Improvement of AlGaN/GaN Heterostructure Field Effect Transistor Characteristics by Using Two-Step Ohmic Contact Process

We attempted a new ohmic contact process for two-step metallization, and demonstrated improvement of the ohmic properties and device characteristics. The contact resistance of the two-step ohmic process was improved from 4.2 Ωmm obtained in a conventional contact to 2.6 Ωmm. The specific contact resistivity of the transmission line method ohmic contacts improved by one order of magnitude, from 10 -4 Ω-cm 2 in the conventional contact sample to 10 -5 Ω-cm 2 in the two-step contact sample treated with Cl 2 plasma. The dc measurements of the HFETs showed improved current-voltage curves in the two-step contact samples. The values of R on of the AlGaN/GaN HFET with the two-step contact process and the conventional HFET were calculated to be 0.23 mΩ-cm 2 and 0.28 mΩ-cm 2 in the linear (ohmic) region, respectively.