Carbon nanotube avalanche photodetector and manufacturing method thereof

Abstract

The invention provides a carbon nano tube avalanche photodetector which is provided with a substrate, a carbon nano tube channel layer is arranged on the substrate, and an n-type contact electrode and a p-type contact electrode are arranged at the two ends of the carbon nano tube channel layer respectively. A first laminated layer of yttrium oxide and hafnium oxide covers the n-type contact electrode and the adjacent carbon nanotube channel extension region; a second laminated layer of yttrium oxide and aluminum oxide covers the part, located on the n-type contact electrode and the adjacent carbon nano tube channel extension region, of the first laminated layer, and the first laminated layer and the second laminated layer jointly form n-type doping on the carbon nano tube adjacent to the n-type contact electrode; and a molybdenum oxide layer covers the p-type contact electrode and the adjacent carbon nanotube channel extension region so as to form p-type doping. The detector is based on an asymmetric electrode and a multilayer electrostatic doping technology, a high-quality p-i-n junction is constructed in a carbon nanotube channel, and the carbon nanotube avalanche photodetector with high performance and low dark current can be obtained.

Description

Technical Field

[0001] This invention relates to a photodetector, and more particularly to a carbon nanotube avalanche photodetector and its fabrication method. Background Technology

[0002] As the application scenarios of infrared detection technology continue to expand in military, communications, medical, and industrial fields, the market has increasingly urgent needs for high-sensitivity detectors capable of detecting faint targets. Against this backdrop, avalanche photodetectors (APDs), with their built-in avalanche gain mechanism, can effectively amplify weak light signals using the impact ionization effect, thereby achieving high-sensitivity and fast-response detection. This gives them unique application advantages in long-distance low-light detection and high-speed optical communication.

[0003] Meanwhile, with the rapid development of information technologies such as 5G, artificial intelligence (AI), and the Internet of Things (IoT), data traffic in global communication networks is experiencing explosive growth. The currently commercially available 1.3-1.6μm optical communication band may face bottlenecks due to insufficient channel capacity in the future. Therefore, developing the 2μm band (1.8-2.1μm) as a new communication window has become a hot research topic in the industry. Furthermore, in applications such as LiDAR (Light Detection and Ranging) and night vision imaging, the 2μm band, being within the eye-safe wavelength range, effectively avoids the risk of eye damage from high-power lasers while achieving longer detection distances, and is considered an ideal choice for next-generation detection and ranging systems.

[0004] However, existing technologies still face numerous challenges in realizing efficient and practical 2μm avalanche photodetectors. First, the impact ionization process relied upon by traditional avalanche photodetectors has inherent randomness. While amplifying the photocurrent, this also introduces significant shot noise, i.e., excessive noise, thus degrading the signal-to-noise ratio and limiting its ability to detect extremely weak signals. Second, traditional commercial photodetectors used in the mid-wavelength infrared (MWIR) band, such as mercury cadmium telluride (HgCdTe) detectors or indium arsenide / indium antimonide (InAs / InAsSb) superlattice detectors, have high intrinsic carrier concentrations, resulting in extremely high dark currents at room temperature. To suppress dark current noise, these detectors typically must operate in cryogenic environments, which undoubtedly increases the system's size, power consumption, and cost, limiting their application in portable and low-cost scenarios.

[0005] Traditional avalanche photodetectors based on bulk semiconductor materials also suffer from inherent performance bottlenecks and integration difficulties. On the one hand, the strong electron-phonon interactions in bulk materials dominate carrier transport, requiring a relatively high external bias voltage (typically tens of volts or even higher) to drive effective impact ionization and achieve ideal avalanche gain. This high operating voltage not only increases the complexity of the driving circuit but also hinders the development of monolithic opto-electronic integrated circuits (OEICs). On the other hand, III-V semiconductor materials, such as gallium arsenide (GaAs), suffer from severe lattice mismatch with the current mainstream silicon-based complementary metal-oxide-semiconductor (CMOS) process platform, making monolithic integration difficult through heteroepitaxial growth and other methods. This significantly impedes the low-cost, large-scale integration of high-performance infrared detectors and silicon-based readout circuits.

