KR101754906B1 - Light emitting device - Google Patents

Abstract

Embodiments relate to a light emitting device and a manufacturing method thereof. The light emitting device according to the embodiment includes the first conductive semiconductor layer, the second conductive semiconductor layer, the first conductive semiconductor layer, and the second conductive semiconductor layer, and the quantum well layer and the quantum barrier layer are alternately stacked And the quantum barrier layers have a thickness such that a plurality of light beams emitted from the quantum well layers satisfy a constructive interference condition. Thereby, the amplitude of light emitted from the multiple quantum wells can be increased to increase the light extraction efficiency.

Description

[0001]

Embodiments relate to a light emitting device capable of inducing a constructive interference of light emitted therefrom.

BACKGROUND ART An LED (Light Emitting Diode) is a device that converts an electric signal into an infrared ray, a visible ray, or a light using the characteristics of a compound semiconductor. The LED is used in household appliances, remote controllers, display boards, The use area is gradually widening.

Meanwhile, the external quantum efficiency, which is the light efficiency of the light emitting device, is determined by the product of the internal quantum efficiency and the light extraction efficiency, and the internal quantum efficiency is determined by the quality of the semiconductor and the efficiency of current injection. The light extraction efficiency is reduced due to total internal reflection due to the difference in refractive index between gallium nitride (GaN) and air in the light emitting device. In order to increase the light extraction efficiency, a vertical type light emitting device has been developed and a method of forming the surface irregularities has been developed.

An embodiment of the present invention provides a light emitting device capable of increasing luminous efficiency by adjusting the thickness of a quantum barrier layer of an active layer to cause constructive interference between emitted light.

According to an embodiment of the present invention, a light emitting device includes a first conductive semiconductor layer, a second conductive semiconductor layer formed between the first conductive semiconductor layer and the second conductive semiconductor layer, and a quantum well layer and a quantum barrier Wherein the quantum barrier layers have a thickness such that a plurality of lights emitted from the quantum well layers satisfy a constructive interference condition.

According to the embodiment, as the light generated in the active layer is emitted to the surface of the light emitting device, the phases thereof become equal to each other, and the constructive interference occurs, so that the light extraction efficiency can be increased by superimposing the wave function.

1 is a cross-sectional view showing a basic structure of a light emitting device according to an embodiment.
2 is a cross-sectional view illustrating an active layer of a light emitting device according to an embodiment.
Fig. 3 is a diagram showing a cross section of the active layer when the reflective layer is present at the lowermost portion.
4 is a graph showing the relationship between the color and the wavelength of light emitted.
FIG. 5 is a table showing the color of light and the thickness of a quantum barrier layer in which a wavelength and constructive interference can occur according to an embodiment.
FIG. 6 is a table summarizing margins of thickness shown in FIG. 5 according to an embodiment.
Fig. 7 is a diagram showing superposition of two waves at the time of constructive interference. Fig.

In the description of the embodiments, it is to be understood that each layer (film), region, pattern or structure may be referred to as being "on", "under", or "on" Quot; on ", " under ", " upper ", and lower " lower " directly "or" indirectly "through " another layer, or structure ".

The thickness and size of each layer in the drawings are exaggerated, omitted, or schematically shown for convenience and clarity of explanation. Also, the size of the component does not entirely reflect the actual size.

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers and / or regions, these elements. Ingredients. Areas. Layers and / or regions should not be limited by these terms.

The thickness and size of each layer in the drawings are exaggerated, omitted, or schematically shown for convenience and clarity of explanation. Also, the size of the component does not entirely reflect the actual size.

Hereinafter, embodiments will be described in detail with reference to FIGS. 1 to 7 attached hereto.

1 is a cross-sectional view showing a basic structure of a light emitting device according to an embodiment.

The light emitting device 100 includes a substrate 110, a first conductive semiconductor layer 120, an active layer 130, a light emitting structure 150 including a second conductive semiconductor layer 140, a first electrode 122, Two electrodes 142, and a light-transmitting electrode layer 160.

The substrate 110 may have a light transmitting property and may be a heterogeneous substrate different from a semiconductor layer such as sapphire (Al ₂ O ₃ ) or a homogeneous substrate such as GaN. The substrate 110 may be made of ZnO, Si, GaP, InP, GaAs ≪ / RTI > Further, it may be a SiC substrate having higher thermal conductivity than a sapphire (Al ₂ O ₃ ) substrate, but is not limited thereto. In addition, a concave-convex pattern may be formed on the upper surface of the substrate 110.

