JPH1012930A - Light emitting diode array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent localization of current flow in an insular semiconductor layer or fluctuation of light emission. SOLUTION: Insular semiconductor layers exhibiting one conductivity type are arranged in row on a semiconductor substrate 1 and a second semiconductor layer 3 exhibiting opposite conductivity type is formed on the first semiconductor layer 2 such that the insular semiconductor layers are exposed partially. A first electrode 4 is then arranged on the exposed part of the first semiconductor layer 2 while being connected therewith and second electrodes 5a, 5b are arranged on the upper surface of the second semiconductor layer 3 while being connected therewith. The second semiconductor layer 3 is provided on the first semiconductor layer 2 such that the circumferential edge part thereof is exposed while being recessed on the plan view and the first electrode 4 is arranged along the exposed part of the first semiconductor layer 2 while being connected therewith.

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 array, and more particularly, to a light emitting diode array used as an exposure light source for a photosensitive drum for a page printer.

[0002]

2. Description of the Related Art FIGS. 6 and 7 show a conventional light emitting diode array. FIG.
FIG. 7 is a sectional view taken along line AA of FIG. 6. 6 and 7, 21 is a semiconductor substrate, 22 is an island-shaped semiconductor layer, 23 is an individual electrode, and 24 is a common electrode.

The semiconductor substrate 21 is made of, for example, silicon (S
i) or a single crystal semiconductor substrate such as gallium arsenide (GaAs). The island-shaped semiconductor layer 22 is made of a compound semiconductor layer of gallium arsenide, aluminum gallium arsenide, or the like, and includes a layer 22a containing impurities of one conductivity type and a layer 22b containing impurities of opposite conductivity type. Layer 22a containing one conductivity type impurity and layer 22b containing opposite conductivity type impurity
A semiconductor junction is formed at the interface portion of. The island-shaped semiconductor layer 22 is formed into an island shape by, for example, mesa etching after forming a single crystal semiconductor layer made of gallium arsenide, aluminum gallium arsenide, or the like by MOCVD or MBE.

[0004] On the surface portion of the island-shaped semiconductor layer 22, for example a protective film 25 made of a silicon nitride film (Si _x N _y)
Are formed, and individual electrodes 23 made of, for example, gold (Au) are formed on the surface of the protective film 25. This individual electrode 23 is connected to a semiconductor layer 22b containing an impurity of the opposite conductivity type via a through hole formed in the protective film 25. This individual electrode 23 is formed of a layer 22 b containing an impurity of the opposite conductivity type in the island-shaped semiconductor layer 22.
Is formed so as to extend alternately to the other end face side for each adjacent island-shaped semiconductor layer 22 from the upper surface part to the vicinity of the end face of the semiconductor substrate 21 via the wall face part. A common electrode 24 is formed on almost the entire back surface of the semiconductor substrate 21.

Each light emitting diode is constituted by the island-shaped semiconductor layer 22, the individual electrode 23, and the common electrode 24. The light emitting diodes are formed on the semiconductor substrate 21 so as to be arranged in a line. In this case, for example, the individual electrode 23 becomes the anode electrode of the light emitting diode, and the common electrode 24 becomes the cathode electrode. The individual electrode 23 is connected to an external circuit at a wide portion thereof by a bonding wire or the like.

In such a light emitting diode array, for example, when a current flows in a forward direction from the individual electrode 23 to the common electrode 24, electrons are injected into the layer 22b containing the reverse conductivity type impurity, and the one conductivity type impurity is Holes are injected into the layer 22a containing. Some of these minority carriers emit light by radiative recombination with majority carriers. In addition, any one of the individual electrodes 2 of the light emitting elements formed in a row
By selecting 3 and causing a current to flow to emit light, it is used, for example, as a light source for discharging a photosensitive drum for a page printer.

