JPH08222763A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE: To improve light lead-out efficiency by restraining the LED light generated inside an element from being reflected by the element surface. CONSTITUTION: The surface of an n-type GaAs substrate 1 is made uneven. By crystal-growing in order an n-type lower clad layer 2, an active layer 3, and a p-type upper clad layer 4 on the substrate surface, a light emitting part 100a is arranged on the substrate 1. The surface form of each of the semiconductor layers 2-4 constituting the light emitting part 100a is made uneven, correspondingly to the uneven surface of the substrate.

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 a device structure for achieving high brightness.

[0002]

2. Description of the Related Art In recent years, LEDs (light emitting diodes) have been spotlighted as indoor and outdoor display devices. In particular, with the increase in brightness, the outdoor display market is expected to grow rapidly in the next few years, and LEDs are expected to grow into display media that will replace neon signs in the future. High-brightness LEDs have been realized in red LEDs having an AlGaAs-based DH (double hetero) structure, and recently, high-brightness LEDs have been realized even in orange to green by AlGaInP-based DH structure LEDs.

AlGaInP-based materials exclude nitrides II
It has the largest direct transition type band gap among I-V group compound semiconductor materials, and is attracting attention as a light emitting device material in the 0.5 to 0.6 μm band.

In particular, a pn junction type light emitting diode (LED) using GaAs as a substrate material and having a light emitting portion made of AlGaInP lattice-matched to it is an indirect transition type material such as GaP or GaAsP as a constituent material of the light emitting portion. It is possible to emit light of high brightness from red to green as compared with the LED using. In order to realize a high-brightness LED, that is, in order to increase the amount of light emitted from the LED, not only the luminous efficiency of the light emitting portion of the element is increased, but also the light generated in the light emitting portion can be efficiently extracted to the outside of the element. How you do it is important.

FIG. 3 is a diagram showing a cross-sectional structure of a conventional LED (see Japanese Patent Laid-Open No. 4-229665) having an AlGaInP light emitting portion. In FIG. 3 (a), the current distribution in the cross-sectional structure is indicated by a dotted line. As shown in FIG. 3 (b),
The way of light emission inside the element is shown by the path (solid line) of the light emitted from the light emitting portion.

In the figure, 10 is a pn junction type light emitting diode (LED), and on the p-GaAs substrate 11,
A laminated structure 10a is provided in which an AlGaInP active layer 13 is sandwiched between a p-AlGaInP lower clad layer 12 and an n-AlGaInP upper clad layer 14, and the laminated structure 10a has a double heterojunction portion, It serves as a light emitting portion from which the light generated in the layer 13 is emitted.
Further, n-GaAs is formed in the central portion on the upper cladding layer 14.
A contact layer 15 is formed, an n-type electrode 15a made of AuGe is provided on the contact layer 15, and AuZ is formed on the entire back surface of the p-GaAs substrate 11.
A p-type electrode 11a made of n is formed.

In the LED 10 having such a structure, the p
When a drive voltage is applied to the mold electrode 11a and the n-type electrode 15a, a current is injected into the portion of the active layer 13 immediately below the n-type electrode 15a and its vicinity, and LED light is generated in this portion.

[0008]

However, the LED 10 having such a structure has the following two problems.

First, as shown in FIG. 3B, the LED light L from the portion directly below the n-type electrode of the active layer 13 to the outside of the n-type electrode arrangement portion on the device surface is above the critical angle and is on the upper surface of the device. The incident light is reflected on the inside of the element on the upper surface of the element, and therefore the light extraction efficiency from the upper surface of the element is very low.

In a high-brightness LED whose LED light is in the range from orange to green, AlGaIn is used as its constituent material.
P mixed crystal semiconductor material is used, and the plane orientation is (100)
When the growth is performed on the surface of the substrate, which is a plane, there is a problem that a natural superlattice is formed in the growth layer.

That is, in this natural superlattice, group III atoms In, Ga and Al form a long-range ordered structure in the <111> direction. Taking GaInP as an example,
The band gap of Ga _0.5 In _0.5 P having such a natural superlattice is about 90 meV smaller than the band gap of Ga _0.5 In _0.5 P having no natural superlattice in an ideal mixed crystal state. Therefore, when a natural superlattice is formed, the wavelength becomes longer than the desired emission wavelength,
It is necessary to increase the Al composition so that the wavelength has an original set value, and this increase in the Al composition causes a problem that the luminous efficiency is reduced and the reliability is reduced.

