KR100631970B1 - Nitride semiconductor light emitting device for flip chip - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device for flip chip, and more particularly, forming a bonding pad of an n-side electrode in the center of an n-type nitride semiconductor layer, and forming an electrode finger extending from the bonding pad, thereby improving current spreading. And a nitride semiconductor light emitting device for flip chip which can prevent a current crowding phenomenon. The present invention, n-type nitride semiconductor layer formed on a light-transmissive substrate; An n-side electrode comprising a bonding pad formed at a substantially center portion on the n-type nitride semiconductor layer and at least one first electrode finger extending from the bonding pad; An active layer and a p-type nitride semiconductor layer sequentially stacked on a region where the n-side electrode is not formed on the n-type nitride semiconductor layer; And it provides a nitride semiconductor light emitting device for flip chip comprising a highly reflective ohmic contact layer formed on the p-type nitride semiconductor layer.

Nitride semiconductor light emitting device, highly reflective ohmic contact layer, electrode, bonding pad, electrode paper

Description

Nitride semiconductor light emitting device for flip chip {FLIP CHIP TYPE NITRIDE SEMICONDUCTOR LIGHT EMITTING DEVICE}

1A is a cross-sectional view showing a light emitting device having a flip chip structure in which a conventional nitride semiconductor light emitting device is mounted, and (b) is a plan view of a conventional nitride semiconductor light emitting device.

2A is a plan view of a nitride semiconductor light emitting device according to an embodiment of the present invention, and (b) is a side cross-sectional view of the nitride semiconductor light emitting device according to an embodiment of the present invention.

3 is a plan view of a nitride semiconductor light emitting device according to another embodiment of the present invention.

4A and 4B are graphs comparing the driving voltage characteristics and the luminance characteristics of the conventional nitride semiconductor light emitting device and the nitride semiconductor light emitting device according to the exemplary embodiment of the present invention shown in FIG. 3, respectively.

* Description of the symbols for the main parts of the drawings *

31 transparent substrate 32 n-type nitride semiconductor layer

33: active layer 34: p-type nitride semiconductor layer

35: highly reflective ohmic contact layer 36a: bonding pad of n-side electrode

36b: first electrode finger 36c: second electrode finger

37: p-side bonding pad 39: passivation layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device for flip chip, and more particularly, forming a bonding pad of an n-side electrode in the center of an n-type nitride semiconductor layer, and forming an electrode finger extending from the bonding pad, thereby improving current spreading. And a nitride semiconductor light emitting device for flip chip which can prevent a current crowding phenomenon.

In general, nitride semiconductors are group III-V semiconductor crystals such as GaN, InN, AlN, and the like, and are widely used in light emitting devices capable of emitting short wavelength light (ultraviolet to green light), especially blue light.

Since the nitride semiconductor light emitting device is manufactured using an insulating substrate such as a sapphire substrate or a SiC substrate that satisfies the lattice matching condition for crystal growth, two electrodes connected to the p-type and n-type nitride semiconductor layers are almost on the top surface of the light emitting structure. The planar structure is arranged horizontally. Due to these structural features, nitride semiconductor light emitting devices are being actively developed as light emitting devices having a flip chip structure.

An example of a flip chip light emitting device equipped with a conventional nitride semiconductor light emitting device light emitting device is shown in FIG. The conventional nitride semiconductor light emitting device 10 employed in the flip chip light emitting device 20 shown in FIG. 1A has a small size having a cross-sectional area of 400 μm × 400 μm or less driven at a low current of 20 mA or less. Have

In the conventional nitride semiconductor light emitting device 10, the n-type nitride semiconductor layer 12, the active layer 13, the p-type nitride semiconductor layer 14, and the ohmic contact layer 15 are sequentially formed on the sapphire substrate 11. The n-side electrode 16 is formed in a region where a portion of the upper surface of the n-type nitride semiconductor layer 13 is exposed, and the p-side electrode 17 is formed on the upper surface of the ohmic contact layer 15.

In the flip chip light emitting device 20 equipped with such a conventional nitride semiconductor light emitting device 10, the nitride semiconductor light emitting device 10 conducts conductive bumps to the electrodes 16 and 17 on the substrate 21 for the support. It has a structure mounted by fusing it on each lead pattern 22a, 22b via 24a, 24b. In the flip chip structure 20, the sapphire substrate 11 of the light emitting device 10 may be used as a light emitting surface because it is transparent. While the ohmic contact layer 15 forms an ohmic contact with the p-type nitride semiconductor layer 14, the ohmic contact layer 15 reflects the light emitted from the active layer 13 toward the light emitting surface (ie, the sapphire substrate 11). It is required to have a high reflectance that can be.

