KR20170024788A - Light emittng device - Google Patents

Abstract

According to an embodiment, the present invention relates to a light emitting device, comprising: a first conductive semiconductor layer; an active layer disposed on the first conductive semiconductor layer; and a second conductive semiconductor layer disposed on the active layer. The active layer is composed of a multiple quantum well structure. A quantum wall closest to the second conductive semiconductor layer among the quantum walls in the multiple quantum well structure operates as an electron blocking layer.

Description

[0001] LIGHT EMITTING DEVICE [0002]

An embodiment relates to a light emitting element.

GaN, and AlGaN are widely used for optoelectronics and electronic devices due to their advantages such as wide and easy bandgap energy.

Particularly, a light emitting device such as a light emitting diode (Ligit Emitting Diode) or a laser diode using a semiconductor material of a 3-5 group or a 2-6 group compound semiconductor has been widely used in various fields such as red, green, blue and ultraviolet It can realize various colors, and it can realize efficient white light by using fluorescent material or color combination. It has low power consumption, semi-permanent lifetime, fast response speed, safety, and environment compared to conventional light sources such as fluorescent lamps and incandescent lamps Affinity.

Therefore, a transmission module of the optical communication means, a light emitting diode backlight replacing a cold cathode fluorescent lamp (CCFL) constituting a backlight of an LCD (Liquid Crystal Display) display device, a white light emitting element capable of replacing a fluorescent lamp or an incandescent lamp Diode lighting, automotive headlights, and traffic lights.

1 is a view showing a conventional light emitting device.

A conventional light emitting device 100 includes a light emitting structure 120 including a first conductive semiconductor layer 122, an active layer 124, and a second conductive semiconductor layer 126 on a substrate 110 made of sapphire or the like The light transmitting conductive layer 150 may be disposed on the second conductive semiconductor layer 126 and the electron blocking layer 130 may be disposed between the active layer 124 and the second conductive semiconductor layer 126 And the first electrode 162 and the second electrode 166 are disposed on the first conductivity type semiconductor layer 122 and the second conductivity type semiconductor layer 126, respectively.

In the light emitting device 100, electrons injected through the first conductive type semiconductor layer 122 and holes injected through the second conductive type semiconductor layer 126 meet to form an energy band inherent to the active layer 124 And emits light having energy determined by the light intensity. The light emitted from the active layer 124 may vary depending on the composition of the material forming the active layer 124.

Electrons have greater mobility than holes and electrons that are not coupled to holes in the active layer 124 can travel in the direction of the second conductivity type semiconductor layer 126. Therefore, an electron blocking layer 130 may be disposed between the active layer 124 and the second conductive semiconductor layer 126.

For example, AlGaN doped with a second conductive dopant may be disposed on the electron blocking layer 130, and a plurality of GaN layers having different aluminum composition ratios may be alternately arranged.

In FIG. 2, the active layer MQW is composed of quantum wells and quantum wells, and the energy band gap E _QB of the quantum well can be larger than the energy band gap E _QW of the quantum well. The energy band gap En of the first conductivity type semiconductor layer (n-GaN) and the energy band gap Ep of the second conductivity type semiconductor layer (p-GaN) are equal to each other. The energy band gap E _QB may be smaller than the energy band gap E _EBL of the electron blocking layer EBL.

However, the conventional light emitting device described above has the following problems.

In the case of a light emitting device emitting blue light or green light, InGaN is contained in the active layer and the content of In (indium) is about 23% in the case of a light emitting device emitting green light. Relative to indium content of 14% .

Since the lattice size of InN is larger than the lattice size of GaN, InGaN, which is an active layer, has a compressive strain larger than that of GaN. In the case of the light emitting device emitting green light, since the indium content is relatively large, a higher compressive stress is applied to the active layer.

Here, the high compressive stress deteriorates the crystallinity of the active layer, limits the thickness to a smaller value, and the piezoelectric polarization phenomenon can be further strengthened.

Further, when the energy levels of the quantum well and the quantum well are not sufficiently large, electrons escaping from the quantum well in the active layer are increased. Such electrons do not contribute to the luminous efficiency, so that the luminous efficiency of the luminous means can be lowered. In order to solve this problem, when the above-described electron blocking layer is disposed immediately before the p-type conductivity-type semiconductor layer, the electron blocking layer may inhibit the movement of holes in addition to the movement of electrons, So that the light efficiency of the light emitting device can be lowered.

