Patent Description:
It is known to generate wavelengths of a desired primary peak wavelength using a pump source light emitting diode (LED) to provide input light and colour conversion materials to convert such input light to light of a desired wavelength. Such colour conversion materials can be phosphor materials or quantum dots (QDs), for example. Of particular importance is to generate light with wavelengths corresponding to red, green and blue light. Such colour light emission has significance in display applications.

In this context, <CIT> discloses an optoelectronic device including an LED that is suited to the emission of a radiation and that includes an active layer, and a conversion layer that extends over the active layer of the LED and that includes a plurality of fluorophores -possibly QDs- suited to the conversion of the radiation emitted by the LED, wherein the conversion layer is confined laterally by a mirror reflecting both the radiation converted by the fluorophores and the radiation not converted by the fluorophores, and vertically between a first and a second multilayer reflective filters forming a resonant Fabry-Perot cavity that blocks the radiation not converted by the fluorophores and has a transmittance peak for the radiation converted by the fluorophores.

Similarly, still in context of RGB LED-based displays, <CIT> discloses wavelength converters coupled with blue LEDs by being preferably integrated inside a resonant optical cavity.

Finally, the article: "<NPL>, discloses monolithic red, green and blue (RGB) micro-light emitting diodes (microLEDs) fabricated using gallium nitride based blue LEDs and QDs. To enhance the color conversion efficiency and the light output intensity, a hybrid Bragg reflector (HBR) was deposited on the bottom side of the monolithic RGB microLEDs, thus reflecting the RGB light emitted to the substrate. To further improve the colour purity of the red and green light, a distributed Bragg reflector (DBR) with high reflection for the blue light was deposited on the top side of the QDs/microLEDs. The red and green light output intensities of the microLEDs with HBR and DBR were enhanced by about <NUM>%.

It is therefore known to provide red, green and blue light from a single wafer of monolithically grown light emitting diode devices that produce light of a particular wavelength (typically blue light), using QD materials to down convert the light. Similarly, red, green and blue light emitting structures comprising quantum wells (QWs) can be stacked on top of one another to produce a stacked device. In such devices, at low current level, the top most QW lights up and by increasing the current level, the middle and bottom QWs are lit up sequentially. However, QD materials are not ready for microLED display applications as such materials typically easily degrade over <NUM>. 2W/cm<NUM> input power. Further, where QDs are used as the colour conversion material, the thickness of the layers of QD material are typically at least <NUM> in order to fully absorb input light. Accordingly, the thickness of QD material needed to provide sufficient conversion of light wavelength is greater than that suitable to provide the pixel size and pitch needed in high resolution microLED arrays. Furthermore, typical colour conversion materials, such as QDs and phosphor materials, result in a large full width half maximum (FWHM) spectrum and hence a reduced colour gamut.

Accordingly, there is a need for sources of distinct and different wavelengths of light, such as red, green and blue light, with an increased colour gamut suitable for microLEDs.

In order to mitigate for at least some of the above-described problems, there is provided a colour conversion resonator system, an array of pixels comprising the same, and a method of forming said colour conversion resonator system in accordance with the appended claims.

There is provided a colour conversion resonator system, comprising: a first partially reflective region configured to transmit light of a first primary peak wavelength and to reflect light of a second primary peak wavelength; a second partially reflective region configured to at least partially transmit light of the first and second primary peak wavelengths and to reflect light of a third primary peak wavelength; a third partially reflective region configured to at least partially reflect light with the third primary peak wavelength; a first colour conversion resonator cavity arranged to receive input light with the first primary peak wavelength through the first partially reflective region and to convert at least some of the light of the first primary peak wavelength to provide light of the second primary peak wavelength, wherein the first colour conversion resonator cavity is arranged such that the second primary peak wavelength resonates in the first colour conversion resonator cavity and resonant light with the second primary peak wavelength is output through the second partially reflective region; and a second colour conversion resonator cavity arranged to receive input light comprising the second primary peak wavelength through the second partially reflective region and to convert at least some of the second primary peak wavelength to provide light of the third primary peak wavelength, wherein the second colour conversion resonator cavity is arranged such that the third primary peak wavelength resonates in the second colour conversion resonator cavity and resonant light with the third primary peak wavelength is output through the third partially reflective region, wherein the first colour conversion resonator cavity and the second resonator cavity are arranged partially to overlap to provide a non-overlapping portion and an overlapping portion thereby to define a first light emitting surface and a second light emitting surface respectively, wherein the first light emitting surface is arranged to provide resonant light of the second primary peak wavelength and the second light emitting surface is arranged to provide resonant light of the third primary peak wavelength.

Preferably, the third partially reflective region is further configured to reflect light with a fourth primary peak wavelength, the colour conversion resonator system further comprising: a fourth partially reflective region configured to at least partially reflect light with the fourth primary peak wavelength; and a third colour conversion resonator cavity arranged to receive input light comprising the third primary peak wavelength through the third partially reflective region and to convert at least some of the third primary peak wavelength to provide light of the fourth primary peak wavelength, wherein the third colour conversion resonator cavity is arranged such that the fourth primary peak wavelength resonates in the third colour conversion resonator cavity and resonant light with the fourth primary peak wavelength is output through the fourth partially reflective region, wherein the second colour conversion resonator cavity and the third colour conversion resonator cavity are arranged partially to overlap to provide a non-overlapping portion and an overlapping portion thereby to define the second light emitting surface and a third light emitting surface respectively, wherein the second light emitting surface is arranged to provide resonant light of the third primary peak wavelength and the third light emitting surface is arranged to provide resonant light of the fourth primary peak wavelength.

Such a configuration forms a monolithic system of epitaxial layers. In contrast to known monolithic LED devices, the colour conversion resonator system of the present invention is able to provide distinct light of different wavelengths in a vertically integrated system. Growing such a colour conversion resonator system monolithically removes the need to use conventional time consuming 'pick and place' methods whereby LEDs are grown individually on a wafer and moved separately onto the display electronics. Furthermore, the partial overlap created between the first and second colour conversion resonator cavities and the second and third colour conversion resonator cavities due to selective etching, allows the system to emit light of different colours with relatively narrow full width half maximum (FWHM) spectra. Furthermore, such a system improves the directionality of light emitted, reducing the need for the integration of collimators or lens, which may require complex processes to implement. Advantageously, improved light output is provided, enabling narrow beam angles and narrow spectra, for example for use in near eye displays. Beneficially, the colour conversion resonator system enables high colour gamut displays and the formation of high resolution micro LED arrays. Advantageously, the optical colour conversion resonator system enables wafer level processing and narrow beam angle emission without collimators, and compressed light emission spectra with reduced efficiency loss.

The colour conversion resonator system can be configured to emit red, green and blue light from the different light emitting surfaces. Such a system is particularly useful in microLED applications for display screens.

Preferably, the first partially reflective region and the second partially reflective region are separated by a distance of (N+<NUM>) multiplied by λconverted_2nd/2n2nd(λconverted_2nd), wherein N is a positive integer number, λconverted_2nd is the second primary peak wavelength and n2nd(λconverted_2nd) is the effective refractive index of the material separating the first partially reflective region and the second partially reflective region, thereby to define the length of the first colour conversion resonator cavity and/or wherein the second partially reflective region and the third partially reflective region are separated by a distance of (N+<NUM>) multiplied by λconverted_3rd/2n3rd(λconverted_3rd), wherein N is a positive integer number, λconverted_3rd is the third primary peak wavelength and n3rd(λconverted_3rd) is the effective refractive index of the material separating the second partially reflective region and the third partially reflective region, thereby to define the length of the second colour conversion resonator cavity, and/or wherein the third partially reflective region and the fourth partially reflective region are separated by a distance of (N+<NUM>) multiplied by λconverted_4th/2n4th(λconverted_4th), wherein N is a positive integer number, λconverted_4th is the fourth primary peak wavelength and n4th(λconverted_4th) is the effective refractive index of the material separating the third partially reflective region and the fourth partially reflective region, thereby to define the length of the third colour conversion resonator cavity.

