Light-emitting diode comprising an aln-based emissive region containing gallium atoms and / or indium atoms

Abstract

The invention relates to a light-emitting diode (100) comprising at least: - a substrate (102); - a portion (108), said to be of a first type, of AlX1Ga(1-X1-Y1)InY1N doped according to a first type of conductivity, where X1 > 0 and X1+Y1 ≤ 1, arranged above the substrate; - an emissive portion (110) comprising a dilute AlN alloy containing gallium atoms and / or indium atoms with a concentration of less than 30%; - a portion (112), said to be of a second type, of AlX2Ga(1-X2-Y2)InY2N doped according to a second type of conductivity, opposite to the first type of conductivity, where X2 > 0 and X2+Y2 ≤ 1, the emissive portion being arranged between the portion of the first type and the portion of the second type.

Description

[0001] LIGHT-EMITTING DIODE COMPRISING AN AIN-BASED EMITTING REGION CONTAINING GALLIUM AND / OR INDIUM ATOMS

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The invention relates to the field of light-emitting diodes, or LEDs, with a broad emission band and based on semiconductors. Advantageously, the invention applies to the production of LEDs emitting light in the ultraviolet (UV) range, in particular in the wavelength range between approximately 230 nm and 310 nm, in particular for fields related to disinfection, conservation and / or agriculture.

[0005] STATE OF THE PRIOR ART

[0006] In particular, the bactericidal effect, and more generally the disinfection effect, of UV radiation arises from the absorption band of the DNA of microorganisms (bacteria, microbes, viruses) in a wavelength range from approximately 230 nm to 310 nm. The damage inflicted on the DNA of microorganisms by the absorption of UV radiation hinders their reproduction and leads to their elimination. A maximum disinfectant effect is obtained with radiation that has a spectral distribution as close as possible to this absorption band of the DNA of the microorganisms to be destroyed.

[0007] Disinfection by exposure to UV radiation is currently carried out using various devices such as KrCI lamps or mercury vapor lamps. However, these devices have disadvantages.

[0008] KrCI lamps are excimer lamps whose emission spectrum is narrow compared to the absorption spectrum of the DNA of the microorganisms to be destroyed and therefore does not provide an optimal disinfectant effect. In addition, these lamps generate ozone, which limits them to niche applications. Mercury vapor lamps, on the other hand, are fragile and have a limited lifespan. They also have narrow emission lines that do not cover the entire absorption spectrum of the DNA of the microorganisms to be destroyed. Finally, these lamps contain mercury, the use of which is ultimately banned due to its high toxicity.

[0009] Semiconductor materials from the III element nitride family, including in particular GaN, AIN, InN or their alloys, in particular ternary and quaternary, are particularly suitable for the production of LEDs emitting in the UV range. Such LEDs are for example produced in the form of a stack of layers, nanowires, or even with a hybrid structure as described in document FR 3 109 470 Al. In these LEDs, the variation of the aluminum content in the composition of the semiconductor of the multi-quantum wells makes it possible to control the emission wavelength of the LEDs. It is therefore possible, with these LEDs, to scan the entire range of desired wavelengths to have an optimal disinfecting effect by varying the aluminum content in the composition of the semiconductor of the multi-quantum wells.However, the sharpness of the emission peaks generally obtained with such LEDs makes it difficult to cover the entire desired wavelength range with a single LED. It is therefore generally necessary to use several LEDs with emission peaks at different wavelengths to cover the entire UV range in particular.

[0010] STATEMENT OF THE INVENTION

[0011] An aim of the present invention is to provide a light-emitting diode whose emission spectrum is as wide as possible in the UV range.

[0012] To achieve this goal, the invention proposes a light-emitting diode comprising at least:

[0013] - a substrate;

[0014] - a portion, called a first type, of AlxiGa(i-xi-Yi)lnyiN doped according to a first type of conductivity, with XI > 0 and Xl+Yl < 1, arranged above the substrate; - an emissive portion comprising a dilute alloy of AIN containing gallium and / or indium atoms with a concentration of less than 30%;

[0015] - a portion, called a second type, of Alx2Ga(i-x2-Y2)lnY2N doped according to a second type of conductivity, opposite to the first type of conductivity, with X2 > 0 and X2+Y2 < 1, the emissive portion being arranged between the portion of the first type and the portion of the second type.

[0016] The LED according to the invention thus comprises an emissive portion formed from a dilute alloy of AlN containing gallium and / or indium atoms, i.e. non-homogeneous at the nanometric scale in terms of distribution of the Al and / or Ga and / or In atoms. The potential felt by the charge carriers circulating and recombining in the emissive portion is locally lowered by the presence of these Ga and / or In atoms randomly incorporated in the dilute alloy, thus inducing a wider band light emission than the LEDs of the prior art.

