JPH11251639A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase an effective solid angle, by providing one electrode in a region other than the ligh ttaking-out surface out of the whole surface in a light taking-out side, by providing the other electrode on a surface opposite to the light taking-out side, and by bending the light taking-out surface in a projection shape. SOLUTION: N- and p-GaAs layers 3 and 4 are formed on an n-GaAs substrate 2, electrode films 8 and 9 are formed on the upper surface of the layer 4 and the lower surface of the substrate 2, the electrode film 8 is etched, and a p-side electrode 5 is formed. A wafer is subjected to dicing for separating for each chip 10 and the surface is etched, thus bending a light taking-out surface 6. Since the light taking-out surface 6 is set to a projection curved surface, light that is emitted in the active layer 3 for reaching the light taking-out surface 6 can nearly vertically enter the surface 6 within an effective solid angle. More specifically, the effective solid can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor light emitting device. In particular, the present invention relates to a semiconductor light emitting device such as a light emitting diode (LED) or a surface emitting laser (LD), which is important in fields such as optical communication or optical information processing.

[0002]

2. Description of the Related Art (First Conventional Example) FIG. 8 is a schematic sectional view showing the structure of a conventional light emitting diode 51. This is n
A p-type semiconductor layer 53 (for example, a p-GaAs layer) is stacked on the p-type semiconductor layer 52 (for example, an n-GaAs layer), and
Forming a p-side electrode 54 at the center of the surface of the type semiconductor layer 53;
The n-side electrode 56 is formed on the entire lower surface of the n-type semiconductor layer 52. Thus, when a voltage is applied between the p-side electrode 54 and the n-side electrode 56, the p-side electrode 54 generates a p-type electrode in a junction region (hereinafter referred to as an active layer) between the p-type semiconductor layer 53 and the n-type semiconductor layer 52. A current is injected into a region facing the side electrode 54, and light is emitted in that region. The light thus emitted is p
The light is emitted from a region of the type semiconductor layer 53 where the p-side electrode 54 is not formed (hereinafter, referred to as a light extraction surface 55).

However, in such a light emitting diode 51, since the light extraction surface 55 is formed flat, a difference in the refractive index between the air and the p-type semiconductor layer 53 on the light extraction surface 55 causes the light extraction surface 55 to have the structure shown in FIG. As shown in (1), light emitted from the active layer is totally reflected by the light extraction surface 55 and is not extracted to the outside. For this reason, in the light emitting diode 51 having the structure as shown in FIG. 8, the amount of light that can be extracted to the outside of the device is extremely small with respect to the amount of light emitted inside the device.

For example, AlGaAs having a flat light extraction surface
The light extraction efficiency of an AlGaAs-based light emitting diode composed of the s layer is obtained as follows. Of the light emitted from the active layer and reaching the light extraction surface, the light extracted outside is only light within the effective solid angle. This is obtained by the Fresnel reflection law. Assuming that the refractive index of Al _0.5 Ga _0.5 As is 3.3 and the refractive index of air is 1.0, the effective solid angle is θ = arcsin (1 / 3.3). = 17.6 ° is obtained. The effective light extraction efficiency η of the light emitting diode is 1-co
sθ, the effective extraction efficiency in this case is η
= 4.7%. That is, only 4.7% of the light emitted from the active layer and reaching the light extraction surface is extracted to the outside.

[0005] Under such circumstances, there has been a demand for a light emitting diode which can extract a larger amount of light to the outside, that is, has a high light extraction efficiency, a high output, and is inexpensive.

(Second Conventional Example) Such total reflection of light on the light extraction surface depends not only on the difference in the refractive index between the semiconductor material and air on the light extraction surface but also on the surface shape of the light extraction surface. . Therefore, attempts have been made to increase the effective solid angle by roughening the light extraction surface of the light emitting diode, thereby improving the light extraction efficiency.

[0007] As shown in Japanese Patent Application Laid-Open No. Hei 3-163883, phosphoric acid: hydrogen peroxide: water = 3:
In this method, the light extraction surface of the p-type semiconductor layer is roughened by immersing it in a 1:21 solution or the like for several minutes. In this method, as shown in FIG. 9, when viewed microscopically, irregularities 58 having various angles are formed on the light extraction surface 55, so that the effective solid angle is increased and the light extraction efficiency of the light emitting diode 57 is improved. I do.

However, since the chip of the light emitting diode is usually potted with resin, in the light emitting diode 57 having such a structure, the unevenness 58 of the light extraction surface 55 is filled with the potting resin, and the effect of rough surface processing is obtained. And the light extraction efficiency could not be increased so much.

