Chiral spin-polarized circular polarized photovoltaic device, preparation and application thereof

Abstract

The application relates to a chiral spin-polarized circularly polarized light photoelectric device, preparation and application, and belongs to the technical field of optoelectronic devices. Specifically, a chiral molecule is introduced on the surface of a semiconductor, and a target of recognizing a light polarization state is realized by using spin polarization induced by a chiral structure. The chiral molecule will generate a Rashba-like spin-orbital coupling effect on the surface through spin exchange interaction, causing symmetry breaking, so as to generate a circularly polarized photocurrent effect under external light conditions. Different chiral (-L / -D) structure molecules have different response effects on polarized light. The chiral spin-polarized optoelectronic device shown in the application has a remarkable circularly polarized light detection effect, the experimental operation is simple and easy to implement, the device preparation cost is low, and the application of the chiral structure in a spin photoelectric device can be greatly expanded.

Description

Technical fields:

[0001] This invention belongs to the field of optoelectronic device fabrication technology and relates to a method for fabricating and applying a chiral spin-polarized circularly polarized optoelectronic device. Background technology:

[0002] Chirality, as a symmetry-breaking property, offers endless possibilities for exploring new physics and mechanisms in materials. The helical spatial structure of chiral molecules, coupled with electrons through spin-orbit coupling, can generate electron spin polarization—an effect known as "chirality-induced spin selectivity." This allows chiral molecules to spin-inject materials cleanly, efficiently, and with low power consumption, without external field assistance. Circularly polarized photocurrent is a common method for studying spin-orbit coupling. It utilizes the interaction between photons and electrons to generate periodically changing photocurrents, and its experimental setup is relatively easy to operate, making it suitable for researching and exploring novel optoelectronic devices. The combination of chiral-induced spin selectivity and circularly polarized photocurrent holds promise for fabricating novel chiral-spin-electrophotonic devices for circularly polarized light detection, which is of great significance for the practical applications of spintronics.

[0003] Current chiral optoelectronic devices are mostly fabricated by adding chiral intercalation layers to perovskites or by constructing plasmons on metal surfaces. These processes are complex, sensitive to environmental changes, and exhibit relatively poor stability, leading to numerous drawbacks in large-scale production applications. Currently, a simple and convenient method for fabricating large-area chiral optoelectronic devices while simultaneously achieving good circularly polarized light detection remains to be explored. Summary of the Invention:

[0004] To achieve the above objectives, this invention aims to propose a circularly polarized optoelectronic device based on chiral spin polarization, its fabrication method, and its application.

[0005] This invention discloses a chiral spin-polarized circularly polarized optoelectronic device that utilizes the spin polarization effect induced by self-assembled chiral molecules AHPA-L / -D to modify the surface of a semiconductor to produce symmetry breaking. It comprises, from bottom to top, a substrate, a semiconductor layer, a metal layer, and a chiral molecular layer.

[0006] The substrate and semiconductor layer are further supported by commercially available p-type doped single-crystal Si grown on a SiO2 substrate. The thickness of the semiconductor layer can range from 100 to 500 μm, specifically 100 μm, 200 μm, 400 μm, 500 μm, etc.

[0007] Furthermore, the material of the metal layer is selected from at least one of Au or Al, and the thickness can be 1 to 5 nm, specifically 1 to 2 nm, 2 to 4 nm, 5 nm, etc.

[0008] Furthermore, the material of the chiral molecular monolayer is selected from at least one of the chiral peptides AHPA-L or AHPA-D, and the thickness of the grown chiral molecular monolayer is approximately 3 nm. Taking AHPA-L as an example, the -SH of the terminal cysteine ​​residue of the chiral molecule forms a thiol bond with the surface of the Au / Al metal layer and is fixed on the metal layer, while the other end of the chiral molecule is suspended; the angle between the chiral molecule and the normal direction of the substrate is 20-70°, such as approximately 50°.

[0009] In the fabrication method of this invention, a commercial semiconductor single crystal is used as the semiconductor layer, a metal layer is formed by magnetron sputtering, and a chiral molecular monolayer is formed by self-assembly. After sequentially fabricating and stacking these layers, a chiral spin-polarized circularly polarized optoelectronic device is obtained. The fabrication scheme is simple, the process cost is low, and the effect is significant, making it promising for future widespread application.

[0010] Secondly, the present invention provides a detailed method for fabricating the above-described optoelectronic device, comprising the following steps:

[0011] (1) The semiconductor layer (commercial p-type doped single crystal Si grown on SiO2, crystal plane (100), resistivity 1-20Ω·cm) is mechanically cut into 5mm×5mm cubes.

