KR20060000464A - Nitride semiconductor light emitting diode having substrate on which rising portions are formed - Google Patents

Abstract

According to the present invention, a nitride semiconductor having a predetermined pattern of protrusions formed on an upper surface of a substrate for growing a nitride semiconductor material and reflecting light emitted toward the substrate toward the light exit surface can extract more light to the outside to improve luminance characteristics. It relates to a light emitting device. The present invention includes a substrate formed on the upper surface of the plurality of protrusions extending from one side to the other side of the upper surface; An n-type nitride semiconductor layer formed on the substrate; An active layer formed on the n-type nitride semiconductor layer; A p-type nitride semiconductor layer formed on the active layer; And an electrode formed on the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, respectively. According to the present invention, the luminance of the nitride semiconductor light emitting device can be improved, and the crystallinity of the nitride semiconductor layer grown on the substrate can be improved.

Substrate, Sapphire, Projection, Nitride Semiconductor Light Emitting Device (LED), Luminance, Crystallinity

Description

NITRIDE SEMICONDUCTOR LIGHT EMITTING DIODE HAVING SUBSTRATE ON WHICH RISING PORTIONS ARE FORMED}             

1 is a cross-sectional view of a conventional nitride semiconductor light emitting device.

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

3 is a perspective view of a substrate used in the nitride semiconductor light emitting device according to the embodiment of the present invention.

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

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

6A and 6B are graphs comparing the light output and the EL intensity of the nitride semiconductor light emitting device according to the present invention and the conventional nitride semiconductor light emitting device.

7A to 7C are graphs showing X-ray analysis results of GaN layers grown on a conventional substrate and GaN layers grown on a substrate according to the present invention.

* Description of the symbols for the main parts of the drawings *

21, 31, 41, 51: substrate 22: n-type nitride semiconductor layer

23 active layer 24 p-type nitride semiconductor layer

25: transparent electrode layer 26a, 26b: n-type, p-type bonding electrode

311, 411, 511: protrusion 311a, 411a, 511a: contact surface

311b, 411b, 511b: vertical plane 311c, 411c, 511c: inclined plane

The present invention relates to a nitride semiconductor light emitting device. More specifically, a nitride having a predetermined pattern on the upper surface of the substrate for growing the nitride semiconductor material to reflect the light emitted toward the substrate toward the light exit surface to extract more light to the outside to improve the luminance characteristics It relates to a semiconductor light emitting device.

In recent years, semiconductor light emitting devices, such as light emitting diodes, can generate light in the green, blue, and ultraviolet regions, and are widely applied to fields such as full color display boards and lighting devices as their brightness is dramatically improved due to continuous technological developments. It is becoming. In particular, nitride semiconductors using nitrides such as GaN have been spotlighted as core materials of optoelectronic materials and electronic devices due to their excellent physical and chemical properties.

Such a nitride semiconductor light emitting device is a light emitting device for obtaining light in a blue or green wavelength band, and has an Al _x In _y Ga _(1-xy) N composition formula (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x). + y ≤ 1). The nitride semiconductor crystal is grown on a nitride single crystal growth substrate such as a sapphire substrate in consideration of lattice matching. Since the sapphire substrate is an electrically insulating substrate, the final nitride semiconductor light emitting device has a structure in which the p-side electrode and the n-side electrode are formed on the same surface.

1 is a cross-sectional view showing the structure of a conventional conventional nitride semiconductor light emitting device. As shown in FIG. 1, in the conventional nitride semiconductor light emitting device, an n-type nitride semiconductor layer 12, an active layer 13, and a p-type nitride semiconductor layer 14 are grown in a stacked structure on a substrate 11. Electrodes 15, 16a, and 16b are formed on the nitride semiconductor layer 12 and the p-type nitride semiconductor layer 13, respectively, and the active layer 13 is formed by recombination of holes and electrons injected from the semiconductor layers 12 and 14, respectively. To generate light. At this time, the light generated in the active layer 13 is emitted to the transparent electrode layer 15 or the substrate 11 on the p-type nitride semiconductor layer 14. The transparent electrode layer 15 is for forming an ohmic contact as a light transmissive electrode made of a metal thin film or a transparent conductive film formed almost on the entire surface of the p-type nitride semiconductor layer 14.

