Lateral current blocking light-emitting diode and method for manufacturing the same

A lateral current blocking light-emitting diode and a method for manufacturing the same are disclosed. The light-emitting diode comprises an insulating substrate, a semiconductor epitaxial structure and electrodes of different conductivity types. The semiconductor epitaxial structure has at least one trench and comprises a first conductivity type semiconductor layer deposed on a portion of the insulating substrate, in which a bottom of the trench is beneath the first conductivity type semiconductor layer, an active layer located on a portion of the first conductivity type semiconductor layer, and a second conductivity type semiconductor layer deposed on the active layer. A first conductivity type electrode is deposed on the exposed portion of the first conductivity type semiconductor layer, and a second conductivity type electrode is deposed on a portion of the second conductivity type semiconductor layer, in which the trench covers the shortest conductive path between the first conductivity type electrode and the second conductivity type electrode, so as to block the current between the first conductivity type electrode and the second conductivity type electrode from flowing through the shortest conductive path.

RELATED APPLICATIONS

The present application is based on, and claims priority from, Taiwan Application Serial Number 94113734, filed Apr. 28, 2005, the disclosure of which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates to a light-emitting diode and a method of manufacturing the same, and more particularly, to a lateral current blocking light-emitting diode and a method for manufacturing the same, which are especially suitable for the application of high-power light-emitting diodes.

BACKGROUND OF THE INVENTION

In the fabrication of light-emitting diodes, III-nitride-based semiconductors, such as GaN, AlGaN, InGaN and AlInGaN, are common. Usually, epitaxial structures of most of the light-emitting devices made of the III-nitride-based semiconductors are grown on an electrically insulating sapphire substrate, which is different from other light-emitting devices utilizing conductive substrates. The sapphire substrate is an insulator, so an electrode cannot be directly formed on the sapphire substrate. Electrodes have to be formed to contact respectively a p-type semiconductor layer and an n-type semiconductor layer directly, so that the light-emitting devices of the aforementioned type can be completed.

Referring toFIGS. 1(a) and1(b),FIG. 1(a) illustrates a top view of a conventional light-emitting diode chip, andFIG. 1(b) illustrates a cross-sectional view of the light-emitting diode chip along the cross-sectional line B-B′ shown inFIG. 1(a). The conventional light-emitting diode200is mainly composed of a transparent substrate202, an epitaxial structure located on the transparent substrate202and two electrodes, in which the epitaxial structure principally includes a first conductivity type semiconductor layer204, an active layer206and a second conductivity type semiconductor layer208stacked in sequence. The first conductivity type semiconductor layer204is deposed on the transparent substrate202, the active layer206is deposed on a portion of the first conductivity type semiconductor layer204to expose the other portion of the first conductivity type semiconductor layer204, and the second conductivity type semiconductor layer208is deposed on the active layer206. A transparent conductive layer210is provided on a portion of the second conductivity type semiconductor layer208for the improvement of current spreading. A second conductivity type electrode pad212is deposed on the exposed portion of the second conductivity type semiconductor layer208and a portion of the transparent conductive layer210, and a stacked structure composed of a first conductivity type electrode214and a first conductivity type electrode pad216is deposed on a portion of the exposed portion of the first conductivity type semiconductor layer204, such as shown inFIG. 1(b).

With respect to the structure illustrated inFIG. 1(b), when an area of the first conductivity type semiconductor layer204is exposed by removing a portion of the epitaxial structure for deposing the first conductivity type electrode214and the first conductivity type electrode pad216, an etching process is performed and stopped at the first conductivity type semiconductor layer204. The conventional light-emitting diode200cannot spread current because the two electrode structures of the light-emitting diode200are typically on the diagonal line of the light-emitting diode chip, which easily causes excessive current density in a local area. Accordingly, when the operating current is increased, because the current distribution between the first conductivity type electrode pad216and the second conductivity type electrode pad212is not uniform, the region A of the light-emitting diode200shown inFIG. 1(a) is easily damaged or the efficiency of the light-emitting diode200is reduced by the excessive current density.

