KR20070027327A - Light emitting diode of vertical electrode type and fabricating method thereof - Google Patents

Abstract

A vertical type light emitting diode and its manufacturing method are provided to promote a flow of a current and to lower an operation voltage by using a vertical type electrode structure. An ohmic layer(110) is formed on a conductive supporting layer(100). A super lattice layer(120) is formed on the ohmic layer. A p-type nitride semiconductor layer(130) is formed on the super lattice layer. An electron blocking layer(140) is formed on the p-type nitride semiconductor layer. An active layer(150) is formed on the electron blocking layer. A current diffusion layer(160) is formed on the active layer to spread an implanted electron to a horizontal direction of the active layer. An n-type nitride semiconductor layer(170) is formed on the current diffusion layer. An n-electrode(180) is formed on the n-type nitride semiconductor layer.

Description

Light emitting diode of vertical electrode type and fabricating method

1 is a cross-sectional view of a conventional nitride based light emitting diode.

2 is a cross-sectional view showing an embodiment of a vertical light emitting diode of the present invention.

3A to 3D are cross-sectional views showing an embodiment of a method of manufacturing a vertical light emitting diode of the present invention.

Explanation of symbols on the main parts of the drawings

100: conductive support film 110: ohmic layer

120: superlattice layer 130: p-type nitride semiconductor layer

140: electron blocking layer 150: active layer

160: current diffusion layer 170: n-type nitride semiconductor layer

180: n-electrode

The present invention relates to a light emitting device, and more particularly, to a vertical light emitting diode and a method of manufacturing the same.

In general, a light emitting diode (LED) is a kind of semiconductor device that transmits and receives a signal by converting electricity into infrared rays or light using characteristics of a compound semiconductor.

The light emitting diode generates energy with high efficiency at low voltage, so it is very energy-saving.In recent years, the luminance problem, which was the limitation of the light emitting diode, has been greatly improved, and the entire industry including a backlight unit, an electronic board, an indicator, a home appliance, and various automation devices It is used throughout.

Particularly, gallium nitride (GaN) -based light emitting diodes have a broad emission spectrum ranging from ultraviolet rays to infrared rays and are environmentally friendly since they do not contain environmentally harmful substances such as arsenic (As) and mercury (Hg). I get a high response.

1 is a cross-sectional view of a conventional nitride based light emitting diode. As shown therein, the undoped GaN layer 11, n-GaN layer 12, active layer 13, and electron blocking layer (EBL) on the sapphire (Al ₂ O ₃ ) substrate 10. 14, the p-GaN layer 15 is sequentially formed,

Mesa is etched from the p-GaN layer 15 to a portion of the n-GaN layer 12, and the transparent electrode 16 and the p-electrode 17 are disposed on the p-GaN layer 15. The m-electrodes 18 are sequentially formed on the mesa-etched n-GaN layer 12.

In the conventional nitride-based light emitting diode configured as described above, the voltage is applied from the n-GaN layer 12 and the p-GaN layer 15 by applying a voltage through the p-electrode 17 and the n-electrode 18. Electrons and holes are injected to emit light while electron-hole recombination occurs in the active layer 13.

Here, the electron blocking layer 14 is made of p-AlGaN, and serves as a potential barrier to prevent electrons injected from the n-GaN layer 12 from moving to the p-GaN layer 15.

In addition, the transparent electrode 16 formed below the p-electrode 17 serves to diffuse current into an area where the p-electrode 17 is not formed.

In other words, the recombination of the electron-hole occurs most actively underneath the electrode where the current flows the most, and since the conventional electrode shields light, light generated directly under the electrode hardly transmits to the outside.

Thus, there is a need for a transparent electrode 16 that diffuses current and allows light to pass through. Here, Ni / Au or ITO (Indium-Tin Oxide) may be used as the transparent electrode 16.

In the conventional GaN-based light emitting diode, since the sapphire, which is an insulating material, is used as the substrate, the p-electrode 17 and the n-electrode 18 must be formed in a substantially horizontal direction, and the n-electrode is applied when a voltage is applied. The current flow from 18 to the p-electrode 17 through the active layer 13 is inevitably formed narrowly along the horizontal direction. Due to this narrow current flow, the light emitting diode has an increased operating voltage and thus lowers current efficiency.

In addition, in the conventional GaN-based light emitting diode, in order to form the n-electrode 18, the area of the active layer 13 must be removed at least wider than the area of the n-electrode 18, so that the emission area is increased. There is a problem in that the luminous efficiency decreases according to the luminance compared to the device size.

