KR20010084332A - III-Nitride Semiconductor White Light Emitting Device - Google Patents

Abstract

PURPOSE: A nitride semiconductor white LED is provided to emit white light by directly generating lights of blue, green and red wavelengths and by color combination. CONSTITUTION: In the nitride semiconductor white LED, an n-type contact layer(220), a nitride semiconductor active layer(240) and a p-type contact layer(260) are sequentially stacked on a substrate(200) and n-type/p-type electrodes are respectively formed on the n-type contact layer(220) and the p-type contact layer(260). A secondary excitation visible ray light emission layer(270) is formed between the p-type contact layer(260) and the p-type electrode. The light emission layer(270) is formed of at least one selected from groups consisting GaAs1-xPx(0<x<1), (AlxGa1-x)yln1-yP(0<x,y<1) or Ga1-xAlxAs(0<x<1).

Description

Nitride Semiconductor White Light Emitting Device {III-Nitride Semiconductor White Light Emitting Device}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride semiconductor white light emitting device. In particular, a secondary excitation visible light emitting layer is further formed on the nitride semiconductor light emitting device to realize red, green, and blue three-color light emission inside the light emitting device. The present invention relates to a nitride semiconductor light emitting device of a light emitting type.

Nitride semiconductor light emitting devices have recently attracted much attention as materials such as blue light emitting diodes (LEDs), blue laser diodes (LDs), and solar cells. In particular, the full-color display area by red, green, and blue LEDs and the replacement market of luminaires by white LEDs are enormous.

Conventional nitride semiconductor white light emitting devices form a fluorescent material layer comprising a YAG phosphor phosphor thermally excited on a blue light emitting device having a wavelength of 430 nm, and thus a color combination between the light in the visible region and the original blue light emitted from the fluorescent material layer. As a method of obtaining white light, the basic structure of the mounted white light emitting device is shown in FIG. 1.

Conventionally, as shown in FIG. 1, a device 110 formed by stacking a multilayer nitride semiconductor thin film on an insulating substrate 100 such as sapphire or SiC, and a lower surface of the substrate 100 on which the device 110 is not formed. In order to prevent light from entering the synthetic resin for die bonding, coating metal such as In, Cu, Pd, Rh, W, Mo, Ti, Ni, Al and Ag or conductive materials such as TiO ₂ , SiO ₂ and BaF ₂ And a die-bonding synthetic resin layer 130 formed using an epoxy resin, a silicon resin, or the like containing Au, Ag, Al, and Cu in order to increase thermal conductivity between the chip and the lead frame. And wires 120 and 125 for connecting the device to the lead frames 135 and 145, and a silicone resin and an amorphous fluorine resin in a gel form. or light-transmitting polyimide (polymide) a color conversion material with a resin and a Y ₃ Al ₅ O type consisting of _two Material layer 150 is formed so as to cover the element 110.

By using the fluorescent material Y ₃ Al ₅ O ₂ in the blue light emitting device having a wavelength of 450 nm as excitation light it is possible to obtain light in the visible light region of 530 ~ 580 nm. It is also possible to replace Al with Ga to shorten the light emission wavelength and to replace Y with Gd to make the long wavelength.

As described above, the white light emitting device manufactured using the conventional blue light as the excitation light source has lower luminous efficiency than the light emitting device in which the white light directly emits light in the device, and because the secondary transition material is used, the overall size of the device is packaged. There is a limit in miniaturization of the white light emitting device, and there is a problem that the unit cost is also high. The conventional method of forming a white light emitting device different from the above-described method is a method of mounting each of the red, green, and blue unit light emitting devices together, and this method requires a separate power supply circuit for each device, so the mounted white LEDs There is a problem in that the manufacturing cost of the high and the size of the device is large.

In addition, high power and ultra-short wavelength light source of 300 nm or less are required for the development of the conventional white light emitting device, but the development of the ultra-short wavelength light emitting device is a research and development stage, which requires a little time to be put into practical use.

Accordingly, an object of the present invention is to provide a nitride semiconductor white light emitting device in which white light is emitted by color combination by directly generating blue, green and red wavelengths of light from the nitride semiconductor light emitting device.

In order to achieve the above object, a nitride semiconductor white light emitting device has an n-type contact layer, a nitride semiconductor active layer, and a p-type contact layer sequentially stacked on a substrate, and n-type and p-type layers on the n-type and p-type contact layers, respectively. A nitride semiconductor light emitting device in which an electrode is formed, characterized in that it comprises a secondary excitation visible light emitting layer between the p-type contact layer and the p-type electrode.

1 is a cross-sectional view schematically showing a nitride semiconductor white light emitting device according to the prior art.

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

3 is a light emission spectrum of the white light emitting device according to the present invention.

