JPH05190897A - Led array light source device - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent light crosstalk in an LED array light source device. [Structure] Edge emitting LEDs 2- on the same substrate 1
1, 2-2 ,. ． 2-i ,. ． Are arranged in one row in a direction parallel to the light emitting surface 2a, and the individual LEDs 2-i are electrically and spatially separated by the separation groove 11 to form each LED 2-i.
The reflective film 5 is formed on the side surface portion intersecting with the arrangement direction via the insulating film 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED array light source device. This light source device can be used as a writing device of an electrophotographic optical printer.

[0002]

2. Description of the Related Art A plurality of edge emitting LEDs are arranged in a row in a direction parallel to a light emitting surface on a single substrate, and each LED is
There is known an LED array light source device in which EDs are electrically and spatially separated by a separation groove (Japanese Patent Laid-Open No. 60-
32373). Since this LED array light source device can arrange minute LEDs at a high density, a high dot density of 600 dpi or more is also possible.

Individual LEs of such an LED array light source device
A desired image can be written as a dot pattern by blinking D according to an image signal and forming an image of a light emission pattern on a photoconductor by an equal-magnification imaging system.

By the way, the conventional LED array light source device has the following problems. That is, when one LED is caused to emit light, the light is emitted from the light emitting surface (the surface from which light is originally to be extracted, which is in an image forming relationship with the photoconductor surface by the same-magnification image forming system in the case of the above writing). Not only the light is emitted also at the separation groove portion that electrically and spatially separates the LEDs from each other, and a part is also emitted from the light emitting surface of the adjacent LED through the light emitting layer of the adjacent LED. This phenomenon is called "light crosstalk."

When there is light crosstalk, when the light emission pattern of the LED array light source device is imaged on the photoconductor by the same-magnification imaging system, the light from the separation groove or the light emitted from the adjacent LED through the separation groove is emitted. The light emitted from the surface acts as stray light, blurs the original dot image, reduces the dot resolution, that is, MTF, and deteriorates the image quality of the image to be written and recorded.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide a novel LED array light source device capable of completely solving the above-mentioned problem of optical crosstalk.

[0007]

The LED array light source device of the present invention comprises a plurality of edge-emitting LEDs arranged in one or more rows on the same substrate. The array direction of the LEDs is a direction parallel to the above-mentioned light emission surface, that is, the surface from which light is to be extracted.

The arranged LEDs are electrically and spatially separated from each other by a separation groove. Then, a reflective film is formed on the LED side surface portion (the side surface portion facing the adjacent LED in the relationship with the adjacent LED) that intersects in the array direction via an insulating film.

Each of the edge emitting LEDs may be configured to include a double heterojunction (claim 2), a single heterojunction or a homojunction, or a P-N junction by diffusion. May be used (claim 3).

According to a second aspect of the present invention, an LED having a double heterojunction has a structure of "a common first conductivity type (N-type or P-type) GaAs substrate and a first conductivity type G
aAs buffer layer, first conductivity type Al _x Ga _1-x As cladding layer, light emitting layer Al _y Ga _1-y As (x> y) active layer, second conductivity type (P-type or N-type) Al _x Ga _1-x As
A structure in which a clad layer and a GaAs cap layer of the second conductivity type are provided "is possible (claim 4).

In such a structure, the separation groove is formed at a depth reaching at least the buffer layer from the cap layer side.

[0012]

In the LED array light source device of the present invention, the light generated in the light emitting layer of the edge emitting type LED is spontaneously emitted and has no directivity and therefore propagates toward the separation groove. Since the reflective film is formed on the side surface portion intersecting with the array direction via the insulating film, the LEs adjacent to each LED are adjacent to each other.
There is no light leakage to D.

[0013]

EXAMPLES Specific examples will be described below.

FIG. 1 shows an embodiment of an LED array light source device embodying the present invention. FIG. 1A shows a part of the device in a perspective view, and FIG. 1B shows a simplified plan view.

Referring to FIG. 1B, reference numeral 1 is a substrate,
Reference numerals 2-1, 2-2 ,. ． ． , 2-i ,. ． , 2-n are edge emitting LEDs, reference numeral 3 is a bonding pad, and reference numeral 11 is a separation groove.

