Light emitting diode

A light emitting diode includes a semiconductor stacked structure, a substrate, a first electrode, a second electrode and a third electrode. The semiconductor stacked structure includes a first semiconductor layer, a second semiconductor layer and a light emitting layer. A light extraction layer with a roughened structure is formed on the doped semiconductor layer to improve the light emitting efficiency of LED. Furthermore, the strength of the semiconductor stacked structure can be enhanced by the light extraction layer, to improve the reliability of the LED and the production yields of manufacturing process.

TECHNICAL FIELD

The technical field relates to a light emitting diode.

BACKGROUND

A light emitting diode (LED) is a semiconductor device constituted mainly by group III-V compound semiconductor materials. Since such semiconductor materials have a characteristic of converting electricity into light, when a current is applied to the semiconductor materials, electrons and holes therein would be combined and release excessive energy in a form of light, thereby achieving an effect of luminosity.

A vertical LED apparatus is a common LED apparatus. In a vertical LED apparatus, an LED chip consists of a silicon substrate and a light emitting layer disposed on the silicon substrate. The silicon substrate is disposed on a carrier board, and the LED chip is electrically connected to the carrier board through a bonding wire. Compared to a conventional face-up LED apparatus, the vertical LED apparatus has good heat dissipation and lower occurrence of current crowding.

Nonetheless, due to a difference in expansion coefficient between the bonding wire and a sealant in the vertical LED apparatus, breakage easily occurs to result in a failure of the apparatus. In addition, uneven distribution of phosphor in the sealant occurs as a consequence of natural deposition of the phosphor itself and excessively large thickness of the bonding wire and the LED chip. Moreover, since the LED chip is electrically connected to the carrier board through the bonding wire, density of the LED chips in the vertical LED apparatus cannot be further decreased. For a projection type light source that requires multiple chips, luminous intensity per unit area cannot be effectively enhanced.

SUMMARY

According to an exemplary embodiment of the disclosure, a light emitting diode (LED) having good device reliability is provided.

According to an exemplary embodiment of the disclosure, a light emitting diode comprises a semiconductor stacked structure, a substrate, a first electrode, a second electrode, and an outer light extraction layer. The semiconductor stacked structure comprises a first semiconductor layer, a second semiconductor layer stacked with the first semiconductor layer, and a light emitting layer disposed between the first semiconductor layer and the second semiconductor layer. The substrate carries the semiconductor stacked structure and faces the second semiconductor layer. The first electrode is disposed between the second semiconductor layer and the substrate and electrically connected to the second semiconductor layer and the substrate. The second electrode is disposed on the first semiconductor layer. The outer light extraction layer is disposed on the first semiconductor layer, wherein the outer light extraction layer forms a roughened structure, and a light refractive index of the outer light extraction layer is less than a light refractive index of the first semiconductor layer.

In the aforementioned LED according to an exemplary embodiment of the disclosure, the roughened structure comprises a plurality of pyramids or a plurality of micro lenses.

In the aforementioned LED according to an exemplary embodiment of the disclosure, the outer light extraction layer comprises a transparent conductive material, and the outer light extraction layer is electrically connected to the second electrode.

In the aforementioned LED according to an exemplary embodiment of the disclosure, the light emitting diode further comprises at least one inner light extraction layer, disposed between the outer light extraction layer and the first semiconductor layer, wherein a light refractive index of the outer light extraction layer is less than a light refractive index of the at least one inner light extraction layer.

In the aforementioned LED according to an exemplary embodiment of the disclosure, the at least one inner light extraction layer comprises a plurality of inner light extraction layers, and a light refractive index of any one of the inner light extraction layers is less than a light refractive index of another one of the inner light extraction layers when a distance between the any one of the inner light extraction layers and the outer light extraction layer is less than a distance between the another one of the inner light extraction layers and the outer light extraction layer.

In the aforementioned LED according to an exemplary embodiment of the disclosure, the at least one inner light extraction layer comprises a transparent conductive material.

In the aforementioned LED according to an exemplary embodiment of the disclosure, the substrate has a first conductive layer and a second conductive layer, and the first electrode is disposed and electrically connected between the second semiconductor layer and the first conductive layer. The light emitting diode further comprises a third electrode and a conductive via. The third electrode is disposed between the semiconductor stacked structure and the second conductive layer, wherein the third electrode is electrically connected to the second conductive layer. The conductive via passes through the semiconductor stacked structure and is electrically connected between the second electrode and the third electrode.

Based on the above, according to the disclosure, the semiconductor stacked structure is bonded to the conductive layer on the substrate by flip-chip bonding. Thus, problems such as uneven distribution of phosphor in a sealant and failure of the LED due to breakage of a bonding wire are unlikely to occur. Accordingly, the LED according to the disclosure has good device reliability. In addition, in the LED according to the disclosure, the second surface of the n-type first semiconductor layer has an opening for disposing the third electrode, and there is a gap between the third electrode and the light emitting layer. Therefore, there is no need to dispose an additional insulating layer between the third electrode and the light emitting layer for electrically isolating the third electrode and the light emitting layer from each other.