In addition, the conventional GaN-based light emitting diode has a large amount of heat generated by an increase in current density, whereas the sapphire substrate 10 has low thermal conductivity, and thus heat emission is not smoothly performed. ) And the GaN-based light emitting structure has a problem that the device is unstable due to the mechanical stress.

Accordingly, an object of the present invention is to remove the sapphire substrate from the conventional light emitting diode and to have electrodes on the upper and lower portions of the light emitting structure, so that the current flows in the vertical direction in the light emitting diode so that the current efficiency and the light efficiency and the heat emission efficiency The present invention provides a vertical light emitting diode and a method of manufacturing the same.

Another object of the present invention is to include a superlattice layer and a current diffusion layer in the light emitting diode to facilitate the injection of holes due to the tunneling effect, to improve the side electron mobility through the potential barrier to reduce the operating voltage and improve the light efficiency The present invention provides a vertical light emitting diode and a method of manufacturing the same.

An embodiment of the vertical light emitting diode of the present invention includes an ohmic layer formed on a conductive support film, a superlattice layer formed on the ohmic layer, a p-type nitride semiconductor layer formed on the superlattice layer, and the p-type nitride semiconductor layer. An electron blocking layer formed thereon, an active layer formed on the electron blocking layer, a current spreading layer spreading the electrons formed on the active layer in a horizontal direction of the active layer, an n-type nitride semiconductor layer formed on the current spreading layer, And an n-electrode formed on the n-type nitride semiconductor layer.

In the embodiment of the manufacturing method of the vertical light emitting diode of the present invention, an n-type nitride semiconductor layer, a current diffusion layer, an active layer, an electron blocking layer, a p-type nitride semiconductor layer, a superlattice layer, an ohmic layer, and a conductive support film are sequentially formed on the substrate. Forming an n-electrode under the n-type nitride semiconductor layer separated from the substrate by separating the substrate from the n-type nitride semiconductor layer by performing a laser lift-off process; Characterized in that made.

Hereinafter, a vertical light emitting diode of the present invention and a manufacturing method thereof will be described in detail with reference to FIGS. 2 to 3. 2 is a cross-sectional view showing an embodiment of a vertical light emitting diode of the present invention.

As shown here, the ohmic layer 110 formed on the conductive support layer 100, the superlattice layer 120 formed on the ohmic layer 110, and the p-type nitride semiconductor layer formed on the superlattice layer 120 ( 130, an electron blocking layer 140 formed on the p-type nitride semiconductor layer 130, an active layer 150 formed on the electron blocking layer 140, a current diffusion layer 160 formed on the active layer 150, and the current And an n-type nitride semiconductor layer 160 formed on the diffusion layer 160 and an n-electrode 180 formed on the n-type nitride semiconductor layer 170.

Here, since the conductive support film 100 serves as a p-electrode, it is preferable to use a metal having excellent electrical conductivity.

In addition, since the heat generated during the operation of the device should be able to be sufficiently dissipated, a metal having high thermal conductivity is used, and the scribing process and the braking may be performed without bringing warp to the entire wafer when forming the conductive support layer 100. Breaking process requires a certain degree of mechanical strength to separate well into separate chips.

Accordingly, the conductive support layer 100 may include a soft metal having good thermal conductivity, such as gold (Au), copper (Cu), silver (Ag), and aluminum (Al), and crystal structures and crystal lattice constants of the metals. Similarly, it is preferable to form an alloy of light metal such as nickel (Ni), cobalt (Co), platinum (Pt), and palladium (Pd) having mechanical strength while minimizing the generation of internal stress in the alloy.

An ohmic layer 110 is formed on the conductive support layer 100. The ohmic layer 110 is formed of a metal thin film of nickel (Ni) / gold (Au). Heat treatment in an oxygen atmosphere forms ohmic contacts having a specific contact resistance of about 10 ⁻³ to 10 ⁻⁴ Ωcm ² .

In the case of using a metal thin film of nickel (Ni) / gold (Au) as the ohmic layer 110, since a high reflectance may effectively reflect light emitted from the active layer 150, a separate reflector is formed. The advantage is that you can get the reflection effect even if you do not.

A supra-lattice layer 120 is formed on the ohmic layer 110, and the superlattice layer 120 is further formed on the active layer 150 of the light emitting diode using a tunneling effect. It is to be able to inject holes.

