Two-dimensional material photoelectric detector based on ferroelectric pyroelectric effect and preparation method thereof

Abstract

The invention discloses a two-dimensional material photoelectric detector based on a ferroelectric pyroelectric effect. The two-dimensional material photoelectric detector comprises a ferroelectric functional layer; the double-layer electrode is positioned above the ferroelectric functional layer; the two-dimensional material thin film is arranged above the double-layer electrode and is in contact with the ferroelectric functional layer; the spontaneous polarization direction of the ferroelectric is perpendicular to the thickness direction of the two-dimensional material film; the double-layer electrode comprises an upper metal layer and a lower metal layer, and the lower metal layer is in contact with the ferroelectric functional layer and is used for enhancing the binding force between the upper metal layer and the ferroelectric functional layer; the upper metal layer has a conductive function; the two-dimensional material film is a photosensitive area of the detector and is used for receiving irradiation of a light source.

Description

Technical Field

[0001] The present invention relates to the field of photoelectric detection technology, in particular to a two-dimensional material photoelectric detector regulated by the pyroelectric effect of a ferroelectric and a preparation method thereof. Background Art

[0002] Photodetectors are devices that can convert light signals into electrical signals. They are an essential type of information sensing device in the field of modern information technology. In order to achieve better performance, photodetectors inevitably need to integrate a variety of high-performance materials and design new structures. However, the current mainstream photodetectors are mainly based on Si, SiO 2 Under the influence of Moore's Law, these traditional semiconductor materials are difficult to meet the design requirements of high integration and high performance of new photodetectors. For example, reducing the thickness of traditional Si, Ge and III-V photodetectors to a few nanometers will lead to a significant increase in surface and internal defects, which will significantly affect their performance. In addition, traditional photodetector technology also has disadvantages such as complex manufacturing process, serious lattice mismatch, and harsh working conditions.

[0003] In recent years, the emergence of two-dimensional materials has brought new opportunities for the development of high-performance photodetectors. Two-dimensional materials represented by graphene, black phosphorus and transition metal dichalcogenides (TMDs) show excellent mechanical, optical and electrical properties compared with traditional materials. Two-dimensional materials are layered materials, and the interlayer van der Waals forces ensure their excellent flexibility and mechanical strength. Their surfaces are naturally passivated and have no dangling bonds, which minimizes defects and improves device performance, while also solving the problem of lattice mismatch in device integration. Although two-dimensional material photodetectors have many advantages, their light absorption is still limited by their atomic-level thickness. At present, there are many strategies to improve the performance of two-dimensional material photodetectors. One of the most efficient methods is to integrate two-dimensional materials with ferroelectrics, and use ferroelectrics to regulate two-dimensional materials and improve their photodetection performance. Ferroelectrics are a class of materials with spontaneous polarization characteristics that can respond to a variety of external stimuli including electric fields, temperature and pressure. At present, most of the two-dimensional material photodetectors based on ferroelectric regulation use the spontaneous polarization effect of ferroelectrics. For example: In 2016, Chu Junhao et al. designed a two-dimensional layered MoTe tuned by a ferroelectric polymer. 2 Photodetector. This detector uses the spontaneous polarization of ferroelectrics to modulate MoTe 2The accumulation or depletion of carriers in the channel achieves high responsivity and specific detection rate in the visible light band. However, the device has a small response in the infrared band, and the reversal of spontaneous polarization requires the application of external voltage, so the detector cannot achieve efficient and simple wide-band detection. In 2020, Wang Jianlu et al. reported a reconfigurable two-dimensional photodetector based on local ferroelectric polarization. The detector uses the ferroelectric polarization of P(VDF-TrEE) (flexible ferroelectric copolymer polyvinylidene fluoride-trifluoroethylene) on MoS 2 The PN junction is successfully doped in the ferroelectric material, and the photogenerated carriers and holes are successfully separated, and finally a high responsivity, a high specific detection rate and an ultra-fast response time are achieved. However, the device realizes the control of the spontaneous polarization of the ferroelectric by local imaging of the piezoelectric force microscope (PFM). This method is complicated to operate and not easy to integrate with other devices, and this method is usually irreversible. CN109950403A discloses a ferroelectric field-regulated two-dimensional material PN junction photodetector, which uses the PFM to polarize the ferroelectric functional layer so that the polarization directions on both sides of the ferroelectric are respectively away from and directed to the two-dimensional material, and then uses the ferroelectric field to regulate the two-dimensional material to form an in-plane PN junction photodetector. This method uses the polarization field of the ferroelectric to regulate the two-dimensional material, and the mechanism is complex. After removing the PFM, the ferroelectric polarization remains unchanged, the PN junction remains unchanged, and it is irreversible. And the device response band is the 520nm visible light band, and there is no response in the near-infrared 1550nm band. In summary, the detection performance of the two-dimensional material photodetector is poor, and the operation of the ferroelectric spontaneous polarization-regulated two-dimensional material photodetector is complex and the performance improvement is limited. Therefore, how to effectively improve the performance of two-dimensional material photodetectors in terms of responsiveness, specific detectivity, 3-dB bandwidth and polarization ratio has become a technical problem that needs to be solved urgently.

