WO2019062036A1

WO2019062036A1 - Led epitaxial structure, and manufacturing method thereof

Info

Publication number: WO2019062036A1
Application number: PCT/CN2018/078656
Authority: WO
Inventors: 程志青; 宋长伟; 徐志波; 林兓兓; 蔡吉明
Original assignee: 厦门三安光电有限公司
Priority date: 2017-09-27
Filing date: 2018-03-12
Publication date: 2019-04-04
Also published as: CN107768494A; CN107768494B

Abstract

An LED epitaxial structure, and manufacturing method thereof. A plurality of magnesium nitride compound-based nucleation structures (8) are inserted between an electron blocking layer (6) and an ultimate barrier layer (5), and the nucleation structures (8) are used as cores to grow a plurality of island structures (9). In this way, total internal reflection at an interface of the electron blocking layer (6) and the ultimate barrier layer (5) is reduced, such that a large portion of light emitted by a multi-quantum well light-emitting layer (4) can enter the electron blocking layer (6), thus improving light-emitting efficiency of the LED epitaxial structure. In addition, the electron blocking layer (6) is used to fill gaps between the island structures (9), thus creating a level surface of the LED epitaxial structure.

Description

Technical field

[0001] The present invention belongs to the field of semiconductor technologies, and in particular, to an LED epitaxial structure and a method for fabricating the same.

Background technique

[0002] An LED is a semiconductor solid-state light-emitting device that utilizes a semiconductor PN junction as a light-emitting structure. Currently, gallium nitride is regarded as a third-generation semiconductor material, and a gallium nitride-based light-emitting diode having an InGaN/GaN active region is regarded as It is the most promising source of light today.

Referring to FIG. 1, a GaN-based blue LED epitaxial structure generally includes a substrate, a buffer layer, a first semiconductor layer, a multiple quantum well light-emitting layer, a final barrier layer, an electron blocking layer, and a second semiconductor layer, and multiple quantum The well light-emitting layer is generally an InGaN/GaN superlattice structure, and the electron blocking layer is a P-type AlGaN structure. However, since the refractive index of the A1 GaN material is lower than that of GaN and InGaN, the light emitted from the multi-quantum well light-emitting layer is likely to be at the final potential. Total reflection occurs at the interface between the barrier layer and the electron blocking layer, resulting in poor light extraction efficiency.

[0004] In the prior art, in order to improve the light extraction efficiency, a P-type layer surface roughening technique is also used. Although this technology can improve the light extraction efficiency to some extent, the interface between the final barrier layer and the electron blocking layer cannot be improved. The resulting light extraction efficiency is lost, and the surface roughening technique is prone to coarsening unevenness, and the color difference between the P electrode and the N electrode of the LED is poor, which makes the automatic wire bonding machine difficult to identify.

[0005] Another common technique for improving the light extraction efficiency is to use a patterned substrate. Although this technology improves the light extraction efficiency to a certain extent without affecting the wire bonding, it cannot completely improve the final barrier layer and the electron blocking. Loss of light extraction efficiency caused by total reflection at the interface of the layer.

[0006] Therefore, at present, there is an urgent need to propose an LED epitaxial structure capable of further improving the light-emitting efficiency of an LED without affecting its wire bonding and a preparation method thereof.

technical problem

Problem solution

Technical solution

In view of the above problems, the present invention first proposes an LED epitaxial structure including a substrate and sequential bits. a first semiconductor layer, a multiple quantum well light emitting layer, a final barrier layer, an electron blocking layer and a second semiconductor layer on the substrate, wherein: a plurality of pixels are interposed between the last barrier layer and the electron blocking layer An island structure that is not continuously arranged.

[0008] Preferably, the refractive index of the island structure is greater than the refractive index of the electron blocking layer is less than or equal to the refractive index of the last barrier layer.

[0009] Preferably, the discontinuously arranged island-like structures are 3D island-like structures, and the shape is a cone or a truncated cone shape or a yurt shape or a polygonal prism shape or a combination of any two or three or four shapes.

[0010] Preferably, the epitaxial structure further includes a plurality of nucleation structures as an island structure forming core between the last barrier layer and the island structure.

[0011] Preferably, the island-shaped structure has the same refractive index as the last barrier layer.

[0012] Preferably, the island structure is Al _x G _ai — _X N, and the electron blocking layer is Al _y G _ai — _y N, where 0≤x

< 1, x < y < l.

[0013] Preferably, the surface of the electron blocking layer is a flat surface.

