WO2012144046A1 - 窒化物半導体紫外線発光素子 - Google Patents
窒化物半導体紫外線発光素子 Download PDFInfo
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- WO2012144046A1 WO2012144046A1 PCT/JP2011/059829 JP2011059829W WO2012144046A1 WO 2012144046 A1 WO2012144046 A1 WO 2012144046A1 JP 2011059829 W JP2011059829 W JP 2011059829W WO 2012144046 A1 WO2012144046 A1 WO 2012144046A1
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- 239000004065 semiconductor Substances 0.000 title claims abstract description 87
- 150000004767 nitrides Chemical class 0.000 title claims description 70
- 238000005253 cladding Methods 0.000 claims abstract description 135
- 229910052751 metal Inorganic materials 0.000 claims abstract description 83
- 239000002184 metal Substances 0.000 claims abstract description 83
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- 238000000034 method Methods 0.000 claims description 29
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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
- H01L33/405—Reflective materials
-
- 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
- H01L33/02—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 semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
Definitions
- the present invention relates to a nitride semiconductor ultraviolet light-emitting device having an emission center wavelength of about 355 nm or less used for a light-emitting diode, a laser diode, etc., and particularly to a technique for improving external quantum efficiency.
- a GaN-based nitride semiconductor is based on an GaN or an AlGaN layer having a relatively small AlN mole fraction (also called an AlN mixed crystal ratio or Al composition ratio), and a light emitting element or a light receiving element having a multilayer structure thereon.
- FIG. 28 shows a crystal layer structure of a typical conventional GaN-based light emitting diode. In the light emitting diode shown in FIG.
- an underlying layer 102 made of AlN is formed on a sapphire substrate 101, a periodic groove structure is formed by photolithography and reactive ion etching, and then ELO (Epitaxial Lateral Overgrowth) -AlN.
- a layer 103 is formed as a template.
- an n-type AlGaN n-type cladding layer 104 having a thickness of 2 ⁇ m, an AlGaN / GaN multiple quantum well active layer 105, and an AlN molar fraction of multiple quantum wells.
- the multiple quantum well active layer 105 has a structure in which five layers of a structure in which a GaN well layer having a thickness of 2 nm is sandwiched between AlGaN barrier layers having a thickness of 8 nm are stacked.
- the multi-quantum well active layer 105, the electron blocking layer 106, the p-type cladding layer 107, and the p-type contact layer 108 thereon are removed by etching until a partial surface of the n-type cladding layer 104 is exposed.
- a Ni / Au p-electrode 109 is formed on the surface of the p-type contact layer 108, and a Ti / Al / Ti / Au n-electrode 110 is formed on the exposed n-type cladding layer 104. ing.
- the emission wavelength is shortened by changing the AlN mole fraction and film thickness, or the emission wavelength is lengthened by adding In, and the wavelength is increased from 200 nm.
- a light emitting diode having an ultraviolet region of about 400 nm can be manufactured.
- a semiconductor laser can be fabricated with a similar configuration.
- the nitride semiconductor light-emitting element that extracts light transmitted through the n-type cladding layer from the back surface side. Then, if at least part of the light traveling toward the p-type cladding layer reaches the interface with the p-electrode without being absorbed by the p-type contact layer and is reflected at the interface, the reflected light is reflected by the n-type cladding layer. It is used effectively by proceeding to the side.
- the amount of light extracted from the nitride semiconductor light emitting device is increased by reflecting the light traveling to the p-type cladding layer side and returning to the n-type cladding layer side with high efficiency. improves.
- Patent Document 1 Attempts to improve external quantum efficiency by efficiently reflecting light traveling toward the p-type cladding layer are disclosed in Patent Document 1, Patent Document 2 and Non-Patent Document 3 below.
- a p-type contact is formed on a p-type contact layer in a mesh shape having an opening, and a p-type electrode electrically connected to the p-type contact layer is exposed.
- a reflective layer using a metal such as silver or Al is formed on the layer and the p electrode, and the light transmitted through the p-type cladding layer and the p-type contact layer is reflected to the active layer side by the reflective layer formed in the opening.
- the structure is designed to improve external quantum efficiency.
- a mesh-like highly reflective metal layer having an opening in ohmic contact with the p-type nitride semiconductor layer is provided on the p-type nitride semiconductor layer, and further exposed to the opening.
- a metal barrier layer is provided on the p-type nitride semiconductor layer and the highly reflective metal layer to assist the reflective action of the highly reflective metal layer, and light transmitted through the p-type nitride semiconductor layer is highly reflective metal layer.
- the external quantum efficiency is improved by reflecting the light at the interface with the metal barrier layer.
- Non-Patent Document 3 a nanopixel type Pd electrode that is in ohmic contact with the p-type nitride semiconductor layer is provided on the p-type nitride semiconductor layer, and an Al reflective layer is provided in the gap between the Pd electrodes.
- the light transmitted through the p-type nitride semiconductor layer is reflected to the active layer side by the reflective layer formed in the gap, and the external quantum efficiency is improved.
- JP 2008-66727 A Japanese Patent Laid-Open No. 2005-210051
- a back-emission type nitride semiconductor light emitting device that extracts light transmitted through the n-type cladding layer from the back side, not all of the light passes through the exit surface and is emitted to the outside. Reflects toward the clad layer side.
- a part of the reflected light reaches the n electrode, and the other part passes through the active layer and reaches the p-type cladding layer or the p electrode, and is absorbed and effective. Not used for.
- the nitride semiconductor ultraviolet light emitting device has a double hetero structure in which an active layer (light emitting layer) is sandwiched between a p-type cladding layer and an n-type cladding layer, and the emission wavelength is the band gap energy (forbidden band width) of the active layer.
- the AlN molar fraction x of Al x Ga 1-x N constituting each cladding layer is set larger than that of the active layer. Accordingly, the AlN mole fraction of each cladding layer increases as the emission wavelength is shortened.
- the AlN mole fraction of each cladding layer is about 60%, and when the emission center wavelength is around 250 nm, the AlN mole fraction of each cladding layer is about 75%. .
- the n-type cladding layer can make ohmic contact with the n-electrode as long as the AlN mole fraction is about 60% even if the AlN mole fraction exceeds 10% compared to the p-type clad layer. For this reason, in general, an n-electrode is formed directly on the n-type cladding layer without providing an n-type contact layer between the n-type cladding layer and the n-electrode.
- the chip area occupied by the single light emitting element on the wafer substrate is the area of the first region where the stacked structure from the active layer 7 to the p-type contact layer 10 on the n-type cladding layer is formed, and the n-type cladding layer. Is the total area of the exposed second region. Therefore, in order to increase the external quantum efficiency per chip area, it is preferable to make the area of the second region as small as possible, and since the area of the second region relative to the chip area is generally kept small, Since the ratio of the light that is reflected at the exit surface and reaches the n-electrode having a small area is relatively small, the light that reaches the n-electrode is not reflected again and effectively used.
