KR20080010138A - Nitride based light emitting diode - Google Patents

Abstract

A nitride based light emitting device is provided to improve inner quantum efficiency by improving the band structure of an active layer through a super lattice layer. A nitride based light emitting device includes a first conductive semiconductor layer(20), a super lattice layer(30), a second conductive semiconductor layer(50), an active layer(60), and a third conductive semiconductor layer(70). The super lattice layer is located on the first conductive semiconductor layer. The second conductive semiconductor layer is located on the super lattice layer. The active layer is located on the second conductive semiconductor layer. The third conductive semiconductor layer is located on the active layer.

Description

Nitride-based light emitting device

1 is a cross-sectional view showing an example of a conventional light emitting device.

2 is a schematic view showing a crystal defect in a conventional light emitting device manufacturing process.

3 is a cross-sectional view showing a thin film structure of the present invention.

4 is an enlarged view of a portion of FIG. 3.

5 is a sectional view showing a first embodiment of the present invention.

6 is a cross-sectional view showing a second embodiment of the present invention.

<Brief description of the main parts of the drawing>

10 substrate 20 first conductive semiconductor layer

30: superlattice layer 31: first layer

32: second layer 40: buffer layer

50: second conductive semiconductor layer 60: active layer

70: third conductive semiconductor layer 80: p-type electrode

90: n-type electrode

The present invention relates to a nitride-based light emitting device, and more particularly to a nitride-based light emitting device that can improve the luminous efficiency and reliability of the light emitting device.

Light Emitting Diodes (LEDs) are well-known semiconductor light emitting devices that convert current into light.In 1962, red LEDs using GaAsP compound semiconductors were commercialized, along with GaP: N series green LEDs. It has been used as a light source for display images of electronic devices, including.

The wavelength of light emitted by such LEDs depends on the semiconductor material used to make the LEDs. This is because the wavelength of the emitted light depends on the band-gap of the semiconductor material, which represents the energy difference between the valence band electrons and the conduction band electrons.

Gallium nitride compound semiconductors (Gallium Nitride (GaN)) have high thermal stability and wide bandgap (0.8 to 6.2 eV), which has attracted much attention in the development of high-power electronic components including LEDs.

One reason for this is that GaN can be combined with other elements (indium (In), aluminum (Al), etc.) to produce semiconductor layers that emit green, blue and white light.

In this way, the emission wavelength can be adjusted to match the material's characteristics to specific device characteristics. For example, GaN can be used to create white LEDs that can replace incandescent and blue LEDs that are beneficial for optical recording.

Due to the advantages of these GaN-based materials, the GaN-based LED market is growing rapidly. Therefore, since commercial introduction in 1994, GaN-based optoelectronic device technology has rapidly developed.

The brightness or output of the LED using the GaN-based material as described above is large, the structure of the active layer, the light extraction efficiency to extract light to the outside, the size of the LED chip, the type and angle of the mold (mold) when assembling the lamp package , Fluorescent material and the like.

On the other hand, one of the reasons why the growth of GaN-based semiconductors is more difficult than other III-V compound semiconductors is that there are no high-quality substrates, that is, wafers made of materials such as GaN, InN, and AlN.

Therefore, the LED structure is grown on a heterogeneous substrate such as sapphire, and many defects are generated, and these defects have a great influence on the LED performance.

As shown in FIG. 1, the basic structure of the LED of the GaN-based material includes an n-type GaN semiconductor layer 1 and an active layer having a quantum well structure adjacent to the n-type GaN semiconductor layer 1. 2) is located and the p-type GaN semiconductor layer 3 is located adjacent to the active layer 2.

In this case, the p-type AlGaN layer 4 may be positioned between the active layer 2 and the p-type GaN semiconductor layer 3 in order to effectively confine the charge in the active layer 2.

In the LED structure, the n-type electrode 5 and the p-type electrode 6 are formed, respectively, so that light emission is possible by the injection of electric charges through the electrodes 5 and 6.

