KR20160105126A - Light emitting diode having strain-enhanced well layer - Google Patents

Abstract

An ultraviolet light emitting diode is disclosed. The ultraviolet light emitting diode includes a first conductivity type semiconductor layer; An active layer located on the first conductivity type semiconductor layer and including alternately stacked barrier layers and well layers; An electron blocking layer positioned on the active layer; And a second conductive semiconductor layer located on the electron blocking layer, wherein at least some of the barrier layers other than the barrier layer located at the top of the barrier layers include a delta layer, The energy is greater than the bandgap energy of the other portion of the barrier layer except for the delta layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a light-emitting diode having a strain-enhanced well layer (LIGHT EMITTING DIODE HAVING STRAIN-ENHANCED WELL LAYER)

The present invention relates to light emitting diodes, and more particularly to light emitting diodes having strain-enhanced well layers.

Group III-V nitride-based laser diodes / light emitting diodes (LD / LED) is generally c- plane (0001), patterning the (Patterned) In _x Ga ₁ on a sapphire substrate of _{- x} N buffer layer, n-GaN layer, InGaN / An active layer of GaN quantum well structure, a p-AlGaN electron blocking layer, and p-GaN.

GaN-based general GaN / In _{0 . 15} Ga _{0 .75} N compressive strain of about 1.6% in the InGaN well layer (Compressive strain) For the quantum well structure is applied. Conventional technology has been developed as a technique for alleviating strain when the strain is applied to the active layer, which is considered to be inefficient.

On the other hand, in general, as the driving current increases in the high-brightness LED, a droop phenomenon occurs in which the light output efficiency is decreased with respect to the applied power. Therefore, in order to obtain a high light output efficiency at a high drive current, it is necessary to alleviate the droop phenomenon of the light emitting diode.

The above information disclosed herein is merely intended to enhance the understanding of the present invention and therefore may not form part of the prior art and may also include information that the prior art does not suggest to a person skilled in the art.

Embodiments of the present invention provide a light emitting diode capable of mitigating the droop phenomenon caused by an increase in driving current.

Another object of the present invention is to provide an ultraviolet light emitting diode having a high luminous efficiency, in particular, an improved internal quantum efficiency.

According to one aspect of the present invention, an ultraviolet light emitting diode includes: a first conductivity type semiconductor layer; An active layer disposed on the first conductive semiconductor layer and including alternately stacked barrier layers and well layers; An electron blocking layer disposed on the active layer; And a second conductive semiconductor layer disposed on the electron blocking layer, wherein at least some of the barrier layers other than the barrier layer located at the top of the barrier layers include a delta layer, The band gap energy of the barrier layer is greater than the band gap energy of the other portion except for the delta layer in the barrier layer.

The barrier layers may include Al _x Ga _(1-x) N (0 < _{x? 1} ), and at least some of the barrier layers other than the topmost barrier layer _y Ga _{(1- y)} N (0 &lt; _{y? 1 )} , where x <y.

The delta layer of a barrier layer of one of the barrier layers may be located closer to a trough layer located above the one barrier layer than a well layer located below the one barrier layer.

The delta layer may be in contact with the trough layer.

The topmost barrier layer may not include the delta layer.

The uppermost barrier layer may contact the electron blocking layer.

The Al composition ratio y of the delta layer may be 0.5 &lt; y? 1.

Other barrier layers other than the topmost barrier layer of the barrier layers may include the delta layer.

The band gap energy of the other portion of the barrier layer excluding the delta layer is defined as E _barrier and the band gap energy of the delta layer is defined as E _{delta layer} , the following expression 1 can be satisfied. (E 1) E _barrier <E _{delta layer} ≤ <E _barrier × 1.11)

Further, the band gap energy of Al _x Ga _(1-x) N and the band gap energy of Al _y Ga _(1-y) N can satisfy the following equation (2). (Equation _{(2) Al x Ga (1-} x) N in the band gap energy _{<Al y Ga (1-y} ) N of the band gap energy _{≤≤ (Al x Ga (1-} x) N in the band gap energy) × 1.11)

The delta layer may further enhance the strain applied to the well layer.

The delta layer of one of the barrier layers may be in contact with a well layer located above the one barrier layer.

In the delta layer, the composition distribution of Al may vary along the horizontal direction.

Further, the composition distribution of Al along the horizontal direction in the delta layer may vary irregularly.

According to embodiments of the present invention, it is possible to provide a light emitting diode capable of mitigating the droop phenomenon due to an increase in driving current by adopting the strain strengthening layer.

Further, according to other embodiments of the present invention, by inserting a delta layer into the barrier layer, an ultraviolet light emitting diode with improved internal quantum efficiency is provided. In particular, at least some of the barrier layers other than the barrier layer located at the top of the barrier layers include a delta layer, so that the internal quantum efficiency of the ultraviolet light emitting diode can be further improved. Furthermore, the delta layer functions as a strain strengthening layer, so that an efficient droop phenomenon can be alleviated.

FIG. 1 is a schematic view for explaining a change in the band structure of a gallium nitride semiconductor according to strain. FIG. 1 (a) shows a normal band structure in which strain is not applied, FIG. 1 The band structure in Fig.
2 is a schematic cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.
3 is a graph for explaining the composition region of the strain enhancement layer.
4 is a schematic cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.
5 is a schematic cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.
6 is a schematic cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.
7 is a schematic cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.
8 is a schematic cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.
9 is a SEM photograph showing the surface of the GaN layer etched using a random pattern of metal.
10 is a graph showing a change in luminous intensity depending on the presence or absence of a strain strengthening layer.
11 is a graph showing the change in external quantum efficiency depending on the presence or absence of the use of the strain strengthening layer.
12 is a cross-sectional view illustrating a structure of a light emitting diode according to an embodiment of the present invention.
13 is a cross-sectional view illustrating a structure of a light emitting diode according to another embodiment of the present invention.
14 is a cross-sectional view illustrating a structure of a light emitting diode according to another embodiment of the present invention.
15A and 15B are enlarged sectional views for explaining the structure of the active layer according to the embodiments of the present invention.
16 (a) and 16 (b) are graphs for comparing light emitting diodes according to embodiments of the present invention with light emitting diodes of a comparative example.
17 is a graph illustrating efficiency droop of light emitting diodes according to embodiments of the present invention.
18 is a graph for comparing the internal quantum efficiency of the light emitting diode according to the embodiments of the present invention.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The dimensions and relative sizes of the layers and regions in the Figures may be exaggerated for clarity. In the drawings, the same reference numerals denote the same elements.