- the area of the second region must be secured to some extent because bumps need to be formed on the n electrode. Therefore, the inventor of the present application examines the possibility that the light reflected by the emission surface and reaching the n electrode can be reflected again and effectively used, and the formation region of the n electrode in the second region is suppressed to the minimum, and n It has been found that there is room for improving the external quantum efficiency by forming a reflective electrode at an excessive portion where no electrode is formed.
- the p-type nitride semiconductor layer is in ohmic contact with the p-type nitride semiconductor layer constituting the uppermost layer of the nitride semiconductor layer constituting the light emitting element.
- a metal electrode partially opened is provided. Since the p-type nitride semiconductor layer constituting the uppermost layer is formed on the entire upper surface of the active layer, in order to reflect light emitted from the active layer by the reflective layer or the highly reflective metal layer formed on the upper layer. It is necessary that the light emission is not absorbed by the p-type nitride semiconductor layer.
- the uppermost layer needs to have a p-type GaN or AlN molar fraction of less than 10%.
- the necessity of using p-type GaN is described in Patent Document 1, and Non-Patent Document 3 describes an example in which p-type GaN is used as the uppermost p-type nitride semiconductor layer.
- the emission wavelength from the active layer is about 355 nm or less, and further shorter, the emission from the active layer is absorbed by the uppermost p-type nitride semiconductor layer.
- Patent Document 1 Even if a part of the layer does not reach the layer, the reflected light is absorbed when it passes through the p-type nitride semiconductor layer again, so that it is not used effectively and the external quantum efficiency is not improved. Therefore, the conventional techniques for improving external quantum efficiency disclosed in Patent Document 1, Patent Document 2, Non-Patent Document 3, and the like cannot be said to be effective techniques for light-emitting elements having an emission wavelength of about 355 nm or less.
- the present invention has been made in view of the above-described problems, and an object thereof is to improve the external quantum efficiency of a nitride semiconductor light emitting device having a light emission center wavelength of about 355 nm or less.
- the band gap energy of the first region in the plane parallel to the surface of the n-type cladding layer on the n-type cladding layer made of an n-type AlGaN-based semiconductor layer is 3.
- An active layer having an AlGaN-based semiconductor layer of 4 eV or more and a p-type cladding layer made of a p-type AlGaN-based semiconductor layer located above the active layer are formed, and the region other than the first region on the n-type cladding layer
- An n-electrode metal layer in ohmic contact with the n-type cladding layer is formed in a region near the first region in the second region, and on the surface of the n-type cladding layer other than the neighboring region in the second region
- a first reflective metal layer that reflects ultraviolet light emitted from the active layer, and the n-electrode metal layer is in contact with the first reflective metal layer on the surface of the n-type cladding layer; region It is disposed between to provide a nitride semiconductor ultraviolet light-emitting device according to the first aspect.
- the nitride semiconductor ultraviolet light-emitting device having the first feature described above it is possible to improve the extraction efficiency in the back-emission type nitride semiconductor light-emitting device that extracts light from the back surface on the lower layer side than the n-type cladding layer. Specifically, a part of the light reflected toward the n-type cladding layer side without passing through the output surface on the back surface is re-reflected toward the output surface by the first reflective metal layer. Light can be used effectively, the amount of light that can be actually extracted from the light emitting element is increased, and the external quantum efficiency is improved.
- the first reflective metal layer covers at least a part of the upper surface of the n-electrode metal layer and is electrically connected to the n-electrode metal layer. It is preferable that they are connected. Thereby, the n-electrode metal layer and the first reflective metal layer can be integrated and used as an electrode pad for flip-chip connection or the like.
- the AlN mole fraction of the n-type cladding layer is larger than the AlN mole fraction of the active layer and not more than 60%.
- FIG. 1 shows measurement data that forms the basis of the present invention.
- An n electrode Ti / Al / Ti / Au: the lowermost layer is Ti and the uppermost layer is Au
- n - type Al x Ga 1-x N layer The relationship between the contact resistance ⁇ C (unit: ⁇ cm 2 ) with the n-type AlGaN layer and the heat treatment temperature T (unit: ° C.) is that the AlN mole fraction x of the n-type AlGaN layer is 0%, 25%, 40%, The result measured about 5 types, 60% and 75% is shown.
- ⁇ C unit: ⁇ cm 2
- T unit: ° C.
- the contact resistance was measured by a known TLM (Transmission Line Model) method.
- the heat treatment temperature was set in the range of 450 ° C. to 1000 ° C., and the sample having an AlN molar fraction x of 0% was also measured even when no heat treatment was performed.
- the sample with an AlN molar fraction x of 0% had the same contact resistance when no heat treatment was performed and when the heat treatment temperature was 450 ° C.
- the sample having an AlN molar fraction x of 75% has an average contact resistance higher than that of a sample having an AlN molar fraction x of 60% at a heat treatment temperature of 950 ° C. When no contact is formed and the heat treatment temperature is 900 ° C. or lower, ohmic contact is not obtained. Furthermore, the sample with an AlN molar fraction x of 75% has a large variation in contact resistance, and a contact resistance that is two orders of magnitude higher is also measured.
- the contact resistance ⁇ C can be adjusted to 0.01 ⁇ cm 2 or less by appropriately selecting the heat treatment temperature T. It can be seen that a good ohmic contact is formed.
- the first reflective metal layer is formed of Al, a metal multilayer film or an alloy containing Al as a main component.
- a p-type contact layer made of a p-type AlGaN-based semiconductor layer that absorbs the ultraviolet light is formed on the p-type cladding layer, and the p-type contact layer Has an opening penetrating to the surface of the p-type cladding layer, and a p-electrode metal layer in ohmic contact or non-rectifying contact with the p-type contact layer on the p-type contact layer completely shields the opening.
- a second reflective metal layer that reflects the ultraviolet light is formed at least on the opening, and the second reflective metal layer directly contacts the surface of the p-type cladding layer exposed through the opening.
- the second feature is that the light is covered with a transparent insulating layer that transmits the ultraviolet light.
- part of the ultraviolet light emitted from the active layer and passing through the p-type cladding layer enters the opening of the p-type contact layer, and the p-type contact Since it reaches the second reflective metal layer and is reflected without being absorbed by the layer, the reflected light can be used effectively, and the external quantum efficiency can be improved.
