Characterization of gate recessed GaN/AlGaN/GaN high electron mobility transistors fabricated using a SiCl₄/SF₆ dry etch recipe

Incorporating GaN capping layers in conjunction with recessing has been identified as a means to maximize the high frequency performance of AlGaN/GaN high electron mobility transistors (HEMTs). Doping the cap heavily n-type is required in order to ensure minimal loss of carriers from the channel. Using a SiCl₄/SF₆ dry etch plasma recipe, 250 nm gate length HEMTs with recess lengths varying from 300 nm to 5 μm are fabricated. Heavily doped n⁺ GaN caps enabled contact resistances of 0.3 mm to be achieved. Recessing using a SiCl₄/SF₆ recipe does not introduce significant numbers of bulk traps. Gate recessing in conjunction with Si₃N₄ passivation reduces rf dispersion to negligible levels.