KR20130077600A

KR20130077600A - Nitride based light emitting device with nano rod of zinc oxide and producing method thereof

Info

Publication number: KR20130077600A
Application number: KR1020110146399A
Authority: KR
Inventors: 김극; 송정섭; 이성학
Original assignee: 일진엘이디(주)
Priority date: 2011-12-29
Filing date: 2011-12-29
Publication date: 2013-07-09

Abstract

PURPOSE: A nitride based light emitting device with the nanorods of zinc oxide and a manufacturing method thereof are provided to improve light extraction efficiency by using a scattering effect. CONSTITUTION: A first nitride semiconductor layer includes a first conductive impurity. An active layer (140) is formed on the first nitride semiconductor layer. A second nitride semiconductor layer has a second conductive impurity. A transparent conduction layer (160) has holes. Zinc oxide nanorods (190) are grown in the holes.

Description

Nitride-based light emitting device in which zinc oxide nanorods are produced and a method of manufacturing the same {NITRIDE BASED LIGHT EMITTING DEVICE WITH NANO ROD OF ZINC OXIDE AND PRODUCING METHOD THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor light emitting device having improved light extraction efficiency, and more particularly, to a nitride semiconductor in which zinc oxide nanorods are grown in at least one hole formed in a transparent conductive layer. A light emitting device and a method of manufacturing a nitride semiconductor light emitting device by growing the zinc oxide nanorods.

Conventional nitride semiconductor devices include, for example, GaN-based nitride semiconductor devices, which include high-speed switching and high-output devices such as blue or green LED light emitting devices, MESFETs and HEMTs, etc. It is applied to the back.

Such a conventional GaN-based nitride semiconductor light emitting device may be a nitride semiconductor light emitting device having an active layer of a multi-quantum well structure. Conventional nitride semiconductor light emitting devices include a sapphire substrate, an n-type nitride layer, an active layer and a p-type nitride layer. The transparent electrode layer and the p-side electrode are sequentially formed on the upper surface of the p-type nitride layer, and the n-side electrode is sequentially formed on the exposed surface of the n-type nitride semiconductor layer.

The conventional GaN-based nitride semiconductor light emitting device injects electrons and holes into the active layer and emits light by combining the electrons and holes.

However, in such a nitride semiconductor light emitting device, the luminous efficiency has emerged as an important problem. The luminous efficiency of the semiconductor light emitting device is determined by the light generation efficiency and the external photon efficiency of the light. The biggest problem among them is the external photon efficiency, that is, the efficiency in which the light generated from the active layer is extracted to the outside is low. Will be.

The decisive factor in reducing the external photon efficiency of the nitride semiconductor light emitting device is reflection characteristics at the interface of the light emitting device, in particular, total internal reflection. That is, due to the large difference in refractive index at the LED device interface, only a part of the generated light is extracted out of the device interface, and light that does not exit the interface is totally reflected at the interface, traveling inside the device, and attenuated by heat. As a result, total internal reflection at the LED device interface increases the amount of heat generated by the LED device and reduces the external extraction efficiency of the device.

In order to solve this problem, various external photon efficiency improvement methods have been proposed. For example, there is a method of forming a surface pattern or surface texture on the surface of the light emitting device such that photons reaching the surface are randomly scattered. For example, Korean Patent Laid-Open Publication No. 2005-0003671 discloses a technique of forming an uneven pattern or surface texture at the edge of a light emitting portion of a light emitting device. See also Daisuke Morita et al. Japanese Journal of Applied Physics, Vol. 43, No. 9A, 2004, pp. 5945-5950 discloses a process of forming an uneven pattern on the upper surface of the light emitting portion of the light emitting device using electron beam lithography and dry etching. However, since the uneven pattern is formed on the upper surface of the GaN-based semiconductor layer by wet etching or dry etching the flat upper surface of the GaN-based semiconductor layer, surface roughness due to the uneven pattern may not be uniform and may damage the active layer.

In order to improve other luminous efficiency, various studies such as surface treatment of the substrate and the formation of roughness inside the undoped GaN have been conducted, but the effect is not so high.

