JPH08167738A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE: To provide a light emitting diode which has a relatively high luminance performance over a wide range from a small-current region to a large-current region. CONSTITUTION: A cathode 19 is formed on the lower surface of a semiconductor substrate composed of a substrate layer 11, a buffer layer 12, an n-type clad layer 13, an active layer 14, a p-type clad layer 15, a first and a second current blocking layers 16a and 16b, and a contact layer 17 and an anode 18 is formed at the center of the upper surface of the semiconductor substrate. The first current blocking layer 16a is positioned below the anode 18 and the second current blocking layer 16b is formed in an annular shape so that the layer 16b can be exposed on the side of the semiconductor substrate. In addition, the upper surface 20 and side 21 of the semiconductor substrate are roughened.

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,
More specifically, it relates to a structure for improving the luminous efficiency of a semiconductor light emitting device.

[0002]

2. Description of the Related Art A semiconductor light emitting diode having a double heterostructure portion in which an active layer made of, for example, AlGaInP is sandwiched by cladding layers is known. This type of light emitting diode has an n-type (first conductivity type) GaA as shown in FIG.
Substrate layer 1, n-type GaAs buffer layer 2, and n-type AlGa
InP clad layer 3, AlGaInP active layer 4, p-type (second conductivity type) AlGaInP clad layer 5, and n-type Al
A semiconductor substrate in which a GaInP current blocking layer 6 and a p-type AlGaAs contact layer 7 are sequentially stacked, and an anode electrode (first electrode) 8 formed on the upper surface of the contact layer 7.
And a cathode electrode (second electrode) 9 formed on the lower surface of the GaAs substrate layer 1. The current blocking layer 6
Is partially formed on the p-type clad layer 5 and is formed below the anode electrode 8 in plan view. The current blocking layer 6 functions to spread the current flowing from the anode electrode 8 to the peripheral side of the device and improve the light extraction efficiency. That is, if the structure is such that the current blocking layer 6 is not formed, the current flowing from the electrode 8 is generated by the contact layer 7.
And the clad layer 5 does not spread so much and is injected into the active layer 4 immediately below the electrode 8 so that the main light emitting region is the anode electrode 8
Occurs directly below. In this way, the light emitting region is the anode electrode 8
When the light is generated immediately below, the light generated in the light emitting region is blocked by the anode electrode 8 and the light extraction efficiency decreases. On the other hand, when the current blocking layer 6 is formed as shown in FIG. 1, the current I flows to the outside of the current blocking layer 6 as shown by the arrow, and the main light emitting region is located outside the anode electrode 8 when viewed in plan. Moving. As a result, the light extraction efficiency is improved.

[0003]

By the way, in the semiconductor element shown in FIG. 1, when the surface (side surface / top surface light extraction surface) of the semiconductor substrate is roughened, the semiconductor light emitting element and the sealing body for covering the same are formed. The total reflection at the interface is reduced, light can be efficiently extracted to the outside of the semiconductor element, and the light extraction efficiency is improved.

However, while the roughening of the device surface is expected to improve the light extraction efficiency, it causes an increase in non-radiative recombination in the vicinity of the side surface of the semiconductor substrate, so that the emission efficiency is improved as expected. The reality is that this cannot be achieved.
This will be described in detail with reference to FIG. Anode electrode 8
In FIG. 4 showing the current I between the cathode electrode 9 and the cathode electrode 9 and the luminous intensity L of the light emission on a logarithmic scale, the characteristic line A shows the characteristic of a normal light emitting diode in which the surface of the semiconductor substrate is not roughened,
A characteristic line B shows the characteristics of the light emitting diode in which the surface of the semiconductor substrate is roughened, and a characteristic line C shows the characteristics of the light emitting diode of the embodiment of the present invention described later. Characteristic line A of a light-emitting diode not roughened and characteristic line B of a light-emitting diode roughened
As is clear from the comparison with, when roughening the surface, in the large current region, the effect of increasing the light extraction effect due to the roughening is exerted, and high luminous intensity is possible, but in the relatively small current region, The effect of non-radiative recombination due to roughening becomes more dominant than the effect of improving light extraction efficiency due to roughening,
The luminous intensity is lower than that of an element not roughened. Nowadays, it is particularly desired to increase the luminous intensity in this relatively small current region. In addition, if the roughened element can achieve high luminous intensity in a relatively small current region, one roughened element can be used for a wide range of applications, which is convenient.

