KR100867499B1 - Nitride Semiconductor Light Emitting Device and Method for Manufacturing the Same - Google Patents

Abstract

The present invention, the substrate; An n-type semiconductor layer, an active layer and a p-type nitride semiconductor layer sequentially formed on the substrate; Provided is a nitride semiconductor light emitting device formed on the p-type nitride semiconductor layer and including a spontaneous quantum dot layer having a plurality of protruding quantum dots.

Nitride semiconductor, light emitting device, LED, light extraction efficiency

Description

Nitride Semiconductor Light Emitting Device and Method for Manufacturing the Same

1A is a cross-sectional view of a nitride semiconductor light emitting device according to the prior art.

FIG. 1B is a view schematically showing an optical path in the light emitting device of FIG. 1A.

2 is a cross-sectional view schematically showing a nitride semiconductor light emitting device according to an embodiment of the present invention.

3 is a view schematically illustrating an optical path in the light emitting device of FIG. 2.

4 is a cross-sectional view of a nitride semiconductor light emitting device according to an embodiment of the present invention.

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

6 is a graph showing strain energy over time when forming a spontaneous quantum dot layer.

7 is a cross-sectional view illustrating a process for forming a spontaneous quantum dot layer.

8 to 10 are cross-sectional views illustrating a method of manufacturing a nitride semiconductor light emitting device according to an embodiment of the present invention.

11 and 12 are cross-sectional views illustrating a method of manufacturing a nitride semiconductor light emitting device according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100, 200, 300: light emitting diode 101: substrate

102: n-type nitride semiconductor layer 103: active layer

104: p-type nitride semiconductor layer 110: spontaneous quantum dot layer

112: spontaneous quantum dot 122a: n-side electrode

124a: p-side electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly, to a nitride light emitting device having an improved light extraction efficiency and a method of manufacturing the same.

Recently, Group III nitride semiconductors (hereinafter, simply referred to as 'nitride semiconductors') have been widely used as light emitting device materials for ultraviolet (UV) light, blue light, and green light in various fields such as LCD backlights, camera flashes, and lighting. In general, the nitride semiconductor has a composition formula of Al _x Ga _y In _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). In order to manufacture such a nitride semiconductor light emitting device (including an LED), an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially grown on a growth substrate such as sapphire to form a light emitting structure.

Nitride semiconductors have a higher refractive index than external environments such as epoxy or air. Due to the large difference in refractive index between the external environment (resin such as air or epoxy) and the nitride semiconductor, a significant part of the photons generated inside the nitride semiconductor light emitting device cannot be escaped to the outside by reflecting at the interface or the wall several times. It is destroyed. Since the optical loss due to the total internal reflection is very large, the external quantum efficiency of the nitride semiconductor light emitting device is not high enough.

1A is a cross-sectional view of a conventional nitride semiconductor light emitting device, and FIG. 1B is a partial cross-sectional view schematically showing an optical path in the light emitting device of FIG. 1A. Referring to FIG. 1A, the light emitting device 10 includes a sapphire substrate 11 and an n-type semiconductor layer 12, an active layer 13, and a p-type semiconductor layer 14 sequentially grown thereon. The n-side electrode 22 and the p-side electrode 24 are formed on some of the n-type semiconductor layer 12 and the p-type semiconductor layer 14 exposed by etching, respectively.

Referring to FIG. 1B, photons emitted at one point of the active layer 13 may have various traveling angles. In order for this photon to be emitted to the outside through the device wall or interface, the traveling direction of the photon must be smaller than the critical angle θc, and photons traveling at an angle larger than this critical angle are totally reflected at the device boundary and trapped inside the device, and eventually lose as heat. do. Due to the total internal reflection and the loss of heat, the external quantum efficiency of the nitride semiconductor light emitting device has a low value.

