JP2005235797A - Semiconductor light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a reliable structure that prevents rapid deterioration because of a short lifetime, and can be manufactured with improved reproducibility having a low forward voltage even if an intermediate band gap layer is not formed in a semiconductor light-emitting device in a structure having a metal oxide window layer (transparent conductive layer). <P>SOLUTION: Mg is used for an additive with a second-conductivity-type cladding layer 5 and a second-conductivity-type contact layer 6 as a second-conductivity type, and Ga<SB>X</SB>In<SB>1-X</SB>P (0≤X≤0.72) is used as the material of the second-conductivity-type contact layer 6 in a semiconductor light-emitting device, having a first-conductivity-type semiconductor substrate 1, an emission section in which an active layer 4 is formed between the first-conductivity-type cladding layer 3 and the second-conductivity-type cladding layer 5, the second-conductivity-type contact layer 6 formed on the emission section, a metal oxide window layer 7 laminated on the second-conductivity-type contact layer, a first electrode 8 formed at one portion of the surface side of the metal oxide window layer, and a second electrode 9 formed entirely or partially on the rear of the substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a structure of a semiconductor light emitting device having a high brightness, high reliability, and low cost provided with a metal oxide window layer.

  Conventionally, LEDs (Light Emitting Diodes) are mostly GaP green and AlGaAs red. However, since it has recently become possible to grow GaN-based and AlGaInP-based crystal layers by the MOVPE method, it has become possible to manufacture orange, yellow, green, and blue high-intensity LEDs.

  An epitaxial wafer formed by the MOVPE (Metal Organic Vapor Phase Epitaxy) method has made it possible to produce an LED capable of emitting light having a short wavelength and high brightness, which has not been possible before. However, in order to obtain high luminance, it is necessary to increase the film thickness of the window layer (current distribution layer) in order to improve current distribution, which increases the manufacturing cost of the epitaxial wafer for LED, and the semiconductor light emitting device. It was difficult to make the

  In order to reduce the cost, it is only necessary to reduce the thickness of the window layer and improve the current dispersion. That is, the resistivity of the window layer itself may be further reduced. In order to obtain an epitaxial layer with low resistance, the mobility is greatly changed. Alternatively, there is a method of increasing the carrier concentration.

  Therefore, as a method for solving these problems, a technique using a material that can obtain a resistance value as low as possible for the window layer has become common.

  For example, in the case of an AlGaInP quaternary LED, GaP or AlGaAs is used as the window layer. However, even if these low-resistivity materials are used, it is difficult to grow a p-type and high carrier concentration epitaxial layer. Therefore, in order to improve the current dispersion effect, the thickness of the window layer is increased to 8 μm or more. It needs to be thick.

  If there are other semiconductors having such characteristics, they can be substituted. However, there are no semiconductors that satisfy such characteristics.

  For example, in the case of a GaN-based LED, as another method, a metal thin film is used as the translucent conductive film. However, it is necessary to make the metal thin film very thin in order to transmit light, and it is necessary to make it thick to obtain sufficient current dispersion. For this reason, if it is going to obtain a favorable current dispersion characteristic, the transmittance | permeability will worsen. That is, the current dispersion and the light transmittance are in a trade-off relationship. Furthermore, the metal thin film is generally formed by a vacuum deposition method, and the evacuation time is long.

  Here, an ITO (Indium Tin Oxide) film, which is a metal oxide conductive film, attracts attention as a film having sufficient translucency and electrical characteristics that can obtain current dispersion. If this ITO film can be used as a current dispersion film, the semiconductor layer has been thickened for the current dispersion film so far, but the epitaxial layer is no longer required, so that a high-brightness LED can be produced inexpensively.

  In the manufacture of this LED, a metal electrode is usually formed on an ITO film (transparent conductive film) as a window layer, but between the uppermost semiconductor layer of the epitaxial wafer and the transparent conductive film that is a metal oxide. There is a problem that contact resistance is generated and the forward operation voltage becomes high.

  On the other hand, a method is also disclosed in which the LED is driven by a tunnel current by increasing the carrier concentration of the semiconductor contact layer (see, for example, Non-Patent Document 1).

