A narrowband near-infrared thermionic photodetector, its fabrication method and application

Abstract

This invention belongs to the field of optoelectronics technology, specifically relating to a narrowband near-infrared thermionic photodetector, its fabrication method, and its applications. A top-layer metal grating absorbs near-infrared light, generating thermionic electrons that are injected into an ultrathin silicon film, where they are collected by the bottom electrode to form a photocurrent. The top-layer metal grating forms a Schottky contact with the silicon thin film, enabling near-infrared light detection below the silicon energy bandgap. The small thickness of the metal grating increases photoemission within the metal, providing more opportunities for thermionic emission over the Schottky barrier, further improving the photodetector efficiency. Simultaneously, by adjusting the width of the metal grating, the resonant wavelength of the detector can be changed, achieving a wavelength-tunable near-infrared photodetector. Due to the thinness of silicon, applying a small bias voltage can induce a strong electric field in the silicon film, triggering an avalanche multiplication effect. This invention broadens the operating wavelength range of traditional silicon-based photodetectors and achieves tunable peak responsivity, showing great promise for applications in silicon-based optoelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic technology, specifically relating to a narrowband near-infrared thermionic photodetector, its fabrication method, and its application. Background Technology

[0002] Silicon photonics and plasma science have attracted academic attention. Among them, photodetectors based on Schottky barriers are competitive with more efficient direct bandgap semiconductor detectors (which are more difficult to integrate) due to their fast response to photons, ease of manufacturing, integration with silicon-based electronic devices, integration with sensors and microelectromechanical systems, and lower cost. They have great potential in fields such as data communication and power monitoring.

[0003] A Schottky barrier photodetector is a device used to detect light radiation with energy below the semiconductor bandgap. Its detection mechanism involves photoemission within a thin metal film, converting photons with energy below the semiconductor bandgap into a photocurrent. There are three formation mechanisms for the Schottky barrier: the first is a thick metal layer on a semiconductor substrate, forming a single Schottky barrier; the second is a thin metal film on a semiconductor substrate, also forming a single Schottky barrier; and the third is a combination of a semiconductor substrate and a thin metal film embedded within the semiconductor, forming two Schottky barriers (one along each metal-semiconductor interface). The formation of a Schottky barrier allows photons with energy below the semiconductor bandgap to be emitted through the barrier and absorbed by the semiconductor to form a photocurrent, indicating that the photodetection range can be extended to the lower-energy near-infrared range. Compared to a thick metal layer, a thin metal film can increase photoemission within the metal. This enhancement occurs through multiple hot electron reflections at the internal metal-semiconductor interface, providing more opportunities for hot electron emission at the Schottky barrier. Consequently, more hot electrons are collected by the semiconductor in the form of photocurrent, enhancing the photoelectric response. (IEEE JOURNALOF QUANTUM ELECTRONICSOL.46, NO.5, MAY 2010) Several experimental inventions have been made regarding Schottky barrier photodetectors. For example, a high-performance self-driven photodetector based on a molybdenum disulfide Schottky barrier diode utilizes a two-dimensional material and a metal-deposited electrode to form a Schottky barrier, which can detect wavelengths from 440 nm to 940 nm with a responsivity on the order of ten to the power of three. However, the detection capability in the near-infrared band beyond 940 nm is lacking. Furthermore, the preparation process of the two-dimensional molybdenum disulfide material requires methods such as mechanical exfoliation, making the preparation process difficult. (Adv. Optical Mater. 2023, 2301900) For example, the gold-silver nanoalloy-type silicon plasmonic Schottky device has high responsivity at wavelengths of 1310 nm and 1550 nm, reaching 7.3 mA / W and 1.9 mA / W, respectively, but its responsivity is still relatively low (ACS Appl. Mater. Interfaces 2024, 16, 8984-8992). Summary of the Invention

[0004] This invention utilizes the phenomenon of metal thin films enhancing the thermionic emission of Schottky barriers to provide a narrowband near-infrared thermionic photodetector based on a nanoscale silicon thin film and metal composite structure, thereby improving photoelectric detection responsivity.

