JP3234344B2 - Light emitting diode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode used in an optical print head.

[0002]

2. Description of the Related Art Conventionally, in order to reduce the size of an optical print head, a side-emitting type light emitting diode has been developed, which is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-107890.
However, since the above-mentioned light emitting diode has a light emitting region formed only on the side surface and does not emit light on the front surface side, the luminance cannot be measured in a wafer state. Therefore, the present applicant has filed a Japanese Patent Application No. 5-2127.
No. 6 filed an application for a light-emitting diode in which the disadvantages were improved, and FIG. 9 shows it. FIG. 9A is a plan view of the light emitting diode, FIG. 9B is a JJ sectional view thereof, and FIG. 9C is a luminance characteristic diagram thereof. In these figures, a light emitting region 43 is formed so as to be exposed on a side surface of a compound semiconductor substrate 41, and an electrode 44 is formed in contact with the light emitting region 43.

[0003]

However, the above-mentioned light emitting diode is formed not only to emit light from the side but also to emit light from the surface so that the luminance can be measured in a wafer state before the element is divided. That is, the end surface 45 of the electrode 44 is formed to be separated from the side surface 46 of the substrate 41 by a predetermined length K (about 100 μm), and the surface of this length K is formed so that surface light emission can be performed in a wafer state. However, in the light-emitting diode after the element division, light emitted from the surface leaks to the side surface 46, so that the luminance characteristic is significantly widened as shown in FIG. 9C.
Therefore, an optical print head in which a plurality of light emitting diodes are arranged has a drawback that the printing quality is deteriorated and cannot be used practically. Accordingly, the present invention has been made in view of the above drawbacks, and provides a side emission type light emitting diode which can easily perform luminance measurement even in a wafer state and can obtain sharp luminance characteristics.

[0004]

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a compound semiconductor substrate and a plurality of first light emitting regions formed on the side surface of the substrate and aligned with the surface of the substrate. A plurality of second light-emitting regions formed on the surface of the substrate apart from the first light-emitting region; and a plurality of second light-emitting regions formed in ohmic contact with each of the first and second light-emitting regions and aligned with the surface of the substrate. A plurality of electrodes are provided, and a window is provided in each of the electrodes so as to partially expose the surface of each of the second light emitting regions. More preferably, the end face of each of the electrodes is positioned within 20 μm from the side surface of the substrate. It is assumed that.

[0006]

[0007]

As described above, since the second light-emitting region is formed apart from the first light-emitting region exposed on the side surface, light traveling from the second light-emitting region to the side surface is transmitted to the first light-emitting region and the second light-emitting region. The light is shielded by the electrode portion between the light emitting region. Therefore, the amount of light emitted from the second light emitting region leaking to the side surface is reduced, so that sharp side surface luminance characteristics can be obtained. In addition, through the window of the electrode formed so as to partially expose the surface of the second light emitting region, the luminance of the surface can be measured even in a wafer state. When the end face of the electrode is provided at a position within 20 μm from the side surface of the substrate, the amount of light leaking from the surface to the side surface sharply decreases, so that the luminance characteristics on the side surface become sharp.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. 1A is a plan view of a light emitting diode according to the present embodiment, FIG. 1B is a cross-sectional view taken along the line AA of FIG.
(C) is a luminance characteristic diagram thereof. In these figures,
The compound semiconductor substrate 1 has an epitaxial layer 3 made of N-type GaAsP formed on a base 2 made of, for example, N-type GaAs by vapor phase epitaxial growth. The light-emitting region 4 is formed by selective diffusion on the substrate 1 and is a P-type region to which zinc is added.
It is an area of 5 μm, 5 to 20 μm in width, and 5 to 20 μm in length. The light-emitting regions 4 are exposed on the side surface 5 of the substrate 1 and are arranged on the surface of the substrate 1 at a pitch of 63,5 μm in the longitudinal direction at a rate of, for example, 128 in a row, 400 dots per inch, and 400 dots per inch.