Various techniques have been proposed to solve the problem of reducing the external quantum efficiency. For example, a technique for deforming the light emitting device structure itself or etching the surface to form a surface texture such as an uneven pattern on the surface of the nitride semiconductor layer has been proposed. However, in order to change the structure of the light emitting device itself, a significant modification of the manufacturing process specification is required and an additional unit process is required. In addition, the method of providing a surface texture by etching the surface of the nitride semiconductor layer may cause a problem of damaging main parts such as the active layer.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a nitride semiconductor light emitting device with improved light extraction efficiency.

Another object of the present invention is to provide a nitride semiconductor light emitting device manufacturing method capable of manufacturing a nitride semiconductor light emitting device having improved light extraction efficiency with high process reliability.

In order to achieve the above technical problem, the present invention, the substrate; An n-type semiconductor layer, an active layer and a p-type nitride semiconductor layer sequentially formed on the substrate; Provided is a nitride semiconductor light emitting device formed on the p-type nitride semiconductor layer and including a spontaneous quantum dot layer having a plurality of protruding quantum dots.

According to an embodiment of the present invention, the spontaneous quantum dot layer has a refractive index larger than that of the p-type nitride semiconductor layer. The spontaneous quantum dot layer may be made of InGaN. The diameter of the quantum dot in the spontaneous quantum dot layer is 5-50nm, the height of the quantum dot may be 1-10nm. In addition, the distribution density of the quantum dots in the spontaneous quantum dot layer may be 1 × 10 ⁸ to 1 × 10 ¹² cm ⁻² .

According to an embodiment of the present invention, the nitride semiconductor light emitting device further includes a p-side electrode formed on the p-type nitride semiconductor layer and an n-side electrode formed on a portion of the n-type nitride semiconductor layer, wherein the n-side electrode The p-side electrode may be disposed on the same side of the light emitting device.

According to another embodiment of the present invention, the nitride semiconductor light emitting device further includes a p-side electrode formed on the p-type nitride semiconductor layer and the n-side electrode formed on the lower surface of the substrate, the substrate may be a conductive substrate.

In order to achieve another object of the present invention, the present invention comprises the steps of forming an n-type nitride semiconductor layer, an active layer and a p-type nitride semiconductor layer on a substrate; It provides a nitride semiconductor light emitting device manufacturing method comprising the step of forming a spontaneous quantum dot layer having a plurality of quantum dots protruding upward on the p-type nitride semiconductor layer.

According to an embodiment of the present invention, the spontaneous quantum dot layer may be grown using a Stranski-Krastanov (hereinafter, simply referred to as S-K) growth method. The spontaneous quantum dot layer may be formed of InGaN.

The quantum dots may be formed to have a diameter of 5-50 nm and a height of 1-10 nm. In addition, the spontaneous quantum dot layer may be formed such that the distribution density of the quantum dots is 1 × 10 ⁸ to 1 × 10 ¹² cm ⁻² .

According to an embodiment of the present invention, in the method of manufacturing a nitride semiconductor light emitting device, a portion of the spontaneous quantum dot layer, the p-type nitride semiconductor layer, the active layer and the n-type nitride semiconductor layer is mesa so that a portion of the n-type nitride semiconductor layer is exposed. Etching; Forming an n-side electrode on the exposed n-type nitride semiconductor layer region; The method may further include forming a p-side electrode on the p-type nitride semiconductor layer. In this case, before the forming of the p-side electrode, the method may further include mesa etching some thicknesses of the spontaneous quantum dot layer and the p-type nitride semiconductor layer in the region where the p-side electrode is to be formed.

According to another embodiment of the present invention, a method for manufacturing a nitride semiconductor light emitting device includes: forming a p-side electrode on the p-type nitride semiconductor layer; The method may further include forming an n-side electrode on the lower surface of the substrate, wherein the substrate may be a conductive substrate. In this case, before the forming of the p-side electrode, the method may further include mesa etching a portion of the spontaneous quantum dot layer and the p-type nitride semiconductor layer in the region where the p-side electrode is to be formed.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Accordingly, the shape and size of elements in the drawings may be exaggerated for clarity, and the elements denoted by the same reference numerals in the drawings are the same elements.