The nitride semiconductor light emitting device 10 attaches a lower part of the substrate to a lead frame or the like and emits light generated by the active layer 13 to the outside of the device using the upper surface of the transparent electrode layer 15 as a light emitting surface.

In the conventional nitride semiconductor light emitting device having such a structure, since the substrate 11 is processed very flat in relation to controlling the laminated structure at an atomic level, the nitride semiconductor layers 12 and 14 and the active layer 13 on the substrate 11 are processed. ) And the transparent electrode layer 15 form a stacked structure parallel to each other. Therefore, half of the light generated in the active layer 13 is transmitted through the transparent electrode layer 15 to the outside of the device, but the other half propagates toward the lower substrate 11. Some of the light propagated toward the substrate 11 is reflected from the upper surface of the substrate to be directed toward the light exit surface, but since the substrate 11 uses a transparent sapphire substrate, some of the light is transmitted through the substrate and emitted downward. When incident at an angle of a predetermined critical angle or more, the inside of the laminated structure of the nitride semiconductor layer propagates laterally and disappears.

As described above, part of the light generated by the active layer 13 is not emitted to the upper surface of the transparent electrode layer 15, which is a light exit surface, but is transmitted through the substrate 11 to be emitted downward and disappears inside. Done. This light loss causes a problem that the luminance characteristics of the light emitted from the nitride semiconductor light emitting device is lowered.

Therefore, there is a need in the art for a technology that can improve the luminance characteristics of the light emitting device by reducing the light loss of the light generated in the active layer of the nitride semiconductor light emitting device to emit more light toward the light emitting surface of the light emitting device. to be.

Accordingly, the present invention has been made to solve the above-described problems of the prior art, the object of which is to form a projection of a predetermined pattern on the upper surface of the semiconductor light emitting element to reflect the light propagating toward the substrate toward the light exit surface, the light is The present invention provides a nitride semiconductor light emitting device capable of preventing the light from passing through a substrate or disappearing inside the light emitting device and increasing light emitted through the light exit surface.

The present invention as a technical configuration for achieving the above object,

A substrate having a plurality of protrusions extending from one side of the upper surface to the other side thereof;

An n-type nitride semiconductor layer formed on the substrate;

An active layer formed on the n-type nitride semiconductor layer;

A p-type nitride semiconductor layer formed on the active layer; And

It provides a nitride semiconductor light emitting device comprising an electrode formed on each of the n-type nitride semiconductor layer and the p-type nitride semiconductor layer.

Preferably, the protrusion includes a contact surface in contact with the substrate, a vertical surface perpendicular to the contact surface, and an inclined surface connecting the contact surface and the vertical surface, the cross section of which is a right triangle. At this time, it is preferable that the width | variety of the said contact surface is 12 micrometers or less, and the height of the said vertical surface is 5000 kPa or less. At least one step may be formed on the inclined surface.

In addition, the plurality of protrusions is preferably formed side by side in the same shape.

Hereinafter, a nitride semiconductor light emitting device including a substrate on which a protrusion is formed according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a cross-sectional view of a nitride semiconductor light emitting device according to one embodiment of the present invention. Referring to FIG. 2, the nitride semiconductor light emitting device 20 according to the exemplary embodiment of the present invention includes a substrate 21 having a plurality of protrusions extending from one side of the upper surface to the other side, and n formed on the substrate 21. The type nitride semiconductor layer 22, the active layer 23 formed on the n-type nitride semiconductor layer 22, the p-type nitride semiconductor layer 24 formed on the active layer 23, and the n-type nitride semiconductor layer And the electrodes 25, 26a, and 26b formed on the p-type nitride semiconductor layer 24, respectively.

Hereinafter, each component of the nitride semiconductor light emitting device 20 according to the exemplary embodiment of the present invention will be described in detail.

Since the substrate 21 has the same crystal structure and crystal structure of the nitride semiconductor material grown thereon, and there is no commercial substrate forming a lattice match, a sapphire substrate is mainly used in consideration of lattice match. The sapphire substrate is a Hexa-Rhombo R3c symmetric crystal with a lattice constant of 13.001Å in the c-axis direction and 4.765Å in the a-axis direction, and has a lattice distance in the sapphire orientation Is characterized by having a C (0001) plane, an A (11 2 0) plane, an R (1 1 02) plane, and the like. In the case of the C surface of the sapphire substrate, the nitride semiconductor material is relatively easy to grow and is stable at high temperature, and thus, the sapphire substrate is mainly used as a substrate for a blue or green light emitting device.

