A fluorine-erbium co-doped tin oxide film and its preparation method and application

Abstract

The present invention discloses a fluorine-erbium co-doped tin oxide film, a preparation method thereof, and an application in the field of near-infrared electroluminescence. The preparation method comprises: introducing a mixed gas of argon and oxygen under vacuum, and using a radio frequency magnetron sputtering method to co-sputter and deposit a thin film on a fluorine-doped tin oxide target and an erbium oxide target; the mass percentage of stannous fluoride in the fluorine-doped tin oxide target is not more than 20%; in an oxygen or nitrogen atmosphere, heating the film obtained by co-sputtering deposition to above 200°C for high-temperature heat treatment, and cooling to obtain a fluorine-erbium co-doped tin oxide film. After the film of the present invention is used to make an electroluminescent device, under the condition of applying a reverse bias, strong electroluminescence can be achieved based on the electron impact ionization effect occurring in the space charge region.

Description

Technical Field

[0001] The invention relates to the technical field of silicon-based optoelectronics, and in particular to a fluorine-erbium co-doped tin oxide film and a preparation method and application thereof. Background Art

[0002] With the rapid development of the microelectronics industry, the process development trend predicted by Moore's Law has reached a bottleneck. Due to the continuous reduction of chip feature line width, signal delay caused by electrical interconnection technology, excessive power consumption and signal crosstalk have restricted the improvement of transistor density. Silicon-based optoelectronic technology based on CMOS (complementary metal oxide semiconductor) technology has become the future trend of the integrated circuit industry due to its high transmission speed, anti-interference ability and low transmission loss.

[0003] At present, silicon-based optical interconnection technology has made breakthrough progress in optical waveguides, optical signal modulators and amplifiers, but there are still serious deficiencies in light sources, especially high-efficiency electroluminescent light sources compatible with mature CMOS processes. Erbium-doped silicon-based light sources have always been the focus of scientific researchers because of the 1535nm characteristic luminescence peak of Er in the minimum loss window of optical fiber transmission and the advantages of being compatible with existing processes.

[0004] In order to further increase the erbium doping concentration and reduce the operating voltage of the device to obtain an efficient electroluminescent light source, researchers have successively doped erbium into silicon, silicon insulating compounds such as silicon oxide, silicon nitride, silicon oxynitride, erbium compounds such as erbium silicate, and narrow-bandgap semiconductors such as gallium arsenide and indium phosphide. However, narrow-bandgap semiconductors such as silicon and gallium arsenide have low erbium ion solid solubility. At the same time, the Auger recombination effect in the matrix leads to strong energy back transfer, which greatly weakens the luminescence efficiency of erbium; in insulating matrices such as silicon oxide and erbium silicate, although the energy back transfer effect is suppressed, the operating voltage of the device is very high, which is not conducive to the development of low-power on-chip integration processes; in addition, the presence of many defects in silicon nitride and silicon oxynitride matrices also restricts the further improvement of device efficiency.

[0005] In order to solve the problem of low operating voltage and low energy back transfer inhibition of erbium-doped electroluminescent devices, which leads to low device efficiency, researchers doped erbium into wide-bandgap semiconductors such as gallium nitride, gallium oxide, and titanium oxide. For example, Houwei Pang, et al., Near-infrared luminescence of erbium doped Ga2O3 films and devices based on silicon: Realization of energy transfer, Optical Materials, Volume 129, 2022, 112462: They completed the doping of erbium in the gallium oxide matrix, and realized electroluminescence based on the energy transfer mechanism in gallium oxide for the first time while maintaining a high erbium concentration and a low mismatch. The device has a luminous voltage of about 13V and a working field strength of about 1.3MV / cm. However, these semiconductor materials all have shortcomings. The presence of nitrogen in gallium nitride will form optically inactive erbium nitride compounds with erbium, resulting in reduced device efficiency. The oxygen present in titanium oxide and gallium oxide can form ErO complexes with erbium with high optical activity. At the same time, the oxygen defects in the matrix can also sensitize erbium ions. However, titanium oxide is an indirect band gap semiconductor with low luminescence efficiency. The gallium element in gallium oxide is a precious metal, and the material growth cost is high. In addition, the electrical properties of the two semiconductor materials are poor, which is not conducive to reducing the operating voltage of electroluminescent devices. Such electroluminescent devices based on energy transfer mechanisms are also difficult to achieve high luminous power.

