KR20160062659A

KR20160062659A - Uv light emitting diode

Info

Publication number: KR20160062659A
Application number: KR1020150045269A
Authority: KR
Inventors: 박승환; 유홍재; 서대웅
Original assignee: 서울바이오시스 주식회사
Priority date: 2014-11-25
Filing date: 2015-03-31
Publication date: 2016-06-02

Abstract

An ultraviolet light emitting diode is disclosed. The ultraviolet light emitting diode includes a first conductivity type semiconductor layer and a second conductivity type semiconductor layer; And an active layer disposed between the first conductive semiconductor layer and the second conductive semiconductor layer, wherein the active layer includes a multiple quantum well structure in which a barrier layer and a well layer are alternately stacked, and the well layer includes a sub- And a delta layer located in the sub-well layer, wherein the sub-well layer has a band gap energy of 84% to 97% of the barrier layer band gap energy and the delta layer has a band of 80% Gap energy.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a UV light emitting diode

The present invention relates to an ultraviolet light emitting diode, and more particularly, to an ultraviolet light emitting diode having enhanced TE light emission intensity.

The light emitting diode is an inorganic semiconductor device which emits light generated by the recombination of electrons and holes. In particular, the ultraviolet light emitting diode can be used as UV curing, sterilization, white light source, medical field, The range is increasing. Particularly, in the case of deep ultraviolet rays (light having a peak wavelength of about 340 nm or less, and further, about 200 nm to about 400 nm), which emits light of a shorter wavelength as compared with near ultraviolet light (light having a peak wavelength in a range of about 340 nm to about 400 nm) A light emitting diode having a peak wavelength in the range of 340 nm has strong luminescence intensity for light in the UV-C region. Therefore, such a deep ultraviolet light emitting diode is expected to play various roles in various fields such as sterilization, purification, detection in biochemistry, medicine, and the like.

In order to produce an ultraviolet light-emitting diode, an active layer is formed of a material having a band gap energy corresponding to an emission wavelength in the ultraviolet band. Therefore, the active layer of the ultraviolet light emitting diode manufactured using the nitride semiconductor includes a nitride semiconductor containing Al, for example, an active layer in which the well layer is formed of AlGaN and the barrier layer is formed of AlGaN or AlN is adopted in the ultraviolet light emitting diode . At this time, it is required that a nitride semiconductor layer having a higher Al composition ratio is applied to the active layer in order to emit light with a relatively short peak wavelength.

However, unlike an active layer based on GaN or InGaN, an ultraviolet light emitting diode including an AlGaN-based active layer emits transverse-magnetic (TM) polarized light. Generally, it is known that the proportion of TM polarized light increases as the content of Al increases in the AlGaN-based active layer, and in the case of AlN, more than 90% of light is emitted as TM polarized light. TM polarized light is emitted in a horizontal direction to the plane of the active layer and TE (transverse-electric) polarized light is emitted in a direction normal to the plane of the active layer, so that TM polarized light The light has a lower light extraction efficiency than the TE polarized light. Therefore, the higher the ratio of the TM polarized light is, the lower the luminous efficiency of the ultraviolet light emitting diode is.

An object of the present invention is to provide an ultraviolet light emitting diode having a high luminous efficiency and in particular to provide an ultraviolet light emitting diode which emits light in a short wavelength band but has a TE polarized light ratio higher than TM polarized light .

According to an aspect of the present invention, there is provided an ultraviolet light emitting diode comprising: a first conductive semiconductor layer and a second conductive semiconductor layer; And an active layer disposed between the first conductive semiconductor layer and the second conductive semiconductor layer, wherein the active layer includes a multiple quantum well structure in which a barrier layer and a well layer are alternately stacked, A sub-well layer and a delta layer located in the sub-well layer, wherein the sub-well layer has a band gap energy of between 84% and 97% of the barrier layer band gap energy, And has a band gap energy of 80% or less of the gap energy.

In the light emitted from the ultraviolet light emitting diode, the ratio of the TE polarized light may be 90% or more.

The well layer may include AlGaN, and the delta layer may have a lower Al composition ratio than the sub-well layer.

The ultraviolet light emitting diode may have a peak wavelength of 300 nm or less.

The delta layer may be located in the middle of the sub-well layer.

According to the present invention, the efficiency of recombination of electrons and holes is increased while emitting light having substantially the same peak wavelength as that of the conventional case, the internal quantum efficiency is improved, the ratio of TE polarized light is increased, An ultraviolet light emitting diode may be provided.

