JP2001144323A - AlGaInP LIGHT-EMITTING DIODE AND MANUFACTURING METHOD THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AlGaInP LED which is equipped with an electrode structure, that is capable of widely diffusing an LED operating current over the entire light-emitting layer in a two-dimensional manner, producing a low forward voltage, and enhancing the LED in other luminous performance. SOLUTION: An electrode structure is so constituted, that an LED drive current fed from a pedestal electrode is made to flow through a light-emitting part from granular ohmic electrodes scattered on a semiconductor layer through the intermediary of a transparent conductive film formed of a conductive oxide layer, where the ohmic electrode is composed of granular electrodes, which are arranged evenly on the surface of the semiconductor layer and 20 μm or smaller in the maximum width on a planar shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-luminance AlGaInP light-emitting diode (LED) having an electrode structure capable of widely diffusing a drive current over a light-emitting portion in a plan view and a method of manufacturing the same.

[0002]

2. Description of the Related Art The general formula is (Al _X Ga _{1 -x} ) _Y In _{1 -Y} P
In an AlGaInP multi-element mixed crystal in which (0 ≦ X ≦ 1, 0 <Y <1), in particular, the indium composition ratio (= 1−Y) is set to 0.5 (Al _X Ga _{1 -X} ) _0.5 In _0.5 P (0 ≦ X ≦
1) has the advantage of achieving good lattice matching with gallium arsenide (GaAs) single crystal, and is used, for example, for forming a light emitting diode (LED) or a laser diode (LD) that emits red-orange light. ing. FIG.
It is sectional drawing which shows the structure of the conventional red-orange AlGaInPLED10 which makes an emission wavelength about 620 nanometer (nm) -630 nm.

A light emitting portion 10a of a conventional AlGaInPLED 10 is formed on an n-type or p-type conductive GaAs single crystal substrate 101 by a vapor phase growth method such as a metalorganic thermal decomposition (MOCVD) method. (Al _x Ga _{1 -x} ) _0.5 In _0.5 P (0 ≦) interposed via the buffer layer 102 and the Bragg reflection layer 103 formed thereon.
It is configured using layers 104 to 106 composed of X ≦ 1). In addition, the light emitting section 10a is provided with a light emitting layer 10 to obtain high intensity light emission by utilizing the "confinement" effect of carriers.
In between the n-type or p-type lower cladding layer 104 and the upper cladding layer 106 each having a band gap larger than 5 (Al _x Ga _{1 -x} ) _0.5 In _0.5 P
P sandwiching the light emitting layer 105 made of (0 ≦ X ≦ 1)
It is customary to use an n-junction type double hetero (DH) structure. That is, AlGaInPLED1
0 denotes a buffer layer 102, a Bragg reflection layer 103, and a lower cladding layer 10 laminated on a GaAs single crystal substrate 101.
4, a structure including a group III-V compound semiconductor layer 10b composed of a light emitting layer 105 and an upper cladding layer 106.

In the conventional AlGaInPLED 10, D
It is customary to arrange a window layer (window layer) 107 in a direction in which light emitted above the light emitting unit 10a having the H structure is taken out. The window layer 107 needs to be made of a transparent material having a large band gap that can sufficiently transmit light emitted from the light emitting layer 105. In the prior art, the window layer 10
No. 7 discloses a means for forming a conductive oxide crystal such as indium oxide, tin oxide, zinc oxide or magnesium oxide (JP-A-11-17220 and US Pat. No. 5,481,122). See specification).

[0005] On the conductive transparent oxide window layer 107,
Gold (Au), aluminum (Al) or titanium (T
A pad electrode 108 for connection such as i) is laid. On the back side of the conductive GaAs substrate 101, a first electrode 109 having ohmic contact is arranged to form an AlGaInPLED 10.

[0006]

The conventional Al shown in FIG.
The cross-sectional structural view of the GaInPLED 10 will be described with reference to the conventional AlGaInPLED 10 including the window layer 107 made of a transparent oxide, in which the window layer 107 is formed of a conductive layer. Oxide Crystal Constituting Layer 107 and III-V Compound Semiconductor Layer 10b
(Especially in the case of the LED structure illustrated in FIG. 1, due to the height of the barrier at the junction with the upper cladding layer 106),
There was a problem that a contact having sufficiently excellent ohmic properties could not be formed between the window layer 107 and the III-V compound semiconductor layer 10b. Therefore, L supplied via the electrode 108
The ED driving current cannot be diffused over a wide area of the light emitting surface.
This hindered the increase in the brightness of the ED. Also, AlGaInPLEDs with reduced forward voltage (Vf) could not be supplied stably.

A window layer 1 made of a conductive transparent oxide
07 and the upper cladding layer 106, zinc (Zn)
Alternatively, a metal film 11 made of a gold-zinc (Au-Zn) alloy
A technique of inserting 0 is also disclosed (JP-A-11-40).
No. 20). In this prior art, the metal film 1
Reference numeral 10 is provided for the purpose of promoting the adhesion between the upper cladding layer 106 and the window layer 107. However, in this prior art, since the metal film 110 is uniformly laid on almost the entire surface of the upper cladding layer 106, light emission is absorbed by the metal film 110, and high brightness AlGaInP
It is disadvantageous for obtaining LEDs.

In addition, since the metal film 110 is laid so as to cover the portion where the pedestal electrode 108 overlaps the surface of the III-V compound semiconductor layer 10b in plan view, the pedestal electrode is difficult to emit light to the outside. The configuration is such that it is impossible to prevent the LED drive current from flowing to the light emitting section in a region immediately below 108. For this reason, a part of the LED operating current is wasted in a region immediately below the pedestal electrode 108, and there is a disadvantage that the efficiency of extracting light emission to the outside is reduced after all.

