KR20090096911A - Semiconductor light emitting device emitting a light having with wide spectrum wavelenth - Google Patents

Abstract

A semiconductor light emitting device emitting a light having with wide spectrum wavelength is provided to secure high color reproducibility by maintaining the distribution of exciting light generated from a fluorescent material wide. In a semiconductor light emitting device emitting a light having with wide spectrum wavelength, a plurality of quantum-well layers are positioned between a p-type nitride semiconductor layer(37) and an n-type nitride semiconductor layer(33). An active layer has a multiple quantum well on which a plurality of quantum barrier layers are laminated. The quantum-well layer of the active layer comprises at least two the quantum-well layer emitting the light of the different wavelength. As the luminescence peak wavelength of the quantum-well layer is shorter, it is adjacent to the p-type nitride semiconductor layer.

Description

Semiconductor light emitting device having a wide emission wavelength spectrum {SEMICONDUCTOR LIGHT EMITTING DEVICE EMITTING A LIGHT HAVING WITH WIDE SPECTRUM WAVELENTH}

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 providing excellent color characteristics when combined with a wavelength conversion member.

Recently, many researches and developments have been conducted to apply white light emitting devices using LEDs to general lighting devices as well as backlights of display devices.

Representatively, the implementation method of the LED white light emitting device is known that a simple combination of blue, red and green LEDs made of individual LEDs and a method using a phosphor. In general, a method of combining individual LEDs of multiple colors on the same printed circuit board requires a complex driving circuit for this purpose, and accordingly has a disadvantage of miniaturization, and thus, a method of manufacturing a white light emitting device using phosphors has recently been widely used.

As a conventional white light emitting device manufacturing method using a phosphor, there is a method using a blue light emitting device and a method using an ultraviolet light emitting device. For example, when a blue light emitting device is used, blue light is converted into white light using a YAG phosphor. That is, the blue wavelength generated from the blue LED may excite the YAG (Yittrium Aluminum Garnet) phosphor to finally emit white light.

As described above, when the fluorescent material is excited by the specific light of the light emitted by the LED chip to provide white light, since the light conversion efficiency of the fluorescent material is low, much loss of the final light amount is caused. In order to realize the high luminance light amount of the final white light, the excitation light must be specified with a wavelength that maximizes the light conversion efficiency of the fluorescent material.

However, the final white light obtained by combining the primary light source of the LED chip and the secondary light source, which is the excitation light specified according to the maximum conversion efficiency, has a limitation in providing at a level that satisfies characteristics such as color temperature by a very narrow wavelength spectrum.

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and an object thereof is to improve the light conversion efficiency in the fluorescent material and to ensure high color reproducibility to maintain a wide distribution of the spectrum of the fluorescent material excitation light in implementing a high brightness white light emitting device. A nitride semiconductor light emitting device can be provided.

In order to solve the above technical problem, the present invention

an active layer having a p-type and n-type nitride semiconductor layer and a multi-quantum well structure in which a plurality of quantum well layers and a plurality of quantum barrier layers are alternately stacked between the p-type and n-type nitride semiconductor layers, The quantum well layer of the active layer includes at least two quantum well layers emitting light of different wavelengths, and the shorter the emission peak wavelength of the quantum well layer is disposed adjacent to the p-type nitride semiconductor layer. A nitride semiconductor light emitting device is provided.

Preferably, the quantum well layer having the maximum light emission peak wavelength and the quantum well layer having the minimum light emission peak wavelength among the at least two quantum well layers are formed such that the light emission peak wavelength difference is 5 to 30 nm.

Further, in a particular embodiment, the plurality of quantum well layers may each be a quantum well layer that emits light of different wavelengths.

The present invention provides two methods (change of the composition or thickness of the quantum well layer) in order to implement the wavelength of each quantum well layer differently.

In one embodiment of the present invention, the at least two quantum well layers have different composition ratios so as to emit different wavelengths. Preferably, the at least two quantum well layers may be formed so that the composition ratio of indium is different.

In another embodiment of the present invention, the at least two quantum well layers have different thicknesses to emit different wavelengths.

Preferably, the quantum well layer having the maximum emission peak wavelength and the quantum well layer having the minimum emission peak wavelength among the at least two quantum well layers may be formed to have a thickness difference of 0.1 to 3 nm. In the case where the plurality of quantum well layers respectively emit light having different wavelengths, the quantum well layers may be formed to have a thickness difference of 0.1 to 1 nm.

