JPH11168239A - Gallium nitride compound semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove obstructions in a light emitting device manufacturing process and to obtain a light emitting device of high optical output by a method wherein the area ratio of a light transmission electrode to a P-type layer is optimized. SOLUTION: An N-type layer 2 and a P-type layer 3 both formed of gallium nitride compound semiconductor thin film are grown on a substrate 1, a P-side transparent electrode 4 is formed on the P-type layer 3, and provided that the surface area of the P-type layer 3 and time area of the P-side transparent electrode 4 are represented by A1 and A2 , A1 and A2 are set so as to satisfy a formula, O.4A1 <=A2 <=0.9A1 , a current injected into the P-type layer 3 is optimized to keep it high in optical output, the P-type layer 3 is prevented from interfering with the N-type layer 2, and a semiconductor light emitting device of this constitution is kept high in yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride-based compound semiconductor light-emitting device used for an optical device such as a blue light-emitting diode, and in particular, to optimize the injection of current into the entire p-type layer to improve the light emission efficiency. The present invention relates to a semiconductor light emitting device which can be kept high.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN and I
Gallium nitride-based compound semiconductors such as nAlGaN have been widely used as semiconductor materials for visible light emitting devices and high-temperature operating electronic devices, and are being developed in the field of blue light emitting diodes.

In the manufacture of a gallium nitride-based compound semiconductor, an insulating sapphire is generally used as a crystal substrate for growing a semiconductor film on its surface. When an insulating crystal substrate such as sapphire is used, unlike a light emitting element using a semiconductor substrate other than gallium nitride, such as GaAs or GaAlP, an electrode cannot be emitted from the crystal substrate side.
The p and n electrodes provided on the semiconductor layer are formed on one side of the crystal substrate.

On the other hand, in the manufacture of light-emitting elements, including those using sapphire as a crystal substrate, the method of growing a gallium nitride-based compound semiconductor thin film by a metal organic chemical vapor deposition method has recently become mainstream. That is, a source gas such as an organometallic compound gas is fed into a reactor by a carrier gas, and an n-type layer and a p-type layer are grown on the surface of the substrate to form a stack. After this growth and formation, a part of the p-type layer is removed by etching to expose the n-type layer. The n-side electrode and the p-type layer are respectively provided on the exposed part of the surface of the n-type layer and the surface of the p-type layer. A light-emitting element can be obtained by joining the p-side electrodes by, for example, an evaporation method.

In recent years, the mainstream is a sapphire crystal substrate using a gallium nitride-based compound semiconductor thin film as a pn junction to make a region of a p-type layer an emission region.
For example, Japanese Patent Application Laid-Open No. 6-314822 discloses a semiconductor light emitting device having a similar configuration.

Incidentally, the p-type layer of the gallium nitride-based compound semiconductor has a higher electric resistance than the n-type layer, so that current hardly flows. Therefore, if an electrode pad for wire bonding is formed on the upper surface of the p-type layer by a vapor deposition method,
Current tends to flow only below the electrode pad portion, and the light emission output from the entire light emission region of the p-type layer is reduced.

On the other hand, as described in the above-mentioned publication, a thin metal conductive film is formed on the upper surface of the p-type layer in order to make it easier to inject current into the entire p-type layer as well as the electrode pad portion. It has been considered effective to form an electrode as an electrode. If the electrode made of the conductive film is made light-transmitting and almost the entire surface of the p-type layer is made a light-transmitting electrode, the upper surface of the p-type layer is made pn
It is possible to assemble the light emitting layer from the light emitting layer in the junction area.

[0008]

In the case where the light-transmitting electrode is provided on the upper surface of the p-type layer, the entire light-transmitting electrode occupies almost the entire light-emitting region when viewed from the light-emitting observation surface side. Good. Therefore, in order to increase the light emission luminance and the light output, it is more effective that the area occupied by the translucent electrode is larger. For example, if a translucent electrode is formed on the entire upper surface of the p-type layer, the entire surface other than the area occupied by the p-side electrode pad for wire bonding can be used as the light extraction surface.

