A method for fabricating a diamond photonic integrated circuit

Abstract

The application discloses a diamond photon integrated circuit preparation method, which comprises the following steps: firstly, ion implantation is adopted on a seed crystal substrate; then, after heat treatment of the implanted single crystal diamond sheet, diamond with low defect density is regrown on the single crystal diamond sheet, so as to realize the preparation of ultrathin single crystal diamond; in addition, a tunable resonator with a diamond H-shaped structure and a high quality factor is prepared; at the same time, a single photon detector is manufactured on the diamond substrate, and the prepared single photon detector is characterized; finally, on the single crystal diamond film with a solid color center light source and a resonator structure, a diamond waveguide is prepared, and finally, an array of superconducting nanowire single photon detectors is prepared, so that the whole photon integrated circuit with diamond as a platform material is manufactured.

Description

Technical Field

[0001] This invention belongs to the field of integrated circuit technology and relates to a method for fabricating diamond photonic integrated circuits. Background Technology

[0002] In photonic integrated circuit applications, the miniaturization of optical devices offers the possibility of a stable and scalable architecture, especially in quantum optics. Exploring the application of quantum mechanics in quantum optical circuits, such as quantum simulators or linear optical quantum computers, holds great promise for surpassing the performance of classical computers. For such photonic integrated circuits, the development of suitable platform materials has a significant impact on future technologies. Diamond possesses excellent mechanical and optical properties, including numerous optical excitation defects, such as solid color centers, which can be applied to single-photon sources, quantum memories, or sensing elements. These properties have inspired the development of diamond photonic integrated circuits and optomechanical circuits. Optical communication offers better bandwidth and speed compared to electrical communication. Currently, Si materials have high broadband infrared transparency, making them a suitable choice for building photonic integrated circuits. Furthermore, silicon's transparency makes it suitable for building passive photonic components such as waveguides. Silicon is also suitable for active devices such as modulators and detectors, but the performance of active devices based on silicon and group III-V semiconductors is inferior to that achievable with active devices made from diamond semiconductor materials. On the other hand, diamond is infrared transparent under the condition of a wide bandwidth of visible to infrared, which can form a wide bandwidth communication.

[0003] Currently, discrete devices related to diamond semiconductors are well-known. However, there is no mature technical path for designing an integrated coupling design that uses diamond as a substrate material and employs the intrinsic color center structure of diamond solid defects as a single photon source for detection under low-temperature conditions.

[0004] For photonic integrated circuits, Si photonic integrated circuits and GaN photonic integrated circuits already exist. Currently, there is no overall design for diamond photonic integrated circuits. Existing technology includes a photonic integrated circuit comprising a substrate and a passive layer. The passive layer is formed on the substrate and includes passive photonic devices. The circuit also includes a III-V material layer disposed in a recess of the passive layer and includes active photonic devices. The III-V material layer is configured to allow light to propagate between the passive and active photonic devices. This photonic integrated circuit offers the advantage of active devices formed from III-V materials in an easily planarizable arrangement, enabling tight integration between the active devices and electronic components. Existing related technologies are primarily focused on Si and SiC / GaN fabrication techniques. Designs of photonic integrated circuits using diamond semiconductors as the platform material are less common. The performance of active devices based on silicon and III-V semiconductors is inferior to that achievable with active devices fabricated from diamond semiconductor materials. On the other hand, diamond is infrared transparent under the condition of a wide bandwidth of visible to infrared, which can form a wide bandwidth communication. Summary of the Invention

[0005] To address the aforementioned issues, this invention utilizes third-generation diamond semiconductors as a platform material to fabricate photonic integrated circuits, forming a photonic integrated circuit with tunable resonant elements based on single-crystal diamond as the main material, diamond as the waveguide material over a wide frequency range, and a highly sensitive nanowire detector.

[0006] The technical solution is a method for fabricating diamond photonic integrated circuits, including the following steps:

[0007] S10, for preparing single-crystal diamond with controllable defects;

[0008] S20, used to fabricate diamond resonators;

[0009] S30, fabrication of nanowire single-photon detectors;

[0010] S40, an integrated fabrication array of superconducting nanowire single-photon detectors;

[0011] Specifically, the following steps are included:

[0012] First, ion implantation is performed on the seed crystal substrate;

[0013] Then, diamond with low defect density is regrowth on the heat-treated single-crystal diamond sheet to achieve the preparation of ultrathin single-crystal diamond.

[0014] In addition, a tunable resonator with a diamond H-type structure and a high quality factor is prepared.

[0015] Meanwhile, a single-photon detector was fabricated on a diamond substrate, and the fabricated single-photon detector was characterized.

