Patent Application
20140183590
This application claims priority to Korean Patent Application No. 10-2012-0156369 filed on Dec. 28, 2013, and all the benefits accruing therefrom under 35 U.S.C. §119, the contents of which is incorporated by reference in its entirety.
1. Technical Field
The present invention relates to a semiconductor light emitting device and a method of manufacturing the same. More particularly, the present invention relates to a nitride semiconductor light emitting device which has excellent light scattering capabilities and adhesion, and a method of manufacturing the same.
2. Description of the Related Art
In recent years, gallium nitride (GaN)-based nitride semiconductor light emitting devices have been mainly studied as nitride semiconductor light emitting devices. Such a GaN-based nitride semiconductor light emitting device is used in various applications, including blue and green light emitting diodes (LEDs), high speed and high output devices, such as MESFETs, HEMTs, and the like.
In order to improve optical efficiency, a nitride semiconductor light emitting device is formed with a current blocking layer under an area in which a p-type metal electrode is placed, and a transparent conductive pattern on the current blocking layer. Here, the transparent conductive pattern acts as an electrode of a p-electrode pad and a current spreading layer.
However, in the nitride semiconductor light emitting device having such a structure, the transparent conductive pattern is formed on the current blocking pattern formed of an insulating material. In this case, since the transparent conductive pattern and the p-electrode pad are formed of metallic materials, there is a problem in rapid deterioration in bonding reliability due to insufficient adhesion therebetween.
Korean Patent No. 10-0793337 (issued on Jan. 11, 2008) discloses a nitride semiconductor light emitting device and a method of manufacturing the same.
Therefore, the present invention is aimed at providing a nitride semiconductor light emitting device which can improve long term durability by securing excellent light scattering capabilities while enhancing adhesion of a p-electrode pad, and a method of manufacturing the same.
In accordance with one aspect of the present invention, a nitride semiconductor light emitting device includes an n-type nitride layer; an active layer formed on the n-type nitride layer; a p-type nitride layer formed on the active layer; a current blocking pattern formed on the p-type nitride layer; a transparent conductive pattern formed to cover upper sides of the p-type nitride layer and the current blocking pattern, and having a contact hole through which a portion of the current blocking pattern is exposed; and a p-electrode pad formed on the current blocking pattern and the transparent conductive pattern, and directly connected to the current blocking pattern.
In accordance with another aspect of the present invention, a method of manufacturing a nitride semiconductor light emitting device includes: (a) sequentially forming an n-type nitride layer, an active layer and a p-type nitride layer on a substrate; (b) forming a current blocking pattern on the p-type nitride layer; (c) forming a transparent conductive layer to cover upper sides of the p-type nitride layer and the current blocking pattern, followed by primary patterning a portion of the transparent conductive layer placed at one edge of the substrate; (d) mesa-etching the p-type nitride layer, the active layer and the n-type nitride layer exposed at the one edge of the substrate to expose a portion of the n-type nitride layer; (e) secondary patterning the transparent conductive layer to form a transparent conductive pattern having a contact hole through which a portion of the current blocking pattern is exposed; and (f) forming a p-electrode pad directly connected to the current blocking pattern, and an n-electrode pad on the exposed portion of the n-type nitride layer.
In the light emitting device according to the present invention, the current blocking pattern is formed on the p-type nitride layer, the transparent conductive pattern having a contact hole is formed on the p-type nitride layer and the current blocking pattern to improve light scattering capabilities, and the p-electrode pad is electrically and physically directly connected to the current blocking pattern formed of an insulating material via the transparent conductive pattern having the contact hole to improve adhesion of the p-electrode pad, thereby enhancing long-term reliability.
The above and other aspects, features, and advantages of the invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, in which:
Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
Referring to
The n-type nitride layer 110 is formed on a substrate 10 or on the buffer layer 105. The n-type nitride layer 110 may have a stack structure in which first silicon (Si)-doped AlGaN layers (not shown) and second undoped GaN layers are alternately stacked one above another. Although the n-type nitride layer may be formed by growing a single nitride layer, it is desirable that the n-type nitride layer be formed in the stack structure including the buffer layer 105 and the first and second layers alternately stacked one above another to secure excellent crystallinity without forming cracks.