1 is a cross-sectional view illustrating an ultraviolet light-emitting diode according to an embodiment of the present invention.
2 is an enlarged cross-sectional view illustrating an active layer of an ultraviolet light emitting diode according to an embodiment of the present invention.
3 is a graph illustrating band gap energy of an active layer of an ultraviolet light emitting diode according to an embodiment of the present invention.
FIG. 4 is a graph illustrating characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention, in comparison with a comparative example.
FIG. 5 is a graph illustrating the characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention, in comparison with a comparative example.
6 is a graph illustrating the characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention in comparison with a comparative example.
7 is a graph for explaining characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention, in comparison with a comparative example.
8 is a graph for illustrating the characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention in comparison with a comparative example.
9 is a graph illustrating characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example so that those skilled in the art can sufficiently convey the spirit of the present invention. Therefore, the present invention is not limited to the embodiments described below, but may be embodied in other forms. In the drawings, the width, length, thickness, etc. of components may be exaggerated for convenience. It is also to be understood that when an element is referred to as being "above" or "above" another element, But also includes the case where there are other components in between. Like reference numerals designate like elements throughout the specification.

The respective composition ratios, growth methods, growth conditions, thicknesses, and the like for the semiconductor layers described below are examples, and the present invention is not limited to the following examples. 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.

FIG. 1 is a cross-sectional view illustrating an ultraviolet light-emitting diode according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view illustrating an active layer of the ultraviolet light-emitting diode.

Referring to FIGS. 1 and 2, the ultraviolet light emitting diode includes a first conductive semiconductor layer 300, an active layer 400, and a second conductive semiconductor layer 500. Furthermore, the light emitting diode may further include a substrate 100 and a buffer layer 200.

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 200 may be located on the substrate 100. The buffer layer 200 may serve as a nucleus layer so that other semiconductor layers formed on the buffer layer 200 can be grown and a lattice constant between the substrate 100 and other semiconductor layers grown on the buffer layer 200 It can play a role in relieving stress caused by difference.

The buffer layer 200 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 200 may be omitted. For example, when the substrate 100 and the first conductivity type semiconductor layer 300 are made of the same material, the first conductivity type semiconductor layer 300 may be grown on the substrate 100 without further forming the buffer layer 200 . In addition, when the substrate 100 is separated and removed, the buffer layer 200 may be removed in the process of separating the substrate 100.

The first conductive semiconductor layer 300 may include a nitride semiconductor such as (Al, Ga, In) N. Since the ultraviolet light emitting diode according to this embodiment emits light in the ultraviolet band, the first conductivity type semiconductor layer 300 may include a nitride semiconductor which does not absorb light in the ultraviolet band. Specifically, when the band gap energy of the nitride semiconductor forming the first conductivity type semiconductor layer 300 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.

Accordingly, the first conductivity type semiconductor layer 300 may include Al, and in particular, may include AlGaN. At this time, the Al composition ratio of the AlGaN can be controlled according to the wavelength of the light emitted from the active layer 400. For example, when the peak wavelength of the light emitted from the active layer 400 is 400 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 400 is 300 nm or less, Al composition ratio. However, the present invention is not limited thereto.

The first conductivity type semiconductor layer 300 may have an n-type or p-type conductivity type including n-type or p-type dopants. For example, the first conductivity type semiconductor layer 300 may be doped with n-type impurity such as Si, Ge or the like as a dopant.

The first conductive semiconductor layer 300 may be a single layer or may be formed of multiple layers including a plurality of layers. When the first conductive semiconductor layer 300 includes a plurality of layers, the first conductive semiconductor layer 300 may include a cladding layer, a contact layer, or a superlattice layer. Furthermore, the first conductivity type semiconductor layer 300 may include a gradation layer continuously changing its composition ratio.

The active layer 400 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 400 may include a multiple quantum well structure (MQW) in which a barrier layer 410 and a well layer 420 are alternately stacked. Hereinafter, the structure of the active layer 400 will be described in detail with reference to FIG.

Referring to FIG. 2, the active layer 400 may include a multiple quantum well structure in which a barrier layer 410 and a well layer 420 are alternately stacked. The well layer 420 may include a sub well layer 421 and a delta layer 423 located in the sub well layer 421.

The barrier layer 410 may comprise a nitride semiconductor having a band gap energy greater than that of the well layer 420 and may include Al _w Ga _(1-w) N (0 < For example, the barrier layer 410 may be formed of AlN. The barrier layer 410 is formed of a nitride semiconductor having a relatively higher Al composition ratio than the well layer 420 so that a plurality of carriers (electrons and holes) are concentrated on the well layer 420. This increases the probability that electrons and holes are combined.

The well layer 420 includes a sub-well layer 421 and a delta layer 423 having a band gap energy smaller than that of the sub-well layer 421. The delta layer 423 may be located within the sub-well layer 421 and the location of the delta layer 423 is not limited within the sub-well layer 421. Accordingly, the well layer 420 may include a region having a relatively small band gap energy and a region having a relatively large band gap energy. In view of the band gap energy profile along the thickness direction, the well layer 420 may be formed in a dip-shaped shape showing a dip-shaped energy profile in a region where the band gap energy is small.

