Tunnel junction and method of fabrication, multi-junction infrared led epitaxial structure and method of fabrication

Abstract

The application provides a tunnel junction and a preparation method, a multi-junction infrared LED epitaxial structure and a preparation method. The tunnel junction comprises, from bottom to top, a first transition layer, a tunnel junction material layer and a second transition layer. The first transition layer and the second transition layer both contain Al components, and the first transition layer and the second transition layer are both doped with different types of dopants. The first transition layer and the second transition layer are both doped concentration gradient layers and Al component gradient layers, which can effectively improve the crystal quality of the tunnel junction and an LED structure on the tunnel junction in the multi-junction infrared LED epitaxial structure, reduce the series resistance and lower the working voltage.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a tunnel junction and its preparation method, and a multi-junction infrared LED epitaxial structure and its preparation method. Background Technology

[0002] Infrared LEDs (IR Light Emitting Diodes) are light-emitting devices that convert electrical energy into near-infrared light. They are mainly used in various optocoupler switches, security monitoring, night vision surveillance, facial and iris recognition, and gas detection. Among these, security monitoring, night vision surveillance, and facial and iris recognition require high brightness in the epitaxial structure of infrared LEDs. To address this, multiple large-size individual infrared LEDs can be connected in series to increase brightness. However, this method results in light-emitting devices with high resistance and high operating voltage, while also occupying a large space and having lower reliability.

[0003] To address these issues, a multi-junction infrared LED epitaxial structure can be employed. This involves connecting multiple LED structures in series using tunnel junctions during the LED epitaxial structure fabrication process to enhance brightness and significantly improve the integration and reliability of the light-emitting device. However, current multi-junction infrared LED epitaxial structures still exhibit relatively high resistance and operating voltage. Summary of the Invention

[0004] The purpose of this invention is to provide a tunnel junction and its preparation method, and a multi-junction infrared LED epitaxial structure and its preparation method, which can reduce the resistance of the multi-junction infrared LED epitaxial structure, thereby reducing the operating voltage of the multi-junction infrared LED epitaxial structure.

[0005] To address the aforementioned problems, the present invention provides a tunnel junction comprising, from bottom to top, a first transition layer, a tunnel junction material layer, and a second transition layer. Both the first and second transition layers contain Al components, and both are doped with different types of dopants. Both the first and second transition layers are doped concentration gradient layers, and both are Al component gradient layers.

[0006] Optionally, the first transition layer is doped with a p-type dopant, the doping concentration of the p-type dopant gradually increases from bottom to top, and the Al component in the first transition layer gradually increases from bottom to top.

[0007] Furthermore, the material of the first transition layer is Al. d Ga 1-d As, where d ranges from 0.3 to 0.4; the doping concentration of the p-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3~1.0×10 19 cm -3 .

[0008] Optionally, the second transition layer is doped with an n-type dopant, the doping concentration of the n-type dopant gradually decreasing from bottom to top, and the Al component in the second transition layer gradually decreasing from bottom to top.

[0009] Furthermore, the material of the second transition layer is Al. e Ga 1-e As, where e ranges from 0.3 to 0.4; the doping concentration of the n-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

[0010] Optionally, the tunnel junction material layer includes, from bottom to top, a first heavily doped layer, an undoped layer, and a second heavily doped layer. Both the first heavily doped layer and the second heavily doped layer are doped with different types of dopants. The undoped layer is used to isolate the first heavily doped layer and the second heavily doped layer.

[0011] Furthermore, the material of the undoped layer is In. c Ga 1-c As, where c ranges from 0.01 to 0.2.

[0012] Furthermore, the thickness of the undoped layer is 0.2 nm to 10 nm.

[0013] Furthermore, the first heavily doped layer is doped with a p-type dopant, and the second heavily doped layer is doped with an n-type dopant, and the doping concentrations of both the first and second heavily doped layers are greater than 2.0 × 10⁻⁶. 19 cm -3 .

[0014] Furthermore, the material of the first doped layer is Al. a Ga 1-a As, where the value of a ranges from 0.2 to 0.8;

[0015] The material of the second doped layer is Ga b In 1-b P, where b ranges from 0.4 to 0.8.

[0016] On the other hand, the present invention also provides a method for preparing a tunnel junction, comprising the following steps:

[0017] A first transition layer is formed, the first transition layer contains an Al component, and the first transition layer is an Al component gradient layer;

[0018] A tunneling junction material layer is formed on the first transition layer; and

[0019] A second transition layer is formed on the tunnel junction material layer. The second transition layer contains an Al component and is an Al component gradient layer. The first and second transition layers are both doped with different types of dopants, and both the first and second transition layers are doped with gradient concentration layers.

[0020] Optionally, the first transition layer is doped with a p-type dopant, the doping concentration of the p-type dopant gradually increases from bottom to top, and the Al component in the first transition layer gradually increases from bottom to top.

[0021] Furthermore, the material of the first transition layer is Al. d Ga 1-d As, where d ranges from 0.3 to 0.4; the doping concentration of the p-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

[0022] Optionally, the second transition layer is doped with an n-type dopant, the doping concentration of the n-type dopant gradually decreasing from bottom to top, and the Al component in the second transition layer gradually decreasing from bottom to top.

