WO2013015035A1 - 半導体発光素子 - Google Patents
半導体発光素子 Download PDFInfo
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- WO2013015035A1 WO2013015035A1 PCT/JP2012/065146 JP2012065146W WO2013015035A1 WO 2013015035 A1 WO2013015035 A1 WO 2013015035A1 JP 2012065146 W JP2012065146 W JP 2012065146W WO 2013015035 A1 WO2013015035 A1 WO 2013015035A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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
- H01L33/04—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with a quantum effect structure or superlattice, e.g. tunnel junction
- H01L33/06—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with a quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier 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 with at least one potential-jump barrier or surface barrier 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 system
- H01L33/32—Materials of the light emitting region containing only elements of group III and group V of the periodic system containing nitrogen
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
- H01S5/2004—Confining in the direction perpendicular to the layer structure
- H01S5/2009—Confining in the direction perpendicular to the layer structure by using electron barrier layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/3407—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers characterised by special barrier layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/34333—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser with a well layer based on Ga(In)N or Ga(In)P, e.g. blue laser
Definitions
- the present invention relates to a semiconductor light emitting device.
- LEDs Light emitting diodes
- LDs semiconductor lasers
- emit light such as blue and green as semiconductor light emitting devices in which an n-side semiconductor layer, an active layer, and a p-side semiconductor layer are stacked in this order on a substrate.
- a GaN layer is formed on a heterogeneous substrate through an intermediate layer such as a low-temperature buffer layer in order to planarize the substrate surface and reduce through pits from the heterogeneous substrate.
- a film is formed, and an n-side semiconductor layer, an active layer, and a p-side semiconductor layer are stacked thereon.
- dislocations and defects once generated in the stacked structure cannot be easily reduced by stacking a semiconductor layer thereon. Further, dislocations and defects tend to further increase as the thickness of the well layer of the active layer increases or the number of stacked layers increases. As a result, due to the light emitting layer with many dislocations and crystal defects, high light emission efficiency cannot be obtained after all. In addition, the increase in the thickness of the well layer or the increase in the number of layers in the active layer in which dislocations and defects exist inherently results in an increase in the series resistance component. Invite the problem of obstructing.
- the present invention has been made in view of the above problems, and suppresses a decrease in light emission efficiency due to dislocations and crystal defects, reduces a series resistance component, and achieves further improvement in light emission efficiency.
- An object is to provide an element.
- the present invention A semiconductor light emitting device in which an n-side semiconductor layer, an active layer, and a p-side semiconductor layer are stacked in this order on a substrate,
- the active layer has a multiple quantum well structure configured to include a plurality of barrier layers and a plurality of well layers adjacent to the barrier layers,
- a final barrier layer disposed on the side of the barrier layer closest to the p-side semiconductor layer, and one or more barrier layers adjacent to the final barrier layer through a well layer are formed in the n-side semiconductor layer.
- It is a semiconductor light emitting element characterized by being thicker than the barrier layer disposed on the near side.
- a semiconductor light emitting device in which an n-side semiconductor layer, an active layer, and a p-side semiconductor layer are stacked in this order on a substrate,
- the active layer has a multiple quantum well structure including a plurality of unit periods composed of a barrier layer and a well layer adjacent to the barrier layer, The film thickness of the unit period arranged on the side closest to the p-side semiconductor layer in the unit period and one or more unit periods adjacent to the unit period are arranged on the side close to the n-side semiconductor layer. It is a semiconductor light emitting element characterized by being thicker than the film thickness of the unit period.
- Such a semiconductor light emitting device preferably includes one or more of the following.
- the active layer includes a unit period disposed on the side close to the n-side semiconductor layer, and has a plurality of adjacent unit periods having the same film thickness and disposed on the side close to the p-side semiconductor layer.
- a plurality of adjacent unit periods having the same film thickness and including unit periods, and the total number of unit periods including unit periods arranged on the side closer to the n-side semiconductor layer is p More than the total number of unit periods including unit periods arranged on the side closer to the side semiconductor layer.
- the barrier layer in the unit period arranged on the side close to the p-side semiconductor layer is thicker than the barrier layer in the unit period arranged on the side close to the n-side semiconductor layer.
- the barrier layer in the unit period arranged on the side close to the p-side semiconductor layer has a thickness of 1.5 times or more the film thickness of the well layer in the unit period arranged on the side close to the p-side semiconductor layer.
- the active layer has a barrier layer disposed on the side close to the n-side semiconductor layer, a plurality of barrier layers having the same film thickness as the barrier layer, and adjacent to the barrier layer via a well layer, a barrier layer disposed on the side close to the p-side semiconductor layer, a plurality of barrier layers having the same film thickness as the barrier layer and adjacent to the barrier layer through a well layer, and the n-side
- the number of barrier layers arranged on the side close to the semiconductor layer and having the same film thickness is larger than the number of barrier layers arranged on the side close to the p-side semiconductor layer and having the same film thickness.
- the final barrier layer has a thickness of 1.5 times or more the thickness of the adjacent well layer.
- the barrier layers and the well layers are alternately stacked.
- the well layer is made of undoped InGaN
- the barrier layer is made of an undoped nitride semiconductor having a band gap energy larger than that of the well layer.
- the well layer is made of undoped InGaN
- the barrier layer is made of undoped GaN, undoped AlGaN, or undoped InGaN having a lower mixed crystal ratio of In than the well layer.
- the mixed crystal ratio of In in the well layer is 0.1 or more and 0.4 or less.
- a cap layer having a composition different from that of the well layer and the barrier layer is provided between the well layer and the barrier layer.
- the semiconductor light emitting device of the present invention it is possible to suppress a decrease in light emission efficiency due to dislocations and crystal defects and reduce a series resistance component, thereby realizing further improvement in light emission efficiency.
- the semiconductor light emitting device of the present invention is a so-called LED.
- an n-side semiconductor layer 2, an active layer 3, and a p-side semiconductor layer 4 are mainly arranged in this order on a substrate 1.
- a stacked semiconductor layer 5 is provided.
- the substrate 1 may not exist in the final form.
- the p-side semiconductor layer 4 has a full-surface electrode 6 connected to substantially the entire upper surface and a p-electrode 7 connected to a part of the full-surface electrode 6.
- n-type contact layer constituting the n-side semiconductor layer 2 is exposed, and the exposed surface
- An n electrode 8 is connected to the first electrode.
- a protective film is formed on a part of the side surface and upper surface of the substrate 1 and the semiconductor layer 5, and optionally on a part of the side surface and upper surface of the p electrode 7 and the n electrode 8.
- “part” includes both part in the plane (part of the region) and part in the film thickness direction.
- the n-side semiconductor layer 2, the active layer 3, and the p-side semiconductor layer 4 are represented by the formula (A) In x Al y Ga 1-x -y N (0 ⁇ x ⁇ 1,0 ⁇ y ⁇ 1,0 ⁇ x + y ⁇ 1) (A) It can form with the compound semiconductor represented by these.
- an element in which B is partially substituted as a group III element may be used, or an element in which a part of N is substituted with P or As may be used as a group V element.
- the n-side semiconductor layer 2 includes a layer containing at least one group IV element or group VI element such as Si, Ge, Sn, S, O, Ti, Zr, and Cd as an n-type impurity. It is a general term for a single layer or a laminated layer on one side with respect to the active layer 3. Of these, Si and Sn are preferable as the n-type impurity.