However, in a general manufacturing process of a gallium nitride compound semiconductor light emitting device, an n-type layer and a p-type layer are sequentially stacked on a sapphire substrate, and a part of the p-type layer is removed by etching. Then, the n-type layer is exposed, and an n-side electrode pad is formed by vapor deposition on the exposed portion. Therefore, when a light-transmitting electrode is formed on the entire surface of the p-type layer by vapor deposition, the light-transmitting electrode may come into contact with the n-side electrode due to poor patterning accuracy of the light-transmitting electrode. And the effect on product yield cannot be ignored. Therefore, although the formation of the translucent electrode over the entire upper surface of the p-type layer itself promotes the improvement of the light emitting performance,
In manufacturing, strict precision and control are required for patterning and the like, and the compatibility in the current manufacturing process is poor.

On the other hand, in order to solve such a problem in the manufacturing process, the area of the translucent electrode may be reduced so as to avoid contact with the n-side electrode. That is, if the design is made such that the light-transmitting electrode is smaller than the outer peripheral edge of the p-type layer and the safety factor against the manufacturing error is increased, product defects due to contact with the n-side electrode can be eliminated. Can be.

As described above, the size of the light-transmitting electrode formed on the upper surface of the p-side electrode affects the product yield if it is too large, and if it is avoided, the size of the light-transmitting electrode is reduced. Insufficiently, the light extraction surface becomes small, and the light emission output is reduced. In other words, in the manufacturing process, limiting the size of the translucent electrode improves the yield, while the product itself decreases the luminous performance. The design philosophy is largely divided by giving priority to the quality of the products.

As described above, the formation of the translucent electrode on the upper surface of the p-type layer can improve the light emission performance.
If the size of the translucent electrode with respect to the mold layer is large, it has not been possible to optimize both the manufacturing and the quality.

The problem to be solved in the present invention is to optimize the ratio of the light-transmitting electrode to the p-type layer so as to eliminate obstacles in the manufacturing process of the light-emitting device and to obtain a light-emitting device having a high light-emitting output. It is to make.

[0014]

SUMMARY OF THE INVENTION The present invention has a laminated structure in which at least an n-type layer and a p-type layer made of a gallium nitride-based compound semiconductor thin film are grown on a substrate. A light-emitting element in which an n-side electrode pad is joined to the exposed portion by exposing the mold layer, and a light-transmitting electrode and a p-side electrode pad are joined on the p-type layer. The area obtained by subtracting the bonding area of the side electrode pad is A
_{When the} area of the light-transmitting electrode is A ₂ , 0.4
Characterized by comprising as the relationship _{A 1 ≦ A 2 ≦ 0.9A 1} .

According to this configuration, the surface area A of the translucent electrode is
Because ₂ has a great influence on the injection of current into the p-type layer, by the relationship between the surface area A ₁ of the p-type layer to optimize this, the light emitting output and producing from the surface of the translucent electrode The yield can be kept high.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 has a laminated structure in which at least an n-type layer and a p-type layer made of a gallium nitride-based compound semiconductor thin film are grown on a substrate. The n-type layer is exposed from the portion, an n-side electrode pad is formed by joining the exposed portion, and the light transmitting electrode and the p-type electrode are formed on the p-type layer.
A light-emitting element joining the side electrode pads, the area obtained by subtracting the bonding area of the p-side electrode pad from the surface area of the p-type layer and A _1, when the area for forming the translucent electrode and A _2,
0.4A ₁ ≦ A ₂ ≦ 0.9A ₁ , and the surface area A ₂ of the translucent electrode and the surface area of the p-type layer
By the relationship between the area A ₁ minus the bonding area of the side electrode pad is identified to be optimum, an effect that allows the light output and improve product yield.

Hereinafter, specific examples of the embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a gallium nitride-based compound semiconductor light emitting device according to an embodiment of the present invention, FIG. 2 is a plan view of the light emitting device of FIG. 1, and FIG.
It is a longitudinal cross-sectional view by the arrow A line.

In FIG. 1, an n-type layer 2 and a p-type layer 3 are respectively formed on a surface of an insulating substrate 1 using sapphire by a well-known metal organic chemical vapor deposition method. , A p-side translucent electrode 4 is joined by an evaporation method, and a p-side electrode pad 5 is fixed on the upper surface of the p-side translucent electrode 4 by an evaporation method. An n-side electrode pad 6 is similarly bonded to the exposed surface of the n-type layer 2 by removing a part of the p-type layer 3 by etching. Also, as shown in FIG.
Between the mold layer 2 and the p-type layer 3, a light-emitting layer 7 formed of a thin film of indium gallium nitride (InGaN) is formed.

