title: Ultrafast carrier trapping of a metal-doped titanium dioxide semiconductor revealed by femtosecond transient absorption spectroscopy.
abstract: We explored for the first time the ultrafast carrier trapping of a metal-doped titanium dioxide (TiO2) semiconductor using broad-band transient absorption (TA) spectroscopy with 120 fs temporal resolution. Titanium dioxide was successfully doped layer-by-layer with two metal ions, namely tungsten and cobalt. The time-resolved data demonstrate clearly that the carrier trapping time decreases progressively as the doping concentration increases. A global-fitting procedure for the carrier trapping suggests the appearance of two time components: a fast one that is directly associated with carrier trapping to the defect state in the vicinity of the conduction band and a slow one that is attributed to carrier trapping to the deep-level state from the conduction band. With a relatively long doping deposition time on the order of 30 s, a carrier lifetime of about 1 ps is obtained. To confirm that the measured ultrafast carrier dynamics are associated with electron trapping by metal doping, we explored the carrier dynamics of undoped TiO2. The findings reported here may be useful for the implementation of high-speed optoelectronic applications and fast switching devices.
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Division of Physical Sciences and Engineering and ‡Advanced Nanofabrication and Imaging Core Lab, King Abdullah University of Science and Technology , Thuwal 23955-6900, Saudi Arabia.
authors.forename: Jingya
authors.initials: J
authors.lastname: Sun
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: Jafar I
authors.initials: JI
authors.lastname: Khan
authors.forename: Erkki
authors.initials: E
authors.lastname: Alarousu
authors.forename: Zaibing
authors.initials: Z
authors.lastname: Guo
authors.forename: Xixiang
authors.initials: X
authors.lastname: Zhang
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Omar F
authors.initials: OF
authors.lastname: Mohammed