In summary, in the prior art for increasing the luminance of an AlGaInPLED, it is not possible to sufficiently achieve a wide diffusion of an LED driving current to a light emitting region and an improvement in the efficiency of extracting light emitted to the outside. The present invention relates to (1) A
Since good ohmic contact with the group III-V compound semiconductor layer constituting the lGaInPLED can be achieved, the LED operating current can be diffused widely over the entire area of the light emitting layer as viewed in plan, and (2) low forward direction. Voltage (V
_f ) is provided, and (3) an AlGaInPLED provided with an electrode structure having an excellent external luminous efficiency because of a shape capable of reducing the rate of blocking light emission.

[0010]

According to the present invention, there is provided a semiconductor substrate having a first electrode formed on a back surface, a semiconductor layer including a light emitting portion made of AlGaInP formed on the semiconductor substrate, A plurality of ohmic electrodes forming ohmic contact with the semiconductor layer formed on a part of the surface; a transparent conductive film formed to cover the semiconductor layer and the ohmic electrode and conducting with the ohmic electrode; and the transparent conductive film In the AlGaInP light-emitting diode having a pedestal electrode that is electrically connected to the transparent conductive film formed on a part of the surface of the device, all of the plurality of ohmic electrodes are formed of granular electrodes having a maximum width of 20 μm or less in a planar shape. It is characterized by.

In the present invention, it is preferable that the ohmic electrodes are scattered and arranged in a portion (open light emitting region) of the surface of the semiconductor layer which does not overlap with the pedestal electrode when viewed in plan. Furthermore, in the present invention, it is particularly desirable that the ratio of the total surface area of the ohmic electrodes in the open light emitting region to the surface area of the open light emitting region (surface coverage) is 3 to 70%.

Further, the present invention is characterized in that the ohmic electrode has a multilayer structure in which the side in contact with the semiconductor layer is an alloy containing gold (Au) and the side in contact with the transparent conductive film is Au. In particular, when the semiconductor layer in contact with the ohmic electrode is made of n-type AlGaInP, the side of the ohmic electrode in contact with the semiconductor layer is preferably made of an alloy of Au and germanium (Ge). When the semiconductor layer in contact with the ohmic electrode is made of p-type AlGaInP, the side of the ohmic electrode in contact with the semiconductor layer is an alloy containing Au and zinc (Zn) or Au and beryllium (Be).
It is desirable to be composed of an alloy containing

Further, the present invention is characterized in that the transparent conductive film is made of indium tin oxide (ITO). That is, the transparent conductive film is preferably made of a metal oxide having a resistivity of 7 × 10 ⁻⁴ Ωcm or less and a band gap of 2.5 eV or more.

Further, according to the present invention, in the above-mentioned method for manufacturing an AlGaInP light-emitting diode, a metal thin film is deposited on the surface of the semiconductor layer, and the metal thin film is condensed by heat treatment to form a plurality of granular ohmic electrodes. It is characterized by.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An AlGaInPLED for describing an embodiment of the present invention according to the first aspect of the present invention.
FIG. 2 shows a schematic plan view of No. 20. FIG. 3 is a schematic diagram showing a cross-sectional structure of the AlGaInPLED 20 shown in FIG. The configurational feature of the LED 20 according to the first embodiment is that, as shown in FIGS.
9, a semiconductor layer 20b including a light emitting portion 20a made of AlGaInP formed on the semiconductor substrate, and an ohmic contact with the semiconductor layer formed on a part of the surface of the semiconductor layer 20b. A plurality of ohmic electrodes 210, a transparent conductive film (= window layer) 207 formed over the semiconductor layer and the ohmic electrode and electrically connected to the ohmic electrode, and formed on part of the surface of the transparent conductive film. In the AlGaInP light-emitting diode 20 having the pedestal electrode 208 electrically connected to the transparent conductive film, the plurality of ohmic electrodes 210 are all formed of granular electrodes having a maximum width of 20 μm or less in a planar shape. In other words, the LED driving current is conveniently applied to the light emitting unit 20a via the transparent conductive film 207 from the pedestal electrode 208 on the bonding surface between the transparent conductive film 207 and the upper cladding layer 206 forming a part of the light emitting unit 20a of the LED 20. It is characterized in that an ohmic electrode 210 for flowing is provided, and the ohmic electrode is composed of a plurality of granular electrodes having a maximum width of 20 μm or less in a planar shape. Here, the upper cladding layer 206 is a cladding layer in a direction in which light is emitted to the outside, and is a layer provided by bonding the transparent conductive film 207.

A method of obtaining the LED 20 having the plurality of ohmic electrodes 210 made of a granular metal will be described with reference to an example in which the ohmic electrode 210 made of a gold (Au) alloy is provided. (1) First, (Al _x Ga _1-x ) is formed on the GaAs substrate 201.
_The semiconductor layer 20b including the upper cladding layer 206 made of _0.5 In _0.5 P is formed by a growth method such as the MOCVD method. Here, for example, the semiconductor layer 20 b includes a buffer layer 202, a Bragg reflection layer 203, a lower cladding layer 204, a light emitting layer 205, and an upper cladding layer 206, which are sequentially laminated on a GaAs substrate 201. In this case, this LED2
The light-emitting portion 20a of the light-emitting layer 20
5. The upper cladding layer 206 is formed. The light emitting unit 20
a shall be made from AlGaInP. (2) Next, on the surface of the upper cladding layer 206,
For example, a thin film having continuity, for example, made of a gold-germanium (Au.Ge) alloy, which is selected as a metal material forming an ohmic contact with (Al _X Ga _{1 -X} ) _0.5 In _0.5 P, which is used as a material, is deposited. . (3) Thereafter, the applied Au.Ge alloy thin film is subjected to an ohmic alloying (alloy) treatment by heat treatment, and at that time, the Au.Ge alloy is condensed due to the surface tension (that is, the Au.Ge alloy is converted into a ball. Then, the continuity of the alloy thin film is broken to form a granular ohmic electrode 210 having a plurality of outer shapes that are substantially spherical. (4) The granular ohmic electrode 210 is formed on the upper cladding layer 2.
06, the upper cladding layer 206 and the ohmic electrode 210 are covered with a transparent conductive film 207 serving as a window layer while being scattered and arranged on the surface of the substrate. (5) Next, the pedestal electrode 2 is provided at the center on the transparent conductive film 207.
08 is laid to configure the LED 20.

