This application claims priority to Taiwan Application Serial Number 101127480, filed Jul. 30, 2012, which is herein incorporated by reference.
1. Technical Field
Embodiments of the present invention relate to a light emitting diode. More particularly, embodiments of the present invention relate to the light emitting diode with undercut.
2. Description of Related Art
Because of having advantages such as long service lifetime, compact size and low power consumption, a light emitting diode (LED) is widely used in various applications of light sources.
A common LED includes an epitaxial stack structure disposed on a substrate. The expitaxial stack structure includes an N-type semiconductor layer, a Multiple Quantum Wells (MQW) and a P-type semiconductor layer stacked sequentially. When the N-type semiconductor layer and the P-type semiconductor layer are applied with a voltage, electrons and electronic holes are driven to be combined in the MQW to emit light. A P-type electrode is disposed on the P-type semiconductor layer. Part of the p-type semiconductor layer and part of the MQW are etched to expose part of the N-type semiconductor layer, so as to dispose an N-type electrode.
The MQW and the P-type semiconductor layer positioned higher than the exposed N-type semiconductor layer are generally called a MESA structure. The lateral wall of the MESA structure vertically stands on the top surface of the N-type semiconductor layer, which may confine lights in the MQW and reduce the illumination efficiency.
In order to improve the illumination efficiency, some manufacturers proposed optical microstructures on the top surface of the MESA structure; nevertheless, these optical microstructures deteriorate the flatness of the P-type semiconductor layer.
A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below.
A light emitting diode (LED) with undercut is provided, and it can achieve high illumination efficiency without reducing the flatness of the surface of the semiconductor layer. In accordance with one embodiment of the present invention, a LED with undercut includes a first semiconductor layer, an illumination layer, a second semiconductor layer, a first electrode and a second electrode. The first semiconductor layer includes a first area and a second area. A side of the first area includes a first slanted wall, and the first area includes a first top surface. A first acute angle is included between the first slanted wall and the first top surface. The illuminating layer is formed on the second area of the first semiconductor layer. The second semiconductor layer is formed on the illuminating layer. The first electrode and the second electrode are respectively formed on the first top surface and the second semiconductor layer. Part of the first semiconductor layer on the second area, the illuminating layer and the second semiconductor layer on the part of the first semiconductor layer form a MESA structure. The MESA structure includes a second slanted wall adjacent to the first area. A second acute angle is included between the second slanted wall and the top surface of the first area.
In accordance with another embodiment of the present invention, a method for manufacturing a light emitting diode with undercut includes steps of: providing a substrate; forming a semiconductor epitaxial structure, wherein the semiconductor epitaxial structure including a buffer layer, a first semiconductor layer stacked on the buffer layer, an illumination layer stacked on the first semiconductor layer and a second semiconductor layer stacked on the illumination layer; forming a first hard mask on a portion of the semiconductor epitaxial structure; applying a first etching step to etch another portion of the semiconductor epitaxial structure not covered by the first hard mask to the first semiconductor layer, so that a part of the first semiconductor layer is exposed as a first area and the unexposed part of the first semiconductor layer is a second area; wherein the illumination layer, the second semiconductor layer and partial of the first semiconductor layer positioned on the second area form a MESA structure on the second area, wherein the MESA structure includes a second slanted wall, and a second acute angle is included between a first top surface of the first area and the second slanted wall; forming a second hard mask covering the MESA structure and partial of the first area; employing a second etching step to etch an area not covered by the second hard mask and forming a first slanted wall, a third slanted wall and a fourth slanted wall respectively on the sides of the first semiconductor layer, the buffer layer and the substrate, wherein a first acute angle is included between the first slanted wall and the first top surface, and the first slanted wall, the third slanted wall and the fourth slanted wall are coplanar.
It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.
The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:
Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
Because the second slanted wall 410 obliquely stands on the first semiconductor layer 100, when the light generated from the illumination layer 200 propagates to the second slanted wall 410, it is more likely to be reflected toward the second semiconductor layer 300 by the second slanted wall 410, thereby improving the illumination efficiency. Further, the first slanted wall 114 can also assist to reflect the light upwards when the light propagates to the first slanted wall 114, thereby improving the illumination efficiency.
