Polarization tunable mid-infrared light emitting diode and preparation method thereof

Abstract

The application belongs to the technical field of semiconductors, and particularly relates to a polarization-adjustable mid-infrared light-emitting diode and a preparation method thereof. The light-emitting diode comprises a heterojunction composed of two p-type black phosphorus films with a partial overlapping area in a mid-infrared region, and the surfaces of the two p-type black phosphorus films have phosphorus oxide; metal electrodes are arranged on the two p-type black phosphorus films respectively, and an intrinsic silicon substrate with an insulating layer on the surface is further arranged below the lower p-type black phosphorus film. The application obtains black phosphorus films with different thicknesses through mechanical exfoliation, forms a phosphorus oxide layer in situ by air exposure treatment, obtains a black phosphorus-phosphorus oxide-black phosphorus heterojunction through simple stacking, and then combines a mature photolithography and evaporation process to prepare the metal electrodes, so that the assembly of the light-emitting diode device can be completed, and the production process is greatly simplified. The application successfully realizes the polarization state regulation of mid-infrared light emission, fills the related technical blank, and expands the application scenarios of the black phosphorus-based light-emitting diode.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a polarization-tunable mid-infrared light-emitting diode and its fabrication method. Background Technology

[0002] The mid-infrared emission spectrum, with its unique wavelength range (2-20 μm) encompassing the molecular fingerprint region and two atmospheric windows, has found wide application in gas sensing, free-space optical communication, and medical imaging. Among these applications, mid-infrared light sources are indispensable core components. Compared to other mid-infrared light sources (such as thermal radiation infrared sources and infrared lasers), mid-infrared light-emitting diodes (MIR-LEDs) are favored due to their narrower spectral lines, lower cost, lower power consumption, and portability. In existing commercial mid-infrared LEDs, III-V compounds, such as InSb and AlInSb, are commonly used active materials with narrow bandgap semiconductors. However, mid-infrared light sources made from these materials are bulky and difficult to integrate with silicon substrates. Black phosphorus, a novel van der Waals layered semiconductor, has attracted widespread attention due to its theoretically higher internal quantum efficiency than most commercial mid-infrared light-emitting device active materials and its ease of integration with silicon substrates. Existing publicly available mid-infrared light-emitting diodes based on black phosphorus, such as those in non-patent literature, *LIGHT: SCIENCE & APPLICATIONS 2020*, Vol. 9, No. 1, starting page 114; and patent application CN111554780A, discloses a type II band structure formed by vertically stacked black phosphorus and a molybdenum disulfide heterojunction. Under electrical excitation, electrons in the conduction band of molybdenum disulfide enter the black phosphorus and recombine with the numerous holes in the black phosphorus to emit light at a wavelength of 3.7 μm. Furthermore, due to the anisotropy of black phosphorus, the device exhibits different luminous intensities in the armchair (AC) and zigzag (ZZ) crystal orientations, with an intensity ratio exceeding 7. Non-patent literature Current Crowding in a High-Efficiency Black Phosphorus Light-Emitting Diode Using a Reflective Back Contact, NANO LETTERS 2025, Vol. 25, No. 30, starting page 11536: This literature reports the placement of a gold layer beneath a black phosphorus-molybdenum disulfide heterojunction to reflect the mid-infrared light radiated downwards by black phosphorus. By adjusting the thickness of black phosphorus and molybdenum disulfide, the device structure is optimized, the reflection enhancement effect is improved, and finally, electroluminescent mid-infrared light with an emission peak position of 3.8 μm at room temperature is achieved.

[0003] Currently, mid-infrared light-emitting diodes (LEDs) based on black phosphorus generally suffer from the following problem: black phosphorus emits light in a linearly polarized state, with the strongest emission along the armchair crystal orientation (AC), but emission is inhibited along the zigzag crystal orientation (ZZ). Current research and technology on black phosphorus-based mid-infrared LEDs focus primarily on improving luminous efficiency, with limited reports on the control of the emission polarization state. This prevents the realization of dynamically adjustable polarization, a function that could significantly improve the integration of mid-infrared optoelectronic systems. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a polarization-tunable mid-infrared light-emitting diode and its preparation method, which solves the technical problem that the existing black phosphorus-based mid-infrared light-emitting diodes can only achieve linear polarization light emission in a single polarization state.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a polarization-tunable mid-infrared light-emitting diode.

[0009] A polarization-tunable mid-infrared light-emitting diode includes a p-type first black phosphorus film and a p-type second black phosphorus film with a bandgap in the mid-infrared region. There is a partial overlap region between the first black phosphorus film and the second black phosphorus film, and phosphorus oxide is present at the surface of the overlap of the two films. The overlap region of the first black phosphorus film and the second black phosphorus film forms a heterojunction. Two metal electrodes are respectively disposed on the surface of the p-type first black phosphorus film and the p-type second black phosphorus film.

