Tunnel junction structure, light-emitting device and preparation method thereof

Abstract

The invention discloses a tunnel junction structure, a light-emitting device and a preparation method thereof, the tunnel junction structure comprises a P-type buried layer and a first N-type contact layer stacked on the P-type buried layer, the P-type buried layer and the first N-type contact layer form a tunnel junction, the P-type buried layer is doped with Mg, and the P-type buried layer is doped with Mg. And at least one hole penetrating through the first N-type contact layer is formed in the first N-type contact layer. The tunnel junction structure is prepared by adopting the first N-type contact layer with the holes, so that the hydrogen diffusion efficiency in the P-type buried layer can be effectively improved, the activation efficiency of Mg can be improved, the hole injection capability in the P-type buried layer can be improved, and the voltage loss can be reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and in particular relates to a tunnel junction structure, a light-emitting device and a preparation method thereof. Background Art

[0002] Deep ultraviolet LED is a semiconductor light-emitting device based on gallium nitride (GaN) or aluminum gallium nitride (AlGaN) materials. Its high energy characteristics give it important application potential in public health and industrial disinfection, and it is regarded as a key technology to replace traditional mercury lamps.

[0003] The P-type GaN layer in the currently widely used deep ultraviolet light-emitting devices has a strong absorption of ultraviolet light, and most of them adopt P-type ohmic contact and use conventional Ni / Au ohmic contact electrodes. This type of ohmic contact electrode significantly absorbs deep ultraviolet light, making the external quantum efficiency of GaN-based deep ultraviolet light-emitting devices low, usually less than 10%, resulting in a significant reduction in the luminescence rate of the light-emitting device.

[0004] In the prior art, tunnel junction technology is used to replace the traditional P-type ohmic contact to improve the hole injection efficiency, thereby improving the luminescence rate of the light-emitting device. However, in the prior art, the Mg-doped P-type buried layer is mostly prepared by the Metal-organic Chemical Vapor Deposition (MOCVD) process in a hydrogen-rich environment, resulting in the Mg in the P-type buried layer being passivated in the form of Mg-H defect clusters, which cannot be effectively activated to generate holes. The binding energy of the Mg-H defect cluster in the conventional P-type buried layer is about 0.7 eV, and the diffusion energy barrier of H in the P-type buried layer is about 0.7 eV. Annealing at a temperature of 550°C for 5 minutes can achieve sufficient dehydrogenation and depassivation. However, in the tunnel junction structure, the P-type buried layer is prepared under the N-type contact layer. The Fermi level of the N-type contact layer is close to the conduction band, which causes the H diffusion energy barrier to rise to 3.4 eV. H cannot be diffused out by high-temperature annealing, resulting in the inability to effectively activate Mg. Therefore, due to the influence of Mg doping tailing and low dehydrogenation efficiency in the tunnel junction structure, the tunnel junction structure in the prior art has high voltage loss and low tunneling current density, which seriously affects the performance of the light-emitting device.

[0005] Therefore, in order to solve the above technical problems, it is necessary to provide a tunnel junction structure, a light-emitting device and a preparation method thereof. Summary of the Invention

[0006] The object of the present invention is to provide a tunnel junction structure, a light-emitting device and a preparation method thereof, which can improve the dehydrogenation efficiency in a P-type buried layer and promote Mg activation.

[0007] In order to achieve the above-mentioned purpose, the technical solution provided by one embodiment of the present invention is as follows:

[0008] A tunnel junction structure includes a P-type buried layer and a first N-type contact layer stacked on the P-type buried layer, wherein the P-type buried layer and the first N-type contact layer form a tunnel junction, the P-type buried layer is doped with Mg, and at least one hole is formed on the first N-type contact layer and penetrates the first N-type contact layer.

[0009] In one embodiment, a plurality of holes penetrating the first N-type contact layer are formed on the first N-type contact layer, and the porosity of the first N-type contact layer is 1% to 50%.

