Optical Reflectance Spectroscopy of Spin-Coated Multilayered ZnO and Al:ZnO Thin Films

Tuesday, 30 May 2017
Grand Ballroom (Hilton New Orleans Riverside)
D. Buckley, R. McCormack, D. McNulty (University College Cork), V. Z. Zubialevich (Tyndall National Institute), P. J. Parbrook (Tyndall National Insitute), and C. O'Dwyer (University College Cork)
Transparent conducting oxides are unique in their ability to be incorporated into a variety of electronic devices such as LCDs, photovoltaic cells and LEDs. This unique ability is due to the oxides having wide band gaps (Eg ~ 3 eV - 4 eV) which gives high transparency (> 80% in visible region) and effective conductivity (>103 Ω-1cm-1) which can be achieved through the introduction of dopants. Zinc oxide is a well-known material of interest due to its wide band gap (Eg ~ 3.3 eV at 300 K) and also for the variety of methods by which it can be processed. Moreover, ZnO is readily able to alloy with other metals in the oxide form and has a lattice that can facilitate interstitial doping. This gives ZnO a key role in the area of optoelectronics, metal oxide thin films and thin film transistor (TFT) technologies.

We show the visible and near-infra red (VIS-NIR) light spectroscopy of ZnO and Al:ZnO multi-layered thin film structures grown on oxidized silicon substrates. Using optical interference, the thickness of the multi-layered deposited ZnO and Al:ZnO can be determined. Using angle-based reflectance spectroscopy measurements and a method derived from reflectivity of dispersive, non-absorbing materials, the optical thickness of thin films samples are calculated. These calculations show an excellent agreement with the actual thickness of ZnO samples with a margin of error of <4% for a 20 layer (500 nm thick) film and <1% for a single-layer ZnO film. This work also investigates the anti-reflection properties of ZnO and Al:ZnO thin films at a variety of angles of incidence. Results show that film’s minimum reflectivity (< 8%) can be tuned in the visible frequency range, based on number of iterative layer depositions and subsequent thickness.