- the p-type contact layer and the p-electrode metal layer are in ohmic contact or non-rectifying contact, a current path from the p-electrode metal layer to the active layer through the p-type contact layer and the p-type cladding layer is secured. Is done. The inventor of the present application has confirmed that the above-described current path is sufficiently ensured and light is emitted well even if the p-type contact layer is not formed on the entire upper surface of the active layer, according to examples described later.
- the AlN molar fraction of the p-type cladding layer is higher than 10%, and the ohmic contact or non-rectifying contact cannot be made with the p-electrode metal layer with low resistance.
- the AlN molar fraction of the p-type contact layer is 0% or more and less than 10%.
- the AlN molar fraction of the p-type contact layer is 0% or more and less than 10%, ohmic contact or low-resistance non-rectifying contact with the p-electrode metal layer is possible.
- p-type GaN having an AlN molar fraction of 0% good ohmic contact can be achieved with low resistance.
- the reflective metal layer is formed on at least the opening and the p-electrode metal layer.
- the reflective metal layer is formed also on the p-electrode metal layer, when the p-electrode metal layer is discretely formed, the discrete p-electrode metal layers are connected to each other and function as an integral p-electrode. Can be made.
- the reflective metal layer is formed of Al, a metal multilayer film or an alloy containing Al as a main component.
- the ratio of the area of the opening to the total area of the p-type contact layer and the opening is preferably 66% or more.
- the higher the ratio the more light is reflected and the higher the external quantum efficiency, but the higher the parasitic resistance on the p-electrode side and the higher the forward voltage, the higher the ratio.
- the light emission efficiency with respect to the electric power input between the anode and the cathode of the light emitting element may decrease.
- the ratio is 66%, the external quantum efficiency can be improved without decreasing the light emission efficiency within a range in which a practical forward voltage can be realized.
- the upper limit of the ratio needs to secure a certain area as the p-electrode metal layer in order to apply the forward voltage to the light emitting element, it depends on the area and the range in which a practical forward voltage can be realized.
- the predetermined value is less than 100%.
- the n-type cladding layer emits the ultraviolet light composed of an insulator layer, a semiconductor layer, or a laminate of an insulator layer and a semiconductor layer. It is preferable to be formed on a transparent template, and it is preferable that the template includes an AlN layer. As a result, it is possible to take out light emission from the back side by passing the template in a state having the template.
- the external quantum efficiency can be reliably improved even for light emission having a center wavelength of about 355 nm or less, which has been difficult with the conventional technology for improving external quantum efficiency.
- a characteristic diagram showing the measurement results of the relationship between the contact resistance between the n-electrode formed on the n-type AlGaN layer and the n-type AlGaN layer, the heat treatment temperature T, and the AlN mole fraction of the n-type AlGaN layer It is sectional drawing which shows typically the laminated structure in 1st Embodiment of the nitride semiconductor ultraviolet light emitting element which concerns on this invention. It is a top view which shows typically the planar structure in 1st Embodiment of the nitride semiconductor ultraviolet light emitting element which concerns on this invention, and the planar view pattern of an n electrode, a p electrode, and a reflective electrode.
- the example in which the n electrode and the reflective electrode are provided on the n type cladding layer and the comparison in which the n electrode is provided on the n type cladding layer and the reflective electrode is not provided It is a characteristic view which shows the measurement result of the characteristic with respect to the forward current of the light emission output of an example.
- the example in which the n electrode and the reflective electrode are provided on the n type cladding layer and the comparison in which the n electrode is provided on the n type cladding layer and the reflective electrode is not provided It is a characteristic view which shows the measurement result of the current voltage characteristic of the forward voltage and forward current of an example.
- the Al mole fraction of the n-type cladding layer is 20%
- the example in which the n electrode and the reflective electrode are provided on the n type cladding layer and the comparison in which the n electrode is provided on the n type cladding layer and the reflective electrode is not provided It is a characteristic view which shows the measurement result of the current voltage characteristic of the forward voltage and forward current of an example. It is a characteristic view which shows the measurement result of the wavelength dependence of the emitted light intensity of the Example provided with the reflective electrode on the n-type clad layer in the case where the Al mole fraction of the n-type clad layer is 55%.
- the present device Embodiments of a nitride semiconductor ultraviolet light emitting device according to the present invention (hereinafter referred to as “the present device” as appropriate) will be described with reference to the drawings.
- the present device for easy understanding of the description, the main contents are emphasized and the contents of the invention are schematically shown. Therefore, the dimensional ratio of each part is not necessarily the same as the actual element. It is not.
- description will be made assuming that the element of the present invention is a light emitting diode.
- the element 1 of the present invention uses, as a template 5, a substrate obtained by growing an AlN layer 3 and an AlGaN layer 4 on a sapphire (0001) substrate 2, and is made of n-type AlGaN on the template 5.
- the active layer 7 has a single-layer quantum well structure including an n-type AlGaN barrier layer 7a having a thickness of 10 nm and an AlGaN well layer 7b having a thickness of 3.5 nm.
- the active layer 7 may be a double heterojunction structure sandwiched between n-type and p-type AlGaN layers having a large Al mole fraction between the lower layer and the upper layer, and the single quantum well structure is multilayered.
- a multiple quantum well structure may be used.
- Each AlGaN layer is formed by a well-known epitaxial growth method such as a metal organic compound vapor phase growth (MOVPE) method or a molecular beam epitaxy (MBE) method.
- MOVPE metal organic compound vapor phase growth
- MBE molecular beam epitaxy
- n-type layer donor impurity for example, Si or p-type
- Mg is used as the acceptor impurity of the layer.
- the AlN layer and the AlGaN layer whose conductivity type is not specified are undoped layers into which impurities are not implanted.
- the AlN molar fraction of the n-type AlGaN layer and the active layer is 60% for the AlGaN layer 4, the n-type cladding layer 6 and the barrier layer 7a, and 35% for the well layer 7b.
- each AlGaN layer other than the active layer 7 is, for example, 2000 nm for the n-type cladding layer 6, 2 nm for the electron blocking layer 8, 540 nm for the p-type cladding layer 9, and 200 nm for the p-type contact layer 10.
- a Ni / Au p-electrode 11 (corresponding to a p-electrode metal layer) is formed on the surface of the p-type contact layer 10.
- a part of the surface of the n-type cladding layer 6 is formed of, for example, Ti / Al / Ti / Au.
- An n-electrode 12 (corresponding to an n-electrode metal layer) is formed, and an Al / Ti / Au reflective electrode 13 (first electrode) is formed on a part of the exposed surface of the n-type cladding layer 6 that is not covered with the n-electrode 12. Corresponding to a reflective metal layer).
- the AlN molar fraction of the n-type cladding layer 6 is 60% from the measurement result shown in FIG. The following is preferred.