[0023] Furthermore, the material of the second transition layer is Al. e Ga 1-e As, where e ranges from 0.3 to 0.4; the doping concentration of the n-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

[0024] Optionally, forming the tunnel junction material layer includes forming a first heavily doped layer, an undoped layer, and a second heavily doped layer sequentially from bottom to top. The first heavily doped layer and the second heavily doped layer are both doped with different types of dopants, and the undoped layer is used to isolate the first heavily doped layer and the second heavily doped layer.

[0025] Furthermore, the material of the undoped layer is In. c Ga 1-c As, where c ranges from 0.01 to 0.2.

[0026] Furthermore, the thickness of the undoped layer is 0.2 nm to 10 nm.

[0027] Furthermore, the first heavily doped layer is doped with a p-type dopant, and the second heavily doped layer is doped with an n-type dopant, and the doping concentrations of both the first and second heavily doped layers are greater than 2.0 × 10⁻⁶. 19 cm -3 .

[0028] Furthermore, the material of the first doped layer is Al. a Ga 1-a As, where the value of a ranges from 0.2 to 0.8;

[0029] The material of the second doped layer is Ga b In 1-b P, where b ranges from 0.4 to 0.8.

[0030] In another aspect, the present invention also provides a multi-junction infrared LED epitaxial structure, including the aforementioned tunneling junction, and further including at least two LED structures stacked on a substrate, wherein a tunneling junction is disposed between each pair of adjacent LED structures.

[0031] Optionally, the LED structure includes, from bottom to top, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer.

[0032] Optionally, the multi-junction infrared LED epitaxial structure further includes a buffer layer and an etch stop layer located between the substrate and the LED structure, wherein the buffer layer and the etch stop layer are sequentially disposed on the substrate.

[0033] Furthermore, the multi-junction infrared LED epitaxial structure comprises, from bottom to top, a first LED structure to an Nth LED structure. Both the first and Nth LED structures further include a current spreading layer and an ohmic contact layer.

[0034] In the first LED structure, both the current spreading layer and the ohmic contact layer are located on the n-type semiconductor layer side; in the Nth LED structure, both the current spreading layer and the ohmic contact layer are located on the p-type semiconductor layer side, where N≥2 and is a positive integer.

[0035] Furthermore, in the first LED structure, the current spreading layer is located between the ohmic contact layer and the n-type semiconductor layer, and the current spreading layer is doped with an n-type dopant; and

[0036] In the Nth LED, the current spreading layer is located between the ohmic contact layer and the p-type semiconductor layer, and the current spreading layer is doped with a p-type dopant.

[0037] In another aspect, the present invention also provides a method for fabricating a multi-junction infrared LED epitaxial structure, comprising the following steps:

[0038] Provide a substrate;

[0039] LED structures and tunnel junctions are alternately formed on the substrate to obtain N LED structures and N-1 tunnel junctions, each tunnel junction being located between two adjacent LED structures, and the Nth LED structure being located on the N-1th tunnel junction, thereby forming a multi-junction infrared LED epitaxial structure, where N≥2 and is a positive integer.

[0040] Optionally, forming the LED structure includes forming an n-type semiconductor layer, an active layer, and a p-type semiconductor layer sequentially from bottom to top.

[0041] Optionally, a buffer layer and an etch stop layer are formed between the substrate and the LED structure, wherein the buffer layer and the etch stop layer are sequentially disposed on the substrate.

[0042] Furthermore, the multi-junction infrared LED epitaxial structure comprises, from bottom to top, a first LED structure to an Nth LED structure. Both the first and Nth LED structures further include a current spreading layer and an ohmic contact layer.

[0043] In the first LED structure, both the current spreading layer and the ohmic contact layer are located on the n-type semiconductor layer side; in the Nth LED structure, both the current spreading layer and the ohmic contact layer are located on the p-type semiconductor layer side.

[0044] Furthermore, in the first LED structure, the current spreading layer is located between the ohmic contact layer and the n-type semiconductor layer, and the current spreading layer is doped with an n-type dopant; and

[0045] In the Nth LED, the current spreading layer is located between the ohmic contact layer and the p-type semiconductor layer, and the current spreading layer is doped with a p-type dopant.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1. By using Al composition gradient layers and doping concentration gradient layers for both the first and second transition layers, the crystal quality of the LED structure located on the tunnel junction in the tunnel junction and the multi-junction infrared LED epitaxial structure is effectively improved, the series resistance is reduced, and the operating voltage is lowered.

[0048] 2. By using a high-Al content first doped layer and a high-bandgap second doped layer as the tunnel junction material, photons passing through the tunnel junction can pass directly through, thereby effectively reducing the absorption of radiated light by the tunnel junction on the LED structure and improving the brightness of the device structure.

[0049] 3. By separating the first heavily doped layer and the second heavily doped layer of different doping types in the tunnel junction material layer with an undoped layer, a built-in electric field can be formed, making the impurity concentration distribution of the first heavily doped layer and the second heavily doped layer steep. This avoids the impurity compensation caused by the mutual diffusion of impurities in the first heavily doped layer and the second heavily doped layer, which would reduce the doping concentration of the first heavily doped layer and the second heavily doped layer.

[0050] 4. Material selection through the undoped layer (i.e., selecting In) c Ga 1-c As material, where c ranges from 0.01 to 0.2), which makes the resistivity of the undoped layer low and the band gap low, thereby improving the peak current of the tunnel junction. The undoped layer is thin, so it absorbs less radiation light from the multi-junction infrared extension LED structure.

