Performance of GaN metal-oxide-semiconductor field-effect transistor with regrown n⁺-source/drain on a selectively etched GaN

We proposed and fabricated normally off GaN MOSFETs with an epitaxially regrown n⁺ GaN source/drain after a short period of dry etching on a sapphire substrate. The regrown S/D MOSFET after dry etching (MOSFET A) exhibited enhanced performance in terms of current drivability and access resistance compared with the same MOSFET without the surface etching before the regrowth (MOSFET B). While MOSFET A has a saturation drain current of 10 mA/mm at V_G = 8 V, a field-effect mobility of 22 cm² V ^-1 s^-1, and a series resistance R_SD of 0.57 kΩ, MOSFET B has 3 mA/mm, 12 cm² V^-1 s^-1, and 0.93 kΩ, respectively. The electrical characteristic of MOSFET A was also much more improved than that of MOSFET B at low temperatures. Mobility degradation at low temperatures was related to the effect of impurity scattering caused by crystal defects generated during the metal organic chemical vapor deposition (MOCVD) growth.