KR101762176B1 - Nano rod light emitting device - Google Patents

Abstract

A light emitting device is disclosed. The disclosed light emitting device includes a mask layer having a through hole; A nano-insertion layer formed in the through-hole and having an energy band structure in which at least one energy barrier is formed in the longitudinal direction of the through-hole; A semiconductor nanocrystal grown from the nano-insertion layer to the outside of the through-hole and doped with a first type; An active layer formed to surround the surface of the semiconductor nanocore; A second semiconductor layer formed to surround the surface of the active layer and doped with a second type; And a first electrode and a second electrode electrically connected to the semiconductor nanocore and the second semiconductor layer, respectively.

Description

[0001] Nano rod light emitting device [0002]

This disclosure is directed to a nanodrode light emitting device.

A light emitting device (LED) refers to a semiconductor device that can emit light of various colors by forming a light emitting source through a PN junction of a compound semiconductor. In recent years, blue LEDs and ultraviolet LEDs realized using nitrides excellent in physical and chemical properties have appeared, and since blue or ultraviolet LEDs and fluorescent materials can be used to form white light or other monochromatic light, ought.

The basic operation principle of the light emitting device is that electrons and holes injected into the active layer combine to emit light. However, in a nitride-based compound semiconductor crystal, many crystal defects generally exist, and when electrons and holes are coupled through the crystal defects, they are emitted as heat energy instead of light energy. Reducing such non-luminescent recombination is important for improving the luminous efficiency of the semiconductor light emitting device.

The crystal defects responsible for the non-luminescent recombination are caused by the lattice constant mismatch between the growth substrate and the compound semiconductor, the difference in the thermal expansion coefficient, and the like. In order to overcome such disadvantages, a technique for forming a nanoscale light emitting structure having a nanorod shape has been studied. Such a structure is known to be capable of large area growth easily on a heterogeneous substrate because it is less affected by the difference in lattice constant and thermal expansion coefficient from the substrate in the case of one-dimensional growth.

Recently, a nano-rod structure in the form of a core / shell has been proposed. One advantage of this structure is that it minimizes the first crystal defect. A typical planar thin film light emitting device has two types of crystal defects. One is a mismatch dislocation formed due to the lattice mismatch between the quantum well layer made of InGaN and the quantum barrier layer made of GaN. In this case, the dislocations are parallel to the growth plane. And the other is a threading dislocation which is formed at the interface between sapphire and gallium nitride and reaches the light emitting layer as the structure of the light emitting device becomes longer in the growth direction during growth. In the nano-rod structure, since the GaN layer can be deformed in the horizontal direction, formation of lattice mismatch dislocation can be reduced as compared with a general planar thin-film light-emitting device. In addition, since the area occupied on the substrate is small, there is a high possibility that only a part of the threading potential is propagated to the active layer, and even if a potential is formed, it moves and disappears to a near surface. Secondly, the active layer is formed along the surface of the core in the form of a shell layer to increase the light emitting surface area and reduce the actual current density, thereby improving the light efficiency.

The present disclosure provides a structure of a nano-rod light-emitting device capable of effectively transferring current to a light-emitting nano-rod having a core-cell structure and increasing the light-emitting efficiency.

A light emitting device according to one type includes: a mask layer having a through hole; A nano-insertion layer formed in the through-hole and having an energy band structure in which at least one energy barrier is formed in the longitudinal direction of the through-hole; A semiconductor nanocrystal grown from the nano-insertion layer to the outside of the through-hole and doped with a first type; An active layer formed to surround the surface of the semiconductor nanocore; A second semiconductor layer formed to surround the surface of the active layer and doped with a second type; And a first electrode and a second electrode electrically connected to the semiconductor nanocore and the second semiconductor layer, respectively.

The nano-insertion layer may include a multiple quantum well structure.

The nano-insertion layer may include an Al _x Ga _1-x N layer, a GaN layer, an In _x Ga _1-x N layer, and a GaN layer. The uppermost layer of the nano- Lt; / RTI >

The mask layer may include at least one of SiO ₂ , TiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , TiN, AlN, ZrO ₂ , TiAlN, and TiSiN.

The horizontal cross-sectional shape of the semiconductor nanocore may be circular, elliptical or polygonal.

And a transparent electrode layer covering the second semiconductor layer, and the second electrode may be provided on the transparent electrode layer.