4 is a comparison graph showing current-voltage characteristics of a conventional nitride semiconductor white light emitting device and a nitride semiconductor white light emitting device according to the present invention;

<Explanation of symbols for the main parts of the drawings>

200: substrate 220: n-type contact layer

240: active layer 260: p-type contact layer

270: secondary excitation light emitting layer

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

GaAs _1-x P _x is a mixed crystal of GaAs and GaP, and the composition ratio x has any value from 0 to 1. At room temperature, the bandgap energy of mixed GaAs _1-x P _x varies from 1.42 eV (GaAs) to 2.26 eV (GaP), and has a direct transition band structure up to x = 0.42, followed by an indirect transition band structure. Has Therefore, correspondingly, the emission wavelength also varies between 880 and 555 nm, and red, orange and yellow light emission can be realized.

In addition, when nitrogen (N) is added to GaP, nitrogen (N) substitutes phosphorus (P) to become an electrically neutral impurity. However, since nitrogen has a higher electron affinity than phosphorus, it traps electrons in the vicinity. Impurities such as nitrogen are called isoelectric traps, and when electrons are trapped, excitons with holes paired by coulomb attraction are formed, and the excitons dissipate and recombine the band gap and Green light can be obtained by subtracting the energy difference.

As a GaP doping method for GaP red light emission around 700 nm, there is a method of simultaneously adding zinc (Zn) and oxygen (O). Zinc forms a low acceptor (E _A = 64 meV) and oxygen forms a deep donor (E _D = 893 meV). When these zinc and oxygen have the nearest lattice point, a complex center is formed. The zinc-oxygen (Zn-O) composite center is electrically neutral, but since oxygen has a deep potential, electrons can be compensated, and when electrons are compensated, holes are drawn and bound energy is formed. Therefore, it disappears by this energy difference and becomes red light emission.

Materials composed of mixed crystals such as (Al _x Ga _1-x ) _y In _1-y P also have a bandgap for the emission region of visible light, and recombination of light absorption and excitons for light with high energy in the bandgap. Red and green light emission can be realized in the process, and like GaAs _1-x P _x , it can be used as a secondary excitation visible light emitting layer of a white light emitting device.

In the present invention, as a method for obtaining the basic three primary colors of red, green, and blue required for the fabrication of white light emitting devices, a vapor phase deposition method (VPE) method on the upper surface of the p-GaN contact layer of the short wavelength light emitting device, organometallic chemistry AlGaAs and GaAsP described above, which can realize red and green visible light emission using a crystal growth apparatus such as a vapor deposition method (hereinafter referred to as a MOCVD) method or a liquid phase epitaxy (LPE) method. And growing a semiconductor crystal thin film such as InGaAlP to induce red and green light emission in the visible light region by re-emission of electrons excited by secondary absorption of ultraviolet light and blue high energy short wavelength light generated in the nitride semiconductor active layer. A white light emitting device was manufactured.

2 is a schematic cross-sectional view of a nitride semiconductor white light emitting device according to an embodiment of the present invention as described above, FIG. 3 is a light emission spectrum of a nitride semiconductor white light emitting device according to an embodiment of the present invention, and FIG. It is a comparative graph showing the current-voltage characteristics of the nitride semiconductor white light emitting device and the nitride semiconductor white light emitting device according to the present invention.

In the nitride semiconductor white light emitting device according to the embodiment of the present invention as shown in FIG. 2, a buffer layer and an n-type contact layer are formed on a substrate, and an n-type cladding layer, an active layer, and a p-type cladding are formed on a predetermined portion of the n-type contact layer. A layer and a p-type contact layer are formed sequentially.

The secondary excitation visible light emitting layer formed of AlGaAs, GaAsP, InGaAlP, etc. on the p-type contact layer reabsorbs and emits blue light generated in the active layer to form a white light source by color sum.

Next, the n-type cladding layer includes n-type contact layers where the n-type cladding layer is not formed, and n-type and p-type, respectively, formed in predetermined portions on the secondary excitation light emitting layer.

Although not shown, a method of forming a nitride semiconductor white light emitting device according to the present invention having the above-described structure may include a buffer layer and an n-type contact by using a MOCVD method on a general substrate for forming a nitride semiconductor thin film such as sapphire. A layer, an n-type cladding layer, an active layer, a p-type cladding layer and a p-type contact layer are sequentially formed, and AlGaAs, GaAsP, and InGaAlP, etc. are deposited on the P-type contact layer by a crystal growth method such as VPE, MOCVD or LPE. To form a secondary excitation light emitting layer. The secondary excitation light emitting layer is composed of general GaAs 1-x Px (0 ≦ x ≦ 1), (AlxGa1-x) yIn1-yP (0 ≦ x, y ≦ 1) or Ga1-xAlxAs (0 <x ≦ 1). It is formed of at least one selected from the group, the secondary excitation light emitting layer is doped with at least one or more impurities selected from the group consisting of Si, Te, Zn, Cd, Mg, N or O of n-type and p-type impurities do.