[0006] Based on the electroluminescent devices prepared by this type of oxide-doped erbium thin film, some work has studied the device structure, such as Chengtao Xia, et al., Electroluminescence from Silicon-Based Light-Emitting Devices with Erbium-Doped ZnO Films: Strong Enhancement Effect of Titanium Codoping, ACS Applied Materials & Interfaces, 202214(39), 44498-44505, by thermally oxidizing a thin layer of SiO2 on a heavily doped n-type silicon wafer. x The erbium layer (about 10nm) is used to generate hot carriers to excite erbium ions, and the crystal field environment is regulated by co-doping Ti elements to obtain a higher electroluminescent intensity. However, this type of device requires a thermal oxidation process to grow a thermal oxide layer on a silicon wafer, which increases the process steps in production. At the same time, its operating voltage is still greater than 10V. There is still a lack of research on erbium-doped electroluminescent devices with simple preparation, low cost and low light-emitting voltage.

[0007] Therefore, the current bottleneck of erbium-doped silicon-based electroluminescent devices is the lack of an excellent erbium-doped matrix material that can suppress the energy back transfer effect and achieve low operating voltage and high-efficiency erbium-doped near-infrared electroluminescence while ensuring electrical properties; at the same time, there is a lack of research on low-cost electroluminescent devices with fewer preparation process steps.

[0008] In view of the shortcomings in this field, namely, ① the lack of an excellent erbium ion luminescent matrix, which allows the erbium-doped electroluminescent device prepared therefrom to have a low operating voltage, while avoiding the energy back transfer effect of erbium to the matrix, and the erbium ion has a high optical activity in the matrix; ② the lack of analysis of the luminescence mechanism of the electroluminescent device and the design of the device macrostructure to obtain more efficient erbium ion near-infrared electroluminescence; ③ the lack of electroluminescent devices with simple process steps, low cost, and growth methods compatible with large-scale industrial production. Therefore, the present invention proposes a new type of fluorine-erbium co-doped tin oxide film. At present, there is no report on the realization of near-infrared electroluminescence of erbium-doped tin oxide film. Dung C, et al. Remarkable enhancement of Er 3+ emission at 1.54μm in Er / Yb co-doped SiO2-SnO2 glass-ceramics[J].Journal of Alloys&Compounds,2018:S092583881831750X reported that by co-doping ytterbium and erbium elements in tin oxide-silicon oxide microcrystalline glass prepared by sol-gel method, very strong near-infrared characteristic luminescence was obtained in the photoluminescence test. Similarly, the current research on erbium-doped tin oxide thin films is limited to photoluminescence, mostly tin oxide is doped into other matrices as a sensitizer to excite erbium ions, lacking the exploration of this excellent erbium-doped matrix, and no near-infrared electroluminescent devices based on tin oxide thin films have been reported, which cannot meet the original intention of using erbium-doped electroluminescent light sources to solve the technical problems existing in silicon-based optoelectronic technology. Summary of the invention

[0009] In view of the above technical problems and the deficiencies in the art, the present invention provides a method for preparing a fluorine-erbium co-doped tin oxide thin film. A dense thin film can be obtained by radio frequency magnetron sputtering. A subsequent heat treatment process is used to passivate some defects in the thin film and fully crystallize the tin oxide thin film. Erbium ions replace tin ions to complete doping. At the same time, fluorine ions replace oxygen ions to further optimize the electrical properties of the thin film and the symmetry of the crystal field in which erbium is located, thereby increasing the carrier concentration in the thin film and the transition probability of erbium ions. After being used to manufacture an electroluminescent device, the operating voltage of the device can be reduced and its working efficiency can be improved. When a reverse bias is applied, strong electroluminescence can be achieved based on the electron impact ionization effect occurring in the space charge region.

