WO2014020080A1

WO2014020080A1 - Radiation emitting device and manufacturing process thereof

Info

Publication number: WO2014020080A1
Application number: PCT/EP2013/066121
Authority: WO
Inventors: Giuseppe Barillaro; Lucanos Marsilio STRAMBINI
Original assignee: Rico - Rappresentanze Industriali E Commerciali Srl; Universita di Pisa
Current assignee: Rico - Rappresentanze Industriali E Commerciali Srl; Universita di Pisa
Priority date: 2012-08-01
Filing date: 2013-07-31
Publication date: 2014-02-06
Anticipated expiration: 2015-02-01
Also published as: ITMI20121364A1

Description

RADIATION EMITTING DEVICE AND MANUFACTURING PROCESS

THEREOF

DESCRIPTION

Field of the invention

The present invention relates to an electromagnetic radiation emitting device, in particular in the visible region.

More particularly the present invention relates to an electromagnetic radiation emitting device which is able to easily and effectively modifying the primary emission spectrum of the device so as to obtain a final electromagnetic radiation centered at a desired wavelength, different from the wavelength of the primary emission.

Furthermore the present invention relates to a manufacturing process of said electromagnetic radiation emitting device.

Correlated Art

It is known in the art that crystalline Silicon is a material that per se does not have photoluminescence property, the latter being a process according to which a material is able to absorbing an electromagnetic radiation (photons) and then to re-emitting it. However, when Silicon is reduced to nanometric dimensions (in the form of Silicon nanoparticles) or when it is obtained in the form of nanostructured Silicon, it acquires photoluminescence properties in the visible light emission spectrum (i.e. in the visible region). Therefore, if the Silicon nanoparticles or the nanostructured Silicon are hit by an electromagnetic radiation having a sufficiently high energy (e.g. with energy equal to or higher than the energy of a blue light), the Silicon is able to emit a radiation that is centered at a wavelength (fundamental wavelength) in the visible light emission spectrum and that is distributed in a given range about said wavelength so as to define a predetermined emission band. Furthermore, by suitably predefining the dimensions of the Silicon or nanostructured Silicon nanoparticles, it is possible to modulate the fundamental wavelength of the emitted radiation and, consequently, to obtain an emitted light of desired color.

Solid-state devices (e.g. LEDs, light emitting diodes) are known in the art that are able to emit electromagnetic radiations (e.g. colored or white light) by using the conversion principle. This principle allows combining electromagnetic radiations of different wavelength so as to obtain a final electromagnetic radiation having predetermined wavelength and color. In detail, starting from a light source (e.g. a LED) that emits a primary radiation at a predetermined wavelength (primary emission) and hits and excites a suitable material having photoluminescence properties, at least part of said primary radiation is converted by said photoluminescent material originating a secondary radiation of different wavelength (secondary emission). The combination of said primary emission with said secondary emission causes the device to create an emitted radiation having a different wavelength - and thus a different color - with respect to the primary and secondary emissions. For instance, the device is able to combine a blue light (primary emission) with a radiation emitted in the yellow range (secondary emission) obtained from the photoluminescent material, thereby generating an emitted final radiation that is spectrally uniform and perceived as a white light by the human eye. Moreover, by suitably varying the concentration and/or the amount of said material, it is possible to obtain different white shades, from a "cold" white that is quite strong to a "warm" white that tends towards the yellow.

In order to make said electromagnetic radiation conversion and to obtain an electromagnetic radiation that is emitted at a wavelength different from the starting original wavelength, nowadays it is known to use materials like phosphors or the nanoparticles of various materials, such as Silicon, some metals (e.g. rare earth metals, among which the lanthanides or lanthanoids like Erbium) and some polymers (e.g. the polysiloxanes). The documents US 7,989,833 B2 and US 8,076,410 B2 disclose, for instance, the use of Silicon nanoparticles in LED devices that allow obtaining as a final result a white colored electromagnetic radiation.

In detail, document US 7,989,833 B2 discloses how to obtain a white light emitting LED starting from a blue or ultraviolet light emitting LED. A wavelength converter layer disposed on an active region of the blue or ultraviolet light emitting LED, said wavelength converter layer comprising a suitable number of Silicon nanoparticles sublayers, each sublayer emitting a light at a predetermined range of wavelengths in the visible light emission spectrum. For instance, a first sublayer emits a light in the red range, a second sublayer emits a light in the range of green and a third sublayer emits a light in the range of blue. The combination of the wavelengths of the light emitted by the first, second and third sublayers with the light emitted by the starting LED originates the desired white light.

The document US 8,076,410 B2 discloses how to obtain a white light emitting LED by starting from a LED that emits at a narrow range of wavelengths. In particular, a wavelength converter layer is associated to an active region of the starting LED, said wavelength converter layer comprising a composite film including a polymer or an organosilicon compound wherein is present a dispersion of Silicon nanoparticles having multiple Si-H termination sites and at least one of said sites being linked to a C of the polymer or of the organosilicon compound to produce a Silicon carbide bond (Si-C). The composite film makes the conversion to obtain the desired wavelength, meanwhile the amount of Silicon nanoparticles is sufficiently limited to avoid any relevant consequence to the properties of the polymer or of the organosilicon compound.

Document US 2007/054426 discloses a method for preparing an optical active layer with 1-lOnm distributed silicon quantum dots. This method adopts high temperature processing and atmospheric -pressure chemical vapor deposition (APCVD) and directly deposit to form a silicon nitride substrate containing 1-10 nm distributed quantum dots, said distribution profile of quantum dot size from large to small is corresponding to from inner to outer layers of film respectively, and obtain a 400-700 nm range of spectrum and white light source under UV photoluminescence or electro-luminescence.

Document US 2012/00631 17 discloses a light source apparatus having a phosphor layer which is subjected to a light beam of a predefined wavelength emitted from a solid light source element as an excitation light beam and which generates fluorescent beam by being excited by the incident excitation light beam and emits the fluorescence beam to outside, and a metal layer which is joined to a predefined surface among outer surfaces of the phosphor layer except an incident surface of the excitation light beam and an outgoing surface of the fluorescence beam for converting excitons excited from a section of the phosphor layer close to the predefined surface into a light beam via surface plasmon polaritons. The light beam converted from the excitons via the surface plasmon polaritons is emitted out of the outgoing surface of the phosphor layer together with the fluorescence beam.

The Applicant has noticed that the devices known in the art that are based on the use of phosphors or nanoparticles of materials like Silicon, as well as the respective manufacturing processes of said devices, have some drawbacks that affect both the reproducibility and the complexity of the manufacturing steps of said devices, and the final quality of the latter.

