UV LEDs

Abstract

The present invention provides an ultraviolet light-emitting diode (UVLED). According to one embodiment, the UV LED comprises: a substrate; an n-type semiconductor layer located on the substrate; a mesa disposed on the n-type semiconductor layer and comprising an active layer and a p-type semiconductor layer; an n-ohmic contact layer contacting the n-type semiconductor layer; a p-ohmic contact layer contacting the p-type semiconductor layer; an n-bump electrically connected to the n-ohmic contact layer; and a p-bump electrically connected to the p-ohmic contact layer. The mesa comprises a plurality of branches, the n-ohmic contact layer surrounds the mesa and is sandwiched between the branches, the n-ohmic contact layer is spaced a constant distance from the mesa, the minimum width of the n-type semiconductor layer exposed between the branches is greater than or equal to the minimum width of the branches, the n-bump and the p-bump respectively cover the upper portion and side surfaces of the mesa, and the p-bump covers at least two of the branches.

Description

[0001] This application is a divisional application of a patent application with application date of July 7, 2017, application number 201780043961.2, and titled “Ultraviolet Light Emitting Diode”. Technical Field

[0002] The present invention relates to an inorganic semiconductor light emitting diode, in particular to a light emitting diode which emits deep ultraviolet light below 300nm. Background Art

[0003] Typically, light-emitting diodes that emit ultraviolet light in the range of 200 to 300 nm can be used for a variety of purposes including as excitation sources for sterilization devices, water or air purification devices, high-density optical recording devices, and bioaerosol fluorescence detection systems.

[0004] Unlike near-ultraviolet or blue-light LEDs, LEDs that emit relatively deep ultraviolet light include well layers containing Al, such as AlGaN. Due to the composition of these gallium nitride-based semiconductor layers, deep ultraviolet LEDs have a structure that is significantly different from blue or near-ultraviolet LEDs.

[0005] In particular, the shape and position of the mesa arranged on the n-type semiconductor layer in the deep ultraviolet light-emitting diode according to the prior art have a structure different from that of blue light-emitting diodes or near-ultraviolet light-emitting diodes. That is, the mesa is formed from the center of the n-type semiconductor layer to one side, and a p-bump is arranged on the mesa, and an n-bump is arranged near the other side opposite to the one side, separated from the mesa. In addition, the existing ultraviolet light-emitting diode is bonded to the substrate (submount) using thermal ultrasonic (TS) bonding technology. For TS bonding, the height of the n-bump and the upper end surface of the p-bump need to be the same. To achieve this, a step adjustment layer is arranged under the n-bump.

[0006] Such existing ultraviolet light-emitting diodes generally have the disadvantages of low light output and high forward voltage. In particular, in order to form an ohmic contact, the p-type GaN layer is included in the p-type semiconductor layer, so the ultraviolet light incident on the p-type semiconductor layer is absorbed by the p-type semiconductor layer and lost. In addition, the n-ohmic contact layer bonded to the n-type semiconductor layer also absorbs light, so the light traveling toward the n-ohmic contact layer is absorbed by the n-ohmic contact layer and lost. For blue light-emitting diodes, although a reflective metal layer is used in the n-ohmic contact layer to reduce light loss, it is difficult to form the n-ohmic contact layer as a reflective metal layer for deep ultraviolet light-emitting diodes, and because the n-ohmic contact layer occupies a relatively wide area, it causes serious problems.

[0007] Furthermore, existing UV LEDs struggle to flexibly utilize the light emitted toward the side surfaces of the mesa, leading to a tendency to minimize the mesa's side surface. In other words, the mesa is made relatively wide. However, a larger mesa width increases the distance from the n-ohmic contact layer to the mesa's center, resulting in poor current dispersion and an increase in forward voltage. Summary of the Invention

[0008] Technical issues

[0009] The problem to be solved by the present invention is to provide an ultraviolet light emitting diode with a novel structure capable of improving electrical characteristics and / or light output.