Accordingly, the present inventors have conducted research and efforts to develop a nitride semiconductor light emitting device having improved luminous efficiency. As a result, when a zinc oxide-based nanorod is formed in a plurality of patterned holes in a transparent conductive layer, the current is not applied to the formed holes. The present invention was completed by confirming that the density is increased and the light extraction efficiency of the light emitting device can be greatly increased by the scattering effect by the zinc oxide nanorods.

Accordingly, an object of the present invention is to provide a nitride semiconductor light emitting device exhibiting excellent luminous efficiency and a method of manufacturing the same.

The nitride light emitting device of the present invention for achieving the above object comprises a first nitride semiconductor layer doped with a first conductivity type impurities; An active layer formed on the first nitride semiconductor layer; A second nitride semiconductor layer formed on the active layer and doped with a second conductivity type impurity; And a transparent conductive layer formed on the second nitride semiconductor layer and having at least one hole formed therein, and including zinc oxide nanorods grown in the hole.

In addition, the method of manufacturing a nitride light emitting device of the present invention comprises the steps of sequentially forming a first nitride semiconductor layer, an active layer, a second nitride semiconductor layer and a transparent conductive layer on a substrate; Etching the transparent conductive layer to form a hole, and growing zinc oxide nanorods in the formed hole.

In the nitride semiconductor light emitting device of the present invention, since the current is not applied to the portion etched in the transparent conductive layer, the current density is increased, and the extraction efficiency of light formed in the active layer can be greatly improved due to the scattering effect by the zinc oxide nanorods. Can be.

1 is a cross-sectional view of a horizontal nitride semiconductor light emitting device according to a first embodiment of the present invention.
2 is a plan view of a transparent conductive layer 160 of the horizontal nitride semiconductor light emitting device according to the first embodiment of the present invention.
3 is a SEM photograph of zinc oxide nanorods grown in a horizontal nitride semiconductor light emitting device manufactured in an embodiment of the present invention.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, a nitride based light emitting device according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Nitride-based light emitting device

1 is a cross-sectional view of a horizontal nitride semiconductor light emitting device according to a first embodiment of the present invention, and FIG. 2 is a plan view of the horizontal nitride semiconductor light emitting device shown in FIG.

Hereinafter, a horizontal nitride semiconductor light emitting device according to a first exemplary embodiment of the present invention will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the horizontal nitride semiconductor light emitting device 100 according to the first exemplary embodiment of the present invention has a buffer layer 120, an n-type nitride layer 130, and an active layer in an upper direction of the substrate 110. 140, a p-type nitride layer 150, a transparent electrode layer 160, a p-side electrode 170 and an n-side electrode 180 may be included.

The buffer layer 120 may be selectively formed to solve the lattice mismatch between the substrate 110 and the n-type nitride layer 130, and may be formed of, for example, AlN or GaN.

The n-type nitride layer 130 is formed on the upper surface of the substrate 110 or the buffer layer 120, and is formed of nitride to which the n-type dopant is doped. The n-type dopant may be silicon (Si), germanium (Ge), tin (Sn), or the like. Here, the n-type nitride layer 130 is a laminated structure in which a first layer made of n-type AlGaN or undoped AlGaN doped with Si and a second layer made of n-type GaN doped with undoped or Si are formed. Can be. Of course, the n-type nitride layer 130 may be grown as a single n-type nitride layer, but may be formed as a laminated structure of the first layer and the second layer to act as a carrier limiting layer having good crystallinity without cracks. .

The active layer 140 may be formed of a single quantum well structure or a multi-quantum well structure between the n-type nitride layer 130 and the p-type nitride layer 150, and electrons flowing through the n-type nitride layer 130, p As holes flowing through the nitride layer 150 are re-combined, light is generated. Here, the active layer 140 has a multi-quantum well structure, wherein the quantum barrier layer and the quantum well layer are each Al _x Ga _y In _z N (where x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≤ 1, 0 ≤ z ≤ 1). The active layer 140 having a structure in which the quantum barrier layer and the quantum well layer are repeatedly formed may suppress spontaneous polarization due to stress and deformation generated.