An insulating layer may further be provided between the transparent electrode layer and the mask layer.

A first semiconductor layer doped with a first type may be further provided on a bottom surface of the mask layer, and the first electrode may be provided on one surface of the first semiconductor layer. In this case, And a reflective metal layer may be provided on the bottom.

The first electrode may be provided on a lower surface of the mask layer. In this case, the first electrode may be formed of a reflective metal material.

The second electrode is made of a reflective metal material and covers the entire surface of the second semiconductor layer. The first electrode is made of a transparent electrode material, and may be provided on a lower surface of the mask layer.

The above-described light emitting element employs a nano-inserted layer below the core in the core-cell type light emitting structure, thereby reducing the leakage current and enabling efficient current transmission in the longitudinal direction of the nanocore.

1 shows a schematic configuration of a light emitting device according to an embodiment of the present invention.
2 is a partially enlarged view showing a detailed structure of a nano-insertion layer employed in the light emitting device of FIG.
FIG. 3 shows the energy band structure in the direction of the arrow in the nano-inserted layer of FIG.
4 shows a schematic configuration of a light emitting device according to another embodiment.
FIG. 5 shows a schematic structure of a light emitting device according to another embodiment.
Description of the Related Art [0002]
100, 200, 300 ... light emitting device 110 ... substrate
120 ... first semiconductor layer 130 ... mask layer
140 ... light emitting nano-rod 142 ... nano-inserted layer
144 ... semiconductor nanocore 146 ... active layer
148 ... second semiconductor layer 160 ... transparent electrode layer
170, 174 ... second electrodes 180, 182, 184 ... first electrodes
190 ... reflective electrode layer

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, like reference numerals refer to like elements, and the size and thickness of each element may be exaggerated for clarity of explanation.

FIG. 1 shows a schematic structure of a light emitting device according to an embodiment of the present invention, FIG. 2 shows a detailed structure of a nano-inserted layer employed in the light emitting device of FIG. 1, Directional energy band structure.

Referring to the drawings, a light emitting device 100 includes a light emitting nano-rod 140, which includes a nano-insertion layer 142 grown from a first semiconductor layer 120, a nano-insertion layer 142 An active layer 146 that surrounds the surface of the semiconductor nanocore 144 and a surface of the active layer 146 that are grown from the first type semiconductor nanocrystal 144 and doped with the first type, And a second semiconductor layer 148.

The more specific configuration is as follows.

The substrate 110 may be a silicon (Si) substrate, a silicon carbide (SiC) substrate, a sapphire substrate, or the like as a growth substrate for semiconductor single crystal growth. In addition, A substrate made of ZnO, GaAs, MgAl ₂ O ₄ , MgO, LiAlO ₂ , LiGaO ₂ , or GaN may be used as a material suitable for growth of one semiconductor layer 120.

A mask layer 130 having a plurality of through holes is provided on a substrate 110. Mask layer 130 is an insulating material, may be made, including silicon oxide or silicon nitride, _{e.g., SiO 2, SiN, TiO 2} , Si 3 N 4, Al 2 O 3, TiN, AlN, ZrO 2 , TiAlN, TiSiN, or the like. The mask layer 130 may be formed by forming a film of such an insulating material on the first semiconductor layer 120 and then etching the desired through-hole pattern by a lithography process. The through-hole may have a cross-sectional shape such as a circle, an ellipse, or a polygon.

A first semiconductor layer 120 doped with a first type may be further formed between the substrate 110 and the mask layer 130. The first semiconductor layer 120 may be a semiconductor layer doped with a first type and may be formed of a III-V group nitride semiconductor material. For example, the first semiconductor layer 120 may be formed of Al _x Ga _y In _z N (0 1, 0? Y? 1, 0? Z? 1, x + y + z = 1). As n-type impurities, Si, Ge, Se, Te and the like can be used. The first semiconductor layer 120 may include at least one selected from the group consisting of hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), metal organic vapor phase epitaxy (MOVPE) A metal organic chemical vapor deposition (MOCVD) method or the like.

Although not shown, a buffer layer may be formed between the substrate 110 and the first semiconductor layer 120 for epitaxial growth, if necessary, and the first semiconductor layer 120 may have a multi-layer structure It is possible. The first semiconductor layer 120 may be omitted in some cases.

