CN114188454A

CN114188454A - Ultraviolet light-emitting diode and light-emitting device

Info

Publication number: CN114188454A
Application number: CN202111470298.9A
Authority: CN
Inventors: 江宾; 臧雅姝; 黄敏; 彭康伟; 曾炜竣; 曾明俊; 陈思河; 龙思怡
Original assignee: Xiamen Sanan Optoelectronics Technology Co Ltd
Current assignee: Quanzhou Sanan Semiconductor Technology Co Ltd
Priority date: 2021-12-03
Filing date: 2021-12-03
Publication date: 2022-03-15
Anticipated expiration: 2041-12-03
Also published as: CN114188454B; CN117613165A

Abstract

The invention provides an ultraviolet light emitting diode and a light emitting device, wherein the ultraviolet light emitting diode comprises: a semiconductor layer sequence comprising a first semiconductor layer, an active layer and a second semiconductor layer stacked in this order and having one or more mesas extending the first semiconductor layer from the second semiconductor layer, the mesas exposing the first semiconductor layer, wherein the first semiconductor layer has a first conductivity and the second semiconductor layer has a second conductivity, the first conductivity being different from the second conductivity; the first ohmic contact electrode is positioned on the table board and forms ohmic contact with the first semiconductor layer; the second ohmic contact electrode is positioned on the second semiconductor layer and forms ohmic contact with the second semiconductor layer; the connecting electrode is formed on the second ohmic contact electrode and is electrically connected with the second semiconductor layer through the ohmic contact electrode; the edge of the connection electrode is positioned inside the edge of the second ohmic contact electrode with a certain distance therebetween.

Description

Ultraviolet light-emitting diode and light-emitting device

Technical Field

The invention relates to the technical field of semiconductors, in particular to an ultraviolet light-emitting diode and a light-emitting device.

Background

The light emitting diode emitting ultraviolet rays having a wavelength in the range of 200 to 300nm can be used for various purposes including a sterilization device, a water or air purification device, a high-density optical recording device, and the like.

Fig. 1 shows a schematic cross-sectional structure of a conventional uv led, which includes a substrate 110, a semiconductor layer sequence 120, a first ohmic contact electrode 131, a second ohmic contact electrode 132, a first connection electrode 133, a second connection electrode 134, a first pad 151, and a second pad 152, wherein the semiconductor layer sequence 120 includes a first semiconductor layer 121, an active layer 122, and a second semiconductor layer 123 sequentially stacked on a surface of the substrate 110, and has one or more mesas extending from the second semiconductor layer to expose the first semiconductor layer, the first ohmic contact electrode 131 forms an ohmic contact with the first semiconductor layer on the mesas, and the second ohmic contact electrode forms an ohmic contact electrode with the second semiconductor layer.

Unlike a near ultraviolet light emitting diode or a blue light emitting diode, a light emitting diode emitting relatively deep ultraviolet light includes a semiconductor layer containing Al such as AlGaN, and the lateral expansion rate of carriers thereof is relatively low, and thus current concentration is likely to occur at a position of a mesa edge, which in turn causes a phenomenon of local overheating and electrode burn, resulting in a reduction in reliability and a reduction in lifetime of an LED chip. As shown in fig. 2, a point explosion occurs at the edge of the ohmic contact electrode.

Disclosure of Invention

One objective of the present invention is to provide an ultraviolet light emitting diode, which can effectively improve the reliability of the ultraviolet light emitting diode.

The invention provides an ultraviolet light-emitting diode, comprising: a semiconductor layer sequence comprising a first semiconductor layer, an active layer and a second semiconductor layer stacked in this order and having one or more mesas extending the first semiconductor layer from the second semiconductor layer, the mesas exposing the first semiconductor layer, wherein the first semiconductor layer has a first conductivity and the second semiconductor layer has a second conductivity, the first conductivity being different from the second conductivity; the first ohmic contact electrode is positioned on the table board and forms ohmic contact with the first semiconductor layer; the second ohmic contact electrode is positioned on the second semiconductor layer and forms ohmic contact with the second semiconductor layer; the connecting electrode is formed on the second ohmic contact electrode and is electrically connected with the second semiconductor layer through the ohmic contact electrode; the edge of the connection electrode is positioned inside the edge of the second ohmic contact electrode with a certain distance therebetween.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts; in the following description, the drawings are illustrated in a schematic view, and the drawings are not intended to limit the present invention.

