Epitaxial structure having low contact resistance and light-emitting apparatus

Abstract

An epitaxial structure having low contact resistance and a light-emitting apparatus. The epitaxial structure comprises a contact layer. The contact layer comprises: a first contact portion arranged on the surface of a P-type layer, the first contact portion at least comprising a plurality of first nanostructures extending in the direction facing away from the P-type layer, adjacent first nanostructures being arranged at intervals, and the first contact portion forming contact with the P-type layer; and a second contact portion at least partially arranged in gaps of the plurality of adjacent first nanostructures, at least part of the second contact portion forming contact with at least part of the first contact portion, the first contact portion and the second contact portion each comprising a nitride semiconductor, and the energy band gap of at least part of the first nanostructures being less than the energy band gap of at least part of the second contact portion. The present application effectively reduces the work function of the contact layer on the basis of the size effect, thus reducing the contact resistance and ensuring ohmic contact.

Description

Epitaxial structure and light-emitting device with low contact resistance Technical Field

[0001] The present application belongs to the technical field of semiconductor light-emitting devices, and specifically relates to an epitaxial structure and a light-emitting device with low contact resistance. Background Art

[0002] AlGaN material has a high work function and a large band gap, so P-type AlGaN easily forms a Schottky contact when in contact with metal. At the same time, Mg doping of P-type AlGaN with a high Al content is difficult, resulting in an excessively low carrier concentration. These factors lead to increased LED turn-on voltage and reduced electro-optical conversion efficiency. To address the above issues, common methods include:

[0003] 1. Since the work function of P-type AlGaN is proportional to the Al content, a P-type AlGaN contact layer with a low Al content is used to reduce the work function difference between the contact layer and the metal, thereby achieving ohmic contact.

[0004] 2. Use high work function metals, such as Au, Ni and Rh, to contact the P-type AlGaN contact layer to reduce the work function difference between the contact layer and the metal, thereby achieving ohmic contact.

[0005] Among them, the first method will lead to serious light absorption effect, especially for deep ultraviolet LEDs, where the light absorption effect is more serious; in the second method, the high work function metals are mostly precious metals, which are expensive and have poor contact with P-type AlGaN with a high Al content. Summary of the Invention

[0006] The purpose of the present application is to provide an epitaxial structure and a light-emitting device with low contact resistance, so as to solve the technical problems existing in the prior art, that is, P-type AlGaN easily forms a Schottky contact when in contact with metal, and that Mg doping of P-type AlGaN with a high Al content is difficult, resulting in an increase in the LED turn-on voltage and a decrease in the electro-optical conversion efficiency.

[0007] To achieve the above purpose, a technical solution adopted in this application is:

[0008] Provided is an epitaxial structure with low contact resistance, comprising a first conductive semiconductor layer, a quantum well active layer, and a second conductive semiconductor layer stacked in sequence, wherein the second conductive semiconductor layer comprises an electron blocking layer, a P-type layer, and a contact layer stacked in sequence in a direction away from the quantum well active layer, wherein a contact surface for connecting to a conductive electrode is formed on a side of the contact layer away from the P-type layer, and the first conductive semiconductor layer, the quantum well active layer, the electron blocking layer, and the P-type layer are all AlGaN-based semiconductor layers;

[0009] The contact layer comprises:

[0010] a first contact portion, arranged on a surface of the P-type layer, the first contact portion comprising at least a plurality of first nanostructures extending in a direction away from the P-type layer, with adjacent first nanostructures spaced apart, and the first contact portion forming contact with the P-type layer;

[0011] a second contact portion, at least partially arranged in gaps between a plurality of adjacent first nanostructures, wherein at least a portion of the second contact portion is in contact with at least a portion of the first contact portion;

[0012] The first contact portion and the second contact portion both comprise nitride semiconductors; and the energy band gap of at least a portion of the first nanostructure is smaller than the energy band gap of at least a portion of the second contact portion.

[0013] In one or more embodiments, at least a portion of the first nanostructure and at least a portion of the second contact portion include Al.

[0014] In one or more embodiments, at least part of the first nanostructure and at least part of the second contact portion both comprise AlGaN, wherein the first nanostructure is AlxGa1-xN, 0≦X≦0.4, and at least part of the second contact portion is AlyGa1-yN, 0.2 <y≦1。

[0015] In one or more embodiments, a difference between the Al mole fraction of the second contact portion and the Al mole fraction of the first nanostructure is greater than 0.5.