[0005] To address the aforementioned technical problems, this application provides the following technical solution:

[0006] The present invention provides a narrowband near-infrared thermionic photodetector, comprising an aluminum thin film, a silicon thin film and a metal grating arranged sequentially; the metal grating is made of a material selected from metal nitrides, metal oxides, a single metal or a multi-metal alloy, and the metal grating and the silicon thin film form a Schottky barrier structure.

[0007] Preferably, the metal in the metal grating material is selected from one or more of gold, silver, copper, aluminum, chromium, and titanium.

[0008] Preferably, the thickness of the metal grating is 5-100 nm.

[0009] Preferably, the silicon thin film is a lightly doped N-type silicon thin film or a P-type silicon thin film.

[0010] Preferably, the resistivity of the silicon thin film is between 1 and 10 Ω·cm.

[0011] Preferably, the thickness of the silicon thin film is 10-500 nm.

[0012] Furthermore, the thickness of the silicon thin film is 60 nm.

[0013] Preferably, the thickness of the aluminum film is 10-500 nm.

[0014] Preferably, the responsivity in the 1200nm-2000nm band can reach 6.19mA / W-19.03mA / W.

[0015] Preferably, the responsivity at a wavelength of 1372nm is 19.03mA / W.

[0016] Simultaneously, adjusting the width of the metal grating allows for adjustable peak responsivity. Applying a small bias voltage induces a strong electric field in the silicon thin film, triggering an avalanche multiplication effect, further increasing the device responsivity by more than three orders of magnitude, reaching the same level as commercial infrared photodetectors.

[0017] The present invention also provides a method for fabricating the above-mentioned narrowband near-infrared thermionic photodetector, comprising the following steps:

[0018] S1: The silicon (SOI) substrate on an insulating substrate is placed in hydrofluoric acid to dissolve the silicon dioxide interlayer, thus obtaining a silicon thin film;

[0019] S2: After transferring the silicon thin film onto a silicon dioxide substrate coated with photoresist, an aluminum thin film is deposited on the side of the silicon thin film away from the silicon dioxide substrate to obtain composite film A;

[0020] S3: After dissolving the photoresist in acetone, the composite film A is transferred to a silicon dioxide substrate coated with a gold layer, so that the aluminum film and the gold layer are connected to obtain the composite film B.

[0021] S4: Coat polymethyl methacrylate (PMMA) onto the silicon film of the composite film B, and expose, develop, and fix the polymethyl methacrylate using electron beam lithography (EBL) to obtain a composite film C containing a PMMA nanograting pattern.

[0022] S5: A metal grating is formed by depositing a metal material into the PMMA nanograting pattern of the composite film C to obtain the composite film D; the metal material is selected from metal nitrides, metal oxides, single metals or multiple metal alloys.

[0023] S6: The PMMA nanograting pattern in the composite film D is stripped to obtain the narrowband near-infrared thermal electron photodetector.

[0024] The present invention also provides the application of the above-mentioned narrowband near-infrared thermionic photodetector in optical communication and near-infrared imaging. By applying a small bias voltage of 2-3V to the narrowband near-infrared thermionic photodetector, the responsivity of the device is further improved by more than 3 orders of magnitude.

[0025] The working principle and effects of the above scheme are as follows: A photodetector utilizing the Schottky barrier property is a device used to detect light radiation with energy below the semiconductor bandgap. Its detection mechanism involves electrons inside a thin metal film absorbing photons and generating hot electrons. Through photoelectric emission within the thin metal film, photons with energy below the semiconductor bandgap are converted into photocurrent. The top-layer metal grating absorbs near-infrared light, generating hot electrons, and forms a Schottky contact with the silicon thin film. Due to the small thickness of the metal grating, multiple hot electron reflections occur at its interface with silicon, increasing the probability of hot electron emission at the Schottky junction and further improving the photodetector efficiency. Adjusting the width of the metal grating changes the detector's response wavelength, realizing a wavelength-tunable near-infrared photodetector.

