# Patent

## Title
Nitride semiconductor light emitting device and fabrication method thereof

## Abstract

Provided is a nitride semiconductor light emitting device including: a first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer; and a delta doped second nitride semiconductor layer formed above the active layer. According to the present invention, the optical power of the nitride semiconductor light emitting device is enhanced, optical power down phenomenon is improved and reliability against ESD (electro static discharge) is enhanced.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application is the U.S. national stage application of International Patent Application No. PCT/KR2005/004120, filed Dec. 5, 2005, the disclosure of which is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
The present invention is relative to a nitride semiconductor light emitting device and fabrication method thereof, and to a nitride semiconductor light emitting device and a fabrication method thereof that can increase the optical power and enhance the reliability by increasing a hole carrier concentration contributing to the electric conductivity in an electrode contact layer to increase the recombination probability of electrons and holes.
BACKGROUND ART
A schematic stack structure of a general nitride semiconductor light emitting device and a fabrication method thereof will now be described.
FIG. 1 is a sectional view of a general nitride semiconductor light emitting device.
Referring to FIG. 1, a conventional nitride semiconductor light emitting device includes a substrate 101, a buffer layer 103, an n-GaN layer 105, an active layer 107 and a p-GaN layer 109. Herein, the substrate 101 can be exemplified by a sapphire substrate.
A fabrication method of the nitride semiconductor light emitting device will now be described. In order to minimize the occurrence of crystal defects due to differences in the lattice constants and the thermal expansion coefficients of the substrate 101 and the n-GaN layer 105, a GaN-based nitride or an AlN-based nitride having an amorphous phase at a low temperature is formed as the buffer layer 103.
The n-GaN layer 105 doped with silicon at a doping concentration of 1018/cm3 is formed at a high temperature as a first electrode contact layer. Thereafter, the growth temperature is lowered and the active layer 107 is formed. Thereafter, the growth temperature is again elevated and the p-GaN layer 109 doped with magnesium (Mg) and having a thickness range of 0.1-0.5 μm is formed as a second electrode contact layer. The nitride semiconductor light emitting device having the aforementioned stack structure is formed in a p-/n-junction structure which uses the n-GaN layer 105 as the first electrode contact layer and uses the p-GaN layer 109 as the second electrode contact layer.
Also, a second electrode material formed on the second electrode contact layer is limited depending on a doping type of the second electrode contact layer. For example, in order to decrease the contact resistance between the second contact material and the p-GaN layer 109 having a high resistance component and enhance the current spreading, a thin transmissive resistance material of a Ni/Au alloy is used as the second electrode material.
To form the p-GaN layer 109 used as the second electrode contact layer, the p-/n-junction light emitting device using the nitride semiconductor employs a doping source of Cp2Mg or DMZn. In the case of DMZn, since Zn is in ‘deep energy level’ within the p-GaN layer 109 and has a very high activation energy, the hole carrier concentration serving as a carrier when a bias is applied is limited to about 1×1017/cm3. Accordingly, Cp2Mg MO (metal organic) having a low activation energy is used as the doping source.
Also, when the Mg-doped p-GaN layer 109 having a thickness range of 0.1-0.5 μm is grown using a doping source of Cp2Mg at the same flow rate or by sequentially varying the flow rate of Cp2Mg, hydrogen (H) gas separated from the doping source and NH3 carrier gas are combined to form an Mg—H complex, in the p-GaN layer 109, which shows a high resistance insulation characteristic of more than  ̃106Ω. Accordingly, in order to emit light during the recombination process of holes and electrons in the active layer 107, an activation process is essentially required to break the bond of Mg—H complex. Since the Mg-doped p-GaN layer 109 has a high resistance, it can not be used without any change. The activation process is performed through an annealing process at a temperature range of 600-800° C. in an ambient of N2, N2/O2. However, since Mg existing in the p-GaN layer 109 has a low activation efficiency, it has a relatively high resistance value compared with the n-GaN layer 105 used as the first electrode contact layer. In real circumstance, after the activation process, the atomic concentration of Mg in the p-GaN layer 109 is in a range of 1019/cm3-1020/cm3, and the hole carrier concentration contributing to a pure carrier conductivity is in a range of 1017/cm3-1018/cm3, which correspond to a difference of maximum 103 times. It is also reported that the hole mobility is 10 cm2/vsec, which is a very low value. FIG. 2 is a schematic view showing a sectional structure of the conventional Mg-doped p-GaN layer and an Mg profile inside the Mg-doped p-GaN layer after the activation process is performed. Referring to FIG. 2, it can be seen that the Mg atomic concentration and the hole carrier concentration show a difference of maximum 103 times.
