Fabrication and integration of metasurfaces and metagratings into organic photodetectors and light emitters
Creators: name: Xu, Xin
Publisher: name: The University of Texas at Austin
Year: 2019
Subjects: Metasurface
Metagrating
OLEDs
Photodetector
Organic electronics

description: The field of optics has been transformed with the advent of high precision nanofabrication techniques that can be used fabricate subwavelength features in the optical regime. Advanced nanofabrication can be used to create engineered materials with optical properties unlike those found in nature and are impossible to achieve using conventional optics. Metasurfaces and metagratings are examples of these new types of engineered materials with unprecedented control over light. These metasurfaces and metagratings are composed of resonators at the nanoscale composed of either plasmonic or dielectric materials. The careful arrangement of these resonators can be used to create interfaces that can steer light in arbitrary directions, control the polarization and manipulate the phase. While there have been many studies into the fundamental design, fabrication, and characterization of these new engineered optical materials, there is relatively fewer work on integrating and implementing these materials into practical optical devices. This work will therefore be focused on the fabrication and integration of metasurfaces and metagratings into organic photodetectors and organic light emitters. In the first part of this work, we integrate a metasurface into an organic photodetector. Ultrathin flexible light sensors have many interesting applications but have drawbacks in their efficiencies because the light absorbing material is too thin to absorb a large degree of the incident light. For this application, the addition of a metasurface can be used to enhance the absorption and make the device appear optical thicker without adding too much additional thickness. We experimentally demonstrate metasurface-enhanced photoresponse in organic photodetectors. We have designed and integrated a metasurface with broadband functionality into an organic photodetector, with the goal of significantly increasing the absorption of light and generated photocurrent from 560 nm up to 690 nm. Our results show large gains in responsivity from 1.5X to 2X between 560 nm and 690 nm. Secondly, we investigate the integration of metagratings into organic light emitting devices with the goal of enhancing emission. Organic light emitting diodes are a common device for mobile screens and televisions but suffer from to a relatively low external quantum efficiency due to generated light being trapped in waveguide modes in the high refractive index organic materials. We incorporated several different types of metagrating to enhance the output light coupling. These included gratings based on a square lattice, 1D periodic lines, and quasicrystal patterns. Discussed are the key parameters for the behavior of the enhancement, such as spacing of the grating from the backside reflector, the periodicity of the grating, and the type of grating. In addition, we study the angular emission pattern and how it differs with differing grating parameters, and also study the polarization dependence of the three patterns as well