2 is a cross-sectional view schematically showing a nitride semiconductor light emitting device according to an embodiment of the present invention. In FIG. 2, the electrode part of the device is not illustrated for convenience, but the n-side electrode and the p-side electrode may be formed on the same or opposite side of the device depending on whether the light emitting device 100 is a horizontal or vertical light emitting device. 4 and FIG. 5 etc.).

Referring to FIG. 2, the n-type nitride semiconductor layer 102, the active layer 103, and the p-type nitride semiconductor layer 104 are sequentially grown on the substrate 101. In particular, the light emitting device 100 includes a spontaneous quantum dot layer 110 formed on the p-type nitride semiconductor layer 104. The spontaneous quantum dot layer 110 serves to effectively increase the light extraction efficiency at the surface of the device, as described below, and includes a plurality of quantum dots 112 protruding upward from the top surface of the layer.

The spontaneous quantum dot layer 110 may be formed of a nitride semiconductor material, and as described later, a p-type semiconductor may be formed by using a Stranski-Krastanov growth method (also referred to simply as a SK growth method). May be grown on layer 104 (see FIG. 6). The spontaneous quantum dot layer 110 may have a refractive index higher than that of the p-type semiconductor layer 104. For example, the p-type semiconductor layer 104 may be formed of GaN or AlGaN, and the spontaneous quantum dot layer 110 may be formed of InGaN. InGaN exhibits a higher refractive index with a larger constant and smaller energy bandgap than GaN or AlGaN.

In this spontaneous quantum dot layer 112, a plurality of protruding quantum dots 112 are distributed, and these protruding structures contribute to suppressing total reflection at the device boundary. These quantum dots 112 are nanostructures of several to tens of nanometers in size. For example, a spontaneous quantum dot layer in which quantum dots having a diameter of 5-50 nm and a height of 1-10 nm are distributed may be formed using S-K growth method or the like. A flat layer portion (two-dimensional growth portion) is formed between the protruding quantum dots 112.

FIG. 3 is a partial cross-sectional view schematically showing an optical path at an element surface portion of the light emitting device 100 of FIG. 2. Referring to FIG. 3, photons generated in the active layer proceed at various angles. Since the refractive index of the spontaneous quantum dot layer 110 is larger than that of the p-type semiconductor layer 104, total reflection does not occur at the interface between the two layers 110 and 104. Between the spontaneous quantum dot layer 110 and the outside (air or encapsulant resin, etc.), some total reflection may occur at the surface of the two-dimensional growth portion, but the light extraction efficiency is considerably increased due to the three-dimensional quantum dot 112. .

Specifically, even if the light proceeds while forming an angle (an angle formed with the vertical line) above the critical angle θ determined by the refractive index of the spontaneous quantum dot layer 110 material (high refractive index) and the external material (low refractive index), The protruding three-dimensional structure allows light to be easily extracted to the outside. When light is scattered at the interface by nano-sized quantum dots, the light can be better escaped. As a result, a significant portion (a, b, d) of the photons starting from the active layer 103 is extracted to the outside and some of the photons (c) are totally reflected at the surface, the overall light extraction efficiency is greatly improved compared with the prior art.

In the above-described embodiment, although the refractive index of the spontaneous quantum dot layer 110 is larger than the refractive index of the p-type nitride semiconductor layer 104 below, the present invention is not limited thereto. Even if the refractive index of the spontaneous quantum dot layer 110 is lower than or equal to that of the p-type nitride semiconductor layer (but higher than the refractive index of an external environment such as air or resin), the effect of increasing light extraction due to the protruding quantum dots can be obtained. Can be.