[0010] In one embodiment, the P-type buried layer is a P-type AlGaN layer, the content of Al component in the P-type AlGaN layer is greater than 0 and less than 1, and the doping concentration is 1E15cm -3 ~1E20cm -3 .

[0011] In one embodiment, the first N-type contact layer is an N-type AlGaN layer, the Al content in the N-type AlGaN layer is greater than 0 and less than 1, and the doping concentration is 1E15cm -3 ~5E20cm -3 .

[0012] Another embodiment of the present invention provides a technical solution as follows:

[0013] A light-emitting device, comprising:

[0014] substrate;

[0015] A light-emitting unit is located above the substrate, the light-emitting unit comprising a second N-type contact layer, a light-emitting layer, an electron blocking layer, and a tunnel junction structure stacked in sequence, the tunnel junction structure being the above-mentioned tunnel junction structure, and a step etched from the tunnel junction structure to the second N-type contact layer on the light-emitting unit;

[0016] The electrodes include a first electrode located on the first N-type contact layer and a second electrode located on the second N-type contact layer.

[0017] In one embodiment, the first electrode includes a metal contact layer and a metal reflective layer sequentially stacked on the first N-type contact layer, and the first electrode covers the first N-type contact layer.

[0018] In one embodiment, the metal contact layer is in a grid shape, a dot shape, or a strip shape.

[0019] In one embodiment, the thickness of the metal reflective layer is 50 nm to 50 μm.

[0020] Another embodiment of the present invention provides a technical method as follows:

[0021] A method for preparing a light-emitting device, comprising the following steps:

[0022] providing a substrate;

[0023] A second N-type contact layer, a light-emitting layer, an electron blocking layer, a P-type buried layer and a first N-type contact layer are sequentially prepared on a substrate, wherein the P-type buried layer forms a tunnel junction with the second N-type contact layer, and the P-type buried layer is doped with Mg;

[0024] Etching the first N-type contact layer to form at least one hole penetrating the first N-type contact layer, and annealing the P-type buried layer;

[0025] The first N-type contact layer, the P-type buried layer, the electron blocking layer and the light-emitting layer are sequentially etched to form a step extending to the second N-type contact layer;

[0026] A first electrode and a second electrode are formed on the first N-type contact layer and the second N-type contact layer respectively.

[0027] In one embodiment, the first N-type contact layer is etched by an electrochemical etching process or a dry etching process to form at least one hole penetrating the first N-type contact layer.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present invention uses a first N-type contact layer with holes to prepare a tunnel junction structure, combined with an annealing dehydrogenation process, to effectively reduce the hydrogen diffusion energy barrier, improve hydrogen diffusion efficiency, increase the activation efficiency of Mg in the P-type buried layer, improve the hole injection efficiency in the P-type buried layer, and reduce voltage loss;

[0030] The present invention adopts a metal contact layer and a metal reflective layer to prepare a reflective first electrode on a tunnel junction structure, thereby reducing the loss of ultraviolet light, improving light extraction efficiency, and enhancing the light output power of the light-emitting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 Schematic diagram of the tunnel junction structure in Example 1 of the present invention;

[0033] Figure 2 Schematic diagram of the structure of the light emitting device in Example 1 of the present invention;

[0034] Figure 3 A top view of the metal contact layer in Example 1 of the present invention;

[0035] Figure 4 is a top view of another metal contact layer in Example 1 of the present invention;

[0036] Figure 5 is a top view of another metal contact layer in Example 1 of the present invention;

[0037] Figure 6 is a top view of another metal contact layer in Example 1 of the present invention;

[0038] Figure 7 is a top view of another metal contact layer in Example 1 of the present invention;

[0039] Figures 8a to 8e This is a process flow chart of a method for preparing a light-emitting device in Example 1 of the present invention;

[0040] Figure 9 Schematic diagram of the electrochemical etching process in Example 1 of the present invention;

