A twisted semi-metal material based cascaded low temperature single photon detector

Abstract

The application relates to a kind of cascade low-temperature single-photon detectors based on torsion semimetal materials, comprising: substrate, cascade structure and electrode;Wherein, the cascade structure is arranged on the substrate;The electrode is arranged on the cascade structure;The cascade structure is formed by the alternating stacking of dielectric layer and Dirac semimetal material;The outermost layer of the cascade structure from bottom to top and from top to bottom is the dielectric layer;The electrode includes a top gate electrode arranged at the top of the cascade structure and a plurality of source / drain metal contact electrodes arranged on the Dirac semimetal material.The beneficial effects of the application are: the Fermi level of the Dirac semimetal material used in the application is adjustable, the internal carrier concentration is controlled by the gate region, and the single-photon energy can excite to generate a photovoltage signal.

Description

Technical Field

[0001] This invention belongs to the field of photon detector technology, and particularly relates to a cascaded low-temperature single-photon detector based on a torsion half-metal material. Background Technology

[0002] Infrared single-photon detection is a highly sensitive detection technique used to detect single photons in the infrared band. Infrared single-photon detection relies on the detector's absorption of a single photon and its conversion into a measurable electrical signal. Due to the low energy of infrared photons, the detector requires extremely high sensitivity and low noise performance to distinguish the signal from background noise. Because the energy of mid- and far-infrared photons is low, the corresponding photoelectric signal is weak and easily drowned out by background noise in the circuit system; therefore, the detector typically operates in a low-temperature environment. Single-photon detectors are widely used in quantum communication, quantum computing, quantum sensing, astronomical observation, biological imaging, and spectral analysis. With the continuous advancement of science and technology, the performance requirements for single-photon detectors are constantly increasing, such as higher detection efficiency, lower dark count rates, and wider spectral response ranges.

[0003] Traditional single-photon detectors mainly include superconducting nanowire single-photon detectors (SNSPDs), photomultiplier tubes, avalanche photodiodes (APDs), and devices based on semiconductor materials such as silicon and germanium. Among them, SNSPDs have become a hot topic in current research and application due to their low dark count rate, low latency, and high repetition rate. However, SNSPDs have a small photosensitive area, requiring precise nanofabrication technology and high-quality materials, making their cost much higher than other single-photon detectors. Photomultiplier tubes have low detection efficiency in the infrared band, especially poor photon response in the band larger than 1 μm, and are large in size, susceptible to interference, have high noise, and a time resolution of only nanoseconds, making it difficult to meet the requirements of high-speed detection. Although avalanche single-photon detectors are suitable for near-infrared light, they have a high dark count rate, significant afterpulse effect, and a detection efficiency of only 20%-50%, which is still far behind the superior performance of superconducting detectors (such as SNSPDs). Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cascaded low-temperature single-photon detector based on torsional semimetal materials.

[0005] In the first aspect, a cascaded low-temperature single-photon detector based on a twisted half-metal material is provided, including: a substrate, a cascaded structure, and electrodes; The cascaded structure is disposed on the substrate; the electrode is disposed on the cascaded structure; the cascaded structure is formed by alternating stacking of dielectric layers and Dirac semimetal materials; the outermost layer of the cascaded structure from bottom to top and from top to bottom is the dielectric layer; the electrode includes a top gate electrode disposed at the top of the cascaded structure and multiple source / drain metal contact electrodes disposed on the Dirac semimetal material.

[0006] Preferably, the substrate is used to provide mechanical support for the device structure and to serve as a back gate for gate control of the semi-metallic material located thereon; the substrate uses a conductive substrate or forms a conductive layer on an insulating layer, and the substrate includes a silicon substrate.

[0007] Preferably, the dielectric layer is used to provide electrical insulation between adjacent structures and to cover / encapsulate a semi-metallic material to achieve physicochemical protection and electrical isolation.

[0008] Preferably, the semi-metallic materials are stacked with relative interlayer twist angles; the Dirac semi-metallic material is a semi-metallic material with a Dirac cone band structure; the Dirac semi-metallic material includes graphene, and the structure of the twisted graphene is selected from twisted monolayer graphene or twisted multilayer graphene.

