KR100638822B1 - Nitride semiconductor light emitting device - Google Patents

Abstract

A nitride semiconductor LED is provided to remarkably improve light extraction efficiency by high reflection effect by introducing a light-penetrating conductive oxide layer and a dielectric reflection layer into a p-side contact structure wherein a plurality of contact holes are arrange din the dielectric reflection layer. A nitride semiconductor light emitting structure includes p-type and n-type nitride semiconductor layers(35,33) and an active layer(34) formed between the p-type and the n-type nitride semiconductor layers. An ohmic contact layer(36a) is formed on the p-type nitride semiconductor layer. A light-penetrating conductive oxide layer(36b) is formed on the ohmic contact layer. Two kinds of dielectric layers having different indexes of refraction are alternately and repeatedly formed on the light-penetrating conductive oxide layer. A dielectric reflection layer(37) has a plurality of contact holes to partially expose the light-penetrating conductive oxide layer. A bonding metal(39) is formed on the dielectric reflection layer, bonded to the light-penetrating conductive oxide layer through the plurality of contact holes. The ohmic contact layer is made of In2O3 including at least one kind selected from a group composed of Cu, Zn and Mg.

Description

Nitride Semiconductor Light Emitting Device {NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE}

1A and 1B are cross-sectional views showing a conventional flip chip type light emitting device, respectively.

2A and 2B show flip-chip type nitride semiconductor light emitting devices according to one embodiment of the present invention, respectively.

FIG. 3 illustrates a form in which the flip chip nitride semiconductor light emitting device of FIG. 2A is die-bonded on a submount substrate.

4A and 4B are graphs showing the reflectance by layer number and the reflectance by wavelength band, respectively, for explaining the reflection effect of the dielectric reflection layer employed in the present invention.

5 is a cross-sectional view showing a vertical nitride semiconductor light emitting device according to another embodiment of the present invention.

<Code Description of Main Parts of Drawing>

31: Sapphire substrate 71: GaN substrate

32,72: buffer layer 33,73: n-type nitride semiconductor layer

34,74: active layer 35,75: p-type nitride semiconductor layer

36a, 76a: ohmic contact layer 36b, 76b: light transmissive conductive oxide layer

37, 77: dielectric reflective layer 38, 78: n-side bonding metal

39,79: p-side bonding metal

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device, and more particularly, to a nitride semiconductor light emitting device in which a reflective metal that adversely affects the reliability of a device is replaced with a dielectric material having a high reflectance.

In general, the nitride semiconductor constituting the nitride semiconductor light emitting device, in particular, the p-type nitride semiconductor layer generally has a wide band gap, which makes it difficult to form ohmic contact with the electrode. Furthermore, in the case of a flip chip type or a specific type of vertical light emitting device, the ohmic contact structure itself requires additional high reflectance for improving luminance.

Japanese Laid-Open Publication No. 2000-183400 (published date: June 6, 2000, Applicant: Toyoda Gosei Co. LTD.) Is a thin film layer 16a, such as nickel (Ni) or cobalt (Co), as shown in FIG. A method of introducing a reflective metal layer 16b such as silver (Ag) is proposed.

As shown in FIG. 1A, the nitride light emitting device 10 has a structure in which a buffer layer 12, an n-type nitride layer 13, an active layer 14, and a p-type nitride layer 15 are sequentially stacked on a sapphire substrate 11. Has On the p-type nitride layer 15, a thin film layer 16a such as Ni or Co is formed for ohmic contact, and a metal layer 16b having high reflectivity is further deposited.

The nitride light emitting device 10 is mounted on the submount substrate 21 on which the conductive pads 22a and 22b are provided by solder bumps 24a and 24b to provide the flip chip nitride light emitting device 20 as shown in FIG. 1B. Can be. The flip chip nitride light emitting device 20 may increase the light efficiency extracted to the sapphire substrate 11 by the reflective metal layer 16b.