Furthermore, at least one light extraction layer can be provided on the first semiconductor layer of any of the LEDs of the aforementioned embodiments in an applicable situation, and a light refractive index of the outer light extraction layer is less than a light refractive index of the first semiconductor layer, to enhance the light emitting efficiency.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

FIG. 1AtoFIG. 1Eare schematic cross-sectional views of a fabrication process of a light emitting diode (LED) according to the first exemplary embodiment. Referring toFIG. 1Afirst, on a carrier substrate200, a first semiconductor material layer210, a light emitting material layer220and a second semiconductor material layer230are formed in sequence. Before the growth of the first semiconductor material layer210, an undoped semiconductor layer is grown to reduce epitaxial defects in number. The carrier substrate200is, e.g., a sapphire substrate or a silicon substrate. In the present exemplary embodiment, the first semiconductor material layer210, the light emitting material layer220and the second semiconductor material layer230are formed by an epitaxy process. Of course, the disclosure is not limited hereto. The above-mentioned material layers may be formed by other suitable processes. The methods of formation are well known by persons of ordinary skill in the art, and thus details thereof are not described herein.

Next, referring toFIG. 1B, portions of the first semiconductor material layer210, the light emitting material layer220and the second semiconductor material layer230are removed to form a first semiconductor layer110, a light emitting layer120and a second semiconductor layer130. The first semiconductor layer110, the light emitting layer120and the second semiconductor layer130constitute a semiconductor stacked structure100. In the present exemplary embodiment, the semiconductor stacked structure100has a thickness of less than 20 μm. The first semiconductor layer110is, e.g., an n-type semiconductor layer, while the second semiconductor layer130is, e.g., a p-type semiconductor layer. Of course, the disclosure is not limited hereto. In other exemplary embodiments, the first semiconductor layer110is, e.g., a p-type semiconductor layer, while the second semiconductor layer130is, e.g., an n-type semiconductor layer.

FIG. 19Ais a schematic top view ofFIG. 1B, whereinFIG. 19does not illustrate the second semiconductor layer130and the light emitting layer120, so as to clearly show a profile of the first semiconductor layer110.FIG. 19Bis a schematic cross-sectional view along line E-E′ inFIG. 19A. Referring toFIG. 1B,FIG. 19AandFIG. 19Btogether, the first semiconductor layer110includes a first surface112and a second surface114opposite to each other. The first semiconductor layer110includes a first region110aand a second region110b. The second semiconductor layer130is disposed on the first region110a. The second region110bincludes an opening H extending from the second surface114to the first surface112. A bottom of the opening H is a third surface116. The bottom of the opening H is located in the first semiconductor layer110. Since the opening H is formed by removing the portions of the first semiconductor material layer210, the light emitting material layer220and the second semiconductor material layer230, a size of the opening H affects an area of the light emitting layer120.

In the present exemplary embodiment, the second region110bis located on an edge of the second surface114. Of course, the disclosure is not limited hereto. In other exemplary embodiment, the second region110bmay not be located on the edge of the second surface114. In other words, the second region110b(not illustrated) may also be completely surrounded by the first region110a, and the second region110bis located at an arbitrary position. It is worth mentioning that it is favorable in terms of process simplification if the second region110bis located on the edge of the second surface114. An area of the third surface116is smaller than or equal to 13% of a total area of the second surface114and the third surface116. Further, an area of the second region is smaller than or equal to 13% of a total area of the first region and the second region. In other exemplary embodiment, the area of the third surface116is smaller than or equal to 10% of the total area of the second surface114and the third surface116. More preferably, the area of the third surface116is smaller than or equal to 3% of the total area of the second surface114and the third surface116. It is to be noted that the size of the opening H is not limited in the disclosure as long as the area of the third surface116is smaller than or equal to 13% of the total area of the second surface114and the third surface116.

Then, referring toFIG. 1C, a first electrode140, a third electrode160and a fourth electrode170are formed on the carrier substrate200, wherein the aforementioned electrodes are formed by, e.g., electroplating. The first electrode140is located on the second semiconductor layer130. The third electrode160is disposed on the second region110b. More specifically, the third electrode160is located in the opening H and on the third surface116. The fourth electrode170is located on a sidewall118of the first semiconductor layer110and connected to the third electrode160.

Next, referring toFIG. 1D, the structure shown inFIG. 1Cis bonded to a substrate300. The substrate300is, e.g., a printed circuit board. In the present exemplary embodiment, the substrate300has a first conductive layer310and a second conductive layer320on its surface. The first electrode140and the third electrode160are connected to the first conductive layer310and the second conductive layer320respectively. Specifically, in the present exemplary embodiment, the first electrode140is located between the second semiconductor layer130and the first conductive layer310, the third electrode160is located between the first semiconductor layer110and the second conductive layer320, and the fourth electrode170is located on the sidewall118of the first semiconductor layer110and a sidewall of the third electrode160. In the present exemplary embodiment, the semiconductor stacked structure100is bonded onto the substrate300by flip-chip bonding. Accordingly, the semiconductor stacked structure100may be electrically connected to a conductive layer (such as the first conductive_layer310and the second conductive layer320) on the substrate300without using a bonding wire. In this way, the chance of uneven distribution of phosphor in a sealant occurring in follow-on processes is reduced.