Furthermore, a GaAs layer is used as a semiconductor contact layer, Zn and C are used as additives, a contact resistance between the semiconductor layer and the metal oxide transparent conductive film is reduced, and a forward operating voltage is lowered. In this method, in order to alleviate the band discontinuity between the GaAs contact layer and the clad layer, a method of inserting an intermediate band gap layer between the GaAs contact layer and the clad layer is disclosed (for example, see Patent Document 1). ). In Patent Document 1, a GaAs layer containing C as an additive is used as the uppermost semiconductor layer, and carbon tetrabromide (CBr ₄ ) is used as a raw material for the C additive. A method of making a luminescent LED is described.
ELECTRONICS LETTERS, 7Th December 1995 (see pages 2210-2212) JP-A-11-307810

  However, when GaAs is used as the semiconductor contact layer and Zn is used as the additive, the lifetime of the semiconductor light emitting device is short and rapidly deteriorates. In other words, there is a problem that the reliability deteriorates.

On the other hand, in the method using GaAs as the semiconductor contact layer, carbon tetrabromide (CBr ₄ ) as the source of the C additive, and C as the additive, the semiconductor light emission with high luminance, low operating voltage, and high reliability is achieved. The device has been successfully manufactured. However, when carbon tetrabromide (CBr ₄ ) is used as a raw material for the C additive, sufficient characteristics can be achieved in the first growth, but the light emission output becomes extremely low after the second growth. . That is, there was a problem in reproducibility.

  In addition, when C is used as an additive, the forward operation voltage is slightly higher than when Zn is used. For this reason, an intermediate band gap layer must be provided between the GaAs contact layer and the cladding layer as in Patent Document 1, and the cost is increased by the amount of the intermediate band gap layer. Further, when a GaAs contact layer is used, there is a problem that defects such as peeling of the metal oxide transparent conductive film and reverse voltage frequently occur at the time of chip cutting, resulting in poor yield.

  Therefore, an object of the present invention is to prevent a semiconductor light emitting device having a structure having a metal oxide window layer (transparent conductive film) from having a short life and rapidly degrading, that is, having high reliability, and Semiconductor light emission that has a low forward operating voltage and can be manufactured with good reproducibility without providing an intermediate bandgap layer, thereby achieving high brightness, high reliability, low cost, and good reproducibility It is to provide an element.

  In order to achieve the above object, the present invention is configured as follows.

The semiconductor light emitting device according to claim 1 is a first conductive type semiconductor substrate, a light emitting portion in which an active layer is provided between the first conductive type cladding layer and the second conductive type cladding layer, and the light emitting device. A second conductivity type contact layer formed on the part, a metal oxide window layer laminated on the second conductivity type contact layer, and a second conductivity type contact layer formed on a part of the surface side of the metal oxide window layer. In a semiconductor light emitting device comprising one electrode and a second electrode formed on the entire back surface of the substrate or partially, the second conductivity type cladding layer and the second conductivity type contact layer are of a second conductivity type. Mg is used as an additive, and Ga _x In _1-X P (0 ≦ X ≦ 0.72) is used as a material of the second conductivity type contact layer.

According to a second aspect of the present invention, in the semiconductor light-emitting device according to the first aspect, the second conductive type cladding layer and the second conductive type Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer A current dispersion layer is provided between them.

According to a third aspect of the present invention, there is provided the semiconductor light emitting device according to the first aspect, wherein the second conductive type cladding layer and the second conductive type Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer are provided. And a current spreading layer is provided, and an undoped layer is provided in a part of the current spreading layer.

According to a fourth aspect of the present invention, there is provided the semiconductor light-emitting device according to the first aspect, wherein the second conductive type cladding layer and the second conductive type Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer are provided. A current spreading layer is provided, an undoped layer is provided in a part of the current spreading layer, and an undoped layer is provided between the second conductivity type cladding layer and the active layer. To do.

According to a fifth aspect of the present invention, in the semiconductor light emitting device according to the second to fourth aspects, the material of the current dispersion layer is GaP or Al _x Ga ₁ -x As (0.8 ≦ X), (Al _x Ga ₁ -x). ) _Y In _1-Y P (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1).

According to a sixth aspect of the present invention, in the semiconductor light emitting device according to the third or fourth aspect, the material of a part of the undoped layer of the current spreading layer is GaP or Al _x Ga ₁ -x As (0.8 ≦ X), ( characterized in that it is a _{al X Ga 1-X) Y} in 1-Y P (0 ≦ X ≦ 1,0 ≦ Y ≦ 1).

According to a seventh aspect of the invention, in the semiconductor light emitting device according to claim 4, wherein the material of the undoped layer between the second-conductivity-type cladding layer and the active _{layer, (Al X Ga 1-X} ) Y In 1-Y P (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1).

According to an eighth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to seventh aspects, the carrier concentration of the second conductivity type Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer is It is characterized by being 1 × 10 ¹⁹ cm ⁻³ or more.

