CN115692561A

CN115692561A - Tunneling junction and preparation method thereof, multi-junction infrared LED epitaxial structure and preparation method thereof

Info

Publication number: CN115692561A
Application number: CN202211399136.5A
Authority: CN
Inventors: 王亚宏; 李森林; 廖寅生; 薛龙; 赖玉财; 董雪振; 谢岚驰
Original assignee: Xiamen Silan Advanced Compound Semiconductor Co Ltd
Current assignee: Xiamen Silan Advanced Compound Semiconductor Co Ltd
Priority date: 2022-11-09
Filing date: 2022-11-09
Publication date: 2023-02-03

Abstract

The invention provides a tunneling junction and a preparation method thereof, a multi-junction infrared LED epitaxial structure and a preparation method thereof, wherein the tunneling junction sequentially comprises a first transition layer, a tunneling junction material layer and a second transition layer from bottom to top, the first transition layer and the second transition layer both contain Al components, the first transition layer and the second transition layer are doped with dopants of different types, the first transition layer and the second transition layer are both doping concentration gradient layers and are both Al component gradient layers, the crystal quality of the LED structure positioned on the tunneling junction in the multi-junction infrared LED epitaxial structure and the tunneling junction can be effectively improved, the series resistance is reduced, and the working voltage is reduced.

Description

Tunneling junction and preparation method thereof, multi-junction infrared LED epitaxial structure and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductors, in particular to a tunneling junction and a preparation method thereof, and a multi-junction infrared LED epitaxial structure and a preparation method thereof.

Background

An infrared LED (infrared Light Emitting Diode) is a Light Emitting device that can convert electric energy into near-infrared Light, and is mainly applied to various photoelectric coupled switches, security monitoring, night vision monitoring, face and iris recognition, gas detection, and other fields, where the security monitoring, night vision monitoring, face and iris recognition, and other fields have high requirements for the brightness of an infrared LED epitaxial structure. For this reason, a plurality of large-sized single infrared LEDs can be used in series to improve the brightness, but the light emitting device obtained in this way has a large resistance and a high operating voltage, and at the same time, occupies a large space and has low reliability.

In order to solve the above problems, a multi-junction infrared LED epitaxial structure may be adopted, that is, in the LED epitaxial structure preparation process, a plurality of LED structures are connected in series by using a tunnel junction (tunnel junction) to improve the brightness, and the integration level and reliability of the light emitting device may also be greatly improved. However, the resistance of the epitaxial structure of the conventional multi-junction infrared LED is still large, and the working voltage is still high.

Disclosure of Invention

The invention aims to provide a tunneling junction and a preparation method thereof, a multi-junction infrared LED epitaxial structure and a preparation method thereof, which can reduce the resistance of the multi-junction infrared LED epitaxial structure, thereby reducing the working voltage of the multi-junction infrared LED epitaxial structure.

In order to solve the above problems, the present invention provides a tunnel junction, which sequentially includes, from bottom to top, a first transition layer, a tunnel junction material layer, and a second transition layer, where the first transition layer and the second transition layer both include Al components, and the first transition layer and the second transition layer are both doped with dopants of different types, and both the first transition layer and the second transition layer are doping concentration gradient layers and are Al component gradient layers.

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 composition in the first transition layer gradually increases from bottom to top.

Further, the material of the first transition layer is Al _d Ga _1-d As, wherein the value range of d is 0.3-0.4; the doping concentration range of the p-type dopant is 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 。

Optionally, the second transition layer is doped with an n-type dopant, the doping concentration of the n-type dopant gradually decreases from bottom to top, and the Al composition in the second transition layer gradually decreases from bottom to top.

Further, the material of the second transition layer is Al _e Ga _1-e As, wherein the value range of e is 0.3-0.4; the doping concentration range of the n-type dopant is 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 。

Optionally, the tunneling junction material layer sequentially includes a first heavily doped layer, a non-doped layer and a second heavily doped layer from bottom to top, the first heavily doped layer and the second heavily doped layer are doped with different types of dopants, and the non-doped layer is used for isolating the first heavily doped layer from the second heavily doped layer.

Further, the material of the undoped layer is In _c Ga _1-c As, wherein the value range of c is 0.01-0.2.

Further, the thickness of the undoped layer is 0.2 nm-10 nm.

Further, the first heavily doped layer is doped with a p-type dopant, the second heavily doped layer is doped with an n-type dopant, and the doping concentration of the first heavily doped layer and the doping concentration of the second heavily doped layer are both greater than 2.0 x 10 ¹⁹ cm ^-3 。

Further, the material of the first heavily doped layer is Al _a Ga _1-a As, wherein a is in a range of 0.2 to 0.8;

the material of the second heavily doped layer is Ga _b In _1-b P, wherein the value range of b is 0.4-0.8.