Subsequently, an n-type electrode is etched by using an etching apparatus to a predetermined depth of the n-type contact layer, and an n-type electrode is formed by using Ti / Al on a portion of the n-type contact layer that is exposed by etching. Ni-Au is used to form the p-type electrode in the predetermined portion.

Finally, each of the n-type and p-type electrodes is assembled to a heat dissipation package by wire bonding to fabricate a nitride semiconductor white light emitting device, and the device is driven by flowing a current through the electrode portion.

The high energy short wavelength blue light generated in the active layer is absorbed by the secondary excitation visible light emitting layer on the surface, and is then excited to generate red and green visible light, and emits white light by hue sum with unabsorbed blue light source. . The red and green secondary excitation light can control the light emission wavelength, the light emission efficiency and the amount of light by the thickness of the grown visible light emitting layer, the composition ratio of the compound and the doping of impurities, and can be controlled by the condition variables during the crystal growth.

In general, the p-type nitride semiconductor has a very limited material used as a doping source, and magnesium (Mg), which is generally used, is also inactivated by hydrogen (H), and thus doping efficiency is not good, and hole mobility and hole concentration are not high. not. The p-type contact layer has a problem in that it is difficult to effectively inject current into a conventional nitride semiconductor device because of a large contact resistance with a metal electrode.

However, GaAsP and InGaAlP secondary-excited visible light emitting layers are relatively easy to dop type impurity dopants, have high hole mobility and hole concentration, and thus have low contact resistance with metal electrodes, thereby lowering the driving voltage of the white light emitting device to implement low power consumption devices. Can be.

In addition, an interface having a high carrier mobility is formed between the p-GaN contact layer and the GaAsP and InGaAlP secondary excitation light emitting layers due to the difference in the band gap, resulting in a two-dimensional current spreading phenomenon, resulting in a uniform light emitting surface of the light emitting device. There is an advantage that can produce a white light emitting device of high light output by inducing one light emission.

3 is a graph showing light emission spectra of a white light emitting device using the secondary excitation visible light emitting layer according to the embodiment of the present invention.

As shown, it can be seen that blue light generated in the active layer emits yellow light around 570 nm generated by reabsorption and emission in the secondary excitation visible light emitting layer. Therefore, such emitted light can form a white light source by the sum of colors.

4 is a graph comparing current-voltage characteristics of a white light emitting device (a) using a secondary excitation visible light emitting layer according to the present invention and a white light emitting device (b) having a conventional structure.

As shown in FIG. 4, when the driving voltage of the current was applied to 20 mA, the case of (a) using the secondary excitation visible light emitting layer was about 3.4V, which was about 0.3V lower than that of (b) which was not used. . The low driving voltage of the light emitting device has an advantage of reducing the power consumed during the operation of the device.

As a result, it can be seen that in addition to the white light emitting effect, the secondary excitation visible light emitting layer has the effect of spreading the current applied to the device and reducing the contact resistance with the metal electrode.

As described above, the nitride semiconductor white light emitting device according to the present invention having the secondary excitation visible light emitting layer using AlGaAs, GaAsP or InGaAlP, etc. has a high luminous efficiency by emitting light directly from the light emitting device without using a phosphor, and thus, device fabrication. The process has a simple advantage.

In addition, the contact resistance with the metal electrode is low, the driving voltage of the white light emitting device can be lowered to implement a device of low power consumption, the two-dimensional current spreading phenomenon due to the difference in the band gap between the p-type contact layer and the secondary excitation light emitting layer This occurs to induce uniform light emission throughout the light emitting surface of the light emitting device has the advantage of producing a white light emitting device of high light output.

Claims (4)

In a nitride semiconductor light emitting device in which an n-type contact layer, a nitride semiconductor active layer, and a p-type contact layer are sequentially stacked on a substrate, and n-type and p-type electrodes are formed on the n-type and p-type contact layers, respectively. A nitride semiconductor white light emitting device comprising a secondary excitation visible light emitting layer between the p-type contact layer and the p-type electrode. The method according to claim 1, wherein the second visible light emitting layer is a general formula GaAs1-xPx (0 ≤ x ≤ 1), (AlxGa1-x) yIn1-yP (0 ≤ x, y ≤ 1) or Ga1-xAlxAs (0 <x ≤ A nitride semiconductor white light emitting device, characterized in that formed at least one selected from the group consisting of 1). The nitride semiconductor white light emitting device of claim 1 or 2, wherein the secondary excitation visible light emitting layer is doped with n-type and p-type impurities. The nitride semiconductor white light emitting device of claim 3, wherein the n-type and p-type impurities are formed of at least one selected from the group consisting of Si, Te, Zn, Cd, Mg, N, or O.