EP2973754A1 - Monolithic light-emitting device - Google Patents

Monolithic light-emitting device

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Publication number
EP2973754A1
EP2973754A1 EP14709339.7A EP14709339A EP2973754A1 EP 2973754 A1 EP2973754 A1 EP 2973754A1 EP 14709339 A EP14709339 A EP 14709339A EP 2973754 A1 EP2973754 A1 EP 2973754A1
Authority
EP
European Patent Office
Prior art keywords
stack
quantum
iii
matrix
planes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP14709339.7A
Other languages
German (de)
French (fr)
Inventor
Benjamin Damilano
Hyonju KIM-CHAUVEAU
Eric Frayssinet
Julien Brault
Philippe DE MIERRY
Sébastien CHENOT
Jean Massies
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Centre National de la Recherche Scientifique CNRS
Original Assignee
Centre National de la Recherche Scientifique CNRS
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Publication date
Application filed by Centre National de la Recherche Scientifique CNRS filed Critical Centre National de la Recherche Scientifique CNRS
Publication of EP2973754A1 publication Critical patent/EP2973754A1/en
Withdrawn legal-status Critical Current

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Classifications

    • 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
    • H01L33/04—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 with a quantum effect structure or superlattice, e.g. tunnel junction
    • H01L33/06—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 with a quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
    • 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
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0075—Processes for devices with an active region comprising only III-V compounds comprising nitride compounds
    • 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
    • H01L33/08—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 with a plurality of light emitting regions, e.g. laterally discontinuous light emitting layer or photoluminescent region integrated within the semiconductor body
    • 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
    • H01L33/325—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen characterised by the doping materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0008—Processes
    • H01L2933/0016—Processes relating to electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2933/00—Details relating to devices covered by the group H01L33/00 but not provided for in its subgroups
    • H01L2933/0008—Processes
    • H01L2933/0033—Processes relating to semiconductor body packages
    • 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
    • H01L33/04—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 with a quantum effect structure or superlattice, e.g. tunnel junction

Definitions

  • the invention relates to a light-emitting device, more particularly to a light-emitting diode and in particular to a white light-emitting diode.
  • the device of the invention comprises in particular a monolithic matrix, preferably made by epitaxial growth, in nitrides of elements III, for example using alloys (Al, Ga, In) N.
  • the invention also relates to a method of manufacturing such a device.
  • Monolithic white diodes known from the prior art comprise a plurality of electroluminescent regions, formed by quantum wells or III element nitride quantum dot planes, emitting at different wavelengths that combine to give light. white. See, for example, US 6,445,009.
  • the luminous efficiency of these devices is limited by that of electroluminescent regions with lower efficiency, especially those emitting in the yellow.
  • the distribution of electrons and holes in the quantum boxes or quantum wells is changed depending on the voltage applied to the diode. The color of the light emitted may therefore vary with the intensity of the electric current.
  • the diodes of this type are not monolithic: for example, in the case of document US2006 / 0124917, the fluorescent region consists of a quantum well stack in semiconductors 11-VI, reported on a blue light-emitting diode in semi -Conductors III-V.
  • US 2003/006430 discloses a monolithic white light-emitting diode comprising a light-emitting region and a fluorescent region consisting of layers of GaN doped Si or Se, exhibiting an emission in the yolk caused by deep energy levels that originate from crystalline defects.
  • the fluorescent emission thus obtained has a limited quantum efficiency, and its wavelength can not be adjusted to obtain a light having a desired tone.
  • the documents US 2004/0227144 and WO 2007/104884 describe monolithic white diodes comprising an active portion (a light-emitting diode), which can be traversed by an electric current, and a passive portion (wavelength converter) which, because of from its position, can not be traversed by an electric current.
  • the active portion comprises a first stack of quantum wells (or quantum dot planes) in semiconductors III-V, emitting blue radiation by electric injection by said electric current, while the passive portion comprises a second quantum well stack ( or quantum dot planes) in semiconductors III-V, emitting yellow, or green and red radiation, by optical pumping by the radiation emitted by the first stack.
  • the passive portion in order not to be traversed by the electric current flowing through the active portion, the passive portion must be carried out first, by epitaxial deposition on a suitable substrate. The active portion must be performed in a second time, above said passive portion.
  • the quantum well or quantum dot plane stack of the passive portion in order to be able to function correctly as a wavelength converter, the quantum well or quantum dot plane stack of the passive portion must have a high indium (In) content - typically greater than 20% - this which makes it unstable when heated above a temperature above about 1050 ° C.
  • Document DE 10 2004 052 245 describes a light-emitting diode comprising an active portion (electroluminescent) and a passive portion (wavelength converter) made above the active portion.
  • This "inverted" structure makes it possible to carry out the passive portion after the active portion, and thus to avoid any risk of thermal degradation.
  • this implies a passage of the electric current through the passive portion, which is not usual and could, in principle, degrade the electrical characteristics of the device, or even induce undesired electroluminescence of the wavelength converter.
  • the invention aims to overcome the aforementioned drawbacks of the prior art, and in particular to provide a monolithic semiconductor device light emitter having a high efficiency, a stable emission spectrum over time, good electrical properties and can be manufactured by standard industrial processes.
  • An object of the invention making it possible to achieve such a goal, consists of a device according to claim 1.
  • Another object of the invention is a method according to claim 6, allowing the manufacture of such a device
  • FIG. 1 the structure of a monolithic white electroluminescent diode in nitride elements III known from the prior art
  • FIG. 8 the structure of a white light-emitting diode according to one embodiment of the invention
  • FIG. 9 the emission spectrum of a monolithic white electroluminescent diode in nitrides of elements III of the type of FIG. 5, acquired on the front face (that is to say opposite the substrate) and on the back side (that is, through the substrate);
  • FIG. 10 the voltage-current characteristic of said monolithic white light-emitting diode made of III element nitrides, compared to that of a conventional blue diode;
  • FIG. 11 the standardized photoluminescence spectra of three wavelength converters that can be used, separately or jointly, in a monolithic white nitride light emitting diode of elements III according to one embodiment of the invention.
  • FIG. 1 illustrates the structure of a monolithic white diode known from the prior art, and particularly from the aforementioned document WO 2007/104884.
  • a diode comprises, from bottom to top:
  • a light-transparent substrate 7 to be emitted by the device for example sapphire, SiC, ZnO or GaN;
  • Superior p-type AIGaInN, typically having a thickness of the order of 200 nm (the p-type AIGaInN being very resistive, it seeks to minimize its thickness).
  • the regions 1, 2, 30, 40, 5 and 6 form a monolithic matrix of element III nitride semiconductor, generally manufactured by epitaxial deposition on the substrate 7. Within this matrix, the regions 1 , 2 and 30 form a light-emitting diode.
  • a "stair step” etching makes it possible to disengage a region of the upper surface of the region 30 to deposit an electrode 9 therein.
  • Another electrode 8 is deposited on the upper layer 1 (its surface must be higher than that of the electrode 9 because of the less favorable electrical properties of the p-type semiconductor
  • the electrode 8 must preferably cover the entire surface of the light-emitting diode so as to ensure homogeneous injection of the current).
  • the electrodes 8 and 9 make it possible to pass an electric current through the diode 1-2-30; we therefore speak of "active portion" of the matrix. On the other hand, it is understood that no current can pass through the layers 40, 5 and 6 ("passive portion"), because of the presence of the "separation" layer 30, undoped and having a relatively large thickness.
  • the deposition of such a layer 3 must be at a high temperature (above 1000 ° C), which may damage the converter 40.
  • FIG. 2 represents a light-emitting diode which does not fall within the scope of the invention, in which an electric current passes through both the "active" portion and the "passive" portion (wavelength converter) of the matrix.
