NiO / MgO / n-si heterojunction ultraviolet detector and preparation method thereof

Abstract

NiO / MgO / n-Si heterojunction ultraviolet detector and preparation method thereof belong to the field of ultraviolet detector, the detector is from bottom to top cathode layer, n-Si, MgO film, NiO film and anode layer, the cathode layer is Al electrode, and the anode layer is Au. N type <100> double-sided polished silicon wafer with resistivity of 1-3 Ω·cm is selected as an electron transport layer, the silicon wafer is first subjected to ultrasonic cleaning and oxide layer removal treatment, then a layer of MgO film is deposited on the clean n-Si as an intermediate medium layer by using a magnetron sputtering method, then a layer of NiO film is deposited as a light absorption layer, then an Au electrode pattern is prepared as an anode layer by using a mask sputtering method, and Al is thermally evaporated as a cathode layer. The device is sensitive to ultraviolet light, the device performance is excellent, the preparation method is green, simple and effective.

Description

Technical Field

[0001] This invention relates to the field of ultraviolet detection technology, and in particular to a NiO / MgO / n-Si heterojunction ultraviolet detector and its preparation method. Background Technology

[0002] Silicon, as the most commonly used photodetector material, boasts advantages such as low production cost, mature and stable fabrication, passivation, and integration processes, and compatibility with CMOS processing technology. However, silicon's high reflectivity and shallow ultraviolet penetration depth lead to low photoresponsivity in the ultraviolet region for silicon-based photodetectors. NiO, a wide-bandgap semiconductor (3.4-4.1 eV), exhibits strong absorption of ultraviolet light. Due to the presence of non-stoichiometric Ni vacancies and oxygen interstitials, NiO displays intrinsic p-type conductivity and possesses high hole mobility. Therefore, choosing NiO as the p-type conductive layer and combining it with n-Si combines the advantages of NiO and silicon, enabling the fabrication of silicon-based PN junction photodetectors with high charge separation and collection efficiency.

[0003] NiO / n-Si devices often exhibit large dark currents and low ultraviolet responsivity and detectivity, primarily due to numerous defects in the NiO / n-Si heterojunction and the extremely small valence band energy difference (0.04 eV) between NiO and n-Si. Therefore, optimizing the structure of NiO / n-Si devices is a crucial issue for improving the performance of ultraviolet detectors. Introducing an intermediate dielectric layer to passivate the interface of the heterojunction can effectively suppress interface defects, thereby reducing the device's dark current. Summary of the Invention

[0004] The purpose of this invention is to provide a NiO / MgO / n-Si heterojunction ultraviolet detector and its fabrication method. This detector has low dark current and good rectification characteristics, and exhibits a sensitive response to ultraviolet light, showing great application potential in the field of ultraviolet detection.

[0005] The NiO / MgO / n-Si heterojunction ultraviolet detector is characterized by having, from bottom to top, a cathode layer, an n-Si layer, a MgO thin film, a NiO thin film, and an anode layer, wherein the cathode layer is an Al electrode and the anode layer is an Au electrode.

[0006] A method for fabricating a NiO / MgO / n-Si heterojunction ultraviolet detector, characterized by the following steps:

[0007] S1, clean n-Si;

[0008] S2, a MgO thin film is sputtered on n-Si by radio frequency magnetron sputtering as an intermediate dielectric layer;

[0009] S3, a NiO thin film is further sputtered on the MgO / n-Si heterojunction as an ultraviolet absorption layer by radio frequency magnetron sputtering;

[0010] S4, Al is thermally evaporated onto the NiO thin film as a cathode layer;

[0011] S5, a masked magnetron sputtered U-shaped Au electrode is used as the anode layer.

[0012] In this invention, the MgO intermediate dielectric layer can passivate dangling bonds on the silicon surface and defect states at the NiO / n-Si interface, reducing carrier recombination, improving carrier transport efficiency, and enhancing photoresponse. Furthermore, the significant valence band energy difference of 3.38 eV between MgO and n-Si can suppress dark current.

[0013] This invention utilizes magnetron sputtering and thermal evaporation processes to obtain high-performance heterojunction optoelectronic devices without high costs and complex steps. The fabrication method is green, simple, and efficient. The fabricated devices exhibit low dark current and good rectification properties, and are highly sensitive to ultraviolet light. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the heterojunction ultraviolet detector in Example 1.

[0015] Figure 2 The image shows the detector IV characteristic curve for Example 1.

[0016] Figure 3 The image shows the log IV characteristic curve of the detector in Example 1.

[0017] Figure 4 The curves showing the relationship between the detector responsivity and detectivity and the applied bias voltage in Example 1 are shown.

[0018] Figure 5 The image shows the IV characteristics of the NiO / Al2O3 / n-Si heterojunction ultraviolet detector under dark conditions and 365 nm ultraviolet light irradiation.

[0019] Figure 6 The logI-V characteristic curves of the NiO / Al2O3 / n-Si heterojunction ultraviolet detector under dark conditions and 365 nm ultraviolet light irradiation are shown.

[0020] Figure 7 The detector curves are for NiO / Al2O3 / n-Si.

[0021] Figure 8 The image shows the IV characteristic curves of NiO / MgO / n-Si devices with different MgO thicknesses. Detailed Implementation

[0022] The present invention will be further described in detail below through specific embodiments, but it should not be construed as limiting the scope of the invention to the following examples. Various substitutions or modifications made based on common knowledge and practice in the art without departing from the above-described methodological spirit of the invention should be included within the scope of the invention.