  The invention of claim 9 is the semiconductor light emitting device according to any one of claims 1 to 8, wherein the metal oxide window layer is made of indium tin oxide, and the method of forming the metal oxide window layer is a vacuum deposition method. It is characterized by being.

A tenth aspect of the present invention is the semiconductor light-emitting device according to any one of the first to ninth aspects, wherein the second conductivity type Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer has a film thickness. It is characterized by being 200 nm or less.

According to an eleventh aspect of the present invention, in the semiconductor light emitting device according to any one of the first to tenth aspects, a first conductivity type cladding layer, an undoped or second conductivity type active layer, and a second conductivity type cladding layer are mainly formed. wherein the material is the _{(Al X Ga 1-X)} Y in 1-Y P (0 ≦ X ≦ 1,0 ≦ Y ≦ 1).

According to a twelfth aspect of the present invention, in the semiconductor light emitting device according to any one of the first to eleventh aspects, a specific resistance of the metal oxide window layer is 1 × 10 ⁻⁵ Ωm or less.

  A thirteenth aspect of the present invention is the semiconductor light emitting device according to the first to twelfth aspects, wherein the metal oxide window layer has a thickness of 50 nm or more.

<Key points of the invention>
In order to achieve the above-mentioned object, the present inventors have intensively studied to solve the above-mentioned problems, and as a result, have reached the present invention.

  That is, the gist of the present invention is that the second conductivity type additive of the semiconductor light emitting device is easily diffused, the conventional second conductivity type additive Zn, and the conventional second conductivity type additive that is likely to remain in the growth furnace. Diffusion of the second conductivity type additive into the active layer by using Mg as the second conductivity type additive, which is difficult to diffuse and less influence on the next growth (hard to remain). Has been found that the second conductivity type additive does not adversely affect the subsequent growth, and this reduces the light emission output due to the diffusion of the second conductivity type additive (Zn). In addition, it has been found that it is possible to prevent deterioration of characteristics, that is, deterioration of reliability, and manufacture with good reproducibility.

In addition, another important point of the present invention is that Mg does not easily enter when the second conductivity type additive is made of Mg by using the conventional GaAs contact layer. Therefore, between the GaAs contact layer and the metal oxide window layer. A sufficient tunnel current could not be generated. However, if the present inventors use Ga _X In _1-X P (0 ≦ X ≦ 0.72), which is a direct transition type P-type semiconductor, as the semiconductor contact layer, a sufficient tunnel current can be obtained. It was found to generate. That is, it has been found that a sufficient tunneling current can be generated by setting the semiconductor contact layer to Ga _X In _1-X P (0 ≦ X ≦ 0.72) to which Mg is added.

Furthermore, the present inventor uses Mg as the second conductivity type additive and direct transition type Ga _X In _1-X P (0 ≦ X ≦ 0.72) as the semiconductor contact layer material. It was found that the band discontinuity between the layer and the second conductivity type cladding layer can be alleviated. That is, it has been found that the forward operating voltage does not increase even if there is no intermediate band gap layer between the semiconductor contact layer and the second conductivity type cladding layer. In addition, the present inventors have improved the adhesion because both the semiconductor contact layer and the metal oxide window layer contain In, which is the same element, and the metal oxide window layer is peeled off during the cutting process. It was found that the number of defects such as these decreased drastically. That is, it has been found that by making the semiconductor contact layer Ga _X In _1-X P (0 ≦ X ≦ 0.72), defects during cutting can be reduced and manufacturing can be performed with high yield.

In short, according to the present invention, the additive of the second conductivity type is Mg, and a direct transition type Ga _X In _1-X P (0 ≦ X ≦ 0) is provided between the metal oxide window layer and the second conductivity type cladding layer. .72) By adopting a structure in which the layer is formed as a contact layer, it is possible to provide a semiconductor light emitting device with extremely low cost, high luminance, high reliability, and low operating voltage. In addition, a semiconductor light emitting device with extremely low cost, high luminance, high reliability, and low operating voltage can be manufactured with good yield and good reproducibility.

  According to the present invention, since Mg is used as an additive for the second conductivity type cladding layer and the second conductivity type contact layer, it is less likely to diffuse than when Zn or C is used, and remains in the growth furnace. Because it is difficult to do, there is little influence on the next growth. Accordingly, it is possible to prevent a decrease in light emission output and deterioration in characteristics (decrease in reliability) due to diffusion of the second conductivity type additive, and to manufacture a semiconductor light emitting device with high reproducibility.

