A high-concentration erbium-doped high-brightness optical communication band silicon-based luminescent film and its preparation method

Abstract

The present invention belongs to the field of optical communications technology, specifically a high-brightness, communication-band silicon-based luminescent film doped with a high concentration of erbium and a method for preparing the same. The present invention uses HSQ as a solvent and erbium nitrate pentahydrate as a source of erbium. Ytterbium ions and independent silicon quantum dots are co-doped, stirred, spin-coated, and subjected to high-temperature annealing to obtain a high-brightness erbium-doped silicon-based luminescent film. HSQ photoresist is used as a precursor material for the preparation of silicon nanocrystal films. After being doped with erbium and subjected to high-temperature annealing, the resulting film contains a large amount of silicon nanocrystals. The silicon nanocrystals act as sensitizers in the energy transfer process, absorbing incident photon energy and then transferring and activating erbium ions to achieve photoluminescence with a central emission wavelength of 1.54 μm. The present invention avoids the numerous defects associated with ion implantation and eliminates the need for maintaining a high vacuum. The resulting erbium-doped film has a high concentration of silicon nanocrystals, which act as erbium luminescence sensitizers, and is simple to prepare and safe to operate.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communications, and in particular relates to a silicon-based light-emitting film and a preparation method thereof. Background Art

[0002] An ideal on-chip integrated light source for optical communication should have an emission wavelength of approximately 1310nm or 1550nm, enabling connection to fiber optic networks. Rare earth ions, due to their unique electronic structure, form a rich array of energy levels that can generate radiation or absorption from the ultraviolet to the infrared. Erbium ions have a radiative transition wavelength of approximately 1550nm, corresponding to the minimum loss window for optical fiber communication. They also have a long luminescence lifetime and easily achieve population inversion. Studies have found that erbium ions doped into crystalline silicon can exhibit sharp, atomic-like, and temperature-independent radiative transitions. This can combine the excellent electrical properties of silicon with the superior optical properties of rare earth ions, enabling the realization of a silicon-based integrated light source for optical communication bands.

[0003] Since Ennen et al. first achieved 1.54μm luminescence from erbium-doped silicon in 1983, erbium-doped silicon-based luminescent systems have been extensively, systematically, and thoroughly studied. Currently, there are two common erbium-doped silicon-based luminescent material systems: erbium-doped bulk silicon and erbium-doped silicon-rich oxide. Compared with the former, because the solid solubility of erbium ions in the silica matrix is ​​more than two orders of magnitude higher than in bulk silicon, and the energy gap of silicon nanocrystals is larger than that of crystalline silicon, this increases the excitation energy required for erbium ion de-excitation to form bound excitons and reduces the free carrier concentration. This effectively suppresses temperature quenching caused by energy backtransfer and Auger recombination, thus offering greater application prospects for erbium-doped silicon-rich oxide-based luminescent materials. In addition, the silicon nanocrystals in the erbium-doped silicon-rich silicon oxide film act as sensitizers, which can transfer the absorbed energy to nearby erbium ions, sensitizing them to emit light. At the same time, the absorption cross-section of silicon nanocrystals is more than four orders of magnitude higher than that of erbium ions, and they can absorb a continuous spectrum, thereby greatly improving the luminescence efficiency of erbium ions and reducing the requirements for the excitation light source.

[0004] Traditional methods for preparing erbium-doped silicon-rich silicon oxide thin films include sol-gel, magnetron multi-target co-sputtering, electron beam evaporation, and ion implantation. Silicon-rich silicon oxide films prepared by the sol-gel method contain a large number of residual hydroxyl groups, which are serious quenching centers, resulting in weak luminescence. Silicon nanocrystals formed after high-temperature annealing in films prepared by magnetron multi-target co-sputtering and electron beam evaporation are large and uneven in size, with a relatively dispersed distribution and a small number. This is highly unfavorable because the energy transfer efficiency between silicon nanocrystals and erbium ions is inversely proportional to the sixth power of the distance between them. Furthermore, during ion implantation, high-speed ions collide with the semiconductor lattice, generating numerous point defects and lattice damage, leading to significant luminescence quenching.