[0023] Example 1: NiO / MgO / n-Si heterojunction ultraviolet detector, from bottom to top: Al cathode layer 1, N-type silicon 2, MgO thin film intermediate dielectric layer 3, NiO thin film absorption layer 4, and Au anode layer 5.

[0024] The fabrication method of the NiO / MgO / n-Si heterojunction ultraviolet detector is as follows:

[0025] S1. The silicon wafer is ultrasonically cleaned in acetone, ethanol and deionized water for 10 min in sequence, and then immersed in hydrofluoric acid with a dilution ratio of 50:1 for 20 s. Finally, the silicon wafer is rinsed with running deionized water and dried with high-purity nitrogen gas for later use.

[0026] The resistivity of the silicon material is 1-3 Ω·cm.

[0027] S2, Under the conditions of sputtering pressure of 5 Pa, power of 100 W and time of 100 s, an intermediate dielectric layer of MgO thin film was prepared on an N-type silicon substrate by radio frequency magnetron sputtering. The thickness of the MgO thin film was 8 nm.

[0028] S3. Under the conditions of sputtering pressure of 0.4 Pa, power of 200 W and time of 50 min, a NiO absorber layer was prepared on a MgO thin film by radio frequency magnetron sputtering. The thickness of the NiO thin film was 198 nm.

[0029] S4, Al is thermally evaporated onto a NiO thin film as a cathode layer.

[0030] S5, a masked magnetron sputtered U-shaped Au electrode is used as the anode layer.

[0031] The heterojunction optoelectronic device obtained in this embodiment was tested to verify its optoelectronic performance.

[0032] like Figure 2 The image shows the IV characteristic curve of the heterojunction ultraviolet detector in Example 1. This heterojunction device exhibits good rectification characteristics, with a rectification ratio of approximately 1.8 × 10³ at ±2V and a dark current as low as 400 nA at a bias voltage of -2V.

[0033] like Figure 3 The graph shows the log IV characteristic curve of the heterojunction ultraviolet detector in Example 1. The photocurrent-to-dark current ratio of this heterojunction device at ±2V is approximately 176.

[0034] like Figure 4 The graph shows the relationship between the responsivity and detectivity of the heterojunction ultraviolet detector in Example 1 and the applied bias voltage. The peak ultraviolet responsivity and detectivity of this heterojunction device are approximately 0.3 A / W and 1.7 × 10¹¹ Jones, respectively, which are 0.1-0.2 A / W higher than the responsivity of commercial ultraviolet detectors and less than 10¹¹ Jones.

[0035] Comparative Example 1: Constructing a NiO / Al2O3 / n-Si heterojunction ultraviolet detector, wherein the thickness of NiO is 198 nm and the thickness of Al2O3 is 10 nm. Figure 5 and Figure 6 The figures show the IV and log IV characteristics of the NiO / Al2O3 / n-Si heterojunction ultraviolet detector under dark conditions and 365nm ultraviolet light illumination, respectively. It can be seen that the device exhibits almost no rectification properties within a ±2 V bias range and possesses a large dark current. Figure 7 The detectivity curves for NiO / Al₂O₃ / n-Si show that the device reaches its peak detectivity at a bias voltage of -1V, which is only 1.24 × 10¹⁰ Jones. For a dielectric layer with the same thickness of 10 nm, the Al₂O₃ device exhibits worse performance than the MgO device. This is mainly due to the excessively large potential barrier (4.03) at the Al₂O₃ / n-Si interface, which hinders carrier transport. Furthermore, the strong insulating properties of Al₂O₃ also contribute to the reduction in photocurrent.

[0036] Comparative Example 2: NiO / MgO / n-Si devices with MgO intermediate dielectric layers of thicknesses of 2 nm, 4 nm, 6 nm, 8 nm, and 10 nm were fabricated, and their IV characteristics under dark conditions were measured for comparison. The results are as follows: Figure 8 As shown, when a bias voltage of -1 V is applied, the dark currents of devices with MgO thicknesses of 2 nm, 4 nm, 6 nm, 8 nm, and 10 nm are 61 μA, 8.9 μA, 2.2 μA, 0.236 μA, and 0.465 μA, respectively. That is, as the thickness of the MgO dielectric layer increases, the dark current of the device first decreases and then increases. The device exhibits the lowest dark current when the MgO thickness is 8 nm. This is mainly because a dielectric layer of a certain thickness can passivate defects at the NiO / n-Si interface, reducing electron-hole recombination. An excessively thick MgO dielectric layer increases the transport distance of electrons and holes, leading to a higher recombination probability and thus increasing the dark current of the device.

Claims

1. A NiO / MgO / n-Si heterojunction ultraviolet detector, characterized in that... From bottom to top, the layers are: cathode layer, n-Si, MgO thin film, NiO thin film, and anode layer. The cathode layer is an Al electrode, and the anode layer is an Au electrode. The MgO film has a thickness of 8 nm; the NiO film has a thickness of 198 nm.

2. The fabrication method of the NiO / MgO / n-Si heterojunction ultraviolet detector as described in claim 1, characterized in that... The preparation method includes the following steps: S1, clean n-Si; S2, an MgO thin film is sputtered on n-Si by radio frequency magnetron sputtering as an intermediate dielectric layer; S3, a NiO thin film is further sputtered on the MgO / n-Si heterojunction as an ultraviolet absorption layer by radio frequency magnetron sputtering; S4, Al is thermally evaporated onto the NiO thin film as a cathode layer; S5, a masked magnetron sputtered U-shaped Au electrode is used as the anode layer.

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