WO2023097683A1 - 紫外发光二极管及发光装置 - Google Patents

紫外发光二极管及发光装置 Download PDF

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Publication number
WO2023097683A1
WO2023097683A1 PCT/CN2021/135485 CN2021135485W WO2023097683A1 WO 2023097683 A1 WO2023097683 A1 WO 2023097683A1 CN 2021135485 W CN2021135485 W CN 2021135485W WO 2023097683 A1 WO2023097683 A1 WO 2023097683A1
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WIPO (PCT)
Prior art keywords
layer
emitting diode
light emitting
ultraviolet light
semiconductor layer
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PCT/CN2021/135485
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English (en)
French (fr)
Inventor
江宾
龙思怡
臧雅姝
彭康伟
曾炜竣
陈思河
曾明俊
Original Assignee
厦门市三安光电科技有限公司
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Application filed by 厦门市三安光电科技有限公司 filed Critical 厦门市三安光电科技有限公司
Priority to PCT/CN2021/135485 priority Critical patent/WO2023097683A1/zh
Priority to CN202180005045.6A priority patent/CN114391185B/zh
Priority to CN202310856270.1A priority patent/CN117253954A/zh
Publication of WO2023097683A1 publication Critical patent/WO2023097683A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/40—Materials therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/36—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes
    • H01L33/38—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the electrodes with a particular shape
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/44—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the coatings, e.g. passivation layer or anti-reflective coating
    • H01L33/46—Reflective coating, e.g. dielectric Bragg reflector

Definitions

  • the invention relates to the technical field of semiconductors, in particular to an ultraviolet light emitting diode and a light emitting device.
  • the existing ultraviolet LED chips In order to uniformly inject the current into the LED element into the light-emitting layer, the existing ultraviolet LED chips usually form a transparent conductive oxide layer (such as ITO, IZO, etc.) on the surface of the p-type semiconductor layer as a current spreading layer for use The current spreads into the light-emitting surface.
  • a transparent conductive oxide layer such as ITO, IZO, etc.
  • Figure 7 shows the absorption rate of different thicknesses of ITO corresponding to the wavelength. It can be seen that the commonly used 110nm ITO layer, when the wavelength is below 280nm, Its absorption rate reaches over 80%, so it is difficult to effectively improve the brightness of the UV LED with this structure.
  • One of the objectives of the present invention is to provide an ultraviolet light emitting diode, which can effectively improve the brightness of the ultraviolet light emitting diode.
  • An ultraviolet light emitting diode comprises: a semiconductor layer sequence, including a first semiconductor layer having a first conductivity, a second semiconductor layer having a second conductivity different from the first conductivity, and an active layer, which is interposed between the first semiconductor layer and the second semiconductor layer, and generates light through the recombination of electrons and holes; an ohmic contact layer, which is formed on the second semiconductor layer, and is connected with the The second semiconductor layer forms an ohmic contact with a thickness of 30 nm or less; a metal current spreading layer is formed on the ohmic contact layer, and is electrically connected to the second semiconductor layer through the ohmic contact layer; a reflective layer is formed on the current spreading layer and cover the exposed surface of the second semiconductor layer.
  • the ohmic contact layer adopts a film structure with a thickness of less than 30nm to form an ohmic contact with the second semiconductor layer, which reduces the absorption of the emission from the active layer by the ohmic contact layer, and forms an ohmic contact layer on the ohmic contact layer.
  • the high reflective layer improves the light extraction efficiency of the light emitting diode.
  • a metal current spreading layer with high reflectivity is used as the current spreading layer at the same time, taking into account the spreading and reflection of the current, and the insulating layer is set as a high reflective structure, so that the area not covered by the metal current spreading layer Reflection can be performed through the insulating layer to effectively improve the luminous efficiency of the light-emitting diode.
  • the light-emitting diode structure further adopts a dense dot-like structure as a metal current spreading layer, and cooperates with a highly reflective insulating layer to further improve the luminous efficiency of the light-emitting diode.
  • the light-emitting diode structure adopts dense point-shaped metal blocks, and a transparent adhesive layer is covered on the surface of the second ohmic contact layer and the point-shaped metal blocks, and a metal reflective layer is formed on the transparent adhesive layer.
  • Layer on the one hand, connects point-shaped metal blocks to form a surface to play the role of expansion, and on the other hand, forms an omnidirectional reflector with the transparent adhesive layer.
  • the point-shaped metal block structure can reserve enough reflection area of the reflective layer, which effectively improves the reflectivity.
  • the point-shaped metal block and the ohmic contact layer can form a good ohmic contact, which solves the problem of metal reflective layer and ohmic contact. The problem of high contact resistance between layers.
  • Fig. 1 is a top view of the ultraviolet light emitting diode provided by the first embodiment of the present invention.
  • Fig. 2 is a schematic longitudinal sectional view taken along the section line A-A of Fig. 1 .
  • Fig. 3 is a top view of the n-type ohmic contact electrode of the ultraviolet light emitting diode provided by the first embodiment of the present invention.
  • Fig. 4 is a top view of the metal current spreading layer of the ultraviolet light emitting diode provided by the first embodiment of the present invention.
  • Figure 5 and Figure 6 show the top view of the reflective layer of the UV light emitting diode provided by the first embodiment of the present invention, wherein Figure 5 shows the reflective area overlapping with the active layer, and Figure 6 shows the area not overlapping with the active layer .
  • Figure 7 shows the absorption rate curve of ITO.
  • Fig. 8 is a top view of the ultraviolet light emitting diode provided by the second embodiment of the present invention.
  • FIG. 9 is a schematic longitudinal sectional view taken along the section line B-B in FIG. 8 .
  • Fig. 10 is a top view of the metal current spreading layer of the ultraviolet light emitting diode provided by the second embodiment of the present invention.
  • Fig. 11 and Fig. 12 show the top view of the reflective layer of the ultraviolet light emitting diode provided by the second embodiment of the present invention, wherein Fig. 11 shows the reflective area overlapping with the active layer, and Fig. 12 shows the area not overlapping with the active layer.
  • FIG. 13 shows the reflectance curve of the reflective layer of the ultraviolet light emitting diode provided by the second embodiment of the present invention.
  • Fig. 14 shows a scatter diagram of the luminance of the ultraviolet light emitting diode provided by the second embodiment of the present invention.
  • Fig. 15 shows a schematic cross-sectional view of an ultraviolet light emitting diode provided by a third embodiment of the present invention.
  • Fig. 16 shows the reflectance curve of the reflective layer of the ultraviolet light emitting diode provided by the third embodiment of the present invention.
  • Fig. 17 shows a scatter diagram of the luminance of the ultraviolet light emitting diode provided by the third embodiment of the present invention.
  • FIG. 1 is a schematic top view of a light emitting diode disclosed in the first embodiment of the present invention
  • FIG. 2 is a schematic longitudinal cross-sectional view taken along line A-A of FIG. 1
  • the LED includes a substrate 110, a semiconductor layer sequence 120 fabricated on the upper surface of the substrate, ohmic contact layers 131 ⁇ 132, a metal current spreading layer 134, pad electrodes 151 ⁇ 152 and an insulating layer 160.
  • 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 forming surface.
  • the light extraction surface S12 is a surface on the opposite side to the first surface S11.
  • the substrate 110 is, for example, a sapphire substrate, but may also be a growth substrate capable of forming a Group III nitride semiconductor film.
  • the substrate is a transparent material or a translucent material.
  • the substrate 110 is preferably thickened, and its thickness can be 250 ⁇ m to 900 ⁇ m.
  • a layer of aluminum nitride is formed on the first surface S11 of the substrate 110 as the bottom layer 111, and the bottom layer 111 is in contact with the first surface S11, and its thickness is preferably less than 1 ⁇ m.
  • the aluminum nitride bottom layer 111 includes a low-temperature layer, an intermediate layer, and a high-temperature layer in order from the side close to the substrate 110, and can grow a semiconductor layer with excellent crystallinity.
  • a series of hole structures are formed in the aluminum nitride bottom layer, which is beneficial to release the stress of the semiconductor layer sequence.
