JP2792781B2 - Light emitting diode and method of manufacturing the same - Google Patents

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 structure of a light emitting diode capable of extracting light efficiently to the outside in a short-wavelength high-brightness LED in an orange to green band, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Light emitting diodes (hereinafter, referred to as LEDs) have high reliability and are therefore used in various display devices as a light source instead of a tungsten lamp, and have been spotlighted as indoor and outdoor display devices. With the increase in brightness of LEDs, in particular, the outdoor display market is expected to accelerate in the next few years, and is expected to grow into a medium that will become a neon sign in the future. High brightness LE
D is GaAlAs-based DH (double hetero) for several years
It is first realized with a red LED with a structure.

Recently, high-brightness InGaAlP-based DH type LEDs have been manufactured in the orange to green band.
In order to increase the luminous efficiency of these LEDs, it is important not only to increase the luminous efficiency inside the LED but also to extract light efficiently to the outside.

FIG. 8 shows an element structure of a green band InGaAlP LED as an example of a conventional LED. (A) is a cross-sectional view of the element structure, showing the flow of current by broken lines,
(B) is a cross-sectional view of the element structure, and a solid line shows a light emission method. The LED 100 of this structure is an n-GaAs substrate 10
1 on the n-GaAs buffer layer 109 (thickness 0.1 μm).
m), n-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P carrier confinement layer (cladding layer) 102 (1.5 μm thick), non-doped In _0.5 (Ga _0.62 Al _0.38 ) _0.5 P active layer 10
3 (0.7 μm), p-In _0.5 (Ga _0.3 Al _0.7 ) _0.5
P window layer (cladding layer) 104 (1.5 μm), p-Ga
_0.3 Al _0.7 As current diffusion layer 105 (5 μm), p-Ga
As ohmic contact layers 106 are grown in this order by MOCVD.

The upper electrode 107 is formed on the p-GaAs ohmic contact layer 106, and the lower electrode 108 is formed on the n-GaAs substrate 101. The upper electrode 107 and the underlying ohmic contact layer 106 are formed by removing the periphery by etching, leaving a size (about 70 μm) where lead bonding can be performed. The current injected from the upper electrode 107 spreads to the current diffusion layer 105 as shown by the broken line in FIG.
n _0.5 (Ga _0.62 Al _0.38 ) _0.5 P is injected into the entire area of the active layer 103 to emit light.

[0006]

In the above conventional example, a current is injected into the entire region of the non-doped In _0.5 (Ga _0.62 Al _0.38 ) _0.5 P active layer 103, but a considerable portion is located in the portion 103 a directly below the upper electrode 107. Concentrate. Therefore, naturally, the light emission amount in this portion increases.

On the other hand, as shown in FIG.
The LED light (I to C) emitted from the portion 103a immediately below the upper electrode 107 and directed to the upper portion is reflected by the upper electrode 107 and is not emitted to the outside. Also, in the light emission (d) emitted from the immediately lower portion 103a and directed outward of the upper electrode 107, the upper surface 105
Those incident on a at a critical angle or more do not go outside. Therefore, a significant portion of the current injected into the active layer 103 is wasted for light that cannot be extracted.

FIG. 9 shows a conventional example improved to solve such a problem. Here, the same layers as those in the conventional example shown in FIG. 8 are denoted by the same reference numerals. A feature of this conventional LED 100 is that a light reflection layer 110 is formed between an n-GaAs buffer layer 109 and an n-InGaAlP carrier confinement layer (cladding layer) 102. Another feature of this conventional example is that p-
The n-InGaAlP (cladding layer) 104 is in contact with and above and above the upper electrode 107.
A P current prevention layer 122 is formed.

The light reflecting layer 110 is made of, for example, InAlP and In.
_0.5 (Ga _0.5 Al _0.5 ) _0.5 P is formed by alternately laminating about 30 layers, and the LED light emitted downward (g, h)
Is reflected at the top. The n-InGaAlP current prevention layer 122 prevents current from being injected into the portion 103a immediately below the upper electrode 107.

