JP2002076436A - Led array - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED array for enhancing the light emitting intensity of each element. SOLUTION: The LED array comprises a one conductivity buffer layer 10, an insertion layer 22, one conductivity semiconductor clad layer 12, a reverse conductivity semiconductor active layer 13 and a reverse conductivity semiconductor clad layer 14 sequentially laminated on one main surface of a semiconductor substrate 9. Further, the LED array comprises a reverse conductivity contact layer 15 and one electrode 16 sequentially laminated near an end on the layer 14. The LED array also comprises another electrode 17 formed on another main surface of the substrate 9. In this case, the etching rate of the layer 11 is larger than those of both layer 10 and the layer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly to an LED array used as a light source for exposure of a photosensitive drum for a page printer.

[0002]

2. Description of the Related Art A conventional LED array disclosed in JP-A-10-242507 will be described with reference to FIG.

According to this LED array, an n-type GaAs buffer layer 2, an n-type AlGaAs cladding layer 3, a p-type AlGaAs active layer 4, a p-type AlGaAs cladding layer 5,
Then, a P-type contact layer 6 is sequentially formed, and a P-side electrode 7 is provided on the surface of the contact layer 6, thereby forming a light emitting element. Further, an n-side electrode 8 is provided on the back surface of the n-type GaAs substrate 1.

In the LED array having the above-described structure, a gentle inverted mesa shape is formed by wet etching at the time of element isolation, thereby increasing luminous efficiency.

[0005] That is, at the time of element separation in an AlGaAs / GaAs LED array, wet etching using sulfuric acid / hydrogen peroxide / water is performed. At that time, anisotropic etching is performed. An inverted mesa shape appears only in a certain direction. When a film was formed on the (100) plane, the (011)
The surface has an inverted mesa shape, and the (0 1 1) surface has a forward mesa shape. There is also a difference in the etching rate between the AlGaAs layer and the GaAs layer. The etching rate of the AlGaAs layer is higher than that of the GaAs layer, and the angle of the inverted mesa shape changes depending on the layer configuration.

[0006] As described above, the light emitting device is usually formed in a gentle inverted mesa shape, and the luminous efficiency is increased by using the reflection at the interface.

[0007]

SUMMARY OF THE INVENTION However, the conventional
In the AlGaAs LED array, the size of each element was reduced due to the arrangement of the light emitting elements at a high density, and therefore, the area ratio of the element covered by the P-side electrode 7 was increased, and light was emitted inside the element. Of the light, the proportion blocked by the P-side electrode 7 tended to increase, and as a result, the luminous intensity was significantly reduced. Accordingly, the present invention has been completed in view of the above, and an object of the present invention is to provide an LED array in which the light emission intensity of each element is increased.

Another object of the present invention is to provide an LED array suitable for a high-density page printer by arranging light-emitting elements at high density.

[0009]

An LED array according to the present invention comprises: a semiconductor substrate having one conductivity type; a buffer layer having one conductivity type; a first cladding layer having one conductivity type;
An active layer, an anti-conductivity type second cladding layer, and a plurality of elements formed sequentially with one electrode are arranged in an island shape, and the other electrode is provided on the back surface of the semiconductor substrate. It is composed of a mesa-type semiconductor light emitting element that emits more light, and further, the one electrode is disposed near the end of each element, and between the buffer layer and the first cladding layer, the etching rate is larger than the etching rate for these layers. A layer having an etching rate is interposed.

In the conventional LED array, since the electrode is provided substantially at the center of the element, the current density immediately below the electrode is increased, and the light emission becomes strongest immediately below the electrode. In addition, since such an electrode is made of metal, it has a light-shielding property, light emission is blocked, and light emission cannot be efficiently emitted.

On the other hand, the LED array of the present invention has a structure in which the buffer layer and the first clad layer are disposed between the buffer layer and the first clad layer as described above.
By interposing a layer having an etching rate higher than the etching rate for these layers, when the light emitting element is separated into islands, the cross section of the light emitting element has a strong inverted mesa shape.

In addition, since the one electrode is disposed near the end of the element, even if the current density immediately below the one electrode is increased, the cross-sectional shape of the light-emitting element forms an inverted mesa shape as described above. As a result, the current is concentrated at a position shifted from immediately below the electrode, and therefore, a structure in which the strongest light emission occurs except immediately below the electrode is obtained. As a result, light emitted from the active layer can be efficiently extracted.

The light emitted from the active layer spreads up, down, left, and right. However, when the light emitted in the lateral direction exits from the inside of the device to the outside having a different refractive index, if the inverted mesa shape becomes strong, the light enters the interface. And the reflectance at the interface increases, thereby increasing the rate of guiding light in the horizontal direction upward, thereby increasing the luminous efficiency.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 is a schematic sectional view of each semiconductor light emitting element arranged in an island shape in the LED head of the present invention.
In this example, a red AlGaAs LED array is exemplified.