FIG. 20is a schematic top view ofFIG. 1C. Referring toFIG. 1C,FIG. 1DandFIG. 20together, inFIG. 1D, the first electrode140is configured to be electrically connected to the first conductive layer310, wherein the first electrode140is connected to the first conductive layer310by its surface140s. A contact area (i.e. the area of the surface140s) between the first electrode140and the first conductive layer310is larger than or equal to 30% of an area of the second surface114, thus enhancing heat dissipation. Preferably, the contact area between the first electrode140and the first conductive layer310is larger than or equal to 50% of the area of the second surface114, so as to further enhance heat dissipation.

In addition, in the case where an LED includes a plurality of semiconductor stacked structures100, since no bonding wire is required for electric connection between the semiconductor stacked structures100and the conductive layer of the substrate300, the density of these semiconductor stacked structures100may be increased, and luminous intensity is effectively enhanced.

Then, referring toFIG. 1E, the carrier substrate200is removed. It is worth mentioning that when the carrier substrate200is being detached from the first semiconductor layer110, since the fourth electrode170is connected to the third electrode160, and the third electrode160is located on the third surface116, the fourth electrode170is unlikely to fall off with the detachment of the carrier substrate200. Next, a second electrode150is formed on the first surface112of the first semiconductor layer110, thereby fabricating an LED100a, wherein the second electrode150is connected to the fourth electrode170. A material of the second electrode150is, e.g., metal or a transparent conductive film.

In addition, with respect to a process of removing the carrier substrate200utilizing laser lift-off (LLO) technology (e.g. growth of GaN on a sapphire substrate), an interlayer (e.g. Al) having a melting point of less than 1000° C. (the highest instantaneous temperature of the LLO process), or an interlayer (e.g. ITO) having a material band gap of less than laser photon energy (KrF: 4.9 eV) is interposed between the fourth electrode170and the carrier substrate200, so as to reduce damage caused to the fourth electrode170during the LLO process due to an impact of laser.

In the present exemplary embodiment, the first semiconductor layer110retracts from the edge of the second surface114to form a containing space (i.e. the opening H). This containing space is configured for disposing the third electrode160, and the third electrode160is electrically connected to the second electrode150on the first surface112through the fourth electrode170. The third electrode160is in place of a metal bonding wire of a conventional vertical LED, transmitting a current of the second electrode150to the second conductive layer320on the substrate300to form a wire-less vertical LED structure. Since the third electrode160and the light emitting layer120have a gap therebetween, an electric isolation effect is achieved without a need to dispose an additional insulating layer between the third electrode160and the light emitting layer120. Based on the above, the LED100aaccording to the present exemplary embodiment has good device reliability.

Several exemplary embodiments will be given hereinafter to describe the disclosure in detail, wherein the same components are denoted by the same reference numerals and descriptions of the same technical content will be omitted. The omitted content may be understood with reference to the aforementioned embodiments, and will not be repeated hereinafter.

FIG. 2is a schematic cross-sectional view of an LED according to the second exemplary embodiment. Referring toFIG. 2, an LED100bof the second exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that in the LED100b, the sidewall118of the first semiconductor layer110is an inclined plane. In the present exemplary embodiment, since the sidewall118of the first semiconductor layer110is an inclined plane, it is easier for the fourth electrode170to be formed on the sidewall118.

FIG. 3is a schematic cross-sectional view of an LED according to the third exemplary embodiment. Referring toFIG. 3, an LED100cof the third exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that the LED100cdoes not include the fourth electrode170as shown inFIG. 1. Specifically, the second electrode150and the third electrode160are respectively located on two opposite sides of the first semiconductor layer110and partially overlap each other. A voltage may be applied to the third electrode160to electrically conduct the second electrode150with the third electrode160. In addition, an ohmic contact layer (not illustrated) is selectively formed between the second electrode150and the first semiconductor layer110and between the third electrode160and the first semiconductor layer110, so as to reduce contact impedance between the second electrode150and the first semiconductor layer110and between the third electrode160and the first semiconductor layer110. In this way, the second electrode150may be electrically connected with the third electrode160, thereby bringing the LED100cinto operation.

FIG. 4is a schematic cross-sectional view of an LED according to the fourth exemplary embodiment. Referring toFIG. 4, an LED100dof the fourth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that in the LED100d, the fourth electrode170is located in the first semiconductor layer110and connected to the second electrode150and the third electrode160.

FIG. 5Ais a schematic cross-sectional view of an LED according to the fifth exemplary embodiment.FIG. 5Bis a schematic top view of the LED inFIG. 5A, whereinFIG. 5Ais a schematic cross-sectional view along a section line A-A′ inFIG. 5B. Referring toFIG. 5AandFIG. 5Btogether, an LED100eof the fifth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that the LED100efurther includes an undoped semiconductor layer180. The undoped semiconductor layer180is located on an edge of the first surface112and surrounds the first surface112, as shown inFIG. 5B. In the present exemplary embodiment, the second electrode150is disposed on the undoped semiconductor layer180and the first surface112of the first semiconductor layer110.

