JP2018074173A - Light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve luminous efficiency of a near ultraviolet light-emitting element.SOLUTION: A light-emitting element comprises: an n-type contact layer including a GaN layer; a p-type contact layer including a GaN layer; and an active region of a multiple quantum well structure located between the n-type contact layer and the p-type contact layer. The active region emits near ultraviolet light within a range of 365 to 390 nm.SELECTED DRAWING: None

Description

The present invention relates to an inorganic semiconductor light emitting device, and more particularly to a near ultraviolet light emitting device.

In general, gallium nitride based semiconductors are widely used for ultraviolet, blue / green light emitting diodes or laser diodes as light sources for full color displays, traffic signals, general lighting and optical communication equipment. In particular, indium gallium nitride (InGaN) compound semiconductors have received much attention due to their narrow band gap.

Light emitting devices using such gallium nitride-based compound semiconductors have various application fields such as large-scale natural color flat panel displays, backlight sources, traffic lights, indoor lighting, high-density light sources, high-resolution output systems, and optical communications. It is used for. In particular, light-emitting elements that emit near-ultraviolet rays are used for counterfeit identification, resin curing, ultraviolet ray treatment, and the like, and can be combined with phosphors to realize visible rays with various hues.

Near-ultraviolet rays generally refer to ultraviolet rays having a wavelength range of about 320 nm to 390 nm. GaN has a band gap energy of about 3.42 eV, which corresponds to light energy with a wavelength of about 365 nm. Therefore, a light emitting device including an InGaN well layer may be used to emit light having a wavelength of 365 nm or more, that is, near ultraviolet rays in the range of 365 nm to 390 nm depending on the In content.

On the other hand, since the light generated in the well layer is emitted to the outside through the barrier layer and the contact layer, a large number of semiconductor layers are positioned on the light traveling path, and light absorption by these semiconductor layers occurs. In particular, if the semiconductor layer has a narrower band gap than the well layer or a band gap similar to the well layer, a considerable amount of light loss occurs. In particular, it is necessary to control light absorption by the n-type contact layer and the p-type contact layer that occupy most of the thickness of the light emitting element.

For this reason, in the conventional near-ultraviolet light emitting device, not only the electron blocking layer but also the barrier layer, the n-type contact layer, and the p-type contact layer are formed of AlGaN having a relatively wide band gap compared to InGaN. Yes. However, since AlGaN is relatively difficult to grow while maintaining good crystallinity, the near-ultraviolet light-emitting element has a relative electrical and optical characteristic relative to that of a blue light-emitting element. It is low and is relatively expensive compared to blue / green light emitting diodes.

The problem to be solved by the present invention is to improve the light output or light emission efficiency of a gallium nitride near-ultraviolet light emitting device.

Another problem to be solved by the present invention is to provide a near-ultraviolet light emitting device that can be more easily manufactured.

A light emitting device according to an embodiment of the present invention includes an n-type contact layer including a gallium nitride layer, a p-type contact layer including a gallium nitride layer, and the n-type contact layer and the p-type contact layer. And an active region having a multiple quantum well structure located therein, and the active region having the multiple quantum well structure emits near ultraviolet rays within a range of 365 nm to 390 nm.

The active region of the multiple quantum well structure includes each barrier layer and each well layer. Meanwhile, each barrier layer may be formed of AlInGaN. When the barrier layer contains In, lattice mismatch between the well layer and the barrier layer can be reduced.

Furthermore, the first barrier layer closest to the n-type contact layer may further contain 10% to 20% of Al as compared with other barrier layers. By forming the first barrier layer from AlInGaN having a relatively small lattice constant compared to other barrier layers, the light output of the light emitting element can be improved. In the present specification, the content of the metal element expressed in percentage is the composition of each metal component expressed in percentage with respect to the sum of the composition of the metal components of the gallium nitride-based layer. . In other words, the Al content of the gallium nitride-based layer represented by Al _x In _y Ga _z N is calculated by 100 × x / (x + y + z) and expressed as%.

Each of the well layers is formed of InGaN and can emit near ultraviolet rays of 375 nm to 390 nm. Other barrier layers other than the first barrier layer include 15% to 25% Al and 1% or less. It may be formed of AlInGaN containing In. Furthermore, the first barrier layer may be formed of AlInGaN containing 30% to 40% Al and 1% or less In.