When an element or layer is referred to herein as being "on" or "connected to" another element, it is to be understood that the element or layer is directly on, or directly connected to, Or intermediate intermediate elements may be present. In contrast, when an element is referred to as being "directly on" another element or layer, or "directly connected" to another element, there is no intermediate element or layer. At least one of X, Y and Z can be interpreted as X only, Y only, Z only or a combination of two or more items X, Y and Z (e.g., XYZ, XYY, YZ, ZZ) It will be understood.

Terms that are spatially relative to each other, such as "under", "under", "under", "above", "above", and the like, May be used to describe a feature as illustrated in Fig. It will be appreciated that the spatially relative terms are intended to encompass various orientations of elements in use or operation in addition to those depicted in the figures. For example, if a device is inverted in the figures, the elements depicted as being "under" or "under" another feature or feature will be "over" the other feature or feature. Thus, the term "below" can encompass both the up and down directions. The elements can also be arranged differently (rotated 90 degrees or in different directions), and the spatially relative descriptive phrases used here are interpreted accordingly.

The respective composition ratios, growth methods, growth conditions, thicknesses, etc. for the semiconductor layers described below are examples, and the present invention is not limited thereto. For example, in the case of being denoted by AlGaN, the composition ratio of Al and Ga can be variously applied according to the needs of ordinary artisans. In addition, the semiconductor layers described below can be grown using a variety of methods commonly known to those of ordinary skill in the art (such as MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydride Vapor Phase Epitaxy). In the growth process of the semiconductor layers, the sources introduced into the chamber may use a source known to those of ordinary skill in the art. For example, when a nitride semiconductor layer is grown using MOCVD, TMGa, TEGa, TMA, TEA, or the like can be used as the Al source. TMI, TEI and the like can be used as the In source, and NH ₃ can be used as the N source. However, the present invention is not limited thereto.

Hereinafter, various embodiments for preventing the droop phenomenon by strengthening the strain applied to the well layer will be described. Wherein the well layer is not limited to c-plane grown polar epi, and includes both non-polar and m-plane (a-plane, r-plane) epi.

1 is a schematic view showing the structure of a conduction band and a valance band in an energy-momentum space of an active layer. (a) shows an energy band in a normal state, and (b) shows an energy band in a state in which a uniaxial strain is applied. In the normal state, since the difference between the energy levels of the holes is not large, the holes can be easily excited, and droop due to Auger recombination under high current driving is likely to occur. However, when the strain is applied, the gap between the energy levels becomes larger, reducing the probability of the hole transitioning to a higher energy level. That is, when the uniaxial strain is applied as shown in Fig. 1 (b), the difference between the levels in the uniaxial direction sharply increases, making it difficult for the hole to be excited to a higher energy level. The difference between the energy levels also increases when biaxial strain is applied. When the difference between the energy levels is increased, the Auger recombination rate is reduced, and thus the droop phenomenon due to Auger recombination can be alleviated.

2 is a schematic cross-sectional view illustrating a light emitting diode according to an embodiment of the present invention.

2, an n-GaN layer 23, for example, an n-contact layer is located on a substrate 21 and a barrier layer 25, a strain enhancement layer 27, Layer 29 is periodically and repeatedly stacked in one unit U1 to form a multiple quantum well structure. The multiple quantum well structure may comprise an Un unit. The top layer of the quantum well structure may be barrier layer 25, but may be well layer 29 or strain enhancement layer 27. A p-GaN layer 31, for example a p-contact layer, is located on the multiple quantum well structure. An electron blocking layer (not shown) may be located between the quantum well structure and the p-GaN layer 31. [

The barrier layer 25 has a lower bandgap composition than the well layer 29, e.g., the well layer may be InGaN and the barrier layer may be GaN. The compressive strain is generally applied to the well layer 29 by the difference in composition of the barrier layer 25 and the well layer 29. The strain enhancing layer 27 may be formed of an InAlGaN-based nitride semiconductor and has a smaller lattice constant than the barrier layer 25. Thus, the strain enhancing layer 27 is configured to strengthen the strain, e.g. compressive strain, applied to the well layer 29. The strain enhancing layer 27 may have a composition that provides a greater compressive strain to the well layer 29 than the compressive strain that is provided to the well layer 25 by the barrier layer 25.

FIG. 3 is a schematic graph for explaining the composition region of the strain-strengthening layer, in which the boiling parameters are omitted and simplified.

As shown in FIG. 3, gallium nitride-based semiconductors are in a triangular region whose composition range is based on AlN, GaN, and InN. When the barrier layer 25 is made of GaN, the composition in the region having a lattice constant smaller than that of GaN becomes the strain strengthening layer 27. For example, when the barrier layer 25 is a GaN layer and the well layer 29 is an InGaN layer, the strain enhancing layer 27 may be formed of an InAlGaN-based nitride semiconductor having a lattice constant smaller than GaN. The semiconductor layer in the composition region having a lattice constant between the well layer 29 and the barrier layer 25 will relax the strain applied to the well layer 29. [

Thus, strain applied to the well layer 29 can be enhanced by aligning a strain enhancing layer of a gallium nitride series with a lower lattice constant than the barrier layer 25 between the barrier layer 25 and the well layer 29, Thus, the droop phenomenon can be alleviated.