FIG. 4 is a schematic view showing steps from the growth and formation of the n-type layer 2 and the p-type layer 3 on the substrate 1 to the deposition of the p-side translucent electrode 4 and the n-side pad 6 in order. These figures are schematic diagrams relating to only one element in a wafer, and in actuality, manufacturing is performed as a wafer in which the elements shown in the figure are repeatedly formed two-dimensionally.

The n-type layer 2 and the p-type layer 3 are formed by a metal organic chemical vapor deposition method. An n-type GaN thin film and a p-type GaN thin film are sequentially laminated on the surface of the substrate 1, respectively. As shown in FIG. 4A, a homojunction light emitting device is obtained.

Next, for the p-type layer 3 of p-type GaN,
As shown in FIG. 4B, a substantially quarter circular area is etched at a position corresponding to the corner of the substrate 1,
A part of the n-type layer 2 is exposed.

The growth of n-type layer 2 and p-type layer 3
After removing part of the mold layer 3 by etching, FIG.
As shown in (c), a p-side light-transmitting electrode 4 having a size covering almost the entire surface of the p-type layer 3 from which a part has been removed is formed by vapor deposition, and the exposed n-type layer is etched. Similarly, a circular n-side electrode pad 6 is formed on the surface of the surface 2a by a vapor deposition method. Then, after the vapor deposition of the p-side translucent electrode 4, as shown in FIG. 1, the p-side electrode pad 5 is formed on the p-side translucent electrode 6 by vapor deposition. As described above, the light emitting layer 7 formed of a thin film of indium gallium nitride (InGaN) is formed of n
It is also well-known that a double heterostructure can be provided between the mold layer 2 and the p-type layer 3, and in this case, a light-emitting element having a higher light-emission output can be obtained. After these steps, the wafer is polished to a thickness of 1
It is thinned to about 00 microns, and is separated as an element as shown in FIG. 1 by scribe or the like.

The light emitting device manufactured in this manner has a p
If each of the side electrode pad 5 and the n-side electrode pad 6 is connected by wire bonding and then sealed with a resin by molding, a light emitting diode as a final product is obtained.

Here, as described in the section of the prior art, the emission output is improved by forming a p-side translucent electrode 4 by developing a thin metal conductive film on the upper surface of the p-type layer 3. It is as follows. The conventional structure is that the ratio of the p-side light-transmitting electrode 4 to the width of the p-type layer 3 and the shape distribution thereof are not listed as special design items. Met.

On the other hand, in the present invention, by optimizing the area ratio of the p-side translucent electrode 4 to the surface area of the p-type layer 3, the yield in the manufacturing process can be improved and the light emitting output of the light emitting device product can be increased. This can be maintained, and this will be described below.

The present inventors have found that a current is injected into the entire p-type layer 3 for the light emitting device having the configuration shown in FIGS.
As a result, the light-emitting area from the light-emitting layer 7 at the pn junction is expanded and the light-emission output is improved. Therefore, the size of the p-side translucent electrode 4 that promotes expansion of the light-emitting area is changed to the p-type layer 3. We investigated what kind of relationship it should have with the surface area of the material, and as a result, obtained the following findings.

First, the relationship between the size of the p-side translucent electrode 4 and the surface area of the p-type layer 3 can be considered separately for the relationship between the size ratio between them and the shape of each.

Regarding the latter shape relationship, it is natural that the planar shapes of the p-type layer 3 and the p-side translucent electrode 4 are completely the same or the p-side translucent electrode 4 is smaller. From the viewpoint of the manufacturing process, the p-side translucent electrode 4 is of course smaller. In a general light emitting element, a substrate 1 having a substantially square planar shape as in the illustrated example is frequently used. Therefore, the p-type layer 3 also has a simple linear element plane except for the etched portion. It has an outer shape. Therefore, in order to simplify the patterning at the time of vapor deposition formation of the p-side translucent electrode 4 and to improve the operability at the time of manufacturing, the outer shape of the p-side translucent electrode 4 is also mainly formed by a linear element. The shape is more convenient, for example, as shown in the illustrated example, the relationship may be similar to the p-type layer 3.