[0041] Figure 10 This is an SEM image of the first N-type contact layer after electrochemical etching in Example 1 of the present invention;

[0042] Figure 11 Schematic diagram of etching the first N-type contact layer using the ICP etching process in Example 1 of the present invention;

[0043] Figure 12 is a graph showing the relationship between the area ratio of the first electrode of the light-emitting device, the light extraction efficiency, and the voltage loss in Example 1 of the present invention;

[0044] Figure 13 Schematic diagram of the structure of the light emitting device in Comparative Example 1 of the present invention;

[0045] Figure 14 Schematic diagram of the structure of the light-emitting device in comparative example 2 of the present invention.

[0046] Description of main reference numerals:

[0047] 10-tunnel junction structure, 101-P-type buried layer, 102-first N-type contact layer, 20-substrate, 30-second N-type contact layer, 40-light-emitting layer, 50-electron blocking layer, 61-first electrode, 611-metal contact layer, 612-metal reflective layer, 62-second electrode, 70-buffer layer, 80-photoresist layer, 901-N-type AlGaN layer, 902-P-type AlGaN layer. DETAILED DESCRIPTION

[0048] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0049] The present invention discloses a tunnel junction structure, which includes a P-type buried layer and a first N-type contact layer stacked on the P-type buried layer. The P-type buried layer and the first N-type contact layer form a tunnel junction. The P-type buried layer is doped with Mg, and at least one hole penetrating the first N-type contact layer is formed on the first N-type contact layer.

[0050] The present invention also discloses a light emitting device, comprising:

[0051] substrate;

[0052] A light-emitting unit is located above the substrate, the light-emitting unit comprising a second N-type contact layer, a light-emitting layer, an electron blocking layer, and a tunnel junction structure stacked in sequence, wherein the tunnel junction structure is the tunnel junction structure described above, and a step is provided on the light-emitting unit, which is etched from the tunnel junction structure to the second N-type contact layer;

[0053] The electrode includes a first electrode located on the first N-type contact layer and a second electrode located on the second N-type contact layer.

[0054] The present invention also discloses a method for preparing a light-emitting device, comprising the following steps:

[0055] providing a substrate;

[0056] A second N-type contact layer, a light-emitting layer, an electron blocking layer, a P-type buried layer and a first N-type contact layer are sequentially formed on the substrate, wherein the P-type buried layer forms a tunnel junction with the second N-type contact layer, and the P-type buried layer is doped with Mg;

[0057] Etching the first N-type contact layer to form at least one hole penetrating the first N-type contact layer, and annealing the P-type buried layer;

[0058] The first N-type contact layer, the P-type buried layer, the electron blocking layer and the light-emitting layer are sequentially etched to form a step extending to the second N-type contact layer;

[0059] A first electrode and a second electrode are prepared on the first N-type contact layer and the second N-type contact layer respectively.

[0060] The present invention is further described below with reference to specific examples.

[0061] Example 1:

[0062] Ginseng Figure 1 As shown, the tunnel junction structure 10 in this embodiment includes a P-type buried layer 101 and a first N-type contact layer 102 stacked on the P-type buried layer 101. The P-type buried layer 101 and the first N-type contact layer 102 form a tunnel junction. The P-type buried layer 101 is doped with Mg. At least one hole is formed on the first N-type contact layer 102 and penetrates the first N-type contact layer 102.

[0063] The P-type buried layer 101 is a P-type AlGaN layer, the content of Al component in the P-type AlGaN layer is greater than 0 and less than 1, preferably P-Al 0.5 Ga 0.5 N layer, doping concentration is 1E15cm -3 ~1E20cm -3 , preferably 5E17cm -3 ~5E18cm -3 The first N-type contact layer 102 is a Si or Ge doped N-type AlGaN layer, the Al content in the N-type AlGaN layer is greater than 0 and less than 1, preferably N-Al 0.45 Ga 0.55 N layer, doping concentration is 1E15cm -3 ~5E20cm -3 , preferably 1E17cm -3 ~4E20cm -3 By properly controlling the doping concentration and distribution in the P-type buried layer 101 and the first N-type contact layer 102 , the lateral current expansion capability between the P-type buried layer 101 and the first N-type contact layer 102 can be effectively improved, thereby improving the current injection efficiency.