Meanwhile, the Mg atomic concentration remaining in the p-GaN layer 109 without a complete activation causes many problems. For example, light emitting from the active layer toward the surface is trapped to lower the optical power, or when a high current is applied, heat is generated due to a relatively high resistance value, so that the life time of the light emitting device is shortened to have a fatal influence on the reliability. Especially, in the case of a large size/high power 1 mm×1 mm light emitting device using a flip chip technique, since a current of 350 mA which is very higher than a conventional current of 20 mA is applied, a junction temperature of more than 100° C. is generated at a junction face, having a fatal influence on the device reliability and causing a limitation to product application in future. The generated much heat is caused by an increase of resistance component due to the Mg atomic concentration remaining in the p-GaN layer 109 used as the second electrode contact layer without being activated as a carrier, and a rough surface property due to the increase of the resistance component.
Also, in the general p-/n-junction light emitting device, the n-GaN layer 105 used as the first electrode contact layer can easily control the hole concentration within 5-6×1018/cm3 within a critical thickness ensuring the crystallinity in proportional to the silicon doping concentration depending on an increase in the flow rate of SiH4 or Si2H6, whilst in the p-GaN layer 109 used as the second electrode contact layer, the hole concentration substantially serving as carriers is limited within a range of 1-9×1017/cm3 although the flow rate of Cp2Mg is increased and Mg atoms of more than maximum  ̃1020/cm3 are doped. To this end, the conventional light emitting device is made in a p-/n-junction structure having an asymmetric doping profile.
As aforementioned, the low carrier concentration and high resistance component of the p-GaN layer 109 used as the second electrode contact layer cause the light emitting efficiency to be decreased.
To solve the above problem, a conventional method for increasing the optical power by employing Ni/Au TM (transparent thin metal) having a good transmission and a low contact resistance has been proposed. However, the conventional method badly influences the device reliability when being applied to a large size/high power light emitting device. This problem still remains unsettled in the light emitting devices using the GaN semiconductor.
DISCLOSURE OF INVENTION
Technical Problem
The present invention provides a nitride semiconductor light emitting device and fabrication method thereof that can enhance the property of p-GaN layer constituting the nitride semiconductor light emitting device.
Also, the present invention provides a nitride semiconductor light emitting device and fabrication method thereof that can enhance the optical power and reliability.
In addition, the present invention provides a nitride semiconductor light emitting device and fabrication method thereof that can overcome the problems caused by the low hole carrier concentration and mobility of the Mg-doped p-GaN layer used as the second electrode contact layer and a high resistance component of Mg atomic concentration (including Mg—H complex) remaining completely inactivated in the p-GaN layer, and enhance the optical power and reliability.
Technical Solution
There is provided a nitride semiconductor light emitting device including: a first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer; and a delta doped second nitride semiconductor layer formed above the active layer.
In another aspect of the present invention, there is provided a nitride semiconductor light emitting device including: a buffer layer; a first nitride semiconductor layer formed above the buffer layer; a first electrode contact layer formed above the first nitride semiconductor layer; an active layer formed above the first nitride semiconductor layer in a single quantum well structure or a multi quantum well structure comprised of a well layer and a barrier layer; and a delta doped second nitride semiconductor layer formed above the active layer.
In another aspect of the present invention, there is provided a method of fabricating a nitride semiconductor light emitting device, the method including: forming a buffer layer above a substrate; forming a first nitride semiconductor layer above the buffer layer; forming an active layer above the first nitride semiconductor layer; and forming a delta doped second nitride semiconductor layer above the active layer.
ADVANTAGEOUS EFFECTS
According to the present invention, the characteristic of the p-GaN layer constituting the nitride semiconductor light emitting device is enhanced, the optical power of the nitride semiconductor light emitting device is enhanced, the optical power down phenomenon is improved, and the reliability against ESD (Electro Static Discharge) is enhanced.