[0012] (2) The metal layer is grown on the semiconductor layer by magnetron sputtering.

[0013] Specifically, the following steps are included:

[0014] (a) Clean the sample from step (1) sequentially with deionized water and ethanol using ultrasonic cleaning for 5-10 minutes each time, and finally dry it with a nitrogen gun.

[0015] (b) The oxide layer on the surface is removed by etching using an ion beam etching method. The etching time is 2-5 min and the beam current is 60-200 mA. After etching, the surface is stored in a vacuum bag.

[0016] (c) Evacuate the coating chamber of the ultra-high vacuum magnetron sputtering system to below 20 Pa using a mechanical pump, then turn on the molecular pump and evacuate to below 10 Pa. -5 Below 20 Pa; place the sample from step (b) on the sample holder and send it into the sample chamber. First, turn on the mechanical pump in the sample chamber to evacuate to below 20 Pa, then turn on the molecular pump to evacuate to below 10 Pa. -3 Below Pa;

[0017] (d) Open the gate valve between the coating chamber and the sample chamber, and feed the sample holder with the substrate from step (b) into the coating chamber via a lateral servo.

[0018] (e) The coating chamber is filled with inert gas to reach the ignition pressure, and pre-sputtering 1 is performed using a DC power supply. After completion, the inert gas flow rate is reduced, and the coating chamber pressure is reduced to the working pressure. At this time, pre-sputtering 2 is performed using a DC power supply. The inert gas includes argon and / or nitrogen. The power of the DC power supply is 180-220W. The working pressure of pre-sputtering 1 is 1.3-2.0 Pa, and the time is 30-60 s. The working pressure of pre-sputtering 2 is 0.3-0.5 Pa, and the time is 30-60 s.

[0019] (f) After completion, open the target baffle to perform formal sputtering. Stop sputtering when the time is up, and remove the sample holder to obtain the grown metal layer.

[0020] (3) A self-assembled chiral molecular monolayer is grown on the metal layer using the Czochralski method;

[0021] The specific preparation method includes the following steps:

[0022] (a) Dissolve the chiral molecule in EtOH to prepare a chiral molecule solution, preferably with a concentration of 1 mmol·L⁻¹. -1 ;

[0023] (b) Place the sample from step (2) upright in the chiral molecular solution, then seal it and let it stand at room temperature, for example, by sealing it with a polytetrafluoroethylene sealing tape and letting it stand at room temperature; so that the chiral molecules assemble in the metal layer for 24-48 hours, for example, 24 hours when a self-assembled molecular monolayer is formed on the Au surface, and 48 hours when a self-assembled molecular monolayer is formed on the Al surface.

[0024] (c) After self-assembly, the sample is removed and the surface is cleaned multiple times with EtOH to remove unassembled molecules; after sample preparation, it is sealed in a vacuum bag and stored at -18°C.

[0025] (4) Use a pressure welding machine to draw out the electrode from the surface of step (3). The electrode material is Al wire and the electrode spacing is 3mm.

[0026] Thirdly, the present invention provides a method for detecting circularly polarized light using the chiral spin-polarized circularly polarized light detector.

[0027] The principle of a chiral optoelectronic device provided by this invention is as follows: molecules with specific chirality allow electrons of a certain spin to pass through more easily, while making it difficult for electrons of another spin to pass through. When chiral molecules are grown on a metal surface through self-assembly, they induce symmetry breaking at the semiconductor interface through spin exchange interactions and spin selection, resulting in Rashba spin splitting. This causes semiconductors that do not inherently exhibit symmetry breaking to generate circularly polarized photocurrents. When external circularly polarized light irradiates the sample surface, a circularly polarized photocurrent effect is generated. Conversely, molecules with different chirality will generate the opposite type of circularly polarized photocurrent.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The method for preparing chiral optoelectronic devices provided by this invention is simple, easy to implement, and low in cost. It achieves high-quality, high-stability, large-area controllable preparation of devices that can be used directly in room temperature air environment, which is conducive to future promotion and application.

[0030] 2. The scheme for circularly polarized light detection using chiral optoelectronic devices provided by this invention has significant effects and high sensitivity. Attached image description:

[0031] Figure 1 This is a schematic diagram of the fabrication process of the chiral optoelectronic device of the present invention.

[0032] Figure 2 This is a test optical path diagram of the chiral optoelectronic device of the present invention.

