Selective-area growth and fabrication of recessed-gate GaN MESFET using plasma-assisted molecular beam epitaxy

For the first time, selective-area growth (SAG) technique has been developed using plasma-assisted molecular beam epitaxy (PAMBE), enabling fabrication of a recessed-gate structure for the metalsemiconductor field-effect transistor (MESFET) without etching. On patterned SiO ₂ samples, polycrystalline GaN and single crystal n ⁺-GaN were observed to grow in the masked and unmasked regions, respectively. The regrown layers were analyzed using AFM. Ohmic contact formed on the n ⁺-GaN exhibited a vastly improved contact resistivity of 1.8 × 10 ^-8 Ω cm ², giving rise to excellent device characteristics including a peak drain current of 360 mA/mm and a maximum transconductance of 46 mS/mm. The advantages of SAG were further investigated by comparing the dc characteristics of recessed-gate and unrecessed MESFET.