BRIEF DESCRIPTION OF THE DRAWINGS
The spirit of the present invention will be understood more apparently from the accompanying drawings. In the drawings:
FIG. 1 is a schematic view showing a stack structure of a general nitride semiconductor light emitting device;
FIG. 2 is a schematic view showing a sectional structure of the conventional Mg-doped p-GaN layer and an Mg profile inside the Mg-doped p-GaN layer after the activation process is performed;
FIG. 3 is a schematic view illustrating a Cp2Mg delta doping flow rate according to a growth time;
FIG. 4 is a graph showing an Mg doping profile before and after a subsequent activation process after a crystal growth for a Cp2Mg delta doped p-GaN is completed;
FIG. 5 is a graph showing an electric field profile after a subsequent activation process of a Cp2Mg delta doped p-GaN layer is completed;
FIG. 6 is a schematic view showing a stack structure of a nitride semiconductor light emitting device according to a first embodiment of the present invention; and
FIG. 7 is a schematic view showing a stack structure of a nitride semiconductor light emitting device according to a second embodiment of the present invention.



BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment according to the spirit of the present invention will be described with reference to the accompanying drawings.
The present invention is characterized in that in the fabrication method of a nitride semiconductor, a Cp2Mg delta doping process is performed to grow a p-GaN layer, and the Cp2Mg delta doping process will be described with reference to FIGS. 3 to 5.
FIG. 3 is a schematic view illustrating a Cp2Mg delta doping flow rate according to a growth time.
Referring to FIG. 3, after an active layer emitting light is grown, an undoped GaN layer of less than 200 Å is grown so as to protect a “V” pit defect formed during the growth of the active layer, and the flow rate of Cp2Mg is adjusted from 0 cc to 1000 cc within a thickness range of 10-200 Å to form a delta doped GaN layer. FIG. 3 shows an Mg-delta doped GaN grown by consecutively repeating one period consisting of undoped GaN layer/delta doped GaN layer. In the above crystal growth method, only the flow rate of Cp2Mg is changed, the growth temperature is fixed to 1000° C. and the other conditions are fixed so as to maintain the crystallinity.
In growing the Mg-delta doped GaN layer, the thickness of each of the undoped GaN layer and the delta doped GaN layer constituting one period may be varied. Also, in repeatedly growing one period of undoped GaN layer/delta doped GaN layer, the dose at each period may be varied. At this time, an overall thickness of the two layers forming one period can be adjusted within a thickness range of 10-300 Å.
FIG. 4 is a graph showing an Mg doping profile before and after a subsequent activation process after a crystal growth for a Cp2Mg delta doped p-GaN is completed.
Referring to FIG. 4, when Cp2Mg delta doping of the same amount is repeated at a constant period before the subsequent activation process, the delta doped GaN layer having a sharp Mg doping profile can be obtained at a boundary between the undoped GaN layers. Thereafter, while the subsequent activation process is performed, Mg is diffused into the undoped GaN layers of both sides, so that a wide Mg doping profile is obtained. Through the above subsequent activation process, the p-GaN layer has a uniform Mg doping profile in whole.
In general, when a forward bias is applied to the undoped GaN layer, it can be seen that the operating voltage increases. In the present invention, the operating voltage can be effectively lowered to less than 3.5 V (20 mA) to increase the optical power of the light emitting device by controlling the thickness of the Cp2Mg delta doped p-GaN layer and the thickness of the undoped GaN layer.
FIG. 5 is a graph showing an electric field profile after a subsequent activation process of a Cp2Mg delta doped p-GaN layer is completed.