(Third conventional example) Japanese Patent Laid-Open No. 3-162
According to the method disclosed in Japanese Patent Publication No. 78-78, a p-side electrode 54 and an n-side electrode 56 are formed on the lower surface of an n-type semiconductor layer 52, and the light is formed on the upper surface of the p-type semiconductor layer 53, as shown in FIG. The extraction surface 55 is processed into a dome shape having a curvature by etching. Such a light emitting diode 59
In Japanese Patent Application Laid-Open No. H11-157, the effective solid angle is increased by giving the light extraction surface 55 a curvature to improve the light extraction efficiency. Further, in such a light emitting diode 59, the influence of resin potting is reduced.

However, in this light emitting diode 59, n
Since the n-side electrode 56 and the p-side electrode 54 are provided on the lower surface of the n-type semiconductor layer 52, an electrode film is formed on the lower surface of the n-type semiconductor layer 52 in the manufacturing process. It must be separated from the n-side electrode 56, and high-precision processing is required. Also, when a bonding wire is connected to the p-side electrode 54 or the n-side electrode 56, high mounting accuracy is required because the p-side electrode 54 and the n-side electrode 56 are close to each other. For this reason, the manufacturing process is complicated and the cost is high.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has as its object to achieve high light extraction efficiency and easy production. An object of the present invention is to provide a semiconductor light emitting device that can be manufactured at low cost.

[0012]

DISCLOSURE OF THE INVENTION The semiconductor light emitting device according to claim 1 has a P
In a surface-emitting type semiconductor light-emitting element having an N-junction and emitting light emitted at the bonding surface to the outside from the light extraction surface, one of the surfaces on the light extraction side is provided in a region excluding the light extraction surface. An electrode is provided, and the other electrode is provided on a surface opposite to a light extraction side, and the light extraction surface is curved in a convex shape.

According to a second aspect of the present invention, there is provided a semiconductor light emitting device having a PN junction, wherein light emitted from the junction surface is extracted from a light extraction surface to the outside. One electrode is provided in a region other than the light extraction surface of the light extraction surface, and the other electrode is provided on a surface opposite to the light extraction surface, and the light extraction surface is concavely curved.

In the semiconductor light emitting device according to the present invention, since the light extraction surface is curved in a convex or concave shape, the effective solid angle at which light emitted from the bonding surface is extracted from the light extraction surface to the outside increases. Therefore, the light extraction efficiency of the semiconductor light emitting element is increased, and a light emitting element with high luminance can be manufactured. Further, even when resin potting is performed as in an element having a light extraction surface with a roughened surface, the light extraction efficiency does not easily decrease. Moreover, in this semiconductor light emitting device, since two electrodes are provided separately on the upper and lower surfaces, high precision processing for forming the electrodes is not required, and the connection work of the bonding wires is also high. No precision is required. Therefore, it is possible to simplify the manufacture of a semiconductor light emitting device having a high light extraction efficiency with a curved light extraction surface, and to reduce the cost.

[0015]

FIG. 1 is a schematic sectional view showing a structure of a light emitting diode (LED) 1 of a full-surface light emitting type according to one embodiment of the present invention. This light emitting diode 1 has n-Ga
An n-GaAs layer 3 and a p-GaAs layer 4 on an As substrate 2
And a p-side electrode 5 is formed in the center of the upper surface of the p-GaAs layer 4, and a light extraction surface 6 around the p-side electrode 5 is curved in a convex shape. Electrode 7
Is formed. Here, the n-GaAs layer 3 is an active layer (therefore, the n-GaAs layer 3 is sometimes referred to as an active layer).

FIG. 2 is a cross-sectional view showing a process for manufacturing the light emitting diode 1, which will be described below according to the manufacturing procedure. First, as shown in FIG.
n-GaAs substrate 2 by quidPhase Epitaxy) method
(GaAs wafer) and n-GaAs layer 3 and p-GaAs
After the s layer 4 is grown, as shown in FIG.
Electrode films 8 and 9 are formed on the upper surface of the GaAs layer 4 and the lower surface of the n-GaAs substrate 2, respectively. Thereafter, as shown in FIG. 2C, the p-side electrode 5 is formed by etching the electrode film 8 on the upper surface side so as to form an electrode pattern of a full light emission type.
The lower electrode film 9 becomes the n-side electrode 7 as it is. Next, the wafer is diced or scribed to separate each chip 10 as shown in FIG. In the chip 10 thus manufactured, the light extraction surface 6 formed around the p-side electrode 5 is flat.