[0009] Preferably, the twisted graphene is used as the absorption region for single photons, and the charge carriers inside the graphene are controlled by an external bias voltage.

[0010] Preferably, the twist angle of the twisted graphene is between 1° and 1.4°.

[0011] Secondly, a method for fabricating a cascaded low-temperature single-photon detector as described in any of the first aspects is provided, comprising: Step 1: A dielectric layer is formed on the substrate to prepare graphene, and a twisted graphene / boron nitride structure is formed by cutting, picking up, and rotating. Step 2: Determine the torsion angle using TEM or STM / STS. Then transfer the structure onto the substrate.

[0012] Step 3: Based on Step 2, prepare source / drain metal contact electrodes of twisted graphene, remove PDMS with dichloromethane and vacuum anneal.

[0013] Step 4: Repeat the steps of forming the dielectric layer, twisting the graphene structure and the source / drain metal electrodes to obtain the cascaded device; Step 5: Fabricate a top gate electrode on top of the cascaded structure.

[0014] Thirdly, a gated single-photon detection system is provided, comprising any of the cascaded low-temperature single-photon detectors, a gated signal generation circuit, a pulse generation circuit, a quenching circuit, a reset circuit, a detection and readout circuit, and a logic control circuit as described in the first aspect.

[0015] Fourthly, a method for operating a gated single-photon detection system is provided, executed by the system described in the third aspect, comprising: Step 1: The logic control circuit sends short pulses to the gate circuit according to the set frequency and width, so that the single detector works under the bias voltage, and works with the pulse generation circuit to synchronously emit photon pulses or perform timing calibration for external events. Step 2: After the photon is captured by the detector, the quenching circuit reduces the bias voltage to prevent the detector from locking up. Step 3: The reset circuit restores the detector to the test state, while the detection readout circuit amplifies, converts analog to digital, and counts the current pulses; Step 4: The logic control unit determines and outputs a valid photon detection event.

[0016] The beneficial effects of this invention are: 1. The Fermi level of the Dirac semimetal material of the present invention is tunable. By controlling the internal carrier concentration in the gate region, a single photon energy can be used to generate a photovoltage signal.

[0017] 2. The strong electron-correlated superconducting state in the torsional Dirac half-metal material of the present invention, and the interlayer coupling with the moiré superlattice formed by the twist, enable the absorption detection of broadband single photons, thereby achieving highly sensitive detection of single photon events.

[0018] 3. This invention utilizes the zero bandgap characteristic of graphene, enabling it to absorb long-wavelength light, particularly mid-infrared light. The low-temperature single-photon detector based on torsional carbon-based half-metal materials possesses broad spectral response and high sensitivity, and is expected to expand the spectral response range, making it suitable for multi-band photon detection applications.

[0019] 4. The fabrication process of this device is relatively simple. Compared with the complex fabrication processes of other single-photon detectors, the fabrication cost of this invention is lower and it is easy to achieve mass production. At the same time, the atomic-level thickness of the two-dimensional structure facilitates device miniaturization and integration. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the cross-sectional structure of a cascaded low-temperature single-photon detector based on a torsion semimetal material. Figure 2 A schematic diagram of the twisted graphene structure; Figure 3 This is a schematic diagram of the device's responsivity; Figure 4This is a schematic diagram of a single-photon detection system; Figure reference numerals: 1. Substrate; 2. Multilayer boron nitride; 3. Multilayer twisted graphene; 4. Composite structure; 5. Cascade structure; 6. Source metal contact electrode; 7. Drain metal contact electrode; 8. Top gate electrode. Detailed Implementation