Referring toFIG. 5AandFIG. 1Atogether, in the present exemplary embodiment, before the formation of the first semiconductor material layer210, the undoped semiconductor layer180is first formed on the carrier substrate200, and then the first semiconductor material layer210, the light emitting material layer220and the second semiconductor material layer230are formed in sequence. The undoped semiconductor layer180serves as a buffer layer to reduce the difference in characteristics between the carrier substrate200and the first semiconductor material layer210, which is favorable for the formation of the first semiconductor material layer210on the carrier substrate200. Then, the steps as shown inFIG. 1BandFIG. 1Care performed. Next, referring toFIG. 5AandFIG. 1Dtogether, the carrier substrate200is removed to expose the undoped semiconductor layer180. Next, referring toFIG. 5AandFIG. 1Etogether, a patterning process is performed to remove a portion of the undoped semiconductor layer180, wherein the portion of the undoped semiconductor layer180on the edge of the first surface112is retained, thus preventing the fourth electrode170from damage during the partial removal of the undoped semiconductor layer180. After that, the second electrode150is formed, so as to form a pattern as shown inFIG. 5B. A material of the undoped semiconductor layer180is a semiconductor material layer that is not doped, including, e.g., gallium nitride or other suitable semiconductor materials.

FIG. 6is a schematic cross-sectional view of an LED according to the sixth exemplary embodiment. Referring toFIG. 6, an LED100fof the sixth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that the LED100ffurther includes a protection layer190alocated at the opening H, wherein the protection layer190ais located on a sidewall of the opening H and on a portion of the second semiconductor layer130around the opening H. A material of the protection layer190ais, e.g., an insulating material. The protection layer190amay further reduce the possibility of a contact between the third electrode160and the light emitting layer120. Specifically, when the semiconductor stacked structure100is bonded onto the substrate300, the third electrode160may be squeezed to deform during the bonding, resulting in the contact between the third electrode160and the light emitting layer120. The arrangement of the protection layer190amay avoid occurrence of the above-mentioned contact.

FIG. 7is a schematic cross-sectional view of an LED according to the seventh exemplary embodiment. Referring toFIG. 7, an LED100gof the seventh exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that while the LED100ahas the third electrode160and the fourth electrode170disposed on only one side of the semiconductor stacked structure100, the LED100ghas third electrodes160as well as fourth electrodes170disposed respectively on two opposite sides of the semiconductor stacked structure100.

FIG. 8is a schematic cross-sectional view of an LED according to the eighth exemplary embodiment. Referring toFIG. 8, an LED100hof the eighth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that the LED100hfurther includes at least one island structure102. The island structure102is located on the third surface116, and the island structure102consists of, e.g., the first semiconductor layer110, the light emitting layer120and the second semiconductor layer130. The present exemplary embodiment provides an example where the LED100hincludes two island structures102. However, the disclosure is not limited hereto. In other exemplary embodiments, only one or two island structures102may be disposed, or three or more island structures102may be disposed.

Referring toFIG. 8andFIG. 1Btogether, the island structures102are formed in a manner of, e.g., being formed concurrently with the opening H. The island structures102are located in the opening H, and the island structures102have top surfaces coplanar with a top surface of the second semiconductor layer130. Next, referring toFIG. 8andFIG. 1Ctogether, during the fabrication of the third electrode160, the third electrode160is filled between the adjacent island structures102. It is worth mentioning that, since the opening H of the present exemplary embodiment has the island structures102therein, and it is easier for a top surface of the formed third electrode160to be coplanar with a top surface of the first electrode140. In this way, in a follow-on flip-chip bonding process, it is ensured that the third electrode160and the first electrode140are smoothly bonded to the conductive layer on the substrate300, and the chance of failure is reduced.

FIG. 9is a schematic cross-sectional view of an LED according to the ninth exemplary embodiment. Referring toFIG. 9, an LED100iof the ninth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that the LED100ifurther includes a protection layer190blocated at the opening H, and that a first electrode140aincludes a mirror layer142, a barrier layer144and a bonding layer146.

The mirror layer142is located on the second semiconductor layer130, the barrier layer144covers the mirror layer142, and the bonding layer146is located on the barrier layer144, wherein the mirror layer142, the barrier layer144and the bonding layer146are all conductive materials. The mirror layer142is, e.g., a conductive material having high reflectivity, such as silver. When light emitted from the light emitting layer120is transmitted to the mirror layer142, the mirror layer142reflects the light to cause the light to exit from the first surface112of the first semiconductor layer110. In this way, luminous efficacy of the LED100iis enhanced. The barrier layer144mainly serves to reduce atomic aggregation or migration from occurring in the mirror layer142under high temperatures, so as to reduce the chance that the mirror layer142decreases in reflectivity, and to further extend the time during which the mirror layer142maintains high reflectivity. The bonding layer146is configured to be connected to the first conductive layer310.

In the present exemplary embodiment, the protection layer190bis, e.g., filled into the opening H before the formation of the third electrode160. Moreover, the protection layer190bfurther covers the sidewall of the opening H, the second semiconductor layer130around the opening H and a portion of the barrier layer144. Next, the third electrode160is formed. Thus, a portion of the third electrode160is located on the protection layer190b. A material of the protection layer190bis, e.g., an insulating material. The protection layer190bfurther reduces the possibility of the contact between the third electrode160and the light emitting layer120. Specifically, when the semiconductor stacked structure100is bonded onto the substrate300, the third electrode160may be squeezed to deform during the bonding, resulting in the contact between the third electrode160and the light emitting layer120. The arrangement of the protection layer190bmay avoid the occurrence of the above-mentioned contact.

