Invented by Su Yeol Lee, Sang Ho Yoon, Doo Go Baik, Seok Beom Choi, Tae Sung JANG, Jong Gun WOO, Samsung Electronics Co Ltd
The Samsung Electronics Co Ltd invention works as followsProvided are vertical LEDs that include an n electrode; an n type GaN underlayer formed beneath the n electrode, with a Ga+N surface containing more Ga than N; an active underlayer formed underneath the n type GaN; a P-type GaN underlayer formed below the active layer; A p -type GaN underlayer formed underthe active layer; A p -electrode under the top p -type GaN; and a structure
Background for Vertical Light Emitting Diode and Method of Manufacturing the Same
The present invention is a vertical light-emitting diode and a manufacturing method that can reduce the contact resistance between a negative electrode and an n type GaN layer on its surface, and improve thermal stability.
Typically, a nitride based semiconductor LED will be grown on a sapphire surface, but sapphire is a rigid, non-conducting material with poor thermal conductivity. There is no way to reduce the cost of manufacturing a nitride based semiconductor LED by shrinking the size or improving chip characteristics. It is crucial to solve the heat-sink issue of the LED because a high current application is required for high power LED. “To solve this problem, it has been suggested a vertical LED where a sapphire sub-strate is removed by Laser Lift-Off.
I will describe a vertical LED in detail, with reference to FIG. 1. FIG. FIG.
As shown in FIG. The conventional vertical LED comprises a structure support 150 in the lowermost part and a positive electrode (p-) 140 on the structure 150. The p-electrode is preferably made of a conductive reflective member that serves as an electrode, and a layer for reflection.
On the p electrode 140, a GaN p-type layer 130 is sequentially formed on top of an active layer 120 and a GaN n-type layer 110, creating a light-emitting structure.
A portion of the upper part of the light-emitting structure, namely the surface of n type GaN layer 110, has surface irregularities for increasing light emission efficiency (not shown). A negative (n) electrode 160 is formed on the n-type GaN surface 110.
In the conventional vertical LED however, the surface that comes into contact with the n electrode 160 is an N face or N polar surface. This surface is in contact with sapphire substrates (not shown), on which the GaN n type layer is formed.
When the n electrode 160 is placed on the GaN n type layer 110 with an N-face, or N-polar, surface, contact resistance increases and a LED’s operational voltage increases. The heating value will increase as a result.
As a result, as the heating value increases and the thermal stability of a vertical LED diminishes, so does the contact resistance, which continuously increases. This leads to deterioration of characteristics and reliability.
The present invention has the advantage that the surface of an N-type GaN is in contact with the n electrode is made of a Ga+N containing more Ga than N. This increases the surface electron density of the n type GaN. The contact resistance between the n type GaN layer and the n electrode with an N-face, or N-polar, surface can be reduced in the vertical LED. Thermal stability can also be improved.
Another benefit of the invention is the method it provides for manufacturing vertical LEDs.
The description will include additional aspects and advantages. Some of these will be evident from the description or can be learned through the practice of this general inventive concept.
According to one aspect of the invention a vertical LED consists of an n electrode; an n type GaN underlayer formed beneath the n electrode, with a Ga+N surface containing more Ga than N; an active underlayer formed underneath the n type GaN; a P-type GaN underlayer formed below the active layer; A p -type GaN underlayer formed beneath the active layer; A p -type GaN underlayer formed underthe p -type GaN;
The n-electrode can be made of a single metal layer consisting of Ti or Ta and Zr. The n-electrode can also be made of a multilayer consisting of more than two layers, including one or more layers composed of metals from the group Ti, Ta and Zr.
The Ga+N layer can be formed on the surface of the GaN layer that is in contact with an n electrode by heat-treating it or laser-treating it.
The p-electrode can be made of a conductive reflective member. The Ga+N layer that comes in contact with n-electrodes may also have surface irregularities.
The method for manufacturing a vertical led, according to another aspect, involves forming the light-emitting structure, in which an n type GaN, an active layer and a Ga+N are sequentially laminated on a substrate, forming the p electrode on the light-emitting structure, removing the substrate so as to expose the GaN n layer, laser-treating this surface to form the Ga layer and the Ga+N layers, which are sequentially laminated from the laser treated surface
Preferably the laser treatment is carried out using a laser wavelength with energy greater than GaN’s energy band gap.
The method consists of forming surface irregularities before forming the n electrode on the surface of the laser-treated n-type GaN.Click here to view the patent on Google Patents.