Ion implantation for isolation of AlGaN/GaN HEMTs using C or Al

Abstract

In this work, we report on the fabrication of electrical isolation for planar AlGaN/GaN high electron mobility transistors (HEMTs) using Al and C ion implantation. Our methodology was to maintain uniform vacancy concentration (>4 × 10 20 cm −3 ) up to the depth of 0.7 µm for both ion species. Electrical measurements have shown that after implantation, the sheet resistance was 1 × 10 11 Ω/□ and increased to 5 × 10 13 –1 × 10 14 Ω/□ after annealing at 400 °C and to 5 × 10 12 –1 × 10 13 Ω/□ after annealing at 600 °C. Further annealing at 800 °C decreased the sheet resistance to 5 × 10 7 Ω/□ and 1 × 10 8 Ω/□, respectively for C and Al implantation. Characterization by XRD, Raman and photoluminescence spectroscopy provides evidence that implantation damages the crystal lattice, yielding insulating properties. It is demonstrated that the isolation is stable up to 600 °C. We also demonstrate AlGaN/GaN HEMTs on semi‐insulating Ammono‐GaN substrates working both in DC ( I DS = 800 mA/mm) and RF (up to 6.5 GHz) mode with isolation prepared by means of the described approach.