- the p-side semiconductor layer 3 is a single layer or a stacked layer on the other side of the active layer 3 in which a layer containing one or more kinds of Mg, Zn, Be, Mn, Ca, Sr, etc. is arranged as a p-type impurity. A generic term for layers.
- the active layer 3 has a multiple quantum well structure.
- the multiple quantum well structure is formed with a plurality of unit periods U each composed of one barrier layer and one well layer adjacent to the barrier layer.
- the multiple quantum well structure is formed to include a barrier layer, one or more barrier layers adjacent to the barrier layer via the well layer, and two or more well layers.
- the number of unit periods, the number of barrier layers, and the number of well layers are not particularly limited, and are each preferably, for example, 50 or less, preferably 30 or less, and more preferably 20 or less. Of these, about 7 to 15 is more preferable.
- the layer adjacent to the n-side semiconductor layer and the p-side semiconductor layer may be a barrier layer or a well layer, but the barrier layer is adjacent to both the n-side semiconductor layer and the p-side semiconductor layer. It is preferable to do. Note that the barrier layer adjacent to the n-side semiconductor layer may be referred to as a first barrier layer, and the barrier layer adjacent to the p-side semiconductor layer may be referred to as a final barrier layer.
- the well layer constituting the active layer 3 preferably contains In in the formula (A), that is, the In mixed crystal ratio (x) is preferably about 0.4 or less. More preferably, it is about 3 or less. Moreover, it is suitable that it is about 0.1 or more.
- the mixed crystal ratio of In becomes a factor for determining the light emission wavelength of the semiconductor light emitting device, and the present invention works particularly advantageously on the light emitting device on the short wavelength side where the mixed crystal ratio of In is low.
- the barrier layer and the well layer have different compositions.
- the barrier layer is preferably made of an undoped nitride semiconductor having a larger band gap energy than the well layer.
- the barrier layer is made of GaN, AlGaN, or InGaN having a smaller In mixed crystal ratio than the well layer. Things.
- the In mixed crystal ratio is compared with values obtained by averaging the In compositions of all well layers and all barrier layers.
- the well layer usually has a thickness in the range of about 1 to 8 nm, preferably about 1.5 to 5 nm, and the barrier layer has a thickness in the range of about 1.5 to 16 nm, preferably about 2 to 10 nm. It has a thickness.
- the barrier layer preferably has a thickness of about 1.5 times or more that of the well layer, and preferably has a thickness of about 2 times or more.
- the final barrier layer preferably has a thickness of about 1.5 times or more that of the adjacent well layer, and preferably has a thickness of about 2 times or more.
- composition and / or film thickness of the well layer may vary, but it is suitable that at least one of the composition and the film thickness, preferably both the composition and the film thickness are constant. If the composition and thickness of the well layer are constant, the wavelength of the light emitted from the active layer is stabilized, and the amount of wavelength change associated with changing the half-value width, current, and temperature is stable, that is, the amount of wavelength change. And the relative output at high temperature with respect to the normal temperature output is improved.
- the barrier layer includes at least a barrier layer disposed on the side closest to the p-side semiconductor layer (hereinafter referred to as a final barrier layer) and one or more barriers adjacent to the final barrier layer through a well layer. It is suitable that the layer is thicker than the barrier layer disposed on the side closer to the n-side semiconductor layer.
- the “barrier layer disposed on the side closer to the n-side semiconductor layer” refers to an arbitrary barrier layer disposed closer to the n-side semiconductor layer than the center of the entire thickness of the active layer among the barrier layers. Point to.
- the final barrier layer and the one or more barrier layers adjacent to the final barrier layer through the well layer may be thicker than any of the barrier layers disposed on the side closer to the n-side semiconductor layer,
- the first barrier layer is preferably thick with respect to all the barrier layers arranged on the n-side semiconductor layer side other than the first barrier layer.
- the final barrier layer is preferably thicker than the first barrier layer.
- the final barrier layer is thicker than the barrier layer disposed on the side closer to the n-side semiconductor layer and closer to the final barrier layer (that is, closer to the p-side semiconductor layer, the final barrier layer and the well layer). If one or more other barrier layers arranged adjacent to each other are thicker than the barrier layer arranged closer to the n-side semiconductor layer, the number of barrier layers, that is, the number of unit periods Can be in the above-mentioned range.
- the “barrier layer disposed on the side close to the final barrier layer (or the side close to the p-side semiconductor layer)” is closer to the p-side semiconductor layer side than the center of the entire film thickness of the active layer among the barrier layers. Refers to any barrier layer placed on the side.
- the other barrier layer preferably has a film thickness equivalent to the final barrier layer (for example, ⁇ 20% thickness).
- the one or more other barrier layers that are thicker than the barrier layer disposed on the side closer to the n-side semiconductor layer and are disposed closer to the p-side semiconductor layer are adjacent to the unit period including the final barrier layer.
- the barrier layer may be one unit period, or may be a plurality of unit period barrier layers that are sequentially adjacent to the unit period including the final barrier layer.
- the barrier layer may be one barrier layer adjacent to the final barrier layer via the well layer, or may be a plurality of barrier layers sequentially adjacent to the final barrier layer via the well layer.
- the well layer 3a, the barrier layers 3bn1 to 3bn4, and the well layer 3a are sequentially formed from the first barrier layer 3b.
- the barrier layer 3 bp 2, the well layer 3 a and the barrier layer 3 bp 1 (that is, the final barrier layer 3 bb), and the unit periods are repeatedly arranged in six periods so as to be arranged in the order of the unit periods UN 1 to UN 4 and the unit periods UP 2 to UP 1.
- the barrier layer 3bp1 (for example, the final barrier layer 3bb closest to the p-side semiconductor layer) disposed on the side close to the p-side semiconductor layer and the barrier layer 3bp2 in the unit cycle UP2 adjacent to the unit cycle UP1 including the barrier layer 3bp1 It is preferable that the barrier layers 3bp1 and 3bp2 have the same thickness and are thicker than the barrier layer 3bn1 disposed on the side closer to the n-side semiconductor layer.
- the barrier layers 3bp1 and 3bp2 are more preferably thicker than the first barrier layer 3b.
- the barrier layer in the unit period UP arranged on the side close to the p-side semiconductor layer for example, the barrier layer 3bp1 in FIG. 2 has the thickness of the well layer 3a in the unit period UP arranged on the side close to the p-side semiconductor layer. It is preferable to have a film thickness of 1.5 or more, and more than twice.
- the film thickness of the unit period arranged on the side closest to the p-side semiconductor layer in the unit period and one or more unit periods adjacent to the unit period is determined by the n-side semiconductor layer. It is suitable that the thickness is larger than the film thickness of the unit period arranged on the near side. That is, in FIG. 2, the total film thickness of the unit period UP1 including the final barrier layer 3bb is an arbitrary unit period (for example, UN1, UN2, etc.) among the unit periods arranged on the side closer to the n-side semiconductor layer. Thicker than the total film thickness is suitable. As described above, the well layer in the active layer usually has a constant composition and / or film thickness.
- the barrier layer 3bp1 disposed on the side closer to the p-side semiconductor layer is preferably thicker than the barrier layer (eg, 3bn1, 3bn2, etc.) disposed on the side closest to the n-side semiconductor layer.
- the barrier layer in the unit period arranged on the side close to the p-side semiconductor layer is preferably thicker than the barrier layer in an arbitrary unit period arranged on the side close to the n-side semiconductor layer.