In the conventional LED 100, the current is injected as shown in FIG. 9A, and the light emission of the LED 100 other than the portion 103a immediately below the upper electrode 107 becomes dominant. The external efficiency increases as compared with the embodiment. However, the LED 100 of this conventional example is shown in FIG.
In the middle, as shown by the dashed line, the active region 10 in which the current is injected also to the portion 103a directly below the active region where the current is not injected.
Carriers diffuse from 3b. In addition, a part (e, f) of the light emitted from the LED 100 is absorbed by the portion 103a immediately below, which is the active region where no light is emitted, so that light is lost inside and the light emission efficiency is reduced.

[0011] As a method of producing this embodiment, MOCVD
After stacking up to the n-InGaAlP current prevention layer 122 by the method, an excess portion is removed by etching, and then the p-GaAlAs current diffusion layer 105 is regrown by the MOCVD method. In this case, the regrowth interfaces 121 to 1
23 are present, and in this case, in particular, the underlying Al
Since the mixed crystal ratio is large, there is also a problem that the crystallinity at the interface is deteriorated and a high-resistance layer is formed.

SUMMARY OF THE INVENTION The present invention has been made to improve the conventional disadvantages described above, and has as its object to reduce the loss of light inside the LED and to provide an LED capable of efficiently extracting light to the outside. And a manufacturing method therefor.

[0013]

A light emitting diode according to the present invention is a surface emitting type light emitting diode in which a current is injected into an active layer from an upper electrode of a growth layer including a double hetero structure and light is emitted from the active layer. Wherein the active layer is formed in a region excluding a portion immediately below the upper electrode,
Thereby, the above object is achieved.

In the method of manufacturing a light emitting diode according to the present invention, a growth layer including a double hetero structure is laminated on a substrate, and a laser beam is selectively irradiated into the growth layer to form a partial active layer. Forming an upper electrode on the surface of the growth layer except directly above the active layer, thereby achieving the above object.

[0015]

In the light emitting diode according to the present invention, the active layer is formed only in the region except the portion immediately below the upper electrode, and the current path not passing through the active layer has a higher resistance than the current path passing through the active layer. . A current is effectively injected into an active layer selectively formed in a region except a portion immediately below the upper electrode, and light is efficiently extracted to the outside. That is, since the active layer is not formed immediately below the upper electrode, the flow of light emitted vertically upward passes through the portion where the upper electrode is not formed. Also, in order to grow the active layer having such a structure, the growth is performed by selectively irradiating light to the active layer at the time of growing the active layer. Can be prevented.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the light emitting diode according to the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the light emitting diode of the present invention. (A) is a cross-sectional view, (b) is a top view, and (c) is a cross-sectional view showing current and light emission.

The LED 10 of this structure is an n-GaAs substrate 1
1, an n-GaAs buffer layer 19, n-InGa
AlP cladding layer 12, InGaAlP active layer 13, p
An -InGaAlP cladding layer 14, a p-GaAlAs current diffusion layer 15, and a p-GaAs contact layer 16 are stacked in this order.

The upper electrode 17 is stacked on the p-GaAs contact layer 16, and the lower electrode 18 is stacked on the n-GaAs substrate 11. The upper electrode 17 has a central electrode 17a formed at the center where lead bonding is performed as shown in the figure.
And a peripheral electrode 17b and a connecting portion 17c connecting them. The peripheral electrode 17b is provided to make the current injection into the InGaAlP active layer 13 more effective. It is not always necessary to form the peripheral electrode 17b and the connecting portion 17c.

In the LED 10 of the present structure, the InGaAlP active layer 13 is formed in a region excluding the portion 13a immediately below the upper electrode 17. Therefore, the InGaAlP active layer 13
As shown in FIG. 1C, the light emission shown by the broken line is emitted vertically upward from the upper electrodes 17a and 17b. This flow of light emission passes through the portion where the central electrode 17a and the peripheral electrode 17b are not formed and is not hindered by the central electrode 17a and the peripheral electrode 17b. For this reason, all the emitted light is extracted to the outside, and the efficiency of extracting the emitted light to the upper part is increased.