[0026] The technical solution of the present invention has the following advantages compared with the prior art:

[0027] To improve the responsivity of photodetectors, this invention provides a narrowband near-infrared thermionic photodetector based on a nanoscale silicon thin film and metal composite structure, achieving a responsivity of 6.19 mA / W-19.03 mA / W in the 1200 nm-2000 nm wavelength range. Furthermore, by adjusting the width of the metal grating, the resonant wavelength of the detector can be changed, realizing a wavelength-tunable near-infrared photodetector. In addition, due to the small thickness of the silicon thin film, applying a small bias voltage can induce a strong electric field within the silicon film, triggering an avalanche multiplication effect, further improving the device responsivity by more than three orders of magnitude, reaching the same level as commercial infrared photodetectors. Attached Figure Description

[0028] Figure 1A front view of a narrowband near-infrared thermionic photodetector structure based on a metal grating.

[0029] Figure 2 This is a comparison of the absorption rates of transverse magnetic waves incident on metal gratings in a narrowband near-infrared thermionic photodetector based on a metal grating structure, with different silicon thin film thicknesses.

[0030] Figure 3 This is a comparison of the absorption rates of transverse magnetic waves incident on metal gratings in a narrowband near-infrared thermionic photodetector based on a metal grating structure under different grating periods.

[0031] Figure 4 This is a comparison of the optical responsivity of a narrowband near-infrared thermionic photodetector based on a metal grating structure under different grating widths.

[0032] Figure 5 This is a flowchart illustrating the experimental fabrication process of a narrowband near-infrared thermionic photodetector based on a metal grating structure.

[0033] Explanation of reference numerals in the attached figures: 1-Silicon thin film, 2-Silicon dioxide intermediate layer, 3-Aluminum thin film, 4-Photoresist, 5-Silicon dioxide substrate, 6-Gold layer, 7-PMMA nanograting pattern, 8-Metal grating. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] Example 1

[0036] like Figure 1 As shown, a narrowband near-infrared thermionic photodetector based on a metal grating structure includes a metal grating 8, a silicon thin film 1, and an aluminum thin film 3. The silicon thin film 1 is disposed on the aluminum thin film 3; the metal grating 8 is disposed on the silicon thin film 1, and the metal grating 8 and the silicon thin film 1 form a Schottky barrier structure.

[0037] The metal grating 8 is made of gold, has a thickness of 15nm, a grating period of 600nm, and a grating width of 400nm.

[0038] The silicon thin film is a lightly doped N-type silicon thin film with a thickness of 60 nm and a resistivity of 1-10 Ω·cm.

[0039] The experimental fabrication process of the narrowband near-infrared thermionic photodetector based on a metal grating structure in this embodiment is as follows: Figure 5As shown. First, the silicon (SOI) substrate on the insulating substrate is immersed in hydrofluoric acid (HF) to dissolve the intermediate silicon dioxide layer (step 1); then, the silicon film floating in the hydrofluoric acid (HF) solution is transferred to the silicon dioxide substrate that has been spin-coated with photoresist (step 2); then, a 100nm thick aluminum film is deposited on the silicon film of this structure (step 3); then, the above structure is immersed in acetone (AC) solution to dissolve the photoresist (step 4), and the upper silicon film and aluminum film structure are transferred to the silicon dioxide substrate with a gold film, and the aluminum film and gold film are connected (step 5).

[0040] A 800 nm thick polymethyl methacrylate (PMMA) layer is spin-coated onto a silicon thin film (step 6); then a grating structure with a period of 600 nm and a width of 400 nm is exposed on the PMMA using electron beam lithography (EBL), and a nano-grating pattern is obtained by development and fixing (step 7, the underlying gold layer and substrate are not shown); then a 15 nm gold thin film is deposited on the surface of the structure (step 8, the underlying gold layer and substrate are not shown); then the PMMA is removed by a liftoff process to obtain a thermionic photodetector (step 9, the underlying gold layer and substrate are not shown).