[0010] Technical Solution

[0011] According to one embodiment of the present invention, an ultraviolet light-emitting diode includes: a substrate; an n-type semiconductor layer located on the substrate; a mesa arranged on the n-type semiconductor layer and including an active layer and a p-type semiconductor layer; an n-ohmic contact layer in contact with the n-type semiconductor layer; a p-ohmic contact layer in contact with the p-type semiconductor layer; an n-bump electrically connected to the n-ohmic contact layer; and a p-bump electrically connected to the p-ohmic contact layer, wherein the mesa includes a main branch and a plurality of sub-branches extending from the main branch, the n-ohmic contact layer surrounds the mesa and is sandwiched between the sub-branches, and the n-bump and the p-bump respectively cover the upper portion and side surfaces of the mesa.

[0012] According to another embodiment of the present invention, an ultraviolet light-emitting diode includes: a substrate; an n-type semiconductor layer located on the substrate; a mesa arranged on the n-type semiconductor layer and including an active layer and a p-type semiconductor layer; an n-ohmic contact layer in contact with the n-type semiconductor layer; a p-ohmic contact layer in contact with the p-type semiconductor layer; an n-bump electrically connected to the n-ohmic contact layer; and a p-bump electrically connected to the p-ohmic contact layer, wherein the mesa includes a plurality of branches, the n-ohmic contact layer surrounds the mesa and is sandwiched between the branches, the n-bump and the p-bump respectively cover the upper portion and side surfaces of the mesa, and the p-bump covers at least two of the branches.

[0013] Beneficial effects

[0014] According to embodiments of the present invention, the n-bumps and p-bumps cover the side surfaces of the mesas, thereby reflecting ultraviolet light off the side surfaces. This reduces the amount of ultraviolet light lost from the side surfaces of the mesas. Furthermore, by employing multiple branches, the surface area of ​​the side surfaces of the mesas can be increased, thereby increasing the area of ​​the light re-incident region between the side surfaces of the mesas and the n-ohmic contact layer. This allows a portion of the ultraviolet light emitted toward the side surfaces of the mesas to re-enter the substrate.

[0015] The advantages and features of the present invention are discussed in detail in or can be made clear through the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. 1 is a plan view for explaining an ultraviolet light emitting diode according to an embodiment of the present invention.

[0017] Figure 2 It is along Figure 1 Cross-sectional view taken along the interception line CC.

[0018] Figure 3 FIG. 1 is a schematic plan view for explaining a table according to an embodiment of the present invention.

[0019] Figure 4 FIG. 1 is a schematic plan view for explaining an ultraviolet light emitting diode according to another embodiment of the present invention.

[0020] Figure 5 FIG. 1 is a schematic plan view for explaining an ultraviolet light emitting diode according to another embodiment of the present invention.

[0021] Figure 6 It is a schematic cross-sectional view for explaining how to mount an ultraviolet light emitting diode according to an embodiment of the present invention on a substrate. DETAILED DESCRIPTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In order to fully convey the idea of ​​the present invention to those skilled in the art, the embodiments described below are provided as examples. Therefore, the present invention is not limited to the embodiments described below, and may be embodied in other forms. In addition, in the accompanying drawings, the width, length, thickness, etc. of the components may be exaggerated for convenience. Furthermore, when it is recorded that a component is located "on" or "on" another component, it not only includes the situation where each part is "directly" located "on" or "on" the other components, but also includes the situation where another component is sandwiched between each component and another component. Throughout the specification, the same reference numerals represent the same components.

[0023] The nitride-based semiconductor layer described below can be grown using a variety of commonly known methods, for example, it can be grown using techniques such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). However, in the embodiments described below, the case where the semiconductor layer is grown in a growth chamber using MOCVD is described. During the growth of the nitride-based semiconductor layer, the source (source) flowing into the growth chamber can be a commonly known source, for example, trimethyl gallium (TMGa), triethyl gallium (TEGa), etc. can be used as a Ga source, trimethyl aluminum (TMAl), triethyl aluminum (TEAl), etc. can be used as an Al source, trimethyl indium (TMIn), triethyl indium (TEIn), etc. can be used as an In source, and NH3 can be used as an N source. However, the present invention is not limited to this.