The present invention is characterized by forming a plurality of projections on the upper surface of the substrate 21 by processing the upper surface of the substrate 21 using a process such as etching. The protrusion may extend from one side of the upper surface of the substrate 21 to the other side. The substrate on which such protrusions are formed will be better understood with reference to FIGS. 3 to 5.

3 is a perspective view illustrating a substrate having a plurality of protrusions formed on an upper surface thereof according to a feature of the present invention. As shown in FIG. 3, in one embodiment of the present invention, a plurality of protrusions 311 are formed on an upper surface of the substrate 31. The protrusion 311 is formed to extend from one side to the other side of the upper surface of the substrate, it is preferably formed side by side in the same shape.

The protrusion 311 serves to increase the light emitted from the light exit surface (upper surface of the transparent electrode layer 25 in FIG. 2) to the outside of the device by reflecting the light traveling toward the substrate back to the upper side among the light generated in the active layer. do. In a conventional substrate having a flat top surface, light is transmitted through the substrate and emitted to the bottom of the substrate, whereas in the present invention, the protrusion 311 is formed to change the incident angle of the light incident on the substrate, thereby reflecting from the upper surface of the substrate to the top without transmitting the substrate. You can. In addition, in a conventional substrate having a flat upper surface, light incident on the upper surface of the substrate at an angle greater than a predetermined critical angle is totally reflected and captured and extinguished in the device, whereas the protrusion 311 adopted in the present invention has an incident angle of light incident on the substrate. It is possible to prevent the total reflection of the light generated on the upper surface of the substrate and to reflect the light toward the light exit surface side of the device.

The inventors of the present invention formed a nitride semiconductor light emitting device by forming protrusions of various shapes on the upper surface of the substrate to test the reflection efficiency of the light on the upper surface of the substrate. As a result, when the cross section of the protrusion is formed in a right triangle, it can be seen that it shows the highest reflection efficiency. 4 is an enlarged cross-sectional view of the substrate for explaining the shape of the protrusions of the substrate according to the embodiment of the present invention. As shown in FIG. 4, the protrusion 411 formed on the upper surface of the substrate 41 includes a contact surface 411a contacting the substrate 41, a vertical surface 411b perpendicular to the contact surface 411a, and the contact surface 411a. It is preferable to have a cross section of a right triangle having an inclined surface 411c connecting the vertical surface 411b). In other words, the protrusion 411 has a right triangular prism shape and is formed on the substrate such that the hypotenuse of the right triangular triangle faces upward. The protrusion 411 extends from one side of the upper surface of the substrate to the other side, and a plurality of protrusions 411 are formed side by side in the same shape.

In consideration of the reflection efficiency of the light reflected from the upper surface of the substrate and the crystallinity of the nitride semiconductor layer grown on the upper surface of the nitride semiconductor element during the manufacturing process, the width of the protrusion 411 and the contact surface 411a and the vertical surface of the protrusion 411 are considered. The height of 411b is determined. In order to maximize the reflection efficiency of the light reflected from the upper surface of the substrate and not affect the crystallinity of the grown nitride at the same time, the width of the contact surface 411a is preferably 12 µm or less, and the height of the vertical surface 411b is 5000 µm or less.

Meanwhile, as shown in FIG. 5, in another embodiment of the present invention, at least one step may be formed on the inclined surface 511c of the protrusion 511 formed on the upper surface of the substrate 51. In the actual etching process, it is very difficult to form the inclined surface 511c in a perfect plane, and thus, it is advantageous to form one or more steps as in the inclined surface 511c shown in FIG. 5.

Referring back to FIG. 2, the n-type nitride semiconductor layer 22 formed on the upper surface of the substrate 21 may have an Al _x In _y Ga _(1-xy) N composition formula, where 0 ≦ x ≦ 1 and 0 ≦ y ≦. 1, 0 ≦ x + y ≦ 1), and representative nitride nitride materials include GaN, AlGaN, and GaInN. As an impurity used for the doping of the n-type nitride semiconductor layer 22, Si, Ge, Se, Te, or C may be used. The n-type nitride semiconductor layer 22 may be formed of a metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hybrid vapor deposition (Hybride Vapor Phase Epitaxy) method. It is formed by growing on the substrate 21 using a known deposition process such as HVPE).