Embodiments provide a light emitting device in which the crystallinity of the active layer is improved, the piezoelectric polarization in the active layer is reduced, and the frequency of coupling of electrons and holes in the quantum well in the active layer is increased to improve the light efficiency.

The embodiment includes a first conductivity type semiconductor layer; An active layer on the first conductive semiconductor layer; And a second conductivity type semiconductor layer on the active layer, wherein the active layer has a multiple quantum well structure, and a quantum wall closest to the second conductivity type semiconductor layer in a quantum wall in the multiple quantum well structure, Emitting layer.

The energy band gap of the quantum wall may be greater than the energy band gap of the first conductivity type semiconductor layer or the energy band gap of the second conductivity type semiconductor layer.

The energy band gap of the first conductivity type semiconductor layer may be the same as the energy band gap of the second conductivity type semiconductor layer.

The first conductivity type semiconductor layer may be an n-type semiconductor layer, and the second conductivity type semiconductor layer may be a p-type semiconductor layer.

The energy band gap of the first conductivity type semiconductor layer and the energy band gap of the second conductivity type semiconductor layer may be 3.42 eV.

The energy bandgap of the quantum wall in the multiple quantum well structure may be 3.62 eV.

The energy band gap of the quantum well in the multiple quantum well structure may be 2.39 eV.

The thickness of the quantum wall serving as the electron blocking layer may be thicker than the thickness of the other quantum wall.

The thickness of the quantum wall may be less than two thirds of the thickness of the quantum well.

Another embodiment includes a first conductive semiconductor layer; An active layer on the first conductive semiconductor layer; And a second conductive semiconductor layer on the active layer, wherein the active layer has a multiple quantum well structure, the quantum wall in the multiple quantum well structure is made of AlGaN, and the quantum well is made of InGaN.

The first conductive semiconductor layer may be made of GaN doped with an n-type dopant.

The second conductivity type semiconductor layer may be made of GaN doped with a p-type dopant.

The composition ratio of Al (aluminum) in the quantum wall may be 0.1.

The composition ratio of In (phosphorus) in the quantum well may be 0.23.

Light in the green wavelength region can be emitted from the active layer.

In the light emitting device according to the embodiments, the energy bandgap of the quantum well and the quantum well is larger than that in the related art, and electrons may be difficult to escape from the quantum well in the active layer. Accordingly, the coupling of electrons and holes in the active layer increases, so that the light efficiency of the light emitting device can be improved.

In addition, since the quantum wall of the active layer in the light emitting device is made of InGaN instead of GaN, the compressive stress applied to the active layer is reduced, so that the crystallinity of the active layer is improved and the piezoelectric polarization phenomenon can be reduced.

1 is a view showing a conventional light emitting device,
FIG. 2 is a view showing an energy band gap of the light emitting device of FIG. 1,
3 is a view illustrating an embodiment of a light emitting device,
4 is a view showing the energy bandgap of the light emitting device of FIG. 3,
5 is a view showing an embodiment of a light emitting device package in which a light emitting device is disposed.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

In the description of the embodiment according to the present invention, in the case of being described as being formed "on or under" of each element, the upper (upper) or lower (lower) or under are all such that two elements are in direct contact with each other or one or more other elements are indirectly formed between the two elements. In addition, when expressed by upper or lower (on or under), it is possible to include not only the upward direction but also the downward direction based on one element.

3 is a view showing an embodiment of a light emitting device.

The light emitting device 200 includes a light emitting structure 220 disposed on a buffer layer 215 on a substrate 210, a light transmitting conductive layer 250 disposed on the light emitting structure 220, The first electrode 262 and the second electrode 266 may be disposed on the transmissive conductive layer 250 and the transmissive conductive layer 250, respectively.

The substrate 210 may be formed of a material suitable for semiconductor material growth or a carrier wafer, may be formed of a material having excellent thermal conductivity, and may include a conductive substrate or an insulating substrate. For example, at least one of sapphire (Al ₂ O ₃ ), SiO ₂ , SiC, Si, GaAs, GaN, ZnO, GaP, InP, Ge and Ga ₂ O ₃ can be used.