Further, according to the present invention, between the second clad layer and the metal oxide window layer, the semiconductor contact layer made of Ga _X In _1-X P of the second conductivity type (0 ≦ X ≦ 0.72) provided Therefore, Mg can easily enter, and a sufficient tunnel current can be generated.

  Therefore, according to the present invention, an LED with extremely low manufacturing cost, high luminance, high reliability, and low forward operation voltage can be stably manufactured with high yield and reproducibility. As a result, the thickness of the epitaxial layer for LEDs can be reduced from one fifth to several tenths. This is because the thickness of the window layer (current dispersion layer) is the thickest among the epitaxial layers constituting the LED. Moreover, the price of the epitaxial wafer for LED was able to be reduced significantly by this.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

In the present embodiment, a light emitting part is formed on the first conductivity type substrate 1 by sandwiching the active layer 4 between the first cladding layer 3 and the second cladding layer 5 having different conductivity types, and the second cladding layer 5 In a semiconductor light emitting device in which a window layer 7 made of metal oxide is formed, a surface electrode 8 is formed on a part of the surface side, and a back electrode 9 made of the entire surface or a partial electrode is formed on the back surface of the substrate. Between the second cladding layer 5 and the metal oxide window layer 7, a semiconductor contact layer 6 made of Ga _x In _1-X P (0 ≦ X ≦ 0.72) of the second conductivity type is provided, and the first A structure using Mg as an additive for the two-conductivity-type cladding layer 5 and the second-conductivity-type contact layer 6 is adopted.

<Embodiment 1>
As a prototype example according to the first embodiment of the present invention, a red light emitting diode epitaxial wafer having a structure as shown in FIG.

An n-type (Se-doped) GaAs buffer layer (film thickness 400 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 2, n-type (Se-doped) is formed on the n-type GaAs substrate 1, which is the first conductivity type substrate, by MOVPE. ) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P first clad layer (first conductivity type clad layer) (film thickness 300 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 3, undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer (film thickness 600 nm) 4, p-type (Mg doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second clad layer (second conductivity type clad layer) (film thickness 300 nm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) 5, p-type (Mg-doped) Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer (second conductivity type contact layer) (film thickness 5 nm, carrier concentration 3 × 10 ¹⁹ cm ⁻³ ) 6 were grown by the MOVPE method.

As Examples 1 to 3, the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 at this time is composed of a Ga _0.72 In _0.28 P layer 6a, a Ga _0.50 In _0.50 P layer 6b, and an InP layer. Three types of 6c were produced. In FIG. 1, these are collectively referred to as a contact layer 6.

  The MOVPE growth was performed at a growth temperature of 650 ° C., a growth pressure of 50 Torr, a growth rate of each layer of 0.3 to 1.0 nm / s, and a V / III ratio of 200 to 600.

Examples of raw materials used in MOVPE growth include organic metals such as trimethylgallium (TMG) or triethylgallium (TEG), trimethylaluminum (TMA), and trimethylindium (TMI), arsine (AsH ₃ ), phosphine (PH ₃ ), and the like. The hydride gas was used.

Hydrogen selenide (H ₂ Se) was used as an additive material for an n-type layer such as the n-type GaAs buffer layer 2. Further, biscyclopentadienylmagnesium (Cp ₂ Mg) was used as an additive material for the p-type layer such as the p _- type Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer 6. In addition, silane (SiH ₄ ), diethyl tellurium (DETe), and dimethyl tellurium (DMTe) can also be used as the n-type layer additive raw material.

An ITO film 7 to be a metal oxide window layer was formed on this epitaxial wafer by about 280 nm by vacuum deposition. The film formation temperature (substrate surface temperature) at this time is 300 ° C. The specific resistance of the ITO film 7 at this time was 6.2 × 10 ⁻⁶ Ωm.

  A first electrode (surface electrode) 8 made of a circular electrode having a diameter of 120 μm was formed on the upper surface of the epitaxial wafer by vapor deposition in a matrix form. The first electrode 8 was formed by depositing nickel and gold in the order of 20 nm and 1000 nm, respectively. Further, a second electrode (back electrode) 9 was formed on the entire bottom surface of the epitaxial wafer. The second electrode 9 was formed by depositing gold, germanium, nickel, and gold in the order of 60 nm, 10 nm, and 500 nm, respectively, and then alloying the electrodes was performed at 400 ° C. for 5 minutes in a nitrogen gas atmosphere.