[0005] This invention proposes a novel erbium-doped silicon-rich silicon oxide (SiO2) light-emitting thin film fabricated using a sol-gel process combined with spin-coating technology. Erbium nitrate pentahydrate crystals are directly dissolved in hydride silsesquioxane (HSQ), avoiding the formation of large amounts of hydroxyl groups in the film while enhancing the solubility of erbium ions. Furthermore, the silicon nanocrystals in the film are uniform in size, evenly distributed, and numerous, facilitating energy transfer and significantly increasing the concentration of optically active erbium ions in the film. Furthermore, by co-doping ytterbium ions with silicon quantum dot colloids, a high-brightness erbium-doped SiO2 light-emitting thin film with superior photoluminescence performance and excellent optical gain is achieved. Summary of the Invention

[0006] The object of the present invention is to provide a silicon-based luminescent film in the optical communication band with high erbium doping concentration, excellent luminescent performance and simple preparation process, and a preparation method thereof.

[0007] The present invention provides a method for preparing a silicon-based light-emitting film. The method uses hydrogenated silsesquioxane (HSQ) photoresist as a solvent, erbium nitrate pentahydrate as an erbium source, and co-doping with ytterbium ions and independent silicon quantum dots. After stirring, spin coating, and high-temperature annealing, a high-brightness erbium-doped silicon-based light-emitting film is obtained. The specific steps are as follows:

[0008] (1) Select a single-side polished silicon wafer as the substrate and clean it to remove impurities on the substrate surface;

[0009] (2) adding erbium nitrate pentahydrate crystals, ytterbium nitrate pentahydrate crystals and silicon quantum dot colloid to HSQ, and stirring at room temperature until completely dissolved to form a mixed sol; wherein the mass of the erbium nitrate pentahydrate crystals is 0.4g-0.5g, the mass of the ytterbium nitrate pentahydrate crystals is 0.1g-0.2g, the volume of the silicon quantum dot colloid is 0.5-3mL, the volume of the HSQ photoresist is 2-4mL, and the stirring time is 45min-60min;

[0010] (3) Spin coating the erbium-doped HSQ mixed sol on the substrate to form an erbium-doped HSQ thin film;

[0011] (4) Place the erbium-doped HSQ film on a constant temperature drying machine for heating and curing;

[0012] (5) Place the solidified erbium-doped HSQ film in the central constant temperature zone of a tubular resistance furnace, introduce a mixed gas of N2 and H2, and heat the tubular resistance furnace from room temperature to 1050°C~1100°C for 100min~120min, and maintain the temperature for 30~120min.

[0013] Further:

[0014] In step (1), the silicon substrate used is P-type silicon with a size of 20 mm×20 mm, a thickness of 525±25 μm, and a resistivity of 0.1 Ω·cm to 0.2 Ω·cm.

[0015] In step (1), the cleaning removes impurities on the surface of the substrate. Specifically, the silicon substrate is cleaned at 200-400° C. using a mixed solution of analytical grade concentrated sulfuric acid and 30% hydrogen peroxide solution for 90 min to 120 min. After cooling, the silicon substrate is alternately rinsed with anhydrous ethanol and deionized water, and then blown dry with a high-purity nitrogen gun.

[0016] In step (2), the silicon quantum dot colloid is extracted and synthesized using triethoxysilane as a precursor, and the specific operation process is as follows:

[0017] a. Under argon atmosphere, hydrochloric acid solution was added dropwise to 10 mL of triethoxysilane and hydrolyzed with stirring at room temperature until a white jelly-like gel was formed. The remaining hydrogen chloride gas was removed by connecting a sodium hydroxide washing bottle.