In some embodiments, the p-type contact layer includes a lower heavily doped layer, an upper heavily doped layer, and a lightly doped layer located between the lower heavily doped layer and the upper heavily doped layer. May be included. The lightly doped layer is thicker than the lower and upper heavily doped layers. By forming the lightly doped layer relatively thick, light absorption by the p-type contact layer can be prevented.

The n-type contact layer may include a lower gallium nitride layer, an upper gallium nitride layer, and an intermediate layer having a multilayer structure positioned between the lower gallium nitride layer and the upper gallium nitride layer. By inserting an intermediate layer having a multilayer structure in the middle of the n-type contact layer, the crystallinity of each epitaxial layer formed on the n-type contact layer can be improved. In particular, the intermediate layer of the multilayer structure may have a structure in which AlInN and GaN are alternately stacked.

Meanwhile, the light emitting device may further include a superlattice layer positioned between the n-type contact layer and the active region, and an electron injection layer positioned between the superlattice layer and the active region. Here, the electron injection layer has a higher n-type impurity doping concentration than the superlattice layer. Since electrons can be successfully injected into the active region by the electron injection layer, the luminous efficiency can be improved.

In a specific embodiment, the superlattice layer may have a structure in which InGaN / InGaN is repeatedly stacked, and the electron injection layer may be formed of GaN or InGaN. Here, InGaN / InGaN indicates that each layer in one cycle constituting the superlattice layer is formed of InGaN, and it is not necessary that these layers contain In having the same composition.

On the other hand, the undoped GaN layer may be located between the n-type contact layer and the superlattice layer. The undoped GaN layer may be in contact with the n-type contact layer, and restores the crystal quality of the n-type contact layer that has been degraded by impurity doping.

The light emitting device is located between the undoped GaN layer and the superlattice layer, and is doped with an n-type impurity at a lower concentration than the n-type contact layer, and the low-concentration GaN. A high-concentration GaN layer positioned between the layer and the superlattice layer and doped with an n-type impurity at a higher concentration than the low-concentration GaN layer may further be included.

It is to be understood that the foregoing general description and the following detailed description are exemplary and are intended to aid in interpretation and to provide further explanation of the claimed invention.

In the conventional near-ultraviolet light emitting element, the n-type contact layer is formed of AlGaN. By forming a contact layer that occupies the thickness of most light-emitting elements excluding the substrate with AlGaN, light loss due to light absorption can be prevented, but the crystal quality of the epi layer is poor, so the light output and light emission efficiency are improved. It ’s difficult. On the other hand, according to the present invention, the crystal quality of the active region can be improved by forming the n-type contact layer and the p-type contact layer all or almost on the gallium nitride layer. Therefore, light loss due to light absorption can be prevented, and the light output of the light emitting element can be improved.

Further, the light output can be further improved by further adding Al to the first barrier layer as compared with other barrier layers. Furthermore, the optical loss due to light absorption can be reduced by improving the crystal quality of the n-type contact layer and the p-type contact layer.

It is sectional drawing for demonstrating the light emitting element which concerns on one Example of this invention. It is sectional drawing for demonstrating the multiple quantum well structure of the light emitting element which concerns on one Example of this invention. It is a graph for demonstrating the light output by content of Al of the 1st barrier layer of a multiple quantum well structure. It is a graph for demonstrating the light output by the thickness of the 1st barrier layer of a multiple quantum well structure.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Each embodiment introduced below is provided as an example to fully convey the idea of the present invention to those skilled in the art. Therefore, the present invention is not limited to the examples described below, and can be embodied in other forms. In the drawings, the width, length, thickness, and the like of components may be exaggerated for convenience. Like reference numerals refer to like elements throughout the specification.

FIG. 1 is a cross-sectional view illustrating a light emitting device according to an embodiment of the present invention, and FIG. 2 is an enlarged cross-sectional view illustrating a multiple quantum well structure of the light emitting device.

Referring to FIG. 1, the light emitting device includes an n-type contact layer 27, an active region 39, and a p-type contact layer 43. Further, the light emitting device includes a substrate 21, a nucleation layer 23, a buffer layer 25, an undoped GaN layer 29, a low concentration GaN layer 31, a high concentration GaN layer 33, a superlattice layer 35, an electron injection layer 37, an electron. A block layer 41 or a delta doving layer 45 may be included.