Such a configuration enables constructive interference of the second primary peak wavelength in the first colour conversion resonator cavity, constructive interference of the third primary peak wavelength in the second colour conversion resonator cavity and constructive interference of the fourth primary peak wavelength in the third colour conversion resonator cavity. Advantageously, careful tuning of the colour conversion resonator cavity enables enhanced output emission.

Preferably, the colour conversion resonator system further comprises at least one LED. More preferably, the colour conversion resonator system comprises a first LED arranged to control light emission from the first light emitting surface and a second LED arranged to control light emission from the second light emitting surface.

More preferably, the colour conversion resonator system comprises a first LED arranged to control light emission from the first light emitting surface, a second LED arranged to control light emission from the second light emitting surface and a third LED arranged to control light emission from the third light emitting surface. Beneficially, such a system allows each pixel to be controlled individually.

For example, a system with at least three individual LEDs and configured to emit red, green and blue light can allow only a blue pixel to emit light, or only a green pixel to emit light or only a red pixel to emit light. Additionally, a combination of the pixels can emit light such that blue and green light is emitted in combination, blue and red light is emitted in combination, red and green light is emitted in combination or red, green and blue light is emitted in combination.

Preferably the input light is at least one of ultraviolet (UV) light and blue light, preferably wherein the input light has a wavelength of between <NUM> and <NUM>. Advantageously, high quality, established input LED sources with shorter wavelengths than the wavelength of further visible light colours required for optical displays are used to provide an input pump source for the colour conversion in the colour conversion resonator cavity.

Preferably, at least one of the colour conversion resonator cavities comprises at least one quantum well layer, preferably wherein the at least one quantum well layer is placed to coincide with an antinode of the colour conversion resonator cavity standing wavelength for converted light, thereby enhancing at least one of the intensity, spectral width and directionality of output light with the resonant converted wavelength of light.

Alternatively or additionally, there is provided the colour conversion resonator system wherein at least one of the colour conversion resonator cavities comprises a quantum well layer comprising at least one quantum well and a further quantum well layer comprising at least one quantum well, wherein the separation of the quantum well layer and the further quantum well layer is N multiplied by λconverted/2n(λconverted), wherein N is a positive integer number, λconverted is the wavelength of the resonant light in the colour conversion resonator cavity and n(λconverted) is the effective refractive index of the material between the quantum well layer and the further quantum well layer at the wavelength of the resonant light in the colour conversion resonator cavity.

Beneficially, such a configuration places each quantum well layer at an antinode of the resonant standing wavelength of light in the colour conversion resonator cavities thereby enabling constructive interference and enhancement of output light.

Preferably, at least one of the colour conversion resonator cavities comprises at least one absorption layer configured to absorb input light thereby to enable transfer of energy from the input light wavelength into the at least one quantum well layer, preferably wherein the absorption layer comprises a material with a lower energy bandgap than the energy of the input light. Advantageously, absorption layers aid the process of enabling carriers to recombine in quantum well layers and thus enabling improved resonance of the converted light emitted by the quantum well layers.

Preferably, the colour conversion resonator system further comprises at least one diffusion barrier arranged to reduce diffusion of carriers from at least one of the colour conversion resonator cavities. Advantageously, the use of diffusion barriers reduces diffusion of carriers and hence enhances emissive recombination in the colour conversion resonator cavity.

Preferably, the colour conversion resonator system comprises at least one further partially reflective region corresponding to at least one of the first, second or third light emitting surfaces. Advantageously, the partially reflective regions are tuned in order to optimise which wavelengths are emitted by light emitting pixels formed by the combination of colour conversion resonator cavity systems and LED devices. Beneficially, light of predefined wavelengths is recycled in the colour conversion resonator cavities in order to enhance the conversion efficiency of input light with a primary peak wavelength to output light with a different primary peak wavelength.

Preferably, at least one of the partially reflective regions and/or the further partially reflective regions comprises a distributed Bragg reflector (DBR), preferably wherein the DBR is at least one of: a double band DBR, a conventional DBR and a vertical stack of two DBRs.

Preferably, at least one of the partially reflective regions comprises a blue wavelength centred low Herpin index distributed Bragg reflector (DBR) or a green wavelength centred low Herpin index DBR or a red wavelength centred low Herpin index DBR.

Preferably, the colour conversion resonator system comprises a blue wavelength centred low Herpin index DBR and a green wavelength centred low Herpin index DBR and a red wavelength centred low Herpin index DBR. Beneficially, such a configuration creates one pixel optimised for blue wavelength light, one pixel optimised for green wavelength light and one pixel optmised for red wavelength light.

Preferably, at least one of the partially reflective regions and the colour conversion resonator cavities comprises an epitaxial crystalline layer, preferably wherein the colour conversion resonator system comprises at least one of a dielectric material and a III-V semiconductor material. Advantageously, the partially reflective region is formed using techniques that enable seamless integration of the functional layers in the colour conversion resonator cavity.

Preferably, the colour conversion resonator system forms an array of pixels, wherein the array comprises a first pixel configured to emit light of a different wavelength to a second pixel and a third pixel configured to emit light of a different wavelength to the first pixel and the second pixel. Preferably the first and/or second pixel and/or third pixel comprises a further partially reflective region corresponding to its light emitting surface. Advantageously, light emitting pixels based on the combination of light emitting devices, such as LED devices, and colour conversion resonator cavities means that high purity colour light emitting pixels can be formed on a scale that means that they can be implemented in high resolution micro scale arrays.

The colour conversion resonator system is preferably produced by forming at least one of the colour conversion resonator cavities on a substrate, preferably wherein forming at least one of the colour conversion resonator cavities on the substrate comprises epitaxial growth of a plurality of layers. The method further comprising forming at least one of the partially reflective regions on the substrate, preferably wherein forming at least one of the partially reflective regions on the substrate comprises sequentially forming at least one of the colour conversion resonator cavities and partially reflective regions on the substrate. The method preferably comprising bonding the colour conversion resonator system to at least one LED and selectively etching the colour conversion resonator system, thereby to provide the light emitting surfaces. Advantageously, forming a colour conversion resonator cavity on a substrate enables large scale formation of colour conversion resonator cavities for integration with light emitting devices. Beneficially, known growth and processing techniques are applied to form structures with high quality, low defect density, material that provides for efficient light input and light conversion for use in light emitting pixels.

Further aspects of the invention will be apparent from the description and the appended claims. The claims define the scope of the present invention.

A detailed description of embodiments of the invention is described, by way of example only, with reference to the figures, in which:.

In order to address disadvantages associated with devices in the prior art at least as described above, a structure and method of forming the structure is described below, with reference to <FIG>. A colour conversion resonator cavity system is described that provides an elegant way to down convert and reuse input light in an efficient manner, in order to provide multi-colour wavelength light output systems. Advantageously, such systems provide high purity, narrow FWHM output light with narrower beam angles, thereby improving light output control and providing systems with a better colour gamut and controlled directionality. Beneficially, the formation and processing of epitaxially grown crystalline layers can be used to provide high quality, and therefore high efficiency, systems for improved light output. Such epitaxially grown crystalline layers can be used to form the colour conversion resonator cavity system in a single growth process or groups of one or more epitaxially grown crystalline layers can be optimised separately and bonded together to form the colour conversion resonator cavity, thereby enabling parallel growth and processing of separately optimised layers.

Further, advantageously, the formation and processing of colour conversion resonator cavities formed from epitaxially grown systems enables the definition of light emitting surfaces associated with the emission of different colours of light, whereby the light emitting surfaces are associated with pixels that can, advantageously, be formed on a scale suitable for implementation in microLED pixel arrays (including high resolution microLED arrays with light emitting surfaces of pixels less than or equal to <NUM><NUM> and preferably less than or equal to <NUM><NUM>, and with pixel pitch less than or equal to <NUM> and preferably less than or equal to <NUM>).