At this stage, the chip 10 is placed on the light extraction surface 6.
Since the difference in the refractive index between the chip 10 and the air is large, and the light extraction surface 6 is flat, the total reflection at the light extraction surface 6 causes the amount of light emitted inside the chip 10 to decrease from the light extraction surface 6. The amount of light taken out is very small.

Therefore, in the present invention, the surface of the chip 10 separated as described above is etched with an appropriate etchant to thereby obtain the light extraction surface 6 (p-GaAs) as shown in FIG. Of the surface of layer 4,
The area exposed from the p-side electrode 5) has a curvature. For example, when immersion is performed for about 10 minutes in an aqueous solution of potassium ferricyanide or the like, the light extraction surface 6 becomes a curved surface by etching. This is because etching hardly progresses at the central portion of the light extraction surface 6 of the chip 10,
This is because the etching proceeds rapidly toward the peripheral portion, and the curvature increases toward the peripheral portion of the light extraction surface 6.

In the light emitting diode 1 manufactured as described above, since the light extraction surface 6 is a convex curved surface, light emitted from the active layer 3 and reaching the light extraction surface 6 is:
The light enters the light extraction surface 6 almost perpendicularly, and can enter the light extraction surface 6 within an effective solid angle. In other words, since the effective solid angle is widened, the light extraction efficiency is improved. Moreover, since the etching does not proceed greatly near the p-side electrode 5 located at the center of the light extraction surface 6,
Under-etch hardly occurs on the p-side electrode 5, and no increase in forward voltage is observed. Further, according to the method of the present invention, the light emitting diode 1 having good light extraction efficiency can be manufactured at a low manufacturing cost because it can be obtained by a simple process of performing etching for several minutes after a general chip separation process. Can be.

(Measurement Results) An n-GaAs layer 3 and a p-GaAs layer 4 are epitaxially grown on an n-GaAs substrate 2 (wafer), and a p-side electrode 5 of full emission type is provided thereon, and an n-side electrode 5 After the provision of 7, the chips were individually separated by dicing. Then, the expanded product was immersed in a potassium ferricyanide solution for 10 minutes to produce a full-surface light emitting diode 1. This chip-shaped light-emitting diode 1 was mounted on a metal stem and molded with resin to prepare a sample.

As a result of measuring the light output using the sample thus obtained, the light output was 2.7 mW / 2 before etching.
What was 0 mA improved to 3.3 mW / 20 mA, and an increase of 22.2% was observed. The forward voltage was 1.24 mV (injection current value I _f = 30 mA), and there was no change before and after immersion in the potassium ferricyanide solution.

(Second Embodiment) FIG. 3 is a sectional view showing a structure of a light emitting diode 11 according to another embodiment of the present invention. This embodiment is a center light emitting type light emitting diode 11, in which a p-side electrode 5 is formed in a flat region on the outer periphery of a chip surface, and a light extraction surface 6 is formed in a window surrounded by the p-side electrode 5. doing. Then, the light extraction surface 6 formed in the center portion has a concave curved surface by being immersed in a potassium ferricyanide solution for 10 minutes.

In such a center emission type light emitting diode 11, when the light extraction surface 6 is flat, the light path of the light emitted in the current injection region of the active layer 3, that is, the outer peripheral portion of the active layer 3, is reduced. In the surface 6, the probability of being outside the effective solid angle increases, and the light output decreases. However, in this embodiment, since the light extraction surface 6 is formed as a concave curved surface, the effective solid angle increases, and the light emitting diode 1
1 increases the light output. Moreover, in the p-side electrode 5 disposed around the light extraction surface 6 as in this embodiment, almost no under-etch occurs under the p-side electrode 5 and the forward direction There is no increase in voltage.

(Third Embodiment) FIG. 4 is a schematic sectional view showing the structure of a light emitting diode 12 according to still another embodiment of the present invention. In this embodiment, a high-resistance layer 13 is formed in a region of the p-GaAs layer 4 facing the p-side electrode 5 in a light emitting diode 12 of the same type as the embodiment of FIG. . The high resistance layer 13 is made of p-G
It is formed by injecting or diffusing an n-type impurity into the aAs layer 4 and controlling the diffusion depth.