Although not shown, a layer or a pattern using a compound semiconductor of Group 2 or Group 6 element is formed on the substrate 110 such that at least one of a ZnO layer (not shown), a buffer layer (not shown) and an undoped semiconductor layer (not shown) Layer may be formed. The buffer layer or the undoped semiconductor layer may be formed using a compound semiconductor of a group III-V element, the buffer layer may reduce a difference in lattice constant with respect to the substrate, and the undoped semiconductor layer may be doped GaN-based semiconductor.

A buffer layer (not shown) and an undoped semiconductor layer may all be formed on the substrate 110, or only one layer may be formed, or both layers may be removed, and the structure is not limited thereto .

The first conductive semiconductor layer 120 may be an n-type semiconductor layer and may provide electrons to the active layer 130. The first conductive semiconductor layer 120 may be formed only of an n-type semiconductor layer or may include an undoped semiconductor layer (not shown) under the n-type semiconductor layer, but the present invention is not limited thereto.

For example, the n-type semiconductor layer may be a semiconductor material having a composition formula of In _x Al _y Ga _{1 -x- y} N (0? X? 1, 0? _Y? 1, 0? _X + y? 1) For example, GaN, AlN, AlGaN, InGaN, InN, InAlGaN, AlInN and the like, and n-type dopants such as Si, Ge and Sn can be doped.

The undoped semiconductor layer (not shown) is a layer formed for improving the crystallinity of the n-type semiconductor layer. The n-type semiconductor layer (not shown) has a lower electrical conductivity than the n- Respectively.

For example, NH 3 and trimetal gallium (TMGa) are supplied on a buffer layer (not shown) to form an undoped semiconductor layer to a predetermined thickness.

A buffer layer (not shown) and an undoped semiconductor layer (not shown) may all be formed on the substrate 110, or only one layer may be formed, or both layers may be removed. .

The reflective layer 112 is disposed on the substrate 110 so that light emitted from the active layer 130 is emitted toward the substrate 110 to reflect the emitted light.

The reflective layer 112 is composed of at least one of silver (Ag), aluminum (Al), lead (Pb), and rhodium (Rh) or an alloy thereof and reflects light traveling toward the substrate 110. Therefore, the luminous efficiency of the light emitting device 100 that emits light through the light emitting structure 150 can be increased.

Meanwhile, the first conductive semiconductor layer 120 may be formed by supplying a SiH ₄ gas including an n-type dopant such as NH ₃ , TMGa, and Si, and may be formed as a multilayer film, .

In addition, the active layer 130 may be formed on the first conductive semiconductor layer 120. The active layer 130 is a region where electrons and holes are recombined. As the electrons and the holes are recombined, the active layer 130 transits to a low energy level and can generate light having a wavelength corresponding thereto.

The active layer 130 includes a semiconductor material having a composition formula of In _x Al _y Ga _{1 -x- y} N (0? X? 1, 0? _Y? 1, 0? _X + y? 1) And may be formed of a single quantum well structure or a multi quantum well (MQW) structure. It may also include a quantum wire structure or a quantum dot structure.

A second conductive semiconductor layer 140 and injects holes to the above-mentioned active layer _{(130), In x Al y} Ga 1 -x- y N (0≤x≤1, 0≤y≤1, 0≤x + y 1, for example, GaN, AlN, AlGaN, InGaN, InN, InAlGaN, AlInN or the like, and a p-type dopant such as Mg, Zn, Ca, have.

Meanwhile, the light emitting structure 150 may include an N-type semiconductor layer or a P-type semiconductor layer on the second conductive semiconductor layer 140. Accordingly, the light emitting structure 150 may include at least one of a P-N junction, an N-P junction, a P-N-P junction, and an N-P-N junction structure.

In the embodiment, the light emitting structure 150 includes an n-type nitride semiconductor layer including an n-type dopant, an active layer formed on the n-type nitride semiconductor layer, and a p-type nitride semiconductor layer including a p- However, the present invention is not limited thereto, and the lamination structure and material of the light emitting structure 150 may be variously modified

The first conductive semiconductor layer 120, the active layer 130 and the second conductive semiconductor layer 140 may be formed using a metal organic chemical vapor deposition (MOCVD) method, a chemical vapor deposition (CVD) method, (PECVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE), which can be used to form And is not limited thereto.

A part of the first conductive semiconductor layer 120 is exposed and a part of the active layer 130 and the second conductive semiconductor layer 140 are partially removed and the upper surface of the exposed first conductive semiconductor layer 120 is coated with titanium The first electrode 122 may be formed.