[0004] Purpose of the Invention

[0005] In view of the problems that traditional material photodetectors are difficult to integrate, two-dimensional material photodetectors have poor detection performance, and two-dimensional material photodetectors controlled by ferroelectric spontaneous polarization are complex to operate and have limited performance improvement, the purpose of the present invention is to adopt a reasonable structure and utilize the pyroelectric effect of ferroelectrics to control two-dimensional material photodetectors, so as to achieve effective improvement of the performance of two-dimensional material photodetection in a wide response band (from visible light to infrared band, especially 1550nm wavelength), such as responsiveness, specific detection rate, 3-dB bandwidth and polarization ratio.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The present invention provides a two-dimensional material photoelectric detector based on the pyroelectric effect of a ferroelectric, the photoelectric detector comprising:

[0008] Ferroelectric functional layer;

[0009] a double-layer electrode located above the ferroelectric functional layer;

[0010] A thin film of two-dimensional material above the double-layer electrode and in contact with the ferroelectric functional layer;

[0011] The spontaneous polarization direction (P) of the ferroelectric is perpendicular to the thickness direction of the two-dimensional material film;

[0012] The double-layer electrode comprises an upper metal layer and a lower metal layer, wherein the lower metal layer is in contact with the ferroelectric functional layer to enhance the bonding force between the upper metal layer and the ferroelectric functional layer; the upper metal layer performs a conductive function;

[0013] The two-dimensional material film is the photosensitive area of ​​the detector, which is used to receive irradiation from the light source. After receiving irradiation from the light source, the two-dimensional material film generates heat and transfers the heat to the ferroelectric functional layer. After the ferroelectric functional layer absorbs the heat, a temperature gradient change occurs, causing the spontaneous polarization intensity of the ferroelectric to change due to the pyroelectric effect, generating pyroelectric charges on the surface of the ferroelectric functional layer. At this time, the spontaneous polarization direction of the ferroelectric is perpendicular to the thickness direction of the two-dimensional material film, and an asymmetric PN junction is formed in the two-dimensional material film. When the light source is removed, the detector PN junction gradually disappears until it returns to its original state.

[0014] As an example, the thickness of the ferroelectric functional layer can be adjusted in the range of 100-500 μm.

[0015] For example, the thickness of the double-layer electrode is in the range of 50-100nm, the thickness of the upper metal layer is in the range of 45-90nm, and the thickness of the lower metal layer is in the range of 5-10nm; the thickness of the two-dimensional material film is 20-100nm, and the difference in thickness with the double-layer electrode is no more than 30nm. If the thickness difference is too large, it is easy to cause the contact edge between the two-dimensional material and the double-layer electrode to break.

[0016] In the present invention, the material of the ferroelectric functional layer is ferroelectric. As an example, the material of the ferroelectric functional layer can be lithium niobate (LiNbO 3 ), lithium tantalate (LiTaO 3 ), lead zirconate titanate (PZT), etc.

[0017] As an example, the material of the two-dimensional material film can be graphene, black phosphorus, transition metal disulfide, etc.

[0018] As an example, the material of the upper metal layer can be gold, silver, aluminum, etc.

[0019] As an example, the material of the lower metal layer may be titanium, chromium, nickel, etc.

[0020] The above-mentioned detector absorbs light signals through two-dimensional material films and converts them into electrical signals; the two-dimensional material film is regulated by the pyroelectric effect of ferroelectrics to improve the performance of the detector.

[0021] The present invention also provides a method for preparing the above-mentioned two-dimensional material photoelectric detector based on the ferroelectric pyroelectric effect, comprising the following steps:

[0022] 1) preparing a substrate, wherein the substrate is made of a ferroelectric material to form a ferroelectric functional layer;

[0023] 2) On the substrate, a double-layer electrode is prepared by laser direct writing or electron beam exposure technology combined with evaporation or sputtering and lift-off process;

[0024] 3) Use a mechanical peeling transfer method to transfer the two-dimensional material film to the substrate and ensure contact with the double-layer electrode.

