JPH0436280Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a light emitting diode for an optical printer suitable for a main scanning long optical printer head.

B. Prior Art In recent years, optical printers using monolithic light emitting diodes (arrays) have been developed.
As shown in the publication, a plurality of light emitting diodes are arranged in a line to match the length of the main scan of an optical printer. It is a so-called one-line head. One of the most important things in such a one-line type head is that the printing quality must not deteriorate even at the joints of the light emitting diodes. In other words, in a single light emitting diode, the light emitting parts are formed at regular intervals and with a predetermined brightness by selective diffusion, etc., but when they are connected, it is especially important to avoid differences in characteristics between adjacent light emitting parts across the seam. It is necessary to However, the light emitting part located at this joint part, in other words, the light emitting part located at the end of the light emitting diode element, is subjected to strain (stress) because the vicinity of the light emitting part is cut when the wafer is cut, and this distortion causes characteristic deterioration. Also, because the crystal edge is close to the PN junction, current and light leak to the edge side, which tends to cause a decrease in brightness. In an optical printer using such a light emitting diode, the printing quality is extremely poor because the seam portion is printed as if there were a white line in the sub-scanning direction. Furthermore, even if the brightness decrease is small, if the interval between the light emitting parts at the seam is even slightly wider than the predetermined interval, the printing will emphasize the differences in characteristics between different light emitting diodes, and the printing quality will deteriorate.

C. Problems to be Solved by the Invention The present invention has been made to correct the above-mentioned problems, and provides a light emitting diode for an optical printer in which the light emitting portion at the end has a high brightness.

D. Means for solving the problem The present invention makes the area of the ohmic contact part of the light emitting part smaller in the area of the light emitting part located at the edge of the light emitting diode (element) than that of the light emitting part in the approximate center of the light emitting diode (device). More preferably, the ohmic contact portion of the light emitting portion located at the end is provided closer to the end of the light emitting diode.

As a result, the current density is higher in the light emitting part at the ends than in the center, resulting in high brightness.The current is supplied from the ohmic contact part to the light emitting part, so the position is biased, and the ends of the light emitting part are biased. The brightness will be higher.

Embodiment FIG. 1 is a plan view a, a sectional view b of a main part, and a luminance characteristic diagram c of a main part of a light emitting diode for an optical printer according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a substrate made of a compound semiconductor such as GaAsP/GaAs, on the surface of which light emitting sections 2, 2, . . . 3, 3' are provided by a selective diffusion method.
The light emitting parts 2, 2...3, 3' are arranged so that the light extraction parts (diffusion area exposed parts) are arranged in a straight line and at equal intervals, and the edges 11, 1 in the alignment direction
The distance between the light-emitting parts 3 and 3' located at the ends of the light-emitting parts 1 and 2 is set to be half or shorter than the alignment interval of the light-emitting parts 2, 2, etc., so that when the light-emitting diodes are arranged in series, the light-emitting parts are equal even at the joints. It is arranged so that the interval is the same.
4, 4... are in ohmic contact with each of the light emitting parts 2, 2, . These are individual electrodes made of vapor-deposited aluminum film.

Here, for example, if the size of the light extraction part of the light emitting parts 2, 2... is 50 μm x 50 μm, the size of the ohmic contact parts 21, 21... is
It is 47μm×45μm (2115μm ² ). On the other hand, the size of the light extraction part of the light emitting part 3, 3' located at the end is
Although the dimensions are the same as 50 μm×50 μm, the ohmic contact portions 31 and 31 are both approximately 1000 μm ² .
The distribution of the current can be made approximately uniform depending on the depth of the light emitting parts 2, 2...3, 3' and the impurity concentration distribution, but if the magnitude of the current is made approximately constant by the driving integrated circuit (driver), The current density depends on the area of the PN junction A at the boundary between the light emitting part and the non-diffused part of the substrate. Therefore, in the light emitting parts 2, 2, located approximately in the center, for example, 3 mA flows through a PN junction of about 4615 μm ² , and in the light emitting parts 3, 3 located at the ends, a current of about 3500 μm ² flows.
The same current flows through the PN junction. Since the brightness is approximately proportional to the current density, it is calculated to be about 32% higher, but in reality, the light under the electrode cannot be extracted, so it is 20 to 25% higher.
The brightness becomes high.

