JP2002050792A - Semiconductor light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an epitaxial semiconductor light-emitting diode, where with no light loss at an upper electrode, current is fully supplied to the entire light-emitting layer for high luminance. SOLUTION: A semiconductor light-emitting diode is provided, which comprises a conductive substrate, an epitaxially grown semiconductor light- emitting layer, and a metal electrode. Here, the metal electrode is arranged so that the light emitted from the semiconductor light-emitting layer is reflected on the metal electrode, which travels to the outside. A metal electrode surface is, for example, tilted by 45 deg. with respect to the light-emitting layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor light emitting diode, and more particularly to a semiconductor light emitting diode having a semiconductor light emitting layer grown on a conductive substrate by epitaxial growth.

[0002]

2. Description of the Related Art The demand for high-luminance semiconductor light-emitting diodes is increasing significantly, mainly for applications such as traffic signals, brake lights and fog lights for automobiles. This semiconductor light emitting diode is manufactured from a semiconductor wafer that has been epitaxially grown.

FIG. 6 shows a structure of an epitaxial semiconductor wafer used for manufacturing a conventional general semiconductor light emitting diode. A light emitting layer 62 and a window layer 63 are epitaxially grown on a GaAs substrate 61. In general, an organic metal vapor phase epitaxy (MOVPE) or a liquid phase epitaxy (LPE) is used to grow the epitaxial layer. Substrate 6 made of n-type GaAs
The light emitting layer 62 above the first layer is composed of four layers: an n-type buffer layer 62a, an n-type cladding layer 62b, an undoped active layer 62c, and a p-type cladding layer 62d. The window layer 63 is also a p-type conductive layer epitaxially grown. The substrate 61 may be made of p-type GaAs, in which case the buffer layer 6
2a and the cladding layer 62b are p-type, and the cladding layer 62d and the window layer 63 are n-type.

FIG. 7 shows a conventional general structure of a light emitting diode manufactured from such a semiconductor epitaxial wafer. The light emitting diode is composed of a chip (for example, processed by dicing, 300 × 300 micrometers) obtained by processing a semiconductor epitaxial wafer, and electrodes provided on both surfaces thereof. A light emitting layer 62 and a window layer 63 epitaxially grown on a GaAs substrate 61; an upper electrode 64 provided on the upper surface of the window layer 63;
It has a lower electrode 65 provided on the lower surface of the substrate. When a current is supplied to the light emitting layer 62 from the upper electrode 64 and the lower electrode 65, the active layer in the light emitting layer 62 emits light. The generated light is extracted to the outside from the portion of the chip upper surface where there is no electrode.

FIG. 8 shows a light emitting state of such a conventional semiconductor light emitting diode. The current is most efficiently supplied to a position directly below the upper electrode 64, but the upper electrode 64 is present at this position, and light emission is reflected by the electrode and cannot be taken out from the upper surface of the chip. Therefore, the light extraction efficiency is low.

Current is supplied to the light emitting layer other than immediately below the upper electrode only in the vicinity of the upper electrode, and the light emitting layer near the outer periphery of the device does not function because the current is not sufficiently supplied. Therefore, the brightness of the entire light emitting diode is low.

In the conventional semiconductor light emitting diode having the structure shown in FIG. 7, since the emitted light is blocked by the metal electrode on the window layer, the light extraction efficiency is low and the light emitting layer is not blocked. Is not supplied with a sufficient current, so that the brightness of this portion is low. As a result, the effective light emitting area is small, and the overall luminance is low.

FIG. 9 shows a conventional semiconductor light emitting diode having another structure. This light-emitting diode has a structure in which a current blocking portion is embedded (current blocking portion embedded structure). A current blocking portion 96 is buried in the window layer 93 directly below the upper electrode 94, so that current is preferentially supplied to the light emitting layer in a portion other than immediately below the upper electrode 94. It is considered that the loss of the emitted light due to the upper electrode 94 is also relatively small. However, as compared with the structure shown in FIG. 7, the area of the upper electrode, that is, the area from which light can be extracted does not change.

