WO2016125993A1

WO2016125993A1 - Ultraviolet light emitting diode

Info

Publication number: WO2016125993A1
Application number: PCT/KR2015/011997
Authority: WO
Inventors: 박승환; 서대웅
Original assignee: 서울바이오시스 주식회사
Priority date: 2015-02-06
Filing date: 2015-11-09
Publication date: 2016-08-11

Abstract

Disclosed is an ultraviolet light emitting diode. The ultraviolet light emitting diode comprises: a first conductive semiconductor layer; an active layer which is disposed on the first conductive semiconductor layer and includes a well layer including B_xAl_yGa_(1-x-y)N and a barrier layer; and a second conductive semiconductor layer disposed on the active layer. The ultraviolet light emitting diode satisfies a relational expression of 0＜y＜0.5, 0＜x＜y, and y = -5x + (0.5~0.7).

Description

Ultraviolet light emitting diode

The present invention relates to an ultraviolet light emitting diode, and more particularly, to an ultraviolet light emitting diode having an active layer structure in which internal quantum efficiency can be improved.

Light emitting diodes are inorganic semiconductor devices that emit light generated by recombination of electrons and holes. In particular, ultraviolet light emitting diodes can be used for UV curing, sterilization, white light source, medical field, and equipment accessory parts. The range is increasing. In particular, deep ultraviolet (light having a peak wavelength of about 340 nm or less, furthermore, about 200 nm to about light) emits shorter wavelengths of light, compared to near ultraviolet (light having a peak wavelength in the range of about 340 nm to about 300 nm) light emitting diodes. A light emitting diode having a peak wavelength in the range of 340 nm has a strong emission intensity with respect to 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, water purification, detection means in the biochemical field, medicine.

In order to manufacture an ultraviolet light emitting diode, an active layer is made of a material having a bandgap energy corresponding to the emission wavelength of the ultraviolet band. Accordingly, an active layer of an ultraviolet light emitting diode manufactured using a nitride semiconductor includes a nitride semiconductor including Al, for example, an active layer in which a well layer is formed of AlGaN and a barrier layer of AlGaN or AlN is adopted for the ultraviolet light emitting diode. . At this time, in order to emit light of a relatively short peak wavelength, a nitride semiconductor layer having a higher Al composition ratio is required to be applied to the active layer.

In addition, unlike the GaN or InGaN-based active layer, the ultraviolet light emitting diode including the AlGaN-based active layer emits TM-polarized light. In general, as the Al content increases in the AlGaN-based active layer, the ratio of TM polarized light is known to be higher, and in the case of AlN, almost 90% or more of the light is emitted as TM polarized light. TM polarized light is emitted in a direction horizontal 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, and thus TM polarized light The light has a lower light extraction efficiency than TE polarized light. Therefore, the higher the ratio of TM polarized light, the lower the luminous efficiency of the ultraviolet light emitting diode.

As such, the characteristics of the active layer including AlGaN are different from those of general blue light emitting diodes, and thus, an active layer structure capable of increasing the internal quantum efficiency of the ultraviolet light emitting diodes is required.

The problem to be solved by the present invention is to provide an ultraviolet light emitting diode having a high luminous efficiency, in particular, the internal quantum efficiency is improved to increase the amount of light.

Ultraviolet light emitting diode according to an aspect of the present invention, the first conductivity type semiconductor layer; An active layer on the first conductivity type semiconductor layer, the active layer including a barrier layer and a well layer including B _x Al _y Ga _(1-xy) N; And a second conductivity-type semiconductor layer located on the active layer, wherein 0 <y <0.5 and 0 <x <y, satisfying a relational expression of y = -5x + (0.5 to 0.7).

The barrier layer may include Al _z Ga _(1-z) N (0 < _z ≦ 1), and the barrier layer may have a greater bandgap energy than the well layer.

Y may be greater than or equal to 0 and less than or equal to 0.2 and 0 <x≤0.12.

Also, 0.06 ≦ x ≦ 0.10.

The y may be 0.2 or more and 0.4 or less and 0 <x ≦ 0.07.

Furthermore, 0.02 ≦ x ≦ 0.06.

In some embodiments, in the light emitted from the active layer, the amount of TE-polarized light may be greater than the amount of TM-polarized light.