In addition, a third conductive semiconductor layer (not shown) including an n-type semiconductor layer or a p-type semiconductor layer may be formed on the second conductive semiconductor layer 140, The semiconductor layer 140 is connected. The doping concentration of the dopant in the first conductive semiconductor layer 120 and the second conductive semiconductor layer 140 may be uniform or non-uniform. That is, the structure of the plurality of semiconductor layers may be variously formed, but the structure is not limited thereto.

A transparent electrode layer 160 may be formed on the second conductive semiconductor layer 140 and a second electrode 142 may be formed on the outer surface of the transparent electrode layer 160 such as nickel (Ni).

It is possible to form irregularities for improving the light extraction efficiency by a predetermined etching method on a part or whole area of the surface of the light transmitting electrode layer 150 or the second conductive semiconductor layer 140 on which the second electrode 142 is not formed have. The second electrode 142 may be formed on a flat surface where unevenness is not formed, or may be formed on an uneven surface, but the present invention is not limited thereto.

The transparent electrode layer 160 may be formed of ITO, IZO (In-ZnO), GZO (Ga-ZnO), AZO (Al-ZnO), AGZO / ITO, Ni / IrOx / Au, and Ni / IrOx / Au / ITO, and is formed on the entire outer surface of the second conductive semiconductor layer 140, have.

2 is a cross-sectional view illustrating an active layer of a light emitting device according to an embodiment.

The active layer 130 is positioned between the first conductive semiconductor layer 120 and the second conductive semiconductor layer 140. The active layer 130 is a region where electrons and holes are recombined. As the electrons and the holes are recombined, the active layer 130 transits to a low energy level and can generate light having a wavelength corresponding thereto.

NH ₃ , TMGa, and trimethyl indium (TMIn) are supplied at a growth temperature of, for example, 780 ° C as a carrier gas to form an active layer 130 made of InGaN 130 may be grown to a thickness of 120 ANGSTROM to 1200 ANGSTROM. At this time, the active layer 130 may have a stacked structure in which the molar ratios of the respective element components of InGaN are different from each other.

The active layer 130 may be formed of one of a single quantum well structure, a multi quantum well (MQW) structure, a quantum wire structure, and a quantum dot structure. However, the present embodiment will be described on the basis of a multiple quantum well structure, but the present invention is not limited thereto.

In the multi-well structure (MQW), more electrons are collected at the lower energy level of the quantum well layer, and as a result, the recombination probability of electrons and holes is increased, and the luminous efficiency can be improved. It may also include a quantum wire structure or a quantum dot structure.

When the active layer 130 has a quantum well structure, for example, quantum wells having a composition formula of In _x Al _y Ga _1-xy N (0? X? 1, 0? _Y? 1, 0? _X + Having quantum barrier layers 210 and 212 having a composition formula of layers 214, 216 and 218 and In _a Al _b Ga _{1 -ab} N (0? A? ₁ , 0? B? ₁ , 0? A + b? 1) It can have a well structure. The quantum well layers 214, 216, and 218 may be formed of a material having a band gap lower than the band gap of the quantum barrier layers 210 and 212.

In addition, the quantum well layers 214, 216, and 218 include InGaN, and the position of the emission wavelength can be changed by changing the amount of In. Specifically, by increasing the composition ratio of In (indium), the emission wavelength position is red shifted, and the depth of the quantum well is increased, resulting in a stronger quantum confinement effect, and the binding force of the carriers can be increased.

In addition, the quantum barrier layers 210 and 212 may specifically include any one of GaN, InGaN, AlInN, and InAlGaN.

Referring to the drawing, the active layer 130 may include quantum barrier layers 210 and 212 and quantum well layers 214, 216, and 218. Although the figure shows two quantum barrier layers 210 and 212 and three quantum well layers, this is only an example, and the number of quantum barrier layers 210 and 212 and quantum well layers is not limited to the drawings.

The light emitted from the quantum well layers 214, 216, and 218 has a wave function, and the waves of light emitted from the quantum well layers 214, 216, and 218 have phases and sizes. When the waves of light emitted from the respective quantum well layers 214, 216, and 218 have the same phase, the magnitude of the wave can be added. The larger the wave size, the greater the brightness of the emitted light. That is, the light extraction efficiency can be increased.

