Bias stress instability involving subgap state transitions in a-IGZO Schottky barrier diodes

Vertical Schottky barrier diodes (SBDs) based on amorphous indium-gallium-zinc-oxide (a-IGZO) with either a top or bottom Schottky contact are fabricated by controlling the oxygen partial pressure during a-IGZO deposition. Although Au electrodes are employed for both Schottky and Ohmic contacts, it is found that Schottky contacts are preferentially formed on a-IGZO film in lower oxygen vacancy concentrations. The effect of negative bias stress on device performance is studied. The Schottky barrier height and series resistance of the a-IGZO SBD are found to increase upon negative bias stress, which is correlated with a reduction of the trap state and background carrier concentration within the a-IGZO film. A physical model based on subgap state transitions from ionized V-O(2+) states to neutralized V-O states is proposed to explain the observed electrical instability behavior.