Fig. 1 is a schematic cross-sectional view of a conventional uv led.

Fig. 2 is an enlarged view of a portion of the light emitting diode shown in fig. 1, showing the appearance of a pop at the mesa edge of the chip.

Fig. 3 is a top view of an ultraviolet light emitting diode according to a first embodiment of the present invention.

Fig. 4 is a schematic longitudinal sectional view taken along the section line a-a of fig. 3.

Fig. 5 is a top view of an n-type ohmic contact electrode of an ultraviolet light emitting diode according to a first embodiment of the present invention.

Fig. 6 is a top view of a connection electrode of an ultraviolet light emitting diode according to a first embodiment of the present invention.

Fig. 7 is a schematic cross-sectional view of an ultraviolet light emitting diode according to a second embodiment of the present invention.

Fig. 8 and 9 are top views illustrating a reflective layer of an ultraviolet light emitting diode according to a first embodiment of the present invention, in which fig. 8 illustrates a reflective region overlapping with an active layer, and fig. 9 illustrates a region not overlapping with the active layer.

Fig. 10 shows the absorption curve of ITO.

Fig. 11 is a top view of an ultraviolet light emitting diode provided by a third embodiment of the present invention.

Fig. 12 is a schematic longitudinal sectional view taken along the section line B-B of fig. 11.

Fig. 13 is a plan view of a connection electrode of an ultraviolet light emitting diode according to a third embodiment of the present invention.

Fig. 14 shows a reflectance curve of a reflective layer of an ultraviolet light emitting diode according to a third embodiment of the present invention.

Fig. 15 shows a luminance scatter diagram of an ultraviolet light emitting diode according to a second embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments; the technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other; all other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 3 and 4, fig. 3 is a schematic top view of a light emitting diode according to a first embodiment of the present invention, and fig. 4 is a schematic longitudinal sectional view taken along a line a-a of fig. 3. The light emitting diode includes a substrate 110, a semiconductor layer sequence 120 formed on an upper surface of the substrate, a first ohmic contact electrode 131, a second ohmic contact electrode 132, a connection electrode 134, a first bonding pad 151, a second bonding pad 152, and an insulating layer 160. In the present embodiment, the light emitting diode is a flip chip having a light extraction surface S12 on the substrate side.

The substrate 110 serves to support the semiconductor layer sequence 110. The substrate has a first surface S11 and a light extraction surface S12. The first surface S11 is a semiconductor layer formation surface. The light extraction surface S12 is a surface on the opposite side of the first surface S11. The substrate 110 may be, for example, a sapphire substrate, or a growth substrate on which a group III nitride semiconductor can be formed. Preferably, the substrate is a transparent material or a translucent material, and in order to enhance the light extraction efficiency of the light S12, especially the effect of light extraction from the substrate surface, the substrate 110 is preferably thickly disposed, and the thickness thereof may be 250 μm to 900 μm.

Preferably, the first surface S11 of the substrate 110 is formed with a layer of aluminum nitride as the underlayer 111, and the underlayer 111 is in contact with the first surface S11 and preferably has a thickness of 1 μm or less. Further, the aluminum nitride underlayer 111 includes a low-temperature layer, an intermediate layer, and a high-temperature layer in this order from the substrate 110 side, and a semiconductor layer with excellent crystallinity can be grown. In other preferred embodiments, a series of holes are formed in the aluminum nitride bottom layer to facilitate stress relief of the semiconductor layer sequence. The series of holes are preferably a series of elongated holes extending along the thickness of the aluminum nitride, and the depth thereof may be, for example, 0.5 to 1.5 μm.