[0014] Preferably, the material of the nucleation structure is a magnesium nitride compound.

[0015] Preferably, a buffer layer is further disposed between the substrate and the first semiconductor layer.

[0016] The present invention also provides a method for preparing an LED epitaxial structure, comprising the following steps:

[0017] Step 1, first providing a substrate;

[0018] Step 2, sequentially depositing a buffer layer and a first semiconductor layer on the substrate;

[0019] Step 3, depositing a multi-quantum well light-emitting layer and a final barrier layer on the first semiconductor layer;

[0020] Step 4, depositing an electron blocking layer on the last barrier layer;

[0021] Step 5, continuing to deposit a second semiconductor layer on the surface of the electron blocking layer;

And [0022] characterized in that: the step 3a of depositing a plurality of discontinuous island structures between the last barrier layer and the electron blocking layer deposition step.

[0023] Preferably, the method for preparing the epitaxial structure further comprises a step 3b of depositing a nucleation structure between the last barrier layer and the island structure, wherein the nucleation structure is a nucleation center of the island structure.

[0024] Preferably, the nucleation structure has a growth temperature of less than 900 ° C and a reaction pressure of 100 to 500 torr.

[0025] Preferably, NH ₃ and CP ₂ Mg are introduced to form a nucleation structure of the magnesium nitride compound.

[0026] Preferably, the island structure has a growth temperature of 700 ° C to 950 ° C. [0027] Preferably, the island structure has a growth temperature of 800 ° C to 900 ° C to facilitate formation of a discontinuous island structure on the nucleation structure of the magnesium nitride compound.

Advantageous effects of the invention

Beneficial effect

[0028] The present invention inserts a plurality of nucleation structures of magnesium nitride compounds between the electron blocking layer and the final barrier layer, and uses the nucleation structure as a core to grow a plurality of island structures to reduce light in the electron blocking layer. The phenomenon of total reflection at the interface with the last barrier layer causes the light emitted from the multi-quantum well light-emitting layer to enter the electron blocking layer more, thereby improving the light-emitting efficiency of the LED epitaxial structure, and filling the island-like structure through the electron blocking layer. A planar epitaxial LED epitaxial structure is then obtained.

Brief description of the drawing

DRAWINGS

The drawings are intended to provide a further understanding of the invention, and are intended to be a part of the description of the invention. In addition, the drawing figures are a summary of the description and are not drawn to scale.

1 is a schematic diagram of an epitaxial structure of an LED in the prior art.

2 is a schematic diagram of an epitaxial structure of an LED according to Embodiment 1 of the present invention.

3 is a flow chart of a method for preparing an epitaxial structure of an LED according to Embodiment 2 of the present invention.

4 is a schematic diagram of an epitaxial structure of an LED according to Embodiment 3 of the present invention.

5 is a flow chart of a method for preparing an epitaxial structure of an LED according to Embodiment 4 of the present invention.

[0035] The figure indicates: 1 : substrate; 2: buffer layer; 3: first semiconductor layer; 4: multiple quantum well light-emitting layer; 5: final barrier layer; 6: electron blocking layer; 8: nucleation structure; 9: island structure.

Embodiments of the invention

The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

Embodiment 1 [0038] The present invention provides an LED epitaxial structure. Referring to FIG. 2, the epitaxial structure includes a substrate 1 and a buffer layer 2, a first semiconductor layer ₃ , and a multiple quantum well light-emitting layer sequentially disposed on the substrate 1. 4. A final barrier layer 5, a plurality of discontinuously arranged island structures 9, an electron blocking layer 6, and a second semiconductor layer 7.

The discontinuously arranged island-like structures 9 are 3D island-like structures 9, which are in the shape of a cone or a truncated cone or a yurt or a polygonal prism or a combination of any two or three or four of the foregoing. In the present embodiment, as shown in FIG. 2, the shape of the island-like structure 9 is a combination of a polygonal prism and a polygonal pyramid, and the bottom pitch of the adjacent island-like structures 9 is larger than the top spacing so as to enter the island-like structure 9. Light energy is emitted from different angles.

