PHOTOELECTROCHEMICAL ETCHING OF HIGH ASPECT RATIO SUBMILLIMETER WAVE-GUIDE FILTERS FROM N+ GAAS WAFERS

A 200 mum high-pass filter has been fabricated using the photoelectrochemical (PEC) etc process to form a series of waveguides through a Si-doped n+ GaAs (I X 10(18) cm-3) substrate. A metal mask on the sample surface with 100 mum square openings and 41 mum spaces was used to locally prevent PEC etching. The sample was etched in a (4:1:50) HCI:HNO3:H2O electrolyte for 1.5 h using an argon ion laser (514 nm) at an intensity of 0.7 W/cm2, and an applied bias of 0. 35 V. The result was a series of highly anisotropic waveguides with a (3: 1) aspect ratio. The transmittance curve had a cutoff of 45 cm-1 and a transmittance of 20% just above the cutoff.