[0018] b. Place the white jelly-like gel in a vacuum drying oven for 5 to 6 hours to dry it to a white solid, then grind it into a white powder in a mortar;

[0019] c. Place the white powder in a quartz boat, push the quartz boat into the central constant temperature zone of a tubular resistance furnace, and introduce a H2:N2 mixed gas for high-temperature annealing to obtain a reddish-brown powder. The temperature setting is as follows: the tubular resistance furnace is heated from room temperature to 1050°C to 1100°C for 60 minutes to 100 minutes, and maintained at this temperature for 30 to 120 minutes; then naturally cool to 200 to 650°C, cool for 2 hours to 3 hours, and pull out the quartz boat;

[0020] d. Grind the reddish-brown powder using a ball mill to obtain fine silicon nanocrystalline powder. Set the ball milling parameters as follows: speed 400-700 rpm, duration 4-15 h;

[0021] e. Add 25 to 60 mL of a mixed solution of deionized water, anhydrous ethanol, and 49% hydrofluoric acid in a volume ratio of 1:1:1 to 1:1:4 to the silicon nanocrystal powder and stir continuously at room temperature to etch the silicon nanocrystals and reduce the size of the silicon nanocrystals;

[0022] f. After etching, 10 to 20 mL of a mixed solution of 1-dodecene and mesitylene in a volume ratio of 3:8 to 5:8 was added to the silicon nanocrystal powder and hydrosilylated in an argon environment to obtain a clear yellow solution at a temperature of 160 to 180 ° C for 1 to 4 h.

[0023] g. Use anhydrous ethanol and methanol to wash away the residual 1-dodecene and trimethylbenzene in the clear yellow solution, and add n-pentane to obtain a uniformly dispersed silicon quantum dot colloid.

[0024] In step (3), the operation of spin coating the erbium-doped HSQ mixed sol is as follows: take 100μL~150μL of the erbium-doped HSQ mixed sol, set the spin coating parameters as follows: first stage speed 300~600rpm, duration 2~5s; second stage speed 2000~4000rpm, duration 5~15s.

[0025] In step (4), the erbium-doped HSQ film is placed on a constant temperature drying machine for heating and curing, the temperature of the constant temperature drying machine is 60-150° C., and the time is 5-20 minutes.

[0026] In step (5), the content of H2 in the mixed gas used is 1% to 10%.

[0027] The present invention uses HSQ photoresist as the precursor material for preparing silicon nanocrystal films. After erbium doping and high-temperature annealing, the resulting film contains a large number of silicon nanocrystals. The silicon nanocrystals act as sensitizers in the energy transfer process, absorbing incident photon energy and then transferring and activating erbium ions. Specifically, the present invention utilizes silicon nanocrystals embedded in a silica matrix to absorb energy from 300nm to 500nm light and transfer it to the erbium ions surrounding the silicon nanocrystals, achieving photoluminescence with the erbium ion luminescence center located at 1.54μm. Because the film prepared by the present invention has a small number of quenching center hydroxyl groups and the silicon nanocrystals are uniformly sized, evenly distributed, and numerous, the resulting film has a high concentration of optically active erbium ions, resulting in superior photoluminescence performance.

[0028] The method of the present invention is different from traditional ion implantation and magnetron sputtering methods for preparing erbium-doped silicon-based films. It avoids the large number of defects caused by the ion implantation method and does not require maintaining a high vacuum degree. The erbium-doped film produced has the characteristics of high doping concentration and high concentration of silicon nanocrystals serving as erbium luminescence sensitizers. The above characteristics result in a higher optical gain of the film in the optical communication band. Compared with erbium-doped silicon-rich films prepared by other methods, the optical gain is 1 to 2 orders of magnitude higher, and the preparation steps are simple and the operation is safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a diagram illustrating the structure of the erbium-doped silicon-based light-emitting thin film of the present invention.

[0030] Figure 2 The figure is a transmission electron microscope (TEM) image of silicon nanocrystals in the erbium-doped silicon-based luminescent film of the present invention, and the inset is a high-magnification transmission electron microscope (HRTEM) image.

[0031] Figure 3 This is a histogram of the size distribution of silicon nanocrystals in the erbium-doped silicon-based luminescent film of the present invention.

[0032] Figure 4 This is the photoexcitation (PL) spectrum of the erbium-doped silicon-based luminescent film of the present invention under 405nm laser excitation.