The well layer 29 may be formed to have a thickness of 3 nm or more. The upper limit of the thickness of the well layer 29 can be selected below the critical thickness. For example, the thickness of the well layer 29 may be 10 nm or less, particularly 7 nm or less.

4 is a cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention. Details of the same components as those described with reference to FIG. 2 will be omitted.

4, the light emitting diode according to the present embodiment has an active layer having a multiple quantum well structure in which a barrier layer 25 and a well layer 29 are periodically formed, and a strain enhancement layer 37 is formed on the quantum well structure unit (U1) and the n-GaN layer (23). The strain enhancing layer 37 is configured to strengthen the strain applied to the well layer 29 as described with reference to Figs. That is, the strain-strengthening layer 37 may be formed of an InAlGaN-based semiconductor having the same composition as the strain-strengthening layer 27 of FIG.

5 is a cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.

Referring to FIG. 5, the light emitting diode according to the present embodiment is substantially similar to the light emitting diode of FIG. 4, except that the strain enhancing layer 47 has a superlattice structure. For example, the strain enhancing layer 47 may have a super lattice structure formed by alternately laminating nitride semiconductor layers having different compositions. The strain enhancing layer 47 has a structure for applying compressive strain to the barrier layer 25. For example, when the barrier layer is GaN, the strain enhancing layer 47 may be formed by laminating InAlGaN / InAlGaN several times. have. Here, the InAlGaN / InAlGaN has a smaller lattice constant than GaN of the barrier layer 25, thus applying a compressive strain to the barrier layer 25, thereby enhancing the strain applied to the well layer 29. That is, the strain enhancing layer 47 with a superlattice structure, together with the barrier layer 25, provides a compressive strain greater than the compressive strain provided only in the barrier layer 25 to the well layer 29 .

6 is a cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.

Referring to FIG. 6, the light emitting diode according to the present embodiment is substantially similar to the light emitting diode according to the embodiment described above with reference to FIG. 4, except that the strain enhancing layer 37 and the active layer (the well layer 29 and the barrier layer (Quantum well structure including the quantum well structure (25)). The electron injection layer 24 is a layer for injecting electrons into the active layer U1 and is formed of an n-type semiconductor layer. The electron injection layer 24 may be formed of a gallium nitride semiconductor having the same composition as the contact layer 23, for example, GaN, but is not limited thereto. The electron injection layer 24 may have a super lattice structure.

The electron injection layer 24 has a thickness sufficient to inject electrons into the active layer. On the other hand, the electron injection layer 24 can attenuate strain applied to the well layer 29 by the strain enhancement layer 37 because the electron injection layer 24 has a relatively large lattice constant as compared with the strain enhancement layer 37. Therefore, the thickness of the electron injecting layer 24 should be sufficiently thin so that strain can be induced in the well layer 29 by the strain enhancing layer 37. The thickness of the electron injection layer 24 may be controlled depending on the doping concentration of the n-type impurity and the composition ratio of the strain enhancing layer 37, and may be about 300 nm to 600 nm.

7 is a cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.

7, the light emitting diode according to the present embodiment includes a substrate 21, an n-GaN layer 23, a barrier layer 25, and a barrier layer 25, as described above in connection with the embodiment shown in Fig. An active layer having a quantum well structure in which a plurality of units U1 of the well layer 29 are stacked, and a p-GaN layer 31. [ The light emitting diode according to the present embodiment has the barrier layer 25 having the quantum dot 25d instead of the strain enhancing layer 27 being aligned between the barrier layer 25 and the well layer 29. [

That is, when forming the barrier layer 25, a quantum dot 25d is formed in the barrier layer 25 to strengthen the strain applied to the well layer 29 by the barrier layer 25. [ The quantum dots 25d have a smaller lattice constant than the barrier layer 25 and the composition of such quantum dots is selected in the strain enhancement region of FIG.

8 is a cross-sectional view illustrating a light emitting diode according to another embodiment of the present invention.

Referring to FIG. 8, the light emitting diode according to the present embodiment includes a substrate 21, an n-GaN layer 23, a barrier layer 25, An active layer of a quantum well structure in which a plurality of units U1 of the p-GaN layer 29 are stacked, and a p-GaN layer 31. The light emitting diode according to the present embodiment is formed by forming the pattern 23a in the n-GaN layer 23 instead of aligning the strain enhancing layer 27 between the barrier layer 25 and the well layer 29 And reinforcing the compressive strain applied to the well layer 29 by growing again using the pattern 23a.

That is, after a part of the n-GaN layer 23 is grown, a part of the grown n-GaN layer is patterned as shown in FIG. 9 to form a concave portion 23a between the protruding portion 23a and the protruding portion 23a 23b. Then, the remaining portion of the n-GaN layer 23 is grown using the flat surface of the projecting portion 23a. As a result, an n-GaN layer 23 having a large dislocation is formed on the protruding portion 23a and an n-GaN layer 23 having a good crystal quality is formed on the concave portion 23b by lateral growth .

It is possible to apply a compressive strain to the semiconductor layer formed on the n-GaN layer 23, for example, the barrier layer 25, by locating the n-GaN layer 23 regions with high dislocation and the region with good crystallinity adjacent to each other Thereby enhancing the compressive strain applied to the well layer 29.

The protrusions 23a may be irregularly formed as shown in FIG. The protrusions 23a are formed by irregularly distributing a metal such as Ni on the partially grown n-GaN layer, patterning the n-GaN layer using the metal as an etching mask, and removing the metal material used as a mask . Thereby, the concave portion 23b is formed between the projecting portions 23a.