The p-type nitride layer 150 is formed by alternately stacking a first layer made of p-type AlGaN or undoped AlGaN doped with Mg, and a second layer made of p-type GaN doped with undoped or Mg. Can be. In addition, the p-type nitride layer 150 may be grown as a single-layer p-type nitride layer similarly to the n-type nitride layer 130, but may be formed as a laminated structure to act as a carrier-limiting layer having good crystallinity without cracks. have.

The transparent electrode layer 160 is a layer provided on the upper surface of the p-type nitride layer 150, the transparent electrode layer 160 is made of a transparent conductive oxide, the material is In, Sn, Al, Zn, Ga, etc. Element, and may be formed of any one of, for example, ITO, CIO, ZnO, NiO, and In ₂ O ₃ .

Next, a hole is formed in the transparent electrode layer 160, and zinc oxide nanorods 190 (ZnO nanorods) are grown in the hole.

Zinc oxide nanorods as used herein refers to a rod-shaped material having a diameter of several nm to several tens of μm, and preferably may be formed of 1 nm to 10 μm.

The hole formed in the transparent electrode layer 160 may be formed as a photoresist pattern having a plurality of holes, but is not limited thereto. In addition, the hole is formed through the transparent electrode layer to expose a portion of the p-type nitride layer 150, in this case, the zinc oxide nano rod 190 may be formed in direct contact with the p-type nitride layer.

In addition, the zinc oxide nanorods 190 are formed sharply in a form in which the thickness thereof gradually decreases upwards, and the height of the zinc oxide nanorods 190 is 1.0 to 3.0 times the thickness of the transparent conductive layer, more preferably 1.5. It is preferred to be formed at ˜2.5 times. If the height of the zinc oxide nanorod 190 is less than the above range, the scattering effect by the zinc oxide nanorod 190 does not appear sufficiently, so the brightness is not greatly improved, and the height of the zinc oxide nanorod 190 is within the above range. When formed in excess, the end portion of the zinc oxide nano rod 190 may be broken so that light may not escape to the outside due to total reflection.

On the other hand, the cross-sectional shape of the hole is preferably circular or rectangular, and it is preferable that the ratio A / B of the total area A of the hole to the cross-sectional area B of the transparent conductive layer is in the range of 0.05 to 0.5.

Meanwhile, about 1 to 5 zinc oxide nanorods 190 may be formed in each hole formed in the transparent conductive layer, and preferably, 2 to 3 zinc oxide nanorods 190 may be formed.

Manufacturing method of nitride based light emitting device

Hereinafter, a method of manufacturing the nitride semiconductor light emitting device 100 according to the first embodiment of the present invention is specifically described below.

In the method of manufacturing the nitride semiconductor light emitting device 100 according to the first embodiment of the present invention, first, the buffer layer 120 and the n-type nitride layer 130 are sequentially formed on the upper surface of the substrate 110.

The buffer layer 120 may be selectively formed on the upper surface of the substrate 110 to eliminate the lattice mismatch between the substrate 110 and the n-type nitride layer 130. Here, the buffer layer 120 may be formed using, for example, AlN or GaN.

The n-type nitride layer 130 may be formed of an n-GaN layer. For example, the n-type nitride layer 130 may be formed by supplying a silane gas including an n-type dopant such as NH ₃ , trimetalgallium (TMG), and Si, thereby converting the n-GaN layer into an n-type nitride layer. Can grow.

Next, the active layer 140 may be provided as a single quantum well structure or a multi quantum well structure in which a plurality of quantum well layers and a quantum barrier layer are alternately stacked. Here, the active layer 140 is made of a multi-quantum well structure, the quantum barrier layer and the quantum well layer is Al _x Ga _y In _z N (where x + y + z = 1, 0≤x≤1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1).