Meanwhile, referring to the plan view of the conventional nitride semiconductor light emitting device shown in FIG. 1B, the conventional nitride semiconductor light emitting device has a generally rectangular shape, and the n-side electrode 16 is formed near the corners of the rectangular shape. do. In the electrode structure of the conventional nitride semiconductor light emitting device, the current is not uniformly diffused as the distance from the n-side electrode 16 increases, and a current crowding phenomenon occurs in which current is concentrated in the vicinity of the n-side electrode. .

That is, referring to FIG. 1A, the conventional nitride semiconductor light emitting device 10 has a planar electrode structure. In particular, since the p-side ohmic contact layer 15 has a lower specific resistance than the p-type nitride semiconductor layer 14, As indicated by the arrow, current crowding occurs where a significant portion of the current is concentrated along the ohmic contact layer 15 in the adjacent portion A of the n-side electrode.

This current crowding not only increases the forward voltage, but also reduces the luminance characteristics by relatively reducing the luminous efficiency of the active layer portion spaced from the n-side electrode. In addition, the amount of heat generated in the portion A where the current is concentrated increases the reliability of the device significantly.

As described above, in the conventional nitride semiconductor light emitting device, since the n-side electrode 16 is positioned near one corner of the nitride semiconductor light emitting device, a vertical structure light emitting device in which two electrodes are disposed on the upper and lower surfaces of the light emitting structure, respectively. In contrast, since the current flow is not uniformly distributed in the entire light emitting area, the effective area participating in the light emission is not large, and the light emitting efficiency per light emitting area is low. In the planar structure semiconductor light emitting device, since the current flow between the two electrodes is concentrated in the shortest path, the current path in which the current density is concentrated becomes narrower than the butter structure structure light emitting device in which the current flow is provided in the vertical direction. Since the current flows in the horizontal direction, a problem arises in that the driving voltage is increased due to the large series resistance.

In particular, due to such a problem, it is considered to be a very difficult problem to ensure high power in a light emitting device for a lighting device having a large size (for example, 600 μm × 600 μm).

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and an object thereof is to reduce driving voltage and heat generation by improving current spreading and preventing occurrence of current crowding in a large nitride semiconductor light emitting device. The present invention provides a nitride semiconductor light emitting device for flip chip having a novel electrode structure capable of improving the light emitting efficiency.

The present invention as a technical configuration for achieving the above object,

An n-type nitride semiconductor layer formed on the light transmissive substrate;

An n-side electrode comprising a bonding pad formed at a substantially center portion on the n-type nitride semiconductor layer and at least one first electrode finger extending from the bonding pad;

An active layer and a p-type nitride semiconductor layer sequentially stacked on a region where the n-side electrode is not formed on the n-type nitride semiconductor layer; And

It provides a nitride semiconductor light emitting device for a flip chip comprising a highly reflective ohmic contact layer formed on the p-type nitride semiconductor layer.

In one embodiment of the present invention, the upper surface of the n-type nitride semiconductor layer may have a substantially rectangular shape, in this case, the first electrode finger is preferably extended from the bonding pad in the corner direction of the n-type nitride semiconductor layer. Do.

In another embodiment of the present invention, it is preferable that the flip chip nitride semiconductor light emitting device further includes at least one second electrode finger extending from the first electrode finger.

Preferably, a passivation layer may be further formed between the n-side electrode and the p-type nitride semiconductor layer for electrical isolation of the n-side electrode and the p-type nitride semiconductor layer.

Preferably, the reflective layer may be formed of at least one layer made of a material selected from the group consisting of Ag, Ni, Al, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and combinations thereof.

More preferably, the reflective layer comprises a first layer made of a material selected from the group consisting of Ni, Pd, Ir, Pt and Zn, and a material made of a material selected from the group consisting of Ag and Al formed on the first layer. It may have a structure including two layers.

Most preferably, the reflective layer has a structure including a first layer made of Ni, a second layer made of Ag formed on the first layer, and a third layer made of Pt formed on the second layer. Can be.