FIG. 10is a schematic cross-sectional view of an LED according to the tenth exemplary embodiment. Referring toFIG. 10, an LED100jof the tenth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that the LED100jfurther includes a protection layer190c. The protection layer190cis disposed between the first semiconductor layer110and the fourth electrode170, extending to cover the third surface116of the opening H, so as to prevent the third electrode160and the fourth electrode170from directly contacting the first semiconductor layer110. In this way, a direct transmission of a current from the third electrode160and the fourth electrode170into the first semiconductor layer110is prevented, thereby reducing the chance of current crowding.

FIG. 11is a schematic cross-sectional view of an LED according to the eleventh exemplary embodiment. Referring toFIG. 11, an LED100kof the eleventh exemplary embodiment has a structure similar to that of the LED100dof the fourth exemplary embodiment. A difference between them lies in that the LED100kfurther includes a protection layer190d. The protection layer190dis disposed between the first semiconductor layer110and the fourth electrode170, extending to cover the third surface116of the opening H, so as to prevent the third electrode160and the fourth electrode170from directly contacting the first semiconductor layer110. In this way, the direct transmission of a current from the third electrode160and the fourth electrode170into the first semiconductor layer110is prevented, thereby reducing the chance of current crowding.

FIG. 12Ais a schematic cross-sectional view of an LED according to the twelfth exemplary embodiment.FIG. 12Bis a schematic bottom view of an LED100linFIG. 12A, wherein the substrate300, the first conductive layer310and the second conductive layer320are omitted fromFIG. 12B. Referring toFIG. 12AandFIG. 12B, the LED100lof the twelfth exemplary embodiment has a structure similar to that of the LED100fof the sixth exemplary embodiment. A difference between them lies in that the LED100lfurther includes a ring-shaped electrode160a. Specifically, the opening H of the present exemplary embodiment is located on the edge of the second surface114, and the opening H surrounds the light emitting layer120. The ring-shaped electrode160ais disposed on the third surface116of the opening H, and thus the ring-shaped electrode160ais, e.g., disposed surrounding the light emitting layer120. The ring-shaped electrode160ais electrically connected to the third electrode160, thus further reducing the chance of current crowding.

FIG. 13Ais a schematic cross-sectional view of an LED according to the thirteenth exemplary embodiment.FIG. 13Bis a schematic top view of an LED100minFIG. 13A, wherein the substrate300is omitted fromFIG. 13B, andFIG. 13Ais a schematic cross-sectional view along a section line B-B′ inFIG. 13B.FIG. 13Cis a schematic bottom view of the LED100minFIG. 13A, wherein the substrate300, the first conductive layer310and the second conductive layer320are omitted fromFIG. 13C. Referring toFIG. 13A,FIG. 13BandFIG. 13C, the LED100mof the thirteenth exemplary embodiment has a structure similar to that of the LED100eof the fifth exemplary embodiment. A difference between them lies in that a second electrode of the LED100mis, e.g., a plurality of first sub-electrodes152, and a third electrode is, e.g., a plurality of second sub-electrodes162. Each of the second sub-electrodes162is connected to the first sub-electrode152corresponding thereto and the second conductive layer320. The present exemplary embodiment includes four first sub-electrodes152disposed at, e.g., four corners on the first surface112. Moreover, the second sub-electrodes162are disposed corresponding to the first sub-electrodes152. In this way, a current is transmitted to the first sub-electrodes152through the second sub-electrodes162at the four corners, thereby reducing the chance of current crowding.

In a general LED, during the LLO process for removing the carrier substrate200, rupture easily occurs at corners of the first semiconductor layer110. Therefore in the present exemplary embodiment, when the second sub-electrodes162are disposed at the corners, due to support of the second sub-electrodes162, the chance of rupture of the first semiconductor layer110is reduced. In this way, manufacturing yield of the LED100mis increased. The present exemplary embodiment provides an example where the LED100mis in a square shape and the LED100mincludes four first sub-electrodes152and four second sub-electrodes162. However, the disclosure is not limited hereto. Depending on their needs, persons of ordinary skill in the art may design LEDs of different shapes, and arrange a plurality of first sub-electrodes and second sub-electrodes at corresponding edges or corners, and the above designs all fall within the scope of the disclosure for which protection is sought.

FIG. 14Ais a schematic cross-sectional view of an LED according to the fourteenth exemplary embodiment.FIG. 14Bis a schematic top view of an LED100ninFIG. 14A, wherein the substrate300and the protection layer190bare omitted fromFIG. 14B, andFIG. 14Ais a schematic cross-sectional view along a section line C-C′ inFIG. 14B.FIG. 14Cis a schematic bottom view of the LED100ninFIG. 14A, wherein the substrate300, the first conductive layer310and the second conductive layer320are omitted fromFIG. 14C. Referring toFIG. 14A,FIG. 14BandFIG. 14C, the LED100nof the fourteenth exemplary embodiment has a structure similar to that of the LED100eof the fifth exemplary embodiment. A difference between them lies in that the second region110bof the present exemplary embodiment is not located on the edge of the second surface114. More specifically, the second region110bof the present exemplary embodiment is surrounded by the first region110a, and the first semiconductor layer110of the present exemplary embodiment includes two second regions110b. The third electrode160is located on the third surface116of the opening H of the second region110b. Moreover, the third electrode160is electrically connected to the second electrode150through the fourth electrode in the first semiconductor layer110.