FIG. 10 shows a conventional semiconductor light emitting diode having another structure. This is done by changing the shape of the upper electrode 64, keeping the area of the upper electrode as much as possible, and expanding the area from which light can be extracted. Since the current is not sufficiently supplied to the thin branches of the upper electrode 64, the brightness is not much improved as compared with the structure of FIG.

[0010]

As described above, the conventional general semiconductor light emitting diode having the structure shown in FIG. 7 has a low light extraction efficiency due to the presence of the metal electrode on the window layer, and has an effective light emitting area. Is small, the overall luminance is low.

The conventional semiconductor light emitting diode having the current blocking portion buried structure of FIG. 9 is the same as that of FIG. 7 in the area from which light can be extracted.

The conventional semiconductor light emitting diode having the structure shown in FIG. 10 also has a small improvement in luminance as compared with the structure shown in FIG.

It is an object of the present invention to provide an epitaxial semiconductor light emitting diode which has no light loss due to the upper electrode and which can supply a high current luminance to the entire light emitting layer so that high light emission luminance can be obtained.

[0014]

In order to achieve the above object, a semiconductor light emitting diode according to the present invention comprises a semiconductor light emitting layer grown on a substrate by epitaxial growth, and a metal electrode provided on the opposite side of the semiconductor light emitting layer from the substrate. In the semiconductor light emitting diode, the metal electrode has light reflectivity, and is arranged so as to reflect light generated from the semiconductor light emitting layer and emit the light in a predetermined emission direction.

The metal electrode is provided so as to have a surface inclined with respect to the surface of the semiconductor light emitting layer epitaxially grown. That is, the extension of the surface of the metal electrode can intersect with the growth surface of the semiconductor light emitting layer that has been epitaxially grown.

A semiconductor light emitting diode having a semiconductor light emitting layer grown on a substrate by epitaxial growth generally has a window layer on the semiconductor light emitting layer grown epitaxially. The window layer is shaped such that its upper surface (the surface far from the semiconductor light emitting layer) is inclined with respect to the semiconductor light emitting layer, and if a metal electrode is provided thereon, the metal electrode is inclined with respect to the epitaxially grown semiconductor light emitting layer. Can be made to have a flat surface.

The metal electrode preferably has an area and a shape that can cover the entire cross section of the columnar body surrounded by a straight line passing through the periphery of the semiconductor light emitting layer and perpendicular to the semiconductor light emitting layer. That is, when the upper surface of the window layer is inclined with respect to the semiconductor light emitting layer and a metal electrode is provided on this surface, it is preferable that the metal electrode covers the entire upper surface of the window layer.

[0018]

FIG. 1 shows a semiconductor light emitting diode (element) according to the present invention. Semiconductor light emitting diodes
On the substrate 1, a thin epitaxial semiconductor light emitting layer 2 composed of four layers, a thick window layer 3, an upper electrode 5 on the inclined upper surface 4 of the window layer 3, and a lower electrode 6 on the opposite side of the substrate 1 are provided. The thickness of the epitaxial semiconductor light emitting layer 2 is, for example, 3 micrometers in total, and the thickness of the window layer 3 is, for example, 200 micrometers. The upper surface 4 of the window layer 3 has a surface 3 a in contact with the epitaxial semiconductor light emitting layer 2.
45 °. In the figure, the direction of current flow is indicated by arrows, and the path of light is indicated by waveform arrows.

FIG. 2 shows details of a cross section of an epitaxial wafer used for manufacturing a semiconductor light emitting diode according to the present invention. The epitaxial semiconductor light emitting layer 2 on the substrate 1 made of n-type GaAs is composed of an n-type GaAs / Te buffer layer 2
a, n-type AlGaAs / Te cladding layer 2b, AlGa
As active layer 2c, p-type AlGaAs / Zn clad layer 2
d. The AlGaAs layer 2c is not doped (/ Te, / Zn, etc. indicate that it is doped with Zn, Te, etc.). The window layer 3 is a conductive layer epitaxially grown and is a p-type AlGaAs / Zn layer. The substrate 1 may be made of p-type GaAs. In this case, the buffer layer 2a and the cladding layer 2b are p-type, and the cladding layer 2d and the window layer 3 are n-type.