In <FIG> there is shown a cross sectional view of a colour conversion resonator system <NUM>, which is an epitaxial structure that has three colour conversion resonator cavities. The epitaxial structure is formed and subsequently processed in order to provide a colour conversion resonator system in combination with light input devices, as described with reference to <FIG>.

The colour conversion resonator system <NUM> is a stack of epitaxial crystalline compound semiconductor layers. The epitaxial crystalline compound semiconductor layers are provided by sequential growth of the epitaxial layers on a growth substrate <NUM>. The growth substrate <NUM>, for example a silicon, silicon carbide, sapphire, gallium nitride, or other suitable growth substrate, may be removed after the epitaxial compound semiconductor crystalline layers have been formed. Beneficially, the growth of such epitaxial compound semiconductor crystalline layers formed in this manner can be controlled with high precision to provide high quality material with low defect densities, as well as controlled thicknesses of layers and efficient emissive recombination of carriers at controlled wavelengths of light.

The three colour conversion resonator cavities of the epitaxial structure are each designed to receive input light from one or more input light sources and to convert input light with a primary peak wavelength from an input light source to provide output light with different, converted, primary peak wavelengths of light. The epitaxial structure is designed such that light of the converted primary peak wavelength resonates in its respective colour conversion resonator cavity of the epitaxial structure and resonant converted light of multiple, different, wavelengths is output from the colour conversion resonator system <NUM> when processed and combined with input light sources. Appropriate processing of the epitaxial structure enables the provision of multi-colour emitters, where multiple colour conversion resonator cavities are associated with different light emitting surfaces for emitting light of different wavelengths, at least as described herein.

<FIG> shows a buffer <NUM> grown on the growth substrate <NUM>. The substrate <NUM> is a silicon substrate and the buffer <NUM> an aluminium gallium nitride (AlGaN) epitaxial layer. In further examples, alternatively or additionally, the buffer <NUM> is formed of at least one of aluminium gallium nitride (AlGaN), aluminium nitride (AIN), and gallium nitride (GaN).

Upon the buffer <NUM> there is grown an etch stop <NUM>. The etch stop <NUM> is an AlGaN layer with relatively high aluminium content. The etch stop <NUM> facilitates accurate control of processing steps that are used to remove material from the epitaxial structure <NUM> in order to provide a processed system.

Atop the etch stop <NUM> there is grown a partially reflective region <NUM>. Upon the partially reflective region <NUM> there is grown a colour conversion resonator cavity <NUM> and a further partially reflective region <NUM>. The colour conversion resonator cavity <NUM> is configured to receive input light of a primary peak wavelength and convert this input light to converted light of a different primary peak wavelength.

Atop the partially reflective region <NUM> there is grown a further colour conversion resonator cavity <NUM> and a further partially reflective region <NUM>. The colour conversion resonator cavity <NUM> is configured to receive input light of another primary peak wavelength and convert this input light to converted light of a different primary peak wavelength. In a further example, an etch stop layer is formed between the partially reflective region <NUM> and the further colour conversion resonator cavity <NUM>. The etch stop layer (not shown) facilitates close control in subsequent steps to remove material from the structure. In further examples, alternative or additional etch stop layers are formed within the structure in order to facilitate control of removal of layers by etching processes.

Atop the partially reflective region <NUM> there is grown a further colour conversion resonator cavity <NUM> and a further partially reflective region <NUM>. The colour conversion resonator cavity <NUM> is configured to receive input light of a further primary peak wavelength and convert this input light to converted light of a different primary peak wavelength. In a further example, an etch stop layer is formed between the partially reflective region <NUM> and the further colour conversion resonator cavity <NUM>. The etch stop layer (not shown) facilitates close control in subsequent steps to remove material from the structure. In further examples, alternative or additional etch stop layers are formed within the structure in order to facilitate control of removal of layers by etching processes.

Colour conversion resonator system <NUM> forms a monolithic system of epitaxial layers. Such epitaxial layers are planar layers. The colour conversion resonator system <NUM> of <FIG> is formed using epitaxial compound semiconductor growth techniques such as metalorganic chemical vapour deposition (MOCVD) and molecular beam epitaxy (MBE). Additionally, or alternatively, the colour conversion resonator system <NUM> is formed using any appropriate technique.

The order of the epitaxial layers is sequentially grown such that when the system is flipped and bonded to an LED, the order of proximity of the colour conversion resonator cavities with respect to the LED is such that shorter wavelength light, such as UV light, from the LED is absorbed in the colour conversion resonator cavity <NUM> and then longer wavelength light, such as blue light, is output from the colour conversion resonator cavity <NUM>. The light output from the colour conversion resonator cavity <NUM> and the LED is absorbed in the colour conversion resonator cavity <NUM>. The colour conversion resonator cavity <NUM> then outputs light with a longer wavelength than the LED and the colour conversion cavity <NUM>, such as green light. Light output from the colour conversion resonator cavity <NUM>, the colour conversion resonator cavity <NUM> and the LED is absorbed in the colour conversion resonator cavity <NUM>, which then outputs yet longer wavelength light, such as red light. This means that input light can be absorbed and emitted by the colour conversion resonator cavities in such a way that the light that is emitted by the successive colour conversion resonator cavities is reused before exiting the eventual structure.

Advantageously, growing the epitaxial structure of the colour conversion resonator system <NUM> in this order means that the colour conversion resonator cavities <NUM>, <NUM>, <NUM> can be handled using the growth substrate <NUM> upon which the layers of the colour conversion resonator system <NUM> are formed, in order to facilitate bonding with LED structures without requiring further processing steps to enable alignment and bonding of the colour conversion resonator system <NUM> with one or more light emitting devices formed on a different underlying substrate.

The colour conversion resonator system <NUM> described with respect to <FIG> is formed from nitride-based materials. In particular, the epitaxial crystalline compound semiconductor layers are Gallium Nitride (GaN) based materials. Whilst the structures described in relation to <FIG> relate to nitride-based semiconductor compound materials, the skilled person understands that the concepts described herein are applicable to other materials, in particular to other semiconductor materials, for example other III-V compound semiconductor materials, or II-VI compound semiconductor materials.

The provision of three colour conversion resonator cavities enables structures that emit multiple, different, primary peak wavelengths of light to be formed. The skilled person understands that alternative or additional structures are used in further examples in order to provide different structures that emit different primary peak wavelengths of light.

The partially reflective region <NUM> and the further partially reflective region <NUM> are separated by a distance of (N+<NUM>) multiplied by λconverted/2n(λconverted) wherein N is a positive integer number, λconverted is the converted primary peak wavelength emitted from the colour conversion resonator cavity <NUM> and n(λconverted) is the effective refractive index of the material separating the partially reflective region <NUM> and the further partially reflective region <NUM>. Such a configuration allows light of the converted primary peak wavelength to resonate in the colour conversion resonator cavity <NUM>. In further examples, the partially reflective region <NUM> and the further partially reflective region <NUM> are separated by a different distance.

Similarly, the partially reflective region <NUM> and the further partially reflective region <NUM> are separated by a distance of (N+<NUM>) multiplied by λconverted/2n(λconverted) wherein N is a positive integer number, λconverted is the converted primary peak wavelength emitted from the colour conversion resonator cavity <NUM> and n(λconverted) is the effective refractive index of the material separating the partially reflective region <NUM> and the further partially reflective region <NUM>. Such a configuration allows light of the converted primary peak wavelength to resonate in the colour conversion resonator cavity <NUM>. In further examples, the partially reflective region <NUM> and the further partially reflective region <NUM> are separated by a different distance.

Additionally, the partially reflective region <NUM> and the further partially reflective region <NUM> are separated by a distance of (N+<NUM>) multiplied by λconverted/2n(λconverted), wherein N is a positive integer number, λconverted is the converted primary peak wavelength emitted from the colour conversion resonator cavity <NUM> and n(λconverted) is the effective refractive index of the material separating the partially reflective region <NUM> and the further partially reflective region <NUM>. Such a configuration allows light of the converted primary peak wavelength to resonate in the colour conversion resonator cavity <NUM>. In further examples, the partially reflective region <NUM> and the further partially reflective region <NUM> are separated by a different distance.

