LED epitaxial structure and preparation method thereof
Technical Field
The invention belongs to the technical field of semiconductors, and particularly relates to an LED epitaxial structure and a preparation method thereof.
Background
An LED is a semiconductor solid-state light emitting device, which uses a semiconductor P-N junction as a light emitting structure, gallium nitride is currently considered as a third generation semiconductor material, and a gallium nitride-based light emitting diode having an InGaN/GaN active region is currently considered as the most potential light emitting source.
Referring to fig. 1, a current 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 last barrier layer, an electron blocking layer and a second semiconductor layer, where the multiple quantum well light emitting layer is generally an InGaN/GaN superlattice structure, and the electron blocking layer is a P-type AlGaN structure, but since the refractive index of AlGaN material is lower than that of GaN and InGaN, light emitted from the multiple quantum well light emitting layer is easily totally reflected at an interface between the last barrier layer and the electron blocking layer, resulting in poor light extraction efficiency.
In the prior art, in order to improve the light extraction efficiency, a P-type layer surface roughening technology is also adopted, although the technology can improve the light extraction efficiency to a certain extent, the loss of light extraction efficiency caused by the phenomenon of the interface between the final barrier layer and the electronic barrier layer cannot be improved, and the identification difficulty of an automatic wire bonder is caused because the surface roughening technology is easy to have poor roughening uneven yield and causes the color difference between a P electrode and an N electrode of an LED.
Another common technique for improving the light extraction efficiency is to use a patterned substrate, which can improve the light extraction efficiency to a certain extent without affecting wire bonding, but cannot completely improve the light extraction efficiency loss caused by the total reflection phenomenon at the interface between the final barrier layer and the electron blocking layer.
Therefore, there is an urgent need to provide an LED epitaxial structure and a method for manufacturing the same, which can further improve the light-emitting efficiency of the LED without affecting the wire bonding.
Disclosure of Invention
In view of the above problems, the present invention provides an LED epitaxial structure, which includes a substrate, and a first semiconductor layer, a multiple quantum well light-emitting layer, a last barrier layer, an electron blocking layer, and a second semiconductor layer sequentially disposed on the substrate, and is characterized in that: and a plurality of island-shaped structures which are discontinuously arranged are inserted between the final barrier layer and the electron blocking layer.
Preferably, the island-like structure has a refractive index greater than that of the electron blocking layer and equal to or less than that of the final barrier layer.
Preferably, the island-shaped structures in discontinuous arrangement are 3D island-shaped structures, and the shapes are cone shapes, frustum shapes, Mongolian pyramid shapes, polygon prisms, or combinations of any two or three or four of the foregoing shapes.
Preferably, the epitaxial structure further comprises a plurality of nucleation structures located between the last barrier layer and the island structures as island structure forming cores.
Preferably, the island-like structure has the same refractive index as the final barrier layer.
Preferably, the island-like structure is AlxGa1-xN, the electron blocking layer is AlyGa1-yN, wherein x is more than or equal to 0 and less than 1, and x is more than or equal to x and less than 1.
Preferably, the surface of the electron barrier layer is a flat surface.
Preferably, the material of the nucleation structure is a magnesium nitride compound.
Preferably, a buffer layer is further provided between the substrate and the first semiconductor layer.
The invention also provides a preparation method of the LED epitaxial structure, which comprises the following steps:
step 1, firstly, providing a substrate;
step 2, depositing a buffer layer and a first semiconductor layer on the substrate in sequence;
step 3, depositing a multi-quantum well light-emitting layer and a final barrier layer on the first semiconductor layer;
step 4, depositing an electronic barrier layer on the final barrier layer;
step 5, continuously depositing a second semiconductor layer on the surface of the electron barrier layer;
the method is characterized in that: and a step 3a of depositing a plurality of discontinuous island-shaped structures is also included between the final barrier layer and the electron barrier layer deposition step.
Preferably, the method for preparing the epitaxial structure further comprises a step 3b of depositing a nucleation structure between the final barrier layer and the island-shaped structure, wherein the nucleation structure is a nucleation center of the island-shaped structure.
Preferably, the growth temperature of the nucleation structure is less than 900 ℃, and the reaction pressure is 100-500 torr.
Preferably, NH is introduced3And CP2Mg, forming a nucleation structure of the magnesium nitride compound.