[0025] The ferroelectric functional layer can be in the form of a thin film or a bulk, and the thin film can be prepared by a sol-gel method, a physical vapor deposition method (PVD), a chemical vapor deposition method (CVD), etc., or the bulk can be prepared by a Czochralski method, a temperature gradient method, etc.

[0026] The working process of the above-mentioned two-dimensional material photodetector based on the ferroelectric pyroelectric effect is as follows:

[0027] When the light source shines on the two-dimensional material film of the detector (i.e., the photosensitive area of ​​the detector), the heat will be transferred to the ferroelectric functional layer. After the ferroelectric functional layer absorbs the heat, the temperature gradient will change, causing the spontaneous polarization intensity of the ferroelectric to change due to the pyroelectric effect, and generating pyroelectric charges on the surface of the ferroelectric functional layer. At this time, the spontaneous polarization direction of the ferroelectric is perpendicular to the thickness direction of the two-dimensional material film, and the ferroelectric will generate different types of pyroelectric net charges in the polarization direction, including electrons and holes. Different types of net charges are injected into the two-dimensional material film in contact with the ferroelectric functional layer, generating different types of doping (P-type or N-type) on the left and right sides of the two-dimensional material film, thereby forming a PN homojunction in the two-dimensional material film. When a forward bias voltage is applied on both sides of the PN junction, the detector can generate a high photocurrent (I light At the same time, the PN junction effectively suppresses the dark current (I dark ), so it is possible to obtain a larger photocurrent (I ph ), I ph =I light -I dark , and finally obtain a higher photoresponsivity (R) and specific detectivity (D * ). At the same time, the asymmetric PN junction can effectively improve the polarization ratio of the two-dimensional material film, greatly improving the polarization detection capability of the detector. When the light source is removed, the detector doping will gradually disappear and return to its original state.

[0028] Compared with the above technology of ferroelectric spontaneous polarization control of two-dimensional material photodetectors, the two-dimensional material photodetector based on ferroelectric pyroelectric effect control has a simple, efficient, reversible and lossless ferroelectric pyroelectric enhancement mechanism; the present invention has good performance in a wide band range, especially in the infrared band; the present invention can achieve efficient polarization detection. The present invention effectively improves the performance of two-dimensional material photodetection, such as responsiveness, specific detection rate, 3dB bandwidth and polarization ratio, and the photodetector of the present invention can achieve simple, efficient, lossless and reversible photodetection. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of an embodiment of a two-dimensional material photoelectric detector based on the ferroelectric pyroelectric effect of the present invention.

[0030] Figure 2 yes Figure 1 A cross-sectional view of the structure shown in the xz plane.

[0031] Figure 3 Based on LiNbO 3 PdSe controlled by pyroelectric effect 2 The photodetector has different incident light powers (P in ) and the photocurrent (I ph )-Bias voltage (V bias )curve.

[0032] Figure 4 Based on LiNbO 3 PdSe controlled by pyroelectric effect 2 The photodetector is irradiated with 1550nm laser and biased with external voltage V bias =2V, the responsivity and detectivity vary with the incident light power.

[0033] Figure 5 The normalized frequency response of the photodetector designed in Example 1 varies with frequency when the incident light power is 1 mW and the wavelength is 1550 nm.

[0034] Figure 6 Based on LiNbO 3 PdSe controlled by pyroelectric effect 2 The photodetector is irradiated with 1550nm laser at different polarization angles and biased by an external voltage V bias =The photocurrent generated when 2V. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0036] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0037] See also Figure 1-Figure 2 , a two-dimensional material photodetector based on ferroelectric pyroelectric effect, comprising a ferroelectric functional layer 1; a double-layer electrode located above the ferroelectric functional layer 1; a two-dimensional material film 6 above the double-layer electrode and in contact with the upper surface of the ferroelectric functional layer 1; the ferroelectric spontaneous polarization direction (P) of the ferroelectric functional layer 1 is perpendicular to the thickness direction of the two-dimensional material film; the double-layer electrode comprises four independent electrodes, namely a first electrode 2, a second electrode 3, a third electrode 4 and a fourth electrode 5, which are respectively distributed at the four corners of the upper surface of the ferroelectric functional layer 1, so as to facilitate the search for the maximum lattice orientation of the light absorption of the anisotropic two-dimensional semiconductor material. Each electrode comprises an upper metal layer and a lower metal layer, wherein the lower metal layer is in contact with the ferroelectric functional layer 1 to enhance the bonding force between the upper metal layer and the ferroelectric functional layer 1; the upper metal layer has the function of conducting electricity.