The thickness of the delta layer 423 can be thinner than the thickness of the sub-well layer 421, can have a thickness in the range of about 1 to 10 angstroms, and can have a thickness of, for example, about 5 angstroms. On the other hand, the thickness of the sub-well layer 421 may be greater than the thickness of the delta layer 423 and may have a thickness of, for example, about 25 ANGSTROM. However, the present invention is not limited thereto.

Since the UV light emitting diode according to this embodiment includes the dip-shaped well layer 420, the spatial separation between the conduction band and the valence band in the well layer 420 is reduced, and the recombination efficiency of electrons and holes Can be improved. Also, as the spatial separation between the conduction band and the valance band is reduced, the transition wavelength of the light emitting diode can be prevented from increasing. This will be described later with reference to Fig.

In addition, the ultraviolet light emitting diode includes a well layer 420 in which a delta layer 423 having a relatively low Al composition ratio is disposed in the sub-well layer 421, so that an internal filed in the active layer 400 . Generally, the lower the Al content of the active layer grown on the AlN substrate, the larger the internal length of the AlGaN active layer. If the internal length of the active layer becomes large, the spatial separation between the conduction band and the valence band becomes intense, and the internal quantum efficiency is reduced. However, if the Al content of the AlGaN active layer is increased in order to reduce the size of the internal field, the crystallinity of the active layer may be significantly lowered due to process limitations and material properties. Therefore, in the conventional case, there is a limit to increase the Al content.

In contrast, according to embodiments of the present invention, the well layer 420 includes the sub-well layer 421 and the delta layer 423 having a lower Al composition ratio than the sub-well layer 421, The stress and the strain generated in the process can be reduced. Accordingly, piezoelectric polarization and spontaneous polarization in the active layer 400 generated by the strain are reduced, and the size of the internal field of the active layer 400 is reduced. When the size of the internal field is reduced, the spatial separation between the wave functions is reduced, and an ultraviolet light emitting diode having a high internal quantum efficiency can be provided. In this regard, it will be described later in detail with reference to Fig.

In addition, the ultraviolet light emitting diode according to embodiments of the present invention may include a well layer 420 including a delta layer 423, thereby reducing the heavy hole effective mass in the valence band. Therefore, it is possible to reduce the carrier density in the sub-band of high energy level and to increase the internal quantum efficiency of the ultraviolet light-emitting diode. In this regard, it will be described later in detail with reference to Fig.

Further, when the composition ratio of Al in the well layer 420 is increased, the piezoelectric field inside the well layer 420 is strengthened and recombination into a TM-emitting crystal spin off band (CH band) As the ratio increases, TM polarized light increases and TE polarized light decreases. However, in order to emit light having a shorter wavelength, the composition ratio of Al must be increased. Therefore, in order to emit light of short wavelength in the conventional ultraviolet light emitting diode structure, the intensity of TE polarized light should be reduced. In contrast, according to embodiments of the present invention, the delta layer 423 is included in the well layer 420 to confine the ground state of the electrons in the delta layer 423 to weaken the piezoelectric field Thereby increasing the ratio of TE polarized light.

2, the sub-well layer 421 and the delta layer 423 may include nitride semiconductors having different band gap energies, and the sub-well layer 421 and the delta layer 423 may have different band- 423), the composition ratio of group III atoms may be determined according to the peak wavelength of light to be emitted from the ultraviolet light emitting diode.

Specifically, for example, a sub-well layer 421 may comprise Al _x Ga _(1-x) N layer (0 <x <1), the delta layer 423 is Al _y Ga _(1-y) N layer (0? Y <1), where x> y. The x and y values may be adjusted according to a transition wavelength (peak wavelength of emitted light) to be emitted from the light emitting diode, and an ultraviolet light emitting diode emitting deep ultraviolet light having a peak wavelength of 300 nm or less may be realized. For example, the sub-well layer 421, the Al _0. ₉₅ Ga ₀ _. ₀₅ N layer and the delta layer 423 is an Al _y Ga _(1-y) N layer, the peak wavelength of the ultraviolet light emitting diode can be controlled by controlling the y value to be within the range of 0? Y? More specifically, as the y value is increased within the range of 0.2 to 0.9, the peak wavelength of the ultraviolet light emitting diode may decrease substantially linearly from about 280 nm to about 220 nm.

Therefore, according to the present invention, the peak wavelength of the ultraviolet light emitting diode can be easily adjusted by changing only the Al composition ratio of the delta layer 423 without changing the composition of the sub-well layer 421. In particular, by forming a delta layer 423 having a relatively low Al composition ratio in the sub-well layer 421 having a relatively high Al composition ratio, the ultraviolet light emitting diode 423 emitting light in the UVC band (about 100 nm to about 290 nm) Can be implemented. Thus, according to the present invention, an ultraviolet light emitting diode having high sterilizing efficiency can be realized. In this regard, it will be described in more detail with reference to FIG.