Preferably, the growth temperature of the island-shaped structure is 700-950 ℃.
Preferably, the growth temperature of the island-shaped structure is 800-900 ℃, so that a discontinuous island-shaped structure can be formed on the magnesium nitride compound nucleation structure.
The invention inserts a plurality of magnesium nitride compound nucleation structures between the electronic barrier layer and the last barrier layer, and takes the nucleation structures as the core to grow a plurality of island-shaped structures so as to reduce the total reflection phenomenon of light at the interface of the electronic barrier layer and the last barrier layer, so that more light emitted from the multi-quantum-well light-emitting layer enters the electronic barrier layer, further the light-emitting efficiency of the LED epitaxial structure is improved, and the island-shaped structures are filled by the electronic barrier layer, thereby obtaining the LED epitaxial structure with a smooth surface.
Description of the drawings:
the accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. Furthermore, the drawing figures are for a descriptive summary and are not drawn to scale.
Fig. 1 is a schematic view of an epitaxial structure of an LED in the prior art.
Fig. 2 is a schematic view of an epitaxial structure of an LED in embodiment 1 of the invention.
Fig. 3 is a flowchart of a method for fabricating an LED epitaxial structure according to embodiment 2 of the present invention.
Fig. 4 is a schematic view of an LED epitaxial structure according to embodiment 3 of the present invention.
Fig. 5 is a flowchart of a method for fabricating an LED epitaxial structure according to embodiment 4 of the present invention.
The following are marked in the figure: 1: a substrate; 2: a buffer layer; 3: a first semiconductor layer; 4: a multiple quantum well light emitting layer; 5: a final barrier layer; 6: an electron blocking layer; 7: a second semiconductor layer; 8: a nucleation structure; 9: an island structure.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.
Example 1
Referring to fig. 2, the LED epitaxial structure provided in this embodiment includes a substrate 1, and a buffer layer 2, a first semiconductor layer 3, a multiple quantum well light-emitting layer 4, a last barrier layer 5, a plurality of island structures 9 discontinuously arranged, an electron blocking layer 6, and a second semiconductor layer 7 sequentially disposed on the substrate 1.
The island-shaped structures 9 in the discontinuous arrangement are 3D island-shaped structures 9, and the shapes of the island-shaped structures are conical shapes, frustum shapes, Mongolian yurt shapes, polygonal prisms shapes or combinations of any two or three or four of the shapes. In the present embodiment, as shown in fig. 2, the island-like structures 9 are in the shape of a combination of polygonal columns and polygonal pyramids, and the distance between the bottom of the adjacent island-like structures 9 is larger than the distance between the top of the adjacent island-like structures 9, so that the light entering the island-like structures 9 can be emitted from different angles.
The refractive index of the island-shaped structure 9 is greater than that of the electron barrier layer 6 and less than or equal to that of the final barrier layer 5, wherein the material of the island-shaped structure 9The material is AlxGa1-xN, the material of the electron blocking layer 6 is AlyGa1-yN, wherein x is more than or equal to 0 and less than 1, x is more than or equal to y and less than 1, preferably, x ranges from 0to 0.1, and y ranges from: x is the number of<y<0.3; the refractive index of the optional island-shaped structure 9 is the same as that of the last barrier layer 5, so in this embodiment, the material of the island-shaped structure 9 and the material of the last barrier layer 5 are both GaN, and a part of light emitted from the quantum well light-emitting layer 4 directly enters the island-shaped structure 9 through the last barrier layer 5 without changing the propagation path of the light, and then enters the electronic barrier layer 6 after being scattered by the island-shaped structure 9.
In this embodiment, the electron blocking layer 6 completely covers the island-shaped structure 9, and a surface with a relatively flat surface is obtained; the substrate 1 is preferably a patterned substrate 1, so that the scattering effect of the bottom of the epitaxial structure on light is increased, and the light extraction efficiency is further improved. The first semiconductor layer 3 and the second semiconductor layer have opposite electrical properties, preferably, the first semiconductor layer 3 is an N-type layer, the second semiconductor layer 7 is a P-type layer, and the multiple quantum well light-emitting layer 4 located between the first semiconductor layer 3 and the second semiconductor layer 7 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.