[0010] An intrinsic silicon substrate with an insulating layer on its surface is disposed below a first black phosphorus film. The insulating layer isolates the first black phosphorus film, located below a second black phosphorus film, from the intrinsic silicon substrate. A bias voltage is applied to the heterojunction via a metal electrode, grounding the upper black phosphorus layer. When a positive bias voltage is applied, holes in the lower black phosphorus layer are blocked from entering the upper black phosphorus layer due to the low valence band of phosphorus oxide, while electrons in the upper black phosphorus layer enter the lower black phosphorus layer unimpeded. Therefore, electron-hole recombination and light emission occur only at the lower black phosphorus layer. When a negative bias voltage is applied, holes in the upper black phosphorus layer are blocked, resulting in light recombination and light emission only at the upper black phosphorus layer.

[0011] Optionally, the thickness of both the first black phosphorus film and the second black phosphorus film is 5~100nm.

[0012] Optionally, the two black phosphorus films have different thicknesses, wherein the thickness of the first black phosphorus film is greater than the thickness of the second black phosphorus film.

[0013] Optionally, the insulating layer is silicon dioxide, and the area of ​​the overlapping region is ≥30μm×30μm.

[0014] Optionally, the metal electrode has a double-layer structure, consisting of a bismuth film with a thickness of 8-15 nm and a gold film with a thickness of 25-35 nm stacked from bottom to top.

[0015] Optionally, the spacing between the overlapping regions of the metal electrodes is 2~5μm.

[0016] Optionally, the polarization-tunable mid-infrared light-emitting diode further includes a hexagonal boron nitride film, which covers the surfaces of the first black phosphorus film, the second black phosphorus film, and the two metal electrodes.

[0017] Optionally, the thickness of the hexagonal boron nitride film is 5~20nm; the area of ​​the hexagonal boron nitride film can completely cover the first black phosphorus film and the second black phosphorus film.

[0018] Secondly, the present invention provides a method for fabricating a polarization-tunable mid-infrared light-emitting diode as described above, comprising the following steps:

[0019] S1. Obtain the first black phosphorus film and the second black phosphorus film in an inert gas environment, respectively;

[0020] S2. Place the first black phosphorus film and the second black phosphorus film in air, and generate an in-situ phosphorus oxide film through oxidation. Then characterize the crystal orientation of the two films respectively.

[0021] S3. In an inert gas environment, the first black phosphorus film is transferred to an intrinsic silicon substrate with an insulating layer on its surface, a portion of the second black phosphorus film is covered on the first black phosphorus film, and the crystal orientation difference between the first black phosphorus film and the second black phosphorus film is controlled.

[0022] S4. Anneal the structure obtained in S3 together with the intrinsic silicon substrate to form a heterojunction between the first black phosphorus film and the second black phosphorus film.

[0023] S5. Metal electrodes are deposited on the surfaces of the first and second black phosphorus films respectively.

[0024] In a preferred embodiment, in step S2, when the first black phosphorus film and the second black phosphorus film are placed in air, the time for laser pumping to characterize the crystal orientation is 30s to 5min.

[0025] In a preferred embodiment, in step S2, the first black phosphorus film and the second black phosphorus film are placed in the air, and the time for in-situ generation of the phosphorus oxide film is 3 to 20 minutes.

[0026] In a preferred embodiment, in step S4, after covering the first black phosphorus film with the second black phosphorus film, the resulting structure together with the intrinsic silicon substrate is annealed at 170~190°C for 15~20 min.

[0027] In a preferred embodiment, when forming the metal electrode by vapor deposition, a bismuth film layer with a thickness of 8-15 nm is first vapor deposited, followed by a gold film layer with a thickness of 25-35 nm.

[0028] In a preferred embodiment, the method further includes step S6, covering the surfaces of the first black phosphorus film, the second black phosphorus film, and the two metal electrodes with a hexagonal boron nitride film.

[0029] (III) Beneficial Effects

[0030] The beneficial effects of this invention are:

[0031] The present invention provides a polarization-tunable mid-infrared light-emitting diode, which significantly enhances the control effect and directional output capability of anisotropic light emission of black phosphorus. The adjustment of the emission polarization state does not require complicated operation, but can be achieved by simply changing the polarity of the applied bias voltage. It has a low operation threshold, fast response, and is convenient for flexible control in practical applications.

[0032] This invention provides a method for fabricating a polarization-tunable mid-infrared light-emitting diode (LED). It eliminates the need for complex equipment or stringent fabrication conditions, requiring only mechanical peeling to obtain black phosphorus films of varying thicknesses. A phosphorus oxide layer is then formed in situ by air exposure for 3 minutes. Simple stacking of these layers yields a black phosphorus-phosphorus oxide-black phosphorus heterojunction. Subsequent electrode fabrication using mature photolithography and evaporation processes completes device assembly, significantly simplifying the production process. Compared to existing black phosphorus mid-infrared LEDs that cannot achieve polarization tunability, this invention successfully achieves polarization state modulation of mid-infrared emission, filling a technological gap and expanding the application scenarios of black phosphorus-based LEDs. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a polarization-tunable mid-infrared light-emitting diode based on black phosphorus-phosphorus oxide-black phosphorus in Embodiment 1 of the present invention;

[0034] Figure 2 This is a magnified view of a portion of the black phosphorus interface between the upper and lower layers of the polarization-tunable mid-infrared light-emitting diode in Example 1.

