Ald grown zno as an alternative material for plasmonic and uncooled infrared imaging applications

Abstract

Plasmonics is touted as a milestone in optoelectronics as this technology can form a bridge between electronics and photonics, enabling the integration of electronics and photonic circuits at the nanoscale. Noble metals such as gold and silver have been extensively used for plasmonic applications due to their ability to support plasmons, yet they suffer from high intrinsic optical losses. Recently, there is an increased effort in the search for alternative plasmonic materials including Si, Ge, III-Nitrides and transparent conductive oxides. The main appeal of these materials, most of them semiconductors, is their lower optical losses, especially in the infrared (IR) regime, compared to noble metals owing to their lower number of free electrons. Other advantages can be listed as low-cost and control on plasma frequency thanks to the tunable electron concentration, i.e. effective doping level. This work focuses on atomic layer deposition (ALD) grown ZnO as a candidate material for plasmonic applications. Optical constants of ZnO are investigated along with figures of merit pertaining to plasmonic waveguides. It is shown that ZnO can alleviate the trade-off between propagation length and mode confinement width owing to tunable dielectric properties. In order to demonstrate plasmonic resonances, a grating structure is simulated using finite-difference-time-domain (FDTD) method and an ultra-wide-band (4-15 µm) infrared absorber is computationally demonstrated. Finally, an all ZnO microbolometer is proposed, where ALD grown ZnO is employed as both the thermistor and the absorber of the microbolometer which is an uncooled infrared imaging unit that relies on the resistance change of the active material (thermistor) as it heats up due to the absorption of incident electromagnetic radiation. The material complexity and process steps of microbolometers could be reduced if the thermistor layer and the absorber layer were consolidated in a single layer. Computational analysis of a basic microbolometer structure using FDTD method is conducted in order to calculate the absorptivity in the long-wave infrared (LWIR) region (8-12 µm). In addition, thermal simulations of the microbolometer structure are conducted using finite element method, and time constant and noise-equivalent-temperature-difference (NETD) values are extracted.