# Patent

## Title
Light-emitting device and manufacturing method thereof

## Abstract

The present disclosure provides a light-emitting device and manufacturing method thereof. The light-emitting device comprising: a light-emitting stack; and a semiconductor layer having a first surface connecting to the light-emitting stack, a second surface opposite to the first surface, and a void; wherein the void comprises a bottom part near the first surface and an opening on the second surface, and a dimension of the bottom part is larger than the dimension of the opening.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application claims the right of priority based on TW application Ser. No. 102138216 filed on Oct. 22, 2013; the contents of which are incorporated herein by reference in its entirety.
FIELD OF DISCLOSURE
The present disclosure relates to a light-emitting device and manufacturing method thereof, in particular to a light-emitting device having voids and manufacturing method thereof.
BACKGROUND OF THE DISCLOSURE
A light-emitting diode (LED) is suitable for diverse lighting and display applications because it has good opto-electrical characteristics of low power consumption, low heat generation, long life, shock tolerance, compact, and swift response. Because the luminous efficiency of an LED is the product of its internal quantum efficiency and light extraction efficiency, the improvement of the light extraction efficiency is one way in addition to the internal quantum efficiency to raise the luminous intensity of LED.
SUMMARY OF THE DISCLOSURE
The present disclosure provides a light-emitting device and manufacturing method thereof. The light-emitting device comprises: a light-emitting stack; and a semiconductor layer having a first surface connecting to the light-emitting stack, a second surface opposite to the first surface, and a void; wherein the void comprises a bottom part near the first surface and an opening on the second surface, and a dimension of the bottom part is larger than the dimension of the opening.
The method for forming the light-emitting device comprises: providing a substrate; forming a light-emitting stack on the substrate; forming a semiconductor layer on the light-emitting stack, the semiconductor layer having a first surface connecting to the light-emitting stack, and a second surface opposite to the first surface, and forming a void in the semiconductor layer; wherein the void comprises a bottom part near the first surface and an opening on the second surface, and a dimension of the bottom part is larger than the dimension of the opening.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a) to 1(g) show a light-emitting device and manufacturing method thereof in accordance with a first embodiment of the present disclosure.
FIG. 2 shows a light-emitting device and manufacturing method thereof in accordance with a second embodiment of the present disclosure.
FIG. 3 shows a light-emitting device and manufacturing method thereof in accordance with a third embodiment of the present disclosure.



