KR102459379B1 - High efficiency long wavelength light emitting device - Google Patents

Abstract

The light emitting device according to an embodiment includes a first conductivity-type semiconductor layer, an active layer positioned on the first conductivity-type semiconductor layer, and having a quantum well structure, a second conductivity-type semiconductor layer positioned on the active layer, and the active layer and an electron blocking layer positioned between the second conductivity type semiconductor layer, and a through region penetrating the electron blocking layer, wherein the active layer includes a plurality of well layers and a plurality of barrier layers, the well layer comprising: a nitride-based semiconductor containing In, wherein the barrier layer is disposed above and below the well layer, and the through region forms an entrance on the upper surface of the second conductivity type semiconductor layer, and has a depth of 200 nm or more from the entrance. have

Description

High-efficiency long-wavelength light-emitting device {HIGH EFFICIENCY LONG WAVELENGTH LIGHT EMITTING DEVICE}

The present invention relates to a light-emitting device, and more particularly, to a high-efficiency light-emitting device emitting light of a long wavelength including green light.

Recently, nitride-based semiconductors are widely used as base materials for light emitting devices such as light emitting diodes. Since the nitride-based semiconductor may have various bandgap energies according to the composition ratio of the group III element, light in various wavelength bands may be realized by controlling the composition ratio of elements such as Al, Ga, and In.

A multi-quantum well structure (MQW) is generally used as the structure of the active layer, and the emission wavelength of the light emitting device is determined according to the composition ratio of the nitride-based semiconductor of the well layer of the multi-quantum well structure. For example, in the case of a light emitting device emitting blue light from an active layer, an InGaN layer containing a small amount of In is used as a well layer, and in the case of an ultraviolet light emitting device, an AlGaN layer is used as a well layer.

Meanwhile, to implement a light emitting device emitting light of a relatively long wavelength, that is, a light emitting device emitting light having a longer wavelength than blue light, a well layer is formed using a nitride-based semiconductor containing a large amount of In. However, a nitride-based semiconductor containing an excessive amount of In such as InGaN has different growth conditions from GaN, so it is difficult to apply a general method of manufacturing a blue light emitting device to the manufacturing of a long wavelength light emitting device as it is.

Furthermore, it is known that a light emitting diode having a well layer containing excessively In is generally more vulnerable to electrostatic discharge and the like than a blue light emitting diode.

The problem to be solved by the present invention is to prevent the occurrence of precipitation and segregation due to site departure of In atoms in a well layer, thereby minimizing wavelength shift and providing a long-wavelength light emitting device with high luminous efficiency will do

Another problem to be solved by the present invention is to provide a long-wavelength light emitting device having high luminous efficiency while preventing device defects from occurring due to electrostatic discharge.

A long wavelength light emitting device according to an embodiment of the present invention, a first conductivity type semiconductor layer; an active layer disposed on the first conductivity-type semiconductor layer and having a quantum well structure; and a second conductivity-type semiconductor layer disposed on the active layer, wherein the active layer includes: at least one well layer including a nitride-based semiconductor containing 21% or more In; at least two barrier layers positioned above and below the well layer; and at least one upper capping layer disposed on the well layer and disposed between the well layer and the barrier layer, wherein the upper capping layer has a higher bandgap energy than the barrier layer, and wherein the upper capping layer has a bandgap energy greater than that of the barrier layer. The ping layer and the well layer are in contact.

Meanwhile, the well layer may include InGaN, the barrier layer may include GaN, and the upper capping layer may include AlGaN.

In addition, AlGaN of the upper capping layer may include 0.1% to 2.5% Al. More specifically, AlGaN of the upper capping layer may contain 1.4% to 1.8% Al, and in this range, good light output and low forward voltage can be achieved.

Meanwhile, a thickness of the upper capping layer may be thinner than a thickness of the barrier layer. In an embodiment, the upper capping layer may have a thickness of 5 Å to 20 Å.

Meanwhile, the long wavelength light emitting device may include a plurality of well layers and a plurality of barrier layers, and a thickness of the uppermost barrier layer positioned at the top of the plurality of barrier layers may be thicker than the other barrier layers.

In addition, the uppermost barrier layer may include a sub-barrier layer having a bandgap energy smaller than an average bandgap energy of the uppermost barrier layer. In particular, the sub-barrier layer may contain In, and the In composition ratio of the sub-barrier layer may be smaller than the In composition ratio of the well layer. The sub-barrier layer has a smaller lattice constant than the well layer, thus mitigating the lattice mismatch between the well layer and the electron blocking layer. Accordingly, the crystal quality of the second conductivity type semiconductor layer may be improved.

The long wavelength light emitting device may further include at least one lower capping layer positioned under the well layer and positioned between the well layer and the barrier layer, wherein the lower capping layer has a larger band than the barrier layer. It may have a gap energy.

The long wavelength light emitting device may further include an electron blocking layer disposed on the active layer.

In some embodiments, the electron blocking layer may include a grading layer in which the Al composition ratio decreases toward the second conductivity type semiconductor layer. By using the Al grading layer, holes can be easily injected into the active layer while blocking electrons. In addition, the electron blocking layer may contain In, and the In composition ratio of the electron blocking layer may be smaller than the In composition ratio of the sub-barrier layer. Accordingly, the In composition ratio gradually decreases in the order of the well layer, the sub-barrier layer, and the electron blocking layer, and the lattice constant decreases. The crystal quality of the electron blocking layer and the second conductivity type semiconductor layer may be improved by gradually decreasing the In composition ratio as described above in a long wavelength light emitting device having a very large In composition ratio. By improving the crystal quality of the second conductivity type semiconductor layer and the electron blocking layer, it is possible to provide a light emitting device resistant to electrostatic discharge.

In other embodiments, the electron blocking layer includes a first electron blocking layer in contact with the active layer, a second electron blocking layer disposed on the first electron blocking layer, and a third electron blocking layer in contact with the second conductivity type semiconductor layer. layer, wherein the second electron blocking layer is doped with Mg at a higher concentration than the first and third electron blocking layers, and the third electron blocking layer may have a superlattice structure. Accordingly, holes can be well injected into the active layer while efficiently blocking electrons using the second electron blocking layer.