[0017] Unlike LEDs of the prior art emitting in the UV range thanks to potential wells formed between n- and p-doped layers, it is proposed to produce an LED whose emissive part is formed by a portion of AlN containing gallium and / or indium atoms in small quantities so as to form a dilute alloy. Unlike a quantum well forming a potential well of defined emission energy, the emissive portion of the LED according to the invention is characterized by an emissive zone where the charge carriers are subjected to a potential having local fluctuations created by the presence of these Ga and / or In atoms and forming emitting zones extending over a range which can go in particular from 230 to 310 nm.

[0018] Furthermore, in the LED according to the invention, the emissive portion may be arranged directly against the n- and p-doped semiconductor portions of the LED (corresponding to the portions of the first type and the second type), unlike the emissive portion of a quantum well which is arranged against barrier layers.

[0019] In the dilute alloy of the emissive portion, the AIN of the emissive portion may comprise gallium and / or indium atoms in random substitution for aluminum atoms, or may comprise gallium and / or indium atoms in substitution for aluminum atoms sufficiently close to each other to locally form a region having the characteristics of an alloy of AIGaN or AlInN or AIGalnN, or may comprise gallium and / or indium atoms bonded to nitrogen atoms and capable of locally forming nanocrystals, or nanocrystallites or aggregates, of AIGaN or AlInN or AIGalnN.

[0020] The fact that the use, to form the emissive portion of the LED, of a diluted alloy of AlN containing gallium and / or indium atoms at a concentration of less than 30% leads to light emission in a broad spectrum of the UV range is surprising and not obvious. Indeed, in a homogeneous alloy of AlN comprising 1% molar fraction of GaN, the gap obtained is 203 nm or 6.1 eV, and for a molar fraction of GaN of 10%, this gap is then 2225 nm or 5.5 eV. A person skilled in the art wishing to produce an AlN-based LED emitting at a wavelength of 280 nm or 4.43 eV would naturally be led to develop a homogeneous ternary alloy which should contain a molar fraction of GaN between 60 and 62%, and not to use a diluted alloy as proposed here.

[0021] With such an emissive portion, the LED according to the invention can emit in a wavelength range much wider than the emission spectrum of a quantum well LED, for example in the wavelength range from about 200 nm to about 350 nm and advantageously in the wavelength range from about 230 nm to about 310 nm. Such an LED is therefore particularly effective when used for disinfectant applications.

[0022] Additionally, compared to a device using multiple LEDs to cover the entire desired spectral range, being able to cover that entire range with a single LED provides similar or higher efficiency while consuming less power.

[0023] Another advantage is that the production of such an LED does not require the formation of multiple quantum wells, and is therefore simpler to produce and allows one to overcome the difficulties inherent in controlling the composition of semiconductors to form such wells.

[0024] The proposed LED is particularly suitable for disinfection applications (bacterial, microbial, viral), in particular of water and / or air. Such an LED can also be used, for example, for skin disinfection applications when its radiation corresponds to light with a wavelength of around 230 nm, the penetration depth of which is limited to the stratum corneum of the epidermis.

[0025] The proposed LED is particularly suitable for general public domestic applications, such as for disinfecting a refrigerator, in a car, purifying water at the outlet of a distribution point such as a fountain or tap, etc.

[0026] The LED may further comprise an intermediate portion of GaN doped according to the first conductivity type arranged between the substrate and the portion of the first type. The presence of such an intermediate portion makes it possible to facilitate the growth of the portion of the first type, particularly when the LED is produced in the form of nanowires.

[0027] The proportion of gallium and / or indium atoms in the material of the emissive portion may advantageously be less than or equal to 10%, or between approximately 1% and 10%, or less than or equal to 5%, or even between 1% and 5%. Such a proportion of gallium and / or indium atoms in the material of the emissive portion allows the LED to emit in the wavelength range particularly well suited to disinfection applications.

[0028] The light-emitting diode may further comprise a buffer layer disposed between the substrate and the portion of the first type, or between the substrate and the intermediate portion when the diode comprises such an intermediate portion.

[0029] The buffer layer material can be based on GaN or AIN or AIGaN.

[0030] The first type of conductivity can correspond to n-type, and the second type of conductivity can correspond to p-type. However, the reverse is possible.

[0031] Advantageously:

[0032] - n-type dopants present in the material of one of the portions either of the first type or of the second type may correspond to atoms of silicon and / or sulfur and / or germanium; - p-type dopants present in the material of the other of the portions either of the first type or of the second type may correspond to atoms of magnesium and / or beryllium.

