Prevention of surface recombination by electrochemical tuning of TiO₂-passivated photocatalysts

We present a systematic study of photoluminescence (PL) spectroscopy of TiO₂-passivated GaAs as a function of electrochemical potential in an ionic liquid solution.^[1] We observe a 7X increase in the PL intensity as the GaAs transitions from accumulation to depletion due to the applied potential. We attribute this to the excellent control over the surface Fermi level enabled by the high capacitance of the electrochemical double layer and TiO₂. In addition to photoluminescence (PL) spectroscopy, we also measured the capacitance-potential (i.e., C-V) characteristics of these samples, which indicate flat band potentials that are consistent with these regimes of ion accumulation observed in the photoluminescence measurements. We have also performed electrostatic simulations of these C-V characteristics, which provide a detailed and quantitative picture of the conduction and valence band profiles and charge distribution at the surface of the semiconductor. These simulations also enable us to determine the range of potentials over which the semiconductor surface experiences depletion, inversion, and accumulation of free carriers.

[1] Bingya Hou, Fatemeh Rezaeifar, Jing Qiu, Guangtong Zeng, Rehan Kapadia and Stephen B. Cronin, Applied Physics Letters, Vol: 111, 141603 (2017)