The substrate 21 is a substrate for growing a gallium nitride based semiconductor layer, and may be a sapphire substrate, a SiC substrate, a spinel substrate, etc., but is not particularly limited thereto. A sapphire substrate (PSS) may be used.

The core layer 23 may be formed of (Al, Ga) N at 400 ° C. to 600 ° C. for growing the buffer layer 25 on the substrate 21, and is preferably formed of GaN or AlN. The core layer may be formed with a thickness of about 25 nm. The buffer layer 25 is a layer for reducing the occurrence of defects such as a potential between the substrate 21 and the n-type contact layer 27, and grows at a relatively high temperature. The buffer layer 25 may be formed of undoped GaN with a thickness of about 1.5 μm, for example.

The n-type contact layer 27 is formed on a gallium nitride based semiconductor layer doped with an n-type impurity, for example, Si, and may have a thickness of about 3 μm, for example. The n-type contact layer 27 includes a GaN layer and may be formed as a single layer or multiple layers. For example, the n-type contact layer 27 may include a lower GaN layer 27a, an intermediate layer 27b, and an upper GaN layer 27c as illustrated. Here, the intermediate layer 27b may be formed of AlInN, or may be formed of a multilayer structure (including a superlattice structure) in which AlInN and GaN are alternately stacked, for example, about 10 periods. The lower GaN layer 27a and the upper GaN layer 27c may be formed to have a similar thickness, for example, about 1.5 μm each. The intermediate layer 27b may be formed to have a relatively small thickness compared to the lower and upper GaN layers 27a and 27c, and may have a thickness of about 80 nm. The intermediate layer 27 b is inserted in the middle of the n-type contact layer 27 as compared with the case where a single GaN layer is continuously grown relatively thick with a thickness of about 3 mm.

Thus, the crystal quality of the epi layer formed on the n-type contact layer 27, particularly the active region 39, can be improved. Meanwhile, the Si doping concentration doped in the n-type contact layer 27 may be in the range of 2 × 10 ¹⁸ / cm ³ to 2 × 10 ¹⁹ / cm ³ , more preferably 1 × 10 ¹⁸ / cm ^3. cm ^{3 to} 2 × 1
It may be within the range of 0 ¹⁹ / cm ³ . In particular, the lower GaN layer 27a and the upper GaN layer 27c may be doped with Si impurities at a high concentration, and the intermediate layer 27b may be doped with Si impurities to the same degree or lower than the upper GaN layer 27c. In some cases, it is not intentionally doped with impurities. Since the lower GaN layer 27a and the upper GaN layer 27c are highly doped with impurities, the resistance component of the n-type contact layer 27 can be reduced. Furthermore, the electrode that contacts the n-type contact layer 27 may contact the upper GaN layer 27c.

The undoped GaN layer 29 is formed of GaN that is not intentionally doped with impurities, and may be formed with a relatively thin thickness compared to the upper GaN layer 27c, for example, a thickness of 80 nm to 300 nm. . By doping the n-type contact layer 27 with an n-type impurity, a residual stress is generated in the n-type contact layer 27 and the crystal quality is degraded. Therefore, when another epitaxial layer is grown on the n-type contact layer 27, it is difficult to grow an epitaxial layer having good crystal quality. However, since the undoped GaN layer 29 is not doped with impurities, it functions as a recovery layer that recovers the deterioration of the crystal quality of the n-type contact layer 27. Therefore, the undoped GaN layer 29 is preferably formed directly on the n-type contact layer 27 and in contact with the n-type contact layer 27. In addition, since the undoped GaN layer 29 has a relatively higher resistivity than the n-type contact layer 27, electrons flowing from the n-type contact layer 27 into the active region 39 pass through the undoped GaN layer 29. It can be uniformly dispersed in the n-type contact layer 27 before performing.