On the other hand, the invention also discloses a preparation method of the tunneling junction, which comprises the following steps:

forming a first transition layer, wherein the first transition layer contains an Al component and is an Al component gradient layer;

forming a tunneling junction material layer on the first transition layer; and

and forming a second transition layer on the tunneling junction material layer, wherein the second transition layer contains an Al component and is an Al component gradient layer, the first transition layer and the second transition layer are both doped with dopants of different types, and the first transition layer and the second transition layer are both doped concentration gradient layers.

Optionally, the forming of the tunneling junction material layer includes sequentially forming a first heavily doped layer, a non-doped layer and a second heavily doped layer from bottom to top, where the first heavily doped layer and the second heavily doped layer are doped with different types of dopants, and the non-doped layer is used to isolate the first heavily doped layer from the second heavily doped layer.

Further, the thickness of the undoped layer is 0.2 nm-10 nm.

In another aspect, the invention further provides a multi-junction infrared LED epitaxial structure, which includes the tunneling junction, and further includes at least two LED structures stacked on the substrate, wherein one tunneling junction is disposed between every two adjacent LED structures.

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

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, and the buffer layer and the etch stop layer are sequentially disposed on the substrate.

Further, the multi-junction infrared LED epitaxial structure sequentially comprises a first LED structure to an Nth LED structure from bottom to top, the first LED structure and the Nth LED structure both further comprise a current expansion layer and an ohmic contact layer,

in the first LED structure, the current spreading layer and the ohmic contact layer are positioned on the side of the n-type semiconductor layer; in the Nth LED structure, the current expansion layer and the ohmic contact layer are both positioned on the side of the p-type semiconductor layer, wherein N is not less than 2 and is a positive integer.

Further, 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

in the nth of the LEDs, 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.

In another aspect, the invention also provides a preparation method of the multi-junction infrared LED epitaxial structure, which comprises the following steps:

providing a substrate;

and alternately forming LED structures and tunneling junctions on the substrate to obtain N LED structures and N-1 tunneling junctions, wherein each tunneling junction is positioned between two adjacent LED structures, and the Nth LED structure is positioned on the N-1 th tunneling junction, so that a multi-junction infrared LED epitaxial structure is formed, wherein N is not less than 2 and is a positive integer.

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

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

in the first LED structure, the current spreading layer and the ohmic contact layer are both positioned on the side of the n-type semiconductor layer; in the Nth LED structure, the current spreading layer and the ohmic contact layer are both positioned on the p-type semiconductor layer side.

Compared with the prior art, the invention has the following beneficial effects:

1. the first transition layer and the second transition layer are both an Al component gradient layer and a doping concentration gradient layer, so that the crystal quality of the tunneling junction and the LED structure positioned on the tunneling junction in the multi-junction infrared LED epitaxial structure is effectively improved, the series resistance is reduced, and the working voltage is reduced.

2. The first heavily doped layer with high Al component of the tunneling junction and the second heavily doped layer with high band gap are used as tunneling junction materials, so that photons passing through the tunneling junction can directly pass through, the absorption of the tunneling junction on the radiation light of the LED structure is effectively reduced, and the brightness of the device structure is improved.

3. The first heavily doped layer and the second heavily doped layer with different doping types are spaced by the undoped layer in the tunneling junction material layer, so that a built-in electric field can be formed, the impurity concentration distribution of the first heavily doped layer and the second heavily doped layer is steep, and the reduction of the doping concentration of the first heavily doped layer and the second heavily doped layer caused by impurity compensation due to the mutual diffusion of impurities in the first heavily doped layer and the second heavily doped layer is avoided.

4. By material selection of the undoped layer (i.e. selection of In) _c Ga _1-c The value range of c is 0.01-0.2), so that the resistivity of the non-doped layer is low, the band gap is low, the peak current of a tunneling junction can be increased, and the thickness of the non-doped layer is thin, so that the radiation light absorption of the multi-junction red epitaxial LED structure is low.

5. The series resistance of the tunneling junction can be effectively reduced through the high doping concentration of the first heavily doped layer and the second heavily doped layer, so that the working voltage is further reduced.

Drawings

Fig. 1 is a schematic structural diagram of a multi-junction infrared LED epitaxial structure according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a tunneling junction according to an embodiment of the present invention;

fig. 3 is a schematic flow chart of a method for fabricating a tunnel junction according to an embodiment of the present invention;

fig. 4 is a schematic flow chart of a method for manufacturing a multi-junction infrared LED epitaxial structure according to an embodiment of the present invention;

fig. 5 is a schematic flow chart of a method for manufacturing a double-junction infrared LED epitaxial structure according to an embodiment of the present invention.