- the thickness of the thick barrier layer is suitably about 200% or less of the thickness of the other barrier layer, preferably about 150% or less, more preferably about 120% or less. preferable. Further, the thickness may be about several percent of the thickness of the other barrier layer, and is preferably about 105% or more.
- the active layer includes a unit period arranged on the side close to the n-side semiconductor layer, has a plurality of adjacent unit periods having the same film thickness, and further close to the p-side semiconductor layer. It is suitable to have a plurality of adjacent unit periods including the arranged unit periods and having the same film thickness.
- the active layer has a barrier layer disposed on the side close to the n-side semiconductor layer, and has the same film thickness as the barrier layer, and has a plurality of barrier layers adjacent to each other through the barrier layer and the well layer.
- At least two types of unit periods are arranged depending on the thickness of the barrier layer.
- a plurality of adjacent unit periods for example, UN2, UN3, UN4, etc.
- Two groups including a unit period UP1 disposed on the side close to the p-side semiconductor layer and a plurality of adjacent unit periods (for example, UP2) having the same film thickness are disposed.
- the total number of unit cycles including unit cycles arranged on the side closer to the n-side semiconductor layer may be larger than the total number of unit cycles including unit cycles arranged on the side closer to the p-side semiconductor layer.
- the number of barrier layers disposed on the side closer to the n-side semiconductor layer and having the same film thickness is larger than the number of barrier layers disposed on the side closer to the p-side semiconductor layer and having the same film thickness. A large amount is preferable.
- the number of unit periodic groups or barrier layer groups arranged on the side closer to the n-side semiconductor layer is about 1.5 times or more, about 2 times or more, or about 3 times or more. In other words, it is preferably 1 or more, 2 or more, 3 or more, 4 or more, 5 or more. As a result, it is possible to effectively improve the light emission efficiency without increasing the series resistance component while sufficiently exhibiting the function as the active layer.
- the total number of unit periods (or barrier layers) including unit periods (or barrier layers) arranged on the side closer to the p-side semiconductor layer is suitably about 2 to 15, About 10 is preferable, and about 2 to 7 is more preferable.
- the total number of unit periods (or barrier layers) including the unit period (or barrier layer) arranged on the side close to the n-side semiconductor layer is the unit period (or barrier) arranged on the side close to the p-side semiconductor layer described above. More than the total number of unit periods (or barrier layers) including the layer), and about 3 to 45 is suitable, preferably about 3 to 30, and more preferably about 3 to 10.
- the first barrier layer adjacent to the n-side semiconductor layer and / or the final barrier layer adjacent to the p-side semiconductor layer described above may be omitted, but it is preferable to arrange both of them.
- the first barrier layer and / or the final barrier layer may be arranged as a barrier layer constituting the above-described two types of film thickness unit period groups or two types of film thickness barrier layers.
- the first barrier layer may be, for example, either a semiconductor layer containing an n-type impurity or a non-doped semiconductor layer, and may have either a single layer structure or a stacked structure.
- a stacked structure in which a semiconductor layer containing an n-type impurity and a non-doped semiconductor layer are stacked adjacent to the n-side semiconductor layer is preferable.
- the film thickness in this case is suitably about 0.5 to 7 nm, for example, and the n-type impurity layer / non-doped layer is preferably about 0.3 to 5 nm / about 0.2 to 2 nm.
- the first barrier layer and making it thicker than the other barrier layers close to the n-side semiconductor it is possible to compensate for the crystal defects in the lower layer, and to improve the quality of the well layer and hence the quality.
- An active layer can be laminated.
- a cap layer 9 having a composition different from that of the well layer and the barrier layer may be formed between the well layer and the barrier layer.
- the cap layer is preferably formed of an AlGaN layer with respect to the InGaN well layer.
- the thickness of the cap layer is preferably, for example, about 20 to 150% with respect to the well layer.
- the active layer may have three or more types of unit period (or three or more types of barrier layers) groups.
- a unit periodic group or a barrier layer group having the thickness of the barrier layer may be arranged. In this way, by adding unit periods or barrier layers having different film thicknesses, the number of unit periods or barrier layers can be increased, and the resistance component, forward voltage Vf, and luminous efficiency can be further reduced. Improvements can be realized.
- the film thickness increases stepwise or gradually from the unit period or barrier layer disposed on the side closer to the n-side semiconductor layer to the unit period or barrier layer disposed on the side closer to the p-side semiconductor layer. Furthermore, these film thicknesses may be changed.
- substrate sapphire whose principal surface is the C-plane, R-plane or A-plane, other insulating substrates such as spinel (MgA 12 O 4 ), SiC (including 6H, 4H, 3C), A semiconductor substrate such as Si, ZnO, GaAs, or GaN can be used.
- the substrate may have an off-angle. By using an off-angled one, the base layer can be grown with good crystallinity, and a high-quality n-side semiconductor layer, active layer, and p-side semiconductor layer can be stacked.
- a buffer layer is preferably formed on the substrate 1.
- the buffer layer include a nitride semiconductor made of Ga d Al 1-d N (0 ⁇ d ⁇ 1), and a layer having an Al mixed crystal ratio of 0.3 or less is preferable, and the Al mixed crystal ratio is 0. .2 or less layers are more preferred. The smaller the Al mixed crystal ratio, the more remarkable the improvement in crystallinity. More preferred is a buffer layer made of GaN. Further, the buffer layer can be finally removed, or can be omitted.
- the film thickness is preferably about 0.002 to 0.5 ⁇ m, preferably about 0.05 to 0.2 ⁇ m, and more preferably about 0.01 to 0.02 ⁇ m.
- the temperature for growing the buffer layer is suitably 200 to 900 ° C., and is preferably adjusted to a range of 400 to 800 ° C. As a result, a good polycrystal can be formed, and the crystallinity of a semiconductor grown on the buffer layer can be made good by using this polycrystal as a seed crystal.
- a semiconductor layer serving as a base layer may be further formed on the buffer layer.
- a nitride semiconductor layer having a dislocation density of 1 ⁇ 10 7 to 5 ⁇ 10 9 cm ⁇ 2 is suitable.
- the nitride semiconductor layer is preferably a GaN layer, but may be an Al 1-x Ga x N layer (0 ⁇ x ⁇ 1).
- This nitride semiconductor layer may be a single layer or a laminated structure of two or more layers.
- the nitride semiconductor layer is preferably a layer having a different composition and / or film formation method. Thereby, the dislocation density can be reduced and the crystallinity can be improved.
- the thickness of the nitride semiconductor layer is, for example, preferably about 1 ⁇ m or more, more preferably about 2 ⁇ m or more, about 3 ⁇ m or more, preferably about 10 ⁇ m or less, more preferably about 5 ⁇ m or less. preferable.
- N-side semiconductor layer In the n-side semiconductor layer, an n-type contact layer and an n-type cladding layer are usually laminated in this order from the substrate 1 side.
- the composition of the n-type contact layer is not particularly limited.
- a layer made of AlGaN or GaN having an Al ratio of 0.2 or less is preferable, and a layer made of a single layer is more preferable. With such a composition, it is easy to obtain a nitride semiconductor layer with few crystal defects.
- the film thickness of the n-type contact layer is not particularly limited, and can be, for example, about 1 ⁇ m or more, preferably about 3 ⁇ m or more.