DETAILED DESCRIPTION OF THE DISCLOSURE
FIG. 1 shows a light-emitting device and manufacturing method thereof in accordance with a first embodiment of the present disclosure. As shown in FIG. 1(a), the method for forming the light-emitting device comprises providing a substrate 101, and forming a light-emitting stack 102 on the substrate 101. The light-emitting stack 102 comprises a semiconductor stack comprising a first conductivity type semiconductor layer 102a, a light-emitting layer 102b on the first conductivity type semiconductor layer 102a, and a second conductivity type semiconductor layer 102c on the light-emitting layer 102b. The first conductivity type semiconductor layer 102a and the second conductivity type semiconductor layer 102c are of different conductivity types. For example, the first conductivity type semiconductor layer 102a is an n-type semiconductor layer, and the second conductivity type semiconductor layer 102c is a p-type semiconductor layer. The first conductivity type semiconductor layer 102a, the light-emitting layer 102b, and the second conductivity type semiconductor layer 102c comprise III-V group material, such as AlGaInP series materials.
Next, as shown in FIG. 1(b), the method further comprises forming a semiconductor layer 103 on the light-emitting stack 102. The semiconductor layer 103 comprises material comprising aluminum, for example, aluminum arsenide (AlAs) and/or aluminum gallium arsenide (AlGaAs). A thickness of the semiconductor layer 103 is about from 1 μm to 10 μm. The semiconductor layer 103 comprises two opposite surfaces, wherein a first surface S1 is connected to the light-emitting stack 102, and a second surface S2 is opposite to the first surface S1. In the present embodiment, the semiconductor layer 103 comprises a first semiconductor layer 103a on the light-emitting stack 102, and a second semiconductor layer 103b on the first semiconductor layer 103a, wherein the aluminum content in the first semiconductor layer 103a is greater than the aluminum content in the second semiconductor layer 103b. For example, the first semiconductor layer 103a comprises aluminum arsenide (AlAs) and/or aluminum gallium arsenide (AlxGa1-xAs), wherein 0.5≦x<1 in one embodiment, and a thickness is about 3 μm; the second semiconductor layer 103b does not contain aluminum. For example, the second semiconductor layer 103b comprises gallium phosphide (GaP) with a thickness of about 50 nm. Furthermore, in the present embodiment, the first semiconductor layer 103a is a two-layer structure. For example, the first semiconductor layer 103a comprises a first aluminum-contained layer 103a1 and a second aluminum-contained layer 103a2, and the aluminum contents are different in these two layers. In the present embodiment, the aluminum content in the first aluminum-contained layer 103a1 is greater than that of the second aluminum-contained layer 103a2. For example, the first aluminum-contained layer 103a1 comprises aluminum arsenide (AlAs), and the second aluminum-contained layer 103a2 comprises aluminum gallium arsenide (AlyGa1-yAs), wherein 0.5≦y<1. Each of the first aluminum-contained layer 103a1 and the second aluminum-contained layer 103a2 has a thickness of about 1.5 μm
Next, a void formation step is performed. As shown in FIG. 1(c), the second semiconductor layer 103b is etched to form a hole for opening 103bo by lithography and etching processes. The hole for opening 103bo provides an opening 103boe on the second surface S2 and functions as an opening of the void. And then, as shown in FIG. 1(d), the first semiconductor layer 103a is etched by a wet etching process. In the present embodiment, an acid solution is used for the wet etching process. For example, citric acid or hydrofluoric acid (HF) is used. The acid solution etches and penetrates the second aluminum-contained layer 103a2 to form a penetrating part 103a2o. This penetrating part 103a2o functions as a middle part of the void 103v. The acid solution etches continuously the first aluminum-contained layer 103a1 to form a bottom hole 103a1ce which functions as a bottom part of the void 103v. 
As mentioned above, it is noted that since the aluminum content in the first aluminum-contained layer 103a1 is different from that in the second aluminum-contained layer 103a2, the etching rates of the acid solution to these two layers are different. The higher aluminum content results in a higher etching rate. Therefore, a hole diameter d2 of the penetrating part 103a2o of the second aluminum-contained layer 103a2 which has a lower aluminum content is smaller than a hole diameter d3 of the bottom hole 103a1ce of the first aluminum-contained layer 103a1 which has a higher aluminum content. In addition, because the penetrating part 103a2o is formed by the etching of the acid solution which infiltrates into the second aluminum-contained layer 103a2 through the hole for opening 103bo of the above second semiconductor layer 103b, the hole diameter d2 of the penetrating part 103a2o is substantially equal to or slightly larger than the hole diameter d1 of the hole for opening 103bo of the second semiconductor layer 103b. In the present embodiment, both the hole diameter d1 of the hole for opening 103bo and the hole diameter d2 of the penetrating part 103a2o are about in the range of 0.1 μm≦d1 (or d2)≦20 μm. The hole diameter d3 of the bottom hole 103a1ce is about in the range of 1.2*d1≦d3≦10*d1. Thus, after the void formation step, the void 103v is formed in the semiconductor layer 103. The void 103v comprises a bottom part near the first surface S1, such as the bottom hole 103a1ce, and an opening located on the second surface S2, such as the opening 103boe, wherein the bottom part of the void 103v has a dimension (d3) larger than the dimension (d1) of the opening.
Based on the teaching of the above embodiment, the person of the ordinary skill of the art should understand that the cross-sectional shape of the void may be adjusted by controlling the aluminum content along the direction which the semiconductor layer 103 is formed. For example, by making the aluminum content in the first aluminum-contained layer 103a1 greater than that of the second aluminum-contained layer 103a2 in the above embodiment, the void can be formed by etching to have the bottom part with a larger dimension than that of the opening. Therefore, in a modified embodiment, all elements are the same as the above embodiment except that the second aluminum-contained layer 103a2 is not formed. In another modified embodiment, the second semiconductor layer 103b is not formed, and the first semiconductor layer 103a (to be more specific, the second aluminum-contained layer 103a2 thereof) is coated with a photo-resistor which is then exposed and developed to have a circular opening, and the second aluminum-contained layer 103a2 and the first aluminum-contained layer 103a1 are etched by an acid solution to form voids. These voids can effectively improve the light extraction efficiency of the light-emitting diode, and enhance luminous intensity of the light-emitting diode.
