Effects of downstream plasma exposure on β-Ga₂O₃ rectifiers

The effects of downstream plasma exposure with O₂, N₂ or CF₄ discharges on Si-doped Ga₂O₃ Schottky diode forward and reverse current-voltage characteristics were investigated. The samples were exposed to discharges with rf power of 50 W plasma at a pressure of 400 mTorr and a fixed treatment time of 1 min to simulate dielectric layer removal, photoresist ashing or surface cleaning steps. Schottky contacts were deposited through a shadow mask after exposure to avoid any changes to the surface. A Schottky barrier height of 1.1 eV was obtained for the reference sample without plasma treatment, with an ideality factor of 1.0. The diodes exposed to CF₄ showed a 0.25 V shift from the I–V of the reference sample due to a Schottky barrier height lowering around 14%. The diodes showed a decrease of Schottky barrier height of 2.5 and 6.5% with O₂ or N₂ treatments, respectively. The effect of plasma exposure on the ideality factor of diodes treated with these plasmas was minimal; 0.2% for O₂ and N₂, 0.3% for CF₄, respectively. The reverse leakage currents were 1.2, 2.2 and 4.8 μA cm^-2 for the diodes treated with O₂, and CF₄, and N₂ respectively. The effect of downstream plasma treatment on diode on-resistance and on-off ratio were also minimal. The changes observed are much less than caused by exposure to hydrogen-containing plasmas and indicate that downstream plasma stripping of films from Ga₂O₃ during device processing is a relatively benign approach.