Furthermore, the third electron blocking layer may have a superlattice structure of AlInGaN/GaN. By adopting the AlInGaN/GaN superlattice structure, the crystal quality of the second conductivity type semiconductor layer formed thereon, for example, the GaN layer can be improved.

Meanwhile, the barrier layer may have a thickness of 120 Å to 150 Å, but is not limited thereto. The barrier layer may have a thickness greater than 150 angstroms. However, the barrier layer has a thickness of 220 angstroms or less. When the barrier layer is thicker than 220 angstroms, the light output decreases and the forward voltage increases. In particular, the barrier layer may have a thickness of 170 angstroms to 200 angstroms, in which high light output and low forward voltage are possible.

Meanwhile, the active layer includes a plurality of barrier layers and a plurality of well layers, and the plurality of barrier layers include barrier layers doped with a relatively high concentration of n-type impurities and a relatively low concentration of n-type impurities among the barrier layers. It may include undoped or undoped barrier layers. The barrier layers doped with the n-type impurity at a relatively high concentration are disposed closer to the first conductivity type semiconductor layer than the second conductivity type semiconductor layer. Electrons and holes are generally likely to recombine in the well layer close to the second conductive current semiconductor layer. Therefore, the electron injection efficiency is improved while preventing non-luminescent recombination by doping the n-type impurity into the barrier layers relatively close to the first conductivity type semiconductor layer compared to the barrier layers around the well layers where electrons and holes recombine. can do it

In addition, the barrier layers may include Mg-doped barrier layers, and the Mg-doped barrier layers may have a higher Mg doping concentration as they are closer to the second conductivity-type semiconductor layer. By doping the barrier layers close to the second conductivity type semiconductor layer with Mg at a relatively high concentration, hole injection efficiency may be improved.

Meanwhile, the first conductivity type semiconductor layer may include a V-pit generation layer. The V-pit generation layer may include a first layer of a single composition doped with an n-type impurity and a second layer of a superlattice structure. By using the V-pit generation layer to form V-pits passing through the active layer, it is possible to provide a light emitting device resistant to electrostatic discharge.

Furthermore, the first layer may be a GaN layer doped with n-type impurities, and the second layer may have an InGaN/GaN superlattice structure. When the second layer has a superlattice structure, the crystal quality of the active layer can be improved. The In content of InGaN in the superlattice structure may be 1% to 5%.

In addition, the V-pit generation layer may have a thickness of 1500 Å to 3000 Å, and the thickness of the second layer of the superlattice structure may be greater than or equal to that of the first layer of the single composition. By making the thickness of the second layer greater than or equal to the thickness of the first layer, it is possible to provide a light emitting device resistant to electrostatic discharge while securing the crystal quality of the active layer.

Meanwhile, the first conductivity-type semiconductor layer may further include an n-type impurity modulation doping layer positioned below the V-pit generation layer, and the doping concentration of the n-type impurity modulation doping layer is n of the first layer. type impurity is higher than the doping concentration. The n-type impurity modulation doping layer may be a contact layer to which an electrode contacts.

In some embodiments, the second layer may be doped with an n-type impurity at a higher concentration than that of the first layer. However, in another embodiment, the second layer may be doped with an n-type impurity at a lower concentration than that of the first layer, or may not be doped.

Meanwhile, the active layer includes a plurality of barrier layers and a plurality of well layers, and the plurality of barrier layers include barrier layers doped with a relatively high concentration of n-type impurities and a relatively low concentration of n-type impurities among the barrier layers. The barrier layers doped with or including undoped barrier layers and doped with the n-type impurity at a relatively high concentration are disposed closer to the first conductivity type semiconductor layer than the second conductivity type semiconductor layer, and the first layer It has a higher n-type impurity doping concentration, and the first layer may be doped with a relatively low concentration of the n-type impurity or may have a higher n-type impurity doping concentration than the undoped barrier layers.

In one embodiment, the light emitting device may include V-pits having an entrance greater than 250 nm.

In another embodiment, the second conductivity type semiconductor layer may include a p-AlGaN layer positioned between the p-GaN layers. The p-AlGaN layer may be disposed closer to a lower surface than the upper surface of the second conductivity type semiconductor layer, wherein the lower surface is a surface located closer to the active layer side than the upper surface.

According to the present invention, there is provided a long-wavelength light emitting device including an upper capping layer disposed between a well layer and a barrier layer and covering the well layer. The upper capping layer prevents thermal damage of the well layer, thereby preventing the escape of In and preventing the crystallinity of the well layer from being deteriorated. In addition, since the upper capping layer has a smaller lattice constant than the well layer and the barrier layer, the strain generated in the well layer can be reduced, thereby reducing the quantum confinement Stark effect, thereby improving luminous efficiency.

In addition, by disposing the V-pit generation layer under the active layer, it is possible to prevent device failure due to electrostatic discharge.

Other features and advantages of the present invention will become more apparent from the following detailed description.

1 to 4 are cross-sectional views illustrating a long wavelength light emitting device and a method of manufacturing a long wavelength light emitting device according to embodiments of the present invention.
5A and 5B are enlarged cross-sectional views and band diagrams for explaining an active layer of a long wavelength light emitting device according to an embodiment.
6A and 6B are enlarged cross-sectional views and band diagrams for explaining an active layer of a long wavelength light emitting device according to another embodiment.
7 is an enlarged cross-sectional view illustrating a first conductivity type semiconductor layer of a long wavelength light emitting device according to an embodiment of the present invention.
8 is an enlarged cross-sectional view illustrating an electron blocking layer of a long wavelength light emitting device according to an embodiment of the present invention.
9 is an enlarged cross-sectional view for explaining an electron blocking layer of a long wavelength light emitting device according to another embodiment of the present invention.
10 is an enlarged cross-sectional view illustrating a second conductivity type semiconductor layer of a long wavelength light emitting device according to an embodiment of the present invention.
11 is an optical photograph showing a surface of a light emitting device according to various embodiments of the present invention.
12 is an electron micrograph showing a cross-section of the V-pit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed 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. And, in the drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. In addition, when one component is described as being “on” or “on” another component, each component is different from each component as well as when each component is “immediately above” or “directly on” the other component. It includes the case where another component is interposed between them. Like reference numerals refer to like elements throughout.

