Photocurrent Characteristics of Mn-Doped Barium Titanate Ferroelectric Single Crystals

We investigated the photocurrent characteristics of ferroelectric single crystals of nondoped barium titanate (BT) and Mn-doped barium titanate (Mn-BT). The introduction of 90° domain structures into the BT crystals markedly increased the photocurrent, which suggests that the separation of photoinduced carriers is significantly enhanced around 90° domain walls (DWs). The Mn doping led to a drastic increase in photocurrent, with a photon energy less than the band gap. Density functional theory calculations show that the large photocurrent observed for the Mn-BT crystals originates from the electron excitation from the O 2p valence band to the Mn eg defect level followed by carrier (hole) injection.