KR20080010135A - Nitride based light emitting diode and method of manufacturing the same - Google Patents

Abstract

A nitride based light emitting device and a manufacturing method thereof are provided to control the polarity of a GaN thin film easily when growing the GaN thin film of the light emitting device. A nitride based light emitting device includes a substrate(10), and a polarity converting layer(30). The polarity converting layer is formed on the substrate. The substrate is nitrided at 1000~150 degrees. A nitridation controlling layer(20) for controlling the surface of the nitrided surface is formed between the substrate and the polarity converting layer. The nitridation controlling layer is an AlN layer with the thickness of 5~10 mono-layers. The AlN layer is grown by an MEE(Migration Enhanced Epitaxy) method at 1000~1150 degrees.

Description

Nitride-based light emitting device and method of manufacturing the same

1 is a schematic diagram showing a general GaN polarity.

2 is a cross-sectional view showing an embodiment of the present invention.

3 is a schematic view showing the thin film growth of the present invention.

4 is a cross-sectional view showing another embodiment of the present invention.

5 is a schematic diagram illustrating a stacking sequence of the present invention.

6 and 7 are surface photographs of N polarity and Ga polarity, respectively.

8 and 9 are AFM images of N polarity and Ga polarity, respectively.

<Brief description of the main parts of the drawing>

10 substrate 20 nitride control layer

30: polarity conversion layer 40: buffer layer

50: n-type semiconductor layer 51: n-type electrode

60: light emitting layer 70: p-type semiconductor layer

71: p-AlGaN cladding layer 72: p-type electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride based light emitting device, and more particularly, to a nitride based light emitting device capable of improving crystallinity and surface properties and a method of manufacturing the same.

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 attracted much attention in the field of high power electronics development due to their high thermal stability and wide bandgap (0.8-6.2 eV). 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.

In addition, in the case of the conventional green LED, it was initially implemented as GaP, which was inefficient as an indirect transition type material, and thus practical pure green light emission could not be obtained. However, as InGaN thin film growth succeeded, high brightness green LED could be realized. It became.

Because of these and other benefits, the GaN series LED market is growing rapidly. Therefore, since commercial introduction in 1994, GaN-based optoelectronic device technology has rapidly developed.

Since the efficiency of GaN light emitting diodes outperformed the efficiency of incandescent lamps and is now comparable to that of fluorescent lamps, the GaN LED market is expected to continue to grow rapidly.

In the GaN semiconductor device described above, a hexagonal sapphire ([0001] direction) substrate is usually used. On the sapphire substrate, GaN crystals having a hexagonal Wurzite structure grow along the c axis of the sapphire substrate.

Figure 1 shows the Wurzite GaN structure formed along the c axis. This structure has no possibility of symmetry in the c-axis direction, i.e., the growth direction, and has the potential to grow a GaN film having two thin crystal growth relationships.

That is, considering a vector of N atoms from GaN atoms, one thin film growth relationship is one in which the vector direction and the growth direction coincide, and the other is a relationship in which the vector direction and the growth direction are different by 180 degrees.

Among these, the polarity of the GaN film having the former thin film growth relation is referred to as Ga polarity and the latter as N polarity. The polarity of GaN film is Ga polarity and N polarity, respectively, by the process of flowing organic metal gas before ammonia gas at the start of thin film growth or nitriding a sapphire substrate with ammonia just before GaN growth using MOCVD method. It is possible to control with.

In particular, the nitriding of the top surface of the sapphire substrate lowered the surface energy by improving the rough surface state of the sapphire substrate and showed that it is effective in improving the growth direction and thin film crystallinity in the nucleation of GaN.

However, GaN thin films grown on nitrided sapphire substrates have a nitrogen-rich surface and thus exhibit hexagonal facet morphology and show a large difference from the flat surface morphology in the case of Ga polarity. There is a need to convert the N polarity to Ga polarity.

When GaN is grown according to the polarity, the surface structure has a difference in crystal growth depending on the polarity of the surface, and brings about a big difference in growth surface shape, defect structure, implantation of impurities, and the like.

Therefore, in the GaN-based thin film manufacturing field, a manufacturing method is required to grow a crystal film that satisfies optimal conditions for growing a high quality semiconductor crystal layer for growing light emitting structures, and in particular, determining and controlling the polarity is very important. Do.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a nitride-based light emitting device capable of improving the crystallinity and surface characteristics of a light emitting device using a GaN semiconductor by growing a GaN semiconductor layer having a Ga polarity surface.

In order to achieve the above technical problem, the present invention is a nitride-based light emitting device, the substrate; It is preferable to include the polarity conversion layer located on the substrate.

The substrate is preferably nitrided, and in this case, it is preferable that the substrate further includes a nitride control layer for controlling the nitrided surface.