[0040] The refractive index of the island structure 9 is greater than the refractive index of the electron blocking layer 6 is less than or equal to the refractive index of the last barrier layer 5, wherein the material of the island structure 9 is Al _x G _ai — _X N, the electron blocking layer 6 The material is Al _y G _ai — _y N, where 0≤χ< 1, x< y < l , preferably, X ranges from 0 to 0.1, and y ranges from: x<y<0.3; optional island The refractive index of the structure 9 is the same as the refractive index of the last barrier layer 5. Therefore, in the present embodiment, the material of the island structure 9 and the material of the last barrier layer 5 are both GaN, which are emitted from the quantum well light-emitting layer 4. The light portion passes through the last barrier layer 5 directly into the island-like structure 9 without changing the propagation path of the light, and then enters the electron blocking layer 6 after being scattered by the island-like structure 9.

[0041] In this embodiment, the electron blocking layer 6 completely covers the island structure 9 and obtains a surface having a relatively flat surface; the substrate 1 is preferably a patterned substrate 1 to increase the scattering effect of the bottom of the epitaxial structure on light, further Improve light extraction efficiency. The first semiconductor layer 3 is electrically opposite to the second conductor layer. Preferably, the first semiconductor layer 3 is an N-type layer, and the second semiconductor layer 7 is a P-type layer, and is located at the first semiconductor layer 3 and the second semiconductor layer 7. The multi-quantum well light-emitting layer 4 is a superlattice structure in which GaN quantum barrier layers and InGaN quantum well layers are alternately stacked; the buffer layer 2 may be GaN, AlN or AlGaN.

[0042] The present invention reduces total light reflection at the interface of the last barrier layer 5 and the electron blocking layer 6 by inserting a plurality of discontinuously arranged island structures 9 between the last barrier layer 5 and the electron blocking layer 6. The probability that the light scatters through the interface between the island structure 9 and the electron blocking layer 6 changes the incident angle of the light entering the electron blocking layer 6, thereby improving the external quantum well efficiency of the LED epitaxial structure. Moreover, the electron blocking layer 6 is used for filling the island structure 9, so that the surface of the prepared epitaxial structure layer is relatively flat, which facilitates automatic wire bonding of the electrodes and improves the reliability of the device.

Embodiment 2

[0044] Embodiments of the present invention provide a method for fabricating an LED epitaxial structure, which is suitable for use in the fabrication example 1. LED epitaxial structure, referring to Figure 3, the preparation method comprises:

[0045] Step 1, first providing a substrate 1, the substrate 1 is a patterned substrate 1, specifically a sapphire patterned substrate 1;

[0046] Step 2, depositing a buffer layer 2, a first semiconductor layer 3 on the substrate 1 in sequence;

The buffer layer 2 is a GaN buffer layer 2 or an A1N buffer layer 2 or an AlGaN buffer layer 2, and the first semiconductor layer 3 is an N-type layer, and is mainly used for supplying electrons.

[0048] Step 3, depositing a multi-quantum well light-emitting layer 4 and a final barrier layer 5 on the first semiconductor layer 3;

[0049] The multiple quantum well light-emitting layer 4 is a superlattice structure in which a GaN quantum barrier layer and an InGaN quantum well layer are alternately stacked, and the number of periods is 2 to 50; the growth conditions and materials of the last barrier layer 5 and the GaN quantum barrier layer are formed. All the same.

[0050] Step 3a, depositing a plurality of discontinuously arranged island-like structures 9 on the last barrier layer 5, the refractive index of the island-like structures 9 being greater than the refractive index of the electron blocking layer 6 being less than or equal to the refractive index of the last barrier layer 5. rate.

[0051] The growth temperature of the island structure 9 is between 700 ° C and 950 ° C, preferably, the growth temperature is 800 ° C to 900 °

°C, to form a discontinuous island structure 9 .

[0052] Step 4, depositing an electron blocking layer 6;

[0053] Specifically, the material of the electron blocking layer 6 is Al _y G _ai — _y N , and the material of the island structure 9 is Al _x Ga ^ _X N, where 0≤χ < 1, x < y < l , preferably The range of X is 0 to 0.1, and the range of y is: x < y < 0.3. The electron blocking layer 6 completely covers the island structure 9 and is formed into a surface flat structure.

[0054] Step 5, depositing a second semiconductor layer 7 on the surface of the electron blocking layer 6, the second semiconductor layer 7 is a P-type layer, including a high-temperature P-type GaN layer and a P-type structural layer.

[0055] wherein, the first semiconductor layer 3, the multiple quantum well light-emitting layer 4, the last barrier layer 5, the island-like structure 9, the electron blocking layer 6, and the second semiconductor layer 7 are all prepared by MOCVD, and the epitaxial structure is in the forming process. Among them, TMG a or TEGa is used as a gallium source, NH _{3 is} used as a nitrogen source, N ^/H _{2 is} used as a carrier gas, CP ₂ Mg is used as a P-type impurity, and SiH _{4 is} used as an N-type impurity.