  • the same reference numerals represent the same elements as in Figure 1. With respect to the device of FIG. 1, the following differences can be observed:
  • the electrode 9 is formed on the rear face of the substrate, which must be conductive (reference 71): a device with a vertical structure is thus produced and the step of "staircase” etching is avoided; the counterpart is that the electric current passes through the whole device, including the converter; this electrode may be transparent, semi-transparent or grid-shaped to allow photon extraction, while it is preferable that the electrode 8, on the "p" side of the device, be a thick metal layer to ensure better electrical contact and also behave like a light reflector;
  • the converter - identified by the reference 4 - differs from the converter 40 of Figure 1 in that it is doped "n" to have a sufficient conductivity (a "p” doping is possible in theory, but less advantageous);
  • the separation region - identified by the reference 3 - may have a much smaller thickness, for example of the order of a few hundred nanometers, or even only 100 nm or less. Indeed, it must no longer ensure the isolation of the converter, which is in any case crossed by the electric current.
  • the converter 4 being doped can provide the electron injection function in the "active" stack 2.
  • Such a thin layer 3 can be carried out by organometallic vapor deposition at a temperature of less than 1000 ° C., for example about 950 ° C. or less, which avoids any risk of damaging the converter 4. .
  • FIG. 3 illustrates a light-emitting diode which does not fall within the scope of the invention, in which an electric current passes through both the "active" portion and the "passive” portion (wavelength converter) of the matrix.
  • This diode also has a vertical structure, but it is performed by flip chip.
  • the epitaxial matrix is separated from its substrate, inverted and deposited on another substrate, 70, which is not necessarily transparent.
  • Reference 80 identifies a solder metal layer, also serving as an electrode.
  • the other The electrode, 90 is deposited on the n-type layer 50 (which corresponds to the "lower” layer 5 of FIGS. 1 and 2, but is now “at the top” of the device).
  • the surface of said layer 50 may be textured to facilitate the extraction of photons.
  • FIGS. 4, 5 and 6 relate to three electroluminescent diodes which do not fall within the scope of the invention, in which an electric current passes through both the "active" portion and the "passive” portion (wavelength converter) of the matrix. These diodes, have a structure closer to that of Figure 1. The only differences concern the thickness of the separation region 3, which is reduced (as in the case of FIGS. 2 and 3), and the fact that the converter 4 has a doping, preferably n-type. Due to the small thickness of the separation layer 3, electrical current lines pass through at least the upper part of the converter 4.
  • the electrical contact 9 is formed on a side portion of the converter. In that of FIG. 5, said contact is made on a lateral portion of the separation region 3. And in the case of FIG. 6 this contact is made on a lateral portion of the lower layer 5.
  • FIG. 7 illustrates the structure of another light-emitting diode which proceeds from a principle different from that at the base of the diodes described above.
  • the key to avoid thermal damage to the converter 4 is not so much in the production of a thin separation layer 3, but in the adoption of an inverted structure, in which said converter is after the "active" stack 2. As in the other examples, this implies the need to allow the passage of an electric current through said converter.
  • the device of FIG. 7 comprises, from bottom to top: an electrode 8 (the structure is of vertical type); a conductive substrate 71, of the p type;
  • an electrode 9 which can be deposited directly above the converter 4, or via an n-type contact layer (not shown).
  • the electrode 9 may be transparent, semi-transparent or grid-shaped to allow extraction of the generated radiation.
  • the advantage of this device is that the converter 4 is made last; it can not be damaged even if other layers are deposited (previously) at high temperature.
  • the main disadvantage of this device lies in the fact that the current must pass through a large thickness of p-type semiconductor (substrate 71, layers 6 and 1 1), which has a high resistivity; in addition, the contact 8 is taken on a p-type region (the substrate 71), which further increases the resistance seen by the current. To reduce this resistance one could achieve an engraving staircase to make contact directly on a portion of the layer 1 January. However, because of the resistivity of said layer, this would lead to a distribution of inhomogeneous current; in addition, the etching operation would be likely to degrade the conductivity of the layers p, while this problem does not arise for n-type layers.
  • FIG. 8 which illustrates an embodiment of the invention, overcomes these disadvantages.
  • the p-type layer 1 1 is replaced by a n-resistive n-type layer 51.
  • the opposite side of the active stack 2 must be provided a layer 3A of type p.
  • a tunnel junction 3B having its p ++ side on the side of the layer 3A and its n ++ side on the side of the converter 4, which has a doping, is introduced. of type n.
  • the tunnel junction 3B has a very small thickness, of the order of a few nanometers, whereas the p-type layer 3A typically has a thickness of the order of 100 nm.
  • devices according to the invention may have a more complex structure, comprising additional layers or by replacing "simple" layers by multilayer structures.
  • the same device may comprise several converters emitting at different wavelengths.
  • the device of Figure 8 is intended for the emission of white light, but this is not an essential feature of the invention.
  • the device of FIG. 8 comprises a conductive substrate 71 (n-type, just like the buffer layer 6), and an electrode 8 deposited on the rear face (opposite to that carrying the matrix) of this substrate.
  • the substrate could be insulating and the electrode 8 could be made in direct contact with the layer 51 by means of staircase etching (see FIG.
  • the matrix could be detached from the substrate, and the electrode 8 could be deposited directly on the rear face of the layer 51.
  • the inventors had to overcome a technical bias. Indeed, it was believed before that the passage of a current Electrical power through the converter 4 would have firstly disturbed the fluorescent emission of said converter, on the other hand degraded the electrical properties of the device in an unacceptable manner. Surprisingly, the present inventors have realized that this is not the case.
  • the matrix of this prototype was entirely realized by EPVOM. It comprises the following stack of layers, starting from the substrate 7 sapphire: a lower layer 5 of thickness of 4.5 ⁇ Si-doped GaN, a converter 4 formed of 20 quantum wells ln 0 , 25Ga 0 , 75N ( 1.2 nm) / GaN: Si (20 nm), a separation layer 3 of GaN: Si (20 nm), an electroluminescent stack 2 formed of 5 quantum wells lno , -iGa 0, .9 N (1 .2 nm) / GaN (10 nm), an upper layer (in fact, a multilayer structure) 1 comprising AI 20 nm thick i-0. 4 Ga 0 .86N: Mg and 235 nm of GaN: Mg.
  • the Si doped layers have n-type conductivity and the Mg-doped layers have a p-type conductivity.
  • Figure 9 shows the emission spectra of this prototype, powered by a current of 20 mA at room temperature.
  • Two spectra were acquired, one "front face” and the other "back face", that is to say through the substrate.
  • a first peak at 380 nm (violet) corresponding to the emission of the active stack 2 and a second peak at 480 nm (yellow) corresponding to the fluorescence of the converter 4 can be noted.
  • the two spectra have been standardized in such a way that that the intensity of the peak at 380 nm is worth 1.
  • the peak at 480 nm is more intense on the rear face than on the front. This is normal because the emission on the front panel also includes the 380 nm photons that have not passed through the converter.
  • Figure 10 compares the current-voltage characteristic of the prototype with that of a conventional violet light-emitting diode (LED), achieved under comparable growth conditions. It comprises the following stack of layers, starting from the substrate 7 in sapphire: a lower layer 5 of 4.5 ⁇ thick Si-doped GaN, an electroluminescent stack 2 formed of 5 quantum wells ln 0 , iGa 0 ,. 9 N (1.2 nm) / GaN (10 nm), an upper layer (in fact, a multilayer structure) 1 comprising 20 nm in thickness of Al 0. 4 Ga 0 .86N: Mg and 235 nm of GaN: mg. It is noted that the current-voltage characteristic of the prototype is not degraded. Surprisingly, this characteristic is even better than that of the reference LED. This indicates that the converter does not add significant resistance to current flow.