[0035] Figure 3 This is a sample image of a mid-infrared light-emitting diode based on black phosphorus-phosphorus oxide-black phosphorus with a crystal orientation difference of 69° prepared in Example 3 of the present invention.

[0036] Figure 4 This is a graph showing the change in electroluminescence intensity of a polarization-tunable light-emitting diode with a crystal orientation difference of 69° as a function of polarization angle in Example 3.

[0037] Figure 5 This is a graph showing the normalized electroluminescence intensity of the polarization-tunable light-emitting diode with a crystal orientation difference of 69° as a function of polarization angle in Example 3.

[0038] Figure 6 This is a graph showing the normalized electroluminescence intensity of a black phosphorus polarization-tunable light-emitting diode with a crystal orientation difference of 50° as a function of polarization angle in Example 4.

[0039] Figure 7 This is a graph showing the normalized electroluminescence intensity of a black phosphorus polarization-tunable light-emitting diode with a crystal orientation difference of 14° as a function of polarization angle in Example 5.

[0040] Figure 8 This is a graph showing the normalized electroluminescence intensity of a black phosphorus polarization-tunable light-emitting diode with a crystal orientation difference of 87° as a function of polarization angle in Example 6.

[0041] Figure 9 This is a schematic diagram of the polarization-tunable mid-infrared light-emitting diode in Example 7.

[0042] Figure 10 The actual photoluminescence intensity of the light-emitting diode with a crystal orientation difference of 50° in Comparative Example 1 is shown.

[0043] Figure 11 The graph shows the normalized electroluminescence intensity of the light-emitting diode with a crystal orientation difference of 50° in Comparative Example 1 as a function of polarization angle.

[0044] Figure 12 The image shows the electroluminescence intensity of the light-emitting diode with a crystal orientation difference of 23° in Comparative Example 2.

[0045] Figure 13 The graph shows the normalized electroluminescence intensity of the light-emitting diode with a crystal orientation difference of 23° in Comparative Example 2 as a function of polarization angle.

[0046] [Explanation of Labels in the Attached Image]

[0047] 1: First black phosphorus film;

[0048] 2: Second black phosphorus film;

[0049] 3: Phosphorus oxide film;

[0050] 4: Silicon dioxide insulating layer;

[0051] 5: Intrinsic silicon substrate;

[0052] 6: Bismuth / gold metal electrode;

[0053] 7: Hexagonal boron nitride thin film. Detailed Implementation

[0054] The inventive principle of this invention lies in providing a polarization-tunable mid-infrared light-emitting diode based on black phosphorus-phosphorus oxide-black phosphorus. The fabrication process is simple and controllable: first, black phosphorus films of different thicknesses are obtained through mechanical peeling; the black phosphorus films are then exposed to air for 3-20 minutes to form a phosphorus oxide layer in situ; then, the black phosphorus films with the oxide layer are stacked together to obtain a black phosphorus-phosphorus oxide-black phosphorus heterojunction; finally, a metal electrode is fabricated on top of the black phosphorus films using a mature photolithography evaporation process to obtain a polarization-tunable mid-infrared light-emitting diode. The polarization state of this mid-infrared light-emitting diode can be controlled simply by changing the polarity of the applied bias voltage, without the need for additional cumbersome operations.

[0055] The polarization-tunable mid-infrared light-emitting diode provided by this invention is characterized by the following method:

[0056] 1) Apply an electrical excitation signal to the target device: Apply an AC square wave voltage to the polarization-tunable mid-infrared light-emitting diode through a signal generator to drive the device to produce an electroluminescence effect;

[0057] 2) Acquisition and noise reduction of mid-infrared emission signal: The mid-infrared emission signal generated by the electrical excitation of the polarization-tunable mid-infrared light-emitting diode is acquired using a Fourier transform infrared spectrometer; the interference of background blackbody radiation noise is filtered out simultaneously using a lock-in amplifier, and finally the electroluminescence (EL) spectrum of the polarization-tunable mid-infrared light-emitting diode is obtained.

[0058] 3) Polarization angle dependence measurement: A mid-infrared polarizer is installed in the light path for collecting the emission signal. The detection angle is adjusted by rotating the polarizer to complete the quantitative test of the electroluminescence intensity of the polarization-tunable mid-infrared light-emitting diode under different polarization angles.

[0059] The polarization-tunable mid-infrared light-emitting diode provided by this invention exhibits an electroluminescent mid-infrared light emission peak position. With a positive bias of 3.53 μm and a negative bias of 3.64 μm, both peak positions fall within the low-loss region (3.5-3.7 μm) of the window core. Compared to the existing technology's 3.8 μm, this represents a wavelength shift of 0.16-0.27 μm, a reduction in atmospheric transmission attenuation rate of approximately 15%-25%, and a significant improvement in light propagation efficiency. Existing technologies only allow peak position adjustment via heterojunction thickness, resulting in a narrow tuning range, slow response, and a fixed peak position of 3.8 μm, limiting application scenarios. In contrast, this invention achieves continuous adjustment of the peak position between 3.53-3.64 μm through positive / negative bias. A single device can be adapted to various scenarios such as portable sensing and short-range infrared communication without structural changes, achieving a tuning response speed at the nanosecond level.

