Enhancement of the LETFEL device optical outcoupling via the fabrication of novel geometry structures

Enhancement of Laterally Emitting Thin Film Electroluminescent (LETFEL) outcoupling efficiency has been achieved via the introduction of a novel outcoupling mechanism, the surface emitting edge emitter. This method incorporates PECVD SiO2 microstructures underlying the device thin films at the device apertures which consequently bend the LETFEL structure at these locations. Additional etching of the bent thin films provides shaped edges at both sides of the aperture which outcouple the internally generated light as conventional edge emitters. Comparison of the conventional non etched and the surface emitting edge device light outputs demonstrates an improvement in the outcoupling efficiency by a factor of 4 at 620 Volts. Additionally, a Gaussian angular distribution with a FWHM approximately 40 degrees has been measured from each edge, being the Gaussian maximum coincident with the microstructure wall side angle. In this research 45 degree wall sided microstructures have been utilized however, perpendicular microstructures are proposed to further enhance the coupling efficiency for the two main LETFEL applications, Head Mounted Displays (HMDs) and Electrophotographic Printing (EP). The fabrication route which successfully defines the surface emitting edge mechanism is presented for the first time; this incorporates Ion Milling as the sputter etch technique to shape the device aperture.