  • a conventional violet light-emitting diode LED
  • the thickness and the composition of the quantum wells of the converter 4 (respectively: the composition and the size of the quantum boxes) one can obtain a fluorescent emission covering the whole visible spectrum: blue (470 nm), green (530 nm) , orange (590 nm) and red (650 nm). This is illustrated in Figure 1 1.
  • the combination of these colors makes it possible in principle to obtain all pure or mixed colors such as white.

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Abstract

Light-emitting device comprising a monolithic matrix of III-nitride elements, said matrix comprising at least one first stack (2) of quantum wells or of planes of quantum dots able to emit photons at at least one first wavelength by electrical injection, a second stack (4) of quantum wells or of planes of quantum dots able to emit photons at at least one second wavelength by optical pumping by said photons emitted by said first stack, and a region (3) separating said two stacks, and first (8) and second (9) electrodes arranged to allow an electrical current to pass through said stacks, said second stack (4) is n-doped, said separating region (3) comprises a tunnel junction (3B) having an n++-doped region arranged on the same side as said second stack (4) and a p++-doped region (3A) arranged on the opposite side, and said first stack (2) is arranged between said separating region (3) and at least one n-doped layer (51). Process for manufacturing such device.

Description

DISPOSITIF MONOLITHIQUE EMETTEUR DE LUMIERE  MONOLITHIC LIGHT EMITTING DEVICE
L'invention porte sur un dispositif émetteur de lumière, plus particulièrement sur une diode électroluminescente et notamment sur une diode électroluminescente blanche. Le dispositif de l'invention comprend en particulier une matrice monolithique, réalisée de préférence par croissance épitaxiale, en nitrures d'éléments III, par exemple en utilisant des alliages (AI,Ga,ln)N.  The invention relates to a light-emitting device, more particularly to a light-emitting diode and in particular to a white light-emitting diode. The device of the invention comprises in particular a monolithic matrix, preferably made by epitaxial growth, in nitrides of elements III, for example using alloys (Al, Ga, In) N.
L'invention porte également sur un procédé de fabrication d'un tel dispositif.  The invention also relates to a method of manufacturing such a device.
Des diodes blanches monolithiques connues de l'art antérieur comprennent une pluralité de régions électroluminescentes, formées par des puits quantiques ou des plans de boîtes quantiques en nitrures d'éléments III, émettant à des longueurs d'ondes différentes qui se combinent pour donner une lumière blanche. Voir par exemple le document US 6,445,009.  Monolithic white diodes known from the prior art comprise a plurality of electroluminescent regions, formed by quantum wells or III element nitride quantum dot planes, emitting at different wavelengths that combine to give light. white. See, for example, US 6,445,009.
Toutefois, le rendement lumineux de ces dispositifs est limité par celui des régions électroluminescentes à plus faible efficacité, notamment celles émettant dans le jaune. En outre, la répartition des électrons et des trous dans les boîtes quantiques ou les puits quantiques est modifiée en fonction de la tension appliquée à la diode. La couleur de la lumière émise peut donc varier avec l'intensité du courant électrique.  However, the luminous efficiency of these devices is limited by that of electroluminescent regions with lower efficiency, especially those emitting in the yellow. In addition, the distribution of electrons and holes in the quantum boxes or quantum wells is changed depending on the voltage applied to the diode. The color of the light emitted may therefore vary with the intensity of the electric current.
Pour éviter ces inconvénients, il est connu de réaliser des diodes électroluminescentes blanches comprenant une région électroluminescente, émettant une lumière bleue ou ultraviolette, et une région fluorescente, pompée par ladite lumière bleue ou ultraviolette et réémettant un rayonnement à plus grande longueur d'onde. Conventionnellement, les diodes de ce type ne sont pas monolithiques : par exemple, dans le cas du document US2006/0124917 la région fluorescente est constituée par un empilement de puits quantiques en semi-conducteurs ll-VI, rapportée sur une diode électroluminescente bleue en semi-conducteurs lll-V. La réalisation séparée de la diode électroluminescente bleue et de la région fluorescente, puis leur assemblage, rendent la fabrication d'un tel dispositif complexe et coûteuse.  To avoid these drawbacks, it is known to produce white light-emitting diodes comprising a light-emitting region, emitting a blue or ultraviolet light, and a fluorescent region, pumped by said blue or ultraviolet light and retransmitting a longer wavelength radiation. Conventionally, the diodes of this type are not monolithic: for example, in the case of document US2006 / 0124917, the fluorescent region consists of a quantum well stack in semiconductors 11-VI, reported on a blue light-emitting diode in semi -Conductors III-V. The separate embodiment of the blue light emitting diode and the fluorescent region, and their assembly, make the manufacture of such a complex and expensive device.
Le document US 2003/006430 décrit une diode électroluminescente blanche monolithique comprenant une région électroluminescente et une région fluorescente constituée par des couches de GaN dopées Si ou Se, présentant une émission dans le jaune provoquée par des niveaux énergétiques profonds qui proviennent de défauts cristallins. L'émission fluorescente ainsi obtenue présente une efficacité quantique limitée, et sa longueur d'onde ne peut pas être ajustée pour obtenir une lumière présentant une tonalité voulue. US 2003/006430 discloses a monolithic white light-emitting diode comprising a light-emitting region and a fluorescent region consisting of layers of GaN doped Si or Se, exhibiting an emission in the yolk caused by deep energy levels that originate from crystalline defects. The fluorescent emission thus obtained has a limited quantum efficiency, and its wavelength can not be adjusted to obtain a light having a desired tone.
Les documents US 2004/0227144 et WO 2007/104884 décrivent des diodes blanches monolithiques comprenant une portion active (une diode électroluminescente), pouvant être parcourue par un courant électrique, et une portion passive (convertisseur de longueur d'onde) qui, en raison de sa position, ne peut pas être parcourue par un courant électrique. La portion active comprend un premier empilement de puits quantiques (ou plans de boîtes quantiques) en semi-conducteurs lll-V, émettant un rayonnement bleu par injection électrique par ledit courant électrique, tandis que la portion passive comprend un deuxième empilement de puits quantiques (ou plans de boîtes quantiques) en semi-conducteurs lll-V, émettant un rayonnement jaune, ou vert et rouge, par pompage optique par le rayonnement émis par le premier empilement.  The documents US 2004/0227144 and WO 2007/104884 describe monolithic white diodes comprising an active portion (a light-emitting diode), which can be traversed by an electric current, and a passive portion (wavelength converter) which, because of from its position, can not be traversed by an electric current. The active portion comprises a first stack of quantum wells (or quantum dot planes) in semiconductors III-V, emitting blue radiation by electric injection by said electric current, while the passive portion comprises a second quantum well stack ( or quantum dot planes) in semiconductors III-V, emitting yellow, or green and red radiation, by optical pumping by the radiation emitted by the first stack.