[0060] To better explain and facilitate understanding of the present invention, exemplary embodiments of the invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. Unless otherwise specified, the technical means employed in this invention are conventional techniques in the art, and the raw materials used can be commercially available products. In this invention, intrinsic silicon refers to pure single-crystal silicon that is free of any impurities and has a complete crystal lattice structure.

[0061] Example 1

[0062] This embodiment provides a polarization-tunable mid-infrared light-emitting diode based on black phosphorus-phosphorus oxide-black phosphorus. Figure 1 , Figure 2 These are a schematic diagram and a partial enlarged view of the device involved in Embodiment 1, respectively. Figure 1 As shown, the mid-infrared light-emitting diode element of this embodiment includes: a p-type first black phosphorus film 1 with a bandgap in the mid-infrared region and a thickness of 5nm~100nm; and a p-type second black phosphorus film 2 with a bandgap in the mid-infrared region and a thickness of 5nm~100nm. The first black phosphorus film 1 and the second black phosphorus film 2 are partially stacked, and a phosphorus oxide film 3 exists at their overlapping interface. An insulating layer 4 made of silicon dioxide is disposed below the first black phosphorus film 1, and an intrinsic silicon substrate 5 is disposed below the insulating layer 4. The insulating layer 4 isolates the first black phosphorus film 1 from the intrinsic silicon substrate 5. Metal electrodes 6, which are bismuth / gold electrodes, are respectively disposed on the outer surfaces of the first black phosphorus film 1 and the second black phosphorus film 2. The intrinsic silicon substrate 5 is a high-purity single-crystal silicon wafer with almost no impurities, a fundamental material for semiconductor manufacturing and microelectronic devices; its atomic arrangement is a perfect diamond crystal structure, with almost no free electrons at absolute zero, making it an excellent insulator.

[0063] In one exemplary embodiment of the present invention, such as Figure 1 In the middle, the polarization-tunable mid-infrared light-emitting diode consists of an intrinsic silicon substrate 5, an insulating layer 4, a first black phosphorus film 1, a phosphorus oxide film 3, a second black phosphorus film 2, and a metal electrode 6, from bottom to top. The first black phosphorus film 1 and the second black phosphorus film 2 are partially overlapped and in contact, and the interface between the first black phosphorus film 1 and the second black phosphorus film 2 is covered by a phosphorus oxide film 3. The metal electrode 6 is disposed on the outer surface of the first black phosphorus film 1 and the p-type second black phosphorus film 2.

[0064] This invention also provides a method for fabricating a polarization-tunable mid-infrared light-emitting diode, comprising the following steps:

[0065] (1) The first black phosphorus film and the second black phosphorus film were obtained by mechanical peeling in an inert gas glove box.

[0066] (2) Remove the first and second black phosphorus films from the inert gas glove box and leave them in the air for 3 to 20 minutes. At this time, due to the presence of oxygen in the air, an oxide layer of phosphorus oxide will be generated in situ on both black phosphorus films.

[0067] (3) Place the two black phosphorus films back into the inert gas glove box and use a PDMS-assisted dry transfer method (place the PDMS with the black phosphorus film sample on the surface onto a glass slide, invert the slide and fix it on the transfer stage fixture, place the intrinsic silicon substrate with a silicon dioxide insulating layer on the sample stage and use a vacuum pump to adsorb it, place the PDMS facing the intrinsic silicon substrate with a silicon dioxide insulating layer on the surface, then lower the fixture to make the PDMS adhere to the substrate, then heat the sample stage, and then slowly raise the fixture, and the black phosphorus film sample will be released onto the substrate) to cover the first black phosphorus film 1 onto the intrinsic silicon substrate 5 with a silicon dioxide insulating layer 4 on the surface, and then cover the first black phosphorus film 1 with the second black phosphorus film 2, so that the overlap area between the two is not less than 30μm×30μm. Phosphorus oxide 3 is present at the interface between the first black phosphorus film 1 and the second black phosphorus film 2.

[0068] (4) In order to improve the quality of the interface between the upper and lower black phosphorus layers, the silicon wafer was placed on the hot table in the inert gas glove box and annealed at 180 degrees Celsius for 20 minutes to form a heterojunction between the upper and lower black phosphorus films.

[0069] (5) A pair of electrode patterns are photolithographically patterned on the first black phosphorus film 1 and the second black phosphorus film 2 of the prepared heterojunction (the electrode pattern area does not contain photoresist, while other areas contain photoresist). Then, a bismuth / gold metal electrode 6 is deposited on the first black phosphorus film 1 and the second black phosphorus film 2. The bismuth / gold metal electrode consists of two metal films: the first layer is bismuth with a thickness of 10 nm, and the second layer is gold with a thickness of 30 nm. The distance between the metal electrode 6 and the overlapping area is 3 μm.

