A lithium niobate waveguide photodetector in the visible light band and its fabrication method

Abstract

This application relates to a lithium niobate waveguide photodetector in the visible light band and its fabrication method. The detector includes a lithium niobate double-ridge waveguide, a silicon crystal layer, a P-type doped region, and an N-type doped region. The lithium niobate double-ridge waveguide includes two spaced-apart ridges. The silicon crystal layer is disposed between the two ridges. A P-type doped region is disposed on the lithium niobate double-ridge waveguide and located on one of the ridges away from the silicon crystal layer, in contact with the silicon crystal layer. An N-type doped region is disposed on the lithium niobate double-ridge waveguide and located on the other ridge away from the silicon crystal layer, in contact with the silicon crystal layer. This application provides a new type of photodetector for visible light communication, making lithium niobate waveguide photodetectors possible in visible light communication.

Description

Technical Field

[0001] This application relates to the field of optical communication device technology, and in particular to a lithium niobate waveguide photodetector in the visible light band and its fabrication method. Background Technology

[0002] Over the past few decades, the explosive growth in data exchange driven by the increasing demand for wireless communication from smartphones and tablets, coupled with the rise of the Internet of Things (IoT), has rendered wireless network capacity insufficient to meet the needs. This necessitates the continuous development of the internet and its infrastructure to meet the demands of current and future multimedia applications.

[0003] Over the past decade, wireless communication traffic has grown at a compound annual growth rate (CAGR) of 60%. If this growth rate continues for another 20 years, bandwidth requirements will be 12,000 times higher than current levels, assuming the same spectral efficiency. To address the increasingly severe spectrum shortage in the radio frequency (RF) field, wireless communication technologies utilizing extremely high frequencies have received widespread attention.

[0004] LiFi (Literal-Light Fiber) is one of the most promising solutions. LiFi is a wireless communication technology that utilizes the infrared and visible light spectra for high-speed data communication. This relatively new technology can utilize a broad spectrum approaching 300 THz, far exceeding the current 300 GHz bandwidth available for communication. In terms of speed, using a single light-emitting diode (LED), LiFi can achieve peak data rates exceeding 10 Gbps. Simultaneously, LiFi offers good security, providing secure wireless communication capabilities without electromagnetic interference issues. Because visible light cannot penetrate opaque objects, it can easily block signals, preventing leakage.

[0005] Lithium niobate (LNO) is one of the most suitable material platforms for integrated photonic circuits due to its unique material properties, including high electro-optic coefficient and second-order nonlinear magnetic susceptibility, as well as a wide optical transparency window (350 nm-5 μm). In recent years, breakthroughs in nanofabrication technology and the emergence of lithium niobate-on-insulator (LNOI) thin films have made it possible to create high-performance integrated nanophotonic devices. The fabrication of high-quality wafer-level devices on LNOI is now fully commercialized, opening the door to applications of lithium niobate in integrated photonics, microwave photonics, and other fields.

[0006] In optical communication systems, photodetectors are crucial components. As the signal receiver, their performance directly impacts the overall communication quality. However, there are few reports on photodetectors using lithium niobate waveguides in visible light communication. Summary of the Invention

[0007] This application provides a lithium niobate waveguide photodetector in the visible light band and its fabrication method, which provides a new type of photodetector for visible light communication, making it possible to use lithium niobate waveguide photodetectors in visible light communication.

[0008] In a first aspect, a lithium niobate waveguide photodetector in the visible light band is provided, comprising:

[0009] A lithium niobate double-ridged waveguide comprising two spaced-apart ridges;

[0010] A silicon crystal layer is disposed between the two ridges;

[0011] A P-type doped region is disposed on the lithium niobate double-ridge waveguide and located on one of the ridges away from the silicon crystal layer, and the P-type doped region is in contact with the silicon crystal layer;

[0012] An N-type doped region is disposed on the lithium niobate double-ridge waveguide and located on the other ridge away from the silicon crystal layer. The N-type doped region is in contact with the silicon crystal layer.

[0013] In some embodiments, the lithium niobate double-ridge waveguide further includes a main body portion, with the ridge portion disposed on the main body portion.

[0014] In some embodiments, a coupling segment for coupling incident light is formed on the main body.

[0015] In some embodiments, a portion of the P-type doped region is located on the ridge and extends toward the silicon crystal layer until it contacts the silicon crystal layer;

[0016] And / or, a portion of the silicon crystal layer is located on the ridge and extends toward the P-type doped region until it contacts the P-type doped region;

[0017] And / or, a portion of the N-type doped region is located on the ridge and extends toward the silicon crystal layer until it contacts the silicon crystal layer;

[0018] And / or, a portion of the silicon crystal layer is located on the ridge and extends toward the N-type doped region until it contacts the N-type doped region.