[0006] To overcome the aforementioned problems, researchers have recently turned their attention to novel low-dimensional materials such as graphene, transition metal sulfides (TMDCs), indium selenide (InSe), and black phosphorus (BP). While avalanche photodetectors based on these materials have achieved high gain levels at relatively low operating voltages to some extent, they generally face key challenges in practical applications, including limited response speed, unstable material chemistry, and difficulty in achieving large-area uniform wafer-level fabrication. Therefore, developing a novel high-performance 2 μm band avalanche photodetector that can operate at room temperature, has low operating voltage and low noise characteristics, and is compatible with CMOS processes is a pressing technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0007] The present invention aims to provide a carbon nanotube avalanche photodetector to overcome the shortcomings of the prior art. The technical problem to be solved by the present invention is achieved through the following technical solution.

[0008] This invention proposes a carbon nanotube avalanche photodetector, which has a substrate, a carbon nanotube channel layer on the substrate, an n-type contact electrode and a p-type contact electrode at both ends of the carbon nanotube channel layer, and the n-type contact electrode and the p-type contact electrode are in full contact with the carbon nanotube channel layer. A first stack of yttrium oxide and hafnium oxide is applied to the middle region of the n-type contact electrode, the carbon nanotube channel layer, and the adjacent carbon nanotube channel extension region to provide intrinsic compensation for the middle region of the carbon nanotube channel. A second layer of yttrium oxide and aluminum oxide is applied over the portion of the first layer located on the n-type contact electrode and the adjacent carbon nanotube channel extension region. The width of the second layer is smaller than that of the first layer. The first layer and the second layer work together to form n-type doping in the carbon nanotube channel region adjacent to the n-type contact electrode. A molybdenum oxide layer is applied to the p-type contact electrode and its adjacent carbon nanotube channel extension region to form p-type doping in the carbon nanotube channel region adjacent to the p-type contact electrode.

[0009] Furthermore, a distributed Bragg grating (DBR) mirror is provided between the substrate and the carbon nanochannel layer.

[0010] Furthermore, the distributed Bragg grating reflector is composed of 30 pairs of alternating dielectric layers of silicon oxide and tantalum oxide.

[0011] Furthermore, the substrate is a silicon substrate, a glass substrate, a quartz substrate, a silicon waveguide, or a silicon nitride waveguide.

[0012] Furthermore, the material of the n-type contact electrode is selected from one of hafnium, scandium, yttrium or titanium, or an alloy or stack composed of the above metals.

[0013] Furthermore, the material of the p-type contact electrode is selected from palladium, molybdenum, nickel, or an alloy or stack of the above metals.

[0014] Another aspect of this application provides a method for fabricating a carbon nanotube avalanche photodetector, comprising the following steps: A substrate is provided on which a carbon nanotube channel layer is formed; The carbon nanotube channel layer is patterned to form an n-type contact electrode pattern and a p-type contact electrode pattern at both ends of the carbon nanotube channel layer, respectively. An n-type contact electrode is formed on the n-type contact electrode pattern, and a p-type contact electrode is formed on the p-type contact electrode pattern; A first yttrium metal layer is deposited on the n-type contact electrode, the intermediate channel region and the carbon nanotube channel layer it contacts, and then oxidized to grow a hafnium oxide layer on the first yttrium metal layer. A second yttrium metal layer is partially deposited on the hafnium oxide layer, oxidized, and an aluminum oxide layer is grown on the second yttrium metal layer to achieve n-type doping of the carbon nanotube channel layer near the n-type contact electrode; A molybdenum oxide layer is deposited on the p-type contact electrode and the carbon nanotube channel layer it contacts, thereby achieving p-type doping of the carbon nanotube channel layer near the p-type contact electrode.

