JPH0438881A - Light emitting element and light emitting element array - Google Patents

Abstract

PURPOSE:To get high resolution and high printing dignity by covering the whole face of the light taking out face of a light emitting part with an electrode for current application, and forming a transparent conductive film, which ohmically contacts with the light taking out face, and a metallic film, which is connected to the transparent conductive film at the position off the light taking out face. CONSTITUTION:In each light emitting part 25, electric energy is supplied, with current density uniform at the whole face of the light taking out face of a P-type diffusion part 26, through a transparent conductive film 27, and the light of uniform brightness is emitted from the whole of the P-N junction between the P-type diffusion part 26 and an N-type epitaxial layer 23, and all lights are emitted to outside through a transparent conductive electrode 27. Moreover, since a metallic film is provided at the place outside the light emitting part 25, the light, which has passed the transparent conductive electrode 27, is all emitted to outside without being screened, and the loss in quantity of light by screening does not occur at all, and the use efficiency of energy becomes extremely high. Accordingly, the shape and the area of each light emitting part 25 become the same, and the overall properties are stabled, and the geometrical center of each light emitting part 25 and the optical center accord completely with each other.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a light emitting element and a light emitting element array used as a light source of Meishin, and in particular, to a light emitting element and a light emitting element array that are capable of emitting light of uniform brightness from the entire surface of the light emitting part. The present invention relates to a light emitting element and a light emitting element array.

(Prior art) Figure 3 shows an example of this type of light emitting element array.
It is a component of an optical writing head 1 that performs optical writing on a photoreceptor in an electrophotographic apparatus.

This optical writing head 1 has a ceramic substrate 3 made of an insulating material laminated on a heat sink 2 made of aluminum, and a plurality of light emitting parts 5 as shown in FIGS. 4 and 5 on this substrate 3. , 5 . The current-carrying electrode 8 and the conductive pattern 7 are connected by bonding wires 9, 9, . . . .

A transparent cover 10 made of glass is adhered onto the outer periphery of the substrate 3 to protect the light emitting element array 4, the conductor pattern 7, the bonding wires 9, and the like.

The optical writing head 1 configured in this way has a length of 11 m.
By energizing a specific conductor pattern 7 based on a signal, a specific light emitting section emits light, and light from this light emitting section is output to the outside via the transparent cover 10 and is used for optical writing.

To further explain the light emitting element array 4 with reference to FIGS. 4 and 5, G is placed on a substrate 12 made of GaAs.
aAsP is epitaxially grown to form an N-type epitaxial layer 13, and this N-type epitaxial layer 13 is
A diffusion mask 14 made of 5102 is formed on the diffusion mask 14, and openings 14a are formed by etching or the like in the portions of this diffusion mask 14 where each light emitting section 5 is to be formed.
From step a, Zll is diffused into the N-type epitaxial layer 13 to form a P-type diffusion section 15 that will become the light emitting section 5. after that,
S + 02 on the diffusion mask 14 and the P-type diffusion part 15
After that, in order to connect the current-carrying electrode 8 and the P-type diffusion part 15, an opening is formed in a portion of the passivation layer 16 on each P-type expanded part 15 by etching or the like. 16a is formed. Thereafter, Aj, which will become the current-carrying electrode 8, is formed entirely on the passivation layer 16, and unnecessary portions are removed by etching or the like, to form each current-carrying electrode 8. Each current-carrying electrode 8 and the P-type diffusion portion 15 are connected to each other through an ohmic contact in which the II wall during current-carrying is removed so that no voltage is generated at the interface. Next, the back electrode 11 is formed by depositing Au or the like on the opposite surface of the substrate 12.

The light-emitting element array 4 formed in this manner is constructed by energizing each current-carrying electrode 8 and the back electrode 11 to connect the P-type diffusion part 15 and the N-type epitaxial layer 13 of each light-emitting part 5. Light is emitted at the pn junction, and the light is emitted to the outside through the passivation 1116 and the transparent cover 10.

(Problems to be Solved by the Invention) However, in the conventional light emitting element array 4, the distribution of the current flowing through the P-type diffusion portion 15 is not uniform, and various problems as described below have occurred.

