KR20080066366A - Semiconductor light emitting device - Google Patents

Abstract

A semiconductor light emitting device is provided to emit white light with high light emitting efficiency and an improved color rendering index by including a color conversion layer made of a semiconductor material that absorbs light emitted from an active layer and has an energy band gap for converting the absorbed light into light of a different wavelength. A light transmitting substrate(11) has first and second main surfaces confronting each other. A semiconductor layer of a first conductivity type is formed on the first main surface of the light transmitting substrate. An active layer(13) is formed on the semiconductor substrate of the first conductivity type. A semiconductor layer of a second conductivity type is formed on the active layer. A color conversion layer(15) is formed on the second main surface of the light transmitting substrate, made of a semiconductor material that absorbs the light emitted from the active layer and converts the absorbed light into light with a different wavelength. The content of a composition of the color conversion layer can be changed to have an energy band gap inclined along its thickness direction.

Description

Semiconductor Light Emitting Device {SEMICONDUCTOR LIGHT EMITTING DEVICE}

1 is a side cross-sectional view showing a semiconductor light emitting device according to one embodiment of the present invention.

FIG. 2 illustrates energy band gaps around an active layer and a color conversion layer in the semiconductor light emitting device of FIG. 1.

3A to 3C illustrate an energy band gap around a color conversion layer in a semiconductor light emitting device according to another embodiment of the present invention.

<Code Description of Main Parts of Drawing>

11: sapphire substrate 12: n-type nitride semiconductor layer

13a: quantum well layer 13b: quantum barrier layer

13: active layer 14: p-type nitride semiconductor layer

15: color conversion layer 16a, 16b: n-side and p-side electrodes

31,31`, 31``: sapphire substrate 35,35`, 35``: color conversion layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device capable of obtaining a high luminous efficiency without using a phosphor and emitting white light having an improved color rendering index.

BACKGROUND A light emitting diode (LED) is a semiconductor device capable of generating light of various colors based on recombination of electrons and holes at a junction portion of a p and n type semiconductor when current is applied thereto. These LEDs have a number of advantages over filament based light emitting devices, such as long life, low power, excellent initial driving characteristics, high vibration resistance, and high tolerance for repetitive power interruptions. In recent years, group III nitride semiconductor light emitting devices capable of emitting light in a blue short wavelength region have been in the spotlight.

In order to use these LEDs as general lighting, it is necessary to obtain white light using the LEDs. There are three ways to implement a white LED.

First, a combination of three LEDs emitting three primary colors of light, red, green, and blue, is used to realize white color. This method requires the use of three LEDs to create one white light source, and involves the hassle of controlling each LED.

Second, a method of realizing white by exciting a yellow phosphor by using a blue LED as a light source is mentioned. This method has a problem that it is difficult to obtain white light close to sunlight because the method has excellent luminous efficiency but low color rendering index and color rendering index changes according to current density.

Finally, there is a method of exciting three primary color phosphors by using an ultraviolet light emitting LED as a light source. This method can be used under high current and has excellent color. However, the three primary phosphor is made of an inorganic phosphor, in particular, the red inorganic phosphor has a problem of low luminous efficiency. In addition, as in the second method, a process such as injecting a phosphor in addition to the light emitting structure has to be accompanied, and thus, the process becomes complicated.

Therefore, there is a need for a semiconductor light emitting device capable of obtaining white light having high color rendering index and high luminous efficiency without using a phosphor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object thereof is to provide a semiconductor light emitting device capable of obtaining high luminous efficiency without emitting a phosphor and emitting white light having improved color rendering index.

In order to solve the above technical problem, in one embodiment of the present invention,

A translucent substrate having first and second main surfaces facing each other, a first conductive semiconductor layer formed on the first main surface of the translucent substrate, an active layer formed on the first conductive semiconductor layer, and an active layer A color conversion layer formed on a second conductive semiconductor layer formed on the second conductive surface and a second main surface of the light transmissive substrate, the color conversion layer comprising a semiconductor material having an energy band gap for absorbing light emitted from the active layer and converting the light into light having a different wavelength; It provides a semiconductor light emitting device comprising.

In order to obtain white light, which is an object of the present invention, preferably, the color conversion layer may include regions having different compositions or contents of the compositions so as to have at least two different energy band gaps.