Description of the reference numerals:

100-a substrate; 110-a buffer layer; 120-an etch stop layer; 200-a first LED structure; 210-a first ohmic contact layer; 220-a first current spreading layer; 230-a first n-type semiconductor layer; 240-first active layer; 250-a first p-type semiconductor layer; 300-tunneling junction; 310 — a first transition layer; 320-a first heavily doped layer; 330-undoped layer; 340-a second heavily doped layer; 350-a second transition layer; 400-a second LED structure; 410-a second n-type semiconductor layer; 420-a second active layer; 430-a second p-type semiconductor layer; 440-a second current spreading layer; 450-second ohmic contact layer.

Detailed Description

The tunneling junction and the preparation method thereof, and the multi-junction infrared LED epitaxial structure and the preparation method thereof according to the present invention will be further described in detail below. The present invention will now be described in more detail with reference to the accompanying drawings, in which preferred embodiments of the invention are shown, it being understood that one skilled in the art may modify the invention herein described while still achieving the advantageous effects of the invention. Accordingly, the following description should be construed as broadly as possible to those skilled in the art and not as limiting the invention.

In the interest of clarity, not all features of an actual implementation are described. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific details must be set forth in order to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art.

In order to make the objects and features of the present invention more comprehensible, embodiments of the present invention are described in detail below with reference to the accompanying drawings. It is to be noted that the drawings are in a very simplified form and are all used in a non-precise ratio for the purpose of facilitating and distinctly aiding in the description of the embodiments of the invention.

Fig. 1 is a schematic structural diagram of a multi-junction infrared LED epitaxial structure provided in this embodiment. Fig. 2 is a schematic structural diagram of the tunnel junction provided in this embodiment. As shown in fig. 1 and 2, the present embodiment provides a tunneling junction 300 for connecting each adjacent two LED structures in a multi-junction infrared LED epitaxial structure to connect all the LED structures in series.

The tunnel junction 300 sequentially includes a first transition layer 310, a tunnel junction material layer, and a second transition layer 350 from bottom to top.

The first transition layer 310 may be doped with a p-type dopant, including but not limited to carbon (C), at a doping concentration in the range of 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 Preferably, the doping concentration of the p-type dopant ranges from 5.0 × 10 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 of doping concentrations, and avoid the diffusion of impurities in the high-doping layer caused by the overlarge concentration gradient of the film layers at the two sides of the first transition layer 310, thereby effectively ensuring that the doping concentration of the high-doping layer reaches the required concentration and reducing the series resistance.

And 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 gradually increases from bottom to top from 5.0 × 10 ¹⁸ cm ^-3 Gradation to 8.0X 10 ¹⁸ cm ^-3 。

The material of the first transition layer 310 is Al _d Ga _1-d As, wherein d is in the range of 0.3 to 0.4, preferably d is in the range of0.3 to 0.35. The first transition layer 310 is an Al composition graded layer, so that the first transition layer 310 has a graded bandgap, which can improve the lattice quality of the tunneling junction 300 and the semiconductor layer in 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 bottom to top from Al _0.3 Ga _0.7 As is graded to Al _0.35 Ga _0.65 As. The thickness of the first transition layer 310 may be 10nm to 50nm, and preferably, the thickness of the first transition layer 310 is 30nm. The first transition layer 310 improves the crystal quality of the tunneling junction 300 and an LED structure on the tunneling junction 300 in the multi-junction infrared LED epitaxial structure through doping concentration gradient and band gap gradient, thereby reducing the series resistance and lowering the operating voltage.

The tunneling junction material layer sequentially comprises a first heavily doped layer 320, a non-doped layer 330 and a second heavily doped layer 340 from bottom to top.

The first heavily doped layer 320 may be doped with a p-type dopant including, but not limited to, carbon (C) at a doping concentration greater than 2.0 x 10 ¹⁹ cm ^-3 Preferably, the doping concentration of the p-type dopant is 8.0 × 10 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.

The material of the first heavily doped layer 320 is Al _a Ga _1-a As, wherein a is in the range of 0.2 to 0.8, preferably, a is 0.4, and Al is a high Al component _a Ga _1-a As is used As a tunneling junction material, photons passing through the tunneling junction can directly pass through, so that the absorption of the tunneling junction 300 on the radiation light of the LED structure can be effectively reduced, and the brightness of the device structure is improved. The thickness of the first heavily doped layer 320 may be 2nm to 50nm, and preferably, the thickness of the first heavily doped layer 320 is 10nm.

The second heavily doped layer 340 may be doped with an n-type dopant including, but not limited to, antimony (Te) at a doping concentration greater than 2.0 x 10 ¹⁹ cm ^-3 Preferably, the doping concentration of the n-type dopant is 1.0 × 10 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.