From the above, the relationship between the respective shapes of the p-type layer 3 and the p-side light-transmitting electrode 4 does not need to be considered so important, and the point is that the specific numerical range of the area ratio is specified. That's it. Consideration should be given to the setting of this numerical range that it does not interfere with the wire bonding area of the n-type layer 2 or the n-side electrode pad 6 after manufacturing, and that a predetermined light emission output can be maintained and there is no reduction in luminance. It is. And it is clear that the former condition is an important factor in the manufacturing process, and the latter corresponds to the items required for the final product.

Here, it is widely known that in a gallium nitride-based compound semiconductor light emitting device, a current tends to hardly flow in the p-type layer 3 layer direction. For this reason, even if a current is injected into the entire region of the p-side translucent electrode 4 and the p-side electrode pad 5, it is difficult to make the entire p-type layer 3 a light emitting region. Therefore, a region where current can be sufficiently injected into the p-type layer 3, that is, a portion where the p-side translucent electrode 4 is formed is a light emitting region when viewed from the light emission observation surface side. Further, since the p-side electrode pad 5 is not light-transmitting, the surface area of the p-side light-transmitting electrode 4 excluding the area covered by the p-side electrode pad 5 is an actual light emitting area.

From the above, the present inventors have found that the p-type layer 3
When the area of the p side translucent electrode 4 made of the surface area between A ₁ and the light-emitting region was designated A _2, these surface areas A ₁ and area A ₂
As a result of repeated studies on the relationship between the light emission output and the light emission output, it was found that the relationship was as shown in FIG. As is apparent from the characteristics of the relative light emission output shown in FIG. 5, it is understood that when A ₂ / A ₁ is 0.4 or more, a relative light emission output of 80% or more of the maximum light emission output can be obtained. Therefore, if A ₂ ≧ 0.4A ₁ is set as a condition for keeping the light emission output high, it can be said that the light emission output is sufficiently effective even in consideration of the application and the field of use of the semiconductor light emitting element.

Incidentally, the light emission output of the light emitting element, including the one using a gallium nitride compound semiconductor, tends to increase with the injected current. And in an actual device, the light emission output is not only the injected current,
It also depends on the luminous efficiency in the luminous region. This luminous efficiency is defined as the ratio of the luminous output obtained with respect to the current injected into the luminous region, and may vary depending on the current injected into the luminous region having a certain area, that is, the current density. Are known. FIG. 6 is a diagram showing the relationship between the current density and the luminous efficiency. As can be seen from the graph, the luminous efficiency is greatly reduced as the current density increases. Such a sharp decrease in luminous efficiency is accompanied by heat generation and the like when the current density is increased, so that the temperature in the luminous region rises and the luminous output is saturated. Therefore, in the gallium nitride-based compound semiconductor light emitting device in which the area of the light emitting region substantially matches the formation area of the p-side translucent electrode 4, in order to keep the light emission output high, It is preferable that the area be equal to or larger than a size at which the luminous efficiency does not greatly decrease.
According to the present invention, as a design item related to the area of the p-side translucent electrode 4, A ₂ ≧ 0.4A _1, which is a condition for keeping the light emission output as described above high, corresponds to the present invention. And others obtained by knowledge.

On the other hand, with respect to production yield, the results of extensive research Similarly, the relationship between the area A ₂ of the p side translucent electrode 4 to the surface area A ₁ of the p-type layer 3, that there is a relationship shown in FIG. 7 There was found. From the relationship between the production yield shown in FIG. 7 and the ratio of the area A ₂ of the p-side translucent electrode 4 to the surface area A ₁ of the p-type layer 3, if A ₂ / A ₁ is larger than 0.9, the production It can be seen that the yield has dropped sharply. According to the investigation and verification of the actually manufactured semiconductor light emitting device, most of the change in the manufacturing yield is such that the p-side translucent electrode 4 is in contact with and interferes with the n-type layer 2. It turns out. That is, when the margin width of the patterning of the p-side translucent electrode 4 formed by patterning on the p-type layer 3 is smaller than about 3 μm, the production yield is significantly reduced due to interference with the n-type layer 2. It is. Therefore,
From the viewpoint of the production yield, it is understood that A ₂ / A ₁ ≦ 0.9 is preferable.