[0033] Figure 3 This is a graph showing the relationship between the circularly polarized photocurrent and the polarization state of the incident light when using the AHPA-L chiral optoelectronic device in this invention.

[0034] Figure 4 This is a graph showing the relationship between the circularly polarized photocurrent and the polarization state of the incident light when using the AHPA-D chiral optoelectronic device in this invention.

[0035] Figure 5 for Figure 5 This is a schematic diagram of the optical transition selection rule involved in this invention, where +1 / 2, -1 / 2, +3 / 2, and -3 / 2 represent the electron angular momentum quantum numbers of light holes and heavy holes. Detailed implementation method:

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that, unless otherwise stated, the technical or scientific terms used in this invention should have the ordinary meaning as understood by one of ordinary skill in the art.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the experimental materials used in the following examples were purchased from conventional biochemical reagent companies.

[0039] This embodiment provides a scheme for detecting circularly polarized light current using chiral optoelectronic devices. By applying chiral molecular modification to ordinary semiconductors, efficient identification of left- or right-polarized light can be achieved.

[0040] In this embodiment, the semiconductor layer used is commercially available p-type doped single-crystal Si grown on SiO2, with a (100) crystal plane, resistivity of 1-20 Ω·cm, and dimensions of 5 mm × 5 mm. The metal layer Au is grown on the semiconductor layer using magnetron sputtering technology, with a thickness of 5 nm. The chiral molecule used is the chiral peptide AHPA-L or AHPA-D, which has a significant spin polarization effect. The electrode spacing in the experiment is 3 mm. The complete sample preparation process is as follows: Figure 1 As shown.

[0041] In this embodiment, the wavelength of the near-infrared excitation light used is 800nm, the laser repetition frequency is 80MHz, and the pulse width is 150fs.

[0042] In this embodiment, the power of the near-infrared excitation light is continuously adjustable between 1-50mW, and the power stability is such that the power fluctuation does not exceed 0.15% within 2 hours. The excitation light spot illuminating the sample is a circular spot with a diameter of 2mm, and the spot intensity follows a Gaussian distribution. 00 mold.

[0043] In this embodiment, the chopping frequency of the optical chopper used is 10-4000Hz, which is continuously adjustable.

[0044] In this embodiment, other optical elements used include apertures, polarizers, quarter-wave plates, and mirrors.

[0045] In this embodiment, the electrical testing equipment used includes a current preamplifier and a lock-in amplifier.

[0046] In this embodiment, other equipment used includes an electric rotary table, a motor, an adapter plate, probes, and wires.

[0047] Specifically, the detailed implementation process of this embodiment is given below:

[0048] In this embodiment, after the device fabrication process is completed according to the above-described device fabrication procedure, the following steps are taken: Figure 2The test optical path shown has an incident light with a power of 5mW. After passing through the aperture, the spot diameter is approximately 2mm. After passing through the polarizer, it reaches a λ / 4 waveplate fixed on an electric rotary stage. As the waveplate rotates continuously within the range of 0°-360°, it periodically generates linearly polarized, left-handed circularly polarized, linearly polarized, and right-handed circularly polarized light. In actual operation, the step length of the electric rotary stage is set to 5°. The excitation light, after undergoing the above transformations, illuminates the sample at an incident angle of 30°. The experimental test environment temperature is room temperature, and the test and control programs are written in LabVIEW software.

[0049] In this embodiment, to avoid the measured photocurrent signal being affected by other signals and noise, phase-sensitive detection technology is used to process the photocurrent signal. Specifically, the chopper is set to a reference frequency, which is then applied to the photocurrent signal. A lock-in amplifier is then used to detect the signal at this frequency, enabling the testing of weak signals. In the experiment, the chopper's reference frequency is set to 2350Hz and connected to the lock-in amplifier. The photocurrent generated by the light spot illuminating the sample enters a current preamplifier through a wire, converting the current signal into a voltage signal and amplifying it. The amplified voltage signal is further input into the lock-in amplifier for photocurrent extraction, and then read by the computer. Simultaneously, the computer acquires the rotation angle of the rotary table, thus obtaining the photocurrent magnitude at each waveplate angle.

[0050] The photocurrent variation curves under different polarization states were plotted using Origin software, with the fitting formula being:

[0051]

[0052] In the above formula, The angle between the quarter-wave plate and the polarizer is shown, with J on the left representing the total photocurrent density, and J on the right representing the angle between the quarter-wave plate and the polarizer. The term represents the circularly polarized photocurrent generated by circularly polarized light excitation. and The term represents the linearly polarized photocurrent effect and the unpolarized photon traction effect generated by linearly polarized light excitation, j0 comes from the thermoelectric effect, photovoltaic effect, Dember effect, etc. caused by the temperature gradient, and is the background current. This is the attenuation term.