Alternatively, as another method, (Al _X G
_{a 1-X) Y In 1} -Y P selectively to a region which does not overlap with the pad electrode 208 in plan view on the surface of the upper cladding layer 206, the Au · Ge alloy thin film is a metal material of the ohmic resistance For example, there is a method in which a granular ohmic electrode is formed by applying an ohmic alloy process after being scattered and attached in isolation from each other using a mask material.

The present invention is characterized in that all of the plurality of ohmic electrodes are formed of granular electrodes having a maximum width of 20 μm or less in a planar shape. Semiconductor layer 20b
A region which does not overlap with the pedestal electrode 208 when viewed in a plane view
That is, when the granular ohmic electrode 210 having a plane area larger than necessary is provided in the open light emitting region 211, the area of the open light emitting region 211 from which light can be extracted from the light emitting portion is reduced, and high intensity light emission can be obtained. It is inconvenient. Therefore, it is preferable that all of the plurality of ohmic electrodes be made of metal particles having a maximum width of 20 μm or less in a planar shape. However, on the other hand, the granular ohmic electrode 210 having an extremely small particle size is disadvantageous because it results in a steep increase in _Vf . The minimum particle size of the ohmic electrode that can be formed stably without inviting an increase in _Vf is about 0.5 μm. The AlGaInPLED 20 exemplified in the schematic plan view of FIG. 2 has an average particle size of about 5 μm.
This is an example of an LED in which granular ohmic electrodes 210 are scattered and provided on the surface of the upper cladding layer 206 that does not overlap with the pedestal electrode 208 in a plan view, that is, on the open light emitting region 211. Granular ohmic electrode 210
When the LED driving current supplied through the transparent conductive film 207 is provided in the open light emitting region, the LED driving current supplied through the transparent conductive film 207 is not densely provided in a part of the surface of the upper cladding layer 206 but is scattered at a substantially uniform surface density. The effect that can be conveniently diffused to 211 is obtained. The preferred density of the granular ohmic electrode 210 in the open light-emitting region 211 is the planar area of the LED, the planar area of the pedestal electrode 208, or the granular ohmic electrode 21.
It varies depending on the average particle size of 0. By way of example, a plane area of the open-emitting region 211 and 5 × 10 ^{over 4} cm ^2, in the case where the average particle diameter of the granular ohmic electrode 210 was assumed 10 [mu] m, a suitable particulate ohmic to be interspersed in the open-emitting region 211 The number of the electrodes 210 is in the range of about 20 to about 445, and therefore, the existence density is in the range of about 3.8 × 10 ⁴ / cm ^{2 to} 8.9 × 10 ⁵ / cm ^2. .

In the embodiment according to the second aspect of the present invention, the ohmic electrodes 210 are scattered in a portion of the surface of the semiconductor layer which does not overlap with the pedestal electrode in a plan view, that is, in the open light emitting region 211. It is preferable to arrange them. The granular ohmic electrode 210 is provided for the purpose of diffusing the LED drive current supplied from the pedestal electrode 208 via the transparent conductive film forming the window layer 207 to a wide area of the open light emitting area 211. Even if an ohmic electrode 210 is provided in a region overlapping with the pedestal electrode 208 and an operating current is supplied to the same region, light emitted from a light emitting portion below the pedestal electrode 208 is shielded by the pedestal electrode 208 and thus extracted to the outside. This is because the emitted light does not increase. In the present invention, the conductive oxide layer forming the transparent conductive film 207 and the group III-V compound semiconductor layer (206 in FIGS. 2 and 3) are directly connected to each other immediately below the pedestal electrode 208. It is preferable to adopt a configuration. At the interface between the transparent conductive film 207 made of an oxide layer and the group III-V compound semiconductor layer, a junction having a relatively high barrier is formed. Therefore, if such a junction is formed in a region directly below the pedestal electrode 208, it is possible to prevent the LED operating current from directly flowing into the region directly below the pedestal electrode 208. In other words, the operating current can be effectively passed through the open light emitting region 211, and the effect of improving the efficiency of external emission of light emission is exhibited.

When the number of granular ohmic electrodes 210 scattered on the surface of the upper cladding layer 206, for example, on the surface of the upper cladding layer 206, especially on the open light emitting region 211 other than the region directly below the pedestal electrode 208, is increased. The area occupied by the electrode 210 in the light emitting region 211 increases.
Thus, the area of the open light emitting region 211 from which light from the light emitting unit can be extracted is reduced. In an LED in which the granular ohmic electrode 210 is arranged so as to occupy an area exceeding 70% (%) of the surface area of the open light emitting region 211, the ratio of light emission blocked by the granular ohmic electrode 210 itself becomes large, and light emission is reduced. As a result, it is impossible to obtain a high-brightness LED. However, an L with only a small ohmic electrode 210 occupying less than 3% of the area
ED is disadvantageous because the forward voltage (V _f ) increases.
Therefore, in the embodiment according to the third aspect of the present invention, the granular ohmic electrode 2 in the open light emitting region 211 is formed.
It is preferable that the total plane area of 10 is not less than 3% (%) and not more than 70% of the surface area of the open light emitting region 211.