[0038] The minimum distance between the electrodes can be adjusted according to the area of ​​the upper surface of the two-dimensional material film. The overall contact area between the two-dimensional material film 6 and the double-layer electrode is preferably less than 1 / 2 of the contact area between the two-dimensional material film and the ferroelectric functional layer. This is because it is necessary to ensure that the two-dimensional material film is not only in contact with the double-layer electrode, but most importantly, in contact with the ferroelectric functional layer. If the contact area with the double-layer electrode is too large, it is easy to cause the two-dimensional material film to be suspended in the air, and it is impossible to ensure contact with the ferroelectric functional layer.

[0039] When the area of ​​the upper surface of the two-dimensional material film 6 is selected to be 15μm×30μm: the minimum distance between the left and right electrodes, that is, between the first electrode 2 and the fourth electrode 5 or between the second electrode 3 and the third electrode 4 is 10-20μm; the minimum distance between the upper and lower electrodes, that is, between the second electrode 3 and the first electrode 2 or between the third electrode 4 and the fourth electrode 5 is 5-10μm.

[0040] The two-dimensional material film 6 is the photosensitive area of ​​the detector, which is used to receive light from the visible to infrared bands, especially light sources with a wavelength of 1550nm.

[0041] Example 1

[0042] Based on LiNbO 3 Pyroelectric Effect of PdSe 2 Photodetector as an example, the PdSe 2 Photodetectors have Figure 1 The structure shown. Among them, LiNbO 3 The thickness of the ferroelectric functional layer is 500μm; the double-layer electrode is Cr / Au (5nm / 90nm, Cr is the lower metal layer, Au is the upper metal layer), the minimum distance between the upper and lower electrodes is 5μm, and the minimum distance between the left and right electrodes is 10μm; PdSe 2 The thickness of the two-dimensional material film is 70nm and the area of ​​the upper surface is 15μm×30μm.

[0043] The photoelectric detector of this embodiment is subjected to the following experiment:

[0044] 1) Under the irradiation of laser with wavelength of 1550nm and different powers, a bias voltage (V bias =-2~2V), test the photocurrent (I ph ) varies with the incident light power and the applied bias voltage.

[0045] Figure 3 Based on LiNbO 3 PdSe controlled by pyroelectric effect 2 The photodetector has different incident light powers (P in ) and the I generated by laser irradiation with a wavelength of 1550nm ph -V bias Curve, photocurrent (I ph ) increases with the increase of incident light power and applied bias voltage. bias =2V, I ph >1200nA, higher than common two-dimensional material photodetectors. bias =-2V, I ph <800nA, significantly less than V bias = Photocurrent at 2V. The asymmetric I ph -V bias The curve is due to the temperature difference caused by laser irradiation, which leads to the 3 A pyroelectric net charge is generated in the polarization direction, which 2 Asymmetric doping was performed to form a unidirectionally conducting PN junction in the material.

[0046] 2) At a wavelength of 1550nm and different incident light powers (P in ) and a bias voltage (V bias =2V), test responsivity R and specific detection rate D * Variation with incident light power.

[0047] Responsivity R and specific detectivity D * It is an important parameter reflecting the performance of the detector. ph / P in and Definition: A higher value indicates higher detection sensitivity. A is the photosensitive area of ​​the photodetector; e is the charge of the elementary charge, which is a constant.

[0048] Figure 4 Based on LiNbO 3 PdSe controlled by pyroelectric effect 2 The photodetector is irradiated with 1550nm laser and biased with external voltage V bias =2V, the responsivity and specific detectivity vary with the incident light power. These two parameters decay exponentially with increasing incident light power, which is due to the enhanced recombination and scattering probability of photogenerated carriers under strong illumination. in =9μW, R and D * It reached 71.5mA / W and 2.13×10 8 Jones. Compared with the existing technology, the performance of the photodetector designed by the present invention has been significantly improved.

[0049] 3) Under the irradiation of laser with a wavelength of 1550nm and an incident light power of 1mW, a bias voltage (V bias =1V), test the change of normalized frequency response with frequency.

[0050] Normalized frequency response (Y) is expressed as Y = 10lg (R X / R max ) calculation, since R = I ph / P in , so the normalized frequency response can be expressed as Y = 10lg (I X / I max ) is simplified. Among them, I X It refers to the photocurrent at a certain incident light frequency, I max It refers to the maximum value of the photogenerated current measured at an incident light frequency of 1 Hz.