[0053] When using AHPA-L as the chiral monolayer to fabricate devices, the photocurrent variation curve is as follows: Figure 3 As shown, the solid line represents the fitted curve of the total photocurrent, and the dashed line represents the fitted curve of the circularly polarized photocurrent term. It can be seen that the fitting effect is good. From... Figure 3As can be seen, when the incident angle is 30° and the incident light wavelength is 800 nm, the circularly polarized photocurrent generated by the AHPA-L chiral optoelectronic device is approximately 154 pA / mW, and it exhibits a larger photocurrent response to right-handed circularly polarized light. This is reflected in the circularly polarized photocurrent term. The C value, normalized using the background current j0, is -0.01878.

[0054] Under the same testing conditions, the AHPA-D chiral optoelectronic device generates a circularly polarized photocurrent of approximately 174 pA / mW. However, unlike the AHPA-L device, the AHPA-D device exhibits a larger photocurrent response to left-handed circularly polarized light, with a C value normalized to the background current j0 of +0.01415. Both devices show higher responses to a specific type of circularly polarized light and possess opposite circularly polarized photocurrent parameters C. These results demonstrate that the chiral optoelectronic device fabricated in this embodiment not only exhibits high sensitivity in polarized light recognition but also allows for large-scale fabrication with a simple and feasible approach.

[0055] This method can be used to detect circularly polarized light because chiral molecules can introduce symmetry breaking and spin-orbit coupling into semiconductors through interface effects, enabling the semiconductors to exhibit characteristic responses to circularly polarized light. Different chiral molecules introduce different symmetry breaking, ultimately leading to opposite values ​​of the circularly polarized light current C. When chiral molecules approach the material surface, they undergo transient charge polarization under the influence of dispersion forces. This charge polarization manifests as spin polarization in chiral molecules, causing an asymmetric spin distribution of surface electrons in momentum space. When the molecular layer thickness is... At the order of magnitude (i.e., within a few helices near the interface layer of the chiral molecule), the interface effect is dominated by spin exchange interactions. When electrons flow through the interface between the chiral molecule and the electrode, the orbital polarization and orbital filtering effects of the chiral molecule, together with the electrode, generate spin polarization and spin filtering effects, introducing symmetry breaking. The interface effect between the chiral molecule and the electrode layer will affect the band symmetry of Si near the interface, resulting in symmetry breaking. The closer to the chiral molecule / electrode layer interface, the stronger the interface effect.

[0056] Due to symmetry breaking, a circularly polarized photocurrent effect occurs when the sample is irradiated with externally polarized light. Electrons are fermions with spin ±1 / 2, and photons are bosons with spin ±1. The photon spin-electron spin interaction satisfies the selection rules for optical transitions, such as... Figure 5As shown, when the incident photon energy is greater than or equal to the semiconductor bandgap, valence band electrons absorb the photon energy and transition to the conduction band. The conduction band and light holes are ±1 / 2 spin states, while heavy holes are ±3 / 2 spin states. When the incident photon is left-handed circularly polarized light with spin +1 (σ+), transitions from the -1 / 2 state of light holes to the +1 / 2 state of the conduction band and from the -3 / 2 state of heavy holes to the -1 / 2 state of the conduction band are possible. When the incident photon is right-handed circularly polarized light with spin -1 (σ-), transitions from the +1 / 2 state of light holes to the 1 / 2 state of the conduction band and from the +3 / 2 state of heavy holes to the +1 / 2 state of the conduction band are possible. Based on this, a photocurrent and its circularly polarized photocurrent term are ultimately generated.