On the other hand, in order to strengthen the compressive strain applied to the well layer 29, the distance between the protrusions 23a and the protrusions 23a is less than 1 um. In particular, these dimensions may be nano-sized below the wavelength of the light generated in the well layer 29. That is, the width of the protrusions 23a and the distance between the protrusions 23a may be nanoscale. If the distance between the protrusions 23a is more than 1 mu m, it is difficult to form the flat n-GaN layer 23 through the horizontal growth, and it is difficult to strengthen the compressive strain applied to the well layer 29. Further, if the width of the protrusions 23a is 1um or more, it is difficult to strengthen the compressive strain applied to the well layer 29. [

On the other hand, the distance between the protrusions 23a and the active layer may be selected in consideration of the critical thickness of the n-GaN layer, and preferably not exceed about 400 nm. If this is exceeded, the effect of using the projections 23a is lost. On the other hand, since horizontal growth must be performed on the protrusions 23a, it must be at least 10 nm.

In this embodiment, the protrusions 23a may be spaced from each other and the recesses 23b may be connected to each other. Alternatively, the protrusions 23a may be connected to each other, and the recesses 23b may be spaced apart from each other.

In the present embodiment, the projections 23a are irregularly formed. However, the present invention is not limited to this, and the projections 23a may be regularly formed. In this case, the projecting portion 23a has a hexagonal columnar or hexagonal prism shape and can be regularly arranged two-dimensionally. By this regular arrangement, it is possible to evenly distribute the dislocation regions and the regions having good crystallinity in the n-GaN layer 23.

On the other hand, the upper surfaces of the protrusions 23a are preferably flat so that the n-GaN layer grows again on the protrusions 23a. Furthermore, the concave portion 23b between the protrusions 23a may be left as an empty space or may be filled with a material other than the n-GaN layer 23, for example, an insulating material or a metal material such as Ag. For example, n-GaN is patterned using Ni as an etching mask to form protrusions 23a and recesses 23b. Then, before removing Ni, a metal layer for filling recesses 23b is formed , The concave portion 23b can be filled by removing Ni and the metal layer located on the projections 23a.

(Experimental Example 1)

In order to investigate the change of the droop characteristics of the light emitting diode due to the adoption of the strain strengthening layer, a light emitting diode (comparative example) in which the strain strengthening layer is omitted together with the light emitting diode Respectively.

Embodiment, the LED is 2um a sentence prompt GaN on a sapphire substrate, Si doped GaN 2um, Al _{0. 25} Ga _{0 . A} Mg-doped AlGaN electron barrier layer was formed by growing a ₇₅ N layer (strain enhancement layer) of about 20 nm, an n GaN electron injection layer of about 500 nm, forming a barrier layer and a well layer of six cycles, Grown GaN. On the other hand, as a comparative example, a light emitting diode in which the strain enhancing layer and the electron injecting layer are omitted was prepared.

The light-emitting diodes were fabricated with 600 x 600 um ² the size of the chip in order to analyze the electrical and optical properties. Pulse power was used to remove the thermal effect, with a pulse period of 100 ns and a tune time of 10%. The luminescence characteristics according to the current are shown in Fig. 10, and the external quantum efficiency according to the current is standardized and shown in Fig.

10 and 11, it can be seen that the light emitting diode of the embodiment in which the strain applied to the well layer is further enhanced exhibits a higher luminous efficiency (EL) as compared with the light emitting diode of the comparative example, and the decrease of the external quantum efficiency As shown in FIG.

FIG. 12 is a cross-sectional view illustrating a structure of a light emitting diode according to an embodiment of the present invention, and FIGS. 15A and 15B are enlarged cross-sectional views illustrating a structure of an active layer according to embodiments of the present invention. 13 and 14 are sectional views for explaining the structure of a light emitting diode according to another embodiment of the present invention, respectively.

12, an ultraviolet light emitting diode according to an exemplary embodiment of the present invention includes a first conductive semiconductor layer 200, an active layer 300, an electron blocking layer 400, (500). Further, the light emitting diode may further include a substrate 100 and a buffer layer 110.

The substrate 100 is not limited as long as it is a substrate for growing a nitride semiconductor layer, and may be, for example, a sapphire substrate, a silicon carbide substrate, a spinel substrate, or a nitride substrate such as a GaN substrate or an AlN substrate.

The substrate 100 may be omitted if necessary. For example, in a vertical type light emitting diode or a flip chip type light emitting diode, the substrate 100 can be separated and removed from the semiconductor layers. For example, the substrate 100 may be removed through a physics-chemical method such as laser lift-off, stress lift-off, chemical lift-off, or lapping or polishing.

The buffer layer 110 is located on the substrate 100. The buffer layer 110 may include a nucleation layer that helps other semiconductor layers grown on the substrate 100 to grow into a single crystal, and may include a three-dimensional growth layer and a recovery layer located on the nucleation layer. The buffer layer 110 may also reduce stress due to the difference in lattice constant between the substrate 100 and other semiconductor layers grown on the buffer layer 110. The buffer layer 110 may include a nitride semiconductor such as (Al, Ga, In) N and may include at least one of GaN, AlGaN, and AlN, for example. In this embodiment, the buffer layer 200 may include AlN.

On the other hand, the buffer layer 110 may be omitted. For example, when the substrate 100 and the first conductivity type semiconductor layer 200 are made of the same material, the first conductivity type semiconductor layer 200 may be grown on the substrate 100 without further forming the buffer layer 110 . Also, when the substrate 100 is separated and removed, the buffer layer 110 may be removed in the process of separating the substrate 100.

The first conductive semiconductor layer 200 is located on the substrate 100. When the buffer layer 110 is further located on the substrate 100, the first conductivity type semiconductor layer 200 may be grown on the buffer layer 110. The first conductive semiconductor layer 200 may include a nitride semiconductor such as (Al, Ga, In) N, and may be doped including a dopant. For example, the first conductive semiconductor layer 200 may be doped with an n-type impurity such as Si, Ge or the like as a dopant.

