Double-Schottky junction silicon-based near-infrared photoelectric detector and preparation method thereof
By adopting a dual Schottky junction structure in silicon-based near-infrared photodetectors, the Schottky junction on the front and back absorbs near-infrared light and reduces dark current, the problem of limited applications of existing silicon-based detectors in the near-infrared band is solved, and efficient photoelectric response and low dark current are achieved.
Patent Information
- Application Number
- CN202411875107.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-19
- Publication Date
- 2025-04-18
AI Technical Summary
The application of existing silicon-based near-infrared photodetectors in the near-infrared communication band is limited by the bandwidth of Si, and cannot effectively absorb photons with wavelengths greater than 1100nm, resulting in low performance and difficult to meet commercial needs.
Using a double Schottky junction structure, the Schottky junction formed on the front and back sides of the detector is respectively formed. The Schottky junction formed by the upper metal layer and the silicon substrate absorbs near-infrared light with a wavelength greater than the width of the Si bandgap, and reduces dark current through the Schottky junction on the back to improve the responsiveness.
Low dark current and high detection degree are achieved, dark current density is reduced by two orders of magnitude, and the responsiveness is increased by 4 times, meeting commercial needs.
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Figure CN119855260A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of photoelectric detection, and in particular relates to a double Schottky junction silicon-based near-infrared photoelectric detector and a preparation method thereof. Background Art
[0002] Silicon is a basic material in the semiconductor field. With the continuous development of the information society, optical communication with photons as information carriers has become the mainstream. At the terminal of the optical network system, it is necessary to convert optical signals into electrical signals to read, process and store information. Therefore, the development of photodetectors that can work in the near-infrared communication band has important application value. On the other hand, silicon-based near-infrared photodetectors integrated on silicon photonic chips are an important link in the development of silicon photonics. Since the band gap width of Si is 1.12eV, it cannot absorb near-infrared light in the communication band with a wavelength greater than 1100nm, which limits its application in the near-infrared band. At present, there are many methods to expand the absorption spectrum of silicon to the near-infrared region, such as internal photoelectron emission effect, surface state absorption, two-photon absorption, surface defect absorption, body defect absorption, etc.
[0003] The internal photoelectron emission effect is realized by using the Schottky junction formed when metal and semiconductor are in contact. Since the work function and Fermi level of metal and semiconductor are different, the flow of carriers during contact will lead to the appearance of a depletion layer near the interface, i.e., the formation of a Schottky barrier. The height of the Schottky barrier is generally smaller than the band gap width of the semiconductor. Therefore, the electrons in the metal can absorb the photon energy of near-infrared light with a wavelength greater than the band gap width of Si, thereby crossing the barrier and transitioning to the conduction band of Si to form a photoelectric response. At present, there have been a number of studies on silicon-based near-infrared photodetectors based on the internal photoelectron emission effect with different structures. However, compared with the mainstream III-V group-based detectors, the performance of existing research detectors is still relatively low and difficult to meet commercial needs. Summary of the invention
[0004] The purpose of the present invention is to provide a double Schottky junction silicon-based near-infrared photodetector with simple preparation process, low cost, low dark current and high detection, and a preparation method thereof.
[0005] The double Schottky junction silicon-based near-infrared photodetector provided by the present invention has a structure as shown in Figure 1As shown, from top to bottom, they are: a front electrode (1), an upper metal layer (2), a silicon substrate (3), a lower metal layer (4), and a back electrode (5); wherein the thickness of the front electrode (1) is 10 nm to 3000 nm, the thickness of the upper metal layer (2) is 1 nm to 100 nm, the thickness of the silicon substrate (3) is 50 μm to 1000 μm, the thickness of the lower metal layer (4) is 1 nm to 1000 nm, and the thickness of the back electrode (5) is 1 μm to 20 μm; the Schottky junction formed by the upper metal layer and the silicon substrate absorbs near-infrared light with a wavelength greater than the Si band gap width to form a photoelectric response; and by introducing a Schottky junction at the back of the detector, the dark current of the detector is further reduced and the response is improved.
[0006] Further:
[0007] The material of the front electrode (1) is selected from transparent conductive films such as ITO, ATO, CTO, AZO, FTO, and IGZO, or selected from metals having a hollow structure such as Al, Ag, Au, Cu, and Al-Si.