In order to improve the aforementioned issue of the conventional light-emitting diode structure, a light-emitting diode300such as illustrated inFIG. 2is provided in U.S. Pat. No. 6,307,218 by Lumileds of the United States of America. A first conductivity type electrode304of the light-emitting diode300is deposed on the exposed portion of a first conductivity type semiconductor layer302, a second conductivity type electrode308is deposed on a transparent electrode306, and most of the first conductivity type electrode304and the second conductivity type electrode308are parallel to improve the distribution of current. Although the light-emitting diode300has parallel electrodes, current cannot be uniformly spread at the electrode edges, such as at a region B and a region C.

For example, if the light-emitting diode shown inFIG. 1(b) is a green light LED (having a wavelength of 525 nm) 14 mil long×14 mil wide, the efficiency of the LED is 50 lm/W; if the green LED is 40 mil long×40 mil wide and is designed as the structure shown inFIG. 2, the efficiency of the LED is lowered to 35 lm/W. As the dimensions are decreased, the efficiency of the LED is decreased, as shown inFIG. 3. Therefore, the parallel electrodes cannot enhance the uniformity of current effectively.

Accordingly, because electrodes of a conventional light-emitting diode are usually deposed on the diagonal line of the light-emitting diode chip, and the etching process used to remove a portion of the epitaxial structure is typically stopped at the first conductivity type semiconductor layer, excessive current density in the local area is easily caused. Particularly, when the light-emitting diode is operated at high power, the area within the shortest path between electrodes is easily damaged by the excessively concentrated current, and the efficiency of the light-emitting diode is decreased with increasing operating power. Accordingly, it is desirable to provide a light-emitting diode without the above shortcomings.

SUMMARY OF THE INVENTION

Therefore, one objective of the present invention is to provide a lateral current blocking light-emitting diode, which includes at least one trench to form electrical insulation, so that the conductive path of injecting current can be restricted for spreading current. Accordingly, the present light-emitting diode has an advantage of highly uniform current, which greatly enhances the efficiency of the light-emitting diode.

Another objective of the present invention is to provide a lateral current blocking light-emitting diode, in which one or more trenches are formed between electrodes of two different conductivity types to adjust one or more conductive paths of injecting current, such that the current between the electrodes can be uniformly distributed, and the illuminant efficiency decay of the light-emitting diode caused by the increasing operating current can be effectively reduced to further enhance the resistance to static electricity and increase reliability.

Still another objective of the present invention is to provide a lateral current blocking light-emitting diode, in which one or more trenches formed in the device can provide the opportunity for the photons created by an active layer of the device to escape from the sidewalls of the trenches, such that the light extraction of the light-emitting diode is greatly enhanced to further increase the illuminant efficiency.

Yet another objective of the present invention is to provide a method for manufacturing a lateral current blocking light-emitting diode, which can effectively improve the illuminant efficiency decay caused by high operating power, so that the method is not only suitable for the fabrication of general light-emitting diodes, but also very suitable for the fabrication of light-emitting diodes with high operating power.

According to the aforementioned objectives, the present invention provides a lateral current blocking light-emitting diode comprising an insulating substrate, a semiconductor epitaxial structure including at least one trench, and comprising a first conductivity type semiconductor layer deposed on a portion of the insulating substrate, wherein a bottom of the trench is beneath the first conductivity type semiconductor layer to form an electrically insulating area in the semiconductor epitaxial structure, an active layer deposed on a portion of the first conductivity type semiconductor layer to expose the other portion of the first conductivity type semiconductor layer, a second conductivity type semiconductor layer deposed on the active layer, a first conductivity type electrode deposed on the exposed portion of the first conductivity type semiconductor layer, and a second conductivity type electrode deposed on a portion of the second conductivity type semiconductor layer, wherein the trench is located between the first conductivity type electrode and the second conductivity type electrode.