From the above, the conditions for maintaining a high light emission output and a high manufacturing yield at the same time are as follows:
The present inventors have found from the knowledge that 0.4A ₁ ≦ A ₂ ≦ 0.9A ₁ .

When the relationship between the surface area A ₁ of the p-type layer 3 and the area A ₂ of the p-side translucent electrode 4 is such that 0.4 A ₁ ≦ A ₂
Under the conditions described above, the light emission output is maintained high. For example,
In general gallium nitride compound semiconductor light emitting devices,
The size of the sapphire substrate 1 having a substantially square planar shape is about 350 μm on one side, and the size of the p-type layer 3 formed on the substrate 1 is also about 7 × 10 ⁴ μm ² . The size of the p-side electrode pad 5 is 130 × 130 μm.
m. Considering the relationship between the size of each of the substrate 1, the p-type layer 3, and the p-side electrode pad 5 and the amount of light that can be extracted from the p-side translucent electrode 4, the above condition is that the light emission output and the luminance 5 cannot be a factor that causes a decrease in
As shown in FIG.

Further, from the condition of A ₂ ≦ 0.9A ₁ , the p-side light-transmitting electrode 4 is separated from the outer edge of the p-type layer 3 by a certain distance as shown in FIG. And a margin 3 having the same width between the edge and the outer periphery of the p-type layer 3.
a can be done. In a general light-emitting element, the length of one side of the p-type layer 3 is about 300 μm, and the error at the time of the vapor deposition patterning operation is in the range of 1 to 2 μm at present. Therefore, with such a size of the p-type layer 3, the width of the margin 3a can be set to a range of 3 μm or more under the condition of A ₂ ≦ 0.9A ₁ , and the p-side light transmission in the manufacturing process is performed. There is no interference of the negative electrode 4 with the n-type layer 2.

[0037]

According to the present invention, the surface area of the light-transmitting electrode and the surface area of the p-type electrode are set so that the light emission performance falls within the minimum range where the light emission performance does not fall below the required value and the maximum range where the light emission performance does not interfere with the n-side. Is optimized, so that a high-performance light-emitting element having a high light-emitting output can be obtained. Further, even in the manufacturing process, it is possible to perform production without contact between the n-side and the translucent electrode, so that the yield is greatly improved and the productivity is also improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a gallium nitride-based compound semiconductor light emitting device according to an embodiment of the present invention.

FIG. 2 is a plan view of the light emitting device of FIG.

FIG. 3 is a longitudinal sectional view taken along line AA of FIG. 2;

FIG. 4 is a graph showing the relationship between p-type growth and n-type layer growth on a substrate.
Schematic diagram sequentially showing the steps up to the deposition of the side translucent electrode and the n-side pad

FIG. 5 is a diagram showing the relationship between the relative light output and the ratio of the area of the p-side translucent electrode to the surface area of the p-type layer.

FIG. 6 is a diagram showing the relationship between current density and luminous efficiency in a gallium nitride based compound semiconductor light emitting device.

FIG. 7 is a diagram showing the relationship between the product yield and the ratio of the area of the p-side translucent electrode to the surface area of the p-type layer.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 n-type layer 2a n-type layer etching surface 3 p-type layer 3a margin 4 p-side translucent electrode 5 p-side electrode pad 6 n-side electrode pad 7 light emitting layer

Continued on the front page (72) Inventor Shunichi Unami 1006 Kazuma Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] A laminated structure in which at least an n-type layer and a p-type layer made of a gallium nitride-based compound semiconductor thin film are grown on a substrate, and an n-type layer is exposed from a part of the p-type layer. A light-emitting element in which an n-side electrode pad is bonded to a portion and a light-transmitting electrode and a p-side electrode pad are bonded on a p-type layer; subtracting the area was a _1, when the area for forming the translucent electrode and the _{a 2, 0.4A 1 ≦ a 2} ≦ 0.9A 1 become a relationship gallium nitride-based compound semiconductor light-emitting device.