The material of the second heavily doped layer 340 is Ga _b In _1-b P, wherein the value range of b is 0.4-0.8, preferably, the value of b is 0.54, and Ga with high band gap _b In _1-b The P is used as a tunneling junction material, so that photons passing through the tunneling junction can directly pass through, the radiation light absorption of the tunneling junction 300 on the LED structure can be effectively reduced, and the brightness of the device structure is improved. The thickness of the second heavily doped layer 340 may be 2nm to 50nm, and preferably, the thickness of the second heavily doped layer 340 is 8nm.

The material of the undoped layer 330 is In _c Ga _1-c As, wherein the value range of c is 0.01 to 0.2, and preferably, the value of c is 0.05, so that the undoped layer 330 has low resistivity and a low band gap, and the peak current of the tunnel junction 300 can be increased. The undoped layer 330 is an unintentional doped layer, that is, the undoped layer 330 is not doped with a dopant during the growth process; the thickness of the undoped layer 330 may be 0.2nm to 10nm, and preferably, the thickness of the undoped layer 330 is 2nm, which results in less absorption of radiation light to the multi-junction red epitaxial LED structure. The undoped layer 330 is disposed between the first and second heavily doped

layers

320 and 340, so that a built-in electric field can be formed, the impurity concentration profile of the first and second heavily doped

layers

320 and 340 is steep, and the decrease of the doping concentration of the first and second heavily doped

layers

320 and 340 due to impurity compensation caused by the mutual diffusion of the impurities in the first and second heavily doped

layers

320 and 340 is avoided.

The second transition layer 350 may be doped with an n-type dopant, including but not limited to silicon (Si), at a doping concentration in the range of 4.0 x 10 ¹⁸ ～1.0×10 ¹⁹ cm ^-3 Preferably, the doping concentration of the n-type dopant is 5.0 × 10 ¹⁸ cm ^-3 ～8.0×10 ¹⁸ cm ^-3 . The second transition layer 350 is a doping concentration gradient layer, which can improve the diffusion of carriers caused by the difference of the doping concentrations, and 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 is from 8.0 × 10 ¹⁸ cm ^-3 Gradation to 5.0X 10 ¹⁸ cm ^-3 。

The material of the second transition layer 350 is Al _e Ga _1-e As, wherein e is in the range of 0.3 to 0.4, preferably d is in the range of 0.3 to 0.35. The second transition layer 350 is an Al composition gradient layer, so that the band gap of the second transition layer 350 is gradually changed, and the lattice quality of the tunneling junction 300 and the semiconductor layer in the LED structure can be improved. The Al component in the second transition layer 350 gradually decreases from bottom to top, that is, the Al component in the second transition layer 350 gradually decreases from bottom to top from Al _0.35 Ga _0.65 As is graded to Al _0.3 Ga _0.7 As. The thickness of the second transition layer 350 may be 10nm to 50nm, and preferably, the thickness of the second transition layer 350 is 20nm. The second transition layer 350 improves the crystal quality of the tunneling junction 300 and the LED structure on the tunneling junction 300 in the multi-junction infrared LED epitaxial structure through the gradual doping concentration change and the gradual band gap change, thereby reducing the series resistance and the working voltage.

Fig. 3 is a schematic flow chart of a method for manufacturing a tunnel junction according to this embodiment. As shown in fig. 3, with continued reference to fig. 1 and fig. 2, the present embodiment further provides a method for fabricating a tunneling junction, including the following steps:

step S11, forming a first transition layer 310, wherein the first transition layer 310 contains an Al component, and the first transition layer 310 is an Al component gradient layer;

step S12, forming a tunneling junction material layer on the first transition layer 310;

step S13, forming a second transition layer 350 on the tunneling junction material layer, wherein the second transition layer 350 contains Al components, and the second transition layer 350 is an Al component gradient layer; and

the first transition layer 310 and the second transition layer 350 are doped with different types of dopants, and the first transition layer 310 and the second transition layer 350 are doped with graded concentrations.

With continued reference to fig. 1 and fig. 2, the present embodiment further provides a multi-junction infrared LED epitaxial structure, which may be a multi-junction reverse-polarity infrared LED epitaxial structure.

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 sequentially includes a first LED structure to an nth LED structure from bottom to top, and a tunneling junction 300, for example, N-1 tunneling junctions 300, is disposed between every two adjacent LED structures, where N is greater than or equal to 2 and is a positive integer.

Wherein the radiation wavelength range of the LED structure is 780 nm-1100 nm.

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

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 being located on the substrate 100, and the etch stop layer 120 being located on the buffer layer 110.