[0051] 5. The high doping concentration of the first and second doping layers can effectively reduce the series resistance of the tunnel junction, thereby further reducing the operating voltage. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of a multi-junction infrared LED epitaxial structure according to an embodiment of the present invention;

[0053] Figure 2 This is a schematic diagram of a tunnel junction provided in an embodiment of the present invention;

[0054] Figure 3 This is a schematic flowchart of a method for preparing a tunnel junction according to an embodiment of the present invention;

[0055] Figure 4 This is a schematic flowchart illustrating a method for fabricating a multi-junction infrared LED epitaxial structure according to an embodiment of the present invention.

[0056] Figure 5 This is a schematic flowchart illustrating a method for fabricating a dual-junction infrared LED epitaxial structure according to an embodiment of the present invention.

[0057] Explanation of reference numerals in the attached figures:

[0058] 100 - Substrate; 110 - Buffer layer; 120 - Etching stop layer; 200 - First LED structure; 210 - First ohmic contact layer; 220 - First current spreading layer; 230 - First n-type semiconductor layer; 240 - First active layer; 250 - First p-type semiconductor layer; 300 - Tunnel junction; 310 - First transition layer; 320 - First heavily doped layer; 330 - Undoped layer; 340 - Second heavily doped layer; 350 - Second transition layer; 400 - Second LED structure; 410 - Second n-type semiconductor layer; 420 - Second active layer; 430 - Second p-type semiconductor layer; 440 - Second current spreading layer; 450 - Second ohmic contact layer. Detailed Implementation

[0059] The following will provide a more detailed description of a tunnel junction and its preparation method, as well as a multi-junction infrared LED epitaxial structure and its preparation method according to the present invention. The present invention will now be described in more detail with reference to the accompanying drawings, which illustrate preferred embodiments of the invention. It should be understood that those skilled in the art can modify the invention described herein while still achieving its advantageous effects. Therefore, the following description should be understood as being of general knowledge to those skilled in the art and is not intended to limit the invention.

[0060] For clarity, not all features of the actual embodiments are described. In the following description, well-known functions and structures are not detailed in detail, as they would obscure the invention with unnecessary detail. It should be understood that in the development of any actual embodiment, numerous implementation details must be made to achieve the developer's specific objectives, such as changes from one embodiment to another according to limitations related to the system or business. Furthermore, it should be understood that such development work may be complex and time-consuming, but is merely routine work for those skilled in the art.

[0061] To make the objectives and features of the present invention more apparent and understandable, the specific embodiments of the present invention will be further described below with reference to the accompanying drawings. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, and are only used to conveniently and clearly assist in illustrating the objectives of the embodiments of the present invention.

[0062] Figure 1 This is a schematic diagram of a multi-junction infrared LED epitaxial structure provided in this embodiment. Figure 2 This is a schematic diagram of the tunnel junction provided in this embodiment. Figure 1 and 2 As shown, this embodiment provides a tunnel junction 300 for connecting every two adjacent LED structures in a multi-junction infrared LED epitaxial structure, so as to connect all the LED structures in series.

[0063] The tunneling junction 300 comprises, from bottom to top, a first transition layer 310, a tunneling junction material layer, and a second transition layer 350.

[0064] The first transition layer 310 may be doped with a p-type dopant, which includes, but is not limited to, carbon (C), and the doping concentration of the p-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 Preferably, the doping concentration of the p-type dopant is in the range of 5.0 × 10⁻⁶. 18 cm -3 ~8.0×10 18 cm -3 The first transition layer 310 is a doping concentration gradient layer, which can improve the diffusion of carriers caused by the difference in doping concentration, and prevent the diffusion of impurities in the highly doped layer due to the excessive concentration gradient on both sides of the first transition layer 310, thereby effectively ensuring that the doping concentration of the highly doped layer reaches the required concentration and reducing the series resistance.

[0065] Furthermore, the doping concentration of the p-type dopant gradually increases from bottom to top; that is, the doping concentration of the p-type dopant in the first transition layer 310 increases from 5.0 × 10⁻⁶ from bottom to top. 18 cm -3 Gradient to 8.0×10 18 cm -3 .

[0066] The material of the first transition layer 310 is Al d Ga 1-d As, where d ranges from 0.3 to 0.4, preferably from 0.3 to 0.35. The first transition layer 310 is an Al composition gradient layer, which makes the band gap of the first transition layer 310 gradually change, which can improve the lattice quality of the semiconductor layer in the tunnel junction 300 and the LED structure. The Al composition in the first transition layer 310 gradually increases from bottom to top, that is, the Al composition in the first transition layer 310 gradually increases from Al to Al. 0.3 Ga 0.7 As gradually changes to Al 0.35 Ga 0.65 As. The thickness of the first transition layer 310 can be 10nm to 50nm, preferably 30nm. The first transition layer 310 improves the crystal quality of the tunnel junction 300 and the LED structure located on the tunnel junction 300 in the multi-junction infrared LED epitaxial structure by gradually varying the doping concentration and bandgap, thereby reducing the series resistance and lowering the operating voltage.

[0067] The tunnel junction material layer comprises, from bottom to top, a first doped layer 320, an undoped layer 330, and a second doped layer 340.