The superlattice structure refers to a structure in which the spatial variation of the semiconductor energy band gap has one-dimensionality or two-dimensional periodicity larger than the lattice constant of the constituent material.

The superlattice structure is similar to the Multi-Quantum-Well (MQW) in structure, but has a distinguishable characteristic from the multi-quantum well. If multiple quantum wells have characteristics such as an array of single quantum wells almost neglecting the interaction between the wells, the superlattice structure is a structure in which the tunneling effect between the wells is important. It mainly determines the role of superlattice structure in semiconductor devices.

Here, the tunneling effect refers to a phenomenon in which electrons or holes that are separated and bound to adjacent wells have little interaction with each other, and these particles easily move to adjacent wells as the barrier becomes thinner.

In the superlattice structure, not only the thickness of the barrier but also the thickness of the well or the barrier composition ratio may affect the tunneling effect.

In the present invention, when considering the maximization of the tunneling effect of the superlattice layer 120, preferably composed of a short period superlattice (Short Period Superlattice) having a period of 10 10 or less, the thickness of the superlattice layer 120 It is preferable to set it as 10-100 Hz.

The superlattice layer 120 is formed by periodically laminating InGaN and GaN, and in order to lower contact resistance, the InGaN and GaN layers are N + doped with a silicon concentration of 1 × 10 ¹⁸ / cm ³ or more. Preferably 1 x 10 ¹⁸ / cm ³ Doping to an impurity concentration of ˜1 × 10 ²⁰ / cm ³ .

In order to form the superlattice layer 120, in addition to InGaN, it is also possible to form a stacked structure with GaN using another known compound semiconductor such as AlGaN or AsGaN.

The p-type nitride semiconductor layer 130 is formed on the superlattice layer 120, and the p-type nitride semiconductor layer 130 has an Al _x In _y Ga _(1-xy) N composition formula, where 0 ≦ x ≦ 1 , 0 ≦ y ≦ 1, 0 ≦ 1-xy ≦ 1), and p-doped. In particular, p-GaN is mainly used as the p-type nitride semiconductor layer 130.

An electron blocking layer (EBL) 140 is formed on the p-type nitride semiconductor layer 130, and the electron blocking layer 140 is formed of p-Al _x GaN (0 <x≤1). . In the case of the electron blocking layer 140, the composition of Al is 10 to 20%, it is preferable to have a thickness of 10 to 100 nm.

The electron blocking layer 140 serves as a potential barrier to prevent electrons injected from the n-type nitride semiconductor layer 160 from moving to the p-type nitride semiconductor layer 130.

The electron blocking layer 140 causes electrons injected from the n-type nitride semiconductor layer 160 to remain in the active layer 150, thereby recombining electron-holes in the active layer 150, thereby emitting light. It is possible to improve the light efficiency of the diode.

An active layer 150 having a quantum well structure is formed on the electron blocking layer 140, and a current spreading layer 160 is formed on the active layer 150, and the current spreading layer 160 is n-Al _x GaN. (0 <x≤1).

The current diffusion layer 160 is injected from the n-electrode 180 to act as a potential barrier to the electrons directed to the active layer 150 to prevent the electrons from being injected directly in the direction perpendicular to the active layer 150. It spreads sufficiently in the horizontal direction to the active layer 150 to be uniformly injected.

In other words, the current diffusion layer 160 improves the lateral electron mobility of electrons injected from the n-electrode 180 so that the current is uniformly spread and injected into the active layer 150, thereby reducing the light output of the light emitting diode. Can be improved.

For example, when the current diffusion layer 160 is absent, electrons injected from the n-electrode 180 are injected only into an area corresponding to a lower portion of the n-electrode 180 in the active layer 150. Since electrons injected only into a region corresponding to the lower portion of the n-electrode 180 by the current diffusion layer 160 meet a kind of potential barrier, they spread in a horizontal direction on the active layer 150, and have a constant level of electron density. In this case, since electrons are injected into the active layer 150 across the potential barrier, electrons are uniformly injected over the entire area of the active layer 150.

An n-type nitride semiconductor layer 170 is formed on the current spreading layer 160. The n-type nitride semiconductor layer 170, like the p-type nitride semiconductor layer 130, is made of Al _x In _y Ga _{(1- 1). xy)} consisting of a nitride semiconductor material having an N composition formula, where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ 1- _xy ≦ 1, and n-doped. In particular, n-GaN is mainly used for the n-type nitride semiconductor layer 170.