The active layer 23 is a layer for emitting light, and is usually formed by growing an InGaN layer as a well and growing an (Al) GaN layer as a barrier layer to form a multi-quantum well structure (MQW). In the blue light emitting diode, a multi-quantum well structure such as InGaN / GaN is used, and in the ultraviolet light emitting diode, a multi-quantum well structure such as GaN / AlGaN, InAlGaN / InAlGaN and InGaN / AlGaN is used. In order to improve the efficiency of the active layer, the internal quantum efficiency of the light emitting diode is improved by controlling the wavelength of light by changing the composition ratio of In or Al, or by changing the depth of the quantum wells, the number of active layers, and the thickness of the active layer. . The active layer 23 is formed on the n-type nitride semiconductor layer 22 using a known deposition process such as organometallic vapor deposition, molecular beam growth, or hybrid vapor deposition, similar to the n-type nitride semiconductor layer 22. Can be formed.

The p-type nitride semiconductor layer 24 is similar to the n-type nitride semiconductor layer 22, Al _x In _y Ga _(1-xy) N composition formula (where 0≤x≤1, 0≤y≤1, 0 ≦ x + y ≦ 1), and typical nitride semiconductor materials include GaN, AlGaN, and GaInN. Impurities used for the doping of the p-type nitride semiconductor layer 24 include Mg, Zn or Be. The p-type nitride semiconductor layer 24 is formed by growing the semiconductor material on the active layer 23 using known deposition processes such as organometallic vapor deposition, molecular beam growth, or hybrid vapor deposition.

The electrodes 25, 26a, and 26b are formed on the upper surface of the transparent electrode layer 25 and the n-type nitride semiconductor layer 26a formed in almost all regions of the upper surface of the p-type nitride semiconductor layer 24. And a p-side bonding electrode 26b formed on the upper surface of the bonding electrode 26a and the transparent electrode layer 25.

The transparent electrode layer 25 is suitable for lowering the contact resistance with the p-type nitride semiconductor layer 24 having a relatively high energy band gap and at the same time has good light transmittance for light emitted from the active layer 23 to be emitted upwards. It is required to be formed of a material. In general, the transparent electrode layer 25 mainly uses a double layer structure of Ni / Au, and has a relatively high contact resistance, but indium tin oxide (ITO), cadmium tin oxide (CTO), or titanium tungsten nitride (TiWN) to ensure good light transmittance. ) Can be used as a material. The transparent electrode layer 25 may be formed by a known deposition method such as chemical vapor deposition (CVD) and an e-beam evaporator, or a process such as sputtering, and ohmic contact. It may be heat-treated at a temperature of about 400 to 900 ℃ to improve the properties of.

The n-side bonding electrode 26a may be formed on the n-type nitride semiconductor layer 22 as a single layer or a plurality of layers made of a material selected from the group consisting of Ti, Cr, Al, Cu, and Au. The n-side bonding electrode 26a may be formed on the n-type nitride semiconductor layer 22 by a known deposition method such as chemical vapor deposition and electron beam evaporation, or a process such as sputtering.

The p-side bonding electrode 26b is formed on the transparent electrode layer 25. The p-side bonding electrode 26b is the outermost electrode layer to be mounted on the lead through wire bonding. In general, the p-side bonding electrode 26b is made of Au or an alloy containing Au, and known deposition methods or sputtering methods such as chemical vapor deposition and electron beam evaporation are performed. It can be formed by a process such as.

The present inventors conducted experiments for comparing various characteristics of the nitride semiconductor light emitting device according to the present invention configured as described above and the conventional nitride semiconductor light emitting device, the results are shown in Figs.

6A is a graph comparing the magnitude of light output according to a change in injection current of a nitride semiconductor light emitting device. As shown in FIG. 6A, when the same current is injected, the light output 61a of the nitride semiconductor light emitting device according to the present invention having the protrusion formed on the upper surface of the substrate is remarkable compared to the light output 61b of the conventional nitride semiconductor light emitting device. It was confirmed that the improvement.