[0019] In some embodiments, the P-type doped region includes a connected heavily doped P-type region and a lightly doped P-type region, and the lightly doped P-type region is located between the heavily doped P-type region and the ridge.

[0020] In some embodiments, the N-type doped region includes an interconnected heavily doped N-type region and a lightly doped N-type region, and the lightly doped N-type region is located between the heavily doped N-type region and the ridge.

[0021] In some embodiments, metal electrodes are provided on both the P-type doped region and the N-type doped region;

[0022] And / or, the P-type doped region is doped with phosphorus or boron, and the N-type doped region is doped with antimony or indium.

[0023] In some embodiments, the lithium niobate double-ridged waveguide is disposed on a silicon dioxide layer, which is disposed on a substrate.

[0024] In some embodiments, the substrate is made of Si or lithium niobate.

[0025] Secondly, a method for fabricating a lithium niobate waveguide photodetector in the visible light band as described above is provided, comprising the following steps:

[0026] Fabrication of lithium niobate double-ridged waveguide;

[0027] Silicon crystals are deposited on the lithium niobate double-ridged waveguide;

[0028] Doping is performed on both sides of the silicon crystal to form a silicon crystal layer in the middle, and P-type doped regions and N-type doped regions on both sides.

[0029] Metal electrodes are fabricated on the P-type doped region and the N-type doped region.

[0030] The beneficial effects of the technical solution provided in this application include:

[0031] This application provides a lithium niobate waveguide photodetector for the visible light band and its fabrication method. Light is coupled into a lithium niobate double-ridged waveguide. Because the refractive index of silicon is greater than that of lithium niobate, the optical signal is ultimately refracted from the lithium niobate double-ridged waveguide into the deposited silicon crystal layer. This reduces the energy density of the optical field in the lithium niobate double-ridged waveguide while increasing the interaction between the optical field in the lithium niobate double-ridged waveguide and the silicon waveguide. Since silicon has a bandgap of 1.12 eV, it exhibits significant absorption in the long-wave infrared band. Therefore, in the visible light wireless communication band, most of the incident light is absorbed by the silicon crystal layer, forming a large number of electron-hole pairs. Thus, the lithium niobate double-ridged waveguide, silicon crystal layer, P-type doped region, and N-type doped region form a photodetector structure for the visible light band, providing a new type of photodetector for visible light communication and making lithium niobate waveguide photodetectors possible in visible light communication.

[0032] This application uses a ridge waveguide structure, which can effectively confine the optical field, maintain the original photoelectric coefficient, and has excellent anti-photorefractive properties. It can simultaneously transmit TE mode and TM mode in the ridge waveguide. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 A cross-sectional view of a lithium niobate waveguide photodetector in the visible light band provided in an embodiment of this application;

[0035] Figure 2 A top view of a lithium niobate waveguide photodetector in the visible light band provided in an embodiment of this application;

[0036] Figure 3 The optical waveguide distribution (TE mode field) provided in the embodiments of this application;

[0037] Figure 4 The optical waveguide distribution (TM mode field) provided for the embodiments of this application.

[0038] In the figure: 1. Lithium niobate double-ridge waveguide; 10. Ridge; 11. Main body; 12. Coupling section; 2. Silicon crystal layer; 3. P-type doped region; 30. P-type heavily doped region; 31. P-type lightly doped region; 4. N-type doped region; 40. N-type heavily doped region; 41. N-type lightly doped region; 5. Metal electrode; 6. Silicon dioxide layer; 7. Substrate. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] See Figure 1 and Figure 2As shown in the illustration, this application provides a lithium niobate waveguide photodetector in the visible light band, comprising a lithium niobate double-ridge waveguide 1, a silicon crystal layer 2, a P-type doped region 3, and an N-type doped region 4. The lithium niobate double-ridge waveguide 1 includes two spaced-apart ridges 10, forming a groove between the two ridges 10. The silicon crystal layer 2 is disposed between the two ridges 10 and located within this groove. The P-type doped region 3 is disposed on the lithium niobate double-ridge waveguide 1, located on the side of one ridge 10 away from the silicon crystal layer 2, and is in contact with the silicon crystal layer 2. The N-type doped region 4 is disposed on the lithium niobate double-ridge waveguide 1, located on the side of the other ridge 10 away from the silicon crystal layer 2, and is in contact with the silicon crystal layer 2. The P-region, N-region, and the intermediate intrinsic semiconductor silicon crystal layer form a PIN photodetector structure.