[0015] Furthermore, a distributed Bragg grating (DBR) mirror is formed on the substrate.

[0016] Furthermore, the material of the n-type contact electrode is selected from one of hafnium, scandium, yttrium or titanium, or an alloy or stack composed of the above metals.

[0017] Furthermore, the material of the p-type contact electrode is selected from palladium, molybdenum, nickel, or an alloy or stack of the above metals.

[0018] The beneficial effects of this invention are as follows: High-quality carbon nanotube pin junctions were constructed, significantly reducing dark current and improving signal-to-noise ratio. This invention employs asymmetric electrodes (n-type electrodes using low work function metals such as hafnium, and p-type electrodes using high work function metals such as palladium) combined with multilayer electrostatic doping technology to achieve precise bandgap control in the carbon nanotube channel. In particular, yttrium oxide / hafnium oxide (YO₂) is utilized... xThe HfO2 stack effectively compensates for the weak p-type state caused by environmental adsorption in the middle region of the carbon nanotube channel, restoring it to the intrinsic (i) state. This, combined with the molybdenum oxide (MoO2) layer in the p-region, further enhances the performance. x Strong acceptor doping and n-region yttrium oxide / aluminum oxide (YO) x Strong donor doping (Al2O3). This design constructs a high-quality pin junction with a clear band structure and a wide depletion region, which greatly suppresses leakage current (dark current) under reverse bias, thereby significantly improving the signal-to-noise ratio of the detector while ensuring avalanche gain.

[0019] The introduction of a distributed Bragg grating (DBR) mirror significantly improves photoelectric responsivity. Addressing the limitation of light absorption cross-section caused by the atomic-level thickness of carbon nanotube films, this invention integrates a distributed Bragg grating mirror optimized for a specific operating wavelength (e.g., 1800 nm) between the substrate and the carbon nanotube channel layer. This structure utilizes the optical interference effect of multilayer dielectric films (e.g., silicon oxide / tantalum oxide) to reflect incident light not absorbed by the carbon nanotube channel back to the channel layer, forming a resonant cavity enhancement effect and achieving secondary absorption of light. This significantly improves the device's light absorption efficiency and external quantum efficiency without increasing the channel thickness to maintain high-speed response.

[0020] Optimized electrode contact structure improves carrier injection efficiency. This invention employs a full-contact metal-semiconductor contact method in electrode fabrication, enabling the metal electrode to not only cover the upper surface of the carbon nanotubes but also achieve sidewall contact. Combined with heavy doping treatment of the epitaxial portion of the contact region, this structure effectively reduces contact resistance and the Schottky barrier, promoting efficient carrier injection and collection, and further enhancing the photoelectric conversion performance of the detector. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the carbon nanotube avalanche photodetector structure of the present invention; Figure 2 A comparison of the transfer characteristic curves of carbon nanotube hole-type field-effect transistors before and after electrostatic doping; Figure 3 A comparison of the output characteristic curves of a carbon nanotube hole-type field-effect transistor before and after electrostatic doping. Figure 4 The photoelectric output curves of carbon nanotube diodes under three different n-region doping lengths: undoped, doped with 1 / 3 of the channel region, and doped with 1 / 2 of the channel region. Figure 5 This is the output curve of the carbon nanotube avalanche photodetector. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] Example 1

[0024] This embodiment provides a high-performance, low-dark-current carbon nanotube avalanche photodetector (APD). This detector utilizes asymmetric electrodes and multilayer electrostatic doping technology to construct a high-quality pin junction within the carbon nanotube channel. For example... Figure 1 As shown, in one specific implementation, the carbon nanotube avalanche photodetector structure of this embodiment includes, from bottom to top: First, a substrate 101 is disposed. In this embodiment, the substrate 101 is preferably a silicon substrate with high flatness. In other embodiments, the substrate may also be quartz, glass, silicon waveguide, or silicon nitride waveguide.