[0010] A method for preparing a fluorine-erbium co-doped tin oxide thin film comprises the following steps:

[0011] (1) Under vacuum, a mixture of argon and oxygen is introduced, and a fluorine-doped tin oxide target and an erbium oxide target are co-sputtered to deposit a thin film by a radio frequency magnetron sputtering method; the mass percentage of stannous fluoride in the fluorine-doped tin oxide target is not more than 20%. If the fluorine doping amount is too high, the scattering of ionized impurities will be enhanced, the collision probability of electrons will be increased, and the electron energy of the excited erbium ions will be reduced; if a pure tin oxide target without fluorine doping is used, the conductivity of the film is poor, and the expected effect cannot be achieved when used to make an electroluminescent device;

[0012] (2) In an oxygen or nitrogen (preferably oxygen) atmosphere, the thin film obtained by co-sputtering deposition is heated to above 200° C. for high-temperature heat treatment, and then cooled to obtain the fluorine-erbium co-doped tin oxide thin film.

[0013] In a preferred embodiment, in step (1), a pre-sputtering is performed before the co-sputtering deposition of the thin film (the time can be set by oneself, for example, more than 5 minutes, etc.), and the sample baffle is opened to start depositing the thin film on the heated substrate.

[0014] The present invention has found that, in step (1), if an erbium target is used instead of an erbium oxide target, erbium in the resulting thin film is prone to phase separation, which has an adverse effect on the thin film and subsequent devices.

[0015] In a preferred embodiment, in step (1), the vacuum refers to a vacuum degree not greater than 5×10 -3 Pa.

[0016] In step (1), the ratio of argon to oxygen in the argon and oxygen mixture mainly affects the film quality of the film, because the appropriate oxygen content in the sputtering atmosphere can effectively reduce oxygen defects in the film. In a preferred embodiment, the volume proportion of argon in the argon and oxygen mixture is not less than 50%.

[0017] In a preferred embodiment, in step (1), the temperature of the heated substrate is above 50°C.

[0018] In a preferred embodiment, in step (1), during sputtering, the power of the fluorine-doped tin oxide target is 10 to 170 watts, the power of the erbium oxide target is 5 to 70 watts, and the pressure of the sputtering chamber is 0.1 to 10 Pa.

[0019] In step (1), the time for sputtering and depositing the thin film on the substrate is preferably 5 to 120 minutes.

[0020] In a preferred embodiment, in step (2), the temperature is not raised or lowered with the furnace, but rather is raised or lowered rapidly. The use of the temperature raised or lowered with the furnace will reduce the carrier concentration in the film and easily form erbium element clusters, which is not conducive to the full performance of the subsequent electroluminescent device. The use of rapid temperature rise and fall can effectively reduce or even avoid the formation of erbium clusters, maintain a high carrier concentration, and thus ensure that the subsequently manufactured device has a low turn-on voltage and light-emitting voltage. Further preferably, in step (2), the heating rate of the heating is greater than 1°C / s, and the cooling rate of the cooling is greater than 1°C / s.

[0021] After the sputtering growth film, heat treatment is required to promote the quality optimization of the fluorine-erbium co-doped tin oxide film and the substitutional doping of erbium ions. Generally speaking, in step (2), the higher the temperature of the high-temperature heat treatment and the longer the residence time, the better the crystallinity of the film but the more obvious the reduction in electrical properties; the lower the temperature of the high-temperature heat treatment and the shorter the residence time, the worse the crystallinity of the film but the more obvious the improvement in electrical properties. This is because the improvement in crystallinity can passivate defects to a certain extent and improve the quality of the film, but too high crystallinity will enhance the grain boundary scattering effect and affect electrical transport. Therefore, the appropriate high-temperature heat treatment temperature and the rate of temperature rise and fall can be selected according to specific needs to obtain the desired crystallinity and electrical properties, thereby obtaining excellent electroluminescence intensity and device stability. In step (2), the temperature of the high-temperature heat treatment is preferably 200 to 1000°C. In step (2), the residence time of the high-temperature heat treatment is preferably 5 to 120 minutes.

[0022] The present invention also provides a fluorine-erbium co-doped tin oxide thin film prepared by the preparation method, wherein fluorine-erbium co-doped tin oxide crystals are formed in the fluorine-erbium co-doped tin oxide thin film.