  • the series of holes are preferably a series of elongated holes extending along the thickness of the aluminum nitride, the depth of which may be, for example, 0.5-1.5 ⁇ m.
  • the semiconductor layer sequence 120 is formed on the aluminum nitride bottom layer 111, including a first semiconductor layer 121, a second semiconductor layer 123 and an active layer 122 between them, for example, the first semiconductor layer 121 is an N-type layer, and the second semiconductor layer The second semiconductor layer 123 is a P-type layer, and the two can also be reversed.
  • the first semiconductor layer 121 is, for example, an n-type AlGaN layer.
  • the active layer 122 is a layer that emits ultraviolet rays, and has a well layer and a barrier layer. The number of repetitions of the well layer and the barrier layer is, for example, 1 or more and 10 or less.
  • the well layer is, for example, an AlGaN layer
  • the barrier layer is, for example, an AlGaN layer.
  • the Al composition of the well layer is 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 formed by sequentially stacking a p-type AlGaN layer and a p-type GaN layer.
  • the second semiconductor layer 123 includes a p-type GaN surface layer, the p-type GaN surface layer has a thickness of 5-50 nm, and the internal quantum luminous efficiency and external quantum luminous efficiency of the device can be taken into account by setting thin-film GaN, Specifically, the p-type GaN layer within this thickness range is conducive to the lateral current expansion of the p-side current without causing excessive light absorption.
  • the edge 121-1 of the first semiconductor layer there is a certain distance between the edge 121-1 of the first semiconductor layer and the edge 110-1 of the substrate. As shown in FIG. 1 and FIG. the inside of the sidewall of the substrate. In the ultraviolet LED chip, increasing the thickness of the substrate 110 is beneficial to improve the luminous efficiency, but increasing the thickness of the substrate also increases the difficulty of cutting the substrate. Therefore, in this embodiment, the edge 121 of the first semiconductor layer A certain distance is kept between -1 and the edge 110-1 of the substrate, so as to ensure that the semiconductor layer sequence will not be damaged when the substrate is cut, thereby improving the reliability of the light emitting diode. Preferably, the distance is more than 2 ⁇ m, such as 4-10 ⁇ m.
  • Part of the semiconductor layer sequence 120 is removed from the second semiconductor layer 123 and the active layer 122 to expose the first semiconductor layer 121 to form one or more mesas 120A, as shown in FIGS. 1 and 2 .
  • the Al content of the n-type semiconductor layer is generally high, which makes it difficult for the current to diffuse, so the current cannot flow uniformly in the active layer and the p-type semiconductor layer.
  • the mesa 120A of the light-emitting diode of this embodiment The area is preferably set to more than 20% and less than 70% of the area of the semiconductor layer sequence 120, and is relatively evenly distributed in the semiconductor layer sequence. In some preferred embodiments, the area of the mesa 120A is 40% to 70% of the area of the semiconductor layer sequence 120. 60%.
  • the shortest distance from each region of the active layer 122 to the mesa is preferably 4-15 ⁇ m, which can protect the current spreading of the n-type semiconductor layer, and is conducive to improving the internal quantum efficiency of the light-emitting diode, thereby helping to reduce the light emission. forward voltage of the diode.
  • the area of the mesa area is too large, the area of the active region of the light emitting diode will be lost too much, which is not conducive to the improvement of the luminous efficiency of the light emitting diode.
  • the first ohmic contact layer 131 is formed on the mesa 120A in direct contact, forming an ohmic contact with the first semiconductor layer.
  • the first ohmic contact layer 131 is selected from one or more of Cr, Pt, Au, Ni, Ti, Al.
  • the first ohmic contact layer 131 needs to be fused at a high temperature to form an alloy after being deposited on the mesa, so as to form a good ohmic contact with the first semiconductor layer, for example, it can be Ti - Al-Au alloys, Ti-Al-Ni-Au alloys, Cr-Al-Ti-Au alloys, Ti-Al-Au-Pt alloys, etc.
  • the second ohmic contact layer 132 is formed in contact on the surface of the second semiconductor layer 123 to form an ohmic contact with the second semiconductor layer.
  • the material of the ohmic contact layer 132 can be an oxide transparent conductive material or a metal alloy such as NiAu, NiAg, NiRh, etc., and its thickness is preferably less than 30 nm, so as to reduce the light absorption rate of this layer as much as possible.
  • a good ohmic contact can be formed with the second semiconductor layer by arranging a thin-film transparent or semi-transparent conductive layer, and on the other hand, an obvious decrease in the light absorption effect caused by excessive thickness can be avoided.
  • the wavelength emitted by the active layer is below 280nm
  • the ohmic contact layer 132 is ITO with a thickness of 5-20nm, for example, 10-15nm.
  • the absorption rate of emitted light can be reduced to within 40%.
  • the distance D1 between the edge of the second ohmic contact layer 132 and the edge of the second semiconductor layer 123 is preferably 2-15 ⁇ m, for example, 5-10 ⁇ m.
  • Risk of electric leakage also called reverse leakage current; abbreviated as IR
  • ESD abnormal electrostatic discharge
  • the distance between the end point or edge of the upper surface of the second ohmic contact layer 132 and the edge of the first ohmic contact layer 131 is greater than or equal to 4 ⁇ m, preferably greater than or equal to 6 ⁇ m. When the distance is too small, leakage is likely to occur. In some embodiments, the distance between the end point or edge of the upper surface of the second ohmic contact layer 132 and the edge of the first ohmic contact layer is greater than or equal to 4 ⁇ m and less than or equal to 10 ⁇ m.
  • the distance between the end point or the edge of the upper surface of the second ohmic contact layer 132 and the edge of the first ohmic contact layer 131 includes that the distance between the first ohmic contact layer 131 and the edge of the upper surface of the second conductivity type semiconductor layer 123 is greater than or equal to 2 ⁇ m, and the distance between the second ohmic contact layer 132 and the edge of the upper surface of the second conductivity type semiconductor layer 123 is greater than or equal to 2 ⁇ m.
  • Such a setting can ensure a certain distance between the second ohmic contact layer 132 and the mesa on the epitaxial structure 20 , so as to prevent leakage and ESD abnormality of the light emitting diode.
  • the second metal current spreading layer 134 is formed on the second ohmic contact layer 132 for spreading current to the entire light emitting region.
  • the metal current spreading layer 134 is preferably a multi-layer metal stack, for example, an adhesion layer and a conductive layer are sequentially deposited on the ohmic contact layer 132 .
  • the adhesion layer can be a Cr metal layer, its thickness is usually 1 ⁇ 10nm
  • the conductive layer can be an Al metal layer, its thickness can be more than 100nm, for example can be 200nm ⁇ 500nm, on the one hand Al has a good conductive layer, on the other hand On the one hand, Al has a high reflectivity to ultraviolet light.
  • the reflectivity of the conductive layer to light emitted by the active layer 122 is above 70%.
  • a stress buffer layer is inserted inside the conductive layer, for example, Al/Ti alternating layers may be used.
  • an etch stop layer Pt, an adhesion layer Ti, etc. may also be formed on the conductive layer.
  • the first metal flow spreading layer 133 is formed on the first ohmic contact layer 131 , as shown in FIG. 4 .
  • the first metal expansion layer 133 and the second metal expansion layer 134 can be formed in the same process, and have the same metal stack structure.
  • the first metal extension layer 133 completely covers the first ohmic contact layer 131 , which can increase the height of the mesa region on the one hand and protect the first ohmic contact layer 131 on the other hand.
  • the metal current spreading layer 134 is retracted compared to the second ohmic contact layer 132, that is, the edge 134-1 of the metal current spreading layer 134 is located at the edge 132-1 of the second ohmic contact layer 132.
  • the distance D5 is greater than or equal to 3 ⁇ m, such as 3 to 15 ⁇ m, to ensure a sufficiently large distance between the second ohmic contact layer 132 at the edge of the mesa and the metal current spreading layer 134, and to improve the ohmic contact near the steps of the deep ultraviolet It can reduce the phenomenon of layer burnt, reduce the proportion of burns in the aging process of products, and improve the aging reliability of deep ultraviolet products.