As shown in the figure, when two orthogonal directions parallel to the surface of the substrate 1 are defined as X and Z directions, a plurality of LEDs 2-i are arranged in the Z direction, and the individual LEDs are electrically separated by a separation groove 11. It is spatially and spatially separated. In FIG. 1B, assuming that the direction orthogonal to the drawing is the Y direction, each LE
The "light emission surface" 2a of D2-i is parallel to the Z-Y plane,
Therefore, the array direction (Z direction) of the LEDs 2-i is parallel to the light exit surface. The individual LEDs have the same structure as each other.

FIG. 1A shows three LEDs 2-1 and 2-2 at the end of the array in the LED array shown in FIG.
2 and 2-3 are shown. As mentioned above, these LEDs
2-1, 2-2 and 2-3 have the same structure, and the same LEDs as these are arranged in one row in the Z direction in the entire device.

Hereinafter, the structure of each LED is shown in FIG.
The LED 2-1 will be described as an example. The substrate indicated by reference numeral 1 is an n-GaAs substrate, on which n-GaAs is formed.
Of the buffer layer _{21, n-Al x Ga 1} -x As (x = 0.
4) clad layer 22, Al _y Ga _1-y As (y = 0.
2) active layer 23, p-Al _x Ga _1-x As (x = 0.
4) Cladding layer 24, p-GaAs cap layer 25
Are stacked in the above order in the Y direction and include a double heterojunction. The active layer 23 is a light emitting layer.

A p-side ohmic electrode 27 is formed on the cap layer 25, and an n-side ohmic electrode 28 is provided on the back surface side of the substrate 1 as a common electrode for all LEDs. In this embodiment, the p-side ohmic electrode 27 is used.
Is Au-Zn / Au, and the n-side ohmic electrode 28 is Au.
-Ge / Ni / Au, respectively.

In FIG. 1 (A), the end surface of each LED that appears on the front side is the light exit surface 2a, which is parallel to the Z-Y plane,
It is located 10 μm from the front edge of the substrate 1. Therefore, the light from each LED is extracted to the negative side in the X direction.

On the front surface side of the substrate 1, the positive side in the X direction with respect to the light emitting surface 2a of each LED is covered with the insulating film 4 including each LED. Therefore, the insulating film 4 is formed so as to cover the “portion excluding the light emission surface” of each LED.
At the top of each LED, a part of the insulating film 4 is removed and a window is opened, and the p-side ohmic electrode 27 is exposed at the opened portion. The insulating film 4 is a SiO ₂ film, but a film of SiN, Al ₂ O ₃ or the like can also be used.

The lead electrodes 3-1, 3-2, 3-3, ... Of the bonding pad 3 (see FIG. 1 (B)) are formed in the windows of the insulating film 4 at the top of each LED. ． ． Corresponding LE
It is connected to the exposed p-side ohmic electrode of D. The bonding pad 3 for wiring is made of Cr / Au, which has a good adhesion to the insulating film 4 and is about Cr: 150Å and Au: about 3000Å which has good step coverage and can be easily bonded.

A reflective film 5 is formed on the side surface portion which intersects the arrangement direction of each LED. In this example, the reflective film 5
Is formed by depositing Au to a thickness of about 3000 Å by a resistance heating vacuum deposition method. As the reflection film 5, a film having a high reflectance such as a film made of a metal such as Al or a dielectric multilayer film can be used.

The above is the structure of the LED array light source device of this embodiment. To make such a device, for example, the following may be performed.

An n-side ohmic electrode is formed on the back side of the substrate 1, and a buffer layer 21, a cladding layer 22,
Active layer 23, cladding layer 24, cap layer 25 and p
Each layer to be the side ohmic electrode 27 is sequentially laminated. Next, dry etching using chlorine gas
A light emitting surface of the ED and a rear end surface parallel to the light emitting surface are formed, and a separation groove 11 reaching the surface portion of the substrate is formed, and the electrically and spatially separated LEDs pass through the separation groove in a direction parallel to the light emitting surface. Realize the state of being arranged.

In this state, the insulating film 4 is formed on the front surface side of the substrate 1. The insulating film 4 is formed by plasma CVD, for example.
Form to a thickness of about 000Å. Then, the reflection film 5 is uniformly formed on the upper portion of the LED array and the separation groove portion,
The reflective film portion on the top may be removed, the insulating film on the front side of the light emitting surface of the LED and the window opening portion on the LED top may be removed, and finally the bonding pad 3 may be formed.

