Metal-dielectric photonic crystals (MDPCs) represent a class of photonic structures which offer unique types of control over the propagation of light. Recent work has demonstrated the ability to form MDPCs using stacked microcavity OLEDs, which enable the generation of complex electroluminescence profiles consisting of multiple emission peaks. Here, we analyze the photonic band formation of idealized MDPCs. We systematically examine the impact of materials parameters on the density of states of the photonic bands and transmission losses through the crystal. We demonstrate the formation and collapse of a Peierls band-gap and the breakdown of the unit cell approach.
A microcavity OLED, consisting of a conventional OLED stack with two metallic mirror electrodes, shows narrow-band emission centered around specific peak resonant wavelengths. These cavity modes are analogous to the energy states found in any resonator system, including musical instrument strings and 1-dimensional quantum square wells. Here we incorporate the microcavity OLED as a unit cell in a photonic crystal. Stacking N microcavities splits the resonant modes into N discrete states. We demonstrate methods to control the photonic density of states and to induce a photonic bandgap. Furthermore, we investigate the effect of various device variables, including N and the thickness of the semi-transparent metal electrodes, on emission properties such as peak wavelength, FWHM, and Q-factor for each of the photonic states. The experimental results are guided by a predictive computational modelling tool, which is critically important for the complex-architecture devices.
A metallic microcavity OLED structure is shown to be an ideal building block for exploring 1D photonic crystals. By stacking N metallic microcavities we demonstrate the formation of photonic energy bands by splitting each single-cavity discrete mode into N hybridized resonance states. The splitting of the local cavity modes is found to directly mimic the formation of energy bands from Bloch and molecular orbital (MO) theory. The resulting energy band structure is manipulated by varying the thickness of the metallic mirrors and the cavities, including the formation of a photonic band gap by the introduction of a Peierls distortion to the 1D crystal. The metallic microcavity OLED structure enables direct observation of the interaction of individual cavity modes with the coupled microcavity superlattice due to the internal broadband emission sources. Recent experimental work confirms the transfer matrix simulations for simple structures and has laid the groundwork for future exploration.