Referring to FIG. 5, it can be seen that the hole carrier concentration profile is relatively high in the Cp2Mg delta doped regions periodically repeated. Therefore, in the Cp2Mg delta doped regions, potential increases to form an electric field doping. Accordingly, like in an HEMT structure 2 DEG (two dimensional electronic well layer) that is a high speed switching device using an energy bandgap difference (AlGaN/GaN junction), potential well can be formed to uniformly and effectively control the flow of holes likewise to effectively control a two-dimensional flow of electrons. In conclusion, it can be seen that hole injection efficiency is increased by the potential well.
As can be seen from the above description, the p-GaN layer grown by the conventional art has a problem that when a forward bias is applied, a high resistance component thereof sharply decreases current flow in inverse proportion with a distance from an electrode contact surface to an upper surface thereof, whilst in the present invention, the potential well layer can more effectively increase the current density to enhance the optical power of the light emitting device.
Also, by the Cp2Mg delta doping, since the doping element is uniformly, repeatedly and periodically doped at a relatively very small amount and then the activation process for the p-GaN layer is optimized and performed, the atomic concentration of Mg, Mg—H complex and the like existing therein can be decreased to suppress the resistance component as much as possible. In other words, the present invention increases the hole carrier concentration purely contributing to the electric conductivity to thereby increase the recombination probability with electrons and in the long run effectively increase the optical power. Thus, the present invention provides a high level crystal growth technique that can decrease the resistance component to enhance the reliability of the light emitting device.
Hereinafter, a concrete embodiment of the nitride semiconductor light emitting device according to the present invention will be described.
FIG. 6 is a schematic view showing a stack structure of a nitride semiconductor light emitting device according to a first embodiment of the present invention.
Referring to FIG. 6, the nitride semiconductor light emitting device according to the present embodiment includes a substrate 401, a buffer layer 403, an In-doped GaN layer 405, an n-GaN layer 407, a low-mole In-doped GaN layer or low-mole InGaN layer 409, an active layer 411, and an Mg-delta doped p-GaN layer 413. The Mg-delta doped p-GaN layer 413 has been described in detail with reference to FIGS. 3 to 5.
Hereinafter, a fabrication method of the nitride semiconductor light emitting device according to a first embodiment will be described in more detail.
First, in the present embodiment, only H2 carrier gas is supplied onto the sapphire substrate 401 at a high temperature to clean the sapphire substrate 401. Thereafter, in step of decreasing the growth temperature to 540° C., NH3 source gas is supplied to perform a nitridation of the sapphire substrate 401, for example for 7 minutes.
Thereafter, the buffer layer 403 having a 1st AlInN/1st GaN/2nd AlInN/2nd GaN structure is grown to a thickness of about 500 Å. Herein, the buffer layer 403 can be formed in a structure selected from the group consisting of a stack structure of AlInN/GaN, a super lattice structure of InGaN/GaN, a stack structure of InxGa1−xN/GaN, and a stack structure of AlxInyGa1−(x+y)N/InxGa1−xN/GaN. Then, the growth temperature is increased up to 1060° C. for 6 minutes, the low temperature buffer layer 403 is recrystallized in a mixture ambient of NH3 source gas and H2 carrier gas for 2 minutes, and at the same growth temperature, the indium-doped GaN layer 405 having about 2 μm thickness is grown in a single crystal.
Thereafter, the growth temperature is decreased to 1050° C., and the n-GaN layer 407 co-doped with silicon and indium at the same growth temperature is grown to a thickness of 2 μm. The n-GaN layer 407 is used as the first electrode layer.