[0008] The material of the upper metal layer (2) is selected from Au, Ag, Cu, Pt, Ti, Ni, Fe, In, Ga, Sn, Al or their alloys, or selected from metal silicides PtSi, FeSi, FeSi2, TiSi2, CoSi2, NiSi.
[0009] The silicon substrate (3) is of P type or N type, and is planar silicon or textured silicon, with a resistivity of 0.01 Ω·cm to 1000 Ω·cm. When the silicon substrate is textured silicon, the depth of the micro-nano structure on the surface of the substrate is 100 nm to 20 μm, and the diameter is 50 nm to 10 μm.
[0010] The material of the metal layer (4) is selected from Au, Ag, Cu, Pt, Ti, Ni, Fe, In, Ga, Sn, Al or their alloys, or selected from metal silicides PtSi, FeSi, FeSi2, TiSi2, CoSi2, NiSi.
[0011] The material of the back electrode (5) is selected from metals Al, Ag, Au, Cu and Al-Si.
[0012] The present invention also provides a method for preparing the above-mentioned double Schottky junction silicon-based near-infrared photodetector, the specific steps of which are:
[0013] (1) Cleaning the silicon substrate to remove impurities on the substrate surface;
[0014] (2) preparing metal layers on both sides of the silicon substrate and annealing them at high temperature to form a Schottky junction between the metal layer and the silicon substrate;
[0015] (3) Prepare a front electrode and a back electrode on the front and back sides respectively, and anneal at high temperature to form an ohmic contact.
[0016] In step 1, the silicon substrate is cleaned to remove impurities on the surface of the substrate, including soaking the silicon substrate in acetone, anhydrous ethanol and pure water for 15 minutes each for ultrasonic treatment to remove impurities and organic matter on the surface of the silicon wafer, and then using the RCA method to clean the silicon substrate: 1) soaking the silicon substrate in a mixed solution of NH3·H2O, H2O2 and pure water at a volume ratio of 1:1:5 at 70°C for 20 minutes to remove organic matter and natural oxide film on the surface of the silicon substrate; 2) soaking in a 1% HF solution for 1 minute to remove oxides on the surface of the silicon substrate; 3) soaking the silicon substrate in a mixed solution of HCl, H2O2 and pure water at a volume ratio of 1:1:6 at 70°C for 10 minutes to remove metal impurities on the surface of the silicon substrate; 4) soaking in a 1% HF solution again for 1 minute to remove oxides while inhibiting the formation of a new oxide film on the surface of the silicon substrate.
[0017] For texturing silicon as the silicon substrate, the substrate is prepared by chemical etching or physical etching.
[0018] The chemical etching refers to immersing the silicon substrate in a mixed etching solution for etching; the etching time is 1 min to 30 min, and the length of the etching time determines the depth and diameter of the micro-nano structure. The longer the etching time, the deeper the depth and the larger the diameter of the micro-nano structure.
[0019] The chemical etching method includes adding a catalyst to accelerate the etching process; the catalyst is selected from Ag, Au, Pt, and Cu; the catalyst can be added by using a physical deposition method such as thermal evaporation to evaporate a layer of a catalyst-containing film on a silicon substrate with a thickness of 1nm to 50nm; or a chemical solution containing a catalyst can be added to the etching solution.
[0020] The physical etching refers to ion beam etching or laser etching; in the ion beam etching, the silicon substrate is placed in an inert gas atmosphere with a gas pressure range of 1KPa to 0.5MPa; the laser etching refers to etching using a pulsed laser; the laser pulse width is 100fs to 100ns, and the wavelength is 200nm to 2000nm; during the etching process, a lens is used to focus the laser on the silicon substrate, and the spot diameter ranges from 1μm to 200μm; the laser scanning speed ranges from 20μm·s -1 ~2000μm·s -1 , energy density is 0.1J / cm 2 ~100J / cm 2 .
[0021] In step (2), the metal layer is prepared on the front and back sides of the silicon substrate by a method selected from pulsed laser deposition, magnetron sputtering, electron beam evaporation, thermal evaporation and chemical vapor deposition; the high temperature annealing has a temperature range of 300°C to 1200°C; the annealing method includes conventional thermal annealing, laser annealing, rapid thermal annealing or vacuum annealing; the annealing atmosphere is N2, O2, Ar, nitrogen-hydrogen mixture or vacuum.