Further, the ultraviolet light emitting diode according to the above-described embodiments can emit TE polarized light with enhanced strength. The ultraviolet rays in the light-emitting diodes, the sub-well layer 421 is Al _x Ga _(1-x) N layer (0 <x <1), and the delta layer 423 is Al _y Ga _(1-y) N layer ( 0 < y < V1, where 0 < = y < have. For example, a sub-well layer 421 is _{Al x Ga (1-x)} N layer (0.5≤≤x <1), and the delta layer 423 is _{Al y Ga (1-y)} N layer (0≤ Y < x), and further, the delta layer 423 may have a y value in the range of 0.2 < = y < V1. As yet another example, a sub-well layer 421 is Al _x Ga _(1-x) N layer and (0.7≤≤x <1), the delta layer 423 is _{Al y Ga (1-y)} N layer (0 Y < x), and further, the delta layer 423 may have a y value in the range of 0.2 < = y < V1.

The band gap energy of the sub-well layer 421 may be about 84% to 97% of the band gap energy of the barrier layer 410 and the band gap energy of the sub- The band gap energy may be less than about 80% of the sub-well layer 421 band gap energy. By adjusting the correlation between the band gap energies of the sub-well layer 421, the delta layer 423 and the barrier layer 410 to the above-described range, the ultraviolet light emitting diode Can be implemented. In this regard, it will be described later in more detail with reference to FIG. In addition, in the light emitted from the ultraviolet light emitting diode, the ratio of the TE polarized light may be 90% or more.

Generally, as the composition ratio of Al increases in the AlGaN well layer, the ratio of TE polarized light decreases and the ratio of TM polarized light increases. According to the present invention, the well layer 420 includes a delta layer 423 having a relatively low Al composition ratio, so that ultraviolet light having an increased proportion of TE polarized light can be emitted. In addition, the ratio of the TE polarized light increases, and the recombination efficiency of electrons and holes increases as described above, and the intensity of the TE polarized light is remarkably improved as compared with the conventional method. As the ratio of the TE polarized light increases, the light extraction efficiency of the light emitted from the ultraviolet light emitting diode is improved and the external quantum efficiency can be improved. In addition, the ratio of TE polarized light can be increased, and the intensity of the total light combined with the TE polarized light and the TM polarized light can also be improved. On the other hand, this will be described later in detail with reference to FIG. 7 and FIG.

Referring again to FIG. 2, the second conductive semiconductor layer 500 is located on the active 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.

Further, the second conductive semiconductor layer 500 may further include a delta doping layer (not shown) for lowering ohmic contact resistance, and may further include an electron blocking layer (not shown).

According to the embodiments described above, an ultraviolet light emitting diode having improved internal quantum efficiency, increased TE polarized light, improved light extraction efficiency, and increased light emission intensity can be provided. In addition, the ultraviolet light emitting diode may emit ultraviolet light having various wavelength ranges, and in particular, an ultraviolet light emitting diode that emits deep ultraviolet light (including light in the UVC band) may be provided.

Hereinafter, an ultraviolet light emitting diode according to embodiments of the present invention and a conventional ultraviolet light emitting diode according to a comparative example will be described with reference to FIGS. 3 to 8. FIG. The following embodiments are provided to aid understanding of the present invention, and the present invention is not limited to the following embodiments.

3 is a graph illustrating band gap energy of an active layer of an ultraviolet light emitting diode according to an embodiment of the present invention.

3 illustrates the band gap energy according to the depth of a portion of the active layer 400 and the band gap energy according to the depth of a portion of the active layer of the conventional light emitting diode according to an embodiment of the present invention. 3 (a) and 3 (b) together show the wave function in each case, C1 means a wave function of a first conduction subband in a conduction band, and HH1 denotes a wave function of a first conduction subband in a conduction band, Means the wave function of the first valence subband.

In the ultraviolet light-emitting diode according to the present embodiment, the sub-well layer 421 is about 25Å thick Al _0. ₉₅ Ga ₀ _. ₀₅ and the N layer, the delta layer 423 is approximately 5Å thick Al _0. ₂ Ga ₀ _. ₈ N layer, and the barrier layer 410 is an AlN layer. The ultraviolet light emitting diode emits light having a transition wavelength of about 280 nm. The band gap energy and the wave function for the active layer of the ultraviolet light emitting diode of the present embodiment are shown in Fig. 3 (a).