- FIG. 3 an example of the planar view pattern of the p electrode 11, the n electrode 12, and the reflective electrode 13 is shown.
- FIG. 3A shows the first region R1 and the second region R2 before the electrodes 11 to 13 are formed.
- the p electrode 11 is formed on almost the entire surface of the first region R1.
- the second region corresponds to a region on the n-type cladding layer 6 excluding the first region.
- the chip size of the element 1 of the present invention shown in FIG. 3 is 800 ⁇ m in both vertical and horizontal directions, and the area of the first region R1 is about 168000 ⁇ m 2 .
- 3 (b) and 3 (c) show the planar view patterns of the n electrode 12 and the reflective electrode 13, respectively.
- FIG. 3 (b) and 3 (c) show the planar view patterns of the n electrode 12 and the reflective electrode 13, respectively.
- the n electrode 12 portion is distinguished by a cross hatch.
- the portion of the reflective electrode 13 is distinguished by a cross hatch.
- the reflective electrode 13 is formed to overlap the upper surface of the n electrode 12, and the reflective electrode 13 and the n electrode 12 are electrically connected.
- the n-electrode 12 is formed along the inner periphery of the reflective electrode 13 facing the first region R1. That is, the n-electrode 12 is formed in the vicinity of the first region R1, and in the example shown in FIG. 2, it is formed so as to surround the first region R1 in an annular shape.
- the contact surface between the reflective electrode 13 and the n-type clad layer 6 is almost the entire region of the first region R2 where the n-electrode 12 is not formed outside the n-electrode 12 (the side far from the first region R1). All the n electrodes 12 are formed so as to cover them, and are formed on the inner side (side closer to the first region R1) of the contact surface.
- the contact area between the n-electrode 12 and the n-type cladding layer 6 and the contact area between the reflective electrode 13 and the n-type cladding layer 6 are about 58000 ⁇ m 2, respectively. And about 313,000 ⁇ m 2 , which corresponds to about 35% and about 186% of the area of the first region R1 (active layer 7).
- the element structure shown in FIG. 2 is basically the same as that of the conventional light emitting diode shown in FIG. 28 except for the n electrode 12 and the reflective electrode 13. Therefore, the element 1 of the present invention is characterized by an n-electrode structure including the n-electrode 12 and the reflective electrode 13.
- the template 5 and each layer from the n-type cladding layer 6 to the p-type contact layer 10 are formed by a well-known growth method as described above.
- a heat treatment is performed at 800 ° C., for example, to activate Mg as an acceptor impurity.
- the first region on the surface of the p-type contact layer 10 is covered with, for example, a Ni mask 14 by a well-known photolithography technique. Subsequently, as shown in FIG.
- the portion located in the second region of each layer from the active layer 7 to the p-type contact layer 10 deposited on the entire surface of the n-type cladding layer 6 is well-known such as reactive ion etching.
- the Ni mask 14 is removed after the surface of the n-type cladding layer 6 is exposed.
- a photoresist (not shown) serving as an inverted pattern of the n electrode 12 is formed on the entire surface of the substrate, and a Ti / Al / Ti / Au four-layer metal film serving as the n electrode 12 is formed on the photoresist.
- deposition is performed by a beam deposition method, the photoresist is removed by lift-off, the four-layer metal film on the photoresist is peeled off, and heat treatment is applied by RTA (instantaneous thermal annealing) or the like.
- the n-electrode 12 is formed on the n-type cladding layer 6.
- the film thickness of the four-layer metal film of Ti / Al / Ti / Au is, for example, 20 nm / 100 nm / 50 nm / 100 nm in the order of description.
- the heat treatment is performed for the purpose of reducing contact resistance.
- the heat treatment temperature is set in consideration of the relationship shown in FIG. 1 or the like so that the contact resistance between the n-electrode 12 and the n-type cladding layer 6 becomes the lowest according to the AlN mole fraction of the n-type cladding layer 6. Is preferred.
- a photoresist (not shown) serving as an inverted pattern of the reflective electrode 13 is formed on the entire surface of the substrate, and an Al / Ti / Au three-layer metal film serving as the reflective electrode 13 is formed thereon by electron beam evaporation.
- the photoresist is removed by lift-off, the photoresist is removed by lift-off, the three-layer metal film on the photoresist is peeled off, and the n-electrode 12 (or at least part of the n-electrode 12) is removed as shown in FIG.
- the reflective electrode 13 is formed on almost the entire surface of the second region so as to cover it.
- the film thickness of the Al / Ti / Au three-layer metal film is, for example, 100 nm / 100 nm / 200 nm in the order of description. Since the reflective electrode 13 formed directly on the n-type cladding layer 6 without covering the n-electrode 12 mainly contains Al that reflects ultraviolet rays, it is reflected from the sapphire substrate 2 side and passes through the n-type cladding layer 6. The light that reaches the second region on the surface of the n-type cladding layer 6 is reflected again toward the sapphire substrate 2 side. Note that no heat treatment is performed on the reflective electrode 13.
- the Al layer in the reflective electrode 13 is not melted by the heat treatment, the function of reflecting the ultraviolet rays is maintained well. Further, since the reflective electrode 13 is in ohmic contact with the n electrode 12, it can be used as an electrode pad for flip chip bonding or wire bonding around the chip.
- a photoresist (not shown) to be an inverted pattern of the p electrode 11 is formed on the entire surface of the substrate, and a Ni / Au two-layer metal film to be the p electrode 11 is formed on the photoresist (not shown).
- the photoresist is removed by lift-off, the two-layer metal film on the photoresist is peeled off, and heat treatment at 450 ° C. is performed by RTA (instantaneous thermal annealing) or the like.
- a p-electrode 11 is formed on the p-type contact layer 10.
- the film thickness of the Ni / Au two-layer metal film is, for example, 60 nm / 50 nm in the order of description. In the heat treatment at 450 ° C., since the melting point of Al is about 660 ° C., the Al layer in the reflective electrode 13 does not melt.
- Examples 1 and 2 of the element 1 of the present invention in which the n-type electrode 12 and the reflective electrode 13 having the pattern shown in FIG. 3 are formed on the n-type cladding layer 6, and the reflective electrode 13 on the n-type cladding layer 6.
- the characteristics of the light emission output P unit: mW
- the forward current If unit: mA
- the forward voltage Vf The measurement results of each of the current-voltage characteristics of the unit: V) and the forward current If are shown in FIGS.
- Example 1 and Comparative Example 1 show the measurement results of Example 1 and Comparative Example 1 for comparison and comparison
- Example 2 and Comparative Example 2 show the measurement results of Example 2 and Comparative Example 2 for comparison and comparison. Yes.