In addition, each composition ratio, growth method, growth condition, thickness, etc. for the nitride-based semiconductor layers described below are examples, and the present invention is not limited as described below. For example, when expressed as InGaN, the composition ratio of In and Ga may be variously applied according to the needs of a person skilled in the art (hereinafter, "a person skilled in the art"). In addition, the nitride-based semiconductor layers described below may be grown using various methods generally known to those skilled in the art, for example, MOCVD (Metal Organic Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydride). Vapor Phase Epitaxy) can be grown using techniques such as. However, in the embodiments described below, it is described that the semiconductor layers are grown in a growth chamber using MOCVD. In the process of growing nitride-based semiconductor layers, sources introduced into the growth chamber may use sources known to those skilled in the art, unless otherwise specified, for example, TMGa, TEGa, etc. may be used as Ga sources, TMAl, TEAl, etc. may be used as the Al source, TMIn, TEIn, etc. may be used as the In source, and NH ₃ may be used as the N source. However, the present invention is not limited thereto. In addition, in the method of manufacturing a long wavelength light emitting device according to embodiments to be described later, the order of each step corresponds to an example, and the order of each step may be changed.

1 to 4 are cross-sectional views illustrating a long wavelength light emitting device and a method of manufacturing a long wavelength light emitting device according to embodiments of the present invention.

First, referring to FIG. 1 , a first conductivity-type semiconductor layer 130 is formed on a substrate 110 . In an embodiment, before the growth of the first conductivity-type semiconductor layer 130 , a buffer layer may be further formed on the substrate 110 .

The substrate 110 is not limited as long as it is a substrate capable of growing a nitride-based semiconductor, and may include, for example, a heterogeneous substrate such as a sapphire substrate, a silicon substrate, a silicon carbide substrate, or a spinel substrate, and also gallium nitride. The substrate may include a substrate of the same type, such as an aluminum nitride substrate. In addition, the substrate 110 may have a non-polar, semi-polar or polar growth surface.

The first conductivity type semiconductor layer 130 is positioned on the growth substrate 110 . The first conductivity-type semiconductor layer 130 may include a nitride-based semiconductor such as (Al, Ga, In)N and be grown and formed on the growth substrate 110 using a method such as MOCVD, MBE, HVPE, etc. have. For example, when the first conductivity type semiconductor layer 130 is grown by using MOCVD, the nitride-based semiconductor layer containing GaN is grown at a predetermined growth rate at a growth temperature of about 950° C. to 1200° C., whereby the first conductivity type semiconductor layer 130 is grown. A type semiconductor layer 130 may be formed. In addition, the first conductivity type semiconductor layer 120 may be n-type doped by including at least one impurity such as Si, C, Ge, Sn, Te, or Pb. However, the present invention is not limited thereto, and the first conductivity type semiconductor layer 130 may be doped with an opposite conductivity type including a p-type dopant. Furthermore, the first conductivity type semiconductor layer 130 may be formed of a single layer or multiple layers. When the first conductivity type semiconductor layer 130 is formed of multiple layers, the first conductivity type semiconductor layer 130 may include a superlattice layer, a contact layer, a modulation doping layer, an electron injection layer, and the like. A case in which the first conductivity-type semiconductor layer 130 is a multi-layer will be described in more detail later with reference to FIG. 7 .

Meanwhile, before growing the first conductivity-type semiconductor layer 130 , a buffer layer 120 may be further formed on the substrate 110 . The buffer layer 120 may include a nitride semiconductor such as GaN, may be grown using MOCVD, and may be grown at a growth temperature within a range of about 450 to 600°C. The buffer layer 120 may improve the crystallinity of the semiconductor layers grown on the substrate 110 in a subsequent process, and may also serve as a seed layer in which nitride-based semiconductor layers may be grown on a heterogeneous substrate. .

Referring to FIG. 2 , the active layer 140 is formed on the first conductivity type semiconductor layer 130 . Furthermore, an electron blocking layer 150 may be further formed on the active layer 140 .

The active layer 140 may include a nitride semiconductor such as (Al, Ga, In)N, and may be grown on the first conductivity type semiconductor layer 130 using a technique such as MOCVD, MBE, or HVPE. . In addition, the active layer 140 may include a quantum well structure QW including at least two barrier layers 141 and at least one well layer 143 , and further, a plurality of barrier layers. It may include a multiple quantum well structure (MQW) including a layer 141 and a plurality of well layers 143 . In addition, the active layer 140 is positioned on the at least one well layer 143 and forms an upper capping layer 145 or 145a interposed between the at least one well layer 143 and the barrier layer 141 . may include more. Furthermore, the active layer 140 is positioned under the at least one well layer 143 and further forms a lower capping layer 145b interposed between the at least one well layer 143 and the barrier layer 141 . may include

Light emitted from the active layer 140 may be light of a relatively long wavelength, for example, green light of a longer wavelength than blue light may be emitted. The wavelength of light emitted from the active layer 140 may be adjusted by controlling the composition ratio of the nitride-based semiconductor layer of the well layer 143 . In this case, the well layer 143 may include a nitride-based semiconductor including In, and the composition ratio of In may be 21% or more. The active layer 140 will be described later in more detail.

The electron blocking layer 150 is positioned on the active layer 140 and prevents electrons from overflowing from the active layer 140 to the upper portion. The electron blocking layer 150 may be formed on the uppermost barrier layer 147 of the active layer 140 . In addition, the average bandgap energy of the electron blocking layer 150 may be greater than the average bandgap energy of the uppermost barrier layer 147 , so that the electrons move toward the second conductivity type semiconductor layer 160 side of the electron blocking layer It can be blocked by an energy barrier of 150.

Referring to FIG. 3 , the second conductivity type semiconductor layer 160 is formed on the active layer 140 or the electron blocking layer 150 .