The present invention has been made to solve the above problems, and it is possible to suppress reflection of LED light generated inside the element on the element surface and improve the light extraction efficiency. The object is to obtain a semiconductor light emitting device that can be manufactured.

Further, according to the present invention, in addition to the improvement of the light extraction efficiency, even when an AlGaInP mixed crystal semiconductor material is used as a constituent material of the device, the generation of natural superlattice is avoided and the emission efficiency is reduced. Another object of the present invention is to obtain a semiconductor light emitting device that can obtain emitted light of a desired emission wavelength without reducing reliability.

[0014]

A semiconductor light emitting device according to the present invention is a compound semiconductor substrate of a first conductivity type, the surface of which is uneven, and at least a first conductive film on the surface of the compound semiconductor substrate. Type lower clad layer, active layer and second conductivity type upper clad layer are sequentially grown to form a light emitting portion for emitting light generated in the active layer and a back surface side of the compound semiconductor substrate. And a second conductivity type electrode formed on the upper side of the light emitting portion. Each semiconductor layer forming the light emitting portion has an uneven surface shape corresponding to the uneven shape of the compound semiconductor substrate surface. Thereby, the above object is achieved.

The present invention provides the above semiconductor light emitting device,
The compound semiconductor substrate has a structure in which a plurality of grooves are formed on the surface of the compound semiconductor substrate so that the surface has an uneven surface, and the plane orientation of the slope of the groove formed on the substrate surface is the (100) plane of the semiconductor crystal. The surface A is based on.

[0016]

In the present invention, the surface of the compound semiconductor substrate is made uneven, and the light emitting portion arranged on the substrate is provided with at least the lower clad layer of the first conductivity type, the active layer and the first conductive type on the surface of the substrate. Since the upper clad layer of the two-conductivity type is sequentially crystal-grown and the surface shape of each semiconductor layer forming the light emitting portion is made to have an uneven shape corresponding to the uneven shape of the substrate surface, The element surface from which the LED light is emitted also becomes uneven, and the proportion of LED light that enters the element surface at a critical angle or more decreases, and even if it enters and reflects at a critical angle or more, it re-enters the surface at a critical angle or less. It will be taken out. As a result, L from the element surface
The extraction efficiency of ED light can be improved.

Further, the active layer, which is the light emitting region of the LED light, also has an uneven structure corresponding to the uneven shape of the substrate surface, and the light emitting area is increased as compared with the flat active layer, so that the LED light Luminous efficiency is increased.

Due to such an increase in light emission efficiency and an improvement in light extraction efficiency, it is possible to increase the brightness of the semiconductor light emitting device.

In the present invention, the compound semiconductor substrate has a structure in which grooves are formed in a plurality of stripes on the surface so that the surface shape is uneven, and the plane orientation of the slope of the groove formed on the surface of the substrate is , The A-plane is based on the (100) plane of the semiconductor crystal.
Even if the AlGaInP mixed crystal semiconductor material is grown by the OCVD method, the natural superlattice is not formed, and it is possible to avoid the wavelength extension of the LED light due to the natural superlattice. Therefore, it is not necessary to adjust the wavelength of the LED light due to the increase in Al composition, and a semiconductor light emitting device with high brightness and high reliability can be realized.

[0020]

【Example】

(Embodiment 1) FIG. 1 is a view for explaining a light emitting diode as an example of a semiconductor light emitting device according to a first embodiment of the present invention, and FIG. 1 (a) is a sectional view showing the structure of the light emitting diode. FIG. 1B is a sectional view showing the structure of a substrate that constitutes the light emitting diode.

In the figure, reference numeral 100 denotes a light emitting diode of this embodiment, which is an n-type Ga constituting the light emitting diode 100.
On the As substrate 1, the n-type lower clad layer 2,
A light emitting portion 100a formed by sequentially crystallizing the active layer 3 and the p-type upper cladding layer 4 is provided, and the light emitting portion 100a is provided.
Has a double heterojunction portion so that the light generated in the active layer 3 is emitted.

