KR20100080094A - Light emitting diode using radial hetero-structure nanorod - Google Patents

Abstract

PURPOSE: As elevation the volume comparison spherically the light emitting diode using the nano rod of the radial shape hetero junction structure forms the light emitting structure in the form of nano rod. The optical extraction efficiency is improved. CONSTITUTION: A reflective electrode(106) is formed on the bearing substrate(103). The first area doped to the first type is perpendicularly formed on the reflective electrode. A plurality of nano rod(200) comprises the second part doped to the active area and the second type. The transparent electrode layer(115) surrounds the surface of nano rod. The epi layer(109) is included of the same material as the first area.

Description

Light emitting diode using radial hetero-structure nanorod

The disclosed light emitting diode relates to a light emitting diode using nano bars of a radial heterojunction structure.

Light emitting diodes (LEDs) using semiconductors are highly efficient and eco-friendly light sources, and are used in various fields such as displays, optical communications, automobiles, and general lighting. Recently, due to the development of the white light LED technology, a general lighting LED technology has attracted much attention. White light LEDs can be made, for example, using blue LEDs or ultraviolet LEDs and phosphors, or a combination of red, green and blue LEDs.

Blue or ultraviolet LED, which is an important component of the white light LED, is mainly made of a gallium nitride (GaN) -based compound semiconductor. The gallium nitride compound semiconductor has a wide band gap and can obtain light in a near-field region from visible light to ultraviolet light depending on the composition of the nitride. Typically, a thin film GaN LED is manufactured by growing a GaN thin film on a sapphire (Al ₂ O ₃ ) substrate. However, when the gallium nitride compound semiconductor is grown in a thin film form on a sapphire substrate, the luminous efficiency is lowered due to lattice constant mismatch or difference in thermal expansion coefficient, and the large area is difficult to grow, resulting in increased production cost.

In order to improve this disadvantage, a technique for forming a nano-scale light emitting diode by forming a p-n junction in the form of nanowires (nanowire, nanopillar, nanocolumn) using a gallium nitride compound semiconductor or zinc oxide. The advantage of such a structure is that one-dimensional growth can be easily grown in large areas on heterogeneous substrates because it is less affected by the lattice constant mismatch with the substrate or the difference in coefficient of thermal expansion than the thin film type.

However, in the application of the nano-rod structure to the light emitting diode, when the p-i-n structure is formed in the longitudinal direction (growth direction), the volume of the i region which is the active layer cannot be increased. In addition, because of the large surface-to-volume ratio, the leakage current at the surface is large and the flow path of the current is small, so the series resistance is large. Therefore, there is a need for a design to increase the amount of light generated from the nanorods and to reduce the resistance.

Embodiments of the present invention in accordance with the above-described needs to provide a light emitting diode having a high luminous efficiency using a radial nano-rod structure.

A light emitting diode according to an embodiment of the present invention includes a support substrate; A reflective electrode formed on the support substrate; A first region vertically grown on the reflective electrode and doped with a first type, an active region radially grown from the first region, and a second region radially grown from the active region and doped with a second type; A plurality of nanorods; And a transparent electrode layer surrounding the surface of the nanorod.

An epitaxial layer made of the same material as the first region may be further provided between the reflective electrode and the plurality of nanorods, and an insulating layer may be further provided on an area between the plurality of nanorods on the epitaxial layer. .

The surface of the second region may be roughened.

The end region of the first region may have a shape in which a cross-sectional area perpendicular to the growth direction becomes smaller along the growth direction, and the end region may not be doped.

The light emitting diode according to an embodiment of the present invention comprises a transparent electrode layer; An epitaxial layer provided on the transparent electrode layer; A first region vertically grown on the epitaxial layer and doped with a first type, an active region radially grown from the first region, and a second region radially grown from the active region and doped with a second type A plurality of nanorods; And a metal layer provided to cover the plurality of nanorods as a whole.

An insulating layer may be further provided in an area between the plurality of nanorods on the epi layer.

The surface of the epi layer in contact with the transparent electrode may be roughened.

The end region of the first region may have a shape in which a cross-sectional area perpendicular to the growth direction becomes smaller along the growth direction, and the end region may be an undoped region.