In detail, the Applicant has noticed that the correct achievement of the desired fundamental wavelength as well as the desired range of emission of an emitting device known in the art considerably depends on the accuracy of the dosing phase of phosphors or Silicon (for instance) nanoparticles of suitable dimensions. In fact, the dimensions of the phosphors or of the Silicon nanoparticles define the fundamental wavelength of the final electromagnetic radiation emitted by the emitting device. Therefore, once the phosphors or the Silicon (for instance) nanoparticles are obtained, the known processes require that intermediate steps of design and successive preparation of the phosphors or the nanoparticles mixture of suitable dimensions are performed in order to obtain said desired fundamental wavelength and range of emission. However said intermediate steps have some drawbacks, such as the difficulty of ensuring a uniform distribution of the phosphors or of the nanoparticles within the mixture, the difficulty of suitably dosing the phosphors or the nanoparticles of different dimensions, the difficulty of carrying out a controlled deposition of the phosphors or of the nanoparticles when more than one layer of said materials has to be produced, and finally the difficulty of suitably handling materials of very small dimensions (nanometric dimensions). It is clear that a wrong (or even only partially wrong) execution of just only one of said intermediate steps can irremediably compromise the final result and the obtained emitting device generates an electromagnetic radiation with characteristics different from the desired ones.

Furthermore, the Applicant has noted that the processes and the devices known in the art which make use of the phosphors or of the nanoparticles of various materials (such as Silicon) may show a further criticality when said phosphors or nanoparticles are not mixed with suitable supporting materials. Therefore an inappropriate choice of said supporting materials can compromise the quality of the final emission and thus the desired working of the emitting device.

Furthermore, the Applicant has noticed that the processes and the devices known in the art which make use of the phosphors or of the nanoparticles of various materials (such as Silicon) may show a further drawback due to a sedimentation phenomenon to which the wavelength converter layer is prone as time goes by. Said phenomenon is particularly disadvantageous since it causes a change in the distribution of the phosphors or of the nanoparticles, fact which causes a consequent change in the optical properties of the emitting device and thus the emission of an electromagnetic radiation that is different from the desired one.

Finally, the Applicant has also noticed the importance of providing a correct and advantageous position for the wavelength converter layer within a radiation emitting device. For instance document US 2012/00631 17 mentioned above describes a LED wherein the light source element is separated from the phosphor layer which is positioned with an inclined orientation with respect to the light source element. According to the LED configuration disclosed in document US 2012/00631 17, the light source element, the phosphor layer and the metal layer present on the backside of the phosphor layer are mounted in a recess portion of the base plate, said recess being successively filled in with a resin that is finally cured, thereby the light source element, the phosphor layer and the metal layer are molded in their entirety by a mold member. The Applicant has noticed that the manufacturing process of such a LED is remarkably complicated since it requires long and difficult steps to be carried out. Moreover, in order to guarantee that each manufactured device gives the same predetermined and desired performances, the Applicant has noticed that it is of extreme relevance that the same and correct positioning of the phosphor layer is always ensured in all the manufactured devices, in particular in terms of angular inclination of the phosphor layer with respect to the light source element

Summary of the invention

The Applicant has perceived the need of making an electromagnetic radiation emitting device and setting a manufacturing process thereof in order to overcome the above mentioned drawbacks of the art.

In particular, the Applicant has perceived the need of arranging an electromagnetic radiation emitting device simpler than the known emitting devices meanwhile ensuring the achievement of the desired optical properties as well as a uniform and stable conversion efficiency of the wavelength of the starting electromagnetic radiation emitted by the device layer made of semiconductor material.

More particularly, the Applicant has perceived the need of suitably coupling to said layer made of semiconductor material possessed by the emitting device a wavelength converter layer - suitable for converting at least partially said starting electromagnetic radiation - that is made from a material different from the phosphors and the Silicon nanoparticles of the manufacturing processes known in the art and that it is easy to be processed and to be conferred the optical properties (in particular the photoluminescence properties) necessary for emitting an electromagnetic radiation centered at a predetermined wavelength.

The Applicant has found that said result can be advantageously obtained by making the wavelength converter layer of the emitting device from a material comprising nanostructured Silicon and by coating said wavelength converter layer on the source element, i.e. on the layer made of semiconductor material.

Therefore, it is a first object of the present invention an electromagnetic radiation emitting device comprising:

• at least one layer made of semiconductor material suitable for emitting a first electromagnetic radiation centered at a first wavelength, and

• at least one wavelength converter layer comprising nanostructured Silicon, said at least one wavelength converter layer being able to at least partially convert said first electromagnetic radiation so that the resultant electromagnetic radiation is emitted by said emitting device centered at a second wavelength different from said first wavelength,

characterized in that said at least one converter layer is coated on said at least one layer made of semiconductor material.

According to the present invention the term "nanostructured Silicon" means a particular Silicon crystal structure obtained by a process of removing Silicon atoms from a crystalline Silicon substrate. Therefore, said structure is formed of nanocrystalline Silicon regions separated by empty regions where only air is contained, both said kinds of regions having dimensions of about or lower than some tens of nanometers. The process of removing Silicon atoms can be, for instance, the Stain Etching or the Electrochemical Etching (ECE), as disclosed in detail in the following of the present description.

Therefore, according to the present invention the term "nanostmctured

Silicon" means a particular Silicon crystal stmcture obtained with the above mentioned processes and having crystals dimensions lower than or equal to 100 nm, preferably lower than or equal to 50 nm. Typically, the term "mesostructured Silicon" indicates Silicon having crystals dimensions from 2 nm to 50 nm, while the term "nanostmctured Silicon" defines Silicon having crystals dimensions lower than or equal to 2 nm.

As mentioned above, according to the present invention and as a relevant difference with respect to some LEDs known in the art, the wavelength converter layer is suitably coupled to the layer made of semiconductor material possessed by the emitting device. More in detail, the wavelength converter layer is disposed on the layer made of semiconductor material possessed by the emitting device, i.e. the wavelength converter layer is coated on the source element that is formed of the LED semiconductor layer.

According to a first embodiment of the emitting device of the present invention, said at least one wavelength converter layer is formed of at least one membrane of nanostmctured Silicon coated on the layer made of semiconductor material of the emitting device.

According to a further embodiment of the emitting device of the present invention, said at least one wavelength converter layer is formed of nanostmctured Silicon microparticles coated on the layer made of semiconductor material of the emitting device.

