Photoelectric detector based on ferroelectric domain wall

Abstract

The invention discloses a ferroelectric domain wall-based photoelectric detector, which comprises a positive domain, a negative domain, a metal film, a waveguide, an insulating layer, a substrate, a first electrode, a second electrode, a third electrode and a fourth electrode, and is characterized in that the waveguide comprises a ridge waveguide, the positive domain and the negative domain are embedded in the ridge waveguide, and a domain wall is formed between the positive domain and the negative domain; the surface of the vertical part is covered with conductive metal films, the conductive metal films are connected to form a first electrode, a second electrode, a third electrode and a fourth electrode, a substrate is arranged on the lower side of the ridge-shaped waveguide, an insulating layer is arranged between the ridge-shaped waveguide and the substrate, and when light passes through the ridge-shaped waveguide, positive and negative charges enter the four corresponding electrodes through the metal films respectively, so that the light is emitted. Therefore, a voltage or current signal is generated. According to the invention, current carriers are generated during illumination and drift is carried out according to domain polarity by utilizing the conductive characteristic and the electric polarization phenomenon of the domain wall of the ferroelectric crystal, and photoelectric detection is carried out by adopting the domain structure of the lithium niobate, so that the preparation is simple.

Description

Technical Field

[0001] The invention relates to a photoelectric detector, and in particular to a photoelectric detector based on a ferroelectric domain wall. Background Art

[0002] The principle of photodetectors is that radiation causes the conductivity of the irradiated material to change. In the visible light or near-infrared band, it is mainly used for ray measurement and detection, industrial automatic control, photometry, etc.; in the infrared band, it is mainly used for missile guidance, infrared thermal imaging, infrared remote sensing, etc. Another application of photoconductors is to use them as camera tube targets. In order to avoid image blur caused by the diffusion of photogenerated carriers, high-resistance polycrystalline materials such as PbS-PbO, Sb2S3, etc. are used for continuous thin film targets. Other materials can be inlaid with the target surface, and the entire target surface is composed of about 100,000 individual detectors. Generally, semiconductor materials with suitable bandgap width or impurity ionization energy have photoelectric effect. However, the manufacture of practical devices also needs to consider factors such as performance, process, and price.

[0003] Photodetectors on lithium niobate are an important part of realizing photon integration. Although lithium niobate materials have rich physical properties, electro-optic modulators based on lithium niobate are still limited to heterogeneous integration. Heterogeneous integration technology is a technology that has just begun to develop, with complex processes and low practicality. Research on carrier regulation and pn junction photodetectors using lithium niobate materials has also just started. Lithium niobate has a photovoltaic phenomenon. When ferroelectric materials are irradiated with uniform light, photovoltaic currents will be generated on both end faces. In nonlinear optics, one phase matching method of ferroelectric crystals is quasi-phase matching (QPM). The characteristic of this phase matching is that it uses the inversion characteristics of ferroelectric domains in ferroelectrics to perform periodic ferroelectric domain inversion, thereby compensating for the phase mismatch generated by the nonlinear coupling process. Quasi-phase matching crystals are also called dielectric superlattices. At present, most of them use electric field polarization methods for domain inversion. According to the wavelength to be compensated, the width of the domain is between submicron and tens of microns. According to the existing technology, the domain wall of ferroelectric crystals has a certain conductivity, and the conductivity of the domain wall is as high as 0.02Ω -1 cm -1 Compared with bulk lithium niobate (about 1×10 -15 Ω -1 cm -1 ) has been improved by 13 orders of magnitude, and the conductive properties of the domain wall can be used to produce logic gate switches and pn junctions. The conductive properties of the domain wall have many advantages. How to use the conductive properties of the domain wall of ferroelectric crystals to form a photodetector is a problem that needs to be solved. Summary of the invention

[0004] Objective of the invention: The objective of the present invention is to provide a photodetector based on ferroelectric domain walls.