[0016] Finally, a diamond waveguide was fabricated on a single-crystal diamond thin film with a solid color center light source and a resonator structure, and an array of superconducting nanowire single-photon detectors was integrated to form the fabrication of an integral photonic integrated circuit with diamond as the platform material.

[0017] Preferably, the preparation of controllable defect single-crystal diamond includes: using a lift-off method, specifically using different implantation conditions to form a damage layer of different depths, evaluating the crystal quality of the formed damage layer, using typical MeV energy for implantation, and evaluating the quality of the diamond epitaxial layer regrowth on the substrate after different lift-off conditions, wherein the different lift-off conditions include ion implantation with different energies and different temperature heat treatment methods.

[0018] Preferably, the fabrication of the diamond resonator includes fabricating a waveguide-based superconducting nanowire single-photon detector structure using a lift-off method.

[0019] Preferably, the fabrication of the diamond resonator includes using a ridge waveguide to limit losses during optical waveguide propagation.

[0020] Preferably, the fabrication of the diamond resonator includes a phase shifter made of diamond, shaped like an H-type resonator, consisting of two double-clamped cantilever beams of the same length, the two beam structures being linked by a central block to form a structure similar to the letter "H". The central block contains an array of holes to form a two-dimensional photonic crystal. The H-type resonator is evanescently coupled to a curved waveguide that supports TE-like polarization single-mode.

[0021] Preferably, the fabrication of the nanowire single-photon detector includes chemical mechanical polishing of the diamond surface, followed by photolithography using electron beam exposure, with NbN material as the single-photon device material, and then forming an Al film on its surface for protection; finally, electrode material is sputtered.

[0022] Preferably, the NbN material is a cubic structure of δ-NbN, or WSi or Nb.

[0023] Preferably, during the fabrication of the superconducting nanowire, the bias current of the nanowire during operation is close to its critical current, and the duty cycle of the nanowire detector is within a preset range while maintaining a preset critical current density.

[0024] Preferably, the test includes testing the performance of the superconducting nanowire single-photon detector. First, the nanowire is tested. After it becomes superconducting and the transition temperature increases, a low-temperature test is performed within a preset temperature range. The bias current is selected to provide a DC bias so that it reaches 95% of the critical current value.

[0025] Preferably, the performance testing of the superconducting nanowire single-photon detector also includes testing the single-photon response, quantum efficiency, dark number rate, reset time, and time jitter of the nanowire.

[0026] The present invention has at least the following beneficial effects:

[0027] 1. This photonic integrated circuit fabrication method utilizes the diamond semiconductor solid-state color center defect structure as a single-photon source and employs an electro-excited single-photon source design. Because it utilizes the color center structure of the substrate material itself, this solid-state circuit exhibits higher integration density, better resolution, and higher transmission efficiency.

[0028] 2. This photonic integrated circuit fabrication method uses diamond waveguides as the photon transmission medium. Diamond has high transmittance in the visible-infrared band, which can form transmission characteristics with high transmission efficiency and wide bandwidth.

[0029] 3. This photonic integrated circuit fabrication method can utilize arrayed single-photon detectors for integration. This allows for higher precision in spatial-temporal resolution. Furthermore, by employing a diamond waveguide and nanowire with the same incident direction, light enters the single-crystal diamond waveguide along the direction of the nanowire, ensuring that the photons interact with the nanowire continuously along its length. This confines the photons within the diamond waveguide, preventing them from escaping. With sufficiently long nanowires, the absorption rate of the incident light can approach 100%.

[0030] 4. This photonic integrated circuit fabrication method couples an optomechanical phase shifter based on optical gradient force, enabling adjustment and control of the optical transmission phase. The overall design of the photonic integrated circuit utilizes a diamond platform material, which allows for circuit miniaturization, good scalability, and high integration. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of the diamond photonic integrated circuit fabrication method according to an embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram of NbN nanowire SNSPD based on diamond waveguide, which is a method for fabricating diamond photonic integrated circuits according to an embodiment of the present invention.

[0033] Figure 3 This is a diamond quantum optical circuit diagram using the diamond photonic integrated circuit fabrication method according to an embodiment of the present invention;

[0034] Figure 4 This is a schematic diagram illustrating the fabrication of a nanowire single-photon detector using a diamond photonic integrated circuit fabrication method according to an embodiment of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0037] Figure 1 The method for fabricating diamond photonic integrated circuits provided in this embodiment of the invention includes the following steps:

[0038] S10, for preparing single-crystal diamond with controllable defects;

[0039] S20, used to fabricate diamond resonators;

[0040] S30, fabrication of nanowire single-photon detectors;

[0041] S40, an integrated fabrication array of superconducting nanowire single-photon detectors;

[0042] Specifically, the following steps are included:

[0043] First, ion implantation is performed on the seed crystal substrate;

[0044] Then, diamond with low defect density is regrowth on the heat-treated single-crystal diamond sheet to achieve the preparation of ultrathin single-crystal diamond.