The nitride control layer may be an AlN layer having a thickness of 5 to 10 atomic layers.

The polarity converting layer may be an Al layer of 2 to 10 atomic layers, and optionally, nitride of any one of B, Al, Ga, and In, or any one of Zn, Cd, and Mg, and any of O, S, and Se. One compound can be used.

It is preferable that such polarity conversion layer converts N polarity into Ga polarity.

A buffer layer on the polarity conversion layer; An n-type semiconductor layer on the buffer layer; A light emitting layer on the n-type semiconductor layer; It may be configured to further include a p- type semiconductor layer positioned on the light emitting layer.

In this case, the substrate may be any one of sapphire, GaN, ZnO.

As another aspect for achieving the above technical problem, the present invention provides a method for manufacturing a nitride-based light emitting device, comprising the steps of: nitriding a substrate; Forming an AlN layer on the nitrided substrate; Forming a polarity conversion layer on the AlN layer; It is preferably configured to include the step of growing a GaN layer on the polarity conversion layer.

The AlN layer or the polarity conversion layer may be formed by a migration enhanced epitaxy (MEE) method.

In this case, the polarity conversion layer is preferably made of any one of nitrides of any one of B, Al, Ga, In, Zn, Cd, Mg, any one of O, S, Se, and Al. .

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

As shown in FIG. 2, the light emitting device of the present invention is first nitrided at 1000 to 1150 ° C. on the sapphire substrate 10.

The nitriding process of the upper surface of the sapphire substrate 10 lowers the surface energy by improving the rough surface state of the sapphire substrate 10 and is effective in improving the growth direction and thin film crystallinity when nucleating GaN.

In this nitrided substrate 10, an AlN layer having a thickness of 5 to 10 atomic layers grown by a migration enhanced epitaxy (MEE) method is formed at a temperature of 1000 to 1150 ° C.

As such, the AIN layer formed on the substrate 10 serves as the nitriding control layer 20 to enhance the migration effect.

Thereafter, on the nitride control layer 20, only the TMAl raw material is injected within a temperature range of 550 to 1100 ° C. to form the polarity conversion layer 30.

The polarity conversion layer 30 has a thickness of 2 to 10 atomic layers of aluminum (Al), which can be grown to form a Ga-polar GaN semiconductor layer having excellent crystallinity. This polarity conversion layer 30 may also be formed by MEE method.

In addition, the polarity conversion layer 30 may be formed of Group 3 element nitrides such as B, Al, Ga, In, and the like, and Group 6 elements such as Zn, Cd, and Mg, and Group 6 such as O, S, and Se. It can be comprised with a compound with an element.

In addition to the sapphire substrate 10, the polarity conversion layer 30 may be applied to the polycrystalline film ZnO on the amorphous substrate 10 such as glass in addition to the GaN single crystal substrate 10.

As shown in FIG. 3, the MEE method is a method of controlling growth to an atomic layer thickness by controlling a shutter of a source material in a vapor deposition method such as MOCVD.

That is, using the AlN layer as an example, Al is delivered by hydrogen gas, which is a carrier gas, using TMAl (tri-methyl aluminum) as a source, and N is also delivered by hydrogen gas, using NH ₃ (ammonia) gas as a source. .

At this time, if there is a time interval (a) between the on-off time of each source, during this time, only one atomic layer of each atomic layer is combined with the lower layer and the remaining atomic layer is the carrier gas (H) flowing during this time interval (a). ₂ ) to be removed.

Therefore, growth is possible in atomic layer units by a purging time through which only such a carrier gas flows.

The buffer layer 40, the n-type semiconductor layer 50, the light emitting layer 60, and the p-type semiconductor layer 70 are sequentially formed on the polarity conversion layer 30.

The buffer layer 40 may be formed of a low temperature buffer layer and a high temperature buffer layer grown by GaN, and a p-AlGaN cladding layer 71 may be further formed between the light emitting layer 60 and the p-type semiconductor layer 70. Can be.

The emission layer 60 may be formed of a material such as InGaN, AlGaN, AlInGaN, GaN.

After the n-type semiconductor layer 50 is viewed to be exposed in the structure thus grown, the n-type electrode 51 and the p-type electrode 72 are formed to form a light emitting device.

Meanwhile, as shown in FIG. 4, in the state where the substrate 10 is removed from the grown structure, the n-type electrode 51 is coupled to the surface from which the substrate 10 is removed to form a vertical light emitting device. It may be.

In this case, the buffer layer 40, the polarity conversion layer 30, and the nitride control layer 20 may also be removed together with the substrate 10.

As described above, the structure in which the substrate 10 is removed is reversed up and down, and the reflective electrode 73 and the support plate 80 supporting the entire structure in the process of removing the substrate 10 are disposed below the p-type electrode 72. Can be configured.

