Electrical control of magnetoresistance in highly insulating Co-doped ZnO

An insulating Zn_0.96Co_0.04O film on a highly conducting Zn_0.99Al_0.01O layer has been deposited on a-plane sapphire substrate by pulsed laser
deposition to study the magnetoresistance (MR) of depleted Co-doped ZnO with low electron concentration (about 1.5x10¹⁷ cm^-3 at 21 K). Au ohmic contact and Pd Schottky contact were deposited on the Zn_0.99Al_0.01O and Zn_0.96Co_0.04O layer, respectively. Positive magnetoresistance (MR) of 30 % with current of 10^-6 A was observed at 5 K. The positive MR decreases drastically at 5 K and changes to negative MR at 50 K with increasing current, which is considered to be due to the bias voltage control of the electron concentration in the Zn_0.96Co_0.04O layer. Our work demonstrates the electrically controllable magnetotransport behavior in insulating ZnO-based diluted magnetic semiconductors.