However, since Ni or Co does not have a high transmittance even when formed as a thin film 16a as a metal, its light loss is large, and thus there is a problem that the luminance improvement effect by the reflective metal layer 16b is not high.

In addition, Ag, which is mainly used as the reflective metal layer 16b, affects defects caused by GaN potential due to migration, and therefore, there is a fatal problem that leakage current occurs.

Accordingly, there is a need in the art for a new reflective ohmic contact structure capable of forming a stable ohmic contact structure with a nitride semiconductor light emitting device while high reflecting effect can be expected in place of the reflective metal layer having an adverse effect.

The present invention is to solve the above problems of the prior art, the purpose is to adopt a dielectric reflective layer composed of a plurality of contact holes with a light-transmitting conductive oxide layer to maximize the reflection effect high brightness nitride that can have a high luminous luminance The present invention provides a semiconductor light emitting device.

In order to achieve the above technical problem, the present invention,

a nitride semiconductor light emitting structure having a p-type and n-type nitride semiconductor layer and an active layer formed therebetween, an ohmic contact layer formed on the p-type nitride semiconductor layer, a light-transmitting conductive oxide layer formed on the ohmic contact layer, and A dielectric reflection layer having a plurality of dielectric films having different refractive indices formed on the light-transmitting conductive oxide layer in alternating times, and having a plurality of contact holes to partially expose the light-transmitting conductive oxide layer, and the dielectric reflecting layer A nitride semiconductor light emitting device including a bonding metal formed on and connected to the light transmissive conductive oxide layer through the plurality of contact holes is provided.

As the ohmic contact layer, various ohmic contact layers may be used. As a preferred ohmic contact layer, In ₂ O ₃ containing at least one selected from the group consisting of copper (Cu), zinc (Zn) and magnesium (Mg) may be used as a material having high light transmittance, and more preferably. Preferably, In ₂ O ₃ containing copper may be used.

In contrast, the ohmic contact layer is an alloy selected from the group consisting of MnNi, LaNi ₅ , ZnNi, MgNi, and ZnMg, but rhodium (Rh), ruthenium (Ru), platinum (Pt), palladium (Pd), and iridium (Ir) It may include a metal or alloy selected from the group consisting of nickel (Ni), cobalt (Co) and alloys thereof.

The preferred transparent conductive oxide layer may include at least one selected from the group consisting of indium tin oxide (ITO) and ZnO, and more preferably, the transparent conductive oxide layer may be ITO. The light transmissive conductive oxide layer preferably has a thickness of about 0.1 μm to 1 μm in consideration of an appropriate current dispersion effect and light transmittance.

The dielectric reflective layer may be formed of an oxide or nitride including an element selected from the group consisting of Si, Zr, Ta, Ti, In, Sn, Mg, and Al, respectively. The two dielectric films constituting the dielectric reflective layer each have a thickness of about 300 kPa to about 900 kPa. The two different dielectric films each have a thickness corresponding to an integer multiple of λ / 4n, where λ is the light emission wavelength of the active layer and n is the refractive index of the dielectric film.

The contact holes of the dielectric reflective layer are preferably arranged at regular intervals over the entire area in consideration of the uniform dispersion effect. The contact holes of the dielectric reflective layer preferably have a cross-sectional area of 0.8 to 50 µm ² , respectively. In order to obtain an adequate reflecting area while ensuring a sufficient current providing area, the cross-sectional area of the entire contact hole is preferably 10 to 30% of the total area of the upper surface of the dielectric reflecting layer.

Hereinafter, with reference to the accompanying drawings will be described the present invention in more detail.

FIG. 2A illustrates a flip chip type nitride semiconductor light emitting device according to an embodiment of the present invention, and FIG. 2B is a top plan view of the nitride semiconductor light emitting device of FIG. 2A when the p-side bonding metal is removed.

As shown in FIG. 2A, the nitride semiconductor light emitting device 30 according to the present embodiment has a buffer layer 32, an n-type nitride layer 33, an active layer 34, and a p-type nitride layer 35 on the sapphire substrate 31. This has a structure stacked sequentially.

