Photoelectrochemical etching of high aspect ratio submillimeter waveguide filters from n+ GaAs wafers

Abstract

A 200 μm high-pass filter has been fabricated using the photoelectrochemical (PEC) etch process to form a series of waveguides through a Si-doped n+ GaAs (1×1018 cm−3) substrate. A metal mask on the sample surface with 100 μm square openings and 41 μm spaces was used to locally prevent PEC etching. The sample was etched in a (4:1:50) HCl: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.