Here, the substrate 10 may be formed of a material suitable for growth of a single crystal nitride semiconductor. For example, the substrate 10 may be a sapphire substrate. In addition, the substrate 10 may be formed of a material selected from zinc oxide (ZnO), gallium nitride (GaN), silicon (Si), silicon carbide (SiC), aluminum nitride (AlN), and the like. Further, the buffer layer 105 is optionally formed on an upper surface of the substrate 10 to relieve lattice mismatch between the substrate 10 and the n-type nitride layer 110. The buffer layer 105 may be formed of AlN, GaN, and the like.
The active layer 120 is formed on the n-type nitride layer 110. The active layer 120 is formed between the n-type nitride layer 110 and the p-type nitride layer 130, and may have a single quantum well structure, or a multi-quantum well (MQW) structure in which quantum well layers and quantum barrier layers are alternately stacked. Specifically, the active layer 120 may have a multi-quantum well structure which includes quantum barrier layers formed of quaternary nitride layers of AlGaInN and quantum well layers of InGaN. The active layer 120 having such a multi-quantum well structure can suppress spontaneous polarization by stress and deformation.
The p-type nitride layer 130 may have, for example, a stack structure formed by alternately stacking a first p-type layer (not shown) composed of p-type AlGaN doped with Mg and a second p-type layer (not shown) composed of p-type GaN doped with Mg. In addition, the p-type nitride layer 130 may act as a carrier restriction layer like the n-type nitride layer 110.
The current blocking pattern 140 is formed on the p-type nitride layer 130. Such a current blocking pattern 140 is formed at a place corresponding to an area (not shown) in which a p-electrode pad described below will be formed.
The current blocking pattern 140 serves to compensate for optical loss due to photon absorption at a lower surface corresponding to the p-electrode pad 160. Further, the current blocking pattern 140 prevents current crowding near the p-electrode pad 160 due to low conductivity of the p-electrode pad 160 having a lower thickness than the n-type nitride layer 110.
Such a current blocking pattern 140 is preferably formed of at least one selected from SiO2, SiNx, and the like. The current blocking pattern 140 preferably has a thickness of 0.01 μm to 0.50 μm, more preferably 0.1 μm to 0.3 μm. When the thickness of the current blocking pattern 140 is less than 0.01 μm, there can be difficulty in realization of the current blocking function. Conversely, when the thickness of the current blocking pattern 140 exceeds 0.50 μm, there can be increase in manufacturing cost and time without significantly improving current blocking.
The transparent conductive pattern 150 is formed to cover upper sides of the p-type nitride layer 130 and the current blocking pattern 140, and has a contact hole (CH) through which a portion of the current blocking pattern 140 is exposed. Such a transparent conductive pattern 150 is formed for the purpose of increasing a current injection area, and may be formed of a transparent conductive material in order to prevent undesirable influence on brightness. Specifically, the transparent conductive pattern 150 may be formed of at least one selected from among indium tin oxide (ITO), indium zinc oxide (IZO), fluorine-doped tin oxide (SnO2) (FTO), and the like.
The p-electrode pad 160 is formed on the current blocking pattern 140 and the transparent conductive pattern 150, and is directly connected to the current blocking pattern 140. In plan view, the p-electrode pad 160 may have a first area and the current blocking pattern 140 has a second area larger than or equal to the first area. This is because the larger area of the current blocking pattern 140 than that of the p-electrode pad 160 is advantageous in compensation for optical loss due to photon absorption. Namely, it is desirable that the overall area of the p-electrode pad 160 overlap the current blocking pattern 140 in plan view. The larger area of the current blocking pattern 140 than that of the p-electrode pad 160 can improve light scattering characteristics.
Particularly, the p-electrode pad 160 is electrically and physically directly connected to the current blocking pattern 140. In this way, since the p-electrode pad 160 is directly connected to the current blocking pattern 140 via the contact hole (CH) of the transparent conductive pattern 150, the p-electrode pad 160 has a T-shaped cross-section formed by a step near the contact hole (CH). Here, since the p-electrode pad 160 and the transparent conductive pattern 150 are formed of metallic materials, there can be a problem of poor adhesion therebetween. However, in the present invention, the p-electrode pad 160 is electrically and physically directly connected to the current blocking pattern 140 formed of an insulating material, thereby improving adhesion of the p-electrode pad 160.
The n-electrode pad 170 is formed in an exposed area of the n-type nitride layer 110. The p-electrode pad 160 and the n-electrode pad 170 may be formed by at least one selected from among electron beam (E-Beam) deposition, thermal evaporation, sputtering, and the like. The p-electrode pad 160 and the n-electrode pad 170 are formed of the same material using the same mask. The p-electrode pad 160 and the n-electrode pad 170 may be formed of one material selected from among Au, Cr—Au alloys, and the like.