[0005] Technical solution: The present invention includes positive domains, negative domains, metal films, waveguides, insulating layers, substrates, first electrodes, second electrodes, third electrodes and fourth electrodes. The waveguide includes a ridge waveguide. The positive domains and negative domains are embedded in the ridge waveguide. Domain walls are formed between the positive domains and the negative domains. The surface of the vertical portion is covered with a conductive metal film. The conductive metal films are connected to form the first electrode, the second electrode, the third electrode and the fourth electrode. The lower side of the ridge waveguide is a substrate. There is an insulating layer between the ridge waveguide and the substrate. When light passes through the ridge waveguide, a photovoltaic effect is generated. Positive and negative charges enter the corresponding four electrodes through the metal film respectively, thereby generating voltage or current signals.

[0006] Furthermore, the positive domains and negative domains are arranged alternately, forming positive domain walls head to head and forming negative domain walls tail to tail.

[0007] Furthermore, the conductive metal film covers the connection of the positive domain wall to form a second electrode and a third electrode.

[0008] Furthermore, the conductive metal film covers the connection of the negative domain wall to form a first electrode and a fourth electrode.

[0009] Furthermore, the first electrode, the second electrode, the third electrode and the fourth electrode are arranged in an upper and lower layer distribution manner, the second electrode and the third electrode are distributed in the same plane, and the first electrode and the fourth electrode are distributed in the same plane.

[0010] Furthermore, the second electrode and the third electrode are distributed in grooves of a pre-fabricated substrate, and the grooves are processed by photolithography.

[0011] Furthermore, an insulating layer is plated on the second electrode and the third electrode, and the first electrode and the fourth electrode are prepared on the insulating layer by photolithography coating.

[0012] Furthermore, the waveguide also includes a strip waveguide, and a whispering gallery microdisk is arranged next to the strip waveguide. Light is transmitted in the strip waveguide, forms evanescent wave coupling through the air gap between the strip waveguide and the whispering gallery microdisk, enters the microdisk and is enhanced.

[0013] Furthermore, the positive domains and negative domains are alternately arranged on the whispering gallery microdisk in a fan-shaped distribution, domain walls are formed between the positive domains and the negative domains, and the vertical surface is covered with a conductive metal film, which is connected to form a first electrode (5) and a second electrode.

[0014] Furthermore, the first electrode collects charges generated on the negative domain wall, and the second electrode collects charges generated on the positive domain wall. The first electrode and the second electrode are distributed in different layers and separated by an insulating layer.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: utilizing the conductive properties and polarization phenomenon of the ferroelectric crystal domain wall, carriers are generated when illuminated and drift according to the domain polarity, so that the electrodes connected to the domain wall generate voltage and current, and finally form a photodetector. The domain structure of lithium niobate itself is used for photoelectric detection, and the preparation is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the present invention;

[0017] Figure 2 A top view of the present invention;

[0018] Figure 3 is a side view of the present invention;

[0019] Figure 4 This is a schematic diagram of the structure of the whispering gallery microdisk used in the present invention;

[0020] Figure 5 This is a side view of the whispering gallery microdisk used in the present invention. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0022] like Figure 1 As shown, the present invention includes a positive domain 12, a negative domain 1, a metal film 9, a waveguide, an insulating layer 3, a substrate 4, a first electrode 5, a second electrode 6, a third electrode 7 and a fourth electrode 8. The waveguide includes a ridge waveguide 2. The positive domain 12 and the negative domain 1 are embedded in the ridge waveguide 2. A domain wall is formed between the positive domain 12 and the negative domain 1. The surface of the vertical portion is covered with a conductive metal film 9. The conductive metal films 9 are connected to form a first electrode 5, a second electrode 6, a third electrode 7 and a fourth electrode 8. The lower side of the ridge waveguide 2 is a substrate 4. The insulating layer 3 is between the ridge waveguide 2 and the substrate 4. When light passes through the ridge waveguide 2, a photovoltaic effect is generated. The positive and negative charges enter the corresponding four electrodes through the metal film 9 respectively, thereby generating voltage or current signals to form a photodetector.

[0023] The optical material for preparing the present invention is a ferroelectric crystal, such as lithium niobate (LiNbO3), lithium tantalate (LiTaO3), potassium titanyl phosphate (KTiOPO4), etc., preferably lithium niobate, or thin film lithium niobate waveguide LNOI, which can be domain reversed by room temperature electric field polarization method. The reversed part is called negative domain 1, and the unreversed part is called positive domain 12. A domain wall with a certain conductivity is formed between the positive domain 12 and the negative domain 1.

