Selective optical filter for RGB LED

#This application is a 35 U.S.C. § 371 national stage application of PCT International Application No. PCT/GB2021/052279, filed on Sep. 9, 2021, which claims the benefit of Great Britain Application No. 2017266.7 filed Sep. 10, 2020, which are hereby incorporated by reference in their entirety.

#The invention relates to light emitting structures and methods of forming light emitting structures. In particular, but not exclusively, the invention relates to improved colour conversion in light emitting diode structures.

#It is known that light emitting diode (LED) devices provide efficient sources of light for a wide range of applications. LED light sources are used to provide conventional white light, and/or multi-colour light emission. For example, multi-colour light emission includes red, green and/or blue emission suitable for display applications. The desired wavelengths of light provided for by LEDs are typically achieved using a combination of a pump source LED with colour conversion layer, such as a phosphor, quantum dots (QDs) or organic semiconductors, for example. Such pump source LEDs generate light with a primary peak wavelength output and stimulate emission of light of a different wavelength in a colour conversion layer. For example, blue light Nitride material LEDs (emitting light with a primary peak wavelength of approximately 450 nm) are used to provide white colour converted light LED emission. Blue Nitride material LEDs are also used to provide red colour converted light LED emission and green colour converted light LED emission.

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

#FIG. 1 shows a cross sectional view of a portion of the light emitting structure comprising a DBR;

#FIG. 2 shows a cross sectional view of a light emitting structure

#The elegant and advantageous implementation of reflecting and partially reflecting layers in light emitting structures with colour conversion layers provides LED devices, such as micro-LED devices capable of realising white LED or multi-colour LED displays suitable for both mass transfer processes of individual micro-LEDs and for monolithic LED arrays. The synergistic combination of different layers in light emitting structures results in a solution for improved light conversion and extraction compared with known structures. Beneficially, implementations enable the improved functionality whilst maintaining the structural crystalline integrity of epitaxial compound semiconductor light emitting structures and also whilst reducing processing requirements.

#The present invention uses distributed Bragg reflectors (DBR) to improve the performance of light emitting devices such as RGB LED and micro-LED devices. Methods of making DBR with GaN material are disclosed in Zhang et al. ACS Photonics, 2, 980 (2015), and more recently by Tongtong et al. “Wafer-scale Fabrication of Non-Polar Mesoporous GaN Distributed Bragg Reflectors via Electrochemical Porosification”, Scientific Reports 7, article number 45344, 2017.

#A method of forming a light emitting structure 100 is described with reference to FIGS. 1-3. The light emitting structure 100 is an LED structure that uses colour conversion layer to provide light with desired wavelengths. The resultant light emitting structure is an LED structure that has a pump source LED and colour conversion layer. The method is described by virtue of cross sectional views through the layers of the light emitting structure 100 at different stages in the process of providing a light emitting structure with improved colour conversion. The layers shown in FIGS. 1-3 provide layers of light emitting structures with different functional properties. The layers of the light emitting structures with different functional properties are formed from one or more layers of different materials that work together to provide the functional properties (for example, light emitting layers may comprise multiple quantum well structures and partially reflective layers may comprise multiple layers of different refractive indices). In further examples, additional or alternative layers are used to facilitate the concepts described herein.