The term " nitride semiconductor light emitting device for flip chip " used in the present invention means a nitride semiconductor light emitting device that is employed in a light emitting device having a flip chip structure, and a surface having a p-side bonding pad and an n-side electrode formed thereon It means the light emitting element which becomes a mounting surface joined to a submount.

Hereinafter, a nitride semiconductor light emitting device for flip chip according to various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the drawings referred to in the description of the present invention, components having substantially the same configuration and function will use the same reference numerals.

2A and 2B are a plan view and a cross-sectional view of a nitride semiconductor light emitting device for flip chip according to an embodiment of the present invention. As shown in FIGS. 2A and 2B, the nitride semiconductor light emitting device 30 for a flip chip according to the exemplary embodiment of the present invention has an n-type nitride semiconductor layer 32 formed on the light transmissive substrate 31. ); An n-side electrode made of a bonding pad 36a formed almost at the center of the n-type nitride semiconductor layer 32 and at least one first electrode finger 36b extending from the bonding pad 36a; An active layer 33 and a p-type nitride semiconductor layer 34 sequentially stacked on a region where the n-side electrode is not formed on the n-type nitride semiconductor layer 32; And a highly reflective ohmic contact layer 35 formed on the p-type nitride semiconductor layer 34.

Since the transparent substrate 31 has the same crystal structure as that of the nitride semiconductor material grown thereon and there is no commercial substrate that forms a lattice match, a sapphire substrate is mainly used in consideration of lattice match. The sapphire substrate is a Hexa-Rhombo R3c symmetric crystal with a lattice constant of 13.001Å in the c-axis direction and 4.765Å in the a-axis direction, and has a lattice distance in the sapphire orientation Is characterized by having a C (0001) plane, an A (11 2 0) plane, an R (1 1 02) plane, and the like. In the case of the C surface of the sapphire substrate, the growth of the GaN thin film is relatively easy and stable at high temperature, and thus, the sapphire substrate is mainly used as a substrate for a blue or green light emitting device.

The n-type nitride semiconductor layer 32 is n-doped with Al _x In _y Ga _(1-xy) N composition formula, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1. It can be made of a semiconductor material, a typical nitride semiconductor material is GaN, AlGaN, GaInN. As an impurity used for the doping of the n-type nitride semiconductor layer 32, Si, Ge, Se, Te, or C may be used. The n-type nitride semiconductor layer 32 may be formed of a metal organic chemical vapor deposition (MOCVD) method, a molecular beam growth method (MBE), or a hybrid vapor deposition method (Hybride Vapor Phase Epitaxy). It is formed by growing on the translucent substrate 31 using a known deposition process such as HVPE).

In general, a buffer layer may be formed between the light transmissive substrate 31 and the n-type nitride semiconductor layer 32 to mitigate lattice mismatch. As the buffer layer, a low temperature nucleus growth layer such as GaN or AlN having a thickness of several tens nm can be usually used.

The n-side electrode includes a bonding pad 36a formed at an almost center portion of an upper surface of the n-type nitride semiconductor layer 32 and at least one electrode finger 36b extending from the bonding pad 36a. The bonding pads 36a may be connected to the lead patterns on the sub-mounts using conductive bumps during flip chip bonding to receive current from the outside. In the present invention, the bonding pads 36a of the n-side electrode are formed in the center of the n-type nitride semiconductor layer 32 in order to improve the current diffusion of the nitride semiconductor light emitting device for flip chip. As such, by arranging the bonding pads 36a of the n-side electrode at the center of the nitride semiconductor light emitting device, the distance between the n-side electrode and the highly reflective ohmic contact layer 35 can be reduced. That is, in the conventional nitride semiconductor light emitting device, the bonding pad of the n-side electrode is formed on one side of the light emitting device so that the current generated due to the long distance between the n-side electrode and the highly reflective ohmic contact layer 35 is not uniformly spread. You can solve the problem.

In addition, the n-side electrode of the present invention includes the first electrode finger 36b extending from the bonding pad 36a formed at the center of the n-type nitride semiconductor layer 32, whereby the n-side electrode and the highly reflective ohmic contact layer are provided. The distance between the 35 can be further reduced.