[0070] In one example embodiment, the thickness of the first black phosphorus film 1 is 50 nm; the thickness of the second black phosphorus film 2 is 20 nm.

[0071] The polarization-tunable mid-infrared light-emitting diode (LED) prepared in this embodiment exhibits polarization-tunable emission because phosphorus oxide has a low valence band. When a positive bias is applied, holes in the first black phosphorus film are blocked from entering the second black phosphorus film, while electrons in the second black phosphorus film enter the first black phosphorus film unimpeded, resulting in light emission only in the first black phosphorus film. When a negative bias is applied, holes in the second black phosphorus film are blocked, resulting in light emission only in the second black phosphorus film. By utilizing the crystal orientation difference between the first and second black phosphorus films, polarization-tunable emission is achieved. Furthermore, the two polarization states of the polarization-tunable mid-infrared LED prepared using the above method are random because the crystal orientations of the two black phosphorus films were not characterized during the stacking of the black phosphorus-phosphorus oxide-black phosphorus heterojunction. Therefore, the crystal orientation difference between the upper and lower black phosphorus films obtained by randomly stacking them without characterizing the crystal orientation is random, and the estimated crystal orientation may deviate from the actual crystal orientation.

[0072] Example 2

[0073] This embodiment provides a method for fabricating a polarization-tunable mid-infrared light-emitting diode based on black phosphorus-phosphorus oxide-black phosphorus. The difference between this embodiment and Embodiment 1 is that after removing the two black phosphorus films from the inert gas glove box, instead of allowing them to stand in air for 3 to 20 minutes, the black phosphorus films are placed on a 100°C hot stage for 30 seconds. The higher temperature increases the oxidation rate, and this method can quickly obtain a 2nm thick phosphorus oxide layer. The specific fabrication method is basically the same as in Embodiment 1, except that in step (2), instead of allowing the black phosphorus films to stand in air for 3 to 20 minutes, the black phosphorus is placed on a 100°C hot stage and heated for 30 seconds. The technical effect produced by this embodiment is the same as that of oxidation by standing in air; both can generate phosphorus oxide and achieve tunable light emission polarization. Simultaneously, this method can accelerate the fabrication speed of polarization-tunable mid-infrared light-emitting diodes and improve production efficiency.

[0074] Example 3

[0075] The polarization-tunable mid-infrared light-emitting diode based on black phosphorus-phosphorus oxide-black phosphorus in this embodiment differs from Embodiment 1 in that, after the first black phosphorus film 1 and the second black phosphorus film 2 are removed from the inert gas glove box, their crystal orientations are characterized. The characterization method utilizes the linear polarization characteristic of black phosphorus emission by irradiating the black phosphorus film with a 520nm laser to induce photoluminescence. Taking advantage of the complete suppression of light emission in the serrated crystal orientation of the black phosphorus film, the serrated crystal orientation is determined by rotating the angle of the polarizer, thus obtaining the crystal orientation information of the black phosphorus film. This method provides precise crystal orientation information for the black phosphorus film. Combined with a displacement stage that can adjust the silicon wafer angle, precise control of the crystal orientation of the upper and lower black phosphorus film layers can be achieved, thereby enabling precise control of the emission polarization state.

[0076] The specific preparation method is as follows:

[0077] (1) In an inert gas glove box, a first black phosphorus film 1 with a thickness of 50 nm and a second black phosphorus film 2 with a thickness of 20 nm were obtained by mechanical peeling.

[0078] (2) The first black phosphorus film 1 and the second black phosphorus film 2 were taken out of the inert gas glove box and their crystal orientations were characterized. The characterization process was carried out in air and the characterization time was controlled within 5 minutes. During this process, a phosphorus oxide layer 3 was generated in situ on the surface of the two black phosphorus films.

[0079] (3) Place the two black phosphorus films back into the inert gas glove box, and then use PDMS-assisted dry transfer method to cover the first black phosphorus film 1 onto the intrinsic silicon substrate 5 with a silicon dioxide insulating layer 4 on the surface; then precisely control the angle of the first black phosphorus film 1 on the silicon substrate (characterizing the known serrated direction of the first black phosphorus film 1). The silicon substrate is vacuum adsorbed on a rotatable sample stage. The sample stage can be rotated to change the orientation of the serrated direction of the first black phosphorus film 1, thereby changing the relationship between the first black phosphorus film 1 and the second black phosphorus film 2. To precisely control the crystal orientation difference between the first and second black phosphorus films, a second black phosphorus film 2 was placed over the first black phosphorus film 1, ensuring an overlap area of ​​no less than 30 × 30 μm. Phosphorus oxide 3 was present at the interface between the first and second black phosphorus films 1 and 2. Subsequently, a Fourier transform infrared spectroscopy (FTIR) instrument was used to induce photoluminescence in the black phosphorus films via laser pumping. Polarization-resolved spectroscopy was used to characterize the results, and the crystal orientation difference between the first and second black phosphorus films 1 and 2 was measured to be 69°.