Next, as shown in FIG. 1(e), a transparent conductive layer 104 is formed on the second surface S2 to seal the opening 103boe. In the present embodiment, the transparent conductive layer 104 comprises a transparent conductive oxide layer, such as one material selected from indium tin oxide (ITO), aluminum zinc oxide (AZO), cadmium tin oxide, antimony tin oxide, zinc oxide (ZnO), and zinc tin oxide.
Next, as shown in FIG. 1(f), wherein FIG. 1(e) is placed upside down, a metal layer 105 is formed on and connects to the transparent conductive layer 104. A first bonding layer 106a1 is formed to connect to the metal layer 105. The metal layer 105 comprises a metal material having a high reflectivity, such as gold (Au), silver (Ag), or aluminum (Al), to function as a reflector. Then, a permanent substrate 107 is provided. The permanent substrate 107 comprises an electrically conductive material, such as silicon (Si) or silicon carbide (SiC). A second bonding layer 106a2 is formed on the permanent substrate 107. The first bonding layer 106a1 and the second bonding layer 106a2 comprise gold (Au), indium (In) or an alloy formed by both. The first bonding layer 106a1 and the second bonding layer 106a2 are bonded together to form the bonding structure 106. As shown in FIG. 1(g), the substrate 101 is removed, and the electrode 109 is formed on the first conductivity type semiconductor layer 102a to form an ohmic contact. In addition, a roughening process is optionally performed to the first conductivity type semiconductor layer 102a to form a roughened surface on the first conductivity type semiconductor layer 102a to increase the light extraction. Finally, a passivation layer 108 is formed on the first conductivity type semiconductor layer 102a to protect the light-emitting device. Because the semiconductor layer 103 comprises aluminum which tends to react with the moisture in the air, the passivation layer 108 is also formed to cover the sidewalls of the semiconductor layer 103 so as to improve the reliability of the light-emitting device. The specific embodiment is shown in FIG. 1(g). A lithography process and an etching process are performed to the light-emitting device to remove the sidewalls of the light-emitting stack 102 and part of the semiconductor layer 103 so that the passivation layer 108 also covers the sidewalls of the semiconductor layer 103 when it is formed. Because the second semiconductor layer 103b in the present embodiment does not contain aluminum, the aforementioned etching process may be performed until the first semiconductor layer 103a is etched and the second semiconductor layer 103b which does not comprises aluminum is exposed. As shown in FIG. 1(g), when light L emitted by the light-emitting stack 102 reaches the void 103v, the reflecting effect and scattering effect occur, so the light extraction efficiency of the light-emitting diode is improved, and the luminous intensity and the luminous uniformity at the light extraction surface of the light-emitting diode is raised.
FIG. 2 shows a light-emitting device and manufacturing method thereof in accordance with a second embodiment of the present disclosure. As mentioned above in FIG. 1(d), the cross-sectional shape of the void may be adjusted by controlling the aluminum content along the direction which the semiconductor layer 103 is formed. In the present embodiment, the semiconductor layer 103 is different from that of the first embodiment. The first aluminum-contained layer 103a1 and the second aluminum-contained layer 103a2 of the first embodiment are exchanged in the present embodiment. That is, the second aluminum-contained layer 103a2 is formed firstly, and then the first aluminum-contained layer 103a1 is formed. As illustrated in the first embodiment, the first aluminum-contained layer 103a1 comprises aluminum arsenide (AlAs), and the second aluminum-contained layer 103a2 comprises aluminum gallium arsenide (AlyGa1-yAs, wherein 0.5≦y<1). Because the first aluminum-contained layer 103a1 which has higher aluminum content is disposed below the second semiconductor layer 103b in the present embodiment, the etching time of the etching process for the acid solution to react can be set shorter than that in the first embodiment to etch only the first aluminum-contained layer 103a1 to form the bottom hole 103a1ce which functions as a bottom part of the void 103v′. The void 103v′ comprises a bottom part near the first surface S1, such as the bottom hole 103a1ce, and an opening located on the second surface S2, such as the opening 103boe, wherein the bottom part of the void 103v′ has a dimension (d3) larger than the dimension (d1) of the opening. The subsequent steps to form the light-emitting device are substantially the same as those illustrated in the first embodiment, so they are not illustrated again. Compared with the first embodiment wherein the first aluminum-contained layer 103a1 which has the higher aluminum content connects to the light-emitting stack 102, in the present embodiment, because the second aluminum-contained layer 103a2 which has the lower aluminum content connects to the light emitting stack 102, a forward voltage (Vf) can be lower than that of the first embodiment.
FIG. 3 shows a light-emitting device and manufacturing method thereof in accordance with a third embodiment of the present disclosure. In the present embodiment, a third aluminum-contained layer 103a3 is added to the semiconductor layer 103 as disclosed in the first embodiment. That is, the third aluminum-contained layer 103a3 is formed firstly, and then the first aluminum-contained layer 103a1 and the second aluminum-contained layer 103a2 of the first semiconductor layer 103a are formed subsequently, and then the second semiconductor layer 103b is formed. In the present embodiment, the third aluminum-contained layer 103a3 and the second aluminum-contained layer 103a2 are the same, and both comprise aluminum gallium arsenide (AlyGa1-yAs, wherein 0.5≦y<1), with a thickness of about 1.5 μm. The subsequent steps to form the light-emitting device are substantially the same as those illustrated in the first embodiment, so they are not illustrated again. Compared with the first embodiment, in the present embodiment, because the third aluminum-contained layer 103a3 which has lower aluminum content connects to the light-emitting stack 102, a forward voltage (Vf) can be lower than that of the first embodiment. In addition, regarding the cross-sectional shape of the voids, compared to the second embodiment, the void 103v in the present embodiment is similar to the void 103v in the first embodiment to comprise a penetrating part 103a2o which functions as a middle part of the void 103v, and therefore the probability for light to be reflected is increased. In other words, the present embodiment comprises the advantages of the two embodiments described above.
The above-mentioned embodiments are only examples to illustrate the theory of the present invention and its effect, rather than be used to limit the present application. Other alternatives and modifications may be made by a person of ordinary skill in the art of the present application without departing from the spirit and scope of the application, and are within the scope of the present application.

