Light-emitting device comprising active nanowires and contact nanowires and method of fabrication

Abstract

A light-emitting device comprises a set of nanowires over the whole surface of a substrate, comprising at least a first series of first nanowires and a second series of second nanowires; the first series comprising first nanowires emitting light under electrical control, connected between a first and a second type of electrical contact to emit light under electrical control, the first nanowires covered by at least one conducting layer transparent at the wavelength of the light-emitting device, layer in contact with the first type of electrical contact; the second series comprising second nanowires, encapsulated in a layer of metal allowing the first electrical contact to be formed; the second electrical contact being on the back face of the substrate, opposite to the face comprising the nanowires, and provided by a conducting layer facing the first series of nanowires. A method of fabrication of the light-emitting device is provided.

Claims

1. A light-emitting device comprising a set of nanowires over the whole surface of a substrate, comprising: a first series of first nanowires; and a second series of second nanowires; said first series comprising first nanowires being active capable of emitting light under electrical control, connected between a first type of electrical contact and a second type of electrical contact in order to avow said device to emit light under electrical control, said first nanowires being covered by at least one conducting layer being transparent at an emission wavelength of said light-emitting device, said layer being in contact with said first type of electrical contact; said second series of second nanowires being contact nanowires connected to said first type of electrical contact; said first type of electrical contact comprising sequentially: said at least one conductor layer deposited on the second nanowires; an adhesion layer wherein the adhesion layer is deposited on and in contact with a portion of the at least one conducting layer in contact with the second nanowires; a layer of metal, encapsulating the second series so that the layer of metal is deposited on both the adhesion layer and another portion of the at least one conducting layer which is in contact with the second nanowires but not with the adhesion layer, and allowing said first type of electrical contact to be formed, the layer of metal not encapsulating the first nanowires; and a contact lug, wherein the contact lug is deposited on and in contact with the layer of metal which is in contact with the adhesion layer, the second type of electrical contact being situated on the back face of said substrate, opposite to the face comprising said nanowires and being provided by another conducting layer facing at least said first series of nanowires.

2. The light-emitting device as claimed in claim 1, wherein said second nanowires are situated around the periphery of said first nanowires.

3. The light-emitting device as claimed in claim 1, comprising a third series of third nanowires being electrically neutral without a conducting layer being transparent at the emission wavelength of said light-emitting device, said third nanowires being able to be situated around the periphery of said first active nanowires and of said second nanowires, defining a region of said device said to be active.

4. The light-emitting device as claimed in claim 1, wherein the thickness of the layer of metal defined on top of said second nanowires is at least ten nanometers and in that the metal layer encapsulating said second nanowires is made of copper or of nickel or of silver.

5. The light-emitting device as claimed in claim 1, comprising a mirror layer situated between two adjacent nanowires, which layer comprises at least one of Al, Ag and Ru.

6. The light-emitting device as claimed in claim 1, wherein the contact lug comprises at least one of gold and an alloy of silver and tin.

7. The light-emitting device as claimed in claim 1, wherein said adhesion layer is discontinuous and comprises at least one of copper and aluminum.

8. A method for the fabrication of a light-emitting device, wherein the light-emitting device comprising: a set of nanowires over the entire surface of a substrate; at least a first series of first nanowires and a second series of second nanowires; said first series comprising first nanowires being active capable of emitting light under electrical control, connected between a first type of electrical contact and a second type of electrical contact in order to allow said device to emit light under electrical control, said first nanowires being covered by at least one first conducting layer being transparent at the emission wavelength of said light emitting device, said layer being in contact with said first type of electrical contact; said second series of second nanowires being contact nanowires connected to said first type of electrical contact; said first type of electrical contact comprising sequentially: said at least one conductor layer deposited on the second nanowires; an adhesion layer wherein the adhesion layer is deposited on and in contact with a portion of the at least one first conducting layer in contact with the second nanowires; a layer of metal, encapsulating the second series so that the layer of metal is deposited on both the adhesion layer and another portion of the at least one first conducting layer which is in contact with the second nanowires but not with the adhesion layer, and allowing said first type of electrical contact to be formed, the layer of metal not encapsulating the first nanowires; and a contact lug, wherein the contact lug is deposited on and in contact with the layer of metal which is in contact with the adhesion layer, the second type of electrical contact being situated on the back face of said substrate, opposite to the face comprising said nanowires, and being provided by another conducting layer at least facing said first series of nanowires, the method comprising carrying out the following steps: growth of the set of nanowires over the whole surface of said substrate; deposition of said first conducting layer; local encapsulation of said second nanowires by said layer of metal; formation of the second type of contact on the back face of the substrate, by said another conducting layer.