[0056] The present invention reduces total light reflection at the interface of the last barrier layer 5 and the electron blocking layer 6 by depositing a plurality of discontinuously arranged island structures 9 between the last barrier layer 5 and the electron blocking layer 6. The probability that the light scatters through the interface between the island structure 9 and the electron blocking layer 6 changes the incident angle of the light entering the electron blocking layer 6, thereby improving the external quantum well efficiency of the LED epitaxial structure.

Embodiment 3 [0058] Referring to FIG. 4, an LED epitaxial structure provided by this embodiment is different from the LED epitaxial structure provided by the embodiment in that: the last barrier layer 5 and the island-like structure 9 further include an island structure 9 formed. The core has a plurality of nucleation structures 8, and the nucleation structure 8 serves as a nucleation center of the island-like structure 9, and its size is smaller than the size of the island-like structure 9.

[0059] Specifically, the LED epitaxial structure provided in this embodiment includes: a substrate 1, a buffer layer 2 on the substrate 1, a first semiconductor layer ₃ , a multiple quantum well light-emitting layer 4, and a final barrier layer 5, The nucleation structure 8, the island structure 9, the electron blocking layer 6, and the second semiconductor layer 7.

[0060] wherein, the material of the nucleation structure 8 is a magnesium nitride compound, the refractive index of the island structure 9 is greater than the refractive index of the electron blocking layer 6 is smaller than the refractive index of the last barrier layer 5, and the material of the island structure 9 is Al. _x G _ai — _X N, the electron blocking layer 6 is Al _y G _ai — _y N, where 0≤χ < 1, x < y < l , preferably, x ranges from 0 to 0.1, and the range of y is: x <y<0.3, the electron blocking layer 6 completely covers the island-like structure 9 and is formed to have a surface flat structure, and the magnesium nitride compound is a Mg ₃ N ₂ structure or a MgN structure.

[0061] In the embodiment of the present invention, a plurality of magnesium nitride compound nucleation structures 8 are inserted between the electron blocking layer 6 and the last barrier layer 5, and the nucleation structure 8 is used as a core to grow a plurality of discontinuous islands. The structure 9 reduces the total reflection phenomenon of light at the interface between the electron blocking layer 6 and the final barrier layer 5, so that the light emitted from the multiple quantum well light-emitting layer 4 enters the electron blocking layer 6 more, thereby improving the epitaxial structure of the LED. The light-emitting efficiency is filled and the island-like structure 9 is filled by the electron blocking layer 6, and then a surface-flat LED epitaxial structure is obtained.

Example 4

The embodiment of the present invention improves a method for preparing an epitaxial structure of an LED, and is suitable for fabricating the epitaxial structure of the LED provided in Embodiment 3. Referring to FIG. 5, the preparation method includes:

[0064] Step 1, first providing a substrate 1, the substrate 1 is a shaped substrate 1, specifically a sapphire patterned substrate 1 [0065] Step 2, sequentially depositing a buffer layer 2 on the substrate 1 , the first semiconductor layer 3;

[0066] The buffer layer 2 is a GaN buffer layer 2 or an A1N buffer layer 2 or an AlGaN buffer layer 2, and the first semiconductor layer 3 is an N-type layer mainly used for supplying electrons.

[0067] Step 3, depositing a multi-quantum well light-emitting layer 4 and a final barrier layer 5 on the first semiconductor layer 3;

[0068] The multi-quantum well light-emitting layer 4 is a superlattice structure in which a GaN quantum barrier layer and an InGaN quantum well layer are alternately stacked, and the number of periods is 2 to 50; the growth conditions and materials of the last barrier layer 5 and the GaN quantum barrier layer are formed. All the same.

[0069] Step 3b, depositing a plurality of nucleation structures 8 on the last barrier layer 5, the nucleation layer material being magnesium nitride Things.

[0070] Step 3a, with the nucleation structure 8 as a core, depositing a plurality of discontinuously arranged island-like structures 9, the refractive index of the island-like structures 9 being greater than the refractive index of the electron blocking layer 6 being smaller than that of the last barrier layer 5. Refractive index.