[0033] Figure 5 This is a fitting curve diagram of the optical net gain of the erbium-doped silicon-based luminescent film of the present invention measured under 405nm laser excitation. DETAILED DESCRIPTION

[0034] The present invention is further described below by way of examples with reference to the accompanying drawings, but is not intended to limit the present invention.

[0035] 1. Raw materials and formula

[0036] Substrate: Single-side polished single crystal (100) orientation P-type silicon wafer, resistivity 0.1Ω·cm to 0.2Ω·cm, size 20mm×20mm, thickness 525±25μm;

[0037] Substrate cleaning solution: concentrated sulfuric acid (analytical grade), 30% hydrogen peroxide, anhydrous ethanol, Sinopharm Chemical Reagent Co., Ltd.

[0038] Raw materials: Erbium nitrate pentahydrate (analytical grade), Ytterbium nitrate pentahydrate (analytical grade), Shanghai Aladdin Biochemical Technology Co., Ltd.

[0039] Precursor materials: Hydrosilsesquioxane, Xuzhou Bokang Information Chemicals Co., Ltd.; Triethoxysilane (analytical grade), Shanghai Aladdin Biochemical Technology Co., Ltd.

[0040] Hydrolysis solution: hydrochloric acid (analytical grade), Sinopharm Chemical Reagent Co., Ltd.

[0041] Etching solution: 49% hydrofluoric acid, anhydrous ethanol, Sinopharm Chemical Reagent Co., Ltd.

[0042] 2. Process parameter setting

[0043] Spin coating conditions: room temperature, clean environment;

[0044] Annealing temperature: 1100℃;

[0045] Annealing gas flow rate: 200 sccm;

[0046] Annealing time: 60min;

[0047] Post-annealing cooling parameters: After power off, the tube is cooled in the furnace at room temperature for 90 minutes;

[0048] 3. Production equipment

[0049] VD650 clean bench, Suzhou Su Clean Chemical Equipment Co., Ltd.

[0050] LS-1D magnetic stirrer, Azov (Shanghai) Trading Co., Ltd.

[0051] KW4A desktop coating machine, Institute of Microelectronics, Chinese Academy of Sciences

[0052] 200-00A Constant Temperature Drying Oven, Huxin Electric Furnace Electric Box Factory

[0053] SK2-2-12 program-controlled tubular resistance furnace, Shanghai Shiyan Circuit Co., Ltd.

[0054] Vertical Planetary Ball Mill, Changsha Deke Instrument Equipment Co., Ltd.

[0055] L550 desktop low-speed centrifuge, Hunan Xiangyi Centrifuge Instrument Co., Ltd.

[0056] 4. Process

[0057] (1) Select a single-sided polished P-type silicon wafer with a resistivity of 0.1Ω·cm to 0.2Ω·cm, a size of 20 mm×20 mm, and a thickness of 525±25 μm and a (100) orientation;

[0058] (2) Immerse the silicon wafer in a 1:1 volume ratio of analytical grade concentrated sulfuric acid and 30% hydrogen peroxide solution, heat at 290°C for 120 min, allow to cool naturally, and then alternately ultrasonically rinse with deionized water and anhydrous ethanol, then blow dry with a high-purity nitrogen gun for later use;

[0059] (3) Under argon atmosphere, hydrochloric acid solution was added dropwise to 10 mL of triethoxysilane, and the mixture was stirred and hydrolyzed at room temperature until a white jelly-like gel was formed. A sodium hydroxide washing bottle was connected to remove the remaining hydrogen chloride gas;

[0060] (4) Place the white jelly-like gel in a vacuum drying oven for 5.5 h to dry into a white solid, then grind it into a white powder in a mortar;

[0061] (5) The white powder was placed in a quartz boat, which was pushed into the central constant temperature zone of a tubular resistance furnace, and a mixed gas of H2:N2 with a volume ratio of 5%:95% was introduced for high temperature annealing to obtain a reddish-brown powder. The temperature was set as follows: the tubular resistance furnace was heated from room temperature to 1100°C for 90 minutes and maintained at this temperature for 90 minutes; then naturally cooled to 500°C for 2 hours, and the quartz boat was pulled out;