The color conversion layer may have a change in content of a part of the composition so as to have an inclined energy bandgap in the thickness direction, and preferably, the energy bandgap increases as the color conversion layer moves away from the translucent substrate.

On the other hand, the first and second conductive type semiconductor layer and the active layer, a nitride semiconductor or a _{Zn x Mg y Cd 1 -x- y} O (0≤x≤1, 0≤y≤1, 0≤x + y≤ It is preferably made of 1), in this case, the active layer may be to emit light having a wavelength of 350 ~ 470nm. Further, the substrate composed of sapphire, SiC, GaN, Ga ₂ O ₃ and _{Zn x Mg y Cd 1 -x- y} O (0≤x≤1, 0≤y≤1, 0≤x + y≤1) It is preferably made of a material selected from the group.

Preferably, the color conversion layer is In _x Ga _(1-x) N (0 <x _{≤ 1} ), Mg _x Zn _{1- x} O (0 _≤ x <1), Al _x Ga _1-x As ( _{0≤x≤1), Zn x Mg y Cd} 1 -x- y O (0≤x≤1, 0≤y≤1, 0≤x + y≤1) , and Al _x In _y Ga _{1 -x- y} It may be made of a material selected from the group consisting of P (0≤x≤1, 0≤y≤1, 0≤x + y≤1).

In a preferred embodiment of the present invention, the color conversion layer may be directly grown on the second main surface of the light transmissive substrate, and the color conversion layer is bonded to the second main surface of the light transmissive substrate by wafer bonding. It may be.

In consideration of the color conversion efficiency of the color conversion layer, the thickness of the color conversion layer is preferably 5 ~ 500㎛.

On the other hand, the color conversion layer may have a doping level by the doped impurities, in this case, the doped impurities, preferably includes both n-type and p-type impurities. In addition, the concentration of the n-type impurities is 5 × 10 ¹⁶ ~ 5 × 10 ¹⁸ / cm 3, and the concentration of the p-type impurity is from 5 × 10 ¹⁷ to It is preferable that it is 5 * 10 <^19> / cm <3>. Herein, the p-type impurity is preferably at least one element selected from the group consisting of Be, Mg, Ca, and Zn, and the n-type impurity is preferably at least one element selected from the group consisting of Si, O, and C. Do.

In another embodiment of the present invention,

A light emitting device comprising a first and a second conductivity type semiconductor layer and an active layer formed therebetween, comprising a semiconductor material having an energy band gap for absorbing the light emitted from the active layer and converting it into light having a different wavelength. The present invention provides a semiconductor light emitting device including a color conversion layer doped with impurities to form a doping level for improving color conversion efficiency.

Also in this case, the doped impurities preferably include both n-type and p-type impurities, and the concentration of the n-type impurities is 5 × 10 ¹⁶ to 5 × 10 ¹⁸ / cm 3, and the concentration of the p-type impurity is from 5 × 10 ¹⁷ to It may be 5 × 10 ¹⁹ / cm 3.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

1 is a side cross-sectional view showing a semiconductor light emitting device according to one embodiment of the present invention.

Referring to FIG. 1, the semiconductor light emitting device 10 according to the present embodiment includes a sapphire substrate 11 and an n-type nitride semiconductor layer sequentially formed on the color conversion layer 15 and the color conversion layer 15. 12), an active layer 13, a p-type nitride semiconductor layer 14 and a p-side electrode 16b. In addition, the n-side electrode 16a is formed on the n-type nitride semiconductor layer 12 upper surface exposed through mesa etching.

The sapphire substrate 11 is a crystal having hexagonal-Rhombo R3c symmetry. An orientation plane includes a C (0001) plane, an A (1120) plane, an R (1102) plane, and the like. In the case of the C surface of the sapphire substrate 11, the nitride thin film is relatively easy to grow and is stable at a high temperature, and thus is mainly used as a nitride growth substrate. In addition, since the sapphire substrate 11 is light-transmitting, light emitted from the active layer 13 may pass through the sapphire substrate 11 and may be absorbed by the color conversion layer 15. However, in the present invention, the light-transmissive substrate is not limited to the sapphire substrate 11, and is not shown in the embodiment of the nitride or Zn _x Mg _y Cd _1-xy O (0≤x≤1, 0≤y≤1 , 0 ≦ x + y ≦ 1) SiC, GaN, Ga ₂ O ₃ , Zn _x Mg _y Cd _1-xy O (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y) ≤1) and the like may be employed.