[0021] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0022] Example 1: The embodiments of this application demonstrate that two-dimensional materials, especially graphene and its derived structures, open up entirely new avenues for ultrasensitive photon detection due to their unique electronic and optical properties. A moiré superlattice is a composite structure formed by superimposing two two-dimensional materials with similar periods through a certain rotation angle or lattice constant mismatch. This structure exhibits many unique physical phenomena due to its special periodic potential field, such as band folding, moiré bands, and novel electronic states. When two graphene sheets are twisted and stacked at a specific angle (e.g., 1.1°), this structure introduces a periodic potential field, leading to significant changes in the electronic band structure, such as the appearance of flat bands near the Dirac point and the generation of superconductivity. When two graphene sheets are twisted and stacked at a specific angle, their lattice periods interfere, forming a moiré superlattice with a larger period. This structure significantly alters the electronic band structure, making the electronic states near the Fermi energy tend to flatten, forming so-called "flat bands," significantly reducing carrier density and significantly enhancing the electronic interactions of the system, thereby enhancing the Coulomb interactions between electrons and leading to the formation of Cooper pairs. This strong correlation effect induces a variety of exotic quantum states, including superconducting states, Mott insulating states, and quantum anomalous Hall states. Among these, the superconducting state is the core characteristic of torsional graphene in single-photon detection.

[0023] Twisted carbon-based half-metals exhibit extremely high responsivity and sensitivity to infrared light, and the Fermi level of twisted carbon-based half-metals can be tunable by adjusting the gate voltage. Furthermore, by applying strain or an external electric field, the electronic band structure and density of states in the moiré superlattice can be tuned, thereby achieving dynamic control of the material's electronic properties. By applying a bias voltage to the gate, the carrier density within graphene can be controlled, reaching levels five orders of magnitude lower than those of conventional superconductors. This results in twisted graphene possessing extremely low carrier density and very small electronic heat capacity, a characteristic that allows even extremely weak energy inputs (such as the energy of a single photon) to significantly affect the temperature balance and state of the electronic system.

[0024] Furthermore, twisted graphene exhibits superconducting behavior at low temperatures. The carrier concentration in twisted graphene can be adjusted by applying an external gate voltage. Due to its extremely low electronic heat capacity and electron-phonon coupling, the local temperature rise caused by the absorption of a single photon is more significant, making it easier to break Cooper pairs and generate photovoltage output, thereby achieving a single-photon level response.

[0025] Therefore, the twisted graphene structure, with its unique electronic structure, low carrier concentration, and ultra-low electronic heat capacity, provides a completely new physical basis and technical path for the design and realization of single-photon detectors. Through the rational design of voltage bias and self-reset circuits, single-photon detectors can achieve highly efficient responses to single-photon events in low-temperature environments, demonstrating advantages that traditional superconducting detectors cannot match.

[0026] Furthermore, Embodiment 1 of this application provides a cascaded low-temperature single-photon detector based on a torsion half-metal material. This detector features ultra-high single-photon sensitivity, low dark count rate, and self-reset capability, making it suitable for applications such as quantum communication, quantum computing, and ultra-high sensitivity sensing. Specifically, as... Figure 1 As shown, the detector includes: a substrate, a cascaded structure, and electrodes; The cascaded structure 5 is disposed on the substrate 1; the electrodes are disposed on the cascaded structure 5; the cascaded structure 5 is formed by alternating stacking of dielectric layers and Dirac semimetal materials; the outermost layer of the cascaded structure 5 from bottom to top and from top to bottom is the dielectric layer; the electrodes include a top gate electrode 8 disposed at the top of the cascaded structure and multiple source metal contact electrodes 6 and drain metal contact electrodes 7 disposed on the Dirac semimetal material. The top gate electrode 8 is in contact with the top dielectric layer, and the source / drain metal contact electrodes have multiple contacts with the Dirac semimetal material. The metal contact electrodes are all composed of chromium and gold.

[0027] Specifically, the substrate is a silicon substrate. Compared to other substrates, silicon has a smooth and flat interface, which provides better adsorption for two-dimensional materials. Furthermore, its reflective properties can increase the absorption of photons by the twisted graphene. The substrate provides mechanical support for the device structure and allows for bias voltage regulation. The substrate can be a conductive substrate or have a conductive layer formed on an insulating layer; the substrate includes, but is not limited to, a silicon substrate.