[0022] In step (3), the electrode preparation method is selected from pulsed laser deposition, magnetron sputtering, electron beam evaporation, thermal evaporation, chemical vapor deposition and atomic layer deposition; after preparing the electrode, the sample is subjected to high temperature annealing in a N2 atmosphere to form an ohmic contact with the electrode; the annealing temperature range is 300°C to 600°C.
[0023] The present invention utilizes the Schottky junction formed by the upper metal layer and the silicon substrate to absorb near-infrared light with a wavelength greater than the Si band gap width to form a photoelectric response. And by introducing a Schottky junction on the back of the detector, the dark current of the detector is further reduced and the responsivity is improved. Compared with a single Schottky junction detector, the dark current density of the present invention is reduced by two orders of magnitude and the responsivity is increased by 4 times. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 It is a structural diagram of the double Schottky junction silicon-based near-infrared photodetector of the present invention.
[0025] Figure 2 It is the near-infrared absorption spectrum of the double Schottky junction silicon-based near-infrared photodetector of the present invention.
[0026] Figure 3 It is the dark current density of the double Schottky junction silicon-based near-infrared photodetector of the present invention.
[0027] Figure 4 It is the responsivity of the double Schottky junction silicon-based near-infrared photodetector of the present invention. DETAILED DESCRIPTION
[0028] The following examples are used to illustrate the present invention but are not intended to limit the present invention.
[0029] 1. Raw materials
[0030] Substrate: double-sided polished silicon wafer, resistivity 1Ω·cm~5Ω·cm, single crystal (100) N-type silicon wafer with size 20mm×20mm×0.20mm;
[0031] Solution for cleaning silicon wafers: acetone, anhydrous ethanol, pure water, 25% NH3·H2O, 30% H2O2; 36% HCl;
[0032] Metal layer: high-purity Au target, purity 99.999%;
[0033] Front electrode: ITO particles, 1mm~3mm, purity 99.99%;
[0034] Back electrode: Al particles, 5mm~10mm, purity 99.99%.
[0035] 2. Equipment used
[0036] VD650 clean bench, Suzhou Su Clean Chemical Equipment Co., Ltd.;
[0037] PLD-450 pulse laser deposition equipment;
[0038] BMDE500 high vacuum coating machine, Dongfang Scientific Instrument Import & Export Group Co., Ltd.;
[0039] DMDE 450 low-temperature coating machine, Beijing Optech Technology Co., Ltd.;
[0040] SK2-12 tubular annealing furnace, Shanghai Shiyan Electric Furnace Co., Ltd.
[0041] 3. Process parameter setting:
[0042] Pulse laser deposition equipment gas pressure: 2.5×10 -4 Pa; Pulse laser wavelength: 532nm; Pulse laser spot size: 1mm 2 ; Repetition rate: 10Hz; Pulse width: 5ns; Energy density: 11J / cm 2 ; Metal layer annealing temperature: 450℃; Metal layer annealing gas flow rate: 200sccm; High vacuum coating machine pressure: 3×10 -4 Pa; Low temperature coating machine pressure: 2×10 -4 Pa; electrode annealing temperature: 450°C; electrode annealing gas flow rate: 200 sccm.
[0043] 4. Preparation process
[0044] (1) Select a double-sided polished single crystal (100) N-type silicon wafer with a size of 20 mm×20 mm×0.20 mm;
[0045] (2) Soak the silicon wafer in a SC-1 mixed solution (a mixed solution of NH3·H2O, H2O2 and pure H2O in a volume ratio of 1:1:5) at 70°C for 20 min to remove organic matter and natural oxide film on the surface of the silicon wafer;
[0046] (3) Soak in 1% HF solution for 1 min to remove oxides on the surface of the silicon wafer;
[0047] (4) Soaking the silicon wafer in a 70°C SC-2 mixed solution (a mixed solution of HCl, H2O2 and pure H2O in a volume ratio of 1:1:6) for 10 min to remove metal impurities on the surface of the silicon wafer;
[0048] (5) Soak again in 1% HF solution for 1 min to remove the oxide and inhibit the formation of a new oxide film on the surface of the silicon wafer;
[0049] (6) Depositing a 30 nm Au film on the front side of the silicon wafer using pulsed laser deposition, and depositing a 3 nm Au film on the back side of the silicon wafer using pulsed laser deposition;
[0050] (7) Annealing the sample at 450°C for 30 min in a H2:N2=5%:95% mixed gas to form a Schottky junction between Au and the silicon wafer;
[0051] (8) Depositing an 80 nm ITO film on the upper surface of the sample by electron beam evaporation;
[0052] (9) Depositing a 1500 nm Al film on the lower surface of the sample by thermal evaporation;
[0053] (10) The device was annealed at 450 °C for 5 min under N2 protection to form an ohmic contact between the electrode and the device.