[0023] In the fluorine-erbium co-doped tin oxide film, if the concentration of erbium is too low, the luminescence effect of the subsequent device is poor. If the concentration of erbium is too high, it is easy to produce concentration quenching effect, resulting in unnecessary energy loss. Preferably, in the fluorine-erbium co-doped tin oxide film, the atomic percentage of erbium is 1% to 5%, based on the total atomic number of erbium and tin as 100%. The erbium content can be adjusted by the sputtering power of the target during co-sputtering.

[0024] The thickness of the fluorine-erbium co-doped tin oxide film is preferably 20-500 nm. If the film is too thin, it is easy to break down. If it is too thick, the electrical performance will be significantly reduced, which is not conducive to the subsequent production of electroluminescent devices. The film thickness is mainly related to the sputtering time.

[0025] The present invention also provides the application of the fluorine-erbium co-doped tin oxide film in the field of near-infrared electroluminescence, for example, for preparing an electroluminescent device based on electron impact ionization effect.

[0026] As a general inventive concept, the present invention also provides a near-infrared electroluminescent device that provides hot electrons based on the avalanche multiplication effect, using the fluorine-erbium co-doped tin oxide film, wherein a metal back electrode for connecting to the negative pole of the power supply is deposited on one side of the substrate, and an oxide transparent electrode for connecting to the positive pole of the power supply is deposited on one side of the fluorine-erbium co-doped tin oxide film.

[0027] In a preferred example, the substrate is silicon, more preferably p-type silicon, and even more preferably lightly doped p-type silicon with a resistivity greater than 0.01 Ω·cm.

[0028] The selection of substrate resistivity will affect the electrical properties and electroluminescent performance of the device, which depends on the width of the space charge region and the field strength, which is mainly determined by the doping concentration of the substrate and the film. For example, if heavily doped p-type silicon with a resistivity not exceeding 0.01Ω·cm is selected as the substrate, the breakdown voltage of the subsequent electroluminescent device will be reduced. This is because the doping concentration of the silicon substrate is too high, and Zener breakdown mainly occurs in the space charge region. The Zener breakdown voltage and electron energy are low, and the erbium ions cannot be fully excited. Considering the electrical properties and the conditions for the occurrence of the avalanche multiplication effect, the present invention preferably uses lightly doped p-type silicon with a resistivity greater than 0.01Ω·cm as the substrate to prepare an electroluminescent device with low light-emitting voltage and high light power.

[0029] The near-infrared electroluminescent device for providing hot electrons based on the avalanche multiplication effect of the present invention has a turn-on voltage lower than 5V and a light-emitting voltage lower than 10V, has high electroluminescent efficiency and long device life, and can be applied to silicon-based integrated light sources, semiconductor light emission, optical communications and other fields.

[0030] The oxide transparent electrode and the metal back electrode in the above-mentioned near-infrared electroluminescent device can be deposited by using existing deposition technologies, such as magnetron sputtering, electron beam evaporation, etc.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The preparation method of the present invention is simple, compatible with the manufacturing process of the microelectronics industry, has low raw material costs, and has broad application prospects in the fields of silicon-based integrated light sources, semiconductor light emission, optical communications, etc. The fluorine-erbium co-doped tin oxide film prepared according to the method of the present invention is highly crystalline, and the erbium element is evenly distributed.