- the measurement results of Examples 1 and 2 are indicated by solid lines or black square marks ( ⁇ )
- the measurement results of Comparative Examples 1 and 2 are indicated by broken lines or white circles ( ⁇ ).
- the light emission output P of the embodiment of the element 1 of the present invention is provided with the reflective electrode 13 regardless of whether the Al mole fraction of the n-type cladding layer 6 is 55% or 20%. It was confirmed that the external quantum efficiency was improved by providing the reflective electrode 13 from the comparative example that did not increase regardless of the forward current If.
- Example 1 and Comparative Example 1 the contact area between the n-electrode 12 and the n-type cladding layer 6 is smaller than that of the Comparative Examples. Therefore, in the embodiment, it is considered that the parasitic resistance of the n-electrode 12 becomes higher and the forward voltage Vf becomes higher.
- the Al mole fraction of the n-type cladding layer 6 is relatively high at 55%, and the contact resistance between the n-electrode 12 and the n-type cladding layer 6 is increased as shown in FIG. Therefore, as shown in FIG. 11, the forward voltage Vf in Example 1 is higher than that in the comparative example.
- the conversion efficiency E (generally referred to as wall plug efficiency) represented by the ratio of the light emission output P to the power injected into the light emitting element (forward voltage Vf ⁇ forward current If) is implemented.
- the example 1 is superior to the comparative example 1, and it can be seen that the improvement of the external quantum efficiency appears more remarkably than the increase of the forward voltage Vf.
- Example 2 and Comparative Example 2 the Al mole fraction of the n-type cladding layer 6 is as small as 20%, and the contact resistance between the n-electrode 12 and the n-type cladding layer 6 is also low as shown in FIG. Since this is suppressed, an increase in the forward voltage Vf in Example 2 is not observed. In FIG. 13, it is considered that the forward voltage Vf in Example 2 is lower than that in Comparative Example 2 within the measurement error range.
- Example 14 and 15 show the results of measuring the wavelength dependence characteristics of the emission intensity LI (arbitrary unit) in Example 1 and Example 2, respectively.
- the Al mole fraction of the well layer 7b of the active layer 7 is also reduced to 40% and 12%, respectively, according to the difference in Al mole fraction of the n-type cladding layer 6. Therefore, the difference in the Al mole fraction appears as a difference in peak emission wavelength (Example 1: about 290 nm, Example 2: about 339 nm).
- the average light emission output P of the three samples of Comparative Example 1 was 2.82 mW, the forward voltage Vf was 4.97 V, and the conversion efficiency E was 2.83%, whereas The average light emission output P of the sample was 3.24 mW, the forward voltage Vf was 5.16 V, and the conversion efficiency E was 3.14%.
- the average light emission output P of the three samples of Comparative Example 2 was 2.78 mW, the forward voltage Vf was 4.74 V, and the conversion efficiency E was 0.98%, whereas the three samples of Example 2
- the average light emission output P was 3.24 mW, the forward voltage Vf was 4.63 V, and the conversion efficiency E was 1.17%.
- the ratio of the light emission output P to the comparative example was 115% in Example 1 and 117% in Example 2.
- the ratio of the forward voltage Vf to the comparative example was 104% in Example 1 and 98% (substantially 100%) in Example 2.
- the conversion efficiency E is higher in Examples 1 and 2 than in Comparative Examples 1 and 2. . From the above, it was confirmed that the external quantum efficiency was improved without sacrificing the conversion efficiency E by providing the reflective electrode 13 in the n-electrode structure portion.
- the external quantum efficiency can be improved by a novel n-electrode structure in which the n-electrode 12 and the reflective electrode 13 are combined, that is, by improving the electrode structure on the n-electrode 12 side.
- the external quantum efficiency can be further improved by improving the electrode structure of both the n-electrode 12 and the p-electrode 11.
- FIG. 17 shows a cross-sectional structure of the element 20 of the present invention in the second embodiment.
- the element 20 of the present invention has a p-type contact layer 10 in which an opening 15 penetrating to the surface of the lower p-type cladding layer 9 is formed by reactive ion etching or the like.
- the p electrode 11 is formed on the surface of the electrode 10, and the reflective electrode 16 (corresponding to the second reflective metal layer) made of Al is formed in the opening 15 of the p-type contact layer 10 and on the p electrode 11, that is,
- the p-electrode structure including the underlying structure and the peripheral structure of the p-electrode 12 is different from the element 1 of the present invention according to the first embodiment shown in FIG.
- the reflective electrode 16 may be a three-layer metal film of Al / Ti / Au instead of an Al single layer.
- the p-type contact layer 10 and the p-electrode 11 are each processed into a lattice-like (or mesh-like), comb-like, or dot-like (or island-like) pattern that covers a part of the first region R1.
- FIG. 18 shows an example of a plan view pattern of the p-electrode 11.
- FIGS. 18 (a) to 18 (c) show cases where the p electrode 11 is a lattice pattern, a comb pattern, or a dot pattern, and the portion of the p electrode 11 is distinguished by a cross hatch. Yes.
- the p-type contact layer 10 and the p-electrode 11 are overlapped in the same pattern, but the p-electrode 11 may be slightly smaller than the p-type contact layer 10. Even if the p-electrode 11 is larger than the p-type contact layer 10 and covers the side surface of the step of the p-type contact layer 10, there is no problem as long as the opening 15 exists.
- the portion excluding the p-type contact layer 10 in the first region R1 is the opening 15, but when the p-electrode 11 is present in the opening 15, the portion where the p-electrode 11 is not formed is an effective opening. Part.
- the opening of the first region R1 on the surface of the p-type contact layer 10 is performed by a known photolithography technique.
- a portion other than the portion where the portion 15 is formed is covered with, for example, a Ni mask (not shown), and the underlying p-type cladding layer 9 exposes the portion of the p-type contact layer 10 not covered with the Ni mask.
- the Ni mask is removed after forming the opening 15 by removing by a known anisotropic etching method such as reactive ion etching. Subsequently, the steps until the formation of the n-electrode 12 and the reflective electrode 13 shown in FIGS. 5 to 8 are performed as described in the first embodiment.
- a photoresist (not shown) to be an inverted pattern of the p electrode 11 is formed on the entire surface of the substrate, and a Ni / Au two-layer metal film to be the p electrode 11 is formed on the photoresist (not shown).
- the photoresist is removed by lift-off, the two-layer metal film on the photoresist is peeled off, and heat treatment is performed at 450 ° C. by RTA or the like, as shown in FIG.
- a p-electrode 11 is formed on the surface of 10.
- the film thickness of the Ni / Au two-layer metal film is, for example, 60 nm / 50 nm in the order of description.