[0068] The first heavily doped layer 320 may be doped with a p-type dopant, which includes, but is not limited to, carbon (C), and the doping concentration of the p-type dopant is greater than 2.0 × 10⁻⁶. 19 cm -3 Preferably, the doping concentration of the p-type dopant is 8.0 × 10⁻⁶. 19 cm -3 The high doping concentration of the first heavily doped layer 320 can effectively reduce the series resistance of the tunnel junction 300, thereby reducing the operating voltage.

[0069] The material of the first heavily doped layer 320 is Al a Ga 1-a As, where the value of a ranges from 0.2 to 0.8, preferably a is 0.4, and the Al content is high. a Ga 1-a As a tunneling junction material, As allows photons passing through the tunneling junction to pass directly through, thereby effectively reducing the absorption of radiated light by the tunneling junction 300 on the LED structure and improving the brightness of the device structure. The thickness of the first heavily doped layer 320 can be 2nm to 50nm, preferably 10nm.

[0070] The second doped layer 340 may be doped with an n-type dopant, including but not limited to antimony (Te), and the doping concentration of the n-type dopant is greater than 2.0 × 10⁻⁶. 19 cm -3 Preferably, the doping concentration of the n-type dopant is 1.0 × 10⁻⁶. 20 cm -3 The high doping concentration of the second heavily doped layer 340 can effectively reduce the series resistance of the tunnel junction 300, thereby reducing the operating voltage.

[0071] The material of the second heavily doped layer 340 is Ga b In 1-b P, where b ranges from 0.4 to 0.8, preferably b is 0.54, for high bandgap Ga b In 1-b P, as a tunneling junction material, allows photons passing through the tunneling junction to pass directly, thereby effectively reducing the absorption of radiated light by the tunneling junction 300 on the LED structure and improving the brightness of the device structure. The thickness of the second heavily doped layer 340 can be 2nm to 50nm, preferably 8nm.

[0072] The undoped layer 330 is made of In. c Ga 1-c As, where c ranges from 0.01 to 0.2, preferably 0.05, resulting in low resistivity and a low bandgap for the undoped layer 330, which improves the peak current of the tunnel junction 300. The undoped layer 330 is an unintentionally doped layer, meaning no dopant is introduced during its growth. The thickness of the undoped layer 330 can be from 0.2 nm to 10 nm, preferably 2 nm. Due to its smaller thickness, it absorbs less radiation from the multi-junction infrared epitaxial LED structure. Placing the undoped layer 330 between the first heavily doped layer 320 and the second heavily doped layer 340 creates a built-in electric field, resulting in a steep impurity concentration distribution between the first and second heavily doped layers 320 and 340. This avoids impurity compensation caused by interdiffusion of impurities in the first and second heavily doped layers 320 and 340, thus preventing a reduction in the doping concentration of the first and second heavily doped layers 320 and 340.

[0073] The second transition layer 350 may be doped with an n-type dopant, including but not limited to silicon (Si), and the doping concentration of the n-type dopant is in the range of 4.0 × 10⁻⁶. 18 ~1.0×10 19 cm -3 Preferably, the n-type dopant concentration is 5.0 × 10⁻⁶. 18 cm -3 ~8.0×10 18 cm -3 The second transition layer 350 is a doping concentration gradient layer, which can improve carrier diffusion caused by differences in doping concentration. Furthermore, the doping concentration of the n-type dopant gradually decreases from bottom to top; that is, the doping concentration of the n-type dopant in the second transition layer 350 increases from 8.0 × 10⁻⁶. 18 cm -3 Gradient to 5.0×10 18 cm -3 .

[0074] The material of the second transition layer 350 is Al e Ga 1-e As, where e ranges from 0.3 to 0.4, and preferably, d ranges from 0.3 to 0.35. The second transition layer 350 is an Al composition gradient layer, which makes the band gap of the second transition layer 350 gradually change, which can improve the lattice quality of the semiconductor layer in the tunnel junction 300 and the LED structure. The Al composition in the second transition layer 350 gradually decreases from bottom to top, that is, the Al composition in the second transition layer 350 decreases from Al to Al from bottom to top.0.35 Ga 0.65 As gradually changes to Al 0.3 Ga 0.7 As. The thickness of the second transition layer 350 can be 10nm to 50nm, preferably 20nm. The second transition layer 350, through gradual doping concentration and bandgap changes, improves the crystal quality of the tunnel junction 300 and the LED structure located on the tunnel junction 300 in the multi-junction infrared LED epitaxial structure, thereby reducing series resistance and lowering the operating voltage.

[0075] Figure 3 This is a schematic flowchart illustrating a method for preparing a tunnel junction according to this embodiment. Figure 3 As shown, please continue reading. Figure 1 and Figure 2 This embodiment also provides a method for preparing a tunnel junction, including the following steps:

[0076] Step S11: A first transition layer 310 is formed, wherein the first transition layer 310 contains an Al component, and the first transition layer 310 is an Al component gradient layer.

[0077] Step S12: A tunnel junction material layer is formed on the first transition layer 310;

[0078] Step S13, forming a second transition layer 350 on the tunneling junction material layer, the second transition layer 350 containing an Al component, and the second transition layer 350 being an Al component gradient layer; and

[0079] The first transition layer 310 and the second transition layer 350 are both doped with different types of dopants, and both the first transition layer 310 and the second transition layer 350 are doping concentration gradient layers.