High resistance layer 1 formed directly below p-side electrode 5
Numeral 3 prevents the current injected from the p-side electrode 5 into the active layer 3 from concentrating directly below the p-side electrode 5. When the high resistance layer 13 is not provided, the current injected from the p-side electrode 5 into the active layer 3 is concentrated in a region of the active layer 3 facing the p-side electrode 5, and the active layer 3 also emits light in this region. The light emitted in such a region is shaded by the p-side electrode 5 and cannot be sufficiently extracted from the light extraction surface 6. On the other hand, when the high-resistance layer 13 is provided immediately below the p-side electrode 5, the current injected from the p-side electrode 5 is injected into the active layer 3, bypassing the high-resistance layer 13 and facing the light extraction surface 6. Light is emitted in the region where Therefore, light is efficiently extracted from the light extraction surface 6 without being shaded by the p-side electrode 5, and the light emitting efficiency of the light emitting diode 12 is improved.

When the high resistance layer 13 is provided, the active layer 3
Of these, the region into which the current is injected is the peripheral portion of the chip, and the probability that the light emitted from the active layer 3 is outside the effective solid angle of the light extraction surface 6 is increased. Since the solid angle can be increased, the output can be improved.

In the embodiment shown in FIG. 4, a high-resistance layer 13 is provided in a light emitting diode 12 of a full-surface light emitting type, but a light emitting diode 14 of a center light emitting type as shown in FIG. The high-resistance layer 13 may be formed on the substrate.

(Fourth Embodiment) FIG. 6 is a schematic sectional view showing the structure of a light emitting diode 15 of a full-surface light emitting type according to still another embodiment of the present invention. This light emitting diode 15
In the above, a high-resistance layer 13 is provided inside the p-GaAs layer 4 as the active layer 3 so as to face the p-side electrode 5, and a multilayer reflective film 16 is provided below the n-GaAs layer 3. Has formed. The multilayer reflective film 16 in this section of the specification multilayer laminated two semiconductor layers of the n-GaAs layer 3 smaller refractive index n ₁ than, n ₂ and alternately each semiconductor layer with a refractive index n _1, n ₂ Are λ / (4n ₁ ) and λ / (4n ₂ ), respectively. Here, λ is the wavelength of light emitted from the active layer 3.

By forming the multilayer reflective film 16 between the active layer 3 and the n-GaAs substrate 2, of the optical path components of the light emitted from the active layer 3, the light traveling in the back direction is reflected by the multilayer reflective film 16.
And can be effectively extracted from the light extraction surface 6. Moreover, since the light extraction surface 6 is curved, the effective solid angle is further increased, and the output of the light emitting diode 15 is improved.

The thickness of each semiconductor layer constituting the multilayer reflective film 16 is changed within a range of ± 15% around λ / (4n ₁ ) and λ / (4n ₂ ). They may be alternately stacked. By making the film thickness uneven, the reflectivity is slightly reduced, but the bandwidth of the reflectivity characteristic can be widened and the emission wavelength λ (peak wavelength) is ± 20 to 30 nm.
Of width.

Such a structure can also be applied to a center light emitting type light emitting diode 17 as shown in FIG.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a structure of a light emitting diode according to an embodiment of the present invention.

FIGS. 2A to 2E are schematic cross-sectional views showing steps of manufacturing the light emitting diode according to the embodiment.

FIG. 3 is a schematic cross-sectional view illustrating a structure of a light emitting diode according to another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a structure of a light emitting diode according to still another embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating a structure of a light emitting diode according to still another embodiment of the present invention.

FIG. 6 is a schematic sectional view showing a structure of a light emitting diode according to still another embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view illustrating a structure of a light emitting diode according to still another embodiment of the present invention.

FIG. 8 is a schematic sectional view showing the structure of a light emitting diode according to a conventional example.

FIG. 9 is a schematic sectional view showing the structure of another conventional light emitting diode.

FIG. 10 is a schematic sectional view showing a structure of a light emitting diode according to another conventional example.

[Explanation of symbols]

 Reference Signs List 2 n-GaAs substrate 3 n-GaAs layer (active layer) 4 p-GaAs layer 5 p-side electrode 6 light extraction surface 7 n-side electrode 13 high-resistance layer 16 multilayer reflection film

Claims (2)

[Claims] 1. A surface-emitting type semiconductor light-emitting device having a PN junction, wherein light emitted at the junction surface is extracted from a light extraction surface to the outside. A semiconductor light emitting device, wherein one electrode is provided in a region excluding the other, and the other electrode is provided on a surface opposite to a light extraction side, and the light extraction surface is curved in a convex shape. 2. A surface-emitting type semiconductor light-emitting device having a PN junction, wherein light emitted at the junction surface is extracted from a light extraction surface to the outside. A semiconductor light emitting device, wherein one electrode is provided in a region excepted, and the other electrode is provided on a surface opposite to a light extraction side, and the light extraction surface is concavely curved.