[0024] The substrate 4 of the present invention is made of the same material as the waveguide material, and has the same thermal expansion coefficient when the environment changes, such as temperature changes, so the device is not easily damaged due to thermal expansion and contraction. In addition, different materials can also be used. For example, when the waveguide uses lithium niobate, the substrate can be made of silicon dioxide, silicon, sapphire, silicon carbide, etc. A thin film with a low refractive index can be prepared between the substrate 4 and the waveguide to ensure the light transmission of the ridge waveguide 2.

[0025] The conductive metal film 9 can be made of materials with high conductivity such as copper, silver, gold, and aluminum.

[0026] The arrangement of domains and electrodes is as follows Figure 2 As shown, the arrangement direction of the domains is as indicated by the arrows, forming a head-to-head and tail-to-tail arrangement structure. Domain walls are formed between domains, and the domain walls are covered with a conductive metal film 9. The conductive metal films 9 are connected to form electrodes. If the negative domain 1 is directed to the right, the positive domain 12 is directed to the left. The direction indicated by the arrow is the +Z direction, and vice versa. The domain in the +Z direction has an electric polarization field in the +Z direction, and the domain in the -Z direction has an electric polarization field in the -Z direction. When there are free carriers in the domain, the carriers drift in the corresponding direction under the action of the electric field, for example, electrons drift in the +Z direction, and holes drift in the -Z direction, and finally gather on the domain wall.

[0027] There are two types of domain walls: Figure 2 The head-to-head domain walls shown are called positive domain walls, and the tail-to-tail domain walls are called negative domain walls. It can be seen that electrons tend to be distributed on the positive domain walls, while holes tend to be distributed on the negative domain walls. A metal film is covered on the vertical surface of the domain wall. The second electrode 6 and the third electrode 7 are formed by connecting the metal film covering the positive domain wall, and the first electrode 5 and the fourth electrode 8 are formed by connecting the metal film covering the negative domain wall.

[0028] When light passes through the ridge waveguide 2, the impurity energy levels in the material absorb photons to generate free carriers. The free carriers drift in a directional manner under the action of the polarization field, gather electrons on the positive domain wall, and gather holes on the negative domain wall. They are collected on the corresponding electrodes through the conductive metal film 9, and a weak positive voltage is generated on the first electrode 5 and the fourth electrode 8, and a weak negative voltage is generated on the second electrode 6 and the third electrode 7. The signals are amplified by an external amplifier circuit to generate photoelectric signals.

[0029] When the light in the ridge waveguide 2 disappears, the free carrier source is no longer continuously generated in the material, and the free carriers gathered on the domain wall return to the initial impurity energy level by diffusion, and the voltage signal on the electrode disappears.

[0030] like Figure 3As shown, in order to avoid the first electrode 5 and the second electrode 6 from crossing, and the third electrode 7 and the fourth electrode 8 from crossing, they are arranged in an upper and lower layer distribution manner. Specifically, the second electrode 6 and the third electrode 7 are distributed in the same plane, and the first electrode 5 and the fourth electrode 8 are distributed in the same plane. Specifically, the second electrode 6 and the third electrode 7 are distributed in the groove of the pre-prepared substrate 4, and the groove is processed by photolithography. A metal film is plated in the groove and connected to the corresponding vertical film. Then, an insulating layer 3 is plated on the second electrode 6 and the third electrode 7. The material of the insulating layer 3 can be photoresist, silicon dioxide, polymer, etc. The first electrode 5 and the fourth electrode 8 are prepared on the insulating layer 3 by photolithography coating, so that the first electrode 5, the fourth electrode 8 and the second electrode 6, the third electrode 7 are insulated.

[0031] Another method of the present invention: In order to enhance the photoelectric detection efficiency, the following method is used: Figure 4 Another method shown in FIG. 1 is characterized in that the whispering gallery microdisk is used to enhance the light intensity, thereby enhancing the photoelectric signal. Figure 4 The basic principle shown is the same as above. Light is transmitted in the strip waveguide, forms evanescent wave coupling through the air gap between the strip waveguide and the whispering gallery microdisk, enters the microdisk and is enhanced. For example, for a resonant cavity with a Q value of more than 1000, it is easy to enhance the intensity in the cavity by 100 times.

