A new photoelectrochemical etching method for the fabrication of GaN MESFETs

A new photoelectrochemical etching method was developed and employed for the fabrication of GaN metal-semiconductor field effect transistors (MESFETs). The unique etching process utilizes a photoresistive mask and a KOH-based etchant. The etching rate of the etchant, with 1.0 mol% of KOH, for n-GaN is as high as 1600 Å/min at a Hg-illumination intensity of 35 mW/cm ². The fabricated GaN MESFET exhibited a current saturation at V _ds = 10 V and a pinch-off at V _gs = -3 V. The peak drain current of the device was about 25 mA/mm at 300 K, and the value remained almost same for 500 K operation. The insensitivity of the device performance to temperature was attributed to the defect-related high activation energy of dopants for ionization and to the band-bending at the subgrain boundaries in GaN thin films.