- the n-type contact layer contains an n-type impurity, and its concentration is preferably high enough not to deteriorate the crystallinity of the nitride semiconductor. For example, it is 1 ⁇ 10 18 / cm 3 or more and 5 ⁇ 10 21 / cm 3 or less.
- the n-type cladding layer may have a single layer structure, but may be a nitride semiconductor composed of at least two kinds of elements having different compositions, for example, a layer composed of the above-described formula (A).
- the n-type cladding layer is preferably formed of a superlattice multilayer film, and Al z Ga 1-z N (0 ⁇ z ⁇ 1) (first layer) and In p Ga 1-p N (0 ⁇ P ⁇ 1)
- a superlattice layer in which layers composed of two types of compositions (second layer) are alternately laminated is more preferable. Any of the first layer and the second layer may be the lowermost layer and / or the uppermost layer.
- the composition of all the layers of the first layer, the second layer, the first layer and the second layer may not necessarily be the same, and the composition may be partially, in a gradient, stepwise or alternately. It may change. Especially, it is preferable that 1st layers and 2nd layers are layers of the same composition.
- the second layer is preferably a layer having p of 0.5 or less, and more preferably a layer having p of 0.2 or less.
- a superlattice multilayer film in which the first layer is GaN and p is 0.2 or less In p Ga 1-p N in the second layer is preferable.
- the layers having different compositions are, for example, suitable to be a laminated film of 20 or more layers, each laminated with 10 or more layers, each having 20 or more layers.
- a laminated film (total of 40 layers or more) is preferable.
- the upper limit of the number of laminated layers of the first layer and the second layer is not particularly limited, for example, 500 layers or less is suitable, and 200 layers or less and 100 layers or less are preferable. By disposing such an n-type cladding layer, it is possible to effectively reduce Vf.
- the thickness of the layer constituting the n-type cladding layer is not particularly limited, but the total thickness is suitably about 50 nm or more, preferably about 65 nm or more, more preferably about 75 nm or more, more preferably about 80 nm or more, Furthermore, about 90 nm or more is even more preferable.
- the upper limit of the total film thickness is not particularly limited, but may be about 500 nm or less, preferably about 400 nm or less, in consideration of manufacturing efficiency and improvement of characteristics. By setting the total film thickness within this range, the crystallinity is improved and the output of the element can be improved.
- the n-type cladding layer may not contain n-type impurities in all layers, and it is sufficient that at least one layer contains n-type impurities.
- only one of the first layer and the second layer described above may not contain n-type impurities, or all layers may contain n-type impurities.
- the types and concentrations of impurities may not be the same in all layers, and may be different from each other or at least one layer.
- both the first layer and the second layer described above are doped with n-type impurities, and by adopting a modulation dope having different concentrations between adjacent nitride semiconductor layers, the light output tends to be further improved. There is.
- the impurity concentration examples include 5 ⁇ 10 16 / cm 3 or more and 3 ⁇ 10 18 / cm 3 or more, and 5 ⁇ 10 18 / cm 3 or more is preferable.
- the upper limit of the n-type impurity concentration is not particularly limited, but is preferably such that the crystallinity is not deteriorated too much, for example, 5 ⁇ 10 21 / cm 3 or less or 1 ⁇ 10 20 / cm 3 or less. By setting such an impurity concentration, Vf can be further reduced.
- the method for forming the n-type cladding layer is not particularly limited.
- MOVPE metal organic vapor phase epitaxy
- HVPE hydride vapor phase epitaxy
- MBE molecular beam epitaxy
- the film formation temperature is not particularly limited, but is preferably 850 ° C. or higher, more preferably 900 ° C. or higher. Thereby, crystallinity can be made more favorable.
- the p-side semiconductor layer preferably includes a p-side cladding layer and a p-type contact layer in order from the active layer side.
- the p-side cladding layer examples include a single layer composed of the above-described formula (A) containing at least a p-type impurity, or at least two laminated layers having different band gap energies or a superlattice multilayer film.
- A Al b Ga 1-b N (0 ⁇ b ⁇ 1) or a stacked layer of at least two semiconductor layers having different band gap energies is preferable.
- the p-side cladding layer has a p-type impurity concentration of, for example, preferably about 1 ⁇ 10 22 / cm 3 or less, and more preferably about 5 ⁇ 10 20 / cm 3 or less.
- the lower limit of the p-type impurity concentration is not particularly limited, but about 5 ⁇ 10 16 / cm 3 or more is suitable.
- the p-type impurity may not be contained in all the layers. Further, the p-type impurity concentration in each layer or a part of the layers may be different or the same.
- the film thickness of the p-side cladding layer is not particularly limited, and may be about 10 nm or more.
- the thickness of the single nitride semiconductor layer is preferably about 10 nm or less, more preferably about 7 nm or less and about 5 nm or less.
- Examples of the p-type contact layer include a layer made of a nitride semiconductor represented by the above-described formula (A). Among them, GaN, AlGaN with an Al ratio of 0.2 or less, InGaN with an In ratio of 0.2 or less A layer made of GaN is preferred, and a layer made of GaN is more preferred. These compositions can provide good ohmic contact with the electrode material.
- the film thickness of the p-type contact layer 10 is not particularly limited, and is preferably about 50 nm or more, and more preferably about 60 nm or more.
- Examples of the impurity concentration include 1 ⁇ 10 18 / cm 3 or more and 5 ⁇ 10 21 / cm 3 or less.
- the whole surface electrode, p electrode and n electrode used in the semiconductor light emitting device of the present invention are not particularly limited, such as the composition of the single layer, the composition and order of the laminated structure, and the film thickness, and any of those known in the art can be used. Can also be adopted.
- the entire surface electrode is preferably formed of a material that does not absorb light emitted from the active layer in consideration of light extraction efficiency, and examples thereof include a conductive oxide (ITO or the like).
- the material and film thickness of the protective film are not particularly limited, but for example, a single layer film or a multilayer film made of SiO 2 , ZrO 2 , TiO 2 , Al 2 O 3 , Nb 2 O 5 , AlN, AlGaN, or the like Is mentioned.
- the film thickness is preferably adjusted as appropriate.
- the semiconductor light emitting device of this example is formed on a substrate 1 made of sapphire.
- a buffer layer made of undoped AlGaN (film thickness: about 15 nm)
- An intermediate layer made of undoped GaN (film thickness: about 3.5 ⁇ m)
- N-type contact layer film thickness: 4.2 ⁇ m) made of GaN doped with 9 ⁇ 10 18 / cm 3 of Si
- a GaN layer r film thickness: 4 nm
- doped with 2.5 ⁇ 10 18 / cm 3 of Si is stacked, an undoped In 0.02 Ga 0.98 N layer q (film thickness: 2 nm)
- Si is 2
- An n-side cladding layer having a superlattice structure of a total of 121 layers in which the GaN layer r (film thickness: 4 nm) doped with .5 ⁇ 10 18 / cm
- the active layer in the laminated structure is First barrier layer: a laminated structure of a layer made of GaN doped with Si at 5 ⁇ 10 18 / cm 3 (film thickness: about 4 nm), a layer made of undoped GaN (film thickness: about 3.5 nm), Above this first barrier layer, A laminated structure in which the unit period of the well layer g (film thickness: about 3.3 nm) made of undoped In 0.2 Ga 0.8 N and the barrier layer h (film thickness: about 5.0 nm) made of undoped GaN is 6 periods.
- n-type contact layer On almost the entire surface of the p-type contact layer, a light-transmitting full-surface electrode 6 made of ITO and a p-electrode 7 containing Ti, Rh, and Au formed thereon are formed, and an exposed n-type contact is formed.