The second conductivity type semiconductor layer 160 may include a nitride-based semiconductor such as (Al, Ga, In)N, and may be grown using a technique such as MOCVD, MBE, or HVPE. The second conductivity type semiconductor layer 160 may be doped with a conductivity type opposite to that of the first conductivity type semiconductor layer 130 . For example, the second conductivity-type semiconductor layer 160 may be doped with p-type including impurities such as Mg. The second conductivity type semiconductor layer 160 may be formed of a p-GaN single layer, but is not limited thereto, and may include an AlGaN layer therein. The Mg doping concentration in the second conductivity type semiconductor layer 160 is highest at the surface of the second conductivity type semiconductor layer 160 and relatively high at the electron blocking layer 150 side, and may have a relatively low profile in the inner layer. have. Furthermore, the Mg doping concentration may include a region having a relatively low profile in the inner layer and a region having a profile in which the doping concentration is relatively increased and then decreased between the electron blocking layer 150 . The AlGaN layer disposed in the second conductivity-type semiconductor layer 160 may be disposed in a region in which the doping concentration decreases between the region having a relatively low Mg doping concentration and the electron blocking layer 150 .

The structure of FIG. 3 may be variously processed, and thus, a long-wavelength light emitting device of various structures may be implemented. For example, referring to FIG. 4 , the long wavelength light emitting device may further include a first electrode 171 and a second electrode 173 to provide a horizontal light emitting device. The first electrode 171 and the second electrode 173 are electrically connected to the first conductivity type semiconductor layer 130 and the second conductivity type semiconductor layer 160 , respectively. However, the present invention is not limited thereto, and the structure of FIG. 3 may be modified into various structures such as a flip-chip type light emitting device and a vertical light emitting device. Also, depending on the shape of the light emitting device, the substrate 110 may be omitted.

Hereinafter, the active layer 140 of the long wavelength light emitting device according to various embodiments will be described in more detail with reference to FIGS. 5A to 6B .

First, FIGS. 5A and 5B are enlarged cross-sectional views and band diagrams for explaining the active layer 140 of the long wavelength light emitting device according to an embodiment.

5A and 5B , the active layer 140 may include at least one well layer 143 , at least two barrier layers 141 , and at least one upper capping layer 145 . In addition, the active layer 140 includes a plurality of well layers 143 , a plurality of barrier layers 141 positioned above and below each of the plurality of well layers 143 , and an upper portion of each of the plurality of well layers 143 . It may include a plurality of upper capping layers 145 positioned on the. Furthermore, the active layer 140 may include an uppermost barrier layer 147 forming the last barrier layer of the active layer 140 .

The well layer 143 is positioned between the barrier layers 141 , and as shown in FIG. 5B , the bandgap energy of the well layer 143 is smaller than the bandgap energy of the barrier layer 141 . The well layer 143 may include or be formed of In _x Ga _(1-x) N (0<x<1), and the composition ratio (x) of In is controlled according to the wavelength emitted by the long-wavelength light emitting device. can be In one embodiment, the composition ratio (x) of In may be 0.21 or more, and further, may be 0.23 or more. Accordingly, the long wavelength light emitting device may emit green light. The barrier layer 141 may include GaN and/or InGaN. Since the bandgap energy of the barrier layer 141 is greater than that of the well layer 143 , when the barrier layer 141 includes InGaN, the In composition ratio of InGaN of the barrier layer 141 is greater than that of the well layer 143 . In _x Ga _(1-x) of N is smaller than the In composition ratio (x).

The upper capping layer 145 is positioned on the well layer 143 , and is positioned between the well layer 143 and the barrier layer 141 . In particular, the upper capping layer 145 may be in contact with the well layer 143 positioned thereunder. The average lattice constant of the upper capping layer 145 may be smaller than the average lattice constant of the well layer 143 and the barrier layer 141 . Also, the bandgap energy of the upper capping layer 145 may be greater than the bandgap energy of the barrier layer 141 . In one embodiment, the upper capping layer 145 may include or be formed of Al _y Ga _(1-y) N (0 < y < 1), and the composition ratio (y) of Al may be 0.001 to 0.025. have. Additionally, when the composition ratio (y) of Al is in the range of 0.014 to 0.017, good light output and low forward voltage can be achieved.

Hereinafter, a manufacturing process of the active layer 140 will be described.

First, the barrier layer 141 may be formed on the first conductivity type semiconductor layer 130 . The barrier layer 141 may be formed of GaN, and may be grown at a temperature of about 900° C. to 1200° C. to a thickness of about 120 Å to 220 Å, and further, a thickness of 170 Å to 200 Å. The thickness of the barrier layer 141 can achieve high light output and low forward voltage in this range. Next, a well layer 143 is formed on the barrier layer 141 . The well layer 143 may be formed of In _x Ga _(1-x) N, and may have a thickness of about 20 Å to about 30 Å. The growth temperature of the well layer 143 may be set to about 150° C. to 200° C. lower than the growth temperature of the barrier layer 141 . When the well layer 143 is grown at too high a temperature, the In content in the well layer 143 may be formed lower than intended, and thus the well layer 143 of a long wavelength light emitting device requiring a relatively high In composition ratio. is grown in the temperature range as described above. Next, an upper capping layer 145 is formed on the well layer 143 . The upper capping layer 145 may be grown at substantially the same temperature as the growth temperature of the well layer 143 . For example, the upper capping layer 145 may be formed of Al _y Ga _(1-y) N grown at a temperature lower than the growth temperature of the barrier layer 141 by about 150° C. to 200° C. The upper capping layer 145 may have a thickness of about 5 Å to 20 Å. Thereafter, the growth temperature is increased again, and the above-described growth process of the barrier layer 141 , the well layer 143 , and the upper capping layer 145 is repeated to provide the active layer 140 structure as shown in FIG. 5A . .