In the active layer 2 having the quantum well structure, a quantum well layer and a quantum barrier layer are repeatedly stacked, and electrons and holes injected from the n-type semiconductor layer 1 and the p-type semiconductor layer 3, respectively. In this active layer 2, they are combined with each other to emit light.

This LED structure is grown on a dissimilar substrate 7 such as sapphire as described above, and due to problems such as lattice mismatch and difference in coefficient of thermal expansion, the LED structure, as shown in FIG. It is formed on the grown GaN buffer layer 8.

Thus, as shown in FIG. 2, crystal defects such as threading dislocation 9 occur, and these crystal defects are transmitted as is to the LED structure described above.

As a result, such crystal defects also affect the active layer in which the LED emits light, which greatly reduces the light emission characteristics, and also degrades the interfacial characteristics between the quantum barrier layer and the quantum well layer of the active layer, thereby greatly reducing the luminous efficiency of the light emitting device. There was a problem.

An object of the present invention is to provide a nitride-based light emitting device that can improve the reliability characteristics by adjusting or suppressing strain and crystal defects of the light emitting device.

In order to achieve the above technical problem, the present invention provides a light emitting device comprising: a first conductive semiconductor layer; A superlattice layer on the first conductive semiconductor layer; A second conductive semiconductor layer on the superlattice layer; An active layer positioned on the second conductive semiconductor layer; It is preferably configured to include a third conductive semiconductor layer located on the active layer.

The superlattice layer may be formed by alternately stacking a high quality GaN layer and a low quality GaN layer.

The superlattice layer may be composed of a high temperature growth layer and a low temperature growth layer made of a GaN material, and may also be formed of a high speed growth layer and a low speed growth layer made of a GaN material.

The high temperature growth layer is grown at a temperature between 900 and 1100 ℃, the low temperature growth layer is preferably grown at a temperature between 600 and 800 ℃.

In addition, the fast growth layer is grown to a thickness of 0.1nm per second, the slow growth layer is preferably grown to a thickness of 2㎛ per hour.

The thickness of each layer constituting the superlattice layer is preferably 1 to 2nm.

The superlattice layer is formed by repeatedly stacking a first layer and a second layer made of a GaN material, and at least one kind of the first layer and the second layer has the same temperature as that of the first conductive semiconductor layer. Can be grown at growth rate conditions.

The first conductive semiconductor layer and the second conductive semiconductor layer may be n-type semiconductor layers, and the third conductive semiconductor layer may be p-type semiconductor layers.

The active layer may include an InGaN quantum well layer and a GaN quantum barrier layer.

In addition, the thickness of the second conductive semiconductor layer is 5 to 10nm, preferably grown at a temperature of 900 to 1100 ℃.

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

As shown in FIG. 3, in the structure of the nitride-based light emitting device of the present invention, a first conductive semiconductor layer 20 is stacked on a substrate 10, and a superconducting layer of GaN material is formed on the first conductive semiconductor layer 20. The lattice layer 30 is stacked.

The first conductive semiconductor layer 20 may be an n-type semiconductor layer, and in some cases, a p-type semiconductor layer may be located. The first conductive semiconductor layer 20 may be grown on the GaN buffer layer 40 grown on the substrate 10.

The superlattice layer 30 may serve to block crystal defects transmitted from the buffer layer 40 and the first conductive semiconductor layer 20 and to mitigate strain.

The high quality second conductive semiconductor layer 50 is grown on the superlattice layer 30.

An active layer 60 is formed on the second conductive semiconductor layer 50, and a third conductive semiconductor layer 70 is formed on the active layer 60.

As described above, when the n-type semiconductor layer is used as the first conductive semiconductor layer 20, the second conductive semiconductor layer 50 and the n-type semiconductor layer are also used, wherein the third conductive semiconductor layer is used. 70 is made of a p-type semiconductor layer.