According to the aforementioned objectives, the present invention further provides a method for manufacturing a lateral current blocking light-emitting diode, comprising providing an insulating substrate, forming a semiconductor epitaxial structure on the insulating substrate, wherein the semiconductor epitaxial structure comprises a first conductivity type semiconductor layer, an active layer and a second conductivity type semiconductor layer stacked in sequence, removing a portion of the second conductivity type semiconductor layer and a portion of the active layer to expose a portion of the underlying first conductivity type semiconductor layer, forming at least one trench in the semiconductor epitaxial structure, wherein the trench penetrates the second conductivity type semiconductor layer, the active layer and the first conductivity type semiconductor layer, and forming a first conductivity type electrode on the exposed portion of the first conductivity type semiconductor layer and a second conductivity type electrode on a portion of the second conductivity type semiconductor layer, wherein the trench is located between the first conductivity type electrode and the second conductivity type electrode.

According to a preferred embodiment of the present invention, the trench covers the shortest distance between the first conductivity type electrode and the second conductivity type electrode to block current between the first conductivity type electrode and the second conductivity type electrode from flowing through the shortest electrically conductible path.

The shortest electrically conductible paths between the first conductivity type electrode and the second conductivity type electrode can be effectively blocked by forming at least one trench penetrating the light-emitting diode, so that the current density with uniform distribution in the semiconductor epitaxial layers can be obtained. Accordingly, when the operating current is increased, the current can uniformly spread at two sides of the current-ejecting conductivity type electrode, which can thereby prevent current from excessively concentrating in the shortest electrically conductible path and consequently degrading the quality of the device and greatly decaying the device efficiency.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses a lateral current blocking light-emitting diode and a method for manufacturing the same, which can greatly enhance the uniformity of current and the light extraction rate to achieve the purpose of increasing the illuminant efficiency of the device. In order to make the illustration of the present invention more explicit and complete, the following description is stated with reference toFIGS. 4(a) through7.

Referring toFIGS. 4(a) to4(d),FIG. 4(a) illustrates a top view of a light-emitting diode in accordance with a first preferred embodiment of the present invention, andFIGS. 4(b) to4(d) respectively illustrate a cross-sectional views of the light-emitting diode along the lines C-C′, D-D′ and E-E′ shown inFIG. 4(a). In the fabrication of a light-emitting diode400, a substrate402is provided, and a first conductivity type semiconductor layer404, an active layer406and a second conductivity semiconductor layer408are formed on the substrate402in sequence by, for example, an epitaxial method, in which the first conductivity type semiconductor layer404, the active layer406and the second conductivity semiconductor layer408comprise a semiconductor epitaxial structure. A material of the substrate402can be an insulating material, such as sapphire or glass. A material of the first conductivity type semiconductor layer404and the second conductivity semiconductor layer408can be, for example, a compound containing AlxInyGa1-x-yN(0≦x≦1; 0≦y≦1; 0≦1−x−y≦1) or a compound containing AltGauIn1-t-uP(0≦t≦1; 0≦u≦1; 0≦1≦t−u≦1). The active layer406can be composed of, for example, a double heterostructure or a quantum well structure. In the other embodiments of the present invention, a buffer layer (not shown) is further formed prior to the formation of the first conductivity type semiconductor layer404for aiding the sequential epitaxial procedure of the semiconductor epitaxial structure. In the present invention, when the first conductivity type is N-type, the second conductivity type is P-type; conversely, when the first conductivity type is P-type, the second conductivity type is N-type.