  Thereafter, the LED epitaxial wafer with an electrode configured as described above was cut so that the circular first electrode 8 was at the center, and a light emitting diode bare chip having a chip size of 300 μm square was produced. Furthermore, this light emitting diode bare chip was mounted on a TO-18 stem (die bonding), and then wire bonding was performed on the further mounted light emitting diode bare chip to produce an LED element.

LED elements of Examples 1 to 3 above, that is, LED elements using Mg as the second conductivity type additive and using the Mg-doped Ga _x In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 The LED characteristics (light emission output at 20 mA energization and forward operating voltage) were examined. The light emission output at 20 mA energization was 2.65 mW with the Ga _0.72 In _0.28 P contact layer 6a (LED of Example 1). Ga _0.50 In _0.50 P contact layer 6b (LED of Example 2) was 2.56 mW, and InP contact layer 6c (LED of Example 3) was 2.50 mW. Moreover, the forward voltage at the time of energizing 20 mA was 1.95V, 1.93V, and 1.90V, respectively. Moreover, when the reliability test of the test condition: 25 ° C. and 50 mA energization was performed, the relative output after the 168 hr energization test (relative output: luminescence output after the 168 hr energization test / initial emission output) was 97%, 99%, It was 98%. Incidentally, the current value at the time of reliability evaluation is 20 mA.

  Further, since the In contained in the ITO film 7 is also contained in the contact layer 6, the adhesion between the ITO film 7 and the contact layer 6 is improved, and the peeling of the ITO film 7 during the cutting operation is reduced. . For this reason, the reverse voltage defect by the leakage current which flows into LED side surface decreased. That is, the failure due to the peeling of the ITO film 7 and the reverse voltage failure could be reduced to 1% or less in total.

<Embodiment 2>
As a prototype example according to the second embodiment of the present invention, a red light-emitting diode epitaxial wafer having a structure as shown in FIG.

An n-type (Se-doped) GaAs buffer layer (film thickness 400 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 2, n-type (Se-doped) (Al _0.7 Ga _0.3 ) is formed on the n-type GaAs substrate 1 by MOVPE. _0.5 In _0.5 P clad layer (film thickness 300 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 3, undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer (film thickness 600 nm) 4, p-type (Mg doped) ( Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer (film thickness 300 nm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) 5, p-type (Mg doped) GaP current dispersion layer (film thickness 500 nm, carrier concentration 5 × 10 ¹⁸ cm ⁻³ ) 10a, p-type (Mg-doped) Ga _0.50 In _0.50 P contact layer (film thickness 5 nm, carrier concentration 3 × 10 ¹⁹ cm ⁻³ ) 6b was grown by MOVPE (Example 4). Also, an epitaxial wafer (Examples 5 and 6) in which the p-type GaP current spreading layer 10a is replaced with a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer 10b and a p-type Al _0.5 Ga _0.5 As layer 10c, Produced simultaneously. In FIG. 2, these are collectively referred to as a current spreading layer 10.

The epitaxial growth method, the method for forming the ITO film 7, the film thickness, the electrode forming method, and the LED element manufacturing method are basically the same as those in the first embodiment. The specific resistance of the ITO film 7 at this time was 6.3 × 10 ⁻⁶ Ωm.

  The LED characteristics of the LED element (light emitting diode) manufactured in this way were evaluated.

Each LED element using an Mg-doped Ga _0.5 In _0.5 P contact layer 6b and further provided with a p-type GaP current dispersion layer 10a, a p-type AlGaInP layer 10b, and a p-type AlGaAs layer 10c in the p-type current dispersion layer 10 (implementation) The emission characteristics of Examples 4 to 6) were as shown in Table 1. The light emission characteristics and reliability evaluation are the same as those in Examples 1-3.

＜実施形態３＞
本発明の第三の実施形態にかかる試作例として、図３のような構造の発光波長６３０nm付近の赤色発光ダイオード用エピタキシャルウェハを作製した。

<Embodiment 3>
As a prototype example according to the third embodiment of the present invention, a red light emitting diode epitaxial wafer having a structure as shown in FIG.

