Effect of Dry Etching to Improve Ohmic Contacts on Bulk, Lightly-Doped β-Ga₂O₃

Abstract

Ti/Au is a typical Ohmic metal contact stack to n-type β-Ga2O3 but there have been few systematic studies of the use of pre-exposure of the surface to plasmas prior to metal deposition in order to lower the contact resistance. The effects of Cl2/Ar inductively coupled plasma exposure of Ga2O3 surfaces prior to deposition of Ti/Au (20/80 nm) contacts were examined through circular transfer length method measurements to determine both the contact resistance and specific contact resistivity. ICP source power, which controls ion density in the plasma is found to be more important than ion energy (~165-490 eV in these experiments). The plasma exposure improved specific contact resistivity by more than a factor of 2 in all cases for lightly n-type (10^17 cm^-3) Ga2O3 and a minimum value of 2x10^-4 Ω.cm^2 was obtained after heating at 550°C.