The colour conversion resonator cavity <NUM> comprises at least one quantum well layer. The quantum well layer comprises multiple quantum wells. In further examples, the quantum well layer comprises a single quantum well. The quantum well layer is placed at an antinode of the colour conversion resonator cavity standing wavelength for the converted primary peak wavelength emitted from the colour conversion resonator cavity <NUM>. Similarly, the colour conversion resonator cavity <NUM> comprises at least one quantum well layer, placed at an antinode of the colour conversion resonator cavity standing wavelength for the converted primary peak wavelength emitted from the colour conversion resonator cavity <NUM>. The quantum well layer comprises multiple quantum wells. In further examples, the quantum well layer comprises a single quantum well. Additionally, the colour conversion resonator cavity <NUM> comprises at least one quantum well layer, placed at an antinode of the colour conversion resonator cavity standing wavelength for the converted primary peak wavelength emitted from the colour conversion resonator cavity <NUM>. The quantum well layer comprises multiple quantum wells. In further examples, the quantum well layer comprises a single quantum well. Such a configuration enhances at least one of the intensity, spectral width and output light with the resonant converted primary peak wavelengths. In further examples, the colour conversion resonator cavities <NUM>, <NUM>, <NUM> each have alternative or additional layers, for example single or multiple quantum wells in the quantum well layers are positioned to coincide with different antinodes of the converted wavelength of light in the respective colour conversion resonator cavities <NUM>, <NUM>, <NUM>.

The colour conversion resonator cavities <NUM>, <NUM> and <NUM> each comprise multiple quantum wells (MQWs). In further examples, the colour conversion resonator cavities <NUM>, <NUM>, <NUM> each comprise a single quantum well (SQW). In further examples, the colour conversion resonator cavities <NUM>, <NUM>, <NUM> comprise different layers from one another. The quantum well layers are designed to enable carriers to recombine such that emissive recombination results in an output of light with a primary peak wavelength that is different to the wavelength of input light that results in the emission of the output light.

In order to enable emission, input light is absorbed by absorption layers associated with respective quantum well layers in each of the colour conversion resonator cavities <NUM>, <NUM>, <NUM>. The input light absorbed at the absorption layers has a primary peak wavelength. In an example, the input light is blue light with a wavelength of approximately <NUM>. The wavelength of light output by the quantum well layers is longer than the wavelength input. The output wavelength of light is the converted wavelength of light. Whilst the input light is blue light, in further examples, additional or alternative wavelengths of input light are used. More preferably, each absorption layer comprises material with a lower energy bandgap than the energy of the input primary peak wavelength.

The epitaxial structure of the colour conversion resonator system <NUM>, once formed, is designed to be inverted and bonded to light emitting devices and the substrate <NUM>, buffer <NUM> and etch stop <NUM> removed. Accordingly, the order of the sequence of layers of input light and subsequent, converted, output light in the epitaxial structure of the colour conversion resonator system <NUM> is considered before growth and the formation of the partially reflective regions is described in more detail with respect to <FIG> and <FIG>, below. The partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> are Distributed Bragg Reflectors (DBRs). In further examples, the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> comprise alternative or additional structures.

Once the system <NUM> has been formed, it is inverted and bonded to an LED structure. This is shown at <FIG>. In <FIG> there is shown a colour conversion resonator system <NUM> that comprises a light emitting diode (LED) <NUM> and substrate device <NUM>. The substrate device is a temporary substrate used to facilitate the processing of the colour conversion resonator system <NUM>. Alternatively, in an example, the substrate device <NUM> is a complementary metal oxide semiconductor (CMOS) backplane that is combined with light emitting devices, such as light emitting diode devices, in order to provide and control input light in the eventual structure. The colour conversion resonator system <NUM> described with respect to <FIG> is combined with the substrate device <NUM> and the LED <NUM> by inverting the colour conversion resonator structure <NUM> described with reference to <FIG> and bonding the uppermost partially reflective region <NUM> epitaxial layer to the LED <NUM> using a bonding layer <NUM>. The substrate <NUM>, buffer, <NUM> and etch stop <NUM> are then removed, leaving the structure shown at <FIG>.

Advantageously, the order of proximity of the colour conversion resonator cavities with respect to the LED <NUM> is such that shorter wavelength light, such as blue light, from the LED <NUM> is absorbed in the first colour conversion resonator cavity, then light output from the first colour conversion resonator cavity and the LED <NUM> is absorbed in the second colour conversion resonator cavity, and light output from the first colour conversion resonator cavity, the second colour conversion resonator cavity and the LED <NUM> is absorbed in the third colour conversion resonator cavity. This means that input light can be absorbed and emitted by the colour conversion resonator cavities in such a way that the light that is emitted by the colour conversion resonator cavities is reused before exiting the eventual structure.

Accordingly the partially reflective region <NUM> is shown directly atop the bonding layer <NUM> on the LED <NUM>. On top of the partially reflective region <NUM> is the colour conversion resonator cavity <NUM> followed by the further partially reflective region <NUM>. On top of the partially reflective region <NUM> is the further colour conversion resonator cavity <NUM> followed by the further partially reflective region <NUM>. On top of the partially reflective region <NUM> is the further colour conversion resonator cavity <NUM> followed by the further partially reflective region <NUM>.

Whilst the colour conversion resonator system <NUM> of <FIG> is processed in order to bond to the LED <NUM>, as shown in <FIG>, in further examples, the epitaxial layers of the colour conversion resonator system <NUM> are grown directly on the LED <NUM>. Beneficially, such direct growth of layers atop the LED <NUM> prevent later bonding steps in the manufacture of such devices.

Whilst the epitaxial layers of the colour conversion resonator system <NUM> described with reference to <FIG> are shown to be grown in a particular order in order to enable bonding of the structure to a light emitting diode structure, in further examples, the order of growth is reversed in order to preserve the efficient absorption and emission of light from shorter to longer wavelengths from the colour conversion resonator cavity nearest to the input LED light source to the colour conversion resonator cavity furthest from the input LED.

In <FIG> there is shown a colour conversion resonator system <NUM>. As described above, the colour conversion resonator system <NUM> is formed by inverting the colour conversion resonator system <NUM> and bonding the colour conversion resonator system <NUM> to the LED <NUM> via the bonding layer <NUM> such that the partially reflective region <NUM> is bonded directly atop the LED <NUM> and the bonding layer <NUM>, and such that the partially reflective region <NUM> is at the top of the colour conversion resonator system <NUM> and subsequently removing the substrate <NUM> and the buffer <NUM> from the colour conversion resonator system <NUM>. The colour conversion resonator system <NUM> may be inverted by handling the substrate <NUM> and the buffer <NUM> of the colour conversion resonator system <NUM> before removing said layers.

The LED <NUM> is bonded to the partially reflective region <NUM> using dielectric bonding. The surface of the LED <NUM> that is to be bonded to the partially reflective region <NUM> is terminated with a high density oxide film in order to facilitate such bonding. The surface of the partially reflective region <NUM> that is to be bonded to the input LED <NUM> is also terminated with a high density oxide film in order to facilitate wafer level oxide bonding. Accordingly, the primary light emitting surface of the LED <NUM> is placed in close proximity or contact with the partially reflective region <NUM> such that light that is output from the LED <NUM> acts as input light for the colour conversion resonator system <NUM>.

In further examples, the LED <NUM> is bonded to the partially reflective region <NUM> using polymer bonding, such as polyimide bonding. In further examples, additional or alternative bonding mechanisms are used in order to attach the LED <NUM> to the partially reflective region <NUM>. Advantageously, the LED <NUM> is bonded to the partially reflective region <NUM> to form a single device with minimal interface loss of light emission from the LED <NUM> at the interface with the colour conversion resonator system <NUM>.

The colour conversion resonator system <NUM> is configured to receive input light of a first primary peak wavelength and convert this input light to light of a second primary peak wavelength. The colour conversion resonator system <NUM> further converts light of the second primary peak wavelength (and light of the first primary peak wavelength) to light of a third primary peak wavelength. Light of the third primary peak wavelength (and the first and second primary peak wavelengths) is then converted to light of a fourth primary peak wavelength.