An n-type (Se-doped) GaAs buffer layer (film thickness 400 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 2, n-type (Se-doped) (Al _0.7 Ga _0.3 ) is formed on the n-type GaAs substrate 1 by MOVPE. _0.5 In _0.5 P clad layer (film thickness 300 nm, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) 3, undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer (film thickness 600 nm) 4, p-type (Mg doped) ( Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer (film thickness 300 nm, carrier concentration 5 × 10 ¹⁷ cm ⁻³ ) 5, p-type (Mg doped) GaP current dispersion layer (film thickness 150 nm, carrier concentration 5 × 10 ¹⁸ cm) ^-3 ) 10a, undoped GaP layer (thickness 200 nm) 11a as a resistance layer, p-type (Mg doped) GaP current dispersion layer (thickness 150 nm, carrier concentration 5 × 10 ¹⁸ cm ^-3 ) 10a, p-type (Mg doped) Ga _0.50 In _0.50 P Ntakuto layer (thickness 5 nm, carrier concentration ^{3 × 10 19 cm -3) 6b} , grown in MOVPE method (Example 7). The p-type GaP current spreading layer 10a is replaced with a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer 10b and a p-type Al _0.85 GaAs layer 10c, and an undoped GaP layer (thickness: 200 nm) as a resistance layer. Epitaxial wafers (Examples 8 and 9) in which 11a was replaced with an undoped Al _0.85 Ga _0.15 As layer 11b were also produced at the same time.

The epitaxial growth method, the method for forming the ITO film 7, the film thickness, the electrode forming method, and the LED element manufacturing method are basically the same as those in the first embodiment. The specific resistance of the ITO film 7 at this time was 6.1 × 10 ⁻⁶ Ωm.

  The LED characteristics of the LED elements thus produced (Examples 7 to 9) were evaluated.

The light emitting characteristics of the LED elements (Examples 7 to 9) using the Mg-doped Ga _0.50 In _0.50 P contact layer 6b as described above and further provided with the p-type current spreading layer 10 and the undoped layer 11 are as shown in Table 2. there were. The light emission characteristics and reliability evaluation are the same as in Example 1.

以上のように、第二導電型の添加物をＭｇにしてＩＴＯ膜７とｐ型クラッド層５、若しくはＬＥＤ膜７と電流分散層１０の間にＭｇを添加したｐ型Ｇａ_XＩｎ_1-XＰ（０≦Ｘ≦０．７２）コンタクト層６を設けた構造とすることにより、低動作電圧であり、且つ良好な発光出力を併せ持つＬＥＤを製作することができた。またアンドープ層１１（抵抗層）を挿入することで、駆動電圧の変動に対しても、強いＬＥＤを製作することができた。更にコンタクト層６をＩｎを含む材料としたことで、該ＩＴＯ膜７の剥がれ不良を少なくし、且つ逆方向電圧不良も少なくすることが出来、歩留りを向上することができた。

As described above, p-type Ga _x In _{1-x in} which Mg is added between the ITO film 7 and the p-type cladding layer 5 or the LED film 7 and the current spreading layer 10 with the second conductivity type additive being Mg. By adopting a structure in which the P (0 ≦ X ≦ 0.72) contact layer 6 is provided, an LED having a low operating voltage and a good light output can be manufactured. Moreover, by inserting the undoped layer 11 (resistive layer), it was possible to manufacture an LED that is strong against fluctuations in the driving voltage. Further, since the contact layer 6 is made of a material containing In, the peeling failure of the ITO film 7 can be reduced and the reverse voltage failure can be reduced, and the yield can be improved.

<Comparative example>
As a comparative example, an epitaxial wafer for a red light emitting diode having a structure as shown in FIG.

The epitaxial growth method, the epitaxial layer thickness, the epitaxial layer structure, the ITO film 7 deposition method, the film thickness, the electrode formation method, and the LED element fabrication method are basically the same as in the first embodiment, and only the contact layer is p-type ( A Zn-doped) GaAs contact layer (film thickness 5 nm) 12a or a p-type (C-doped) GaAs contact layer (film thickness 50 nm) 12b was grown by the MOVPE method. The carrier concentration of the GaAs layer contact layer 12 is 1 × 10 ¹⁹ cm ⁻³ .

  The LED characteristics of the LED elements thus manufactured (Comparative Examples 1 and 2) were evaluated.

  The light emission output of the LED element using the Zn-doped GaAs contact layer 12a according to Comparative Example 1 was 2.4 mW when energized with 20 mA. The forward operating voltage was 1.94V. Further, the relative output of the LED element after energization for 168 hours was 41%. (Current value at the time of output evaluation is 20 mA). The reason why the relative output is low and the characteristics are deteriorated, that is, the reliability is lowered, is that Zn in the Zn-doped GaAs contact layer 12a diffuses into the active layer to create defects, and non-radiative recombination increases.

The light emission output of the LED element using the C-doped GaAs contact layer 12b (C additive raw material = CBr ₄ ) according to Comparative Example 2 was 2.35 mW when energized with 20 mA. The forward operating voltage was 2.21V. Furthermore, the relative output of the LED element after energization for 168 hours was 98% (current value at the time of output evaluation was 20 mA). For this reason, almost good LED was obtained.