In the nitride semiconductor light emitting device according to the present invention, by maintaining the spectral distribution of the excitation light wide, it is possible to improve the light conversion efficiency in the fluorescent material and further ensure high color reproducibility. Therefore, the nitride semiconductor light emitting device according to the present invention can be very advantageously applied to a high brightness white light emitting device using a phosphor.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention;

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

Referring to FIG. 1, the nitride semiconductor light emitting device 10 according to the exemplary embodiment of the present invention includes an n-type nitride semiconductor layer 13, an active layer 15, and a p-type nitride semiconductor layer sequentially formed on a substrate 11. (17).

As in the present embodiment, a transparent electrode layer 18 for ohmic contact is formed on the p-type nitride semiconductor layer 17, and n-side and on the n-type nitride semiconductor layer 12 and the transparent electrode layer 18, respectively. The p-side electrodes 19a and 19b may be provided.

The active layer 15 has a multi-quantum well structure in which a plurality of quantum well layers 15a and a plurality of quantum barrier layers 15b are alternately stacked. The present invention provides a method of extending the spectrum of total emitted light by forming at least two quantum well layers of the quantum well layer 15a such that the wavelength regions of the emitted light are different from each other.

In this embodiment, as shown in Fig. 2, the plurality of quantum well layers 15a are arranged such that the energy band gap becomes larger as the closer to the p-type nitride semiconductor layer 17, each having a different emission wavelength (Eg1 < Eg2 <Eg3 <Eg4).

This difference in energy band gap can be realized by forming different ratios of quantum well layers, respectively. For example, the plurality of quantum well layers 15a may be formed of In _x Ga _1-x N (0 ≦ _x ≦ ₁ ), and the In composition ratio (x) of each quantum well layer 15a may be p-type. The closer it is to the nitride semiconductor layer 17, the lower and smaller it can be realized.

In the case of a nitride semiconductor light emitting device, the hole injection length is relatively shorter than that of electrons, and the longer the quantum well layer emitting the longer wavelength, the deeper the quantum well.

In order to solve this problem, in the present invention, the quantum well layer close to the p-type nitride semiconductor layer 17 side is arranged so as to have an energy band gap smaller than that of the quantum well layer close to the n-type nitride semiconductor layer 13. In the active layer 15 of the well structure, it is planned to have a uniform distribution of holes. As a result, the current in the active layer 15 is smoothly provided, and the improvement of luminous efficiency can be expected.

In addition, by varying the emission light wavelength of each quantum well layer in the present invention it is possible to secure a broad spectrum of the final light emission wavelength, as a result can improve the light conversion efficiency by the phosphor and color reproducibility.

In this respect, the emission wavelength range of the quantum well layer is preferably limited within a certain range. Preferably, the quantum well layer having the maximum emission peak wavelength and the quantum well layer having the minimum emission peak wavelength may be formed such that the difference in the emission peak wavelength is 5 to 30 nm.

3 is a side cross-sectional view of a nitride semiconductor light emitting device according to another embodiment of the present invention. In this embodiment, a method of controlling the thickness of the quantum well layer with the emission wavelength of each quantum well layer is provided.

Referring to FIG. 3, the nitride semiconductor light emitting device 30 according to another embodiment of the present invention is similar to the previous embodiment, the n-type nitride semiconductor layer 33 and the active layer 35 sequentially formed on the substrate 31. And a p-type nitride semiconductor layer 37. The p-side and n-side electrodes 39b and 39a are formed on the transparent electrode layer 38 formed on the p-type nitride semiconductor layer 37 and on the n-type nitride semiconductor layer 32, respectively.

The active layer 35 has a multi-quantum well structure in which a plurality of quantum well layers 35a and a plurality of quantum barrier layers 35b are alternately stacked.

In the present embodiment, the plurality of quantum well layers 35a have different thicknesses so as to have different emission wavelengths. The thicker the quantum well layer 35a having the same composition ratio, the longer the wavelength becomes.

By using this tendency, the closer the quantum well layer 35a is to the p-type nitride semiconductor layer 37, the thinner its thickness is disposed (ta1> ta2> ta3> ta4). Through such thickness adjustment and arrangement, an effect similar to that of the energy band gap shown in FIG. 4 may be obtained. That is, the thinner the thickness of the quantum well layer has the effect of increasing the actual energy band gap (Ea1 <Ea2 <Ea3 <Ea4), and may have different wavelengths of emitted light depending on the thickness.