  • the insulating layer 160 is formed on the metal current spreading layer 134 and the side surfaces of the semiconductor layer sequence and the side surface S13 of the mesa 120A to insulate the first metal current spreading layer 133 and the second metal current spreading layer 134 .
  • the insulating layer 160 has a first opening 171 and a second opening 172 , exposing the first metal current spreading layer 133 and the second metal current spreading layer 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 includes silica gel or glass, and the dielectric material includes aluminum oxide, silicon nitride, silicon oxide, titanium oxide, or magnesium fluoride.
  • the insulating layer 160 may be silicon dioxide, silicon nitride, titanium oxide, tantalum oxide, niobium oxide, barium titanate or a combination thereof, such as a Bragg reflector (DBR) formed by stacking two materials repeatedly.
  • DBR Bragg reflector
  • the insulating layer 160 is preferably a reflective insulating layer.
  • the light-emitting diode has a large-area mesa structure, and the second metal current spreading layer 134 is only partially formed on the second ohmic contact layer 132, so by setting the insulating layer 160 as a highly reflective structure, it can The light extraction efficiency of the light emitting diode is effectively improved.
  • Figure 5 and Figure 6 show the reflective area of the ultraviolet light emitting diode described in this embodiment, wherein the oblique shaded part in Figure 5 represents the reflective area overlapping with the active layer, specifically the edge 123-1 to the second semiconductor layer In the region between the edge 134-1 of the second metal current spreading layer, the light emitted by the active layer corresponding to this part to the electrode side can be directly reflected by the reflective layer to avoid being absorbed by the electrode below. Preferably, this region accounts for 5-20% of the area of the upper surface of the substrate, for example, it may be 10%.
  • the area that does not overlap with the active layer including the area between the outer edge 134-1 of the second metal current spreading layer and the edge 110-1 of the substrate, and the area between the second metal current spreading layer
  • the area between the inner edge 134-2 of the extension layer and the edge 123-1 of the second semiconductor layer is the area near the mesa. Preferably, this area accounts for 15-40% of the area of the upper surface of the substrate, for example, 25%.
  • the first pad 151 and the second pad 152 are located on the insulating layer 160, the first pad 151 is electrically connected to the first metal current spreading layer 133 through the first opening 171, and the second pad 152 is connected through the second opening 172
  • the second metal current spreading layer 134 is electrically connected.
  • the first pad 41 and the second pad 42 may be formed together using the same material in the same process, and thus may have the same layer configuration. Materials of the first and second pads may be selected from one or more of Cr, Pt, Au, Ni, Ti, Al, and AuSn.
  • Figure 7 shows the absorption rate of ITO with different thicknesses.
  • ITO When ITO is used as a current spreading layer, a sufficient thickness is required, generally above 100nm, such as 110nm.
  • the light yield for ultraviolet wavelengths is very high, so the luminous efficiency of light-emitting diodes is difficult. promote.
  • the ohmic contact layer 132 of this embodiment adopts a film structure with a thickness of less than 30nm, which is only used to form an ohmic contact with the second semiconductor layer, reducing the absorption of the emission from the active layer by the ohmic contact layer 133.
  • the insulating layer 260 is set as a highly reflective structure, so that the area not covered by the metal current spreading layer can reflect through the insulating layer, further improving the luminous efficiency of the light emitting diode.
  • FIG. 8 is a schematic top view of a light-emitting diode disclosed in a second embodiment of the present invention
  • FIG. 9 is a schematic longitudinal cross-sectional view taken along line B-B in FIG. 8
  • This embodiment discloses an ultraviolet light-emitting diode.
  • the metal current spreading layer 134 adopts a dense dot-like structure, and cooperates with a highly reflective insulating layer 161 to further improve the light emission of the light-emitting diode. efficiency.
  • the ultraviolet light emitting diode includes: a substrate 110, a semiconductor layer sequence 120 fabricated on the upper surface of the substrate, an ohmic contact layer 131 ⁇ 132, a metal current spreading layer 134, a connecting electrode 142, pad electrodes 151 ⁇ 152, The first insulating layer 161 and the second insulating layer 162 .
  • the substrate and the semiconductor layer sequence, the first ohmic contact electrode, and the second ohmic contact layer can be arranged with reference to the first embodiment. In this embodiment, it is more suitable for light-emitting diode chips of medium and large sizes, for example, the side length of the chip is 20 above mil.
  • the semiconductor layer sequence 120 has a plurality of mesas 120A open to each other, which are distributed inside the semiconductor layer sequence.
  • the plurality of mesa structures have at least one or more fingers.
  • the first ohmic contact electrode 131 is formed on the plurality of mesas and forms ohmic contact with the first semiconductor layer
  • the second ohmic contact layer 132 is formed on the second semiconductor layer and forms ohmic contact with the second semiconductor layer.
  • the metal current spreading layer 134 is formed on the second ohmic contact layer 132, and includes a series of densely distributed dot-like metal blocks.
  • the diameter D2 of each dot-like metal block can be 10-50 ⁇ m, adjacent to each other.
  • the distance D3 of the metal block is 10-100 ⁇ m, so that the metal can play the role of current expansion.
  • the contact resistance between the metal block and the ohmic contact layer 132 may increase, resulting in an increase in forward voltage; when the value of D3 is less than 10 ⁇ m, it is difficult to reserve a large reflection area; When the value of D2 exceeds 50 ⁇ m or the value of D3 exceeds 100 ⁇ m, it will be difficult to achieve a dense distribution of point-shaped metal blocks, resulting in poor current uniform expansion, and it is difficult to achieve the effect of current expansion.
  • the diameter D3 of the dot-shaped metal block is preferably 15-35 ⁇ m, and the distance D3 between adjacent metal blocks is preferably 15-35 ⁇ m.
  • the dot-shaped metal block can achieve current expansion
  • enough reflection windows can be reserved to reduce the light absorption effect of the metal block.
  • the forward voltage of the LED is guaranteed by controlling the distance between the metal blocks.
  • the stacked structure of metal blocks can be set with reference to the first embodiment.
  • the first metal current spreading layer 133 can be formed on the first ohmic contact electrode 131 , which can protect the first ohmic contact electrode on the one hand and reduce the height of the mesa area on the other hand.
  • the first insulating layer 161 is formed on the metal current spreading layer 134 and the side surface of the semiconductor layer sequence and the side surface S13 of the mesa 120A to insulate the first metal current spreading layer 133 and the second metal current spreading layer 134 .
  • the first insulating layer 161 has a first opening 171 and a third opening 173, wherein the first opening exposes the first metal current spreading layer 133, and the second opening corresponds to the metal block of the second metal current spreading layer 134, specifically, Each metal block has a third opening 173 above it.
  • the first insulating layer 161 is preferably a reflective insulating layer, and the material may include aluminum oxide, silicon nitride, silicon oxide, titanium oxide, or magnesium fluoride.
  • Figure 11 and Figure 12 show the reflective area of the ultraviolet light emitting diode described in this embodiment, wherein the oblique shaded part in Figure 11 represents the reflective area overlapping with the active layer, specifically the removal of the second metal current in the second semiconductor layer
  • the light emitted from the corresponding active layer to the electrode side can be directly reflected by the reflective layer to avoid being absorbed by the electrode below.
  • this region accounts for more than 30% of the area of the upper surface of the substrate, for example, it may be 40-70%.
  • the area between the inner edge 134-2 of the extension layer and the edge 123-1 of the second semiconductor layer is the area near the mesa. Preferably, this area accounts for 15-30% of the area of the upper surface of the substrate. For example, it can be 15%.
  • connection electrode 142 is formed on the first insulating layer 161 and connected to the metal current spreading layer 134 through the third opening electrode, so as to connect all the metal blocks into a plane and play the role of current spreading. Furthermore, the connection electrode 142 may have a high reflection capability, which can complement the large-angle reflection capability of the first insulating layer, thereby further improving the light extraction efficiency of the light emitting diode.
  • a first connection electrode (not shown in the figure) can also be formed on the first metal current spreading layer 133 , so that the height difference between different electrodes can be reduced, which is beneficial to the setting of subsequent pad electrodes.