The semiconductor light emitting diode of the present invention is manufactured by the following method. An epitaxial wafer having the cross section shown in FIG. 2 is manufactured by the LPE method. A chip is manufactured from the epitaxial wafer by dicing. The chip is fixed at an angle of 45 ° and the window layer 3 is polished.

FIG. 3 shows a method of polishing a chip to obtain a top surface of a window layer inclined at 45 °. The chip is set at 45 ° so that the upper surface 3b of the window layer 3 of a certain chip 11 is located in the same plane as the interface 3a between the epitaxial semiconductor light emitting layer 2 and the window layer 3 of the adjacent chip 12.
The window layer 3 is polished to a flat surface as shown in FIG.

When an upper electrode 5, for example, an AuZn—Ni—Au laminated electrode is deposited on the upper surface 4 of the window layer 3 inclined at 45 °, and a lower electrode 6, for example, an AuGe electrode is deposited on the lower surface of the substrate 1, as shown in FIG. A semiconductor light emitting diode device is completed.

[0023]

EXAMPLES The effects of the present invention will be specifically described below with reference to examples. An epitaxial wafer having the cross section shown in FIG. 2 was manufactured by the LPE method, and a square chip having a side of 200 μm was manufactured by dicing. As shown in FIG. 3, the window layer 3 is polished to a flat surface by a thickness of 140 micrometers in the vertical direction, and the polished surface (the upper surface 4 of the window layer 3)
An AuZn—Ni—Au laminated electrode as the upper electrode 5,
An AuGe electrode was deposited as a lower electrode 6 on the lower surface of the substrate 1 to obtain a semiconductor light emitting diode device shown in FIG.

For comparison, in addition to the semiconductor light-emitting diode element A of the present invention, an epitaxial semiconductor light-emitting diode B having a general structure shown in FIG. 7 and a structure (C) in which the shape of the upper electrode shown in FIG. The epitaxial semiconductor light emitting diodes D having a current blocking portion embedded structure shown in FIG. 9 were also manufactured. The size of each chip was a square with a side of 200 micrometers, and the upper electrode was a circle with a diameter of 130 micrometers.

In order to compare the performance of the semiconductor light emitting diode device A of the present invention and the conventional semiconductor light emitting diode devices B, C and D, the emission luminance was measured.

FIG. 4 shows the light emission luminance of the present invention and the conventional semiconductor light emitting diode device. The device C in which the shape of the upper electrode is changed and the device D having the current blocking portion embedded structure are about 1.2 to 1.4 times as large as the epitaxial semiconductor light emitting diode B having a general structure. The device A exhibited a light emission luminance approximately twice that of the conventional semiconductor light emitting diode device B.

FIG. 5 shows a semiconductor light emitting diode element A,
The area of the light-extractable portions B, C, and D is shown. The element D having the current blocking portion embedded structure is the same as the light emitting element B having the general structure. The element C having the shape of the upper electrode is 1.1 times the element B, whereas the light emitting diode element A according to the present invention has the same structure. It is 1.3 times that of the element B. Whereas the conventional light emitting device has weak light emission at a portion from which light can be extracted (even in the device D having the current blocking portion embedded structure, light emission is mainly near the electrodes), whereas the light emitting device of the present invention has light emission of the entire light emitting layer. Can be taken out, so that the difference in the amount of light emission is further increased (see FIG. 4).

[0028]

According to the present invention, light loss due to the upper electrode can be avoided, and sufficient current can be supplied to the entire light emitting layer, so that an epitaxial semiconductor light emitting diode having high light emission luminance can be obtained.

A semiconductor light emitting diode according to the present invention comprises: a semiconductor light emitting layer grown on a substrate by epitaxial growth;
In a semiconductor light emitting diode having a metal electrode provided on a side opposite to a substrate of a semiconductor light emitting layer, the metal electrode has light reflectivity, and reflects light generated from the semiconductor light emitting layer to emit light in a predetermined direction. The light generated from the semiconductor light emitting layer can be extracted outside without being blocked by the metal electrode.