The longer the length of the first electrode finger 36b may reduce the area of the active layer 33 that generates light, but by further reducing the distance to the highly reflective ohmic contact layer 35 to improve current spreading. The forward voltage (driving voltage) can be lowered and the amount of heat generated can be reduced. Therefore, as shown in FIG. 2A, when the upper surface of the n-type nitride semiconductor layer 32 has a substantially rectangular shape, the first electrode finger 32b is removed from the bonding pad 32a. It is suitable for extending the edge direction of the n-type nitride semiconductor layer 32 to ensure sufficient length of the first electrode finger 32a.

In addition, in FIG. 2A, the first electrode fingers 32b are illustrated as four extending to each corner. However, the number of the first electrode fingers 32b may be appropriately adjusted according to the application of the flip chip nitride semiconductor according to the present invention. It does not limit the present invention as it exists.

The active layer 33 and the p-type nitride semiconductor layer 34 are sequentially formed in the upper region of the n-type nitride semiconductor layer 32 where the n-side electrode is not formed.

The active layer 33 is a layer for emitting light and is composed of a nitride semiconductor layer such as GaN or InGaN having a single or multiple quantum well structure. The active layer 33 may be formed using a known deposition process such as an organometallic vapor deposition method, a molecular beam growth method, or a hybrid vapor deposition method like the n-type nitride semiconductor layer 32.

Like the n-type nitride semiconductor layer 32, the p-type nitride semiconductor layer 34 has an Al _x In _y Ga _(1-xy) N composition formula (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0). ≦ x + y ≦ 1), and typical nitride semiconductor materials include GaN, AlGaN, and GaInN. Impurities used for the doping of the p-type nitride semiconductor layer 34 include Mg, Zn, or Be. The p-type nitride semiconductor layer 34 is formed by growing the semiconductor material on the active layer 33 using a known deposition process such as organometallic vapor deposition, molecular beam growth, or hybrid vapor deposition.

The highly reflective ohmic contact layer 35 has a high reflectance in consideration of the structural aspect of the nitride semiconductor light emitting device for flip chip, and has a contact resistance with the p-type nitride semiconductor layer 34 having a relatively high energy band gap. It is required to be formed of a material suitable for lowering. In order to satisfy the conditions of improving the high reflectivity and contact resistance, the highly reflective ohmic contact layer 35 is composed of Ag, Ni, Al, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and combinations thereof. It may be formed of at least one layer of a material selected from the group, preferably having a reflectance of at least 70%. More preferably, the highly reflective ohmic contact layer 35 includes a first layer made of a material selected from the group consisting of Ni, Pd, Ir, Pt, and Zn, and a group formed of Ag and Al on the first layer. It may be formed of a two-layer structure comprising a second layer of a material selected from. Most preferably, the highly reflective ohmic contact layer 35 comprises a first layer made of Ni, a second layer made of Ag formed on the first layer, and a third layer made of Pt formed on the second layer. It may be formed in a three-layer structure comprising a. The highly reflective ohmic contact layer 35 may be formed by a known deposition method such as chemical vapor deposition (CVD) and an e-beam evaporator, or a process such as sputtering. In order to improve the properties of the ohmic contact, the heat treatment may be performed at a temperature of about 400 to 900 ° C.

The p-side bonding pad 37 for flip chip bonding may be formed on the highly reflective ohmic contact layer 35. One or more p-side bonding pads 37 may be formed as necessary, and are fused to lead patterns on a substrate for a support using conductive bumps during flip chip bonding. As shown in FIG. 2A, in this embodiment, the p-side bonding pad 37 may be formed on the upper surface of the highly reflective ohmic contact layer 35 positioned between the first electrode fingers 36b. have.

In addition, a passivation layer 39 may be formed therebetween for electrical isolation of the p-type nitride semiconductor layer 34 and the n-side electrode. The passivation layer 39 electrically isolates the p-type nitride semiconductor layer 34 and the n-side electrode. The passivation layer 39 may be made of an oxide or nitride having electrical insulation.

3 shows a nitride semiconductor light emitting device for flip chip according to another embodiment of the present invention. Referring to FIG. 3, the flip chip nitride semiconductor light emitting device according to the present embodiment includes a second electrode finger extending from each of the first electrode fingers 36b of the flip chip nitride semiconductor light emitting device of the embodiment shown in FIG. 2. (36c) is further included. Although FIG. 3 illustrates a structure having two second electrode fingers 36c extending in a vertical direction from each of the first electrode fingers 36b, the extension direction and the number of the second electrode fingers 36c are not limited to the present invention. It is not limited. Preferably, the second electrode finger 36c extends far from the bonding pad 36a and the first electrode finger 36b.