[0028] The dielectric layer is composed of multiple layers of boron nitride 2. Compared with other materials, boron nitride is easy to mechanically peel off, and its excellent insulating properties can effectively suppress the tunneling current of the gate. In addition, due to its excellent mechanical properties and chemical resistance, boron nitride can also serve as a protective layer for twisted graphene, and the coating effect of boron nitride on graphene is good.

[0029] The Dirac semimetal material includes multiple layers of twisted graphene 3, that is, graphene stacked together at a specific relative angle to form a twisted graphene structure. The Dirac semimetal material and the dielectric layer are alternately stacked along the vertical direction in space to form a cascaded structure.

[0030] In this method, the multilayer twisted graphene 3 is used as the absorption region for single photons. Since the Fermi level of graphene is tunable, the charge carriers inside the graphene can be controlled by an external bias voltage.

[0031] Furthermore, the twist angle of the multilayer twisted graphene 3 is between 1° and 1.4°, for example, the optimal twist angle is 1.1°.

[0032] It should be noted that the composite structure 4 formed by multilayer twisted graphene 3 and multilayer boron nitride 2 utilizes the complementary advantages of graphene layers with different twist angles in band structure and optical absorption spectrum. Through multi-level absorption and carrier gain cascade, it achieves high efficiency photon capture and multi-level multiplication in a wide band. At the same time, the atomically smooth insulating layer of boron nitride not only isolates interface trap states and charge scattering, ensuring the high mobility of graphene, but also suppresses thermal excitation phenomena, thus significantly reducing dark current and dark count rate. Therefore, high quantum gain is obtained while maintaining extremely low noise.

[0033] Furthermore, the detector described above needs to operate at low temperatures to ensure that the tortuous graphene is in a superconducting state. In this state, a constant bias voltage is applied to the detector. This bias voltage sets the detector's operating point at the transition edge between the superconducting and normal states. At this point, the system is extremely sensitive to minute external perturbations (such as photon absorption), and any energy input may trigger the destruction of the superconducting state.

[0034] When an incident photon is absorbed by the detector, its energy far exceeds the superconducting bandgap of the twisted graphene. This allows even a small energy from a single photon to trigger a rapid increase in local temperature, disrupting the stability of Cooper pairs in the superconducting system and generating a large number of quasiparticles. These quasiparticles diffuse within the two-dimensional graphene structure, weakening or destroying the superconducting state in localized areas, forming a "hotspot" region. This localized superconducting instability is a crucial step in detecting single-photon events.

[0035] Under normal operating conditions, the detector operates in a superconducting state, achieving resistance-free transmission via Cooper pairs. The device exists in a sensitive equilibrium between the superconducting and normal states, making it highly susceptible to energy disturbances. The system is extremely sensitive to temperature and excitation, with the entire superconducting state at a critical equilibrium. In this state, the energy released after absorbing a photon is sufficient to break the local Cooper pairs, causing this region to rapidly transition from the superconducting to the normal state. This transition causes a sudden increase in local resistance, generating a significant voltage pulse signal in the external circuitry, thus enabling the detection of a single photon.

[0036] Example 2: Based on Example 1, Example 2 of this application provides a method for fabricating a cascaded low-temperature single-photon detector, including: Step 1: Preparation of twisted graphene structure Specifically, monolayer graphene can be prepared using chemical vapor deposition (CVD), molecular beam epitaxy (MBE), or mechanical exfoliation. The monolayer graphene is then pre-cut and pre-treated using an atomic force microscope (AFM) tip, creating artificial notches for reference. This step divides a single graphene sheet into two parts (graphene A and graphene B). The hexagonal boron nitride (BON) sheet grown by CVD is mechanically exfoliated using a polydimethylsiloxane (PDMS) stamp to pick up and transfer the BON. The PDMS stamp with BON picks up the first graphene sheet (graphene A), lifts the stamp, and simultaneously rotates the second graphene sheet (graphene B) precisely to the required angle. The PDMS stamp is then pressed down again to pick up the second graphene sheet (graphene B), forming a twisted graphene-BON structure.