[0024] According to one embodiment of the present invention, an ultraviolet light-emitting diode includes: a substrate; an n-type semiconductor layer located on the substrate; a mesa arranged on the n-type semiconductor layer and including an active layer and a p-type semiconductor layer; an n-ohmic contact layer in contact with the n-type semiconductor layer; a p-ohmic contact layer in contact with the p-type semiconductor layer; an n-bump electrically connected to the n-ohmic contact layer; and a p-bump electrically connected to the p-ohmic contact layer, wherein the mesa includes a main branch and a plurality of sub-branches extending from the main branch, the n-ohmic contact layer surrounds the mesa and is sandwiched between the sub-branches, and the n-bump and the p-bump respectively cover the upper portion and side surfaces of the mesa.

[0025] In conventional UV LEDs, the p-bumps are placed on the upper portion of the mesa, preventing them from reflecting light emitted toward the side surfaces of the mesa. In contrast, in embodiments of the present invention, the side surfaces of the mesa are partially covered by the n-bumps and p-bumps. Therefore, these n-bumps and p-bumps can reflect UV light emitted toward the side surfaces of the mesa, allowing it to re-enter the substrate.

[0026] Furthermore, the mesas can be located not only under the p-bumps but also under the n-bumps, so that the mesas can be distributed over a wide area of ​​the substrate.

[0027] Furthermore, according to embodiments of the present invention, the mesa includes main branches and sub-branches, thereby increasing the surface area of ​​the mesa side surface. Consequently, the area between the mesa and the n-ohmic contact layer is increased, allowing ultraviolet light emitted toward the mesa side surface to re-enter the substrate through this area, thereby increasing light output.

[0028] Furthermore, the minimum width of the n-type semiconductor layer exposed between the sub-branches can be greater than or equal to the minimum width of the sub-branches. In conventional UV LEDs, the mesa width is typically formed to be relatively larger than the width of the exposed n-type semiconductor layer. However, in the present invention, the mesa width is formed to be narrower. This facilitates current dispersion within the mesa and further reduces the forward voltage.

[0029] In some embodiments, the minimum width of the main branch may be greater than the minimum width of the sub-branch. However, the present invention is not limited thereto, and the main branch and the sub-branch may also have the same width, and the sub-branch may also have a larger width.

[0030] In addition, the main branch may include: a first main branch extending along a side edge portion of the substrate; and a second main branch extending along another side edge portion adjacent to the side edge portion of the substrate, and the sub-branches may include sub-branches extending from the first main branch and sub-branches extending from the second main branch.

[0031] In this specification, a "main branch" refers to a branch that branches out into multiple branches at a point between its two ends, and a "sub-branch" refers to a branch that is connected to the main branch at one end and is free standing at the other end. Furthermore, a branch with two ends is considered a single branch, while "multiple branches" means there are three or more ends.

[0032] The sub-branches may be parallel to each other and branch off from the same side surface of the main branch.

[0033] Furthermore, the sub-branches may be parallel to a diagonal line of the substrate.

[0034] Furthermore, the sub-branches may have different lengths. Therefore, by adjusting the lengths of the sub-branches, the mesas can be arranged over a wider area of ​​the substrate.

[0035] Furthermore, the substrate may be a quadrilateral with four edge portions, and the shortest distance from each edge portion to the mesa is less than half the shortest distance from each edge portion to the center of the substrate. In existing UV LEDs, the mesa is positioned toward one edge portion of the substrate. However, in the UV LED of the present invention, the mesa can be positioned wider in the center of the substrate.

[0036] In addition, the ultraviolet light emitting diode may further include: an n pad metal layer covering the n ohmic contact layer; and a p pad metal layer covering the p ohmic contact layer, wherein the n bump and the p bump may be connected to the n pad metal layer and the p pad metal layer respectively.

[0037] In some embodiments, the n-ohmic contact layer may be a metal alloy layer including Cr, Ti, Al, and Au, the n-pad metal layer includes Ti layer / Au layer / Ti layer, and the n-pad metal layer is connected to the n-ohmic contact layer.

[0038] The UV LED may further include an insulating layer interposed between the n-pad metal layer, the p-pad metal layer, and the n-bump and the p-bump, and having an opening exposing the n-pad metal layer and the p-pad metal layer. The insulating layer may be formed, for example, as a single SiO2 layer or as multiple layers. In particular, the insulating layer may be a distributed Bragg reflector formed by alternating insulating layers with different refractive indices.