When a forward bias is applied between the electrodes 27 and 28, the active layer 23 emits light. This light emission is due to natural light emission and has no directivity, and is emitted in all directions in the light emitting layer. However, since the side surface of the LED that intersects the array direction is formed with the reflection film 5, the light eventually comes out. Will be ejected from.

FIG. 2C shows LEDs 2-1 and 2-.
2 ,. ． , 2-i ,. ． 2-n shows the arrangement status. When the above-mentioned reflective film 5 is not provided, any LED2-
The light generated by i is emitted not only from the light emitting surface 2a but also from the side surface portion 2b and is also emitted from the light emitting surface of the adjacent LED (light crosstalk). Therefore, the light emitting portion (light emitting surface) of the LED array light source device The light emission pattern (near field pattern) on the (arrangement surface of) is a series of bimodal light intensity distributions as shown in FIG. Reference sign a indicates an overlapping region of the light intensity distribution. As described above, when the reflective film is not provided, the light emission pattern of each LED is blurred, so that the written image has a low MTF.

On the other hand, in the LED array light source device of the present invention, since light hardly leaks from the LED side surface portion 2b, the light emission pattern is the light emission pattern of each LED as shown in FIG. 2B. They are unimodal and well separated from each other. Therefore, it is possible to write an image having a high MTF.

FIG. 3 shows another embodiment. In order to avoid complications, if you think that there is no fear of confusion,
The same reference numerals as in FIG. 1 were used. FIG. 3 (A) shows a part of the apparatus in a perspective view, and FIG. 3 (B) shows an AA cross section in the above (A) figure as an end view. The simplified plan view is similar to that in FIG.

The first difference between the embodiment shown in FIG. 3 and the embodiment shown in FIG. 1 is that the surface side of the substrate 1 including each LED is covered with an insulating film 4. Due to this coating structure, each of the LEDs 2-1, 2-2 ,. ． Etc., the light emitting surface thereof is also covered with the insulating film 4 (FIG. 3 (A)),
When each LED is caused to emit light, the light is emitted to the negative side of the X axis via the insulating film 4 covering the light emitting surface. The insulating film 4 is a film of SiO ₂ as in the embodiment of FIG. 1, but a film of SiN, Al ₂ O ₃ or the like can also be used.

Of course, each of the LEDs 2-1, 2-2 ,. ． ． Etc. are arranged in the Z direction in the figure, and the individual LEDs are electrically and spatially separated by the separation groove 11. The “light emitting surface” of each LED is parallel to the Z-Y plane, and thus the LED array direction (Z direction) is parallel to the light emitting surface.

The individual LEDs have the same structure as each other and include a double heterojunction. As shown in FIG. 3B, the substrate 1,
Buffer layer 21, clad layer 22, active layer (light emitting layer) 2
3, the clad layer 24, and the cap layer 25 are laminated in the above-mentioned order in the Y direction, but these are the same as those described in connection with the embodiment of FIG.

The p-side ohmic electrode 27 is formed on the cap layer 25, and the n-side ohmic electrode 28 is provided on the back surface side of the substrate 1 as a common electrode for all LEDs, which is different from the embodiment shown in FIG. It is the same. p-side ohmic electrode 2
7 is made of Au—Zn / Au as in the embodiment of FIG. 1, and the n-side ohmic electrode 28 is made of Au—Ge / Ni / Au in this embodiment.

In FIG. 3A, the light emission surface of each LED covered with the insulating film 4 is parallel to the Z-Y plane and is located at a position 10 μm from the front edge of the substrate 1. ing.

At the top of each LED, a part of the insulating film 4 is removed to open a window, and the p-side ohmic electrode 27 exposed at the opened part has lead electrodes 3-1 and 3- of the bonding pad. 2,3-3 ,. ． ． Are connected. The bonding pad is formed as in the embodiment of FIG.

A reflective film 5 is formed on the side surface intersecting with the arrangement direction of each LED by depositing Au to a thickness of about 3000 Å by the resistance heating vacuum deposition method as in the embodiment of FIG. As the reflection film 5, a film having a high reflectance such as a film made of a metal such as Al or a dielectric multilayer film can be used.