The buffer layer 110 may be a GaAs buffer layer 110, and the buffer layer 110 can reduce defects and dislocations occurring in the multi-junction infrared LED epitaxial structure due to 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 may be 100nm to 500nm, and preferably, the thickness of the buffer layer 110 is 300nm. The material of the corrosion stop layer is GaInP, the thickness of the corrosion stop layer can be 100 nm-500 nm, preferably, the thickness of the corrosion stop layer is 200nm, and the corrosion stop layer can be matched with the subsequent process of the multi-junction infrared LED epitaxial structure, so that the multi-junction infrared LED epitaxial structure has very high photoelectric efficiency.

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

The n-type semiconductor layer serves to supply electrons and limit the optical field distribution. The n-type semiconductor layer is made of Al _h Ga _1-h As, h can be in the range of 0.2-0.4, preferably, h is 0.3. The thickness of the n-type semiconductor layer is 200nm to 600nm, and preferably, the thickness of the n-type semiconductor layer is 400nm.

The active layer sequentially comprises a first space layer, a multi-quantum well layer and a second space layer from bottom to top, and the first space layer is made of Al _i Ga _1-i And As, wherein the value range of i is 0.1-0.3, the first space layer is an unintentional doping layer, namely, the first space layer is not doped with a dopant in the growth process. The material of the second space layer is Al _j Ga _1-j And As, wherein j ranges from 0.1 to 0.3, and the second space layer is an unintentional doping layer, that is, the second space layer is not doped with a dopant during the growth process.

The multi-quantum well layer is of a multi-quantum well structure with a well layer and a barrier layer of preset period number P alternately growing, wherein the value range of the preset period number P is 3-15. The material of the well layer is In _x Ga _1-x And As, wherein x ranges from 0 to 0.5, and the thickness of the single-layer well layer can range from 4nm to 15nm. The barrier layer is made of Al _y Ga _1-y As _z P _1-z Wherein y ranges from 0 to 0.4, z ranges from 0.5 to 1, and the thickness of the single-layer barrier layer can range from 5nm to 50nm.

The p-type semiconductor layer is used for providing holes and limiting optical field distribution, and the material of the p-type semiconductor layer is Al _k Ga _1-k As, wherein k is in the range of 0.2-0.4, preferably, k is 0.3. The thickness of the p-type semiconductor layer may be 200nm to 600nm, and preferably, the thickness of the p-type semiconductor layer is 400nm.

Each of the first and nth LED structures may further include a current spreading layer and an ohmic contact layer. In the first LED structure, the current spreading layer and the ohmic contact layer are both located on the n-type semiconductor layer side, and in particular, in the first LED structure, the current spreading layer is located between the ohmic contact layer and the n-type semiconductor layer, and in this case, the doping type of the current spreading layer is the same as that of the n-type semiconductor layer, for example, both are n-type doping; in the nth LED structure, the current spreading layer and the ohmic contact layer are located on the p-type semiconductor layer side, and in particular, in the nth LED structure, the current spreading layer is located between the ohmic contact layer and the p-type semiconductor layer, and at this time, the doping type of the current spreading layer is the same as that of the p-type semiconductor layer, for example, both are p-type doping. The current spreading layer is beneficial to subsequent processes, the brightness of a product can be improved, and the ohmic contact layer is used for providing ohmic contact when an electrode is formed subsequently.

The current spreading layer is made of Al _g Ga _1-g As, g is in the range of 0.1 to 0.4, preferably 0.2. The thickness of the current spreading layer may be 0.2 μm to 10 μm. The current spreading layer may be doped with an n-type dopant or a p-type dopant, and when the current spreading layer is positioned at the n-type semiconductor layer side, the current spreading layer is doped with an n-type dopant, and when the current spreading layer is positioned at the p-type semiconductor layer side, the current spreading layer is doped with a p-type dopant.

The material of the ohmic contact layer includes, but is not limited to, gaAs and GaP, the thickness of the ohmic contact layer can be 50 nm-150 nm, and preferably, the thickness of the ohmic contact layer is 100nm. The ohmic contact layer may be doped with an n-type dopant or a p-type dopant, and when the ohmic contact layer is positioned on the n-type semiconductor layer side, the ohmic contact layer is doped with the n-type dopant, and when the ohmic contact layer is positioned on the p-type semiconductor layer side, the ohmic contact layer is doped with the p-type dopant.