  • the second insulating layer 162 is formed on the connection electrode 142, so that the second connection electrode 142 is electrically isolated from the first metal current spreading layer 133 (or the first connection electrode 141), and has a fourth opening 174 and a fifth The opening 175 , wherein the fourth opening corresponds to the position corresponding to the first opening 171 .
  • the first pad 151 and the second pad 152 are formed on the second insulating layer 162, wherein the first pad 151 is electrically connected to the first semiconductor layer through the fourth opening, and the second pad is electrically connected to the connecting pad through the fifth opening. electrode 142 .
  • the disclosed thin film structure is used as the ohmic contact of the second semiconductor layer, which can effectively reduce the light absorption problem of the ohmic contact electrode; dense point-shaped metal blocks are used, and the second ohmic contact Layers, dot-shaped metal blocks and exposed semiconductor layer sequences are covered with an insulating reflective layer, and connecting electrodes 142 are formed on the insulating reflective layer to connect the dot-shaped metal blocks to form a surface for expansion.
  • the point-shaped metal block structure 132 can reserve enough reflection area of the insulating reflection layer, especially the area overlapping with the active layer, which effectively improves the reflectivity;
  • the metal block can also be used as an etching stop layer to solve the etching problem of the insulating reflective layer and ensure the reliability of the light emitting diode.
  • Figure 13 shows the reflectance curves of LEDs with different structures.
  • the dotted curve corresponds to the reflectivity of the light-emitting diode described in this embodiment, wherein the second ohmic contact layer adopts ITO with a thickness of about 11 nm, the second metal current spreading layer adopts the array shown in Figure 11, and the first insulating Layer 161 adopts a DBR reflective layer structure;
  • the triangular curve corresponds to the reflectance of an existing light-emitting diode using NiAu alloy as the second electrode, wherein the second electrode uses Ni with a thickness of about 20nm and Au with a thickness of about 350nm for high temperature Fusion can achieve the effect of ohmic contact and current expansion. It can be seen from the figure that the reflectance of the LED structure described in this embodiment can reach about 90% when the wavelength is 260-300nm, which is much higher than that of the existing NiAu electrodes.
  • Fig. 14 shows the brightness scatter diagram of different LED chip structures with the same epitaxial structure at an input current of 350mA, where the dot curve represents the brightness of the light emitting diode in this embodiment at different wavelengths, and the x curve represents the existing A light emitting diode using NiAu as the second electrode for brightness. It can be seen from the figure that under the same epitaxial structure and the same input current, the brightness of the light emitting diode described in this embodiment is greatly improved compared with the existing light emitting diode with NiAu electrode structure.
  • Fig. 15 is a schematic cross-sectional structure diagram of a light emitting diode disclosed in the third embodiment of the present invention.
  • the reflective effect of aluminum among metals is the best, but the contact between pure aluminum Al and ITO has poor adhesion and high contact resistance. Therefore, Cr is used as an adhesion layer between ITO and Al in the industry. The reflective effect will be reduced.
  • this embodiment discloses an ultraviolet light emitting diode, which differs from the second embodiment in that: Al is used as the reflective layer 143, and a transparent adhesive layer 163 is provided between the ITO and Al layers.
  • the ultraviolet light emitting diode includes: a substrate 110, a semiconductor layer sequence 120 fabricated on the upper surface of the substrate, an ohmic contact layer 131 ⁇ 132, a metal current spreading layer 134, a transparent adhesive layer 163, an Al reflective layer 143, Pad electrodes 151 ⁇ 152, insulating layer 164.
  • the substrate and the semiconductor layer sequence, the first ohmic contact electrode, and the second ohmic contact layer can be set with reference to the first embodiment, and the mesa 120A, dense dot-like metal block array 134, etc. can be set with reference to the second embodiment to set.
  • the transparent adhesive layer 163 covers the second ohmic contact layer 134 , the metal current spreading layer 134 and the semiconductor layer sequence.
  • the transparent adhesive layer 163 is preferably an insulating material, so that the first metal current spreading layer 133 and the second metal current spreading layer 134 can be insulated from each other at the same time.
  • the transparent adhesive layer 163 has a first opening 171 and a third opening 173, wherein the first opening 171 exposes the first metal current spreading layer 133, and the second opening corresponds to the metal block of the second metal current spreading layer 134, specifically , there is a third opening 173 above each metal block.
  • the material of the transparent adhesive layer 163 may include aluminum oxide, silicon nitride, silicon oxide, titanium oxide, or magnesium fluoride.
  • the transparent adhesive layer 163 is made of silicon dioxide, and its thickness is less than 100 nm.
  • the Al metal reflective layer 143 is formed on the transparent adhesive layer 163, and is electrode-connected to the metal current spreading layer 134 through the third opening 173, so as to connect all the metal blocks into a plane and play the role of current spreading at the same time.
  • an Al layer (not shown in the figure) can also be formed on the first metal current spreading layer 133 , so that the height difference between different electrodes can be reduced, which is beneficial to the setting of subsequent pad electrodes.
  • the thickness of the Al metal reflective layer 143 is preferably more than 80nm, for example, 100-300nm. On the one hand, it can have good reflection ability, and on the other hand, it can achieve good conductivity.
  • a thin-film structure is used as the ohmic contact of the second semiconductor layer, which can effectively reduce the light absorption problem of the ohmic contact electrode; dense point-shaped metal blocks are used, and the second ohmic contact layer,
  • the surface of the point-shaped metal block is covered with a transparent adhesive layer, and an Al metal reflective layer 143 is formed on the transparent adhesive layer.
  • the attached layer forms an omnidirectional reflector.
  • the point-shaped metal block structure 132 can reserve enough reflective area of the Al reflective layer, especially the area overlapping with the active layer, which effectively improves the reflectivity.
  • the point-shaped metal block and ITO can form a good ohmic contact, which solves the problem of high contact resistance between Al and ITO.
  • Figure 16 shows the reflectance curves of LEDs with different structures.
  • the dot curve corresponds to the reflectivity of the Al metal reflective layer
  • the triangle curve corresponds to the reflectivity of an existing light-emitting diode using CrAl alloy as the second electrode
  • the x curve corresponds to the existing one using NiAu alloy as the second electrode reflectivity of light-emitting diodes. It can be seen from the figure that the reflectance of the light emitting diode structure described in this embodiment is greater than 80% during the wavelength range of 260-300 nm, which is much higher than that of the existing NiAu electrodes or CrAl.
  • Fig. 17 shows the brightness scatter diagram of different LED chip structures with the same epitaxial structure at an input current of 40mA, where the dot curve represents the brightness of the light emitting diode of this embodiment at different wavelengths, and the x curve represents the existing The brightness of a light-emitting diode using CrAl as the second electrode. It can be seen from the figure that under the same epitaxial structure and the same input current, the brightness of the light-emitting diode described in this embodiment is greatly improved compared with the light-emitting diode with the existing CrAl electrode structure.
  • the light emitting device may be a light emitting device for UV products or UVC products.