For example, a square LED chip having a side of 250 μm (plane area ≒ 6.3 × 10 ^-4)
in central cm ^2), In the circular seat electrode 208 (plane area ≒ 1.1 × 10 ^-4 cm ²⁾ is laid AlGaInPLED20 to 120μm in diameter, the surface area of the open-emitting region 211 is approximately 5 2 × 10 ⁻⁴ cm ² .
In the open light emitting region 211 having this surface area, granular ohmic electrodes 210 (planar area ≒ 7.9 × 10 ⁻⁷ cm ² ) approximate to a circular shape having an average particle size of 5 μm are provided at a total of about 50 places. In this case, the coverage of the ohmic electrode 210 in the open light emitting region 211 is about 7.6%.

In the case where a granular ohmic electrode is formed by utilizing ball-up during heat treatment for forming an ohmic alloy of the electrode, the granular ohmic electrode 210 is used.
Can be adjusted depending on the thickness of the thin film which is a material of the electrode metal constituting the ohmic electrode 210 and the conditions of an alloying (alloy) treatment for imparting ohmic properties thereto. When the alloy conditions are the same, the thinner the film thickness, the smaller the ohmic electrode 21 having a smaller particle size.
It can be set to 0. Therefore, a granular ohmic electrode 210 having a small coverage can be formed. For thin films of the same thickness, the heat treatment temperature for alloying (alloy temperature)
The higher the temperature, the smaller the size of the granular ohmic electrode 21
0 is obtained. Generally, the alloy temperature is in the range of about 400 ° C. to about 550 ° C., and the processing time is about
It is suitable to be within 0 minutes. The longer the processing time, the easier it is to obtain granular electrodes due to condensation. For example, a gold-germanium alloy (A) having a thickness of about 50 nanometers (nm)
u93% by weight, Ge 7% by weight alloy) on the surface of the semiconductor layer, and then, at 500 ° C. in a hydrogen (H ₂ ) atmosphere, at 3 ° C.
Performing the alloying process for 0 minutes results in a granular ohmic electrode 210 having an average diameter of about 5 μm. The alloy treatment can be performed in a non-oxidizing atmosphere such as nitrogen (N ₂ ) or argon (Ar) in addition to hydrogen. However, according to the heat treatment in an atmosphere mainly containing hydrogen, the particle size can be made more uniform. There is the advantage of providing a granular ohmic electrode. The particle diameter is the diameter of a circumscribed circle when the planar shape of the granular ohmic electrode is regarded as a circumscribed circle.

In the case where a granular ohmic electrode is manufactured by using ball-up, the granular ohmic electrode having a substantially uniform surface density is disposed on the surface of the semiconductor layer. It is necessary to make the thickness uniform on the surface of the semiconductor layer in advance. If there is a region where the film thickness is non-uniform and the film thickness is large in a part of the region, it becomes easy to form a granular ohmic electrode having a large particle diameter due to condensation in the region, and the ohmic electrode 210 is opened. Light emitting area 2
11 cannot be scattered at a uniform density. For example, a thin film having a uniform thickness of ± 10% or less for a 50 nm Au—Ge alloy film is advantageous for promoting the formation of the ohmic electrode 210 having a uniform surface density. A thin film having such uniformity can be formed by a general vacuum evaporation method, a sputtering method, or the like.

Further, as described in the embodiment according to the fourth aspect of the present invention, in forming the granular ohmic electrode 210, a part of the light emitting portion 20a is formed (Al _X
When the side that makes contact with the Ga _1-x ) _0.5 In _0.5 P upper cladding layer 206 is made of a gold alloy, an electrode 210 having excellent ohmic properties is obtained. Further, when the side in contact with the transparent conductive film 207, which is the upper layer of the gold alloy layer, is made of gold,
Ohmic electrode 2 having excellent adhesion to transparent conductive film 207
10 can be configured. That is, since the ohmic electrode 210 has a multilayer structure in which the side in contact with the semiconductor layer is made of an alloy containing gold (Au) and the side in contact with the transparent conductive film 207 is Au, the ohmic electrode 210 and the upper cladding layer 206 of the AlGaInPLED 20 are different from each other. The granular ohmic electrode 21 having excellent contact properties and excellent adhesion to the transparent conductive film 207
0 results. By making the granular ohmic electrode 210 excellent in adhesion to the transparent conductive film 207, the drive current supplied through the transparent conductive film 207 can be stably supplied to the ohmic electrode 210. For an ohmic electrode having a multilayer structure in which the lower layer is a gold alloy layer and the upper layer is a gold layer, for example, a gold alloy film is first deposited using a general vacuum deposition method, and then a gold film is deposited thereon. It can be formed by attaching it. From the viewpoint of obtaining an ohmic electrode having low contact resistance, it is desirable that the layer thickness of the gold alloy thin film is approximately 10 nm or more. A typical thickness is about 50 nm. It is desirable that the thickness of the gold thin film is also about 10 nm or more. Further, the total thickness of the gold alloy thin film and the gold thin film is preferably smaller than the thickness of the oxide layer included in the transparent conductive film 207.

In the embodiment according to the fifth aspect of the present invention, a part of the light emitting section 20a is formed (Al _x Ga _{1 -x} ).
_{When the 0.5} In _0.5 P upper cladding layer 206 is an n-type conductive layer, a preferable electrode configuration for providing a granular ohmic electrode is a gold alloy of an electrode material on the side joining with the upper cladding layer 206, particularly Gold-germanium alloy. Other gold alloys that have ohmic contact with the n-type (Al _x Ga _{1 -x} ) _0.5 In _0.5 P layer include gold and tin (Au.
Sn) alloys and gold-indium (Au-In) alloys are listed, but Au-Ge alloys stably provide the best ohmic contact. In the Au.Ge alloy, the higher the germanium (Ge) weight content, the better the ohmic contact property and the easier it is to condense, so that the granular ohmic electrode 210 is easily provided.

