Dry Etching Damage Effect on Ohmic Characteristics of GaN

Abstract

ABSTRACTWe 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 GaxOy during etching process, and the weakening of the bonding by ion bombardments might be responsible for the difference in the ohmic characteristics.