However, in this conventional light emitting diode array, the individual electrodes 23 are provided on the island-like semiconductor layer 22 formed on the surface side of the semiconductor substrate 21 and the semiconductor substrate 2
Since the common electrode 24 is provided on the back surface side of the device 1, the process of forming the individual electrode 23 and the common electrode 24 is performed twice, and there is a problem that the manufacturing process becomes complicated. In addition, when the individual electrode 23 and the common electrode 24 are on both the front and back surfaces of the semiconductor substrate 21, there is a problem that the connection work is difficult when connecting to an external circuit by a wire bonding method or the like.

Accordingly, the applicant of the present application has filed Japanese Patent Application No. 7-1928.
No. 57, as shown in FIGS. 8 and 9, a lower semiconductor layer 22a containing one conductivity type impurity is provided on a semiconductor substrate 21 and an upper layer containing an opposite conductivity type impurity is formed on the lower semiconductor layer 22a. The semiconductor layer 22b is provided to have a smaller area than the lower semiconductor layer 22a, the common electrode 24 is connected to an exposed portion of the lower semiconductor layer 22a, and the individual electrode 23 is connected to the upper semiconductor layer 22b. Proposed.

With this configuration, the individual electrode 23 and the common electrode 24 can be provided on the same side of the semiconductor substrate 21 and the individual electrode 23 and the common electrode 24 can be formed simultaneously in one step, so that the light emitting diode array And the common electrode 24 is located on the same side as the individual electrode 23, so that the connection with an external circuit by a wire bonding method or the like is facilitated. Note that FIG.
Reference numeral 25 denotes an insulating film made of a silicon nitride film or the like.

Further, as shown in FIG.
Are provided in two groups so as to belong to different groups for each adjacent island-shaped semiconductor layer 22, and the individual electrodes 23 are provided such that the adjacent island-shaped semiconductor layers 22 are connected by the same individual electrode 23. I have.

In such a light emitting diode, as shown by an ellipse in FIG.
The current flows the most strongly from the connection part to the connection part between the lower semiconductor layer 22a and the common electrode 24, and the light is emitted most strongly.

However, in this conventional light emitting diode array, as shown in FIG. 10, the connection portion 24a between the common electrode 24 and the first semiconductor layer 22a is elongated in the same direction as the arrangement direction A of the island-shaped semiconductor layers 22. Although it is formed so that the connection part 23 of the individual electrode 23 and the second semiconductor layer 22b
Since a is formed such that the direction intersecting with the arrangement direction A of the island-shaped semiconductor layers 22 becomes longer, the current flow in the island-shaped semiconductor layers 22 is locally increased as shown by the arrow B in the figure. At the same time, there is a problem that the position of the island-like semiconductor layer 22 in the depth direction of the current flow tends to vary, and the emission variation occurs.

As shown in FIG. 11, a region 22b having a reverse conductivity type is provided in a semiconductor substrate 21 having one conductivity type, and a common electrode 24 is provided on the back surface side of the semiconductor substrate 21. U is formed on the periphery of the surface of the region 22b to be presented.
It has also been proposed to provide a character-shaped or annular individual electrode 23 (see, for example, JP-A-59-22372).
However, in this conventional light emitting diode array, there is a problem that the current flows still locally since the current flows substantially perpendicularly from the individual electrodes 23 to the common electrode 24.

The present invention has been made in view of such problems of the prior art, and has solved the problem that the current flow in the island-shaped semiconductor layer is localized and the light emission varies. An object is to provide a light emitting diode array.

[0015]

In order to achieve the above object, in a light emitting diode array according to the present invention, island-like semiconductor layers having one conductivity type are provided in a row on a semiconductor substrate,
A second semiconductor layer having a reverse conductivity type is provided on the first semiconductor layer so that a part of the semiconductor layer is exposed, and a first electrode is provided on an exposed portion of the first semiconductor layer. In the light-emitting diode array provided by connecting and providing the second electrode on the upper surface of the second semiconductor layer, the peripheral portion of the first semiconductor layer is exposed in a concave shape when viewed in a plan view. The second semiconductor layer is provided by being laminated on the first semiconductor layer, and the first electrode is connected along a concave portion of the first semiconductor layer.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a view showing one embodiment of a light emitting diode array according to the present invention, and FIG. 2 is a sectional view taken along line AA of FIG. 1 and 2, 1 is a semiconductor substrate, 2 is a first semiconductor layer, 3 is a second semiconductor layer, 4 is a second electrode (individual electrode), 5a and 5b are first electrodes (common electrodes). ).