- An n electrode 8 made of the same laminated material as the p electrode is formed on the surface of the layer.
- Such a semiconductor light emitting device 10 can be manufactured by the following method.
- substrate A substrate 1 made of sapphire (C-plane) is set in a MOCVD reaction vessel, and the substrate temperature is raised to about 900 ° C. to 1200 ° C. while flowing hydrogen to clean the substrate.
- the temperature is set to about 500 ° C.
- hydrogen is used as a carrier gas
- ammonia is used as a carrier gas
- TMG trimethylgallium
- TMA trimethylaluminum
- the substrate is made of undoped Al 0.05 Ga 0.95 N.
- a buffer layer is grown to a thickness of about 1.5 ⁇ m.
- the temperature is set to about 800 ° C.
- hydrogen is used as the carrier gas
- ammonia and TMG are used as the source gas
- an intermediate layer made of undoped GaN is grown on the buffer layer to a thickness of about 3.5 ⁇ m. .
- an n-type contact layer made of GaN doped with Si is grown to a thickness of about 4 ⁇ m using TMG, ammonia gas as source gas, and silane gas as impurity gas.
- N-type cladding layer (N-type cladding layer) Subsequently, using a TMG and ammonia at a temperature of about 800 ° C. to 1000 ° C., a Si-doped GaN layer (film thickness: 4 nm) is stacked, and then a non-doped GaN layer (film thickness: 2 nm) is stacked.
- the barrier layer a layer made of GaN containing Si is grown by about 4 nm, and a layer made by undoped GaN is grown by a film thickness of about 3.5 nm. Then, using TMG, TMI, and ammonia, a well layer made of undoped In 0.2 Ga 0.8 N and a barrier layer made of undoped GaN with a thickness of about 4.4 nm are alternately stacked in six layers. Further, the well layer made of undoped In 0.2 Ga 0.8 N is about 3.3 nm, and the barrier layer made of undoped GaN is about 5.25 (1.05 times thick), respectively. Three layers (that is, the seventh layer to the ninth layer) are alternately stacked to grow an active layer having a multiple quantum well structure in which the unit period of the well layer and the barrier layer is nine periods (total film thickness: about 75 nm). .
- a p-side cladding layer made of Mg-doped p-type Al 0.2 Ga 0.8 N is grown to a thickness of about 15 nm.
- TMG, TMA, and ammonia are used at a temperature of about 900 ° C. to 1000 ° C., and a layer made of undoped GaN is grown to a thickness of about 50 nm, on which TMG, ammonia, and Cp 2 Mg are used.
- a layer made of Mg-doped p-type GaN is grown to a thickness of about 50 nm, and a layer made of Mg-doped p-type GaN is further grown to a thickness of about 15 nm.
- the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 300 ° C. to 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-side layer.
- the wafer is taken out from the reaction container, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer, and etching is performed from the p-type contact layer side with an RIE (reactive ion etching) apparatus to form an n-type contact. Expose the surface of the layer.
- RIE reactive ion etching
- a translucent full-surface electrode made of ITO is formed on almost the entire surface of the p-type contact layer as the uppermost layer.
- a laminated film containing Ti, Rh, and Au is formed on the n-type contact layer exposed by p-etching on the entire surface electrode, and patterned to form a p-electrode and an n-electrode, respectively.
- the obtained laminated structure was cut into each chip to obtain a semiconductor light emitting device having an output wavelength of 440 to 480 nm, for example. Further, the same structure as in Example 1a except that the thick film of the barrier layer was changed to a 1.1 times thick film (5.5 nm) instead of a 1.05 times thick film (5.25 nm). A semiconductor light emitting device of Example 1b was prepared.
- the thickness of the barrier layer is 1.05 times (Example 2a) and 1.1 times (Example 2b) in the fifth to ninth layers, and the well layer and the barrier layer have nine cycles ( (Layer thickness: 76 nm and 77 nm)