[0041] Example 2

[0042] A narrowband near-infrared thermionic photodetector based on a metal grating structure includes a metal grating 8, a silicon thin film 1, and an aluminum thin film 3. The silicon thin film 1 is disposed on the aluminum thin film 3; the metal grating 8 is disposed on the silicon thin film 1, and the metal grating 8 and the silicon thin film 1 form a Schottky barrier structure.

[0043] The metal grating 8 is made of gold and has a thickness of 15 nm.

[0044] The silicon thin film is a lightly doped N-type silicon thin film with a thickness of 60 nm and a resistivity of 1-10 Ω·cm.

[0045] The preparation method is as described in Example 1.

[0046] Example 3

[0047] A narrowband near-infrared thermionic photodetector based on a metal grating structure includes a metal grating 8, a silicon thin film 1, and an aluminum thin film 3. The silicon thin film 1 is disposed on the aluminum thin film 3; the metal grating 8 is disposed on the silicon thin film 1, and the metal grating 8 and the silicon thin film 1 form a Schottky barrier structure.

[0048] The metal grating 8 is made of aluminum nitride, with a thickness of 5nm, a grating period of 600nm, and a grating width of 400nm.

[0049] The silicon thin film is a lightly doped N-type silicon thin film with a thickness of 10 nm and a resistivity of 1-10 Ω·cm.

[0050] The preparation method is the same as in Example 1, except that the gold film is replaced with an aluminum nitride film with a thickness of 5 nm. The aluminum film has a thickness of 50 nm.

[0051] Example 4

[0052] A narrowband near-infrared thermionic photodetector based on a metal grating structure includes a metal grating 8, a silicon thin film 1, and an aluminum thin film 3. The silicon thin film 1 is disposed on the aluminum thin film 3; the metal grating 8 is disposed on the silicon thin film 1, and the metal grating 8 and the silicon thin film 1 form a Schottky barrier structure.

[0053] The metal grating is made of copper oxide. The thickness of the metal grating 8 is 100nm, the grating period is 600nm, and the grating width is 400nm.

[0054] The silicon thin film is a lightly doped P-type silicon thin film with a thickness of 500 nm and a resistivity of 1-10 Ω·cm.

[0055] The preparation method is the same as in Example 1, except that the gold film is replaced with a copper oxide film with a thickness of 100 nm; the aluminum film has a thickness of 100 nm.

[0056] Example 5

[0057] A narrowband near-infrared thermionic photodetector based on a metal grating structure includes a metal grating 8, a silicon thin film 1, and an aluminum thin film 3. The silicon thin film 1 is disposed on the aluminum thin film 3; the metal grating 8 is disposed on the silicon thin film 1, and the metal grating 8 and the silicon thin film 1 form a Schottky barrier structure.

[0058] The metal grating 8 is made of silver, with a thickness of 15nm, a grating period of 600nm, and a grating width of 400nm.

[0059] The silicon thin film is a lightly doped N-type silicon thin film with a thickness of 60 nm and a resistivity of 1-10 Ω·cm.

[0060] The preparation method is the same as in Example 1, except that the gold film is replaced with a silver film with a thickness of 15 nm, and the aluminum film has a thickness of 100 nm.

[0061] Example 6

[0062] A narrowband near-infrared thermionic photodetector based on a metal grating structure includes a metal grating 8, a silicon thin film 1, and an aluminum thin film 3. The silicon thin film 1 is disposed on the aluminum thin film 3; the metal grating 8 is disposed on the silicon thin film 1, and the metal grating 8 and the silicon thin film 1 form a Schottky barrier structure.

[0063] The metal grating 8 is made of chromium-titanium alloy, with a thickness of 15nm, a grating period of 600nm, and a grating width of 400nm.

[0064] The silicon thin film is a lightly doped N-type silicon thin film with a thickness of 60 nm and a resistivity of 1-10 Ω·cm.

[0065] The preparation method is the same as in Example 1, except that the gold film is replaced with a chromium-titanium alloy film with a thickness of 15 nm. The aluminum film has a thickness of 100 nm.

