Investigation of AlGaN/GaN fluorine plasma treatment enhancement-mode high electronic mobility transistors by frequency-dependent capacitance and conductance analysis

This paper reports fluorine plasma treatment enhancement-mode HEMTs (high electronic mobility transistors) EHEMTs and conventional depletion-mode HEMTs DHEMTs fabricated on one wafer using separate litho-photography technology. It finds that fluorine plasma etches the AlGaN at a slow rate by capacitance–voltage measurement. Using capacitance–frequency measurement, it finds one type of trap in conventional DHEMTs with \tau_T=(0.5–6) ms and D_T= (1–5) × 10¹³ cm^-2·eV^-1. Two types of trap are found in fluorine plasma treatment EHEMTs, fast with τ_T(f)=(0.2–2) μs and slow with \tau_T(s)=(0.5–6) ms. The density of trap states evaluated on the EHEMTs is D_T(f)=(1–3) × 10¹² cm^-2·eV^-1 and D_T(s)=(2–6) × 10¹² cm^-2·eV^-1 for the fast and slow traps, respectively. The result shows that the fluorine plasma treatment reduces the slow trap density by about one order, but introduces a new type of fast trap. The slow trap is suggested to be a surface trap, related to the gate leakage current.