According to the present invention, an ultraviolet light emitting diode includes a well layer including BAlGaN, thereby providing an ultraviolet light emitting diode having improved internal quantum efficiency. Also, by forming a BAlGaN well layer having a composition ratio of Al and B in a predetermined range, the light amount of TE-polarized light can be increased, so that the substantial light amount of light emitted from the ultraviolet light emitting diode can be increased.

1 is a cross-sectional view illustrating a structure of an ultraviolet light emitting diode according to an embodiment of the present invention.

2 is an enlarged cross-sectional view illustrating the structure of an active layer according to an embodiment of the present invention.

3 to 6 are graphs for explaining characteristics of light emitting diodes according to exemplary embodiments of the present invention and a comparative example.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; The following embodiments are provided as examples to sufficiently convey the spirit of the present invention to those skilled in the art to which the present invention pertains. Accordingly, the present invention is not limited to the embodiments described below and may be embodied in other forms. In the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. In addition, when one component is described as "on" or "on" another component, each component is different from each other as well as when the component is "just above" or "on" the other component. It also includes a case where another component is interposed therebetween. Like numbers refer to like elements throughout.

Each composition ratio, growth method, growth conditions, thickness, etc. for the semiconductor layers described below correspond to an example, and the present invention is not limited as described below. For example, in the case of AlGaN, the composition ratio of Al and Ga may be variously applied according to the needs of those skilled in the art. In addition, the semiconductor layers described below can be grown using a variety of methods generally known to those skilled in the art (hereinafter referred to as "normal technician"), for example, MOCVD (Metal Organic Chemical) It may be grown using techniques such as Vapor Deposition, Molecular Beam Epitaxy (MBE), or Hydride Vapor Phase Epitaxy (HVPE). During the growth of the semiconductor layers, sources introduced into the chamber may use a source known to a person skilled in the art. For example, when growing a nitride semiconductor layer using MOCVD, TMGa, TEGa, etc. may be used as a Ga source. and, as an Al source, and you can take advantage of a TMA, TEA, etc., as the In source may be used, and TMI, TEI, NH ₃ may be used as the N source. However, the present invention is not limited thereto.

1 is a cross-sectional view illustrating a structure of a light emitting diode according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view illustrating a structure of an active layer 400 according to an embodiment of the present invention.

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. In addition, 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 as necessary. For example, in a vertical light emitting diode or a flip chip light emitting diode, the substrate 100 may be separated and removed from the semiconductor layers. For example, the substrate 100 may be removed through laser lift off, stress lift off, chemical lift off, or physicochemical methods through lapping or polishing.

The buffer layer 200 is located on the substrate 100. The buffer layer 200 may include a nuclear 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 positioned on the nuclear layer. The buffer layer 200 may also serve to alleviate stress caused by a difference in lattice constant between the substrate 100 and other semiconductor layers grown on the buffer layer 200. The buffer layer 200 may include a nitride semiconductor such as (Al, Ga, In) N, and may include, for example, at least one of GaN, AlGaN, and AlN. In the present embodiment, the buffer layer 200 may include AlN.

Meanwhile, the buffer layer 200 may be omitted. For example, when the substrate 100 and the first conductive semiconductor layer 300 are the same material, the first conductive semiconductor layer 300 is grown on the substrate 100 without additionally forming the buffer layer 200. Can be. In addition, when the substrate 100 is separated and removed, the buffer layer 200 may also be removed in the process of separating the substrate 100.

The first conductivity type semiconductor layer 300 may include a nitride semiconductor such as (Al, Ga, In) N. Since the ultraviolet light emitting diode according to the present embodiment emits light in the ultraviolet band, the first conductivity type semiconductor layer 300 may include a nitride semiconductor that does not absorb light in the ultraviolet band. Specifically, when the bandgap energy of the nitride semiconductor forming the first conductivity type semiconductor layer 300 is smaller than the energy corresponding to the wavelength of the light of the ultraviolet band, the light of the ultraviolet band may be absorbed by the nitride semiconductor. When the light is absorbed by the nitride semiconductor, the luminous efficiency of the ultraviolet light emitting diode may be very low.

Therefore, the first conductivity type semiconductor layer 300 may include Al, and in particular, may include AlGaN. In this case, the Al composition ratio of the AlGaN may be adjusted according to the wavelength of 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, the AlGaN is about 0.4. It may have an Al composition ratio of more than. However, the present invention is not limited thereto.