After the second conductivity type semiconductor layer408is formed, a portion of the second conductivity type semiconductor layer408and a portion of the active layer406are directly removed by, for example, dry etching or wet etching, to expose a portion of the first conductivity type semiconductor layer404, such as shown inFIG. 4(d). The exposed portion of the first conductivity type semiconductor layer404is provided for an electrode fabricated thereon. In the other embodiments of the present invention, the substrate402is not the growth substrate on which the semiconductor epitaxial structure is epitaxially formed, but instead is an insulating substrate adhered to the semiconductor epitaxial structure by, for example, sticking after the epitaxial procedure is completed and the growth substrate is removed by, for example, an etching method or a laser heating method. During the step of exposing the area of the first conductivity type semiconductor layer404, a portion of the first conductivity type semiconductor layer404is usually removed for process reliability concerns. Then, another portion of the second conductivity type semiconductor layer408, the active layer406and the first conductivity type semiconductor layer404are removed by, for example, a dry etching method or a wet etching method, to form one or more trenches420in the semiconductor epitaxial structure and expose the underlying substrate402. That is, the trench420passes through the second conductivity type semiconductor layer408, the active layer406and the first conductivity type semiconductor layer404, and the bottom of the trench420is beneath the first conductivity type semiconductor layer404, such as shown inFIGS. 4(b) and4(c). In the other embodiments of the present invention, when a buffer layer is interposed between the first conductivity type semiconductor layer404and the substrate402, the trench420can expose the buffer layer or the substrate402. The amount and the shapes of the trenches420may be changed and modified according to the locational relation between electrodes of two different conductivity types. The trench420is formed between the electrodes of two different conductivity types, and the area of the trench420at least covers the shortest electrically conductible path between the electrodes of two different conductivity types, so as to block the current flowing between the electrodes of different conductivity types from flowing through the shortest electrically conductible path, such as shown inFIG. 4(a).

Accordingly, one feature of the present invention is that at least one trench420is formed in the semiconductor epitaxial structure of the light-emitting diode400to block the shortest electrically conductible path between the electrodes of different conductivity types, and the bottom of the trench420reaches to the depth beneath the first conductivity type semiconductor layer404, so that the trench420forms an electrically insulating area in the semiconductor epitaxial structure. As a result, current can be effectively blocked by the trench420, and the conductive path of the injecting current can be modified, so as to uniformly distribute current between the electrodes. Accordingly, it can prevent current from excessively concentrating on the shortest electrically conductible path between the electrodes of two different conductivity types, which can thereby enhance the device quality and prolong the device life. In addition, photons created by the active layer406can escape from the sidewall of the trench420, so that the light extraction of the light-emitting diode400can be increased to achieve the effect of enhancing the illuminant efficiency.

After the trench420is formed, an insulating material (not shown) may be filled into the trench420to prevent a short circuit from unexpectedly occurring. The trench420may be filled with the insulating material by, for example, a vacuum deposition method or a coating method. The insulating material may be dielectric or organic material, in which the dielectric can be, for example, silicon nitride (SiNx) or silicon oxide (SiOx). Next, the electrodes can be formed immediately, or a transparent conductive layer410can be firstly formed on the second conductivity type semiconductor layer408by a deposition method to enhance the effect of spreading current. Then, a first conductivity type electrode416is formed on the exposed portion of the first conductivity type semiconductor layer404, and a first conductivity type electrode pad418is formed on a portion of the first conductivity type electrode416, and a second conductivity type electrode412and a second conductivity type electrode pad414are respectively formed on the transparent conductive layer410a portion of the second conductivity type electrode412and a portion of the transparent conductive layer410in sequence by, for example, a thermal evaporation, an e-beam evaporation or an ion sputtering method, such as shown inFIG. 4(b). The materials of the first conductivity type electrode416, the first conductivity type electrode pad418, the second conductivity type electrode412and the second conductivity type electrode pad414are preferably metal. For the time being, the light-emitting diode400is substantially completed.