Such a set up allows the colour conversion resonator cavity <NUM> to receive input light of the first primary peak wavelength from the LED <NUM> before the further colour conversion resonator cavities <NUM> and <NUM>. This is efficient when the colour conversion resonator cavity <NUM> is configured for resonant light of the second primary peak wavelength wherein this wavelength is less than the third primary peak wavelength and the fourth primary peak wavelength. The third primary peak wavelength is greater than the second primary peak wavelength and less than the fourth primary peak wavelength.

For example, the colour conversion resonator cavity <NUM> can be optimised for a wavelength of light corresponding to blue light (e.g., approximately <NUM> whereby the input light has a shorter wavelength, e.g., UV light at approximately <NUM>), the further colour conversion resonator cavity <NUM> can be optimised for a wavelength of light corresponding to green light (e.g., approximately <NUM>, whereby the input light has a shorter wavelength, e.g., blue light and UV light), and the further colour conversion resonator cavity <NUM> can be optimised for a wavelength of light corresponding to red light (e.g., approximately <NUM>, whereby the input light has a shorter wavelength, e.g., green light, blue light and UV light).

In order to enable resonance of wavelengths of light, the partially reflective regions <NUM>, <NUM>, <NUM>, <NUM> are configured to improve the passage of light through the colour conversion resonator system <NUM> from the light input LED <NUM> to a light emitting surface.

The partially reflective region <NUM> has a relatively high reflectivity for the wavelength of converted light generated in the colour conversion resonator cavity <NUM> and a relatively high transmissivity for the wavelength of the input light. In an example, the partially reflective region <NUM> has a relatively low reflectivity, e.g., less than <NUM>% of the primary peak wavelength of the input light from the LED <NUM> bonded to the partially reflective region <NUM> and a relatively high reflectivity, e.g., more than <NUM>%, of converted light generated by absorption of the input light and re-emission in the colour conversion resonator cavity <NUM>. In further examples, different reflectivity values are used for the partially reflective region <NUM>. In an example, the partially reflective region <NUM> has a reflectivity of input light of less than <NUM>% and a reflectivity of converted light of greater than <NUM>%. In a further example, the partially reflective region <NUM> has a reflectivity of input light of less than <NUM>% and a reflectivity of converted light of greater than <NUM>%. Similarly, the partially reflective region <NUM> has a relatively high reflectivity for the wavelength of converted light generated in the colour conversion resonator cavity <NUM> and a relatively high transmissivity for the wavelength of the input light.

In an example, the partially reflective region <NUM> has a relatively low reflectivity, e.g., less than <NUM>% of the primary peak wavelength of the input light and a relatively high reflectivity, e.g., more than <NUM>%, of converted light generated by absorption of the input light and re-emission in the colour conversion resonator cavity <NUM>. In further examples, different reflectivity values are used for the partially reflective region <NUM>. In an example, the partially reflective region <NUM> has a reflectivity of input light of less than <NUM>% and a reflectivity of converted light of greater than <NUM>%. In a further example, the partially reflective region <NUM> has a reflectivity of input light of less than <NUM>% and a reflectivity of converted light of greater than <NUM>%. Additionally, the partially reflective region <NUM> has a relatively high reflectivity for the wavelength of converted light generated in the colour conversion resonator cavity <NUM> and a relatively high transmissivity for the wavelength of the input light.

In an example, the partially reflective region <NUM> has a relatively low reflectivity, e.g., less than <NUM>% of the primary peak wavelength of the input light and a relatively high reflectivity, e.g., more than <NUM>%, of converted light generated by absorption of the input light and re-emission in the colour conversion resonator cavity <NUM>. In further examples, different reflectivity values are used for the partially reflective region <NUM>. In an example, the partially reflective region <NUM> has a reflectivity of input light of less than <NUM>% and a reflectivity of converted light of greater than <NUM>%. In a further example, the partially reflective region <NUM> has a reflectivity of input light of less than <NUM>% and a reflectivity of converted light of greater than <NUM>%.

The partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> are formed from alternating epitaxial crystalline layers of different refractive indices. The refractive indices of the layers, and the thicknesses of the layers, are selected in order to provide a reflectivity response as a function of the wavelength of light incident at the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM>. Growth of a DBR in this manner enables seamless formation of a high crystalline quality colour conversion resonator system <NUM>.

Whilst the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> are DBRs, in further examples, alternative or additional regions are used. In a further example, the partially reflective region <NUM> comprises a DBR or a vertical stack of two different DBRs or a double band DBR. In a further example, the partially reflective region <NUM> is omitted. In a further example, the partially reflective region <NUM> and/or the partially reflective region <NUM> and/or the partially reflective region <NUM> comprise a DBR with relatively high reflectivity of converted wavelengths of light and low reflectivity of input wavelengths. For example, as a filter for high reflectivity of blue light and low reflectivity of green and red light, or as a filter for low reflectivity of blue light and high reflectivity of green and red light. Reflectivity of light either side of a range of wavelengths may also be implemented. Where 'H' defines a quarter wavelength thick, high refractive index material, 'L' defines a quarter wavelength thick, low refractive index material, for N layers, a <MAT> and <MAT> stack can be used to suppress the reflectivity of the short and long wavelength side, respectively, a <MAT> stack can be used as a filter for high reflectivity of blue light and low reflectivity of green and red light and a <MAT> stack can be used as a filter for low reflectivity of blue light and high reflectivity of green and red light. In other examples, other arrangements are used selectively to filter light.

Whilst the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> are DBRs formed of nitride-based epitaxial layers, in further examples the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> are additionally, or alternatively formed using different methods whilst maintaining the functionality of enabling reflection of some wavelengths of light and transmission of different wavelengths of light. For example, the partially reflective region <NUM> and/or the partially reflective region <NUM> and/or the partially reflective region <NUM> and/or the partially reflective region <NUM> are/is formed from dielectric stacks. In a further example, the partially reflective region <NUM> and/or the partially reflective region <NUM> and/or the partially reflective region <NUM> and/or the partially reflective region <NUM> are/is formed from alternating layers of GaN and porous GaN. The porosity of the epitaxial crystalline GaN layers forming the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> is controlled in order to provide the desired reflectivity response as a function of wavelength, since the porosity of the epitaxial crystalline layers is linked to their refractive index. Advantageously, DBRs formed in this manner can be provided using GaN alone.

Preferably, there is provided at least one diffusion barrier arranged to reduce diffusion of carriers from the colour conversion resonator cavities <NUM>, <NUM> and <NUM>. Diffusion barriers are incorporated in the structure in order to enhance resonant light emission of converted light in the colour conversion resonator cavities.

In <FIG> there is shown a colour conversion resonator system <NUM> comprising the LED <NUM>, the bonding layer <NUM>, the partially reflective region <NUM>, the colour conversion resonator cavity <NUM>, the further partially reflective region <NUM> and the further colour conversion resonator cavity <NUM>. Each of these layers is grown sequentially as described above (e.g., either in the order shown in <FIG> and flipped, or in the order shown in <FIG>, without being flipped). Atop this series of layers partially etched layers from the structure described with respect to <FIG> and <FIG> is shown. The etched layers are the partially reflective region <NUM>, the colour conversion resonator cavity <NUM> and the partially reflective region <NUM>. These layers have been etched such that said layers <NUM>, <NUM> and <NUM> form a partially overlapping region with remaining layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

The colour conversion resonator system <NUM> is formed by selectively etching the colour conversion resonator system <NUM> in a first region. The surface of the partially reflective region <NUM> is selectively patterned according to known techniques. Such selective patterning allows for selective etching of regions of the colour conversion resonator system (e.g., using known wet or dry etching techniques). As shown at <FIG>, a first etch has removed the partially reflective regions <NUM>, <NUM> and the colour conversion resonator cavity <NUM> from the colour conversion resonator system <NUM> in the first region. The use of an etch stop (not shown) between the colour conversion resonator cavity <NUM> and the partially reflective region <NUM> facilitates control of the removal of material by etching. In further examples, additionally or alternatively, the partially reflective region <NUM> is not removed during the first etch process. The first etch process forms a light emitting surface region associated with the partially reflective region <NUM>. Whilst one region is shown as the partially reflective region <NUM>, in further examples, multiple regions are etched to provide light emitting surfaces associated with the partially reflective region <NUM>. Such multiple regions are used to form arrays.