4 illustrates a nitride semiconductor light emitting device according to one embodiment, in particular, a cross-sectional view of a 'horizontal' light emitting device in which an n-side electrode and a p-side electrode are disposed on the same side of the device. Referring to FIG. 4, the light emitting device 200 includes an n-type nitride semiconductor layer 102, an active layer 103, and a p-type nitride semiconductor layer 104 sequentially grown on a growth substrate 101a such as a sapphire substrate. It includes. An n-side electrode 122a is formed on a portion of the n-type semiconductor layer 102 exposed by mesa etching of the semiconductor layers 102, 103, 104, and p is formed on a portion of the p-type semiconductor layer 104. The side electrode 124a is formed.

As shown in FIG. 4, a spontaneous quantum dot layer 110 is formed on the p-type semiconductor layer 104 other than the p-side electrode formation region. If the spontaneous quantum dot layer 110 can have a higher refractive index than the p-type semiconductor layer 104, for example, it may be formed of InGaN having a higher In composition than the p-type semiconductor layer 104. A plurality of quantum dots 112 protruding upward are distributed on the spontaneous quantum dot layer 110, and the quantum dots contribute to light extraction efficiency as described above.

5 shows a nitride semiconductor light emitting device according to another embodiment, and in particular, is a cross-sectional view of a 'vertical' light emitting device in which an n-side electrode and a p-side electrode are disposed to face each other. Referring to FIG. 5, the nitride semiconductor light emitting device 300 includes an n-type nitride semiconductor layer 102, an active layer 103, and a p-type nitride semiconductor layer 104 sequentially formed on the conductive substrate 101b. The conductive substrate 101b may be, for example, a GaAs, SiC, GaN substrate, or Si substrate. The p-side electrode 124a is formed on the p-type nitride semiconductor layer 104, and the n-side electrode 122b is formed on the lower surface of the conductive substrate 101b.

Also in this embodiment, on the p-type nitride semiconductor layer 104, a spontaneous quantum dot layer 110 (eg, formed on In-type GaN layer and formed of InGaN) including a plurality of protruding quantum dots 112 is grown. It is. Therefore, the effect of increasing the light extraction efficiency as described above can be obtained.

FIG. 6 is a graph showing strain energy due to lattice mismatch with growth time in a process of growing a spontaneous quantum dot layer. In particular, the graph of Figure 6 shows the change in strain energy when growing the spontaneous quantum dot layer by using the Stransky-Crastanov (S-K) growth method. For example, the S-K growth method can be used to grow a spontaneous quantum dot layer of InGaN (with a relatively large lattice constant) on a p-type GaN layer (with a relatively small lattice constant). The spontaneous quantum dot layer forming process through the S-K growth method is schematically illustrated in the cross-sectional views of FIGS. 7A to 7C.

6 and 7, in the early stage of growth of the spontaneous quantum dot layer, the InGaN layer 110a grows on the p-type GaN layer 104 with stable 2D growth and then the critical wetting layer thickness tcw. If it exceeds, it grows in a metastable two-dimensional growth (metastable 2D growth) and continues to grow in two dimensions (Fig. 7 (a)). In this two-dimensional growth phase (Step A of FIG. 6), the strain energy of the InGaN layer increases with growth time for lattice matching with the GaN layer below.

When the strain energy reaches the critical point X, the strain energy decreases, causing the InGaN material to agglomerate at many points, resulting in a large number of InGaN three-dimensional structures (initial forms of quantum dot structures) in the layer (Fig. 7 ( b)). At this time, the corresponding 2D-3D growth transition (2D-3D transition) represented by B period (B period) of FIG. 6 shows a decrease in strain energy along with growth of the initial form of the quantum dot structure.

Thereafter, a three-dimensional quantum dot growth is stabilized (ripening phase (step C of FIG. 6)) and the strain energy is kept constant (Fig. 7 (c)). After passing through this ballast, as shown in FIG. 7C, a spontaneous quantum dot layer 110c having a plurality of quantum dots 112 protruding upwards is obtained.