[0080] Please continue reading. Figure 1 and Figure 2 This embodiment also provides a multi-junction infrared LED epitaxial structure, which can be a multi-junction anti-polarity infrared LED epitaxial structure.

[0081] The multi-junction infrared LED epitaxial structure includes at least two LED structures stacked on the substrate 100, for example, N LED structures. That is, the multi-junction infrared LED epitaxial structure includes the first LED structure to the Nth LED structure from bottom to top. A tunnel junction 300 is provided between each two adjacent LED structures, for example, N-1 tunnel junctions 300, where N≥2 and is a positive integer.

[0082] The radiation wavelength range of the LED structure is 780nm to 1100nm.

[0083] The substrate 100 is, for example, doped with an n-type dopant, and the substrate 100 includes, but is not limited to, GaAs (gallium arsenide) substrates and Si substrates. Preferably, the substrate 100 is a GaAs substrate.

[0084] A buffer layer 110 and an etch stop layer 120 are also formed between the substrate 100 and the LED structure. The buffer layer 110 is located on the substrate 100, and the etch stop layer 120 is located on the buffer layer 110.

[0085] The buffer layer 110 can be a GaAs buffer layer 110. The buffer layer 110 can reduce defects and dislocations in the multi-junction infrared LED epitaxial structure caused by surface defects of the substrate 100, and provide good surface quality for the next subsequent process (i.e., forming the etch stop layer 120). The thickness of the buffer layer 110 can be 100nm to 500nm, preferably 300nm. The etch stop layer is made of GaInP, and its thickness can be 100nm to 500nm, preferably 200nm. The etch stop layer can cooperate with the subsequent processes of the multi-junction infrared LED epitaxial structure to enable the multi-junction infrared LED epitaxial structure to have very high photoelectric efficiency.

[0086] The LED structure comprises, from bottom to top, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer.

[0087] The n-type semiconductor layer is used to provide electrons and confine the light field distribution. The material of the n-type semiconductor layer is Al. h Ga 1-h As, where h can range from 0.2 to 0.4, preferably h is 0.3. The thickness of the n-type semiconductor layer is 200 nm to 600 nm, preferably 400 nm.

[0088] The active layer comprises, from bottom to top, a first spatial layer, a multiple quantum well layer, and a second spatial layer. The material of the first spatial layer is Al. i Ga 1-i As, where i ranges from 0.1 to 0.3, the first space layer is an unintentionally doped layer, meaning no dopant is introduced during its growth. The material of the second space layer is Al. j Ga 1-j As, where j ranges from 0.1 to 0.3, and the second space layer is an unintentionally doped layer, meaning that no dopant is introduced into the second space layer during its growth.

[0089] The multiple quantum well layer is a structure in which well layers and barrier layers are grown alternately with a predetermined period number P, wherein the predetermined period number P ranges from 3 to 15. The material of the well layer is In. x Ga 1-x As, where x ranges from 0 to 0.5, and the thickness of a single well layer can be from 4 nm to 15 nm. The barrier layer material is Al. y Ga 1-y As z P 1-z Where y ranges from 0 to 0.4, z ranges from 0.5 to 1, and the thickness of a single barrier layer can be from 5 nm to 50 nm.

[0090] The p-type semiconductor layer is used to provide holes and confine the light field distribution; the material of the p-type semiconductor layer is Al. k Ga 1-k As, where k ranges from 0.2 to 0.4, preferably k is 0.3. The thickness of the p-type semiconductor layer can be from 200 nm to 600 nm, preferably 400 nm.

[0091] Both the first and Nth LED structures may further include a current spreading layer and an ohmic contact layer. In the first LED structure, both the current spreading layer and the ohmic contact layer are located on the n-type semiconductor layer side. Specifically, in the first LED structure, the current spreading layer is located between the ohmic contact layer and the n-type semiconductor layer. In this case, the doping type of the current spreading layer is the same as the doping type of the n-type semiconductor layer, for example, both are n-type doped. In the Nth LED structure, the current spreading layer and the ohmic contact layer are located on the p-type semiconductor layer side. Specifically, in the Nth LED, the current spreading layer is located between the ohmic contact layer and the p-type semiconductor layer. In this case, the doping type of the current spreading layer is the same as the doping type of the p-type semiconductor layer, for example, both are p-type doped. The current spreading layer is beneficial for subsequent processes and can improve product brightness. The ohmic contact layer is used to provide ohmic contact during subsequent electrode formation.

[0092] The material of the current spreading layer is Al. g Ga 1-gAs, where g ranges from 0.1 to 0.4, preferably 0.2. The thickness of the current spreading layer can be from 0.2 μm to 10 μm. The current spreading layer can be doped with n-type or p-type dopant. When the current spreading layer is located on the n-type semiconductor layer side, it is doped with n-type dopant; when the current spreading layer is located on the p-type semiconductor layer side, it is doped with p-type dopant.

[0093] The ohmic contact layer is made of materials including, but not limited to, GaAs and GaP. The thickness of the ohmic contact layer can be 50 nm to 150 nm, preferably 100 nm. The ohmic contact layer can be doped with either an n-type or p-type dopant. When the ohmic contact layer is located on the n-type semiconductor layer side, it is doped with n-type dopant; when it is located on the p-type semiconductor layer side, it is doped with p-type dopant.

