gas pressure and is used as bombardment particles to perform DC sputtering on a Pt target, thereby preparing a ZnSnN2 homojunction with good rectification characteristics and good photovoltaic effect.

[0054] Preferably, in the method for preparing the ZnSnN2 homojunction, the ZnSnN2:Ag film needs to be prepared in advance. For example, the P-type ZnSnN2 film used in this invention is the ZnSnN2:Ag film prepared above. P-type ZnSnN2 films prepared under other conditions can also be used to prepare ZnSnN2 homojunctions in this invention.

[0055] In the method for preparing the ZnSnN2 homojunction, the argon gas is 99.995% high-purity argon gas to minimize the interference of impurity gases on the preparation of the homojunction, thereby improving the quality of the ZnSnN2 homojunction. At the same time, it ensures that the gas pressure of the entire system is stable at 1 Pa, which means that even at the sputtering gas pressure of 1 Pa, Pt as an electrode can better bond with the ZnSnN2:Ag thin film, and the thickness of the Pt electrode is more uniform.

[0056] Preferably, the flow rate of the argon gas is 30 sccm. ZnSnN2 homojunctions prepared under the above-mentioned flow rate of argon gas have low carrier concentrations and excellent quality.

[0057] The present invention also provides a ZnSnN2 homojunction, wherein it is prepared by the method described above.

[0058] The present invention will be described in detail below through embodiments.

[0059] Example 1

[0060] A zinc-tin alloy target with a Zn:Sn ratio of 3:1 was fixed on the RF target site. ITO was used as the substrate, and the base voltage of the sputtering system was pumped to 5.0 × 10⁻⁶. -4 High-purity argon gas (8 sccm) and high-purity nitrogen gas (5 sccm) were introduced to deposit a thin film at a working pressure of 5.0 Pa. Before sputtering, the target was pre-sputtered for 5 minutes to remove oxides and impurities from the target surface. During film sputtering deposition, the sputtering power of the zinc-tin alloy target was 35 W, and the substrate temperature was 50 °C. After sputtering, the sputtering source and inlet valve were turned off. Once the substrate temperature had cooled to room temperature, the vacuum pump, power supply, and other switches were turned off sequentially. The film sample was then removed for testing.

[0061] When preparing ZnSnN2:Ag thin films on this sample, the RF sputtering power on the zinc-tin alloy target with a Zn:Sn ratio of 3:1 was 35W, the DC sputtering power on the Ag target was 3W, and the background pressure was 5.0 × 10⁻⁶. -4 Three groups of TO / ZnSnN2 / ZnSnN2:Ag structure samples were obtained at room temperature with fixed argon flow rate of 8 sccm, nitrogen flow rate of 5 sccm, sputtering pressure of 5 Pa, sputtering time of 2 h, 3 h and 4 h respectively.

[0062] Finally, Pt electrodes were deposited, and the Pt target was mounted on a DC target position. The power of the Pt target was fixed at 20W, and sputtering was performed using 99.995% high-purity argon gas. An ITO / ZnSnN2 / ZnSnN2:Ag structure was used as the substrate. The base pressure was 4.0 × 10⁻⁶. -4 A ZnSnN2 homojunction sample was obtained by setting the argon gas flow rate to 30 sccm, the sputtering pressure to 1 Pa, and the sputtering time to 30 min. After the sputtering coating was completed, the sputtering source and inlet valve were turned off. After the substrate temperature dropped to room temperature, the vacuum pump, power supply, and other switches were turned off in sequence. The homojunction sample was then removed for testing.

[0063] Figure 1 , Figure 2 , Figure 3The images show dark-state IV diagrams of samples sputtered for 2h, 3h, and 4h. The figures demonstrate that the homojunction exhibits good and stable rectification characteristics. Figure 4 , Figure 5 , Figure 6 The images show the illumination conditions of the samples after sputtering for 2 hours, 3 hours, and 4 hours. Photovoltaic effects were observed in all samples.

[0064] As can be seen from the above embodiments, this preparation method can obtain a ZnSnN2 homojunction with good rectification characteristics and photovoltaic effect.

[0065] Under constant sputtering parameters (including zinc-tin alloy target power, working gas flow rate, and chamber pressure), the deposition flux of zinc and tin can be considered to remain stable during sputtering. Since the Zn:Sn atomic ratio in the target material is 3:1, this process essentially constitutes a zinc-rich deposition environment.

[0066] From the perspective of gas-phase chemical potential, since nitrogen is actively introduced as the reactant gas, while oxygen mainly originates from the residual gas in the vacuum chamber, the chemical potential of nitrogen is significantly higher than that of oxygen. As the substrate temperature decreases, the chemical potentials of both nitrogen and oxygen show an increasing trend, and the difference gradually decreases. Moreover, oxygen has higher chemical reactivity, and its chemical potential increases more significantly at low temperatures.

[0067] When the substrate temperature is 50°C, the higher oxidation potential and enhanced adsorption stability work together to significantly increase the oxygen concentration in the ZnSnN2 thin film. Under these conditions, oxygen atoms more readily occupy nitrogen sites through substitution mechanisms, forming donor-type doping centers (denoted as O). N ).