[0064] Compared with the P-type GaN layer, the P-type AlGaN layer has better light transmittance, with a transmittance of about 60% for 280nm ultraviolet light. Although the P-type GaN layer has excellent characteristics such as high carrier concentration and good crystal quality, it has strong absorption of 280nm deep ultraviolet light and its transmittance is only 5%.

[0065] Specifically, in this embodiment, a plurality of holes are formed on the first N-type contact layer 102 that penetrate the first N-type contact layer 102. The porosity of the first N-type contact layer 102 is 1% to 50%, preferably 10% to 30%. When the porosity changes, the electron concentration of the first N-type contact layer is almost linearly related to the porosity. When the porosity changes from 10% to 30%, the electron concentration of the first N-type contact layer will increase from 10% to 30%. 20 cm -3 Down to 10 19 cm -3The electron mobility decreases by no more than 20%. At the same time, a porosity range of 10% to 30% enables sufficient dehydrogenation of the P-type buried layer. Therefore, when the porosity is within the range of 10% to 30%, the tunnel junction structure can simultaneously achieve optimal hydrogen diffusion paths and current conductivity.

[0066] It should be understood that the porosity of the first N-type contact layer is the percentage of the volume of the pores in the first N-type contact layer to the total volume of the first N-type contact layer in a natural state.

[0067] More specifically, the holes are preferably cylindrical and distributed on the first N-type contact layer. The hole diameter is 10nm to 5μm, and the spacing between adjacent holes is 50nm to 50μm. By controlling the porosity of the first N-type contact layer, the hole diameter, and the spacing between adjacent holes, the hydrogen diffusion path and current conductivity can be controlled and optimized.

[0068] Ginseng Figure 2 As shown, the light-emitting device having the tunnel junction structure 10 in this embodiment includes:

[0069] substrate 20;

[0070] A light-emitting unit is located above the substrate 20. The light-emitting unit includes a second N-type contact layer 30, a light-emitting layer 40, an electron blocking layer 50, and a tunnel junction structure 10 stacked in sequence. A step is provided on the light-emitting unit, which is etched from the tunnel junction structure 10 to the second N-type contact layer 30.

[0071] The electrodes include a first electrode 61 located on the first N-type contact layer 102 and a second electrode 62 located on the second N-type contact layer 30 .

[0072] Among them, the substrate 20 is a sapphire substrate, a nitride intrinsic substrate or a silicon substrate, the second N-type contact layer 30 is also an N-type AlGaN layer doped with Si or Ge, the light-emitting layer 40 is composed of multiple AlGaN quantum well layers, and the luminescence performance of the light-emitting layer is controlled by controlling the Al content in the AlGaN quantum well layer. The electron blocking layer 50 selects a conventional electron blocking layer, which will not be repeated here.

[0073] Specifically, the size of the light emitting device in this embodiment is 150 μm×150 μm.

[0074] Furthermore, the first electrode 61 in this embodiment covers the first N-type contact layer 102. The first electrode 61 includes a metal contact layer 611 and a metal reflective layer 612 sequentially stacked on the first N-type contact layer 102, forming a reflective electrode to improve the reflection efficiency of ultraviolet light, reduce light loss, and enhance the light extraction efficiency of the light-emitting device.

[0075] Specifically, the metal contact layer 611 is preferably a Ti / Al / Ni / Au composite metal layer to ensure good ohmic contact with the first N-type contact layer 102 and provide stable contact resistance. The metal reflective layer 612 is preferably an Al metal layer, which has excellent ultraviolet reflection properties (>90%) and can effectively reflect ultraviolet light emitted by the light-emitting device.