The end face 7 of the electrode 6 is located on the same plane as the side face 5 of the substrate 1, the electrode 6 makes ohmic contact with the light emitting region 4 near the side face 5, and the other part is provided on the surface of the substrate 1 with an insulating layer. 8
The other portion described above is a wiring region 9 for wire bonding. A window 10 is formed between the end face 7 of the electrode 6 and the ohmic contact so as to partially expose the surface of the light emitting region 4. Although a round hole is shown as the window 10 in FIG. 1A, the shape is not limited to this and may be a square hole or a polygonal hole, and may have any shape. In this manner, the electrode 6 has the partition 11 formed between the end face 7 and the window 10.

The insulating layer 8 is made of, for example, silicon nitride or the like.
It is formed by the VD method or the like so as to cover the entire surface of the substrate 1 except for a region surrounded by a broken line shown in FIG. The back surface electrode 12 is made of gold or the like, and is formed on the entire back surface of the substrate 1. These members constitute the light emitting diode 13 of the present embodiment. The size of the light emitting diode 13 is, for example, about 400 μm in thickness and about 8 mm in length.

Next, the luminance characteristics of the present light emitting diode will be described with reference to FIG. The horizontal axis shows the height position with the back surface of the back electrode 12 of the light emitting diode 13 as the origin, and the vertical axis shows the luminance (cd / m ² ). From this figure, it can be seen that the luminance characteristic becomes sharp and the remarkable spread unlike the conventional case is eliminated. The reason is that the light emitted from the side surface 5 through the window 10 at the electrode 6 does not leak to the side surface 5 side by the partitioning portion 11 formed between the window 10 and the side surface 5, so that the light from the side surface 5 is Because it becomes sharp.

Further, an inspection in a wafer state before the light emitting diode 13 is divided into elements will be described with reference to FIG.
FIG. 2 is a plan view of the wafer 14. One wafer 1
4, several hundred light emitting diodes 13 are formed. 1
As described above, for example, 128 combinations of the light emitting region 4 and the electrode 6 are formed in each of the light emitting diodes 13 (FIG. 2).
Then four are shown for simplicity). Using the back electrode as a common electrode, a lead wire from a measuring device prober is connected to one electrode 6 and energized, and the luminance and forward voltage-current characteristics of light from the light emitting region 4 are measured through the window 10. The above measurement was taken as 1
The process is performed on each of the 28 electrodes 6, and a mark indicating that the light emitting diode 13 is within a predetermined numerical value range is provided.

After the wafer 14 is divided into elements, only the light-emitting diodes 13 marked above are taken out by a chip mounter to obtain non-defective light-emitting diodes 13. Since the luminance can be measured in the state of the wafer 14 in this manner, the operation can be easily performed because an automatic inspection machine can be used.

Further, in the light-emitting diode disclosed in Japanese Patent Application No. 5-212276, the electrode in ohmic contact with the light-emitting region exposed on the side and the ohmic contact with another light-emitting region formed on the other surface of the substrate. An embodiment in which other electrodes are provided separately is also shown. However, it is difficult to measure the forward voltage-current characteristics in the wafer state by connecting the lead wire to the electrode, and to measure the luminance characteristics by connecting the lead wire to another electrode again.

On the other hand, the light emitting diode 1 of this embodiment
In FIG. 3, the electrode 6 connected to the light emitting region 4 exposed on the side surface 5 and the light emitting region 4 through the window 10 for surface light emission measurement.
Are the same. Therefore, in the state of the wafer 14 as described above, the forward voltage-current characteristics and the luminance characteristics on the surface side can be performed without reconnecting the lead lines. Therefore, the work of reconnecting becomes unnecessary, and the work time is shortened.

Next, a second embodiment in which a light emitting diode is easier to divide than a first embodiment will be described with reference to the plan view of FIG.
The description will be given with reference to the BB cross-sectional view of FIG. 3B and the luminance characteristic diagram of FIG. In these figures, the electrode 15 is formed such that the length C between the end face 16 of the electrode 15 and the side face 5 of the light emitting diode 17 is within 20 μm, preferably in the range of 5 to 10 μm.

By providing the end face 16 of the electrode 15 inside the side face 5 as described above, when the side face 5 is cut off after dicing or scribing, deformation of the electrode due to the entire coating of the electrode or short-circuit between the electrodes or Deformation of the light emitting region 4 can be prevented. Further, according to the measurement by the present inventors, it was found that if the above-mentioned length C is within 20 μm, there is no remarkable spread of the luminance characteristics. This length is 20 μm
It was also found that the luminance characteristics were significantly widened when exceeding.