Also, to adjust the strain of the active layer 411, the low-mole In-doped GaN layer or low-mole InGaN layer 409 having 5% indium content (wavelength: 480 nm) is grown to a thickness of 300 Å at 750° C. The indium content can be adjusted in a range of 1-5%. The low-mole In-doped GaN layer or low-mole InGaN layer 409 is intentionally controlled in ‘spiral growth mode’ having a uniform profile. Herein, in the low-mole In-doped GaN layer or low-mole InGaN layer 409, as the ‘spiral density’ intentionally controlled increases, the area of the active layer 411 increases. Accordingly, the low-mole In-doped GaN layer or low-mole InGaN layer 409 can perform a role that can increase the light emitting efficiency.
Thereafter, at the same growth temperature, the active layer 411 having a single quantum well (SQW) of undoped InGaN/InGaN structure is grown. In the grown active layer 411, the barrier layer has an indium content of less than 5% and a thickness of about 250 Å. At this time, the active layer 411 can be formed in the multi quantum well layer.
Thereafter, the growth temperature is again increased to 1000° C., an overall thickness is fixed to 0.1 μm, the flow rate of TMGa is also fixed, and only the flow rate of Cp2Mg is switched on/off from 0 cc to 1000 cc to thereby perform the delta doping process. In order to effectively perform the Cp2Mg delta doping, after the active layer 411 emitting light is grown, the undoped GaN layer is first grown in a thickness range of 10-200 Å to completely protect the active layer 411 such that Mg atoms are not internally diffused into the “V” pit crystal formed on a surface of the active layer 411, and then the Cp2Mg delta doping process is performed in a thickness range of 10-200 Å. The Cp2Mg delta doping process sets the undoped GaN/delta doped GaN structure as one period and continuously repeats the one period within an overall thickness of 0.1 μm to form a light emitting device having a p-/n-junction structure such that resistance component is decreased by Mg atomic concentration (including Mg atomic and Mg—H complex) after the activation and uniform carrier concentration is obtained.
After the nitride semiconductor light emitting device is completed by the aforementioned processes, mesa etching is performed using an ICP etching apparatus and the nitride semiconductor light emitting device is made in a size of 330 μm×205 μM. Electrical property variation of the fabricated nitride semiconductor light emitting device is analyzed and investigated to verify its performance. As a result, the operating voltage (20 mA) in a forward bias is below 3.4 V, which is the same value as that of the conventional art, but the optical power is increased by 50-100%.
Why the optical power is increased is that an inner diffusion into the “V” pit defect formed in the surface of the active layer emitting light is suppressed, and an absolute amount of Mg atomic (including Mg—H complex) remaining in the layer after the subsequent activation process is decreased by an Mg doping profile lower than that of the conventional art, but the hole carrier concentration contributing to the electric conductivity is increased.
FIG. 7 shows a nitride semiconductor light emitting device according to a second embodiment of the present invention.
Referring to FIG. 7, the nitride semiconductor light emitting device according to a second embodiment of the present invention includes a substrate 401, a buffer layer 403, an In-doped GaN layer 405, an n-GaN layer 407, a low-mole In-doped GaN layer or low-mole InGaN layer 409, an active layer 411, an Mg-delta doped p-GaN layer 413, and an n-InGaN layer 515.
Compared with the first embodiment, the above second embodiment has a difference in that the nitride semiconductor light emitting device further includes the n-InGaN layer 515. Therefore, only the n-InGaN layer 515 will be additively described and descriptions of other elements will be referred from that of the first embodiment.
To fabricate an n-/p-/n-junction structure light emitting device, in addition to the p-/n-junction structure light emitting device, the second embodiment of the present invention grows the Mg-delta doped p-GaN layer 413 and then grows the n-InGaN layer 515 to use as the second electrode contact layer.