The n-type nitride semiconductor layer 12 and the p-type nitride semiconductor layer 14 are Al _x In _y Ga _(1-xy) N composition formula (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + n? impurity and p type impurity doped with a semiconductor material doped with y ≦ 1), and typically GaN, AlGaN, InGaN. In addition, Si, O, C, etc. may be used as the n-type impurity, and the p-type impurity may be representative of Be, Mg, Ca, Zn, and the like. The n-type and p-type nitride semiconductor layers 12 and 14 may be grown by known growth processes such as organometallic vapor deposition (MOCVD), molecular beam growth (MBE), hybrid vapor deposition (HVPE), and the like.

The active layer 13 emits visible light (about 350 to 680 nm wavelength range), ultraviolet light, etc. by recombination of electrons and holes, and is composed of a semiconductor layer having a single or multiple quantum well structure. As described above, in the present embodiment, the light emitted from the active layer 13 is absorbed by the color conversion layer 15, and the color conversion layer 15 emits light having a longer wavelength than the light, so that white light Implement More details on this will be described with reference to FIG. 2.

Meanwhile, the active layer 13 may be grown by organometallic vapor deposition, molecular beam growth, hybrid vapor deposition, and the like as the n-type and p-type nitride semiconductor layers 12 and 14.

As described above, the color conversion layer 15 employed in the present invention absorbs the light emitted from the active layer 13 and then emits long wavelength light, thereby providing a white semiconductor light emitting device 10 ) Can be implemented. In the present embodiment, the color conversion layer 15 may be made of nitride such as In _x Ga _(1-x) N (0 <x≤1), in which case the energy band gap is controlled by the indium content. . Specifically, since the energy band gap decreases as the indium content increases, the indium content may be adjusted to have a smaller energy band gap than the quantum well layer of the active layer, so that light having a relatively long wavelength may be emitted.

In this case, when the thickness t of the color conversion layer is too thin, it is difficult to obtain white light having a high luminous efficiency, whereas when too thick, the light extraction efficiency may be lowered. Therefore, in consideration of the color conversion efficiency of the color conversion layer 15, the thickness t of the color conversion layer is preferably 5 ~ 500㎛.

As illustrated in FIG. 1, the color conversion layer 15 may be formed on the second main surface of the sapphire substrate 11 (corresponding to the bottom surface of the sapphire substrate based on FIG. 1). 15 may be bonded to the sapphire substrate 11 through a wafer bonding process. As such, when the color conversion layer 15 is bonded, another semiconductor layer may not be grown on the color conversion layer 15 having relatively low crystallinity due to the high indium content. Therefore, the crystallinity of the n-type and p-type nitride semiconductor layers 12 and 14 and the active layer 13 formed on the sapphire substrate 11 is not lowered due to the color conversion layer 15. The semiconductor light emitting device 10 can expect high luminous efficiency and reliability.

Further, as the color conversion layer 15 can be formed by bonding, the color conversion layer 15 is not limited to nitride as in the present embodiment, and Mg _x Zn _{1 -x} O (0 ≦ x < _{1), Al x Ga 1-} x As (0≤x≤1), Zn x Mg y Cd 1 -x- y O (0≤x≤1, 0≤y≤1, 0≤x + y≤1) and _{Al x in y Ga 1 -x- y} P (0≤x≤1, 0≤y≤1, 0≤x + y≤1) short wavelength light by absorbing an energy band gap structure which is capable of emitting long wavelength, such as Other materials having may be employed. However, in the present invention, the color conversion layer 15 may be directly grown on the second main surface of the sapphire substrate 11 in addition to the case where the color conversion layer 15 is bonded to the sapphire substrate 11.

FIG. 2 illustrates energy band gaps around an active layer and a color conversion layer in the semiconductor light emitting device of FIG. 1.

Referring to FIG. 2, the active layer 13 has a structure in which a plurality of quantum well layers 13a and a quantum barrier layer 13b are alternately stacked, and the active layer is formed by an energy band gap of the quantum well layer 13a. The wavelength of the light emitted at (13) is determined.

In the present embodiment, in order to implement a white light emitting device by absorbing and emitting the color conversion layer 15, the light L1 emitted from the active layer 13 is light of blue series, specifically, the light. It is preferable that the wavelength of (L1) is 350-470 nm, but ultraviolet light may be emitted in another embodiment.