9. The method of fabrication of light-emitting devices as claimed in claim 8, comprising: formation of thick photoresist patterns on the surface of said first nanowires leaving said second nanowires not covered by said photoresist; deposition of said layer of metal on the surface of said second nanowires in order to provide the first type of electrical contact; removal of said photoresist patterns from said first nanowires.

10. The method of fabrication of light-emitting devices as claimed in claim 9, comprising formation of the contact lug, wherein the deposition of the layer of metal and/or the formation of the contact lug are carried out by an electrodeposition operation.

11. The method of fabrication of light-emitting devices as claimed in claim 8, comprising a step for removal of the first conducting layer which is transparent at the emission wavelength of said light-emitting device from nanowires situated around the periphery of said first and second nanowires, in such a manner as to define a third series of third nanowires.

12. The method of fabrication of light-emitting devices as claimed in claim 11, comprising deposition of said adhesion layer designed for the adhesion of said layer of metal, said deposition being able to be implemented: in a discontinuous manner at the ends of said nanowires and between two adjacent nanowires onto said substrate or; between two adjacent nanowires onto said substrate.

13. The method of fabric of light-emitting device as claimed in claim 12, comprising an operation for removal of said adhesion layer from said third nanowire or from said third nanowires and said first nanowires.

14. The method of fabrication of light-emitting devices as claimed in claim 8, comprising the deposition of a mirror layer between two adjacent nanowires, said deposition being prior to or after the deposition of said transparent first conducting layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood and other advantages will become apparent upon reading the description that follows presented by way of non-limiting example and thanks to the appended figures amongst which:

(2) FIG. 1 illustrates a first example of an LED comprising nanowires according to the prior art;

(3) FIG. 2 illustrates a second example of an LED comprising nanowires according to the prior art;

(4) FIG. 3 shows a photograph of a set of nanowires separated by regions without growth in which defects are present in a configuration of the prior art;

(5) FIGS. 4a to 4i illustrate the various steps of one example of a method of fabrication of a light-emitting device of the invention;

(6) FIG. 5 illustrates one example of configuration of a thick contact layer on the surface of a set of nanowires NTic, situated between first nanowires NTia and third nanowires NTin.

(7) FIG. 6 illustrates an overall view of one example of a device according to the invention mounted onto a housing.

(8) FIGS. 7a to 7d illustrate the various steps of a second example of a method of fabrication of a light-emitting device of the invention;

(9) FIGS. 8a and 8b illustrate the steps of a third example of a method of fabrication of a light-emitting device of the invention.

DETAILED DESCRIPTION

(10) The light-emitting device of the present invention comprises, generally speaking, a substrate covered with nanowires over the entirety of its surface, in order not to leave open areas in which there could be growth defects during the formation of the nanowires. Thus, according to the invention, even the regions dedicated to the contacts allowing the nanowires to be controlled use the top surface of certain nanowires.

(11) The present invention will be described hereinafter in more detail by virtue of the steps of the method of fabrication allowing the device of the invention to be obtained. The various steps are illustrated by means of FIGS. 4a to 4i.

(12) Step 1 Illustrated in FIG. 4a:

(13) Starting from a substrate 100, which can advantageously be made of silicon, the growth of the nanowires NT.sub.i, is carried out over the entirety of this substrate.

(14) Step 2 Illustrated in FIG. 4b:

(15) The deposition of a layer 200 is then carried out allowing the nanowires to be partially encapsulated, via a dielectric which can typically be SiO.sub.2, Al.sub.2O.sub.3, HfO.sub.2 or Si.sub.xN.sub.y with x and y being molar fractions.

(16) Step 3 Illustrated in FIG. 4c:

(17) The deposition of a conducting layer 300, being transparent at the wavelength of operation of the light-emitting device, is carried out. Typically, this layer may be deposited onto a first layer of nickel, palladium or platinum a few nanometers (5 nm) thick. The transparent conducting layer may be of ITO with a thickness of the order of ten to a hundred nanometers. The transparent conducting layer may equally be of FTO, AZO or GZO.

(18) In order to redirect the beams toward the top of the chip, the deposition of a mirror structure 400 may advantageously also be provided, where this mirror structure may have been deposited prior to the deposition of the transparent conducting layer or afterwards. This mirror structure may be a bi-layer structure of the Ti/Al type or of the Ti/Ag type or of the Ti/Ru type. The various alternatives are shown in FIG. 4c.