The p-type nitride layer 150 may be formed, for example, by alternately stacking a first layer of p-type AlGaN doped with Mg and a second layer of p-type GaN doped with Mg. In addition, the p-type nitride layer 150 can be grown into a single-layer p-type nitride layer similarly to the n-type nitride layer 130.

The transparent electrode layer 160 is formed on the upper surface of the p-type nitride layer 150. The transparent electrode layer 160 is made of a transparent conductive oxide, the material of which includes elements such as In, Sn, Al, Zn, Ga, for example, ITO, CIO, ZnO, NiO, In ₂ O ₃ Can be formed.

After forming the transparent electrode layer 160 as described above, one region of the n-type nitride layer 130 may be exposed by lithography etching from the transparent electrode layer 160 to one region of the n-type nitride layer 130. .

When one region of the n-type nitride layer 130 is exposed, the n-side electrode 180 may be formed in one region of the n-type nitride layer 130 exposed. The p-side electrode 170 may be formed on an upper surface of the transparent electrode layer 160.

Next, the transparent conductive layer is etched to form a hole, and the hole may be formed as a photoresist pattern, and the pattern may be formed by nanoimprint lithography, laser interference lithography, electron beam lithography, ultraviolet lithography, or holographic methods. Lithography or liquid immersion lithography may be used, but is not limited thereto. In this case, the hole is preferably formed through the transparent conductive layer through the transparent electrode layer.

The zinc oxide (ZnO) nanorods are grown in the formed holes, and the zinc oxide nanorods may be formed by hydrothermal synthesis. More specifically, the zinc oxide nanorods grow in the pores by immersing and heating the device having a hole in the transparent conductive layer in a culture solution containing zinc salt and a precipitant.

The generation mechanism of the nanorods is as follows. The zinc salt produces zinc ions and the precipitant provides NH ⁴ ⁺ and OH ⁻ . In addition, NH ⁴ ⁺ and OH ⁻ react to form NH ₃ , and NH ₃ , OH ^−, and Zn ² ⁺ react with each other to form Zn (NH ₃ ) ₄ ²⁺ and Zn (OH, corresponding to growth factors of the zinc oxide nanorods. ) ₄ ^2- can be generated.

The growth factors Zn (NH ₃ ) ₄ ²⁺ and Zn (OH) ₄ ^2- generate zinc oxide nanorods according to Schemes 1 and 2, respectively.

[Reaction Scheme 1]

_{^{Zn (NH 3) 4 2+ +}} 2OH - → ZnO + 4 NH 3 + H ₂ O

[Reaction Scheme 2]

_{^{Zn (OH) 4 2- → ZnO}} + H 2 O + 2OH -

Meanwhile, OH ⁻ contained in the culture solution may corrode zinc oxide to generate a Zn (OH) ₂ corrosive as shown in Scheme 3 below. Is generated.

The zinc salt is selected from zinc nitrate, zinc acetate, zinc oxide, zinc oxide, zinc chloride, zinc sulfate, and zinc hydroxide. One or more compounds may be used, preferably zinc nitrate. In addition, the precipitant may be used at least one compound selected from diethylenetriamine, hexamethylenetetraamine, NH ₄ OH, NaOH and KOH, preferably diethylenetriamine, NH ₄ OH.

In addition, the precipitant is preferably used in a ratio of 0.1 to 10 moles with respect to 1 mole of zinc salt, and more preferably may be used in a ratio of 0.5 to 5 moles, but is not limited thereto. By adjusting the height, thickness, etc. of the nanorods can be adjusted.

Ion is low ^- the other hand it is preferred that pH is adjusted to 7.5 ~ 10 range of the culture solution, pH will not exceed 10, and may result in damage to the zinc nanorods oxidation due to the widow formula, pH is equal OH is less than 7.5 There is a problem that the formation of the nanorod is not well made.

The hydrothermal reaction is made by applying the reaction heat, it can be made in the temperature range of 60 ~ 120 ℃ at atmospheric pressure, it is preferable to proceed for 1 to 2 hours.

Hereinafter, the nitride semiconductor light emitting device of the present invention will be described in more detail with reference to the following Preparation Examples of the present invention.