The light emitting diode according to the embodiment of the present invention is advantageous to grow on a heterogeneous substrate by forming a light emitting structure in the form of a nano-rod, and has a low effective refractive index and a high surface area ratio to volume, so that the light extraction efficiency is high. In addition, since the p-i-n structure is radially formed, the light emitting layer for generating light can be increased, and since the injection of current is performed on the surface of the nanorod, the leakage current is small and the series resistance is small.

Hereinafter, exemplary 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 of each element in the drawings may be exaggerated for clarity and convenience of description.

1 is a perspective view showing a schematic structure of a light emitting diode according to an embodiment of the present invention. Referring to the drawings, the light emitting diode 100 includes a support substrate 103, a reflective electrode 106 formed on the support substrate 103, a plurality of nano bars 200 arranged vertically on the reflective electrode 106, The transparent electrode layer 115 surrounding the surface of the nano bar 200 is included. An epitaxial layer 109 may be further provided between the reflective electrode 106 and the plurality of nanorods 200, and the insulating layer 112 may be formed in an area between the nanorods 200 on the epitaxial layer 109. This may be further provided.

The nano-rod 200 has a light emitting structure in the form of pin, for example, to generate and emit light, the pin structure is radially formed, and the generated light is emitted through the surface of the nano-rod 200. It has a structure. A more detailed structure will be described later in the description of FIGS. 2 to 9 illustrating various embodiments.

The first electrode 118 and the second electrode 121 are contact regions for supplying current to the nanorods 200, one region on the transparent electrode layer 115 and one region on the reflective electrode 106, respectively. Is provided. However, this is exemplary and may be variously changed. For example, when the support substrate 103 is a conductive substrate, the second electrode 121 may be provided on one surface of the support substrate 103.

As the support substrate 103, for example, a heavily doped silicon (Si) substrate, a heavily doped germanium (Ge) substrate, a heavily doped compound semiconductor substrate or a metal substrate may be used. In addition, the support substrate 103 may use a conductive metal having good thermal conductivity, such as copper (Cu), to release heat generated from the nanorods ().

The reflective electrode 106 is provided to serve as an electrode and a reflecting plate. That is, a current path for supplying current to the nanorods 200 is formed, and also, the light generated from the nanorods 200 is reflected to the upper portion. The reflective electrode 106 may be formed by, for example, growing ZrN, ZrB 2, TiN, HfN, or the like on the support substrate 103.

The epitaxial layer 109 is provided between the reflective electrode 106 and the nanorods 200, which is not essential to the light emission principle, but is accompanied by a manufacturing process of growing the nanorods 200. For example, an epitaxial layer 109 is formed over the reflective electrode 106, and the nanorods 200 are grown thereon.

The insulating layer 112 is provided in the region between the nano bars 200 on the epi layer 109 and is intended to reduce unnecessary current paths that do not contribute to light generation. Therefore, the thickness is appropriately determined to the extent that the epitaxial layer 109 and the transparent electrode layer 106 can be insulated from each other. As the material of the insulating layer 112, an oxide such as silicon dioxide (SiO ₂ ) or a transparent insulating resin such as a silicone resin or an epoxy resin may be used.

The transparent electrode layer 115 is used to form a current path for supplying current to the nanorods 200 together with the reflective electrode 106. The transparent electrode layer 115 may be formed of a transparent conductive oxide (TCO), for example, may be formed of indium tin oxide (ITO), aluminum zinc oxide (AZO), indium zinc oxide (IZO), or the like. have. Or a thin Ni / Au layer.

Looking at the path of the light is extracted from the light emitting diode 200 according to an embodiment of the present invention as follows. When a current is applied to the nanorods 200 through the first electrode 118 and the second electrode 121, light is generated in the active region of the nanorods 200. Since the light emission in the active region is spontaneous emission, there is no special directivity and thus it is directed in all directions, largely, light emitted through the surface of the nanorod 200 and light toward the bottom of the light emitting diode 100. Can be seen. Among them, the light toward the lower portion of the light emitting diode 100 is reflected by the reflective electrode 206 to be emitted to the upper portion of the light emitting diode 100.

2 to 9 are cross-sectional views illustrating various embodiments 201 to 209 that may be employed as the nanorods 200 of the light emitting diode 100 of FIG. 1.