Referring toFIG. 4(a) again, the first conductivity type electrode416is substantially C-shaped and is principally composed of a vertical portion and two horizontal portions substantially perpendicular to the vertical portion, and the second conductivity type electrode412is interposed between the horizontal portions of the first conductivity type electrode416and is parallel and equidistant to the horizontal portions of the first conductivity type electrode416. The rear ends of the horizontal portions of the first conductivity type electrode416are adjacent to the second conductivity type electrode pad414, and the rear end of the second conductivity type electrode412is adjacent to the first conductivity type electrode pad418, so that the shortest electrically conductible paths between the two electrodes fall in the two regions. Accordingly, one trench420is installed between the first conductivity type electrode pad418and the second conductivity type electrode412and between the second conductivity type electrode pad414and the first conductivity type electrode416, respectively, to block the shortest electrically conductive paths between the two electrodes. Thus, the trench420can prevent the current injecting from the second conductivity type electrode pad414from excessively concentrating in local regions, such as in the shortest electrically conductive paths between the electrodes. By properly designing the shapes and locations of the electrodes and introducing the trenches420, the current injecting into the first conductivity type electrode416can be uniformly transmitted.

FIG. 5illustrates a top view of a light-emitting diode in accordance with a second preferred embodiment of the present invention. The structure of a light-emitting diode500may be approximately the same as that of the aforementioned light-emitting diode400. A first conductivity type electrode510and a first conductivity type electrode pad516are deposed on the exposed portion of a first conductivity type semiconductor layer504, and a second conductivity type electrode514and a second conductivity type electrode pad508are deposed on a transparent conductive layer506. Trenches512penetrate an illuminant epitaxial structure and expose an insulating substrate502underlying the first conductivity type semiconductor layer504. Similar to the light-emitting diode400, the first conductivity type electrode510is substantially C-shaped and is principally composed of a vertical portion and two horizontal portions substantially perpendicular to the vertical portion, and the second conductivity type electrode514is interposed between the horizontal portions of the first conductivity type electrode510, in which the second conductivity type electrode514is parallel and equidistant to the horizontal portions of the first conductivity type electrode510. In the light-emitting diode500, the shortest electrically conductive paths between the electrodes fall in the regions which are between the rear ends of the horizontal portions of the first conductivity type electrode510and the second conductivity type electrode pad508and between the rear end of the second conductivity type electrode514and the first conductivity type electrode pad516. Accordingly, two trenches512are respectively installed between the rear ends of the horizontal portions of the first conductivity type electrode510and the second conductivity type electrode pad508and between the rear end of the second conductivity type electrode514and the first conductivity type electrode pad516, so as to block the shortest electrically conductive paths between the two electrodes. By properly designing the shapes and adjusting the locations of the electrodes and by introducing the trenches512, the injecting current from the second conductivity type electrode pad508to the horizontal portions of the first conductivity type electrode can be uniformly transmitted. As a result, when the injecting current is increased, the current can separately flow at two sides of the second conductivity type electrode514to halve the current and make the current uniformly distributed at the two sides, thereby postponing the formation of a breakdown and avoiding the excessive current concentration in local areas as exhibited by the conventional light-emitting diode.

FIG. 6illustrates a top view of a light-emitting diode in accordance with a third preferred embodiment of the present invention. The structure of a light-emitting diode600may also be approximately the same as that of the aforementioned light-emitting diode400. A first conductivity type electrode610is deposed on the exposed portion of a first conductivity type semiconductor layer604, and a second conductivity type electrode614and a second conductivity type electrode pad608are deposed on a transparent conductive layer606. In the light-emitting diode600, the second conductivity type electrode pad608is deposed at an edge of the light-emitting diode600, and the second conductivity type electrode614is deposed at the central region of the light-emitting diode600, in which the second conductivity type electrode pad608is connected with the second conductivity type electrode614by a connecting portion616. The first conductivity type electrode610includes four parts respectively on four corners of the light-emitting diode600. In order to block the shortest electrically conductive paths between the first conductivity type electrodes610and the second conductivity type electrode structure (which is composed of the second conductivity type electrode pad608, the connecting portion616and the second conductivity type electrode614), a trench612is formed surrounding the second conductivity type electrode pad608and the connecting portion616. In addition, one trench612is further formed between the second conductivity type electrode614and each part of the first conductivity type electrode610, such as shown inFIG. 6. The trenches612penetrate an illuminant epitaxial structure of the light-emitting diode600and expose an insulating substrate602underlying the first conductivity type semiconductor layer604. The shapes and the locations of the trenches612are determined according to the shapes and the locations of the electrodes of the light-emitting diode600, and current between electrodes of different conductivity types can be effectively distributed with the formation of the trenches612.

