|
Transparent conducting oxides (TCOs) have long been used in optics and electronics for their unique combination of both high transmission and high electrical conductivity. In recent years, the impact of such TCOs has been felt in the subgenre of nanophotonics and plasmonics.1-3 Specifically, the TCOs provide plasmonic response in the near infrared and infrared region,4 epsilon-near-zero (ENZ) properties in the telecom band, tunable static optical properties through deposition/annealing control,5 and the potential for dynamic control of their properties under electrical or optical biasing.6-8 Due to the combination of these interesting properties, TCOs such as In:SnO (ITO), Al:ZnO (AZO), and Ga:ZnO (GZO) have become leaders in the drive to produce high-performance dynamic and alternative nanophotonic devices and metamaterials. In our work, we have studied the potential for optical control of AZO thin films using both above bandgap and below bandgap excitation, noting strong changes in reflection/transmission with enhancement due to the ENZ as well as ultrafast response times less than 1 ps. Using a photo-modified carrier density and recombination to model above bandgap excitation, we demonstrated 40%/30% change in the reflection/transmission of a 350 nm AZO film with an 88 fs recombination time, corresponding to a modification of the carrier density by 10%.6 Below bandgap excitation has experimentally shown the potential for similar variations in the reflection and transmission under increased fluences with a factor of ~8x increase in the normalized ΔR at ENZ. Current efforts are focused to model the material response as well as to investigate electrical modulation of AZO films. In summary, our work has demonstrated the potential for optical control of AZO films both above and below bandgap on an ultrafast timescale which can be enhanced through ENZ. Combining this with traditional nanophotonic and metamaterial devices opens a broad range of high impact studies such as tunable optical components, on-chip photonic elements, and controllable nonlinear enhancement.
|