The semiconductor substrate 1 is made of, for example, silicon (Si).
And a single crystal semiconductor substrate such as gallium arsenide (GaAs).

The first semiconductor layer 2 is made of gallium arsenide or gallium arsenide and aluminum gallium arsenide (Al _x Ga _{1 -x}
And a semiconductor impurity having one conductivity type. This first semiconductor layer 2 is made of, for example, M
It is formed by the OCVD method or the MBE method. That is, when the semiconductor substrate 1 is formed of silicon, the natural oxide film
MOCVD removes the high-temperature amorphous gallium arsenide at a low temperature of 450 ° C or less.
After growing to a thickness of about 0.1 to 2 μm by the MBE method or the MBE method, the temperature is raised to 500 to 700 ° C. and recrystallized to grow a gallium arsenide single crystal (two-stage growth method). In this case, the raw material of gallium is trimethylgallium ((C
H ₃ ) ₃ Ga) or the like is used, and arsine (AsH ₃ ) or the like is used as a source of arsenic. Then 750 ° C ~
Anneal at a high temperature of 1000 ° C. When a two-layer structure of gallium arsenide and aluminum gallium arsenide is used, trimethyl aluminum ((CH ₃ ) ₃ Al) or the like is used as a raw material of aluminum.

On the first semiconductor layer 2, a second semiconductor layer 3 is formed. The second semiconductor layer 3 is also made of a compound semiconductor film such as aluminum gallium arsenide and contains impurities of the opposite conductivity type. A semiconductor junction is formed at the interface between the first semiconductor layer 2 containing one conductivity type impurity and the second semiconductor layer 3 containing the opposite conductivity type impurity. The first semiconductor layer 2 is made of a semiconductor impurity such as Zn,
10 ¹⁸ contained about ~10 ¹⁹ atm / cm ^3, the second semiconductor layer 3, S, Se, Te, Ge , a semiconductor impurity, such as Si containing approximately ^{1 × 10 16 ~10 19 atm /} cm 3. The second semiconductor layer 3 is made of aluminum arsenide (A
1As) and gallium arsenide (GaAs).

After the first semiconductor layer 2 and the second semiconductor layer 3 are formed on the entire surface or a part of the semiconductor substrate 1 by lamination, the first semiconductor layer 2 and the second semiconductor layer 3 are separated from the island. So that the peripheral portion of the first semiconductor layer 2 is exposed in a concave shape when viewed in a plan view.
Is etched.

The first semiconductor layer 2 and the second semiconductor layer 3 formed in an island shape are covered with a protective film 6 made of, for example, a silicon nitride film or the like, and are aligned with the concave exposed portions of the first semiconductor layer 2. Then, for example, gold (A)
u) etc. are formed in a concave shape. That is, the first semiconductor layer 2 is divided into two groups and connected to first common electrodes 5a and 5b which are different for each group.

The second electrode 4 is formed so as to extend from the surface of the second semiconductor layer 3 to the vicinity of the end face of the semiconductor substrate 1 via the wall surface. The second electrode 4 is formed so as to be located substantially at the center of the concave portion of the first electrode 5. One second electrode 4 is formed for each adjacent second semiconductor layer 3. That is, the second electrode 4 is provided for each adjacent light emitting diode belonging to a different group. The wide portion of the second electrode 4 becomes an electrode pad for performing wire bonding for connection to an external circuit.

As described above, the first electrodes 5a and 5b are provided along the concave exposed portions of the first semiconductor layer 2, and the second electrode 4 is formed on the concave portions of the first electrodes 5a and 5b. When formed so as to be located substantially in the center, the first semiconductor layer 2
The distance between the first electrodes 5a and 5b and the second electrode 4 via the first and second semiconductor layers 3 is uniform over a wide area, and the current flow in the island-like semiconductor layer is uniform over substantially the entire area.