However, the problem is that the forward operating voltage is high (2 V or more). When an LED element using the C-doped GaAs contact layer 12b (C additive raw material: CBr ₄ ) was manufactured again and evaluated, the light emission output was 1.2 mW when energized with 20 mA. The forward operating voltage was 2.18V. Thereafter, no matter how many times the LED element (not molded with resin) was manufactured, the light emission output was about 0.7 to 1.4 mW, and an LED element having good light emission characteristics could not be manufactured. The reason why the light emission output did not increase was investigated by SIMS analysis. As a result, it was found that a large amount of C (carbon) and O (oxygen) was mixed in the epitaxial layer including the light emitting layer. That is, it has been found that by using CBr ₄ as the additive material for C, a large amount of C and O remain in the growth furnace after growth. For this reason, it was confirmed that the cause of the low light emission output of the LED element manufactured in the second and subsequent growths was due to CBr ₄ .

<Reason for optimal conditions>
If the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 has a low carrier concentration, it becomes difficult for a tunnel current to flow, and forward operation due to band discontinuity with the p-type cladding layer 5. Since the voltage rises, the carrier concentration of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is preferably 1 × 10 ¹⁹ cm ⁻³ or more. Further, the carrier concentration of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is preferably as high as possible.

The Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 may have a band gap smaller than the band gap of the active layer 4 in some cases. For this reason, when a composition having a band gap smaller than the band gap of the active layer 4 is used, it becomes an absorption layer for the emitted light, and the light emission output as the LED is lowered. Therefore, when the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 has a composition having a band gap smaller than the band gap of the active layer 4, the thinner one is desirable. However, if the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is made too thin, tunnel current will not flow. For this reason, there is an optimum value for the film thickness of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6. Therefore, the film thickness of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is preferably about 1 to 200 nm, and more preferably 2 to 30 nm.

  When the specific resistance of the metal oxide window layer (ITO film 7) is high, the tunnel current does not flow or does not flow easily. For this reason, a forward operation voltage becomes high. In addition, the current dispersion effect is reduced and the light emission output is lowered. Therefore, the specific resistance of the metal oxide window layer (ITO film 7) is preferably as low as possible.

The specific resistance of the metal oxide window layer (ITO film 7) is preferably 1 × 10 ⁻⁵ Ωm, more preferably 7 × 10 ⁻⁶ Ωm or less.

  If the thickness of the metal oxide window layer (ITO film 7) is thin, the current dispersion effect is reduced and the light emission output is lowered. Therefore, the thickness of the metal oxide window layer (ITO film 7) is preferably as thick as possible. The film thickness of the metal oxide window layer 7 is preferably 50 nm or more, more preferably 200 nm or more.

When the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is grown at a high temperature, the crystallinity is improved. When the crystallinity is good, the tunnel current hardly flows even at the same carrier concentration. For this reason, a forward operation voltage becomes high. In addition, the forward operating voltage is likely to increase due to band discontinuity with the p-type cladding layer 5, and the forward operating voltage is increased. Therefore, the crystallinity of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 should be not so good. Therefore, it is preferable that the growth temperature of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is lower. That is, the growth temperature of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is preferably low. A more preferable growth temperature of the Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer 6 is 450 to 650 ° C.

<Other Embodiments and Modifications>
In the above embodiment, Mg having a small diffusion is used as the second conductivity type additive, but there is a slight diffusion. For this reason, it is good also as a structure which provides a diffusion suppression layer between the said active layer 4 and the said p-type clad layer 5, and this may be used together with this invention. The diffusion suppression layer may be an undoped layer, a low concentration first conductivity type (carrier concentration: 1 × 10 ¹⁷ cm ⁻³ or less), or a low concentration second conductivity type (carrier concentration: 1 × 10 ¹⁷ cm ⁻³ or less). good. However, if the diffusion suppression layer is too thick, the series resistance increases and the forward voltage increases. In addition, the manufacturing cost increases. Therefore, when providing a diffusion suppression layer, 1500 nm or less is desirable.

  It can be easily analogized that the same effect can be obtained even in an LED having an emission wavelength of 560 to 650 nm manufactured using an AlGaInP-based material.

  The same effect can be obtained by using a multiple quantum well for the active layer. The same effect can be obtained with a structure in which a DBR layer as a light reflecting layer is inserted between the buffer layer 2 and the n-type cladding layer 3. Further, the structure in which the buffer layer 2 is removed has the same effect.