[0016] In one or more embodiments, at least a portion of the first nanostructure is GaN, and at least a portion of the second contact portion is AlN or AlGaN with an Al mole fraction greater than 0.5.

[0017] In one or more embodiments, the contact layer has a thickness of 1-20 nm.

[0018] In one or more embodiments, the first nanostructure has a cross-section that is circular, rectangular, square, trapezoidal, triangular, prismatic, or irregular.

[0019] In one or more embodiments, the maximum lateral outer dimension of the first nanostructure is 1-30 nm; the minimum distance between two adjacent first nanostructures is smaller than the maximum lateral outer dimension of the first nanostructure, and the minimum distance between two adjacent first nanostructures is 0.5-10 nm.

[0020] In one or more embodiments, the energy band gap of the second contact portion is greater than the energy band gap of the P-type layer.

[0021] In one or more embodiments, the contact surface is formed by the end of the first nanostructure facing away from the P-type layer and the end of the second contact portion facing away from the P-type layer, and the other end of the first nanostructure and the other end of the second contact portion are in contact with the P-type layer.

[0022] In one or more embodiments, the second contact portion fills a gap between adjacent first nanostructures and extends in a direction away from the P-type layer to form a connection layer covering ends of the first nanostructures, and the contact surface is formed by the connection layer.

[0023] In one or more embodiments, the thickness of the connecting layer is 0.1-3 nm.

[0024] In one or more embodiments, the connecting layer is AlN.

[0025] To achieve the above purpose, another technical solution adopted by this application is:

[0026] A light-emitting device is provided, comprising the epitaxial structure described in any one of the above embodiments.

[0027] Different from the prior art, the present invention has the following advantages:

[0028] The contact layer of the present application includes a first contact portion, which includes a plurality of first nanostructures, adjacent first nanostructures are spaced apart, and second contact portions are filled in the gaps between adjacent first nanostructures, thereby forming a contact layer with a nanolattice structure. Based on the size effect, the work function of the contact layer can be effectively reduced, thereby significantly reducing the work function difference between the contact layer and the conductive electrode, reducing the contact resistance, and ensuring ohmic contact;

[0029] The first nanostructure of the first contact portion of the contact layer of the present application and the second contact portion can be closely fitted, and a polarization induction effect exists on the ultra-thin contact surfaces of different components, thereby activating deep energy levels; the second contact portion has a higher band gap than the first nanostructure, thereby generating a large number of hole carriers and improving the contact performance of the contact layer;

[0030] The second contact portion of the present application with a higher energy band gap is filled into the spacing space of the nanostructure of the first contact portion. The lattice structure formed by the contact can increase the specific surface area of ​​the contact layer, increase the surface state in the P-AlGaN band gap, increase the polarization induction effect, facilitate hole injection, improve the contact effect, and reduce resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a schematic structural diagram of an embodiment of an epitaxial structure with low contact resistance according to the present invention;

[0032] FIG2 is a schematic structural diagram of another embodiment of the epitaxial structure with low contact resistance according to the present application.

[0033] Reference numerals: substrate 10; AlN substrate layer 20; AlGaN transition layer 30; N-type AlGaN layer 40; quantum well active layer 50; P-type AlGaN electron blocking layer 60; P-type AlGaN layer 70; contact layer 80; contact surface 801; first contact portion 802; first nanostructure 803; second contact portion 804; connection layer 805; DETAILED DESCRIPTION

[0034] The present application will be described in detail below with reference to the various embodiments shown in the accompanying drawings. However, these embodiments do not limit the present application, and any structural, methodological, or functional modifications made by a person skilled in the art based on these embodiments are included within the scope of protection of the present application.

[0035] Due to the high work function and large band gap of AlGaN material, the work function difference between AlGaN material and conductive electrode is large, the contact resistance is high, and the contact performance is affected; at the same time, it is difficult to dope Mg in P-type AlGaN with high work function, resulting in too low carrier concentration.

[0036] In the prior art, in order to solve the above problems, the work function of the contact layer is generally reduced by reducing the molar fraction of the Al component of the contact layer, or the work function of the conductive electrode is increased by using a metal with a high work function.