FIG. 7illustrates a top view of a light-emitting diode in accordance with a fourth preferred embodiment of the present invention. Similarly, the structure of a light-emitting diode700may also be approximately the same as that of the aforementioned light-emitting diode400. A first conductivity type electrode710is deposed on the exposed portion of a first conductivity type semiconductor layer704, and a second conductivity type electrode714and a second conductivity type electrode pad708are deposed on a transparent conductive layer706. A trench712penetrates an illuminant epitaxial structure of the light-emitting diode700and exposes an insulating substrate702underlying the first conductivity type semiconductor layer704. In the light-emitting diode700, the second conductivity type electrode pad708is deposed at one edge, and the second conductivity type electrode714is deposed at the central region, in which the second conductivity type electrode pad708is connected with the second conductivity type electrode714by a connecting portion716. The first conductivity type electrode710is at a portion of the rim region of the light-emitting diode700. Due to the shape of the second conductivity type electrode714being an octagon, the inner sides of the first conductivity type electrode710also are octagonal. In order to block the shortest electrically conductive paths between the first conductivity type electrodes710and the second conductivity type electrode structure (which is composed of the second conductivity type electrode pad708, the connecting portion716and the second conductivity type electrode714), a trench712is formed surrounding the second conductivity type electrode pad708and the connecting portion716. The shape and the location of the trench712are determined according to the shapes and the locations of the electrodes of the light-emitting diode700, and current between electrodes of different conductivity types can be effectively distributed with the formation of the trench712.

In the present invention, the shape of the light-emitting diode chip may be a rectangle, a square or any polygon. The focus of the present invention is to use the design and the formation of the trench to achieve the objective of uniformly distributing current between the extended first conductivity type electrode and the extended second conductivity type electrode. Moreover, the shape of the trench is not limited, but the scope of the trench has to include the shortest electrically conductive path between the first conductivity type electrode and the second conductivity type electrode. In addition, the conductive path of current is restricted by the electrically insulating effect resulting from the trench formed in the light-emitting diode, so that current is spread to obtain a superior uniform effect and further enhance the illuminant efficiency of the light-emitting diode. Accordingly, the present invention is also very well suited to a high power light-emitting diode.

According to the aforementioned description, one advantage of the present invention is that the present lateral current blocking light-emitting diode includes at least one trench having an electrically insulating effect, so that the conductive path of injecting current can be modified for spreading current. Therefore, the present light-emitting diode has an advantage of having highly uniform current, which thereby prolongs the life of the device, greatly reduces the decay of the illuminant efficiency caused by the increasing operating current, enhances the efficiency, increases the resistance to static electricity and improves the reliability of the light-emitting diode.

According to the aforementioned description, another advantage of the present invention is that the formation of one or more trenches can provide the opportunity for the photons created by an active layer to escape from the sidewalls of the trenches, greatly enhancing the illuminant efficiency by increasing the light extraction of the light-emitting diode.

According to the aforementioned description, a further advantage of the present invention is that the decay of the illuminant efficiency caused by the high operating power can be effectively reduced by forming one or more trenches in a light-emitting diode, so that the method is not only suitable for the fabrication of general light-emitting diodes, but also very suitable for the fabrication of light-emitting diodes with high operating power.