In general, if the growth temperature is increased while the surface of the well layer 143 is exposed after growth of the well layer 143 , the probability that In atoms in the well layer 143 are separated from the site of the semiconductor layer increases. rises In this case, In may be precipitated or In segregation may occur on the surface of the well layer 143 as the growth temperature rises. In this case, the crystallinity of the well layer 143 becomes coarse or the surface morphology deteriorates. In addition, when In atoms are separated from the site of the semiconductor layer, the In composition ratio of the well layer 143 becomes smaller than intended, so that light having a shorter wavelength than the intended wavelength is emitted from the light emitting device. However, according to the above-described embodiments, the barrier layer 141 is not formed by raising the temperature immediately after the growth of the well layer 143 is completed, and the upper portion grown at substantially the same temperature as the growth temperature of the well layer 143 . After the capping layer 145 is formed, the barrier layer 141 is formed. Accordingly, the upper capping layer 145 may cover the upper portion of the well layer 143 to protect the well layer 143 from heat. Accordingly, it is possible to prevent In atoms from being separated from the well layer 143 , thereby preventing deterioration of the surface morphology of the well layer 143 and shifting of the wavelength to a shorter wavelength. In addition, due to the formation of the upper capping layer 145, the growth temperature of the barrier layer 141 can be increased to a temperature at which the crystallinity of the barrier layer 141 can be improved, so that the crystallinity of the entire active layer 140 is improved to emit light. It is possible to improve the luminous efficiency of the device.

Meanwhile, since the upper capping layer 145 is formed of Al _y Ga _(1-y) N grown at a relatively low temperature, the crystalline quality of the upper capping layer 145 itself may not be relatively good. However, since the thickness of the upper capping layer 145 is controlled to be about 5 Å to 20 Å, it has a very thin thickness compared to the barrier layer 141 , so that the crystallinity degradation of the entire active layer 140 due to the upper capping layer 145 hardly occurs. I never do that. Accordingly, a decrease in luminous efficiency due to the crystallinity of the upper capping layer 145 hardly occurs.

Also, in general, a long-wavelength light emitting device such as a green light emitting device is subjected to relatively strong stress and strain due to a difference in lattice constant between the well layer and the barrier layer due to the high In content of the well layer. Due to this, a strong quantum confined stark effect (QCSE) appears, resulting in a decrease in luminous efficiency and a change in luminous wavelength. On the other hand, according to embodiments, by forming the upper capping layer 145 having an average lattice constant smaller than that of the barrier layer 141 and the well layer 143 in the difference between the barrier layer 141 and the well layer 143 , Reduce the strain acting on the layer (143). As the quantum confinement Stark effect in the well layer 143 is weakened due to the reduction in strain, luminous efficiency may be improved and a change in emission wavelength due to band bending may be reduced.

Furthermore, according to embodiments, the thickness of the upper capping layer 145 is about 5 Å to 20 Å, and the thickness of the barrier layer 141 is formed to be about 120 Å to 220 Å, particularly 170 Å to 200 Å, thereby optimizing the luminous efficiency. can By forming the upper capping layer 145 within the above-described range, strain due to a difference in lattice constant can be minimized, and degradation of crystallinity due to the upper capping layer 145 can be minimized. In addition, by forming the thickness of the barrier layer 141 within the above-described range in consideration of the thickness of the upper capping layer 145 , the average crystallinity of the entire active layer 140 may be improved, thereby improving luminous efficiency.

Referring back to FIGS. 5A and 5B , the uppermost barrier layer 147 positioned immediately below the electron blocking layer 150 among the barrier layers may have a thickness greater than the average thickness of the remaining barrier layers 141 . Also, the uppermost barrier layer 147 may include a sub-barrier layer 147a having a bandgap energy that is less than the average bandgap energy of the uppermost barrier layer 147 .

Meanwhile, in some embodiments, the light emitting device may have a multi-quantum well structure in which a plurality of barrier layers 141 and a plurality of well layers 143 are alternately stacked. In this case, since the mobility of the electrons is greater than that of the holes, the electrons and the holes mainly recombine in the well layer 143 close to the second conductivity type semiconductor layer 160 (or the electron blocking layer 150 ). Therefore, in the barrier layers 141 of the active layer 140 in which recombination of electrons and holes does not occur well, that is, in the barrier layers 141 close to the first conductivity-type semiconductor layer 130, n-type impurities such as Si It is possible to improve the electron injection efficiency by doping the , thereby lowering the forward voltage of the light emitting device. In this case, the plurality of barrier layers 141 include barrier layers doped with a relatively high concentration of n-type impurities and undoped barrier layers doped with a relatively low concentration of n-type impurities. In particular, the barrier layers 141 doped with a relatively high concentration of n-type impurities are disposed closer to the first conductivity-type semiconductor layer 130 than the second conductivity-type semiconductor layer 160 .

In general, it is preferable that an n-type impurity such as Si is not doped around at least two well layers 143 close to the second conductivity type semiconductor layer 160 . For example, when the number of barrier layers 141 is 10, Si is added at a relatively high concentration, for example, about 5×10 ¹⁸ /cm 3 , to the five barrier layers 141 close to the first conductivity type semiconductor layer 130 . After doping, the five barrier layers close to the second conductivity type semiconductor layer 160 may be doped with Si at a low concentration, for example, about 5×10 ¹⁷ /cm 3 . In addition, it is not necessary for all of the Si-doped barrier layers 141 to have the same Si doping concentration, and the doping concentration may gradually decrease as the distance from the first conductivity-type semiconductor layer 130 increases.

Meanwhile, the n-type impurity doping concentration of the barrier layers 141 doped with the n-type impurity at a relatively high concentration is the n-type doped n-type doped layer (133 in FIG. 7 ) of the first conductivity-type semiconductor layer 130 . Although lower than the doping concentration of the impurity, it is higher than the doping concentration of the n-type impurity in the V-pit generation layer (137 in FIG. 7 ). This will be described again later.

Meanwhile, the barrier layers 141 may be doped with a p-type impurity such as Mg. The p-type impurity may be doped to improve hole injection efficiency, and thus, barrier layers close to the second conductivity-type semiconductor layer 160 are mainly doped. Furthermore, the closer to the second conductivity type semiconductor layer 160, the more Mg may be doped. However, the Mg doping concentration doped in the barrier layers is relatively lower than the Mg doping concentration doped in the electron blocking layer 150 or the second conductivity type semiconductor layer 160 .

Further, in various embodiments, as shown in FIGS. 6A and 6B , the active layer 140 may further include an upper capping layer 145a and a lower capping layer 145b.