In short, the process of forming the spontaneous quantum dot layer using the SK growth method is a two-dimensional growth period in which two-dimensional growth is dominant, two-dimensional three-dimensional growth in which three-dimensional growth occurs at a plurality of points in the layer. 2D-3D transition period, a ripening phase in which three-dimensional quantum dot growth is stabilized.

Next, the manufacturing method of a nitride semiconductor light emitting element is demonstrated.

8 to 10 are cross-sectional views illustrating a method of manufacturing a nitride semiconductor light emitting device according to one embodiment.

Referring to FIG. 8, an n-type nitride semiconductor layer 102, an active layer 103, and a p-type nitride semiconductor layer 104 are sequentially grown on a growth substrate 101a such as a sapphire substrate. For example, after forming an undoped GaN layer on a sapphire substrate using MOCVD, an n-type GaN layer, a multi-quantum well structure active layer of InGaN / GaN, and a p-type GaN layer can be grown thereon.

On the p-type nitride semiconductor layer 104, a spontaneous quantum dot layer 110 in which a plurality of quantum dots 112 are distributed is grown using the SK growth method as described above. The spontaneous quantum dot layer 110 may be formed of, for example, InGaN, and may have a larger refractive index than the p-type nitride semiconductor layer 104 below. The quantum dots 112 in the spontaneous quantum dot layer 110 may be formed to have a diameter of 5-50 nm and a height of 1-10 nm. In addition, the distribution density of the quantum dots 112 may be adjusted within the range of 1 × 10 ⁸ to 1 × 10 ¹² cm ⁻² . By having such a quantum dot size and quantum dot distribution density, the spontaneous quantum dot layer 110 can extract light more efficiently from the upper surface of the light emitting device.

Thereafter, as shown in FIG. 9, the spontaneous quantum dot layer 110, the p-type semiconductor layer 104, the active layer 103, and some thicknesses of the n-type semiconductor layer 102 are exposed to expose a portion of the n-type semiconductor layer 102. The semiconductor layer 102 is mesa etched. In addition, the spontaneous quantum dot layer 110 and the P-type semiconductor layer 104 having a partial thickness may be mesa-etched in a region where the P-side electrode is to be formed.

Then, as shown in FIG. 10, the n-side electrode 122a is formed on the n-type semiconductor layer 102 region exposed by mesa etching, and the p-side electrode (p-type electrode) is formed on the p-type nitride semiconductor layer 104. 124a). As a result, a horizontal nitride semiconductor light emitting device having improved light extraction efficiency can be obtained.

11 and 12 are cross-sectional views illustrating a method of manufacturing a nitride semiconductor light emitting device according to another embodiment. In this embodiment, a vertical nitride semiconductor light emitting element in which the n-side electrode and the p-side electrode are disposed opposite to each other is manufactured.

Referring to FIG. 11, the n-type semiconductor layer, the active layer, and the p-type semiconductor layers 102 to 104 are sequentially grown on a conductive substrate 101b such as GaAs, GaN, SiC, or Si, and then, as described above. A spontaneous quantum dot layer 110 (eg made of InGaN) with grown quantum dots 112 is grown. The semiconductor layers 102 to 104 may each be an n-type GaN layer, an InGaN / GaN multi-quantum well structure active layer, or a p-type GaN layer. For subsequent p-side electrode formation, the spontaneous quantum dot layer and the p-type semiconductor layer of some thickness may be mesa-etched in the region P in which the p-side electrode is to be formed.

12, the p-side electrode 124a is formed on the p-type semiconductor layer 104, and the n-side electrode 122b is formed on the lower surface of the conductive substrate 101b. As a result, a vertical nitride semiconductor light emitting device having improved light extraction efficiency can be obtained.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. In addition, it will be apparent to those skilled in the art that the present invention may be substituted, modified, and changed in various forms without departing from the technical spirit of the present invention described in the claims.

