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Patent Issued for Reflection Curved Mirror Structure of a Vertical Light-Emitting Diode

September 10, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Chen, Fu-Bang (Taichung, TW); Yen, Wei-Yu (Taichung, TW); Chou, Li-Ping (Taichung, TW); Tseng, Wei-Chun (Taichung, TW); Chang, Chih-Sung (Taichung, TW), filed on July 10, 2013, was published online on August 26, 2014.

The assignee for this patent, patent number 8816379, is High Power Opto, Inc. (Taichung, TW).

Reporters obtained the following quote from the background information supplied by the inventors: "FIG. 1 shows a conventional vertical LED. The conventional vertical LED includes a sandwich structure formed by an N-type semiconductor layer 1, a light-emitting layer 2 and a P-type semiconductor layer 3. Below the P-type semiconductor layer 3, a mirror layer 4, a buffer layer 5, a binding layer 6, a silicon substrate 7 and a P-type electrode 8 are disposed in sequence. A surface of the N-type semiconductor layer 1 is processed by a roughening treatment for increasing an optical emission rate. An N-type electrode 9 is further disposed on the roughened surface of the N-type semiconductor layer 1.

"By applying a voltage between the N-type electrode 9 and the P-type electrode 8, the N-type semiconductor layer 1 is enabled to provide electrons and the P-type semiconductor layer 3 is enabled to provide holes. Light is produced by the electrons and holes combining at the light-emitting layer 2 to further generate excited light through energy level jump.

"Again referring to FIG. 1, a region right below the N-type electrode 9 has a highest current density, and so a main light-emitting region of the light-emitting layer 2 falls right below the N-type electrode 9. However, since the N-type electrode 9 is opaque and occupies 10% to 23% of an overall area of the LED and the main light-emitting region is right below the N-type electrode 9, a substantial ratio of excited light 2A is shielded. As a result, the loss of the excited light may reach as high as 15% to 38% such that light extraction efficiency suffers.

"Referring to FIG. 2, to, increase the light extraction efficiency, a current blocking layer 3A is often disposed between the P-type semiconductor layer 3 and the mirror layer 4. The current blocking layer 3A is disposed right below the N-type electrode 9, inferring to that a current can only reach the light-emitting layer 2 by first bypassing the current block layer 3A. Thus, the main light-emitting region of the light-emitting layer 2 is no longer situated right below the N-type electrode 9, so that the excited light shielded by the N-type electrode 9 is reduced to increase the light extraction efficiency.

"However, the presence of the current block layer 3A leads to increased resistance that reduces light-emitting efficiency of the LED. Further, a transmission speed of a horizontal current is greater than that of a vertical current. When the current block layer 3A is utilized for guiding the current not to pass through the light-emitting layer 2 right below the N-type electrode 9, the light-emitting layer 2 right below the N-type electrode 9 still has considerable brightness due to the transmission of the horizontal current. As a result, a substantial amount of light remains being shielded by the N-type electrode 9 to lead 5% to 20% loss. In conclusion, the light extraction efficiency is limited and fails to fulfill actual requirements.

"In another conventional approach for increasing the light extraction efficiency, a thickness of an epitaxy layer is enlarged or a doping concentration is increased to improve a current transmission capability. Through the high current transmission capability, the area of the N-type electrode 9 can be reduced to further decrease a shielded region. However, regardless whether the thickness of the epitaxy layer is enlarged or the doping concentration is increased, a quality of the epitaxy is severely degraded. Further, a current density gets larger as the current increases, such that problems of a boosted forward voltage and burning the electrode are likely incurred.

"In yet another conventional approach for increasing the light extraction efficiency, a reflection metal is disposed right below the N-type electrode 9 to reflect the excited light shielded by the N-type electrode 9. It should be noted that, in a vertical LED, as previously stated, the mirror layer 4 is already disposed below the P-type semiconductor layer 3. When the reflection metal is disposed right below the N-type electrode, the excited light is incessantly reflected between the reflection metal and the mirror layer 4 till the excited light is fully depleted. Consequently, the excited light is still not extracted, namely the light extraction efficiency cannot be increased."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Therefore, the primary object of the present invention is to provide a structure capable of increasing light extraction efficiency by guiding a projection of excited light.

"A reflection curved mirror structure of a vertical light-emitting diode (LED) is provided according to one embodiment of the present invention. The reflection curved mirror structure is applied to an LED structure which comprises a P-type electrode, a permanent substrate, a binding layer, a buffer layer, a mirror layer, a P-type semiconductor layer, a light-emitting layer, an N-type semiconductor layer and an N-type electrode that are stacked in sequence. Between the P-type semiconductor layer and the mirror layer is a filler. The filler is made of a transparent material, and forms a protruding curved surface right below the N-type electrode. The protruding curved surface faces the light-emitting layer. The mirror layer forms a mirror structure along the protruding curved surface.

"Thus, with the mirror structure of the present invention, when excited light generated by the light-emitting layer which is located right below the N-type electrode is emitted downwards, the excited light is reflected by the mirror structure towards two sides of the mirror structure. That is to say, by means of the mirror structure, the excited light generated by the light-emitting layer right below the N-type electrode can dodge the N-type electrode without being shielded, thereby increasing the light extraction efficiency.

"The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings."

For more information, see this patent: Chen, Fu-Bang; Yen, Wei-Yu; Chou, Li-Ping; Tseng, Wei-Chun; Chang, Chih-Sung. Reflection Curved Mirror Structure of a Vertical Light-Emitting Diode. U.S. Patent Number 8816379, filed July 10, 2013, and published online on August 26, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8816379.PN.&OS=PN/8816379RS=PN/8816379

Keywords for this news article include: Electronics, High Power Opto, High Power Opto Inc., Light-emitting Diode, Semiconductor.

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Source: Electronics Newsweekly


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