According to the invention, the plurality of discontinuously arranged island-shaped structures 9 are inserted between the last barrier layer 5 and the electronic barrier layer 6, so that the probability of total reflection of light at the interface between the last barrier layer 5 and the electronic barrier layer 6 is reduced, the light is scattered through the interface between the island-shaped structures 9 and the electronic barrier layer 6, the incident angle of the light entering the electronic barrier layer 6 is changed, and the external quantum well efficiency of the LED epitaxial structure is improved. Moreover, the electronic barrier layer 6 is used for filling and leveling the island-shaped structure 9, so that the surface of the prepared epitaxial structure layer is relatively flat, the automatic routing of electrodes is facilitated, and the reliability of the device is improved.
Example 2
The embodiment of the invention provides a preparation method of an LED epitaxial structure, which is suitable for manufacturing the LED epitaxial structure provided by the embodiment 1, and with reference to the attached drawing 3, the preparation method comprises the following steps:
step 1, firstly, providing a substrate 1, wherein the substrate 1 is a patterned substrate 1, in particular to a sapphire patterned substrate 1;
step 2, depositing a buffer layer 2 and a first semiconductor layer 3 on the substrate 1 in sequence;
the buffer layer 2 is a GaN buffer layer 2 or an AlN 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.
Step 3, depositing a multiple quantum well light-emitting layer 4 and a final barrier layer 5 on the first semiconductor layer 3;
the multi-quantum well light-emitting layer 4 is of a superlattice structure formed by alternately laminating a GaN quantum barrier layer and an InGaN quantum well layer, and the cycle number of the multi-quantum well light-emitting layer is 2-50; and finally, the growth conditions and the materials of the barrier layer 5 and the GaN quantum barrier layer are the same.
And 3a, depositing a plurality of discontinuously arranged island-shaped structures 9 on the last barrier layer 5, wherein the refractive index of the island-shaped structures 9 is greater than that of the electron blocking layer 6 and is less than or equal to that of the last barrier layer 5.
The growth temperature of the island-shaped structure 9 is 700-950 ℃, preferably 800-900 ℃, so as to form a discontinuous island-shaped structure 9.
Step 4, depositing an electron barrier layer 6;
specifically, the material of the electron blocking layer 6 is AlyGa1-yN, the island-shaped structure 9 is made of AlxGa1-xN, wherein x is more than or equal to 0 and less than 1, x is more than or equal to y and less than 1, preferably, x ranges from 0to 0.1, and y ranges from: x is the number of<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 5, continuously depositing a second semiconductor layer 7 on the surface of the electron blocking layer 6, wherein the second semiconductor layer 7 is a P-type layer and comprises a high-temperature P-type GaN layer and a P-type structure layer.
The first semiconductor layer 3, the multiple quantum well light-emitting layer 4, the last barrier layer 5, the island-shaped structure 9, the electronic barrier layer 6 and the second semiconductor layer 7 are all prepared by an MOCVD method, and in the forming process of the epitaxial structure, TMGa or TEGa is used as a gallium source and NH3As nitrogen source, N2and/H2As carrier gas, CP2Mg as a P-type impurity, SiH4As an N-type impurity.
According to the invention, the plurality of discontinuously arranged island-shaped structures 9 are deposited between the final barrier layer 5 and the electronic barrier layer 6, so that the probability of total reflection of light at the interface between the final barrier layer 5 and the electronic barrier layer 6 is reduced, the light is scattered through the interface between the island-shaped structures 9 and the electronic barrier layer 6, the incident angle of the light entering the electronic barrier layer 6 is changed, and the external quantum well efficiency of the LED epitaxial structure is improved.
Example 3
Referring to fig. 4, the difference between the LED epitaxial structure provided in this embodiment and the LED epitaxial structure provided in this embodiment is: and finally, a plurality of nucleation structures 8 which are used as island structures 9 to form cores are also arranged between the barrier layer 5 and the island structures 9, and the nucleation structures 8 are used as nucleation centers of the island structures 9 and have smaller sizes than the island structures 9.
Specifically, the LED epitaxial structure provided in this embodiment sequentially includes: the semiconductor device comprises a substrate 1, and a buffer layer 2, a first semiconductor layer 3, a multiple quantum well light-emitting layer 4, a final barrier layer 5, a nucleation structure 8, an island-shaped structure 9, an electron blocking layer 6 and a second semiconductor layer 7 which are positioned on the substrate 1.