[0039] In addition, the openings are covered by the n-bump and the p-bump, respectively. Therefore, the n-pad metal layer and the p-pad metal layer exposed through the openings can be covered by the n-bump and the p-bump, respectively, and thus protected from external environments such as moisture.

[0040] In addition, the spacing distance between the n-ohmic contact layer and the mesa can be constant. However, the present invention is not necessarily limited thereto, and the spacing distance can also be adjusted to be different depending on the position.

[0041] In addition, the n-bumps and the p-bumps may be arranged parallel to each other.

[0042] In one embodiment, the mesa may include a protrusion on a side surface. The protrusion further increases the surface area of ​​the mesa side surface. Furthermore, the n-ohmic contact layer may be spaced apart from the mesa at a predetermined interval along the side surface of the mesa. Therefore, the n-ohmic contact layer is arranged according to the shape of the protrusion on the side surface of the mesa, thereby increasing the overall area of ​​the region between the n-ohmic contact layer and the mesa.

[0043] According to another embodiment of the present invention, an ultraviolet light-emitting diode includes: a substrate; an n-type semiconductor layer located on the substrate; a mesa arranged on the n-type semiconductor layer and including an active layer and a p-type semiconductor layer; an n-ohmic contact layer in contact with the n-type semiconductor layer; a p-ohmic contact layer in contact with the p-type semiconductor layer; an n-bump electrically connected to the n-ohmic contact layer; and a p-bump electrically connected to the p-ohmic contact layer, wherein the mesa includes a plurality of branches, the n-ohmic contact layer surrounds the mesa and is sandwiched between the branches, the n-bump and the p-bump respectively cover the upper portion and side surfaces of the mesa, and the p-bump covers at least two of the branches.

[0044] The branches may include a main branch and a plurality of sub-branches extending from the main branch.

[0045] Furthermore, the main branch may include: a first main branch extending along an edge portion of one side of the substrate; and a second main branch perpendicular to the first main branch.

[0046] Furthermore, the p-bump may completely cover the first main branch and partially cover the second main branch. Furthermore, a portion of the sub-branch may be separated from the p-bump and partially overlap with the n-bump.

[0047] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0048] Figure 1 is a schematic plan view for illustrating an ultraviolet light emitting diode according to an embodiment of the present invention, Figure 2 It is along Figure 1 The cross-sectional view is taken along the cutting line CC. Figure 3 FIG. 1 is a schematic plan view for explaining a table according to an embodiment of the present invention.

[0049] Reference Figure 1 、 Figure 2 and Figure 3 According to this embodiment, the ultraviolet light emitting diode includes a substrate 121, an n-type semiconductor layer 123, an active layer 125, a p-type semiconductor layer 127, an n-ohmic contact layer 129a, a p-ohmic contact layer 129b, an n-pad metal layer 133a, a p-pad metal layer 133b, an insulating layer 135, an n-bump 137a, a p-bump 137b, and an anti-reflection layer 139.

[0050] The substrate 121 is not limited as long as it is a substrate that can grow nitride-based semiconductors. For example, it can include a sapphire substrate, a silicon substrate, a silicon carbide substrate, or a heterogeneous substrate such as a spinel substrate, and can include the same type of substrate such as a gallium nitride substrate and an aluminum nitride substrate.

[0051] The n-type semiconductor layer 123 is located on the substrate 121. For example, the n-type semiconductor layer 123 may include an AlN buffer layer (approximately 3.79 μm) and an n-type AlGaN layer. The n-type AlGaN layer may include a lower n-type AlGaN layer (approximately 2.15 μm) with an Al molar ratio of 0.8 or more, an intermediate n-type AlGaN layer (approximately 1.7 nm) with an Al molar ratio of 0.7 to 0.8, and an upper n-type AlGaN layer with a thickness of approximately 66.5 nm. The n-type semiconductor layer 123 is formed as a nitride-based semiconductor having a band gap higher than that of the active layer, so that light generated in the active layer can be transmitted. In the case of growing the gallium nitride-based semiconductor layer on the sapphire substrate 121, in order to improve the crystal quality, the n-type semiconductor layer 123 may generally include multiple layers.