Example : ZnO Nano rod formed GaN Manufacture of nitride light emitting device

GaN was applied to each layer for forming the nitride-based light emitting device as shown in FIG. 1, and the transparent conductive layer was formed of indium tin oxide (ITO). A photoresist pattern having a plurality of holes (diameter about 1 nm to 10 μm) in the transparent conductive layer was formed by using nanoimprinting.

Next, while keeping the temperature of the thermostat at 70 ° C, 0.025 mol of Zn (NO ₃ ) ₂ .6H ₂ O and 0.025 mol of diethylenetriamine were added to water to prepare a culture solution (pH 9.0).

A device having a transparent conductive layer having a hole formed in the culture solution was immersed and reacted at 90 ° C. for 2 hours to grow zinc oxide nanorods.

The SEM photograph of the grown zinc oxide nanorods is shown in FIG. 3, and as shown in the SEM photographs, it was confirmed that the zinc oxide nanorods were formed at about 2.0 times the thickness of the ITO layer.

Experimental Example : Comparison of Luminous Efficiency

The light emission output in the upper direction was measured at 20 mA, and a light emitting device without growing zinc oxide nanorods was used as a comparative example in order to compare the light emitting efficiency of the light emitting device of the above embodiment. The measurement results are shown in Table 1 below.

Po (mW) Example 196 mW Comparative example 185 mW

As shown in Table 1, the light emitting device of the example in which the zinc oxide nanorods were formed in the transparent conductive layer was confirmed to have improved light output characteristics by about 6% or more as compared with the comparative example.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. . Accordingly, the true scope of the present invention should be determined by the following claims.

100 semiconductor light emitting device 110 substrate
120: buffer layer 130: n-type nitride layer
140: active layer 150: p-type nitride layer
160: transparent electrode layer 170: p-side electrode
180: n-side electrode 190: zinc oxide nano rod

Claims

A first nitride semiconductor layer doped with a first conductivity type impurity;
An active layer formed on the first nitride semiconductor layer;
A second nitride semiconductor layer formed on the active layer and doped with a second conductivity type impurity; And
A transparent conductive layer formed on the second nitride semiconductor layer and having at least one hole formed therein;
A nitride semiconductor light emitting device comprising a zinc oxide nanorod (ZnO nanorod) grown in the hole.

The method of claim 1,
The height of the zinc oxide nanorods is a nitride semiconductor light emitting device, characterized in that 1.0 to 3.0 times the thickness of the transparent conductive layer.

The method of claim 1,
The hole penetrates the transparent conductive layer and exposes a part of the second nitride semiconductor layer.

The method of claim 1,
And a ratio (A / B) of the total hole area A to the cross-sectional area B of the transparent conductive layer is in the range of 0.05 to 0.5.

Sequentially forming a first nitride semiconductor layer, an active layer, a second nitride semiconductor layer, and a transparent conductive layer on the substrate;
Etching the transparent conductive layer to form holes; and
A method of manufacturing a nitride semiconductor light emitting device comprising growing a zinc oxide nanorod (ZnO nanorod) in the hole.

The method of claim 5, wherein
The zinc oxide nanorods are grown by hydrothermal synthesis method.

The method according to claim 6,
A method for manufacturing a nitride light emitting device comprising growing a zinc oxide-based nanorod in a hole by dipping a device having a hole in a transparent conductive layer in a culture solution containing a zinc salt and a precipitant.

The method of claim 7, wherein
The zinc salt is selected from zinc nitrate, zinc acetate, zinc oxide, zinc oxide, zinc chloride, zinc sulfate, and zinc hydroxide. A method for producing a nitride light emitting device, characterized in that at least one compound.

The method of claim 7, wherein
The precipitant is a method of manufacturing a nitride light emitting device, characterized in that at least one compound selected from diethylenetriamine, hexamethylenetetraamine, NH ₄ OH, NaOH and KOH.

The method of claim 7, wherein
PH of the culture solution is a manufacturing method of the nitride light emitting device, characterized in that in the range of 7.5 ~ 10.