[0045] In addition, a tunable resonator with a diamond H-type structure and a high quality factor is prepared.

[0046] Meanwhile, single-photon detectors are fabricated on Si or SiC substrates, and the fabricated single-photon detectors are characterized.

[0047] Finally, a superconducting nanowire single-photon detector array was integrated onto the single-crystal diamond film of the fabricated resonator.

[0048] The fabrication of controllable defect single-crystal diamond involves the following steps: To prepare high-quality, thin diamond films, we employ a lift-off method. Different implantation conditions result in damage layers of varying depths. The crystal quality of these damage layers is evaluated in detail. This method utilizes typical MeV implantation energies. The quality of the diamond epitaxial layer regrowth on the substrate is evaluated under different lift-off conditions (different ion implantation energies and different thermal treatment methods). Specifically, this refers to a double-crystal rocking curve below 30 arcseconds.

[0049] Fabrication of diamond resonators includes the fabrication of diamond waveguides, which are the most fundamental and core component of every photonic integrated circuit. This is because the optical waveguide assembly runs throughout the entire photonic chip and connects to various optical devices. Waveguides are typically composed of dielectric strips with rectangular cross-sections, which confine light within a two-dimensional space and guide its propagation in three dimensions. A lift-off method is used to fabricate waveguide-based SNSPD (Superconducting nanowire single-photon detector) structures. The wavelengths used in photonic integrated circuits are mainly concentrated in the visible range of 380nm to 800nm, as well as the near-infrared wavelength range used in communications. The near-infrared wavelength includes the C- and L-bands (1530-1625nm) for long-distance transmission. To minimize light loss during waveguide propagation, appropriate dimensions need to be designed. We will use ridged waveguides to limit losses during optical waveguide propagation; see [link to relevant documentation]. Figure 2 11 represents a diamond waveguide, 12 a NbN nanowire, 13 a SiO2, and 14 a schematic diagram of light propagation. Unlike conventional SNSPDs, SNSPDs on optical waveguides do not require the fabrication of long, winding superconducting nanowires. Instead, nanowires only tens of micrometers long are sufficient to achieve near-100% light absorption. This ensures quantum efficiency while significantly increasing the maximum count rate of the SNSPD.

[0050] Fabricating diamond resonators involves using phase shifters made of diamond. In photonic integrated circuits, we use phase shifters made of diamond, such as H-type resonators (see [link]). Figure 3The structure consists of a single-photon detector (10), a single-crystal diamond waveguide (20), an optically driven phase shifter (30), and a single-photon source (40). It comprises two identical double-clamped cantilever beams, typically tens of micrometers long, with widths on the order of hundreds of nanometers. The two beams are linked by a central block, forming a structure resembling the letter "H". The central block contains an array of holes, forming a two-dimensional photonic crystal. The H-resonator is evanescently coupled to a curved waveguide that supports TE-like polarization single-mode. The interaction length between the waveguide and the mechanical oscillator is calculated to be Lint = 12 μm, and the H-resonator and waveguide are parallel to each other. The waveguide is approximately 1 μm wide, and the distance between the waveguide and the H-resonator is approximately 150 nm. Both the waveguide and the H-resonator are fabricated using photolithography lift-off and etching, with a diamond material thickness of approximately 600 nm. The specific resonator is... Figure 3 30-channel optical drive phase shifter.

[0051] For the fabrication process of nanowire single-photon detectors, please refer to [link / reference]. Figure 4 The diamond surface is chemically and mechanically polished; then, an electron beam lithography mask is applied, typically using NbN as the single-photon device material. This NbN material is a cubic δ-NbN structure, which has high intrinsic quantum efficiency and a roughness generally around 2.5 nm. Other single-photon materials, such as WSi and Nb, can also be used. An Al film is then formed on the surface for protection; finally, electrode materials are sputtered.

[0052] This also includes the fabrication of superconducting nanowires: to ensure high quantum efficiency of the SNSPD, the bias current Ib of the nanowire must be very close to its critical current IC (typically Ib > 0.95IC). This places high demands on the thickness and width uniformity of the superconducting nanowire over a large area, because the critical current of the entire superconducting nanowire depends on the region with the smallest cross-sectional area. If, due to some undesirable factors during fabrication, a small portion of the nanowire has a much smaller cross-sectional area than other areas, this will reduce the critical current of the entire nanowire. Consequently, most areas of the nanowire cannot operate with a bias current very close to the local critical current, thus affecting the quantum efficiency of the entire detector. Furthermore, while maintaining a certain critical current density, the nanowire detector needs a suitable duty cycle. Too high or too low a duty cycle will significantly reduce the critical current of the nanowire.