Therefore, the nanostmctured Silicon, both in the form of membrane and of microparticles, can be advantageously used to manufacture an emitting device of colored or white light by suitably combining the nanostmctured Silicon with a known electromagnetic radiation emitting device, e.g. a LED. The electromagnetic radiation emitted by the device centered at a first predetermined wavelength initially chosen by the operator is partially absorbed by the nanostmctured Silicon and successively re-emitted centered at a second wavelength different from the first one and dependent on the photoluminescence properties of the nanostmctured Silicon. The remaining electromagnetic radiation (i.e. the portion of electromagnetic radiation emitted centered at the first wavelength and non- absorbed by the nanostmctured Silicon) combines with the electromagnetic radiation emitted by the nanostmctured Silicon originating a final electromagnetic radiation emitted in the visible region that can be colored or white, i.e. of the desired color as a function of the selected fundamental wavelength of the radiation emitted by the nanostmctured Silicon, as well as of the emission band about said fundamental wavelength. Furthermore, by acting on the nanostmctured Silicon microparticles dosage or on the nanostmctured Silicon membrane thickness, it is possible to modify the portion of electromagnetic radiation emitted by the commercial device and absorbed by the nanostmctured Silicon, in case up to a complete absorption. In this latter case the emitted electromagnetic radiation depends only on the photoluminescence properties of the nanostmctured Silicon.

Moreover, the Applicant has perceived the need of setting an easy and reliable manufacturing process that solves the problems of the above known art.

Therefore, it is a second object of the present invention a manufacturing process of an electromagnetic radiation emitting device comprising the steps of:

• providing at least one layer made of semiconductor material of the electromagnetic radiation emitting device;

• providing at least one crystalline Silicon substrate;

• carrying out a dissolution step of said crystalline Silicon substrate to produce a nanostmctured Silicon membrane, and • coating said at least one layer of material comprising nanostmctured silicon on at least one layer made of semiconductor material so as to form at least one wavelength converter layer of said electromagnetic radiation emitting device.

Therefore, according to a first embodiment the manufacturing process of the present invention comprises the step of producing a nanostmctured Silicon membrane.

According to a further embodiment of the manufacturing process of the present invention, said process comprises the step of grinding said nanostmctured Silicon membrane so as to obtain a plurality of nanostmctured Silicon microparticles.

Further characteristics and advantages of the present invention will appear from the detailed description of some preferred but non-exclusive embodiments of an emitting device and of a manufacturing process of said device in accordance with the present invention.

Brief description of the figures

The following description is given with reference to the enclosed drawings that are provided for an explanatory and thus non-limitative purpose, wherein:

Figure 1 and 2 show the cells used in the electrochemical and chemical processes respectively for the production of nanostmctured Silicon;

- Figure 3 shows a schematic representation of a manufacturing process of a nanostmctured Silicon membrane and of nanostmctured Silicon microparticles;

Figure 4 shows a schematic representation of some manufacturing steps of a LED according to the present invention;

- Figure 5 shows some prototypes of emitting devices (LED) according to the present invention;

Figure 6 shows some commercial LED;

Figure 7 show the emission spectmm and the chromaticity coordinates of a commercial LED, and

Figures from 8 to 1 1 show the emission spectra and the chromaticity coordinates of some prototypes of emitting devices according to the present invention.

Detailed description of the preferred embodiments

Figures 1 and 2 schematically show the cells used for obtaining nanostmctured Silicon according to an electrochemical process (ECE) and a chemical process (STAIN) respectively, both said processes basing on the chemical dissolution (erosion) in hydrofluoric acid (HF) aqueous solution of at least part of the crystalline Silicon substrate that is submitted to attack.

The obtained structure of nanostmctured Silicon has a porous matrix that alternates empty zones (the pores) with zones of crystalline Silicon, the porous matrix (i.e. the porous Silicon) having a high luminous efficiency at room temperature, particularly advantageous for making the emitting device of the present invention.

In Figure 1 the crystalline Silicon substrate 20, from which the nanostmctured Silicon layer will be obtained, is the anode of the electrochemical cell 10, while the cathode 30 is formed of an inert material, typically Platinum. The electrochemical cell is made of a material inert to hydrofluoric acid, e.g. Teflon. The electrochemical solution is typically formed of highly pure (48%) hydrofluoric acid diluted with ethanol and/or water. Since the electrochemical attack occurs along the electrical current streamlines, it is important the shape and the reciprocal position of the electrodes in order to obtain a uniform distribution of the electrical field. Furthermore the stirring of the electrolytic solution and the temperature control are very important too.

The electrochemical process is very versatile, ensures a high reproducibility and allows obtaining nanostmctured Silicon layers with high dimensional and morphological uniformity, as well as excellent mechanical and optical properties. In particular the morphological and dimensional properties of the porous layer of nanostructured Silicon remarkably depend on the anodization process conditions: a) type of doping and resistivity of the Silicon substrate; b) composition and temperature of the electrolytic solution; c) polarization regimen (current and voltage) and geometry of the electrolytic cell; d) preparation conditions of the substrate. It is expedient pointing out that the present invention applies to any kind of nanostructured Silicon substrate, independently of the presence or the absence of a doping substance, as well as of the doping type, said aspect being able to modify some emission properties of the emitting device.

In Figure 2 the crystalline Silicon substrate 50 is immersed within cell 40 into a highly oxidant solution, e.g. an aqueous solution of nitric acid also containing hydrofluoric acid. The chemical process does not require a polarization system since it is an open-circuit process.

The nanostructured Silicon layers that are obtained with the chemical process are structurally comparable to those obtained with the electrochemical process since the chemical reaction which causes the crystalline Silicon dissolution is the same, with surface areas that casually behave as localized cathodes and anodes on which the oxidation-reduction reactions and the charge transfer occur. In detail, at the local anodes the oxidation reactions occur, while at the local cathodes the nitric acid reduction occurs. Successively the Silicon oxide is removed by the hydrofluoric acid, thereby completing the crystalline Silicon dissolution.

However, although the chemical process is easier than the electrochemical process, it has the drawback of generating porous layers having a worse homogeneity and a lower luminous efficiency, in addition to some problems of reproducibility.

By acting on the crystalline Silicon substrate (e.g. by acting on the type and the doping level of said substrate), as well as on the parameters of the chemical (STAIN) or electrochemical (ECE) attack for removing the Silicon (e.g. by acting on the composition and the concentration of the electrolytic solution, on the temperature, etc) it is possible to change the morphology and the dimensions of the nanostmctured Silicon. In particular, as far as the nanostmctured Silicon dimensions are concerned, it is possible to operate both on the thickness of the layer to be produced, and on the smallest and average dimensions of the Silicon nanocrystals. In so doing, since the beginning it is possible to easily and effectively modulate the photoluminescence properties of the nanostmctured Silicon, thereby allowing selecting both the fundamental wavelength of the radiation that it is desired to be emitted by the device, and the emission band about said fundamental wavelength.