The reason why the current distribution in the P-type diffusion part 15 which becomes the light emitting part 5 becomes non-uniform is because the connection part between the P-type diffusion part 15 which becomes the supply &1 of the electrical circuit 1' and the current-carrying electrode 8 is formed by the passivation layer 16. The opening 16a is limited to the opening 16a.
This is because a is very small compared to the P-type diffusion section 15 which becomes the light emitting section 5.

That is, although the Pt diffusion portion 15 and the current-carrying electrode 8 are in ohmic contact in this opening portion 16a, the current flowing through the PN junction between the P-type diffusion portion 15 and the N-type epitaxial layer 13 The density is f! As shown by the arrow in Fig. 4, the current distribution becomes non-uniform in the part facing the ohmic contact part, that is, the part located directly below the opening part 16a in Fig. 4, because it becomes smaller as it moves away from there. It ends up.

The brightness of the light emitted by the light emitting part 5 tends to increase as the current increases (the larger the current), so the brightness distribution in the light emitting part 5 also has a single brightness in the part facing the ohmic contact, and the A-mink It becomes smaller as it fills from the contact area.

To explain this brightness distribution using FIGS. 6(a), (b) (cl), the brightness distribution in the P-type pad 15 is maximum at the part facing the A-mic contact, as shown in N<b> of the same figure. In plan view, the same luminance distribution spreads out in the form of ripples around the ohmic contact portion, as shown in FIG.

In this way, in the conventional light emitting element array 4, 1. Since the luminance distribution of light emission in the P-type diffuser 15 that becomes the light-emitting section 5 is not uniform, the low-luminance part becomes useless as a light source, and the truncated P-type diffuser 15 is not effectively utilized. The current density and brightness density are maximum in the part of the passivation layer 16 facing the ohmic contact in the opening 168 part, but this part is below the current-carrying electrode 8 made of AN and having zero translucency. Then,
The part that can emit light becomes the P-type diffusion part 15 that is not covered by the current-carrying electrode 8, as shown in FIG. It was not utilized and its utilization efficiency was poor. Furthermore, considering the positional deviation between the current-carrying electrode 8 and the P-type diffusion section 15 during pattern formation, it is difficult to keep the shape of the portion of the P-type diffusion section 15 directly below the current-carrying electrode 8 small. Met.

For example, in the optical writing head 1 of 300DPr,
20 to 30% of the area of the P-type diffusion section 15 is directly under the current-carrying electrode 8, resulting in a loss of optical output of 30 to 50%.
There was the inconvenience that it reached .

Furthermore, the optical center of the light emitted at the PN junction at the interface between the P-type diffusion part 15 and the N-type epitaxial layer 13 is the brightest part near the current-carrying electrode 8, but Pτ! Diffusion part 15
does not coincide with the geometric center formed by the intersection of the diagonal lines, so if the current-carrying electrodes 8 of each light-emitting section 5 are provided on opposite sides in the direction in which the light-emitting sections 5 are arranged, as shown in FIG. ,
Even if the light emitting sections 5 are arranged in a straight line, the optical centers of the light emitting sections 5 are substantially arranged in a staggered manner, which degrades printing quality. Particularly in the case of A-resolution, the deterioration in printing quality becomes remarkable.

In order to prevent this, it has been proposed to connect the current-carrying electrodes 8 to each light emitting part 5 from the same direction, as shown in FIG. 7, so that the optical centers are aligned in a straight line. As shown above, the energy usage efficiency is poor, and the current-carrying electrode 8
Compared to the case where electrodes 8 and bonding wires 9 are provided alternately on opposite sides, the width of the connection between the current-carrying electrode 8 and the bonding wire 9 must be made smaller. The process becomes difficult and the yield decreases accordingly, resulting in high costs.

Further, since the width of the connecting portion cannot be made smaller than a certain level, there is a limit to the arrangement density of the light emitting portions 5 based on this, and it is impossible to obtain a light emitting element array with high resolution.