Once the first etch process has been performed in order selectively to remove material associated with the colour conversion resonator cavity <NUM>, a second etch process is performed. This is shown at <FIG>.

In <FIG> there is shown a colour conversion resonator system <NUM> comprising the LED <NUM>, the bonding layer <NUM>, the partially reflective region <NUM> and the colour conversion resonator cavity <NUM>. These layers, grown sequentially, as described above, remain unetched. Atop said layers <NUM>, <NUM>, <NUM> and <NUM>, is the partially reflective region <NUM> and the further colour conversion resonator cavity <NUM>. The partially reflective region <NUM> and the colour conversion resonator cavity <NUM> have selectively been etched such that layers <NUM> and <NUM> form a partially overlapping region with remaining layers <NUM>, <NUM>, <NUM> and <NUM>. As described above, atop layers <NUM> and <NUM> is the further partially reflective region <NUM>, the further colour conversion resonator cavity <NUM> and the further partially reflective region <NUM> such that said layers <NUM>, <NUM> and <NUM> form a partially overlapping region with layers <NUM> and <NUM>. The use of an etch stop (not shown) between the colour conversion resonator cavity <NUM> and the partially reflective region <NUM> facilitates control of the removal of material by etching. In further examples, additionally or alternatively, the partially reflective region <NUM> is not removed during the second etch process. The second etch process forms an exposed light emitting surface region associated with the colour conversion resonator cavity <NUM> and an exposed light emitting surface region associated with the colour conversion resonator cavity <NUM>. Whilst the etch process is described with respect to a cross-sectional view of three exposed regions associated with different layers of colour conversion resonator cavities, in further examples, multiple regions are etched to provide light emitting surfaces associated with different layers of colour conversion resonator cavities in order to form arrays, with two dimensional arrays of light emitting pixels, each light emitting pixel having an associated light emitting surface.

The colour conversion resonator system <NUM> is formed by etching the colour conversion resonator system <NUM> in a second region. A second etch has removed the partially reflective region <NUM> and the colour conversion resonator cavity <NUM> from the colour conversion resonator system <NUM> in the second region.

Beneficially, such a system creates a colour conversion resonator system <NUM> with light emitting surfaces associated with different regions, where the light emitting surfaces are provided by the exposed regions and enable light of three different primary peak wavelengths to be emitted from the colour conversion resonator system <NUM>.

In <FIG> there is shown a colour conversion resonator system <NUM> where the colour conversion resonator system <NUM> described with reference to <FIG> has been further processed to provide a first further partially reflective region <NUM>, a second further partially reflective region <NUM>, and a third further partially reflective region <NUM>. The third further partially reflective region <NUM> associated with the colour conversion resonator cavity <NUM> is provided instead of the partially reflective region <NUM> formed in the initial epitaxial structure. Alternatively, the partially reflective region <NUM> remains in place and the third further partially reflective region <NUM> is not formed in the structure shown at <FIG>. The first further partially reflective region <NUM> is formed atop the exposed surface of the colour conversion resonator cavity <NUM>. The second further partially reflective region <NUM> is formed atop the exposed surface of the colour conversion resonator cavity <NUM>.

The partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> and/or the further partially reflective regions <NUM>, <NUM>, <NUM> comprise a Distributed Bragg Reflector (DBR). Such a DBR is preferably one of a double band DBR, a conventional DBR and a vertical stack of two DBRs. More preferably, the partially reflective regions <NUM>, <NUM> and <NUM> comprise a low Herpin index DBR whilst the partially reflective region <NUM> and the further partially reflective regions <NUM>, <NUM> and <NUM> comprise a double band DBR, a conventional DBR and a vertical stack of two DBRs.

In an example, the partially reflective regions <NUM>, <NUM>, <NUM> and <NUM> comprises a blue wavelength centred low Herpin index DBR, or a green wavelength centred low Herpin index DBR, or a red wavelength centred low Herpin index DBR. For example, the partially reflective region <NUM> may have a blue wavelength centred low Herpin index DBR such that the first pixel is optimised for blue wavelength light. The partially reflective region <NUM> may have a green wavelength centred low Herpin index DBR such that the second pixel is optimised for green wavelength light. The partially reflective region <NUM> may have a red wavelength centred low Herpin index DBR such that the third pixel is optimised for red wavelength light.

Such a configuration provided by the colour conversion resonator system <NUM> enables light emitting surfaces to be provided in order to form arrays of pixels. The etching and deposition of partially reflective regions described above results in the creation of a first pixel with the first further partially reflective region <NUM> as a top layer, a second pixel with the second further partially reflective region <NUM> as a top layer and a third pixel with the third further partially reflective region <NUM> as a top layer. The first pixel has a pixel dimension <NUM>. The second pixel has a pixel dimension <NUM>. The third pixel has a pixel dimension <NUM>. Whilst the pixel dimensions <NUM>, <NUM>, <NUM> are shown in cross section, the skilled person understands that in plan view the pixels have exposed light emitting surfaces associated with the dimensions <NUM>, <NUM>, <NUM> (for example, pixels with square light emitting surface areas - in further examples, pixels of different forms of arrays and shaped light emitting surfaces are formed). Further, whilst the first and second partially reflective regions <NUM>, <NUM> are shown to abut partially reflectively regions <NUM> and <NUM> respectively, in further examples, the first and second partially reflective regions <NUM>, <NUM> have different surface coverage. Further, whilst the relative thicknesses of the cross sectional image are shown in the Figures, the skilled person understands that in further examples the layers have different relative dimensions.

In <FIG> there is shown a colour conversion resonator system <NUM> showing the colour conversion resonator system <NUM> bonded to a CMOS backplane <NUM> further showing input light of the first primary peak wavelength <NUM>, converted light of the second primary peak wavelength <NUM>, converted light of the third primary peak wavelength <NUM> and converted light of the fourth primary peak wavelength <NUM>.

The partially reflective region <NUM> is designed such that light of the first primary peak wavelength <NUM> is transmitted and light of the second primary peak wavelength <NUM> is reflected. The partially reflective region <NUM> is configured such that light of the first primary peak wavelength <NUM> and light of the second primary peak wavelength <NUM> is partially transmitted and light of the third primary peak wavelength <NUM> is reflected. The partially reflective region <NUM> is configured such that light of the first primary peak wavelength <NUM>, light of the second primary peak wavelength <NUM> and light of the third primary peak wavelength <NUM> is partially transmitted and light of the fourth primary peak wavelength <NUM> is reflected.

Input light of the first primary peak wavelength <NUM> is emitted from the LED <NUM> through the colour conversion resonator system <NUM>. In the example of <FIG>, the first primary peak wavelength <NUM> corresponds to UV light. Light of the first primary peak wavelength <NUM> is transmitted through the partially reflective region <NUM> into the colour conversion resonator cavity <NUM>, where the light is absorbed and down converted by emissive recombination. Light of the first primary peak wavelength <NUM> is converted in the colour conversion resonator cavity <NUM> to light of the second primary peak wavelength <NUM>. In the example of <FIG>, light of the second primary peak wavelength corresponds to blue light.