[0054] Results and Analysis
[0055] Based on the above specific examples, a double Schottky junction silicon-based near-infrared photodetector is obtained. This detector uses the Schottky junction formed by Au and N-type Si to absorb near-infrared light with a wavelength greater than the Si band gap width, and aggregates Au to form Au nanoparticles through thermal annealing, and uses the surface plasmon effect to generate hot electrons to improve the near-infrared response. Figure 2 As shown in the figure, the average absorption rate of the sample after adding Au in the near-infrared band greater than 1100nm is increased from about 2% to nearly 15%. Due to the small amount of Au on the back of the detector, the infrared response of the double Schottky junction sample does not show a significant improvement compared with the single Schottky junction. After absorbing near-infrared light, hot electrons are excited in the Au nanoparticles through plasmon induction and transported to the Au / Si interface. Hot electrons with sufficient energy can cross the Schottky barrier to reach the conduction band of Si and be collected by the external circuit, thereby generating a photoelectric response. In the absence of light, it is difficult for electrons to cross the Schottky barrier, thereby suppressing the dark current of the detector. Compared with the single Schottky junction device, under the illumination of 10mW, wavelength of 1319nm, and external bias of -0.1V, the dark current density of the double Schottky junction device increases from 1.71×10 -5 A / cm 2 Down to 1.42×10 -8 A / cm2 , reduced by two orders of magnitude, such as Figure 3 As shown in Figure 2, the responsivity is increased from 0.49mA / W to 1.98mA / W, a 4-fold increase. Figure 4 As shown, the specific detection is 2.09×10 8 cm·(Hz) 1 / 2 / W increased to 9.30×10 9 cm·(Hz) 1 / 2 / W.
Claims
1. A double Schottky junction silicon-based near-infrared photodetector, characterized in that: Its structure from top to bottom is: front electrode (1), upper metal layer (2), silicon substrate (3), lower metal layer (4), back electrode (5); wherein the thickness of the front electrode (1) is 10nm to 3000nm, the thickness of the upper metal layer (2) is 1nm to 100nm, the thickness of the silicon substrate (3) is 50μm to 1000μm, the thickness of the lower metal layer (4) is 1nm to 1000nm, and the thickness of the back electrode (5) is 1μm to 20μm; Among them, the Schottky junction formed by the upper metal layer and the silicon substrate absorbs near-infrared light with a wavelength greater than the Si band gap width, forming a photoelectric response; and by introducing a Schottky junction on the back of the detector, the dark current of the detector is further reduced and the response is improved.
2. The double Schottky junction silicon-based near-infrared photodetector according to claim 1, characterized in that: The material of the front electrode (1) is selected from transparent conductive films such as ITO, ATO, CTO, AZO, FTO, and IGZO, or selected from metals having a hollow structure such as Al, Ag, Au, Cu, and Al-Si.
3. The double Schottky junction silicon-based near-infrared photodetector according to claim 1, characterized in that: The material of the upper metal layer (2) is selected from Au, Ag, Cu, Pt, Ti, Ni, Fe, In, Ga, Sn, Al or their alloys, or selected from metal silicides PtSi, FeSi, FeSi2, TiSi2, CoSi2, NiSi.
4. The double Schottky junction silicon-based near-infrared photodetector according to claim 1, characterized in that: The silicon substrate is P-type or N-type, planar silicon or textured silicon, with a resistivity of 0.01Ω·cm to 1000Ω·cm; when the silicon substrate is textured silicon, the depth of the micro-nano structure on the surface of the substrate is 100nm to 20μm, and the diameter is 50nm to 10μm.