[0032] like Figure 4 The dark part of the microdisk shown is the positive domain 12, and the light part is the negative domain 1, which is distributed in a fan shape. The first electrode 5 collects the charges generated on the negative domain wall, and the second electrode 6 collects the charges generated on the positive domain wall. Figure 5 As shown, the first electrode 5 and the second electrode 6 are distributed in different layers in the same manner as described above and are separated by the insulating layer 3 .

Claims

1. A photodetector based on ferroelectric domain walls, Features: The invention comprises a positive domain (12), a negative domain (1), a metal film (9), a waveguide, an insulating layer (3), a substrate (4), a first electrode (5), a second electrode (6), a third electrode (7) and a fourth electrode (8); the waveguide comprises a ridge waveguide (2) and is made of lithium niobate, lithium tantalate or potassium titanyl phosphate; the positive domain (12) and the negative domain (1) are embedded in the ridge waveguide (2); a domain wall is formed between the positive domain (12) and the negative domain (1); a surface of a vertical portion is covered with a conductive metal film (9); the conductive metal films (9) are connected to form a first electrode (5), a second electrode (6), a third electrode (7) and a fourth electrode (8); the lower side of the ridge waveguide (2) is a substrate (4); an insulating layer (3) is provided between the ridge waveguide (2) and the substrate (4); when light passes through the ridge waveguide (2), a photovoltaic effect is generated; positive and negative charges respectively enter the corresponding four electrodes through the metal film (9), thereby generating a voltage or current signal.

2. The ferroelectric domain wall-based photodetector according to claim 1, Features: The positive domains (12) and negative domains (1) are arranged alternately, forming positive domain walls head to head and negative domain walls tail to tail.

3. The ferroelectric domain wall based photodetector according to claim 1, Features: The conductive metal film (9) covers the connection of the positive domain wall to form a second electrode (6) and a third electrode (7).

4. The ferroelectric domain wall based photodetector according to claim 1, Features: The conductive metal film (9) covers the connection of the negative domain wall to form a first electrode (5) and a fourth electrode (8).

5. The ferroelectric domain wall based photodetector according to claim 1, Features: The first electrode (5), the second electrode (6), the third electrode (7) and the fourth electrode (8) are arranged in an upper and lower layer distribution manner, the second electrode (6) and the third electrode (7) are distributed in the same plane, and the first electrode (5) and the fourth electrode (8) are distributed in the same plane.

6. The ferroelectric domain wall based photodetector according to claim 1, Features: The second electrode (6) and the third electrode (7) are distributed in a groove of a pre-prepared substrate (4), the groove is processed by photolithography, and the substrate (4) is made of the same material as the waveguide or silicon dioxide, silicon, sapphire, or silicon carbide.

7. The ferroelectric domain wall based photodetector according to claim 1, Features: An insulating layer is plated on the second electrode (6) and the third electrode (7), and the first electrode (5) and the fourth electrode (8) are prepared on the insulating layer by photolithography coating.

8. The ferroelectric domain wall based photodetector according to claim 1, Features: The waveguide also includes a strip waveguide (10), and a whispering gallery microdisk (11) is arranged next to the strip waveguide. Light is transmitted in the strip waveguide, forms evanescent wave coupling through the air gap between the strip waveguide and the whispering gallery microdisk, enters the microdisk and is enhanced.

9. The ferroelectric domain wall based photodetector according to claim 8, Features: The positive domains (12) and the negative domains (1) are alternately arranged on the whispering gallery microdisk (11) in a fan-shaped distribution, a domain wall is formed between the positive domains (12) and the negative domains (1), and the vertical portion of the surface is covered with a conductive metal film (9), and the conductive metal films (9) are connected to form a first electrode (5) and a second electrode (6).

10. The ferroelectric domain wall based photodetector according to claim 9, Features: The first electrode (5) collects charges generated on the negative domain wall, and the second electrode (6) collects charges generated on the positive domain wall. The first electrode (5) and the second electrode (6) are distributed in different layers and separated by an insulating layer (3).

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