The first conductive semiconductor layer 300 may have an n-type or p-type conductive type, including an n-type or p-type dopant. For example, the first conductivity type semiconductor layer 300 may be doped to n-type by including impurities such as Si, Ge, and the like as a dopant. The first conductivity type semiconductor layer 300 may be a single layer or may be formed of multiple layers including a plurality of layers. When the first conductivity type semiconductor layer 300 includes a plurality of layers, the first conductive semiconductor layer 300 may include a clad layer, a contact layer, a superlattice layer, or the like. In addition, the first conductivity type semiconductor layer 300 may include a gradient layer in which the composition ratio continuously changes.

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, as shown in FIG. 2, the active layer 400 may include a multi-quantum well structure (MQW) in which the well layer 410 and the barrier layer 420 are alternately stacked.

The barrier layer 420 may include a nitride semiconductor having a greater bandgap energy than the well layer 410, and may include Al _z Ga _(1-z) N (0 < _z ≦ 1). For example, the barrier layer 420 may be formed of AlN. The barrier layer 420 is formed of a nitride semiconductor having a relatively higher bandgap energy than the well layer 410, thereby allowing a plurality of carriers (electrons and holes) to concentrate on the well layer 410. This increases the probability that electrons and holes combine.

The well layer 410 may include a nitride semiconductor having a bandgap energy smaller than the barrier layer 420. In particular, the well layer 410 includes B (boron), for example, B _x Al _y Ga _(1-xy) N (0 <x <1, 0 <y <1 and x <y). have. Since the well layer 410 further includes B in addition to AlGaN, an absolute value of an internal field inside the well layer 410 may be reduced. This is achieved by the well layer 410 further comprising B, whereby the degree of lattice mismatch is reduced. Accordingly, spatial separation of the conduction and valence bands in the active layer 400 may be reduced, thereby improving recombination efficiency of electrons and holes. In addition, as the spatial separation of the conduction band and the valence band is reduced, the phenomenon of increasing the transition wavelength of the light emitting diode can be prevented.

In addition, in B _x Al _y Ga _(1-xy) N of the well layer 410, the composition ratio of Al may be greater than 0 and less than 0.5. In this case, the effect of increasing the luminous efficiency when B is added to AlGaN can be further improved. When the composition ratio of Al is 0.5 or more, the addition of B causes the uppermost subband in the valence band to change from a heavy-hole band to a crystal-field splittoff hole band, thus transverse-electric ) -Polarized light is reduced and transverse-magnetic (TM) -polarized light is increased. That is, when the composition ratio of Al is 0.5 or more, the luminous efficiency of the light emitting diode is reduced. Therefore, in the ultraviolet light emitting diode emitted light of this embodiment, the light amount of TE-polarized light is larger than the light amount of TM-polarized light.

In addition, in B _x Al _y Ga _(1-xy) N of the well layer 410, the composition ratio of B has a constant dependency on the composition ratio of Al. As described above, the composition ratio x of B in B _x Al _y Ga _(1-xy) N is lower than the composition ratio y of Al. For example, when the composition ratio y of Al is greater than 0 and 0.2 or less, the composition ratio x of B may be greater than 0 and 0.12 or less, and further, the composition ratio x of B may be 0.06 or more and 0.10 or less. As another example, when the composition ratio (y) of Al is 0.2 or more and 0.4 or less, the composition ratio (x) of B may be more than 0 and 0.07 or less, and further, the composition ratio (x) of B may be 0.02 or more and 0.06 or less. Furthermore, in B _x Al _y Ga _(1-xy) N of the well layer 410, the higher the Al composition ratio, the lower the optimum composition ratio of B, and the Al composition ratio and the B composition ratio may be in a linear relationship with each other. The relation of -5x + (0.5 ~ 0.7) can be satisfied. In B _x Al _y Ga _(1-xy) N of the well layer 410, the AlGaN well layer containing no B is determined by determining the composition ratio x of B and the composition ratio y of Al in the above-mentioned ranges. Luminous efficiency can be improved compared with the case where it is used.

With regard to the configuration of the well layer 410 described above, it will be described in more detail with reference to FIGS. 3 to 6 are graphs for explaining characteristics of light emitting diodes according to exemplary embodiments of the present invention and a comparative example.