6A and 6B , the lower capping layer 145b is positioned below the well layer 143 , and is positioned between the well layer 143 and the barrier layer 141 . In particular, the lower capping layer 145b may be in contact with the well layer 143 disposed thereon. The average lattice constant of the lower capping layer 145b may be smaller than the average lattice constant of the well layer 143 and the barrier layer 141 . Also, the bandgap energy of the lower capping layer 145b may be greater than the bandgap energy of the barrier layer 141 . In an embodiment, the lower capping layer 145b may include or be formed of Al _z Ga _(1-z) N (0 < z < 1), and the Al composition ratio (z) may be 0.001 to 0.025. have. The upper capping layer 145a and the lower capping layer 145b may include or be formed of AlGaN having substantially the same Al composition ratio. However, the present invention is not limited thereto, and the Al composition ratio of the upper capping layer 145a may be different from the Al composition ratio of the lower capping layer 145b. By further including the lower capping layer 145b, the strain of the well layer 143 may be further reduced.

7 is an enlarged cross-sectional view illustrating the first conductivity type semiconductor layer 130 of the long wavelength light emitting device according to an embodiment of the present invention.

Referring to FIG. 7 , the first conductivity type semiconductor layer 130 is disposed on the substrate 110 . When the substrate 110 is a heterogeneous substrate such as a sapphire substrate (including a patterned sapphire substrate), the buffer layer 120 may be first formed on the substrate 110 .

The first conductivity type semiconductor layer 130 may include, for example, an undoped semiconductor layer 131 , a modulation doped layer 133 , a strain relaxed buffer layer 135 , and a V-pit generation layer 137 . The V-pit generation layer 137 may include a first layer 137a having a single composition and a second layer 137b having a superlattice structure.

The undoped semiconductor layer 131 may be formed of GaN, and is preferably not doped with Si in order to improve crystal quality. However, in another embodiment, a semiconductor layer lightly doped with Si may be used.

The modulation doped layer 133 may be formed of GaN, and is modulated and doped with an n-type impurity such as Si. Accordingly, a region doped with an n-type impurity and an undoped region, or a region doped with a relatively high concentration of an n-type impurity and a region doped with a relatively low concentration are alternately repeated. The doping concentration of an impurity, eg, Si, in the region doped with the n-type impurity or the region doped with a relatively high concentration of the n-type impurity is the doping concentration of the n-type impurity in the barrier layers 141 heavily doped with the n-type impurity. higher than The modulation doped layer 133 is a layer to which the n-electrode 171 is contacted, and the region doped with the n-type impurity or the region doped with a relatively high concentration of the n-type impurity is relatively high in order to lower the contact resistance and disperse the current. Si may be doped at a concentration of, for example, 5×10 ¹⁸ /cm 3 or more, and further, at a concentration of 1×10 ¹⁹ /cm 3 or more. In addition, for a stable ohmic contact, the region doped with the n-type impurity or the region doped with a relatively high concentration of the n-type impurity is thicker than the thickness of the undoped region or the region doped with the n-type impurity at a relatively low concentration. .

The strain relaxed buffer layer 135 may be formed to relieve strain applied to the active layer 140 and help distribute current. The strain relaxed buffer layer 135 may be formed of, for example, five pairs of n-AlGaU/u-GaN superlattice layers in which an AlGaN layer doped with an n-type impurity and an undoped GaN layer are alternately stacked. The doping concentration of an n-type impurity doped in n-AlGaN, for example, Si, is substantially similar to that of Si doped in the modulation doped layer 133, for example, 5×10 ¹⁸ /cm 3 or more, and further, 1×10 ¹⁹ / It may be a concentration of cm 3 or more. However, the strain relaxed buffer layer 135 may be omitted.

The V-pit generation layer 137 generates V-pits in portions where threading dislocations are formed. The V-pit generation layer 137 is 750 ° C. to 950 ° C., specifically 800 ° C. to 900 ° C., more specifically 800 ° C. to 850 ° C. Using TEGa (Triethylgallium) as a Ga source and N ₂ carrier It can be formed using gas. This condition produces V-pits that are generally uniform in size.

V-pits are formed through the active layer 140 . The breakdown voltage in the V-pit represents a difference from the breakdown voltage of the active region around the V-pit, and accordingly, it is possible to distribute the current through the V-pits during electrostatic discharge, thereby preventing the destruction of the active region.

In the present embodiment, the V-pit generation layer 137 includes a first layer 137a having a single composition and a second layer 137b having a superlattice structure. The first layer 137 may be formed of a GaN layer doped with an n-type impurity, for example, Si. The doping concentration of the n-type impurity in the first layer 137 is lower than the Si doping concentration of the modulation doped layer 133 and further lower than the doping concentration of the n-type impurity in the barrier layers 141 doped with the n-type impurity at a high concentration. can

Meanwhile, the second layer may be formed of, for example, an InGaN/GaN superlattice structure. The second layer may be undoped or doped with an n-type impurity. However, the doping concentration of the n-type impurity in the second layer is lower than the Si doping concentration of the modulation doped layer 133 and further lower than the doping concentration of the n-type impurity in the barrier layers 141 doped with the n-type impurity at a high concentration. The active layer 140 may be directly formed on the second layer, and thus, the crystal quality of the active layer 140 may be improved by forming the second layer 137b in a superlattice structure including InGaN. The composition ratio of In of the InGaN layer in the second layer may be 1% to 5%.

Meanwhile, the thickness of the V-pit generation layer 137 affects the light output and forward voltage of the light emitting diode. The thickness of the V-pit generation layer 137 may be, for example, in the range of 1500 Å to 3000 Å. Over 90% of the maximum light output can be achieved in this range. More specifically, the thickness of the V-pit generation layer 137 may be, for example, in the range of 2000 Angstroms to 3000 Angstroms, in which an optical output greater than 95% of the maximum optical output and a relatively low forward voltage may be achieved.

In this case, the second layer 137b has a thickness equal to or greater than that of the first layer 137a. By securing the second layer 137b at least as thick as the first layer 137a, the crystal quality of the active layer 140 can be improved while creating V-pits in a limited thickness range. In particular, the second layer 137b may have a thickness of 1000 Å or more.

8 is an enlarged cross-sectional view for explaining the electron blocking layer 150 of the long wavelength light emitting device according to an embodiment of the present invention.

