JPH04174567A - Surface-emitting light emitting diode array - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a surface-emitting light emitting diode array.

Conventional technology A plurality of surface-emitting light emitting diodes are arranged to extract light generated in a plurality of active layers provided on a common substrate from light extraction surfaces formed on the substrate side and the opposite side of the active layer. Surface-emitting light emitting diode arrays have been provided in the past, and are used as light sources for printer exposure heads, displays, and the like. This surface-emitting light emitting diode array is generally produced by epitaxial growth such as vapor phase growth or liquid phase growth on a common semiconductor substrate.
It is manufactured by forming an n-junction or the like.

Problems to be Solved by the Invention However, in the surface-emitting type light-emitting diode array produced as described above, the light emission intensity of the plurality of light-emitting diodes constituting the array may not be uniform in some cases. If such a surface-emitting type light emitting diode array in which the light emitting intensity of each light emitting diode is not uniform is used as a light source for an exposure head of a printer, for example, uneven printing may occur. On the other hand, it is possible to make the light emitting intensity of each light emitting diode uniform by providing an appropriate resistance in the electric circuit that drives the surface emitting type light emitting diode array, but in this case, the surface emitting type light emitting diode It is unavoidable that the structure of an exposure head etc. equipped with an array becomes complicated, and the light emitting intensity of the other light emitting diodes is matched to the light emitting diode with the lowest light emitting intensity, so the light emitting intensity of each light emitting diode Attempting to ensure sufficient power consumption has the disadvantage of increasing power consumption.

In addition, in the above-mentioned surface-emitting type light emitting diode array,
Of the light emitted from each light emitting diode, the light directed toward the substrate may be absorbed by the substrate or the like, resulting in insufficient light emission intensity. This is especially true when a large number of light emitting diodes are arranged on a substrate and the light extraction surface of each light emitting diode is made very small, such as in a surface-emitting light emitting diode array used as a light source for exposure. It is.

If sufficient luminous intensity is not obtained in this way, for example when used as an exposure light source for a printer, the exposure of the photoreceptor becomes insufficient and the resolution of characters, images, etc. decreases. There were such problems.

The present invention has been made against the background of the above-mentioned circumstances, and its object is to provide a surface-emitting type light emitting diode array in which the light emitting intensity of each light emitting diode can be uniformly and sufficiently obtained.

Means for Solving the Problems The gist of the present invention for achieving the above object is to direct light generated within a plurality of active layers provided on a common substrate to the side of the active layer opposite to the substrate side. A surface-emitting type light-emitting diode array comprising a plurality of surface-emitting type light-emitting diodes that are arranged to be extracted from light extraction surfaces respectively formed in the surface-emitting type, the surface-emitting type light-emitting diode array comprising a plurality of surface-emitting type light-emitting diodes, each of which is formed of a semiconductor multilayer film. A light reflecting layer is provided between the active layer and the common substrate and reflects the light through light wave interference.

Operation and Effects of the Invention As described above, a semiconductor multilayer film is formed between the active layer of a plurality of light emitting diodes of a surface emitting type light emitting diode array and a common substrate, and light generated from the active layer is transmitted by light wave interference. By providing respective light reflecting layers, the light emission intensity of each light emitting diode could be made more uniform. The reason for this is that dislocations, which are linear lattice defects present in the substrate, are allowed to escape along the surface direction of the semiconductor multilayer film constituting the light reflecting layer and propagate to the active layer. This is presumed to be due to the fact that the reduction in the light emitting intensity of the light emitting diode caused by the dislocation of the substrate was prevented. When a surface-emitting type light emitting diode array in which the light emitting intensity of each light emitting diode is uniform in this manner is used, for example, as an exposure light source of a printer, printing unevenness can be suitably prevented.

Moreover, since the light reflection layer made of a semiconductor multilayer film is formed by crystal growth together with the active layer etc. in a common chamber, the surface-emitting light emitting diode array is formed so that the light emitting intensity of each light emitting diode is uniform. Compared to the case where a resistor is provided in the driving electric circuit, the structure of an exposure head etc. equipped with a surface-emitting light emitting diode array can be simplified, and the emission intensity is the lowest compared to the case where a resistor is provided in the electric circuit. Since it is not necessary to match the light emitting intensity of the light emitting diode with that of other light emitting diodes, sufficient light emitting intensity of each light emitting diode can be ensured without increasing power consumption.