Une telle structure est attrayante, mais difficile à réaliser. En effet, afin de ne pas être parcourue par le courant électrique qui traverse la portion active, la portion passive doit être réalisée la première, par dépôt épitaxial sur un substrat adapté. La portion active doit être réalisée en un deuxième temps, au-dessus de ladite portion passive. Or, pour pouvoir fonctionner correctement en tant que convertisseur de longueur d'onde, l'empilement de puits quantiques ou de plans de boîtes quantiques de la portion passive doit présenter une teneur en Indium (In) élevée - typiquement supérieure à 20% - ce qui la rend instable en cas de chauffage au-delà d'une température supérieure à 1050 ° C environ. Cela sigrifie que la croissance de la portion active doit être réalisée à « basse » température (moins de 1000 ° C, de préférence 950 °C ou moins), ce qui exclut le recouis aux techniques d'épitaxie en phase vapeur aux organométallique (EPVOM, ou MOCVD de l'anglais Such a structure is attractive, but difficult to achieve. Indeed, in order not to be traversed by the electric current flowing through the active portion, the passive portion must be carried out first, by epitaxial deposition on a suitable substrate. The active portion must be performed in a second time, above said passive portion. However, in order to be able to function correctly as a wavelength converter, the quantum well or quantum dot plane stack of the passive portion must have a high indium (In) content - typically greater than 20% - this which makes it unstable when heated above a temperature above about 1050 ° C. It sigrifies that the growth of the active portion must be carried out at "low" temperature (less than 1000 ° C, preferably 950 ° C or less), which excludes the recipe for organometallic vapor phase epitaxy techniques (EPVOM , or MOCVD of English
« Métal Organic Chemical Vapor Déposition »), qui sont les plus couramment employées dans l'industrie. Il est intéressant de noter que le document US 2004/0227144 précité décrit un procédé de fabrication comprenant une étape de croissance de la portion active effectuée à une température de 1020 - 1040 °C ce qui, compte tenu du temps nécessaire pour sa réalisation, conduirait nécessairement à une altération (et notamment à un noircissement) du convertisseur dans la portion passive. "Organic Chemical Chemical Vapor Deposition"), which are most commonly used in the industry. It is interesting to note that the aforementioned document US 2004/0227144 describes a manufacturing process comprising a step growth of the active portion carried out at a temperature of 1020 - 1040 ° C which, given the time required for its completion, would necessarily lead to alteration (and in particular blackening) of the converter in the passive portion.
Le document DE 10 2004 052 245 décrit une diode électroluminescente comprenant une portion active (électroluminescente) et une portion passive (convertisseur de longueur d'onde) réalisée au-dessus de la portion active. Cette structure « inversée » permet de réaliser la portion passive après la portion active, et donc d'éviter tout risque de dégradation thermique. Toutefois, cela implique un passage du courant électrique à travers la portion passive, ce qui n'est pas usuel et pourrait, en principe, dégrader les caractéristiques électriques du dispositif, voire induire une électroluminescence non souhaitée du convertisseur de longueur d'onde.  Document DE 10 2004 052 245 describes a light-emitting diode comprising an active portion (electroluminescent) and a passive portion (wavelength converter) made above the active portion. This "inverted" structure makes it possible to carry out the passive portion after the active portion, and thus to avoid any risk of thermal degradation. However, this implies a passage of the electric current through the passive portion, which is not usual and could, in principle, degrade the electrical characteristics of the device, or even induce undesired electroluminescence of the wavelength converter.
L'invention vise à pallier les inconvénients précités de l'art antérieur, et notamment à procurer un dispositif semi-conducteur monolithique émetteur de lumière présentant un rendement élevé, un spectre d'émission stable dans le temps, de bonnes propriétés électriques et pouvant être fabriqué par des procédés industriels standard.  The invention aims to overcome the aforementioned drawbacks of the prior art, and in particular to provide a monolithic semiconductor device light emitter having a high efficiency, a stable emission spectrum over time, good electrical properties and can be manufactured by standard industrial processes.
Un objet de l'invention, permettant d'atteindre un tel but, est constitué par un dispositif selon la revendication 1 .  An object of the invention, making it possible to achieve such a goal, consists of a device according to claim 1.
Un autre objet de l'invention est un procédé selon la revendication 6, permettant la fabrication d'un tel dispositif,  Another object of the invention is a method according to claim 6, allowing the manufacture of such a device,
Les revendications dépendantes portent sur des modes de réalisation avantageux d'un tel dispositif et d'un tel procédé.  The dependent claims relate to advantageous embodiments of such a device and such a method.
D'autres caractéristiques, détails et avantages de l'invention ressortiront à la lecture de la description faite en référence aux dessins annexés donnés à titre d'exemple et qui représentent, respectivement :  Other characteristics, details and advantages of the invention will emerge on reading the description given with reference to the accompanying drawings given by way of example and which represent, respectively:
La figure 1 , la structure d'une diode électroluminescente blanche monolithique en nitrures d'éléments III connue de l'art antérieur ;  FIG. 1, the structure of a monolithic white electroluminescent diode in nitride elements III known from the prior art;
- les figures 2 à 7, des structures de diodes électroluminescentes blanches données à titre d'exemple et ne relevant pas de l'invention ; - la figure 8 la structure d'une diode électroluminescente blanche selon un mode de réalisation de l'invention FIGS. 2 to 7, white light-emitting diode structures given by way of example and not falling within the scope of the invention; FIG. 8 the structure of a white light-emitting diode according to one embodiment of the invention
- La figure 9, le spectre d'émission d'une diode électroluminescente blanche monolithique en nitrures d'éléments III du type de la figure 5, acquis en face avant (c'est-à-dire à l'opposé du substrat) et en face arrière (c'est-à-dire à travers le substrat) ;  FIG. 9, the emission spectrum of a monolithic white electroluminescent diode in nitrides of elements III of the type of FIG. 5, acquired on the front face (that is to say opposite the substrate) and on the back side (that is, through the substrate);
La figure 10, la caractéristique tension-courant de ladite diode électroluminescente blanche monolithique en nitrures d'éléments III, comparée à celle d'une diode bleu conventionnelle ; et  FIG. 10, the voltage-current characteristic of said monolithic white light-emitting diode made of III element nitrides, compared to that of a conventional blue diode; and
- La figure 1 1 , les spectres de photoluminescence normalisés de trois convertisseurs de longueur d'onde pouvant être utilisés, séparément ou conjointement, dans une diode électroluminescente blanche monolithique en nitrures d'éléments III selon un mode de réalisation de l'invention.  FIG. 11, the standardized photoluminescence spectra of three wavelength converters that can be used, separately or jointly, in a monolithic white nitride light emitting diode of elements III according to one embodiment of the invention.
La figure 1 illustre la structure d'une diode blanche monolithique connue de l'art antérieure, et particulièrement du document WO 2007/104884 précité. Une telle diode comprend, du bas vers le haut :  FIG. 1 illustrates the structure of a monolithic white diode known from the prior art, and particularly from the aforementioned document WO 2007/104884. Such a diode comprises, from bottom to top:
un substrat 7 transparent à la lumière qui doit être émise par le dispositif, par exemple en saphir, , SiC, ZnO ou GaN ;  a light-transparent substrate 7 to be emitted by the device, for example sapphire, SiC, ZnO or GaN;
une ou plusieurs couches tampons 6 en AIGalnN intrinsèque ou, plus précisément non intentionnellement dopée (n.i.d.) ; « AIGalnN » est ici une formule générale qui signifie AlxGaylnzN, avec x+y+z=1 et où un ou deux des coefficients stœchiométriques x, y ,z peuvent également être nuls ; one or more buffer layers 6 in intrinsic AIGalnN or, more precisely, unintentionally doped (nest); "AIGalnN" is here a general formula which means Al x Ga y ln z N, with x + y + z = 1 and where one or two of the stoichiometric coefficients x, y, z can also be zero;
une couche 5 dite « inférieure » en AIGalnN de type n.i.d. - un « convertisseur » formé par un empilement 40 de puits quantiques ou plans de boîtes quantiques en lnxGa-i-xN / GaN susceptibles d'absorber un rayonnement à une première longueur d'onde (typiquement dans le bleu) et de réémettre un rayonnement à une deuxième longueur d'onde, plus élevée (typiquement dans le jaune) ; le coefficient stœchiométrique x est généralement supérieur ou égal à 0,2 ; a so-called "lower" layer 5 in AIGalnN of nest type - a "converter" formed by a stack 40 of quantum wells or quantum well planes in ln x Ga-i- x N / GaN capable of absorbing radiation at a first wavelength (typically in blue) and re-emit radiation at a second wavelength, higher (typically in the yellow); the stoichiometric coefficient x is generally greater than or equal to 0.2;
une région (couche ou structure multicouche) 30, dite « de séparation », en AIGalnN de type n, présentant typiquement une épaisseur de l'ordre de 2 μιη ; un empilement 2 de puits quantiques ou plans de boîtes quantiques en lnxGa-i-xN / GaN (avec typiquement x<0,2), susceptible d'émettre un rayonnement à ladite première longueur d'onde par injection électronique ; et a region (layer or multilayer structure) 30, called "separation", in AIGalnN type n, typically having a thickness of the order of 2 μιη; a stack 2 of quantum wells or quantum dot planes in ln x Ga-i- x N / GaN (with typically x <0.2) capable of emitting radiation at said first wavelength by electronic injection; and
- une région (couche ou structure multicouche) 1 , dite a region (layer or multilayer structure) 1, called
« supérieure », en AIGaInN de type p, présentant typiquement une épaisseur de l'ordre de 200 nm (la AIGaInN de type p étant très résistif, on cherche à minimiser son épaisseur). "Superior", p-type AIGaInN, typically having a thickness of the order of 200 nm (the p-type AIGaInN being very resistive, it seeks to minimize its thickness).