Further, since the semiconductor light emitting diode of the present invention has a structure in which light from the light emitting layer can be extracted outside without being blocked by the metal electrode, the area of the metal electrode for supplying current to the light emitting layer is limited. The current is sufficiently supplied to the entire light emitting layer without receiving the light, so that high light emission luminance can be obtained.
Conventional semiconductor light-emitting diodes of the same type have a structure in which light from the light-emitting layer is blocked by the metal electrode, so the area of the metal electrode is limited and the area of the light-emitting layer where light is effectively emitted is small. In the structure of the semiconductor light emitting diode of the present invention, the area of the metal electrode can be made large so as to occupy a wide portion or the whole of the light emitting layer.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a semiconductor light emitting diode (element) according to the present invention.

FIG. 2 is an explanatory sectional view of an epitaxial wafer used for manufacturing a semiconductor light emitting diode according to the present invention.

FIG. 3 is an explanatory sectional view showing a method of polishing a window layer of a chip.

FIG. 4 is a graph showing light emission luminances of the present invention and a conventional semiconductor light emitting diode device.

FIG. 5 is a graph showing an area of a light-extractable portion of the semiconductor light-emitting diode element.

FIG. 6 is an explanatory view showing a structure of an epitaxial semiconductor wafer used for manufacturing a conventional semiconductor light emitting diode.

FIG. 7 is an explanatory view showing the structure of a conventional semiconductor light emitting diode.

FIG. 8 is an explanatory diagram showing a light emitting state of a conventional semiconductor light emitting diode.

FIG. 9 is an explanatory diagram showing a conventional semiconductor light emitting diode and its light emitting state.

FIG. 10 is an explanatory view showing the structure of a conventional semiconductor light emitting diode.

[Explanation of symbols]

Reference Signs List 1 substrate 2 epitaxial semiconductor light emitting layer 2a n-type GaAs / Te buffer layer 2b n-type AlGaAs / Te cladding layer 2c AlGaAs active layer 2d p-type AlGaAs / Zn cladding layer 3 window layer 3a interface between epitaxial semiconductor light emitting layer and window layer 3b Upper surface of window layer 4 Upper surface of inclined window layer 5 Upper electrode 6 Lower electrode 11 Chip 12 Chip 61 GaAs substrate 62 Light emitting layer 62a N-type buffer layer 62b N-type cladding layer 62c Undoped active layer 62d P-type cladding layer 63 Window layer 64 Upper electrode 65 Lower electrode 93 Window layer 94 Upper electrode 96 Current blocking portion

Claims (5)

[Claims] 1. A semiconductor light emitting diode comprising: a semiconductor light emitting layer grown on a substrate by epitaxial growth; and a metal electrode provided on the side of the semiconductor light emitting layer opposite to the substrate, wherein the metal electrode has light reflectivity. The semiconductor light emitting diode is arranged so as to reflect light generated from the semiconductor light emitting layer and emit the light in a predetermined emission direction. 2. The semiconductor light emitting diode according to claim 1, wherein said metal electrode is provided so as to have a surface inclined with respect to a surface of said epitaxially grown semiconductor light emitting layer. 3. The semiconductor device according to claim 2, wherein the metal electrode has a shape capable of covering the entire cross section of the columnar body surrounded by a straight line perpendicular to the semiconductor light emitting layer through the periphery of the semiconductor light emitting layer. The semiconductor light emitting diode according to claim 1 or 2. 4. A semiconductor light emitting diode comprising: a semiconductor light emitting layer grown on a substrate by epitaxial growth; a window layer provided on the semiconductor light emitting layer; and a metal electrode provided on the window layer. The surface of the window layer on which the metal electrode is provided is inclined with respect to the semiconductor light emitting layer. The metal electrode has light reflectivity, reflects light generated from the semiconductor light emitting layer, and has a predetermined shape. A semiconductor light emitting diode, which is arranged to emit light in an emission direction. 5. The semiconductor light emitting diode according to claim 4, wherein said metal electrode is provided so as to cover the entire surface of said window layer.