Referring to the drawings, the nanorod 201 is vertically grown on the epi layer 109 and doped as a first type 210, an active region 220 radially grown from the first region 210. And a second region 230 radially grown from the active region 220 and doped with the second type. For example, the first region 210 may be doped p-type and the second region 230 may be doped n-type, whereas the first region 210 may be doped n-type and the second region doped. 230 may be doped with a p-type. The nanorod 201 is a heterojunction structure using, for example, group III-V binary, ternary, quaternary materials such as GaN / InGaN, ZnO / MgZnO, GaAs / InGaAs, InP, InAs, AlGaInP, and AlGaInAs with a pin structure. Can be formed. For example, when the nanorods 200 are made of GaN-based semiconductor material, the first region 210 is formed of p-Al _x Ga _y In _z N (x + y + z = 1), and the second region 230 is formed. ) May be composed of n-Al _x Ga _y In _z N. The active region 220 may be formed of a single or multiple quantum well structure made by adjusting the band spacing by periodically changing the x, y, z values in Al _x Ga _y In _z N. In addition, when the nano-rod 200 is formed of a ZnO-based semiconductor, the first region 210 is formed of p-Mg _x Zn _y O (x + y = 1), and the second region 230 is n-Mg. _x Zn _y O. In addition, the active region 220 may have a single or multiple quantum well structure formed by controlling a band gap by periodically changing x and y values in Mg _x Zn _y O.

In the manufacturing process, the reflective electrode 106 is formed on the support substrate 103, and then, for example, an epitaxial layer may be formed of the same material as that of the first region 210 corresponding to the core of the nanorod 200. 109 is formed, and the first region 210 is vertically grown on the epitaxial layer 109. For example, VLS (vapor-liquid-solid), hybrid gas phase crystal growth (hydride) using metal nanoparticles such as Fe, Ni, and Au as a growth catalyst, using n-GaN as a growth mode in which axial growth is dominant. growth by vapor phase epitaxy (HVPE), molecular beam crystal growth (MBE), metal organic vapor phase epitaxy (MOVPE), and halogen chemical vapor deposition (HCVD). Subsequently, the multi-quantum well and p-GaN are sequentially grown to form the active region 220 and the second region 230 by switching to a mode in which radial growth is dominant. The multi quantum well (MQW) can be adjusted to emit white light by adjusting the mole fraction and thickness of In.

The shape of the end region of the nanorod 201 grown as described above may vary according to a specific growth method. In the case of using the catalyst, it may be formed flat, or, as shown, the end region of the first region 210 may have a shape in which the cross-sectional area perpendicular to the growth direction is reduced along the growth direction. As such, when the end region has a pyramid shape, current crowding may occur in this portion. In an embodiment of the present invention, in order to prevent such current concentration, the end region of the first region 210 may be formed. It is formed into an undoped region. That is, in the nanorod 202 shown in FIG. 3, when the first region 210 is grown, doping is not performed during the growth of the last end region 212 so that light is not generated in this portion.

In addition, the shape of the remaining regions other than the end region may have a shape in which the cross-sectional area perpendicular to the growth direction is constant along the growth direction, decreases along the growth direction, or increases along the growth direction.

The nanorod 203 shown in FIG. 4 has a shape in which the cross-sectional area of the first region 210 increases along the growth direction, and the end region 212 having a conical shape is formed as an undoped region.

The nano-rod 204 shown in FIG. 5 has a shape in which the cross-sectional area of the first region 210 decreases along the growth direction, and the conical end region 212 is formed as an undoped region.

The nanorods 205 to 208 shown in FIGS. 6 to 9 differ from the embodiments of FIGS. 2 to 5 in that the surface of the second region 230 is composed of a roughened textured surface 230a. have. The texturing surface 230a of the second region 230 is provided in such a manner that light generated in the active region 220 may be emitted without being totally reflected, and is processed through, for example, etching. Although not shown, such texturing may also be performed on the surface of the transparent electrode layer 115 surrounding the nanorods 205 to 208.