Therefore, an object of the present invention is to provide a semiconductor light emitting device capable of increasing the luminous intensity in a low current region.

[0006]

The present invention for achieving the above object comprises at least a first conductivity type cladding layer, an active layer, a second conductivity type cladding layer opposite to the first conductivity type, and a first conductivity type cladding layer. A semiconductor substrate in which a conductivity type current blocking layer and a second conductivity type contact layer are sequentially arranged; a first electrode connected to the contact layer on one main surface of the semiconductor substrate; In a semiconductor light emitting device having a second electrode disposed on the other main surface and electrically connected to the first conductivity type cladding layer, the first electrode is one main surface of the semiconductor substrate. The current blocking layer is provided in a central portion of the surface, and the current blocking layer includes first and second current blocking layers, and the first current blocking layer has a portion overlapping with the first electrode in plan view. Is arranged and said second current block A layer relating to a semiconductor light-emitting device, characterized in that the layer is formed so as to surround the first current blocking layer via the contact layer in plan view and to be exposed at a side surface of the semiconductor substrate. Is. It is desirable that the side surface of the semiconductor substrate is roughened as described in claim 2. Further, as described in claim 3, it is desirable to roughen both the side surface and the main surface.

[0007]

According to the invention of each claim, since the second current blocking layer is formed so as to be exposed at the side surface of the semiconductor substrate, the current does not substantially flow in the vicinity of the side surface.
The vicinity of the side surface of the semiconductor substrate has minute cracks due to dicing or the like, and includes many traps in which non-radiative recombination occurs. Therefore, even if a current flows in the vicinity of the side surface, recombination that does not contribute to light emission occurs, resulting in a decrease in light emission efficiency. In contrast,
In the present invention, since the current does not flow in the vicinity of the side surface due to the function of the second current blocking layer, the amount of current that does not contribute to light emission is reduced and efficiency is improved. When the side surface described in claim 2 is roughened, total reflection on the side surface of the light emitted in the side surface direction is blocked, and the light extraction efficiency is improved. Note that the roughening causes cracks and the like near the side surface of the semiconductor substrate to increase recombination which does not contribute to light emission, but the current near the side surface is limited by the second current blocking layer. In particular, it is possible to reduce the decrease in efficiency particularly in the small current region. When the main surface is also roughened as described in claim 3, total reflection is prevented here, and the efficiency can be increased particularly in a large current region.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor light emitting device, that is, a light emitting diode according to an embodiment of the present invention will be described below with reference to FIGS. The light emitting diode (L
ED) is an n-type GaAs substrate layer 11, an n-type GaAs buffer layer 12, an n-type AlGaInP clad layer 13 and Al.
GaInP active layer 14, p-type AlGaInP clad layer 15, first and second n-type AlGaInP current blocking layers 16a and 16b, and p-type AlGaAs contact layer 17
A semiconductor substrate in which layers are sequentially stacked, an anode electrode (first electrode) 18 formed on the upper surface of the contact layer 17,
It has a cathode electrode (second electrode) 19 formed on the lower surface of the substrate layer 11. The portion of the light emitting diode of FIG. 2 excluding the first and second current blocking layers 16a and 16b is substantially the same as that of FIG.

As shown by the chain line in FIG. 3, the anode electrode 18 is formed in the central portion of the upper surface of the contact layer 17 in plan view and has a substantially circular planar shape. The planar shape of the anode electrode 18 is not limited to the circular shape, and may be a substantially rectangular planar shape in accordance with the planar shape of the element. A region on the upper surface of the contact layer 17 where the anode electrode 18 is not formed, that is, a ring-shaped region surrounding the anode electrode 18 in plan view becomes a light extraction region 20. Although the cathode electrode 19 is formed on the entire lower surface of the GaAs substrate layer 11, the outer edge of the cathode electrode 19 may be slightly spaced inward from the outer edge of the element.