[0052] The mesa M is disposed on a portion of the n-type semiconductor layer 123. The mesa M includes an active layer 125 and a p-type semiconductor layer 127. Typically, after the n-type semiconductor layer 123, the active layer 125, and the p-type semiconductor layer 127 are sequentially grown, the p-type semiconductor layer 127 and the active layer 125 are patterned by a mesa etching process to form the mesa M.

[0053] The active layer 125 can be a single quantum well or multi-quantum well structure including a well layer and a barrier layer. The well layer can be formed using AlGaN or AlInGaN, and the barrier layer can be formed using AlGaN or AlInGaN having a band gap wider than the well layer. For example, each well layer can be formed to a thickness of about 3.1 nm using AlGaN having an Al mole ratio of about 0.5, and each barrier layer can be formed to a thickness of about 9 nm or more using AlGaN having an Al mole ratio of 0.7 or more. In particular, the first barrier layer can be formed to a thickness of more than 12 nm, that is, formed thicker than the other barrier layers. In addition, AlGaN layers with an Al mole ratio of 0.7 to 0.8 adjacent to the upper and lower well layers can be arranged to a thickness of about 1 nm respectively. However, considering the connection with the electron blocking layer, the Al mole ratio of the AlGaN layer adjacent to the last well layer can be greater than 0.8.

[0054] In addition, the p-type semiconductor layer 127 may include an electron blocking layer and a p-type GaN contact layer. The electron blocking layer prevents electrons from overflowing from the active layer into the p-type semiconductor layer, thereby increasing the recombination rate of electrons and holes. The electron blocking layer may be formed, for example, using p-type AlGaN with an Al molar ratio of approximately 0.8 and may be formed to a thickness of, for example, 55 nm. In addition, the p-type GaN contact layer may be formed to a thickness of approximately 300 nm.

[0055] The mesa M includes a plurality of branches M1, M2, S1, S2, S3, and S4. For example, the mesa M may include main branches M1 and M2 and sub-branches S1, S2, S3, and S4. Figure 5 As shown, the mesa M may include a first main branch M1 extending along a side edge of the substrate 121 or the n-type semiconductor layer 123; and a second main branch M2 extending along another side edge adjacent to the first side edge. For example, sub-branches S1 and S2 may extend from the first main branch M1, and sub-branches S3 and S4 may extend from the second main branch M2. For ease of illustration, the first main branch M1 and the second main branch M2 are described separately, but they are a single main branch. Alternatively, the second main branch M2 may be omitted.

[0056] Furthermore, the sub-branches S1, S2, S3, and S4 may have different lengths and may be parallel to each other. In particular, the sub-branches S1, S2, S3, and S4 may be arranged parallel to the diagonal lines of the substrate 121. Figure 5 As clearly shown in FIG, the main branches M1, M2 and the sub-branches S1, S2, S3, and S4 are arranged across a relatively wide area of ​​the substrate 121. For example, the substrate 121 is a quadrangular shape having four edge portions, such as a rectangle. The shortest distance from each edge portion of the substrate 121 to the mesa M can be less than 1 / 2 of the shortest distance from each edge portion to the center of the substrate 121.

[0057] In addition, refer to Figure 3 The minimum width W2 of the n-type semiconductor layer 123 exposed between the sub-branches S1, S2, S3, and S4 can be greater than 1 / 2 of the minimum width W1 of the sub-branches S1, S2, S3, and S4. Furthermore, the minimum width W2 of the n-type semiconductor layer 123 exposed between the sub-branches S1, S2, S3, and S4 can be greater than or equal to the minimum width W1 of the sub-branches S1, S2, S3, and S4. Compared to the prior art, the widths of the sub-branches S1, S2, S3, and S4 are formed to be relatively small, and the width of the n-type semiconductor layer 123 exposed between the sub-branches S1, S2, S3, and S4 is relatively increased. By arranging the sub-branches S1, S2, S3, and S4 across a wider area of ​​the substrate 121, rather than forming the sub-branches S1, S2, S3, and S4 to be relatively narrow, the side surface area of ​​the mesa M is increased.

[0058] The main branches M1 and M2 may have a width wider than the sub-branches S1, S2, S3, and S4, but are not limited thereto. The main branches M1 and M2 may have a width equal to or narrower than the sub-branches S1, S2, S3, and S4.