FIG. 4A is a plan view, FIG. 4B is a sectional view taken along the line DD, and FIG. The description will be made according to the drawings. In these figures, the window portion 18 is divided right and left with respect to one electrode and formed as a pair. In this way, since the window 18 has a larger area than the window 10 of the light emitting diode 17 of the second embodiment, the brightness of the light from the front side becomes larger, and the brightness measurement becomes easier.

Further, a fourth embodiment having sharper luminance characteristics than the third embodiment will be described with reference to the plan view of FIG.
The description will be given with reference to the EE cross-sectional view of FIG. 5B and the luminance characteristic diagram of FIG. In these figures, a compound semiconductor substrate 1 has an epitaxial layer 3 formed on a base 2.
The first light emitting region 20 is exposed on the side surface 5 of the substrate 1 and
Are arranged in a single row on the surface of. The second light emitting region 21 is separated from the first light emitting region 20 and is separated from the first light emitting region 20.
Are formed on the surface of the substrate 1 as a pair. The electrode 22 is in ohmic contact with the first and second light emitting regions 20 and 21 and is formed on the surface of the substrate 1 via an insulating layer 23. Window 24 is formed so as to partially expose the surface of second light emitting region 21.

The window 2 for taking out the light on the front side as described above.
By providing 4 at a position relatively far from side surface 5, the amount of light on the front surface side leaking to side surface 5 is reduced, so that the luminance characteristics become sharper.

FIG. 6A is a plan view of a fifth embodiment having a sharper luminance characteristic than the fourth embodiment.
This will be described with reference to the FF cross-sectional view of FIG. 6B and the luminance characteristic diagram of FIG. In these figures, the second light emitting region 25 is the substrate 1
Is formed on the surface of the substrate 1 located in the vicinity of the other side surface 26 opposite to the side surface 5. The window 27 is the second light emitting area 25
And is distributed to the left and right with respect to one electrode 28 to form a pair. By providing the window 27 for taking out the light on the front surface side near the other side surface 26 opposite to the side surface 5 in this manner, the amount of light on the front surface side leaking to the side surface 5 is reduced, so that the luminance characteristics are further sharpened. .

Next, a sixth embodiment in which the first light emitting region is less susceptible to stress distortion than the fifth embodiment will be described with reference to the plan view of FIG.
The description will be given with reference to a GG sectional view of FIG. 7B and a luminance characteristic diagram of FIG. 7C. In these figures, the first light-emitting regions 29 are formed in a line in a row on the surface of the substrate 1 which extends from the side surface 5 of the substrate 1 by a length H (H = 10 to 30 μm). An electrode 30 is formed in ohmic contact with the first and second light emitting regions 29 and 25, and a window 31 is formed near the other side surface 26.

By forming the first light emitting region 29 at a position slightly distant from the side surface 5 of the substrate 1 as described above, stress distortion to the first light emitting region 29 when the wafer is cut can be reduced, and the light emitting diode can be formed. Lifespan can be extended.

Further, the seventh aspect in which light on the front side does not leak to the side faces at all.
An embodiment will be described with reference to FIG. FIG. 8A is a plan view of a light-emitting diode on which fine metal wires are wired, and FIG. 8B is a cross-sectional view of the light-emitting diode II. In these figures, the first light emitting region 20 is formed so as to be exposed on the side surface 5 of the substrate 1, the second light emitting region 25 is formed near the other side surface 26 of the substrate 1, and the electrodes 32 are formed on the first and second sides. The window 33 is formed in contact with the second light emitting regions 20 and 25, and is formed near the other side surface 26.
These members constitute the light emitting diode 34 of this embodiment.

Further, in a wafer state before the light emitting diode 34 is divided into elements, the brightness of light to the front side through the window 33 is measured. Thereafter, the device is divided, a plurality of light emitting diodes 34 are aligned and mounted on a substrate (not shown), and a metal is disposed between the electrode 32 of the light emitting diode 34 and a conductive pattern (not shown) on the substrate. It is wired by a thin wire 35. Desirably, when the wiring place of the thin metal wire 35 is made on the electrode 32 near the window 33, light emitted to the front side is completely blocked by the thin metal wire 35, so that light from the side surface 5 is light from the surface. Is completely unaffected by
A sharper luminance characteristic can be obtained.