An n-electrode 180 is formed on the n-type nitride semiconductor layer 170, and a transparent electrode (not shown) is further included between the n-type nitride semiconductor layer 170 and the n-electrode 180. Can be formed.

The recombination of electron-holes in the active layer 150 occurs most actively underneath the electrode where the current flows most, and since the light shields the light, the light generated directly under the electrode hardly transmits to the outside. I can't.

Therefore, there is a need for a transparent electrode to diffuse current and transmit light. Here, Ni / Au or ITO (Indium-Tin Oxide) may be used as the transparent electrode.

As described above, according to the present invention, a vertical electrode structure is formed by providing electrodes on the upper and lower portions of the light emitting diode, thereby smoothing the flow of current, lowering the operating voltage of the device, and conducting a material having excellent thermal conductivity. By using it as a supporting film, problems caused by heat dissipation can be solved.

In addition, by forming the N + doped superlattice layer, it is possible to improve the injection of holes due to the tunneling effect, and to prevent the electrons injected from the n-electrode through the electron blocking layer from moving to the p-type nitride semiconductor. By activating the recombination of electrons and holes in the electron and uniformly injecting electrons into the active layer through the current diffusion layer, it is possible to increase the recombination efficiency of electron-holes in the active layer, thereby improving the light efficiency.

3A to 3D are cross-sectional views showing an embodiment of a method of manufacturing a vertical light emitting diode of the present invention. As shown in the drawing, first, the n-type nitride semiconductor layer 210, the current diffusion layer 220, the active layer 230, the electron blocking layer 240, the p-type nitride semiconductor layer 250, and the superlattice on the substrate 200. The light emitting structure is formed by sequentially stacking the layer 260 and the ohmic layer 270 (FIG. 3A).

Here, the substrate 200 uses sapphire (Al ₂ O ₃ ), silicon carbide (SiC) or the like. In particular, a sapphire substrate is typically used because the crystal structure of the nitride semiconductor material grown on the substrate 200 is the same and there is no commercial substrate that forms a lattice match.

The n-type nitride semiconductor layer 210, the current diffusion layer 220, the active layer 230, the electron blocking layer 240, and the p-type nitride semiconductor layer 250 are sequentially formed on the substrate 200.

In this case, before forming the n-type nitride semiconductor layer 210 on the substrate 200, to overcome the difference between the lattice constant and the coefficient of thermal expansion between the substrate 200 and the n-type nitride semiconductor layer 210. In order to form the undoped GaN layer, the crystallinity of the n-type nitride semiconductor layer 210 can be improved.

The current diffusion layer 220 is formed of n-Al _x GaN (0 <x≤1), and the electron blocking layer 240 is formed of p-Al _x GaN (0 <x≤1). In addition, in the electron blocking layer 240, Al has a composition of 10 to 20% and is formed to have a thickness of 10 to 100 nm.

InGaN and GaN are periodically stacked on the p-type nitride semiconductor layer 250, and a short-period superlattice layer 260 having a thickness of 10 to 100 μs is formed.

The superlattice layer 260 is N + doped with a silicon doping concentration of 1 x 10 ¹⁸ / cm ³ or more, but 1 x 10 ¹⁸ / cm ³ Preference is given to doping at ˜1 × 10 ²⁰ / cm ³ .

In addition, the superlattice layer 260 is preferably formed in a nitrogen atmosphere in order to have excellent conductivity and crystallinity.

On the superlattice layer 260, an ohmic layer 270 made of a metal thin film of nickel (Ni) / gold (Au) is formed. The metal thin film based on the nickel is heat-treated in an oxygen atmosphere so that 10 ^-3 to 10 ^It forms an ohmic contact with a specific contact resistance of about ^-4 Ωcm ² .

In the case of using the metal thin film of nickel (Ni) / gold (Au) as the ohmic layer 270, since the reflectance is high, the light emitted from the active layer 230 can be effectively reflected, so that a separate reflective film is not required. The advantage is that the reflection effect can be obtained.

Next, a conductive support film 280 is formed on the ohmic layer 270 (FIG. 3B). Here, the conductive support layer 280 is used as a p-electrode, and titanium (Ti) / gold (Au), nickel (Ni) / gold (Au), platinum (Pt) / gold (Au), nickel (Ni ) / Aluminum (Al) or the like, and is formed of an alloy of light metals such as titanium (Ti), nickel (Ni), platinum (Pt), and soft metals such as gold (Au) and aluminum (Al).