In this embodiment, the first transition layer 310 and the second transition layer 350 of the tunnel junction 300 are both an Al composition gradient layer and a doping concentration gradient layer, so that the crystal quality of the tunnel junction 300 and the LED structure on the tunnel junction 300 in the multi-junction infrared LED epitaxial structure is effectively improved, the series resistance is reduced, and the operating voltage is reduced; the first heavily doped layer 320 with high Al component of the tunnel junction 300 and the second heavily doped layer 340 with high band gap are used as tunnel junction materials, so that photons passing through the tunnel junction can directly pass through, the absorption of the tunnel junction 300 on the radiation light of the LED structure is effectively reduced, the brightness of the device structure is improved, and the series resistance of the tunnel junction 300 can be effectively reduced due to the high doping concentration of the first heavily doped layer 320 and the second heavily doped layer 340, so that the working voltage is further reduced; by further separating the first heavily doped layer 320 and the second heavily doped layer 340 with different doping types by the undoped layer 330 in the tunnel junction material layer, a built-in electric field can be formed, so that the impurity concentration distribution of the first heavily doped layer 320 and the second heavily doped layer 340 is steep, and the reduction of the doping concentration of the first heavily doped layer 320 and the second heavily doped layer 340 caused by impurity compensation due to the mutual diffusion of impurities in the first heavily doped layer 320 and the second heavily doped layer 340 is avoided; meanwhile, the material of the undoped layer 330 is selected (i.e., inGaAs material is selected), so that the undoped layer 330 has low resistivity and a lower bandgap, which can increase the peak current of the tunnel junction 300, and the undoped layer 330 has a thinner thickness, which has less radiation light absorption to the multi-junction red epitaxial LED structure.

It should be noted that, because the multi-junction infrared LED epitaxial structure includes N LED structures and N-1 tunneling junctions, the specific compositions of the semiconductor layers in each LED structure are the same or different, for example, al is the material of the N-type semiconductor layer in each LED structure _h Ga _1-h H in As, al As the material of the first space layer _i Ga _1-i I in As, material Al of the second space layer _j Ga _1-j J of As and In the material of the well layer _x Ga _1-x X in As and barrier layer material Al _y Ga _1-y As _z P _1-z Z in (b) and Al which is a material of the p-type semiconductor layer _k Ga _1-k K in As, al which is a material of the current spreading layer _g Ga _1-g The g in As may be the same or different, respectively.

Likewise, the material of the first transition layer 310 in each of the tunnel junctionsAl _d Ga _1-d D in As, al which is the material of the first heavily doped layer 320 _a Ga _1-a A in As, ga material of the second heavily doped layer 340 _b In _1-b B In P, in which is the material of the undoped layer 330 _c Ga _1-c C in As, al which is the material of the second transition layer 350 _e Ga _1-e E in As may be the same or different, respectively.

Referring to fig. 1, the multi-junction infrared LED epitaxial structure is exemplified as a double-junction infrared LED epitaxial structure.

The double-junction infrared LED epitaxial structure sequentially comprises a substrate 100, a buffer layer 110, an etching stop layer 120, a first LED structure 200, a tunneling junction 300 and a second LED structure 400 from bottom to top.

The first LED structure 200 sequentially includes, 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. Wherein the first ohmic contact layer 210 and the first current spreading layer 220 are both doped with n-type dopant, the thickness of the first current spreading layer 220 may be 3 μm to 10 μm, and preferably, the thickness of the first current spreading layer 220 is 8 μm. The material of the first ohmic contact layer 210 is GaAs. The barrier layer material of the MQW 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 And when the value of the preset period number P is 12, the radiation wavelength of the multi-quantum well layer is 850nm.

The second LED structure 400 sequentially includes, from bottom to top, 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. Wherein the second current spreading layer 440 and the second ohmic contact layer 450 are both doped with a p-type dopant, the thickness of the second current spreading layer 440 may be 0.2 μm to 4 μm, and preferably, the thickness of the second current spreading layer 440 is 2 μm. The material of the second ohmic contact layer 450 is GaP. Barrier layer material of the MQW layer of the second active regionIs Al _y Ga _1-y As _z P _1-z When y =0, the barrier layer material is GaAs _z P _1-z And when the preset period number P is 6, the radiation wavelength of the multi-quantum well layer is 850nm.

Fig. 4 is a schematic flow chart of a method for manufacturing a multi-junction infrared LED epitaxial structure according to this embodiment. As shown in fig. 4 and referring to fig. 1 and fig. 2, this embodiment further provides a method for manufacturing a multi-junction infrared LED epitaxial structure, where each step of the method may adopt any one of an MOCVD process, a molecular beam epitaxy process, an HVPE process, a plasma-assisted chemical vapor deposition (pecvd) process, and a sputtering process, and preferably, each step of the method adopts an MOCVD process. The preparation method comprises the following steps:

step S21, providing a substrate 100;

step S22, alternately forming LED structures and tunneling junctions 300 on the substrate 100 to obtain N LED structures and N-1 tunneling junctions 300, wherein each tunneling junction 300 is located between two adjacent LED structures, and the Nth LED structure is located on the N-1 th tunneling junction 300, so that a multi-junction infrared LED epitaxial structure is formed, wherein N is greater than or equal to 2 and is a positive integer.