Further, on the p-type upper clad layer 4 of the light emitting portion 100a, a p-type GaAs contact layer 8 is provided,
A p-type electrode 111 made of AuZn is arranged. In addition, on the entire back surface of the n-type GaAs substrate 1, AuG
An n-type electrode 110 made of e is formed.

In this embodiment, the surface of the n-type GaAs substrate 1 has a V-shaped groove 1a having a depth of 5 μm and a width of 20 μm.
Are formed in a stripe shape, and the surface of the substrate 1 is uneven. Further, here, the inclination angle of the slope of the groove 1a is 30 degrees.

The lower clad layer 2, the active layer 3 and the upper clad layer 4 are (Al _x Ga _{1 -x} ) _{1 -y} In _{y, respectively.}
P (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). In the lower clad layer 2 and the upper clad layer 4, for example, the composition ratio x,
y is x = 0.70, y = 0.50, the layer thickness is 1.0 μ
m, and the Si carrier concentration of the lower cladding layer 2 and the Zn carrier concentration of the upper cladding layer 4 are both 1 × 10.
^{It is 18} cm ^-3 . Further, in the active layer 3, for example, the composition ratios x and y are x = 0.30, y = 0.50, and the layer thickness thereof is 0.50 μm.

Further, the p-type GaAs contact layer 8 is formed.
Are arranged in a circular region having a diameter of 200 μm at the center of the light emitting part 100a, and the Zn carrier concentration thereof is 3
It is × 10 ¹⁸ cm ^-3 and the layer thickness is 1 μm.

Next, the manufacturing method will be described.

First, a groove having a depth of 5 μm and a width of 20 μm having an inclined surface angle of, for example, 30 degrees is formed in a plurality of stripes on the surface of the n-type GaAs substrate 1 by etching (see FIG. 1B). .

Next, the semiconductor layers 2 to 4 and 8 are formed on the etched substrate 1 by MOCVD.

That is, after the above etching treatment, n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P is used as the n-type lower cladding layer 2 on the substrate 1 and the Si carrier concentration is 1 × 10 ¹⁸ cm 2.
It grows to a thickness of about 1.0 μm to become ⁻³ . continue,
(Al _0.3 Ga _0.5 ) _0.5 In _0.5 P is used as the active layer 3.
It is formed to a thickness of about 50 μm, and a p-type (A
1 _0.7 Ga _0.3 ) _0.5 In _0.5 P is grown as a p-type upper cladding layer 4 to a Zn carrier concentration of 1 × 10 ¹⁸ cm ⁻³ with a layer thickness of about 1 μm.

At this time, the surface shape of the substrate 1 is almost inherited by the semiconductor layer grown thereon. For this reason, the active layer 3 has a corrugated plate-like structure, and a plurality of grooves each having a slope plane orientation of about 30 degrees are formed on the surface of the p-type upper cladding layer 4, and the surface has an uneven shape.

Subsequently, p-type Ga is formed on the upper cladding layer 4.
The As layer has a Si carrier concentration of 3 × 1 and a thickness of about 1 μm.
It grows to become 0 ¹⁸ cm ^-3 . After that, the p-type GaAs
An AuZn layer is formed on the layer, and an AuGe layer 110 as an n-type electrode is formed on the back surface side of the n-type substrate 1.
After that, the n-type GaAs layer and the AuZn layer are selectively etched so that a circular region having a diameter of 200 μm located on the center of the light emitting portion 100a remains to form an n-type GaAs contact layer 8 and a p-type electrode 111. . As a result, the light emitting diode 100 is completed (see FIG. 1A).

When a voltage (2 V) was applied in the forward direction and a current (20 mA) was applied to the semiconductor light emitting device according to this example, LE having a peak wavelength of 595 nm exceeding 3 cd was obtained.
D light was obtained.

When the composition x, y of the (Al _x Ga _1-x ) _1-y In _y P active layer is set to x = 0.50 and y = 0.50, the luminous intensity at a peak wavelength of 565 nm is 1 cd. A green light emission exceeding that was obtained.