On the p-type nitride layer 35, an ohmic contact layer 36a and a transparent conductive oxide layer 36b are formed in this order. The ohmic contact layer 36a may be formed of a suitable metal and alloy to lower the contact resistance with the p-type nitride layer 35. For example, the ohmic contact layer 36a may be an alloy selected from the group consisting of MnNi, LaNi ₅ , ZnNi, MgNi, and ZnMg, or rhodium (Rh), ruthenium (Ru), platinum (Pt), palladium (Pd), It may be formed of a metal or alloy selected from the group consisting of iridium (Ir), nickel (Ni), cobalt (Co) and alloys thereof. However, since the metal or alloy is difficult to ensure high light transmittance, it is required to form a thickness of 5 ~ 100Å.

The ohmic contact layer 36a material which may be more preferably employed in the present invention is an indium oxide (In ₂ O) containing at least one selected from the group consisting of copper (Cu), zinc (Zn), and magnesium (Mg). ₃ ). The indium oxide not only acts as an excellent conductive material for forming ohmic contact with the p-type nitride layer by containing copper, zinc or magnesium, and also ensures high light transmittance, thereby ensuring excellent light efficiency. The indium oxide based ohmic contact layer 36a having light transmissivity may be formed to a relatively large thickness, and may preferably have a thickness of about 5 to 500 kPa.

A light transmissive conductive oxide layer 36b is formed on the ohmic contact layer 36a. The light transmissive conductive oxide layer 36b may be formed of at least one selected from the group consisting of indium tin oxide (ITO) and ZnO. The light-transmitting conductive oxide layer 36b employed in the present invention not only has excellent light transmittance, but also has a low conductivity compared to metal, and thus a current dispersion effect can be expected.

A dielectric reflective layer 37 is formed on the light transmissive conductive oxide layer 36b. The dielectric reflective layer may be formed by alternately forming two kinds of dielectric films 37a and 37b having different refractive indices. The two dielectric films 37a and 37b constituting the dielectric reflecting layer 37 each have an integer multiple of λ / 4n when λ is an emission wavelength of the active layer 34 and n is a refractive index of the dielectric film. It is preferable to have a thickness corresponding to

As described above, the dielectric reflective layer 37 employed in the present invention can obtain a high reflectance of 90%, preferably 95% or more through the sprayed Bragg reflection (DBR) principle. This will be described in more detail with reference to FIGS. 4A and 4B.

In addition, the dielectric reflective layer 37 has a plurality of contact holes h such that the light-transmitting conductive oxide layer 36b is partially exposed. In general, since the dielectric material has electrical insulation, a separate path for connecting the p-side bonding metal 39 and the transparent conductive oxide layer 36b should be provided. The present invention proposes a method of arranging a plurality of contact holes h as the connection paths. As shown, an additional current dispersion effect can be expected through the arrangement of the plurality of contact holes (h).

Further, in order to further improve the current dispersion effect side, the plurality of contact holes h formed in the dielectric reflective layer 37 are preferably arranged at regular intervals over the entire area as shown in FIG. 2B. It is preferable that the diameter of the spherical contact hole h like this embodiment is at least 1 micrometer. The cross-sectional shape of the contact hole of the dielectric reflective layer may be employed in various ways. In this case, it is preferable that the cross-sectional area of the individual contact hole has a cross-sectional area of 0.8 to 50 μm ² for electrical connection and proper arrangement of the plurality of holes. Further, in consideration of the trade-off between sufficient electrical connection area and reflection area, the cross-sectional area of the entire contact hole h is preferably 10 to 30% of the total area of the upper surface of the dielectric reflective layer 37.

P-side and n-side bonding metals 39 and 38 are formed on the upper surface of the dielectric reflective layer 37 and the n-type nitride layer 35, respectively. The p-side bonding metal 39 may be connected to the light-transmitting conductive oxide layer 36b through the contact hole h of the dielectric reflective layer 37. Therefore, unlike the conventional bonding metal structure, the p-side bonding metal 39 of the present invention is not limited to the wire bonding region but is formed widely over the area where the contact hole h is formed.