[0076] It is worth noting that the thickness of the Al metal layer serving as the metal reflective layer is 50 nm to 50 μm, ensuring sufficient reflection capability while not affecting the current injection performance.

[0077] Ginseng Figure 3 As shown, the metal contact layer 611 in this embodiment is in a grid shape, and a number of metal strips arranged in parallel along the X direction and a number of metal strips arranged in parallel along the Y direction intersect vertically to form a metal contact layer 611 with pores, which can further improve the reflectivity of the first electrode, avoid the loss caused by multiple reflections, and improve the output power of light.

[0078] It is worth mentioning that Figure 4 As shown, the sizes of the metal strips arranged in parallel along the X direction and the metal strips arranged in parallel along the Y direction can be different. The sizes of the metal strips arranged in parallel along the same direction can also be different. It is only necessary that the contact area between the metal contact layer and the first N-type contact layer can achieve ohmic contact and electron extraction.

[0079] In addition, Figure 5 As shown, in other embodiments, a single metal strip can be arranged along the Y direction and perpendicular to a plurality of metal strips arranged parallel to the X direction. Figure 6 、 Figure 7 As shown, in other embodiments, the metal contact layer may also be in the form of dots or strips in an array.

[0080] It should be understood that, in addition to the above examples, other shapes that can facilitate adjustment of the contact area between the metal contact layer and the first N-type contact layer are possible, to ensure that the reflectivity and resistivity of the first electrode can be adjusted by adjusting the contact area between the metal contact layer and the first N-type contact layer.

[0081] In addition, the second electrode 62 in this embodiment is the same as the metal contact layer 611 in the first electrode 61 , which is a Ti / Al / Ni / Au composite metal layer. Furthermore, the light emitting device in this embodiment further includes a buffer layer 70 located between the substrate 20 and the second N-type contact layer 30 .

[0082] The method for preparing the light-emitting device in this embodiment includes the following steps:

[0083] S1. Provide a substrate 20.

[0084] S2. A second N-type contact layer 30, a light-emitting layer 40, an electron blocking layer 50, a P-type buried layer 101 and a first N-type contact layer 102 are sequentially prepared on the substrate 20. The P-type buried layer 101 forms a tunnel junction with the second N-type contact layer 102. The P-type buried layer 101 is doped with Mg.

[0085] Ginseng Figure 8a As shown, in this embodiment, a buffer layer 70 is first prepared on the substrate 20, and then a second N-type contact layer 30, a light-emitting layer 40, an electron blocking layer 50, a P-type buried layer 101 and a first N-type contact layer 102 are epitaxially grown on the buffer layer 70 in sequence.

[0086] More specifically, the first N-type contact layer 102 and the second N-type contact layer 30 are both Si- or Ge-doped N-type AlGaN layers, the P-type buried layer 101 is a Mg-doped P-type AlGaN layer, and both the P-type AlGaN layer and the N-type AlGaN layer are prepared by MOCVD process.

[0087] S3 , etching the first N-type contact layer 102 to form at least one hole penetrating the first N-type contact layer 102 , and annealing the P-type buried layer 101 .

[0088] Ginseng Figure 8b and combined Figure 9 、 Figure 10 As shown, in this embodiment, an electrochemical etching process is used to etch the first N-type contact layer to form a plurality of holes penetrating the first N-type contact layer, which specifically includes the following steps:

[0089] 1. Prepare electrolyte.

[0090] Specifically, nitric acid or KOH is used as an electrolyte to prepare an electrolyte, a platinum electrode is used as a cathode, and the first N-type contact layer contacts an indium electrode as an anode.

[0091] 2. Apply a reverse bias voltage between the first N-type contact layer and the electrolyte to etch the first N-type contact layer through an electrochemical reaction.

[0092] Specifically, the hole diameter and the porosity of the first N-type contact layer are precisely controlled by adjusting the voltage, the concentration of the electrolyte and the etching time. Preferably, the voltage is set to 10V to 100V.