[0059] Refer again Figure 1 and Figure 2 An n-ohmic contact layer 129a is disposed on the n-type semiconductor layer 123 exposed around the mesa M. The n-ohmic contact layer 129a can be formed by stacking multiple metal layers and then alloying them using a rapid thermal alloying (RTA) process. For example, the n-ohmic contact layer 129a can be sequentially stacked with Cr / Ti / Al / Ti / Au and then alloyed using an RTA process, such as at 935°C for several seconds or tens of seconds. As a result, the n-ohmic contact layer 129a becomes an alloy layer containing Cr, Ti, Al, and Au.

[0060] The n-ohmic contact layer 129a surrounds the mesa M along its perimeter. Furthermore, the n-ohmic contact layer 129a is also interposed in the region between the sub-branches S1, S2, S3, and S4. The n-ohmic contact layer 129a may be spaced a predetermined distance apart from the mesa M and formed over a majority of the n-type semiconductor layer 123. The n-ohmic contact layer 129a is formed along the side surface of the mesa M, thereby forming a region without the n-ohmic contact layer 129a between the mesa M and the n-ohmic contact layer 129a. Light emitted toward the side surface of the mesa M through this region may be incident again on the n-type semiconductor layer 123 and emitted to the outside through the substrate 121. The spacing distance between the n-ohmic contact layer 129a and the mesa M may be constant along the perimeter of the mesa M, but is not necessarily limited thereto.

[0061] After forming the n-ohmic contact layer 129a, a p-ohmic contact layer 129b is formed on the mesa M. The p-ohmic contact layer 129b can be formed, for example, by depositing Ni / Au and then performing an RTA process at a temperature of approximately 590°C for approximately 80 seconds. The p-ohmic contact layer 129b makes ohmic contact with the p-type semiconductor layer 127 and covers a majority of the upper region of the mesa M, for example, at least 80%.

[0062] In addition, an n-pad metal layer 133a and a p-pad metal layer 133b are formed on the n-ohmic contact layer 129a and the p-ohmic contact layer 129b, respectively. The n-pad metal layer 133a and the p-pad metal layer 133b can be formed as the same metal layer in the same process. For example, the n-pad metal layer 133a and the p-pad metal layer 133b can be formed as a Ti layer. / Au layer / Ti layer

[0063] Conventional technology requires a step adjustment layer under the n-bump for thermosonic bonding, but the embodiments of the present invention utilize solder paste or AuSn bonding, eliminating the need for a step adjustment layer. Therefore, the n-pad metal layer 133a can directly connect to the n-ohmic contact layer 129a.

[0064] In addition, Figure 2 (a) shows that the n-pad metal layer 133a and the p-pad metal layer 133b are arranged on the n-ohmic contact layer 129a and the p-ohmic contact layer 129b respectively with the same area as the n-ohmic contact layer 129a and the p-ohmic contact layer 129b, but the present invention is not limited thereto. The n-pad metal layer 133a and the p-pad metal layer 133b may have a smaller area than the n-ohmic contact layer 129a and the p-ohmic contact layer 129b and be arranged on the n-ohmic contact layer 129a and the p-ohmic contact layer 129b. In contrast, as shown in FIG. Figure 2 As shown in (b), the n-pad metal layer 133a and the p-pad metal layer 133b can cover the upper surface and side surface of the n-ohmic contact layer 129a and the p-ohmic contact layer 129b, respectively. Since the n-pad metal layer 133a and the p-pad metal layer 133b cover not only the upper surface of the n-ohmic contact layer 129a and the p-ohmic contact layer 129b but also their side surfaces, when solder or AuSn is bonded, the n-ohmic contact layer 129a and the p-ohmic contact layer 129b can be better protected from the effects of the solder or the like.

[0065] Insulating layer 135 covers n-pad metal layer 133a and p-pad metal layer 133b. However, insulating layer 135 includes opening 135a that exposes n-pad metal layer 133a, and opening 135b that partially exposes p-pad metal layer 133b above mesa M. Opening 135a overlaps with n-ohmic contact layer 129a, and opening 135b overlaps with p-ohmic contact layer 129b. Openings 135a and 135b may be arranged offset toward opposing edges.