[0025] A distributed Bragg grating reflector (DBR) 102 is disposed on the aforementioned silicon substrate to reflect incident light that is not absorbed by the carbon nanotube channel layer back to the channel layer, thereby significantly improving the device's light absorption efficiency and photoelectric response. Specifically, this DBR is designed for a center reflection wavelength of 1800 nm and is composed of 30 pairs of alternating dielectric layers. Following the design principle of dielectric thickness T = λ / 4n, where λ is the center wavelength (1800 nm) and n is the effective refractive index of the material, the first dielectric layer is silicon oxide (SiO2, n≈1.46), with a thickness of 308 nm; the second dielectric layer is tantalum oxide (Ta2O5, n≈2.11), with a thickness of 212 nm. This DBR structure achieves a reflectivity exceeding 90% in the wavelength range of 1600–2000 nm, with a peak reflectivity of 99% at 1800 nm.

[0026] A thin film composed of high-purity semiconductor carbon nanotubes (CNTs) is formed on the aforementioned DBR, serving as the carbon nanotube channel layer 103 of the device. In this embodiment, carbon nanotubes with an average diameter of 1.5 nm are preferably used, and the carbon nanotube film density is preferably greater than 400 nanotubes per micrometer. The total length of the entire channel layer is designed to range from 100 nm to 1000 nm. At both ends of the aforementioned carbon nanotube channel layer, a p-type contact electrode 104 and an n-type contact electrode 105 are respectively disposed for injecting or collecting charge carriers when a bias voltage is applied. Specifically, the material of the p-type contact electrode 104 is palladium (Pd), and the material of the n-type contact electrode 105 is hafnium (Hf), forming an asymmetric contact. Among them, the p-type contact electrode 104 and the n-type contact electrode 105 use a full-contact metal-semiconductor contact method. Before depositing the metal electrode, a portion of the carbon nanotubes on the substrate is etched away in advance, so that while the metal covers the upper surface of the carbon nanotubes, it can also achieve sidewall contact. This can promote more efficient injection of charge carriers into the carbon nanotube channel layer and further reduce the contact resistance. On this basis, the interdigitated electrode method is used to increase the channel width, reduce the overall resistance of the device, and increase the current.

[0027] This embodiment precisely controls the electrical properties of the carbon nanotube channel by covering the electrode and the carbon nanotube channel extension region in contact with the electrode with a specific doping layer, forming p-regions, i-regions, and n-regions. The specific structure is as follows: The i-region (intrinsic region): a 250 nm long intermediate region of carbon nanotube channels located between the p-region and the n-region. This intermediate region is covered with 1.5 nm of yttrium (naturally oxidized to YO₂). x YO is formed by combining 10nm thick hafnium oxide (HfO2) with other materials. x / HfO2 electrostatic doping layer 106. Due to the aggregation of surface polymers and the adsorption of water and oxygen from the air, the channels of carbon nanotubes themselves exhibit weak p-type doping, therefore a relatively thin 1.5nm yttrium layer (naturally oxidized to YO2) is required. x ) and 10nm thick hafnium oxide (HfO2) to dope the threshold in the middle of the channel back to the intrinsic i-region properties.

[0028] n-region: A composite n-type doped stack is deposited on the n-type contact electrode (Hf) and its adjacent 200 nm long carbon nanotube channel extension region. In YO x On top of the HfO2 electrostatic doped layer 106, a 3nm yttrium (naturally oxidized to YO) layer is deposited. x Add a 30nm thick layer of alumina (Al2O3) to form YO x / Al2O3 electrostatic doping layer 107, under the combined effect of the two electrostatic doping layers, can achieve n-type doping near the n-type contact electrode (Hf).

[0029] p-region: A 5nm thick layer of molybdenum oxide (MoO2) is sputtered onto the p-type contact electrode (Pd) and its adjacent 150nm long carbon nanotube channel extension region. x ) layer 108. MoO x As a strong electron acceptor, applying strong p-type electrostatic doping to the channel region of carbon nanotubes to form heavily doped p-regions is beneficial for the effective injection and collection of holes.