By selecting a combination of the second electrode 4 and the first electrodes 5a and 5b and passing an electric current, an individual light emitting diode can be selected to emit light. That is,
As shown in FIGS. 1 and 2, the semiconductor substrate 1 is a p-type or an n-type having a high resistance (1000 to 3000 Ω · cm), the first semiconductor layer 2 is an n-type, and the second semiconductor layer 3 is a p-type. If there is, when a current flows in the forward direction between the second semiconductor layer 3 and the first semiconductor layer 2, one first electrode 5a is opened while the other first electrode 5b is opened. Is grounded, only the light emitting diode connected to the first electrode 5b emits light. Therefore, even if a common second electrode 4 is provided for each adjacent second semiconductor layer 3, the first electrodes 5a and 5b are separately connected, and thus the first electrodes 5a and 5b are connected to each other.
By changing the voltage application state between b and the semiconductor substrate 1, it becomes possible to selectively cause adjacent light emitting diodes to emit light.

The present invention is not limited to the case where the island-like semiconductor layers are divided into two groups and connected to the first electrodes 5a and 5b, and the second electrode 4 is provided for each island-like semiconductor layer belonging to a different group.
The first electrode 5 and the second electrode 4 may be provided in more groups, and the first electrode 5 and the second electrode 4 may be provided for each individual island-shaped semiconductor layer.

FIGS. 3 and 4 show a second embodiment. The light-emitting diode of this embodiment is almost the same as the light-emitting diode array shown in FIGS. 1 and 2, but in this embodiment, a common first semiconductor layer 2 is provided for each adjacent island-shaped semiconductor layer. Two second semiconductor layers 3 are provided for each common first semiconductor layer 2. With this configuration, the width of the light emitting diode array can be reduced without reducing the light emitting region of the light emitting diode.

FIG. 5 is a diagram showing a third embodiment.
This embodiment is almost the same as the embodiment shown in FIGS. 3 and 4, but in this embodiment, the second electrodes 4 are provided alternately for each adjacent first semiconductor layer 2.

[0028]

As described above, according to the light-emitting diode array according to the present invention, the first semiconductor layer is exposed to the first semiconductor layer in a concave shape when viewed from above. Since the first electrode is connected and provided along the concave portion of the first semiconductor layer, the flow of current in the semiconductor layer is increased, and the light emission variation of each light emitting diode is increased. Can be eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a light emitting diode array according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a view showing a second embodiment of the light emitting diode array according to the present invention.

FIG. 4 is a sectional view taken along line AA of FIG. 3;

FIG. 5 is a diagram showing a third embodiment according to the present invention.

FIG. 6 is a view showing a conventional light emitting diode array.

FIG. 7 is a sectional view taken along line AA of FIG. 6;

FIG. 8 is a diagram showing another conventional light emitting diode array.

FIG. 9 is a sectional view taken along line AA of FIG. 8;

FIG. 10 is a diagram for explaining a current flow in another conventional light emitting diode array.

FIG. 11 is a diagram showing another conventional light emitting diode array.

[Explanation of symbols]

1 ... semiconductor substrate, 2 ... first semiconductor layer, 3 ...
A second semiconductor layer, 4 ... first electrodes, 5a, 5b
..Second electrode, 6 ... Protective film

Claims (1)

[Claims] An island-shaped semiconductor layer having one conductivity type is provided in a row on a semiconductor substrate, and a second semiconductor layer having a reverse conductivity type is provided on the first substrate so that a part of the semiconductor layer is exposed. And a first electrode connected to an exposed portion of the first semiconductor layer, and a second electrode connected to an upper surface of the second semiconductor layer. In the light-emitting diode array, the second semiconductor layer is provided on the first semiconductor layer so as to be concavely exposed when the peripheral portion of the first semiconductor layer is viewed in a plan view. A light emitting diode array, wherein said first electrode is connected along a concave portion of a semiconductor layer.