When the quantum well layers 214, 216 and 218 are referred to as a first quantum well layer 214, a second quantum well layer 216 and a third quantum well layer 218, light emitted from the third quantum well layer 218 Passes through the second quantum well layer 216 past the second quantum barrier layer 212. Light emitted from the second quantum well layer 216 reaches the first quantum well layer 214 through the first quantum barrier layer 210. At this time, when the emitted light proceeds, the light passes through the quantum barrier layers 210 and 212, and the phases of the light emitted from the second and third quantum well layers 216 and 218 coincide with the thickness of the quantum barrier layers 210 and 212 .

When the phases of the waves of light emitted from the second quantum well layer 216 and the third quantum well layer 218 coincide with each other, the magnitude of each light can be amplified. In this case, the amount of light emitted to the outside of the light emitting device 100 through the first quantum well layer 214 can be increased.

Fig. 3 is a diagram showing a cross section of the active layer when the reflective layer is present at the lowermost portion.

The light emitted from the second quantum well layer 216 is reflected by the reflective layer 112 under the active layer 130 and passes through the second barrier layer 216 to the upper portion of the active layer 216, .

Since the refractive index of the quantum well layer is larger than that of the quantum barrier layer and the refractive index of the quantum barrier layer is larger than the refractive index of the metal forming the reflective layer, light emitted from the second quantum well layer 216 is free-end reflected.

The term "free end half" refers to a case where light propagates to a medium having a relatively low refractive index in a medium having a refractive index, and is reflected, and there is no change in phase.

으로 계산할 수 있으며, T는 상기 양자장벽층(210,212)의 두께,

λ는 진공에서의 파장, n은 상기 양자장벽층(210,212)을 구성하는 물질의 굴절률 및 m은 정수를 나타낸다. 즉, 양자장벽층의 두께는 파장의 정수배여야 한다. The thickness of the quantum barrier layer depends on the conditions under which constructive interference can occur in the absence of phase change

T is the thickness of the quantum barrier layers 210 and 212,

lambda is a wavelength in a vacuum, n is a refractive index of a material constituting the quantum barrier layers 210 and 212, and m is an integer. That is, the thickness of the quantum barrier layer should be an integral multiple of the wavelength.

Light emitted from the second quantum well layer 216 is reflected toward the reflective layer 112 and reflected by the reflective layer 112 and light emitted from the second quantum well layer 216 It is possible to increase the light extraction efficiency in the case where the phase of the light emitted by the light source is coincident with the phase of the constructive interference.

According to the embodiment, the light emitted from the first quantum well layer 214 moves toward the reflection layer 112 and is reflected by the reflection layer 112 and the light when the first quantum well layer 214 or the second quantum well 214, The light extraction efficiency can be increased when the phases of the light beams emitted from the layer 216 to the upper portion of the active layer 130 coincide with each other and interfere constructively.

In this case, since there is no phase change as a result of free-end reflection, the conventional equation can be applied, and the amplitude of the composite wave becomes twice as large as the floor and the floor or the bone and the valley of two waves having the same phase.

4 is a graph showing the relationship between the color and the wavelength of light emitted.

5 is a table showing the color of light and the thickness of a quantum barrier layer in which a wavelength and constructive interference may occur according to an embodiment.

FIG. 6 is a table summarizing margins of thickness shown in FIG. 5 according to an embodiment.

According to the drawing, the x-axis represents the wavelength of light and the y-axis represents the intensity of light. In the case of blue light, it has a wavelength of about 420 nm to 470 nm, and in the case of green light, it has a wavelength of about 530 nm to 580 nm. In the case of red light, it has a wavelength of about 690 nm to 690 nm. The center wavelength is 450 nm or 460 nm for blue light, 540 nm or 550 nm for green light, and 670 nm or 680 nm for red light.

λ는 진공에서의 파장, n은 상기 양자장벽층(210,212)을 구성하는 물질의 굴절률 및 m은 정수를 나타낸다. 실시예에 따른 양자장벽층(210,212)을 구성하는 물질이 GaN인 경우, 굴절률 n은 2.487이고 일단 m은 1이라고 하면, 청색광의 경우 보강간섭이 일어나는 양자장벽층(210,212)의 두께는 168 내지 189nm이고, 녹색광의 경우는 213 내지 234nm이며, 적색광의 경우, 257 내지 278nm이다. The equation for calculating the thickness of the quantum barrier layers 210 and 212 according to the wavelength of light is T = lambda / nxm, T is the thickness of the quantum barrier layers 210 and 212,

lambda is a wavelength in a vacuum, n is a refractive index of a material constituting the quantum barrier layers 210 and 212, and m is an integer. When the material constituting the quantum barrier layers 210 and 212 according to the embodiment is GaN, when the refractive index n is 2.487 and the m is 1, the thickness of the quantum barrier layers 210 and 212 in which the constructive interference occurs in the case of blue light is 168 to 189 nm In the case of the green light, 213 to 234 nm in the case of the red light, and 257 to 278 nm in the case of the red light.