In the ultraviolet light-emitting diode according to the comparative example, the well layer is about 25Å thick Al _0.5 Ga _0.5 N layer, a barrier layer is an AlN layer. The ultraviolet light emitting diode of the comparative example emits light having a transition wavelength of about 280 nm. The band gap energy and the wave function for the active layer of the UV light emitting diode according to the comparative example are shown in Fig. 3 (b).

As shown in FIG. 3 (a), the ultraviolet light emitting diode of this embodiment includes a well layer 420 including a region having a relatively large band gap energy and a region having a relatively small band gap energy. The well layer 420 may be formed in a dip-shaped shape showing a dip-shaped energy profile in a region where the band gap energy is small. On the other hand, as shown in FIG. 3 (b), the well layer of the ultraviolet light emitting diode according to the comparative example shows a band gap energy profile having a relatively wide width.

3 (a) and 3 (b), the UV light emitting diode according to the present embodiment is superior to the comparative light emitting diode in the spatial separation of the conduction band and the valence band in the well layer 420, And the spatial separation between C1 and HH1 is also reduced. Therefore, the ultraviolet light emitting diode emits light having a transition wavelength similar to that of a conventional light emitting diode, and has a higher coupling efficiency of electrons and holes, and has a high internal quantum efficiency. Thus, according to the embodiment of the present invention, an ultraviolet light emitting diode having a high luminous efficiency can be provided.

FIG. 4 is a graph illustrating characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention, in comparison with a comparative example.

In the ultraviolet light-emitting diode according to the present embodiment, the sub-well layer 421 is about 25Å thick Al _0. ₉₅ Ga ₀ _. _5N layer, the delta layer 423 is an Al _y Ga _(1-y) N layer about 5 Å thick, and the barrier layer 410 is an AlN layer. 4A shows the size of the internal field (field due to piezoelectric polarization and spontaneous polarization) of the well layer 420 according to the Al composition ratio (y value) of the delta layer 423, and FIG. (b) shows the transition wavelength depending on the Al composition ratio (y value) of the delta layer 423.

In the ultraviolet light emitting diode according to the comparative example, the well layer is an Al _z Ga _(1-z) N layer with a thickness of about 25 Å, and the barrier layer is an AlN layer. 4 (a) shows the size of the internal field of the well layer according to the Al composition ratio (z value) of the well layer, and FIG. 4 (b) shows the transition wavelength according to the Al composition ratio .

The size of the internal field in FIG. 4A is a value calculated using a periodic boundary condition, and a positive or negative number of the internal field means the direction of the field, &Lt; / RTI > The transition wavelength in FIG. 4 (b) is a value calculated assuming that the carrier density (N _2D ) is 20 × 10 ¹² cm ^-2 .

Referring to FIG. 4A, the internal length of the well layer of the UV LED according to the comparative example decreases as the Al composition ratio increases. Specifically, when the Al composition ratio (z value) of the well layer is about 0.2, the size of the internal field is 5.4 MV / cm, which decreases to about 1 MV / cm as the z value increases. On the other hand, the internal length of the well layer of the ultraviolet light emitting diode according to the present embodiment decreases as the Al composition ratio of the delta layer 423 increases, and then increases again. In particular, when the Al composition ratio (y value) of the delta layer 423 is about 0.6, the internal length is reduced to nearly zero. In addition, whatever the Al composition ratio (y value) of the delta layer 423 has, the internal length of the well layer 420 is lower than that of the comparative example.

Next, referring to FIG. 4B, it can be seen that the transition wavelength of the ultraviolet light emitting diode according to the comparative example decreases as the Al composition ratio (z value) of the well layer increases. On the other hand, also in the ultraviolet light emitting diode of this embodiment, the transition wavelength becomes shorter as the Al composition ratio (y value) of the delta layer 423 is increased.

As described above, the ultraviolet light emitting diode of this embodiment may include a well layer 420 having a lower internal field size than the comparative example. That is, according to the embodiment of the present invention, the spatial separation of the wave function in the well layer 420 can be reduced, and the recombination efficiency of electrons and holes can be increased. In addition, the ultraviolet light emitting diode of this embodiment can emit light having a transition wavelength of about 240 nm to about 280 nm when the Al composition ratio (y value) of the delta layer 423 is about 0.2 to 0.5, And may include a well layer 420 having an internal length much smaller than that of the comparative ultraviolet light emitting diode that emits light of a transition wavelength. Therefore, according to the embodiment of the present invention, the size of the internal field of the well layer is reduced while emitting light of the UVC band wavelength (in particular, light having a peak wavelength within the range of about 240 nm to about 280 nm) A light emitting diode may be provided.

FIG. 5 is a graph illustrating the characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention, in comparison with a comparative example.