5. The double Schottky junction silicon-based near-infrared photodetector according to claim 1, characterized in that: The material of the lower metal layer (4) is selected from Au, Ag, Cu, Pt, Ti, Ni, Fe, In, Ga, Sn, Al or their alloys, or selected from metal silicides PtSi, FeSi, FeSi2, TiSi2, CoSi2, NiSi.
6. The double Schottky junction silicon-based near-infrared photodetector according to claim 1, characterized in that: The material of the back electrode (5) is selected from metals Al, Ag, Au, Cu and Al-Si.
7. A method for preparing a double Schottky junction silicon-based near-infrared photodetector according to any one of claims 1 to 6, characterized in that: The specific steps are: (1) cleaning the silicon substrate to remove impurities on the substrate surface; (2) preparing metal layers on both sides of the silicon substrate and annealing them at high temperature to form a Schottky junction between the metal layer and the silicon substrate; (3) Prepare a front electrode and a back electrode on the front and back sides respectively, and anneal them at high temperature to form an ohmic contact.
8. The preparation method according to claim 7, characterized in that: In step 1, the silicon substrate is cleaned to remove impurities on the surface of the substrate, including soaking the silicon substrate in acetone, anhydrous ethanol and pure water for 15 minutes each, ultrasonically removing impurities and organic matter on the surface of the silicon wafer, and then using the RCA method to clean the silicon substrate: 1) soaking the silicon substrate in a mixed solution of NH3·H2O, H2O2 and pure water at a volume ratio of 1:1:5 at 70°C for 20 minutes to remove organic matter and natural oxide film on the surface of the silicon substrate; 2) soaking in a 1% HF solution for 1 minute to remove oxides on the surface of the silicon substrate; 3) soaking the silicon substrate in a mixed solution of HCl, H2O2 and pure water at a volume ratio of 1:1:6 at 70°C for 10 minutes to remove metal impurities on the surface of the silicon substrate; 4) soaking in a 1% HF solution again for 1 minute to remove oxides while inhibiting the formation of a new oxide film on the surface of the silicon substrate; For texturing silicon as a silicon substrate, the texturing silicon substrate is prepared by chemical etching or physical etching; The chemical etching is to immerse the silicon substrate in a mixed etching solution for etching; the etching time is 1min to 30min, and the length of the etching time determines the depth and diameter of the micro-nano structure. The longer the etching time, the deeper the depth and the larger the diameter of the micro-nano structure. The chemical etching method includes adding a catalyst to accelerate the etching process; the catalyst is selected from Ag, Au, Pt, and Cu; the catalyst is added by using a physical deposition method such as thermal evaporation to deposit a catalyst-containing film on the silicon substrate with a thickness of 1nm to 50nm; or a chemical solution containing the catalyst is added to the etching solution; The physical etching is ion beam etching or laser etching; in the ion beam etching, the silicon substrate is placed in an inert gas atmosphere with a gas pressure range of 1KPa to 0.5MPa; in the laser etching, a pulsed laser is used for etching; the laser pulse width is 100fs to 100ns, and the wavelength is 200nm to 2000nm; during the etching process, a lens is used to focus the laser on the silicon substrate, and the spot diameter ranges from 1μm to 200μm; the laser scanning speed is 20μm·s -1 ~2000μm·s -1 , energy density is 0.1J / cm 2 ~100J / cm 2 .
9. The preparation method according to claim 7, characterized in that: In step (2), the metal layer is prepared on the front and back sides of the silicon substrate by a method selected from pulsed laser deposition, magnetron sputtering, electron beam evaporation, thermal evaporation and chemical vapor deposition; the high temperature annealing is performed at a temperature of 300°C to 1200°C; the annealing method includes conventional thermal annealing, laser annealing, rapid thermal annealing or vacuum annealing; the annealing atmosphere is N2, O2, Ar, nitrogen-hydrogen mixture or vacuum.
10. The preparation method according to claim 7, characterized in that: The electrode preparation method in step (3) is selected from pulsed laser deposition, magnetron sputtering, electron beam evaporation, thermal evaporation, chemical vapor deposition and atomic layer deposition; after preparing the electrode, the sample is subjected to high temperature annealing in a N2 atmosphere to form an ohmic contact with the electrode; the annealing temperature is 300°C to 600°C.