The semiconductor layer sequence 120 is formed on the aluminum nitride bottom layer 111, and sequentially includes a first semiconductor layer 121, a second semiconductor layer 123, and an active layer 122 therebetween, for example, the first semiconductor layer 121 is an N-type layer, and the second semiconductor layer 123 is a P-type layer, which may also be inverted. The first semiconductor layer 121 is, for example, an n-type AlGaN layer. The active layer 122 is a layer that emits ultraviolet light, and includes a well layer and a barrier layer, the number of repetitions of the well layer and the barrier layer being, for example, 1 or more and 10 or less, the well layer being, for example, an AlGaN layer, and the barrier layer being, for example, an AlGaN layer, but the Al composition of the well layer being lower than that of the barrier layer. The second semiconductor layer 123 is, for example, a p-type AlGaN layer or a p-type GaN layer, or a layer in which a p-type AlGaN layer and a p-type GaN layer are stacked in this order. In this embodiment, the second semiconductor layer 123 includes a p-type GaN surface layer, the thickness of the p-type GaN surface layer is 5 to 50nm, the internal quantum light emitting efficiency and the external quantum light emitting efficiency of the device can be considered by providing the thin film GaN, and specifically, the p-type GaN layer within the thickness range contributes to lateral current spreading of p-side current and does not cause too much light absorption.

In a preferred embodiment, the edge 121-1 of the first semiconductor layer is at a distance from the edge 110-1 of the substrate, as shown in fig. 1 and 2, and the sidewall of the first semiconductor layer is located inside the sidewall of the substrate. In the ultraviolet LED chip, the increase of the thickness of the substrate 110 is beneficial to improving the light emitting efficiency, but the increase of the thickness of the substrate also increases the difficulty in cutting the substrate, so that in this embodiment, a certain distance is reserved between the edge 121-1 of the first semiconductor layer and the edge 110-1 of the substrate, so that the semiconductor layer sequence is not damaged during the cutting of the substrate, and the reliability of the light emitting diode is improved. Preferably, the distance is 2 μm or more, for example, 4 to 10 μm.

The second semiconductor layer 123 and the active layer 122 are removed from the semiconductor layer sequence 120, exposing the first semiconductor layer 121, and forming one or more mesas 120A, as shown in fig. 3 and 4. In this embodiment, it is preferable to form a plurality of mesas 120A, the plurality of mesas 120A are used to form the first ohmic contact electrode 131, the distribution of the mesas 120A is not limited to that shown in fig. 4, and may be designed according to an actual chip size and shape, and the plurality of mesas 120A may be connected together or separated from each other. In the ultraviolet light emitting diode, since the Al content of the n-type semiconductor layer is generally high and diffusion of current is difficult, and thus current cannot flow uniformly in the active layer and the p-type semiconductor layer, the area of the mesa 120A of the light emitting diode of the present embodiment is preferably set to be 20% or more and 70% or less of the area of the semiconductor layer sequence 120 and relatively uniformly distributed in the semiconductor layer sequence. Preferably, the shortest distance from each region where the active layer 122 is maintained to the mesa is preferably 4 to 15 μm, so that the current spreading of the n-type semiconductor layer can be protected, which is beneficial to improving the internal quantum efficiency of the light emitting diode, and is beneficial to reducing the forward voltage of the light emitting diode. When the area of the mesa region is too large, the area loss of the active region of the light emitting diode is too large, which is not favorable for improving the light emitting efficiency of the light emitting diode.

As shown in fig. 5 and 3, the first ohmic contact electrode 131 is formed on the mesa 120A in direct contact with the first semiconductor layer 121. The first ohmic contact electrode 131 is selected from one or more of Cr, Pt, Au, Ni, Ti, and Al. Since the first semiconductor layer has a high Al composition, the first ohmic contact electrode 131 needs to be alloyed at a high temperature after being deposited on the mesa, so as to form a good ohmic contact with the first semiconductor layer, which may be, for example, a Ti-Al-Au alloy, a Ti-Al-Ni-Au alloy, a Cr-Al-Ti-Au alloy, a Ti-Al-Au-Pt alloy, or the like.

