Dry Etching Damage Effect on Ohmic Characteristics of GaN

Abstract

We report on the dry etching damage effects on the Ohmic contact characteristics of Sidoped n-type GaN. The 2-µm thick n-type GaN samples whose carrier concentrations are ∼7 × 10¹⁷/cm³ are grown on c-plane sapphire substrates by metalorganic chemical vapor deposition(MOCVD). The samples are processed to measure the transmission line method(TLM). We evaporated Ti/Al/Ni/Au=150/2700/400/4000 Å on the samples using an ebeam evaporator under 5 × 10⁻⁷ torr and annealed at 700 °C for lminute using a rapid thermal annealer(RTA). AES and XPS data show that the surface stoichiometry of the sample etched with H₂ gas is gallium- richer than that of the one etched with Cl₂ gas. According to the previous report[l], N-vacancy acts as shallow donor in GaN. However, specific contact resistivity of the sample etched with H₂ gas is 3.03 × 10⁻⁶ Ω cm ², which is much higher than that of the sample etched with C1₂ gas, 7.9 × 10 ⁻⁷ Ω cm². The difference of the N- vacancy formed during the etching process cannot completely explain the result. We suggest that formation of Ga_xO_y during etching process, and the weakening of the bonding by ion bombardments might be responsible for the difference in the ohmic characteristics.