Since the ultraviolet light emitting diode according to the present embodiment emits light in the ultraviolet band, the first conductivity type semiconductor layer 200 may include a nitride semiconductor which has a low absorption rate with respect to light in the ultraviolet band or does not absorb the ultraviolet light can do. Specifically, when the band gap energy of the nitride semiconductor forming the first conductivity type semiconductor layer 200 is smaller than the energy corresponding to the wavelength of light in the ultraviolet band, the light in the ultraviolet band can be absorbed by the nitride semiconductor. If the light is absorbed in the nitride semiconductor, the light emitting efficiency of the ultraviolet light emitting diode may be significantly lowered. Therefore, the first conductivity type semiconductor layer 200 may include Al, and in particular, may include AlGaN. At this time, the Al composition ratio of AlGaN can be controlled according to the wavelength of light emitted from the active layer 300. For example, when the peak wavelength of the light emitted from the active layer 300 is 300 nm or less, the AlGaN may have an Al composition ratio of about 0.2 or more. When the peak wavelength of the light emitted from the active layer 300 is 300 nm or less, Al composition ratio. However, the present invention is not limited thereto.

The first conductive semiconductor layer 200 may be a single layer or may be formed of multiple layers including a plurality of layers. When the first conductive semiconductor layer 200 includes a plurality of layers, the first conductive semiconductor layer 200 may include a clad layer, a contact layer, an intermediate layer, or a superlattice layer. Furthermore, the first conductivity type semiconductor layer 200 may include a gradation layer continuously changing its composition ratio.

12, the first conductivity type semiconductor layer 200 may include a lower first conductivity type semiconductor layer 210, an upper first conductivity type semiconductor layer 230, and a lower first conductivity type semiconductor layer 230. [ And an intermediate layer 220 interposed between the semiconductor layer 210 and the upper first conductivity type semiconductor layer 230. At this time, the lower and upper first conductivity type semiconductor layers 210 and 230 and the intermediate layer 220 may each include n-type doped AlGaN. The Al composition ratio of the intermediate layer 220 may be higher than the Al composition ratio of the lower and upper first conductivity type semiconductor layers 210 and 230. Further, the thickness of the intermediate layer 220 may be thinner than the thickness of the lower and upper first conductivity type semiconductor layers 210 and 230, and the thickness of the upper first conductivity type semiconductor layer 230 may be less than the thickness of the intermediate layer 220. [ It can be thin. For example, the lower first conductivity type semiconductor layer 210 may be formed of AlGaN having a thickness of about 1000 nm and an Al composition ratio of about 50%, and the intermediate layer 220 may have an Al composition ratio of about 63% And the upper first conductivity type semiconductor layer 230 may be formed of AlGaN having a thickness of about 70 nm and an Al composition ratio of about 50%. However, the present invention is not limited thereto.

When an intermediate layer 220 having a high Al composition ratio is formed on the lower first conductivity type semiconductor layer 210, biaxial stress is generated. By forming the upper first conductivity type semiconductor layer 210 having an Al composition ratio lower than that of the intermediate layer 220 on the intermediate layer 220, the biaxial stress can be alleviated. Accordingly, the stress applied to the lattice due to the stress change is alleviated, the crystallinity can be improved, and the potential can be reduced or the propagation of the potential can be blocked. In addition, since the Al composition ratio of the intermediate layer 220 is relatively high, the band gap energy of the intermediate layer 220 is relatively higher than that of the lower and upper first conductivity type semiconductor layers 210 and 230. Therefore, the electrons traveling in the vertical direction can be evenly dispersed in the horizontal direction, and the current can be evenly dispersed in the horizontal direction in the light emitting diode.

The active layer 300 is located on the first conductive semiconductor layer 200. The active layer 300 may include a nitride semiconductor such as (Al, Ga, In) N, and may control the composition ratio of the nitride semiconductor to emit light having a peak wavelength in a desired ultraviolet region. In addition, the active layer 300 may include a multiple quantum well structure (MQW) in which the well layer 310 and the barrier layer 320 are alternately stacked by at least 13 or more cycles. Hereinafter, the structure of the active layer 300 will be described in detail with reference to FIGS. 15A and 15B.

15A and 15B, the active layer 300 includes a multiple quantum well structure in which a barrier layer 320 and a well layer 310 are alternately stacked. At this point, some of the barrier layers 320 include a delta layer 321 located therein.

The barrier layer 320 may include a nitride semiconductor having a bandgap energy greater than that of the well layer 310 and the barrier layer 320 and the well layer 310 may comprise Al _x Ga _(1-x) N ( 0 <x? 1) and Al _y Ga _(1-y) N (0 <y? 1, y <x). For example, the barrier layer 320 is Al _{0. 5} Ga _(1-0.5) N, the well layer 310 may be formed of AlGaN having an Al composition ratio of less than 0.5, for example, Al _{0 . 4} Ga _(1-0.4) N. The barrier layer 320 is formed of a nitride semiconductor having a relatively higher Al composition ratio than the well layer 310 so that a plurality of carriers (electrons and holes) are concentrated on the well layer 310. This increases the probability that electrons and holes are combined. However, the barrier layer 320 and the well layer 310 are not limited thereto, and may include, for example, a four-component nitride semiconductor such as AlInGaN. In this case, the composition ratio of Al, In, and Ga is adjusted so that the nitride semiconductor forming the layers 310 and 320 is formed so that the band gap energy of the barrier layer 320 is larger than the band gap energy of the well layer 310 You can decide.

Among the barrier layers 320, at least some of the remaining barrier layers 320 except for the topmost barrier layer 320a include a delta layer 321 located therein. Further, among the barrier layers 320, all the barrier layers 320 except for the barrier layer 320a located at the top may include a delta layer 321 located therein. That is, during the growth of the active layer 300, the delta layer 321 is inserted during the growth of at least some of the other barrier layers 320 except for the last grown barrier layer 320a. Accordingly, the lastly grown barrier layer 320a can be in contact with the electron blocking layer 400. However, the present invention is not limited thereto, and another layer may be further interposed between the uppermost barrier layer 320a and the electron blocking layer 400. Delta layer 321 includes _{Al w Ga (1-w)} N (0 <w≤1), In this case, the Al composition ratio of the delta layer 321 is higher than the Al composition ratio of other parts of the barrier layer 320 . Therefore, the relation of x &lt; w can be established. For example, in Al _w Ga _(1-w) N of the delta layer 321, the Al composition ratio w may be more than 0.5 and not more than 1. However, the Al composition ratio w of the delta layer 321 can be variously adjusted according to the Al composition ratio of the well layer 310 and the barrier layer 320, and is not limited to the above range.