[0080] (4) In order to improve the quality of the interface between the upper and lower black phosphorus layers, the intrinsic silicon substrate was placed on a hot stage in an inert gas glove box and annealed at 180°C for 20 minutes to form a heterojunction between the upper and lower black phosphorus films.

[0081] (5) A pair of electrode patterns are photolithographically etched on the first black phosphorus film 1 and the second black phosphorus film 2 of the prepared heterojunction (the electrode pattern area does not contain photoresist, while other areas contain photoresist). Then, bismuth / gold metal electrodes 6 are deposited on the first black phosphorus film 1 and the second black phosphorus film 2 respectively. The distance between the metal electrodes 6 and the overlapping area is 3 μm. The pair of metal electrodes consists of two metal films: the first layer is bismuth with a thickness of 10 nm, and the second layer is gold with a thickness of 30 nm.

[0082] In addition, it should be noted that since the characterization is performed by using laser pumping to make black phosphorus emit light, the oxidation process of black phosphorus will be accelerated by the laser. Therefore, when stacking the second black phosphorus film 2 onto the first black phosphorus film 1 in step (3), extra care should be taken to ensure that the overlapping area avoids the laser irradiation area; and the characterization time should be controlled within 3 minutes.

[0083] The polarization-tunable mid-infrared light-emitting diode prepared above was observed under an optical microscope, as follows: Figure 3 As shown in the figure, the solid line area represents the upper black phosphorus film (Top BP), i.e., the second black phosphorus film 2, and the dashed line represents the lower black phosphorus film (Bottom BP), i.e., the first black phosphorus film 2. The scale bar is 30 μm. Using a Fourier transform infrared spectroscopy (FTIR) spectrometer, laser pumping was used to induce photoluminescence in the black phosphorus film. Polarization-resolved characterization revealed a crystal orientation difference of 69°. Subsequently, a signal generator was used to apply an external bias voltage to the device. First, a positive bias voltage of 3V was applied, followed by a negative bias voltage of -3V. By changing the bias voltage polarity and rotating the polarizer angle, the variation of the electroluminescence intensity of the device with the polarization angle was measured. The results are shown below. Figure 4 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 3V. The device exhibits a difference in luminescence intensity between the armchair (AC) and zigzag (ZZ) crystal orientations, with an intensity ratio exceeding 38. It emits electroluminescent mid-infrared light with a peak emission position of 3.53μm at room temperature. The star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -3V. The device also shows a difference in luminescence intensity between the armchair (AC) and zigzag (ZZ) crystal orientations, with an intensity ratio exceeding 27. It emits electroluminescent mid-infrared light with a peak emission position of 3.64μm at room temperature. The solid lines represent scattered points using I=cos... 2 The fitted value of (θ+φ). The graph showing the change in electroluminescence intensity as a function of polarization angle after normalizing the luminescence intensity is shown below. Figure 5 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 3V, and the star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -3V; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ) shows a more pronounced change in the polarization state of the emitted light under different polarities, as observed in the figure. With an applied bias voltage (top black phosphorus grounded) of +5V, the calculated external quantum efficiency (calculated as the number of emitted photons divided by the number of injected electrons) at room temperature is 0.16%; with an applied bias voltage of -5V, the calculated external quantum efficiency at room temperature is 0.072%.

[0084] The mid-infrared light-emitting diode (LED) fabricated in this invention exhibits a blue shift of the emission peak to 3.53 μm under positive bias and to 3.64 μm under negative bias, both falling within the 3-5 μm mid-infrared atmospheric transmission window. Furthermore, the device demonstrates significantly improved luminous intensity and external quantum efficiency, indicating that bias control achieves both precise peak optimization and enhanced luminous efficiency. The overall performance of the device is significantly superior to existing technologies. This invention enables continuous adjustment of the peak position between 3.53 and 3.64 μm via positive / negative bias, allowing a single device to be adapted for various scenarios such as portable sensing and short-range infrared communication without structural changes, achieving a tuning response speed in the nanosecond range.

[0085] Example 4

[0086] The fabrication method of the polarization-tunable mid-infrared light-emitting diode provided in this embodiment is the same as that in Embodiment 3, except that the angle difference between the serrated directions of the first and second black phosphorus films is controlled during the dry transfer in step 3. The normalized electroluminescence intensity of the device with a crystal orientation difference of 50° changes with the polarization angle as follows: Figure 6 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 6V, and the star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -4V; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ).

[0087] Example 5

[0088] The fabrication method of the polarization-tunable mid-infrared light-emitting diode provided in this embodiment is the same as that in Embodiment 3, except that the angle difference between the serrated directions of the first and second black phosphorus films is controlled during the dry transfer in step 3. The normalized electroluminescence intensity of the device with a crystal orientation difference of 14° changes with the polarization angle as follows: Figure 7 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 3V, and the star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -3V; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ).