[0033] The material of the other of the portions of the first type and the second type may comprise indium atoms, which makes it possible to increase the quantity of p dopants, in particular magnesium atoms, incorporated into the material of this other portion, thus facilitating its doping.

[0034] The material of the portion of the first type and / or the portion of the second type may comprise AIN. This configuration makes it possible to prevent the portions of the first type and the second type from having a barrier effect with respect to the emissive portion which is based on AIN.

[0035] In a first embodiment, the LED may comprise a plurality of nanowires extending from the substrate, each of the nanowires comprising at least the first type and second type portions and the emissive portion.

[0036] In a second embodiment, at least the portions of the first type and the second type and the emissive portion may form a stack of layers disposed on the substrate.

[0037] The invention also proposes a method for producing a light-emitting diode, comprising at least:

[0038] - production, on a substrate, of a portion, called a first type, of AlxiGa(i-xi-Yi)lnyiN doped according to a first type of conductivity, with XI > 0 and Xl+Yl < 1;

[0039] - production, on the portion of the first type, of an emissive portion comprising a diluted alloy of AIN containing gallium and / or indium atoms at a concentration of less than 30%, and advantageously less than 10% or even less than 5%;

[0040] - production, on the emissive portion, of a portion, called a second type, of Alx2Ga(i-x2-Y2)lriY2N doped according to a second type of conductivity, opposite to the first type of conductivity, with X2 > 0 and X2+Y2 < 1. Throughout the document, the term "on" is used without distinction of the orientation in space of the element to which this term relates. For example, in the characteristic "an element produced on a substrate", the face of the substrate on which the element is produced is not necessarily oriented upwards but can correspond to a face oriented in any direction.Furthermore, the arrangement of a first element on a second element should be understood as being able to correspond to the arrangement of the first element against the second element, without any intermediate element between the first and second elements, or as being able to correspond to the arrangement of the first element on the second element with one or more intermediate elements arranged between the first and second elements.

[0041] BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be better understood by reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0043] - figure 1 represents an LED comprising an emissive portion based on AIN containing gallium and / or indium atoms and forming a diluted alloy, object of the present invention, according to a first embodiment;

[0044] - figure 2 represents an emission spectrum of the LED according to the first embodiment;

[0045] - figure 3 represents an LED comprising an emissive portion based on AIN containing gallium and / or indium atoms and forming a diluted alloy, object of the present invention, according to a second embodiment.

[0046] Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the transition from one figure to another.

[0047] The different parts represented in the figures are not necessarily shown on a uniform scale, in order to make the figures more readable. The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other.

[0048] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0049] Figure 1 described below represents an LED 100 according to a first embodiment of the invention.

[0050] In the description below, the term "thickness" is used to designate the dimension parallel to the Z axis shown in Figures 1 and 3, i.e. the dimension parallel to the direction in which the nanowires of the LED 100 extend in the first embodiment, or the stacking direction of the different layers of the LED 100 in the second embodiment.

[0051] The LED 100 comprises a substrate 102 on which the other elements of the LED 100 are arranged and serving as a mechanical support for these other elements. In this first embodiment, the substrate 102 comprises, for example, sapphire. Other types of substrate may be used, comprising, for example, a semiconductor material such as silicon. The thickness of this substrate 102 is, for example, equal to several hundred microns.

[0052] In these figures, the LED 100 also comprises a buffer layer 104 arranged on the substrate 102. Advantageously, the buffer layer 104 comprises AIN or AIGaN or even GaN. The thickness of the buffer layer 104 is for example between approximately 0.5 pm and 3 pm. It may optionally be electrically doped and contain other chemical elements and in particular indium or boron. This buffer layer promotes the growth of the portion 106.

[0053] The LED 100 comprises, on the buffer layer 104, a plurality of nanowires extending substantially in the direction of the thickness of the LED 100, that is to say in a direction substantially perpendicular to the surface of the substrate 102 on which the buffer layer 104 is formed. In FIG. 1, all the nanowires are represented as being perpendicular to the surface of the buffer layer 104 on which the nanowires are made. In practice, these nanowires may not all be perfectly perpendicular to this surface of the buffer layer 104, and the angles formed between the growth surface of these nanowires and the growth directions of these nanowires may vary by several degrees, or even by ten degrees or more. For example, the diameter of each nanowire and the distance between the growth axes of two neighboring nanowires, that is to say their periodicity, may be between approximately 100 nm and 300 nm.Furthermore, the LED 100 may comprise a number of nanowires of between approximately 1 million (for an area of ​​100x100 pm. 2 ) and 10 million (for a surface of 300x300 pm 2 ), with an average density for example equal to approximately 100 threads / pm 2 on substrate 102.