[0094] In this embodiment, by using Al composition gradient layers 310 and 350 of the tunnel junction 300 as Al composition gradient layers and doping concentration gradient layers, the crystal quality of the tunnel junction 300 and the LED structure located on the tunnel junction 300 in the multi-junction infrared LED epitaxial structure is effectively improved, reducing series resistance and lowering operating voltage. Furthermore, by using a high-Al composition first heavily doped layer 320 and a high-bandgap second heavily doped layer 340 of the tunnel junction 300 as tunnel junction materials, photons can directly pass through the tunnel junction, effectively reducing the absorption of radiated light by the LED structure and improving the brightness of the device structure. Additionally, the high doping concentration of the first heavily doped layer 320 and the second heavily doped layer 340 effectively reduces the series resistance of the tunnel junction 300, further reducing... The operating voltage; furthermore, by spacing the first heavily doped layer 320 and the second heavily doped layer 340 with different doping types between the undoped layer 330 in the tunnel junction material layer, a built-in electric field can be formed, making the impurity concentration distribution of the first heavily doped layer 320 and the second heavily doped layer 340 steep, avoiding impurity compensation caused by the interdiffusion of impurities in the first heavily doped layer 320 and the second heavily doped layer 340, thus reducing the doping concentration of the first heavily doped layer 320 and the second heavily doped layer 340; at the same time, the material selection of the undoped layer 330 (i.e., InGaAs material) makes the resistivity of the undoped layer 330 low and the band gap low, which can improve the peak current of the tunnel junction 300; the thickness of the undoped layer 330 is relatively thin, resulting in less absorption of the radiation light of the multi-junction infrared extension LED structure.

[0095] It should be noted that, since the multi-junction infrared LED epitaxial structure includes N LED structures and N-1 tunnel junctions, the specific composition of each semiconductor layer in each LED structure may be the same or different. For example, the material Al of the n-type semiconductor layer in each LED structure may be different. h Ga 1-h h in As, and Al, the material of the first space layer i Ga 1-i i in As, and Al, the material of the second space layer j Ga 1-j j in As, and the material In of the well layer x Ga 1-x x in As, the barrier layer material Al y Ga 1-y As z P 1-z z in the text, and Al, the material of the p-type semiconductor layer. k Ga 1-k k in As, and Al, the material of the current spreading layer g Ga 1-g In As, the 'g' can be the same or different.

[0096] Similarly, the material Al of the first transition layer 310 in each of the tunneling junctions d Ga 1-d d in As, and Al, the material of the first doped layer 320. a Ga 1-a In As, α, and the material of the second doped layer 340, Ga... b In 1-b b in P, the material In of the undoped layer 330 c Ga 1-c c in As, Al, the material of the second transition layer 350 e Ga 1-e In As, the 'e' can be the same or different.

[0097] Please see Figure 1 The following example illustrates the concept of a dual-junction infrared LED epitaxial structure as an example of a multi-junction infrared LED epitaxial structure.

[0098] The dual-junction infrared LED epitaxial structure comprises, from bottom to top, a substrate 100, a buffer layer 110, an etch stop layer 120, a first LED structure 200, a tunnel junction 300, and a second LED structure 400.

[0099] The first LED structure 200 comprises, from bottom to top, a first ohmic contact layer 210, a first current spreading layer 220, a first n-type semiconductor layer 230, a first active layer 240, and a first p-type semiconductor layer 250. Both the first ohmic contact layer 210 and the first current spreading layer 220 are doped with n-type dopants. The thickness of the first current spreading layer 220 can be 3 μm to 10 μm, preferably 8 μm. The material of the first ohmic contact layer 210 is GaAs. The barrier layer material of the multi-quantum well layer of the first active layer 240 is Al. y Ga 1-y As z P 1-z When y = 0, the barrier layer material is GaAs. z P 1-z When the preset period number P is 12, the radiation wavelength of the multi-quantum well layer is 850nm.

[0100] The second LED structure 400, from bottom to top, includes a second n-type semiconductor layer 410, a second active layer 420, a second p-type semiconductor layer 430, a second current spreading layer 440, and a second ohmic contact layer 450. Both the second current spreading layer 440 and the second ohmic contact layer 450 are doped with p-type dopant. The thickness of the second current spreading layer 440 can be 0.2 μm to 4 μm, preferably 2 μm. The material of the second ohmic contact layer 450 is GaP. The barrier layer material of the multi-quantum well layer in the second active region is Al. y Ga 1-y As z P 1-z When y = 0, the barrier layer material is GaAs. z P 1-z When the preset period number P is 6, the radiation wavelength of the multi-quantum well layer is 850nm.

[0101] Figure 4 This is a schematic flowchart illustrating a method for fabricating a multi-junction infrared LED epitaxial structure provided in this embodiment. Figure 4 As shown, please also refer to Figure 1 and Figure 2 This embodiment also provides a method for fabricating a multi-junction infrared LED epitaxial structure. Each step of the fabrication method can employ any one of MOCVD, molecular beam epitaxy, HVPE, plasma-assisted chemical vapor deposition, and sputtering processes. Preferably, each step of the fabrication method employs MOCVD. The fabrication method includes the following steps:

[0102] Step S21, provide a substrate 100;

[0103] Step S22: LED structures and tunnel junctions 300 are alternately formed on the substrate 100 to obtain N LED structures and N-1 tunnel junctions 300. Each tunnel junction 300 is located between two adjacent LED structures, and the Nth LED structure is located on the N-1th tunnel junction 300, thereby forming a multi-junction infrared LED epitaxial structure, where N≥2 and is a positive integer.