[0089] Example 6

[0090] The fabrication method of the polarization-tunable mid-infrared light-emitting diode provided in this embodiment is the same as that in Embodiment 3, except that the angle difference between the serrated directions of the first and second black phosphorus films is controlled during the dry transfer in step 3. The normalized electroluminescence intensity of the device with a crystal orientation difference of 87° changes with the polarization angle as follows: Figure 8 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 3V, and the star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -3V; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ).

[0091] Example 7

[0092] A schematic diagram of the polarization-tunable mid-infrared light-emitting diode involved in this embodiment is shown below. Figure 9 As shown, the difference from Example 3 is that after stacking the black phosphorus-phosphorus oxide-black phosphorus heterojunction in step (3), a hexagonal boron nitride film 7 is also covered on top of the heterojunction in an inert gas glove box to achieve encapsulation and isolate oxygen. The preparation method of the polarization-tunable mid-infrared light-emitting diode in this embodiment includes the following steps:

[0093] (1) In an inert gas glove box with a nitrogen atmosphere, a first black phosphorus film 1 with a thickness of 30 nm, a second black phosphorus film 2 with a thickness of 15 nm and a hexagonal boron nitride film 7 with a thickness of 10 nm were obtained by mechanical stripping.

[0094] (2) The first black phosphorus film 1 and the second black phosphorus film 2 were removed from the inert gas glove box. Using a Fourier transform infrared spectrometer, the black phosphorus films were photoluminescent using laser pumping. The crystal orientation of the black phosphorus film 1 and the black phosphorus film 2 were characterized by polarization resolution, and the time was controlled within 5 minutes. At this time, since the characterization process was carried out in the air, an oxide layer of phosphorus oxide 3 was present on both black phosphorus films.

[0095] (3) Place the two black phosphorus films back into the inert gas glove box, and then use a PDMS-assisted dry transfer method to cover the first black phosphorus film 1 onto the intrinsic silicon substrate 5 with a silicon dioxide insulating layer 4 on its surface; then precisely control the angle of the first black phosphorus film 1 on the silicon substrate, and cover the second black phosphorus film 2 on top of the black phosphorus film 1, so as to achieve precise control of the crystal orientation difference between the first black phosphorus film 1 and the second black phosphorus film 2, and make the overlap area not less than 30μm×30μm. Phosphorus oxide 3 is present at the interface between the first black phosphorus film 1 and the second black phosphorus film 2. Then cover the first black phosphorus film 1 and the second black phosphorus film 2 with a hexagonal boron nitride film 7.

[0096] (4) In order to improve the quality of the interface between the upper and lower black phosphorus films, the silicon wafer was placed on the hot table in the inert gas glove box and annealed at 180°C for 20 minutes to form a heterojunction between the upper and lower black phosphorus films.

[0097] (5) Using photolithography, a pair of electrode patterns are photolithographically etched on the first black phosphorus film 1 and the second black phosphorus film 2 of the heterojunction prepared above (the electrode pattern area does not contain photoresist, while other areas contain photoresist). Then, bismuth / gold metal electrodes 6 are deposited on the first black phosphorus film 1 and the second black phosphorus film 2 respectively. The distance between the metal electrodes 6 and the overlapping area is 3 μm. This pair of metal electrodes consists of two metal films: the first layer is bismuth with a thickness of 10 nm, and the second layer is gold with a thickness of 30 nm.

[0098] (6) In an inert gas glove box, a hexagonal boron nitride film 7 is placed over the first black phosphorus film 1 and the second black phosphorus film 2 to achieve encapsulation and isolate oxygen. In addition, it should be noted that the thickness of the hexagonal boron nitride film 7 should be less than 20 nm to reduce the attenuation of the light-emitting effect of the device; at the same time, the area of ​​the hexagonal boron nitride film 7 should not only be larger than the overlapping area of ​​the first black phosphorus film 1 and the second black phosphorus film 2, but also completely cover the first black phosphorus film 1 and the second black phosphorus film 2 to prevent oxygen from continuing to erode the overlapping area of ​​black phosphorus after the black phosphorus in the non-overlapping area is completely oxidized, thereby ensuring the stability of the light-emitting device.

[0099] Comparative Example 1

[0100] This comparative example is based on Example 3, but differs from Example 3 in that: after obtaining the first black phosphorus film 1 and the second black phosphorus film 2, no oxide layer was introduced; instead, the two were directly stacked to form a heterojunction. Then, using a Fourier transform infrared spectroscopy, the black phosphorus film was photoluminescently induced by laser pumping. Polarization-resolved characterization revealed a crystal orientation difference of 56°. Figure 10 As shown in the figure, the circular dots represent the actual photoluminescence intensity of the lower layer of black phosphorus, and the star-shaped dots represent the actual photoluminescence intensity of the upper layer of black phosphorus; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ) was then obtained. Subsequently, a signal generator was used to apply an external bias voltage to the device. First, a positive bias voltage of 10V was applied, followed by a negative bias voltage of -8V, thus changing the bias polarity. The change in the device's electroluminescence intensity as a function of the polarization angle was measured by rotating the polarizer angle, as shown below. Figure 11 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 10V, and the star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -8V; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ). Comparing the actual test results of the emission polarization state of each device, it can be seen that without the introduction of the phosphorus oxide layer, the device is difficult to achieve the function of adjustable emission polarization.