At least some of the other barrier layers 320 except for the uppermost barrier layer 320a include a delta layer 321 to enhance the internal quantum efficiency of the light emitting diode. At least some of the barrier layers 320 include a delta layer 321 having a relatively high energy band gap, increasing the probability that the carrier is confined in the well layer 310. Therefore, the concentration of carriers in the well layer can be increased and the internal quantum efficiency can be improved.

On the other hand, the Al composition ratio of the delta layer 321 may be determined according to the Al composition ratio of the other portions of the barrier layer 320. The Al composition ratio of the delta layer 321 may be larger at a ratio of about 11% or less, although the band gap energy of the delta layer 321 is larger than the band gap energy of the barrier layer 320. That is, the relationship of the following equation (1) can be established between the band gap energy of the delta layer 321 and the band gap energy of the barrier layer 320.

[Formula 1]

In the barrier layer, when the band gap energy E _barrier and the band gap energy E _{delta layer} of the delta layer are other than the _{delta layer} ,

E _barrier <E _{delta layer} ≤ E _barrier × 1.11

As described above, when the barrier layer 320 includes the delta layer 321, the probability that the carriers are confined in the well layer 310 increases, and the recombination efficiency of electrons and holes can be improved. However, as the bandgap energy of the entire barrier layer 320 increases, the probability of electrons and holes being transferred into the well layer decreases, increasing the probability of auger recombination at high currents. The delta layer 321 and the delta layer 321 in consideration of the degree of increase in the probability that the carrier is confined in the well layer 310 and the degree of increase in the probability of recombination of the erasures, The band gap energy can be determined. When the above formula (1) is satisfied, it is possible to obtain the best efficiency droop characteristic in the tradeoff relation between the probability that the carrier is confined in the well layer (310) and the erasure reuse probability. Therefore, the Al composition ratio of the other portion of the barrier layer 320 other than the delta layer 321 and the Al composition ratio of the delta layer 321 can be determined so as to have the band gap energy satisfying Equation (1).

The delta layer 321 may also include one or more well layers 310 located in the upper portion of the one barrier layer 320 in the one barrier layer 320, Lt; RTI ID = 0.0 &gt; 310 &lt; / RTI &gt; 15A, the delta layer 321 is positioned within the upper region of the one barrier layer 320, assuming that one barrier layer 320 is divided into an upper region and a lower region of substantially the same thickness. can do. Further, as shown in FIG. 15B, the delta layer 321 can contact the well layer 310 located in the upper portion of the one barrier layer 320 within the barrier layer 320. The thickness of the delta layer 321 may be thinner than the thickness of the barrier layer 320 in other portions except for the delta layer 321, and may have a thickness within a range of, for example, about 1 A to 10 A.

The lattice constant of the delta layer 321 is higher than the lattice constant of the delta layer 321 in the barrier layer 320 because the Al composition ratio of the delta layer 321 is higher than the Al composition ratio of the other portions except for the delta layer 321 in the barrier layer 320. [ ) Is lower than the lattice constant of the other portions. The delta layer 321 is located closer to the top layer 310 located above the one barrier layer 320 than the one well layer 310 located below the one barrier layer 320 The strain applied to the tear layer 310 can be strengthened, as described above. That is, the delta layer 321 may serve as the strain enhancing layer 27 described in the embodiment of FIG. In particular, when the delta layer 321 is in contact with the top layer 310 located above the delta layer 321, the strain applied to the top layer 310 can be further strengthened. Thus, the efficiency drop phenomenon of the light emitting diode can be mitigated.

In addition, in various embodiments, the Al compositional distribution in the delta layer 321 may vary along the horizontal direction within the delta layer 321. In particular, the Al composition ratio in the delta layer 321 may be irregularly distributed along the horizontal direction. When the strain of the well layer 310 is strengthened by the delta layer 321, the efficiency droop characteristic is improved, but the piezoelectric field is strengthened and the internal quantum efficiency can be lowered due to polarization of the electronization hole. At this time, the Al composition ratio in the horizontal direction in the delta layer 321 can be irregularly formed so that the uneven compressive strain is applied in the horizontal direction in the well layer 310. In this case, when a relatively low density current is applied to the ultraviolet light emitting diode, the recombination rate of electrons and holes is high and the recombination time is shortened because there is little polarization in a region where the strain is small. do. Further, when a current with a relatively high density is applied to the ultraviolet light emitting diode, the piezoelectric electric field that causes polarization is screened by the carrier and canceled, and due to the efficient droop mitigation characteristic due to the hole level separation phenomenon described above In the region where the strain is strong, luminescence can mainly occur. Therefore, by changing the Al composition ratio in the delta layer 321 along the horizontal direction, it is possible to improve the luminous efficiency at the time of low current application and to relax the efficiency droop at the time of high current application.

The delta layer 321 having an Al composition ratio changing along the horizontal direction can be provided through a heat treatment process after the growth of the delta layer 321. [ By controlling the time of the heat treatment process, the distribution of the Al composition ratio and the like can be controlled. Specifically, after the delta layer 321 growth is completed, the Al remaining in the growth chamber is deposited on the delta layer during the time for changing the growth condition for growth of the well layer 310. [ At this time, the delta layer 321 is etched by the hydrogen gas in the growth chamber. In this process, the Al bonding force is stronger than the Ga bonding force, so that there is a difference in the etching rate, and the probability that the remaining Al source forms the Al-to-Al bond increases. Therefore, as the time for changing the growth condition becomes longer, . Therefore, the Al compositional change in the horizontal direction of the delta layer 321 can be adjusted depending on the concentration ratio of the hydrogen carrier gas, the Al source residual amount, the heat treatment temperature and time, and the like.