The second difference of this embodiment from the embodiment shown in FIG. 1 is that the reflection film 5 is formed shorter than the length of each LED in the light emission direction (X direction). The reflection film 5 is ideally provided for each L as in the embodiment of FIG.
It is better to form the full length of the ED in the X direction, but L
In the process of manufacturing the ED array light source device, when the LED and the reflective film 5 are aligned, the length of the LED in the X direction and the length of the reflective film 5 in the X direction are made different from each other, so that the reflective film 5 is formed. It can be easily formed.

The LED array light source device of this embodiment can be manufactured, for example, as follows. The buffer layer 21, the clad layer 22, and the active layer 2 are provided on the front surface side of the substrate 1.
3, the clad layer 24, the cap layer 25, and the respective layers to be the p-side ohmic electrode 27 are sequentially laminated, and then the light emitting surface of the LED and the rear end surface parallel thereto are formed by a dry etching method using chlorine gas. At the same time, the separation groove 11 that reaches the surface portion of the substrate is formed, and a state in which the electrically and spatially separated LEDs are arranged in the direction parallel to the light emission surface via the separation groove is realized.

In this state, the insulating film 4 is formed on the front surface side of the substrate 1.
Is formed, for example, by plasma CVD to a thickness of about 4000Å, the reflective film 5 is uniformly formed on the upper part of the LED array and the separation groove part, and then the reflective film part on the LED top is removed to form a window opening part on the LED top. Of the lead electrodes 3-1, 3-
2 ,. ． ． To the corresponding LEDs 2-1, 2-2. ． Of P
The n-type ohmic electrode may be formed on the back surface of the substrate 1 by connecting to the type ohmic electrode 27.

When forward bias is applied between the electrodes 27 and 28 to cause light emission in the active layer 23, the light is emitted in all directions in the light emitting layer, but the LEDs intersect in the array direction.
Since the reflection film 5 is formed on the side surface, the light is emitted from the light emission surface via the insulating film 4.

Comparing the embodiment of FIG. 3 with the embodiment of FIG. 1, since it is not necessary to remove the insulating film at the light emitting end face side of the LED after the insulating film 4 is formed, the manufacturing becomes simpler. ..

4 and 5 show another embodiment. In order to avoid complication, the same reference numerals as those in FIGS. 1 and 2 are used for those which are considered not to be confused. Figure 4
(A) shows a part of the device in a perspective view, and (B) shows the BB cross section in the above (A) view as an end view. FIG. 5 shows a simplified plan view of the LED light source device of this embodiment.

The embodiment shown in FIGS. 4 and 5 is a modification of the embodiment shown in FIG. 3, and is different from the embodiment shown in FIG. 3 in that the lead of the bonding pad 3A (FIG. 5) is shown in the figure. Electrodes 3A-1, 3A-2, 3A-3 ,. ． ． ． Each LED
The tip part connected to has an area spread, and each LE
The only difference is that it is formed so as to cover the upper surface of D and the side surface portion in the LED array direction, and the side surface portion also serves as a reflection film. Of course, to ensure the independence of the lead electrodes,
The lead electrode portion that also serves as the reflection film must be separated from each other at the separation groove 11 that spatially and electrically separates the individual LEDs. The bonding pad 3A is generally formed of a metal film (in this embodiment, as in the above-described two embodiments, formed as a thin film of Cr / Au composed of about Cr: 150Å and Au: 3000Å) and is high. Since it has a reflectance, it can be effectively used as a reflective film.

The individual LEDs have the same structure as each other and include a double heterojunction, and are sequentially laminated in the Y direction as shown in FIG. 4 (B). The substrate 1, the buffer layer 21, and the cladding layer 2 are laminated.
2, the active layer (light emitting layer) 23, the cladding layer 24, and the cap layer 25 are the same as those described in the embodiment of FIG. 1, and the p-side ohmic electrode formed on the cap layer 25. 27 and the n-side ohmic electrode 28 formed on the back surface side of the substrate 1 are the same as those described with reference to the embodiment of FIG.

In FIG. 4 (A), the light emitting surface of each LED covered with the insulating film 4 is parallel to the Z-Y plane and is located at a position 10 μm from the front edge of the substrate 1. ing.