[0033] 2. The present invention adopts the fluorine-doped tin oxide thin film prepared by radio frequency magnetron sputtering-high temperature rapid thermal treatment as the substrate of the erbium-doped electroluminescent device. ① Tin oxide has a wide band gap (3.9 eV) and can avoid the energy back transfer caused by the Auger effect, thereby improving the electroluminescence intensity and efficiency of the device; ② Tin oxide has low cost and good electrical properties. The fluorine-doped tin oxide material prepared by co-doping fluorine element has high carrier concentration and conductivity, and has a higher lattice matching degree with commercial indium tin oxide and fluorine tin oxide transparent electrodes. The prepared electroluminescent device The electroluminescent device has high performance and can reduce the turn-on voltage and light-emitting voltage of the device; ③ Tin oxide has excellent optical properties, and its ultraviolet-visible-near infrared transmittance is greater than 80%. It still has good optical properties under the premise of ensuring high carrier concentration. As a light-emitting layer material, its internal light loss is low and the light extraction efficiency is high; ④ The structure of tin oxide is a tetragonal rutile structure. Erbium is replaced by the site of tin ions. By co-doping with fluorine elements, the crystal field environment of erbium ions is affected, the lattice symmetry is reduced, and the optical activity of erbium is improved; ⑤ By The structure is designed to obtain an electroluminescent device based on the avalanche multiplication effect. The light-emitting device based on this mechanism has excellent electrical performance, low turn-on voltage and light-emitting voltage, minority electrons are injected from the metal back electrode from the p-type silicon side into the fluorine-erbium co-doped tin oxide light-emitting layer, and holes are injected from the oxide transparent electrode side into the fluorine-erbium co-doped tin oxide light-emitting layer, and the fluorine-erbium co-doped tin oxide film obtained by the radio frequency magnetron sputtering of the present invention has fewer defects and better uniformity than the traditional PLD (pulsed laser deposition) and spin coating preparation methods, and electrons directly collide with erbium ions under the acceleration of the space charge region, thereby obtaining Strong near-infrared characteristic electroluminescence; this mechanism is based on the avalanche multiplication effect in the space charge region of the diode under reverse bias to obtain high-energy thermal electron collisions to excite erbium ions. Compared with the traditional method of relying on a thermal oxide layer to obtain high-energy electrons, the process steps are simple and can reduce the cost in industrial production. Due to the excellent electrical properties of the fluorine-erbium co-doped tin oxide light-emitting layer, its turn-on voltage and light-emitting voltage are low, and the current flowing through the device during operation is small. The device has a longer life and optical power, and has a higher luminous intensity than electroluminescent devices with energy transfer mechanisms.

[0034] 3. The present invention successfully prepared an electroluminescent device based on electron impact ionization by using fluorine-erbium co-doped tin oxide as the erbium luminescent matrix through the radio frequency magnetron sputtering-high temperature rapid thermal treatment method and the design of the device structure. This type of device has fewer preparation steps and lower raw material costs. Its preparation and testing methods are highly compatible with existing processes, the technology is mature, the production process is simple and has certain industrial application prospects; its lower turn-on voltage can also ensure the working life and stability of the device.

[0035] 4. Due to the co-doping of fluorine, the electrical properties of the film of the present invention are enhanced, the turn-on voltage is significantly reduced, and electroluminescence can be detected at a voltage of 8V. At the same time, the symmetry of the crystal field where the erbium ions are located is reduced. The device has a strong near-infrared electroluminescence intensity and working stability, and the output light power can reach 2.37μW / cm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Rutherford backscattering element content spectrum of the prepared film.

[0037] Figure 2 is the UV-visible-infrared transmission spectrum of the film.

[0038] Figure 3 This is the X-ray diffraction pattern of the film after heat treatment, and the crystal plane corresponding to tin oxide is marked in the figure.

[0039] Figure 4 Scanning electron microscope (left) and atomic force microscope (right) photographs of the film after heat treatment.

[0040] Figure 5 High-angle annular dark field image (HAADF, left) of the heat-treated film and the energy dispersion spectrum at the corresponding position (right).

[0041] Figure 6 This is a schematic diagram of the structure of a fluorine-erbium co-doped tin oxide near-infrared electroluminescent device based on the avalanche multiplication effect (small picture in the figure) and a volt-ampere characteristic curve.

[0042] Figure 7 This is the electroluminescence spectrum of the fluorine-erbium co-doped tin oxide near-infrared electroluminescent device. The labels in the figure represent the current and voltage conditions of the electroluminescence test.

[0043] Figure 8 This is the near-infrared light power density diagram of the fluorine-erbium co-doped tin oxide near-infrared electroluminescent device at 1550nm.

[0044] Fig. 9 This is the X-ray diffraction pattern of the thin film prepared by erbium target sputtering in Comparative Example 1.

[0045] Fig.10 This is a comparison chart of the electroluminescence intensity of devices prepared using pure tin oxide target and fluorine-doped tin oxide target.

[0046] Fig.11 Schematic diagram of the theoretical model structure of erbium-doped tin oxide thin films without fluorine (left) and with fluorine (right). DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The raw materials in the following examples and comparative examples are all commercially available products without any other additional treatment.