[0037] The low Al content P-type AlGaN contact layer used in the former will lead to severe light absorption effect, especially for deep ultraviolet LEDs, where the light absorption effect is even more serious; the latter uses high work function metals, mostly precious metals, which are expensive and have poor contact with high Al content P-type AlGaN.

[0038] To address the above issues, the applicant has developed a novel epitaxial structure that utilizes the material size effect to reduce the work function of the P-type AlGaN contact layer, thereby reducing the work function difference between the contact layer and the conductive electrode, improving contact, and reducing the difficulty of Mg doping.

[0039] Specifically, please refer to FIG1 , which is a schematic structural diagram of an embodiment of an epitaxial structure with low contact resistance according to the present application.

[0040] The epitaxial structure is arranged on a substrate 10 and includes a first conductive semiconductor layer, a quantum well active layer 50, and a second conductive semiconductor layer. The first conductive semiconductor layer includes an AlN base layer 20, an AlGaN transition layer 30, and an N-type AlGaN layer 40 stacked in a direction away from the substrate 10. The second conductive semiconductor layer includes a P-type AlGaN electron blocking layer 60, a P-type AlGaN layer 70, and a contact layer 80 stacked in a direction away from the substrate 10.

[0041] In one embodiment, the epitaxial structure can be applied to a deep ultraviolet light-emitting chip, wherein the substrate 10 can be a sapphire substrate 10, Si-based or SiC, etc., or other substrate 10 materials that can be applied to deep ultraviolet light-emitting chips can be used.

[0042] The AlN substrate layer 20 is used to grow an epitaxial layer and has a sufficiently high Al component to ensure UV light transmission. The thickness of the AlN substrate layer 20 can be set based on actual needs and is not limited here.

[0043] The AlGaN transition layer 30 is used to balance the lattice difference between the AlN substrate layer 20 and the N-type AlGaN layer 40 , thereby achieving better matching.

[0044] The N-type AlGaN layer 40 is used for electron injection, and the molar fraction of the Al component thereof may be 0.4-0.6.

[0045] The quantum well active layer 50 is made of multiple alternating stacks of thicker quantum barrier layers and thinner quantum well layers. Preferably, the number of loops in the quantum well active layer 50 is 5 to ensure the quantum confinement effect.

[0046] The P-type AlGaN electron blocking layer 60 is used to limit electron transmission, and the molar fraction of the Al component thereof may be 0.6-1.

[0047] The P-type AlGaN layer 70 is used to transport holes, and the molar fraction of the Al component thereof may be 0.4-0.7.

[0048] The contact layer 80 is used to form an ohmic contact with a conductive electrode, and a contact surface 801 for connecting with the conductive electrode is formed on a side facing away from the P-type AlGaN layer 70 .

[0049] The contact layer 80 includes a first contact portion 802 including a plurality of first nanostructures 803 . The first nanostructures 803 of the first contact portion 802 extend from the surface of the P-type AlGaN layer 70 to the contact surface 801 , and adjacent first nanostructures 803 are spaced apart.

[0050] The contact layer 80 also includes a second contact portion 804, which is arranged between adjacent first nanostructures 803 and extends from the contact surface 801 to the surface of the p-type AlGaN layer 70. The first nanostructures 803 and the second contact portion 804 extend to the same length; the bottoms of the first nanostructures 803 and the second contact portion 804 contact the p-type layer; and the ends of the first nanostructures 803 and the second contact portion 804 together form the contact surface 801.

[0051] The energy band gaps of the first nanostructure 803 and the second contact portion 804 may be different. In one embodiment, the first nanostructure 803 and the second contact portion 804 may both include Al, for example, both may be made of AlGaN material; or, in another embodiment, the first nanostructure 803 and the second contact portion 804 may not both include Al, for example, the first nanostructure 803 may be made of GaN material, and the second contact portion 804 may be made of AlN or AlGaN material, which can also achieve the effect of this embodiment.

[0052] Specifically, in one embodiment, the first nanostructure 803 and the second contact portion 804 can both be made of AlGaN material. The first nanostructure 803 can be made of AlXGa1-XN material, where x can be 0-0.4, and the second contact portion 804 can both be made of AlYGa1-YN material, where y can be 0.2-1, preferably 0.6-1. In some embodiments, the materials of the first nanostructure 803 and the second contact portion 804 can also be doped with a small amount of indium to achieve the effects of this embodiment.