As described above, in the present embodiment, the spectrum of the final light emission wavelength can be more widely secured by adjusting the thickness of the quantum well layer 35a to change the emission light wavelength. As a result, the light conversion efficiency by the phosphor can be improved and color reproducibility can be improved. Preferably, the quantum well layer having the maximum emission peak wavelength and the quantum well layer having the minimum emission peak wavelength may be formed such that the difference in the emission peak wavelength is 5 to 30 nm.

In order to ensure a desired wavelength band for improving the phosphor conversion efficiency, the quantum well layer having the maximum emission peak wavelength and the quantum well layer having the minimum emission peak wavelength may be formed to have a thickness difference of 0.1 to 3 nm. Preferably, each quantum well layer 35a may be formed to have a thickness difference of 0.1 to 1 nm.

The present invention proposes two methods, namely, change of quantum well layer composition and quantum well layer thickness, to implement different wavelengths of each quantum well layer. Of course, the present invention may employ simultaneously changing the thickness of the quantum well layer with the composition of the quantum well layer.

Hereinafter, a method of expanding the wavelength spectrum by adjusting the thickness of the quantum well layer as in the embodiment shown in FIGS. 3 and 4 will be described in more detail with reference to the graph of FIG. 5.

Simulations were carried out using six pairs of In _0.07 Ga _0.93 N quantum well layers and GaN quantum barrier layers under the assumption of an active layer having a multi-quantum well structure. The six quantum well layers were set so that their thicknesses had 4.5 nm, 4.0 nm, 3.5 nm, 3.0 nm, 2.5 nm, and 2.0 nm, respectively, in the order of growth.

In addition, as an example (R), six active pairs of multi-quantum well structures having a thickness of 3.0 nm were assumed.

As shown in Fig. 5, in the reference example (R), the wavelength value was about 384 nm, and the spectrum was very narrow. In this case, as described above, even if only a slight deviation from the excitation wavelength of the phosphor, the conversion efficiency is greatly lowered, and color reproducibility is inferior depending on the product.

In contrast, when the thickness of the quantum well layer is implemented differently, the emission wavelength peak is different according to each quantum well layer. The light emission wavelength peak of each quantum well layer exhibits a wavelength shift of about 4 to 6 nm with the light emission wavelength peak of the adjacent quantum well layer, and it can be seen that the light emission wavelength peak is located over a band of about 25 nm as a whole. Therefore, even if a slight difference with the excitation wavelength of a given phosphor occurs, the conversion efficiency can be maintained at a constant level, and as a result, excellent color reproducibility can be expected.

The present invention is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims, and the appended claims. Will belong to the technical spirit described in.

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

FIG. 2 is an energy band diagram of an active layer of the nitride semiconductor light emitting device shown in FIG.

3 is a side cross-sectional view of a nitride semiconductor light emitting device according to another embodiment of the present invention.

FIG. 4 is an energy band diagram of an active layer of the nitride semiconductor light emitting device shown in FIG.

FIG. 5 is a graph showing wavelength spectrum of a nitride light emitting device enlarged using thickness control of a quantum well layer as an embodiment of the present invention.

Claims (8)

an active layer having a p-type and n-type nitride semiconductor layer and a multi-quantum well structure in which a plurality of quantum well layers and a plurality of quantum barrier layers are alternately stacked between the p-type and n-type nitride semiconductor layers, The quantum well layer of the active layer includes at least two quantum well layers emitting light of different wavelengths, and the shorter the emission peak wavelength of the quantum well layer is disposed adjacent to the p-type nitride semiconductor layer. A nitride semiconductor light emitting device. The method of claim 1, The light emitting peak wavelength difference between the quantum well layer having the maximum light emission peak wavelength and the quantum well layer having the minimum light emission peak wavelength among the at least two quantum well layers is 5 to 30 nm. The method of claim 1, The quantum well layer is a nitride semiconductor light emitting device, characterized in that each of the quantum well layer for emitting light of different wavelengths. The method of claim 1, And the at least two quantum well layers have different composition ratios so as to emit different wavelengths. The method of claim 4, wherein The at least two quantum well layers are nitride semiconductor light emitting device, characterized in that the composition ratio of indium is different. The method of claim 1, And the at least two quantum well layers have different thicknesses to emit different wavelengths. The method of claim 6, The nitride semiconductor light emitting device of claim 2, wherein the quantum well layer having the maximum light emission peak wavelength and the quantum well layer having the minimum light emission peak wavelength are formed to have a thickness difference of 0.1 to 3 nm. The method of claim 7, wherein The plurality of quantum well layers each emit light of different wavelengths, and the nitride semiconductor light emitting device, characterized in that formed to have a thickness difference of 0.1 ~ 1nm.

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