The first current blocking layer 16a is arranged so as to face the anode electrode 18, and the second current blocking layer 16 is provided.
b is arranged so as to surround the first current block layer 16a with a space therebetween when seen in a plan view. The first current blocking layer 16a has the same circular planar shape as the anode electrode 18, and slightly protrudes outward from the outer edge of the anode electrode 18 over the entire circumference in plan view. That is, as shown in FIG. 3, when viewed in plan, the anode electrode 1
8 is included inside the first current blocking layer 16a.
The outer edge of the anode electrode 18 and the first current blocking layer 16a
The distance from the outer edge of the first current blocking layer 16a, that is, the width L1 of the projection of the first current blocking layer 16a from directly below the anode electrode 18 is equal over the entire circumference. First current blocking layer 16a
The upper surface and the side surface of are contacted with the contact layer 17 to form a pn junction at the interface. In addition, the first current blocking layer 16
The lower surface of a is in contact with the upper surface of the p-type AlGaInP cladding layer 15 to form a pn junction at the interface. As shown in FIG. 3, the second current blocking layer 16b has a contact layer 1
The first current block layer 16a is separated from the first current block layer 16a by a ring shape 7 and is formed in a ring shape on the element peripheral side, and is exposed on the side surface of the semiconductor substrate. The distance L2 between the first current blocking layer 16a and the second current blocking layer 16b is equal over the entire circumference. The upper surface and the inner peripheral side surface of the second current block layer 16b are in contact with the contact layer 17, and a pn junction is formed at the interface. The lower surface of the second current block layer 16b is in contact with the p-type AlGaInP clad layer 15 to form a pn junction at its interface. As a result,
The upper surface of the p-type AlGaInP cladding layer 15 is in contact with the contact layer 17 in a ring shape. The annular contact layer 17 between the first and second current blocking layers 16a and 16b serves as a current path, and the upper portion thereof is the light extraction upper surface 20.

The side surface 21 and the light extraction top surface 20 of the semiconductor substrate are preferably rough surfaces having minute irregularities in the height range of 1 to 20 μm. For the roughening of the side surface 21, the wafer is diced with a diamond single blade high-speed rotary blade, and this dicing surface is subjected to HCl: H ₂ O ₂ :
It is formed by etching with an etching solution of H ₂ O = 6: 1: 6. The region near the side surface 21 is a region where recombination that does not contribute to light emission occurs due to dicing and / or roughening. The second current blocking layer 16b according to the present invention is formed corresponding to the non-radiative recombination region near the side surface 21. The upper surface 20 of the semiconductor substrate is
The surface is roughened by not mirror-finishing it.

This light emitting diode element has a first current blocking layer 16a immediately below the anode electrode 18, and is annularly adjacent to the side surface 21 so as to surround the first current blocking layer 16b at a distance. Second current blocking layer 16b
Have. Therefore, the current flowing from the anode electrode 18 toward the cathode electrode 19 is the first current blocking layer 1
It flows into the active layer 14 through between 6a and the second current blocking layer 16b. As a result, the main light emitting region is formed immediately below between the first current blocking layer 16a and the second current blocking layer 16b. Since the anode electrode 18 is not present on the main light emitting region, the light extracted upward is not blocked by the anode electrode 18. In addition, since the current flow toward the vicinity of the side surface 21 is suppressed by the second current blocking layer 16b, the problem of increase of non-radiative recombination near the side surface caused by roughening the side surface 21. Has been resolved. For this reason, the effect of improving the light extraction efficiency by roughening the surface can be satisfactorily exhibited without being reduced by the non-radiative recombination even in the current region where the light extraction efficiency is relatively small. Of course, even in a large current region, the effect of improving the light extraction efficiency is satisfactorily exhibited. As a result, as shown by the characteristic line C in FIG. 4, high luminous intensity is realized in a wide range from a small current region to a large current region.

