Kink effects are studied in conventional AlGaN/GaN high-electron-mobility transistors by measuring their current-voltage characteristics with various bias sweeping conditions at drain and gate terminals. It is found that the kink effect is induced by drain and gate pumping. The magnitude of kink is directly related to the maximum drain voltage and current levels during on-state operation. The hot electrons in the 2-D electron gas channel generated under high drain bias could be injected into the adjacent epitaxial buffer layer where they can be captured by donor-like traps. Hot electron trapping and the subsequent field-assisted de-trapping is suggested to be the dominant mechanism of kink generation in the studied device. The extracted activation energy of the traps accounting for the kink effect is 589 +/- 67 meV from temperature-dependent transient measurement, and is close to the energy of the E-2 trap widely reported in GaN layers.

Improvement of the AlGaN/GaN high-electron mobility transistor's (HEMT's) OFF-state breakdown voltage is achieved by implanting (19)F(+) ions at an energy of 50 keV and dose of 1 x 10(12) cm(-2) under the gate region using BF(3) 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-off)(2)/R(on) are achieved in the enhanced back barrier HEMT.

This paper presents a fabrication technology of enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) using standard fluorine ion implantation. An 80 nm silicon nitride layer was deposited on the AlGaN as an energy-absorbing layer that slows down the high energy (similar to 25 keV) fluorine ions so that majority of the fluorine ions are incorporated in the AlGaN barrier. The threshold voltage was successfully shifted from -1.9 to +1.8 V, converting depletion mode HEMTs to enhancement-mode ones. The fluorine ion distribution profile was confirmed by Secondary Ion Mass Spectrometry (SIMS). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3562273] All rights reserved.