4A and 4B are graphs comparing driving voltage characteristics and luminance characteristics of a nitride semiconductor light emitting device according to an exemplary embodiment of the present invention shown in FIG. 3 with a conventional nitride semiconductor light emitting device.

First, referring to FIG. 4A, the curve 31 showing the driving voltage according to the current of the nitride semiconductor light emitting device according to the related art has not only a large driving voltage but also a saturation when the current reaches 300 mA. It can be seen that. In addition, as shown in FIG. 4B, not only the brightness is low but also the current reaches 300 mA, resulting in saturation even in the curve 33 showing the brightness according to the current of the conventional nitride semiconductor light emitting device. . As such, it can be seen that the electrode structure of the conventional nitride semiconductor light emitting device is not suitable for a large size high power nitride semiconductor light emitting device.

In contrast, the nitride semiconductor light emitting device according to the exemplary embodiment of the present invention has a lower driving voltage and shows a saturation even at a current of 300 mA or more as compared with the conventional nitride semiconductor light emitting device as shown by the curve 32 shown in FIG. Did. In addition, as the curve 34 shown in (b) of FIG. 4 increases as the current increases, the luminance increases and does not show a saturation state.

The comparison result shows that the nitride semiconductor light emitting device according to the present invention forms the bonding pad of the n-side electrode at the center of the n-type nitride semiconductor layer and forms the electrode paper extending from the bonding pad, thereby providing a highly reflective ohmic contact layer and the n-side. This is because the current crowding phenomenon in which the current is uniformly diffused and the current is concentrated in the vicinity of the n-side electrode is reduced by reducing the distance between the electrodes.

The present invention is not limited by the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims, and various forms of substitution, modification, and within the scope not departing from the technical spirit of the present invention described in the claims. It will be apparent to those skilled in the art that changes are possible.

As described above, according to the present invention, in the nitride semiconductor light emitting device for flip chip, by forming a bonding pad of the n-side electrode in the center of the n-type nitride semiconductor layer and forming an electrode finger extending from the bonding pad, By reducing the distance between the ohmic contact layer and the n-side electrode, there is an effect of improving the current crowding phenomenon that the current is uniformly diffused and the current is concentrated in the vicinity of the n-side electrode. In addition, this can greatly reduce the driving voltage, there is an effect that can improve the brightness.

Claims (7)

An n-type nitride semiconductor layer formed on the light transmissive substrate; An n-side electrode comprising a bonding pad formed at a substantially center portion on the n-type nitride semiconductor layer and at least one first electrode finger extending from the bonding pad; An active layer and a p-type nitride semiconductor layer sequentially stacked on a region where the n-side electrode is not formed on the n-type nitride semiconductor layer; And A nitride semiconductor light emitting device for flip chip comprising a highly reflective ohmic contact layer formed on the p-type nitride semiconductor layer. The method of claim 1, The upper surface of the n-type nitride semiconductor layer has a substantially rectangular shape, the first electrode finger is a nitride semiconductor light emitting device for flip chip, characterized in that extending from the bonding pad in the corner direction of the n-type nitride semiconductor layer. The method of claim 2, And at least one second electrode finger extending from the first electrode finger. The method of claim 1, And a passivation layer formed between the n-side electrode and the highly reflective p-type nitride semiconductor layer and electrically isolating the n-side electrode and the p-type nitride semiconductor layer to each other. . The method of claim 1, The highly reflective ohmic contact layer is formed of at least one layer made of a material selected from the group consisting of Ag, Ni, Al, Rh, Pd, Ir, Ru, Mg, Zn, Pt, Au, and combinations thereof. Nitride semiconductor light emitting device for flip chip. The method of claim 1, The highly reflective ohmic contact layer comprises a first layer made of a material selected from the group consisting of Ni, Pd, Ir, Pt, and Zn, and a material made from a material selected from the group consisting of Ag and Al formed on the first layer. A nitride semiconductor light emitting device for flip chip, comprising two layers. The method of claim 1, The highly reflective ohmic contact layer includes a first layer made of Ni, a second layer made of Ag formed on the first layer, and a third layer made of Pt formed on the second layer. A nitride semiconductor light emitting device for flip chip.

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