[0053] In one embodiment, the extension length of the first nanostructure 803 and the second contact portion 804 in the epitaxial stacking growth direction may be 1 to 20 nm.

[0054] It can be understood that since the contact layer 80 is composed of multiple first nanostructures 803 and second contact parts 804, the original bulk material is reduced to a nano-lattice structure. Based on the size effect, the work function of the contact layer 80 can be effectively reduced, thereby significantly reducing the work function difference between the contact layer 80 and the conductive electrode, reducing the contact resistance, and ensuring ohmic contact.

[0055] To ensure the work function reduction effect of the contact layer 80 , in one embodiment, the maximum lateral peripheral dimension of the first nanostructure 803 may be 1 to 30 nm, and the minimum distance D between adjacent first nanostructures 803 may be 0.5 to 10 nm.

[0056] In this embodiment, the first nanostructure 803 is a cylindrical structure. In other embodiments, the cross-section of the first nanostructure 803 may also be other shapes, such as circular, rectangular, square, trapezoidal, triangular, prism-shaped, etc., or may be an irregular shape, to ensure that multiple first nanostructures 803 are arranged at nanometer-sized intervals, and the second contact portion 804 is arranged between adjacent first nanostructures 803, so as to achieve the effect of this embodiment.

[0057] Furthermore, in this embodiment, the molar fraction of the Al component of the second contact portion 804 can be greater than the molar fraction of the Al component of the first nanostructure 803, so that there is a polarization induction effect at the ultra-thin contact surface of the P-AlGaN with different Al components in the contact layer 80 formed by the first nanostructure 803 and the second contact portion 804, thereby activating the deep energy level acceptor state, generating a large number of hole carriers, and improving the contact performance of the contact layer 80.

[0058] Specifically, in one embodiment, the first nanostructure 803 can be made of AlxGa1-xN material, where x is 0-0.4; the second contact portion 804 is made of AlyGa1-yN material, where y is 0.4-1; the Al content of the second contact portion is higher than that of the first contact portion to ensure the polarization induction effect.

[0059] To further enhance the polarization induction effect, in one embodiment, the difference between y and x may be greater than 0.5.

[0060] In another embodiment, referring to FIG. 2 , FIG. 2 is a schematic structural diagram of another embodiment of the epitaxial structure with low contact resistance of the present application. In order to further enhance the polarization induction effect generated at the contact area and facilitate the growth of the second contact portion 804 on the first nanostructure 803 of the first contact portion 802, the second contact portion 804 can fill the gap between the first nanostructure 803 and grow in a direction away from one side of the P-type AlGaN layer 70 to form a connecting layer 805, so that the second contact portion 804 alone forms the entire contact surface 801.

[0061] The thickness of the connecting layer 805 may be 0.1-3 nm, preferably 0.1-2 nm.

[0062] In this embodiment, the energy band gap of the second contact portion 804 is larger than that of the first nanostructure 803, and the first nanostructure 803 and the second contact portion 804 are tightly fitted, and multiple polarization contact surfaces are formed between the bottom of the connecting layer 805 and the top surface of the first nanostructure 803, and between the side surfaces of multiple first nanostructures 803 and the side surfaces of the second contact portion 804, thereby further increasing the contact area and increasing the polarization induction effect, so that a polarization induction effect exists on the P-AlGaN ultra-thin contact surface between the second contact portion 804 and the first nanostructure 803, so that the deep energy level acceptor state is activated, a large number of hole carriers are generated, and the contact performance of the contact layer 80 is improved.

[0063] In each of the above-described embodiments, the plurality of first nanostructures 803 are formed into nanometer-sized structures and cooperate with the second contact portion 804 of a higher energy band to form a contact surface. This utilizes the nanoscale effect to reduce the work function of the contact layer 80, and, combined with the polarization-induced effect, improves the hole injection efficiency, thereby reducing resistance and voltage. The epitaxial contact layer 80 prepared in this embodiment has a low work function and can form an ohmic contact with a low-work-function metal, thereby improving contact.