[0104] The following example illustrates the concept of a dual-junction infrared LED epitaxial structure as an example of a multi-junction infrared LED epitaxial structure.

[0105] Figure 5 This is a schematic flowchart illustrating a method for fabricating a dual-junction infrared LED epitaxial structure provided in this embodiment. Figure 5 As shown, please also refer to Figure 1 and Figure 2 The multi-junction infrared LED epitaxial structure is a double-junction infrared LED epitaxial structure. The fabrication method includes the following steps:

[0106] Step S31, provide a substrate 100;

[0107] In step S32, a first LED structure 200, a tunnel junction 300, and a second LED structure 400 are sequentially stacked on the substrate 100 to form a double-junction infrared LED epitaxial structure.

[0108] In this embodiment, an infrared LED with an area of ​​350μm*350μm was prepared using a reverse polarity infrared LED process. Compared with the traditional single-junction reverse polarity infrared LED, the brightness of the dual-junction infrared LED in this embodiment is increased by 50% to 60%, and the operating voltage of the dual-junction infrared LED is less than twice that of the single-junction reverse polarity infrared LED.

[0109] In summary, this invention provides a tunnel junction and its fabrication method, as well as a multi-junction infrared LED epitaxial structure and its fabrication method. The tunnel junction, from bottom to top, comprises a first transition layer, a tunnel junction material layer, and a second transition layer. Both the first and second transition layers contain Al components and are doped with different types of dopants. Both the first and second transition layers are doping concentration gradient layers and are Al composition gradient layers. By using Al composition gradient layers and doping concentration gradient layers for both the first and second transition layers of the tunnel junction, this invention effectively improves the crystal quality of the LED structure located on the tunnel junction in the tunnel junction and the multi-junction infrared LED epitaxial structure, reduces series resistance, and lowers the operating voltage.

[0110] Furthermore, it should be noted that, unless otherwise specified or indicated, the terms "first" and "second" in the specification are used only to distinguish the various components, elements, steps, etc. in the specification, and are not used to indicate the logical or sequential relationships between the various components, elements, steps, etc.

[0111] It is understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A tunnel junction, characterized in that, From bottom to top, it includes a first transition layer, a tunnel junction material layer, and a second transition layer. Both the first and second transition layers contain Al components. The first transition layer is doped with a p-type dopant, and the second transition layer is doped with an n-type dopant. Both the first and second transition layers are doping concentration gradient layers and are Al component gradient layers.

2. The tunneling junction as described in claim 1, characterized in that, The doping concentration of the p-type dopant gradually increases from bottom to top, and the Al component in the first transition layer gradually increases from bottom to top.

3. The tunneling junction as described in claim 2, characterized in that, The material of the first transition layer is Al d Ga 1-d As, where d ranges from 0.3 to 0.4; the doping concentration of the p-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

4. The tunneling knot as described in claim 1, characterized in that, The doping concentration of the n-type dopant gradually decreases from bottom to top, and the Al component in the second transition layer gradually decreases from bottom to top.

5. The tunneling junction as described in claim 4, characterized in that, The material of the second transition layer is Al e Ga 1-e As, where e ranges from 0.3 to 0.4; the doping concentration of the n-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

6. The tunneling junction as described in claim 1, characterized in that, The tunnel junction material layer comprises, from bottom to top, a first heavily doped layer, an undoped layer, and a second heavily doped layer. Both the first heavily doped layer and the second heavily doped layer are doped with different types of dopants. The undoped layer is used to isolate the first heavily doped layer and the second heavily doped layer.

7. The tunnel joint as described in claim 6, characterized in that, The material of the undoped layer is In. c Ga 1-c As, where c ranges from 0.01 to 0.

2.

8. The tunnel junction as described in claim 6, characterized in that, The thickness of the undoped layer is 0.2 nm to 10 nm.

9. The tunnel joint as described in claim 6, characterized in that, The first heavily doped layer is doped with a p-type dopant, and the second heavily doped layer is doped with an n-type dopant, with both the doping concentration of the first and second heavily doped layers being greater than 2.0 × 10⁻⁶. 19 cm -3 .

10. The tunneling knot as described in claim 6, characterized in that, The material of the first doped layer is Al a Ga 1-a As, where the value of a ranges from 0.2 to 0.8; The material of the second doped layer is Ga b In 1-b P, where b ranges from 0.4 to 0.

8.

11. A method for preparing a tunnel junction, characterized in that, Includes the following steps: A first transition layer is formed, the first transition layer contains an Al component, and the first transition layer is an Al component gradient layer; A tunneling junction material layer is formed on the first transition layer; as well as A second transition layer is formed on the tunnel junction material layer. The second transition layer contains an Al component and is an Al component gradient layer. The first transition layer is doped with a p-type dopant, the second transition layer is doped with an n-type dopant, and both the first and second transition layers are doped concentration gradient layers.

12. The method for preparing a tunnel junction as described in claim 11, characterized in that, The doping concentration of the p-type dopant gradually increases from bottom to top, and the Al component in the first transition layer gradually increases from bottom to top.