The multi-junction infrared LED epitaxial structure is exemplified as a double-junction infrared LED epitaxial structure.

Fig. 5 is a schematic flow chart of a method for manufacturing a double-junction infrared LED epitaxial structure according to this embodiment. Referring to fig. 5 and fig. 1 and 2, the multi-junction infrared LED epitaxial structure is a double-junction infrared LED epitaxial structure. The preparation method comprises the following steps:

step S31, providing a substrate 100;

in step S32, a first LED structure 200, a tunneling junction 300, and a second LED structure 400 are sequentially formed on the substrate 100, so as to form a double-junction infrared LED epitaxial structure.

In this embodiment, the reverse polarity infrared LED process is used to prepare an infrared LED with an area of 350 μm × 350 μm, and compared with the conventional unijunction reverse polarity infrared LED, the brightness of the double-junction infrared LED of this embodiment is improved by 50% to 60%, and the operating voltage of the double-junction infrared LED is less than twice the operating voltage of the unijunction reverse polarity infrared LED.

In summary, the present invention provides a tunneling junction and a manufacturing method thereof, a multi-junction infrared LED epitaxial structure and a manufacturing method thereof, in which the tunneling junction sequentially includes, from bottom to top, a first transition layer, a tunneling junction material layer, and a second transition layer, the first transition layer and the second transition layer both include Al components, the first transition layer and the second transition layer are doped with dopants of different types, and the first transition layer and the second transition layer are both doped concentration gradient layers and are both Al component gradient layers. According to the invention, the first transition layer and the second transition layer of the tunneling junction are both the Al component gradient layer and the doping concentration gradient layer, so that the crystal quality of the tunneling junction and the LED structure positioned on the tunneling junction in the multi-junction infrared LED epitaxial structure is effectively improved, the series resistance is reduced, and the working voltage is reduced.

In addition, unless otherwise specified or indicated, the description of the terms "first" and "second" in the specification is only used for distinguishing various components, elements, steps and the like in the specification, and is not used for representing logical relationships or sequential relationships among the various components, elements, steps and the like.

It is to be understood that while the present invention has been described in conjunction with the preferred embodiments thereof, the foregoing description is not intended to limit the invention. It will be apparent to those skilled in the art that many changes and modifications can be made, or equivalents employed, to the presently disclosed embodiments without departing from the intended scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.

Claims

1. A tunneling junction is characterized by sequentially comprising a first transition layer, a tunneling junction material layer and a second transition layer from bottom to top, wherein the first transition layer and the second transition layer both comprise Al components, the first transition layer and the second transition layer are both doped with dopants of different types, and the first transition layer and the second transition layer are both doping concentration gradient layers and are both Al component gradient layers.

2. The tunnel junction according to claim 1 wherein 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 composition in the first transition layer gradually increases from bottom to top.

3. The tunneling junction of claim 2, wherein the material of the first transition layer is Al _d Ga _1-d As, wherein the value range of d is 0.3-0.4; the doping concentration range of the p-type dopant is 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 。

4. The tunneling junction according to claim 1, wherein the second transition layer is doped with an n-type dopant, the doping concentration of the n-type dopant gradually decreases from bottom to top, and the Al composition in the second transition layer gradually decreases from bottom to top.

5. The tunneling junction of claim 4, wherein the material of the second transition layer is Al _e Ga _1-e As, wherein the value range of e is 0.3-0.4; the doping concentration range of the n-type dopant is 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 。

6. The tunnel junction according to claim 1, wherein the tunnel junction material layer comprises a first heavily doped layer, an undoped layer and a second heavily doped layer in sequence from bottom to top, the first heavily doped layer and the second heavily doped layer are doped with different types of dopants, and the undoped layer is used for isolating the first heavily doped layer from the second heavily doped layer.

7. The tunneling junction of claim 6, wherein the undoped layer is In _c Ga _1-c As, wherein the value range of c is 0.01-0.2.

8. The tunneling junction according to claim 6, wherein the undoped layer has a thickness of 0.2nm to 10nm.

9. The tunnel junction of claim 6 wherein said first heavily doped layer is doped with a p-type dopant and said second heavily doped layer is doped with an n-type dopant, and wherein the doping concentration of said first heavily doped layer and the doping concentration of said second heavily doped layer are each greater than 2.0 x 10 ¹⁹ cm-3。

10. The tunneling junction of claim 6,

the material of the first heavily doped layer is Al _a Ga _1-a As, wherein a is in a range of 0.2 to 0.8;

11. A preparation method of a tunneling junction is characterized by comprising the following steps:

forming a tunneling junction material layer on the first transition layer; and

and forming a second transition layer on the tunneling junction material layer, wherein the second transition layer contains an Al component and is an Al component gradient layer, the first transition layer and the second transition layer are both doped with dopants of different types, and the first transition layer and the second transition layer are both doped with doping concentration gradient layers.