## Claims

1. A light-emitting device comprising:
a light-emitting stack; and
a semiconductor layer having a first surface connecting to the light-emitting stack, a second surface opposite to the first surface, and a void; wherein the void comprises a bottom part near the first surface and an opening on the second surface, and a dimension of the bottom part is larger than the dimension of the opening, wherein the semiconductor layer comprises a first semiconductor layer and a second semiconductor layer, and the second semiconductor layer is closer to the second surface than the first semiconductor layer is, and wherein an aluminum content in the first semiconductor layer is greater than the aluminum content in the second semiconductor layer.

2. The light-emitting device of claim 1, further comprising a transparent conductive layer on the second surface to seal the opening.

3. The light-emitting device of claim 1, wherein the semiconductor layer comprises aluminum arsenide (AlAs) or aluminum gallium arsenide (AlxGa1-xAs).

4. The light-emitting device of claim 1, wherein the first semiconductor layer comprises aluminum arsenide (AlAs) or aluminum gallium arsenide (AlxGa1-xAs, wherein 0.5≦x<1).

5. The light-emitting device of claim 1, wherein the second semiconductor layer does not comprise aluminum (Al).

6. The light-emitting device of claim 1, wherein a diameter of the opening is about equal to d, a diameter of the bottom part is about equal to D, and 1.2*d≦D≦10*d, wherein 0.1 μm≦d≦20 μm.

7. The light-emitting device of claim 1, wherein the semiconductor layer comprises a plurality of layers comprising semiconductor material, and each of the layers comprising semiconductor material has different aluminum contents.

8. A method for forming a light-emitting device, comprising:
providing a substrate;
forming a light-emitting stack on the substrate;
forming a semiconductor layer comprising a second semiconductor layer disposed on a first semiconductor layer formed on the light-emitting stack, the first semiconductor layer having a first surface connecting to the light-emitting stack, and the second semiconductor layer has a second surface opposite to the first surface, wherein the first semiconductor layer comprises aluminum (Al), and an aluminum content in the second semiconductor layer is smaller than the aluminum content in the first semiconductor layer; and
forming a void in the semiconductor layer; wherein the void comprises a bottom part near the first surface and an opening on the second surface, and a dimension of the bottom part is larger than the dimension of the opening.

9. The method of claim 8, further comprising forming a transparent conductive layer on the second surface to seal the opening.

10. The method of claim 8, wherein the first semiconductor layer comprises aluminum arsenide (AlAs) or aluminum gallium arsenide (AlxGa1-xAs, wherein 0.5≦x<1).

11. The method of claim 8, wherein the second semiconductor layer does not comprise aluminum (Al).

12. The method of claim 9, further comprising forming a metal layer connecting to the transparent conductive layer.

13. The method of claim 12, further comprising forming a first bonding layer connecting to the metal layer.

14. The method of claim 13, further comprising providing a permanent substrate; forming a second bonding layer on the permanent substrate; bonding the first bonding layer and the second bonding layer; and removing the substrate.

15. The method of claim 14, wherein the permanent substrate comprises an electrically conductive substrate.

16. The method of claim 8, further comprising forming the opening by a dry etching method, and forming the bottom part by a wet etching method.