6B is a graph comparing EL (ElectroLuminescence) spectra of nitride semiconductor light emitting devices. As shown in Fig. 6B, when a current of 20 mA is injected into each element, the EL intensity 62a of the nitride semiconductor light emitting device of the present invention and the EL intensity 62b of the conventional nitride semiconductor light emitting device are almost similar, When the current is injected into each element, it can be seen that the EL intensity 63 of the nitride semiconductor light emitting element of the present invention is improved by 10 times or more compared with the EL intensity 63b of the conventional nitride semiconductor light emitting element.

6A and 6B show that the nitride semiconductor light emitting device according to the present invention adopts a substrate having protrusions formed on an upper surface thereof, thereby increasing the light output to the outside of the device, thereby improving luminance characteristics.

7A to 7C are graphs showing the results of X-ray analysis experiments on GaN layers grown on substrates having flat top surfaces and GaN layers grown on substrates having protrusions according to the present invention, respectively. As shown in FIG. 7A, the half-width (FWHM) of the curve was 269.6 arcsec. In the X-ray analysis of a GaN layer grown on a substrate having a conventional flat top surface. On the other hand, as shown in FIG. 7B, in the X-ray analysis of the GaN layer grown on the substrate on which the protrusion was formed, the half width of the curve was 226 arcsec. In the direction in which the protrusion was formed (0 °). 228 arcsec. In the direction perpendicular to the direction in which the was formed. In addition, as shown in FIG. 7C, in the X-ray analysis of the GaN layer grown on the substrate on which the protrusions having the height of about 2000 μs were formed, the half width of the curve was 254 arcsec. In the direction in which the protrusions were formed (0 °). It was 260 arcsec. In the direction perpendicular (90 °) to the direction in which the protrusion was formed.

Thus, the result showed a smaller half width value in the GaN layer grown on the substrate on which the protrusions were formed, and this result indicates that the GaN layer grown on the substrate on which the protrusions were formed has better crystallinity. In general, the sapphire substrate and the GaN layer grown thereon have a problem that the crystallinity of the GaN layer grown by the stress due to the lattice constant difference is reduced. The above experimental result is considered to be because the formation of the projections on the substrate to generate a different stress for each position of the projections to suppress the stress between the substrate and the GaN layer.

As can be seen from the above experiments, by forming the protrusions on the upper surface of the substrate, the luminance characteristics of the nitride semiconductor light emitting device can be improved, and the crystallinity of the nitride semiconductor layer grown on the substrate can be improved.

The present invention is not limited by the above-described embodiment and the accompanying drawings, but is intended to be limited by the appended claims, and various forms of substitution, modification, and within the scope not departing from the technical spirit of the present invention described in the claims. It will be apparent to those skilled in the art that changes are possible.

According to the nitride semiconductor light emitting device of the present invention as described above, by forming a plurality of projections on the upper surface of the substrate for growing the nitride semiconductor material, the light propagated to the substrate side is reflected from the upper surface of the substrate toward the light exit surface to the outside of the light emitting device There is an effect of increasing the emitted light and the brightness.

In addition, by forming a plurality of protrusions on the upper surface of the substrate to have a different stress for each position of the protrusions to suppress the stress between the substrate and the nitride semiconductor layer, thereby growing a nitride semiconductor layer having better crystallinity It works.

Claims (6)

A substrate having a plurality of protrusions extending from one side of the upper surface to the other side thereof; An n-type nitride semiconductor layer formed on the substrate; An active layer formed on the n-type nitride semiconductor layer; A p-type nitride semiconductor layer formed on the active layer; And And an electrode formed on the n-type nitride semiconductor layer and the p-type nitride semiconductor layer, respectively. The method of claim 1, And the projection portion includes a contact surface in contact with the substrate, a vertical surface perpendicular to the contact surface, and an inclined surface connecting the contact surface and the vertical surface, the cross section being a right triangle. The method of claim 2, The nitride semiconductor light emitting device, characterized in that the width of the contact surface is 12㎛ or less. The method of claim 2, The height of the vertical plane is a nitride semiconductor light emitting device, characterized in that less than 5000Å. The method of claim 2, The inclined surface is nitride semiconductor light emitting device, characterized in that at least one step is formed. The method according to any one of claims 1 to 5, The plurality of protrusions are formed side by side in the same shape nitride semiconductor light emitting device.

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