The n-InGaN layer 515 used as the second electrode contact layer is grown to a thickness of 50 Å with being doped with silicon at a growth temperature decreased to 800° C. in a mixture gas ambient of NH3 source gas and N2 carrier gas. At this time, the n-InGaN layer 515 is used as the second electrode contact layer and is designed to have the super grading (SG) structure in which indium content is adjusted to control the energy bandgap profile on whole. By the aforementioned method, the n-/p-/n-junction structure nitride semiconductor light emitting device can be obtained.
MODE FOR THE INVENTION
In addition to the above embodiments, a plurality of other examples can be provided on the basis of the same spirit.
First, a transparent electrode may be further formed on the n-InGaN layer 515. The transparent electrode can be formed of one selected from the group consisting of ITO, IZO(In—ZnO), GZO(Ga—ZnO), AZO(Al—ZnO), AGZO(Al—Ga ZnO), IGZO(In—Ga ZnO), IrOx, RuOx, RuOx/ITO, Ni/IrOx/Au, and Ni/IrOx/Au/ITO.
Also, while the second embodiment illustrates that the n-InGaN layer 515 is formed as the second electrode contact layer, an n-InGaN/InGaN super lattice structure may be formed as the second electrode contact layer. Alternatively, a Si-doped GaN layer may be further formed between the n-InGaN/InGaN super lattice layer and the Mg-delta doped p-GaN layer 413.
In addition, the first and second embodiments illustrate that Mg is delta doped in the delta doping process. However, through a similar process, Mg—Al, Mg—Al—In or the like as well as Mg can be delta doped. At this time, TMAl, TMIn MO (metal organic) can be used as a doping source.
Further, the delta doped p-GaN layer can be formed with one period consisting of undoped AlGaN/delta doped p-GaN structure, the two layers constituting the one period can be repeatedly grown at least two times, the undoped AlGaN layer is grown within a thickness range of 10-300 Å with an Al composition range of 0.01-0.02.
Furthermore, the delta doped p-GaN layer can be formed with one period consisting of undoped InGaN/delta doped p-GaN structure, the two layers constituting the one period can be repeatedly grown at least two times, the undoped InGaN layer is grown within a thickness range of 10-300 Å with an Al composition range of 0.01-0.1.
Also, the delta doped p-GaN layer can be formed with one period consisting of undoped GaN/undoped AlGaN cap/delta doped p-GaN structure, the three layers constituting the one period can be repeatedly grown at least two times, the undoped AlGaN cap layer is grown within a thickness range of 5-200 Å with an Al composition range of 0.01-0.02.
Additionally, the delta doped p-GaN layer can be formed with one period consisting of undoped InGaN/undoped AlGaN cap/delta doped p-GaN structure, the three layers constituting the one period can be repeatedly grown at least two times, the undoped AlGaN cap layer is grown within a thickness range of 5-200 Å with an Al composition range of 0.01-0.02.
Also, in the first and second embodiments, the n-GaN layer serving as the first electrode contact layer can be an n-GaN layer formed by a co-doping of Si and In, and it can be formed at a doping concentration of 1-9×1019/cm3 in a thickness range of 1-4 μm.
Additionally, the first electrode contact layer can be formed with one period consisting of undoped-AlGaN/doped-GaN super lattice structure, the two layers constituting the one period can be repeatedly grown at least two times with an overall thickness of 1-2 μm and an Al composition of 0.05-0.3. The doped-GaN layer can be formed within a thickness range of 200-500 Å.
Further, the active layer can be made in a single quantum well structure or a multi quantum well structure comprised of well layer/SiNx cluster layer/barrier layer, and the SiNx cluster layer can be grown by a Si-delta doping method. The SiNx cluster layer can be grown by the Si-delta doping using a doping source of SiH4 or SiH6 alone.
INDUSTRIAL APPLICABILITY
According to the nitride semiconductor light emitting device and fabrication method thereof provided by the present invention, the optical power is enhanced, the power down phenomenon is improved, and the reliability against ESD (Electro Static Discharge) is enhanced.
Also, the present invention can be applied to a lighting apparatus requiring high optical power and high reliability.