[0048] Example

[0049] In this embodiment, the preparation of the fluorine-erbium co-doped tin oxide thin film electroluminescent device adopts radio frequency magnetron co-sputtering to grow a thin film on a (100) crystal orientation single-side polished p-type CZ single crystal silicon wafer with a resistivity of ρ of 0.15-0.3Ω·cm. When sputtering the thin film, the substrate heating temperature is 200°C, and the back vacuum degree of the radio frequency magnetron sputtering equipment is 2×10 -3 Pa, the sputtering gas is a mixture of oxygen and argon, the gas introduction rate is a volume ratio of oxygen and argon of 1:1, the total flow rate is 50sccm, the tin oxide target is doped with stannous fluoride, the stannous fluoride content is 5wt%, the sputtering power of the fluorine-doped tin oxide target is 90 watts, the sputtering power of the co-sputtered erbium oxide target is 50 watts, the sputtering chamber pressure is 1.0Pa, and the sample baffle is removed after 15 minutes of pre-sputtering to start sputtering, and the sputtering deposition time of the film is 20 minutes. After sputtering, the film is heat treated at a heating rate of 30℃ / s in an oxygen atmosphere at 900℃ for 15 minutes, and then rapidly cooled at a cooling rate of 7.5℃ / s. Subsequently, a gold electrode was sputtered on the back of p-type silicon by DC magnetron sputtering, and then an ITO transparent electrode was grown on one side of the film. The prepared film was kept at 300°C in a nitrogen atmosphere for 30 minutes to obtain good ohmic contact, resulting in an electroluminescent device with an Au / p-Si / SnO2:F:Er / ITO structure, in which the thickness of the ITO transparent electrode and the Au electrode were 100nm respectively, and the thickness of the fluorine-erbium co-doped tin oxide film (SnO2:F:Er) was 70nm.

[0050] The specific preparation method is as follows:

[0051] (1) For p-type silicon wafers, standard RCA cleaning was performed after processing. Before sputtering, anhydrous ethanol was first used to ultrasonically remove organic pollutants on the surface. Then, a dilute hydrofluoric acid solution (10 wt%) was used to remove the oxide layer on the surface of the silicon wafer. The silicon wafer was rinsed with deionized water to remove residual hydrofluoric acid. The p-type silicon wafer was placed in a radio frequency magnetron sputtering device, and then the vacuum was pumped to 2×10 -3Pa, and at the same time, heat the substrate silicon wafer to 200°C; co-sputter the stannous fluoride target and the erbium oxide target under the conditions of oxygen and argon (the oxygen and argon introduction rates are both 25 sccm) and a sputtering pressure of 1.0 Pa, block the substrate with a sample baffle, perform pre-sputtering for 15 minutes, and then open the baffle to sputter and deposit the fluorine-erbium co-doped tin oxide film on the silicon substrate. Figure 1 As shown in Figure 2, fluorine and erbium elements were successfully doped into the tin oxide matrix, where the erbium content accounted for 3.64 at% of the cation content; the optical transmittance of the co-doped film is shown in Figure 2. Figure 2 As shown, the film has high transmittance in the range of 300-1700nm, wherein the transmittance at 1550nm is about 90%, and the optical band gap is about 3.72eV, which is consistent with the literature reports and has excellent performance.

[0052] (2) The fluorine-erbium co-doped tin oxide thin film obtained by the sputtering is heat treated in an oxygen atmosphere by a high-temperature tube furnace, rapidly heating, then keeping the temperature at 900°C for 15 minutes, and then rapidly cooling, so that the erbium is evenly distributed in the thin film and the tin oxide is fully crystallized. Figure 3 As shown. The heat-treated film has high crystallinity, and no diffraction peaks of erbium and erbium oxide are detected, indicating that the erbium element is fully doped into the matrix; Figure 4 As shown in the figure, the surface of the film is very flat, without cracks or undulations, and its surface root mean square roughness is only 0.42nm; Figure 5 As shown in the middle left figure, the thickness of the fluorine-erbium co-doped film is about 70nm, and the energy dispersion spectrum imaging at the same position is as follows Figure 5 As shown in the middle right figure, each element is evenly distributed inside the film, and the high erbium content does not cause the generation of erbium clusters, which shows that the fluorine-doped tin oxide of the present invention is an excellent doping matrix for erbium.