In FIG. 2, reference numeral 9 denotes a semiconductor substrate. On one main surface of the semiconductor substrate 9, a buffer layer 10 of one conductivity type, the layer 11 having a large etching rate, and one conductivity type of the first cladding layer. A semiconductor cladding layer 12, a reverse conductivity type semiconductor active layer 13, and a reverse conductivity type semiconductor cladding layer 14, which is the second cladding layer, are sequentially laminated, and a reverse conductivity type contact is formed near an end on the reverse conductivity type semiconductor cladding layer 14. The layer 15 and the one electrode 16 are sequentially laminated.

On the other main surface of the semiconductor substrate 9, another electrode 17 is formed. The semiconductor substrate 9 contains 1 × 1 impurity of one conductivity type.
0 ¹⁷ to 10 ¹⁹ atoms / cm ^{3, from} a single crystal semiconductor substrate such as silicon (Si), gallium arsenide (GaAs) or indium phosphide (InP) or a single crystal insulating substrate such as sapphire (Al ₂ O ₃ ) Become.

In the case of a single crystal semiconductor substrate, the (100) plane is <011>
A substrate that is turned off by 2 to 7 degrees in the direction is preferably used. In the case of sapphire, a C-plane substrate is preferably used.

The buffer layer 10 is made of gallium arsenide (GaAs) or the like, and contains one conductivity type impurity (Si or the like) at 1 × 10 ¹⁷ to 10 ¹⁹ atoms.
/ cm ^3, and formed to a thickness of about 2 to 4 μm to prevent or reduce misfit dislocation due to lattice mismatch between the semiconductor substrate 9 and the semiconductor layer.

Layer 11 having high etching rate
(Hereinafter referred to as the insertion layer 11) is made of aluminum arsenide (AlA
s) or aluminum gallium arsenide (AlGaAs) having a higher Al composition than the one-conductivity-type semiconductor cladding layer 12.

The thickness of the insertion layer 11 is 0.05 to 2 μm.
m is preferably set to 0.1 to 1.0 μm, which has an advantage that a rise in driving voltage due to the insertion layer 11 is suppressed and a strong inverted mesa shape is obtained.

The one conductivity type semiconductor cladding layer 12 is configured as an electron injection layer. And, formed of aluminum gallium arsenide (AlGaAs), contains about 1 × 10 ¹⁶ to 10 ¹⁹ atoms / cm ³ of one conductivity type semiconductor impurity such as silicon,
The thickness is about 0.2 to 4 μm.

The opposite conductivity type semiconductor active layer 13 is formed of aluminum gallium arsenide (AlGaAs), and contains about 1 × 10 ¹⁶ to 10 ²¹ atoms / cm ³ of opposite conductivity type semiconductor impurities such as zinc (Zn). The thickness is about 4 μm.

The opposite conductivity type semiconductor cladding layer 14 is formed of aluminum gallium arsenide (AlGaAs), contains about 1 × 10 ¹⁶ to 10 ²¹ atoms / cm ³ of opposite conductivity type semiconductor impurities such as zinc (Zn), and has a thickness of 0.2 to 10 × 10 ²¹ atoms / cm ^3. The thickness is about 4 μm.

The mixed crystal ratio of aluminum arsenide (AlAs) and gallium arsenide (GaAs) of the opposite conductivity type semiconductor active layer 13 and the opposite conductivity type semiconductor cladding layer 14 is considered in consideration of the carrier confinement effect and light transmittance. I make them different.

The ohmic contact layer 15 is formed of gallium arsenide (GaAs) and contains about 1 × 10 ¹⁹ to 10 ²⁰ atoms / cm ³ of a reverse conductivity type semiconductor impurity such as zinc (Zn).
The thickness is about μm.

Next, a method of manufacturing the semiconductor light emitting device having the above configuration will be described. First, the semiconductor substrate 9 is hydrogenated by MOCVD.
The temperature is raised from 700 ° C. to 1000 ° C. in an atmosphere of (H ₂ ) and arsine gas (AsH ₃ ) to remove oxides on the surface of the semiconductor substrate 9.

Next, trimethylgallium (hereinafter, TMG), arsine gas (AsH ₃ ), and silane gas (SiH ₄ ) are supplied as dopant gases at a substrate temperature of 500 ° C. to 800 ° C. to supply the buffer layer 1.
0 is formed at 2 to 4 μm.

Further, TMG, trimethylaluminum (hereinafter, TMA), arsine gas (AsH ₃ ) and silane gas (SiH ₄ ) are used as source gases as dopant gases, and the insertion layer 11 is formed.
To form

After that, the one conductivity type semiconductor clad layer 12 is formed using silane gas (SiH ₄ ) as a dopant gas. Using dimethylzinc (hereinafter referred to as DMZ) as a dopant gas thereon, a reverse conductive semiconductor active layer 13, a reverse conductive semiconductor clad layer 14, and an ohmic contact layer 15 are formed.
Are sequentially formed.

By sequentially laminating and etching each layer as described above, each element has a strong inverted mesa shape as shown in FIG.