## Claims

1. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
a delta doped second nitride semiconductor layer; and
an active layer between the first nitride semiconductor layer and the delta doped second nitride semiconductor layer;
wherein the delta doped second nitride semiconductor layer includes a delta doped nitride semiconductor layer and an un-doped nitride semiconductor layer between the delta doped nitride semiconductor layer and the active layer.

2. The nitride semiconductor light emitting device according to claim 1, further comprising a third nitride semiconductor layer on the delta doped second nitride semiconductor layer.

3. The nitride semiconductor light emitting device according to claim 2, wherein the third nitride semiconductor layer is formed of an n-InGaN layer with an SG (super grading) structure in which indium content is gradually varied, or of an n-InGaN/InGaN super lattice structure layer.

4. The nitride semiconductor light emitting device according to claim 2, further comprising a Si-doped GaN layer between the third nitride semiconductor layer and the delta doped second nitride semiconductor layer.

5. The nitride semiconductor light emitting device according to claim 2, further comprising a transparent electrode on the third nitride semiconductor layer.

6. The nitride semiconductor light emitting device according to claim 5, wherein the transparent electrode includes at least one selected from the group consisting of ITO, IZO(In—ZnO), GZO(Ga—ZnO), AZO(Al—ZnO), AGZO(Al—Ga ZnO), IGZO(In—Ga ZnO), IrOx, RuOx, RuOx/ITO, Ni/IrOx/Au, and Ni/IrOx/Au/ITO.

7. The nitride semiconductor light emitting device according to claim 1, further comprising:
a buffer layer under the first nitride semiconductor layer; and
a substrate under the buffer layer.

8. The nitride semiconductor light emitting device according to claim 7, further comprising a strain control layer on the buffer layer.

9. The nitride semiconductor light emitting device according to claim 7, wherein the buffer layer includes at least one structure selected from the group consisting of a stack structure of AlInN/GaN, a super lattice structure of InGaN/GaN, a stack structure of InxGa1−xN/GaN, and a stack structure of AlxInyGa1−(x+y)N/InxGa1−xN/GaN.

10. The nitride semiconductor light emitting device according to claim 1, further comprising a low mole indium-containing nitride layer between the first nitride semiconductor layer and the active layer, wherein the low mole indium-containing nitride layer has an indium content of 1-5%.

11. The nitride semiconductor light emitting device according to claim 1, wherein the delta doped second nitride semiconductor layer is grown in a thickness range of 10-300 Å.

12. The nitride semiconductor light emitting device according to claim 1, wherein the delta doped second nitride semiconductor layer includes at least one repeatedly grown structure selected from the group consisting of undoped GaN/delta doped p-GaN, undoped AlGaN/delta doped p-GaN, undoped InGaN/delta doped p-GaN, undoped GaN/undoped AlGaN cap/delta doped p-GaN, and undoped InGaN/undoped AlGaN cap/delta doped p-GaN structures.

13. The nitride semiconductor light emitting device according to claim 1, wherein the delta doped second nitride semiconductor layer is formed with at least one period consisting of layers where the doping dose is changed, wherein the period is repeatedly grown in the delta doped second nitride semiconductor layer.

14. The nitride semiconductor light emitting device according to claim 1, wherein the delta doped second nitride semiconductor layer comprises at least one selected from the group consisting of Mg delta doped GaN layer, Mg—Al delta doped GaN layer and Mg—Al—In delta doped GaN layer.

15. The nitride semiconductor light emitting device according to claim 1, wherein the delta doped second nitride semiconductor layer is grown repeatedly at least two times where one period is one selected from the group consisting of undoped GaN layer/delta doped p-GaN layer, undoped AlGaN layer/delta doped p-GaN layer, undoped InGaN layer/delta doped p-GaN layer, undoped GaN layer/undoped AlGaN cap layer/delta doped p-GaN layer, and undoped InGaN layer/undoped AlGaN cap layer/delta doped p-GaN layer structures such that the selected layers constituting the one period have different thicknesses.

16. The nitride semiconductor light emitting device according to claim 15, wherein the undoped AlGaN layer is grown in a thickness range of 10-300 Å with an Al composition of 1-2%.

17. The nitride semiconductor light emitting device according to claim 15, wherein the undoped InGaN layer is grown in a thickness range of 10-300 Å with an In composition of 1-2%.

18. The nitride semiconductor light emitting device according to claim 15, wherein the undoped AlGaN cap layer is grown in a thickness range of 5-200 Å with an Al composition of 1-2%.

19. The nitride semiconductor light emitting device according to claim 1, wherein the first nitride semiconductor layer is an n-GaN layer formed by a Si—In simultaneous doping in a doping concentration range of 1×1019/cm3-9×1019/cm3 at a thickness range of 1-4 μm.

20. The nitride semiconductor light emitting device according to claim 1, wherein the first nitride semiconductor layer is formed in an overall thickness less than 2 μm by growing repeatedly at least two times an undoped-AlGaN/doped-GaN super lattice structure.

21. The nitride semiconductor light emitting device according to claim 20, wherein the undoped-AlGaN layer is formed in a thickness range of 10-200 Å with an Al composition of 0.05-0.3, and the doped-GaN layer is formed in a thickness range of 200-500 Å.