- a photoresist (not shown) serving as a reverse pattern of the reflective electrode 16 is formed on the entire surface of the substrate, and an Al / Ti / Au three-layer metal film serving as the reflective electrode 16 is formed thereon by electron beam evaporation.
- the photoresist is removed by lift-off, etc., the photoresist is removed by lift-off, the three-layer metal film on the photoresist is peeled off, and the p-type cladding exposed in the p-electrode 11 and the opening 15 as shown in FIG.
- the reflective electrode 16 is formed on almost the entire surface of the first region R1 so as to cover the layer 9.
- the film thickness of the Al / Ti / Au three-layer metal film is, for example, 100 nm / 100 nm / 200 nm in the order of description. Note that no heat treatment is performed on the reflective electrode 16. As a result, since the Al layer in the reflective electrode 16 is not melted by the heat treatment, the function of reflecting the ultraviolet rays is maintained well. Further, since the reflective electrode 16 is in ohmic contact with the p-electrode 11, it can be used as an electrode pad for flip chip bonding or wire bonding.
- an opening 15 is formed in the first region R1 on the surface of the p-type contact layer 10, and the p-type cladding layer 9 exposed in the opening 15 is covered with the p-electrode 11
- the effect of forming the reflective electrode 16 on almost the entire surface of the one region R1 will be described. That is, in the first embodiment, it has been confirmed that the external quantum efficiency is improved by forming the reflective electrode 13 in the n-electrode structure portion, but in the second embodiment, the reflective electrode 16 is provided in the p-electrode structure portion. It is confirmed that the external quantum efficiency is improved by forming.
- n electrode structure portion used in the first embodiment. Therefore, as an example of the inventive element 20 of the second embodiment, n A sample having no reflective electrode 13 in the electrode structure portion was used.
- Example 3 (with the reflective electrode 16 and without the reflective electrode 13) of the element 20 of the present invention, the p-type contact layer 10 and the p-electrode 11 are formed on almost the entire surface of the p-type cladding layer 9, and the reflective electrode 16 is formed.
- the wavelength dependence of the light emission intensity LI (arbitrary unit), the characteristics of the light emission output P (unit: mW) with respect to the forward current If (unit: mA), the forward voltage Vf (unit) : V) and the current-voltage characteristics of the forward current If are shown in FIGS.
- p-type GaN was used as the p-type contact layer 10.
- each AlGaN layer is, for example, 60% for the n-type cladding layer 6, 50% for the barrier layer 7a, 35% for the well layer 7b, 100% for the electron blocking layer 8, and p-type cladding layer 9 Is 40%.
- FIG. 22 (a) and 22 (b) show the wavelength dependences of the emission intensity LI on the vertical axis expressed in a linear scale and a logarithmic scale, respectively.
- each forward current If of Example 3 and Comparative Example 3 is 60 mA.
- FIG. 23A shows the characteristic of the light emission output P with respect to the forward current If.
- FIG. 23B shows the characteristic obtained by normalizing the measurement result of Example 3 with the measurement result of Comparative Example 3 with respect to the same measurement result. Is shown.
- FIG. 24 shows current-voltage characteristics of the forward voltage Vf and the forward current If.
- the measurement result of Example 3 is indicated by a solid line or a black square mark ( ⁇ )
- the measurement result of Comparative Example 3 is indicated by a broken line or a white circle ( ⁇ ).
- the emission intensity LI of Example 3 is significantly higher than that of Comparative Example 3 on the shorter wavelength side than the emission center region, and the peak emission wavelength is also slightly shorter.
- the peak wavelength of Comparative Example 3 was about 307.0 nm, and the emission intensity LI was about 252.5 [arbitrary unit].
- the peak wavelength of Example 3 was about 304.6 nm, and the emission intensity LI was about 301.0 [arbitrary unit]. From the above measurement results, it was confirmed that the external quantum efficiency was improved over the entire emission wavelength region. Furthermore, from the result shown in FIG. 23, the light emission output P of Example 3 increased from the comparative example irrespective of the forward current If, and it was confirmed that the external quantum efficiency was improved.
- Example 3 Although the external quantum efficiency of Example 3 is improved compared to Comparative Example 3, the area of the p-type contact layer 10 is one third of that of the Comparative Example and the ohmic contact area is reduced. Since the parasitic resistance on the electrode 11 side is high, the forward voltage Vf is higher in Example 3 as shown in FIG.
- Example 3 and Comparative Example 3 used p-type GaN as the p-type contact layer 10, and Example 3 used 67% as the aperture ratio.
- the patterns of the p-type contact layer 10 and the p-electrode 11 three types were prepared with the same aperture ratio, and Examples 3A to 3C were used.
- Examples 3A to 3C and Comparative Example 3 the light emission output P and the forward voltage Vf were measured for each of three samples, the conversion efficiency E was calculated, and the average value of each is shown in FIG.
- the pattern of Example 3A is a grid pattern shown in FIG. 18A
- the pattern of Example 3B is a comb pattern shown in FIG. 18B
- the pattern of Example 3C is shown in FIG. This is a dot pattern shown in FIG.
- the average light emission output P of the three samples of Comparative Example 3 was 5.85 mW, the forward voltage Vf was 6.23 V, and the conversion efficiency E was 1.57%, whereas the three samples of Example 3A
- the voltage Vf is 7.90 V
- the conversion efficiency E is 1.61%
- the average light emission output P of the three samples of Example 3C is 7.70 mW
- the forward voltage Vf is 7.81 V
- the conversion efficiency E is 1. It was 64%.
- the ratio of the light emission output P to Comparative Example 3 was 129% in Example 3A, 130% in Example 3B, and 132% in Example 3C.
- the ratio of the forward voltage Vf to Comparative Example 3 was 119% in Example 3A, 127% in Example 3B, and 125% in Example 3C.
- the conversion efficiency E is higher in Examples 3A to 3C than in Comparative Example 3.
- the patterns of the p-type contact layer 10 and the p-electrode 11 are different, but the aperture ratio is the same, so that there is no significant difference in the light emission output P and the forward voltage Vf.
- Example 3C the light emission output P tends to be good in Example 3C, and the conversion efficiency E tends to be good in Example 3A.
- Example 3 67% was used as the aperture ratio.
- the forward voltage Vf is the same, the light emission output P naturally increases and the forward voltage Vf also increases as the aperture ratio increases.
- the aperture ratio is Larger is more advantageous.
- the aperture ratio becomes too large, the p-type contact layer 10 and the p-electrode 11 cannot be patterned, and the forward voltage Vf may increase beyond the practical range. There is an upper limit according to the structure, manufacturing process, electrical specifications, etc.
- the effect of improving the external quantum efficiency by providing the reflective electrode 13 in the n-electrode structure portion will be described.