Further, it can be set to have an error within +/- 10% of the thickness satisfying the constructive interference condition. When the margin is set to about 10%, the thicknesses of the quantum barrier layers 210 and 212 are 151.2 to 207 nm for blue light, 191.7 nm to 257 nm for green light, and 231.3 to 305.8 nm for red light.

However, depending on the purpose and the choice of color, there may be a change in the wavelength in the case of blue light, green light, and red light, and the thickness of the quantum barrier layers 210 and 212 may vary, and the quantum barrier layers 210 and 212 May be varied. Therefore, the wavelengths and thicknesses shown in the table are not limited, and may be variously expressed according to the color of light to be realized in the light emitting device.

For example, when Al is alloyed with In by about 15% of GaN, the refractive index becomes about 2.52. When the quantum barrier layers 210 and 212 are made of different materials, there may be differences in thickness, The thickness of the quantum barrier layers 210 and 212 can be controlled by changing the wavelength depending on whether the color of the light is green or light green among the green light.

The thickness of the quantum barrier layers 210 and 212 can be controlled by controlling the growth time according to the calculated thickness if the quantum barrier layers 210 and 212 can be grown in the active layer, 210 and 212 can be adjusted.

Fig. 7 is a diagram showing superposition of two waves at the time of constructive interference. Fig.

Constructive interference occurs when two waves of the same phase are superimposed on each other. The amplitude of the composite wave is doubled because the floor and the floor or the valley and the valley meet.

As a result of the moments when two waves with the same amplitude and frequency pass through the same region at a certain moment, the waves that occur at the moment of superposition of the two waves have the same original wave and frequency, and the amplitude is doubled.

The light emitting device 100 according to the embodiment may be mounted in a package, and a plurality of light emitting device packages having the light emitting device 100 mounted thereon may be arrayed on a substrate, and a light guide plate, A prism sheet, a diffusion sheet, and the like may be disposed. Such a light emitting device package, a substrate, and an optical member can function as a light unit. Still another embodiment may be implemented as a display device, an indicating device, and a lighting system including the light emitting device or the light emitting device package described in the above embodiments. For example, the lighting system may include a lamp and a streetlight.

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 exemplary embodiments, but, on the contrary, It should be understood that various modifications may be made by those skilled in the art without departing from the spirit and scope of the present invention.

100: light emitting device 110: substrate
112: reflective layer 120: first conductive semiconductor layer
122: first electrode 130: active layer
140: second conductive semiconductor layer 142: second electrode
150: light emitting structure 160: translucent electrode layer
210, 212: quantum barrier layer 214, 216, 218: quantum well layer

Claims (8)

A first conductive semiconductor layer;
A second conductive semiconductor layer; And
An active layer formed between the first conductive semiconductor layer and the second conductive semiconductor layer, the active layer including a quantum well layer and a quantum barrier layer alternately stacked a plurality of times and a lowermost portion formed of a reflective layer,
Wherein the quantum well layer has a refractive index greater than a refractive index of a quantum barrier layer and a refractive index of the quantum barrier layer is greater than a refractive index of a metal forming the reflective layer, Wherein the quantum barrier layers have a thickness such that a plurality of lights emitted from the quantum well layers satisfy a constructive interference condition. The method according to claim 1,
The constructive interference condition

T is the thickness of the quantum barrier layer,

lambda is a wavelength in a vacuum, n is a refractive index of a material constituting the quantum barrier layer, and m is an integer. The method according to claim 1,
Wherein the quantum well layer comprises
Wherein the quantum well structure comprises InGaN, and the amount of In is variable. The method according to claim 1,
Wherein the quantum barrier layer comprises:
GaN, InGaN, AlInN, and InAlGaN. The method according to claim 1,
When the light emitted from the active layer is blue light,
Lt; RTI ID = 0.0 > nm. ≪ / RTI > The method according to claim 1,
When the light emitted from the active layer is red light,
Lt; RTI ID = 0.0 > nm. ≪ / RTI > The method according to claim 1,
When the light emitted from the active layer is green light,
Lt; RTI ID = 0.0 > nm. ≪ / RTI > 8. The method according to any one of claims 5 to 7,
Wherein the quantum barrier layer has an error range within +/- 10% of a thickness satisfying a constructive interference condition.

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