22. The nitride semiconductor light emitting device according to claim 1, wherein the first nitride semiconductor layer includes n-type impurities and the delta doped second nitride semiconductor layer includes p-type impurities.

23. The nitride semiconductor light emitting device according to claim 1, wherein the un-doped nitride semiconductor layer is formed in a thickness range of 10-200 Å.

24. The nitride semiconductor light emitting device according to claim 1, wherein the un-doped nitride semiconductor layer is formed in a thickness less than 200 Å.

25. The nitride semiconductor light emitting device according to claim 1, wherein the delta doped second nitride semiconductor layer includes at least two delta doped nitride semiconductor layers.

26. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
an active layer on the first nitride semiconductor layer in a single quantum well structure or a multi quantum well structure comprising a well layer and a barrier layer; and
an Mg-delta doped second nitride semiconductor layer on the active layer.

27. The nitride semiconductor light emitting device according to claim 26, wherein the Mg-delta doped second nitride semiconductor layer is a second electrode contact layer.

28. The nitride semiconductor light emitting device according to claim 26, further comprising an n-type second electrode contact layer on the Mg-delta doped second nitride semiconductor layer.

29. The nitride semiconductor light emitting device according to claim 26, wherein the active layer further comprises an SiNx cluster layer interposed between the well layer and the barrier layer.

30. The nitride semiconductor light emitting device according to claim 29, wherein the SiNx cluster layer is grown using a Si-delta doping method.

31. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
an active layer formed above the first nitride semiconductor layer; and
a delta doped second nitride semiconductor layer formed above the active layer,
wherein the delta doped second nitride semiconductor layer is formed with at least one period consisting of layers where the doping dose is changed, wherein the period is repeatedly grown in the delta doped second nitride semiconductor layer.

32. The nitride semiconductor light emitting device according to claim 31, wherein the first nitride semiconductor layer includes n-type impurities and the delta doped second nitride semiconductor layer includes p-type impurities.

33. The nitride semiconductor light emitting device according to claim 32, wherein the p-type impurities include Mg.

34. The nitride semiconductor light emitting device according to claim 31, wherein the delta doped second nitride semiconductor layer is grown in a thickness range of 10-300 Å.

35. The nitride semiconductor light emitting device according to claim 31, wherein the layers where the doping dose is changed includes an un-doped nitride semiconductor layer formed in a thickness range of 10-200 Å.

36. The nitride semiconductor light emitting device according to claim 31, wherein the layers where the doping dose is changed includes an un-doped nitride semiconductor layer formed in a thickness less than 200 Å.

37. The nitride semiconductor light emitting device according to claim 31, wherein the delta doped second nitride semiconductor layer includes at least two delta doped nitride semiconductor layers.

38. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
an active layer on the first nitride semiconductor layer in a single quantum well structure or a multi quantum well structure comprising a well layer and a barrier layer; and
an Mg-delta doped second nitride semiconductor layer on the active layer,
wherein Mg-delta doped second nitride semiconductor layer includes Al.

39. The nitride semiconductor light emitting device according to claim 38, wherein the Mg-delta doped second nitride semiconductor layer includes AlGaN.

40. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
an active layer formed above the first nitride semiconductor layer;
a delta doped second nitride semiconductor layer formed above the active layer; and
a third nitride semiconductor layer on the delta doped second nitride semiconductor layer,
wherein the third nitride semiconductor layer is formed of an n-InGaN layer with an SG (super grading) structure in which indium content is gradually varied, or of an n-InGaN/InGaN super lattice structure layer.

41. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
an active layer formed above the first nitride semiconductor layer;
a delta doped second nitride semiconductor layer formed above the active layer;
a third nitride semiconductor layer on the delta doped second nitride semiconductor layer; and
a Si-doped GaN layer between the third nitride semiconductor layer and the delta doped second nitride semiconductor layer.

42. A nitride semiconductor light emitting device comprising:
a first nitride semiconductor layer;
an active layer formed above the first nitride semiconductor layer; and
a delta doped second nitride semiconductor layer formed above the active layer,
wherein the first nitride semiconductor layer is formed in an overall thickness less than 2 μm by growing repeatedly at least two times an undoped-AlGaN/doped-GaN super lattice structure.