Wherein the nucleating structure 8 is made of magnesium nitride compound, the island-shaped structure 9 has a refractive index larger than that of the electron blocking layer 6 and smaller than that of the final barrier layer 5, and the island-shaped structure 9 is made of AlxGa1-xN, the electron blocking layer 6 is AlyGa1-yN, wherein x is more than or equal to 0 and less than 1, x is more than or equal to y and less than 1, preferably, x ranges from 0to 0.1, and y ranges from: x is the number of<y<0.3, the electron blocking layer 6 completely covers the island-like structure 9 and forms a surface-flattened structure, and the magnesium nitride compound is Mg3N2A structure or a MgN structure.
In the embodiment of the invention, a plurality of magnesium nitride compound nucleation structures 8 are inserted between the electronic barrier layer 6 and the last barrier layer 5, and a plurality of discontinuous island-shaped structures 9 are grown by taking the nucleation structures 8 as cores to reduce the total reflection phenomenon of light at the interface of the electronic barrier layer 6 and the last barrier layer 5, so that more light emitted from the multi-quantum well light-emitting layer 4 enters the electronic barrier layer 6, the light-emitting efficiency of the LED epitaxial structure is further improved, and the island-shaped structures 9 are filled by the electronic barrier layer 6, and then the LED epitaxial structure with a smooth surface is obtained.
Example 4
The embodiment of the invention provides a method for manufacturing an LED epitaxial structure, which is suitable for manufacturing the LED epitaxial structure provided by the embodiment 3, and with reference to the attached drawing 5, the method comprises the following steps:
step 1, firstly, providing a substrate 1, wherein the substrate 1 is a patterned substrate 1, in particular a sapphire patterned substrate 1
Step 2, depositing a buffer layer 2 and a first semiconductor layer 3 on the substrate 1 in sequence;
the buffer layer 2 is a GaN buffer layer 2 or an AlN 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.
Step 3, depositing a multiple quantum well light-emitting layer 4 and a final barrier layer 5 on the first semiconductor layer 3;
the multi-quantum well light-emitting layer 4 is of a superlattice structure formed by alternately laminating a GaN quantum barrier layer and an InGaN quantum well layer, and the cycle number of the multi-quantum well light-emitting layer is 2-50; and finally, the growth conditions and the materials of the barrier layer 5 and the GaN quantum barrier layer are the same.
And 3b, depositing a plurality of nucleation structures 8 on the final barrier layer 5, wherein the nucleation structures are made of magnesium nitride compounds.
And 3a, taking the nucleation structure 8 as a core, and depositing a plurality of discontinuously arranged island-shaped structures 9, wherein the refractive index of the island-shaped structures 9 is larger than that of the electron blocking layer 6 and is smaller than that of the final barrier layer 5.
The growth temperature of the island-shaped structure 9 is 700-950 ℃, preferably 800-900 ℃, so that a discontinuous island-shaped structure 9 is formed by taking a magnesium nitride compound nucleation structure 8 as a core, and the magnesium nitride compound is Mg3N2A structure or a MgN structure.
Step 4, depositing an electron barrier layer 6;
specifically, the material of the electron blocking layer 6 is AlyGa1-yN, the island-shaped structure 9 is made of AlxGa1-xN, wherein x is more than or equal to 0 and less than 1, x is more than or equal to y and less than 1, preferably, x ranges from 0to 0.1, and y ranges from: x is the number of<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 5, continuously depositing a second semiconductor layer 7 on the surface of the electron blocking layer 6, wherein the second semiconductor layer 7 is a P-type layer and comprises a high-temperature P-type GaN layer and a P-type structure layer.
According to the invention, the plurality of discontinuously arranged island-shaped structures 9 are deposited between the final barrier layer 5 and the electronic barrier layer 6, so that the probability of total reflection of light at the interface between the final barrier layer 5 and the electronic barrier layer 6 is reduced, the light is scattered through the interface between the island-shaped structures 9 and the electronic barrier layer 6, the incident angle of the light entering the electronic barrier layer 6 is changed, and the external quantum well efficiency of the LED epitaxial structure is improved.
It should be understood that the above-mentioned embodiments are preferred examples of the present invention, and the scope of the present invention is not limited to these examples, and any modification made according to the present invention is within the scope of the present invention.