Referring to FIG. 8 , the electron blocking layer 150 may include a grading layer 153 in which the Al composition ratio decreases toward the second conductivity type semiconductor layer 160 . Furthermore, the electron blocking layer 150 may further include an interfacial layer 151 having a predetermined composition between the grading layer 153 and the active layer 140 .

The electron blocking layer 150 may be formed of AlGaN or AlInGaN, and has a relatively high bandgap to prevent electrons from moving from the active layer 140 to the second conductivity type semiconductor layer 160 to improve luminous efficiency. do. The electron blocking layer 150 should allow holes to be injected into the active layer 140 region while blocking the flow of electrons. The In composition ratio in the sub-barrier layer 147a is smaller than the In composition ratio in the well layer 143 , and the In composition ratio in the electron blocking layer 150 is smaller than the In composition ratio in the sub-barrier layer 147a. Accordingly, the lattice mismatch between the well layer 143 and the electron blocking layer 150 can be reduced by decreasing the In content in the order of the well layer 143 , the sub-barrier layer 147a , and the electron blocking layer 150 . , the good electron blocking layer 150 and the second conductivity type semiconductor layer 160 can be grown.

The Al composition ratio of the grading layer 153 may gradually decrease from the Al composition ratio of the interfacial layer 151 , and finally the Al composition ratio may become zero. Since the Al composition of the grading layer 153 decreases toward the second conductivity type semiconductor layer 160 , the energy barrier decreases toward the second conductivity type semiconductor layer 160 . Accordingly, holes can be better injected into the active layer 140 beyond the grading layer 153 .

In addition, a p-type impurity such as Mg may be doped into the electron blocking layer 150 , and a doping concentration grading characteristic in which the doping concentration is lowered toward the active layer 140 in the electron blocking layer 150 may be exhibited. The doping concentration grading may be formed within the grading layer 153 or within the interfacial layer 151 .

In the present embodiment, the description will be given that the interfacial layer 151 having a predetermined thickness is formed before the grading layer 153 is formed. However, the interfacial layer 151 may be omitted.

9 is an enlarged cross-sectional view for explaining the electron blocking layer 150 of the long wavelength light emitting device according to another embodiment of the present invention.

Referring to FIG. 9 , the electron blocking layer 150 may include a first electron blocking layer 151 , a second electron blocking layer 155 , and a third electron blocking layer 157 .

The first electron blocking layer 151 may have the same single composition as the interfacial layer 151 described above with reference to FIG. 8 and is in contact with the active layer 140 . The first electron blocking layer 151 may be formed of AlGaN or AlInGaN. The first electron blocking layer 151 may be doped with a p-type impurity such as Mg. The doping concentration of the p-type impurity in the first electron blocking layer 151 may be lower than the doping concentration of the p-type impurity in the second conductivity-type semiconductor layer 160 . In addition, the doping concentration of the p-type impurity in the first electron blocking layer 151 may have a grading characteristic that decreases toward the active layer 140 .

The second electron blocking layer 155 may be formed of AlGaN or AlInGaN having a lower Al composition ratio than that of the first electron blocking layer 151 . Furthermore, the second electron blocking layer 155 may have a single composition or may have a superlattice structure. The second electron blocking layer 155 is doped with a higher concentration of p-type impurities than the first and third electron blocking layers 151 and 157 . A doping concentration of a p-type impurity, for example, Mg, doped into the second electron blocking layer 155 may be substantially similar to a concentration of a p-type impurity in the second conductivity-type semiconductor layer 160 .

The third electron blocking layer 157 is in contact with the second conductivity type semiconductor layer 160 . The third electron blocking layer 157 may have a superlattice structure to improve the crystal quality of the second conductivity type semiconductor layer 160 . For example, the third electron blocking layer 157 may have a superlattice structure of AlInGaN/GaN. The third electron blocking layer 157 may also be doped with a p-type impurity, for example, Mg, and the doping concentration is lower than the doping concentration of the p-type impurity in the second conductivity-type semiconductor layer 160 , and furthermore, the first electron blocking layer 157 . It may be lower than the doping concentration of the layer 151 .

In the present embodiment, the second electron blocking layer 155 is disposed between the first electron blocking layer 151 and the third electron blocking layer 157 , and is disposed on the first and third electron blocking layers 151 and 157 . It has a relatively low bandgap. In addition, the second electron blocking layer 155 is highly doped with a p-type impurity. Accordingly, holes in the second conductivity type semiconductor layer 160 may be easily injected into the active layer 140 through the electron blocking layer 150 .

10 is an enlarged cross-sectional view illustrating a second conductivity type semiconductor layer of a long wavelength light emitting device according to an embodiment of the present invention.

Referring to FIG. 10 , the second conductivity type semiconductor layer 160 may include a first layer 161 , a second layer 163 , and a third layer 165 . The second conductivity type semiconductor layer 160 may be formed of a single p-GaN single layer having a single composition, but in this embodiment, a plurality of layers will be described.

The first layer 161 is in contact with the electron blocking layer 150 . The first layer 161 is grown in an N2 atmosphere and is formed along the V-pit. The first layer 161 is formed of p-GaN. The Mg doping concentration of the first layer 161 is lower than the doping concentration of the electron blocking layer 160 , but is relatively higher than the doping concentration of the second layer 163 .

The second layer 163 is disposed on the first layer 161 and is formed of p-AlGaN. The Mg doping concentration of the second layer 163 is relatively lower than that of the first layer 161 . The AlGaN layer is generally grown at a relatively high temperature compared to the GaN layer, but since the second conductivity-type semiconductor layer 160 is grown on the active layer 140 , there is a limit in increasing the growth temperature. Accordingly, the second layer 163 lowers the Mg doping concentration than the first layer to prevent deterioration of crystal quality.

The second layer 163 may be disposed as a p-AlGaN single layer in the second conductivity type semiconductor layer 160 , but is not limited thereto, and a plurality of p-AlGaN layers may be disposed with a GaN layer interposed therebetween. . Here, the Al composition ratio of AlGaN may be 10% or less, and more specifically, 5% or less. Even if the Al content is increased to 5%, the driving voltage increase is hardly seen, but when it exceeds 5%, the driving voltage is increased. In particular, when the Al content exceeds 10%, the injection of holes is excessively prevented, thereby greatly increasing the driving voltage of the light emitting device.