Preferably, the chemical dissolution step (erosion step) of the crystalline Silicon substrate is preceded by some preliminary preparation steps of said substrate, as schematically shown in Figure 3.

Firstly, the native oxide that is generally present on the crystalline Silicon substrate 100 (Figure 3a) is subject to a removing step. Said removing step is typically carried out through a chemical attack (e.g. by using an aqueous solution of hydrofluoric acid and ammonium fluoride) at room temperature.

In case the manufacturing process of the nanostmctured Silicon layer is of the electrochemical type (ECE), successively to the native oxide removing step, on the backside (i.e. on the supporting surface) of the crystalline Silicon substrate 100 it is carried out the deposition (Figure 3b) of a thin metallic film 1 10 (e.g. Aluminum) having the function of increasing the electrical contact between the substrate 100 and the electrochemical cell, thereby reducing the contact voltage drop and ensuring a more uniform distribution of the electric potential and thus of the electrical current streamlines.

The chemical dissolution step (performed with the above mentioned chemical or electrochemical processes or with alternative processes, such as the "spark" erosion, the synthesis of Silicon clusters containing luminescent molecules like siloxene, the etching by means of hydrofluoric acid and nitric acid vapors) causes the formation of a nanostmctured Silicon layer 120 (Figure 3c).

Following the chemical dissolution step a drying step of the obtained nanostmctured Silicon layer is performed in order to remove from the pores the hydrofluoric acid solution that has been used during the chemical attack.

Successively to the drying step, the manufacturing process envisages a removing step (Figure 3d) of the nanostmctured Silicon layer (membrane) 120 from the crystalline Silicon substrate 100.

According to an embodiment of the present invention, once the nanostmctured Silicon layer 120 is obtained, in order to easily and effectively coating said layer on the layer made of semiconductor material possessed by the emitting device, the manufacturing process advantageously comprises a step of embedding said nanostmctured Silicon layer in a supporting matrix made of inert material, said material being also transparent both to the starting electromagnetic radiation emitted by the device and to the electromagnetic radiation emitted by the nanostmctured Silicon layer. Furthermore, the material of said supporting matrix has to guarantee both a stable positioning of the nanostmctured Silicon layer and a suitable protection of the latter from the surrounding environmental conditions so as to remarkably reduce the risk of contamination and ageing of the nanostmctured Silicon layer. Therefore, said inert material is requested to have stable chemical- mechanical properties as time goes by and, as mentioned above, to have a good transparency in the visible light emission spectmm. Suitable materials for carrying out this function are, for instance, some polymeric materials, such as the silicone resins.

According to a further embodiment of the present invention, said step of coating the obtained nanostmctured Silicon layer on one layer made of semiconductor material possessed by the emitting device is preceded by a grinding step of said nanostmctured Silicon 120 (Figure 3e) so as to obtain microparticles 130 of the latter.

Said grinding step can be done, for instance, by using ultrasounds or mechanically.

The ultrasonic impact grinding requires the immersion of the previously obtained nanostmctured Silicon layer into a suitable solvent (e.g. isopropanol) and the successive immersion of the Silicon/solvent system into an ultrasonic bath at a frequency of about 40 kHz. The grinding requires a first step lasting about one hour in which the nanostmctured Silicon layer (typically already partially ground due to the drying step, as mentioned above) is reduced to pieces having dimensions of hundreds of micron, and a second step lasting many hours (e.g. 10-12 hr) in which pieces of the desired dimensions of few tens of micron are obtained.

However, the ultrasonic impact grinding has some drawbacks such as, for instance, the fact that it is not uniform with time (therefore pieces of considerable dimensions are still present even after many hours of process) and that, at the end of the procedure, the microparticles are in solution and it is necessary an additional step of solvent removing, which is very difficult since there's a high risk that a remarkable amount of the produced microparticles is lost during the solvent removal. Furthermore, a qualitative evaluation has indicated that this grinding technique causes a deterioration of the luminous intensity of the electromagnetic radiation emitted by the microparticles with respect to the starting nanostmctured Silicon layer.

The mechanical grinding can be carried out manually by using a common tool of suitable dimensions or can be advantageously automated to obtain the microparticles of desired dimensions.

The mechanical grinding has some advantages with respect to the ultrasonic impact grinding. For instance, it is a process that can be performed quite uniformly and does not require the use of solvents, fact particularly advantageous since there's no need for additional steps of solvents removal and the thus obtained microparticles are immediately usable in the successive embedding step that will be detailed in the following of the present description. Furthermore, the mechanical grinding reduces to a minimum the risk of material loss and, by making a qualitative analysis identical to what previously described for the ultrasonic impact grinding, it has been pointed out that this type of grinding does not cause an important deterioration of the luminous intensity of the electromagnetic radiation emitted by the microparticles with respect to the starting nanostructured Silicon layer.

Successively, analogously to what described above with reference to the embodiment of the nanostructured Silicon layer (membrane), the nanostructured Silicon microparticles are embedded into a supporting matrix and then coated on the layer made of semiconductor material possessed by the emitting device, thereby completing the manufacturing of the latter in accordance with the present invention.

It can be pointed out that the LED and the manufacturing process thereof according to the present invention show a plurality of advantages with respect to the LED devices known in the art, e.g. the LED configuration described in document US 2012/00631 17.

For instance (as it will be clear e.g. from the Figures 8, 9 and 10 in the following example section of the present description), the present invention allows the manufacturer to decide a priori (i.e. to predetermine on the basis of the desired result to be achieve) the microparticles percentage (concentration) to be embedded in the polymeric supporting matrix and thus to define how will be the final radiation emitted by the emitting device (LED). In fact, by increasing the microparticles amount, a greater amount of the radiation emitted by the starting blue LED is converted into red light by said microparticles. The LED and the manufacturing process of document US 2012/00631 17 do not allow to decide a priori and then to suitably modulate the nanostmctured Silicon concentration for emitting exactly the desired electromagnetic radiation. In fact, since the phosphor layer is separated from the source element, only a portion of the radiation emitted by the source element is conveyed towards the phosphor layer and thus converted and re-emitted, while the remaining portion (probably the major part) passes through the mold member (i.e. the resin) and thus it is emitted as it is, i.e. without being converted. On the contrary, since the wavelength converter layer of the present invention is coated on (disposed on) the layer made of semiconductor material (i.e. the source element), all the radiation emitted by the latter passes through the wavelength converter layer and, on the basis of the predefined nanostmctured Silicon microparticles concentration (low, medium or high concentration), the radiation emitted by layer made of semiconductor material can be partially or even completed converted. Therefore, it is apparent that the manufacturing process of the present invention is particularly versatile, easy to be carried out, allows to suitably define and modulate a priori (i.e. in the design phase) the desired emitted electromagnetic radiation and it shows a great and advantageous flexibility which leads to the obtainment of even very different results (emitted radiations) by suitably varying the characteristics of the wavelength converter material (e.g. microparticles concentration, dimensions, and even materials).