- Layer thickness: 76 nm and 77 nm A semiconductor light emitting device having the same structure was obtained except that the layers were stacked.
- the thickness of the barrier layer is 1.05 times (Example 3a) and 1.1 times (Example 3b) in the third to ninth layers, and the well layer and the barrier layer have nine periods ( (Layer thickness: 76.5 nm and 78 nm)
- Layer thickness: 76.5 nm and 78 nm A semiconductor light emitting device having a similar structure was obtained except that the layers were stacked.
- Comparative Example 1 A semiconductor light emitting device having a similar structure was obtained except that the well layer and the barrier layer were stacked for nine periods (layer thickness: 75 nm) without changing the thickness of the barrier layer in the active layer.
- the semiconductor light-emitting device of the present invention can be used for various light sources such as a full-color LED display, a traffic signal light, and an image scanner light source, for example, as a high-intensity blue LED or pure green LED.
Abstract
Description
これらの半導体発光素子を製造する方法としては、一般に、異種基板上に低温バッファ層等の中間層等を介して、基板表面の平坦化及び異種基板からの貫通ピットを低減するためにGaN層を成膜し、その上に、n側半導体層、活性層及びp側半導体層を積層する。
一方、高輝度でかつ高発光効率を有する半導体発光素子を得るために、井戸層の厚みを変化させること、あるいは、活性層の障壁層及び井戸層の単位周期数を、n側半導体層側よりもp側半導体層側で多く設定することなどが提案されている(例えば、特許文献1)。
基板上に、n側半導体層、活性層及びp側半導体層がこの順に積層された半導体発光素子であって、
前記活性層は、複数の障壁層とこれら障壁層に隣接する複数の井戸層とを含んで構成された多重量子井戸構造を有し、
前記障壁層のうちの前記p側半導体層に最も近い側に配置された最終障壁層と、該最終障壁層に井戸層を介して隣接する1以上の障壁層とが、前記n側半導体層に近い側に配置する障壁層よりも厚膜であることを特徴とする半導体発光素子である。
前記活性層は、障壁層と該障壁層に隣接する井戸層とからなる複数の単位周期を含んで構成された多重量子井戸構造を有し、
前記単位周期のうちの前記p側半導体層に最も近い側に配置された単位周期と、該単位周期に隣接する1以上の単位周期との膜厚が、前記n側半導体層に近い側に配置された単位周期の膜厚よりも厚いことを特徴とする半導体発光素子である。
前記活性層は、前記n側半導体層に近い側に配置された単位周期を含み、互いに同じ膜厚を有して隣接する複数の単位周期と、前記p側半導体層に近い側に配置された単位周期を含み、互いに同じ膜厚を有して隣接する複数の単位周期とを有し、かつ
前記n側半導体層に近い側に配置された単位周期を含む単位周期の合計数が、前記p側半導体層に近い側に配置された単位周期を含む単位周期の合計数よりも多い。
前記p側半導体層に近い側に配置された単位周期における障壁層が、前記n側半導体層に近い側に配置された単位周期における障壁層よりも厚膜である。
前記p側半導体層に近い側に配置された単位周期における障壁層は、前記p側半導体層に近い側に配置された単位周期における井戸層の膜厚の1.5倍以上の膜厚を有する。
前記活性層は、前記n側半導体層に近い側に配置された障壁層と、該障壁層と同じ膜厚を有し、該障壁層と井戸層を介して隣接する複数の障壁層と、前記p側半導体層に近い側に配置された障壁層と、該障壁層と同じ膜厚を有し、該障壁層と井戸層を介して隣接する複数の障壁層とを有し、かつ
前記n側半導体層に近い側に配置され、互いに同じ膜厚を有する障壁層の数が、前記p側半導体層に近い側に配置され、互いに同じ膜厚を有する障壁層の数よりも多い。
前記最終障壁層は、隣接する前記井戸層の膜厚の1.5倍以上の膜厚を有する。
前記障壁層と前記井戸層とが交互に積層される。
前記井戸層は、アンドープInGaNからなり、
前記障壁層は、前記井戸層よりもバンドギャップエネルギーが大きいアンドープの窒化物半導体からなる。
前記井戸層は、アンドープInGaNからなり、
前記障壁層は、アンドープGaN、アンドープAlGaN又は前記井戸層よりもInの混晶比が低いアンドープInGaNからなる。
前記井戸層のInの混晶比が、0.1以上0.4以下である。
前記井戸層と障壁層との間に、該井戸層及び障壁層と組成の異なるキャップ層を有する。
さらに、p側半導体層4は、その上面の略全面に接続された全面電極6及びこの全面電極6の一部に接続されたp電極7を有している。また、p側半導体層4及び活性層3の一部ならびにn側半導体層2の一部が除去されて、n側半導体層2を構成するn型コンタクト層が露出しており、その露出した面にn電極8が接続されている。
ここでの「一部」とは、面内における一部(領域の一部)及び膜厚方向の一部の双方を含む。
InxAlyGa1-x-yN(0≦x≦1、0≦y≦1、0≦x+y≦1) (A)
で表される化合物半導体によって形成することができる。これに加えて、III族元素としてBが一部に置換されたものを用いてもよいし、V族元素としてNの一部をP、Asで置換されたものを用いてもよい。
p側半導体層3は、p型不純物として、Mg、Zn、Be、Mn、Ca、Sr等を1種類以上含有している層が配置されている、活性層3に対する他方側の単層又は積層層の総称である。
活性層3は、多重量子井戸構造を有している。多重量子井戸構造は、1つの障壁層とこの障壁層に隣接する1つの井戸層とからなる単位周期Uを複数有して形成されている。言い換えると、多重量子井戸構造は、障壁層と、その障壁層に井戸層を介して隣接する1以上の障壁層と、2以上の井戸層とを有して形成されている。単位周期の数、障壁層及び井戸層の数は、特に限定されず、それぞれ、例えば、50以下であることが適しており、30以下であることが好ましく、20以下であることがより好ましい。なかでも、7~15程度がさらに好ましい。
活性層では、通常、井戸層は1~8nm、好ましくは1.5~5nm程度の範囲内の厚みを有し、障壁層は、1.5~16nm、好ましくは2~10nm程度の範囲内の厚みを有する。一般に、障壁層は、井戸層の1.5倍程度以上の膜厚を有していることが適しており、2倍程度以上の膜厚を有していることが好ましい。特に、最終障壁層は、隣接する井戸層の1.5倍程度以上の膜厚を有していることが適しており、2倍程度以上の膜厚を有していることが好ましい。障壁層を井戸層よりも厚膜とすることにより、Inの混晶によって、さらに、Inの混晶比を高くすることによって発生し得る欠陥を補填することができ、良好な品質の井戸層、ひいては良質の活性層を得ることができる。
p側半導体層に近い側に配置された単位周期UPにおける障壁層、例えば、図2における障壁層3bp1は、p側半導体層に近い側に配置された単位周期UPにおける井戸層3aの膜厚の1.5以上、さらに2倍以上の膜厚を有することが好ましい。
つまり、図2において、最終障壁層3bbを含む単位周期UP1の総膜厚が、n側半導体層に近い側に配置された単位周期のうちの任意の単位周期(例えば、UN1、UN2等)の総膜厚よりも厚いことが適している。なお、上述したように、活性層における井戸層は、通常、その組成及び/又は膜厚が一定であることが好ましいため、上述したように、p側半導体層に近い側に配置する障壁層3bp1(例えば、最もp側半導体層に近い最終障壁層3bb)が、n側半導体層に近い側に配置する障壁層(例えば、3bn1、3bn2等)よりも厚膜であることが好ましい。言い換えると、p側半導体層に近い側に配置された単位周期における障壁層が、n側半導体層に近い側に配置された任意の単位周期における障壁層よりも厚膜であることが好ましい。