The second layer 163 is grown in an H2 atmosphere to fill the V-pits. The V-pits start from the V-pit generation layer 137 and increase in size significantly while growing the active layer 140 including an excess of In. In addition, since the electron blocking layer 150 and the first layer 161 are grown in an N2 atmosphere, the V-pit cannot be filled. Before growing the second layer 163, the V-pit may be formed to a depth of about 200 nm or more. Since the AlGaN layer 163 grown in the H2 atmosphere has a relatively slow growth rate, it can fill the relatively large V-pits well.

The third layer 165 is a layer positioned on the upper surface side of the second conductivity-type semiconductor layer 160 . The third layer 165 may be formed of p-GaN. The third layer 163 has a higher Mg doping concentration region than the electron blocking layer 150 on the surface side, and is relatively higher than the doping concentration of the second layer 163 on the second layer 163 side, but the first layer The region may have an Mg doping concentration lower than the doping concentration of 161 , and may have an Mg doping concentration region lower than the doping concentration of the second layer 163 therein. The heavily doped region on the surface of the third layer 165 is for an ohmic contact. The concentration region lower than the doping concentration of the second layer 163 is to evenly distribute the holes in the surface of the second conductivity-type semiconductor layer 160 and may be omitted.

In this embodiment, the second layer 163 is disposed closer to the electron blocking layer 150 than the top surface of the second conductivity type semiconductor layer 160 . Accordingly, the V-pit may be quickly filled during the growth of the second conductivity type semiconductor layer 160 , and the third layer 165 having a flat region may be formed relatively thickly.

In the present embodiment, it has been described that the V-pits are filled by using the AlGaN layer 163, but V-pits may be left on the surface of the light emitting device by growing or omitting the AlGaN layer 163 in an N2 atmosphere. .

11 (a) is an optical photograph showing the surface of the light emitting device having the surface planarized by filling in the V-pits according to the embodiment of FIG. 10 , and FIG. It's an optical picture. FIG. 12 is an electron micrograph showing a cross-section of the V-pit of FIG. 11( b ).

As shown in FIG. 11( a ), the V-pits may be filled using the AlGaN layer 163 described above to make the surface flat, and as shown in FIG. 11( b ), the V-pits may be maintained.

By not using a layer filling the V-pits, it is possible to form a large amount of V-pits having an entrance width exceeding about 250 nm in the long-wavelength light emitting device. Moreover, the depth of the V-pits may be greater than the total thickness of the second conductivity type semiconductor layer 160 and the electron blocking layer 150 . The density of the V-pits may be, for example, in the range of 1×10 ⁴ to 1×10 ⁷ /cm 2 . The V-pit remaining on the surface of the light emitting device reduces total internal reflection and increases light extraction efficiency. Furthermore, by increasing the surface area of the second conductivity-type semiconductor layer 160 , the electrode formation area is increased, and thus the driving voltage can be reduced.

Conventionally, a roughened surface is formed on a surface through intentional etching, but it is difficult to form a roughened surface on a relatively thin p-GaN layer, and it is also difficult to control the size. Furthermore, since the roughened surface formed on the p-GaN layer must be limited on the active layer, the depth cannot be greater than the total thickness of the second conductivity type semiconductor layer 160 and the electron blocking layer 150 . In addition, when the surface of the second conductivity-type semiconductor layer 160 is etched to form a roughened surface, the distance between the electrode formed thereon and the active layer is shortened, making it difficult to distribute current, and thus it is particularly vulnerable to electrostatic discharge. On the other hand, when the V-pit is used, it is possible to provide the second conductivity-type semiconductor layer 160 which is advantageous in current dispersion and has strong resistance to static discharge by using a relatively high resistance characteristic in the V-pit. Moreover, since there is no need to separately perform a process of forming the roughened surface, a process for increasing light extraction efficiency is further simplified.

As mentioned above, various modifications and changes are possible in the above embodiments without departing from the technical spirit of the present invention, and the present invention includes all of the technical spirit of the present invention.

Claims (10)

a first conductivity type semiconductor layer;
an active layer disposed on the first conductivity-type semiconductor layer and having a quantum well structure;
a second conductivity-type semiconductor layer positioned on the active layer;
an electron blocking layer positioned between the active layer and the second conductivity-type semiconductor layer; and
a penetrating region penetrating the electron blocking layer;
the active layer comprises a plurality of well layers and a plurality of barrier layers;
the well layer includes a nitride-based semiconductor including In, and the barrier layer is disposed above and below the well layer;
The through region forms an entrance on the upper surface of the second conductivity type semiconductor layer, and the light emitting device has a depth of 200 nm or more from the entrance. The method according to claim 1,
The width of the entrance formed in the second conductivity-type semiconductor layer is 250nm or more light emitting device. The method according to claim 1,
The light emitting device includes an electrode electrically connected to the second conductivity type semiconductor layer,
The electrode is a light emitting device formed along the surface of the through region. The method according to claim 1,
The plurality of inlets are formed in the light emitting device to form a roughened surface on the surface of the second conductivity type semiconductor layer. The method according to claim 1,
The through region is a light emitting device formed to extend from the electron blocking layer to the active layer. 6. The method of claim 5,
The electron blocking layer includes a grading layer having a reduced Al composition, and an Al composition ratio of 0 in a region in contact with the second conductivity-type semiconductor layer. The method according to claim 1,
The plurality of barrier layers includes an n-type impurity, and the light emitting device includes a region doped with a relatively high concentration of the n-type impurity and a region doped with a low concentration. 8. The method of claim 7,
The heavily doped region of the plurality of barrier layers is disposed closer to the first conductivity type semiconductor layer than the second conductivity type semiconductor layer. The method according to claim 1,
An In content of the well layer is 21% or more, and the well layer emits light of a green wavelength. 3. The method according to claim 2,
The density of the inlet is a light emitting device having a range of 1×10 ⁴ to 1×10 ⁷ /cm 2 .

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