Off-state breakdown and dispersion optimization in AlGaN/GaN heterojunction field-effect transistors utilizing carbon doped buffer

An example of GaN buffer structure optimization in AlGaN/GaN heterojunction field-effect transistors is demonstrated. Transistors fabricated on four epitaxial structures with buffer consisting of unintentionally doped GaN channel (35 nm or 100 nm) and carbon doped GaN:C layers (∼1 × 1018 cm−3 or ∼1 × 1017 cm−3) are compared. As the criteria for optimization off-state breakdown voltage (Vbr) and drain current dispersion are used. The observed trade-off between the two parameters and dependency of Vbr on the carbon concentration and on the channel thickness are explained by a potential barrier formed due to GaN:C part of the buffer.