In this embodiment, a rough surface suitable for improving the light extraction efficiency is formed on the side surface (cut surface) at the time of dicing the wafer, and is used as it is as a rough surface for preventing total reflection. There is. Therefore, simplification of the manufacturing process is achieved. For example, if a wafer having a roughened main surface is used, a semiconductor chip having a rough surface on the upper surface 20 and the side surface 21 suitable for improving the light extraction efficiency can be obtained substantially only by braking or dicing. When a wafer whose main surface is not roughened is used, it can be roughened by etching the element surface (top surface, side surface) after dicing. At this time, only the upper surface may be selectively etched.

[0014]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) If the p-type AlGaInP cladding layer 15 is too thick or the impurity concentration is too high, the p-type AlGaInP is too thick.
In the P clad layer 15, the current tends to spread in the planar direction of the element, and the effect of forming the second current blocking layer 16b may be impaired. Therefore, p-type A
It is desirable that the thickness and the impurity concentration of the 1GaInP cladding layer 15 be 1 μm or less and 5 × 10 ¹⁷ cm ⁻³ or less, respectively. That is, in practice, it is desirable to set the ND product (impurity concentration × thickness) to 5 × 10 ¹² cm ⁻² or less,
When the thickness is about 0.5 μm, the impurity concentration is 1 × 1.
It is desirable to set it to about 0 ⁷ cm ^-3 or less. (2) It is desirable that the impurity concentration of the p-type AlGaInP clad layer 15 be low in order to prevent the current from spreading laterally. The effect of overflow due to the decrease in the height of the potential barrier with respect to 14 becomes significant. In such a case, p-type Al
On the active layer 14 side of the GaInP clad layer 15, it is preferable to form a layer (overflow suppression layer) whose impurity concentration is partially increased. If the overflow layer is too thin, the effect of suppressing the overflow will not be fully exerted, and if it is too thick, the current will spread laterally.
It is desirable to set it in the range of 00 to 500 angstrom. (3) Even if the side surface 21 or only the light emitting region of the side surface 21 is roughened without particularly roughening the upper surface 20, some effects can be obtained. (4) The first current blocking layer 16a is the anode electrode 1
It suffices that it is located substantially below 8 and may be divided into a plurality of parts. The second current blocking layer 16b is preferably ring-shaped, but may be divided into a plurality if it is substantially ring-shaped. (5) The rough surface according to the present invention may be, for example, one having irregularities scattered at intervals of 1 to 20 μm, or one having irregularities arranged in a stripe shape, a lattice shape, or the like.

[Brief description of drawings]

FIG. 1 is a central longitudinal sectional view showing a conventional light emitting diode.

FIG. 2 is a central vertical sectional view showing a light emitting diode according to an embodiment of the present invention.

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

FIG. 4 is a characteristic diagram showing a relationship between current and luminous intensity of a conventional light emitting diode having a non-roughened surface and a light emitting diode of an embodiment of the present invention.

[Explanation of symbols]

 13 n-type clad layer 14 active layer 15 p-type clad layer 16a, 16b first and second current blocking layers 17 contact layer 18 anode electrode

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[Procedure amendment]

[Submission date] June 2, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

Claims (3)

[Claims] 1. A clad layer of a first conductivity type, an active layer, a clad layer of a second conductivity type opposite to the first conductivity type, a current blocking layer of a first conductivity type, and a contact layer of a second conductivity type. Are sequentially arranged, a first electrode connected to the contact layer on one main surface of the semiconductor substrate, and a first electrode of the first conductivity type provided on the other main surface of the semiconductor substrate. In a semiconductor light emitting device including a second electrode electrically connected to a clad layer, the first electrode is provided in a central portion of one main surface of the semiconductor substrate, and the current blocking layer is a first electrode. And a second current blocking layer, wherein the first current blocking layer is arranged so as to have a portion that overlaps with the first electrode when seen in a plan view, and the second current blocking layer is seen in a plan view. Through the contact layer The semiconductor light emitting device characterized in that it is formed so that the first current blocking layer is exposed on the side surfaces of the enclosure to and the semiconductor substrate. 2. A semiconductor light emitting device, wherein at least a light emitting region on a side surface of the semiconductor substrate is formed into a rough surface. 3. The semiconductor light emitting device according to claim 2, wherein at least a side surface of the semiconductor substrate and a light emitting region of the one main surface are formed into a rough surface.