Optimization of photogenerated charge carrier lifetimes in ald grown tio₂ for photonic applications

Abstract

<p>Titanium dioxide (TiO<sub>2</sub>) thin films are widely employed for photocatalytic and photovoltaic applications where the long lifetime of charge carriers is a paramount requirement for the device efficiency. To ensure the long lifetime, a high temperature treatment is used which restricts the applicability of TiO<sub>2</sub> in devices incorporating organic or polymer components. In this study, we exploited low temperature (100–150<sup>◦</sup> C) atomic layer deposition (ALD) of 30 nm TiO<sub>2</sub> thin films from tetrakis(dimethylamido)titanium. The deposition was followed by a heat treatment in air to find the minimum temperature requirements for the film fabrication without compromising the carrier lifetime. Femto-to nanosecond transient absorption spectroscopy was used to determine the lifetimes, and grazing incidence X-ray diffraction was employed for structural analysis. The optimal result was obtained for the TiO<sub>2</sub> thin films grown at 150<sup>◦</sup> C and heat-treated at as low as 300<sup>◦</sup> C. The deposited thin films were amorphous and crystallized into anatase phase upon heat treatment at 300–500<sup>◦</sup> C. The average carrier lifetime for amorphous TiO<sub>2</sub> is few picoseconds but increases to >400 ps upon crystallization at 500<sup>◦</sup> C. The samples deposited at 100<sup>◦</sup> C were also crystallized as anatase but the carrier lifetime was <100 ps.</p>