Design and fabrication of a GaAs vertical MESFET

Vertically oriented GaAs MESFET's were fabricated on thick epitaxial conductive layers grown by molecular-beam epitaxy on a semi-insulating substrate. The vertical channel pattern was defined by electron-beam lithography and included structures as small as 0.3- 0.4 µm on a total period of 1.0 µm. The vertical channels were formed by reactive ion etching, and the gate contact was formed by dual-angle evaporation. The top ohmic contacts were interconnected by a metal bridge supported by a dielectric layer. The drain characteristics displayed a drain punchthrough effect, indicating that a very short gate length was achieved. Microwave measurements indicated a maximum oscillation frequency of 12 GHz.