12. The method of claim 11, wherein 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 composition in the first transition layer gradually increases from bottom to top.

13. The method of claim 12, wherein the first transition layer is made of Al _d Ga _1-d As, wherein the value range of d is 0.3-0.4; the doping concentration range of the p-type dopant is 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 。

14. The method of claim 11, wherein the second transition layer is doped with an n-type dopant, the doping concentration of the n-type dopant gradually decreases from bottom to top, and the Al content in the second transition layer gradually decreases from bottom to top.

15. The method of claim 14, wherein the second transition layer is made of Al _e Ga _1-e As, wherein the value range of e is 0.3-0.4; the doping concentration range of the n-type dopant is 4.0 x 10 ¹⁸ cm ^-3 ～1.0×10 ¹⁹ cm ^-3 。

16. The method according to claim 11, wherein forming the tunnel junction material layer comprises sequentially forming a first heavily doped layer, a non-doped layer and a second heavily doped layer from bottom to top, wherein the first heavily doped layer and the second heavily doped layer are doped with different types of dopants, and the non-doped layer is used for isolating the first heavily doped layer from the second heavily doped layer.

17. The method of claim 16, wherein the undoped layer is formed of In _c Ga _1-c As, wherein, c is takenThe value range is 0.01 to 0.2.

18. The method of claim 16, wherein the undoped layer has a thickness of 0.2nm to 10nm.

19. The method of claim 16, wherein the first heavily doped layer is doped with a p-type dopant, the second heavily doped layer is doped with an n-type dopant, and the doping concentration of the first heavily doped layer and the doping concentration of the second heavily doped layer are both greater than 2.0 x 10 ¹⁹ cm ^-3 。

20. The method of fabricating a tunnel junction according to claim 16,

21. A multi-junction infrared LED epitaxial structure comprising the tunnel junction according to any one of claims 1 to 10, further comprising at least two LED structures stacked on a substrate, one tunnel junction being disposed between each adjacent two of the LED structures.

22. The multi-junction infrared LED epitaxial structure of claim 21, wherein the LED structure comprises, in order 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 of claim 21, further comprising a buffer layer and an etch stop layer between the substrate and the LED structure, the buffer layer and etch stop layer being disposed sequentially on the substrate.

24. The multi-junction infrared LED epitaxial structure of claim 22, wherein the multi-junction infrared LED epitaxial structure comprises, in order from bottom to top, a first LED structure to an nth LED structure, each of the first LED structure and the nth LED structure further comprising a current spreading layer and an ohmic contact layer,

in the first LED structure, the current spreading layer and the ohmic contact layer are both positioned on the side of the n-type semiconductor layer; in the Nth LED structure, the current expansion layer and the ohmic contact layer are both positioned on the side of the p-type semiconductor layer, wherein N is more than or equal to 2 and is a positive integer.

25. The multi-junction infrared LED epitaxial structure of claim 24,

in the first LED structure, the current spreading layer is positioned between the ohmic contact layer and the n-type semiconductor layer, and the current spreading layer is doped with n-type dopant; and

26. A preparation method of a multi-junction infrared LED epitaxial structure is characterized by comprising the following steps:

providing a substrate;

and alternately forming LED structures and tunneling junctions on the substrate to obtain N LED structures and N-1 tunneling junctions, wherein each tunneling junction is positioned between two adjacent LED structures, and the Nth LED structure is positioned on the N-1 th tunneling junction, so that a multi-junction infrared LED epitaxial structure is formed, wherein N is more than or equal to 2 and is a positive integer.

27. The method of claim 26, wherein forming the LED structure comprises sequentially forming an n-type semiconductor layer, an active layer, and a p-type semiconductor layer from bottom to top.

28. The method of claim 26, further comprising forming a buffer layer and an etch stop layer between the substrate and the LED structure, the buffer layer and the etch stop layer being disposed sequentially on the substrate.

29. The method of claim 27, wherein said multi-junction infrared LED epitaxial structure comprises, in order from bottom to top, a first LED structure to an Nth LED structure, each of said first LED structure and said Nth LED structure further comprising a current spreading layer and an ohmic contact layer,

in the first LED structure, the current spreading layer and the ohmic contact layer are positioned on the side of the n-type semiconductor layer; in the Nth LED structure, the current spreading layer and the ohmic contact layer are positioned on the side of the p-type semiconductor layer.

30. The method of claim 29, wherein the epitaxial structure of the multi-junction infrared LED is prepared by the steps of,

in a first one of the LED structures, 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