# US 9,520,538 B2 · LED epitaxial structure and fabrication method thereof

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- Number: US 9,520,538 B2
- Document ID: US9520538B2
- Status: Granted
- Kind: B2
- Application number: 14/748,195
- Filed: 2015-06-23
- Published: 2015-11-05
- Granted: 2016-12-13
- Earliest claimed: 2013-04-19
- Assignees: Xiamen Sanan Optoelectronics Technology Co., Ltd.
- Applicants: Xiamen Sanan Optoelectronics Technology Co., Ltd.
- Inventors: Qi Nan; Hsiang-Pin Hsieh; Nan Qiao; Wenyan Zhang; Hongmin Zhou; Lan Li; Wei Cheng; Zhijun Xu; Honghao Wu
- Web page: https://patentgrep.com/patent/US9520538B2

## CPC

- H10H 20/84: Coatings, e.g. passivation layers or antireflective coatings
- H10H 20/01335: {the light-emitting regions comprising nitride materials}
- H10H 20/811: having quantum effect structures or superlattices, e.g. tunnel junctions
- H10H 20/812: within the light-emitting regions, e.g. having quantum confinement structures
- H10H 20/813: having a plurality of light-emitting regions, e.g. multi-junction LEDs or light-emitting devices having photoluminescent regions within the bodies
- H10H 20/815: having stress relaxation structures, e.g. buffer layers
- H10H 20/825: containing nitrogen, e.g. GaN
- H10P 14/3216: {Nitrides}
- H10P 14/3252: {Alternating layers, e.g. superlattice}
- H10P 14/3254: {Graded layers}
- H10P 14/3416: {Nitrides}
- H10H 20/034: {of coatings}
- H10H 20/036: {of packages}
- H10H: INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10

## Abstract

An LED epitaxial structure includes a substrate; a GaN nucleating layer; a superlattice buffer layer comprising a plurality pairs of alternately stacked AlGaN/n-GaN structures; an n-GaN layer; a MQW light-emitting layer, a p-GaN layer and a p-type contact layer. Al(n) represents Al composition value of the nth AlGaN/n-GaN superlattice buffer layer pair; N(n) represents n-type impurity concentration value of the nth AlGaN/n-GaN superlattice buffer layer pair; variation trend of Al(n) is from gradual increase to gradual decrease, and for N(n) is from gradual increase to gradual decrease. The structure can effectively and sufficiently release the lattice stress due to lattice mismatch between the sapphire substrate and GaN at the bottom layer growth section, thereby greatly reducing wrapping of the epitaxial wafer throughout high-temperature growth process, improving wavelength concentration and yield of the epitaxial wafer, improving GaN lattice quality, reducing lattice dislocation density and improving stability of photoelectric characteristics.

## Claims

### Claim 1

An LED epitaxial structure, from bottom to up, comprising: a substrate; a GaN nucleating layer; a superlattice buffer layer comprising a plurality pairs of alternately stacked AlGaN/GaN structures; an n-type GaN layer; a MQW light-emitting layer, a p-type GaN layer, and a p-type contact layer; wherein an Al composition value of an nth AlGaN/GaN superlattice buffer layer pair is represented by Al(n); an n-type impurity concentration value of the nth AlGaN/GaN superlattice buffer layer pair is represented by N(n); a variation trend of Al(n) is from gradual increase to gradual decrease, and a variation trend of N(n) is from gradual increase to gradual decrease.

### Claim 2 (depends on 1)

The LED epitaxial structure of claim 1, wherein the variation trends of Al(n) and N(n) satisfy a relational expression: Al(n)=Yn*Al(n−1) and N(n)=Yn*N(n−1), wherein Yn follows a parabolic linear equation
Yn
=
-
a
⁡
(
n
-
N
+
1
2
)
2
+
a
⁡
(
N
+
1
)
2
4
,
wherein a is a fixed constant; n represents an nth superlattice buffer layer, in which 1<n≦≦ a total number of pairs of superlattice buffer layers, and 0<a≦18.

### Claim 3 (depends on 1)

The LED epitaxial structure of claim 1, wherein each group of lattice buffer layer pair comprises a plurality of AlGaN/GaN superlattice buffer layer pairs, in which, Al(m) represents an Al composition value of an mth group AlGaN/GaN superlattice buffer layer pair; N(m) represents an n-type impurity concentration value of the mth group AlGaN/GaN superlattice buffer layer pair; the variation trends of Al(m) and N(m) satisfy a relational expression: Al(m)=Ym*Al(m−1) and N(m)=Ym*M(m−1), wherein, Ym follows a parabolic linear equation
Ym
=
-
a
⁡
(
m
-
M
+
1
2
)
2
+
a
⁡
(
M
+
1
)
2
4
,
wherein a is a fixed constant; M represents a total number of groups comprising a plurality pairs of superlattice buffer layers; and m represents an mth group superlattice buffer layer pair, in which 1<m≦M and 0<a≦18.

### Claim 4 (depends on 1)

The LED epitaxial structure of claim 1, wherein a number of AlGaN/GaN superlattice buffer layer pairs varies from 3 to 40.

### Claim 5 (depends on 1)

The LED epitaxial structure of claim 1, wherein the substrate comprises at least one of sapphire (Al2O3), silicon carbide (SiC), silicon (Si), germanium (Ge), gallium nitride (GaN), aluminum gallium nitride (AlGaN), or aluminum nitride (AlN).

### Claim 6 (depends on 1)

The LED epitaxial structure of claim 1, wherein in each pair of AlGaN/GaN superlattice buffer layers, an n-type doping impurity in the n-type GaN layer is Si, and a p-type doping impurity in the p-type GaN layer is Mg.

### Claim 7 (depends on 1)

The LED epitaxial structure of claim 1, wherein Al composition of the AlGaN layer of each pair of AlGaN/GaN superlattice buffer layers varies from 0% to 40%.

### Claim 8 (depends on 1)

The LED epitaxial structure of claim 1, wherein an n-type impurity concentration of the n-type GaN layer of each pair of AlGaN/GaN superlattice buffer layers varies from 5×1016 cm−3 to 1×1019 cm−3.

### Claim 9 (depends on 1)

The LED epitaxial structure of claim 1, wherein a thickness of the AlGaN layer of each pair of AlGaN/GaN superlattice buffer layers varies from 0.1 nm to 40 nm.

### Claim 10 (depends on 1)

The LED epitaxial structure of claim 1, wherein a thickness of the n-type GaN layer of each pair of AlGaN/GaN superlattice buffer layers varies from 0.3 nm to 120 nm.

### Claim 11 (depends on 1)

The LED epitaxial structure of claim 1, wherein a thickness ratio of the AlGaN layer and corresponding n-type GaN layer of each pair of AlGaN/GaN superlattice buffer layers is 1:5-1:1.