The second ohmic contact electrode 132 is contactingly formed on the surface of the second semiconductor layer 123 to form an ohmic contact with the second semiconductor layer. Preferably, the material of the ohmic contact electrode 132 may be an oxide transparent conductive material or a metal alloy such as NiAu, NiAg, NiRh, etc. In one embodiment, the distance D1 between the edge of the second ohmic contact electrode 132 and the edge of the second semiconductor layer 123 is preferably 2 to 15 μm, for example, 5 to 10 μm, which can reduce the risk of the light emitting diode 1 from generating electrical leakage (also called reverse leakage; abbreviated as IR) and electrostatic discharge (ESD) abnormality. Further, the distance between the end point or edge of the upper surface of the second ohmic contact electrode 132 and the edge of the first ohmic contact electrode 131 is 4 μm or more, and when the distance is excessively small, a phenomenon of leakage easily occurs. In some embodiments, the end point or edge of the upper surface of the second ohmic contact electrode 132 is spaced apart from the edge of the first ohmic contact electrode by 4 μm or more and 10 μm or less. The interval between the end point or edge of the upper surface of the second ohmic contact electrode 132 and the edge of the first ohmic contact electrode 131 includes an interval between the first ohmic contact electrode 131 and the edge of the upper surface of the second conductive type semiconductor layer 123 of 2 μm or more, and an interval between the second ohmic contact electrode 132 and the edge of the upper surface of the second conductive type semiconductor layer 123 of 2 μm or more. With such a configuration, the second ohmic contact electrode 132 can be spaced from the mesa on the epitaxial structure 20, thereby preventing the light emitting diode from leakage and ESD abnormality. Meanwhile, a certain distance between the second insulating layer 33 and the mesa on the epitaxial structure 20 can be ensured, and the etching of the insulating layer with sufficient thickness on the sidewall of the epitaxial structure 20 is realized, so as to ensure that the light emitting diode 1 has better insulating protection and anti-leakage performance.

The second connection electrode 134 is formed on the second ohmic contact electrode 132 for diffusing current to the entire light emitting region. The connection electrode 134 is preferably a multi-layered metal stack, for example, an adhesion layer and a conductive layer are sequentially deposited on the ohmic contact electrode 132. The adhesion layer may be a Cr metal layer, the thickness of which is usually 1 to 10nm, and the conductive layer may be an Al metal layer, the thickness of which may be more than 100nm, for example, 200nm to 500nm, on one hand, Al has a good conductive layer, on the other hand, Al has a high reflectance to ultraviolet light, and preferably, the reflectance of the conductive layer to light emitted by the active layer 122 is more than 70%. Furthermore, a stress buffer layer is preferably inserted into the conductive layer, and may be, for example, an Al/Ti alternating layer. Further, an etch stop layer Pt, an adhesion layer Ti, or the like may be formed on the conductive layer. Preferably, the first metal flow spreading layer 133 is formed on the first ohmic contact electrode 131, as shown in fig. 4. The first metal extension layer 133 may be formed in the same process as the second metal extension layer 134, and has the same metal stack structure. Preferably, the first metal extension layer 133 completely covers the first ohmic contact electrode 131, on one hand, the height of the mesa region may be increased, and on the other hand, the first ohmic contact electrode 131 may be protected.

In the deep ultraviolet light emitting diode structure, the lateral expansion rate of carriers of the semiconductor layer is relatively low, so that current concentration is likely to occur at the edge (close to the mesa) of the second ohmic contact electrode, and further, local overheating and electrode burning phenomena are caused, thereby causing the reliability of the LED chip to be weakened and the service life to be shortened. Therefore, in a preferred embodiment, the connecting electrode 134 is recessed compared to the second ohmic contact electrode 132, i.e. the edge 134-1 of the connecting electrode 134 is located inside the edge 132-1 of the second ohmic contact electrode 132, and a distance D5 is provided therebetween, so as to adjust the current spreading and reduce the failure rate of the product due to excessive edge current accumulation. Preferably, the distance D5 is greater than or equal to 3 μm, and more preferably 5 to 15 μm, so that a sufficiently large distance is ensured between the second ohmic contact electrode 132 and the connection electrode 134 at the edge of the mesa, the phenomenon that the ohmic contact electrode of the deep ultraviolet light emitting diode near the mesa is burnt is improved, the burn ratio of the product in the aging process is reduced, and the aging reliability of the deep ultraviolet product is improved.