Claims

1. An application of a chiral spin-polarized circularly polarized optoelectronic device, characterized in that, For the detection of circularly polarized light, molecules with specific chiralities allow electrons of one spin to pass through more easily, while making it difficult for electrons of another spin to pass through. When chiral molecules are grown on a metal surface through self-assembly, they induce symmetry breaking at the semiconductor interface through spin exchange interactions and spin selection, resulting in Rashba spin splitting. This causes semiconductors that do not inherently have symmetry breaking to generate circularly polarized photocurrents. When external circularly polarized light irradiates the sample surface, a circularly polarized photocurrent effect is generated. Conversely, molecules with chiralities will generate the opposite type of circularly polarized photocurrent. The chiral spin-polarized circularly polarized optoelectronic device utilizes the spin polarization effect induced by the self-assembled chiral molecule AHPA-L / -D to modify the surface of a semiconductor to produce symmetry breaking. It comprises, from bottom to top, a substrate, a semiconductor layer, a metal layer, and a chiral molecule monolayer. The substrate and semiconductor layer are commercially available low-doped single-crystal p-Si grown on a SiO2 substrate. The semiconductor layer has a thickness of 100–500 μm. The metal layer is selected from at least one of Au or Al, with a thickness of 1–5 nm. The chiral molecule monolayer is selected from at least one of the chiral peptides AHPA-L or AHPA-D. Electrodes are led out from the surface of the chiral molecule monolayer, with Al wire as the electrode material and an electrode spacing of 3 mm.

2. The application of the chiral spin-polarized circularly polarized optoelectronic device according to claim 1, characterized in that, The -SH of the cysteine ​​residue at the end of the chiral molecule forms a thiol bond with the surface of the metal layer and is fixed on the metal layer, while the other end of the chiral molecule is suspended; the angle between the chiral molecule and the normal direction of the substrate is 20-70°.

3. The application of the chiral spin-polarized circularly polarized optoelectronic device according to claim 1 or 2, characterized in that, A method for fabricating a chiral spin-polarized circularly polarized optoelectronic device includes the following steps: using a commercial semiconductor single crystal as the semiconductor layer, forming a metal layer by magnetron sputtering, forming a chiral molecular monolayer by self-assembly, and sequentially stacking the layers to obtain the chiral spin-polarized circularly polarized optoelectronic device. (1) The semiconductor layer, namely commercial p-type doped single crystal Si grown on SiO2, with a crystal plane (100) and a resistivity of 1-20 Ω·cm, is mechanically cut; (2) The metal layer is grown on the semiconductor layer using a magnetron sputtering method; (3) A self-assembled chiral molecular monolayer is grown on the metal layer; (4) Use a pressure welding machine to draw out the electrode from the surface of step (3). The electrode material is Al wire and the electrode spacing is 3 mm.

4. The application according to claim 3, characterized in that, Step (2) specifically includes the following steps: (a) Clean the sample from step (1) sequentially with deionized water and ethanol using ultrasonic cleaning for 5-10 minutes each time, and finally dry it with a nitrogen gun. (b) The oxide layer on the surface was removed by etching using an ion beam etching method. The etching time was 2-5 min and the beam current was 60-200 mA. After etching, the surface was stored in a vacuum bag. (c) Evacuate the coating chamber of the ultra-high vacuum magnetron sputtering system to below 20 Pa using a mechanical pump, then turn on the molecular pump and evacuate to below 10 Pa. -5 Below 20 Pa; place the sample from step (b) on the sample holder and send it into the sample chamber. First, turn on the mechanical pump in the sample chamber to evacuate to below 20 Pa, then turn on the molecular pump to evacuate to below 10 Pa. -3 Below Pa; (d) Open the gate valve between the coating chamber and the sample chamber, and feed the sample holder with the substrate from step (b) into the coating chamber via a lateral servo. (e) Inert gas is introduced into the coating chamber to achieve the ignition pressure, and pre-sputtering 1 is performed using a DC power supply. After completion, the inert gas flow rate is reduced, and the pressure in the coating chamber is reduced to the working pressure. At this time, pre-sputtering 2 is performed using a DC power supply. The inert gas includes argon and / or nitrogen. The power of the DC power supply is 180~220 W. The working pressure of pre-sputtering 1 is 1.3~2.0 Pa, and the time is 30~60 s. The working pressure of pre-sputtering 2 is 0.3~0.5 Pa, and the time is 30~60 s. (f) After completion, open the target baffle to begin the actual sputtering. Stop sputtering after the allotted time has elapsed, and remove the target. Once the sample holder is removed, the grown metal layer is obtained. Step (3) The specific preparation method includes the following steps: (a) Dissolve the chiral molecules in EtOH to prepare a chiral molecule solution with a concentration of 1 mmol·L⁻¹. -1 ; (b) Place the sample from step (2) upright in the chiral molecule solution, then seal and let it stand at room temperature; allowing the chiral molecules to assemble in the metal layer for 24-48 hours. (c) After self-assembly, the sample is removed and the surface is cleaned multiple times with EtOH to remove unassembled molecules; after sample preparation, it is sealed in a vacuum bag and stored at -18 °C.

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