Hole conductivity and acceptor density of p-type CuGaO2 nanoparticles determined by impedance spectroscopy: The effect of Mg doping

Delafossite materials like CuGaO2 have appeared as promising p-type semiconductor materials for their exploitation in tandem dye sensitized solar cells and water splitting photoelectrochemical cells. However, the intrinsic electronic properties of this material once nanostructured have not been extensively studied and fundamental knowledge is required in order to further develop photovoltaic and photoelectrochemical devices. In the present study, we report the main electrical properties of CuGaO2 nanoparticles and evaluate the effect of Mg doping. We determine for the first time the hole conductivity of mesoporous CuGaO2 using impedance spectroscopy, extracting values ranging from 1 to 10 x S cm(-1) in the interval of applied bias tested. We show that after Mg doping, the optical bandgap is red-shifted 0.15 eV and the conductivity increased one order of magnitude, indicating real p-type doping of the materials. Furthermore, after Mg doping the capacitance showed a Mott-Schottky behaviour reflecting the band bending of the semiconductor. In these conditions, the estimated acceptor density and the flat band potential were N-A =10(19) cm(-3) and V-FB = 0.23 V vs Ag/Ag+, respectively. When the material is not intentionally doped, the measured capacitance corresponds to the double layer capacitance, since the semiconductor is fully depleted in the testing conditions. (C) 2013 Elsevier Ltd. All rights reserved.