[0093] It is worth noting that, in other embodiments, the first N-type contact layer may be etched by a dry etching process. Figure 11As shown, a patterned photoresist layer 80 made of AZ5214 photoresist is used as a mask to etch holes in the first N-type contact layer using an inductively coupled plasma (ICP) process. Although dry etching can introduce a large number of surface defects, affecting the current injection performance of the tunnel junction structure, it has significant advantages in large-scale production.

[0094] Ginseng Figure 8c As shown in the figure, after etching is completed, the tunnel junction structure is annealed to promote the dehydrogenation and activation of Mg in the P-type buried layer. During the annealing process, the Mg-H defect clusters in the P-type buried layer break, releasing hydrogen atoms. The released hydrogen atoms escape through the holes in the first N-type contact layer, avoiding the influence of the hydrogen diffusion barrier on Mg activation.

[0095] Specifically, the annealing temperature is set to 700° C. to 850° C., and the annealing time is 10 min to 30 min.

[0096] S4 , etching the first N-type contact layer 102 , the P-type buried layer 101 , the electron blocking layer 50 and the light-emitting layer 40 in sequence to form a step etched to the second N-type contact layer 30 .

[0097] Ginseng Figure 8d As shown, AZ5214 photoresist is first spin-coated on the first N-type contact layer 102, and a patterned photoresist layer 80 is prepared by a photolithography process; then, the patterned photoresist layer 80 is used as a mask, and the first N-type contact layer 102, the P-type mask layer 101, the electron blocking layer 50 and the light-emitting layer 40 are etched in sequence by an inductively coupled plasma etching process, and the etching rate is preferably 70nm / min to 100nm / min, until the second N-type contact layer 30 is etched.

[0098] It should be understood that the etching time needs to be properly controlled to ensure that the second N-type contact layer is etched to the right level while not being over-etched.

[0099] More specifically, after etching is completed, the photoresist layer is removed, and the epitaxial wafer is placed in a KOH solution, and a wet treatment process is used to repair the damage caused by the dry etching process. The concentration of the KOH solution is 0.5 mol / L to 3 mol / L, the temperature of the wet treatment is set to 80°C, and the treatment time is 5 minutes to 30 minutes.

[0100] S5, ginseng Figure 8e As shown, a first electrode 61 and a second electrode 62 are formed on the first N-type contact layer 101 and the second N-type contact layer 30 respectively.

[0101] Specifically, the preparation process of the first electrode is as follows: first, a metal contact layer of the first electrode is prepared on the first N-type contact layer using a photolithography process combined with a coating process, and a Ti metal layer, an Al metal layer, a Ni metal layer and an Au metal layer are sequentially deposited on the first N-type contact layer using an electron beam evaporation process, a magnetron sputtering process or an electroplating process to form a Ti / Al / Ni / Au composite metal layer; then, an Al metal layer is prepared on the metal contact layer as a metal reflective layer.

[0102] It is worth noting that the material of the second electrode is consistent with that of the metal contact layer in the first electrode and can be deposited simultaneously with the metal contact layer to simplify the preparation process, reduce production costs, and enhance the industrial application capability of the device.

[0103] In addition, after the deposition of the first electrode and the second electrode is completed, the electrodes need to be annealed to ensure that the first electrode and the second electrode form good contact with the first N-type contact layer and the second N-type contact layer respectively, thereby improving the contact quality.

[0104] It should be understood that after the preparation of the first electrode and the second electrode is completed, the light-emitting device is packaged, tested, and characterized.

[0105] Specifically, the current injection path of the encapsulated light-emitting device must be effective and well connected to the power source. At the same time, the encapsulation material must have good thermal conductivity to ensure good heat dissipation of the light-emitting device during operation.