The present invention has been made in view of these points, and provides a light emitting element array that can emit light with uniform brightness from the entire light emitting group to the outside, has high energy utilization efficiency, and has a plurality of light emitting parts. provides a light-emitting element and a light-emitting element array in which the characteristics of each light-emitting part are the same, the geometrical center and the optical center coincide, and high resolution and high printing quality can be obtained. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the light emitting element of the present invention according to claim 1 has a light emitting part that emits light using electrical energy, and a current-carrying electrode that supplies electrical energy to the light emitting part.
In the light emitting element, the transparent conductive film has 74 current-carrying poles that supply electrical energy to the light extraction surface of the light emitting section, which covers at least the entire surface of the light extraction surface of the light emitting section and is in ohmic contact with the light extraction surface. And gold j! is connected to the transparent N-conducting film at a position away from the light extraction surface. The light emitting element array according to claim 2, characterized in that it is formed of a film, has a plurality of light emitting parts that emit light using electrical energy, arranged at predetermined positions, and supplies electrical energy to each light emitting part. In the light-emitting element array, the current-carrying electrode is provided with a current-carrying electrode for supplying electrical energy to the light-extracting surface of each of the light-emitting parts, and the current-carrying electrode covers at least the entire surface of the light-extracting surface of the light-emitting part. It is characterized in that it is formed by a transparent conductive film that is in ohmic contact and a metal film that is connected to the transparent conductive film at a position away from the light extraction surface.

[For production]

In the single light emitting element of claim 1 and each of the light emitting elements of claim 2, electrical energy is supplied with a uniform current density to the entire light extraction surface of the light emitting part via the transparent conductive film, and the light emitting element is emitted. Light of uniform brightness is emitted from the entire group, and all the light is emitted to the outside through the transparent conductive film. In addition, since the gold film is provided in a place other than the light emitting part, all of the light that passes through the transparent conductive film is emitted to the outside without being blocked, and the loss of light amount due to light blocking as in the conventional method is eliminated. No energy is generated at all, and the energy usage efficiency is extremely high.

Furthermore, in the light emitting element array of claim 2, the shape and area of each light emitting part are the same, the overall characteristics are stable, and the geometric center and optical center of each light emitting part are the same. The print quality is extremely high.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 and 2.

1 and 2 show an embodiment of the light emitting element array of the present invention.

The light emitting element array 20 of this example is formed in the cross-sectional shape shown in FIG. That is, an N-type epitaxial cell layer 23 is formed by growing N-type GaAsP one bitaxially on a substrate 22 made of GaAS. After forming a diffusion mask 24 made of SiO2 on the entire surface of the N-type epitaxial layer 23, a plurality of openings 24a, 24a, . Established by. Next, in order to form the light emitting section 25, Zn is diffused into the N-type epitaxial layer 823 through the opening 24a to form the PP! :! The diffusion portion 26 is formed to a depth of approximately 3 μm. In this case, in order to stabilize the ohmic contact, it is preferable that the P-type concentration in the surface layer of several hundreds of layers from the surface of the P9 extension part 26 be set to be a higher than that in other parts. Next, a transparent conductive film 27 is formed on the entire upper surface of the diffusion mask 24 and the P-type diffusion section 26. In this case, the transparent 'S' electric film 27 and the upper surface of the P-type diffusion section 26 are in ohmic contact. As the material of this transparent conductive film 27, it is preferable to use an oxide of indium and 1/2. Thereafter, unnecessary portions of the transparent conductive film 27 are removed by etching or the like, and each transparent conductive N film 27 covers the entire light extraction part (top surface in FIG. 1) of the light emitting part 25, that is, the P-type diffusion part 26. A metal film 2 is placed at a position away from this P-type expanded portion 26.
8. In addition, each transparent S electric film 27
The gold Iil film 28 is placed on the opposite side in order in the column direction of the light emitting section 25.
The shape is such that it can be formed.

Next, W
A metal film 28 for connection with the outside is formed on each of I.

This metal 1!128 also serves to lower the electrical resistance of the transparent conductive jII27. As this metal film 28, metal film 2
When bonding wire 9 is bonded to bonding wire 8, Aj or AU is used to stabilize the connection, and gold lag! is used when bonding by flip-chip method. It is preferable to use N1 or the like so that 28 holds the solder bump and serves as a solder barrier layer.

Finally, the back electrode 21 is formed by depositing Au or the like on the opposite surface of the substrate 22, thereby completing the light emitting element array 20.