[0066] N-bump 137a covers opening 135a and is connected to n-pad metal layer 133a through opening 135a. N-bump 137a is electrically connected to n-type semiconductor layer 123 through n-pad metal layer 133a and n-ohmic contact layer 129a.

[0067] The p-bump 137b covers the opening 135b and is connected to the p-pad metal layer 133b through the opening 135b. The p-bump 137b is electrically connected to the p-type semiconductor layer 127 through the p-pad metal layer 133b and the p-ohmic contact layer 129b.

[0068] For example, the n-bump 137a and the p-bump 137b may be formed using Ti / Au / Cr / Au. Figure 1As shown, n-bump 137a and p-bump 137b can be arranged parallel to each other. The openings 135a and 135b are covered by n-bump 137a and p-bump 137b, thereby preventing moisture or solder from penetrating from the outside through the openings 135a and 135b, thereby improving reliability.

[0069] Furthermore, the n-bump 137 a and the p-bump 137 b partially cover the side surface of the mesa M. The n-bump 137 a and the p-bump 137 b have reflectivity for ultraviolet rays, and thus can reflect light emitted toward the side surface of the mesa M and allow the light to enter the mesa M again.

[0070] In addition, if Figure 2 As shown, due to the height difference between the mesa M and the n-pad metal layer 133 a , the top surfaces of the n-bump 137 a and the p-bump 137 b may be uneven.

[0071] Antireflection layer 139 is disposed on the light-emitting surface side of substrate 121. Antireflection layer 139 is formed of a transparent insulating layer such as SiO2, for example, with a thickness that is an integral multiple of ¼ of the wavelength of ultraviolet light. Alternatively, a bandpass filter composed of layers with different refractive indices can be used as antireflection layer 139.

[0072] Figure 4 FIG. 1 is a schematic plan view for explaining an ultraviolet light emitting diode according to another embodiment of the present invention.

[0073] Reference Figure 4 The light-emitting diode according to this embodiment is substantially similar to the light-emitting diode described above, with the difference being that the number of sub-branches S1 to S6 increases. As the number of sub-branches S1 to S6 increases, the width of the sub-branches S1 to S6 becomes smaller. The sub-branches S1 to S6 may have substantially similar widths, and the minimum width W1 of the sub-branches S1 to S6 may be less than twice the minimum width W2 of the n-type semiconductor layer 123 exposed between the sub-branches. Furthermore, the minimum width W1 of the sub-branches S1 to S6 may be less than or equal to the minimum width W2 of the n-type semiconductor layer 123 exposed between the sub-branches. In addition, the widths of the first main branch M1 and the second main branch M2 may be greater than the widths of the sub-branches S1 to S6, but are not necessarily limited thereto, and may also be less than or equal to the widths of the sub-branches S1 to S6.

[0074] Since the structure is substantially similar to the ultraviolet light emitting diode of the above-mentioned embodiment except for the shape of the mesa M, detailed description is omitted to avoid repetition and the drawings are briefly shown.

[0075] Figure 5 FIG. 1 is a schematic plan view for explaining an ultraviolet light emitting diode according to another embodiment of the present invention.

[0076] Reference Figure 5 The ultraviolet light emitting diode according to this embodiment is different from the reference Figures 1 to 3 The aforementioned ultraviolet light emitting diodes are substantially similar, with the difference being that a protrusion P is formed on the side surface of the mesa M. The protrusion P can be formed together with the mesa M during the mesa etching process.

[0077] Since the protrusions P are formed on the side surface of the mesa M, the surface area of ​​the side surface of the mesa M can be increased.

[0078] In addition, the n-ohmic contact layer 129a may be formed to be spaced apart from the side surface of the mesa M by a predetermined interval, and thus may have a recessed portion corresponding to the protrusion P along the side surface shape of the mesa M. The p-ohmic contact layer 129b may also be formed to have a protrusion along the side surface shape of the mesa M.

[0079] Figure 6 It is a schematic cross-sectional view for explaining how to mount an ultraviolet light emitting diode according to an embodiment of the present invention on a substrate.

[0080] Reference Figure 6 The ultraviolet light emitting diode is flip-chip bonded on a mounting substrate 200. The mounting substrate 200 may have electrode pads 201a and 201b on an insulating substrate such as AlN.