[0053] (3) After applying a small amount of dilute hydrofluoric acid on the back side of the heat-treated sample (one side of the silicon wafer) to remove the surface oxide layer, clean the back side with a nitrogen air gun, place the sample in the RF magnetron sputtering chamber, and evacuate to a vacuum degree of 3×10 -3 Pa, under the conditions of introducing argon gas (50sccm) and a sputtering pressure of 3.0Pa, a layer of gold electrode was sputtered on the back of the sample using a high-purity gold target.

[0054] (4) Place the front side of the heat-treated sample (the side of the fluorine-erbium co-doped tin oxide film) into a DC magnetron sputtering chamber and evacuate the chamber to a vacuum of 2×10 -3 Pa, and at the same time the sample is heated to 150°C; under the conditions of passing argon gas (50sccm) and a sputtering pressure of 0.2Pa, a layer of ITO transparent electrode is sputtered on the front of the sample using an indium tin oxide target, and then the sample is placed in a nitrogen atmosphere at 300°C for 30 minutes to complete the preparation of the electroluminescent device.

[0055] (5) Further testing of electroluminescent devices based on fluorine-erbium co-doped tin oxide thin films. The device structure is as follows: Figure 6 As shown in the small figure, under reverse bias, that is, the gold electrode is connected to the negative and the ITO electrode is connected to the positive, the volt-ampere characteristic curve of the device is tested, such as Figure 6 As shown, the device has an electrical turn-on voltage of 4.3 V (current reaches 1 mA / cm 2 ). Hall effect tests show that the carrier concentration of fluorine-erbium co-doped tin oxide film is about 10 19 cm -3 , which is a heavily doped n-type semiconductor, the voltage of the device will be concentrated on the lightly doped silicon substrate side, and the silicon substrate will undergo avalanche breakdown, causing the heterojunction device in the reverse bias state to turn on.

[0056] (6) The prepared device was subjected to an electroluminescence test. The test results are as follows: Figure 7 As shown, it can be seen that the device produces a characteristic luminescence peak based on erbium ions in the near-infrared band, corresponding to 4 I 13 / 2 arrive 4 I 15 / 2 As the voltage increases, the luminous intensity of the electroluminescent device also increases, and the luminous voltage can be as low as 8V. The output light power density of the device when working is as follows: Figure 8 As shown in the figure, the detection limit of the optical power meter is slightly higher than that of the spectrometer, so the luminescence is detected from 10V. The optical power density output by the device increases with the voltage. When saturation is reached, the luminous power in the near-infrared band can reach 2.37μW / cm 2 This type of device has a low turn-on voltage, which is lower than most reported electroluminescent systems based on electron impact excitation. Strong electroluminescence was monitored at a voltage of 8V.

[0057] The fluorine-erbium co-doped tin oxide film prepared by the present invention has a high erbium doping concentration and the ability to suppress the energy back transfer effect while ensuring excellent optical and electrical properties. This type of film has the potential to obtain high output light power, low turn-on voltage and light-emitting voltage, compatible with CMOS manufacturing process and low application cost. This invention is expected to be applied to silicon-based integrated light sources, semiconductor light emission, optical communications and other fields.

[0058] Comparative Example 1

[0059] The only difference from the embodiment is that a metal erbium target is used instead of an erbium oxide target, and the other operating conditions are the same. The X-ray diffraction results of the heat-treated film are shown in FIG. Fig. 9As shown, the diffraction peak of erbium oxide (Er2O3) can be observed, which means that the sputtering of the erbium target causes erbium to not be completely incorporated into the fluorine-doped tin oxide matrix, but rather forms erbium clusters, which will produce serious concentration quenching effect in the electroluminescence test. Therefore, erbium oxide target is preferred as the target material.

[0060] Comparative Example 2

[0061] The only difference from the embodiment is that a pure tin oxide target is used instead of a fluorine-doped tin oxide target, and the other operating conditions are the same. Fig.10 The electroluminescent intensity comparison of the electroluminescent device of the Au / p-Si / SnO2:F:Er / ITO structure prepared in Example 2 and the electroluminescent device of the Au / p-Si / SnO2:Er / ITO structure prepared in Comparative Example 2 is shown. It can be seen that after doping with fluorine element, when the same injection current (about 28 mA) is reached, the injection voltage of the two devices differs by about 4 times. This is because fluorine incorporation improves the electrical properties of the device. At the same time, the electroluminescent intensity of the sample after fluorine doping is increased by about 245 times.