[0030] Using the aforementioned p-region, i-region, and n-region device structure, a pin junction structure was formed in a 600 nm carbon nanotube channel. This structure effectively widens the depletion region, greatly suppresses dark current under reverse bias, and provides a sufficiently long acceleration path in the avalanche multiplication region, thereby achieving high-gain and high-signal-to-noise ratio avalanche photodetector performance.

[0031] In other embodiments, the region lengths of p, i, and n can be adjusted according to performance requirements: For low operating voltage, low gain, and high bandwidth applications, short-channel devices can be selected, with the i-region being relatively thin at 50-100 nm and the p-region and n-region each at 100 nm. (2) For high gain and low dark current applications, the channel length of the device can be increased. Increasing the i-region length will increase the operating voltage and decrease the dark current. In addition, the carbon nanotube material (CNTs) of the channel can be replaced. If it is a 1.3 nm diameter carbon nanotube, compared with the currently used 1.5 nm diameter carbon nanotube, the band gap will increase, and the dark current of the device of the same size will be reduced.

[0032] Figure 2 A comparison of the transfer characteristic curves of carbon nanotube hole-type field-effect transistors before and after electrostatic doping was performed, including a comparison of undoped and (YO)-doped transistors. x After performing two yttrium-doped hafnium oxide layers with different thicknesses ( / HfO2=3 / 15), the threshold voltage of the device can be seen to have shifted from greater than +60V to around -60V, indicating a significant n-type doping effect on the overall channel.

[0033] Figure 3 A comparison of the output characteristic curves of a carbon nanotube hole-type field-effect transistor before and after electrostatic doping shows that after two yttrium-hafnium oxide doping treatments with different thicknesses, the output current at 1V decreased from over 300µA to around 1µA, indicating significant n-type doping throughout the channel. For clarity, Figure 2 – Figure 3 The device shown adopts a YOx / HfO2=3 / 15nm structure, which has slightly different parameters from that of Example 1, but the principle is the same.

[0034] Figure 4The photoelectric output curves of the carbon nanotube diode are shown for three cases: undoped, doped with 1 / 3 of the channel region, and doped with 1 / 2 of the channel region. The comparison shows that after doping the n-region, the dark current of the diode is significantly reduced, while the photoelectric response and signal-to-noise ratio are significantly improved. Figure 5 Typical output curves of the carbon nanotube avalanche photodetector are shown in linear and logarithmic coordinates. Under high reverse bias voltage, the carriers in the APD device channel undergo collisional ionization, resulting in a sharp increase in dark current and photocurrent, leading to avalanche phenomena and avalanche breakdown at -4.9V. Under high reverse bias conditions, significant avalanche multiplication of photocurrent can be observed when the device is illuminated at 1.55μm with a power of -21.1dBm and at 2μm with a power of -30.7dBm, while the photoelectric response and signal-to-noise ratio of the device remain at a high level.

[0035] Example 2

[0036] This embodiment provides a method for fabricating a carbon nanotube avalanche photodetector as described in Embodiment 1, specifically including the following steps: Step 1: Substrate and DBR Fabrication. A clean silicon substrate is provided. Using vacuum deposition techniques such as magnetron sputtering or electron beam evaporation, 30 pairs of alternating silicon oxide (SiO2) and tantalum oxide (Ta2O5) dielectric layers are deposited on the substrate. The thickness of each layer is precisely controlled, resulting in a silicon oxide layer thickness of 308 nm and a tantalum oxide layer thickness of 212 nm, thereby forming a high-reflectivity distributed Bragg grating (DBR) mirror targeting a center wavelength of 1800 nm.

[0037] Step 2: Formation of the carbon nanotube channel layer. A semiconductor carbon nanotube network film with an average diameter of 1.5 nm is uniformly deposited on the DBR using solution spin coating or transfer technology to form the carbon nanotube channel layer.