The nano-insertion layer 142 is formed in the through-hole and is provided to reduce the leakage current when the current is injected into the semiconductor nanocore 142. For this purpose, the nano-insertion layer 142 may have a shape having an energy band structure in which one or more energy barrier is formed in the longitudinal direction of the through hole. Nano insertion layer 142 may be formed in a single quantum well (single quantum well) or a multiple quantum well (multi quantum well) structure, for example, as shown in Figure 2, Al _x Ga _{1 - x} N layer (0? _X? 1), a GaN layer, an In _x Ga _1-x N layer (0 _{? X?} 1), and a GaN layer. However, the present invention is not limited to such a four-layer structure, and may be composed of a plurality of layers smaller than 4 or a single layer. Or a structure in which the above-described structure is repeated, for example, a structure in which the above-described structure is repeated in a form in which the Al content is changed. The uppermost layer of the nano-inserted layer 142 may be doped with the same first type as the semiconductor nanocore 144, and the doping concentration may be formed to be equal to or lower than the semiconductor nanocore 144.

Referring to FIG. 3, the energy band structure of the nano-inserted layer 142 is illustrated as an example along the arrow direction of FIG. Two energy barriers having different heights are formed in the direction crossing the nano-insertion layer 142, that is, the longitudinal direction of the through holes. The provision of the nano-insertion layer 142 prevents current leakage that may occur at the interface between the semiconductor nanocore 144 and the nano-insertion layer 142, and enables efficient current transmission to the core-cell light-emitting structure .

The semiconductor nanocore 144 is vertically grown from the nano-insertion layer 142 to the outside of the through-hole, and is made of a semiconductor material doped with the first type. n-Al _x Ga _y In _z N (0? x? 1, 0? y? 1, 0? z? 1, x + y + z = 1). The semiconductor nanocore 144 has a cross-sectional shape such as a circle, an ellipse, and a polygon along the cross-sectional shape of the through-hole.

In the drawing, the width of the semiconductor nanocore 144 is shown to be the same as the width of the through hole as a whole, but this is exemplary. The portion where the semiconductor nanocore 144 is grown outside the through hole is usually formed to be somewhat wider than the width of the through hole. In addition, although the upper end of the semiconductor nanocore 144 is shown as being flat, this is an example, and it may have a horn shape or a truncated cone shape that becomes narrower toward the upper side depending on a manufacturing process.

The active layer 146 is a layer that emits light by electron-hole recombination. The active layer 146 is a single quantum well (Al _x Ga _y In _z N) layer in which band intervals are varied by periodically changing x, y, ) Or a multi quantum well structure. For example, the quantum well layer and the barrier layer may form a quantum well structure in the form of InGaN / GaN, InGaN / InGaN, InGaN / AlGaN or InGaN / InAlGaN, The gap energy can be controlled and the emission wavelength band can be adjusted. Normally, when the mole fraction of In changes by 1%, the emission wavelength is shifted by about 5 nm.

The second semiconductor layer 148 is formed so as to cover the surface of the active layer 146. The second semiconductor layer 148 may be made of p-Al _x Ga _y In _z N (0? X? 1, 0? Y? 1, 0? Z? 1, x + y + z = Type impurities may be Mg, Zn, Be, and the like.

An electron blocking layer (not shown) is formed between the second semiconductor layer 148 and the active layer 146 to block electrons flowing from the first semiconductor layer 120, which is n-type, from moving to the p- layer may be further provided.

The first electrode 180 and the second electrode 170 are electrically connected to the first semiconductor layer 120 and the second semiconductor layer 146 to apply a voltage for electron and hole injection to the active layer 143 . The first electrode 180 may be formed on the first semiconductor layer 120. The second electrode 170 may be provided on the transparent electrode layer 160 covering the plurality of light emitting nano-rods 140. The transparent electrode layer 160 serves as a path for supplying a current to the light emitting nano-rod 140 and is formed of a transparent conductive oxide (TCO) so as to transmit light emitted from the light emitting nano- . For example, ITO (Indium Tin Oxide), AZO (Aluminum Zinc Oxide), IZO (Indium Zinc Oxide), or the like.

Although not shown, an insulating layer may be further provided between the mask layer 130 and the transparent electrode layer 160, and the thickness of the insulating layer to be inserted may be properly determined for an efficient current path.