The light L1 emitted from the active layer 13 passes through the sapphire substrate 11 having a high energy band gap and is absorbed by the color conversion layer 15. This is due to the principle that when high energy light passes through a region having a relatively low energy band gap, the light is absorbed in the region and emits light corresponding to the energy band gap of the region. That is, the light L1 emitted from the active layer 13 is absorbed by the color conversion layer 15 having a lower energy bandgap than the quantum well layer 13a. Accordingly, the color conversion layer 15 ) Can emit light (L2, L3, L4) corresponding to the three primary colors. That is, white light is realized by the combination of the lights L1, L2, L3, and L4 emitted from the active layer 13 and the color conversion layer 15, respectively.

Meanwhile, as shown in FIG. 2, the energy band gap of the color conversion layer 15 tends to increase gradually in a direction away from the sapphire substrate 11, that is, in a thickness direction of the color conversion layer 15. As shown, the wavelength change can emit continuous light. That is, since the color conversion layer 15 may emit other light showing continuous wavelength changes in addition to the light L2, L3, and L4 shown in FIG. 2, the energy bandgap structure of the color conversion layer 15 Can contribute to obtaining white light having excellent color rendering index. In this regard, the energy bandgap structure of the color conversion layer 15 may be controlled by an indium content as described above, and the indium content included in the color conversion layer 15 may be the sapphire substrate 11. Away from), gradually decreasing.

In addition, referring to the energy level indicated by the dotted line in the energy band gap of the color conversion layer 15, the color conversion layer 15 is doped level doped with n-type impurities and doped level doped with p-type impurities, respectively. Has In this case, the doping levels doped with the n-type and p-type impurities improve the recombination efficiency of electrons and holes, thereby improving the color conversion efficiency of the color conversion layer 15. In this case, it is most preferable that the n-type impurity is Si, and the p-type impurity is Mg, and considering the aspect of improving color conversion efficiency, the concentration of the n-type impurity is 5 × 10 ^16- 5 × 10 ¹⁸ / cm 3, and the concentration of p-type impurities is 5 × 10 ¹⁷ to It is preferable that it is 5 * 10 <^19> / cm <3>.

As described above, in the present invention, the color conversion layer 15 is unique in that it also improves the color conversion efficiency by impurity doping. Accordingly, the formation position of the color conversion layer 15 as in the present embodiment is It is not limited to the second main surface of the sapphire substrate 11. That is, in another embodiment, the color conversion layer 15 is made of a semiconductor material having an energy bandgap for absorbing the light emitted from the active layer and converting it into light of a different wavelength, and doping for improving the light conversion efficiency. The impurity may be doped to form a level, and may be formed without limitation as long as it is a position capable of performing the above function.

On the other hand, in the present invention, the energy bandgap structure of the color conversion layer 15 is not limited to the form of decreasing linearly as in the present embodiment, which will be described with reference to FIGS. 3A to 3C. 3A to 3C illustrate an energy band gap around a color conversion layer in a semiconductor light emitting device according to another exemplary embodiment of the present invention, and n-type and p-type nitride semiconductor layers and active layer portions are omitted.

3A to 3C, the color conversion layers 35, 35 ′ and 35 ″ are formed adjacent to the sapphire substrates 31, 31 ′ and 31 ″ as in FIG. 1, and FIG. 3A. The color conversion layer 35 of Figure 3b is a step of increasing in the form, the color conversion layer 35` of Figure 3b is reduced in a linear form, the color conversion layer 35`` of Figure 3c is increased in a curved form Each has an energy band gap of. In addition, although not shown, an energy bandgap structure (eg, step reduction, curve reduction, etc.) of a color conversion layer for obtaining white light having a high color rendering index, which is an object of the present invention, may be appropriately adopted.

In the above embodiments, when the first and second conductivity-type semiconductor layers, the active layer, and the color conversion layer are nitride, that is, the nitride semiconductor light emitting device has been described, the present invention is not limited thereto. That is, even in a semiconductor light emitting device made of a material such as Zn _x Mg _y Cd _{1 -x- y} O (0≤x≤1, 0≤y≤1, 0≤x + y≤1), which is not nitride, The white light may be emitted through the process of absorbing and re-emitting the color conversion layer.