- the second embodiment the external quantum efficiency by providing the reflective electrode 13 in the n-electrode structure portion.
- the improvement effect was explained.
- the increase rate of the light emission output P was 115% (Example 1), whereas in the second embodiment, the increase rate of the light emission output P was 129% to 132% (implementation). Examples 3A to 3C), and the rate of increase was about twice that of the first embodiment.
- the reflective electrode 13 in the n-electrode structure portion is not directly reflected from the active layer 7 as the reflective electrode 16 in the p-electrode structure portion to improve the external quantum efficiency, but is reflected on the emission surface. Since the external quantum efficiency is improved by further re-reflecting some light emission, the external quantum efficiency improvement effect is expected to be considerably lower than that of the reflective electrode 16 in the p-electrode structure portion. As described above, if the area of the contact surface between the reflective electrode 13 and the n-type cladding layer 6 is secured to about 180 to 200% of the area of the first region R1, about half of the effect of improving the reflective electrode 16 in the p-electrode structure portion. A degree is obtained. An increase rate of the light emission output P by the two reflective electrodes 13 and 16 can be expected to be about 150%.
- the reflective electrode 16 may be formed after depositing a transparent insulating film 17 such as SiO 2 , AlN, or HfO 2 that transmits ultraviolet rays (particularly, ultraviolet rays in the emission wavelength region).
- a transparent insulating film 17 such as SiO 2 , AlN, or HfO 2 that transmits ultraviolet rays (particularly, ultraviolet rays in the emission wavelength region).
- the opening 15 is formed by forming the p-type contact layer 10 on the entire surface of the p-type cladding layer 9 and then removing a part thereof by reactive ion etching or the like.
- a mask for selective growth such as SiO 2 is formed in a portion to be the opening 15 on the p-type cladding layer 9, and then a p-type contact layer 10 of p-type GaN is formed on the p-type cladding layer 9.
- selective growth may be performed so that a mask portion for selective growth is formed as the opening 15.
- the reflective electrode 16 can be formed thereon without removing the mask portion.
- FIG. 27 shows the dependence of the AlN mole fraction on the current-voltage characteristics indicating the contact resistance characteristics at the interface between the p-electrode and p-type AlGaN used in this embodiment.
- the current value on the vertical axis in FIG. 27 is a relative value. It can be seen that p-type GaN with an AlN molar fraction of 0% shows good ohmic characteristics with low resistance.
- p-type AlGaN having an AlN molar fraction of 9.5% shows a varistor-like non-linear current-voltage characteristic, but it shows a low-resistance non-rectifying resistance characteristic when a voltage of 1 V or higher is applied. I understand.
- p-type AlGaN having an AlN molar fraction of 19.3% is not practical because its resistance value is 30 times higher than that of p-type GaN.
- p-type AlGaN having an AlN molar fraction of 32.8% has a resistance value that is about four orders of magnitude higher than that of p-type GaN and cannot be used.
- the reflective electrode 13 in the n-electrode structure portion and the reflective electrode 16 in the p-electrode structure portion need not have the same composition and structure.
- one may be an Al single layer film and the other may be a three-layer film of Al / Ti / Au.
- the reflective electrode 13 is formed after the n-electrode 12 is formed and the reflective electrode 16 is formed after the p-electrode 11 is formed has been described.
- the electrodes 12 and the p-electrode 11 may be formed after the formation, and the order of formation between the reflecting electrodes 13 and 16 is not particularly limited, and may be formed simultaneously.
- the template 5 shown in FIGS. 2 and 17 is taken as an example of the template constituting the elements 1 and 20 of the present invention.
- the template 5 is not limited to the template 5, and for example, AlN
- the layer 3 may be an ELO-AlN layer shown in FIG. 28, the AlGaN layer 4 may be omitted, and another substrate may be used instead of the sapphire (0001) substrate 2.
- the film thickness and AlN mole fraction of each layer of AlGaN or GaN constituting the elements 1 and 20 of the present invention exemplified in the above embodiments are examples, and can be appropriately changed according to the specifications of the element.
- the electronic block layer 8 was provided was illustrated in each said embodiment, the electronic block layer 8 does not necessarily need to be provided.
- the p electrode 11 when the p electrode 11 is Ni / Au, the n electrode 12 is Ti / Al / Ti / Au, and the reflective electrodes 13 and 16 are Al or Al / Ti / Au.
- the material and film thickness of each electrode are not limited to those described above.
- the electrode material of the p-electrode 11 and the n-electrode 12 can make ohmic contact (or non-rectifying contact with low contact resistance) between the p-type contact layer 10 and the n-type cladding layer 6 which are the respective underlayers. Any metal material may be used, and the multilayer structure is not necessarily required. Further, the layer structure may be alloyed by heat treatment.
- the n electrode 12 has exemplified the case of using Ti as a metal material (adhesive layer) for enhancing the adhesiveness with the n-type cladding layer 6, but Cr may be used instead of Ti. It is not necessary to provide such an adhesive layer.
- the reflective electrodes 13 and 16 need to contain a metal that reflects ultraviolet rays, for example, Al as a main component, but do not necessarily have ohmic contact with the base layer.
- the reflective electrode 16 when the reflective electrode 16 is formed, the reflective electrode 16 is formed on the substantially entire surface of the first region so as to cover the p electrode 11, but the reflective electrode 16 is formed on the active region formed in the first region. It is also a preferred embodiment to form the layer 7 to the p-type contact layer 10 on the side wall surface of the laminate. In this case, in order to prevent each layer of the laminate from being electrically short-circuited, it is necessary to form a sidewall insulating film with SiO 2 or the like between the sidewall surface of the laminate and the reflective electrode 13.
- the sidewall insulating film is formed by depositing an insulating film such as SiO 2 on the entire surface of the substrate, and removing the insulating film deposited by anisotropic etching, so that the side wall surface of the stacked body is removed.
- the insulating film remaining in the wall shape is formed as a sidewall insulating film.
- a photoresist to be an inverted pattern of the reflective electrode 16 is formed on the entire surface of the substrate so as not to cover the sidewall insulating film, and the material film of the reflective electrode 16 is deposited in the manner described above.
- the reflective electrode 16 that covers the side wall surface of the stacked body is formed. Further, instead of the reflective electrode 16, the reflective electrode 13 is also preferably formed on the side wall surface of the laminate from the active layer 7 formed in the first region to the p-type contact layer 10 in the same manner as described above. It is an embodiment.
- the nitride semiconductor ultraviolet light-emitting device according to the present invention can be used for a light-emitting diode having an emission center wavelength of about 355 nm or less, and is effective in improving external quantum efficiency.