A reflective electrode layer 190 may be further formed on the lower surface of the substrate 110. The reflective electrode layer 190 reflects light emitted from the light emitting nano-rod 140 upward. Since the light generated in the active layer 146 of the light emitting nano-rod 140 is spontaneous emission, there is no particular directionality and the light is directed in all directions. Of these, the light directed downward is reflected upward, as shown in Fig. The reflective electrode layer 190 may include a reflective metal such as silver (Ag), aluminum (Al), or an alloy containing silver or aluminum.

4 shows a schematic configuration of a light emitting device 200 according to another embodiment. The present embodiment is different from the light emitting device 100 of FIG. 1 in the position of the first electrode 182. The substrate (110 in FIG. 1) used as a semiconductor growth substrate is removed, and the first electrode 182 is formed on the lower surface of the first semiconductor layer 120. In the case where the substrate (110 in FIG. 1) is a conductive substrate, it is also possible to form the first electrode 182 on the lower surface of the substrate without removing the substrate (110 in FIG. 1). The first electrode 182 may also be formed of a reflective metallic material so that the light generated by the light emitting nano-rod 140 may be reflected back toward the front surface.

FIG. 5 shows a schematic configuration of a light emitting device 300 according to another embodiment. The present embodiment differs from the light emitting device 100 of FIG. 1 and the light emitting device 200 of FIG. 4 in that the light emitting direction is a back surface. The second electrode 174 is formed of a reflective metallic material and surrounds the surface of the light emitting nano-rod 140. The first electrode 184 is made of a transparent electrode material and is provided on the lower surface of the first semiconductor layer 120. Accordingly, the light generated by the light emitting nano-rod 140 is reflected by the reflective metal material that is in contact with the surface of the light emitting nano-rod 140, and is all directed toward the back surface.

The light emitting device having various structures using the light emitting nano-rod 140 having the nano-inserted layer 142 under the semiconductor nanocore 144 in the through-hole of the mask layer 130 has been described above. For example, the electrode structure, the specific shape of the upper end of the light emitting nano-rods, and the like can be variously modified. Although the first type is an n-type and the second type is a p-type, they are mutually interchangeable.

Although the light emitting device of the present invention has been described with reference to the embodiments shown in the drawings for the sake of understanding, the light emitting device of the present invention is merely an example, and various modifications and equivalent embodiments can be made by those skilled in the art I will understand the point. Accordingly, the true scope of the present invention should be determined by the appended claims.

Claims (13)

A mask layer having a through hole;
A nano-insertion layer formed in the through-hole and having an energy band structure in which at least one energy barrier is formed in the longitudinal direction of the through-hole;
A semiconductor nanocrystal grown from the nano-insertion layer to the outside of the through-hole and doped with a first type;
An active layer formed to surround the surface of the semiconductor nanocore;
A second semiconductor layer formed to surround the surface of the active layer and doped with a second type;
And a first electrode and a second electrode electrically connected to the semiconductor nanocore and the second semiconductor layer, respectively. The method according to claim 1,
Wherein the nano-inserted layer comprises a multiple quantum well structure. The method according to claim 1,
Wherein the nano-insertion layer is composed of an Al _x Ga ₁ -xN (0 _{? X} ? 1) layer, a GaN layer, an In _x Ga ₁ -xN (0 _{? X} ? 1) layer, and a GaN layer. The method of claim 3,
Wherein the uppermost layer of the nano-inserted layer is doped with a first type same as that of the semiconductor nanocore. delete delete 5. The method according to any one of claims 1 to 4,
And a transparent electrode layer covering the second semiconductor layer,
And the second electrode is provided on the transparent electrode layer. delete 8. The method of claim 7,
A first semiconductor layer doped with a first type is further provided on a lower surface of the mask layer,
Wherein the first electrode is provided in one region of the upper surface of the first semiconductor layer. 10. The method of claim 9,
And a reflective metal layer is formed under the first semiconductor layer. 8. The method of claim 7,
A first semiconductor layer doped with a first type is further provided on a lower surface of the mask layer,
Wherein the first electrode is provided on a lower surface of the first semiconductor layer. 12. The method of claim 11,
Wherein the first electrode is made of a reflective metal material. 5. The method according to any one of claims 1 to 4,
Wherein the second electrode is made of a reflective metal material and is provided so as to cover the entire surface of the second semiconductor layer,
A first semiconductor layer doped with a first type is further provided on a lower surface of the mask layer,
Wherein the first electrode is made of a transparent electrode material and is provided on a lower surface of the first semiconductor layer.

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