[0054] In the exemplary embodiment of Figure 1, each nanowire comprises an intermediate portion 106 of GaN doped according to a first type of conductivity (n-type in the exemplary embodiment of Figure 1). For example, the thickness of the intermediate portion 106 is between approximately 100 nm and 1 micron.

[0055] Alternatively, it is possible that the nanowires of the LED 100 do not include these intermediate portions 106.

[0056] In each nanowire, the intermediate portion 106 is surmounted by a portion 108, called a first type, of AIXlGa(l-Xl-Yl)lnYlN doped according to the first type of conductivity, with XI > 0 and Xl+Yl < 1. According to an advantageous embodiment, the material of this portion 108 comprises sulfur and / or silicon and / or germanium atoms and / or corresponds to AIN. For example, the thickness of the portion 108 is between approximately 100 nm and 1 pm.

[0057] According to an exemplary embodiment, the n-type doping of the semiconductors of the portions 106, 108 is obtained by incorporating silicon atoms into the semiconductors of the portions 106, 108, for example implemented during the semiconductor depositions used to produce these portions. The concentration of dopants in the semiconductors of the portions 106, 108 is for example between approximately 1016 at / cm 3 and 1021 at / cm 3 .

[0058] The portion 108 of each nanowire is topped with an emissive portion 110, or active portion, of AIN containing gallium and / or indium atoms. The proportion, or concentration, of Ga and / or In atoms in the AIN of the emissive portion 110 is less than 30% and for example between approximately 1% and 10% or even between 1% and 5%. For example, the thickness of the emissive portion 110 is between approximately 25 nm and 100 nm.

[0059] In each nanowire, the emissive portion 110 is surmounted by a portion 112, said to be of a second type, of Alx2Ga(i-x2-Y2)lriY2N doped according to a second type of conductivity (p type in the exemplary embodiment of FIG. 1), opposite to the first type of conductivity, with X2 > 0 and X2+Y2 < 1. According to an advantageous embodiment, the material of this portion 112 comprises beryllium and / or magnesium atoms and / or corresponds to AlN. For example, the thickness of the portion 112 is between approximately 10 nm and 100 nm, and advantageously between approximately 10 nm and 50 nm. The material of portion 112 may comprise indium atoms, which makes it possible to increase the quantity of p dopants, in particular magnesium atoms, incorporated into the material of this portion 112, thus facilitating its doping.

[0060] According to an exemplary embodiment, the p-type doping of the semiconductor of the portion 112 is obtained by incorporation of magnesium atoms into the semiconductor of the portion 112, for example during the deposition of this semiconductor. The concentration of dopants in the semiconductor of the portion 112 is for example between approximately 1016 at / cm 3 and 1021 at / cm 3 .

[0061] Finally, the portion 112 of each nanowire is surmounted by an ohmic contact layer 114 arranged on the tops of the nanowires and forming an electrical contact for one of the electrodes of the LED 100. This ohmic contact layer 114 comprises at least one electrically conductive material transparent to the wavelengths intended to be emitted by the LED 100, such as for example ITO or advantageously diamond, or else highly electrically doped semiconductor.

[0062] Figure 2 represents the emission spectrum of a set of nanowires of the LED 100 described above, when the emissive portion 110 comprises AIN containing gallium atoms. In this spectrum, the amplitude is expressed in arbitrary units. This spectrum clearly illustrates the light emission obtained in the wavelength range from approximately 230 nm to 340 nm, covering in particular the absorption range of the DNA of the microorganisms intended to be eliminated when this LED 100 is used to destroy these microorganisms. An example of a method for producing the LED 100 is described below.

[0063] The buffer layer 104 is first produced on the substrate 102, for example by implementing a MOCVD type deposition (chemical vapor deposition from metal-organic precursors).

[0064] A growth mask is then produced on the buffer layer 104 in order to produce the nanowires. This mask comprises, for example, circular openings produced, for example, by lithography in a layer of material suitable for producing this mask. The diameter and periodicity of these openings may be, for example, between approximately 100 nm and 300 nm.

[0065] The intermediate portions 106 are then produced by growth or deposition through the openings of this mask, on the buffer layer 104.

[0066] The doping of the 106 portions is then carried out, for example by incorporation of silicon atoms into the semiconductor formed by growth.

[0067] The portions 108 of the first type are then produced on the portions 106, by growth or deposition through the openings of the mask.

[0068] The doping of the 108 portions is then carried out, for example by incorporation of silicon and / or sulfur and / or germanium atoms.

