Improvement of the Off-State Breakdown Voltage With Fluorine Ion Implantation in AlGaN/GaN HEMTs

Improvement of the AlGaN/GaN high-electron mobility transistor´s (HEMT´s) off -state breakdown voltage is achieved by implanting ¹⁹F⁺ ions at an energy of 50 keV and dose of 1 × 10¹² cm^-2 under the gate region using BF₃ as the source. The charge state of the implanted fluorine ions changes from positive to negative in the AlGaN/GaN structure because of fluorine´s strong electronegativity. The negative-charged fluorine ions at the back side of the two-dimensional electron gas can raise the energy barrier of the GaN buffer layer under the channel, effectively blocking the current injected from the source to the high-field region of the GaN channel when the HEMT is biased at off-state. The source-injected electrons, if not blocked, could flow to the high-field region and initiate a premature three-terminal off-state breakdown in a conventional AlGaN/GaN HEMT. A 38% improvement of the three-terminal off-state breakdown voltage and 40% improvement of the power figure-of-merit V_BD-off²/R_on are achieved in the enhanced back barrier HEMT.