In the ultraviolet light-emitting diode according to the present embodiment, the sub-well layer 421 is about 25Å thick Al _0. ₉₅ Ga ₀ _. ₀₅ and the N layer, the delta layer 423 is approximately 5Å thick Al _0. ₂ Ga ₀ _. ₈ N layer, and the barrier layer 410 is an AlN layer. 5 (a) shows a valence band structure in the active layer 400 of the ultraviolet light-emitting diode as a function of an in-plane wave vector.

In the ultraviolet light-emitting diode according to the comparative example, the well layer is about 25Å thick Al _0.5 Ga _0.5 N layer, a barrier layer is an AlN layer. 5 (b) shows a valence band structure represented by a function of an in-plane wave vector in the active layer of the ultraviolet light-emitting diode.

The graphs of FIGS. 5 (a) and 5 (b) were derived according to a self-consistent solution, assuming that the carrier density (N _2D ) is 20 × 10 ¹² cm ^-2 .

5A and 5B, it can be seen that in the active layer of the ultraviolet light-emitting diode of this embodiment, the effective mass of the heavy-hole around the highest valence band is greatly reduced compared to the case of the comparative example. If the hole effective mass is about 2.27m _0, heavy in this embodiment the active layer (400) - for instance, the active layer of the comparative example in the heavy-hole effective mass is about 0.87 m _0. It can also be seen that, in the active layer structure of this embodiment, the energy gap between the first two subbands (HH1 and LH1) and the higher subbands (HH2 and LH2) is increased, The number of carriers in the energy-rich subband in the active layer can be reduced. Therefore, the internal quantum efficiency of the ultraviolet light emitting diode of this embodiment can be improved as compared with the comparative example.

6 is a graph illustrating the characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention in comparison with a comparative example.

In the ultraviolet light-emitting diode according to the present embodiment, the sub-well layer 421 is about 25Å thick Al _0. ₉₅ Ga ₀ _. ₀₅ and the N layer, the delta layer 423 is approximately 5Å thick Al _0. ₂ Ga ₀ _. ₈ N layer, and the barrier layer 410 is an AlN layer. 6A shows an optical matrix element value (| M | ² ) expressed as a function of an in-plane wave vector in the active layer 400 of the ultraviolet light emitting diode .

In the ultraviolet light-emitting diode according to the comparative example, the well layer is about 25Å thick Al _0.5 Ga _0.5 N layer, a barrier layer is an AlN layer. 6 (b) shows an optical matrix element value (| M | ² ) expressed as a function of an in-plane wave vector in the active layer of the ultraviolet light-emitting diode.

The graphs of FIGS. 6 (a) and 6 (b) were derived according to a self-consistent solution, assuming that the carrier density (N _2D ) is 20 × 10 ¹² cm ^-2 .

6A and 6B, it can be seen that the magnitude of TE polarized light at the C1-V1 transition of the ultraviolet light emitting diode according to this embodiment is larger than that of the comparative example. The internal field inside the ultraviolet light emitting diode of this embodiment is lower than that of the comparative example, and the intensity of the TE polarized light is increased.

Therefore, according to this embodiment, an ultraviolet light emitting diode having an increased intensity of TE polarized light can be provided. Accordingly, the light extraction efficiency of the ultraviolet light emitting diode can be improved, and the light emission intensity can also be improved.

7 is a graph for explaining characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention, in comparison with a comparative example.

In the ultraviolet light-emitting diode according to the present embodiment, the sub-well layer 421 is about 25Å thick Al _0. ₉₅ Ga ₀ _. _5N layer, the delta layer 423 is an Al _y Ga _(1-y) N layer about 5 Å thick, and the barrier layer 410 is an AlN layer. FIG. 7 shows the wavelength and the spontaneous emission coefficient according to the Al composition ratio (y value) of the delta layer 423, and particularly shows the case where the y value is 0.2 and 0.5.

In the ultraviolet light emitting diode according to the comparative example, the well layer is an Al _z Ga _(1-z) N layer with a thickness of about 25 Å, and the barrier layer is an AlN layer. FIG. 7 shows the wavelength and the spontaneous emission coefficient according to the Al composition ratio (z value) of the well layer. Particularly, the z value is 0.5 and 0.7.

The graph of FIG. 7 was derived according to a self-consistent solution, and the solution was calculated assuming a carrier density (N _2D ) of 20 × 10 ¹² cm ^-2 .

Referring to FIG. 7, the ultraviolet light emitting diode of this embodiment emits ultraviolet light having a peak wavelength of about 280 nm when the Al _0.2 Ga _0.8 N layer is included as a delta layer, and the ultraviolet light emitting diode of the comparative example emits Al ₀ _. ₅ Ga ₀ _. ₅ N layer, it emits ultraviolet light having a peak wavelength of about 280 nm. In addition, the ultraviolet light emitting diode of this embodiment has a delta layer of Al ₀ _. ₅ Ga ₀ _. ₅ N those containing layer emits ultraviolet light having a peak wavelength of about 245nm, and the UV light-emitting diode of the comparative example is Al ₀ as the well _layer. ₇ Ga ₀ _. ₇ N layer, it emits ultraviolet light having a peak wavelength of about 245 nm.