Les régions 1 , 2, 30, 40, 5 et 6 forment une matrice monolithique en semi-conducteur de type nitrure d'éléments III, fabriquée généralement par dépôt épitaxial sur le substrat 7. A l'intérieur de cette matrice, les régions 1 , 2 et 30 forment une diode électroluminescente.  The regions 1, 2, 30, 40, 5 and 6 form a monolithic matrix of element III nitride semiconductor, generally manufactured by epitaxial deposition on the substrate 7. Within this matrix, the regions 1 , 2 and 30 form a light-emitting diode.
Une gravure en « marche d'escalier » permet de dégager une région de la surface supérieure de la région 30 pour y déposer une électrode 9. Une autre électrode 8 est déposée sur la couche supérieure 1 (sa surface doit être plus élevée que celle de l'électrode 9 en raison des propriétés électriques moins favorables du semi-conducteur de type p. L'électrode 8 doit recouvrir de préférence toute la surface de la diode électroluminescente afin d'assurer une injection homogène du courant). Les électrodes 8 et 9 permettent de faire passer un courant électrique à travers la diode 1 -2-30 ; on parle donc de « portion active » de la matrice. Par contre, on comprend qu'aucun courant ne peut traverser les couches 40, 5 et 6 (« portion passive »), en raison de la présence de la couche « de séparation » 30, non dopée et présentant une épaisseur relativement importante.  A "stair step" etching makes it possible to disengage a region of the upper surface of the region 30 to deposit an electrode 9 therein. Another electrode 8 is deposited on the upper layer 1 (its surface must be higher than that of the electrode 9 because of the less favorable electrical properties of the p-type semiconductor The electrode 8 must preferably cover the entire surface of the light-emitting diode so as to ensure homogeneous injection of the current). The electrodes 8 and 9 make it possible to pass an electric current through the diode 1-2-30; we therefore speak of "active portion" of the matrix. On the other hand, it is understood that no current can pass through the layers 40, 5 and 6 ("passive portion"), because of the presence of the "separation" layer 30, undoped and having a relatively large thickness.
Comme mentionné plus haut, le dépôt d'une telle couche 3 doit se faire à une température élevée (supérieure à 1000 ° C), ce qui risque d'endommager le convertisseur 40.  As mentioned above, the deposition of such a layer 3 must be at a high temperature (above 1000 ° C), which may damage the converter 40.
La figure 2 représente une diode électroluminescente ne relevant pas de l'invention, dans laquelle un courant électrique traverse aussi bien la portion « active » que la portion « passive » (convertisseur de longueur d'onde) de la matrice. Les mêmes chiffres de référence représentent les mêmes éléments que sur la figure 1 . Par rapport au dispositif de la figure 1 on peut remarquer les différences suivantes : FIG. 2 represents a light-emitting diode which does not fall within the scope of the invention, in which an electric current passes through both the "active" portion and the "passive" portion (wavelength converter) of the matrix. The same reference numerals represent the same elements as in Figure 1. With respect to the device of FIG. 1, the following differences can be observed:
l'électrode 9 est réalisée sur la face arrière du substrat, qui doit être conducteur (référence 71 ) : on réalise ainsi un dispositif à structure verticale et on évite l'étape de gravure « en marche d'escalier » ; la contrepartie est que le courant électrique traverse tout le dispositif, y compris le convertisseur ; cette électrode peut être transparente, semi-transparente ou en forme de grille pour permettre l'extraction des photon, alors qu'il est préférable que l'électrode 8, du côte « p » du dispositif, soit une couche métallique épaisse pour assurer un meilleur contact électrique et se comporter également comme un réflecteur de lumière;  the electrode 9 is formed on the rear face of the substrate, which must be conductive (reference 71): a device with a vertical structure is thus produced and the step of "staircase" etching is avoided; the counterpart is that the electric current passes through the whole device, including the converter; this electrode may be transparent, semi-transparent or grid-shaped to allow photon extraction, while it is preferable that the electrode 8, on the "p" side of the device, be a thick metal layer to ensure better electrical contact and also behave like a light reflector;
le convertisseur - identifié par la référence 4 - se différencie du convertisseur 40 de la figure 1 en ce qu'il est dopé « n » afin de présenter une conductivité suffisante (un dopage « p » est possible en théorie, mais moins avantageux) ;  the converter - identified by the reference 4 - differs from the converter 40 of Figure 1 in that it is doped "n" to have a sufficient conductivity (a "p" doping is possible in theory, but less advantageous);
la région de séparation - identifiée par la référence 3 - peut présenter une épaisseur beaucoup plus faible, par exemple de l'ordre de quelques centaines de nanomètres, voire seulement de 100 nm ou moins. En effet, elle ne doit plus assurer l'isolement du convertisseur, qui est en tout cas traversé par le courant électrique. En outre, le convertisseur 4, étant dopé, peut assurer la fonction d'injection d'électrons dans l'empilement « actif » 2.  the separation region - identified by the reference 3 - may have a much smaller thickness, for example of the order of a few hundred nanometers, or even only 100 nm or less. Indeed, it must no longer ensure the isolation of the converter, which is in any case crossed by the electric current. In addition, the converter 4, being doped, can provide the electron injection function in the "active" stack 2.
La croissance d'une couche 3 aussi mince peut s'effectuer par dépôt en phase vapeur aux organométalliques à une température inférieure à 1000 °C, par exemple d'environ 950 °C ou moins, cequi évite tout risque d'endommagement du convertisseur 4.  The growth of such a thin layer 3 can be carried out by organometallic vapor deposition at a temperature of less than 1000 ° C., for example about 950 ° C. or less, which avoids any risk of damaging the converter 4. .
La figure 3 illustre une diode électroluminescente ne relevant pas de l'invention, dans laquelle un courant électrique traverse aussi bien la portion « active » que la portion « passive » (convertisseur de longueur d'onde) de la matrice. Cette diode présente également une structure verticale, mais elle est réalisée par retournement de puce (« flip chip »). Autrement dit, la matrice épitaxiale est séparée de son substrat, retournée et déposée sur un autre substrat, 70, qui n'est pas nécessairement transparent. La référence 80 identifie une couche métallique de brasure, servant également d'électrode. L'autre électrode, 90, est déposée sur la couche de type n 50 (qui correspond à la couche « inférieure » 5 des figures 1 et 2, mais se trouve maintenant « en haut » du dispositif). La surface de ladite couche 50 peut être texturée pour faciliter l'extraction des photons. FIG. 3 illustrates a light-emitting diode which does not fall within the scope of the invention, in which an electric current passes through both the "active" portion and the "passive" portion (wavelength converter) of the matrix. This diode also has a vertical structure, but it is performed by flip chip. In other words, the epitaxial matrix is separated from its substrate, inverted and deposited on another substrate, 70, which is not necessarily transparent. Reference 80 identifies a solder metal layer, also serving as an electrode. The other The electrode, 90, is deposited on the n-type layer 50 (which corresponds to the "lower" layer 5 of FIGS. 1 and 2, but is now "at the top" of the device). The surface of said layer 50 may be textured to facilitate the extraction of photons.