[0101] Comparative Example 2

[0102] This comparative example is based on Example 3, but differs from Example 3 in that the first and second black phosphorus films were subjected to a very short static oxidation time in air, only 1 minute, and were subsequently stacked in a glove box to form a heterojunction. Then, using a Fourier transform infrared spectroscopy (FTIR) spectrometer, the black phosphorus films were photoluminescently induced by laser pumping. Polarization-resolved characterization revealed a crystal orientation difference of 23°. Figure 12 As shown in the figure, the circular dots represent the actual photoluminescence intensity of the lower layer of black phosphorus, and the star-shaped dots represent the actual photoluminescence intensity of the upper layer of black phosphorus; the solid line represents scattered points using I=cos 2The fitted value of (θ+φ) was then obtained. Subsequently, a signal generator was used to apply an external bias voltage to the device. First, a positive bias voltage of 8V was applied, followed by a negative bias voltage of -10V, thus changing the bias polarity. The change in the device's electroluminescence intensity as a function of the polarization angle was measured by rotating the polarizer angle, as shown below. Figure 13 As shown in the figure, the circular dots represent the actual electroluminescence intensity at a bias voltage of 8V, and the star-shaped dots represent the actual electroluminescence intensity at a bias voltage of -10V; the solid line represents scattered points using I=cos 2 The fitted value of (θ+φ). Comparing the actual test results of the emission polarization state of each device, it can be seen that when the formation time of the phosphorus oxide layer is too short, the device will also find it difficult to achieve the function of adjustable emission polarization.

[0103] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0104] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0105] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," or "on top" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," or "beneath" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0106] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0107] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A polarization-tunable mid-infrared light-emitting diode, characterized in that, It includes: The first and second black phosphorus films of type p have band gaps in the mid-infrared region. There is a partial overlap region between the first and second black phosphorus films, and phosphorus oxide is present at the surface where the two films overlap. The overlap region of the first and second black phosphorus films forms a heterojunction. Two metal electrodes are respectively disposed on the surfaces of the p-type first black phosphorus film and the p-type second black phosphorus film; An intrinsic silicon substrate with an insulating layer on its surface is disposed below a first black phosphorus film, and the insulating layer isolates the first black phosphorus film, which is located below a second black phosphorus film, from the intrinsic silicon substrate.

2. The polarization-tunable mid-infrared light-emitting diode as described in claim 1, characterized in that, The thickness of both the first and second black phosphorus films is 5~100nm.

3. The polarization-tunable mid-infrared light-emitting diode as described in claim 1 or 2, characterized in that, The thickness of the first black phosphorus film is greater than the thickness of the second black phosphorus film.

4. The polarization-tunable mid-infrared light-emitting diode as described in claim 1, characterized in that, The insulating layer is silicon dioxide, and the area of ​​the overlapping region is ≥30μm×30μm.

5. The polarization-tunable mid-infrared light-emitting diode as described in claim 1, characterized in that, The metal electrode has a double-layer structure, consisting of a bismuth film with a thickness of 8-15 nm and a gold film with a thickness of 25-35 nm stacked from bottom to top.

6. The polarization-tunable mid-infrared light-emitting diode as described in any one of claims 1-5, characterized in that, It also includes a hexagonal boron nitride film, which covers the surfaces of the first black phosphorus film, the second black phosphorus film, and the two metal electrodes.

7. The polarization-tunable mid-infrared light-emitting diode as described in claim 6, characterized in that, The thickness of the hexagonal boron nitride film is 5~20nm; the area of ​​the hexagonal boron nitride film can completely cover the first black phosphorus film and the second black phosphorus film.

8. A method for fabricating a polarization-tunable mid-infrared light-emitting diode as described in any one of claims 1-7, comprising the following steps: S1. Obtain the first black phosphorus film and the second black phosphorus film in an inert gas environment, respectively; S2. Place the first black phosphorus film and the second black phosphorus film in air, and generate an in-situ phosphorus oxide film through oxidation. Then characterize the crystal orientation of the two films respectively. S3. In an inert gas environment, the first black phosphorus film is transferred to an intrinsic silicon substrate with an insulating layer on its surface, a portion of the second black phosphorus film is covered on the first black phosphorus film, and the crystal orientation difference between the first black phosphorus film and the second black phosphorus film is controlled. S4. Anneal the structure obtained in S3 together with the intrinsic silicon substrate to form a heterojunction between the first black phosphorus film and the second black phosphorus film. S5. Metal electrodes are deposited on the surfaces of the first and second black phosphorus films respectively.

9. The preparation method according to claim 8, characterized in that, In step S2, when the first black phosphorus film and the second black phosphorus film are placed in air, the time for characterizing the crystal orientation using the laser pumping method is 30s~5min.

10. The preparation method according to claim 8, characterized in that, It also includes step S6, covering the surface of the first black phosphorus film, the second black phosphorus film and the two metal electrodes with a hexagonal boron nitride film.

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