Effect of Photon-Induced Charge Transfer on Transport Characteristic in Au-TiO2 Schottky Diode
C.Y. Tsai2,1*, C.T. Liang2, H.R. Chen3, Y.C. Chang2,4
1Electrophysics, National Chiao Tung University, Taiwan
2Research Center for Applied Sciences, Academic Sinica, Taiwan
3Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Taiwan
4Department of Physics, National Cheng-Kung University, Taiwan
* presenting author:Chih-Ya Tsai, email:walkingyaya@gmail.com
We investigate the photo-induced charge transfer mechanism and its influence on current transport characteristics in an Au-TiO2 Schottky diode via I-V measurements under photo illumination from visible to ultraviolet (UV). The effective-mass approximation reveals that the photo-excited charge transfer from Au to TiO2 increases as the applied reverse bias increases because of the enhancement of effective density of states. The interfacial barrier potential and the tunneling width change under charge transfer since most of the transferred charges tend to accumulate in the space-charge region. Therefore, the current transport characteristic is modified. According to the electrostatics and WKB approximation, the evaluated injected carrier concentration is higher than 10^18 cm-3 and the effective barrier height is lower than 0.53 eV under light excitation of 60 mW. Furthermore, the carrier tunneling enhances under light illumination and quenches at the termination of illumination, which illustrates a photon-assisted tunneling phenomenon. This is equivalent to an optical bias with ~0.1 eV above Fermi-level at the metal-side.

Keywords: charge transfer, Schottky diode, Au-TiO2