Les figures 4, 5 et 6 se rapportent à trois diodes électroluminescente ne relevant pas de l'invention, dans lesquelles un courant électrique traverse aussi bien la portion « active » que la portion « passive » (convertisseur de longueur d'onde) de la matrice. Ces diodes., présentent une structure plus proche de celle de la figure 1 . Les seules différences concernent l'épaisseur de la région de séparation 3, qui est réduite (comme dans le cas des figures 2 et 3), et le fait que le convertisseur 4 présente un dopage, préférentiellement de type n. En raison de la faible épaisseur de la couche de séparation 3, des lignes de courant électrique traversent au moins la partie supérieure du convertisseur 4.  FIGS. 4, 5 and 6 relate to three electroluminescent diodes which do not fall within the scope of the invention, in which an electric current passes through both the "active" portion and the "passive" portion (wavelength converter) of the matrix. These diodes, have a structure closer to that of Figure 1. The only differences concern the thickness of the separation region 3, which is reduced (as in the case of FIGS. 2 and 3), and the fact that the converter 4 has a doping, preferably n-type. Due to the small thickness of the separation layer 3, electrical current lines pass through at least the upper part of the converter 4.
Dans le cas de la figure 4, le contact électrique 9 est réalisé sur une portion latérale du convertisseur. Dans celui de la figure 5, ledit contact est réalisé sur une portion latérale de la région de séparation 3. Et dans le cas de la figure 6 ce contact est réalisé sur une portion latérale de la couche inférieure 5. Ces trois variantes sont sensiblement équivalentes ; on remarquera seulement que, pour pouvoir réaliser le contact sur la région de séparation 3, il faut contrôler très précisément la gravure « en marche d'escalier » en raison de la faible épaisseur de cette couche.  In the case of Figure 4, the electrical contact 9 is formed on a side portion of the converter. In that of FIG. 5, said contact is made on a lateral portion of the separation region 3. And in the case of FIG. 6 this contact is made on a lateral portion of the lower layer 5. These three variants are substantially equivalent ; it will be noted only that, in order to be able to make the contact on the separation region 3, it is necessary to control very precisely the engraving "in step" because of the small thickness of this layer.
La figure 7 illustre la structure d'une autre diode électroluminescente qui procède d'un principe différent de celui à la base des diodes décrites ci-dessus. En effet, dans ce cas, la clé pour éviter l'endommagement thermique du convertisseur 4 ne réside pas tant dans la réalisation d'une couche de séparation 3 mince, quant dans l'adoption d'une structure inversée, dans laquelle ledit convertisseur est réalisé après l'empilement « actif » 2. Comme dans les autres exemples, cela implique la nécessité d'autoriser le passage d'un courant électrique à travers ledit convertisseur.  FIG. 7 illustrates the structure of another light-emitting diode which proceeds from a principle different from that at the base of the diodes described above. Indeed, in this case, the key to avoid thermal damage to the converter 4 is not so much in the production of a thin separation layer 3, but in the adoption of an inverted structure, in which said converter is after the "active" stack 2. As in the other examples, this implies the need to allow the passage of an electric current through said converter.
Ainsi le dispositif de la figure 7 comprend, du bas vers le haut : une électrode 8 (la structure est de type vertical) ; un substrat conducteur 71 , de type p ; Thus the device of FIG. 7 comprises, from bottom to top: an electrode 8 (the structure is of vertical type); a conductive substrate 71, of the p type;
une couche tampon 6 en AIGalnN de type p. ;  a p-type AIGalnN buffer layer 6. ;
une couche 1 1 en AIGalnN de type p ;  a layer 1 1 AIGalnN p type;
un empilement électroluminescent 2 de puits quantiques ou plans de boîtes quantiques de semi-conducteur lll-V ;  an electroluminescent stack 2 of quantum wells or semiconductor quantum dot planes III-V;
une région de séparation 3, de type n ou n.i.d., dont l'épaisseur n'est pas critique ;  a separation region 3, of type n or n.d.d, whose thickness is not critical;
un convertisseur 4, présentant un dopage de type n ;  a converter 4 having n-type doping;
une électrode 9 qui peut être déposée directement au- dessus du convertisseur 4, ou par l'intermédiaire d'une couche de contact de type n (non représentée). De préférence l'électrode 9 peut être transparente, semi-transparente ou en forme de grille pour permettre l'extraction du rayonnement généré.  an electrode 9 which can be deposited directly above the converter 4, or via an n-type contact layer (not shown). Preferably the electrode 9 may be transparent, semi-transparent or grid-shaped to allow extraction of the generated radiation.
L'avantage de ce dispositif est que le convertisseur 4 est réalisé en dernier ; il ne peut donc pas être endommagé même si d'autres couches sont déposées (préalablement) à haute température.  The advantage of this device is that the converter 4 is made last; it can not be damaged even if other layers are deposited (previously) at high temperature.
Le principal inconvénient de ce dispositif réside dans le fait que le courant doit traverser une épaisseur importante de semi-conducteur de type p (substrat 71 , couches 6 et 1 1 ), qui présente une résistivité élevée ; en outre, le contact 8 est pris sur une région de type p (le substrat 71 ), ce qui accroît encore la résistance vue par le courant. Pour réduire cette résistance on pourrait réaliser une gravure en marche d'escalier afin de prendre un contact directement sur une portion de la couche 1 1 . Cependant, en raison de la résistivité de ladite couche, cela conduirait à une répartition du courant peu homogène ; en outre, l'opération de gravure serait susceptible de dégrader la conductivité des des couches p, alors que ce problème ne se pose pas pour des couches de type n.  The main disadvantage of this device lies in the fact that the current must pass through a large thickness of p-type semiconductor (substrate 71, layers 6 and 1 1), which has a high resistivity; in addition, the contact 8 is taken on a p-type region (the substrate 71), which further increases the resistance seen by the current. To reduce this resistance one could achieve an engraving staircase to make contact directly on a portion of the layer 1 January. However, because of the resistivity of said layer, this would lead to a distribution of inhomogeneous current; in addition, the etching operation would be likely to degrade the conductivity of the layers p, while this problem does not arise for n-type layers.
Des problèmes semblables se posent dans le cas du dispositif illustré par la figure 2 du document DE 10 2004 052 245 précité.  Similar problems arise in the case of the device illustrated in Figure 2 of DE 10 2004 052 245 supra.
La structure de la figure 8, qui illustre un mode de réalisation de l'invention, permet de remédier à ces inconvénients. Dans ce dispositif, la couche 1 1 de type p est remplacée par une couche 51 de type n, moins résistive. En contrepartie, du côté opposé de l'empilement actif 2 il faut prévoir une couche 3A de type p. Mais comme, en général, on ne souhaite pas réaliser un convertisseur 4 avec dopage de type p, on introduit une jonction tunnel 3B ayant son côté p++ du côté de la couche 3A et son côté n++ du côté du convertisseur 4, qui a un dopage de type n. La jonction tunnel 3B présente une épaisseur très faible, de l'ordre de quelques nanomètres, tandis que la couche 3A, de type p, présente typiquement une épaisseur de l'ordre de 100 nm. The structure of Figure 8, which illustrates an embodiment of the invention, overcomes these disadvantages. In this device, the p-type layer 1 1 is replaced by a n-resistive n-type layer 51. In return, the opposite side of the active stack 2 must be provided a layer 3A of type p. But since, in general, it is not desired to make a p-type doping converter 4, a tunnel junction 3B having its p ++ side on the side of the layer 3A and its n ++ side on the side of the converter 4, which has a doping, is introduced. of type n. The tunnel junction 3B has a very small thickness, of the order of a few nanometers, whereas the p-type layer 3A typically has a thickness of the order of 100 nm.
