Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Of specified material other than unalloyed aluminum
Reexamination Certificate
2002-09-30
2004-08-17
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Of specified material other than unalloyed aluminum
C257S081000, C257S094000, C257S099000
Reexamination Certificate
active
06777805
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a Group III nitride compound semiconductor device. The invention is adapted for improvement in electrodes of a Group III nitride compound semiconductor light-emitting device such as a blue light-emitting diode.
BACKGROUND ART
In a Group III nitride compound semiconductor light-emitting device such as a blue light-emitting diode, various proposals have been made for obtaining uniform light emission from the whole surface of the device.
For example, in Unexamined Japanese Patent Publication No. Hei. 8-340131 and Unexamined Japanese Patent Publication No. Hei. 10-117017, a p auxiliary electrode is provided radially on an upper surface of a p contact layer to attain uniformity of electric current density injected into the p contact layer. On the other hand, for example, as described in Unexamined Japanese Patent Publication No. 10-275934, a translucent electrode may be stuck on an upper surface of a p-type contact layer so that a p seat electrode is provided thereon. In this example, a p auxiliary electrode is extended from the p seat electrode along sides of the device.
Unexamined Japanese Patent Publication No. Hei. 9-97922 and Unexamined Japanese Patent Publication No. 2000-22210 have disclosed the case where an n auxiliary electrode is provided along sides of the device from an n seat electrode formed in a corner portion of the device, by way of example.
Unexamined Japanese Patent Publication No. 2000-164930 has disclosed a comb-like electrode.
According to the present inventors' examination, it has been found that it is preferable to increase the chip size of light-emitting diodes used in a signal or the like in which high luminance is demanded and light-emitting diodes of one color are collectively used. This is because if the number of light-emitting diodes used can be reduced by increase in chip size, a circuit for evenly distributing an electric current to respective light-emitting diodes can be designed easily and simply as well as the number of steps for assembling the light-emitting diodes can be reduced to attain reduction in production cost.
Therefore, the inventors have made examination again and again to increase the chip size of light-emitting diodes. As a result, the following problems have been found.
Since the resistance of an n contact layer (a layer on which an n electrode is formed) in a light-emitting diode is relatively high, an electric current cannot sufficiently go around to a portion far from then electrode so that light emission is reduced in the portion. On the other hand, intensive light emission is obtained in a portion near the n electrode, so that light emission becomes uneven on the whole of the device. In a conventional small-size device (300 to 400 &mgr;m□) viewed from this point, the portion far from the n electrode was more or less dark, but was limited to a very small area so that the unevenness of light emission was substantially not a large obstacle.
If the chip size becomes large, the amount of an electric current applied to the p seat electrode must be increased when preferable current density injected per unit light-emitting area is to be kept. The current applied to the p seat electrode flows from the p seat electrode into the translucent electrode. If the amount of the current becomes large, there is a high possibility that burning (burning off the translucent electrode in a joint portion by generated Joule heat) may occur between the p seat electrode and the translucent electrode. The area of an interface between the p seat electrode and the translucent electrode is a factor for deciding the amount of the current (permissible current quantity) permitted to be injected into the p seat electrode. It is conceived that the permissible current quantity can increase as the area increases.
If one p seat electrode and one n seat electrode are used in combination when preferred current density is to be secured in an effective light-emitting surface of a large-size chip having an outermost diameter of not smaller than 700 &mgr;m, there is a fear that mold resin may be burned by heat generated in a bonding wire portion or the bonding wire itself may be broken by heat unfavorably.
DISCLOSURE OF THE INVENTION
The invention is provided to solve at least one of the aforementioned problems. That is, in the present invention, there is provided a Group III nitride compound semiconductor device which is a device having an outermost diameter of not smaller than 700 &mgr;m, wherein a distance from an n electrode to a farthest point of a p electrode is not larger than 500 &mgr;m.
According to the Group III nitride compound semiconductor device configured as described above, the farthest point of the p electrode from the n electrode is with in the aforementioned distance. Hence, even in the case where the resistance of an n-type semiconductor layer is high, electrons are sufficiently injected into the farthest device portion from the n electrode (electric current is diffused). As a result, light is emitted more evenly from the whole surface of the device.
Incidentally, the current density and the luminous output of the light-emitting device have such relation that the luminous output is saturated when the current density exceeds a predetermined value. That is, even in the case where current density exceeding the predetermined value is injected, it is impossible to obtain increase in the luminous output in accordance with the current density. It is therefore preferable that current density near the predetermined value is achieved on the whole region of the device in order to achieve both high luminous output and high luminous efficiency. When the distance between the n electrode and the p electrode is defined as in the invention, the preferred current density can be obtained on the whole region of the device and, accordingly, a device excellent in luminous efficiency can be provided.
Incidentally, in this specification, the n electrode has an n seat electrode, and an n auxiliary electrode extended from then seat electrode whereas the p electrode has a p seat electrode, and a p auxiliary electrode extended from the p seat electrode. The outermost diameter of the device is the length of the longest one of lines allowed to be drawn on the device in a plan view of the device. When the device is rectangular, the outermost diameter of the device is the length of a diagonal line. When the device is rhombic, the outermost diameter of the device is likewise the length of a diagonal line. When the device is circular or elliptic, the outermost diameter of the device is the length of a line passing through the center of a circle or ellipse. As described above, the shape of the device is not particularly limited. Besides the aforementioned shapes, polygonal shapes such as a hexagonal shape, an octagonal shape, etc. may be used as the device shapes.
The upper limit of the distance between the n electrode and the p electrode located farthest from the n electrode is selected to be more preferably 400 &mgr;m, further more preferably 350 &mgr;m.
In the case of a rectangular chip, such configuration is preferably applied to a chip having a length of 500 &mgr;m or more on one side (700 &mgr;m or more in outermost diameter). In a conventional n electrode configuration, if the chip size becomes large as described above, there is fear that a portion which is darkened because it is too far from the n electrode to obtain sufficient current density may form an unacceptably large region, and that the region may appear in the central portion of the device to make the luminous form unsuitable. In the case of a rectangular chip, the length of a side is selected to be more preferably not smaller than 600 &mgr;m, further more preferably not smaller than 700 &mgr;m, most preferably not smaller than 800 &mgr;m.
In an aspect of the invention, configuration that the n auxiliary electrode is extended from the n seat electrode to the central portion of the device is used so that the distance between any point of the p electrode and
Hirano Atsuo
Nagasaka Naohisa
Ota Koichi
Uemura Toshiya
McGinn & Gibb PLLC
Nelms David
Nguyen Dao H.
Toyoda Gosei Co,., Ltd.
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