[0066] Effect Evaluation 1

[0067] Figure 2 As shown, the absorptivity of a narrowband near-infrared thermionic photodetector based on a metal grating structure was compared under different silicon thin film thicknesses. When the silicon thin film thickness increased from 40 nm to 70 nm, the absorptivity of the metal grating increased from 0.39 to 0.53 and then decreased to 0.51. Excessive increase in silicon thin film thickness led to a decrease in the absorptivity of the metal grating.

[0068] Figure 3 As shown, the absorptivity of a narrowband near-infrared thermionic photodetector based on a metal grating structure was compared under different grating periods. With a fixed grating width of 400 nm, changing the grating period had no effect on the modulation of the resonant wavelength, but it did affect the absorptivity of the metal grating. When the grating period increased from 600 nm to 1000 nm, the absorptivity of the metal grating decreased from 0.53 to 0.43.

[0069] Figure 4 As shown, the optical responsivity of a narrowband near-infrared thermionic photodetector based on a metal grating structure was compared under different grating widths. With a fixed period of 600 nm, changing the grating width affected the modulation of the resonant wavelength. As the grating width changed from 350 nm to 500 nm, the resonant wavelength redshifted from 1372 nm to 1868 nm. At a grating width of 350 nm, the responsivity reached 19 mA / W, nearly 1000 times higher than other silicon-based near-infrared photodetectors.

[0070] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. The application of a narrowband near-infrared thermionic photodetector in optical communication and near-infrared imaging, characterized in that, Applying a small bias voltage of 2-3V to the narrowband near-infrared thermionic photodetector further improves the device responsivity by more than 3 orders of magnitude; the narrowband near-infrared thermionic photodetector includes an aluminum thin film (3), a silicon thin film (1) and a metal grating (8) arranged sequentially; the material of the metal grating (8) is selected from metal nitrides, metal oxides, single metals or multiple metal alloys, and the metal grating (8) and the silicon thin film (1) form a Schottky barrier structure; the silicon thin film (1) is a lightly doped N-type silicon thin film with a resistivity of 0.1-10 Ω·cm and a thickness of 10-60nm; the narrowband near-infrared thermionic photodetector has a responsivity of 6.19mA / W-19.03mA / W in the 1200nm-2000nm band; and a responsivity of 19.03mA / W at a wavelength of 1372nm; the thickness of the metal grating (8) is 5-100nm.

2. The application of the narrowband near-infrared thermionic photodetector according to claim 1 in optical communication and near-infrared imaging, characterized in that, The metal in the material of the metal grating (8) is selected from one or more of gold, silver, copper, aluminum, chromium and titanium.

3. The application of the narrowband near-infrared thermionic photodetector according to claim 1 in optical communication and near-infrared imaging, characterized in that, The thickness of the aluminum film (3) is 10-500 nm.

4. The application of the narrowband near-infrared thermionic photodetector according to claim 1 in optical communication and near-infrared imaging, characterized in that, The fabrication method of the narrowband near-infrared thermionic photodetector includes the following steps: S1: Place the silicon substrate on the insulating substrate in hydrofluoric acid to dissolve the silicon dioxide interlayer (2) to obtain a silicon thin film (1). S2: After transferring the silicon thin film (1) onto a silicon dioxide substrate (5) coated with photoresist (4), an aluminum thin film (3) is deposited on the side of the silicon thin film (1) away from the silicon dioxide substrate to obtain composite film A; S3: After dissolving the photoresist (4) in acetone, the composite film A is transferred to a silicon dioxide substrate coated with a gold layer (6) to connect the aluminum film (3) with the gold layer (6) to obtain the composite film B. S4: Coat polymethyl methacrylate on the silicon thin film (1) of the composite film B, expose the polymethyl methacrylate by electron beam lithography, develop and fix it to obtain a composite film C containing PMMA nanograting pattern (7). S5: A metal grating (8) is formed by depositing a metal material in the PMMA nanograting pattern (7) of the composite film C to obtain the composite film D; the metal material is selected from metal nitrides, metal oxides, single metals or multiple metal alloys; S6: Peel off the PMMA nanograting pattern (7) in the composite film D to obtain the narrowband near-infrared thermal electron photodetector.

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