- SYMBOLS 1,20 Nitride semiconductor ultraviolet light emitting element 2,101: Sapphire substrate 3: AlN layer 4: AlGaN layer 5: Template 6,104: N-type clad layer (n-type AlGaN) 7: Active layer 7a: Barrier layer 7b: Well layer 8,106: Electron block layer (p-type AlGaN) 9, 107: p-type cladding layer (p-type AlGaN) 10, 108: p contact layer (p-type GaN) 11, 109: p-electrode 12, 110: n-electrode 13: reflective electrode (first reflective metal layer) 14: Ni mask 15: Opening 16: Reflective electrode (second reflective metal layer) 17: Transparent insulating film 102: Underlayer (AlN) 103: ELO-AlN layer 105: Multiple quantum well active layer R1: first region R2: second region
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Abstract
Description
図2に示すように、本発明素子1は、サファイア(0001)基板2上にAlN層3とAlGaN層4を成長させた基板をテンプレート5として用い、当該テンプレート5上に、n型AlGaNからなるn型クラッド層6、活性層7、Alモル分率が活性層7より大きいp型AlGaNの電子ブロック層8、p型AlGaNのp型クラッド層9、p型GaNのp型コンタクト層10を順番に積層した積層構造を有している。n型クラッド層6より上部の活性層7、電子ブロック層8、p型クラッド層9、p型コンタクト層10の一部が、n型クラッド層6の一部表面が露出するまで反応性イオンエッチング等により除去され、n型クラッド層6上の第1領域(R1)に活性層7からp型コンタクト層10までの積層構造が形成されている。また、活性層7は、一例として、膜厚10nmのn型AlGaNのバリア層7aと膜厚3.5nmのAlGaNの井戸層7bからなる単層の量子井戸構造となっている。活性層7は、下側層と上側層にAlモル分率の大きいn型及びp型AlGaN層で挟持されるダブルヘテロジャンクション構造であれば良く、また、上記単層の量子井戸構造を多層化した多重量子井戸構造であっても良い。
上記第1実施形態では、n電極12と反射電極13を組み合わせた新規なn電極構造により、つまり、n電極12側での電極構造の改良により、外部量子効率が改善できることを説明した。第2実施形態では、n電極12とp電極11の両電極での電極構造の改良により、外部量子効率が更に改善できることを説明する。
〈1〉上記第2実施形態では、反射電極16を、開口部15内において、p型クラッド層9表面上に直接形成する場合を説明したが、例えば、図26に示すように、開口部15内に紫外線(特に、発光波長域の紫外線)を透過するSiO2、AlN、HfO2等の透明絶縁膜17を堆積した後、反射電極16を形成するようにしても良い。
2,101: サファイア基板
3: AlN層
4: AlGaN層
5: テンプレート
6,104: n型クラッド層(n型AlGaN)
7: 活性層
7a: バリア層
7b: 井戸層
8,106: 電子ブロック層(p型AlGaN)
9,107: p型クラッド層(p型AlGaN)
10,108: pコンタクト層(p型GaN)
11,109: p電極
12,110: n電極
13: 反射電極(第1反射金属層)
14: Niマスク
15: 開口部
16: 反射電極(第2反射金属層)
17: 透明絶縁膜
102: 下地層(AlN)
103: ELO-AlN層
105: 多重量子井戸活性層
R1: 第1領域
R2: 第2領域
Claims (11)
- n型AlGaN系半導体層からなるn型クラッド層上の前記n型クラッド層の表面と平行な面内の第1領域に、バンドギャップエネルギが3.4eV以上のAlGaN系半導体層を有する活性層と、前記活性層より上層に位置するp型AlGaN系半導体層からなるp型クラッド層が形成され、
前記n型クラッド層上の前記第1領域以外の第2領域内における前記第1領域の近傍領域に、前記n型クラッド層とオーミック接触するn電極金属層が形成され、
前記第2領域内の前記近傍領域以外の前記n型クラッド層の表面上に、前記活性層から発光される紫外光を反射する第1反射金属層が形成され、
前記n電極金属層が前記n型クラッド層表面の前記第1反射金属層と接触する領域と前記第1領域の間に配置されていることを特徴とする窒化物半導体紫外線発光素子。 - 前記第1反射金属層が、前記n電極金属層の上面の少なくとも一部を覆って接触し、前記n電極金属層と電気的に接続していることを特徴とする請求項1に記載の窒化物半導体紫外線発光素子。
- 前記n型クラッド層のAlNモル分率が、前記活性層のAlNモル分率より大きく、且つ、60%以下であることを特徴とする請求項1または2に記載の窒化物半導体紫外線発光素子。
- 前記第1反射金属層が、Al、或いは、Alを主成分とする金属多層膜または合金で形成されていることを特徴とする請求項1~3の何れか1項に記載の窒化物半導体紫外線発光素子。
- 前記p型クラッド層上に前記紫外光を吸収するp型AlGaN系半導体層からなるp型コンタクト層が形成され、
前記p型コンタクト層が前記p型クラッド層表面まで貫通する開口部を有し、
前記p型コンタクト層上に前記p型コンタクト層とオーミック接触または非整流性接触するp電極金属層が、前記開口部を完全に遮蔽しないように形成され、
少なくとも前記開口部上に前記紫外光を反射する第2反射金属層が形成され、
前記第2反射金属層が、前記開口部を通して露出した前記p型クラッド層表面を、直接または前記紫外光を透過する透明絶縁層を介して覆っていることを特徴とする請求項1~4の何れか1項に記載の窒化物半導体紫外線発光素子。 - 前記p型コンタクト層のAlNモル分率が0%以上10%未満であることを特徴とする請求項5に記載の窒化物半導体紫外線発光素子。
- 前記第2反射金属層が少なくとも前記開口部上と前記p電極金属層上に形成されていることを特徴とする請求項5または6に記載の窒化物半導体紫外線発光素子。
- 前記第2反射金属層が、Al、或いは、Alを主成分とする金属多層膜または合金で形成されていることを特徴とする請求項5~7の何れか1項に記載の窒化物半導体紫外線発光素子。
- 前記p型コンタクト層と前記開口部の合計面積に対する前記開口部の面積の比率が66%以上であることを特徴とする請求項5~8の何れか1項に記載の窒化物半導体紫外線発光素子。
- 前記n型クラッド層が、絶縁体層、半導体層、または、絶縁体層と半導体層の積層体からなる前記紫外光を透過するテンプレート上に形成されていることを特徴とする請求項1~9の何れか1項に記載の窒化物半導体紫外線発光素子。
- 前記テンプレートがAlN層を含むことを特徴とする請求項10に記載の窒化物半導体紫外線発光素子。
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