Since the substrate 210 and the light emitting structure 220 are different materials, lattice mismatch is very large and the difference in thermal expansion coefficient between them is very large. Therefore, dislocations that deteriorate the crystallinity, melt-back, crack, pit, and surface morphology defects may occur.

A buffer layer 215 may be formed between the substrate 210 and the light emitting structure 220 to solve the above-described problems.

The light emitting structure 220 may include a first conductive semiconductor layer 222, an active layer 224, and a second conductive semiconductor layer 226.

The first conductive semiconductor layer 222 may be formed of a compound semiconductor such as Group III-V or Group II-VI, and may be doped with a first conductive dopant.

More specifically, the first conductive semiconductor layer 222 is a semiconductor having a composition formula of Al _x In _y Ga _(1-xy) N (0? X? 1, 0? _Y? 1, 0? _X + Material, AlGaN, GaN, InAlGaN, AlGaAs, GaP, GaAs, GaAsP, and AlGaInP.

When the first conductivity type semiconductor layer 222 is an n-type semiconductor layer, the first conductivity type dopant may include n-type dopants such as Si, Ge, Sn, Se, and Te. The first conductive semiconductor layer 222 may be formed as a single layer or a multilayer, but the present invention is not limited thereto.

The active layer 224 is disposed between the first conductivity type semiconductor layer 222 and the second conductivity type semiconductor layer 226 and may include a single well structure, a multiple well structure, a single quantum well structure, a multi quantum well (MQW) Well structure, a quantum dot structure, or a quantum wire structure, and may be formed of, for example, a multiple quantum well structure.

InGaN / InGaN, InGaN / InGaN, AlGaN / GaN, InAlGaN / GaN, GaAs (InGaAs), and AlGaN / AlGaN / InGaN / GaN, / AlGaAs, GaP (InGaP) / AlGaP, and InGaN / AlGaN.

The well layer may be formed of a material having an energy band gap smaller than the energy band gap of the barrier layer. When the active layer 224 emits light in the green wavelength region, the active layer 224 may be composed of a multiple quantum well structure, for example, a quantum well / quantum wall of an InGaN / AlGaN structure, in _{0 .23} may be a GaN / Al _{0 .1} multiple quantum well structure is a pair (pair) structure of the GaN quantum well structure layer / quantum byeokcheung of more than one period, the quantum well will include a second conductive dopant, which will be described later .

The second conductive semiconductor layer 226 may be formed of a semiconductor compound. The second conductive semiconductor layer 226 may be formed of a compound semiconductor such as a Group III-V or a Group II-VI, and may be doped with a second conductive dopant. The second conductive semiconductor layer 226 may be a semiconductor material having a composition formula of In _x Al _y Ga _{1 -xy} N (0? X? 1, 0? _Y? 1, 0? _X + y? For example, the second conductivity type semiconductor layer 226 may be formed of Al _x Ga _(1-x) N. The second conductivity type semiconductor layer 226 may be formed of Al _x Ga _{y (1-x)} N.

When the second conductivity type semiconductor layer 226 is a p-type semiconductor layer, the second conductivity type dopant may be a p-type dopant such as Mg, Zn, Ca, Sr, and Ba. The second conductivity type semiconductor layer 226 may be formed as a single layer or a multilayer, but is not limited thereto.

FIG. 4 is a diagram showing the energy bandgap of the light emitting device of FIG. 3. FIG.

The active layer MQW is made of a quantum wall and a quantum well, and the energy band gap E _QB of the quantum well can be larger than the energy band gap E _QW of the quantum well. The energy band gap En of the first conductivity type semiconductor layer (n-GaN) and the energy band gap Ep of the second conductivity type semiconductor layer (p-GaN) may be equal to each other.

Here, the energy band gap E _QB of the quantum wall is equal to the energy band gap En of the first conductivity type semiconductor layer (n-GaN) and the energy band gap Ep of the second conductivity type semiconductor layer (p-GaN) So that the quantum wall closest to the first conductivity type semiconductor layer (p-GaN) in the quantum wall can act as the electron blocking layer (EBL).