[0026]

According to the first aspect of the present invention, as described above, the amount of light leaking from the surface to the side surface is sharply reduced by providing the end surface of the electrode at a position within 20 μm from the side surface of the substrate. The brightness characteristics in are sharpened. Also, through the window of the electrode formed so as to partially expose the surface of the light emitting region, it is possible to measure the luminance on the front side even in a wafer state.

The second aspect of the present invention is the first aspect of the present invention,
Since the second light emitting region is formed apart from the light emitting region,
Light that exits the second light emitting region and travels to the side surface is blocked by a portion of the electrode between the first light emitting region and the second light emitting region. Therefore, the amount of light emitted from the second light emitting region leaking to the side surface is reduced, so that sharp side surface luminance characteristics can be obtained. In addition, through the window of the electrode formed so as to partially expose the surface of the second light emitting region, it is possible to measure the luminance on the front side even in a wafer state.

As described above, in the first and second aspects of the present invention, by measuring the luminance characteristics on the surface side, the luminance characteristics due to the light emitting region formed on the side surface of the substrate can be estimated. This is because the luminance characteristics are determined by the epitaxial state of the epitaxial layer and the diffusion state of the light emitting region.
As a result, by measuring the brightness on the front surface side in the wafer state, it becomes easy to inspect non-defective and defective products of each light emitting diode.

[Brief description of the drawings]

1 (a) is a plan view of a light emitting diode according to a first embodiment of the present invention, FIG. 1 (b) is a sectional view taken along the line AA thereof, and FIG. 1 (c) is a luminance characteristic diagram thereof. .

FIG. 2 is a plan view of a wafer state before a light emitting diode according to the first embodiment of the present invention is divided into elements.

3 (a) is a plan view of a light emitting diode according to a second embodiment of the present invention, FIG. 3 (b) is a BB sectional view thereof, and FIG. 3 (c) is a luminance characteristic diagram thereof. .

4 (a) is a plan view of a light emitting diode according to a third embodiment of the present invention, FIG. 4 (b) is a DD sectional view thereof, and FIG. 4 (c) is a luminance characteristic diagram thereof. .

5 (a) is a plan view of a light emitting diode according to a fourth embodiment of the present invention, FIG. 5 (b) is an EE sectional view thereof, and FIG. 5 (c) is a luminance characteristic diagram thereof. .

6 (a) is a plan view of a light emitting diode according to a fifth embodiment of the present invention, FIG. 6 (b) is a sectional view taken along the line FF thereof, and FIG. 6 (c) is a luminance characteristic diagram thereof. .

FIG. 7A is a plan view of a light emitting diode according to a sixth embodiment of the present embodiment, FIG. 7B is a GG sectional view thereof,
FIG. 7C is a luminance characteristic diagram thereof.

FIG. 8 (a) is a plan view of a light emitting diode according to a seventh embodiment of the present invention in which thin metal wires are wired, and FIG. 8 (b) is a II sectional view thereof.

FIG. 9A is a plan view of a conventional light emitting diode,
FIG. 9B is a JJ cross-sectional view thereof, and FIG. 9C is a luminance characteristic view thereof.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 4 Light-emitting area 6 Electrode 7 End face 10 Window

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-33685 (JP, A) JP-A-61-88575 (JP, A) JP-A-5-31955 (JP, A) JP-A-3-3195 180078 (JP, A) JP-A-6-237015 (JP, A) JP-A-5-8444 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 33/00

Claims (1)

(57) [Claims] 1. A compound semiconductor substrate and a side surface of the substrate.
Exposed on the substrate and formed in alignment with the surface of the substrate.
A first light emitting region and a surface of the substrate separated from the first light emitting region;
A plurality of second light-emitting regions formed on the surface;
The substrate is in ohmic contact with the light emitting region and is
A plurality of electrodes formed in a row,
A window is formed in each of the electrodes so as to partially expose the surface of the light area.
A light emitting diode characterized by being formed.