Furthermore, as shown in FIG. 1a, the ohmic contact parts 31, 31' of the light emitting parts 3, 3' located at the ends are shaped like triangles, steps, or strips, so that the ends of the light emitting parts 3, 3' are If the ohmic contact area on the 11, 11 side is made larger, the brightness characteristics will change as shown by the curve 32 in FIG.
The curves 22, 22... showing the characteristics of 2... have higher brightness, and the brightness can be made higher toward the ends. As a result, even if the seam of the light emitting diodes in an optical printer head using this light emitting diode is somewhat wide, that part will be printed with high density and will not be noticeable.

FIG. 2 shows another example of the present invention, in particular, strip-shaped electrodes 41, 4 extending from individual electrodes 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 40, 4, 5, 5, 4, 5, 4, 5, 4, 5, 4, 5, 4, 5, 3, 3, 3, 3, 3, 4
1... is placed as an example. At this time as well, the ohmic contact area is made smaller than that of the other light emitting parts 20, 20, . . . by the amount of the light emitting part 30 located at the end portion 12. Furthermore, the strip electrode 4
1, 41... serve to uniformly flow current throughout the light emitting parts 20, 20... 30, but as shown in the curves 23, 23... in FIG. 2b, the strip electrodes 41,
41... creates a shadow. Therefore, in the light emitting section 30 at the end, it is preferable to not only position the strip electrode 41 at the end rather than the center but also to make it thinner, because not only the brightness at the end side becomes higher as shown by the curve 33, but also the shaded area becomes narrower. .

In the above examples, the current density increases in the light emitting parts located at the ends, but as long as the current density does not become too high, rapid deterioration will not occur due to good heat dissipation. Practical effective area ratio between the substantially central light emitting section and the end light emitting section is 1:0.9 to 1:0.7. In addition, in the above example, the ohmic contact area was reduced only for one light emitting part located at the end, but if the light emitting diode is long or the light emitting parts are dense, it may be applied to one to several light emitting parts from the end. You can.

G. Effect of the invention As described above. The brightness of the light emitting part at the edge of the light emitting diode (near the seam) is increased, or the brightness characteristics of the light emitting part are set so that the end side has higher brightness, so there is a possibility that the brightness will be lower than the original due to deterioration. Even as I get older, I still haven't reached the level of white line printing,
Further, even if the seam widens to some extent, the photoreceptor of the optical printer can be exposed to light to an unnoticeable extent, and deterioration of printing quality due to the seam can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a plan view a, a sectional view b of a main part, and a diagram c of a main part luminance characteristic diagram of a light emitting diode for an optical printer according to an embodiment of the present invention, and Fig. 2 is a plan view of a main part of a light emitting diode for an optical printer according to another embodiment. Figure a and its luminance characteristic diagram b. 1...Substrate, 2, 2...3, 3', 20, 20
...30... Light emitting part, 4,4...40,40...
Individual electrodes.

Claims (1)

[Claims for Utility Model Registration] (1) A plurality of light emitting parts arranged in alignment on the surface,
In a light emitting diode for an optical printer, which has individual electrodes in ohmic contact with each of the light emitting parts, the ohmic contact area of the light emitting parts located at the ends of the light emitting diode is equal to the ohmic contact area of the light emitting part located approximately at the center of the light emitting diode. A light emitting diode for optical printers that is characterized by its smaller size. (2) Claim 1 of the above-mentioned utility model registration claim, characterized in that the light emitting part located at the end of the light emitting diode is in ohmic contact with the individual electrode on the end side of the light emitting diode from the center of the light emitting part. The light emitting diode for optical printers described.