In the nitride semiconductor light emitting device according to the embodiment, the current blocking pattern is formed on the p-type nitride layer and the transparent conductive pattern having the contact hole is formed on the upper sides of the p-type nitride layer and the current blocking pattern to improve optical scattering characteristics. In addition, the p-electrode pad is electrically and physically directly connected to the current blocking pattern 140 formed of an insulating material through the contact hole of the transparent conductive pattern to improve adhesion of the p-electrode pad, thereby enhancing long-term reliability.
Next, a method of fabricating a nitride semiconductor light emitting device according to one embodiment of the invention will be described.
Referring to
Referring to
The n-type nitride layer 110 may have a stack structure in which first silicon (Si)-doped AlGaN layers (not shown) and second undoped GaN layers are alternately stacked one above another. The active layer 120 may have a single quantum well structure, or a multi-quantum well (MQW) structure in which quantum well layers and quantum barrier layers are alternately stacked one above another. In addition, the p-type nitride layer 130 may have, for example, a stack structure formed by alternately stacking a first p-type layer (not shown) composed of p-type AlGaN doped with Mg and a second p-type layer (not shown) composed of p-type GaN doped with Mg.
Although not shown in the drawings, a buffer layer (not shown) may be further formed on the substrate 10 before formation of the n-type nitride layer 110. Here, the buffer layer serves to relieve lattice mismatch between the substrate 10 and the n-type nitride layer 110, and may be formed of AlN, GaN, and the like.
Referring to
Although not shown in the drawings, the current blocking pattern 140 may be formed by depositing at least one selected from among SiO2, SiNx, and the like to a thickness of 0.01 μm to 0.50 μm over an upper surface of the p-type nitride layer 130 to form a current blocking material layer (not shown), followed by photolithography using a first mask (not shown). Although not shown in the drawings, photolithography may be performed by depositing a photoresist material to a certain thickness over the upper sides of the p-type nitride layer 130 and the current blocking pattern 140 to form a photomask (not shown), selectively exposing and developing the photomask, selectively etching the p-type nitride layer 130 and the current blocking pattern 140 using the photomask, and removing the remaining photomask using a stripping liquid.
Here, the current blocking pattern 140 is preferably formed to a thickness of 0.01 μm to 0.50 μm. When the thickness of the current blocking pattern 140 is less than 0.01 μm, there can be difficulty in realization of the current blocking function. Conversely, when the thickness of the current blocking pattern 140 exceeds 0.50 μm, there can be increase in manufacturing cost and time without significantly improving the current blocking effect
Referring to
Next, referring to
Referring to
Referring to
Some of the current blocking pattern 140 is exposed through the contact hole (CH). Preferably, the contact hole (CH) is formed to expose half or more the area of the current blocking pattern 140 therethrough in order to secure a contact area between the current blocking pattern 140 and a p-electrode pad 160 described hereinafter.
Referring to
In plan view, the p-electrode pad 160 may have a first area and the current blocking pattern 140 has a second area larger than or equal to the first area such that the overall area of the p-electrode pad 160 overlaps the current blocking pattern 140. This is because the larger area of the current blocking pattern 140 than that of the p-electrode pad 160 is advantageous in compensation for optical loss due to photon absorption, thereby improving light scattering characteristics.
In the nitride semiconductor light emitting device formed through such a 4-mask process according to the embodiment of the invention, the current blocking pattern is formed on the p-type nitride layer and the transparent conductive pattern having the contact hole is formed on the upper sides of the p-type nitride layer and the current blocking pattern to improve optical scattering characteristics. In addition, the p-electrode pad is electrically and physically directly connected to the current blocking pattern formed of an insulating material through the contact hole of the transparent conductive pattern to improve adhesion of the p-electrode pad, thereby enhancing long-term reliability.
Although the nitride semiconductor light emitting device is described as being formed by sequentially stacking the n-type nitride layer, the active layer, the p-type nitride layer, the current blocking pattern, the transparent conductive pattern, the p-electrode pad and the n-electrode pad in the above embodiments, it should be understood that these embodiments are provided for illustration only and the nitride semiconductor light emitting device according to the present invention may have a structure in which the n-side and the p-side are stacked in reverse sequence.
Although some embodiments have been described herein, it should be understood by those skilled in the art that these embodiments are given by way of illustration only, and that various modifications, variations and alterations can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be limited only by the accompanying claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2012-0156369 | Dec 2012 | KR | national |