[0053] Testing the performance of SNSPD: After testing the nanowire and obtaining the expected results (superconductivity and high transition temperature), we used a low-temperature testing system to test it. The bias current was selected to provide DC bias to reach 95% of the critical current value. The single-photon response, quantum efficiency, dark number rate, reset time, and time jitter of the nanowire were tested.

[0054] The method of the present invention is as follows:

[0055] 1. A single-photon excitation source with NV color centers is formed by using an electrically driven method;

[0056] 2. This allows single photons to be confined within the diamond waveguide and to have low loss over a wide bandwidth, resulting in a high-fidelity transmission signal;

[0057] 3. Modulate the frequency and phase of the signal using a diamond optical resonator;

[0058] 4. Under low-temperature conditions, a single-photon detector integrated with a diamond waveguide is used to read out a single-photon source at a certain frequency, and the detection efficiency is calculated to form a detection system based on a diamond photonic integrated circuit.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for fabricating a diamond photonic integrated circuit, characterized in that, Includes the following steps: S10, for preparing single-crystal diamond with controllable defects; S20, used to fabricate diamond resonators; S30, fabrication of nanowire single-photon detectors; S40, an integrated fabrication array of superconducting nanowire single-photon detectors; Specifically, the following steps are included: First, ion implantation is performed on the seed crystal substrate; Then, diamond with low defect density is regrowth on the heat-treated single-crystal diamond sheet to achieve the preparation of ultrathin single-crystal diamond and solid color center light source. In addition, a tunable resonator with a diamond H-type structure and a high quality factor is prepared. In S30, a single-photon detector is fabricated on a diamond substrate, and the fabricated single-photon detector is characterized. Finally, a diamond waveguide was fabricated on a single-crystal diamond thin film with a solid color center light source and a resonator structure, and an array of superconducting nanowire single-photon detectors was integrated to form the fabrication of an integral photonic integrated circuit with diamond as the platform material.

2. The method for fabricating a diamond photonic integrated circuit according to claim 1, characterized in that, The preparation of controllable defect single-crystal diamond includes: using a lift-off method, specifically using different implantation conditions to form a damage layer of different depths, evaluating the crystal quality of the formed damage layer, using typical MeV energy for implantation, and evaluating the quality of the diamond epitaxial layer regrowth on the substrate after different lift-off conditions, wherein the different lift-off conditions include ion implantation with different energies and different temperature heat treatment methods.

3. The method for fabricating a diamond photonic integrated circuit according to claim 2, characterized in that, The fabrication of the diamond resonator includes the fabrication of a waveguide-based superconducting nanowire single-photon detector structure using a lift-off method.

4. The method for fabricating a diamond photonic integrated circuit according to claim 2, characterized in that, The fabrication of the diamond resonator includes using a ridge waveguide to limit losses during optical waveguide propagation.

5. The method for fabricating a diamond photonic integrated circuit according to claim 4, characterized in that, In S20, the diamond resonator is an H-type resonator, which consists of two double-clamped cantilever beams of the same length. The two beam structures are linked by a central block to form a structure resembling the letter "H". The central block contains an array of holes to form a two-dimensional photonic crystal. The H-type resonator is evanescently coupled to a curved waveguide that supports TE-like polarization single-mode.

6. The method for fabricating a diamond photonic integrated circuit according to claim 5, characterized in that, The fabrication of the nanowire single-photon detector in S30 includes chemical mechanical polishing of the diamond surface, followed by photolithography using electron beam exposure, with NbN material as the single-photon device material, and then forming an Al film on its surface for protection; finally, electrode material is sputtered.

7. The method for fabricating a diamond photonic integrated circuit according to claim 6, characterized in that, The NbN material has a cubic structure of δ-NbN.

8. The method for fabricating a diamond photonic integrated circuit according to claim 6, characterized in that, In the fabrication of superconducting nanowires, the bias current of the nanowire during operation is close to its critical current, and the duty cycle of the nanowire detector is within a preset range while maintaining a preset critical current density.

9. The method for fabricating a diamond photonic integrated circuit according to claim 6, characterized in that, The test includes evaluating the performance of a superconducting nanowire single-photon detector. First, the nanowire is tested. After it becomes superconducting and the transition temperature increases, a low-temperature test is performed within a preset temperature range. The bias current is selected to provide a DC bias so that it reaches 95% of the critical current value.

10. A method for fabricating a diamond photonic integrated circuit according to claim 9, characterized in that, The testing of the performance of the superconducting nanowire single-photon detector also includes testing the single-photon response, quantum efficiency, dark number rate, reset time, and time jitter of the nanowire.

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