10 is a perspective view showing a schematic structure of a light emitting diode 300 according to another embodiment of the present invention. Referring to the drawings, the light emitting diode 300 includes a transparent electrode layer 303, an epitaxial layer 306 provided on the transparent electrode layer 303, and a plurality of nanorods 400 vertically arranged on the epitaxial layer 306. It includes a metal layer 312 is provided to cover the nano bar 400 of the entire. An insulating layer 309 may be further provided in an area between the plurality of nano bars 400 on the epi layer 306.

This embodiment differs from the embodiment of FIG. 1 in that light generated from the nanorod 400 is emitted to the bottom surface of the light emitting diode 300.

With a description of the manufacturing process, looking at the specific configuration as follows. An epi layer 306 is formed on a predetermined growth substrate, not shown, and a plurality of nano bars 400 are grown thereon. The growth process of the nanorod 400 is substantially the same as described in the embodiment of FIG.

Next, an insulating layer 309 is formed in the region between the nano bars 400 on the epi layer 306. The insulating layer 309 is intended to reduce unnecessary current paths that do not contribute to light generation. Therefore, the thickness is appropriately determined to the extent that the epitaxial layer 306 and the metal layer 312 can be insulated. As the material of the insulating layer 309, an oxide such as silicon dioxide (SiO ₂ ) or a transparent insulating resin such as a silicone resin or an epoxy resin may be used.

Next, the metal layer 312 is formed to cover the plurality of nanorods 400. The metal layer 312 is provided to reflect the light emitted from the nano bar 400 to face the bottom surface of the light emitting diode 300. The metal layer 312 may be made of silver (Ag), aluminum (Al), or an alloy including silver or aluminum, for example.

Next, the metal layer 312 is bonded to the support substrate 315. The support substrate 315 may be a conductive substrate, for example, a heavily doped silicon (Si) substrate, a heavily doped germanium (Ge) substrate, a heavily doped compound semiconductor substrate, a metal substrate, or the like. Can be used.

Next, the structure bonded to the support substrate 315 is separated from the growth substrate (not shown) by a laser lift off or chemical lift off method, and the separated surface is roughened by, for example, etching to texturize. It forms in the surface 316a.

Next, the transparent electrode layer 303 is formed on the texturing surface 316a. The transparent electrode layer 303 may be formed of a transparent conductive oxide (TCO) to supply current to the nanorods 400 and transmit light emitted from the nanorods 400. For example, it may be formed of indium tin oxide (ITO), aluminum zinc oxide (AZO), indium zinc oxide (IZO), or the like. Or a thin Ni / Au layer.

Looking at the path of the light is extracted from the light emitting diode 300 according to an embodiment of the present invention as follows. When a current is applied to the nanorods 400 through the metal layer 312 and the transparent electrode layer 303, light is generated in the active region of the nanorods 400. Since the light emission in the active region is spontaneous emission, there is no special directivity, so it is directed in all directions, which is largely viewed as light directed toward the surface of the nanorod 400 and light directed toward the bottom of the light emitting diode 300. Can be. Among these, light directed toward the surface of the nanorod 400 is reflected by the metal layer 312 which is in contact with the surface of the nanorod 400, toward the lower portion of the light emitting diode 300, and emitted through the transparent electrode layer 303. do.

11 to 14 are cross-sectional views illustrating various embodiments 401 to 404 that may be employed as the nanorods 400 of the light emitting diode 300 of FIG. 10.

Referring to the drawings, the nano-rod 401 is vertically grown on the epi layer 306 and doped with a first type 410, the active region 420 radially grown from the first region 410 And a second region 430 radially grown from the active region 420 and doped with a second type. For example, the first region 410 may be doped with p-type and the second region 430 may be doped with n-type, or vice versa. Looking at the manufacturing process, the first region 410 corresponding to the core of the nano-rod 400, for example, n-GaN is grown in a growth mode in which axial growth is dominant, and then radial growth is dominant mode. After the conversion, the multi-quantum wells and p-GaN are sequentially grown to form the active region 420 and the second region 430. The multi quantum well (MQW) can be adjusted to emit white light by adjusting the mole fraction and thickness of In.

The shape of the end region of the nanorods 400 grown as described above may vary according to a specific growth method and may be flat. As shown, the cross-sectional area of the end region of the first region 410 perpendicular to the growth direction is shown. It can become a shape which becomes small according to this growth direction. As such, when the end region 410 has a pyramid shape, current crowding may occur in this portion. In one embodiment of the present invention, in order to prevent such current concentration, the first region 410 may be formed. The end region is formed as an undoped region. In addition, the shape of the remaining region except for the end region is also a shape in which the cross-sectional area perpendicular to the growth direction is constant along the growth direction or decreases along the growth direction.