Comparing these, it can be seen that the ultraviolet light emitting diode of this embodiment has much higher light emission intensity, although it emits light of similar or substantially the same peak wavelength. Since the ultraviolet light emitting diode of this embodiment has an increased optical matrix element value compared with that of the comparative example, the intensity of the emitted light can also be increased.

Therefore, according to the present invention, it is possible to provide an ultraviolet light emitting diode having an increased light emission intensity while emitting light of similar or substantially the same peak wavelength.

8 is a graph for illustrating the characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention in comparison with a comparative example.

In the ultraviolet light-emitting diode according to the present embodiment, the sub-well layer 421 is about 25Å thick Al _0. ₉₅ Ga ₀ _. _5N layer, the delta layer 423 is an Al _y Ga _(1-y) N layer about 5 Å thick, and the barrier layer 410 is an AlN layer. 8 shows the wavelength depending on the Al composition ratio (y value) of the delta layer 423, the spontaneous emission coefficient of the TE polarized light, and the spontaneous emission coefficient of the TM polarized light, and particularly shows a case where the y value is 0.2 to 0.9 .

In the ultraviolet light emitting diode according to the comparative example, the well layer is an Al _z Ga _(1-z) N layer with a thickness of about 25 Å, and the barrier layer is an AlN layer. FIG. 8 shows the wavelength depending on the Al composition ratio (z value) of the well layer, the spontaneous emission coefficient of TE polarized light, and the spontaneous emission coefficient of TM polarized light. Particularly, the z value is 0.2 to 0.9.

The graph of FIG. 8 was derived according to a self-consistent solution, and the solution was calculated assuming a carrier density (N _2D ) of 20 × 10 ¹² cm ^-2 .

8, in the case where the delta layer 423 of this embodiment and the well layer of the comparative example each have a predetermined Al composition ratio (y value and z value), the ultraviolet light emitting diode of this embodiment emits much TE polarized light Emitting device. Specifically, when the Al composition ratio (y value and z value) is within the range of about 0.2 to 0.75, the intensity of the TE polarized light in both the present embodiment and the comparative example is larger than that of the TM polarized light. However, when comparing the present embodiment and the comparative example having the Al composition ratios (y value and z value) within the above range, it can be seen that TE polarized light of higher intensity is emitted in the ultraviolet light emitting diode of this embodiment.

That is, as the ratio of the TE polarized light increases, the light extraction efficiency of the light emitted from the ultraviolet light emitting diode of the present embodiment can be improved and the external quantum efficiency can be improved. In addition, the ratio of TE polarized light can be increased, and the intensity of the total light combined with the TE polarized light and the TM polarized light can also be improved.

9 is a graph illustrating characteristics of an ultraviolet light emitting diode according to another embodiment of the present invention.

The graphs shown in Figs. 9 (a) and 9 (b) are simulation results showing the cases of including the delta layer and the ratio of the TE polarized light when the delta layer is not included, according to the composition ratio. In each case, the well layer is an N layer Al _x Ga _(1-x) of about 25Å thick, the barrier layer is an AlN layer of about 100Å thickness, the delta layer is between about 5Å thick Al _y Ga _{(1-y )} N layer. In each graph, x means the Al composition ratio of the well layer, and the ratio of the TE polarized light according to the change of the Al composition ratio (y) of the delta layer (FIG. 9A) in the state where the Al composition ratio of the well layer is fixed, ) And an emission wavelength (Fig. 9 (b)). In this experiment, the AlGaN-based semiconductor layer is modified in band gap by controlling the Al composition ratio. However, this is for simplifying the experimental parameters and the present invention is not limited thereto. Therefore, similar results can be obtained by changing the composition ratio of Ga even in an InGaN-based semiconductor layer.

First, the band gap energy of the well layer, the emission wavelength (peak wavelength), and the transmittance (TE) of the TE layer depend on the Al composition ratio (y) of the delta layer, when the Al composition ratio x of the sub- Represents the occupation rate of the polarized light. The occupation ratio of the TE polarized light is equal to (TE polarized light / (TE polarized light + TM polarized light)). Also, in Table 1, the data of the portion expressed by 'No delta' indicates the case where there is no delta layer.