Referring again to FIG. 12, the electron blocking layer 400 is located on the active layer 300. The electron blocking layer 400 may comprise a nitride semiconductor, such as (Al, Ga, In) N, and may include, for example, AlGaN. The electron blocking layer 400 prevents the electrons supplied from the first conductivity type semiconductor layer 200 to the active layer 300 from moving toward the second conductivity type semiconductor layer 500 to lower the coupling efficiency, It is preferable that the band gap energy of the barrier layer 400 is larger than the band gap energy of the barrier layer 320. Therefore, the electron blocking layer 400 may include AlGaN having a higher Al composition ratio than the AlGaN of the barrier layer 320, and may be formed of AlGaN having an Al composition ratio of about 0.5 or more, for example.

In addition, the electron blocking layer 400 may be doped to have the same conductivity type as that of the second conductive semiconductor layer 500, and may be doped with a p-type dopant including a dopant such as Mg. At this time, the doping concentration of the electron blocking layer 400 may be higher than the doping concentration of the second conductivity type semiconductor layer 500. The hole injection efficiency into the active layer 300 can be improved by doping the electron blocking layer 400 into p-type. The thickness of the electron blocking layer 400 is not limited, but may be formed to a thickness of, for example, about 80 nm.

The second conductive semiconductor layer 500 is located on the electron blocking layer 400. The second conductive semiconductor layer 500 may include a nitride semiconductor such as (Al, Ga, In) N, and may include, for example, AlGaN. The second conductivity type semiconductor layer 500 may be doped with a conductivity type opposite to that of the first conductivity type semiconductor layer 300 and may have a p-type conductivity type including, for example, a Mg dopant. The second conductive semiconductor layer 500 may further include a delta doping layer (not shown) for lowering ohmic contact resistance. The second conductivity type semiconductor layer 500 may have a relatively low Al composition ratio as compared with the first conductivity type semiconductor layer 200 to form a smooth ohmic contact with the electrode. However, the second conductivity type semiconductor layer 500 is not limited thereto.

According to the above-described embodiments, a light emitting diode having a high internal quantum efficiency shown in FIG. 12 can be provided. The light emitting diode may be modified into various forms through additional processes. For example, the light emitting diode may be applied to a vertical type light emitting diode or a horizontal type light emitting diode as shown in FIGS. 13 and 14, respectively.

13, the ultraviolet light emitting diode includes a first conductive semiconductor layer 200, an active layer 300, an electron blocking layer 400, a second conductive semiconductor layer 500, first and second electrodes 610 , 620). 13, the substrate 100 is removed from the ultraviolet light emitting diode of FIG. 12, and the first and second electrodes 610 (610) are formed on the first and second conductive semiconductor layers 200 and 500, respectively, , 620).

14, the ultraviolet light emitting diode includes a first conductive semiconductor layer 200, an active layer 300, an electron blocking layer 400, a second conductive semiconductor layer 500, (610, 620). 14, a mesa including a second conductive type semiconductor layer 500, an electron blocking layer 400, and an active layer 300 is formed from the ultraviolet light emitting diode of FIG. 12 to form a first conductive type semiconductor layer The first and second electrodes 610 and 620 are formed on the exposed portions of the first conductivity type semiconductor layer 200 and the second conductivity type semiconductor layer 500, .

As described above, according to the embodiments of the present invention, ultraviolet light emitting diodes having high internal quantum efficiency can be provided.

(Experimental Example 2)

Hereinafter, the ultraviolet light emitting diodes according to the embodiments of the present invention and the ultraviolet light emitting diodes according to the comparative example will be described with reference to the graphs of FIG. 16 and FIG.

First, referring to FIG. 16, an ultraviolet light emitting diode (example) including a delta layer and an ultraviolet light emitting diode (excluding example) including no delta layer are compared and described. The ultraviolet light emitting diodes of the above embodiments and comparative examples each include the same n-type semiconductor layer and p-type semiconductor layer, and an electron blocking layer. However, the ultraviolet light emitting diode of the above-described embodiment has the structure of Al _{0 . 5} Ga _{0 .5} N barrier layer and Al _{0 . 8} Ga _{0 .8} N delta layer, and the ultraviolet light emitting diode of the above comparative example includes Al _{0 . 5} and Ga _{0 .5} includes a multiple quantum well structure of the active layer including the barrier layer, N.

16 (a) and 16 (b) show the concentration of electrons and holes according to a vertical distance, respectively. The larger the vertical distance, the closer to the p-type semiconductor layer. As shown in Figs. 16 (a) and 16 (b), in the case of the embodiment, the carrier concentration is higher than that of the comparative example, which is interpreted as a result of an improvement in carrier confinement efficiency.

17, the ultraviolet light emitting diodes (Examples 1 to 3) including delta layers having different Al composition ratios and the ultraviolet light emitting diodes not containing the delta layer (Comparative Example) are compared . The ultraviolet light emitting diodes of Examples 1 to 3 were Al _{0 . 5} Ga _{0 .5} N barrier layers, each of the ultraviolet light emitting diodes of Examples 1 to 3 comprising Al _{0 . 8} Ga _{0 .8} N delta layer, Al _{0 . 7} Ga _{0 .7} N delta layer and Al _{0 . 6} Ga _{0 .6} N delta layer. The ultraviolet light emitting diode of the comparative example includes an active layer of a multiple quantum well structure including an Al _0.5 Ga _0.5 N barrier layer.

