Light-emitting device and manufacturing method thereof

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.

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.

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.

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.

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.

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 102 a , a light-emitting layer 102 b on the first conductivity type semiconductor layer 102 a , and a second conductivity type semiconductor layer 102 c on the light-emitting layer 102 b . The first conductivity type semiconductor layer 102 a and the second conductivity type semiconductor layer 102 c are of different conductivity types. For example, the first conductivity type semiconductor layer 102 a is an n-type semiconductor layer, and the second conductivity type semiconductor layer 102 c is a p-type semiconductor layer. The first conductivity type semiconductor layer 102 a , the light-emitting layer 102 b , and the second conductivity type semiconductor layer 102 c 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 S 1 is connected to the light-emitting stack 102 , and a second surface S 2 is opposite to the first surface S 1 . In the present embodiment, the semiconductor layer 103 comprises a first semiconductor layer 103 a on the light-emitting stack 102 , and a second semiconductor layer 103 b on the first semiconductor layer 103 a , wherein the aluminum content in the first semiconductor layer 103 a is greater than the aluminum content in the second semiconductor layer 103 b . For example, the first semiconductor layer 103 a comprises aluminum arsenide (AlAs) and/or aluminum gallium arsenide (Al x Ga 1-x As), wherein 0.5≦x<1 in one embodiment, and a thickness is about 3 μm; the second semiconductor layer 103 b does not contain aluminum. For example, the second semiconductor layer 103 b comprises gallium phosphide (GaP) with a thickness of about 50 nm. Furthermore, in the present embodiment, the first semiconductor layer 103 a is a two-layer structure. For example, the first semiconductor layer 103 a comprises a first aluminum-contained layer 103 a 1 and a second aluminum-contained layer 103 a 2 , and the aluminum contents are different in these two layers. In the present embodiment, the aluminum content in the first aluminum-contained layer 103 a 1 is greater than that of the second aluminum-contained layer 103 a 2 . For example, the first aluminum-contained layer 103 a 1 comprises aluminum arsenide (AlAs), and the second aluminum-contained layer 103 a 2 comprises aluminum gallium arsenide (Al y Ga 1-y As), wherein 0.5≦y<1. Each of the first aluminum-contained layer 103 a 1 and the second aluminum-contained layer 103 a 2 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 103 b is etched to form a hole for opening 103 bo by lithography and etching processes. The hole for opening 103 bo provides an opening 103 boe on the second surface S 2 and functions as an opening of the void. And then, as shown in FIG. 1( d ) , the first semiconductor layer 103 a 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 103 a 2 to form a penetrating part 103 a 2 o . This penetrating part 103 a 2 o functions as a middle part of the void 103 v . The acid solution etches continuously the first aluminum-contained layer 103 a 1 to form a bottom hole 103 a 1 ce which functions as a bottom part of the void 103 v.

As mentioned above, it is noted that since the aluminum content in the first aluminum-contained layer 103 a 1 is different from that in the second aluminum-contained layer 103 a 2 , 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 d 2 of the penetrating part 103 a 2 o of the second aluminum-contained layer 103 a 2 which has a lower aluminum content is smaller than a hole diameter d 3 of the bottom hole 103 a 1 ce of the first aluminum-contained layer 103 a 1 which has a higher aluminum content. In addition, because the penetrating part 103 a 2 o is formed by the etching of the acid solution which infiltrates into the second aluminum-contained layer 103 a 2 through the hole for opening 103 bo of the above second semiconductor layer 103 b , the hole diameter d 2 of the penetrating part 103 a 2 o is substantially equal to or slightly larger than the hole diameter d 1 of the hole for opening 103 bo of the second semiconductor layer 103 b . In the present embodiment, both the hole diameter d 1 of the hole for opening 103 bo and the hole diameter d 2 of the penetrating part 103 a 2 o are about in the range of 0.1 μm≦d 1 (or d 2 )≦20 μm. The hole diameter d 3 of the bottom hole 103 a 1 ce is about in the range of 1.2*d 1 ≦d 3 ≦10*d 1 . Thus, after the void formation step, the void 103 v is formed in the semiconductor layer 103 . The void 103 v comprises a bottom part near the first surface S 1 , such as the bottom hole 103 a 1 ce , and an opening located on the second surface S 2 , such as the opening 103 boe , wherein the bottom part of the void 103 v has a dimension (d 3 ) larger than the dimension (d 1 ) 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 103 a 1 greater than that of the second aluminum-contained layer 103 a 2 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 103 a 2 is not formed. In another modified embodiment, the second semiconductor layer 103 b is not formed, and the first semiconductor layer 103 a (to be more specific, the second aluminum-contained layer 103 a 2 thereof) is coated with a photo-resistor which is then exposed and developed to have a circular opening, and the second aluminum-contained layer 103 a 2 and the first aluminum-contained layer 103 a 1 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 S 2 to seal the opening 103 boe . 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 106 a 1 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 106 a 2 is formed on the permanent substrate 107 . The first bonding layer 106 a 1 and the second bonding layer 106 a 2 comprise gold (Au), indium (In) or an alloy formed by both. The first bonding layer 106 a 1 and the second bonding layer 106 a 2 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 102 a to form an ohmic contact. In addition, a roughening process is optionally performed to the first conductivity type semiconductor layer 102 a to form a roughened surface on the first conductivity type semiconductor layer 102 a to increase the light extraction. Finally, a passivation layer 108 is formed on the first conductivity type semiconductor layer 102 a 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 103 b in the present embodiment does not contain aluminum, the aforementioned etching process may be performed until the first semiconductor layer 103 a is etched and the second semiconductor layer 103 b 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 103 v , 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 103 a 1 and the second aluminum-contained layer 103 a 2 of the first embodiment are exchanged in the present embodiment. That is, the second aluminum-contained layer 103 a 2 is formed firstly, and then the first aluminum-contained layer 103 a 1 is formed. As illustrated in the first embodiment, the first aluminum-contained layer 103 a 1 comprises aluminum arsenide (AlAs), and the second aluminum-contained layer 103 a 2 comprises aluminum gallium arsenide (Al y Ga 1-y As, wherein 0.5≦y<1). Because the first aluminum-contained layer 103 a 1 which has higher aluminum content is disposed below the second semiconductor layer 103 b 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 103 a 1 to form the bottom hole 103 a 1 ce which functions as a bottom part of the void 103 v ′. The void 103 v ′ comprises a bottom part near the first surface S 1 , such as the bottom hole 103 a 1 ce , and an opening located on the second surface S 2 , such as the opening 103 boe , wherein the bottom part of the void 103 v ′ has a dimension (d 3 ) larger than the dimension (d 1 ) 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 103 a 1 which has the higher aluminum content connects to the light-emitting stack 102 , in the present embodiment, because the second aluminum-contained layer 103 a 2 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 103 a 3 is added to the semiconductor layer 103 as disclosed in the first embodiment. That is, the third aluminum-contained layer 103 a 3 is formed firstly, and then the first aluminum-contained layer 103 a 1 and the second aluminum-contained layer 103 a 2 of the first semiconductor layer 103 a are formed subsequently, and then the second semiconductor layer 103 b is formed. In the present embodiment, the third aluminum-contained layer 103 a 3 and the second aluminum-contained layer 103 a 2 are the same, and both comprise aluminum gallium arsenide (Al y Ga 1-y As, 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 103 a 3 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 103 v in the present embodiment is similar to the void 103 v in the first embodiment to comprise a penetrating part 103 a 2 o which functions as a middle part of the void 103 v , 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.