The insulating layer 160 is formed on the connection electrode 134 and on the side of the semiconductor layer sequence and on the side S13 of the mesa 120A, insulating the first connection electrode 133 from the second connection electrode 134. The insulating layer 160 has a first opening 171 and a second opening 172 exposing the first connection electrode 133 and the second connection electrode 134. The material of the insulating layer 160 includes a non-conductive material. The non-conductive material is preferably an inorganic material or a dielectric material. The inorganic material comprises silica gel or glass and the dielectric material comprises alumina, silicon nitride, silicon oxide, titanium oxide, or magnesium fluoride. For example, the insulating layer 160 may be silicon dioxide, silicon nitride, titanium oxide, tantalum oxide, niobium oxide, barium titanate, or a combination thereof, which may be, for example, a bragg reflector (DBR) formed by repeatedly stacking two materials.

The first pads 151 and the second pads 152 are positioned on the insulating layer 160, the first pads 151 are electrically connected to the first connection electrodes 133 through the first openings 171, and the second pads 152 are electrically connected to the second connection electrodes 134 through the second openings 172. The first pad 41 and the second pad 42 may be collectively formed using the same material in the same process, and thus may have the same layer configuration. The material of the first and second bonding pads can be one or more selected from Cr, Pt, Au, Ni, Ti, Al and AuSn.

Fig. 3 is a schematic diagram showing a simple flow of current after the light emitting diode is powered on, when the light emitting diode shown in fig. 4 is powered on, the current L1 injected through the first pad flows preferentially from the nearest distance to the active layer, the current density is strongest in the edge region near the mesa; the current L2 injected from the second pad flows first into the second ohmic contact electrode 132 through the second connection electrode, since the second connection electrode 134 is recessed with respect to the second ohmic contact electrode 132, only a portion of the current L23 reaches the edge region of the second semiconductor layer after passing through the lateral extension of the second ohmic contact electrode, therefore, the current is prevented from being gathered at the edge area of the second ohmic contact electrode close to the table top, the problem that the ohmic contact electrode of the deep ultraviolet light-emitting diode is burnt at the position close to the table top is effectively solved, and the aging reliability of the deep ultraviolet product is improved.

Fig. 7 is a schematic cross-sectional view of a second embodiment of the present invention, and reference is made to fig. 3 for a corresponding top view. The light emitting diode of the present embodiment is similar to the light emitting diode disclosed in the first embodiment, except that the ultraviolet light emitting diode disclosed in the present embodiment further improves the light emitting efficiency of the light emitting diode by providing a high reflection structure. Specifically, the thickness of the second ohmic contact electrode 132 is preferably 30nm or less, and the light absorption rate of the layer is reduced as much as possible. By arranging the thin film type transparent or semitransparent conductive layer as the contact electrode, on one hand, good ohmic contact can be formed between the thin film type transparent or semitransparent conductive layer and the second semiconductor layer, and on the other hand, the phenomenon that the light absorption effect is obviously reduced due to overlarge thickness is avoided. In a preferred embodiment, the wavelength emitted by the active layer is less than 280nm, the ohmic contact electrode 132 is ITO, the thickness is 5-20 nm, for example, 10-15 nm, and the absorption rate of the ITO layer to the light emitted by the active layer can be reduced to less than 40%.

Further, the insulating layer 160 of the present embodiment is preferably a reflective insulating layer. As shown in the figure, the light emitting diode has a mesa structure with a large area, and the second connection electrode 134 is only partially formed on the second ohmic contact electrode 132, so that the light emitting efficiency of the light emitting diode can be effectively improved by setting the insulating layer 160 to be a highly reflective structure. Fig. 8 and 9 show the reflective region of the ultraviolet light emitting diode according to this embodiment, wherein the hatched portion in fig. 8 represents the reflective region overlapping with the active layer, specifically, the region between the edge 123-1 of the second semiconductor layer and the edge 134-1 of the second connection electrode, and the light emitted from the active layer to the electrode side corresponding to this portion can directly pass through the reflective layer for reflection, and is prevented from being absorbed by the electrode below. Preferably, the area occupies 5 to 20% of the area of the upper surface of the substrate, and may be, for example, 10%. The hatched portions in fig. 9 indicate regions not overlapping with the active layer, including a region between the outer edge 134-1 of the second connection electrode and the edge 110-1 of the substrate and a region between the inner edge 134-2 of the second connection electrode and the edge 123-1 of the second semiconductor layer, i.e., a region near the mesa, which preferably occupies 15 to 40% of the area of the upper surface of the substrate, for example, 25%.