17 (a) shows the recombination rate of electrons and holes according to the vertical distance when a current of 20 A / cm ² density is applied to the ultraviolet light emitting diodes. The larger the vertical distance, the closer to the p-type semiconductor layer. As shown in FIG. 17 (a), it can be seen that as the Al composition ratio of the delta layer increases, the recombination rate increases, and the internal quantum efficiency increases accordingly.

However, as the Al composition ratio of the delta layer increases, the recombination rate in the well layer increases as the p-side, that is, the well layer located relatively close to the p-type semiconductor layer. That is, as the Al composition ratio of the delta layer increases, the band gap energy of the barrier layer becomes larger, so that carriers (particularly, holes) are less likely to be transferred. Therefore, as the ultraviolet light emitting diode includes a delta layer having a high Al composition ratio, the recombination rate is increased toward the p-type semiconductor layer side. If the probability of the holes being transferred to the well layers is reduced, the probability of recombination of the electrons increases and the efficiency droop characteristics deteriorate. Therefore, it is preferable that the Al composition ratio of the delta layer is determined so that the band gap energy of the delta layer becomes a predetermined ratio of energy to the band gap energy of the other portion except the delta layer in the barrier layer.

17 (b), as the Al composition ratio of the delta layer increases, the maximum internal quantum efficiency increases, but when the current density increases according to the Al composition ratio of the delta layer, the ratio of the efficiency droop Is different. When driving the ultraviolet light emitting diodes of Examples 1 to 3 at a current density of about 300 A / cm ² or more, which is a substantial high current driving region, when the Al composition ratio of the delta layer is 0.7, the Al composition ratio of the delta layer is 0.8 It can be seen that the internal quantum efficiency is lowered. That is, when the Al composition ratio of the delta layer exceeds 0.7, the efficiency droop characteristic deteriorates. Therefore, if a delta layer is inserted into the barrier layer, but the barrier layer does not have a band gap energy of 11% or more other than the delta layer, ultraviolet light emitting diodes having low efficiency droop characteristics can be provided.

However, as described above, the efficiency of the droplet may be reduced by changing the Al composition ratio of the delta layer irregularly along the horizontal direction, depending on the difference in band gap energy.

(Experimental Example 3)

The internal quantum efficiency of the ultraviolet light emitting diode according to the embodiments of the present invention and the ultraviolet light emitting diodes according to the comparative example will be compared and described. 18 shows the Al quantum efficiency according to the Al thickness of the delta layer and the presence or absence of the delta layer in the light emitting diode having the thickness, the Al composition ratio, the dopant and the doping concentration as shown in Table 1 below. The presence and characteristics of the delta layers of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in Table 2 below.

Referring to FIG. 18, it can be seen that the internal quantum efficiency of Examples 1 to 3 is higher than that of Comparative Example 1 which does not include a delta layer. Accordingly, it can be seen that the internal quantum efficiency of the light emitting diode according to the present embodiments is higher than that of the light emitting diode not including the delta layer. On the other hand, in the case of Comparative Examples 2 and 3, the internal quantum efficiency was decreased rather than Comparative Example 1. That is, it can be seen that the internal quantum efficiency is improved when a delta layer is inserted into the barrier layer but no delta layer is formed in the barrier layer located at the top of the active layer.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit of the invention. Accordingly, it is intended that the present invention cover the modifications and variations of this invention provided they fall within the scope of the appended claims or their equivalents.

Claims (14)

A first conductive semiconductor layer;
An active layer disposed on the first conductive semiconductor layer and including alternately stacked barrier layers and well layers;
An electron blocking layer disposed on the active layer; And
And a second conductive type semiconductor layer located on the electron blocking layer,
Wherein at least a portion of the barrier layers other than the topmost barrier layer comprises a delta layer and the band gap energy of the delta layer is greater than the band gap energy of the other portion of the barrier layer except for the delta layer, Ultraviolet light emitting diodes larger than energy.
The method according to claim 1,
Wherein the barrier layers comprise Al _x Ga _(1-x) N (0 _{&lt; x} &lt;
At least some of the barrier layers, other than the topmost barrier layer, include a delta layer comprising Al _y Ga _(1-y) N (0 < _{y? 1} ) y. &lt; / RTI &gt;
The method according to claim 1,
Wherein the delta layer of a barrier layer of one of the barrier layers is positioned closer to a trough layer located above the one barrier layer than a well layer located below the one barrier layer.
The method of claim 2,
Wherein the delta layer is in contact with the trough layer.
The method according to claim 1,
Wherein the topmost barrier layer does not include the delta layer.
The method of claim 4,
And the uppermost barrier layer is in contact with the electron blocking layer.
The method of claim 2,
Wherein an Al composition ratio y of the delta layer is 0.5 &lt; y &amp;le; 1.
The method according to claim 1,
Wherein all of the barrier layers other than the barrier layer located at the top of the barrier layers comprise the delta layer.
The method according to claim 1,
The band gap energy of the other portion of the barrier layer excluding the delta layer is defined as E _barrier and the band gap energy of the delta layer is defined as E _{delta layer} , the ultraviolet light emitting diode satisfying the following expression (1).
(Equation 1)
E _barrier <E _{delta layer} ≤ <E _barrier × 1.11
The method of claim 2,
Wherein the band gap energy of Al _x Ga _(1-x) N and the band gap energy of Al _y Ga _(1-y) N satisfy the following formula (2).
(Equation 2)
_{Al x Ga (1-x)} N in the band gap energy _{<Al y Ga (1-y} ) N of the band gap energy _{≤≤ (Al x Ga (1-} x) N in the band gap energy) × 1.11
The method according to claim 1,
Wherein the delta layer further strengthens strain applied to the well layer.
The method of claim 11,
Wherein the delta layer of one of the barrier layers is in contact with a well layer located above the one barrier layer.
The method according to claim 1,
Wherein a compositional distribution of Al varies in the horizontal direction in the delta layer.
14. The method of claim 13,
Wherein a composition distribution of Al varies along the horizontal direction in the delta layer irregularly.

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