The low-concentration GaN layer 31 is located on the undoped GaN layer 29 and has an n-type impurity doping concentration doped at a lower concentration than the n-type contact layer 27. The low-concentration GaN layer 31 may have, for example, a Si doping concentration within a range of 5 × 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ , and is relatively smaller than the undoped GaN layer 29. It may be formed with a small thickness, for example, a thickness of 50 nm to 150 nm. On the other hand, the high-concentration GaN layer 33 is located on the low-concentration GaN layer 31 and has a higher n-type impurity doping concentration than the low-concentration GaN layer 31. The high-concentration GaN layer 33 may have a Si doping concentration that is substantially similar to the n-type contact layer 27. The high-concentration GaN layer 33 may be formed with a relatively thinner thickness than the low-concentration GaN layer 31, for example, a thickness of about 30 nm.

The n-type contact layer 27, the undoped GaN layer 29, the low-concentration GaN layer 31, and the high-concentration GaN layer 33 may be continuously grown by supplying a metal source gas into the chamber. As a raw material for the metal source gas, organic substances such as Al, Ga, and In, for example, TMA (trimethylaluminum), TMD (trimethylgallium), and / or TMI (trimethylindium) are used. On the other hand, SiH ₄ may be used as the Si source gas. These layers may be grown at a first temperature, eg, 1050 ° C. to 1150 ° C.

The superlattice layer 35 is located on the high concentration GaN layer 33. The superlattice layer 35 may be formed, for example, by alternately stacking first InGaN layers and second InGaN layers having different compositions from each other with a thickness of 20 and approximately 30 periods. The In composition ratio contained in the first InGaN layer and the second InGaN layer is smaller than the In composition ratio contained in each well layer 39w in the active region 39. The superlattice layer 35 may be formed in an undoped layer without intentionally doping with impurities. Since the superlattice layer 35 is formed in the undoped layer, the leakage current of the light emitting element can be reduced.

The electron injection layer 37 has an n-type impurity doping concentration that is relatively higher than that of the superlattice layer 35. Further, the electron injection layer 37 may have substantially the same n-type impurity doping concentration as the n-type contact layer 27. For example, the n-type impurity doping concentration may be in the range of 1 × 10 ¹⁹ / cm ^{3 to} 5 × 10 ¹⁹ / cm ³ , more preferably 1 × 10 ¹⁹ / cm ^{3 to} 3 × 10 ^19. It may be within the range of / cm ³ . The electron injection layer 37 is doped at a high concentration, so that electrons are smoothly injected into the active region 39. The electron injection layer 37 may be formed with a thickness of, for example, about 20 nm so as to have a thickness that is similar to or relatively smaller than the high-concentration GaN layer 33. Further, the electron injection layer 37 may be grown at a pressure of about 300 Torr and at a temperature of about 820 ° C to 850 ° C.

An active region 39 is located on the electron injection layer 37. FIG. 2 is an enlarged cross-sectional view showing the active region 39.

Referring to FIG. 2, the active region 39 has a multiple quantum well structure including barrier layers 39b and well layers 39w that are alternately stacked. Each of the well layers 39w has a composition that emits near ultraviolet rays in a range of 365 nm to 390 nm. For example, the well layer 39w may be formed of InGaN or AlInGaN, and particularly may be formed of InGaN. At this time, the content of In contained in the well layer 39w is determined by the required near-ultraviolet wavelength. For example, the In content contained in the well layer 39w may be in the range of about 2% to 5% (and thus Ga is about 95% to 98%). In addition, throughout this specification, the content of the compound in each layer is similarly expressed in mole percent. The well layer 39w may be formed to a thickness of about 20 to 30 inches. The well layer 39w may be grown at a temperature higher than that of a general blue light emitting diode, for example, 800 ° C. to 820 ° C. and a pressure of 300 Torr. In this way, the crystal quality of the well layer may be improved.

Each barrier layer 39b may be formed of a gallium nitride based semiconductor layer having a wider band gap than the well layer, for example, GaN, InGaN, AlGaN, or AlInGaN. In particular, each of the barrier layers 39b may be formed of AlInGaN, but by containing In, lattice mismatch between the well layer 39w and the barrier layer 39b can be reduced.

The barrier layer 39b may be grown at a growth temperature slightly higher than the growth temperature of the well layer 39w. For example, the barrier layer 39b may be grown at a temperature of 820 ° C. to 850 ° C. under a pressure of 300 Torr.