  In the above embodiment example, the shape of the surface electrode and the metal layer is circular, but it can be easily inferred that the same effect can be obtained even if the shape is different, for example, square, rhombus, polygon.

1 is a cross-sectional structure diagram of an AlGaInP-based red LED epitaxial wafer according to a first embodiment of the present invention. It is a cross-section figure of the epitaxial wafer for AlGaInP type | system | group red LED concerning 2nd embodiment of this invention. It is a cross-section figure of the epitaxial wafer for AlGaInP type | system | group red LED concerning 3rd embodiment of this invention. It is a cross-section figure of the epitaxial wafer for AlGaInP type red LEDs concerning a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Buffer layer 3 First clad layer 4 Active layer 5 Second clad layer 6 Contact layer 7 ITO film (metal oxide window layer)
8 First electrode (surface electrode)
9 Second electrode (back electrode)
10 Current distribution layer 11 Undoped layer (resistance layer)

Claims (13)

A first conductivity type semiconductor substrate;
A light emitting part in which an active layer is provided between the first conductivity type cladding layer and the second conductivity type cladding layer;
A second conductivity type contact layer formed on the light emitting portion;
A metal oxide window layer laminated on the second conductivity type contact layer;
A first electrode formed on a part of the surface side of the metal oxide window layer;
In a semiconductor light emitting device comprising a second electrode formed entirely or partially on the back surface of the substrate,
Mg is used as an additive for making the second conductivity type cladding layer and the second conductivity type contact layer a second conductivity type,
2. A semiconductor light emitting device using Ga _x In _1-X P (0 ≦ X ≦ 0.72) as a material of the second conductivity type contact layer. The semiconductor light-emitting device according to claim 1.
Between the second-conductivity-type cladding layer and the second conductivity type _{Ga X In 1-X P (} 0 ≦ X ≦ 0.72) contact layer, a semiconductor light-emitting, characterized in that the current spreading layer is provided element. The semiconductor light-emitting device according to claim 1.
A current spreading layer is provided between the second conductivity type cladding layer and the second conductivity type Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer, and part of the current spreading layer A semiconductor light-emitting element, comprising an undoped layer. The semiconductor light-emitting device according to claim 1.
A current spreading layer is provided between the second conductivity type cladding layer and the second conductivity type Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer, and part of the current spreading layer An undoped layer is provided, and an undoped layer is provided between the second conductivity type cladding layer and the active layer. The semiconductor light emitting device according to claim 2,
The material of the current spreading layer is GaP or Al _x Ga _1-X As (0.8 ≦ X), (Al _x Ga _1-x ) _Y In _1-Y P (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1) A semiconductor light-emitting element. The semiconductor light emitting device according to claim 3 or 4,
Materials Some of the undoped layers of the current spreading layer, GaP or _{Al X Ga 1-X As (} 0.8 ≦ X), (Al X Ga 1-X) Y In 1-Y P (0 ≦ X ≦ 1 , 0 ≦ Y ≦ 1). The semiconductor light-emitting device according to claim 4.
Material of an undoped layer between the second-conductivity-type cladding layer and the active layer, that is _{(Al X Ga 1-X)} Y In 1-Y P (0 ≦ X ≦ 1,0 ≦ Y ≦ 1) A semiconductor light emitting device characterized. In the semiconductor light emitting device according to any one of claims 1 to 7,
A semiconductor light-emitting element, wherein the second conductivity type Ga _X In _1-X P (0 ≦ X ≦ 0.72) contact layer has a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ or more. In the semiconductor light-emitting device according to any one of claims 1 to 8,
A semiconductor light emitting element, wherein the metal oxide window layer is made of indium tin oxide, and the method of forming the metal oxide window layer is a vacuum deposition method. In the semiconductor light-emitting device according to claim 1,
The semiconductor light-emitting device, wherein the thickness of said second conductivity type _{Ga X In 1-X P (} 0 ≦ X ≦ 0.72) contact layer is 200nm or less. In the semiconductor light emitting device according to any one of claims 1 to 10,
First-conductivity-type cladding layer, an undoped or second conductive type active layer, a main material for forming the second-conductivity-type cladding layer is _{(Al X Ga 1-X)} Y In 1-Y P (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1). A semiconductor light-emitting element, wherein The semiconductor light-emitting device according to claim 1,
A specific resistance of the metal oxide window layer is 1 × 10 ⁻⁵ Ωm or less. The semiconductor light emitting device according to claim 1,
A semiconductor light emitting element, wherein the metal oxide window layer has a thickness of 50 nm or more.

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