[0062] (6) Grind the reddish-brown powder using a ball mill to obtain silicon nanocrystal fine powder. The ball milling parameters are set as follows: speed 600 rpm, duration 10 h;

[0063] (7) adding 30 mL of a mixed solution of deionized water, anhydrous ethanol, and 49% hydrofluoric acid in a volume ratio of 1:1:1 to the silicon nanocrystal fine powder, and stirring continuously at room temperature to etch the silicon nanocrystals and reduce the size of the silicon nanocrystals;

[0064] (8) Add 11 mL of a mixed solution of 1-dodecene and mesitylene in a volume ratio of 3:8 to the etched silicon nanocrystal powder and perform hydrosilylation in an argon environment to obtain a clear yellow solution at 165 °C for 3 h.

[0065] (9) Using anhydrous ethanol and methanol to wash away the residual 1-dodecene and trimethylbenzene in the clear yellow solution, and adding n-pentane to obtain a uniformly dispersed silicon quantum dot colloid;

[0066] (10) 0.4 g of erbium nitrate pentahydrate crystals, 0.2 g of ytterbium nitrate pentahydrate crystals, and 1 mL of the silicon quantum dot colloid prepared above were placed in 2 mL of HSQ and stirred at 300 rpm on a magnetic stirrer at room temperature for 45 min until the solids were completely dissolved to form a clear pink sol;

[0067] (11) The cleaned silicon substrate was placed on the tray of the spin coater, and 150 μL of the erbium-doped HSQ mixed sol was dropped onto the substrate surface. The spin coating parameters were set as follows: first stage speed 500 rpm, duration 3 s; second stage speed 3000 rpm, duration 10 s;

[0068] (12) Place the spin-coated film sample on a constant temperature drying machine to bake and solidify the film at 80°C for 10 min;

[0069] (13) After the baked sample is cooled to room temperature, it is placed on a cleaned quartz substrate and pushed into the central constant temperature zone of the tubular resistance furnace. A mixed gas of H2:N2=5%:95% is introduced, and the mixed gas flow rate is 200sccm. The tubular resistance furnace is set to heat from room temperature to 1100℃, the heating time is 100min, and it is maintained at 1100℃ for 60min. Then the power is turned off and the sample is taken out after cooling in the furnace for 90min.

[0070] Results and Analysis

[0071] By specific embodiments, such as Figure 1 As shown in Figure 1, a high-concentration erbium-doped silicon-based light-emitting film in the optical communication band was successfully prepared on a silicon substrate; Figure 2 Shown is a transmission electron micrograph of the prepared film, showing that the film contains uniformly distributed silicon nanocrystals; Figure 3 The silicon nanocrystals in the film were counted and the size of the silicon nanocrystals in the film was found to be 2.89±0.14nm, which was uniform in size. Figure 4As shown in Figure 1, when the sample is excited by the non-resonant excitation light of erbium ions at 405 nm, strong erbium ion photoluminescence is observed at 1.54 μm. The optical net gain is tested by the variable aperture length-moving excitation point (VSL-SES) method, as shown in Figure 1. Figure 5 As shown in Figure 2, the optical net gain at 1.54 μm is 272 cm -1 or 24.35dB cm -1 , which is the highest optical net gain at 1.54μm among the erbium-doped silicon-rich silicon oxide films reported so far.