As described above, by forming a spontaneous quantum dot layer having a plurality of quantum dots protruding upward on the p-type nitride semiconductor layer, the light extraction efficiency at the surface of the device can be greatly improved. In addition, unlike the conventional method, since the uneven surface is not formed by etching, damage to the element layer due to etching can be prevented, and the manufacturing process is simple and easy.

Claims (16)

Board; An n-type semiconductor layer, an active layer, and a p-type nitride semiconductor layer sequentially formed on the substrate; And And a spontaneous quantum dot layer having a plurality of quantum dots protruding upward from the p-type nitride semiconductor layer by using the Stranski-Crastanoff growth method. The method of claim 1, The spontaneous quantum dot layer is nitride semiconductor light emitting device, characterized in that having a refractive index larger than the refractive index of the p-type nitride semiconductor layer. The method of claim 1, The spontaneous quantum dot layer is nitride semiconductor light emitting device, characterized in that made of InGaN. The method of claim 1, The nitride semiconductor light emitting device, characterized in that the diameter of the quantum dot in the spontaneous quantum dot layer is 5-50nm, the height of the quantum dot is 1-10nm. The method of claim 1, The nitride semiconductor light emitting device of claim ⁹ , wherein the distribution density of the quantum dots in the spontaneous quantum dot layer is 1 × 10 ⁸ to 1 × 10 ¹² cm ⁻² . The method of claim 1, And a p-side electrode formed on the p-type nitride semiconductor layer and an n-side electrode formed on a portion of the n-type nitride semiconductor layer, wherein the n-side electrode and the p-side electrode are disposed on the same side of the light emitting device. A nitride semiconductor light emitting device, characterized in that. The method of claim 1, And a p-side electrode formed on the p-type nitride semiconductor layer and an n-side electrode formed on the lower surface of the substrate, wherein the substrate is a conductive substrate. Forming an n-type nitride semiconductor layer, an active layer and a p-type nitride semiconductor layer on the substrate; And And forming a spontaneous quantum dot layer having a plurality of quantum dots protruding upward by using the Stranski-Crastanoff growth method on the p-type nitride semiconductor layer. delete The method of claim 8, The spontaneous quantum dot layer is a method of manufacturing a nitride semiconductor light emitting device, characterized in that formed with InGaN. The method of claim 8, The quantum dot is a method of manufacturing a nitride semiconductor light emitting device, characterized in that formed to have a diameter of 5-50nm and a height of 1-10nm. The method of claim 8, The spontaneous quantum dot layer is a method of manufacturing a nitride semiconductor light emitting device, characterized in that the distribution density of the quantum dot is formed to 1 × 10 ⁸ to 1 × 10 ¹² cm ^-2 . The method of claim 8, Mesa etching a portion of the spontaneous quantum dot layer, a p-type nitride semiconductor layer, an active layer, and an n-type nitride semiconductor layer to expose a portion of the n-type nitride semiconductor layer; Forming an n-side electrode on the exposed n-type nitride semiconductor layer region; And A method of manufacturing a nitride semiconductor light emitting device further comprising the step of forming a p-side electrode on the p-type nitride semiconductor layer. The method of claim 13, And mesa etching a portion of the spontaneous quantum dot layer and the p-type nitride semiconductor layer in a region where the p-side electrode is to be formed before the forming of the p-side electrode. . The method of claim 8, Forming a p-side electrode on the p-type nitride semiconductor layer; And The method may further include forming an n-side electrode on the lower surface of the substrate. The substrate is a method of manufacturing a nitride semiconductor light emitting device, characterized in that the conductive substrate. The method of claim 15, Before the forming of the p-side electrode, further comprising mesa etching a portion of the spontaneous quantum dot layer and the p-type nitride semiconductor layer in the region where the p-side electrode is to be formed. Manufacturing method.

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