FIG. 3 shows a form in which the nitride semiconductor light emitting device 30 of FIG. 2A is flip chip bonded onto the submount substrate 41.

As shown in FIG. 3, the flip chip light emitting device 40 includes a submount substrate 41 provided with conductive pads 42a and 42b. The nitride light emitting device 30 may be mounted on the submount substrate 4 by connecting the bonding metals 38 and 39 and the conductive pads 42a and 42b through the solder bumps 44a and 44b, respectively. In the flip chip light emitting device 40 having such a mounting structure, the sapphire substrate 31 side is provided with a main light exit surface.

As indicated by " R ", the light generated from the active layer 35 reaches the dielectric reflective layer 37 through the ohmic contact structures 36a and 36b having excellent light transmittance, which is then again desired by the dielectric reflective layer 37. It may be emitted in the light exit direction. At this time, the light reaching the dielectric reflective layer 37 has a very small loss through the light transmissive conductive oxide layer 36b such as ITO and the ohmic contact layer 36a such as indium oxide. Excellent improvement can be made.

4A and 4B are graphs showing the reflectance for each layer and the reflectance for each wavelength band of the dielectric reflecting layer employing Al ₂ O ₃ and Si ₃ N ₄ as two different dielectric films, respectively.

Referring to FIG. 4A, the reflectance of the Al ₂ O ₃ / Si ₃ N ₄ dielectric reflector layer with respect to 460 nm wavelength light is shown. The thickness of each dielectric film was formed under the condition that λ is the light emission wavelength of the active layer and n is the refractive index of the dielectric film, each having a thickness corresponding to an integer multiple of λ / 4n. That is, the thickness of the Al ₂ O ₃ film (n = 1.6) is about 72 nm, and the thickness of the Si ₃ N ₄ film (n = 2.05 to 2.25) is about 49 nm, and the growth is repeated alternately from one to five times. I was. The low reflectance of 40% in one case was found to have a high reflectance of 90% in four or more times and 95% in five repeated growths.

FIG. 4B is a result of measuring reflectance for each wavelength band of the dielectric reflective layer repeatedly grown five times in FIG. 4A. It was shown to have a high reflectance of 95% at 460 nm. This is the result of setting the thickness of each dielectric film in consideration of the wavelength of 460 nm.

Two different kinds of dielectric films constituting the dielectric reflective layer may be designed to have high reflectivity at an appropriate thickness, provided they have different refractive indices. 4A and 4B, an oxide reflective layer having a high reflectivity may be formed by selecting an oxide or nitride including an element selected from the group consisting of Si, Zr, Ta, Ti, In, Sn, Mg, and Al. .

As shown in FIG. 5, the present invention can be advantageously applied to the vertical nitride semiconductor light emitting device 70.

The vertical nitride semiconductor light emitting device 70 shown in Fig. 5 has a buffer layer 72, an n-type nitride layer 73, an active layer 74 and a p-type nitride layer 75 on a GaN substrate 71 which is a conductive substrate. This has a structure stacked sequentially. Here, the conductive substrate is not limited to the GaN substrate 75, and other hetero substrates may be satisfied as long as the transparent substrate has conductivity. The p-side and n-side bonding metals 78 and 79 are formed at predetermined positions so as to be connected on the opposing p-type nitride layer 75 and the n-type GaN substrate 71.

Since the vertical light emitting device 70 is also provided with a main light exit surface on the substrate 71 side like a conventional flip chip light emitting device, the electrode structure provided in the p-type nitride layer will have a high reflectance along with the ohmic contact. Required.