As described above, in this embodiment, the surface of the n-type GaAs substrate 1 is made uneven, and the light emitting portion 100a arranged on the substrate 1 is provided on the surface of the n-type lower cladding layer 2, The active layer 3 and the p-type upper clad layer 4 are sequentially crystal-grown, and the surface shape of each of the semiconductor layers 2 to 4 constituting the light emitting unit 100a has an uneven shape corresponding to the uneven shape of the substrate surface. As a result, the element surface from which the LED light is emitted also has an irregular shape, and the proportion of LED light incident on the element surface at a critical angle or more is reduced,
Even if the light enters and is reflected at a critical angle or more, it is again incident on the surface at a critical angle or less and is extracted to the outside. Thereby, the extraction efficiency of the LED light from the element surface can be improved.

Further, the active layer 3 which is a light emitting region of the LED light
Also has a corrugated plate-like structure corresponding to the uneven shape on the front surface of the substrate, and the light emitting area is increased as compared with the flat active layer, so that the luminous efficiency of LED light is increased.

Due to such an increase in light emission efficiency and an improvement in light derivation efficiency, the brightness of the light emitting diode 100 can be increased.

(Embodiment 2) FIG. 2 is a sectional view for explaining a light emitting diode (semiconductor light emitting element) according to a second embodiment of the present invention, in which 200 is a light emitting diode of this embodiment, The n-type GaAs substrate 21 constituting the light emitting diode 200 has a depth of 4.3 μm and a width of 6 μm on the surface, where the plane orientation of the slope is (111) A plane, for example.
The V-shaped groove 21a is formed in a plurality of stripes.

The other structure of the light emitting diode 200 is the same as that of the light emitting diode 100 of the first embodiment. That is, on the substrate 21 having the above structure, a light emitting portion having a double heterojunction portion, in which an n-type lower clad layer 22, an active layer 23 and a p-type upper clad layer 24 are sequentially grown on the surface thereof. 200a is provided, and the light emitting section 200a is adapted to emit the light generated in the active layer 23. On the p-type upper clad layer 24 of the light emitting part 200a, a Zn carrier concentration of 3 × 10 ¹⁸ cm ^−3.
The p-type electrode 211 made of AuZn is disposed via the p-type GaAs contact layer 28 of FIG. An n-type electrode 210 made of AuGe is formed on the entire back surface of the n-type GaAs substrate 21.

Here, the p-type GaAs contact layer 2 is formed.
The plane patterns of the 8 and p-type electrodes 211 have a circular shape with a diameter of 200 μm as in the above embodiment. Further, the n-type lower clad layer 22, the active layer 23, and the p-type clad 24
Are the same as in the first embodiment (Al _x G
a _1-x ) _1-y In _y P, and the composition of the n-type lower clad layer 22 and the p-type upper clad layer 24, the carrier concentration, and the layer thickness, and the composition of the active layer 23 are also as described above. First
The same as in the embodiment of FIG.

When a voltage (2 V) was applied in the forward direction and a current (20 mA) was applied to the semiconductor light emitting device according to this example, LE having a luminous intensity at a peak wavelength of 585 nm of more than 3 cd was obtained.
D light was obtained.

When the composition x, y of the (Al _x Ga _1-x ) _1-y In _y P active layer is x = 0.50 and y = 0.50, the luminous intensity at a peak wavelength of 555 nm is 1 cd. A green light emission exceeding that was obtained.

In this embodiment having such a structure, n-type Ga is used.
The As substrate 21 has a structure in which grooves 21a are formed in a plurality of stripes on the surface so that the surface shape is uneven, and the plane orientation of the inclined surface of the grooves 21a formed on the substrate surface is
(111) A based on the (100) plane of the GaAs crystal
Since it is a surface, in addition to the effect of the first embodiment,
On this substrate surface, a natural superlattice is not formed even if an AlGaInP mixed crystal semiconductor material is grown by MOCVD. That is, (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P as an active layer grown by MOCVD on the GaAs substrate 21.
The crystal will have no natural superlattice in it. Therefore, it is possible to prevent the wavelength of the LED light from becoming longer due to the natural superlattice. As a result, due to the increase in Al composition, L
Since it is not necessary to adjust the wavelength of the ED light, a semiconductor light emitting device having high brightness and high reliability can be realized.

The present invention is not limited to the above-mentioned first and second embodiments. Particularly in the first embodiment, the active layer is made of an AlGaInP-based semiconductor material, but the active layer is made of AlGaAs or AlG.
It may be an aInN-based or MgZnSSe-based semiconductor material, and by changing the constituent material of the active layer, it is possible to obtain LED light in the visible light range from red to blue. This also applies to the clad layer.