[0081] N-bump 137a and p-bump 137b can be bonded to electrode pads 201a and 201b of mounting substrate 200 via solder paste 203a and 203b. Since the UV LEDs are bonded via solder paste 203a and 203b, unlike conventional thermosonic bonding, the top end surfaces of n-bump 137a and p-bump 137b can be at different heights.

[0082] Although the case of bonding using solder paste is described in this embodiment, the ultraviolet light emitting diode may be bonded to the mounting substrate 200 by solder bonding using AuSn.

[0083] The above embodiments can be modified and altered in various ways without departing from the technical concept based on the scope of the claims of the present invention, and the present invention includes all technical concepts based on the scope of the claims.

Claims

1. An ultraviolet light emitting diode, emitting deep ultraviolet light with a wavelength of less than 300 nm, comprising: substrate; An n-type semiconductor layer is located on the substrate; a mesa disposed on the n-type semiconductor layer and comprising an active layer and a p-type semiconductor layer; an n-ohmic contact layer, contacting the n-type semiconductor layer; A p-ohmic contact layer, contacting the p-type semiconductor layer; an n bump electrically connected to the n ohmic contact layer; as well as A p-bump electrically connected to the p-ohmic contact layer, The table includes a main branch and a plurality of sub-branches extending from the main branch. The main branch has a width wider than the plurality of sub-branches, The n-bump and the p-bump respectively cover the upper portion and the side surface of the mesa to reflect ultraviolet rays from the side surface of the mesa. The n-bump and the p-bump are arranged at intervals between the n-ohmic contact layer and the mesa, thereby reflecting ultraviolet rays traveling toward the n-ohmic contact layer from side surfaces of the mesa.

2. The ultraviolet light emitting diode according to claim 1, wherein A minimum width of the n-type semiconductor layer exposed between the plurality of sub-branches is greater than or equal to a minimum width of the plurality of sub-branches.

3. The ultraviolet light emitting diode according to claim 1, wherein The multiple sub-branches are parallel to each other.

4. The ultraviolet light emitting diode according to claim 3, wherein: The plurality of sub-branches are parallel to a diagonal line of the substrate.

5. The ultraviolet light emitting diode according to claim 1, wherein The plurality of sub-branches have different lengths from each other.

6. The ultraviolet light emitting diode according to claim 1, wherein: The substrate is in a quadrangular shape having four edge portions, and the shortest distance from each edge portion to the mesa is less than 1 / 2 of the shortest distance from each edge portion to the center of the substrate.

7. The ultraviolet light emitting diode according to claim 1, further comprising: an n pad metal layer covering the n ohmic contact layer; and a p pad metal layer covering the p ohmic contact layer, The n-bump and the p-bump are connected to the n-pad metal layer and the p-pad metal layer respectively.

8. The ultraviolet light emitting diode according to claim 7, wherein: The n-ohmic contact layer is a metal alloy layer containing Cr, Ti, Al and Au. The n pad metal layer includes a Ti layer / Au layer / Ti layer, The n pad metal layer is connected to the n ohmic contact layer.

9. The ultraviolet light emitting diode according to claim 8, further comprising: The insulating layer is interposed between the n-pad metal layer, the p-pad metal layer, and the n-bump and the p-bump, and has an opening for exposing the n-pad metal layer and the p-pad metal layer.

10. The ultraviolet light emitting diode according to claim 9, wherein: The openings are covered by the n-bump and the p-bump respectively.

11. The ultraviolet light emitting diode according to claim 1, wherein: The spacing distance between the n-ohmic contact layer and the mesa is constant.

12. The ultraviolet light emitting diode according to claim 1, wherein: The n-bumps and the p-bumps are arranged parallel to each other.

13. The ultraviolet light emitting diode according to claim 1, wherein: The n-ohmic contact layer is spaced apart from the mesa at a predetermined interval along a side surface of the mesa.

14. The ultraviolet light emitting diode according to claim 1, wherein: The n-type semiconductor layer is formed using a nitride-based semiconductor having a band gap higher than that of the active layer, so that light generated in the active layer can be transmitted.

15. The ultraviolet light emitting diode according to claim 1, wherein: The active layer of the mesa includes a barrier layer, and the barrier layer is formed using AlGaN with a molar ratio of Al being greater than or equal to 0.7.

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