13. The method for preparing a tunnel junction as described in claim 12, characterized in that, The material of the first transition layer is Al d Ga 1-d As, where d ranges from 0.3 to 0.4; the doping concentration of the p-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

14. The method for preparing a tunnel junction as described in claim 11, characterized in that, The doping concentration of the n-type dopant gradually decreases from bottom to top, and the Al component in the second transition layer gradually decreases from bottom to top.

15. The method for preparing a tunnel junction as described in claim 14, characterized in that, The material of the second transition layer is Al e Ga 1-e As, where e ranges from 0.3 to 0.4; the doping concentration of the n-type dopant ranges from 4.0 × 10⁻⁶. 18 cm -3 ~1.0×10 19 cm -3 .

16. The method for preparing a tunnel junction as described in claim 11, characterized in that, The tunnel junction material layer is formed by sequentially forming a first heavily doped layer, an undoped layer, and a second heavily doped layer from bottom to top. Both the first heavily doped layer and the second heavily doped layer are doped with different types of dopants. The undoped layer is used to isolate the first heavily doped layer and the second heavily doped layer.

17. The method for preparing a tunnel junction as described in claim 16, characterized in that, The material of the undoped layer is In. c Ga 1-c As, where c ranges from 0.01 to 0.

2.

18. The method for preparing a tunnel junction as described in claim 16, characterized in that, The thickness of the undoped layer is 0.2 nm to 10 nm.

19. The method for preparing a tunnel junction as described in claim 16, characterized in that, The first heavily doped layer is doped with a p-type dopant, and the second heavily doped layer is doped with an n-type dopant, with both the doping concentration of the first and second heavily doped layers being greater than 2.0 × 10⁻⁶. 19 cm -3 .

20. The method for preparing a tunnel junction as described in claim 16, characterized in that, The material of the first doped layer is Al a Ga 1-a As, where the value of a ranges from 0.2 to 0.8; The material of the second doped layer is Ga b In 1-b P, where b ranges from 0.4 to 0.

8.

21. A multi-junction infrared LED epitaxial structure, characterized in that, The device includes a tunnel junction as described in any one of claims 1 to 10, and further includes at least two LED structures stacked on a substrate, with a tunnel junction disposed between each pair of adjacent LED structures.

22. The multi-junction infrared LED epitaxial structure as described in claim 21, characterized in that, The LED structure comprises, from bottom to top, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer.

23. The multi-junction infrared LED epitaxial structure as described in claim 21, characterized in that, The multi-junction infrared LED epitaxial structure further includes a buffer layer and an etch stop layer located between the substrate and the LED structure, wherein the buffer layer and the etch stop layer are sequentially disposed on the substrate.

24. The multi-junction infrared LED epitaxial structure as described in claim 22, characterized in that, The multi-junction infrared LED epitaxial structure comprises, from bottom to top, a first LED structure to an Nth LED structure. Both the first and Nth LED structures further include a current spreading layer and an ohmic contact layer. In the first LED structure, both the current spreading layer and the ohmic contact layer are located on the n-type semiconductor layer side; in the Nth LED structure, both the current spreading layer and the ohmic contact layer are located on the p-type semiconductor layer side, where N≥2 and is a positive integer.

25. The multi-junction infrared LED epitaxial structure as described in claim 24, characterized in that, In the first LED structure, the current spreading layer is located between the ohmic contact layer and the n-type semiconductor layer, and the current spreading layer is doped with an n-type dopant. as well as In the Nth LED, the current spreading layer is located between the ohmic contact layer and the p-type semiconductor layer, and the current spreading layer is doped with a p-type dopant.

26. A method for fabricating a multi-junction infrared LED epitaxial structure, characterized in that, Includes the following steps: Provide a substrate; LED structures and tunnel junctions as described in any one of claims 1 to 10 are alternately formed on the substrate to obtain N LED structures and N-1 tunnel junctions, each of the tunnel junctions being located between two adjacent LED structures, and the Nth LED structure being located on the (N-1)th tunnel junction, thereby forming a multi-junction infrared LED epitaxial structure, wherein N ≥ 2 and is a positive integer.

27. The method for fabricating a multi-junction infrared LED epitaxial structure as described in claim 26, characterized in that, The formation of the LED structure includes forming an n-type semiconductor layer, an active layer, and a p-type semiconductor layer from bottom to top.

28. The method for fabricating a multi-junction infrared LED epitaxial structure as described in claim 26, characterized in that, It also includes forming a buffer layer and an etch stop layer between the substrate and the LED structure, wherein the buffer layer and the etch stop layer are sequentially disposed on the substrate.

29. The method for fabricating a multi-junction infrared LED epitaxial structure as described in claim 27, characterized in that, The multi-junction infrared LED epitaxial structure comprises, from bottom to top, a first LED structure to an Nth LED structure. Both the first and Nth LED structures further include a current spreading layer and an ohmic contact layer. In the first LED structure, both the current spreading layer and the ohmic contact layer are located on the n-type semiconductor layer side; in the Nth LED structure, both the current spreading layer and the ohmic contact layer are located on the p-type semiconductor layer side.

30. The method for fabricating a multi-junction infrared LED epitaxial structure as described in claim 29, characterized in that, In the first LED structure, the current spreading layer is located between the ohmic contact layer and the n-type semiconductor layer, and the current spreading layer is doped with an n-type dopant. as well as In the Nth LED, the current spreading layer is located between the ohmic contact layer and the p-type semiconductor layer, and the current spreading layer is doped with a p-type dopant.

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