The ultraviolet light emitting diode characteristic illustrated in FIGS. 3 to 6 is B _x Al ₀ _. Value calculated from an ultraviolet light emitting diode having a 2.5 nm thick well layer comprising ₂ Ga _(0.8-x) N and a barrier layer comprising AlN. Specifically, FIG. 3 is graphs illustrating a valence band structure according to a change in the composition ratio x of B. FIG. 3A to 3C show valence band structures in which the energy of each subband when x is 0, 0.06 and 0.12, respectively, as a function of an in-plane wave vector (k _∥ ) do. FIG. 4A shows an optical matrix element value (| M│ ² ) when x is 0, 0.06 and 0.12 as a function of an in-plane wave vector (k _∥ ). 4B shows the strain and the internal field of the well layer according to the composition ratio of B. FIG. 5A shows a spontaneous emission coefficient according to the wavelength when x is 0, 0.02, 0.06, 0.10 and 0.12, and FIG. 5B shows the spontaneous emission coefficient according to the composition ratio of B. (spontaneous emission coefficient). 6 (a) to 6 (c) show potential profiles and wave functions when x is 0, 0.06, and 0.12 according to positions, and FIG. 6 (d) shows pseudo Fermi levels according to the composition ratio of B (Quasi−). A graph showing the separation of fermi level).

The graph of FIG. 3 was derived according to a self-consistent solution, which was calculated assuming a carrier density (N _2D ) of 20 × 10 ¹² cm ⁻² . 'HHn', 'LHn' and 'CHn' in FIGS. 3 and 6 are 'n-th heavy-hole subband', 'n-th light-hole subband' and 'n-th crystal splitting hole subband (crystal), respectively. -field splittoff hole subband) '.

Referring to FIG. 3, it can be seen that the energy of each subband changes according to the composition ratio x of B. In particular, when B is not added ((a)), the uppermost subband of the valence band is represented by HH1. When B is added to AlGaN ((b), (c)), the energy of the crystal splitting hole subband CH1 increases and is located between LH1 and HH2. Meanwhile, the heavy-hole effective mass increases as B is added to AlGaN. For example, when the composition ratio (x) of B in the BAlGaN / AlN quantum well structure is 0 and 0.12, the heavy-hole effective mass is respectively. 1.75m ₀ and 2.97m ₀ .

Referring to FIG. 4 (a), it can be seen that the light amount of TE-polarized light increases as the composition ratio x of B increases. However, when the x value is 0.1 or more, the amount of light of the TE-polarized light is drastically reduced when the plane wave vector k _∥ increases above a certain size. This is interpreted as the uppermost subband in the valence band is changed from the heavy-hole band (HH) to the crystal splitting hole band (CH) when the amount of B added is more than a predetermined value.

Also, as B is added to the well layer, lattice mismatch is reduced. Furthermore, as shown in (b) of FIG. 4, as the composition ratio (x) of B increases, the internal field and strain decrease, thereby reducing the spatial separation of the electron and the space and the spatial separation of the wave function. This may increase the internal quantum efficiency, thereby increasing the luminous efficiency of the ultraviolet light emitting diode. Thus, increases as the Figure 4, as shown in (a), the band edges (k _∥ = 0) optical matrix required value (│M│ ²⁾ increases the composition ratio (x) of B in.

Next, referring to FIG. 5 (a), it can be seen that the emission wavelength is shortened as the composition ratio x of B increases from 0 to 0.12, and the amount of light of TE-polarized light increases. In addition, referring to FIG. 5 (b), it can be seen that when the composition ratio y of Al is less than 0.5, the amount of light of TE-polarized light increases by adding B to the well layer. That is, as described with reference to FIGS. 3 and 4, by adding B to the well layer, the luminous efficiency of the ultraviolet light emitting diode is improved.

However, when the composition ratio x of B exceeds the threshold of the predetermined ratio, it can be seen that the amount of light emitted from the light emitting diode is reduced. Specifically, as shown in (a) and (b) of FIG. 5, in the B _x Al _y Ga _(1-xy) N of the well layer 410, when the composition ratio y of Al is 0.2, B Increasing the composition ratio (x) from 0 to 0.08 increases the amount of light, and when setting the composition ratio (x) of B to more than 0.08, the amount of light decreases with the increase in the B composition ratio. In addition, referring to FIG. 5 (b), when the composition ratio y of Al is 0.4, when the composition ratio x of B is increased from 0 to 0.04, the amount of light increases, but the composition ratio x of B is greater than 0.04. When set, the amount of light decreases with the increase in the B composition ratio. Furthermore, when the composition ratio y of Al is 0.6, the amount of light decreases even if B is added.