Seuls des dispositifs comportant un convertisseur 4 avec dopage n ont été décrits en détail. Si le dopage du convertisseur était de type p, celui des autres couches de la matrice devrait changer en conséquence. Toutefois, il est connu que les convertisseurs de type p sont moins efficaces que ceux de type n.  Only devices comprising a converter 4 with n doping have been described in detail. If the doping of the converter was of type p, that of the other layers of the matrix should change accordingly. However, it is known that p-type converters are less efficient than n-type converters.
Un seul mode de réalisation de l'invention a été décrit ; plusieurs autres variantes sont cependant possibles. En particulier, des dispositifs selon l'invention peuvent présenter une structure plus complexe, comprenant des couches additionnelles ou en remplaçant des couches « simples » par des structures multicouches. En particulier, un même dispositif peut comprendre plusieurs convertisseurs émettant à différentes longueurs d'onde.  Only one embodiment of the invention has been described; however, several other variants are possible. In particular, devices according to the invention may have a more complex structure, comprising additional layers or by replacing "simple" layers by multilayer structures. In particular, the same device may comprise several converters emitting at different wavelengths.
Le dispositif de la figure 8 est destiné à l'émission d'une lumière blanche, mais il ne s'agit pas là d'une caractéristique essentielle de l'invention.  The device of Figure 8 is intended for the emission of white light, but this is not an essential feature of the invention.
Le dispositif de la figure 8 comprend un substrat 71 conducteur (de type n, tout comme la couche tampon 6), et une électrode 8 déposée sur la face arrière (opposée à celle portant la matrice) de ce substrat. En variante, le substrat pourrait être isolant et l'électrode 8 être réalisée en contact direct avec la couche 51 grâce à une gravure en marche d'escalier (cf. la figure 6). Selon une autre variante, la matrice pourrait être détachée du substrat, et l'électrode 8 être déposée directement sur la face arrière de la couche 51 . Ces exemples ne sont pas limitatifs. Dans tous les cas, grâce à l'utilisation de la jonction tunnel 3B on parvient à minimiser l'épaisseur des régions dopées p traversées par le courant et à assurer que les contacts électriques soient pris sur des régions dopées n.  The device of FIG. 8 comprises a conductive substrate 71 (n-type, just like the buffer layer 6), and an electrode 8 deposited on the rear face (opposite to that carrying the matrix) of this substrate. In a variant, the substrate could be insulating and the electrode 8 could be made in direct contact with the layer 51 by means of staircase etching (see FIG. According to another variant, the matrix could be detached from the substrate, and the electrode 8 could be deposited directly on the rear face of the layer 51. These examples are not limiting. In any case, thanks to the use of the tunnel junction 3B, it is possible to minimize the thickness of the p-doped regions traversed by the current and to ensure that the electrical contacts are taken on n-doped regions.
Pour parvenir à l'invention, les inventeurs on dû surmonter un préjugé technique. En effet, il était cru auparavant que le passage d'un courant électrique à travers du convertisseur 4 aurait d'une part perturbé l'émission fluorescente dudit convertisseur, d'autre part dégradé les propriétés électriques du dispositif d'une manière inacceptable. De manière inattendue, les présents inventeurs se sont rendu compte que ce n'est pas le cas. To achieve the invention, the inventors had to overcome a technical bias. Indeed, it was believed before that the passage of a current Electrical power through the converter 4 would have firstly disturbed the fluorescent emission of said converter, on the other hand degraded the electrical properties of the device in an unacceptable manner. Surprisingly, the present inventors have realized that this is not the case.
Cela a été démontré expérimentalement en réalisant un prototype présentant la structure de la figure 5. La matrice de ce prototype a été entièrement réalisée par EPVOM. Elle comprend l'empilement de couches suivant, en partant du substrat 7 en saphir : une couche inférieure 5 de 4,5 μιτι d'épaisseur en GaN dopé Si, un convertisseur 4 formé de 20 puits quantiques ln0,25Ga0,75N (1 .2 nm) / GaN : Si (20 nm), une couche de séparation 3 de GaN : Si (20 nm), un empilement électroluminescent 2 formé de 5 puits quantiques lno,-iGa0,.9N (1 .2 nm) / GaN (10 nm), une couche supérieure (en fait, une structure multicouches) 1 comprenant 20 nm d'épaisseur de AI0.-i4Ga0.86N : Mg et 235 nm de GaN : Mg. Les couches dopées Si présentent une conductivité de type n et les couches dopées Mg une conductivité de type p. This has been demonstrated experimentally by making a prototype with the structure of Figure 5. The matrix of this prototype was entirely realized by EPVOM. It comprises the following stack of layers, starting from the substrate 7 sapphire: a lower layer 5 of thickness of 4.5 μιτι Si-doped GaN, a converter 4 formed of 20 quantum wells ln 0 , 25Ga 0 , 75N ( 1.2 nm) / GaN: Si (20 nm), a separation layer 3 of GaN: Si (20 nm), an electroluminescent stack 2 formed of 5 quantum wells lno , -iGa 0, .9 N (1 .2 nm) / GaN (10 nm), an upper layer (in fact, a multilayer structure) 1 comprising AI 20 nm thick i-0. 4 Ga 0 .86N: Mg and 235 nm of GaN: Mg. The Si doped layers have n-type conductivity and the Mg-doped layers have a p-type conductivity.
La figure 9 montre les spectres d'émission de ce prototype, alimenté par un courant de 20 mA à température ambiante. Deux spectres ont été acquis, l'un « face avant » et l'autre « face arrière », c'est-à-dire à travers le substrat. On peut noter un premier pic à 380 nm (violet) correspondant à l'émission de l'empilement actif 2 et un deuxième pic à 480 nm (jaune) correspondant à la fluorescence du convertisseur 4. Les deux spectres ont été normalisés de telle sorte que l'intensité du pic à 380 nm vaille 1 . On peut remarquer que le pic à 480 nm est plus intense en face arrière qu'en face avant. Cela est normal car l'émission en face avant comprend aussi les photons à 380 nm qui n'ont pas traversé le convertisseur.  Figure 9 shows the emission spectra of this prototype, powered by a current of 20 mA at room temperature. Two spectra were acquired, one "front face" and the other "back face", that is to say through the substrate. A first peak at 380 nm (violet) corresponding to the emission of the active stack 2 and a second peak at 480 nm (yellow) corresponding to the fluorescence of the converter 4 can be noted. The two spectra have been standardized in such a way that that the intensity of the peak at 380 nm is worth 1. It can be noted that the peak at 480 nm is more intense on the rear face than on the front. This is normal because the emission on the front panel also includes the 380 nm photons that have not passed through the converter.