In addition, the light generated from the active layer toward the substrate side is not absorbed by the substrate, etc., but is reflected by the light reflection layer, and the reflected light is also extracted from the light extraction surface. Sufficient luminous intensity can be obtained. Therefore, even if such a surface-emitting type light-emitting diode array is used as a light source for exposure in a printer, and the light extraction surface of each light-emitting diode is very small, sufficient luminous intensity can be obtained, so that the photoreceptor exposure can be carried out suitably, and sufficient resolution of characters, images, etc. can be ensured.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a perspective view showing a part of a surface-emitting type light emitting diode array according to an embodiment of the present invention, which is used as a light source for an exposure head of a printer. In FIG. 1, a surface-emitting type light-emitting diode array (hereinafter simply referred to as a light-emitting diode array) 10 has, for example, 0.7
A common substrate 12 made of n-GaAs single crystal and having a size of s X 4.5 rrm X O, 5 m (thickness)
For example, 128 surface-emitting type light emitting diodes (hereinafter simply referred to as light emitting diodes) 14 (14-I, 14
-2.14-8. ...) are arranged and configured. Each of the light emitting diodes 14 has a similar structure, and as shown in FIG.
A crand layer 18 made of S, made of p-GaAs,
For example, an active layer 20 that generates light with a wavelength of 880 nm,
A cladding layer 22 made of PGao, ssA1o, and asAs, and a cap layer 24 made of p-CyaAs are sequentially laminated to form a double heterostructure. A light extraction portion 26 (made of p”-GaAs) is formed in a part of the cap layer 24 by an impurity diffusion method.
A portion surrounded by a broken line in FIG. 2) is formed. Note that the substrate 12 has a thickness of, for example, 500 μm, and a cladding layer 18.
22 is, for example, 2 μm, and the active layer 20 is, for example, 0.2 μm.
m, the cap layer 24 and the light extraction part 26 are, for example, 1
Each layer is provided with a film thickness of μm.

The light reflecting layer 16 is composed of a semiconductor multilayer film and reflects the light incident from the active layer 20 by a light wave interference effect.
A 1 nm thick n-GaAS layer 28 and, for example, a 72 nm thick
The active layer 20 is composed of a so-called superlattice layer in which, for example, 20 pairs of n-AIAS layers 30 having a film thickness of
The wavelength selection characteristic is such that the light having the wavelength of 880 nm from the 880 nm wavelength has the maximum reflectance.

Each light emitting diode 14 first has a light reflecting N16° cladding layer 18. Active layer 20. After the cladding layer 22° and the cap layer 24 are sequentially grown in a single crystal state over the entire upper surface of the common substrate 12 by, for example, metalorganic chemical vapor deposition, the layers 16, 18, 20 . 22
．． It is formed by removing a part of 24 along a predetermined line by photolithography or the like.

As shown in FIGS. 1 and 2, on the cap layer 24 of each light emitting diode 14, an insulating layer 32 made of 5izN4 with a thickness of 0.5 μm is interposed.
Upper electrodes 34 (shaded portions in FIG. 1) made of i/Au are respectively attached over substantially the entire surface. An opening 36 is provided at a position corresponding to the light extraction portion 26 of each upper electrode 34, and a portion located on the inner peripheral side of the opening 36 on the upper surface of each light extraction portion 26 is The upper electrode 34 serves as a light extraction surface 38 for extracting the emitted light, and the peripheral edge of the opening 36 of each upper electrode 34 is brought into contact with the light extraction portion 26 . The light extraction surface 38 has a rectangular shape as shown in FIG. 1 and has a very small area (for example, 40×70 μmZ
)have. Further, the lower surface of the substrate 12 is made of AuGe.
A lower electrode 40 made of /Ni and common to each light emitting diode 14 is attached over the entire surface. The upper electrode 34 and the lower electrode 40 are each ohmic electrodes.

A large number of light emitting diode arrays 10 configured as described above are installed in an exposure head (not shown) of a printer.
Each light emitting diode 1 corresponds to the characters or images to be printed.
Light is generated from within the active layer 20 by passing a forward driving current between the upper electrodes 34 of the active layer 4 and the lower common electrode 40 . Above the active layer 20 (cladding layer 2
2 side) is emitted from the light extraction surface 38 of the light extraction section 26 toward the photosensitive drum (not shown), and the light directed downward (toward the substrate 12 side) from the active layer 20 is also reflected by the light reflection layer 16. The light is emitted from the light extraction surface 38 toward the photosensitive drum.

As a result, the photosensitive drum is exposed to light according to the characters, images, etc., and printing is performed in the same manner as normal dry copying. Note that the drive current for each light emitting diode 14 flows only from the peripheral edge of the opening 36 of the upper electrode 34 via the light extraction portion 26 to the cladding layer 22 and active layer 20 located directly below the light extraction portion 26, and is activated. Light is emitted only in the portion of the layer 20 located directly below the light extraction portion 26, and as a result, the drive current is completely cut off.