To this end, an ohmic contact layer 76a and a transparent conductive oxide layer 76b are sequentially formed on the p-type nitride layer 75 similarly to FIG. 2A. A dielectric reflective layer 77 is formed on the light transmissive conductive oxide layer 76b. The dielectric reflective layer 77 forms a DBR structure having a high reflectivity in which two dielectric layers 77a and 77b having different refractive indices are alternately grown, and a plurality of contact holes h are formed thereon. A connection path between the p-side bonding metal 79 and the transparent conductive oxide layer 76b to be provided is provided.

As described above, the vertical nitride light emitting device improves light extraction efficiency by using the dielectric reflecting layer 77 having a high reflectance, and at the same time, due to the plurality of contact holes h arranged over the dielectric reflecting layer 77, It is possible to provide uniform current flow over the entire area. In particular, when the ohmic contact layer 76a is formed of indium oxide such as copper-indium oxide, high transmittance is ensured, and thus a high brightness and high efficiency light emitting device can be provided.

As such, the invention is not to be limited by the foregoing embodiments and the accompanying drawings, which are intended to be limited by the appended claims. Accordingly, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

As described above, according to the present invention, by introducing a dielectric reflective layer in which a plurality of contact holes are arranged together with a light-transmitting conductive oxide layer in the p-side contact structure, the light extraction efficiency can be greatly improved through high reflection effect. By the arrangement of the contact holes of the dielectric reflecting layer, the current dispersing effect is further improved, and the luminous efficiency of the device can be greatly improved.

Claims (12)

a nitride semiconductor light emitting structure having a p-type and n-type nitride semiconductor layer and an active layer formed therebetween; An ohmic contact layer formed on the p-type nitride semiconductor layer; A transparent conductive oxide layer formed on the ohmic contact layer; Two dielectric layers having different refractive indices formed on the light-permeable conductive oxide layer alternately a plurality of times, and a dielectric reflecting layer having a plurality of contact holes to partially expose the light-permeable conductive oxide layer; And And a bonding metal formed on the dielectric reflective layer and connected to the light transmissive conductive oxide layer through the plurality of contact holes. The method of claim 1, The ohmic contact layer is nitride semiconductor light emitting device, characterized in that made of In ₂ O ₃ including at least one selected from the group consisting of copper (Cu), zinc (Zn) and magnesium (Mg). The method of claim 1, The ohmic contact layer is nitride semiconductor light emitting device, characterized in that made of an alloy selected from the group consisting of MnNi, LaNi ₅ , ZnNi, MgNi and ZnMg. The method of claim 1, The ohmic contact layer is a metal selected from the group consisting of rhodium (Rh), ruthenium (Ru), platinum (Pt), palladium (Pd), iridium (Ir), nickel (Ni), cobalt (Co) and alloys thereof. A nitride semiconductor light emitting device comprising an alloy. The method of claim 1, The light-transmitting conductive oxide layer is at least one selected from the group consisting of indium tin oxide (ITO) and ZnO. The method of claim 5, The light-transmitting conductive oxide layer has a thickness of 0.1 ~ 1㎛ nitride semiconductor light emitting device. The method of claim 1, The dielectric reflective layer is nitride semiconductor light emitting device, characterized in that consisting of an oxide or nitride containing an element selected from the group consisting of Si, Zr, Ta, Ti, In, Sn, Mg and Al, respectively. The method of claim 7, wherein The two kinds of dielectric films constituting the dielectric reflective layer each have a thickness of 300 mW to 900 mW. The method of claim 8, The two dielectric films constituting the dielectric reflective layer each have a thickness corresponding to an integer multiple of λ / 4n, wherein λ is a light emission wavelength of the active layer, and n is a refractive index of the dielectric film. The method of claim 1, The contact hole of the dielectric reflective layer is nitride semiconductor light emitting device, characterized in that arranged at regular intervals over the entire area. The method of claim 1, The contact hole of the dielectric reflective layer has a cross-sectional area of 0.8 to 50㎛ ² each nitride semiconductor light emitting device. The method of claim 1, The cross-sectional area of the entire contact hole is a nitride semiconductor light emitting device, characterized in that 10 to 30% of the total area of the upper surface of the dielectric reflective layer.

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