[0041] The photodetector provided in this application couples light into a lithium niobate double-ridged waveguide. Since the refractive index of silicon is greater than that of lithium niobate, the optical signal is ultimately refracted from the lithium niobate double-ridged waveguide into the deposited silicon crystal layer. This reduces the energy density of the optical field in the lithium niobate double-ridged waveguide while increasing the interaction between the optical fields in the lithium niobate double-ridged waveguide and the silicon waveguide. Because silicon has a bandgap of 1.12 eV, it exhibits significant absorption in the long-wave infrared band. Therefore, in the visible light wireless communication band, most of the incident light is absorbed by the silicon crystal layer, forming a large number of electron-hole pairs. Thus, the lithium niobate double-ridged waveguide, silicon crystal layer, P-type doped region, and N-type doped region form a photodetector structure for the visible light band.

[0042] This application utilizes a ridge waveguide structure, which effectively confines the optical field, maintains the original photoelectric coefficient, exhibits superior resistance to photorefractive properties, and can simultaneously transmit TE and TM modes within the ridge waveguide. Figure 3 and Figure 4 As shown.

[0043] The dimensions of the lithium niobate double-ridge waveguide 1 can be determined according to actual needs. For example, as an example, the height is 300-600nm (including the ridge), the length is 10-100um, and the width is 800nm-2um, which can ensure good single-mode transmission conditions and improve absorption efficiency.

[0044] The size of silicon crystal layer 2 can be determined according to actual needs. For example, as an example, it can be 10-100 μm long and 100-400 nm wide, which can achieve a good balance between bandwidth and absorption efficiency.

[0045] See Figure 1 As shown, in some preferred embodiments, the lithium niobate double-ridge waveguide 1 further includes a main body 11, with ridges 10 disposed on the main body 11, and P-type doped regions and N-type doped regions also deposited on the main body 11.

[0046] See Figure 1As shown, in some preferred embodiments, a coupling segment 12 for coupling incident light is formed on the main body 11 to facilitate coupling of the incident light.

[0047] See Figure 1 As shown, in some preferred embodiments, a portion of the P-type doped region 3 is located on the ridge 10 and extends toward the silicon crystal layer 2 until it contacts the silicon crystal layer 2.

[0048] A portion of the silicon crystal layer 2 is located on the ridge 10 and extends toward the P-type doped region 3 until it contacts the P-type doped region 3.

[0049] A portion of the N-type doped region 4 is located on the ridge 10 and extends toward the silicon crystal layer 2 until it contacts the silicon crystal layer 2.

[0050] A portion of the silicon crystal layer 2 is located on the ridge 10 and extends toward the N-type doped region 4 until it contacts the N-type doped region 4.

[0051] In fact, during fabrication, the silicon crystal layer 2, the N-type doped region 4, and the P-type doped region 3 are all formed from silicon crystals deposited on the lithium niobate double-ridged waveguide 1.

[0052] Specifically, doping is performed on both sides of the silicon crystal to form an N-type doped region 4 and a P-type doped region 3, while the remaining part of the silicon crystal forms a silicon crystal layer 2.

[0053] See Figure 1 As shown, in some preferred embodiments, the P-type doped region 3 includes a P-type heavily doped region 30 and a P-type lightly doped region 31 connected to each other, and the P-type lightly doped region 31 is located between the P-type heavily doped region 30 and the ridge 10.

[0054] See Figure 1 As shown, in some preferred embodiments, the N-type doped region 4 includes an interconnected N-type heavily doped region 40 and an N-type lightly doped region 41, with the N-type lightly doped region 41 located between the N-type heavily doped region 40 and the ridge 10.

[0055] Light doping is used to improve capacitance, increase breakdown voltage, and reduce metal absorption losses. Heavy doping is used to improve conductivity and form good ohmic contacts.

[0056] The ranges for light and heavy doping can be determined based on actual needs. For example, heavy doping might be around 10. 20 / cm 3 Lightly doped at approximately 10 18 / cm 3 .

[0057] See Figure 1 As shown, in some preferred embodiments, metal electrodes 5 are provided on both the P-type doped region 3 and the N-type doped region 4.

[0058] See Figure 1 As shown, in some preferred embodiments, the P-type doped region 3 is doped with phosphorus or boron, and the N-type doped region 4 is doped with antimony or indium.