In fact, it can be further pointed out that the present invention can allow the simultaneous use of different materials so that the electromagnetic radiation can be re-emitted centered at different fundamental wavelengths. This can be obtained, for instance, by producing two or more membranes of nanostmctured Silicon in which the Silicon nanocrystals in the two membranes are different (this can be achieved by suitably selecting the parameters of the electrochemical processes). Thereafter, the microparticles obtained by grinding the two different membranes can be embedded together in the same supporting polymeric matrix and then coated on the layer made of semiconductor material.

The step of coating can be performed, for instance, by applying the microparticles embedded in the polymeric matrix through a dispensing device such as a pipette or a sprayer. For instance, the microparticles embedded in the polymeric matrix can be dispersed in an ink and then printed (with an inkjet printer) on the layer made of semiconductor material. Alternatively, the nanostructured Silicon layer, obtained in the end of the erosion step (e.g. by chemical dissolution) of the crystalline Silicon substrate, is coated as it is (i.e. in the form of membrane) on the layer made of semiconductor material of the emitting device. Therefore, in this case the grinding step described above is not necessary and is not contemplated in the manufacturing process of the device according to the invention. However, the embedding step in a supporting polymeric matrix can still be envisaged for a suitable adhesion of the membrane to the layer made of semiconductor material.

For example, in order to coat said membrane on the layer made of semiconductor material, a small amount (e.g. one drop or very few drops) of polymeric material is positioned onto the layer made of semiconductor material, then the membrane is applied and finally a further small amount of polymeric material is placed on top of the membrane. Generally, this coating step is completed by heating the assembly so that the polymeric material becomes hardened (cured) and it stably fixes the membrane to the layer made of semiconductor material.

At the end of the detaching step of the nanostructured Silicon layer from the crystalline Silicon substrate, it can be advantageously envisaged a chemical (e.g. in nitric acid) or thermal (e.g. carried out at a temperature of 1000-1050°C in pure oxygen atmosphere) oxidation step, said step being able to modulate the dimensions of the crystalline part of the porous matrix. In so doing, then, besides modulating the photoluminescence properties of the material, it is also possible to further protect the Silicon from the ageing thanks to the Silicon oxide layer obtained on the Silicon surface during the oxidation step.

It is apparent that the advantages over the prior art mentioned above with respect to the nanostmctured Silicon microparticles embedded in the polymeric supporting matrix apply also to the case in which the membrane of nanostmctured Silicon is directly coated on the layer of semiconductor material (i.e. the source element). In fact, as mentioned above, the manufacturing process of the present invention allows to act on the crystalline Silicon substrate (e.g. on the type and the doping level of the substrate), on the parameters of the electrochemical attack for removing the Silicon (e.g. on the composition and the concentration of the electrolytic solution, on the temperature), thereby changing the morphology and the dimensions (thickness of the layer and Silicon nanocrystals dimensions), fact which allows to modulate the photoluminescence properties of the nanostmctured Silicon and thus to select the fundamental wavelength of the radiation that it is desired to be emitted by the device, and the emission band centered about said fundamental wavelength.

For illustrative purpose only, in the form of examples, herein below are illustrated the main steps of the manufacturing process of some prototypes of an emitting device of the present invention.

Example 1

Example 1 describes the production of a nanostmctured Silicon layer by using an electrochemical process (ECE).

The electrochemical cell 10 of the type shown in Figure 1 has been connected to a SMU (Source Meter Unit - Keithley SMU 2400) suitable for setting the polarization current and reading the potential difference produced between the cathode 30 and the anode 20. The anode consisted of an Aluminum disk directly contacting with a crystalline Silicon substrate, while the cathode consisted of a ring shaped Platinum wire positioned at a distance of 3 mm from the crystalline Silicon substrate surface. This configuration has guaranteed a uniform distribution of the electrical current streamlines over the whole substrate area subject to the electrochemical attack, thereby promoting a uniform growth of the nano structured Silicon layer and a uniform porosity in a direction parallel to the substrate surface.

The starting crystalline Silicon substrate was chosen to be a p-type Silicon

(p-type doping obtained by using Boron as dopant) which is able to produce a microporous nanostructured Silicon, i.e. having pores diameter and inter-pore distance lower than 10 nm. This aspect is particularly relevant since it allows to obtain a photo luminescent material, since the photoluminescence properties of the nanostructured Silicon highly depend on the dimensions of the material porous matrix.

The SMU was connected to an elaboration unit (personal computer) suitable for receiving and processing the data obtained during the electrochemical process, as well as for setting the parameters necessary for carrying out said process.

As mentioned above, the manufacturing process of a nanostructured Silicon layer started with a removing step of the native oxide (Figure 3a) present on the crystalline Silicon substrate 100, removing step that has been conducted by chemical attack in BHF (Buffered HF, i.e. an aqueous solution of hydrofluoric acid and ammonium fluoride) at room temperature.

Successively, the deposition of an Aluminum film 1 10 (Figure 3b) having a thickness of about 500 nm was carried out on the backside of the crystalline Silicon substrate 100 by using a thermal evaporator.

Thereafter, once the preliminary steps of sample preparation (i.e. preparation of the crystalline Silicon substrate) was completed, the production of the nanostructured Silicon layer (membrane) 120 (Figure 3c) was carried out by means of the electrochemical process (ECE), i.e. attacking the sample in an aqueous solution of hydrofluoric acid at anodic polarization conditions. By suitably setting the ECE parameters a nanostructured Silicon layer having the desired (predetermined) porosity and thickness was obtained.

The electrolytic solution used in the cell was a mixture of hydrofluoric acid (48% in water) and highly pure ethanol (99,998%) in 1 : 1 volume ratio so as to make a hydrofluoric acid volume concentration equal to 24%. In the cell the electrolytic solution had a height of 30 mm so as to submerging only the area of crystalline Silicon substrate subjected to said attack. Said expedient allowed for a greater uniformity of the electrochemical attack and for a substantial saving and maximum efficiency of the electrolytic solution. The starting crystalline Silicon substrates had dimensions of 15 mm x 15 mm and thicknesses of about 500 - 600 μιη.