Band gap energy
(eV) Delta-layer
Al composition ratio (y) Wavelength (nm) TE Polarization share
( TE / ( TE + TM )) x = 0.95 5.99 0.86 215 2% 5.81 0.80 221 23% 5.62 0.74 228 42% 5.41 0.67 236 64% 5.18 0.59 246 81% 4.82 0.47 263 95% 4.48 0.36 281 100% 4.26 0.29 294 100% x = 0.7 5.35 0.65 240 39% 4.9 0.50 259 71% 4.84 0.48 262 75% 4.74 0.45 267 82% 4.64 0.41 272 90% 4.31 0.30 291 96% 4.15 0.25 310 99% 3.7 0.10 340 100% x = 0.6 5.02 0.54 256 39% 4.87 0.49 264 48% 4.69 0.43 275 63% 4.36 0.32 292 86% 4.06 0.22 330 95% 3.55 0.05 355 95% No delta 5.84 0.81 220 3% 5.49 0.70 233 19% 4.99 0.53 256 50% 4.78 0.46 265 63% 4.46 0.35 282 87% 4.17 0.26 300 95% 3.68 0.09 336 97% 3.4 0.00 360 97%

Referring to Table 1 and FIGS. 9 (a) and 9 (b), it can be seen that as the Al composition ratio of the well layer increases, the ratio of TE polarized light gradually decreases. For example, in the case where the Al composition ratio of the well layer is 0 and the well layer is GaN, the ratio of the TM polarized light from the case where the TE polarized light occupies 97% Lt; / RTI > A wavelength of 270 nm to 280 nm is the main application area of sterilization, and the Al composition ratio thereof is about 0.4 to 0.5. At this time, the share of the TE polarized light is 87%.

When there is a delta layer in the well layer, if the Al composition ratio of the delta layer is smaller than the well layer, a ground state is formed in the delta layer as described above. When the Al composition ratio of the sub-well layer was 0.6, 0.7, and 0.95, the TE mode occupancy was observed while varying the Al composition ratio of the delta layer. As can be seen from the experimental results, when the delta layer is inserted into the well layer, it can be seen that the occupancy of the TE polarized light is not always higher than in the case where the delta layer is not included in all cases. As shown in Table 1 and FIG. 5, it can be seen that when the Al composition ratio of the well layer is 0.6, for example, when the delta layer is inserted, the ratio of the TE polarized light becomes lower than when the delta layer is not inserted.

From the above-described experimental results, it is confirmed that the concentration range of the well layer in which the TE polarized light is increased by the delta layer is 65 to 95% of the Al composition ratio of the barrier layer. In terms of the bandgap, it can be seen that the band gap energy of the well layer is about 84% to 97% of the band gap band gap energy based on the band gap energy of 6.1 eV of AlN and 3.44 eV of GaN. If the Al composition ratio of the well layer is too low, the probability distribution function of the delta layer is extended to the barrier layer, so that the confinement factor is lowered and the recombination efficiency is lowered.

Also, it can be seen that when the Al composition ratio of the well layer is 0.95, the TE polarized light decreases when the Al composition ratio of the delta layer exceeds 0.36. Similarly, when the Al composition ratio of the well layer is 0.7, the Al composition ratio of the delta layer exceeds 0.25, the Al composition ratio of the well layer is 0.6, and the Al composition ratio of the delta layer exceeds 0.22, the TE polarized light It can be seen that a reduction occurs. From these results, it can be seen that when the Al composition ratio of the delta layer is about 35% to 37% of the Al composition ratio of the well layer, the effect of TE polarized light increase due to insertion of the delta layer is maximized. Converting these results into band gap energy is shown in [Table 2].

Al composition ratio of well layer Delta layer Al composition ratio Band gap energy of the delta layer / band gap energy of the well layer 0.95 0.36 74% 0.70 0.25 77% 0.60 0.22 80%

Therefore, it can be seen that when the band gap energy of the delta layer is 80% or less of the band gap energy of the well layer, the ratio of the TE polarized light in the light emitted from the ultraviolet light emitting diode is 90% or more.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Variations and changes are possible.

Claims

A first conductivity type semiconductor layer and a second conductivity type semiconductor layer; And
And an active layer disposed between the first conductive semiconductor layer and the second conductive semiconductor layer,
Wherein the active layer comprises a multiple quantum well structure in which a barrier layer and a well layer are alternately laminated, the well layer comprising a sub-well layer and a delta layer located in the sub-well layer,
Wherein the sub-well layer has a band gap energy of 84% to 97% of the barrier layer band gap energy, and the delta layer has a band gap energy of 80% or less of the sub-well layer band gap energy.

The method according to claim 1,
Wherein the ratio of the TE polarized light in the light emitted from the ultraviolet light emitting diode is 90% or more.

The method according to claim 1,
Wherein the well layer comprises AlGaN and the delta layer has a lower Al composition ratio than the sub-well layer.

The method according to claim 1,
Wherein the ultraviolet light emitting diode emits light having a peak wavelength of 300 nm or less.

The method according to claim 1,
Wherein the delta layer is located in the middle of the sub-well layer.