[0038] Step 3: Electrode Patterning and Deposition. Using standard photolithography or electron beam lithography, electrode patterns are defined on the carbon nanotube channel layer. Subsequently, through electron beam evaporation and lift-off, palladium (Pd) is deposited at one end of the pattern as a p-type contact electrode, and hafnium (Hf) is deposited at the other end as an n-type contact electrode. The electrode formation simultaneously defines an effective channel with a length of 600 nm.

[0039] Step 4: Electrostatic doping construction of the pin junction. This step is the core of this method and is completed through precisely controlled multi-step masking and deposition processes: p-region doping: Using the first mask, only the p-type contact electrode (Pd) and its adjacent 150nm channel region are exposed. A 5nm thick layer of molybdenum oxide (MoO) is deposited on this exposed region using magnetron sputtering.x () layer, forming a heavily doped p region.

[0040] i-region compensation doping: Using a second mask, the central 250nm channel region (i-region) and the 200nm channel region (n-region) on the n-type electrode side are exposed. A 1.5nm layer of metallic yttrium (Y) is first deposited using atomic layer deposition (ALD) or reactive magnetron sputtering, which then naturally oxidizes to YO under ambient conditions or a specific atmosphere. x Then, 10 nm of hafnium oxide (HfO2) is grown. After this step, the intermediate channel region is effectively compensated as the intrinsic i-region.

[0041] n-region heavy doping: Using a third mask, only the n-type contact electrode (Hf) and its adjacent 200 nm channel region are exposed. The YO₂ already formed in the previous step... x Above the HfO2 layer, a 3nm layer of metallic yttrium (Y) is deposited (also oxidized to YO). x Then, 30 nm of alumina (Al₂O₃) is grown. Finally, YO₂ is formed in the n-region. x Al2O3 is superimposed on YO x The composite doping structure above / HfO2 enables heavy doping of the n-region.

[0042] After testing, compared with the device without fine doping, the detector fabricated in this embodiment has significantly reduced dark current, and the photoelectric response and signal-to-noise ratio are greatly improved, verifying the effectiveness of the pin structure design.

[0043] Example 3

[0044] This embodiment provides a carbon nanotube avalanche photodetector suitable for low operating voltage and high bandwidth applications. Its basic structure and fabrication method are similar to those of Embodiments 1 and 2, with the main difference being the adjustment of the channel size. In this embodiment, the total channel length of the device is designed to be shorter, for example, 300 nm. The lengths of the p-region and n-region are both designed to be approximately 100 nm, while the length of the central i-region is correspondingly shortened to 50-100 nm. The thinner i-region shortens the carrier transit time, which is beneficial for improving the device's response speed and operating bandwidth, while also enabling avalanche multiplication at a lower operating voltage. The p-type contact electrode material can be palladium (Pd), molybdenum (Mo), or nickel (Ni) and their alloys, while the n-type contact electrode material can be hafnium (Hf), scandium (Sc), yttrium (Y), or titanium (Ti) and their alloys.

[0045] Example 4

[0046] This embodiment provides a carbon nanotube avalanche photodetector designed to achieve higher gain and lower dark current. Its structure and fabrication method are similar to those of Embodiments 1 and 2, with the main difference being the optimization of the channel material and size. In this embodiment, the total length of the channel can be appropriately increased, for example, to 800 nm or 1 µm, while primarily increasing the length of the i-region. A longer i-region means that under the same electric field, carriers have a longer path for collisional ionization, thus achieving higher avalanche gain, but the operating voltage will be correspondingly increased. More importantly, this embodiment uses smaller diameter carbon nanotubes, such as 1.3 nm diameter carbon nanotubes, instead of the 1.5 nm diameter carbon nanotubes in Embodiment 1. Due to the quantum confinement effect, smaller diameter carbon nanotubes have a larger band gap, which can fundamentally reduce the intrinsic carrier concentration caused by thermal excitation, thereby further significantly suppressing the dark current of the device under the same size and operating conditions.

