Enhancement mode HEMT using fluorine implantation below the channel^*

¹ CNRS, LAAS, 7 avenue du Colonel Roche, 31400 Toulouse, France
² Université de Toulouse, LAAS, 31400 Toulouse, France
³ GET/LPE, Lebanese University, Hadath Campus, Beirut, Lebanon
⁴ Université de Toulouse, UPS, LAAS, 31400 Toulouse, France
⁵ CEA Tech Midi-Pyrénées, 135 avenue de Rangueil, INSA Bât. 8, 31400 Toulouse, France

^a e-mail: shamady@laas.fr

Received: 31 January 2015
Revised: 28 April 2015
Accepted: 15 May 2015
Published online: 24 June 2015

Abstract

Gallium nitride based high electron mobility transistors (HEMT) are powerful candidates for high frequency and high power applications. While switching applications demand normally-off operation, these devices are normally-on. Recent normally-off HEMTs were demonstrated by implanting fluorine above the channel, in the barrier layer. During implantation, fluorine ions penetrate into the channel and cause mobility degradation. In this paper, we propose and simulate an alternative approach in which fluorine ions are implanted below the channel of the HEMT rather than above it. The simulation tool ATLAS is calibrated using experimental data from a real HEMT device. Simulation results have shown that implanting fluorine ions below the channel is capable of achieving normally-off operation. When compared to the implantation in the barrier layer, the proposed approach offers better confinement for the two dimensional electron gas (2DEG) below the gate, eliminates the scattering of fluorine ions with channel electrons and is more efficient when it comes to the fluorine concentration required to achieve a desired threshold voltage. This technique neither affects the breakdown voltage nor the off-state current.