Subsequently, a laser lift off (LLO) process is performed to separate the substrate 200 from the light emitting structure (FIG. 3C).

That is, when focusing and irradiating excimer laser light having a wavelength of a predetermined region on the substrate 200, thermal energy is applied to an interface between the substrate 200 and the n-type nitride semiconductor layer 210 of the light emitting structure. As the interface of the n-type nitride semiconductor layer 210 is concentrated and separated into gallium and nitrogen molecules, separation of the substrate 200 occurs instantaneously at a portion where the laser light passes.

After performing the laser lift-off process, the rough surface of the lower portion of the n-type nitride semiconductor layer 210 may be polished by an ICP / RIE (Inductively Coupled Plasma / Reactive Ion Etching) method.

Thereafter, an n-electrode 290 is formed under the n-type nitride semiconductor layer 210 where the substrate is separated and exposed (FIG. 3D). In this case, in order to increase the light efficiency of the light emitting diode, a transparent electrode may be formed on the n-type nitride semiconductor layer 210, and then an n-electrode 290 may be formed.

On the other hand, while the present invention has been shown and described with respect to specific preferred embodiments, various modifications and variations of the present invention without departing from the spirit or field of the invention provided by the claims below It will be readily apparent to one of ordinary skill in the art that it can be used.

According to the present invention, a vertical electrode structure is formed by providing electrodes on the top and bottom of the light emitting diode, respectively, so that the current flows smoothly, the operating voltage of the device can be reduced, and a material having excellent thermal conductivity is formed of a conductive support film. By using it, problems caused by heat dissipation can be solved.

In addition, by forming the N + doped superlattice layer, it is possible to improve the injection of holes due to the tunneling effect, and to prevent the electrons injected from the n-electrode through the electron blocking layer from moving to the p-type nitride semiconductor. By activating the recombination of electrons and holes in the carrier and uniformly injecting carriers into the active layer through the current diffusion layer, it is possible to increase the recombination efficiency of electron-holes in the active layer, thereby improving the light efficiency of the light emitting diode.

Claims (11)

An ohmic layer formed on the conductive support film; A superlattice layer formed on the ohmic layer; A p-type nitride semiconductor layer formed on the superlattice layer; An electron blocking layer formed on the p-type nitride semiconductor layer; An active layer formed on the electron blocking layer; A current diffusion layer formed on the active layer to spread the injected electrons in a horizontal direction of the active layer; An n-type nitride semiconductor layer formed on the current spreading layer; And And a n-electrode formed on the n-type nitride semiconductor layer. The method of claim 1, wherein the conductive support film is any one selected from gold (Au), copper (Cu), silver (Ag), and aluminum (Al), and nickel (Ni), cobalt (Co), and platinum (Pt). And an alloy of any one metal selected from palladium (Pd). The vertical type light emitting diode of claim 1, wherein the ohmic layer is formed of a metal thin film of nickel (Ni) / gold (Au). The vertical light emitting diode of claim 1, wherein the superlattice layer has a thickness of about 10 to about 100 microns. The vertical light emitting diode of claim 1, wherein the superlattice layer is formed by periodically stacking InGaN and GaN. The method of claim 1, wherein the superlattice layer is silicon 1 x 10 ¹⁸ / cm ³ A vertical type light emitting diode, which is doped at a concentration of ˜1 × 10 ²⁰ / cm ³ . The vertical light emitting diode of claim 1, wherein the electron blocking layer is formed of p-Al _x GaN (0 <x≤1) and has a thickness of 10 to 100 nm. The vertical type light emitting diode of claim 7, wherein the Al blocking composition has 10 to 20% of the electron blocking layer. The vertical light emitting diode of claim 1, wherein the current spreading layer is formed of n-Al _x GaN (0 &lt; x _{≤ 1} ). Sequentially forming an n-type nitride semiconductor layer, a current diffusion layer, an active layer, an electron blocking layer, a p-type nitride semiconductor layer, a superlattice layer, an ohmic layer, and a conductive support layer on the substrate; Separating the substrate from the n-type nitride semiconductor layer by performing a laser lift off process; And And forming an n-electrode under the n-type nitride semiconductor layer exposed by separating the substrate. 12. The method of claim 10, further comprising polishing the surface of the lower portion of the n-type nitride semiconductor layer by ICP / RIE (Inductively Coupled Plasma / Reactive Ion Etching) before forming the n-electrode. Method of manufacturing a vertical light emitting diode.

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