Hereinafter, operations of the nitride control layer 20 and the polarity conversion layer 30 will be described in detail with reference to FIG. 5. 5 shows an embodiment in which an Al 2 atomic layer is used as the polarity conversion layer 30.

If the GaN thin film is grown directly on the nitrided sapphire substrate 10 described above, the substrate 10 exhibits a hexagonal facet surface shape since the substrate 10 has a nitrogen-rich surface.

When the GaN thin film stacked on the substrate 10 has N polarity, it is necessary to convert the N polarity to the Ga polarity in order to apply it to the device.

That is, when a GaN thin film is grown on the nitrided substrate 10 without forming the polarity conversion layer 30, Wurzite GaN has a structure called (AB) (AB) (AB) when Ga is A and N is B. It has a stacking sequence of.

In this case, when the polarity conversion layer 30 is formed, the stacking sequence of the GaN thin film deposited thereafter is changed to (AB) (AB) (AB) (AA ') (BA) (BA) so that the polarity is changed from the N polarity. Can be changed to Ga polarity. (AA ') represents the polarity conversion layer 30.

As described above, the GaN-based semiconductor layer having a Ga polar surface does not bond well with a material that acts as an impurity as compared to the N polar surface, and does not have a hexagonal surface shape that hinders crystal growth. The light emitting structure may be formed of the semiconductor layer.

6 and 7 show surface photographs of GaN thin films having N polarity and Ga polarity, respectively. When the polarity conversion layer 30 is absent, the thin film may have N polarity.

8 and 9 show AFM images of GaN thin films having N polarity and Ga polarity, respectively.

As described above, the nitride control layer 20 of the present invention can be grown to have a Ga-polar GaN semiconductor layer having excellent crystallinity by increasing the migration effect and forming the polarity conversion layer 30.

The polarity conversion layer 30 of the present invention may be formed by MBE or MOCVD.

In the present invention, the term polarity conversion layer 30 is formed so that the GaN thin film can have a Ga polar surface when the GaN semiconductor layer is grown on the N polar surface formed by the nitriding process of the initial stage of growth. Refers to the crystalline layer.

As such, the present invention can improve the crystallinity and surface properties of the GaN semiconductor layer to be subsequently grown by providing the polarity conversion layer 30 on the nitrided sapphire substrate 10, that is, immediately before the GaN buffer layer 40 is formed. have.

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, in growing the GaN thin film constituting the light emitting device it is possible to easily control the polarity of the GaN thin film.

Second, compared to the GaN semiconductor layer having an N polar surface, the GaN semiconductor layer having Ga polarity having excellent crystallinity and surface characteristics without dislocations and defects is possible.

Third, the light emitting device of the GaN semiconductor light emitting device may be improved by forming a light emitting device using the high quality GaN semiconductor layer.

Claims (12)

In the nitride-based light emitting device, A substrate; A nitride-based light emitting device comprising a polarity conversion layer located on the substrate. The nitride-based light emitting device of claim 1, wherein the substrate is nitrided. The nitride-based light emitting device according to claim 2, further comprising a nitride control layer for controlling the nitrided surface between the substrate and the polarity converting layer. The nitride-based light emitting device according to claim 3, wherein the nitride control layer is an AlN layer having a thickness of 5 to 10 atomic layers. The nitride-based light emitting device of claim 1, wherein the polarity conversion layer is an Al layer of 2 to 10 atomic layers. According to claim 1, wherein the polarity conversion layer is nitride of any one of B, Al, Ga, In or any one of Zn, Cd, Mg and O, S, Se compound Light emitting device. The nitride-based light emitting device according to claim 1, wherein the polarity conversion layer converts the N polarity into a Ga polarity. According to claim 1, On the polarity conversion layer, A buffer layer; An n-type semiconductor layer on the buffer layer; A light emitting layer on the n-type semiconductor layer; And a p-type semiconductor layer positioned on the light emitting layer. The nitride-based light emitting device according to claim 1, wherein the substrate is any one of sapphire, GaN, and ZnO. In the method of manufacturing a nitride-based light emitting device, Nitriding the substrate; Forming an AlN layer on the nitrided substrate; Forming a polarity conversion layer on the AlN layer; A method of manufacturing a nitride-based light emitting device comprising the step of growing a GaN layer on the polarity conversion layer. The method of claim 10, wherein the AlN layer or the polarity conversion layer is formed by a migration enhanced epitaxy (MEE) method. The method of claim 10, wherein the polarity conversion layer, A nitride, light-emitting device comprising a nitride of any one of B, Al, Ga, In, any one of Zn, Cd, Mg, any one of O, S, Se, and Al. .

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