(19) Step 4 Illustrated in FIG. 4d:

(20) The deposition is carried out of a structure 500 of adhesion layer(s) for the thick metal designed to enable the contact to be made. This structure may for example be composed of a first layer of titanium with a thickness of the order of 100 nm and of a layer of copper of the order of 400 nm, and may be obtained by a PVD process. This bi-layer structure may be formed over all of the nanowires and the voids between nanowires, or else in a discontinuous manner. These various possibilities are illustrated in FIG. 4d and may be obtained by adjusting the thicknesses of the bi-layer or by etching.

(21) The bi-layer structures may also be formed by the following depositions: a first layer of TiN or of Ti under a second layer of Cu or of Al using PVD or CVD or evaporation process or sputtering process.

(22) Step 5 Illustrated in FIG. 4e:

(23) A lithography of the photoresist patterns 600 is carried out allowing the later positioning of the upper contacts and thus the active region of the light-emitting device to be defined and at the same time allowing their size to be individualized as described hereinafter.

(24) Step 6 Illustrated in FIG. 4f:

(25) The deposition of a thick layer of metal is carried out which can typically have a thickness of around ten nm on top of said nanowires and which can reach several microns, between the photoresist patterns, allowing two series of nanowires to be identified: a first series of first nanowires under the photoresist patterns, said photoresist being designed to be removed so as to leave said first nanowires behind; a second series of second nanowires under the patterns of thick metal.

(26) The thick layer of metal can typically be made of copper or of nickel and formed by an electrodeposition process.

(27) Bonding lugs 800 can then be formed on this thick layer of metal which are designed to enable the connection with another functionalized support, of the SnAg type for example, which yields the multilayer Cu/Ni/SnAg, followed by an annealing operation at 260 C. These bonding lugs may also be made of Au.

(28) Step 7 Illustrated in FIG. 4g:

(29) The removal of the photoresist patterns is then carried out in such a manner as to leave behind the first nanowires designed to be active.

(30) Step 8 Illustrated in FIG. 4h:

(31) Then, in the case of the use of an adhesion structure 500, on the transparent conducting layer 300 or on a mirror structure 400, the selective chemical etching of this structure can be carried out.

(32) It should be noted that, in the case of an adhesion layer made of Ti/AI, this layer may be conserved so as to be used as mirror layer.

(33) Typically, this type of selective etching can be carried out in the pairs: Ti/Cu with respect to ITO or with respect to a mirror structure Ti/AI, by using for example a solution of: H.sub.2O.sub.2/H.sub.2SO.sub.4, in the case of copper; HF 0.25% in the case of titanium.

(34) The elimination of the adhesion structure may also be carried out by a dry etching operation.

(35) Step 8 Illustrated in FIG. 4i:

(36) Finally, the removal of the transparent conducting layer 300 may advantageously be carried out, around the periphery of the whole set of the first nanowires and of the second nanowires, in such a manner as to circumscribe the active part of the device, neutralizing nanowires, thus defined as being neutral, without having to resort to operations for elimination of these said nanowires.

(37) One example of a device according to the present invention is thus obtained comprising: the first series of first nanowires which are exposed and are referred to as active NTi.sub.a; the second series of second nanowires, under the patterns of thick metal, known as contact nanowires NTi.sub.c. a third series of third neutral nanowires NTi.sub.n, lacking the transparent conducting layer and bounding the light-emitting device part on the substrate having given rise to a global operation for growth of nanowires over the whole surface of said substrate.

(38) As a variant of the method previously described, it is just as possible to envision the formation of the neutral nanowires NTi.sub.n at the start of the method prior to the steps for formation of photoresist patterns, by carrying out the removal of the conducting layer 300 on the nanowires around the periphery.

(39) In the case of the use of an adhesion layer 400 on top of the conducting layer 300, the removal of the two layers around the periphery is then implemented in order to define the nanowires destined to be neutral nanowires.

(40) In the two cases that the layer 300 is on top of or underneath the layer 400, these two layers need to be removed in the region of the neutral nanowires.

(41) FIG. 5 illustrates a top view of one exemplary configuration of thick contact layer 700 on the surface of a set of nanowires NTi.sub.c situated between first nanowires NTi.sub.a and third nanowires NTi.sub.n.

(42) Generally speaking, the second type of contact for controlling the light-emitting device is on the back face. This may typically be a layer of metal deposited on the back face of the substrate which can be advantageously made of silicon.