[0106] Testing and characterization include electro-optical performance testing: testing the current-voltage characteristics (IV curve), external quantum efficiency (EQE), luminous power and electro-optical conversion efficiency of the LED; UV output testing: verifying the effect of the reflective electrode design on improving UV light extraction efficiency through UV intensity testing; thermal stability testing: conducting stability tests on the packaged light-emitting devices in a high-temperature environment to ensure reliability during long-term use.

[0107] Ginseng Figure 12 The figure shows the relationship between the area ratio of the first electrode of the light-emitting device in this embodiment and the light extraction efficiency and voltage loss. In this embodiment, the thickness of the first N-type contact layer is 200nm. In conventional GaN-based light-emitting devices, the absorption coefficient of the P-type GaN layer is 1.7×10 5 / cm, the reflectivity of Ni and Au is calculated to be 0.4. Combined with the data in the figure, it is estimated that when the first electrode accounts for 100% of the area, the light extraction efficiency reaches 3.4%. At the same time, when the first electrode accounts for 20%, the voltage loss of the light-emitting device is only 6.2V. This shows that the reflective first electrode can improve light extraction efficiency while taking into account voltage loss.

[0108] Comparative Example 1:

[0109] Ginseng Figure 13 As shown, the light-emitting device in this comparative example is a light-emitting device with a conventional tunnel junction structure. Meanwhile, the first electrode 61 is a V / Al / Ti / Pt / Au composite electrode, and no reflective layer is prepared.

[0110] Conventional tunnel junction structures are also prepared by stacking P-type AlGaN layers and N-type AlGaN layers in sequence. However, since the P-type AlGaN layer is buried under the N-type AlGaN layer, the Fermi level of the N-type AlGaN layer is close to the conduction band, which increases the H diffusion energy barrier. H cannot be diffused and escaped through high-temperature annealing, resulting in ineffective activation of Mg, which seriously affects the performance of the light-emitting device.

[0111] Meanwhile, the first electrode 61 in this comparative example is a conventional electrode and does not adopt the design of a reflective electrode, which seriously affects the light extraction efficiency of the light-emitting device and greatly limits the ultraviolet light output.

[0112] Comparative Example 2:

[0113] Ginseng Figure 14 As shown, the light-emitting device in this comparative example is a light-emitting device with a conventional reflective electrode, and no tunnel junction structure is prepared.

[0114] The light-emitting device in this comparative example is an AlGaN-based light-emitting device, which includes a buffer layer 70, an N-type AlGaN layer 901, a light-emitting layer 40, an electron blocking layer 50 and a P-type AlGaN layer 902 stacked in sequence on a substrate 20, and is formed with a step etched to the N-type AlGaN layer 901. An Rh metal layer is provided on the P-type AlGaN layer 902 as a first electrode 61, which is prepared as a light-reflecting electrode. A second electrode 62 is provided on the N-type AlGaN layer 901, and the second electrode 62 is a conventional electrode.

[0115] The P-type AlGaN layer in this comparative example is P-Al 0.65 Ga 0.35 N layer, P-Al 0.65 Ga 0.35 The N layer has a transmittance of more than 50% for deep ultraviolet light with a wavelength of 270nm. By replacing the P-type GaN layer as the contact layer of the first electrode, combined with the design of the reflective electrode, the light extraction rate of the device can be effectively improved.

[0116] However, in ultraviolet light-emitting devices, the P-type AlGaN layer serving as the first electrode contact layer is also doped with Mg. As the Al component increases, the lattice constant of AlGaN decreases, and the effective Mg doping concentration decreases. Secondly, during the MOCVD epitaxial growth process, H acts as a carrier gas to form Mg-H with Mg, causing Mg to lose its acceptor activity. Moreover, as the Al component in the P-type AlGaN layer increases, the band gap widens, and the ionization energy of the Mg acceptor increases (GaN ionization energy is approximately 160meV, and AlN ionization energy reaches 510meV). In the AlGaN layer with a high Al component, the diffusion coefficient of H is low, and the activation efficiency of Mg decreases. At the same time, the work function of the P-type AlGaN layer is large, ranging from about 7.5 (x=0) to 8.1 (x=1). Combined with the above factors, the driving voltage of the light-emitting device in this comparative example increases significantly, seriously affecting its performance.