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Abstract

一种紫外发光二极管及发光装置，包括：半导体层序列（120），包含具备第一导电性的第一半导体层（121），具备与第一导电性不同的第二导电性的第二半导体层（123），及有源层（122），其介于第一半导体层与第二半导体层之间，并通过电子和空穴的复合而生成光；欧姆接触层（132），形成于第二半导体层上，并与第二半导体层形成欧姆接触，厚度为30nm以下；金属电流扩展层（134），形成于欧姆接触层上，通过欧姆接触层与第二半导体层形成电性连接；反射层（143），形成于金属电流扩展层上，并覆盖裸露出的第二半导体层表面。该发光二极管可以有效提高发光效率。

Description

紫外发光二极管及发光装置 技术领域
本发明涉及半导体技术领域，特别涉及一种紫外发光二极管及发光装置。
 背景技术
近年来，紫外光LED特别是深紫外光LED的巨大的应用价值引起了人们的高度关，成为了新的研究热点。为使通入LED元件的电流均匀注入发光层，现有的紫外LED芯片通常在p型半导体层的表面形成一透明导电氧化物层（例如ITO、IZO等）等作为电流扩展层，用于使电流扩展至发光面内。然而在紫外光波长，特别是深紫外波段，ITO的吸光效应严重，图7显示了不同厚度的ITO对应波长的吸收率，可以看到现有常用的110nm的ITO层，当波长在280nm以下，其吸收率达到约80%以上，因此该结构较难有效提升紫外发光二极管的亮度。
 技术解决方案
本发明的目的之一在于：提供一种紫外发光二极管，其可以有效提升紫外发光二极管的亮度。
本发明所述的一种紫外发光二极管，包括：半导体层序列，包含具备第一导电性的第一半导体层，具备与第一导电性不同的第二导电性的第二半导体层，及有源层，其介于所述第一半导体层与所述第二半导体层之间，并通过电子和空穴的复合而生成光；欧姆接触层，形成于所述第二半导体层上，并与所述第二半导体层形成欧姆接触，厚度为30nm以下；金属电流扩展层，形成于所述欧姆接触层上，通过所述欧姆接触层与所述第二半导体层形成电性连接；反射层，形成于所述电流扩展层上，并覆盖裸露出的第二半导体层表面。
本发明所述的紫外发光二极管，欧姆接触层采用厚度30nm以下的薄膜结构用于与第二半导体层形成欧姆接触，减少了欧姆接触层对有源层发射的吸收，并在欧姆接触层上形成高反射层，从而提升发光二极管的出光效率。
在一些实施例中，同时采用具有高反射率的金属电流扩展层作为电流扩展层，兼顾了电流的扩展及反射，并将绝缘层设置为高反射结构，如此未被金属电流扩展层覆盖的区域可以通过绝缘层进行反射，有效提升发光二极管的发光效率。
在一些实施例中，所述发光二极管结构进一步采用密集的点状结构作为金属电流扩展层，并配合高反射的绝缘层，进一步提高发光二极管的发光效率。
在一些实施例中，所述发光二极管结构采用密集的点状金属块，并在第二欧姆接触层、点状金属块的表面上覆盖透明粘附层，在该透明粘附层上形成金属反射层，一方面将点状金属块连接成面起到扩展作用的作用，另一方面与透明粘附层形成全方位反射镜。点状的金属块结构一方面可以预留足够的反射层反射面积，有效提升了反射率,另一方面点状金属块与欧姆接触层可以形成良好的欧姆接触，解决了金属反射层与欧姆接触层之间接触电阻大的问题。
 有益效果
本发明的其它特征和有益效果将在随后的说明书中阐述，并且，部分地从说明书中变得显而易见，或者通过实施本发明而了解。本发明的目的和其他有益效果可通过在说明书、权利要求书等内容中所特别指出的结构来实现和获得。
 附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作一简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图；在下面描述中附图所述的位置关系，若无特别指明，皆是图示中组件绘示的方向为基准。
图1是本发明第一实施例提供的紫外发光二极管俯视图。
图2是沿图1的截取线A-A截取的纵向剖面示意图。
图3是本发明第一实施例提供的紫外发光二极管的n型欧姆接触电极的俯视图。
图4是本发明第一实施例提供的紫外发光二极管的金属电流扩展层的俯视图。
图5和图6显示了本发明第一实施例提供的紫外发光二极管的反射层的俯视图，其中图5显示了与有源层重叠的反射区域，图6显示了不与有源层重叠的区域。
图7显示了ITO的吸收率曲线。
图8是本发明第二实施例提供的紫外发光二极管的俯视图。
图9是沿图8的截取线B-B截取的纵向剖面示意图。
图10是本发明第二实施提供的紫外发光二极管的金属电流扩展层的俯视图。
图11和图12显示了本发明第二实施提供的紫外发光二极管的反射层的俯视图，其中图11显示了与有源层重叠的反射区域，图12显示了不与有源层重叠的区域。
图13显示了本发明第二实施例提供的紫外发光二极管的反射层的反射率曲线。
图14显示了本发明第二实施例提供的紫外发光二极管的亮度散点图。
图15显示了本发明第三个实施例提供的紫外发光二极管的剖面示意图。
图16显示了本发明第三实施例提供的紫外发光二极管的反射层的反射率曲线。
图17显示了本发明第三实施例提供的紫外发光二极管的亮度散点图。
 本发明的实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例是本发明一部分实施例，而不是全部的实施例；下面所描述的本发明不同实施方式中所设计的技术特征只要彼此之间未构成冲突就可以相互结合；基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
请参阅图1和图2，图1是本发明第一实施例公开的发光二极管的俯视结构示意图，图2是沿图1的截取线A-A截取的纵向剖面示意图。该发光二极管包括衬底110、制作在衬底上表面的半导体层序列120、欧姆接触层131\132、金属电流扩展层134、焊盘电极151\152及绝缘层160层。在本实施例，该发光二极管为在衬底一侧具有光提取表面S12的倒装芯片。
衬底110用于支持半导体层序列110。衬底具有第一表面S11和光提取表面S12。第一面S11为半导体层形成面。光提取表面S12是第一面S11的相反侧的面。衬底110例如是蓝宝石基板，此外也可以是能够进行III族氮化物半导体的成膜的生长基板。优选的，该衬底为透明材料或者半透明材料，为了增强出光S12的光萃取效率，特别是光从衬底面萃取的效果，优选地加厚设置衬底110，其厚度可以为250μm至900μm。
优选地，衬底110的第一表面S11形成有一层氮化铝作为底层111，该底层111与第一面S11接触，其厚度优选为1μm以下。进一步地，该氮化铝底层111从靠近衬底110一侧起依次包括低温层、中间层和高温层，能够使结晶性优异的半导体层生长。在另一些优选实施例中，该氮化铝底层中形成一系列的孔洞结构，有利于释放半导体层序列的应力。该系列孔洞优先为一系列沿着该氮化铝的厚度延伸的细长孔，其深度例如可以为0.5~1.5μm。
半导体层序列120形成于氮化铝底层111上，依次包括第一半导体层121、第二半导体层123和位于两者之间的有源层122，例如第一半导体层121为N型层，第二半导体层123为P型层，两者也可以倒置。第一半导体层121例如是n型AlGaN层。有源层122是发出紫外线的层，具有阱层和势垒层，阱层和势垒层的重复次数例如为1以上且10以下，阱层例如是AlGaN层，势垒层例如是AlGaN层，但阱层的Al组成比势垒层的Al组成低。第二半导体层123例如是p型AlGaN层或者p型GaN层，或者依次层叠p型AlGaN层和p型GaN层而成的层。在本实施例，该第二半导体层123包括p型GaN表面层，该 p型GaN表面层的厚度为5~50nm，通过设置薄膜型GaN能够兼顾器件的内量子发光效率及外量子发光效率，具体的，该厚度范围内的p型GaN层有助于进行p侧电流的横向电流扩展，且不会导致吸光过于严重。