Once the chemical dissolution was concluded, a drying step of the obtained nanostmctured Silicon layer was performed by evaporation at room temperature. In detail, after removal of the electrolytic solution, the nanostmctured Silicon layer was immersed into ethanol and then into deionized water. The great wettability of the nanostmctured Silicon with respect to ethanol ensured a complete removal of the electrolytic solution from the porous matrix. Successively, the deionized water was removed from the pores through evaporation at room temperature and atmospheric pressure.

The above mentioned electrolytic solution was used to carry out some electrochemical attacks where the polarization current density was set in the range from 75 mA/cm 2 to 600 mA/cm 2 and the electrochemical attack duration was set in the range from 0 s to 300 s, in order to obtain the desired porosity level and thickness for the nanostmctured Silicon layer.

On the basis of the results obtained with the electrochemical attacks carried out by suitably varying the above parameters, Table 1 shows the electrochemical process main parameters values that have been chosen for manufacturing the nanostmctured Silicon layer. Table 1

By making a qualitative evaluation of both the efficiency of use of the starting crystalline Silicon and the conversion efficiency, the latter being carried out by exciting the obtained nanostmctured Silicon layers with a blue LED (λ = 450 nm - manufactured by .i.C.O. Sri) positioned over (i.e. coated on) said layers, Table 2 shows the configuration of compromise that has been chosen for manufacturing the nanostmctured Silicon layers.

Table 2

The parameters values reported in Table 2 lead to the production of nanostmctured Silicon layers having porosity of about 85% and thickness of about 40 μηι.

Once the drying step was completed, the removing step (Figure 3d) of the nanostmctured Silicon layer 120 from the crystalline Silicon substrate 100 was successively performed. Said removing step was very easily carried out by means of a slight mechanical action performed on the supporting surface of the crystalline Silicon substrate 100. Typically the dimensions of the nanostmctured Silicon layers were comprised from some centimeter up to 20 cm in diameter.

Example 2

The nanostmctured Silicon layer obtained according to Example 1 was successively subjected to a mechanical grinding step for obtaining nanostmctured Silicon microparticles (Figure 3e). In detail, said nanostmctured Silicon layer was placed inside a Pyrex^® container and manually ground by using a steel tool for obtaining microparticles of dimensions lower than 1 μηι and up to some tens of μηι.

Successively, the obtained nanostructured Silicon microparticles were embedded in a supporting matrix for simplifying the assembly of said microparticles with a commercial blue LED.

More in detail, the inert material that was chosen for embedding the nanostructured Silicon microparticles was the Sylgard^® 184 material (manufactured by Dow Corning), a silicone resin transparent in the visible region and suitable for ensuring a good physical and thermal protection of the blue LED and of the nanostructured Silicon microparticles. Figure 4 schematically shows said embedding step, as well as the coupling (coating) step of the obtained embedded microparticles with the blue LED used as starting emitting device. In detail, Figure 4a shows the Sylgard^® 184 material that is provided in two distinct liquid components: a base component A and a cure agent B that, suitably mixed (10: 1 weight ratio), cause the polymerization of the silicone elastomer. In order to ensure a uniform polymerization, the two starting components need to be carefully mixed, thereby eliminating the air bubbles potentially present. For instance, it is possible to promote expulsion of the air trapped within the mixture by applying thereto a light vacuum (e.g. 712 - 762 mm Hg). In order to properly mixing said two components a period of time of at least 30 minutes is needed.

Thereafter the obtained elastomeric compound was mixed with the nanostructured Silicon microparticles (Figure 4b). This step is particularly delicate since it is in this manufacturing process step that the nanostructured Silicon microparticles amount to be associated to the starting blue LED is defined.

Once the microparticles dosing step and the mixing step of said microparticles into the supporting matrix were concluded, also in this case carrying out the removal of air bubbles possibly present in the compound, the step of coating the obtained mixture on the starting blue LED surface 140 (Figure 4c) is performed in order to obtain a wavelength converter layer 150 positioned over the layer made of semiconductor material possessed by said LED. According to the present invention, said wavelength converter layer is designated to convert at least partially the primary (original) electromagnetic radiation emitted by the starting blue LED so that the obtained secondary electromagnetic radiation exiting from the emitting device is emitted centered at a second wavelength different from said first wavelength. It is necessary to wait for the completion of the polymerization before using the modified LED. The polymerization was carried out at room temperature since the coating step was done with a LED already provided with the external polarization connections. A polymerization that is carried out at higher temperatures, in any case born by the Sylgard^® 184 material, would have damaged the LED connections already provided and placed for the LED correct operation.

Example 3

The nanostructured Silicon microparticles embedded in the polymeric matrix as shown in Example 2 were used for the manufacturing of some LED prototypes according to the present invention. In particular, said embedded microparticles have been associated to some commercial blue LED manufactured by R.i.C.O. Sri, arranged in a matrix configuration of two columns, each column having 4 groups of blue LED. The LED have been connected so that each group of LED were individually polarizable and in each group the 5 LED were parallel connected so that the polarization of one group caused the simultaneous lighting of all the LED of the same group. This configuration allowed measuring the electric power absorbed by the whole group, but not the electric power absorbed by each single LED.

Some distinct prototypes have been provided which had different concentrations of the nanostructured Silicon microparticles in the polymeric mixture, said mixture having been prepared with low, medium and high concentration of nanostructured Silicon microparticles.

Figure 5 shows the LED prototypes according to the present invention, in the absence of polarization (turned off LED - Figure 5a) and in the presence of polarization (turned on LED - Figure 5b) respectively. The blue light emitted by the starting blue LED was partially absorbed and partially converted by the nanostructured Silicon microparticles (which created the wavelength converter layer of the present invention), and, combined with the electromagnetic radiation emitted by the microparticles, had originated a reddish light. Therefore, this fact proved that the starting (original) blue light of the starting blue LED was converted into a light of a different color thanks to the use of the nanostructured Silicon microparticles. Furthermore, Figure 5 shows how the red shade of the light emitted by the 5 LED was different from one LED to another since said 5 LED have been coated with different concentrations of nanostructured Silicon microparticles.

Figure 6 shows a comparative example wherein the same starting blue LED have been used, but devoid of the nanostructured Silicon microparticles. Said LED are shown in the absence of polarization (turned off LED - Figure 6a) and in the presence of polarization (turned on LED - Figure 6b) respectively. The comparison between Figure 5b and Figure 6b clearly shows the contribution given by the wavelength converter layer according to the invention: the blue light emitted by the LED of Figure 6b was transformed into a reddish light by the modified LED of Figure 5b.