In detail, the first conductive semiconductor layer and the second conductive semiconductor layer may each be made of GaN, and may have a thickness of 340 nm to 380 nm, for example, 363 nm. An energy band gap (En, Ep) can each be 3.42 eV. And, both wall forming the active layer (MQW) is Al _{0 .1} made of GaN may be a thickness of 320 nanometers to 360 nanometers, for example 342 may be nano-meter, the energy band gap (E _QB) is 3.62 eV. Further, the quantum well is made of a GaN In _{0 .14} may be a thickness of 500 nanometers to 550 nanometers and can be for example 520 nanometers, an energy band gap (E _QB) forming the active layer (MQW) is 2.39 eV. Further, the thickness of the quantum wall may be 2/3 or less of the thickness of the quantum well.

The thickness of the quantum wall closest to the first conductivity type semiconductor layer (p-GaN) which can serve as the electron blocking layer among the quantum wells may be thicker than the thickness of the other quantum wells.

The light-transmitting conductive layer 250 may be disposed on the light-emitting structure 220. The transmissive conductive layer 250 acts to uniformly inject holes injected into the second electrode 266 into the second conductive type semiconductor layer 226. For example, the transparent conductive layer 250 may be formed of indium tin oxide (ITO), indium zinc oxide ), IZTO (indium zinc tin oxide), IZO (indium aluminum zinc oxide), IGZO (indium gallium zinc oxide), IGTO (indium gallium tin oxide), AZO IrOx / AuO, and Ni / IrOx / Au / IrOx / ITO, gallium zinc oxide, IZON, IZON, AGZO, IGZO, InGaZO, ZnO, IrOx, RuOx, NiO, And may include at least one of ITO, Ag, Ni, Cr, Ti, Al, Rh, Pd, Ir, Sn, In, Ru, Mg, Zn, Pt, Au, and Hf. .

A part of the first conductivity type semiconductor layer 222 may be exposed by mesa etching from the light transmitting conductive layer 250 to a part of the height of the first conductivity type semiconductor layer 222 in a part of the light emitting device 200 .

The first electrode 262 and the second electrode 266 may be disposed on the exposed first conductive semiconductor layer 222 and the second conductive semiconductor layer 226, respectively.

The first electrode 262 and the second electrode 266 may include at least one of Al, Ti, Cr, Ni, Cu, Or a multi-layer structure.

As shown in FIG. 3, the side surface of the light emitting structure 220 may be disposed in an inclined manner, and a passivation layer may be disposed around the light emitting structure to protect the light emitting structure. The passivation layer may be made of an insulating material, and the insulating material may be made of a non-conductive oxide or nitride. As an example, it may be composed of a passivation layer silicon oxide (SiO ₂ ) layer, an oxynitride layer, and an aluminum oxide layer.

3, the energy bandgaps of the first conductivity type semiconductor layer 222, the active layer 224, and the second conductivity type semiconductor layer 226 of the above-described structure are the same as those of the vertical light emitting device or the light emitting device And can also be applied to a flip chip type light emitting device.

In the conventional light emitting device emitting blue light, the energy band gap of the quantum well and the electron blocking layer was about 0.96 eV. However, since the energy band gap of the quantum well and the quantum well is about 1.23 eV, It may be difficult for electrons to escape from the well. Accordingly, the coupling of electrons and holes in the active layer increases, so that the light efficiency of the light emitting device can be improved.

In addition, since the content of In (indium) in the quantum well in the active layer in the light emitting device is as high as about 23%, since the quantum wall is made of InGaN instead of GaN, the compressive stress applied to the active layer is reduced, Polarization phenomena can also be reduced.

5 is a view showing an embodiment of a light emitting device package in which a light emitting device is disposed.

The light emitting device package 300 may include a first lead frame 322 and a second lead frame 326 disposed in a package body 310 having a cavity and the first lead frame 322 and the second lead frame 322 The lead frame 326 is disposed through the package body 310 but may be disposed in a different shape.