Fig. 10 shows the absorption rate of ITO with different thicknesses, and when ITO is used as the current spreading layer, a sufficient thickness is required, generally more than 100nm, for example, 110nm, and the light yield for the ultraviolet wavelength is high, so that the light emitting efficiency of the light emitting diode is difficult to be improved. The ohmic contact electrode 132 of the present embodiment has a thin film structure with a thickness of 30nm or less, and is used only for forming ohmic contact with the second semiconductor layer, thereby reducing absorption of the ohmic contact electrode 133 to the light emitted from the active layer, for example, when ITO with a thickness of 11nm is used, the absorption rate is 30% or less with respect to ultraviolet light with a thickness of 310nm or less, and at the same time, a connection electrode with a high reflectance is used as a current spreading layer, thereby achieving both current spreading and current reflection. Further, the insulating layer 260 is configured to have a high reflection structure, so that the region not covered by the connection electrode can be reflected by the insulating layer, thereby further improving the light emitting efficiency of the light emitting diode.

Referring to fig. 11 and 12, fig. 11 is a schematic top view of a light emitting diode according to a second embodiment of the present invention, and fig. 12 is a schematic longitudinal sectional view taken along line B-B of fig. 11. The present embodiment discloses an ultraviolet light emitting diode, which is different from the second embodiment in that: the connection electrode 134 is of a dense point structure and is matched with the metal reflective layer, so that the light emitting efficiency of the light emitting diode is further improved.

In the deep ultraviolet light emitting diode structure, aluminum has the best reflection effect, but pure aluminum Al is in contact with ITO and has the conditions of poor adhesion, large contact resistance and the like, so Cr is arranged between ITO and Al as an adhesion layer, and the reflection effect is poor. To solve this problem, this embodiment discloses an ultraviolet light emitting diode, which uses Al as the reflective layer 143, and a transparent adhesive layer 163 is disposed between the ohmic contact electrode and the Al reflective layer.

Specifically, the ultraviolet light emitting diode includes: the semiconductor device comprises a substrate 110, a semiconductor layer sequence 120, ohmic contact electrodes 131\132, a connecting electrode 134, a transparent adhesion layer 163, an Al reflecting layer 143, pad electrodes 151\152 and an insulating layer 164, wherein the semiconductor layer sequence is manufactured on the upper surface of the substrate. The first and second

ohmic contact electrodes

131 and 132 may be provided as described in the first embodiment. The embodiment is more advantageous when applied to a middle-sized and large-sized led chip, for example, one side of the chip is more than 20 mil. In the present exemplary embodiment, the semiconductor layer sequence 120 has a plurality of mesas 120A, which are open to each other, distributed within the semiconductor layer sequence. Preferably, the second semiconductor layer is rectangular or square in a length direction, the mesas are arranged in parallel with each other in a direction perpendicular to the length direction of the chip, and the first ohmic contact electrodes 131 are formed on the mesas and form ohmic contact with the first semiconductor layer. The second ohmic contact electrode 132 is formed on the second semiconductor layer and forms an ohmic contact with the second semiconductor layer.

As shown in fig. 12 and 13, the connection electrode 134 is formed on the second ohmic contact electrode 132 and includes a series of densely distributed dot-shaped metal blocks, [ z1 ]. The diameter D2 of each dot-shaped metal block can be 10-50 μm, and the distance D3 of the adjacent metal blocks is 10-100 μm, so that the metal can play a role in current spreading. When the value of D2 is smaller than 10 μm, the contact resistance between the metal block and the ohmic contact electrode 132 may be increased, thereby increasing the forward voltage; when the value of D3 is less than 10 μm, a larger reflection area is difficult to reserve; when the value of D2 exceeds 50 μm or the value of D3 exceeds 100 μm, the point-like metal blocks are difficult to densely distribute, so that the uniform current spreading is poor, and the current spreading effect is difficult to achieve. In a preferred embodiment, the diameter D3 of the dot-shaped metal blocks is preferably 15-35 μm, and the distance D3 of the adjacent metal blocks is preferably 15-35 μm, within this range, on one hand, the dot-shaped metal blocks can achieve the effect of current expansion, and on the other hand, enough reflective windows can be reserved to reduce the light absorption effect of the metal blocks. In the embodiment, the forward voltage of the light emitting diode is ensured by controlling the spacing of the metal blocks. The stacked structure of the metal blocks may be arranged with reference to the connection electrodes of the first embodiment. Further, the first connection electrode 133 may be formed on the first ohmic contact electrode 131, and may protect the first ohmic contact electrode on the one hand and may have a height of a mesa region on the other hand.