When B is added to B _x Al _y Ga _(1-xy) N of the well layer 410 at a predetermined composition ratio or more, the amount of light decreases. As described above, the uppermost subband in the valence band has a heavy-hole band ( It is interpreted as changing from HH) to crystal splitting hole band (CH). It is also interpreted that the light amount of the TM-polarized light increases simultaneously with the decrease in the light amount of the TE-polarized light.

Next, referring to FIGS. 6A to 6C, B _x Al ₀ _. Increasing the B composition ratio (x) from ₂ Ga _(0.8-x) N to 0.12 reduces the spatial separation of the energy bands and the spatial separation of the wavefunction. As described above, this is an effect due to the reduction of the internal field, and thus, by adding B, the internal quantum efficiency of the ultraviolet light emitting diode can be increased. In addition, referring to FIG. _6D , it can be seen that the pseudo Fermi level separation (ΔE _fc + ΔE _fν ) decreases as the B composition ratio increases. At this time, the pseudo Fermi level separation (ΔE _fc + ΔE _fν ) is defined as the difference between the energy of the pseudo Fermi level and the energy of the ground state. Accordingly, it can be seen that the luminous efficiency improves with the addition of B. However, when the composition ratio of B exceeds 0.8, the value of ΔE _fc + ΔE _fν is lower than ΔE _fc , and it is interpreted that the amount of light of TE-polarized light decreases with increasing B again.

That is, the matrix element is related to the transition probability of electrons and holes, and as the TE optical matrix element increases, the emission intensity increases, but the maximum value is determined because the separation energy of the quasi fermi level gradually decreases. . However, when the Al component exceeds 0.5, the optimum point disappears because the TE optical matrix element suddenly decreases regardless of the separation energy of the pseudo Fermi level. Therefore, while satisfying the above relation, satisfying 0 <y <0.5 and 0 <x <y, the TE optical matrix element can be maximized to obtain higher luminous efficiency.

Referring back to FIG. 1, the second conductivity type semiconductor layer 500 is located on the active layer 400.

The second conductivity-type semiconductor layer 500 may include a nitride semiconductor such as (Al, Ga, In) N, and may include, for example, AlGaN or GaN. 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, for example, a p-type conductivity type including an Mg dopant.

In addition, the second conductivity-type 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 emission intensity can be provided. In addition, the ultraviolet light emitting diode may implement ultraviolet light of various wavelengths, and in particular, an ultraviolet light emitting diode that emits deep ultraviolet light (including light in the UVC band) may be provided.

The structure of the ultraviolet light emitting diode of FIG. 1 may be modified in various forms. For example, by performing an additional process to the ultraviolet light emitting diode structure of FIG. 1, light emitting diodes having various known structures, such as a horizontal type, a vertical type, or a flip chip type, may be implemented.

In the above, various embodiments of the present invention have been described, but the present invention is not limited to the various embodiments and features described above, and various modifications may be made without departing from the technical spirit of the claims of the present invention. Modifications and variations are possible.

Claims

A first conductivity type semiconductor layer;

An active layer on the first conductivity type semiconductor layer, the active layer including a barrier layer and a well layer including B x Al y Ga (1-xy) N; And

A second conductivity type semiconductor layer on the active layer,

An ultraviolet light emitting diode in which 0 <y <0.5 and 0 <x <y, and satisfying a relational expression of y = -5x + (0.5 to 0.7).
The method according to claim 1,

The barrier layer includes Al z Ga (1-z) N (0 < z ≦ 1), and the barrier layer has a greater bandgap energy than the well layer.
The method according to claim 1,

Y is greater than 0 and less than or equal to 0.2, and wherein 0 <x≤0.12.
The method according to claim 3,

An ultraviolet light emitting diode wherein 0.06 ≦ x ≦ 0.10.
The method according to claim 1,

Y is 0.2 or more and 0.4 or less and 0 <x≤0.07.
The method according to claim 5,

An ultraviolet light emitting diode wherein 0.02 ≦ x ≦ 0.06.
The method according to claim 1,

In the light emitted from the active layer, the amount of light of TE-polarized light is greater than the amount of TM-polarized light.