In the embodiment according to the sixth aspect of the present invention, a part of the light emitting section 20a is formed (Al _x Ga _{1 -x} ).
_{When the 0.5} In _0.5 P upper cladding layer 206 is a p-type conductive layer, the gold alloy of the electrode material on the side joining with the upper cladding layer 206 may be gold-zinc (Zn) alloy or gold-beryllium (Au-Be). ) Alloy. If an Au.Zn alloy or an Au.Be alloy is used, a granular ohmic electrode can be formed most conveniently.

In the present invention, a transparent conductive film 207 made of a conductive oxide layer is formed as a window layer so as to cover the surface of the semiconductor layer and the granular ohmic electrodes 210 scattered on the surface. By forming the electrical contact by covering the ohmic electrode 210 with the transparent conductive film 207, the pedestal electrode 208 is formed.
The supplied LED driving current can be uniformly supplied to the granular ohmic electrode 210. In other words, the transparent conductive film 207 has a function of flowing an operating current to the ohmic electrode 210 due to its conductivity while forming a barrier that inhibits conduction with the group III-V compound semiconductor layer as described above. Have. In addition, a portion of the semiconductor layer surface between the granular ohmic electrodes 210 is sufficiently larger than the forbidden band width corresponding to the emission wavelength of the LED, specifically, 2.5 eV or more that can transmit green band light. By laying a transparent conductive film made of an optically transparent oxide layer having a band gap, light can be transmitted to the outside without being shielded and transmitted through the transparent conductive film. For this reason, high brightness LE
This is convenient for obtaining D. L to ohmic electrode 210
Metal oxides having conductivity suitable for supplying an ED driving current and having sufficiently excellent transmission of light emission having a band gap exceeding 2.5 eV at room temperature include indium tin oxide (ITO) and zinc oxide (ZnO). ) And magnesium oxide (MgO). In particular, ITO having a low specific resistance, which has a forbidden band width of 2.5 eV or more and a resistivity of 7 × 10 ⁻⁴ Ω · cm or less, is favorable as a material of the transparent conductive film 207.

The thickness of the transparent conductive film 207 is
Is set so as to give a high transmittance for the emission wavelength of. For example, for red-orange light emission having a wavelength of about 620 nm, a window layer having a transmittance exceeding 90% can be formed by forming the transparent conductive film 207 from ITO having a layer thickness of about 600 nm. Further, a transparent conductive film can be formed from two or more metal oxide layers so that a transparent conductive film is formed from an ITO layer and a ZnO layer. However, the transparent conductive film 207 is formed from two or more metal oxide layers. In such a case, an optimum configuration is such that an oxide layer having a smaller refractive index is sequentially stacked in the direction of light emission. For example, ITO (refractive index ≒ 2.
In the case where a transparent conductive film is formed from a multilayer structure of (0) and ZnO (refractive index: ≒ 2.2), it is recommended that the lower layer be made of ZnO and the upper layer be made of ITO in the emission direction of light emission.

[0029]

EXAMPLES (Example 1) Hereinafter, the present invention will be described in detail based on examples. FIG. 4 shows the AlGaIn according to the first embodiment.
1 shows a schematic plan view of a PLED 30. FIG. FIG. 5 is a schematic sectional view of the AlGaInPLED 30 shown in FIG.

The LED 30 is formed on a GaAs single crystal substrate 301 having a p-type (001) plane doped with zinc (Zn) as a semiconductor layer 30b in the order of Zn-doped p-type GaAs.
s buffer layer 302, both p-type Al doped with Zn
_0.40 Ga _0.60 As layer Bragg reflector consisting of 10 layers at a time stacked periodic structure alternately and p-type Al _{0. 95} Ga _0.05 As layer (DBR) layer 303, Zn-doped p-type (Al _0.7 Ga
_0.3 ) p-type lower cladding layer 30 made of _0.5 In _0.5 P
4. Undoped n-type (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P
And it has a light-emitting layer 305, and silicon (Si) doped n-type a (Al _0.7 Ga _{0 .3)} upper cladding layer 306 made of _0.5 an In _0.5 P stacked structure consisting of a mixed crystal. This L
The light emitting portions of the ED 30 are a lower cladding layer 304, a light emitting layer 305, and an upper cladding layer 3 made of AlGaInP, respectively.
06.

Each of layers 302 to 3 constituting semiconductor layer 30b
06 is trimethylaluminum ((CH ₃ ) ₃ Al),
It was formed by a reduced pressure MOCVD method using trimethyl gallium ((CH ₃ ) ₃ Ga) and trimethyl indium ((CH ₃ ) ₃ In) as a group III element material. Diethyl zinc ((C ₂ H ₅ ) ₂ Zn) was used as a doping material for zinc (Zn) as a p-type impurity. Disilane (Si ₂ ) is used as a doping material for silicon (Si) which is an n-type impurity.
H ₆₎ was used. Arsine (AsH ₃ ) or phosphine (PH ₃ ) was used as a raw material of the group V element. The formation temperature of each of the layers 302 to 306 of the semiconductor layer 30b was unified to 730 ° C. The carrier concentration of the buffer layer 302 was about 5 × 10 ¹⁸ cm ^−3, and the layer thickness was about 1 μm. D
The layer thicknesses of the p-type Al _0.40 Ga _0.60 As layer and the p-type Al _0.95 Ga _0.05 As layer forming the BR layer 303 were each about 40 nm. The carrier concentration of the lower cladding layer 304 is about 3 × 10
¹⁷ cm ^-3 and the layer thickness was about 1 μm. Light emitting layer 30
5 has a thickness of about 0.5 μm and a carrier concentration of about 5 × 1.
It was set to 0 ¹⁶ cm ^-3 . The carrier concentration of the upper cladding layer 306 was about 2 × 10 ¹⁸ cm ^−3, and the layer thickness was about 5 μm.