This etching step will be described with reference to FIGS. In the present invention, the etching rate of the insertion layer 11 is set higher than the etching rates of both the one conductivity type buffer layer 10 and the one conductivity type semiconductor clad layer 12.

According to this structure, a mesa structure is formed on the crystal layer after the growth by using a sulfuric acid / hydrogen peroxide-based etching solution. As shown in FIG. 3, a gentle inverted mesa shape is formed. Reference numeral 18 denotes a resist mask used for etching.

Thereafter, the etching proceeds, and when the insertion layer 11 having a high Al composition appears, the etching rate increases,
Then, the etching in the lateral direction greatly proceeds, and the etching of this layer results in a strong inverted mesa shape as shown in FIG.

Thereafter, as shown in FIG. 5, a buffer layer having a low etching rate appears, and the buffer layer has an inverted mesa shape.

Thereafter, one electrode 16 is formed of gold / germanium (AuGe) or the like by using an evaporation method or a sputtering method.
And the other electrode 17 is formed.

Thus, according to the LED array of the present invention,
One conductivity type buffer layer 10 and one conductivity type semiconductor cladding layer 1
2 and the insertion layer 11 having the above-described configuration,
When the light-emitting elements are separated into islands, the cross-sectional shape of the light-emitting elements becomes a strong inverted mesa shape, and the current density immediately below one of the electrodes 16 is increased by disposing one electrode near the end of each element. Even if it is, the current is concentrated at a position shifted from immediately below the electrode, thereby providing a structure in which the strongest light emission occurs except immediately below the one electrode 16, and as a result, light emitted from the active layer can be efficiently extracted. did it.

[0036]

As described above, according to the LED array of the present invention, a buffer layer having one conductivity type, a first cladding layer having one conductivity type, and an active layer are provided on a semiconductor substrate having one conductivity type. And a plurality of elements formed by sequentially forming an anti-conductivity type second cladding layer and one electrode are arranged in an island shape, and the other electrode is provided on the back surface of the semiconductor substrate, and light is emitted from above the second cladding layer. A mesa-type semiconductor light emitting device, and the one electrode is disposed near the end of each device,
Further, a layer having an etching rate higher than the etching rate for these layers is interposed between the buffer layer and the first cladding layer.

As a result, in the conventional LED array, since the electrode is provided almost at the center of the element, the current density immediately below the electrode is increased, whereby the light emission is generated immediately below the electrode. Since such an electrode is made of metal, it has a light-shielding property, light emission is blocked, and light emission cannot be efficiently emitted.
On the other hand, the LED array of the present invention has a light emission by interposing a layer having an etching rate higher than the etching rate for these layers between the buffer layer and the first cladding layer as described above. When the element is separated into islands, the cross-sectional shape of the light emitting element becomes a strong inverted mesa shape,
Moreover, by disposing one electrode near the end of the element,
On the other hand, even if the current density immediately below the electrode increases, the cross-sectional shape of the light-emitting element forms a strong inverted mesa shape as described above, so that the current is concentrated at a position displaced from immediately below the electrode. The structure that generated the strongest light emission was obtained. As a result, light emitted from the active layer could be efficiently extracted.

Further, according to the present invention, the light emitted from the active layer spreads up, down, left and right, but the light emitted in the lateral direction has an inverted mesa shape at the interface from the inside of the device to the outside having a different refractive index. When it becomes stronger, the angle of incidence on the interface increases, and the reflectivity at the interface increases. As a result, the rate of guiding the light in the horizontal direction upward increases, and the luminous efficiency also significantly increases at that point.

Further, in the present invention, the light emission intensity of each element is increased, and the light emitting elements are arranged at a high density.
An LED array suitable for a high-density page printer could be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a light emitting element of a conventional LED array.

FIG. 2 is a sectional view of a light emitting element of the LED array according to the present invention.

FIG. 3 is a view showing one step when the LED array of the present invention is manufactured.

FIG. 4 is a process chart when the LED array of the present invention is manufactured.

FIG. 5 is a process chart when the LED array of the present invention is manufactured.

[Explanation of symbols]

 Reference Signs List 9 ... Semiconductor substrate 10 ... One conductivity type buffer layer 11 ... Insertion layer 12 ... One conductivity type semiconductor clad layer 13 ... Reverse conductivity type semiconductor active layer 14 ... Reverse conductivity type semiconductor clad Layer 15: reverse conductivity type contact layer 16: one electrode 17: other electrode 18: resist mask

Claims (1)

[Claims] 1. A semiconductor substrate having one conductivity type, a buffer layer having one conductivity type, a first cladding layer having one conductivity type, an active layer, and a second cladding layer having an anti-conductivity type. A plurality of elements sequentially formed with electrodes are arranged in an island shape,
The other electrode is provided on the back surface of the semiconductor substrate, and in the LED array that emits light from the upper part of the second clad layer, the one electrode is disposed near an end of each element, and the one electrode is disposed between the buffer layer and the first clad layer. An LED array, characterized in that a layer having an etching rate higher than an etching rate for these layers is interposed between the layers.