The light emitting device 200 is electrically connected to the first lead frame 322 and the second lead frame 326 by wires 330. The cavity is filled with the molding portion 340 and the molding portion 340 ) May include a phosphor 345. [

In the light emitting device package 300 of FIG. 5, the light of the first wavelength range, for example, green wavelength range is emitted from the light emitting device 200, and the phosphor 345 is excited by the light of the first wavelength range It is possible to emit light of a second wavelength range having a longer wavelength and to mix light of the first wavelength range and light of the second wavelength range to realize light of the third wavelength range, for example, white light.

The light emitting device package may include one or more light emitting devices according to the above-described embodiments, but the present invention is not limited thereto.

The above-described light emitting device package can be used as a light source of an illumination system, and can be used, for example, in an image display device and a lighting device.

The above-described light emitting device package may be arranged in a line on a circuit board to be used in a lighting apparatus or as an edge type light source in an image display apparatus.

In the light emitting device package, a plurality of light emitting devices may be arranged in a plurality of rows and columns on a circuit board, and in particular, a direct light type light source may be used in a video display device.

When the above-described light emitting devices are used as a light source of an image display device or a lighting device, the light efficiency of the light emitting device is improved, the crystallinity of the active layer is improved, and the polarization polarization phenomenon is also reduced. Further, a light emitting element that emits green light is used, so that the color rendering property is improved and the half width of light is reduced, so that the color reproducibility can be improved.

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, It will be understood that various modifications and applications are possible. For example, each component specifically shown in the embodiments can be modified and implemented. It is to be understood that all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

100, 200: light emitting device 110, 210:
120: 220: light emitting structure 122, 222: first conductivity type semiconductor layer
124, 224: active layer 126, 226: second conductivity type semiconductor layer
130: electron blocking layer
150, 250: transmissive conductive layer 162, 261: first electrode
166, 266: second electrode 215: buffer layer
300: light emitting device package 310: package body
322: first lead frame 326: second lead frame
330: wire 340: molding part
345: Phosphor

Claims (15)

A first conductive semiconductor layer;
An active layer on the first conductive semiconductor layer; And
And a second conductivity type semiconductor layer on the active layer,
Wherein the active layer has a multiple quantum well structure and a quantum wall closest to the second conductivity type semiconductor layer among the quantum wells in the multiple quantum well structure acts as an electron blocking layer. The method according to claim 1,
Wherein an energy band gap of the quantum wall is larger than an energy band gap of the first conductivity type semiconductor layer or an energy band gap of the second conductivity type semiconductor layer. The method according to claim 1,
Wherein the energy band gap of the first conductivity type semiconductor layer is equal to the energy band gap of the second conductivity type semiconductor layer. The method according to claim 1,
Wherein the first conductivity type semiconductor layer is an n-type semiconductor layer, and the second conductivity type semiconductor layer is a p-type semiconductor layer. The method according to claim 1,
And the energy band gap of the first conductivity type semiconductor layer and the energy band gap of the second conductivity type semiconductor layer are 3.42 eV. The method according to claim 1,
And the energy band gap of the quantum wall in the multiple quantum well structure is 3.62 eV. The method according to claim 1,
And the energy band gap of the quantum well in the multiple quantum well structure is 2.39 eV. The method according to claim 1,
Wherein the thickness of the quantum wall serving as the electron blocking layer is thicker than the thickness of the other quantum wall. The method according to claim 1,
Wherein the thickness of the quantum well is 2/3 or less of the thickness of the quantum well. A first conductive semiconductor layer;
An active layer on the first conductive semiconductor layer; And
And a second conductivity type semiconductor layer on the active layer,
Wherein the active layer has a multiple quantum well structure, the quantum wall in the multiple quantum well structure is made of AlGaN, and the quantum well is made of InGaN. 11. The method of claim 10,
Wherein the first conductivity type semiconductor layer is made of GaN doped with an n-type dopant. 11. The method of claim 10,
And the second conductivity type semiconductor layer is made of GaN doped with a p-type dopant. 11. The method of claim 10,
And the composition ratio of Al (aluminum) in the quantum wall is 0.1. 11. The method of claim 10,
And the composition ratio of In (phosphorus) in the quantum well is 0.23. 15. The method according to any one of claims 1 to 14,
Wherein the active layer emits light in a green wavelength range.

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