GaAs single crystal substrate by MOCVD
Each layer 302 to 306 of the semiconductor layer 30b is formed on 301
After that, electrodes were formed on the front and back surfaces of the wafer.
First, the general surface of the n-type upper cladding layer 306 is
And gel with a thickness of about 50 nm by a typical vacuum evaporation method
Manium alloy (Au 93% by weight-Ge 7% by weight)
A continuous film was once deposited. Continue to reduce the film thickness to about 5
A gold (Au) film having a thickness of 0 nm is formed on the surface of an Au—Ge alloy film.
Deposited on top. Next, the Au—Ge alloy film and the Au coating
With the film left on the surface of the upper cladding layer 306
And hydrogen (H _Two) In air stream at 500 ° C for 30 minutes
Was subjected to a heat treatment for alloying. As a result, during deposition
The above Au—Ge alloy film / Au coating exhibiting continuity
Ball-up, condensed into granular and ohmic contact
An ohmic electrode 307 having a touch was obtained. Normal optics
Diameter of granular ohmic electrode 307 measured by microscope
The average value of (particle size) is about 8 μm and the maximum width is 20 μm or less.
it was under.

Next, the n-type upper cladding layer 306 and the ohmic electrode 307 are covered with the granular ohmic electrode 307 remaining on the n-type upper cladding layer 306, and the transparent conductive film 309 is formed by a general magnetron sputtering method. Indium tin oxide (ITO) film
Deposited at 00 ° C. Thus, the granular ohmic electrode 307 was surrounded by the transparent conductive film 309. The specific resistance of the ITO layer is about 4 × 10 ⁻⁴ Ω · cm, and the layer thickness is about 600 nm.
And According to the general X-ray diffraction analysis method, the ITO film
It was shown that the film was a polycrystalline film preferentially oriented in the <001> direction (C-axis).

Next, the transparent conductive film 3 for transmitting light emission
After a general organic photoresist material was applied to the surface of the substrate 09, a region where the pedestal electrode 310 was to be provided was patterned using a known photolithography technique. Thereafter, a gold (Au) film was deposited on the entire surface by a vacuum deposition method while the patterned resist material was left. The thickness of the gold (Au) film was about 700 nm. Thereafter, as the resist material is removed, the pedestal electrode 310 is formed by well-known lift-off means.
The Au film was left only in the region where the film was to be formed. Thus, a circular pedestal electrode 310 made of an Au film having a diameter of about 110 μm was formed. The plane area of the pedestal electrode 310 was about 0.95 × 10 ⁻⁴ cm ² .

Subsequently, the back of the p-type GaAs single crystal substrate 301
Ohmic contact made of gold-zinc (Au-Zn) alloy on the surface
After forming the p-type first electrode 311 having a touch,
Wafers are cut into individual pieces by the scribe method
Then, LED 30 was formed. LED30 is 260μ on one side
m, flat area about 6.8 × 10^-Fourcm^TwoAnd a square
As a result, the open light emitting area 308 of the LED 30
The area is 5.9 × 10^-Fourcm ^TwoIt became. LED3
Granular ohmics scattered on the surface of the open emission region 308 of zero
The number of the electrodes 307 is 436, and the
Area density of the ohmic electrode 307 is about 7.4 × 10^FivePcs / c
m^TwoIt was calculated. Also, the surface area of the open light emitting area 308
In contrast, a granular ohmic electrode with an average particle size of about 8 μm
Total plane area occupied by pole 307 (2.2 × 10^-Fourcm
^Two) Accounted for about 37%.

When a current was passed in the forward direction between the p-type first electrode 311 and the pedestal electrode 310 of the LED 30, red-orange light having a wavelength of about 620 nm was emitted through the open light-emitting region 308. The half width of the emission spectrum measured by the spectroscope was about 20 nm, and light emission having excellent monochromaticity was obtained. The intensity of light emission of the LED 30 when a current of 20 mA, which is simply measured in a state where the visibility was corrected using an integrating sphere, was about 74 millicandela (mcd). Further, in the LED 30 of the present embodiment,
Due to the effect of the uniform distribution of the operating current due to the scattered arrangement of the ohmic electrodes, light emission is also observed in the peripheral region of the LED 30 and the open light emitting region 308
The distribution of the light emission intensity in Example 2 was uniform. Also, 20
LED 30 when a current of milliamp (mA) flows
The forward voltage (V _f : ＠ 20 mA) was about 2.1 volts (V), reflecting the good ohmic characteristics exhibited by the distributed ohmic electrodes 307.

Example 2 In Example 2, an LED in which a p-type semiconductor layer was arranged in the direction of extracting light was manufactured. FIG. 6 is a schematic cross-sectional view of an LED 50 according to the second embodiment.