When an LED, such as the light emitting device <NUM>, is coupled with the colour conversion resonator system <NUM>, the angular distribution of light emission of the input LED <NUM> is altered. Once the input light from an LED <NUM> with such a Lambertian distribution of light emission has been absorbed in the MQWs and pump absorbing layers of the colour conversion resonator cavity <NUM>, electron hole pairs are generated in the MQWs and pump absorbing layers. The electrons and holes generated in the pump absorbing layers move to the MQWs. Therefore, the emitted light wavelength is determined by MQW transitions wavelength. This transition wavelength has a spectral range (FWHM: full width half maximum) of ~<NUM> for green and ~<NUM> for Red when QW materials are AlxInyGa1-x-yN. In general, AlxInyGa1-x-yN or AlxInyGa1-x-yP MQWs emit the light all directions but the colour conversion cavity resonator enhances the emission meeting the cavity condition. The results are narrow beam angle and concentrated emission spectrum of the light of the second primary peak wavelength <NUM> that is emitted from the colour conversion resonator system <NUM> of <FIG>. Similar absorption and transmission occurs in the other colour conversion resonator cavities <NUM>, <NUM> in accordance with their respective absorption and emission properties.

Light of the second primary peak wavelength <NUM> resonates in the colour conversion resonator cavity <NUM> and is transmitted at least in part through the partially reflective region <NUM>. Light of the second primary peak wavelength <NUM> is also transmitted through the first further partially reflective region <NUM> and emitted from the associated light emitting surface.

The relative properties of the partially reflective regions <NUM>, <NUM> on the colour conversion resonator cavity <NUM> are such that resonant converted light <NUM> is emitted from a first pixel associated (e.g., pixel with dimension <NUM> of <FIG>) with the partially reflective region <NUM> and such that any converted light with the second primary peak wavelength <NUM> and light with the first primary peak wavelength pass through the partially reflective region <NUM> such that the light in parts of the colour conversion resonator system <NUM> are efficiently reused.

Accordingly, at regions associated with a second and a third pixel (e.g., the regions associated with pixel dimensions <NUM> and <NUM> of <FIG>), light of the second primary peak wavelength <NUM> is received in the colour conversion resonator cavity <NUM> through the partially reflective region <NUM>. Light of the first primary peak wavelength <NUM> that has not been converted is also received in the colour conversion resonator cavity <NUM>.

Light of the first primary peak wavelength <NUM> and light of the second primary peak wavelength <NUM> is at least partially converted in the colour conversion resonator cavity <NUM> to light of the third primary peak wavelength <NUM>. In the example of <FIG>, the third primary peak wavelength corresponds to green light.

Light of the third primary peak wavelength <NUM> resonates in the colour conversion resonator cavity <NUM> and is transmitted through the partially reflective region <NUM>. Light of the third primary peak wavelength <NUM> is also transmitted through the second further partially reflective region <NUM> and emitted.

At a second pixel (e.g., the pixel associated with pixel dimension <NUM> of <FIG>), light of the third primary peak wavelength <NUM> is transmitted through the second further partially reflective region <NUM> and emitted. At a third pixel (e.g., the pixel associated with pixel dimension <NUM> of <FIG>), light of the first primary peak wavelength <NUM>, second primary peak wavelength <NUM> and third primary peak wavelength <NUM> is received in the colour conversion resonator cavity <NUM> through the partially reflective region <NUM>. Light of the third primary peak wavelength <NUM> is converted in the colour conversion resonator cavity <NUM> to light of the fourth primary peak wavelength <NUM>. Light of the fourth primary peak wavelength <NUM> corresponds to red light.

Light of the fourth primary peak wavelength <NUM> resonates in the colour conversion resonator cavity <NUM> and is transmitted through the partially reflective region <NUM> and/or the third further partially reflective region <NUM> to be emitted.

Preferably, input light of the first primary peak wavelength <NUM> has a wavelength corresponding to ultraviolet (UV) wavelength light. Alternatively, or additionally, input light of the first primary peak wavelength <NUM> has a wavelength corresponding to blue light. In further examples, different wavelengths of light are used.

Whilst a system showing colour conversion to provide blue, green and red converted light output is demonstrated, in further examples, blue light is used as the first primary peak wavelength. Advantageously, one of the colour conversion resonator cavities and the associated partially reflective layers need not be used where red, green and blue light outputs are desired.

Input light of the first primary peak wavelength <NUM> has a wavelength corresponding to UV wavelength light. The converted light of the second primary peak wavelength <NUM> corresponds to blue wavelength light such that the first pixel emits light of the colour blue.

The converted light of the third primary peak wavelength <NUM> corresponds to green wavelength light such that the second pixel emits light of the colour green. The converted light of the fourth primary peak wavelength <NUM> corresponds to red wavelength light such that the third pixel emits light of the colour red. Such an embodiment allows for a monolithic integration of red, green and blue pixels to provide a monolithic colour conversion system.

In examples, the first pixel, the second pixel and the third pixel are isolated and individually addressable by the CMOS backplane <NUM>, thereby enabling the formation of a multicolour light emitting display.

Whilst <FIG> illustrates the LED <NUM>, in further examples, individual light emitting diodes are used selectively to provide light to light emitting surfaces associated with particular colour conversion resonator cavities and associated output light. In <FIG> there is shown an alternative embodiment of a colour conversion resonator system <NUM>. The colour conversion resonator system <NUM> comprises the first LED <NUM>, a second LED <NUM> and a third LED <NUM>. The LEDs <NUM>, <NUM> and <NUM> are placed adjacent to one another. Atop the LEDs <NUM>, <NUM> and <NUM> are layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> sequentially grown and in the selectively etched configuration of colour conversion resonator system <NUM>.

The first LED <NUM> is bonded such that input light from the first LED <NUM> is provided to the first pixel with the pixel dimension <NUM>, the second LED <NUM> is bonded such that input light from the second LED <NUM> is provided to the second pixel with the pixel dimension <NUM>, the third LED <NUM> is bonded such that input light from the third LED <NUM> is provided to the third pixel with the pixel dimension <NUM>. The LEDs <NUM>, <NUM>, <NUM> are bonded to the colour conversion resonator cavity system in accordance with the techniques described herein with reference to <FIG>. The LEDs <NUM>, <NUM>, <NUM> are individually addressable LED devices that can be addressed using a suitable backplane, such as a Si based CMOS backplane.

Beneficially the colour conversion resonator system <NUM> allows controlled light emission from each of the three pixels individually. The improved angular distribution, intensity and colour purity illustrated herein provides significant benefits, particularly in respect of augmented reality applications that use high resolution arrays of LEDs to form displays in close proximity to users. Further, beneficially, the use of epitaxially grown layers to form colour conversion resonator cavity systems means that the size constraints imparted by quantum-dot based colour conversion systems are overcome and smaller light emitting surfaces of light emitting pixels based on micro LEDs can be provided, and arrays of light emitting pixels with reduced pixel pitch can be provided.

Whilst <FIG> illustrate epitaxially grown colour conversion resonator systems that are formed by sequential growth of layers upon a substrate, in further examples, a series of layers is epitaxially grown and subsequently bonded to another series of epitaxial layers. Advantageously, by this method, individual colour conversion resonator cavities, or groups of colour conversion resonator cavities, can be optimised independently and bonded together, thereby to provide high crystalline quality colour conversion resonator cavities that are optimised for their particular wavelength of resonant light.

In <FIG> there is shown an alternative embodiment of a colour conversion resonator system <NUM>. The colour conversion resonator system <NUM> comprises the colour conversion resonator cavity <NUM> epitaxially grown atop the partially reflective region <NUM> and subsequently bonded to the input LED <NUM> and the substrate device <NUM> via the bonding layer <NUM>. Atop this series of layers there is bonded the partially reflective region <NUM> and the colour conversion resonator cavity <NUM> via the bonding layer <NUM>. Additionally, atop this series of layers there is bonded the partially reflective region <NUM>, the colour conversion resonator cavity <NUM> and, optionally, the partially reflective region <NUM> via the bonding layer <NUM>. Effectively, each colour conversion resonator cavity <NUM>, <NUM>, <NUM> and its respective partially reflective regions are provided separately and bonded together to form the structure of <FIG>. Advantageously, each colour conversion resonator cavity <NUM>, <NUM>, <NUM> and its respective partially reflective regions can be optimised separately prior to being bonded together to form the eventual structure. Such individual optimisation means, for example, that blue and green light emitting structures may be formed based on nitrides materials, whereas red light emitting structures may be formed using different materials, such as phosphide materials. In further examples, different combinations of materials are used in order to provide optimised structures for colour conversion and resonance at particular frequencies of light.