In each of the above embodiments, (Al _x G
By adjusting the Al composition x of a _1-x ) _1-y In _y P, it is possible to obtain LED light in the visible light region ranging from red to blue.

Needless to say, the effect of the present invention can be obtained even if the constituent materials of the active layer and the composition ratio of the constituent materials are changed.

Such changes in constituent materials and composition ratios can be made to the clad layer and contact layer other than the active layer.

[0047]

As described above, according to the semiconductor light emitting device of the present invention, the surface of the compound semiconductor substrate is made uneven, and the light emitting portion arranged on the substrate is provided at least on the substrate surface. A structure in which a lower clad layer of one conductivity type, an active layer, and an upper clad layer of a second conductivity type are sequentially crystal-grown, and the surface shape of each semiconductor layer forming the light emitting portion is made into an uneven shape of the substrate surface. Since it has a corresponding uneven shape, the element surface from which the LED light is emitted has an uneven shape, the proportion of the LED light incident on the element surface at a critical angle or more is reduced, and at the same time it is incident and reflected at a critical angle or more. However, the light is again incident on the surface at a critical angle or less and is extracted to the outside, whereby the extraction efficiency of the LED light from the element surface can be improved.

Further, the active layer, which is the light emitting region of the LED light, also has an uneven structure corresponding to the uneven shape of the surface of the substrate, and the light emitting area is increased as compared with the flat active layer. Luminous efficiency is increased.

Due to such an increase in light emission efficiency and an improvement in light extraction efficiency, there is an effect that the brightness of the semiconductor light emitting element can be increased.

Further, according to the invention, in the above semiconductor light emitting device, the compound semiconductor substrate has a structure in which grooves are formed in a plurality of stripes on the surface so that the surface shape is uneven, and the compound semiconductor substrate is formed on the substrate surface. Since the plane orientation of the inclined surface of the groove is the A plane with reference to the (100) plane of the semiconductor crystal, AlGa is formed by MOCVD on the substrate surface.
Even if the InP mixed crystal semiconductor material is grown, the natural superlattice is not formed, and it is possible to prevent the LED light from having a long wavelength due to the natural superlattice. As a result, there is no need to adjust the wavelength of LED light due to the increase in Al composition, and there is an effect that a semiconductor light emitting device with high brightness and high reliability can be realized.

[Brief description of drawings]

1A and 1B are views for explaining a light emitting diode according to a first embodiment of the present invention, FIG. 1A is a sectional view showing the structure of the light emitting diode, and FIG. It is sectional drawing which shows the structure of the board | substrate which comprises.

FIG. 2 is a sectional view showing a structure of a light emitting diode according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view for explaining a conventional light emitting diode (LED), FIG. 3 (a) shows a current flow in the LED, and FIG. 3 (b) shows how to emit light in the LED. There is.

[Explanation of symbols]

 1, 21 n-type GaAs substrate 1a, 21a groove 2, 22 n-type AlGaInP lower clad layer 3, 23 AlGaInP active layer 4, 24 p-type AlGaInP upper clad layer 8, 28 p-type GaAs contact layer 100, 200 light emitting diode (semiconductor) Light emitting element) 100a, 200a Light emitting part 110, 210 n-type electrode 111, 211 p-type electrode

Claims (2)

[Claims] 1. A compound semiconductor substrate of a first conductivity type whose surface is uneven, and at least a lower clad layer of a first conductivity type, an active layer and a second conductivity type on the surface of the compound semiconductor substrate. A light emitting portion formed by sequentially performing crystal growth on the upper clad layer to emit light generated in the active layer, a first conductivity type electrode formed on the back surface side of the compound semiconductor substrate, and an upper side of the light emitting portion. And a second conductivity type electrode formed on the semiconductor light emitting element, wherein each semiconductor layer forming the light emitting portion has an uneven surface shape corresponding to the uneven shape of the compound semiconductor substrate surface. 2. The semiconductor light emitting device according to claim 1, wherein the compound semiconductor substrate has grooves formed in a plurality of stripes on its surface so that the surface shape is uneven, and the sloped surface of the groove. The semiconductor light emitting device has a plane orientation of A plane with reference to the (100) plane of the semiconductor crystal.