The LED 50 of the second embodiment is made of silicon (S
i) A semiconductor layer 50 is formed on a GaAs single crystal substrate 501 having a surface that is 2 ° off from the n-type (001) direction by doping.
b, the Si-doped n-type GaAs buffer layer 502
Both are n-type Al _0.40 Ga _0.60 As doped with Si.
Layer (DBR) layer 5 having a periodic structure in which 10 layers and n-type Al _0.95 Ga _0.05 As layers are alternately laminated in layers of 10 layers.
03, Si-doped n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
A lower cladding layer 504 of undoped n-type (A
a light-emitting layer 505 made of l _0.2 Ga _0.8 ) _0.5 In _0.5 P, and a magnesium (Mg) -doped p-type (Al _0.7 Ga _0.3 )
_It has a structure in which an upper cladding layer 506 made of _0.5 In _0.5 P is laminated. The light emitting portion of the LED 50 includes a lower cladding layer 504, a light emitting layer 505, and an upper cladding layer 506 made of AlGaInP.

Each layer 502-5 constituting the semiconductor layer 50b
06 is trimethylaluminum ((CH ₃ ) ₃ Al),
A film was formed by a reduced-pressure MOCVD method using trimethylgallium ((CH ₃ ) ₃ Ga) and trimethyl indium ((CH ₃ ) ₃ In) as a raw material of a group III constituent element. As a doping material of magnesium (Mg) which is a p-type impurity, biscyclopentadienyl magnesium (bis- (C ₅
H _{5) 2} Mg) was used. Disilane (Si ₂ H ₆ ) was used as a doping material for Si, which is an n-type impurity. The formation temperature of each of the layers 502 to 506 of the semiconductor layer 50b is 730
° C. The carrier concentration of the buffer layer 502 is about 3 × 1
0 ¹⁸ cm ^-3 and a layer thickness of about 0.5 μm. DB
N-type Al _0.40 Ga _0.60 As layer forming R layer 503 and n-type A
The layer thickness of each l _0.95 Ga _0.05 As layer was about 40 nm. The carrier concentration was about 2 × 10 ¹⁸ cm ⁻³ . The carrier concentration of the lower cladding layer 504 is about 3 × 1
0 ¹⁸ cm ^-3 and a layer thickness of about 400 nm. The thickness of the light emitting layer 505 is about 10 nm, and the carrier concentration is about 1 nm.
× 10 ¹⁷ cm ^-3 . The carrier concentration of the upper cladding layer 506 is about 4 × 10 ¹⁷ cm ^−3, and the thickness of the layer is about 3 μm.
m.

After the layers 502 to 506 of the semiconductor layer 50b were formed on the GaAs single crystal substrate 501 by MOCVD, electrodes were formed on the front and back surfaces of the wafer.
First, gold / zinc (A) having a thickness of about 40 nm is formed on the entire surface of the upper cladding layer 506 by a general vacuum deposition method.
u · Zn) alloy thin film was deposited. Next, with the Au—Zn alloy thin film left on the surface of the p-type upper cladding layer 506, the film was heated at 480 ° C. for 2 hours in a stream of hydrogen (H ₂ ).
An alloying heat treatment was performed for 5 minutes. As a result, the Au / Zn film, which exhibited continuity at the time of vapor deposition, became a granular ohmic electrode 507 exhibiting granular and ohmic contact properties by condensation. The average value of the diameter (particle size) of the granular ohmic electrode 507 measured by a normal optical microscope is about 10
μm, and the maximum width was 20 μm or less.

Next, with the granular ohmic electrode 507 remaining on the p-type upper cladding layer 506, the p-type upper cladding layer 506 and the granular ohmic electrode 507 are covered by a general magnetron sputtering method to form a transparent conductive film. As 509, an indium tin oxide (ITO) film is used.
Deposited at 50 ° C. The specific resistance of this ITO film is about 3 × 1
0 ⁻⁴ Ω · cm, and the layer thickness was about 590 nm. According to a general X-ray diffraction analysis method, it was shown that the ITO film was a polycrystalline film preferentially oriented in the <001> direction (C axis).

Next, a general organic photoresist material is applied to the entire surface of the transparent conductive film 509, and then the pedestal electrode 51 is applied.
A region where 0 was to be provided was patterned using a known photolithography technique. Thereafter, an aluminum (Al) film was deposited on the entire surface by an electron beam vacuum evaporation method while leaving the patterned resist material. The thickness of the Al film was about 800 nm. Thereafter, as the resist material is removed, a well-known lift-off (l
If-off) means, the Al film was left only in the area where the pedestal electrode 510 was to be formed. Thus, A having a diameter of about 120 μm and a plane area of 1.1 × 10 ⁻⁴ cm ² is used.
A circular pedestal electrode 510 made of an l film was formed.

Subsequently, after forming a first electrode 511 having an ohmic contact made of a gold-germanium (Au.Ge) alloy on the back surface of the n-type GaAs single crystal substrate 501, the wafer is cut by a normal scribing method. It was subdivided individually to make LED50. LED50 is 260μ on one side
m, and the area of the open light-emitting region 508 is 5.7 × 10 ⁻⁴ , because the square area is 6.8 × 10 ⁻⁴ cm ^2.
cm ² . Further, the number of the granular ohmic electrodes 507 scattered on the surface of the open light emitting region 508 is 220, and the total plane area of the granular ohmic electrodes 507 is about 1.
It was 7 × 10 ⁻⁴ cm ² . Therefore, the open light emitting area 50
The ratio occupied by the total plane area (= 1.7 × 10 ⁻⁴ cm ² ) of the granular ohmic electrode 507 with respect to the surface area of No. 8, ie, the so-called coverage was about 30%.

When a current was passed in the forward direction between the n-type first electrode 511 and the pedestal electrode 519 of the LED 50, red-orange light having a wavelength of about 620 nm was emitted through the open light emitting region 508. The half width of the emission spectrum measured by the spectroscope was about 20 nm, and light emission having excellent monochromaticity was obtained. Also, due to the effect of arranging the ohmic electrodes 507 in a dispersed manner, light emission is also recognized in the peripheral area of the LED 50, and is simply measured in a state where visibility is corrected using an integrating sphere. The light emission intensity of the LED when the current was passed was about 55 millicandela (mcd). It has been shown that the LED 50 of this embodiment is an LED that emits light with uniform intensity by the effect of the uniform distribution of the operating current by the granular ohmic electrode 507 in the open light emitting region 508. The forward voltage (V _f : 20 mA) of the LED 50 when a current of 20 mA (mA) is passed reflects the good ohmic characteristics of the dispersed ohmic electrodes 507 of about 2. 1 volt (V).