[0037] Subsequently, specific characterization methods are used to determine whether the relative torsion angle of the formed graphene meets the requirements. For example, transmission electron microscopy (TEM) can accurately measure the torsion angle of graphene; scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can also accurately measure the torsion angle of graphene.

[0038] Finally, the twisted graphene-boron nitride structure is transferred onto a clean substrate, with the boron nitride in contact with the substrate and the twisted graphene on top of the boron nitride.

[0039] Step 2: Prepare source / drain metal contact electrodes based on Step 1.

[0040] Specifically, photoresist is first uniformly applied to the transferred hexagonal boron nitride-twisted graphene structure, and electrode patterns are drawn using a laser direct-write device. Then, a diluted developer is used for development. Finally, metal deposition of the electrodes is performed using a magnetron sputtering system, vapor deposition, or chemical synthesis. Finally, acetone solution is used to strip away any remaining photoresist until the electrode patterns are exposed. In addition, the device is placed in a dichloromethane solution to remove polydimethylsiloxane, and then vacuum annealed.

[0041] Step 3: Repeat the steps of forming the dielectric layer and preparing and transferring the twisted graphene structure to form a cascade structure, and prepare source / drain metal contact electrodes on the twisted graphene according to the method in Step 2.

[0042] Step 4: Form a top gate electrode on top of the cascaded structure.

[0043] Specifically, a new hexagonal boron nitride sheet is picked up using a polydimethylsiloxane (PDMS) stamp and transferred onto the cascade structure, covering the twisted graphene with boron nitride. Photoresist is uniformly applied to the device surface, i.e., the boron nitride sheet, and electrode patterns are drawn using a laser direct writing device. Subsequently, a diluted developer is used for development. Finally, metal deposition of the electrodes is performed using a magnetron sputtering system, vapor deposition, or chemical synthesis. Finally, acetone solution is used to strip away any remaining photoresist until the top gate metal electrode pattern is exposed.

[0044] The materials used in the above preparation steps are for illustrative purposes only. The semi-metallic materials and dielectric layer materials used in this invention can be two-dimensional materials. The semi-metallic materials used in this invention are not limited to graphene, but should also include other Dirac semi-metallic materials and materials with semi-metallic characteristics. The structure of the twisted graphene mentioned is selected from at least one of twisted monolayer graphene, twisted bilayer graphene, twisted trilayer graphene, and derived twisted multilayer graphene. The dielectric layer is used to provide electrical insulation between adjacent structures and to cover / encapsulate the semi-metallic material to achieve physicochemical protection and electrical isolation. The material of the dielectric layer is not limited to boron nitride, and any dielectric material known to those skilled in the art that can achieve the above-mentioned insulation and encapsulation of the semi-metallic material can be used, or any combination thereof.

[0045] It should be noted that the method provided in this embodiment is the same as the method of the detector provided in Embodiment 1. Therefore, the parts that are the same as or similar to those in Embodiment 1 in this embodiment can be referred to each other, and will not be repeated in this application.

[0046] Example 3: Based on Embodiment 1, Embodiment 3 of this application provides a gated single-photon detection system, including a cascaded low-temperature single-photon detector, a gated signal generation circuit, a pulse generation circuit, a quenching circuit, a reset circuit, a detection readout circuit, and a logic control circuit as described in any of the first aspects.

[0047] When a device absorbs a photon, it instantly transitions from a superconducting (or low-resistivity) state to a high-resistivity state, generating a measurable voltage signal. However, without a dedicated reset circuit, the detector will lock into the high-resistivity state. Once the detector is "locked" into the normal state, it loses its superconducting or low-resistivity operating point, and even if subsequent photons are absorbed, they will no longer cause significant impedance jumps or voltage pulses, thus losing its detection function.

[0048] Furthermore, embodiments of this application also provide a method for operating a gated single-photon detection system, including: Step 1: The logic control circuit sends short pulses to the gate circuit according to the set frequency and width, so that the single detector works under the bias voltage, and works with the pulse generation circuit to synchronously emit photon pulses or perform timing calibration for external events. Step 2: After the photon is captured by the detector, the quenching circuit reduces the bias voltage to prevent the detector from locking up. Step 3: The reset circuit restores the detector to the test state, while the detection readout circuit amplifies, converts analog to digital, and counts the current pulses; Step 4: The logic control unit determines and outputs a valid photon detection event.