In the LED 10 of this structure, in the current path not passing through the InGaAlP active layer 13, the pn junction has a large band gap of n-In _0.5 (Ga _0.3 Al _0.7 ).
It is composed of _0.5 P and p-In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P, and the built-in voltage is inevitably high.

On the other hand, in the current path passing through the InGaAlP active layer 13, In has a relatively small band gap.
_{A 0.5} (Ga _0.62 Al _0.38 ) _0.5 P active layer 13 is present. For this reason, the built-in voltage is also relatively small, and the resistance of the current path passing through the InGaAlP active layer 13 is lower than that of the current path that does not pass. Therefore, the current is changed to In
Injection can be concentrated in the GaAlP active layer 13.

Further, the entire periphery of the InGaAlP active layer 13 is embedded with a crystal having a large band gap.
For this reason, diffusion of carriers and light are not guided out of the InGaAlP active layer 13 and absorbed, thereby increasing the internal efficiency. In this embodiment, the planar I
The shape of the nGaAlP active layer 13 is rectangular.

FIG. 2 shows a light emitting diode according to a second embodiment of the present invention. The LED 10 of this embodiment has an upper electrode 17
Shows a simplified cross-sectional structure. That is, the upper electrode 17 is formed only on the center electrode 17a, and the ones corresponding to the peripheral electrode 17b and the connecting portion 17c are not formed. And
Since the InGaAlP active layer 13 is formed in a region other than the center electrode 17a, its shape is also different. The InGaAlP active layer 13 is formed up to both side edges, and is not formed only in the center. Since other structures are the same as those of the first embodiment, the description of the structure is omitted here.

The LED 10 of the first embodiment shown in FIG.
When the device was mounted on a 5 mmφ lamp by molding, high luminance of 3 candela was obtained at a wavelength of 555 nm when a current of 20 mA was applied. This LED 10 is formed by growing the InGaAlP active layer 13 and then leaving the necessary portions.
The active layer 13 is removed by etching, and p-
Although it is also formed by regrowing the InGaAlP window layer (cladding layer) and thereafter, the conventional LED shown in FIG.
As described in the manufacturing method of No. 100, if there is a regrowth interface, the regrowth interface becomes high in resistance and may adversely affect device characteristics, which is not preferable.

The LED 10 of this embodiment is a photo-excitation type MO.
It is desirable to manufacture it by the following steps using a CVD apparatus. FIG. 3 shows a main part of a typical MOCVD apparatus 40 used for manufacturing the LED 10 of the present embodiment. This M
The OCVD apparatus 40 includes a reactor 31 made of quartz.
And a flow channel 35 provided inside the reactor 31, and a susceptor 32 projecting from the side inside the reactor 31. Cooling water 37 flows on the outer peripheral wall of the reactor 31, and a high-frequency coil 36 is wound around the outer peripheral wall. A laser introduction hole 46 is formed in the upper part of the outer peripheral wall, and a gas introduction hole 3 is formed inside the reactor.
4, 34 ', 34 "have been introduced.

The substrate 10 is placed on a carbon susceptor 32 projecting from a support rod 33, and a high-frequency coil 36
Heated by Material gas is supplied to the gas introduction pipes 34, 3
4 'feeds into the flow channel 35. H ₂ is injected from the gas introduction pipe 34 ″ to the vicinity of the laser introduction hole 46 so that this portion is not stained.

The laser beam is irradiated onto the substrate 10 by, for example, reflecting the 246 nm light 41 (KrF) of the excimer laser 42 at a right angle on the mirror 43. At this time, by passing through the mask 44 for selective growth and the optical system 45,
Light can be applied only to a desired area. By selectively irradiating a laser beam as described above, the above I
The nGaAlP active layer 13 and the like are grown and formed.