[0071] The growth temperature of the island structure 9 is between 700 ° C and 950 ° C, preferably, the growth temperature is 800 ° C to 900 ° C, in order to benefit from the nucleation structure 8 of the magnesium nitride compound. A discontinuous island-like structure 9 is formed, and the magnesium nitride compound is a Mg ₃ N ₂ structure or a MgN structure.

[0072] Step 4, depositing an electron blocking layer 6;

[0073] Specifically, the material of the electron blocking layer 6 is Al _y G _ai — _y N, and the material of the island structure 9 is Al _x Ga _X N, where 0≤χ< 1, x< y < l , preferably, The range of x is 0 to 0.1, and the range of y is: x < y < 0.3, and the electron blocking layer 6 completely covers the island-like structure 9 and is formed to have a surface flat structure.

[0074] Step 5, further depositing a second semiconductor layer 7 on the surface of the electron blocking layer 6, the second semiconductor layer 7 is

The P-type layer includes a high-temperature P-type GaN layer and a P-type structural layer.

[0075] The present invention reduces total light reflection at the interface of the last barrier layer 5 and the electron blocking layer 6 by depositing a plurality of discontinuously arranged island-like structures 9 between the last barrier layer 5 and the electron blocking layer 6. The probability that the light scatters through the interface between the island structure 9 and the electron blocking layer 6 changes the incident angle of the light entering the electron blocking layer 6, thereby improving the external quantum well efficiency of the LED epitaxial structure.

It is to be understood that the above-described embodiments are a preferred embodiment of the present invention, and the scope of the present invention is not limited to the embodiment, and any modifications made in accordance with the present invention are within the scope of the present invention.

Claims

Claim

[Claim 1] An LED epitaxial structure comprising a substrate and a first semiconductor layer, a multiple quantum well light-emitting layer, a final barrier layer, an electron blocking layer, and a second semiconductor layer sequentially disposed on the substrate, characterized in that The method comprises: inserting a plurality of discontinuous island structures between the last barrier layer and the electron blocking layer.

[Claim 2] An LED epitaxial structure according to claim 1, wherein: the island structure has a refractive index greater than a refractive index of the electron blocking layer and less than or equal to a refractive index of the last barrier layer

[Claim 3] The LED epitaxial structure according to claim 1, wherein: the discontinuously arranged island-like structure is a 3D island-like structure having a shape of a cone or a truncated cone or a yurt or more Prismatic or any combination of the two or three or four of the foregoing.

[Claim 4] The LED epitaxial structure according to claim 1, wherein: the epitaxial structure further comprises an island structure forming core between the last barrier layer and the island structure Multiple nucleation structures.

[Claim 5] An LED epitaxial structure according to claim 2, wherein: the island-like structure has the same refractive index as the last barrier layer.

[Claim 6] The LED epitaxial structure according to claim 1, wherein: the island-shaped structural material is Al _x Ga ! _X N N, and the electron blocking layer material is Al _y Ga ^ _y N Where 0≤x< 1

, x< y < l.

[Claim 7] An LED epitaxial structure according to claim 1, wherein: the surface of the electron blocking layer is a flat surface.

[Claim 8] An LED epitaxial structure according to claim 4, wherein: the material of the nucleation structure is a magnesium nitride compound.

[Claim 9] A method for preparing an LED epitaxial structure, comprising the following steps:

Step 1. providing a substrate;

Step 2, sequentially depositing a buffer layer and a first semiconductor layer on the substrate;

Step 3, depositing a multi-quantum well light-emitting layer and a final barrier layer on the first semiconductor layer; Step 4, depositing an electron blocking layer on the last barrier layer; Step 5, further depositing a second semiconductor layer on the surface of the electron blocking layer; wherein: the step of depositing a plurality of discontinuous island structures between the final barrier layer and the electron blocking layer deposition step 3a.

[Claim 10] The method for fabricating an LED epitaxial structure according to claim 9, wherein: the method for preparing the epitaxial structure further comprises depositing a nucleation structure between the last barrier layer and the island structure. Step 3b, the nucleation structure is a nucleation center of the island structure.

[Claim 11] A method for fabricating an LED epitaxial structure according to claim 10, wherein: the nucleation structure has a growth temperature of less than 900 ° C and a reaction pressure of 100 to 500 torr.

[Claim 12] A method for fabricating an LED epitaxial structure according to claim 10, wherein:

₂ Mg, forming a nucleation structure of the magnesium nitride compound.

[Claim 13] The method for fabricating an LED epitaxial structure according to claim 9, wherein the island structure has a growth temperature of 700 ° C to 950 ° C.