[0045]

According to the present invention, L supplied from the pedestal electrode
An ED drive current can be passed through the transparent conductive film made of a conductive oxide layer to the light emitting portion from each of the granular ohmic electrodes scattered on the semiconductor layer, and the ohmic electrode is formed on the surface of the semiconductor layer. Since it is made up of granular electrodes having a maximum width of 20 μm or less in a planar shape arranged evenly, the LED driving current can be evenly diffused in the open light emitting region, and the uniformity of the light emitting intensity and the high brightness of AlGa
An InPLED is obtained.

According to the present invention, a granular ohmic electrode can be produced by utilizing the condensation (ball-up) of an electrode metal material during heat treatment for ohmic alloying.
A desired ohmic electrode can be efficiently produced with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of a conventional AlGaInPLED.

FIG. 2 is a schematic plan view of an AlGaInPLED according to the present invention.

FIG. 3 is a schematic sectional view of the AlGaInPLED shown in FIG.

FIG. 4 shows an AlGaInPLE according to the first embodiment of the present invention.
It is a plane schematic diagram of D.

FIG. 5 is a schematic cross-sectional view of the AlGaInPLED shown in FIG.

FIG. 6 shows an AlGaInPLE according to a second embodiment of the present invention.
It is a plane schematic diagram of D.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 AlGaInPLED 10a Light emission part 10b III-V group compound semiconductor layer 101 GaAs single crystal substrate 102 Buffer layer 103 Bragg reflection layer 104 Lower cladding layer 105 Light emission layer 106 Upper cladding layer 107 Window layer 108 Pedestal electrode 109 First electrode 110 Metal film Reference Signs List 20 AlGaInPLED 20a Light emitting portion 20b Semiconductor layer 201 GaAs single crystal substrate 202 Buffer layer 203 Bragg reflective layer 204 Lower clad layer 205 Light emitting layer 206 Upper clad layer 207 Transparent conductive film 208 Pedestal electrode 209 First electrode 210 Ohmic electrode 211 Open light emitting region 30, 50 AlGaInPLED 30b, 50b Semiconductor layer 301, 501 GaAs single crystal substrate 302, 502 Buffer layer 303, 503 Bragg reflection layer 304, 504 Head layer 305,505 emitting layer 306,506 upper clad layer 307,507 ohmic electrodes 308,508 open-emitting region 309,509 transparent conductive film 310, 510 pad electrode 311, 511 first electrode

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takashi Udagawa 1505 Shimokagemori, Chichibu-shi, Saitama F-term (reference) 5F041 AA04 AA05 CA34 CA65 CA82 CA91

Claims (9)

[Claims] 1. A semiconductor substrate having a first electrode formed on a back surface, a semiconductor layer including a light emitting portion made of AlGaInP formed on the semiconductor substrate, and a semiconductor layer formed on a part of the surface of the semiconductor layer. A plurality of ohmic electrodes forming an ohmic contact with the semiconductor layer; a transparent conductive film formed to cover the semiconductor layer and the ohmic electrode and electrically connected to the ohmic electrode; and a part formed on a part of the surface of the transparent conductive film. An AlGaInP light-emitting diode having the transparent conductive film and a pedestal electrode which conducts, wherein all of the plurality of ohmic electrodes are formed of granular electrodes having a maximum width of 20 μm or less in a planar shape. 2. The AlGaInP light emission according to claim 1, wherein said ohmic electrodes are scattered and arranged in a portion (open light emission region) which does not overlap with the pedestal electrode when viewed in plan of the surface of the semiconductor layer. diode. 3. A method according to claim 1, wherein the ratio of the total surface area of the ohmic electrodes in the open light emitting region to the surface area of the open light emitting region (surface coverage) is 3 to 70%. 2. The AlGaInP light-emitting diode according to item 1. 4. The ohmic electrode according to claim 1, wherein said ohmic electrode has a multilayer structure in which the side in contact with the semiconductor layer is made of an alloy containing gold (Au) and the side in contact with the transparent conductive film is Au. An AlGaInP light emitting diode as described. 5. The semiconductor device according to claim 1, wherein said semiconductor layer is in contact with said ohmic electrode.
The AlGaInP according to claim 4, wherein the ohmic electrode is made of an alloy of Au and germanium (Ge) on the side in contact with the semiconductor layer.
P light emitting diode. 6. The semiconductor layer in contact with the ohmic electrode is p-type.
5. The AlGaInP light-emitting diode according to claim 4, wherein the ohmic electrode is made of an alloy containing Au and zinc (Zn) or an alloy containing Au and beryllium (Be). . 7. The transparent conductive film is made of indium tin oxide (I
7. An AlGaInP light-emitting diode according to claim 1, comprising TO). 8. The transparent conductive film has a resistivity of 7 × 10 ⁻⁴ Ω.
The AlGaInP light-emitting diode according to claim 1, wherein the AlGaInP light-emitting diode is made of a metal oxide having a band gap of 2.5 cm or less and a band gap of 2.5 eV or more. 9. The AlGaInP according to claim 1, wherein
A method for manufacturing a light-emitting diode, comprising: depositing a metal thin film on the surface of the semiconductor layer; and condensing the metal thin film by heat treatment to form a plurality of granular ohmic electrodes.