Example 4

The prototypes of Example 3 were subjected to optical characterization by using a spectrophotometer (CS-2000 model manufactured by Konica Minolta) and software (CS-SIOW Professional produced by Konica Minolta) for remote management of the equipment by means of a personal computer. The small dimensions (2 mm x 2 mm in plant) of the blue LED had requested also the use of a lens for close-ups (CS-A35 from Konica Minolta) in order to take measurements at a distance of about 7 cm. Measurements have been carried out for each prototype at different values of the polarization current and at two values of the solid angle (0.1° and 1° respectively). Six measurements with solid angle equal to 0.1° and three measurements with solid angle equal to 1° have been carried out for each value of the polarization current. The decision of using two different measurements solid angles allowed to change the measurement area (i.e. the area through which the light emitted by the prototype is detected), thereby passing from a circular area having diameter comprised between 0.1 mm and 0.2 mm at a solid angle equal to 0.1° to a circular area having diameter comprised between 1.0 mm and 2.0 mm at a solid angle equal to 1°. For the polarization current a range from 200 mA to 600 mA was selected.

The optical characterization of the prototypes was aimed at identifying the light (electromagnetic radiation) color emitted by each device, by determining both the chromaticity coordinates x and y and the luminance L_v, and the light emission spectrum. In particular, the first information gives important indications on the result of the chromatic combination between the light emitted by the starting blue LED and the light converted by the nanostmctured Silicon microparticles, combination that depends on the dosage of said microparticles. On the contrary, the light emission spectmm provides information also on the single component of the luminous radiation emitted by the microparticles and thus on the photoluminescence of the nanostmctured Silicon. Under optical stimulation with radiation having wavelength equal to 450 nm (blue light), in fact it is possible to deduce the dominant wavelength and the emission band of the radiation emitted by the nanostmctured Silicon microparticles, these properties being directly correlated to the dimensions of the crystalline part of the porous matrix of the nanostmctured Silicon and to the state (type of chemical terminal group being present) of the surface of the nanostmctured Silicon.

Figure 7 shows the light emission spectmm and the chromaticity coordinates x and y of the starting blue LED, i.e. of the commercial LED not provided with the nanostmctured Silicon microparticles. The measurements shown in the graphs (referred to a solid angle equal to 0.1°) prove that the blue light emitted by the LED has a dominant wavelength of 450 nm.

Figures 8, 9 and 10 show the light emission spectrum and the chromaticity coordinates x and y of the three prototypes of Example 3 that, as mentioned above, are different from each other because, respectively, of the low, medium and high concentration of the nanostmctured Silicon microparticles embedded in the supporting polymer matrix. Said figures indicate also the measures obtained for different values of the total polarization current (bias current) (i.e. the reported current values refer to each group of 5 blue LED and not to a single blue LED).

The analysis of Figures 8, 9 and 10 leads to the following considerations. From a chromatic standpoint, by increasing the dosage (i.e. the amount) of the nanostmctured Silicon microparticles, the shade of the red light emitted by the prototype has varied from a blue-red (Figure 8) to a bright red (Figure 10). Notwithstanding this variation (very clear when looking at the emission spectmm graphs), all the color data points reported on the standard CIE 1931 chromaticity diagram ideally move along a straight line that intercepts the white-light line in the region of warm white (below 2000 K). This means that the nanostmctured Silicon microparticles embedded in the polymeric matrix have all the same properties and, then, the color change is only due to the different dosage of said microparticles. From the chromaticity standpoint, the result of the different polarization current of the prototype does not seem to be substantial.

From the emission spectmm standpoint, independently from the dosage of the nanostmctured Silicon microparticles, can be easily identifiable the emission band of the blue LED (comparable with that of Figure 7) and the band of the light emitted by the nanostmctured Silicon as a consequence of the stimulation with the blue light of the starting LED. In particular, it can be noted that the light emitted by the nanostructured Silicon starting from yellow (λ = 550 - 570 nm) extends up to infrared with a dominant wavelength about 670 nm. Furthermore, it can be noted a secondary peak, very narrow around 690 nm. The band width of the light emitted by the nanostructured Silicon microparticles indicates the possible presence in the crystalline part of the porous matrix of the nanostructured Silicon of a distribution of crystals having different dimensions, with predominance of those crystals to which a photoluminescence at the peak wavelength can be attributed. The result of the polarization total current is to increase the intensity of the emitted radiation, noting that by increasing this intensity an increase of the luminance is obtained at any wavelength (in the band of the blue LED and of the nanostructured Silicon). The comparison between the various dosages of the nanostructured Silicon microparticles (Figures 8, 9 and 10) shows that, by increasing the microparticles amount, a greater amount of the radiation emitted by the starting blue LED is converted into red light by said microparticles, shifting from an intensity associated to λ = 450 nm (peak of blue) that is remarkably higher than that associated to λ = 670 nm (peak of red) in case of low dosage (Figure 8), to an equality of the intensities of said peaks in case of medium dosage (Figure 9), to an overturn in case of high dosage (Figure 10).

Example 5

A further prototype was manufactured by the Applicant by using a nanostructured Silicon layer obtained from a crystalline Silicon substrate analogous to that described in Example 1, but having an amount of dopant (Boron) equal to2 xl0¹⁹÷6xl0¹⁹ atoms/cm³.

In fact, the Applicant has noticed that, by starting from crystalline Silicon substrates in accordance with the values of Table 2, nanostructured Silicon layers with a sponge-like morphology are obtained, while, by using a crystalline Silicon substrate having the above mentioned Boron amount, nanostructured Silicon layers with a column-like morphology are obtained. This property confers to the thus obtained nanostructured Silicon layer a mechanical resistance that is sufficient to keep intact the layer, even after the drying step. Therefore, since the nanostructured Silicon layer did not exhibit any crashing, not even a partial crashing, said layer was not subjected to any embedding step in a polymeric supporting matrix and was directly coated on starting blue LED (i.e. to the layer made of semiconductor material of said LED). Nanostructured Silicon layers having thickness of 40 μηι have been used for manufacturing the prototype.

Therefore, Figure 1 1 shows the emission spectrum and the chromaticity coordinates x and y (standard CIE 1931 diagram) of said prototype for different values of the polarization total current (i.e. the current values refer to each group of 5 blue LED and not to a single blue LED). By analyzing the graphs of Figure 1 1 it can be noticed a remarkable attenuation of the luminous power, with a nearly entire cancellation of the blue light band and the presence of an emission band in the red that is very narrow if compared to that of the prototypes obtained with nanostructured Silicon microparticles of the previous examples. Said emission band in the red has a peak wavelength of about 690 nm, peak that is present also in the spectra of the prototypes manufactured with nanostructured Silicon microparticles. This behavior can be explained taking into account that the different morphology of the above mentioned nanostructured Silicon does not allow the formation, in the crystalline part of the porous matrix, of crystals having dimensions sufficiently small to exhibit photoluminescence properties. Therefore, the most part of the blue radiation emitted by the starting LED is absorbed by the nanostructured Silicon layer without being emitted as light of different color, fact that explains the observed high attenuation. However an emission of the nanostructured Silicon layer is in any case present and has a very narrow emission band. This result reveals in the porous matrix the presence of Silicon nanocrystals the dimensions of which, in addition to allowing photoluminescence, are distributed over a very narrow range about the average value. The present invention allows that a plurality of advantages can be obtained, in particular with respect to the manufacturing processes of the known emitting devices.