A transparent adhesive layer 163 covers the second ohmic contact electrode 134, the connection electrode 134 and the semiconductor layer sequence. In the present embodiment, the transparent adhesive layer 163 is preferably an insulating material, and thus the first connection electrode 133 and the second connection electrode 134 can be simultaneously insulated from each other. The transparent adhesive layer 163 has a first opening 171 and a third opening 173, wherein the first opening 171 exposes the first connection electrode 133, the second opening corresponds to the metal blocks of the second connection electrode 134, and specifically, each metal block has a third opening 173 above. The material of the transparent adhesive layer 163 may include aluminum oxide, silicon nitride, silicon oxide, titanium oxide, or magnesium fluoride. In one embodiment, the transparent adhesion layer 163 is silicon dioxide and has a thickness of 100nm or less. The Al metal reflective layer 143 is formed on the transparent adhesive layer 163 and is electrode-connected to the connection electrode 134 through the third opening 173, thereby connecting all the metal blocks into a plane while functioning as current spreading. In some embodiments, an Al metal reflective layer (not shown) may be further formed on the first connection electrode 133, so that a height difference between different electrodes may be reduced, which is beneficial for the arrangement of a subsequent pad electrode. In the embodiment, the thickness of the Al metal reflective layer 143 is preferably 80nm or more, for example, 100 to 300nm, which can achieve good reflective performance and good conductive performance.

In the light emitting diode structure described in this embodiment, firstly, the thin film structure is used as the ohmic contact of the second semiconductor layer, so that the problem of light absorption of the ohmic contact electrode can be effectively reduced; dense point-shaped metal blocks are adopted, the surfaces of the second ohmic contact electrode and the point-shaped metal blocks are covered with transparent adhesive layers, and Al metal reflecting layers 143 are formed on the transparent adhesive layers, so that the point-shaped metal blocks are connected into a plane to play a role in expansion, and form an omnidirectional reflector together with the transparent adhesive layers. Sufficient Al reflecting layer reflecting area can be reserved on one hand to the punctiform metal block structure 132, especially with the region of active layer overlap, has effectively promoted the reflectivity, and on the other hand punctiform metal block can form good ohmic contact with ITO, has solved the problem that contact resistance is big between Al and the ITO, and the adhesion problem of ITO and Al metal layer has been solved to transparent adhesion layer.

Fig. 14 shows reflectance curves for different configurations of leds. The dot curve corresponds to the reflectivity of the Al metal reflecting layer, the triangular curve corresponds to the reflectivity of the existing light-emitting diode adopting CrAl alloy as the second electrode, and the x curve corresponds to the reflectivity of the existing light-emitting diode adopting NiAu alloy as the second electrode. It can be seen from the figure that, in the light emitting diode structure of the present embodiment, the reflectivity is greater than 80% when the wavelength is 260 to 300nm, which is much higher than the reflectivity of the existing NiAu electrode or CrAl electrode.

Fig. 15 shows a luminance scatter diagram of a light emitting diode chip structure with different epitaxial structures under an input current of 40mA, wherein the dot curves show the luminance of the light emitting diode of the present embodiment at different wavelengths, and the x curves show the luminance of a conventional light emitting diode using CrAl as the second electrode. As can be seen from the figure, under the same epitaxial structure and the same input current, the luminance of the light emitting diode according to the embodiment is greatly improved compared with the light emitting diode with the existing CrAl electrode structure.

The present embodiment discloses a light emitting device, which adopts the light emitting diode structure provided in any of the above embodiments, and details of the structure and technical effects are not repeated. The light emitting device may be a light emitting device for a UV product or a UVC product.