In this way, according to this embodiment, the light emitting diode array l
A common substrate 1 with the active layer 20 of each light emitting diode 14 of O
2, a semiconductor multilayer film G a A s /
Each of the light reflecting layers 16 made of an AIAs superlattice layer was provided, thereby making it possible to make the light emission intensity of each light emitting diode 14 more uniform. The reason for this is that the substrate 12 usually has a large number of dislocations, which are linear lattice defects, and the substrate 120 dislocations are active [
When propagating toward the active layer 20 side, the dislocations are allowed to escape along the boundary surfaces of the respective films of the superlattice layer, and the dislocations in the substrate 12 propagate to the active layer 20 .
It is presumed that this is because electrons and holes are prevented from recombining without emitting light at the dislocations of the substrate 12, thereby preventing a decrease in the light emission intensity of the light emitting diode 140 caused by the dislocations of the substrate 12. . In this way, by making the light emission intensity of the light emitting diodes 14 of each light emitting diode array 10 as an exposure light source more uniform, it is possible to suitably prevent printing unevenness.

According to this embodiment, the light reflection layer 16 made of a semiconductor multilayer film is formed by crystal growth together with the active layer 20 and the like in a common chamber, so that the light emission intensity of each light emitting diode is uniform. Compared to the case where an appropriate resistance is provided in the electric circuit that drives the light emitting diode array, the structure of the exposure head equipped with the light emitting diode array 10 can be simplified, and the case where the electric circuit is provided with a resistor Since it is not necessary to match the light emitting intensity of the other light emitting diodes to the light emitting diode with the lowest light emitting intensity, the light emitting intensity of each light emitting diode 14 can be ensured sufficiently without increasing power consumption.

Further, according to this embodiment, the light generated from the active layer 20 toward the substrate 12 is not absorbed by the substrate 12 but is reflected by the light reflecting layer 16, and the reflected light is also reflected from the light extraction surface 38. Since the light is emitted, the light emitting intensity of the light emitting diodes 14 constituting the light emitting diode array 10 can be sufficiently obtained. The solid line in FIG. 4 shows an example of the light output characteristics with respect to the amount of current flowing through the light emitting diode 14, and the light output is more than twice that of the conventional case shown by the broken line where no light reflective layer is provided. Obtained. and,
In this way, even in the case of the light emitting diode array 10 in which each light extraction surface 38 is small, it is possible to obtain sufficient light emission intensity from each light emitting diode 14, so that the photosensitive drum can be sufficiently exposed to light such as characters, images, etc. It is possible to suitably secure the resolution of .

Although one embodiment of the present invention has been described above based on the drawings,
The invention may also be implemented in other embodiments.

For example, each light emitting diode 14 of the light emitting diode array 10 of the above embodiment has G a A s / A I G
Although it forms an aAs double heterostructure, Gap.

The present invention can also be applied to surface-emitting light-emitting diode arrays comprising double heterostructure or single-heterostructure surface-emitting light-emitting diodes made of other compound semiconductors such as Ink and InGaAsP, or surface-emitting light-emitting diodes having a homostructure. may be applied as well.

Further, the light reflecting layer 16 of the above embodiment is made of GaAs/AlAs.
Although it is composed of a superlattice layer, it is also possible to use a multilayer light reflecting layer made of other semiconductor materials in consideration of refractive index and the like.

Furthermore, in the above embodiment, the present invention was applied to a surface-emitting light emitting diode array used as an exposure light source of a printer, but the present invention is also applicable to a surface-emitting light emitting diode array used as a display device. Even when the invention is applied, the effect of the invention is obtained in that the light emission intensity is uniform and sufficient in each light emitting diode.

Although other examples are not provided, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a part of a surface-emitting type light emitting diode array which is an embodiment of the present invention. FIG. 2 is an enlarged view of a cross section taken along line 1 in FIG. FIG. 3 is an enlarged cross-sectional view of a part of the light-reflecting layer shown in FIG. 2. FIG. FIG. 4 is a diagram showing an example of the light output characteristics of the light emitting diodes constituting the surface emitting type light emitting diode array shown in FIG. This is the time to show. 10: Surface emitting type light emitting diode array 12: Substrate 14: Surface emitting type light emitting diode 16; Light reflecting layer 20: Active layer 38: Light extraction surface Figure 1 Figure 3 Figure 4 Current (mA)

Claims (1)

[Claims] A plurality of surface-emitting type light emitting devices that extract light generated in a plurality of active layers provided on a common substrate from light extraction surfaces formed on the substrate side and the opposite side of the active layer, respectively. A surface-emitting type light-emitting diode array consisting of diodes arranged, the surface-emitting type light-emitting diode array comprising a semiconductor multilayer film, each provided between the active layer of the plurality of surface-emitting type light-emitting diodes and the common substrate, and capable of emitting light waves. A surface-emitting light emitting diode array comprising a light reflecting layer that reflects the light by interference.