[0069] The emissive portions 110 are then produced on the portions 108, for example by growth or deposition. Gallium and / or indium atoms are incorporated therein in order to form the dilute alloy of these portions 110.

[0070] The portions 112 of the second type are then produced on the emissive portions 110, for example by growth or deposition.

[0071] The doping of the 112 portions is then carried out, for example by incorporation of magnesium and / or beryllium atoms.

[0072] The ohmic contact layer 114 is then produced on the tops of the nanowires, for example by deposition.

[0073] The growth or deposition steps described above correspond, for example, to molecular beam epitaxy (MBE) or MOCVD deposition. The doping can be implemented in situ in this growth or deposition equipment. Figure 3 described below represents the LED 100 according to a second embodiment.

[0074] Compared to the LED 100 according to the first embodiment previously described, the LED 100 according to this second embodiment is not formed by a set of nanowires made on the buffer layer 104, but by a stack of layers of materials made on the buffer layer 104, the length and width (dimensions along the X and Y axes in FIG. 3) of each of these layers corresponding to the length and width of the LED 100. The materials of these layers 106, 108, 110 and 112 in FIG. 3, as well as the thicknesses of these layers, are for example similar to those of the portions 106, 108, 110 and 112 of materials of each of the nanowires of the LED 100 according to the first embodiment.

[0075] As a variant of the first and second embodiments described above, it is possible that the LED 100 does not include the buffer layer 104, the nanowires or the layers being in this case produced directly on the substrate 102.

Claims

DEMANDS 1. Light-emitting diode (100) comprising at least: - a substrate (102); - a portion (108), called of a first type, of AlxiGa(i-xi-Yi)lnyiN doped according to a first type of conductivity, with XI > 0 and Xl+Yl < 1, disposed above the substrate (102); - an emissive portion (110) comprising a dilute alloy of AIN containing gallium and / or indium atoms with a concentration of less than 30%; - a portion (112), called of a second type, of Alx2Ga(i-x2-Y2)lny2N doped according to a second type of conductivity, opposite to the first type of conductivity, with X2 > 0 and X2+Y2 < 1, the emissive portion (110) being disposed between the portion (108) of the first type and the portion (112) of the second type.

2. Light-emitting diode (100) according to claim 1, further comprising an intermediate portion (106) of GaN doped according to the first type of conductivity disposed between the substrate (102) and the portion (108) of the first type.

3. Light-emitting diode (100) according to any one of claims 1 or 2, wherein the proportion of gallium and / or indium atoms in the material of the emitting portion (110) is less than or equal to 10%, and in particular less than or equal to 5%.

4. Light-emitting diode (100) according to any one of the preceding claims, further comprising a buffer layer (104) disposed between the substrate (102) and the portion (108) of the first type or between the substrate (102) and the intermediate portion (106) when the light-emitting diode (100) comprises such an intermediate portion (106).

5. Light-emitting diode (100) according to claim 4, wherein the buffer layer material (104) is based on GaN or AIN or AIGaN.

6. Light-emitting diode (100) according to any one of the preceding claims, wherein: - n-type dopants present in the material of one of the portions (108, 112) of either the first type or the second type correspond to silicon and / or sulfur and / or germanium atoms; - p-type dopants present in the material of the other of said portions (108, 112) either of the first type or of the second type correspond to magnesium and / or beryllium atoms.

7. Light-emitting diode (100) according to any one of the preceding claims, wherein the material of portion (108) of the first type and / or portion (112) of the second type comprises NAIN.

8. Light-emitting diode (100) according to any one of the preceding claims, comprising a plurality of nanowires extending from the substrate (102), each of the nanowires comprising at least the portions (108, 112) of the first type and the second type and the emitting portion (110).

9. Light-emitting diode (100) according to any one of claims 1 to 7, wherein at least the portions (108, 112) of the first type and the second type and the emitting portion (110) form a stack of layers arranged on the substrate (102).

10. Method for making a light-emitting diode (100), comprising at least: - realization, on a substrate (102), of a portion (108), called of a first type, of AlxiGa(i-xi-Yi)lnyiN doped according to a first type of conductivity, with XI > 0 and Xl+Yl < 1; - production, on the portion (108) of the first type, of an emissive portion (110) comprising a dilute alloy of AIN containing gallium and / or indium atoms at a concentration of less than 30%; - realization, on the emissive portion (110), of a portion (112), called of a second type, of Alx2Ga(i-x2-Y2)lnY2N doped according to a second type of conductivity, opposite to the first type of conductivity, with X2 > 0 and X2+Y2 < 1.

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