[0047] It should be noted that the above detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A carbon nanotube avalanche photodetector, comprising a substrate, a carbon nanotube channel layer thereon, and an n-type contact electrode and a p-type contact electrode at each end of the carbon nanotube channel layer, characterized in that, The n-type contact electrode and the p-type contact electrode are in full contact with the carbon nanotube channel layer; A first stack of yttrium oxide and hafnium oxide is applied to the middle region of the n-type contact electrode, the carbon nanotube channel layer, and the adjacent carbon nanotube channel extension region to provide intrinsic compensation for the carbon nanotube channel region. A second layer of yttrium oxide and aluminum oxide is applied over the portion of the first layer located on the n-type contact electrode and the adjacent carbon nanotube channel extension region. The width of the second layer is smaller than that of the first layer. The first layer and the second layer work together to form n-type doping in the carbon nanotube channel region adjacent to the n-type contact electrode. A molybdenum oxide layer is applied to the p-type contact electrode and its adjacent carbon nanotube channel extension region to form p-type doping in the carbon nanotube channel region adjacent to the p-type contact electrode.

2. The carbon nanotube avalanche photodetector as described in claim 1, characterized in that, A distributed Bragg grating reflector is provided between the substrate and the carbon nanotube channel layer.

3. The carbon nanotube avalanche photodetector as described in claim 2, characterized in that, The distributed Bragg grating reflector is composed of multiple pairs of alternating dielectric layers of silicon oxide and tantalum oxide.

4. The carbon nanotube avalanche photodetector as described in claim 1, characterized in that, The substrate is a silicon substrate, a glass substrate, a quartz substrate, a silicon waveguide, or a silicon nitride waveguide.

5. The carbon nanotube avalanche photodetector as described in claim 1, characterized in that, The material of the n-type contact electrode is selected from one of hafnium, scandium, yttrium or titanium, or an alloy or stack of the above metals.

6. The carbon nanotube avalanche photodetector as described in claim 1, characterized in that, The material of the p-type contact electrode is selected from palladium, molybdenum, or nickel, or an alloy or stack of the above metals.

7. A method for fabricating a carbon nanotube avalanche photodetector, characterized in that, A substrate is provided on which a carbon nanotube channel layer is formed; The carbon nanotube channel layer is patterned to form an n-type contact electrode pattern and a p-type contact electrode pattern at both ends of the carbon nanotube channel layer, respectively. An n-type contact electrode is formed on the n-type contact electrode pattern, and a p-type contact electrode is formed on the p-type contact electrode pattern; A first yttrium metal layer is deposited on the n-type contact electrode, the intermediate channel region and the carbon nanotube channel layer it contacts, and then oxidized to grow a hafnium oxide layer on the first yttrium metal layer. A second yttrium metal layer is partially deposited on the hafnium oxide layer, oxidized, and an aluminum oxide layer is grown on the second yttrium metal layer to achieve n-type doping of the carbon nanotube channel layer near the n-type contact electrode; A molybdenum oxide layer is deposited on the p-type contact electrode and the carbon nanotube channel layer it contacts, thereby achieving p-type doping of the carbon nanotube channel layer near the p-type contact electrode.

8. The method for fabricating a carbon nanotube avalanche photodetector as described in claim 7, characterized in that, A distributed Bragg grating reflector is formed on the substrate.

9. The method for fabricating a carbon nanotube avalanche photodetector as described in claim 7, characterized in that, The material of the n-type contact electrode is selected from one of hafnium, scandium, yttrium or titanium, or an alloy or stack of the above metals.

10. The method for fabricating a carbon nanotube avalanche photodetector as described in claim 7, characterized in that, The material of the p-type contact electrode is selected from palladium, molybdenum, or nickel, or an alloy or stack of the above metals.

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