On the other hand, among the barrier layers 39b1, 39b, 39bn, the first barrier layer 39b1 closest to the electron injection layer 37 or the n-type contact layer 27 may have a higher Al content than other barrier layers. . For example, the Al content of the first barrier layer 39b1 may be 10% to 20% higher than that of the other barrier layers 39b. For example, when the other barrier layers 39b and 39bn contain about 20% Al, the first barrier layer 39b1 may contain about 30% to 40% Al. The In content contained in these barrier layers 39b1, 39b, 39bn is about 1% or less. In particular, when each of the well layers 39w is formed of InGaN and emits near ultraviolet rays of 375 nm to 390 nm, the other barrier layers 39b and 39bn other than the first barrier layer 39b1 include 15% to 25% Al and 15% to 25%. The first barrier layer 39b1 may be formed of AlInGaN containing 30% to 40% Al and 1% or less of In.

In general, the barrier layers in the light emitting device are formed to have the same composition. However, in this embodiment, the first barrier layer 39b1 has an Al content that is 10% to 20% higher than the other barrier layers 39b. In the present invention, the electron injection layer 37, the n-type contact layer 27, and the like are formed of GaN. The well layer 39w and GaN that emit near-ultraviolet rays have a relatively small band gap difference. Accordingly, the first barrier layer 39b1 is formed to have a relatively high band gap as compared with the other barrier layers 39b, so that the first barrier layer 39b1 has carriers in the active region 39. The function of confinement can be performed. In particular, when an AlGaN barrier layer is used, the movement speed of the holes is significantly slowed down, which may increase the electron overflow rate. In this case, it is conceivable to increase the thickness of the electron blocking layer 41 to prevent the overflow of electrons, but in order to facilitate the injection of holes into the active region, the increase in the thickness of the electron blocking layer 41 is Done restrictively.

Therefore, by forming the first barrier layer 39b1 so as to have a wider band gap (about 0.5 eV or more) than the other barrier layers, the movement speed of electrons is reduced and the overflow of electrons is effectively prevented. can do. However, when the Al content contained in the first barrier layer 39b1 excessively increases to about 20% or more, the first barrier layer 39b1 and the electron injection layer 37 and between the first barrier layer 39b1 and the well layer The lattice mismatch with 39w is increased, and the crystal quality of the active region 39 can be lowered.

The thickness of the first barrier layer is approximately equal to or greater than the remaining barrier layer except the last barrier layer closest to the electron blocking layer 41 or the p-type contact layer 43 (for example, about 40 mm). It is preferable. The first barrier layer may have a thickness of, for example, 40 to 60 mm, particularly about 45 mm.

The active region 39 may be in contact with the electron injection layer 37. The barrier layer and the quantum well layer of the active region 39 may be formed in an undoped layer that is not doped with impurities in order to improve the crystal quality of the active region. The entire active region may be doped with impurities.

Referring to FIG. 1 again, a p-type contact layer 43 may be located on the active region 39, and an electron blocking layer 41 may be located between the active region 39 and the p-type contact layer 43. The electron blocking layer 41 may be formed of AlINGaN or AlInGaN in order to reduce lattice mismatch between the p-type contact layer and the active region 39. At this time, the electron block layer 41 may contain 36% Al and 3% In. The electron blocking layer 41 may be doped with a p-type impurity, for example, Mg with a doping density of 5 × 10 ¹⁹ / cm ³ to 2 × 10 ²⁰ / cm ³ .

The p-type contact layer 43 may include a lower heavily doped layer 43a, a lightly doped layer 43b, and an upper heavily doped layer 43c. The lower heavily doped layer 43a and the upper heavily doped layer 43c may be doped with p-type impurities, for example, Mg with a doping density of 5 × 10 ¹⁹ / cm ³ to 2 × 10 ²⁰ / cm ³ . The lightly doped layer 43b has a relatively low doping concentration compared to the lower and upper heavily doped layers 43a and 43c, and is interposed between the lower heavily doped layer 43a and the upper heavily doped layer 43c. To position. The low-concentration doping layer 43b may block the supply of Mg source gas (for example, Cp ₂ Mg) during the growth.