At the top of each LED, a part of the insulating film 4 is removed and a window is opened to form the lead electrode 3 of the bonding pad.
A-1, 3A-2 ,. ． The tip portion of each LE together with the p-side ohmic electrode 27 exposed in the portion where the window is opened.
It covers the upper and side surfaces of D.

To manufacture the LED array light source device of this embodiment, for example, the following may be carried out. The buffer layer 21, the clad layer 22, and the active layer 2 are provided on the front surface side of the substrate 1.
3, the clad layer 24, the cap layer 25, and the respective layers to be the p-side ohmic electrode 27 are sequentially laminated, and then the light emitting surface of the LED and the rear end surface parallel thereto are formed by a dry etching method using chlorine gas. At the same time, the separation groove 11 that reaches the surface portion of the substrate is formed, and a state in which the electrically and spatially separated LEDs are arranged in the direction parallel to the light emission surface via the separation groove is realized.

In this state, the insulating film 4 is formed on the front surface side of the substrate 1.
Is formed to a thickness of about 4000Å by plasma CVD, for example, and the insulating film on the window opening part on the LED top is removed.
Bonding pads are formed, and each lead electrode 3-1 and
3-2 .. ． ． Corresponding to the tip of the LED2-1,
2-2. ． ． To cover the upper surface and the side surface of the substrate, to form a portion which is connected to the P-type ohmic electrode 27 and also serves as a reflection surface, each lead electrode is removed at the separation groove 11, and finally the back surface of the substrate 1 is n-type. An ohmic electrode may be formed. Since the lead electrode portion of the bonding pad also serves as a reflective film, there is no need to form a dedicated reflective film, and the LED
The manufacturing process of the array light source device is further simplified as compared with the embodiment of FIG.

When forward bias is applied between the electrodes 27 and 28 to cause light emission in the active layer 23, light is emitted in all directions in the light emitting layer, but the LEDs intersect in the array direction.
Since the side surface portion is formed with the lead electrode film which also serves as the reflection film, the light is emitted from the light emitting surface through the insulating film 4.

In each of the above-mentioned embodiments, the LED array is one.
Although the case of a row is described, two or more rows of LED arrays similar to the above are formed, and the light emitting state of one row is monitored by a photosensor so as to compensate for the temporal change of the light emitting state of the LEDs. Good. In each of the above embodiments, the first
Although the conductivity type is described as N-type and the second conductivity type is described as P-type, the opposite case is of course possible.

[0052]

As described above, according to the present invention, a novel LED array light source device can be provided. Since this light source device is configured as described above, in an electronic printer or the like that uses the LED array light source device as a writing device, light crosstalk, which has been a problem in the past, can be completely prevented, and even in the case of high density recording, dot An excellent image with high resolution can be written.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining the effect of the above embodiment.

FIG. 3 is a diagram for explaining another embodiment.

FIG. 4 is a diagram for explaining another embodiment.

5 is a simplified plan view of the LED array light source device of the embodiment shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2-i LED 2a Light emission surface 4 Insulating film 5 Reflective film 11 Separation groove

Claims (4)

[Claims] 1. A plurality of edge emitting LEDs are arranged on the same substrate in one or more rows in a direction parallel to a light emitting surface, and individual LEDs are electrically and spatially separated by a separating groove. An LED array light source device, wherein a reflective film is formed on a side surface portion of each LED intersecting with the array direction via an insulating film. 2. The LED array light source device according to claim 1, wherein each of the edge-emitting LEDs includes a double heterojunction. 3. The LED array light source device according to claim 1, wherein each of the edge-emitting LEDs includes a single heterojunction, a homojunction, or a diffusion P-N junction. 4. The edge emitting type LEDs according to claim 2, wherein each of the edge emitting type LEDs has a common first conductivity type (N type or P type) GaAs substrate, a first conductivity type GaAs buffer layer, and a first conductivity type Al. _x
Ga _1-x As clad layer, light emitting layer of Al _y Ga _1-y A
s (x> y) active layer, second conductivity type (P type or N type)
An LED having a structure in which an Al _x Ga _1-x As clad layer and a GaAs cap layer of the second conductivity type are provided.
Array light source device.