It is intended that the invention not be limited by the foregoing embodiments and the accompanying drawings, but rather by the claims appended hereto. Accordingly, various forms of substitution, modification, and alteration may be made by those skilled in the art without departing from the technical spirit of the present invention described in the claims, which are also within the scope of the present invention. something to do.

As described above, according to the present invention, it is possible to obtain a semiconductor light emitting device capable of obtaining high luminous efficiency without emitting phosphor and emitting white light having improved color rendering index.

Claims (19)

A translucent substrate having first and second main surfaces facing each other; A first conductivity type semiconductor layer formed on the first main surface of the light transmissive substrate; An active layer formed on the first conductivity type semiconductor layer; A second conductivity type semiconductor layer formed on the active layer; And And a color conversion layer formed on a second main surface of the light transmissive substrate, the color conversion layer comprising a semiconductor material having an energy band gap for absorbing light emitted from the active layer and converting the light into light having a different wavelength. The method of claim 1, The color conversion layer is a semiconductor light emitting device, characterized in that it comprises a region having a different composition or content of the composition to have at least two different energy band gap. The method of claim 1, The color conversion layer is a semiconductor light emitting device, characterized in that the content of the composition is changed to have an inclined energy bandgap according to the thickness direction. The method of claim 3, The color conversion layer is a semiconductor light emitting device, characterized in that the energy band gap increases as the distance from the transparent substrate. The method of claim 1, The first and second conductivity type semiconductor layers and the active layer are formed of a nitride semiconductor or Zn _x Mg _y Cd _1-xy O (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A semiconductor light emitting device, characterized in that. The method of claim 5, The active layer is a semiconductor light emitting device, characterized in that for emitting light having a wavelength of 350 ~ 470nm. The method of claim 5, The substrate from the _{sapphire, SiC, GaN, Ga 2 O} 3 and _{Zn x Mg y Cd 1 -x- y} O the group consisting of (0≤x≤1, 0≤y≤1, 0≤x + y≤1 ) A semiconductor light emitting device comprising a selected material. The method of claim 1, The color conversion layer is In _x Ga _(1-x) N (0 <x _{≤ 1} ), Mg _x Zn _{1- x} O (0 _≤ x <1), Al _x Ga _{1 - x} As (0 ≤ _x ≤ _{1), Zn x Mg y Cd} 1 -x- y O (0≤x≤1, 0≤y≤1, 0≤x + y≤1) , and _{Al x In y Ga 1 -x- y} P (0≤ and a material selected from the group consisting of x ≦ 1, 0 ≦ y ≦ 1, and 0 ≦ x + y ≦ 1). The method of claim 1, The color conversion layer is a semiconductor light emitting device, characterized in that directly grown on the second main surface of the transparent substrate. The method of claim 1, And the color conversion layer is bonded to the second main surface of the light transmissive substrate by wafer bonding. The method of claim 1, The thickness of the color conversion layer is a semiconductor light emitting device, characterized in that 5 ~ 500㎛. The method of claim 1, And the color conversion layer has a doping level due to doped impurities. The method of claim 12, The doped impurity may include both n-type and p-type impurities. The method of claim 13, The concentration of the n-type impurities is 5 × 10 ¹⁶ ~ 5 × 10 ¹⁸ / cm 3, and the concentration of the p-type impurity is from 5 × 10 ¹⁷ to A semiconductor light emitting device, characterized in that 5 × 10 ¹⁹ / cm 3. The method of claim 13, The p-type impurity is at least one element selected from the group consisting of Be, Mg, Ca and Zn. The method of claim 13, The n-type impurity is at least one element selected from the group consisting of Si, O and C semiconductor light emitting device. A light emitting device comprising a first and a second conductivity type semiconductor layer and an active layer formed therebetween, Comprising a semiconductor material having an energy bandgap for absorbing the light emitted from the active layer and converting it to light of a different wavelength, comprising a color conversion layer doped with impurities to form a doping level for improving color conversion efficiency Semiconductor light emitting device. The method of claim 17, The doped impurity may include both n-type and p-type impurities. The method of claim 18, The concentration of the n-type impurities is 5 × 10 ¹⁶ ~ 5 × 10 ¹⁸ / cm 3, and the concentration of the p-type impurity is from 5 × 10 ¹⁷ to A semiconductor light emitting device, characterized in that 5 × 10 ¹⁹ / cm 3.

Images