In FIG. 4, a detailed structure of the first conductive semiconductor layer 20 to the active layer 60 is illustrated.

The superlattice layer 30 positioned on the first conductive semiconductor layer 20 includes a first layer 31 made of high quality GaN and a second layer 32 made of GaN of lower quality than the first layer 31. ) Is repeatedly stacked.

The buffer layer 40 and the first conductive semiconductor layer 20 may be grown at a temperature condition of 900 to 1100 ° C., in this embodiment, at 1050 ° C.

The superlattice layer 30 grown on the first conductive semiconductor layer 20 includes a first layer 31 having excellent crystallinity by varying growth rate and temperature, and a low quality second layer 32 containing many defects. ) To grow crosswise to form a superlattice structure.

In this case, the first layer 31 may be grown at a low temperature at a high temperature to form a high quality thin film.

That is, the first layer 31 may be grown at a temperature between 900 and 1100 ° C. in the same manner as the first conductive semiconductor layer 20 or the second conductive semiconductor layer 50.

The growth rate at this time can be grown at a low speed while achieving a high quality with a thickness of 2㎛ per hour.

In addition, the second layer 32 may be grown at a high speed at a relatively low temperature compared to the first layer 31 to form a relatively low quality thin film.

That is, the second layer 32 may be grown to a thickness of 0.1 nm per second at a temperature between 600 and 800 degrees.

The thickness of each layer 31 and 32 constituting the superlattice layer 30 is preferably 1 to 2 nm.

As described above, the superlattice layer 30 is formed by repeatedly stacking the first layer 31 and the second layer 32 made of GaN material, and the first layer 31 and the second layer 32. At least one kind of layer may be grown at the same temperature and growth rate as the first conductive semiconductor layer.

After the growth process of the superlattice layer 30 structure, the second conductive semiconductor layer 50 may be grown at a high temperature to improve crystallinity of the superlattice layer 30 structure.

That is, the structure of the superlattice layer 30 may block the lattice defects and strains that start from the upper side of the substrate 10 and continue through the buffer layer 40 and the first conductive semiconductor layer 20.

The second layer 32 of the superlattice layer 30 may block the above-described lattice defects and strains, and the high quality first layer 31 located between the second layers 32 may include the second layer ( The quality of the thin film degraded by 32 can be restored.

In addition, the second conductive semiconductor layer 50 grown at a high temperature on the superlattice layer 30 has an effect of performing heat treatment.

Such a high temperature heat treatment effect, in particular, when forming a vertical light emitting device structure because there is a metal support plate can solve the disadvantage that later heat treatment is not possible.

As such, the active layer 60 having an InGaN / GaN structure is formed on the second conductive semiconductor layer 50 formed on the superlattice layer 30.

That is, in the active layer 60, an InGaN layer may be used as a quantum well layer, and a GaN layer may be used as a quantum barrier layer.

In addition, an AlGaN layer or an AlInGaN layer may also be used as a quantum well layer, and an InGaN or AlInGaN layer may be used as a quantum barrier layer.

As a specific embodiment of the present invention, the growth method is as follows.

First, an n-type GaN layer was grown as the first conductive semiconductor layer 20 at 1050 ° C. in the growth conditions of the superlattice layer 30.

Thereafter, the growth temperature is lowered to 650 to 750 ° C., and the growth rate is increased to grow the second layer 32 containing a lot of defects. ) Slow growth.

The first layer 31 and the second layer 32 intersect and grow to block dislocations that may flow into the active layer 60 and to control strain, thereby improving light emission characteristics. .

The n-type GaN layer was grown on the superlattice layer 30 again as the second conductive semiconductor layer 50 at 1050 ° C.

5 shows an example of a horizontal light emitting device having the above-described structure.