在一个优选实施方式中，第一半导体层的边缘121-1与衬底的边缘110-1之间具有一定的距离，如图1和图2所示，第一半导体层的侧壁位于所述衬底的侧壁的内侧。在紫外LED芯片中通过增加衬底110的厚度有利于提升发光效率，但是增加衬底的厚度同时也增加了衬底的切割难度，因此在本实施例中，通过将第一半导体层的边缘121-1与衬底的边缘110-1之间保留一定的距离，如此可以保证在衬底切割时不会损伤半导体层序列，从而提升发光二极管的可靠性。优选的，该距离为2μm以上，例如4~10μm。
该半导体层序列120部分区域被移除第二半导体层123、有源层122，裸露出第一半导体层121，形成一个或者多个台面120A，如图1和2所示。在本实施例中，优选形成多个台面120A，该多个台面120A用于形成第一欧姆接触层131，台面120A的分布并不局限于图2所示，可以根据实际的芯片尺寸及形状进行设计，该多个台面120A可以连接在一起，也可以彼此分离。在紫外发光二极管中，n型半导体层的含Al量通常较高导致电流难以进行扩散，因此电流不能够在有源层和p型半导体层中均匀地流动，本实施例发光二极管的台面120A的面积优选设置为半导体层序列120面积的20%以上且70%以下，且相对均匀地分布于半导体层序列中，在一些较佳实施例中，台面120A的面积为半导体层序列120面积的40~60%。较佳地，保持有源层122的各个区域到该台面的最近距离优选是4~15μm，如此可以保护n型半导体层的电流扩展，有利于提高发光二极管的内量子效率，从而有助降低发光二极管的正向电压。当台面区域的面积过大将导致发光二极管的有源区面积损失过多，不利于发光二极管的发光效率的提升。
结合图3和图2所示，第一欧姆接触层131直接接触地形成于该台面120A上，与第一半导体层形成欧姆接触。该第一欧姆接触层131选自Cr、Pt、Au、Ni、Ti、Al的一种或者多种。由于第一半导体层具有较高的Al组份，因此该第一欧姆接触层131在沉积于该台面后需要进行高温熔合形成合金，从而与第一半导体层形成良好的欧姆接触，例如可以为Ti-Al-Au合金、Ti-Al-Ni-Au合金、Cr-Al-Ti-Au合金、Ti-Al-Au-Pt合金等。
第二欧姆接触层132接触式地形成于第二半导体层123的表面上，与第二半导体层形成欧姆接触。优选的，该欧姆接触层132的材料可以为氧化物透明导电材料或者NiAu、NiAg、NiRh等金属合金，其厚度优选为30nm以下，尽可能降低该层的光吸收率。通过设置薄膜式的透明或者半透明导电层一方面可以与第二半导体层形成良好的欧姆接触，另一方面避免厚度过大而导致吸光效应明显上降。在一个较佳的实施样态中，有源层发射的波长为280nm以下，该欧姆接触层132为ITO，厚度为5~20nm，例如可以为10~15nm，此时该ITO层对于有源层发射的光线的吸收率可以降低至40%以内。在一个具体的实施例中，该第二欧姆接触层132的边缘与第二半导体层123的边缘的距离D1优选为2~15μm，例如可以为5~10μm，此种设置，可以降低发光二极管1发生漏电（也称反向漏电流；简称为IR）和静电放电（ESD）异常的风险。进一步地，第二欧姆接触层132的上表面的端点或边缘与第一欧姆接触层131的边缘的间距为大于等于4μm，优选为大于等于6μm，当该距离过小时，容易发生漏电的现象。在一些实施例中，第二欧姆接触层132的上表面的端点或边缘与第一欧姆接触层的边缘的间距为大于等于4μm且小于等于10μm。第二欧姆接触层132的上表面的端点或边缘与第一欧姆接触层131的边缘的间距包括第一欧姆接触层131与第二导电类型半导体层123的上表面的边缘之间的间距大于等于2μm，及第二欧姆接触层132与第二导电类型半导体层123的上表面的边缘之间的间距大于等于2μm。如此设定，可保证第二欧姆接触层132与外延结构20上的台面具有一定的间距，防止发光二极管发生漏电和ESD异常。同时可保证第二绝缘层33与外延结构20上的台面具有一定间距，实现刻蚀外延结构20的侧壁具有足够厚的绝缘层，以确保发光二极管1具有较好的绝缘保护及防漏电性能。
第二金属电流扩展层134形成于在第二欧姆接触层132上，用于使电流扩散至整个发光区域。该金属电流扩展层134优选为多层金属叠层，例如在欧姆接触层132上依次沉积粘附层、导电层。其中粘附层可以为Cr金属层，其厚度通常为1~10nm，导电层可以为Al金属层，其厚度可以为100nm以上，例如可以为200nm~500nm，一方面Al具有良好的导电层，另一方面Al对紫外光具有较高的反射率，优选地，该导电层对于有源层122发射的光线的反射率为70%以上。进一步的，优先该导电层内部插入应力缓冲层，例如可以为Al/Ti交替层。进一步的，还可以在导电层上形成蚀刻截止层Pt、粘附层Ti等。优选地，第一金属流扩展层133形成于第一欧姆接触层131之上，如图4所示。该第一金属扩展层133可以与第二金属扩展层134在同一道工艺中形成，具有相同的金属叠层结构。优选的，该第一金属扩展层133完全覆盖第一欧姆接触层131，一方面可以增加台面区域的高度，另一方面可以保护第一欧姆接触层131。
在深紫外发光二极管结构中，半导体层的载流子的横向扩展速率相对较低，因此在欧姆接触层的边缘（靠近台面）的位置容易出现电流聚集，进而导致局部过热和电极烧伤的现象，从而导致LED芯片的可靠性变弱及寿命缩短。因此，在一个优选的实施方式中，金属电流扩展层134相较于第二欧姆接触层132内缩，即金属电流扩展层134的边缘134-1位于第二欧姆接触层132的边缘132-1的内侧，两者之间具有一间距D5，一方面起到调节电流扩展的作用，另一方面减小产品因边缘电流过渡聚集而导致的失效比例。优选地，该距离D5大于或者等于3μm，例如3~15μm，保证在台面边缘处的第二欧姆接触层132与金属电流扩展层134之间具有足够大的间距，改善深紫外近台阶处欧姆接触层烧毁的现象，降低产品在老化过程中出现的烧伤比例，提升深紫外产品老化的可靠性。
绝缘层160形成在金属电流扩展层134上及半导体层序列的侧面及台面120A的侧面S13,使第一金属电流扩展层133和第二金属电流扩展层134绝缘。该绝缘层160具有第一开口171和第二开口172，裸露出第一金属电流扩展层133和第二金属电流扩展层134。绝缘层160的材料包含非导电材料。非导电材料优选地为无机材料或者介电材料。无机材料包含硅胶或玻璃，介电材料包含氧化铝、氮化硅、氧化硅、氧化钛、或氟化镁。例如，绝缘层160可以是二氧化硅、氮化硅、氧化钛、氧化钽、氧化铌、钛酸钡或者其组合，其组合例如可以是两种材料重复堆叠形成的布拉格反射镜（DBR）。
在本实施例中，该绝缘层160优选为反射率绝缘层。如图所示，该发光二极管具有较大面积的台面结构，且第二金属电流扩展层134仅部分地形在第二欧姆接触层132上，因此通过将绝缘层160设置为高反射的结构，可以有效地提高发光二极管的出光效率。图5和图6显示了本实施例所述紫外发光二极管的反射区域，其中图5中的斜线阴影部分表示与有源层重叠的反射区域，具体为第二半导体层的边缘123-1到第二金属电流扩展层的边缘134-1之间的区域，此部分对应的有源层向电极一侧发射的光线可以直接经过该反射层的反射，避免被下方的电极吸收。优选的，该区域占衬底上表面的面积的5~20%，例如可以为10%。图6中的斜线阴影部分表示不与有源层重叠的区域，包含了第二金属电流扩展层的外边缘134-1与衬底的边缘110-1之间的区域，及第二金属电流扩展层的内边缘134-2与第二半导体层的边缘123-1之间的区域，即为台面附近的区域，优选的，该区域占衬底上表面的面积的15~40%，例如可以为25%。
第一焊盘151与第二焊盘152位于绝缘层160上，第一焊盘151是通过第一开口171电连接第一金属电流扩展层133上，第二焊盘152是通过第二开口172电连接第二金属电流扩展层134。第一焊盘41和第二焊盘42可在同一工艺中利用相同材料一并形成，因此可具有相同的层构造。第一、第二焊盘的材料可以选自Cr、Pt、Au、Ni、Ti、Al、AuSn中的一种或多种。