[0117] It can be seen from the above technical solution that the present invention has the following beneficial effects:

[0118] The present invention uses a first N-type contact layer with holes to prepare a tunnel junction structure, combined with an annealing dehydrogenation process, to effectively reduce the hydrogen diffusion energy barrier, improve hydrogen diffusion efficiency, increase the activation efficiency of Mg in the P-type buried layer, improve the hole injection efficiency in the P-type buried layer, and reduce voltage loss;

[0119] The present invention adopts a metal contact layer and a metal reflective layer to prepare a reflective first electrode on a tunnel junction structure, thereby reducing the loss of ultraviolet light, improving light extraction efficiency, and enhancing the light output power of the light-emitting device.

[0120] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0121] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A tunnel junction structure, characterized in that: The tunnel junction structure includes a P-type buried layer and a first N-type contact layer stacked on the P-type buried layer, the P-type buried layer and the first N-type contact layer form a tunnel junction, the P-type buried layer is doped with Mg, and at least one hole is formed on the first N-type contact layer and penetrates the first N-type contact layer.

2. The tunnel junction structure according to claim 1, wherein: A plurality of holes penetrating the first N-type contact layer are formed on the first N-type contact layer, and the porosity of the first N-type contact layer is 1% to 50%.

3. The tunnel junction structure according to claim 1, wherein: The P-type buried layer is P-type AlGaN, the content of Al component in the P-type AlGaN layer is greater than 0 and less than 1, and the doping concentration is 1E15cm -3 ~1E20cm -3 .

4. The tunnel junction structure according to claim 1, wherein: The first N-type contact layer is an N-type AlGaN layer, the Al content in the N-type AlGaN layer is greater than 0 and less than 1, and the doping concentration is 1E15cm -3 ~5E20cm -3 .

5. A light emitting device, characterized in that: The light emitting device comprises: substrate; A light-emitting unit located above the substrate, the light-emitting unit comprising a second N-type contact layer, a light-emitting layer, an electron blocking layer, and a tunnel junction structure stacked in sequence, the tunnel junction structure being the tunnel junction structure according to any one of claims 1 to 4, the light-emitting unit being provided with a step etched from the tunnel junction structure to the second N-type contact layer; The electrodes include a first electrode located on the first N-type contact layer and a second electrode located on the second N-type contact layer.

6. The light emitting device according to claim 5, characterized in that The first electrode includes a metal contact layer and a metal reflective layer sequentially stacked on the first N-type contact layer, and the first electrode covers the first N-type contact layer.

7. The light emitting device according to claim 6, characterized in that The metal contact layer is in a grid shape, a dot shape or a strip shape.

8. The light emitting device according to claim 5, characterized in that The thickness of the metal reflective layer is 50 nm to 50 μm.

9. A method for preparing a light-emitting device, characterized in that: The preparation method comprises the following steps: providing a substrate; A second N-type contact layer, a light-emitting layer, an electron blocking layer, a P-type buried layer and a first N-type contact layer are sequentially prepared on a substrate, wherein the P-type buried layer forms a tunnel junction with the first N-type contact layer, and the P-type buried layer is doped with Mg; Etching the first N-type contact layer to form at least one hole penetrating the first N-type contact layer, and annealing the P-type buried layer; The first N-type contact layer, the P-type buried layer, the electron blocking layer and the light-emitting layer are sequentially etched to form a step extending to the second N-type contact layer; A first electrode and a second electrode are formed on the first N-type contact layer and the second N-type contact layer respectively.

10. The method for preparing a light-emitting device according to claim 9, wherein: The first N-type contact layer is etched by an electrochemical etching process or a dry etching process to form at least one hole penetrating the first N-type contact layer.

Images