[0062] Fig.11 The schematic diagram of the structure of ErO6 (undoped with fluorine) and ErO4F2 (doped with fluorine) in the supercell is constructed using VESTA software, and the doping amount of the model is determined by the Rutherford backscattering element content spectrum in the embodiment. The change of the bond length around erbium after fluorine doping is simulated by the generalized gradient approximation theory to describe the crystal field symmetry, and the results are shown in Table 1. After doping, the bond length around the erbium element has changed significantly, and the standard deviation of the bond length has increased by about 6.2 times, which shows that the symmetry of the crystal field where the erbium element is located has decreased, which can increase the transition luminescence probability of erbium. Therefore, the incorporation of fluorine elements can improve the electrical properties and luminescence intensity of the device, so a fluorine-doped tin oxide target is preferably used as a target material.

[0063] Table 1

[0064]

[0065] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a fluorine-erbium co-doped tin oxide thin film, characterized in that: Includes steps: (1) Under vacuum, a mixture of argon and oxygen is introduced to co-sputter a fluorine-doped tin oxide target and an erbium oxide target by a radio frequency magnetron sputtering method to deposit a thin film; the mass percentage of stannous fluoride in the fluorine-doped tin oxide target is not more than 20%; (2) In an oxygen or nitrogen atmosphere, heating the film obtained by co-sputtering deposition to above 200° C. for high-temperature heat treatment, and cooling to obtain the fluorine-erbium co-doped tin oxide film; In step (2), the temperature is not raised or lowered with the furnace, but is raised or lowered rapidly; the heating rate of the heating is greater than 1°C / s, and the cooling rate of the cooling is greater than 1°C / s.

2. The preparation method according to claim 1, characterized in that: In step (1): the vacuum refers to a vacuum degree not greater than 5×10 -3 Pa; The volume proportion of argon in the argon and oxygen mixture is not less than 50%; The substrate temperature is heated to above 50°C; During sputtering, the power of the fluorine-doped tin oxide target is 10~170 watts, the power of the erbium oxide target is 5~70 watts, and the pressure of the sputtering chamber is 0.1~10 Pa.

3. The preparation method according to claim 1, characterized in that: In step (2): The temperature of the high temperature heat treatment is 200-1000°C.

4. The fluorine-erbium co-doped tin oxide thin film prepared by the preparation method according to any one of claims 1 to 3, characterized in that: Fluorine-erbium co-doped tin oxide crystals are formed in the fluorine-erbium co-doped tin oxide film.

5. The fluorine-erbium co-doped tin oxide thin film according to claim 4, characterized in that: In the fluorine-erbium co-doped tin oxide thin film, the atomic percentage of the erbium element is 1% to 5%, based on the total atomic number of the erbium element and the tin element being 100%.

6. The fluorine-erbium co-doped tin oxide thin film according to claim 4, characterized in that: The thickness of the fluorine-erbium co-doped tin oxide film is 20-500 nm.

7. Use of the fluorine-erbium co-doped tin oxide thin film according to any one of claims 4 to 6 in the field of near-infrared electroluminescence.

8. A near-infrared electroluminescent device providing hot electrons based on avalanche multiplication effect, characterized in that: The fluorine-erbium co-doped tin oxide thin film according to any one of claims 4 to 6 is used, wherein a metal back electrode for connecting to the negative pole of the power supply is deposited on one side of the substrate, and an oxide transparent electrode for connecting to the positive pole of the power supply is deposited on one side of the fluorine-erbium co-doped tin oxide thin film.

9. The near-infrared electroluminescent device for providing hot electrons based on avalanche multiplication effect according to claim 8, characterized in that: The substrate is silicon.

10. The near-infrared electroluminescent device for providing hot electrons based on avalanche multiplication effect according to claim 8, characterized in that: The turn-on voltage of the near-infrared electroluminescent device providing hot electrons based on the avalanche multiplication effect is lower than 5V.

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