As shown, an n-type semiconductor layer as a buffer layer 40, an n-type semiconductor layer as the first conductive semiconductor layer 20, a superlattice layer 30, and a second conductive semiconductor layer 50 on the substrate 10. The layer, the active layer 60, and the p-type semiconductor layer as the third conductive semiconductor layer 70 have the structure of the above-described light emitting element.

In this structure, the p-type electrode 80 and the n-type electrode 90 are provided after the first conductive semiconductor layer 20 is etched to be exposed.

6 shows an example of a vertical light emitting device having the above structure.

The structure of the above-described light emitting device comprising the first conductive semiconductor layer 20, the superlattice layer 30, the second conductive semiconductor layer 50, the active layer 60, and the third conductive semiconductor layer 70 as described above. Is formed on a substrate (not shown), and the substrate is separated in a state where the support layer 83 formed of a metal or a conductive semiconductor layer is positioned to form a state as shown in FIG. 6.

A p-type electrode 80 is positioned between the third conductive semiconductor layer 70 and the support layer 83, and the p-type electrode 80 may be formed of an ohmic electrode 81 and a reflective electrode 82. have.

In this case, the ohmic electrode 81 may be a transparent electrode.

The light emitting device manufactured in such a form can greatly increase the luminous efficiency by mitigating crystal defects and strain transmitted to the active layer 60 by the action of the superlattice layer 30 described above.

The above embodiment is an example for explaining the technical idea of the present invention in detail, and the present invention is not limited to the above embodiment, various modifications are possible, and various embodiments of the technical idea are all protected by the present invention. It belongs to the scope.

The present invention as described above has the following effects.

First, the light emitting device according to the present invention can improve the internal quantum efficiency by improving the band structure of the active layer by the superlattice layer.

Second, the superlattice layer of the present invention can control the stress distribution and crystal defects in the active layer grown thereon to improve the optical properties.

Claims (12)

In the light emitting device, A first conductive semiconductor layer; A superlattice layer on the first conductive semiconductor layer; A second conductive semiconductor layer on the superlattice layer; An active layer positioned on the second conductive semiconductor layer; A nitride-based light emitting device comprising a third conductive semiconductor layer located on the active layer. The nitride-based light emitting device of claim 1, wherein the superlattice layer comprises a high temperature growth layer and a low temperature growth layer made of a GaN material. The nitride of claim 2, wherein the high temperature growth layer of the superlattice layer is grown at a temperature between 900 and 1100 ° C., and the low temperature growth layer of the superlattice layer is grown at a temperature between 600 and 800 ° C. 4. Light emitting device. The nitride-based light emitting device according to claim 1, wherein the superlattice layer comprises a fast growth layer and a slow growth layer made of a GaN material. The nitride layer of claim 4, wherein the high growth layer of the superlattice layer is grown to a thickness of 0.05 to 1.5 nm per second, and the slow growth layer of the superlattice layer is grown to a thickness of 1 to 3 μm per hour. Light emitting device. The superlattice layer of claim 1, wherein the superlattice layer is formed by repeatedly stacking a first layer and a second layer made of a GaN material, and at least one kind of the first layer and the second layer is formed of the first conductive layer. A nitride-based light emitting device characterized in that the growth at the same temperature and growth rate conditions as the semiconductor layer. The nitride-based light emitting device according to claim 1, wherein the thickness of each layer constituting the superlattice layer is 1 to 2 nm. The nitride-based light emitting device according to claim 1, wherein the first conductive semiconductor layer and the second conductive semiconductor layer are n-type semiconductor layers. The nitride-based light emitting device according to claim 1, wherein the third conductive semiconductor layer is a p-type semiconductor layer. The nitride-based light emitting device according to claim 1, wherein the active layer comprises an InGaN quantum well layer and a GaN quantum barrier layer. The nitride-based light emitting device according to claim 1, wherein the thickness of the second conductive semiconductor layer is 5 to 10 nm. The nitride-based light emitting device of claim 1, wherein the second conductive semiconductor layer is grown at a temperature of 900 to 1100 ° C.

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