Next, the operation of this embodiment will be explained.

According to the light emitting element array 20 of this embodiment, each light emitting section 25
In this case, electric energy is supplied with uniform current density to the light extraction area (top surface in FIG. 1) of the P-type diffusion part 26 through the transparent conductive film 27, and the P-type diffusion part 26 and the N-type epitaxial layer are connected to each other. Light of uniform brightness is emitted from the entire PN junction between the transparent conductive film 2
The light is emitted to the outside through 7. Further, since the metal R2B is provided in a place other than the light emitting part 25, the transparent conductive film 27
All of the light that has passed through is emitted to the outside without being blocked, and the loss caused by blocking of light as in the conventional case does not occur at all, resulting in extremely high energy utilization efficiency.

Therefore, the shape and area of each light emitting part 25 are the same b, and the overall characteristics are stable. Also, the geometrical center and optical center of each light emitting part 25 completely match, so that the printing device If used as an optical writing head, the printing quality will be extremely high.

Therefore, according to this embodiment, the back electrode and the gold bottom film 28
When used as an optical writing head, by energizing a desired light emitting section 25 through the printhead, high-resolution and extremely high-quality printing that appropriately corresponds to a printing command can be performed.

Furthermore, in this embodiment, the transparent conductive film 27 can be formed directly on the diffusion mask 24, and the conventional passivation layer 16 can be omitted, making manufacturing easy and inexpensive.

In addition, although the plurality of light emitting parts 25 are arranged in a straight line in the above embodiment, the arrangement method may be changed as necessary.

Alternatively, only a single light emitting section 25 may be provided to form a light emitting element and used as a single light source.

Furthermore, the present invention is not limited to the above embodiments,
It can be changed as necessary.

〔Effect of the invention〕

As explained above, the light-emitting element and light-emitting element array of the present invention are configured and operate, so that light with uniform brightness can be emitted from the entire light-emitting group to the outside, and energy utilization efficiency is high. In a light emitting element array having light emitting parts, the characteristics of each light emitting part are the same,
The geometric center and optical center match, high resolution, and
This has the effect of achieving high printing quality.

[Brief explanation of the drawing]

1 and 2 show an embodiment of the light emitting element array of the present invention, in which FIG. 1 is a vertical side view, FIG. 2 is a plan view, and FIG.
The figure is a vertical side view of an optical writing head equipped with a conventional light emitting element array, Figure 4 is a vertical side view of a conventional light emitting element array, Figure 5 is a plan view of Figure 4, and Figure 6 (a) is FIG. 6(b) is a characteristic diagram showing the luminance distribution on the longitudinal side surface of the light emitting section, FIG. 6(C) is a characteristic diagram showing the luminance distribution on the plane of the light emitting section, and FIG. 7 is a characteristic diagram showing the luminance distribution on the plane of the light emitting section. FIG. 7 is a plan view showing another conventional example. 20... Light emitting element array 25... Light emitting section, 26.
...P9 expansion part, 27...transparent conductive film, 28...gold lll film. Guno Qfu

Claims (1)

[Scope of Claims] 1) In a light-emitting element having a light-emitting part that emits light using electrical energy and a current-carrying electrode that supplies electrical energy to the light-emitting part, electric energy is transferred to the light extraction surface side of the light-emitting part. a transparent conductive film that covers at least the entire surface of the light extraction surface of the light emitting section and is in ohmic contact with the light extraction surface, and is connected to the transparent conductive film at a position away from the light extraction surface. A light emitting element characterized in that it is formed of a metal film. 2) In a light-emitting element array in which a plurality of light-emitting parts that emit light by electrical energy are arranged at predetermined positions and a current-carrying electrode is provided for supplying electric energy to each light-emitting part, the light extraction surface of each light-emitting part A current-carrying electrode for supplying electrical energy to the transparent conductive film covers at least the entire surface of the light extraction surface of the light emitting section and is in ohmic contact with the light extraction surface, and a transparent conductive film that covers at least the entire surface of the light extraction surface of the light emitting section, and a transparent conductive film that supplies electrical energy to the light extraction surface at a position away from the light extraction surface. A light emitting element array comprising a transparent conductive film and a metal film connected to the transparent conductive film.