In the present exemplary embodiment, the third electrodes160in different second regions110bare connected together. In addition, in the present exemplary embodiment, the protection layer190bis disposed to reduce the possibility of the contact between the third electrode160and the light emitting layer120. Of course, the number of the second regions110bis not limited in the disclosure, and persons of ordinary skill in the art may set by themselves the number of contact positions between the third electrode160and the second electrode150, depending on their needs.

FIG. 15Ais a schematic cross-sectional view of an LED according to the fifteenth exemplary embodiment.FIG. 15Bis a schematic top view of an LED100oinFIG. 15A, wherein the substrate300is omitted fromFIG. 15B, andFIG. 15Ais a schematic cross-sectional view along a section line D-D′ inFIG. 15B.FIG. 15Cis a schematic bottom view of the LED100oinFIG. 15A, wherein the substrate300, the first conductive layer310and the second conductive layer320are omitted fromFIG. 15C. Referring toFIG. 15A,FIG. 15BandFIG. 15C, the LED100oof the fifteenth exemplary embodiment has a structure similar to that of the LED100nof the fourteenth exemplary embodiment. A difference between them lies in that the first semiconductor layer110of the present exemplary embodiment includes one second region110b, and the second region110bis located at, e.g., the center of the first semiconductor layer110. In addition, the protection layer190ais located between the third electrode160and the light emitting layer120, and there is a gap between the protection layer190aand the third electrode160.

FIG. 16is a schematic cross-sectional view of an LED according to the sixteenth exemplary embodiment. Referring toFIG. 16, an LED100pof the sixteenth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that in the LED100pof the present exemplary embodiment, the first surface112of the first semiconductor layer110has a roughened structure V. The arrangement of the roughened structure V effectively enhances light emitting efficiency of the LED100p.

FIG. 17is a schematic cross-sectional view of an LED according to the seventeenth exemplary embodiment. Referring toFIG. 17, an LED100qof the seventeenth exemplary embodiment has a structure similar to that of the LED100aof the first exemplary embodiment. A difference between them lies in that in the LED100qof the present exemplary embodiment, the first surface112of the first semiconductor layer110has a photonic crystal P. The arrangement of the photonic crystal P effectively enhances light emitting directivity of the LED100q. Specifically, the photonic crystal P further decreases a light emitting angle of the LED100q. Thus, a higher light utilization rate is achieved as compared to a conventional face-up LED.

FIG. 18Ais a schematic cross-sectional view of an LED according to the eighteenth exemplary embodiment.FIG. 18Bis a schematic top view of the LED inFIG. 18A, wherein the substrate300and the protection layer190bare omitted fromFIG. 18B, andFIG. 18Ais a schematic cross-sectional view along a section line E-E′ inFIG. 18B.FIG. 18Cis a schematic bottom view of the LED inFIG. 18A, wherein the substrate300, the first conductive layer310and the second conductive layer320are omitted fromFIG. 18C. Referring toFIG. 18A,FIG. 18BandFIG. 18C, an LED100rof the eighteenth exemplary embodiment has a structure similar to that of the LED100eof the fifth exemplary embodiment. A difference between them lies in that a connected part between the second electrode150and the fourth electrode170of the present exemplary embodiment is in the first semiconductor layer110.

Specifically, during the fabrication, the third electrode160and the fourth electrode170are, e.g., formed in an opening (not illustrated) in the first semiconductor layer110, and do not contact the undoped semiconductor layer180. Accordingly, when the carrier substrate200is removed to be detached from the undoped semiconductor layer180, the fourth electrode170is unlikely to fall off with the lift-off of the carrier substrate200. Then, a dry etching process is performed to remove a portion of the undoped semiconductor layer180and a portion of the first semiconductor layer110(not illustrated), thereby exposing the fourth electrode170located in the first semiconductor layer110. Next, the roughened structure V is formed on the first surface112of the first semiconductor layer110, so as to enhance light emitting efficiency of the LED100r. Next, the second electrode150is formed on the first surface112of the first semiconductor layer110. In addition, the third electrode160of the present exemplary embodiment has a larger surface area (as shown inFIG. 18C), which is thus favorable for follow-on processes.

As to the embodiments illustrated inFIGS. 16-18, a roughened structure V (or a photonic crystal P) can be formed on the first surface112of the first semiconductor layer110to enhance light emitting efficiency of the LEDs100p,110qor100r. However, the disclosure is not limited thereto, wherein the roughened structure V or the photonic crystal P can be applied to any appropriate LED structures. For example, a light extraction layer with a roughened structure can be formed on the doped semiconductor layer. In other words, an LED having a light extraction layer with a roughened structure over a doped semiconductor layer is provided in the disclosure, and some exemplary embodiments are further illustrated hereinafter.