この場合、第1障壁層及び/又は最終障壁層は、上述した2種類の膜厚の単位周期群又は2種類の膜厚の障壁層群を構成する障壁層として配置してもよいし、各群を構成しない障壁層として配置していてもよい。各群を構成する障壁層として配置する場合には、これらの膜厚関係に従って適切な膜厚に調整することが好ましい。なかでも、最終障壁層は、群を構成する障壁層として配置することが好ましい。
特に、第1障壁層を配置すること、さらにn側半導体に近い他の障壁層よりも厚膜とすることにより、下層の結晶欠陥を補填することができ、より良質の井戸層、ひいては良質の活性層を積層することができる。
基板1としては、C面、R面又はA面を主面とするサファイア、その他、スピネル(MgA12O4)のような絶縁性の基板の他、SiC(6H、4H、3Cを含む)、Si、ZnO、GaAs、GaN等の半導体基板を用いることができる。
基板は、オフアングルを有していてもよい。オフアングルしたものを用いることにより、下地層を結晶性よく成長させることができ、良質のn側半導体層、活性層及びp側半導体層を積層することができる。
バッファ層としては、例えば、GadAl1-dN(0<d≦1)からなる窒化物半導体が挙げられ、Al混晶比が0.3以下の層が好ましく、Al混晶比が0.2以下の層がより好ましい。Al混晶比が小さいほど結晶性の改善が顕著となる。より好ましくはGaNからなるバッファ層が挙げられる。また、バッファ層は最終的に除去することもできるし、それ自体省略することもできる。
例えば、転位密度が1×107~5×109cm-2である窒化物半導体層を備えていることが適している。この窒化物半導体層はGaN層であることが好ましいが、Al1-xGaxN層(0<x<1)としてもよい。この窒化物半導体層は、単一層でも、2層以上の積層構造であってもよい。窒化物半導体層は、積層構造として形成される場合、組成及び/又は成膜方法等の異なる層で有ることが好ましい。これによって、転位密度を低減することができるとともに、結晶性を向上させることができる。
n側半導体層は、基板1側から、通常、n型コンタクト層及びn型クラッド層がこの順に積層されている。
n型コンタクト層としては、その組成は特に限定されるものではなく、例えば、Al比率が0.2以下のAlGaN又はGaNからなる層が好ましく、単一層からなる層がより好ましい。このような組成にすると、結晶欠陥の少ない窒化物半導体層が得やすい。
n型コンタクト層は、n型不純物を含有しており、その濃度は、窒化物半導体の結晶性を悪化しない程度に高いことが好ましい。例えば、1×1018/cm3以上、5×1021/cm3以下が挙げられる。
n型クラッド層は、単層構造でもよいが、組成の異なる少なくとも2種類以上の元素からなる窒化物半導体、例えば、上述した式(A)からなる層であってもよい。特に、n型クラッド層は、超格子多層膜によって形成されていることが好ましく、AlzGa1-zN(0≦z<1)(第1層)とInpGa1-pN(0<p<1)(第2層)との2種類の組成からなる層が交互に積層された超格子層がより好ましい。第1層及び第2層は、いずれが最下層及び/又は最上層であってもよい。ただし、必ずしも第1層同士、第2層同士、第1層及び第2層の全ての層の組成が同じでなくもよく、部分的に、傾斜的に、段階的に又は交互にその組成が変化してもよい。なかでも、第1層同士及び第2層同士が、同じ組成の層であることが好ましい。
第2層は、pが0.5以下の層が好ましく、pが0.2以下の層がより好ましい。
なかでも、n型クラッド層としては、第1層がGaNであり、第2層においてpが0.2以下のInpGa1-pNである超格子多層膜が好ましい。
p側半導体層は、例えば、活性層側から順に、p側クラッド層及びp型コンタクト層を含むことが好ましい。
p側クラッド層としては、p型不純物を含有する、上述した式(A)からなる単一層又はバンドギャップエネルギーの異なる少なくとも2層の積層層又は超格子多層膜が挙げられる。なかでも、AlbGa1-b N(0≦b≦1)からなる単一層又はバンドギャップエネルギーの異なる少なくとも2層の半導体層の積層層が好ましい。
p側クラッド層は、p型不純物濃度が、例えば、1×1022/cm3程度以下が好ましく、5×1020/cm3程度以下がより好ましい。p型不純物濃度の下限は特に限定されないが、5×1016/cm3程度以上が適している。
積層層又は超格子多層膜においては、全ての層にp型不純物が含有されていなくてもよい。また、各層又は一部の層においてp型不純物濃度が異なっていてもよいし、同じでもよい。
p型コンタクト層は、例えば、上述した式(A)で表される窒化物半導体からなる層が挙げられ、なかでも、GaN、Al比率0.2以下のAlGaN、In比率0.2以下のInGaNからなる層が好ましく、GaNからなる層がより好ましい。これらの組成は、電極材料と良好なオーミックコンタクトを得ることができる。
不純物濃度は、例えば、1×1018/cm3以上、5×1021/cm3以下が挙げられる。
本発明の半導体発光素子において用いられる全面電極、p電極及びn電極は、その単一層の組成、積層構造の組成及び積層順序、膜厚等、特に限定されず、当該分野で公知のもののいずれをも採用することができる。
特に、全面電極は、光の取出効率を考慮して、活性層から出射される光を吸収しない材料によって形成されることが好ましく、例えば、導電性酸化物(ITO等)等が挙げられる。
保護膜としては、特にその材料及び膜厚は限定されないが、例えば、SiO2、ZrO2、TiO2、Al2O3、Nb2O5、AlN、AlGaN等からなる単層膜又は多層膜等が挙げられる。その膜厚は適宜調整することが好ましい。
実施例1a及び1b
この実施例の半導体発光素子は、図1に示すように、サファイアからなる基板1上に、
アンドープAlGaNからなるバッファ層(膜厚:約15nm)、
アンドープGaNからなる中間層(膜厚:約3.5μm)、
Siを9×1018/cm3ドープしたGaNからなるn型コンタクト層(膜厚:4.2μm)、
Siを2.5×1018/cm3ドープしたGaN層r(膜厚:4nm)を積層した上に、アンドープIn0.02Ga0.98N層q(膜厚:2nm)、Siを2.5×1018/cm3ドープしたGaN層r(膜厚:4nm)がこの順で、GaN層qとGaN層rの積層を繰り返した合計121層の超格子構造からなるn側クラッド層(膜厚:364nm)、
活性層(膜厚:膜厚約75nm)、
Mgを1×1020/cm3ドープしたp型Al0.2Ga0.8Nからなるp側クラッド層(膜厚:約25nm)及び
アンドープGaNからなる層(膜厚:約50nm)、Mgを1×1020/cm3ドープしたp型GaNからなる層(膜厚:約50nm)及びMgを5×1020/cm3ドープしたp型GaNからなる層(膜厚:約15nm)が順に積層されたp型コンタクト層がこの順に積層されて構成されている。
第1障壁層:Siを5×1018/cm3ドープしたGaNからなる層(膜厚:約4nm)、アンドープGaNからなる層(膜厚:約3.5nm)の積層構造と、
この第1障壁層の上の、
アンドープIn0.2Ga0.8Nからなる井戸層g(膜厚:約3.3nm)及びアンドープGaNからなる障壁層h(膜厚:約5.0nm)の単位周期を6周期の積層構造と、この積層構造の上の、
アンドープIn0.2Ga0.8Nからなる井戸層w(膜厚:約3.3nm)及びアンドープGaNからなる障壁層t(膜厚:約5.25nm)の単位周期を3周期の積層構造とから構成される多重量子井戸構造を有する。
p型コンタクト層上のほぼ全面には、ITOからなる透光性の全面電極6と、その上に形成されたTi、Rh及びAuを含むp電極7が形成されており、露出したn型コンタクト層上の表面にはp電極と同じ積層材料からなるn電極8が形成されている。
(基板)
サファイア(C面)からなる基板1をMOCVDの反応容器内にセットし、水素を流しながら、基板の温度を900℃~1200℃程度まで上昇させ、基板のクリーニングを行う。
続いて、温度を500℃程度にして、キャリアガスに水素、原料ガスにアンモニア、TMG(トリメチルガリウム)及びTMA(トリメチルアルミニウム)を用い、基板上にアンドープAl0.05Ga0.95Nからなるバッファ層を約1.5μmの膜厚で成長させる。
続いて、温度を800℃程度にして、キャリアガスに水素、原料ガスにアンモニア、TMG(トリメチルガリウム)を用い、バッファ層上にアンドープGaNからなる中間層を約3.5μmの膜厚で成長させる。
次に、同じく原料ガスにTMG、アンモニアガス、不純物ガスにシランガスを用い、SiをドープしたGaNからなるn型コンタクト層を約4μmの膜厚で成長させる。
続いて、温度800℃~1000℃程度で、TMG、アンモニアを用い、SiをドープしたGaN層(膜厚:4nm)を積層した上に、ノンドープのGaN層(膜厚:2nm)を積層する。
次に、障壁層として、Siを含むGaNよりなる層を約4nm成長させ、アンドープGaNよりなる層を約3.5nmの膜厚で成長させる。
その後、TMG、TMI、アンモニアを用いアンドープIn0.2Ga0.8Nよりなる井戸層を約3.3nm及びアンドープGaNよりなる障壁層を約4.4nmの膜厚でそれぞれ6層交互に積層して、さらに、アンドープIn0.2Ga0.8Nよりなる井戸層を約3.3nm及びアンドープGaNよりなる障壁層を約5.25(1.05倍厚膜)nmの膜厚でそれぞれ3層(つまり、7層目~9層目)交互に積層して、井戸層及び障壁層の単位周期が9周期(総膜厚:約75nm)の多重量子井戸構造よりなる活性層を成長させる。
