IMPACT IONIZATION IN ALGAN-GAN HETEROSTRUCTURE FIELD-EFFECT TRANSISTORS ON SAPPHIRE SUBSTRATES

The authors report on the impact ionisation in AlGaN-GaN heterostructu re field effect transistors (HFETs) grown on sapphire substrates. The measured characteristic electric field of the impact ionisation is sim ilar to 2.8-3.15 MV/cm at room temperature. This result is in good agr eement with the theoretical predictions for the breakdown field in GaN and with recent results for AlGaN-GaN HFETs on 6H-SiC substrates.