No abstract

Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFNI). The contact resistance decreased from about 0.45 Ohmmm for unetched ohmics to a minimum of 0.27 Ohmmm for 70 A etched ohmics. The initial thickness of the AlGaN layer was 250 Angstrom. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs

High electron mobility transistors (HEMTs) with different gate recess depth were fabricated on an Al0.33Ga0.67N/GaN heterostructure, utilizing low power Cl-2 reactive ion etching. An increase in extrinsic transconductance and a positive threshold shift were observed with an increase of etching time. The etch depth was measured by atomic force microscopy (AFM) and determined to be nonlinear with etching time. The two terminal gate-drain leakage increased from about 0.005 mA/mm to 0.05 mA/mm. The destructive three-terminal breakdown voltage was about 120 V for all devices, etched and un-etched. Power measurements were performed in class A/B at a frequency of 8 GHz. The output power varied between 2.5 and 4.5 W/mm with the increase of bias voltage from 25 to 50 V. Independently of etch depth, there was no evidence of device failure even for the highest bias. The low increase in leakage, and no change in breakdown voltage support that low power RIE etching is a viable solution for low damage gate recess etch