FIGS. 4A to 4C show L of the first embodiment.
A manufacturing process for manufacturing the ED 10 will be described. In order to manufacture the LED 10 of the first embodiment shown in FIG. 1, the temperature of the n-GaAs substrate 11 is set to 700 ° C., and TEG (triethylgallium), TEA (triethylaluminum), TMI (trimethylindium), PH3 (Phosphine) or other material gas is supplied.

Next, after growing up to the n-InGaAlP carrier confinement layer (cladding layer) 12, FIG.
The temperature of the n-GaAs substrate 11 is lowered to 500 ° C.
Then, as shown in FIG. 4B, laser light is selectively irradiated to grow the InGaAIP active layer 13. Since only the portion irradiated with light has a temperature of 600 ° C. or more, which is the decomposition temperature of PH ₃ , a partial InGaAIP active layer 13 is grown.

Thereafter, as shown in FIG. 4C, the temperature of the substrate 11 is raised to 700 ° C. again, and p-
An InGaAlP cladding layer 14, a p-GaAlAs current diffusion layer 15, and a p-GaAs contact layer 16 are grown on the surface. In the LED 10, after the upper electrode 17 and the lower electrode 18 are grown, a pattern as shown in FIG. 1 is formed by etching. If such a manufacturing method is used, InGa
Since there is no regrowth interface around the AIP active layer 13, a very good crystal can be produced and the resistance of the device becomes small.

FIG. 5 shows a third embodiment of the light emitting diode of the present invention. This embodiment is applied to an AlGaAs system. The LED 20 of this embodiment has an n-GaAs buffer layer 29 and an n-type Ga
_A light reflection layer 29a composed of _0.5 Al _0.5 As / AlAs (10 layers), an n-Ga _0.3 Al _0.7 As carrier confinement layer (cladding layer) 22, and a non-doped Ga _0.62 Al _0.38 A
An s active layer 23, a p-Ga _0.3 Al _0.7 As window layer (cladding layer) 24, and a p-GaAs ohmic contact layer 26 are laminated. The upper electrode 27 is formed on the p-GaAs ohmic contact layer 26 and the lower electrode 28
Is formed on the n-GaAs substrate 21. This LE
Also in D20, light emission is taken out from the upper part of the element.
The feature is that the GaAIAs active layer 23 is formed in a substantially circular shape. As in the case of the first embodiment, the layers other than the GaAs active layer 23 are grown by a normal MOCVD method (at a growth temperature of 760 ° C.).
The temperature of the n-GaAs substrate 21 is reduced to about 500 ° C. only for the growth of the IAS active layer 23. Then, light is irradiated only to a portion where the InGaIP active layer 23 is to be selectively grown, and
The growth was carried out at a temperature higher than the decomposition temperature of AsH ₃ .

In the LED 20 of this configuration, the current is G
It is implanted intensively in the aAIAs active layer 23. This is because the pn junction in the current path that does not pass through the GaAlAs active layer 23 has a high Al mixed crystal ratio of n-Ga _0.3 Al _0.7 As.
The reason for this is that the built-in voltage is high in that part because it is made of p-Ga _0.3 Al _0.7 As.
According to the measurement results, the characteristics of this LED 20 were such that when 5 mmφ was mounted, the luminance was 10 candelas at a wavelength of 655 nm (red) under a current of 20 mA.

FIG. 6 shows the structure of a light emitting diode according to a fourth embodiment of the present invention. This LED 50 is made of InGaAs
1P-based, and selectively non-doped In _0.5 (G
a _0.6 Al _0.4 ) _0.5 P active layer 53 is formed. In this LED 50, a luminance of 3.2 candela was obtained at a wavelength of 555 nm (5 mmφ, 20 mA).

The material system in the present invention is the above-mentioned InGa
It is not limited to AlP or GaAlAs,
nSSe, CdZnS-based or the like may be adopted. The light source used for the light excitation is not limited to the excimer laser light, and an Ar laser, a He-Cd laser, a halogen lamp, a mercury lamp, or the like may be used.