Particularly, as mentioned above, the manufacturing process of an emitting device having a wavelength converter layer made from a material comprising nanostmctured Silicon according to the invention allows to define and predetermine in a single process step both the fundamental wavelength and the emission band of the electromagnetic radiation emitted by the device, In detail, by varying the intensity of the applied current, it is possible to vary the dimensions of the nanostmctured Silicon crystals and then to select in a single process step both the fundamental wavelength and the emission band of the electromagnetic radiation emitted by the device. This aspect is particularly advantageous in terms of versatility of the manufacturing process and of costs correlated thereto, and thus also of manufacturing cost of the device.

Furthermore, said manufacturing process has a good reproducibility and an effective use of the starting Silicon since, once the obtained nanostmctured Silicon membrane has been removed, the remaining crystalline Silicon substrate can be reused to obtain a new membrane, thereby allowing the use of the substrate for its whole thickness with a remarkable reduction of the production scraps.

Furthermore, the dimensions of the nanostmctured Silicon membranes and microparticles are suitable for simplifying the assembly steps of the final emitting device and a great stability of the properties of the emission spectmm of the light emitted by the device is guaranteed.

The emitting device according to the present invention can be applied in any technological field where a light source in the visible light emission spectrum is envisaged, being it a white or colored light, even where a light source of small dimensions is required.

A first example is represented by the lighting field that may include: a) public or private, indoor or outdoor lighting systems, where luminous sources having high efficiency and low consumptions are requested (in terms of energy saving and environmental impact reduction); b) luminous signs for means of transport, where luminous sources are required to be colored and well visible even in difficult atmospheric conditions; c) artistic and architectural lighting systems, where white or colored luminous sources are required to be versatile and of easy configuration; d) artificial view systems, where a bright, focused and homogeneous light is requested.

A second example is represented by the medicine field that may include: a) chromotherapy, where sources of colored light are requested for treating specific pathologies; b) photobiomodulation, where sources of athermic lights are requested that should not have to cause damages to the treated tissue cells; c) electromedical analysis equipment, e.g. the endoscope, where luminous sources of small dimensions are requested.

A further example is represented by the agriculture field, where the plantation can be made more efficient by selecting for each type of cultivation the luminous source having suitable wavelength and emission band.

Claims

1. Electromagnetic radiation emitting device comprising:

• at least one wavelength converter layer comprising nanostructured Silicon, said at least one wavelength converter layer being able to at least partially convert said first electromagnetic radiation so that the resultant electromagnetic radiation is emitted by said emitting device centered at a second wavelength different from said first wavelength, characterized in that said at least one wavelength converter layer is coated on said at least one layer made of semiconductor material.

2. Electromagnetic radiation emitting device according to claim 1, wherein said at least one wavelength converter layer is made of microparticles of nanostructured Silicon.

3. Electromagnetic radiation emitting device according to claim 2, wherein said microparticles of nanostructured Silicon are embedded in a supporting polymeric matrix.

4. Electromagnetic radiation emitting device according to claim 3, wherein said supporting polymeric matrix is a Silicone resin.

5. Electromagnetic radiation emitting device according to claim 1, wherein said at least one wavelength converter layer comprises at least one membrane of nanostructured Silicon.

6. Electromagnetic radiation emitting device according to any one of claims 1 to 5, wherein said device is a light Emitting Diode (LED).

7. Electromagnetic radiation emitting device according to any one of claims 1 to 6, wherein the crystals dimensions of said nanostructured Silicon are lower than or equal to 100 nm.

8. Electromagnetic radiation emitting device according to claim 7, wherein said crystals dimensions are lower than or equal to 50 nm.

9. Manufacturing process of an electromagnetic radiation emitting device according to claims 1 to 8, comprising the steps of:

· providing at least one layer made of semiconductor material of said electromagnetic radiation emitting device;

• providing at least one crystalline Silicon substrate;

• carrying out a dissolution step of said crystalline Silicon substrate to produce a nanostmctured Silicon membrane, and

· coating said at least one layer of material comprising nanostmctured

Silicon on said at least one layer made of semiconductor material so as to form at least one wavelength converter layer of said electromagnetic radiation emitting device.

10. Manufacturing process according to claim 9, comprising the step of removing said nanostmctured Silicon membrane from said crystalline Silicon substrate.

1 1. Manufacturing process according to claim 9, wherein said dissolution step is performed electrochemically.

12. Manufacturing process according to claim 9, wherein said dissolution step is performed chemically.

13. Manufacturing process according to any one of claims 9 to 12, comprising a step of removing the native oxide possessed by said crystalline Silicon substrate.

14. Manufacturing process according to claim 13, wherein said removing step of the native oxide is performed before said dissolution step.

15. Manufacturing process according to claim 9, comprising a deposition step of a metallic film on the backside surface of said crystalline Silicon substrate.

16. Manufacturing process according to any one of claims 9 to 15, comprising a drying step of said nanostmctured Silicon membrane.

17. Manufacturing process according to claim 10, comprising a step of grinding said nanostmctured Silicon membrane for producing a plurality of microparticles of nanostmctured Silicon, said grinding step being performed after the removing step of said nanostmctured Silicon membrane from said crystalline Silicon substrate.

18. Manufacturing process according to claim 17, wherein said grinding step is performed mechanically or by means of ultrasounds.

19. Manufacturing process according to claim 10, comprising a step of oxidizing said nanostmctured Silicon membrane, said oxidizing step being performed after the removing step of said nanostmctured Silicon membrane from said crystalline Silicon substrate.

20. Manufacturing process according to claim 17, comprising a step of embedding said plurality of microparticles of nanostmctured Silicon in a supporting polymeric matrix.

21. Manufacturing process according to claim 20, wherein said embedding step comprises a step of dosing an amount of microparticles of nanostmctured Silicon.

22. Manufacturing process according to claim 20, wherein said embedding step comprises a step of mixing said plurality of microparticles of nanostmctured Silicon with the polymeric material of said supporting polymeric matrix.