In the nanorod 402 illustrated in FIG. 12, the cross-sectional area of the first region 410 has a constant shape along the growth direction, and the conical end region 412 is formed as an undoped region.

The nanorod 403 shown in FIG. 13 has a shape in which the cross-sectional area of the first region 410 becomes smaller along the growth direction. This shape is intended to allow the light generated in the nano bar 400 to be well extracted to the lower region.

The nanorod 404 illustrated in FIG. 14 has a shape in which the cross-sectional area of the first region 410 decreases along the growth direction, and the conical end region 412 is formed as an undoped region.

The light emitting diodes 100 and 300 described above have an advantage in that the nanorod structure is adopted, that is, the effective refractive index is low and the volume to surface area ratio is high, so that the light extraction efficiency is high. Further, the light emitting layer in which light is generated is made larger and injection of electric current is made on the surface of the nanorod, which reduces the resistance, and therefore, the luminous efficiency is high.

Such a light emitting diode of the present invention has been described with reference to the embodiment shown in the drawings for clarity, but this is only an example, and those skilled in the art that various modifications and equivalent other embodiments are possible therefrom. I will understand the point. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

1 is a perspective view showing a schematic configuration of a light emitting diode according to an embodiment of the present invention.

2 to 9 are cross-sectional views illustrating various embodiments of nanorods that may be employed in the light emitting diode of FIG. 1.

10 is a perspective view showing a schematic configuration of a light emitting diode according to another embodiment of the present invention.

11 to 14 are cross-sectional views illustrating various embodiments of nanorods that may be employed in the light emitting diode of FIG. 1.

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

100,300 ... Light Emitting Diodes 200 ~ 208, 400 ~ 404 ... Nano Rods

103,315 ... support substrate 109,306 ... epi layer

106 ... reflective electrode 112,309 ... insulating layer

115, 303 ... transparent electrode layer 312 ... metal layer

Claims (14)

Support substrate; A reflective electrode formed on the support substrate; A first region vertically grown on the reflective electrode and doped with a first type, an active region radially grown from the first region, and a second region radially grown from the active region and doped with a second type A plurality of nanorods; And And a transparent electrode layer surrounding the surface of the nanorod. The method of claim 1, A light emitting diode further comprising an epitaxial layer formed of the same material as the first region between the reflective electrode and the plurality of nanorods. The method of claim 2, The light emitting diode further provided with an insulating layer in the region between the plurality of nano-rods on the epi layer. The method of claim 3, The transparent electrode layer is a light emitting diode formed along the surface of the nano-rod and the insulating layer. The method of claim 1, The light emitting diode of which the surface of the second region is roughened. 6. The method according to any one of claims 1 to 5, The end area of the first region has a shape in which the cross-sectional area perpendicular to the growth direction is reduced along the growth direction. The method of claim 6, And the end region is undoped light emitting diode. The method of claim 7, wherein The light emitting diode of the first region, except for the end region, has a shape in which a cross-sectional area perpendicular to the growth direction is constant, becomes smaller, or becomes larger along the growth direction. Transparent electrode layer; An epitaxial layer provided on the transparent electrode layer; A first region vertically grown on the epitaxial layer and doped with a first type, an active region radially grown from the first region, and a second region radially grown from the active region and doped with a second type A plurality of nanorods; And a metal layer formed to cover the plurality of nanorods as a whole. 10. The method of claim 9, The light emitting diode further provided with an insulating layer in the region between the plurality of nano-rods on the epi layer. 10. The method of claim 9, The surface of the light emitting diode is in contact with the transparent electrode is roughened (roughening). The method according to any one of claims 9 to 11, The end area of the first region has a shape in which the cross-sectional area perpendicular to the growth direction is reduced along the growth direction. The method of claim 12, And the end region is undoped light emitting diode. The method of claim 12, The light emitting diode of the first region except for the end region has a shape in which a cross-sectional area perpendicular to the growth direction is constant or smaller in the growth direction.

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