The LED <NUM> is bonded to the partially reflective region <NUM> using dielectric bonding. The surface of the LED <NUM> that is to be bonded to the partially reflective region <NUM> is terminated with a high density oxide film in order to facilitate such bonding. The surface of the partially reflective region <NUM> that is to be bonded to the input LED <NUM> is also terminated with a high density oxide film in order to facilitate wafer level oxide bonding. Accordingly, the primary light emitting surface of the LED <NUM> is placed in close proximity or contact with the partially reflective region <NUM> such that light that is output from the LED <NUM> acts as input light for the colour conversion resonator system <NUM>. Similarly, the colour conversion resonator cavity <NUM> and the partially reflective region <NUM> are terminated with a high density oxide film to facilitate wafer level oxide bonding. Additionally, the colour conversion resonator cavity <NUM> and the partially reflective region <NUM> are terminated with a high density oxide film to facilitate wafer level oxide bonding.

In further examples, the LED <NUM> is bonded to the partially reflective region <NUM> using polymer bonding, such as polyimide bonding. Similarly, the colour conversion resonator cavity <NUM> is bonded to the partially reflective region <NUM> using polymer bonding, such as polyimide bonding. Further, the colour conversion resonator cavity <NUM> is bonded to the partially reflective region <NUM> using polymer bonding, such as polyimide bonding. In further examples, additional or alternative bonding mechanisms are used in order to attach the corresponding layers. Advantageously, the layers are bonded to form a single device with minimal interface loss of light emission from the LED <NUM> at the interface with the colour conversion resonator system <NUM>.

Whilst the layers are shown to be bonded in <FIG> with bonding layers <NUM>, <NUM>, <NUM>, in further example additional and/or alternative bonding layers are used to form the structure <NUM> of <FIG>.

In <FIG> there is shown a colour conversion resonator system <NUM> comprising the LED <NUM>, the bonding layer <NUM>, the partially reflective region <NUM>, the colour conversion resonator cavity <NUM>, the bonding layer <NUM>, the further partially reflective region <NUM> and the further colour conversion resonator cavity <NUM>. Each of these layers is grown sequentially and subsequently bonded as described above in <FIG>. Atop this series of layers partially etched layers from the structure described with respect to <FIG> is shown. The etched layers are the bonding layer <NUM>, the partially reflective region <NUM>, the colour conversion resonator cavity <NUM> and the partially reflective region <NUM>. These layers have been etched such that said layers <NUM>, <NUM> and <NUM> and <NUM> form a partially overlapping region with remaining layers <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

In further examples, the colour conversion resonator system <NUM> is provided by bonding layers that have already been etched in order to provide the partially overlapping region. For example, arrays of etched layers are provided and bonded together to provide partially overlapping regions corresponding to different light output wavelengths.

In <FIG> there is shown a colour conversion resonator system <NUM> comprising the LED <NUM>, the bonding layer <NUM>, the partially reflective region <NUM> and the colour conversion resonator cavity <NUM>. These layers, grown and bonded sequentially, as described above, remain unetched. Atop said layers <NUM>, <NUM>, <NUM> and <NUM>, is the bonding layer <NUM>, the partially reflective region <NUM> and the further colour conversion resonator cavity <NUM>. The bonding layer <NUM>, the partially reflective region <NUM> and the colour conversion resonator cavity <NUM> have selectively been etched such that layers <NUM>, <NUM> and <NUM> form a partially overlapping region with remaining layers <NUM>, <NUM>, <NUM> and <NUM>. As described above, atop layers <NUM>, <NUM> and <NUM> is the bonding layer <NUM> the further partially reflective region <NUM>, the further colour conversion resonator cavity <NUM> and the further partially reflective region <NUM> such that said layers <NUM>, <NUM>, <NUM> and <NUM> form a partially overlapping region with layers <NUM>, <NUM> and <NUM>. The use of an etch stop (not shown) between the colour conversion resonator cavity <NUM> and the bonding layer <NUM> facilitates control of the removal of material by etching. The second etch process forms an exposed light emitting surface region associated with the colour conversion resonator cavity <NUM> and an exposed light emitting surface region associated with the colour conversion resonator cavity <NUM>. In further examples, the colour conversion resonator system <NUM> is provided by bonding layers that have already been etched in order to provide the partially overlapping region. For example, arrays of etched layers are provided and bonded together to provide partially overlapping regions corresponding to different light output wavelengths.

Whilst the LED <NUM> is shown as a single LED, in further examples the LED <NUM> is formed from individually addressable LED devices with individual LED devices corresponding to light output at one or more pixels formed from the partially overlapping regions of the colour conversion resonator system <NUM>. In such a way, high resolution displays can be formed.

In a further example, different combinations of cavities are grown together and subsequently bonded together. For example, the colour conversion resonator cavity <NUM> and the colour conversion resonator cavity <NUM> can be grown in one step with the partially reflective regions <NUM> and <NUM>. These epitaxially grown layers can then be bonded to the colour conversion resonator cavity <NUM> and partially reflective regions <NUM> and <NUM> via a bonding layer. Beneficially, such a process allows the colour conversion resonator cavities <NUM> and <NUM> to be grown from similar materials to provide high quality cavities and allows colour conversion resonator cavity <NUM> to be grown from a different material which is more optimal for the required wavelength of light in the colour conversion resonator cavity <NUM>. For example, the colour conversion resonator cavity <NUM> can correspond to blue wavelength light and the colour conversion resonator cavity <NUM> can correspond to green wavelength light. As such, it may be optimal to grow colour conversion resonator cavities <NUM> and <NUM> together from nitride based materials. The colour conversion resonator cavity <NUM> can correspond to red wavelength light. As such, it may be optimal to grow the colour conversion resonator cavity <NUM> separately from phosphide based materials.

In order to facilitate the bonding processes described with reference to <FIG>, handling wafers or growth substrates for the individual components are used and removed at appropriate stages in the device processing.

Accordingly, the colour conversion resonator system <NUM> can be used to provide an array of pixels, such as a high resolution micro LED array of pixels that emit light of different wavelengths in a manner similar to that described with the colour conversion resonator systems of <FIG>.

Claim 1:
A colour conversion resonator system (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>), comprising:
a first partially reflective region (<NUM>) configured to transmit light (<NUM>) of a first primary peak wavelength and to reflect light (<NUM>) of a second primary peak wavelength;
a second partially reflective region (<NUM>) configured to at least partially transmit light of the first and second primary peak wavelengths and to reflect light (<NUM>) of a third primary peak wavelength;
a third partially reflective region (<NUM>) configured to at least partially reflect light with the third primary peak wavelength;
a first colour conversion resonator cavity (<NUM>) arranged to receive input light with the first primary peak wavelength through the first partially reflective region and to convert at least some of the light of the first primary peak wavelength to provide light of the second primary peak wavelength, wherein the first colour conversion resonator cavity is arranged such that the second primary peak wavelength resonates in the first colour conversion resonator cavity and resonant light with the second primary peak wavelength is output through the second partially reflective region; and
a second colour conversion resonator cavity (<NUM>) arranged to receive input light comprising the second primary peak wavelength through the second partially reflective region and to convert at least some of the second primary peak wavelength to provide light of the third primary peak wavelength, wherein the second colour conversion resonator cavity is arranged such that the third primary peak wavelength resonates in the second colour conversion resonator cavity and resonant light with the third primary peak wavelength is output through the third partially reflective region, wherein the first colour conversion resonator cavity and the second resonator cavity are arranged partially to overlap to provide a non-overlapping portion and an overlapping portion thereby to define a first light emitting surface and a second light emitting surface respectively, wherein the first light emitting surface is arranged to provide resonant light of the second primary peak wavelength and the second light emitting surface is arranged to provide resonant light of the third primary peak wavelength.