图7显示了不同厚度的ITO的吸收率，当ITO用作电流扩展层时需要足够的厚度，一般为100nm以上，例如110nm，对于紫外波长的光收率很高，因此发光二极管的发光效率难以提升。本实施例的欧姆接触层132采用厚度30nm以下的薄膜结构，仅用于与第二半导体层形成欧姆接触，减少了欧姆接触层133对有源层发射的吸收，例如采用厚度为11nm的ITO时，对于310nm以下的紫外光，其吸收率为30%以下，同时采用具有高反射率的金属电流扩展层作为电流扩展层，兼顾了电流的扩展及反射。进一步地，将绝缘层260设置为高反射结构，如此未被金属电流扩展层覆盖的区域可以通过绝缘层进行反射，进一步提高发光二极管的发光效率。
请参阅图8和图9，图8是本发明第二个实施例公开的发光二极管的俯视结构示意图，图9是沿着图8的截取线B-B截取的纵向剖面示意图。本实施例公开了一种紫外发光二极管，与第一个实施例的不同之处在于：金属电流扩展层134采用密集的点状结构，并配合高反射的绝缘层161，进一步提高发光二极管的发光效率。
具体的，所述紫外发光二极管包括：衬底110、制作在衬底上表面的半导体层序列120、欧姆接触层131\132、金属电流扩展层134、连接电极142、焊盘电极151\152、第一绝缘层161和第二绝缘层162。其中衬底及半导体层序列、第一欧姆接触电极、第二欧姆接触层可以参照第一个实施例的进行设置。在本实施例中，比较适用于中大尺寸的发光二极管芯片，例如芯片的边长为20 mil以上。在本实施例中，半导体层序列120具有多个彼此公开的台面120A，分布于发半导体层序列的内部，优选地，该多个台面结构至少具有一个或者多个呈指状。第一欧姆接触电极131形成于该多个台面上，并与所述第一半导体层形成欧姆接触，第二欧姆接触层132形成于第二半导体上，并与该第二半导体层形成欧姆接触。
如图9和10所示，金属电流扩展层134形成于第二欧姆接触层132上，包含一系列密集分布的点状金属块，各个点状金属块的直径D2可以为10~50μm，相邻的金属块的距离D3为10~100μm，如此该金属可以起到电流扩展的作用。当D2的取值小10μm，可能导致金属块与欧姆接触层132之间的接触电阻增加从而导致正向电压升高；当D3的取值小于10μm时，则难以预留较大的反射面积；当D2的取值超过50μm或者D3的取值超过100μm时，则点状金属块将难以做到密集分布，从而导致电流均匀扩展变差，难以达到电流扩展的作用。在一个较佳实施例中，点状金属块的直径D3优选为15~35μm，相邻的金属块的距离D3优选为15~35μm，在此范围内，一方面点状金属块可以达到电流扩展的作用，另一方面可以预留足够的反射窗口，减少金属块的吸光效应。在本实施例，通过控制金属块的间距保证发光二极管的正向电压。金属块的叠层结构可以参照第一个实施例进行设置。进一步地，可以在第一欧姆接触电极131上形成第一金属电流扩展层133，一方面可以保护第一欧姆接触电极，另一方面可以台面区域的高度。
第一绝缘层161形成在金属电流扩展层134上及半导体层序列的侧面及台面120A的侧面S13,使第一金属电流扩展层133和第二金属电流扩展层134绝缘。该第一绝缘层161具有第一开口171和第三开口173，其中第一开口裸露出第一金属电流扩展层133，第二开口对应于第二金属电流扩展层134的金属块，具体的，每个金属块的上方均具有一第三开口173。第一绝缘层161优选为反射率绝缘层，材料可以包含氧化铝、氮化硅、氧化硅、氧化钛、或氟化镁。图11和图12显示了本实施例所述紫外发光二极管的反射区域，其中图11中的斜线阴影部分表示与有源层重叠的反射区域，具体为第二半导体层中去除第二金属电流扩展层的区域，此部分对应的有源层向电极一侧发射的光线可以直接经过该反射层的反射，避免被下方的电极吸收。优选的，该区域占衬底上表面的面积30%以上，例如可以为40~70%。图12中的斜线阴影部分表示不与有源层重叠的区域，包含了第二金属电流扩展层的外边缘134-1与衬底的边缘110-1之间的区域，及第二金属电流扩展层的内边缘134-2与第二半导体层的边缘123-1之间的区域，即为台面附近的区域，优选的，该区域点衬底上表面的面积的15~30%，例如可以为15%。
连接电极142形成于第一绝缘层161上，并通过第三开口电极连接到金属电流扩展层134，从而将所有的金属块连成面，起到电流扩展的作用。进一步的，该连接电极142可以具有高反射的能力，如此可以补足第一绝缘层的大角度反射方面的能力，从而进一步提高发光二极管的出光效率。在一些实施例中，还可以在第一金属电流扩展层133上形成第一连接电极（图中未示出），如此可以减少不同电极之间的高度差，有利于后续焊盘电极的设置。
第二绝缘层162形成于连接电极142之上，使得第二连接电极142与第一金属电流扩展层133（或者第一连接电极141）之间电性隔离，具有第四开174口和第五开口175，其中第四开口对应于在第一开口171对应的位置。第一焊盘151和第二焊盘152形成于第二绝缘层162上，其中第一焊盘151通过第四开口电连接到第一半导体层，第二焊盘通过第五开口电连接到连接电极142。
本实施例所述的发光二极管结构中，首先采用分别公开薄膜结构作为第二半导体层的欧姆接触，可以有效减少欧姆接触电极的吸光问题；采用密集的点状金属块，并在第二欧姆接触层、点状金属块及裸露出的半导体层序列的表面上覆盖绝缘反射层，在绝缘反射层上形成连接电极142，将点状金属块连接成面起到扩展作用的作用。其中，点状的金属块结构132一方面可以预留足够的绝缘反射层反射面积，特别是与有源层重叠的区域，有效提升了反射率；另一方面，由于第三开口均对位于点状金属块上方，该金属块同时可以作为蚀刻截止层，解决绝缘反射层的蚀刻问题，保证的发光二极管的可靠性。
图13显示了不同结构的发光二极管的反射率曲线。其中圆点曲线对应的是采用本实施例所述的发光二极管的反射率，其中第二欧姆接触层采用厚度约11nm的ITO，第二金属电流扩展层采用图11所示的阵列，第一绝缘层161采用DBR反射层结构；三角形曲线对应的是现有的一种采用NiAu合金作为第二电极的发光二极管的反射率，其中第二电极采用厚度约20nm的Ni和厚度约350nm的Au进行高温熔合，可以达到欧姆接触和电流扩展的作用。从图中可以看出，本实施例所述的发光二极管结构在波长为260~300nm期间，其反射率可以达到约90%，远高于现有的采用NiAu电极的反射率。
图14显示了同一外延结构不同的发光二极管芯片结构在输入电流为350mA下的亮度散点图，其中圆点曲线表示为本实施例发光二极管在不同波长的亮度，x曲线表示的是现有的一种采用NiAu为作为第二电极的发光二极管的亮度。从图中可以看出，在相同的外延结构下和相同的输入电流下，本实施例所述的发光二极管相对于现有的NiAu电极结构的发光二极管，其亮度大幅度的提升。
图15是本发明第三个实施例公开的发光二极管的剖面结构示意图。在深紫外发光二极管结构中，金属中铝的反射效果最好，但是纯铝Al与ITO接触存在粘附性差以及接触电阻大等情况，因此业内在ITO与Al之间设置Cr作为粘附层，如此反射效果将变差。针对该问题，本实施例公开了一种紫外发光二极管，与第二个实施例的不同之处在于：采用Al作反射层143，在ITO与Al层之间设置透明粘附层163。
具体的，所述紫外发光二极管包括：衬底110、制作在衬底上表面的半导体层序列120、欧姆接触层131\132、金属电流扩展层134、透明粘附层163、Al反射层143、焊盘电极151\152、绝缘层164。其中衬底及半导体层序列、第一欧姆接触电极、第二欧姆接触层、可以参照第一个实施例的进行设置，台面120A、密集型点状金属块阵列134等可以参照第二个实施例进行设置。