Furthermore, during the growth of the lightly doped layer 43b, the impurity content can be reduced by using N ₂ gas as a carrier gas instead of using H ₂ gas. Further, the lightly doped layer 43b is formed relatively thicker than the lower and upper heavily doped layers 43a and 43c. For example, the lightly doped layer 43b may be formed with a thickness of about 60 nm, and the lower and upper heavily doped layers 43a and 43c may be formed with a thickness of 10 nm. As a result, the p-type contact layer 43
By improving the crystal quality and reducing the impurity concentration, the loss of near ultraviolet rays by the p-type contact layer 43 can be prevented or alleviated.

Meanwhile, a delta doping layer 45 for reducing ohmic contact resistance may be positioned on the p-type contact layer 43. The delta doping layer 45 is doped with an n-type or p-type impurity at a high concentration, and reduces ohmic resistance between the electrode formed thereon and the p-type contact layer 43. The delta doping layer 45 may be formed with a thickness of about 2 to 5 mm.

Meanwhile, a light emitting device having a horizontal structure or a light emitting device having a flip chip structure may be manufactured by patterning each epitaxial layer grown on the substrate 21, and a light emitting device having a vertical structure may be formed by removing the substrate 21. May be manufactured.

(Experimental example 1)

In order to confirm the light output change due to the Al composition of the first barrier layer 39b closest to the n-type contact layer 27, the MOCVD equipment is used, and only the Al composition of the first barrier layer is changed, and other conditions are as follows. Each epi layer was grown in the same manner, and the light output by the Al composition was measured. FIG. 3 is a graph showing the light output by the Al composition of the first barrier layer. The Al compositions of the other barrier layers other than the first barrier layer were all the same. The Al content of each barrier layer was measured using an atomic probe, and the other barrier layer contained about 20% Al.

Referring to FIG. 3, when the Al composition contained in the first barrier layer is 14% larger than that of the other barrier layers, the light output of the light emitting device is relatively high. On the other hand, when Al was not contained in the first barrier layer, the light output of the light emitting device was shown to be relatively low. In addition, a sample light emitting device having an Al composition contained in the first barrier layer of about 47% and 27% higher than the other barrier layers is a light emitting device having the same Al composition as the other barrier layers. The light output was shown to be lower.

(Experimental example 2)

In order to investigate the light output change due to the thickness of the first barrier layer 39b closest to the n-type contact layer 27, the MOCVD equipment is used, and the other conditions are all the same, and each epi layer is grown. The light output according to the thickness of the first barrier layer was measured by changing only the thickness of the barrier layer. FIG. 4 is a graph showing the light output according to the thickness of the first barrier layer. The thicknesses of the other barrier layers other than the first barrier layer are all about 45 mm except for the last barrier layer closest to the p-type contact layer 43, and the last barrier layer is relatively about 75 mm. It was formed thick. Also, the Al composition of the first barrier layer was all about 34%, and the Al composition of the other barrier layers was all about 20%.

Referring to FIG. 4, when the thickness of the first barrier layer was 45 mm, which was the same as the thickness of the other barrier layers, the light output was relatively high. On the other hand, when the thickness of the first barrier layer was 25 mm, the light output was low, and when the first barrier layer was thickly 75 mm, the light output was relatively low.

In the conventional near-ultraviolet light emitting element, the n-type contact layer is formed of AlGaN. By forming a contact layer that occupies the thickness of most light-emitting elements excluding the substrate with AlGaN, light loss due to light absorption can be prevented, but the crystal quality of the epi layer is poor, so the light output and light emission efficiency are improved. It ’s difficult. On the other hand, according to the present invention, the crystal quality of the active region can be improved by forming the n-type contact layer and the p-type contact layer all or almost on the gallium nitride layer. Therefore, light loss due to light absorption can be prevented, and the light output of the light emitting element can be improved.

Further, the light output can be further improved by further adding Al to the first barrier layer as compared with other barrier layers. Furthermore, the optical loss due to light absorption can be reduced by improving the crystal quality of the n-type contact layer and the p-type contact layer.

It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. It is intended that the present invention include such modifications and variations made within the scope of the claims and their equivalents.

Claims (1)

An n-type contact layer including a gallium nitride layer; a p-type contact layer including a gallium nitride layer; and an active region having a multiple quantum well structure positioned between the n-type contact layer and the p-type contact layer. The active region of the multiple quantum well structure is in the range of 365 nm to 309 nm.

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