[0049] It should be noted that the method provided in this embodiment is the system and working method corresponding to the detector provided in Embodiment 1. Therefore, the parts that are the same as or similar to those in Embodiment 1 in this embodiment can be referred to each other, and will not be repeated in this application.

Claims

1. A cascaded low-temperature single-photon detector based on a torsion half-metal material, characterized in that, include: Substrate, cascade structure, and electrodes; The cascaded structure is disposed on the substrate; the electrode is disposed on the cascaded structure; the cascaded structure is formed by alternating stacking of dielectric layers and Dirac semimetal materials; the outermost layer of the cascaded structure from bottom to top and from top to bottom is the dielectric layer; the electrode includes a top gate electrode disposed at the top of the cascaded structure and multiple source / drain metal contact electrodes disposed on the Dirac semimetal material.

2. The cascaded low-temperature single-photon detector based on torsional semimetallic materials according to claim 1, characterized in that, The substrate is used to provide mechanical support for the device structure and to act as a back gate for gate control of the semi-metallic material located thereon; the substrate uses a conductive substrate or forms a conductive layer on an insulating layer, and the substrate includes a silicon substrate.

3. The cascaded low-temperature single-photon detector based on torsional semimetal material according to claim 2, wherein the dielectric layer is used to provide electrical insulation between adjacent structures and to cover / encapsulate the semimetal material to achieve physicochemical protection and electrical isolation.

4. The cascaded low-temperature single-photon detector based on torsional semimetallic materials according to claim 3, characterized in that, The semi-metallic materials are stacked with relative interlayer twist angles; the Dirac semi-metallic material is a semi-metallic material with a Dirac cone band structure; the Dirac semi-metallic material includes graphene, and the structure of the twisted graphene is selected from twisted monolayer graphene or twisted multilayer graphene.

5. The cascaded low-temperature single-photon detector based on a torsion half-metal material according to claim 4, characterized in that, The twisted graphene is used as the absorption region for single photons, and the charge carriers inside the graphene are controlled by an external bias voltage.

6. The cascaded low-temperature single-photon detector based on a torsion half-metal material according to claim 5, characterized in that, The twisted graphene has a twist angle between 1° and 1.4°.

7. A method for fabricating a cascaded low-temperature single-photon detector as described in any one of claims 1 to 6, characterized in that, include: Step 1: Prepare a dielectric layer on a substrate to prepare graphene, and use a cutting, picking, and rotating method to prepare a twisted graphene / boron nitride structure. Step 2: Determine the torsion angle using TEM or STM / STS. Then transfer the structure to the substrate; Step 3: Based on Step 2, prepare the source / drain metal contact electrode of twisted graphene, remove PDMS with dichloromethane and vacuum anneal; Step 4: Repeat the steps of forming the dielectric layer, twisting the graphene structure and the source / drain metal electrodes to obtain the cascaded device; Step 5: Fabricate a top gate electrode on top of the cascaded structure.

8. A gated single-photon detection system, characterized in that, It includes the cascaded low-temperature single-photon detector, gating signal generation circuit, pulse generation circuit, quenching circuit, reset circuit, detection readout circuit and logic control circuit as described in any one of claims 1 to 6.

9. A method for operating a gated single-photon detection system, characterized in that, Performed by the system of claim 8, comprising: Step 1: The logic control circuit sends short pulses to the gate circuit according to the set frequency and width, so that the single detector works under the bias voltage, and works with the pulse generation circuit to synchronously emit photon pulses or perform timing calibration for external events. Step 2: After the photon is captured by the detector, the quenching circuit reduces the bias voltage to prevent the detector from locking up. Step 3: The reset circuit restores the detector to the test state, while the detection readout circuit amplifies, converts analog to digital, and counts the current pulses.

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