透明粘附层163覆盖在第二欧姆接触层134、金属电流扩展层134上及半导体层序列。在本实施例中，该透明粘附层163优选为绝缘性的材料，因此可以同时使第一金属电流扩展层133和第二金属电流扩展层134彼此绝缘。该透明粘附层163具有第一开口171和第三开口173，其中第一开口171裸露出第一金属电流扩展层133，第二开口对应于第二金属电流扩展层134的金属块，具体的，每个金属块的上方均具有一第三开口173。透明粘附层163的材料可以包含氧化铝、氮化硅、氧化硅、氧化钛、或氟化镁。在一个具体的实施样态中，该透明粘附层163采用二氧化硅，其厚度为100nm以下。Al金属反射层143形成在透明粘附层163上，并通过第三开口173电极连接到金属电流扩展层134，从而将所有的金属块连接成面，同时起到电流扩展的作用。在一些实施例中，还可以在第一金属电流扩展层133上形成Al层（图中未示出），如此可以减少不同电极之间的高度差，有利于后续焊盘电极的设置。在本实施例，该Al金属反射层143厚度优选为80nm以上，例如可以为100~300nm，一方面可以具有良好的反射能力，另一方面可以达到良好的导电性能。
本实施例所述的发光二极管结构中，首先采用薄膜结构作为第二半导体层的欧姆接触，可以有效减少欧姆接触电极的吸光问题；采用密集的点状金属块，并在第二欧姆接触层、点状金属块的表面上覆盖透明粘附层，在该透明粘附层上形成Al金属反射层143，一方面将点状金属块连接成面起到扩展作用的作用，另一方面与透明粘附层形成全方位反射镜。点状的金属块结构132一方面可以预留足够的Al反射层反射面积，特别是与有源层重叠的区域，有效提升了反射率,另一方面点状金属块与ITO可以形成良好的欧姆接触，解决了Al与ITO之间接触电阻大的问题。
图16显示了不同结构的发光二极管的反射率曲线。其中圆点曲线对应的是Al金属反射层的反射率，三角形曲线对应的是现有的一种采用CrAl合金作为第二电极的发光二极管的反射率，x曲线对应的是现有的一种采用NiAu合金作为第二电极的发光二极管的反射率。从图中可以看出，本实施例所述的发光二极管结构在波长为260~300nm期间，其反射率大于80%，远高于现有的采用NiAu电极或者CrAl的反射率。
图17显示了同一外延结构不同的发光二极管芯片结构在输入电流为40mA下的亮度散点图，其中圆点曲线表示的是本实施例发光二极管在不同波长的亮度，x曲线表示的是现有的一种采用CrAl作为第二电极的发光二极管的亮度。从图中可以看出，在相同的外延结构下和相同的输入电流下，本实施例所述的发光二极管相对于现有的CrAl电极结构的发光二极管，其亮度大幅度的提升。
本实施例公开一种发光装置，该发光装置采用上述任意实施例提供的发光二极管结构，其具体结构与技术效果不再赘述。该发光装置可以是用于UV产品或UVC产品的发光装置。
另外，本领域技术人员应当理解，尽管现有技术中存在许多问题，但是，本发明的每个实施例或技术方案可以仅在一个或几个方面进行改进，而不必同时解决现有技术中或者背景技术中列出的全部技术问题。本领域技术人员应当理解，对于一个权利要求中没有提到的内容不应当作为对于该权利要求的限制。
最后应说明的是：以上各实施例仅用以说明本发明的技术方案，而非对其限制；尽管参照前述各实施例对本发明进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分或者全部技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本发明各实施例技术方案的范围。

Claims (23)

  1. 一种紫外发光二极管，包括：
    半导体层序列，包含具备第一导电性的第一半导体层，具备与第一导电性不同的第二导电性的第二半导体层，及有源层，其介于所述第一半导体层与所述第二半导体层之间，并通过电子和空穴的复合而生成光；
    欧姆接触层，形成于所述第二半导体层上，并与所述第二半导体层形成欧姆接触，厚度为30nm以下；
    金属电流扩展层，形成于所述欧姆接触层上，通过所述欧姆接触层与所述第二半导体层形成电性连接；
    反射层，形成于所述电流扩展层上，并覆盖裸露出的第二半导体层表面。
  2. 根据权利要求1所述的紫外发光二极管，其特征在于：所述第二半导体层包含AlGaN层和GaN层，该GaN层的厚度为50nm以下。
  3. 根据权利要求1所述的紫外发光二极管，其特征在于：所述欧姆接触层为透明导电氧化物，其与所述第二半导体层的边缘具有一间距，该间距为2~15μm。
  4. 根据权利要求1所述的紫外发光二极管，其特征在于：所述金属电流扩展层为多层结构，自所述欧姆接触层起依次包含粘附层、导电层及蚀刻截止层。
  5. 根据权利要求4所述的紫外发光二极管，其特征在于：所述导电层对于所述有源层发射的光线具有70%以上的反射率。
  6. 根据权利要求1所述的紫外发光二极管，其特征在于：所述包含一系列金属块组成的阵列，裸露出部分所述欧姆接触层。
  7. 根据权利要求6所述的紫外发光二极管，其特征在于：所述金属块均匀地分布于所述欧姆接触层上，其间距为10~100μm。
  8. 根据权利要求6所述的紫外发光二极管，其特征在于：所述反射层为一绝缘反射层，同时覆盖裸露出的金属电流扩展层、欧姆接触层及半导体层序列的侧表面，并在所述金属块对应的位置形成导电通孔。
  9. 根据权利要求8所述的紫外发光二极管，其特征在于：所述反射层包含高、低折射率层的材料层交替叠层。
  10. 根据权利要求9所述的紫外发光二极管，其特征在于：所述反射层的材料包括二氧化硅、二氧化铪、三氧化二铝、氟化镁、氮化硅、氧化钛。
  11. 根据权利要求8所述的紫外发光二极管，其特征在于：还包括连接电极，形成所述绝缘反射层之上，并通过所述通孔结构与所述金属块形阵列形成电连接。
  12. 根据权利要求6所述的紫外发光二极管，其特征在于：包括一透明粘附层，该透明粘附层覆盖所述金属电流扩展层及裸露出的欧姆接触层，所述反射层为金属反射层，形成于所述透明粘附层上。
  13. 根据权利要求12所述的紫外发光二极管，其特征在于：所述透明粘附层的材料是二氧化硅、二氧化铪、三氧化二铝、氟化镁、氮化硅、氧化钛。
  14. 根据权利要求12所述的紫外发光二极管，其特征在于：所述金属反射层对于所述有源层发射的光线具有75%以上的反射率。
  15. 根据权利要求1所述的紫外发光二极管，其特征在于：所述有源层发射的中心波长为220~400nm，所述第一半导体层为n型AlGaN半导体层。
  16. 根据权利要求15所述的紫外发光二极管，其特征在于：所述半导体层序列部分区域被移除所述第二半导体层、有源层，裸露出所述第一半导体层，形成一个或者多个台面。
  17. 根据权利要求16所述的紫外发光二极管，其特征在于：还包括n型欧姆接触电极，其形成于所述台面上，与所述第一半导体层形成欧姆接触。
  18. 根据权利要求17所述的紫外发光二极管，其特征在于：所述n型欧姆电极的材料选自Cr、Pt、Au、Ni、Ti、Al中的一种或多种。
  19. 根据权利要求17所述的紫外发光二极管，其特征在于：还包括一第一连接电极和第二连接电极，其中第一连接电极与所述n型欧姆接触电极电连接，所述第二连接电极形成于所述反射层之上，并与所述金属扩展电极形成电连接。
  20. 根据权利要求19所述的紫外发光二极管，其特征在于：所述第一、第二连接电极的材料选自Cr、Pt、Au、Ni、Ti、Al中的一种或多种。
  21. 根据权利要求17所述的紫外发光二极管，其特征在于：还包括第二绝缘层、第一焊盘电极和第二焊盘电极，所述第二绝缘层形成于第一、第二连接电极上，具有第一开口和第二开口，其中第一开口裸露出所述第一连接电极，第二开口裸露出第二连接电极，所述第一焊盘电极通过所述第一开口电连接所述第一连接电极，所述第二焊盘电极通过所述第二开口电连接所述第二连接电极。
  22. 根据权利要求1所述的紫外发光二极管，其特征在于：所述衬底的厚度为250~900μm，所述第一半导体层的边缘与所述衬底的边缘具有一间距，该间距大于等于2μm。
  23. 一种发光装置，其特征在于，采用如权利要求1至22中任一项所述的紫外发光二极管。
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