[0064] The present application also provides a light-emitting device, which may include an epitaxial structure of any of the above-mentioned embodiments. The light-emitting device can deposit a conductive electrode with a low work function on the contact surface 801 of the above-mentioned epitaxial structure and ensure ohmic contact, thereby effectively solving the problem of poor contact performance between the ohmic contact layer and the P-type electrode in the traditional epitaxial structure.

[0065] The foregoing description of the present disclosure is provided to enable any person skilled in the art to implement or use the present disclosure. Various modifications to the present disclosure will be readily apparent to those skilled in the art, and the general principles herein may be applied to other variations without departing from the scope of the present disclosure. Therefore, the present disclosure is not limited to the examples and designs described herein, but is intended to be consistent with the widest range of principles and novel features disclosed herein.

Claims

1. An epitaxial structure with low contact resistance, characterized in that: It includes a first conductive semiconductor layer, a quantum well active layer, and a second conductive semiconductor layer that are stacked in sequence. The second conductive semiconductor layer includes an electron blocking layer, a P-type layer, and a contact layer that are stacked in sequence in a direction away from the quantum well active layer. A contact surface for connecting to a conductive electrode is formed on a side of the contact layer facing away from the P-type layer. The first conductive semiconductor layer, the quantum well active layer, the electron blocking layer, and the P-type layer are all AlGaN-based semiconductor layers; The contact layer includes: A first contact portion disposed on the surface of the P-type layer. The first contact portion at least includes a plurality of first nanostructures extending in a direction away from the P-type layer. Adjacent first nanostructures are spaced apart, and the first contact portion makes contact with the P-type layer; A second contact portion at least partially disposed in the gaps between a plurality of adjacent first nanostructures, and at least part of the second contact portion makes contact with at least part of the first contact portion; Wherein, both the first contact portion and the second contact portion include nitride semiconductors; the energy band gap of at least part of the first nanostructures is less than the energy band gap of at least part of the second contact portion.

2. The epitaxial structure according to claim 1, characterized in that: At least part of the first nanostructures and at least part of the second contact portion both include Al.

3. The epitaxial structure according to claim 2, characterized in that: At least part of the first nanostructures and at least part of the second contact portion both include AlGaN. Among them, the first nanostructures are AlxGa1-XN, where 0 < X ≦ 0.4, and at least part of the second contact portion is AlyGa1-yN, where 0.2 < y ≦ 1.

4. The epitaxial structure according to claim 2, characterized in that: The difference in the Al mole fraction between the second contact portion and the first nanostructures is greater than 0.

5.

5. The epitaxial structure according to claim 1, characterized in that: At least part of the first nanostructures are GaN, and at least part of the second contact portion is AlN or AlGaN with an Al mole fraction greater than 0.

5.

6. The epitaxial structure according to any one of claims 1 to 5, characterized in that: The thickness of the contact layer is 1 - 20 nm.

7. The epitaxial structure according to any one of claims 1 to 5, characterized in that: The first nanostructures are circular, rectangular, square, trapezoidal, triangular, rhombic, or irregular in cross-section.

8. The epitaxial structure according to any one of claims 1 to 5, characterized in that: The maximum lateral peripheral dimension of the first nanostructures is 1 - 30 nm; the minimum distance between two adjacent first nanostructures is less than the maximum lateral peripheral dimension of the first nanostructures, and the minimum distance between two adjacent first nanostructures is 0.5 - 10 nm.

9. The epitaxial structure according to any one of claims 1 to 5, characterized in that: The energy band gap of the second contact portion is greater than the energy band gap of the P-type layer.

10. The epitaxial structure according to claim 1, characterized in that: The contact surface is formed by the ends of the first nanostructures facing away from the P-type layer and the ends of the second contact portion facing away from the P-type layer. The other ends of the first nanostructures and the other ends of the second contact portion are in contact with the P-type layer.

11. The epitaxial structure according to claim 1, characterized in that: The second contact portion fills the gaps between adjacent first nanostructures and extends in a direction away from the P-type layer to form a connection layer covering the ends of the first nanostructures, and the contact surface is formed by the connection layer.

12. The epitaxial structure according to claim 11, characterized in that: The thickness of the connection layer is 0.1 - 3 nm, and / or the connection layer is AlN.

13. A light emitting device, characterized in that: An epitaxial structure according to any one of claims 1 to 12.

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