[0051] Response time (T) is another key factor of the detector, reflecting the response speed of the detector. The response time of the detector is usually related to the 3-dB bandwidth (f 3-dB ) is related to Definition. The 3-dB bandwidth (f 3-dB ) depends on its response speed to changes in optical power, that is, the frequency at which the detected electrical signal power drops to half of its maximum value.

[0052] Figure 5 is the change of the normalized response of the photodetector designed in Example 1 with frequency under the irradiation of laser with incident light power of 1 mW and wavelength of 1550 nm. 3-dB =13.871kHz, response time T=0.11ms. Compared with the prior art, the response time of the photodetector designed in the present invention is further improved.

[0053] 4) Under the irradiation of laser with wavelength of 1550nm, incident light power of 1mW and different polarization angles, a bias voltage (V bias =2V), and test the change of photogenerated current with polarization angle.

[0054] In addition to light intensity, frequency and phase, polarization is another important property of light. Polarization ratio (PR) is a parameter used to describe the polarization sensitivity of photodetectors, usually expressed as PR = I ph_max / I ph_min , where I ph_max and I ph_min It is the maximum and minimum value of the photogenerated current under laser irradiation at different polarization angles.

[0055] Figure 6 Based on LiNbO 3 PdSe controlled by pyroelectric effect 2 The photodetector is irradiated with 1550nm laser at different polarization angles and biased by an external voltage V bias =2V, the photocurrent generated can be calculated to be PR≈4.2. 2 Compared with LiNbO photodetectors, 3 Under the influence of the pyroelectric effect, the PR of the device increased by more than 3 times. This is because the ferroelectric forms an asymmetric PN junction inside the two-dimensional material through the pyroelectric effect, which improves the asymmetry of the device. It can be seen that the pyroelectric effect of the ferroelectric can effectively improve the polarization detection capability of the two-dimensional material detector.

Claims

1. A two-dimensional material photoelectric detector based on ferroelectric pyroelectric effect, characterized in that: include: Ferroelectric functional layer; a double-layer electrode located above the ferroelectric functional layer; A thin film of two-dimensional material above the double-layer electrode and in contact with the ferroelectric functional layer; The spontaneous polarization direction of the ferroelectric is perpendicular to the thickness direction of the two-dimensional material film; The double-layer electrode comprises an upper metal layer and a lower metal layer, wherein the lower metal layer is in contact with the ferroelectric functional layer to enhance the bonding force between the upper metal layer and the ferroelectric functional layer; the upper metal layer performs a conductive function; The two-dimensional material film is the photosensitive area of ​​the detector, which is used to receive irradiation from a light source.

2. The detector according to claim 1, characterized in that: The thickness of the ferroelectric functional layer is 100-500 μm.

3. The detector according to claim 1, characterized in that: The thickness of the double-layer electrode is in the range of 50-100nm, the thickness of the upper metal layer is in the range of 45-90nm, and the thickness of the lower metal layer is in the range of 5-10nm; the thickness of the two-dimensional material film is 20-100nm, and the difference in thickness with the double-layer electrode is no more than 30nm.

4. The detector according to claim 1, characterized in that: The double-layer electrode includes four independent electrodes, namely a first electrode, a second electrode, a third electrode and a fourth electrode, which are respectively distributed on four corners of the upper surface of the ferroelectric functional layer.

5. The detector according to claim 1, characterized in that: The material of the ferroelectric functional layer is lithium niobate, lithium tantalate, or lead zirconate titanate.

6. The detector according to claim 1, characterized in that: The material of the two-dimensional material film is graphene, black phosphorus or transition metal disulfide.

7. The detector according to claim 1, characterized in that: The material of the upper metal layer is gold, silver or aluminum.

8. The detector according to claim 1, characterized in that: The material of the lower metal layer is titanium, chromium or nickel.

9. A method for preparing the detector according to claims 1-7, comprising the following steps: 1) preparing a substrate, wherein the substrate is made of a ferroelectric material to form a ferroelectric functional layer; 2) On the substrate, a double-layer electrode is prepared by using laser direct writing or electron beam exposure technology, combined with evaporation or sputtering, and a lift-off process; 3) Use a mechanical peeling transfer method to transfer the two-dimensional material film to the substrate and ensure contact with the double-layer electrode.

10. The method according to claim 8, characterized in that The ferroelectric functional layer is in the form of a thin film or a block, and the thin film is prepared by a sol-gel method, a physical vapor deposition method, or a chemical vapor deposition method, or the block is prepared by a Czochralski method or a temperature gradient method.

Images