(43) FIG. 6 shows schematically the mounting of one example of a device according to the invention onto a housing, and the electrical connection from the two types of contact: p contact and n contact. The p contact is provided from the NTi.sub.c and the contact lugs 800 and 800. The housing B.sub.o is covered with a layer of metal M.sub.1 which can be of copper, with a thin metal layer M.sub.2 which may typically be a flash of gold, said housing thus being rigidly attached to the light-emitting device on the back face via the substrate comprising a metal layer M.sub.3 which can typically be based on Ti/Au and providing the contact of the n type, via an intermediate layer which may be a Co bonding layer.

(44) It should be noted that the bonding lugs can have smaller lateral dimensions and may not occupy the whole top surface of the patterns of thick metal 700, such as the bonding lugs 800 effectively shown in FIG. 6.

(45) Second Example of a Method of Fabrication of a Light-Emitting Device of the Invention

(46) It is also advantageously possible to form the contacts by metal deposition using a serigraphic process. FIGS. 7a to 7d illustrate the main steps of this type of process, which only shows the formation of a single sub-assembly of contact nanowires NTi.sub.c, even if the nanowires NTi.sub.a may advantageously be included between two sub-assemblies of nanowires NTi.sub.c.

(47) The first steps may be identical to those described in FIGS. 4a and 4c.

(48) Starting from a substrate 100 comprising nanowires NTi covered by a transparent conducting layer 300 and locally by a mirror layer 400 as illustrated in FIG. 7a, a mask M comprising openings is placed facing the nanowires designed to form the contact nanowires, as illustrated in FIG. 7b.

(49) Through said mask M, the deposition of a metal ink E is carried out which can typically be of silver, as illustrated in FIG. 7c. Subsequently, the thickness of the metal contacts thus formed is made uniform by means of a scraper R, as illustrated in FIG. 7d, and the contact nanowires NTi.sub.c are thus defined, covered by a thick metal layer, contiguous with the active nanowires NTi.sub.a.

(50) In an analogous manner to what is shown in FIG. 4i, but not shown in the present example, it is advantageously possible to proceed with the removal of the transparent conducting layer 300 and of the mirror layer 400, around the periphery of the whole set of the first nanowires and of the second nanowires, in such a manner as to circumscribe the active part of the device, neutralizing nanowires, thus defined as being neutral, without having to resort to operations for elimination of these said nanowires.

(51) According to this method, the electrical connection (bonding) with another metalized support, from the first contact thick layer, can be formed directly.

(52) Third Example of a Method of Fabrication of a Light-Emitting Device of the Invention

(53) It is furthermore advantageously possible to form the contacts by localized deposition of metal using a dispenser. FIGS. 8a and 8b illustrate this third example of a method of fabrication of a light-emitting device of the invention which only shows the formation of a single sub-assembly of contact nanowires NTi.sub.c, even if the nanowires NTi.sub.a may advantageously be included between two sub-assemblies of nanowires NTi.sub.c.

(54) The first steps can be identical to those described in FIGS. 4a and 4c.

(55) Starting from a substrate 100 comprising nanowires NTi covered by a transparent conducting layer 300 and locally by a mirror layer 400, the localized deposition of a drop of metal G is carried out by means of a dispenser D, as illustrated in FIG. 8a. The dispenser D may typically be a syringe. This metal deposition thus forms the contacts on the contact nanowires NTi.sub.c contiguous with the active nanowires NTi.sub.a, as illustrated in FIG. 8b. In an analogous manner to what is shown in FIG. 4i, but not shown in the present example, it is advantageously possible to proceed with the removal of the transparent conducting layer 300 and of the mirror layer 400 around the periphery of the whole set of the first nanowires and of the second nanowires, in such a manner as to circumscribe the active part of the device, neutralizing nanowires, thus defined as being neutral, without having to resort to operations for elimination of these said nanowires.

(56) According to this method, the electrical connection (bonding) with another metalized support, from the first contact thick layer, can be formed directly.

(57) Fourth Example of a Method of Fabrication of a Light-Emitting Device of the Invention

(58) It is yet again advantageously possible to form the contacts by localized deposition of metal using an inkjet process.

(59) Thus, according to the present invention, the size of the LEDs becomes customizable, by virtue of the positioning of the regions of thick metal, and this may be carried out advantageously fairly late in the process steps.

(60) Beyond the non-deterioration of certain nanowires, by removal operations, a gain in the number of process steps may be made (notably all the steps required in the case of elimination of nanowires).

(61) It is also advantageously possible to position intermediate upper contacts in the center of large matrices, while at the same time benefiting from the possibility of electrodepositing bonding lugs following the formation of the thick metal contact layer.

(62) Lastly, it should be noted that the principle of the present invention allows devices to be fabricated at a particularly advantageous cost.