Applied Physics Letters, Volume 103, Issue 3, id. 033524 (5 pages) (2013).
Zhang, Yuhao ; ; Sun, Min ; Joglekar, Sameer J. ; Fujishima, Tatsuya.
Microsystems Technology Laboratories, Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Abstract
This paper demonstrates the compensation of the intrinsic positive charges in Al2O3 gate dielectric by fluorine ions in GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs). Negatively-charged fluorine ions diffused into the oxide from the AlGaN barrier during the 250 °C atomic layer deposition compensate the intrinsic positive charge present in the Al2O3. This compensation is key to control the threshold voltage (Vth) of enhancement-mode (E-mode) transistors. A comprehensive analytical model for the Vth of fluorinated MOS-HEMTs was established and verified by experimental data. This model allows the calculation of the different charge components in order to optimize the transistor structure for E-mode operation. Using the proposed charge compensation, the Vth increases with gate dielectric thickness, exceeding 3.5 V for gate dielectrics 25 nm thick.