[0068] Due to Sn zn and O N The low formation energy of defects like Sn and Zn results in a high intrinsic carrier concentration, making it difficult to achieve p-type ZnSnN2 materials. Therefore, Ag is chosen to dope ZnSnN2 to achieve p-type doping. Ag atoms tend to occupy Zn sites in the material, forming Agzn. Since Ag is typically in the +1 valence state while Zn is in the +2 valence state, Agzn is an acceptor defect, capable of accepting an electron and creating a hole in the valence band. In experiments, by controlling the Ag doping concentration, the Sn doping energy can be compensated for. zn The excess electrons provided by the donor defect eventually convert the conductivity type to P-type, resulting in P-type ZnSnN2 material.

[0069] Under a substrate temperature of 50°C and Zn-rich sputtering conditions, the electrical performance optimization we observed is essentially a precise process of defect synergistic modulation. Its physical essence can be described as follows: the introduced O impurities act as donor centers (O... NThis triggers lattice charge rearrangement. To maintain the system's electroneutrality, the Zn-rich environment suppresses the dominant donor defect Sn antisite by lowering the Sn chemical potential. zn The formation of the acceptor defect Zn inversion (Zn) is also facilitated by this condition. Sn The generation of ) and its relationship with O N Donors form electrically neutral defect complexes. This defect reconstruction path achieves the transformation from discrete charged defects to neutral complexes. It not only reduces the net donor concentration, allowing the material to enter the non-degenerate region, but also achieves a suitable carrier concentration because the scattering cross-section of neutral defects for charge carriers is significantly smaller than that of charged impurities. This electrical performance modulation achieved through defect engineering provides an ideal material basis for the application of ZnSnN2 in photovoltaic devices.

[0070] Pt is used as the metal electrode in the homojunction because it hardly oxidizes in air and maintains its metallic state even at high temperatures, which is crucial in device fabrication. Furthermore, Pt has a work function of 5.65 eV, one of the highest known work functions among metals, enabling it to form ohmic contacts with ZnSnN2:Ag (a P-type semiconductor). Therefore, the ZnSnN2 homojunction has significant value in photovoltaic applications.

[0071] In summary, the method for preparing ZnSnN2 homojunctions in this invention is a simple, large-area, and low-cost preparation method. The ZnSnN2 homojunctions prepared by this method exhibit good rectification characteristics and stable photovoltaic performance. The ZnSnN2 homojunctions prepared using the method described in this invention are highly suitable for photovoltaic research and are of great significance for improving the application of ZnSnN2 in the photovoltaic industry.

[0072] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a ZnSnN2 homojunction, characterized in that, Including the following steps: First, a Zn:Sn = 3:1 alloy target is fixed on the RF target position. The sputtering system is evacuated, and nitrogen and argon gases are continuously introduced while maintaining a stable gas pressure. Then, zinc and tin are simultaneously deposited on ITO using RF sputtering to obtain ITO / ZnSnN2. Next, the Zn:Sn = 3:1 alloy target is fixed on the RF target position, and the Ag target is placed on the DC target position. The ITO / ZnSnN2 is placed in the sputtering chamber. After evacuating to the required vacuum level, a mixture of nitrogen and argon gases is continuously introduced while maintaining a stable working gas pressure. Then, in RF and DC co-sputtering mode, the zinc-tin target and the Ag target are sputtered simultaneously to obtain the ITO / ZnSnN2 / ZnSnN2:Ag structure. The thin film structure was then placed into a sputtering system, which was evacuated. Nitrogen and argon were continuously introduced while maintaining a stable pressure. Pt was then deposited on the structure using DC sputtering to obtain a ZnSnN2 homojunction.

2. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The nitrogen gas used is 99.999% high-purity nitrogen gas, and the argon gas used is 99.995% high-purity argon gas.

3. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The nitrogen flow rate is 5 sccm, the argon flow rate for preparing the ZnSnN2 thin film is 8 sccm, the argon flow rate for preparing ZnSnN2:Ag is 8 sccm, and the argon flow rate for preparing the ZnSnN2 homojunction is 30 sccm.

4. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The RF sputtering power of the zinc-tin alloy target is 35W, and the power of the DC sputtering Ag target is 3W.

5. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The gas pressure for preparing the ZnSnN2 thin film is 5 Pa, the gas pressure for preparing the ZnSnN2:Ag thin film is 5 Pa, and the gas pressure for preparing the Pt thin film layer is 1 Pa.

6. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The substrate needs to be heated to 50°C before ZnSnN2 thin film deposition.

7. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The ITO / ZnSnN2 structure is deposited at room temperature during ZnSnN2:Ag thin film deposition.

8. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The ZnSnN2:Ag thin film was prepared by co-sputtering with radio frequency sputtering and DC sputtering to form P-type doping.

9. The method for preparing a ZnSnN2 homojunction according to claim 1, characterized in that, The Pt thin film was prepared using a DC sputtering method.

10. A ZnSnN2 homojunction, characterized in that, Prepared by the method described in any one of claims 1 to 9.

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