次に、TMG、TMA、アンモニア、Cp2Mg(シクロペンタジエニルマグネシウム)を用い、Mgドープp型Al0.2Ga0.8Nからなるp側クラッド層を約15nmの膜厚で成長させる。
続いて、温度900℃~1000℃程度で、TMG、TMA、アンモニアを用い、アンドープのGaNからなる層を約50nmの膜厚で成長させ、この上に、TMG、アンモニア、Cp2Mgを用い、Mgドープp型GaNからなる層を約50nmの膜厚で、さらにその上にMgドープp型GaNからなる層を約15nmの膜厚で成長させる。
その後、ウエハを反応容器から取り出し、最上層のp型コンタクト層の表面に所定の形状のマスクを形成し、RIE(反応性イオンエッチング)装置でp型コンタクト層側からエッチングを行い、n型コンタクト層の表面を露出させる。
全面電極上pエッチングにより露出させたn型コンタクト層の上に、Ti、Rh、Auを含む積層膜を成膜し、パターニングすることにより、p電極及びn電極をそれぞれ形成する。
また、上記実施例1aにおいて、障壁層の厚膜を、1.05倍の厚膜(5.25nm)に代えて、1.1倍の厚膜(5.5nm)とした以外、同様の構造の半導体発光素子を作製した(実施例1b)。
活性層において、障壁層の膜厚を、5~9層目において1.05倍(実施例2a)及び1.1倍(実施例2b)の厚膜として、井戸層及び障壁層を9周期(層膜厚:76nm及び77nm)積層した以外、同様の構造の半導体発光素子を得た。
活性層において、障壁層の膜厚を、3~9層目において1.05倍(実施例3a)及び1.1倍(実施例3b)の厚膜として、井戸層及び障壁層を9周期(層膜厚:76.5nm及び78nm)積層した以外、同様の構造の半導体発光素子を得た。
活性層において障壁層の膜厚を変化させることなく、井戸層及び障壁層を9周期(層膜厚:75nm)積層した以外、同様の構造の半導体発光素子を得た。
上記実施例1a~3b及び比較例1で得られた半導体発光素子について、順方向電圧と出力とを測定した。評価は500×290μmサイズのチップに順方向電流20mAをパルスで印加した状態で行った。
その結果を図3に示す。図3において、白棒は障壁層の厚みが1.05倍厚膜、斜線は障壁層の厚みが1.1倍厚膜の活性層を備える発光素子の出力を示す。比較例の発光素子の出力を基準として、実施例1a~実施例3bのいずれも、0.2~0.5mV程度の増加が認められた。
また、これらの実施例の全てにおいて、比較例のVfに対して、同等以下のVfが測定された。
このような結果から、Vfの低下及び出力の向上のバランスを図り、より高い発光効率を実現することができる。
Claims (12)
- 基板上に、n側半導体層、活性層及びp側半導体層がこの順に積層された半導体発光素子であって、
前記活性層は、複数の障壁層とこれら障壁層に隣接する複数の井戸層とを含んで構成された多重量子井戸構造を有し、
前記障壁層のうちの前記p側半導体層に最も近い側に配置された最終障壁層と、該最終障壁層に井戸層を介して隣接する1以上の障壁層とが、前記n側半導体層に近い側に配置する障壁層よりも厚膜であることを特徴とする半導体発光素子。 - 基板上に、n側半導体層、活性層及びp側半導体層がこの順に積層された半導体発光素子であって、
前記活性層は、障壁層と該障壁層に隣接する井戸層とからなる複数の単位周期を含んで構成された多重量子井戸構造を有し、
前記単位周期のうちの前記p側半導体層に最も近い側に配置された単位周期と、該単位周期に隣接する1以上の単位周期との膜厚が、前記n側半導体層に近い側に配置された単位周期の膜厚よりも厚いことを特徴とする半導体発光素子。 - 前記活性層は、前記n側半導体層に近い側に配置された単位周期を含み、互いに同じ膜厚を有して隣接する複数の単位周期と、前記p側半導体層に近い側に配置された単位周期を含み、互いに同じ膜厚を有して隣接する複数の単位周期とを有し、かつ
前記n側半導体層に近い側に配置された単位周期を含む単位周期の合計数が、前記p側半導体層に近い側に配置された単位周期を含む単位周期の合計数よりも多い請求項2に記載の半導体発光素子。 - 前記p側半導体層に近い側に配置された単位周期における障壁層が、前記n側半導体層に近い側に配置された単位周期における障壁層よりも厚膜である請求項3に記載の半導体発光素子。
- 前記p側半導体層に近い側に配置された単位周期における障壁層は、前記p側半導体層に近い側に配置された単位周期における井戸層の膜厚の1.5倍以上の膜厚を有する請求項4に記載の半導体発光素子。
- 前記活性層は、前記n側半導体層に近い側に配置された障壁層と、該障壁層と同じ膜厚を有し、該障壁層と井戸層を介して隣接する複数の障壁層と、前記p側半導体層に近い側に配置された障壁層と、該障壁層と同じ膜厚を有し、該障壁層と井戸層を介して隣接する複数の障壁層とを有し、かつ
前記n側半導体層に近い側に配置され、互いに同じ膜厚を有する障壁層の数が、前記p側半導体層に近い側に配置され、互いに同じ膜厚を有する障壁層の数よりも多い請求項1に記載の半導体発光素子。 - 前記最終障壁層は、隣接する前記井戸層の膜厚の1.5倍以上の膜厚を有する請求項1に記載の半導体発光素子。
- 前記障壁層と前記井戸層とが交互に積層される請求項1に記載の半導体発光素子。
- 前記井戸層は、アンドープInGaNからなり、
前記障壁層は、前記井戸層よりもバンドギャップエネルギーが大きいアンドープの窒化物半導体からなる請求項1~8のいずれか1つに記載の半導体発光素子。 - 前記井戸層は、アンドープInGaNからなり、
前記障壁層は、アンドープGaN、アンドープAlGaN又は前記井戸層よりもInの混晶比が低いアンドープInGaNからなる請求項1~8のいずれか1つに記載の半導体発光素子。 - 前記井戸層のInの混晶比が、0.1以上0.4以下である請求項9又は10に記載の半導体発光素子。
- 前記井戸層と障壁層との間に、該井戸層及び障壁層と組成の異なるキャップ層を有する請求項1~11のいずれか1つに記載の半導体発光素子。
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US9524869B2 (en) * | 2004-03-11 | 2016-12-20 | Epistar Corporation | Nitride-based semiconductor light-emitting device |
US10553749B2 (en) | 2004-03-11 | 2020-02-04 | Epistar Corporation | Nitride-based semiconductor light-emitting device |
WO2013132812A1 (ja) * | 2012-03-05 | 2013-09-12 | パナソニック株式会社 | 窒化物半導体発光素子、光源及びその製造方法 |
JP5468709B2 (ja) * | 2012-03-05 | 2014-04-09 | パナソニック株式会社 | 窒化物半導体発光素子、光源及びその製造方法 |
US8866127B2 (en) | 2012-03-05 | 2014-10-21 | Panasonic Corporation | Nitride semiconductor light-emitting element including Si-doped layer, and light source |
CN107004740A (zh) * | 2014-12-01 | 2017-08-01 | 欧司朗光电半导体有限公司 | 具有波长的温度补偿的发光二极管芯片 |
US10217896B2 (en) | 2014-12-01 | 2019-02-26 | Osram Opto Semiconductors Gmbh | Light emitting diode chip having temperature compensation of the wavelength |
Also Published As
Publication number | Publication date |
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EP2738824A1 (en) | 2014-06-04 |
EP2738824B1 (en) | 2022-08-24 |
TW201316546A (zh) | 2013-04-16 |
JP6079628B2 (ja) | 2017-02-15 |
US9123851B2 (en) | 2015-09-01 |
US20140166980A1 (en) | 2014-06-19 |
JPWO2013015035A1 (ja) | 2015-02-23 |
TWI585995B (zh) | 2017-06-01 |
EP2738824A4 (en) | 2015-04-22 |
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