FIG. 7 shows the structure of a light emitting diode according to a fifth embodiment of the present invention. In this LED 60, the center electrode 67a, which is the upper electrode 67, and the square annular electrodes 67b and 67c are p
The lower electrode 68 is formed on the n-GaAs substrate 61. The center electrode 67a and the rectangular annular electrodes 67b and 67c are connected by a connecting portion 67d. The InGaAIP active layer 63 includes a central electrode 67a, square annular electrodes 67b and 67c.
7A is formed in a region excluding the portion 63a immediately below.

It is shown that the shape of the InGaAIP active layer 63 is not limited to a special shape, but may be formed in a large number.

[0037]

According to the light emitting diode of the present invention, the active layer is formed only in the region except the portion immediately below the upper electrode, and the current path not passing through the active layer has a higher resistance than the current path passing through the active layer. I have. A current is effectively injected into an active layer selectively formed in a region except a portion immediately below the upper electrode, and the flow of light emission passes through a portion where the upper electrode is not formed and is not hindered by the upper electrode. For this reason, the loss of extracting light is reduced, and light can be efficiently extracted to the outside of the element. In order to grow an active layer having such a structure, the active layer is grown by selectively irradiating light to the active layer at the time of growing the active layer, thereby preventing generation of an undesirable high-resistance layer without a regrowth interface. .

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of the structure of the light emitting diode of the present invention, wherein (a) is a cross-sectional view of the LED, (b) is a plan view of the LED, and (C) is a current flow and light emission. Indicate the direction.

FIG. 2 is a schematic view showing another embodiment of the structure of the light emitting diode of the present invention.

FIG. 3 is a cross-sectional view showing a conventional light emitting diode manufacturing apparatus.

FIG. 4 is a sectional view showing the manufacturing process of the light emitting diode of the first embodiment.

5A and 5B are schematic views showing an embodiment of the structure of the light emitting diode of the present invention, wherein FIG. 5A is a sectional view of the LED, and FIG. 5B is a plan view of the LED.

FIG. 6 is a schematic view showing an embodiment of the structure of the light emitting diode of the present invention, wherein (a) is a cross-sectional view of the LED, and (b) is a plan view of the LED.

FIGS. 7A and 7B are schematic views showing an embodiment of the structure of the light emitting diode of the present invention, wherein FIG. 7A is a cross-sectional view of the LED, and FIG.

FIG. 8 is a cross-sectional view illustrating a structure of a conventional light emitting diode.

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

[Explanation of symbols]

10, 20, 50, 60 LED 11, 21, 51, 61 n-GaAs substrate 12, 22, 52, 62 n-InGaAlP cladding layer 13, 23, 53, 63 InGaAlP active layer 14, 24, 54, 64 p- InGaAlP cladding layer (window) 15, 55 p-GaAlAs current diffusion layer 16, 26, 56 p-GaAs contact layer 19, 29, 59 n-GaAs buffer layer 17, 27, 57, 67 upper electrode 18, 28, 58, 68 Lower electrode 22 n-GaAlAs cladding layer 23 GaAlAs active layer 24 p-GaAlAs cladding layer (window) 29a, 59a Light reflection layer

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Saburo Yamamoto 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-4-282875 (JP, A) JP-A-3-3 3373 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 33/00

Claims (2)

(57) [Claims] 1. A surface-emitting type light-emitting diode in which a current is injected from an upper electrode of a growth layer including a double heterostructure to an active layer to emit light from the active layer, except for a portion directly below the upper electrode. active layer is formed in a region, the active
The top and both sides of the layer are covered by a single semiconductor layer
Light-emitting diodes are. 2. A step of laminating a growth layer including a double heterostructure on a substrate; a step of selectively irradiating a laser beam into the growth layer to form a partial active layer; Forming an upper electrode on the surface of the growth layer except directly above the light emitting diode.