[0059] See Figure 1 As shown, in some preferred embodiments, the lithium niobate double-ridged waveguide 1 is disposed on the silicon dioxide layer 6, which is disposed on the substrate 7. The substrate 7 is made of Si or lithium niobate.

[0060] This application also provides a method for fabricating a lithium niobate waveguide photodetector in the visible light band, which includes the following steps:

[0061] 101: Fabrication of lithium niobate double-ridge waveguide using lithium niobate thin-film chip fabrication process 1.

[0062] 102: Silicon crystals are deposited on lithium niobate double-ridged waveguide 1 using vapor phase epitaxy (VPE) or chemical vapor deposition (CVD) techniques.

[0063] 103: Doping is performed on both sides of the silicon crystal to form a silicon crystal layer 2 in the middle, and a P-type doped region 3 and an N-type doped region 4 on both sides.

[0064] 104: Fabricate metal electrodes 5 on P-type doped region 3 and N-type doped region 4.

[0065] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0066] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0067] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A lithium niobate waveguide photodetector in the visible light band, characterized in that, It includes: A lithium niobate double-ridged waveguide (1) comprising two spaced-apart ridges (10). A silicon crystal layer (2) is disposed between the two ridges (10); A P-type doped region (3) is disposed on the lithium niobate double-ridge waveguide (1) and located on one of the ridges (10) away from the silicon crystal layer (2). The P-type doped region (3) is in contact with the silicon crystal layer (2). An N-type doped region (4) is disposed on the lithium niobate double-ridge waveguide (1) and located on the other ridge (10) away from the silicon crystal layer (2). The N-type doped region (4) is in contact with the silicon crystal layer (2). The silicon crystal layer (2), the N-type doped region (4) and the P-type doped region (3) are all formed by silicon crystal deposited on the lithium niobate double-ridge waveguide (1); The P-type doped region (3) includes a P-type heavily doped region (30) and a P-type lightly doped region (31) connected to each other, and the P-type lightly doped region (31) is located between the P-type heavily doped region (30) and the ridge (10); The N-type doped region (4) includes an N-type heavily doped region (40) and an N-type lightly doped region (41) connected to each other, and the N-type lightly doped region (41) is located between the N-type heavily doped region (40) and the ridge (10); A portion of the P-type doped region (3) is located on the ridge (10) and extends toward the silicon crystal layer (2) until it contacts the silicon crystal layer (2); And / or, a portion of the silicon crystal layer (2) is located on the ridge (10) and extends toward the P-type doped region (3) until it contacts the P-type doped region (3); And / or, a portion of the N-type doped region (4) is located on the ridge (10) and extends toward the silicon crystal layer (2) until it contacts the silicon crystal layer (2); And / or, a portion of the silicon crystal layer (2) is located on the ridge (10) and extends toward the N-type doped region (4) until it contacts the N-type doped region (4).

2. The lithium niobate waveguide photodetector in the visible light band as described in claim 1, characterized in that: The lithium niobate double-ridge waveguide (1) also includes a main body (11), with the ridge (10) disposed on the main body (11).

3. The lithium niobate waveguide photodetector in the visible light band as described in claim 2, characterized in that: The main body (11) has a coupling segment (12) for coupling incident light.

4. The lithium niobate waveguide photodetector in the visible light band as described in claim 1, characterized in that: Metal electrodes (5) are provided on both the P-type doped region (3) and the N-type doped region (4); And / or, the P-type doped region (3) is doped with phosphorus or boron, and the N-type doped region (4) is doped with antimony or indium.

5. The lithium niobate waveguide photodetector in the visible light band as described in claim 1, characterized in that: The lithium niobate double-ridge waveguide (1) is disposed on the silicon dioxide layer (6), and the silicon dioxide layer (6) is disposed on the substrate (7).

6. The lithium niobate waveguide photodetector in the visible light band as described in claim 5, characterized in that: The substrate (7) is made of Si or lithium niobate.

7. A method for fabricating a lithium niobate waveguide photodetector in the visible light band as described in any one of claims 1 to 6, characterized in that, It includes the following steps: Fabrication of lithium niobate double-ridged waveguide (1); Silicon crystals are deposited on the lithium niobate double-ridged waveguide (1); Doping is performed on both sides of the silicon crystal to form a silicon crystal layer (2) in the middle and P-type doped regions (3) and N-type doped regions (4) on both sides. Metal electrodes (5) are fabricated on the P-type doped region (3) and the N-type doped region (4).

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