In addition, it will be appreciated by those skilled in the art that, although there may be many problems with the prior art, each embodiment or aspect of the present invention may be improved only in one or several respects, without necessarily simultaneously solving all the technical problems listed in the prior art or in the background. It will be understood by those skilled in the art that nothing in a claim should be taken as a limitation on that claim.

Claims

1. An ultraviolet light emitting diode comprising:

a semiconductor layer sequence comprising a first semiconductor layer, an active layer and a second semiconductor layer stacked in this order and having one or more mesas extending the first semiconductor layer from the second semiconductor layer, the mesas exposing the first semiconductor layer, wherein the first semiconductor layer has a first conductivity and the second semiconductor layer has a second conductivity, the first conductivity being different from the second conductivity;

the first ohmic contact electrode is positioned on the table board and forms ohmic contact with the first semiconductor layer;

the second ohmic contact electrode is positioned on the second semiconductor layer and forms ohmic contact with the second semiconductor layer;

the connecting electrode is formed on the second ohmic contact electrode and is electrically connected with the second semiconductor layer through the ohmic contact electrode;

the method is characterized in that: the edge of the connection electrode is positioned inside the edge of the second ohmic contact electrode with a certain distance therebetween.

2. The uv led of claim 1, wherein: the second semiconductor layer includes an AlGaN layer and a GaN layer having a thickness of 50nm or less.

3. The uv led of claim 1, wherein: the edge of the second ohmic contact electrode is positioned on the inner side of the edge of the second semiconductor layer, and the edge of the second ohmic contact electrode and the edge of the second semiconductor layer have a distance of 2-15 mu m.

4. The uv led of claim 1, wherein: the second ohmic contact electrode has a thickness of 150nm or less.

5. The uv led of claim 1, wherein: and the distance between the edge of the connecting electrode and the edge of the second ohmic contact electrode is more than or equal to 5 μm.

6. The uv led of claim 1, wherein: the connection electrode includes a multi-metal stack layer, and includes an adhesion layer, a conductive layer, and an etch stop layer in order from the second ohmic contact electrode.

7. The ultraviolet light emitting diode of claim 6, wherein: the conductive layer has a reflectance of 70% or more with respect to light emitted from the active layer.

8. The uv led of claim 1, wherein: the semiconductor device further comprises an insulating layer which is formed on the connecting electrode, the side face of the semiconductor layer sequence and the side face of the table top and enables the first ohmic contact electrode and the second connecting electrode to be insulated.

9. The uv led of claim 8, wherein: the insulating layer is an insulating reflecting layer.

10. The uv led of claim 1, wherein: the connection electrode includes a series of metal block arrays forming ohmic contacts with the second ohmic contact electrode and a metal reflective layer.

11. The uv led of claim 10, wherein: the metal blocks are uniformly distributed on the second ohmic contact electrodes, and the distance between the metal blocks is 10-100 mu m.

12. The uv led of claim 10, wherein: the metal block array is formed on the first ohmic contact electrode and the metal block array, and the metal reflection layer is electrically connected to the metal block through the first opening.

13. The uv led of claim 12, wherein: the transparent adhesion layer is made of silicon dioxide, hafnium dioxide, aluminum oxide, magnesium fluoride, silicon nitride and titanium oxide.

14. The uv led of claim 10, wherein: the metal reflective layer has a reflectivity of 75% or more with respect to light emitted from the active layer.

15. The uv led of claim 1, wherein: the center wavelength emitted by the active layer is 220-400 nm, and the first semiconductor layer is an n-type AlGaN semiconductor layer.

16. The uv led of claim 1, wherein: the material of the first type ohmic electrode is selected from one or more of Cr, Pt, Au, Ni, Ti and Al.

17. The uv led of claim 1, wherein: the material of the connecting electrode is selected from one or more of Cr, Pt, Au, Ni, Ti and Al.

18. The uv led of claim 1, wherein: the thickness of the substrate is 250-900 microns, a distance is formed between the edge of the first semiconductor layer and the edge of the substrate, and the distance is larger than or equal to 2 microns.

19. The uv led of claim 1, wherein: the thickness of the substrate is 250-900 mu m, and the nearest distance between the second semiconductor layer and the side wall of the substrate is more than or equal to 30 mu m.

20. A light-emitting device, characterized in that the ultraviolet light-emitting diode according to any one of claims 1 to 19 is used.