Claims

1. A method for preparing a silicon-based light-emitting thin film, characterized in that: Using HSQ photoresist as a solvent and erbium nitrate pentahydrate as the source of erbium, high-brightness erbium-doped silicon-based light-emitting thin films were obtained by co-doping ytterbium ions and independent silicon quantum dots, stirring, spin coating, and high-temperature annealing. The specific steps are as follows: (1) Select a single-side polished silicon wafer as the substrate and clean it to remove impurities on the substrate surface; (2) adding erbium nitrate pentahydrate crystals, ytterbium nitrate pentahydrate crystals and silicon quantum dot colloid to HSQ, and stirring at room temperature until completely dissolved to form a mixed sol; wherein the mass of the erbium nitrate pentahydrate crystals is 0.4g-0.5g, the mass of the ytterbium nitrate pentahydrate crystals is 0.1g-0.2g, the volume of the silicon quantum dot colloid is 0.5-3mL, the volume of the HSQ photoresist is 2-4mL, and the stirring time is 45min-60min; (3) Spin coating the erbium-doped HSQ mixed sol on the substrate to form an erbium-doped HSQ thin film; (4) Place the erbium-doped HSQ film on a constant temperature drying machine for heating and curing; (5) Place the solidified erbium-doped HSQ film in the central constant temperature zone of a tubular resistance furnace, introduce a mixed gas of N2 and H2, and heat the tubular resistance furnace from room temperature to 1050°C~1100°C for 100min~120min, and maintain the temperature for 30~120min.

2. The preparation method according to claim 1, characterized in that The cleaning described in step (1) removes impurities on the surface of the substrate. Specifically, the silicon substrate is cleaned at 200-400° C. using a mixed solution of analytical grade concentrated sulfuric acid and 30% hydrogen peroxide solution for 90 min to 120 min. After cooling, the silicon substrate is alternately rinsed with anhydrous ethanol and deionized water, and then blown dry with a high-purity nitrogen gun.

3. The preparation method according to claim 1, characterized in that The silicon quantum dot colloid described in step (2) is extracted and synthesized using triethoxysilane as a precursor. The specific operation process is as follows: a. Under argon atmosphere, hydrochloric acid solution was added dropwise to 10 mL of triethoxysilane and hydrolyzed with stirring at room temperature until a white jelly-like gel was formed. The remaining hydrogen chloride gas was removed by connecting a sodium hydroxide washing bottle. b. Place the white jelly-like gel in a vacuum drying oven for 5 to 6 hours to dry it to a white solid, then grind it into a white powder in a mortar; c. Place the white powder in a quartz boat, push the quartz boat into the central constant temperature zone of a tubular resistance furnace, and introduce a H2:N2 mixed gas for high-temperature annealing to obtain a reddish-brown powder. The temperature setting is as follows: the tubular resistance furnace is heated from room temperature to 1050°C to 1100°C for 60 minutes to 100 minutes, and maintained at this temperature for 30 to 120 minutes; then naturally cool to 200 to 650°C, cool for 2 hours to 3 hours, and pull out the quartz boat; d. Grind the reddish-brown powder using a ball mill to obtain fine silicon nanocrystalline powder. Set the ball milling parameters as follows: speed 400-700 rpm, duration 4-15 h; e. Add 25 to 60 mL of a mixed solution of deionized water, anhydrous ethanol, and 49% hydrofluoric acid in a volume ratio of 1:1:1 to 1:1:4 to the silicon nanocrystal powder and stir continuously at room temperature to etch the silicon nanocrystals and reduce the size of the silicon nanocrystals; f. After etching, 10 to 20 mL of a mixed solution of 1-dodecene and mesitylene in a volume ratio of 3:8 to 5:8 was added to the silicon nanocrystal powder and hydrosilylated in an argon environment to obtain a clear yellow solution at a temperature of 160 to 180 ° C for 1 to 4 h. g. Use anhydrous ethanol and methanol to wash away the residual 1-dodecene and trimethylbenzene in the clear yellow solution, and add n-pentane to obtain a uniformly dispersed silicon quantum dot colloid.

4. The preparation method according to claim 1, characterized in that The operation of spin coating the erbium-doped HSQ mixed sol in step (3) is as follows: take 100 μL to 150 μL of the erbium-doped HSQ mixed sol, and set the spin coating parameters as follows: first stage speed 300 to 600 rpm, duration 2 to 5 s; second stage speed 2000 to 4000 rpm, duration 5 to 15 s.

5. The preparation method according to claim 1, characterized in that In step (4), the erbium-doped HSQ film is placed on a constant temperature drying machine for heating and curing at a temperature of 60 to 150° C. for 5 to 20 minutes.

6. The preparation method according to claim 1, characterized in that The H2 content in the mixed gas used in step (5) is 1% to 10%.

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