Specifically, the third slanted wall 610 of the buffer layer 600 is adjacent to the first slanted wall 114, and the third slanted wall 610 and the first slanted wall 114 are on the same plane. In other words, the angle between the third slanted wall 610 and the first slanted wall 114 is about 180 degrees. Still in other words, the slanted angle of the third slanted wall 610 is equal to the slanted angle of the first slanted wall 114. Therefore, the third slanted wall 610 can assist to reflect the light when the light propagates to the third slanted wall 610, thereby improving the illumination efficiency.
Specifically, the substrate 700 is positioned beneath the bottom surface 620 of the buffer layer 600, and the fourth slanted wall 710 is adjacent to the third slanted wall 610 of the buffer layer 600. The fourth slanted wall 710 and the third slanted wall 610 are on the same plane, namely, the slanted angle of the fourth slanted wall 710 is equal to the slanted angle of the third slanted wall 610. Therefore, the fourth slanted wall 710 can assist to reflect the light when the light propagates to the fourth slanted wall 710, thereby improving the illumination efficiency.
Referring back to
In some embodiments, by the slope shape of the second slanted wall 410, the cross-sectional area of the MESA structure 400 gradually increases along the direction from the first semiconductor layer 100 to the second semiconductor layer 300. In other words, the projections of the illumination layer 200 and the second semiconductor layer 300 that are projected to the first semiconductor layer 100 cover part of the first area 110.
In some embodiments, by the slope shape of the first slanted wall 114, the cross-sectional area of the first semiconductor layer 100 gradually increases along the direction from the first semiconductor layer 100 to the second semiconductor layer 300.
In some embodiments, the first acute angle 116 ranges from about 30 degrees to about 89 degrees. In some embodiments, the second acute angle 420 ranges from about 30 degrees to about 89 degrees.
In some embodiments, the first semiconductor layer 100 is an N-type semiconductor layer, and the first electrode 510 is an N electrode. The second semiconductor layer 300 is a P-type semiconductor layer, and the second electrode 520 is a P electrode. For example, the first semiconductor layer 100 is formed by a nitride semiconductor doped with N-type impurity, such as n-GaN, which is formed by doping the group 4A elements, such as Silicon, in the pure GaN. The second semiconductor layer 300 is a nitride semiconductor doped with P-type impurity, which is formed by doping the group 2A elements, such as Magnesium, in the pure GaN.
In some embodiments, the first semiconductor layer 100 is a P-type semiconductor layer, and the first electrode 510 is a P electrode. The second semiconductor layer 300 is an N-type semiconductor layer, and the second electrode 520 is an N electrode. For example, the first semiconductor layer 100 is a nitride semiconductor doped with P-type impurity, which is formed by doping the group 2A elements, such as Magnesium, in the pure GaN. The second semiconductor layer 300 is formed by a nitride semiconductor doped with N-type impurity, such as n-GaN, which is formed by doping the group 4A elements, such as Silicon, in the pure GaN.
In some embodiments, the illumination layer 200 includes a plurality of quantum wells to assist the electrons and the electronic holes provided by the first semiconductor layer 100 and the second semiconductor layer 300 to combine therein.
In some embodiments, the buffer layer 600 may include, but is not limited to include, a nitride semiconductor without doping impurity, such as U-GaN.
In some embodiments, the substrate 700 may be, but is not limited to be, a sapphire substrate.
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Specifically, the first etching step in
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In some embodiments, another step can be further included, and in this step, the first electrode 510 and the second electrode 520 (See
In some embodiments, another step can be further included, and in this step, the substrate 700 can be removed, so as to form the structure similar to which is shown in
In some embodiments, another step can be further included, and in this step, the buffer layer 600 and the substrate 700 can be removed, so as to form the structure similar to which is shown in
Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.
Number | Date | Country | Kind |
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101127480 | Jul 2012 | TW | national |