La figure 10 permet de comparer la caractéristique courant- tension du prototype avec celle d'une diode électroluminescente (DEL) violette conventionnelle, réalisée dans des conditions de croissance comparables. Elle comprend l'empilement de couches suivant, en partant du substrat 7 en saphir : une couche inférieure 5 de 4,5 μιτι d'épaisseur en GaN dopé Si, un empilement électroluminescent 2 formé de 5 puits quantiques ln0,iGa0,.9N (1 .2 nm) / GaN (10 nm), une couche supérieure (en fait, une structure multicouches) 1 comprenant 20 nm d'épaisseur de AI0. 4Ga0.86N : Mg et 235 nm de GaN : Mg. On constate que la caractéristique courant-tension du prototype n'est pas dégradée. De manière surprenante, cette caractéristique est même meilleure que celle de la DEL de référence. Ceci indique que le convertisseur n'ajoute pas une résistance significative au passage du courant. Figure 10 compares the current-voltage characteristic of the prototype with that of a conventional violet light-emitting diode (LED), achieved under comparable growth conditions. It comprises the following stack of layers, starting from the substrate 7 in sapphire: a lower layer 5 of 4.5 μιτι thick Si-doped GaN, an electroluminescent stack 2 formed of 5 quantum wells ln 0 , iGa 0 ,. 9 N (1.2 nm) / GaN (10 nm), an upper layer (in fact, a multilayer structure) 1 comprising 20 nm in thickness of Al 0. 4 Ga 0 .86N: Mg and 235 nm of GaN: mg. It is noted that the current-voltage characteristic of the prototype is not degraded. Surprisingly, this characteristic is even better than that of the reference LED. This indicates that the converter does not add significant resistance to current flow.
Les résultats expérimentaux des figures 9 et 10 concernent des dispositifs qui ne relèvent pas de l'invention ; toutefois, ils peuvent être extrapolés au cas d'un dispositif selon l'invention, du type illustré sur la figure 8.  The experimental results of Figures 9 and 10 relate to devices that do not fall within the scope of the invention; however, they can be extrapolated to the case of a device according to the invention, of the type illustrated in FIG.
En faisant varier l'épaisseur et la composition des puits quantiques du convertisseur 4 (respectivement : la composition et la taille des boîtes quantiques) on peut obtenir une émission fluorescente couvrant tout le spectre visible : bleu (470 nm), vert (530 nm), orange (590 nm) et rouge (650 nm). Cela est illustré sur la figure 1 1 . La combinaison de ces couleurs permet en principe d'obtenir toutes les couleurs pures ou mélangées comme le blanc.  By varying the thickness and the composition of the quantum wells of the converter 4 (respectively: the composition and the size of the quantum boxes) one can obtain a fluorescent emission covering the whole visible spectrum: blue (470 nm), green (530 nm) , orange (590 nm) and red (650 nm). This is illustrated in Figure 1 1. The combination of these colors makes it possible in principle to obtain all pure or mixed colors such as white.

Claims

REVENDICATIONS
1 . Dispositif émetteur de lumière comprenant une matrice monolithique de nitrures l l l-V, ladite matrice comportant au moins un premier empilement (2) de puits quantiques ou de plans de boîtes quantiques de nitrures d'éléments III, un deuxième empilement (4) de puits quantiques ou de plans de boîtes quantiques de nitrures lll-V, et une région (3) dite de séparation, séparant les deux dits empilements de puits quantiques ou de plans de boîtes quantiques, ainsi qu'une première (8) et une deuxième (9) électrode agencées pour permettre le passage d'un courant électrique à travers ledit premier empilement de puits quantiques ou de plans de boîtes quantiques de nitrures d'éléments III et également à travers au moins une partie dudit deuxième empilement de puits quantiques ou de pians de boîtes quantiques de nitrures d'éléments III,, dans lequel ledit premier empilement de puits quantiques ou de pians de boîtes quantiques de nitrures d'éléments III est apte à émettre des photons à au moins une première longueur d'onde par injection électrique par ledit courant électrique et ledit deuxième empilement de puits quantiques ou de plans de boîtes quantiques de nitrures d'éléments III est apte à émettre des photons à au moins une seconde longueur d'onde par pompage optique par lesdits photons émis par ledit premier empilement, ladite matrice étant réalisée par dépôt épitaxial, caractérisé en ce que ledit deuxième empilement (4) de puits quantiques ou de plans de boîtes quantiques de nitrures lll-V présente un dopage de type n, en ce que ladite région de séparation (3) comprend une jonction tunnel (3B) ayant une région dopée n++ agencé du côté dudit deuxième empilement (4) et une région dopée p++ agencée du côté opposé, ainsi qu'au moins une couche dopée p (3A) agencée du côté de la région de séparation opposée audit deuxième empilement, et en ce que ledit premier empilement (2) de puits quantiques ou de plans de boîtes quantiques de nitrures d'éléments III est agencé entre ladite région de séparation (3) et au moins une couche (51 ) présentant un dopage de type n.  1. A light emitting device comprising a monolithic matrix of nitrides 11 IV, said matrix comprising at least a first stack (2) of quantum wells or III quantum element quantum box planes, a second quantum well stack (4) or quantum dot boxes of nitride III-V, and a so-called separation region (3), separating the two said quantum well or quantum dot plane stacks, as well as a first (8) and a second (9) electrodes arranged to allow passage of an electric current through said first quantum well stack or quantum dot planes of element III nitrides and also through at least a portion of said second quantum well stack or box planes quantum element III nitrides, in which said first quantum well stack or IEC III nitride quantum dot body pans is capable of emitting being photons at at least a first wavelength by electric injection by said electric current and said second stack of quantum wells or quantum dot planes of element III nitrides is capable of emitting photons at least a second length waveform by optical pumping by said photons emitted by said first stack, said matrix being made by epitaxial deposition, characterized in that said second stack (4) of quantum wells or quantum dot planes of nitrides III-V has a doping n-type, in that said separation region (3) comprises a tunnel junction (3B) having an n ++ doped region arranged on the side of said second stack (4) and a p ++ doped region arranged on the opposite side, and at least one a p-doped layer (3A) arranged on the side of the separation region opposite to said second stack, and in that said first stack (2) of quantum wells or pla ns of quantum boxes of nitride elements III is arranged between said separation region (3) and at least one layer (51) exhibiting n-type doping.
2. Dispositif selon la revendication 1 dans lequel ladite région de séparation (3) présente une épaisseur inférieure ou égale à 1 000 nm et de préférence inférieure ou égale à 500 nm. 2. Device according to claim 1 wherein said separation region (3) has a thickness less than or equal to 1000 nm and preferably less than or equal to 500 nm.
3. Dispositif selon l'une des revendications précédentes, dans lequel ladite première et la deuxième électrode sont agencées de part et d'autre de ladite matrice monolithique de nitrures d'éléments III, moyennant quoi ledit courant électrique circule dans une direction sensiblement perpendiculaire auxdits puits quantiques ou plans de boîtes quantiques. 3. Device according to one of the preceding claims, wherein said first and the second electrode are arranged on either side of said monolithic matrix of element nitrides III, whereby said electric current flows in a direction substantially perpendicular to said quantum wells or quantum dot planes.
4. Dispositif selon l'une des revendications précédentes dans lequel lesdites première et deuxième longueurs d'onde sont choisies de telle sorte que leur combinaison donne une lumière blanche. 4. Device according to one of the preceding claims wherein said first and second wavelengths are chosen so that their combination gives a white light.
5. Dispositif selon l'une des revendications précédentes dans lequel ladite matrice est déposée sur un substrat (7) conducteur ledit deuxième empilement (4) étant agencé du côté de ladite matrice opposé audit substrat et ledit premier empilement (2) étant agencé entre ledit substrat et ledit deuxième empilement, 5. Device according to one of the preceding claims wherein said matrix is deposited on a substrate (7) conductive said second stack (4) being arranged on the side of said matrix opposite said substrate and said first stack (2) being arranged between said substrate and said second stack,
6. Procédé de fabrication d'un dispositif selon l'une des revendications précédentes comportant la réalisation de ladite matrice monolithique de nitrures d'éléments III par croissance épitaxiale. 6. A method of manufacturing a device according to one of the preceding claims comprising the realization of said monolithic matrix of nitride elements III by epitaxial growth.
7. Procédé selon la revendication 6 dans lequel ladite croissance épitaxiale est entièrement réalisée en phase vapeur aux organométalliques. 7. The method of claim 6 wherein said epitaxial growth is entirely carried out in the organometallic vapor phase.
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