FIG. 21Ais a schematic top view of a semiconductor stacked structure of an LED according to further an exemplary embodiment of the disclosure.FIG. 21Bis a schematic cross-sectional view of the LED inFIG. 21Aalong line A-A′. As shown inFIG. 21AandFIG. 21B, a light emitting diode100scomprises a semiconductor stacked structure100, a substrate300, a first electrode140, a second electrode150, a third electrode160, and a conductive via165. The material of the semiconductor stacked structure100may comprise GaN or AlN, for example.

In the present embodiment, the semiconductor stacked structure100comprises a first (e.g. N-type) semiconductor layer110, a second (e.g. P-type) semiconductor layer130, and a light emitting layer120. The second semiconductor layer130is stacked with the first semiconductor layer110. The light emitting layer120is disposed between the first semiconductor layer110and the second semiconductor layer130.

The substrate300carries the semiconductor stacked structure100and faces the second semiconductor layer130. The substrate300has a first conductive layer310and a second conductive layer320. The first electrode140is disposed between the second semiconductor layer130and the first conductive layer310and electrically connected to the second semiconductor layer130and the first conductive layer310. The second electrode150is disposed on the first semiconductor layer110. The third electrode160is disposed between the semiconductor stacked structure100and the second conductive layer320, wherein the third electrode160is electrically connected to the second conductive layer320. The conductive via165passes through the semiconductor stacked structure100and electrically connected between the second electrode150and the third electrode160.

As shown inFIG. 21AandFIG. 21B, an outer light extraction layer500is disposed on the first semiconductor layer110and forms a roughened structure502. Herein, the outer light extraction layer500may be made of a transparent insulation material, such as silicone. Alternatively, the outer light extraction layer500may be made of a transparent conductive material and electrically connected to the first semiconductor layer110, such as aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), indium zinc oxide (IZO), indium tin oxide (ITO), grapheme, etc.

In the case that the outer light extraction layer500is made of a transparent conductive material and electrically connected to the second electrode150, the outer light extraction layer500and the second electrode150together serve as an electrode of large area, and thus the current spreading on the first semiconductor layer110can be improved. In addition, the outer light extraction layer500may be a complete layer covering the entire top surface of the first semiconductor layer110. Or, the outer light extraction layer500may be a patterned layer, such as a meshed layer. The profile of the outer light extraction layer500is not limited in the disclosure and may be varied due to different practical requirements.

Furthermore, a light refractive index of the outer light extraction layer500is less than a light refractive index of the first semiconductor layer110in the current embodiment. For example, a light refractive index of silicone is about 1.4, a light refractive index of ITO is about 1.9, and a light refractive index of gallium nitride is about 2.4.

In an LED structure without the outer light extraction layer500, the light emitted from the light emitting layer120may pass through the first semiconductor layer110and transmitted to the outside. However, since the air of the outside has a much lower light refractive index (about 1) than the first semiconductor layer110, a large portion of the light may be reflected due to total internal reflection (TIR) at the junction between the first semiconductor layer110and the outside, and may be trapped in the semiconductor stacked structure100.

Instead, the present embodiment provides the outer light extraction layer500between the first semiconductor layer110and the outside. The light refractive index of the outer light extraction layer500is ranged between the light refractive index of the air and the light refractive index of the first semiconductor layer110. Furthermore, the roughened structure502is formed on the outer light extraction layer500to eliminate the total internal reflection (TIR) at the junction between the outer light extraction layer500and the outside. Therefore, most of the light emitted from the light emitting layer120can effectively pass through the first semiconductor layer110, the outer light extraction layer500, the roughened structure502, and then is transmitted to the outside.

Furthermore, the roughened structure502may be varied in other embodiments of the disclosure.FIG. 22andFIG. 23are partial enlarged view of the semiconductor stacked structures100of LEDs according to different exemplary embodiments of the disclosure. Referring toFIG. 22, the roughened structure502comprises a plurality of pyramids504; and referring toFIG. 23, the roughened structure502comprises a plurality of micro lenses506.

In addition to the outer light extraction layer500, one or more inner light extraction layers can be formed between the outer light extraction layer500and the first semiconductor layer110to improve the light extraction effect.

FIG. 24andFIG. 25are partial enlarged view of the semiconductor stacked structures100of LEDs according to different exemplary embodiments of the disclosure.

Referring toFIG. 24, an inner light extraction layer510is disposed between the outer light extraction layer500and the first semiconductor layer110. And, a light refractive index of the outer light extraction layer500is less than a light refractive index of the inner light extraction layer510. Herein, the material of the inner light extraction layer510can be selected from those of the outer light extraction layer500mentioned above. For example, the inner light extraction layer510can be made of s transparent conductive material, such as ITO.

Referring toFIG. 25, an inner light extraction layer512and an inner light extraction layer514are disposed between the outer light extraction layer500and the first semiconductor layer110, wherein the inner light extraction layer512is closer to the outer light extraction layer500than the inner light extraction layer514is. A light refractive index of the outer light extraction layer500is less than a light refractive index of the inner light extraction layer512, and a light refractive index of the inner light extraction layer512is less than a light refractive index of the inner light extraction layer514. Herein, the material of the inner light extraction layers512and514can be selected from those of the outer light extraction layer500mentioned above.

However, the number of the inner light extraction layers may be more than two in other exemplary embodiments of the disclosure. In those cases, a light refractive index of any one of the inner light extraction layers is less than a light refractive index of another one of the inner light extraction layers when a distance between the any one of the inner light extraction layers and the outer light extraction layer is less than a distance between the another one of the inner light extraction layers and the outer light extraction layer.

FIG. 26Ais a schematic top view of a semiconductor stacked structure of an LED according to further another exemplary embodiment of the disclosure.FIG. 26Bis a schematic cross-sectional view of the LED inFIG. 26Aalong line B-B′. As shown inFIG. 26AandFIG. 26B, the light emitting diode100tof the present embodiment is similar to the light emitting diode100sofFIG. 21AandFIG. 21B, except that a first conductive via165aand a second conductive via165bare respectively provided nearby two opposite sides of the semiconductor stacked structure100. In addition, the outer light extraction layer500is electrically connected to the third electrode160through both of the first conductive via165a, the second conductive via165band interconnections165c(or circuits). An insulation layer195is formed to electrically isolate the first conductive via165a, the second conductive via165band the interconnections165cfrom the light emitting layer120and the second semiconductor layer130. The first electrode140and the third electrode160are located at two opposite sides of the bottom of the semiconductor stacked structure100, and are respectively bonded to the first conductive layer310and the second conductive layer320. It is noted that the portion113of the semiconductor stacked structure100which is not bonded to the first conductive layer310and the second conductive layer320is prone to be cracked due to the thin thickness of the semiconductor stacked structure100; however, the outer light extraction layer500on the first semiconductor layer110helps to increase the strength of the semiconductor stacked structure100and thereby enhances the reliability of LED and improves the production yields of manufacturing process.

The LEDs100s-100tas shown in the above embodiment are lateral type LEDs wherein the two electrodes are disposed at the same side of an LED, and the LEDs100s-100tare suitable for being bonded to the substrate300by surface mount technique (e.g. flip-chip technique). However, application of the light extraction layers on the first semiconductor layer110is not limited thereto. In other embodiment of the disclosure, the light extraction layers may further be applied to different types of LED, such as a vertical type LED.

FIG. 27is a schematic cross-sectional view of an LED according to further another exemplary embodiment of the disclosure. As shown inFIG. 27, the light emitting diode100ucomprises a semiconductor stacked structure100, a reflective layer530, and an outer light extraction layer500. The semiconductor stacked structure100comprises a first semiconductor layer110, a second semiconductor layer130, and a light emitting layer120. The second semiconductor layer130is stacked with the first semiconductor layer110. The light emitting layer120is disposed between the first semiconductor layer110and the second semiconductor layer130. The reflective layer530is disposed on the bottom of the second semiconductor layer130. And, the outer light extraction layer500is disposed on the top of the first semiconductor layer110. The outer light extraction layer500forms a roughened structure502comprising such as comprises a plurality of pyramids504(as shown inFIG. 22) or a plurality of micro lenses506(as shown inFIG. 23). Furthermore, the light refractive index of the outer light extraction layer500is less than a light refractive index of the first semiconductor layer110. Details of the outer light extraction layer500or may be even additional inner light extraction layers510,512,514as shown inFIG. 22andFIG. 23can be referred to the description of the aforementioned exemplary embodiment, and are not repeated hereinafter.

It is worth mentioning that the designs of the aforementioned exemplary embodiments may be combined with one another for designing an LED having good luminous efficacy. For example, the first electrode140aof the ninth exemplary embodiment may be designed to have the same structure as the first electrode140of the first exemplary embodiment. Or, the structure of the first electrode140of the first to eighth exemplary embodiments may be the same as that of the first electrode140aof the ninth exemplary embodiment. Or, the outer light extraction layer500with the roughened structure502thereon or the inner light extraction layers510,512,514can be applied to the LEDs100a-100rof the aforementioned embodiments. Persons of ordinary skill in the art may design a satisfactory LED according to their needs. It is to be noted that the various technical solutions designed as a result of combinations of the aforementioned exemplary embodiments all meet the spirit of the disclosure, and all fall within the scope of the disclosure for which protection is sought.

In summary, in the LED according to the above embodiments, the semiconductor stacked structure is bonded to the conductive layer on the substrate by flip-chip bonding. Thus, problems such as uneven distribution of phosphor in a sealant and failure of the LED due to breakage of a bonding wire are unlikely to occur. Based on the above, the LED according to the disclosure has good device reliability.

In addition, in the LED according to the disclosure, the second surface of the first semiconductor layer has an opening for disposing the third electrode, and there is a gap between the third electrode and the light emitting layer. Therefore, there is no need to dispose an additional insulating layer between the third electrode and the light emitting layer for electrically isolating the third electrode and the light emitting layer from each other.

Furthermore, a light extraction layer with a roughened structure can be formed on the doped semiconductor layer to improve the light emitting efficiency of LED. Furthermore, the strength of the semiconductor stacked structure can be enhanced by the light extraction layer, to improve the reliability of the LED and the production yields of manufacturing process. It is noted that the light extraction layer can be more suitable for formed on a smooth top surface of the first semiconductor layer, especially to those manufactured by a plane sapphire substrate, rather than a pattern sapphire substrate. In some embodiments, the roughness (Ra) of the smooth top surface of the first semiconductor layer is less than 0.1 μm, or further less than 0.01 μm, or even less than 0.2 nm.