Fabrication of bulk and epitaxial germanium field emitter arrays by dry etching techniques

We present the fabrication and characterization of novel high density field emitter arrays (FEAs) on CVDgrown epitaxial germanium on (001) silicon. In particular we propose a heterostructure made up of silicon as substrate and of germanium as active layer, exploiting the infrared transparency of Si and the infrared sensitivity of Ge to realize a semi-transparent photo-assisted electron beam source. We used a completely dry etching process in fluorinated gases (SF6) due to its significant under-etching for both silicon and germanium. High aspect ratio silicon and germanium FEAs, with minimum tip radii of 25 nm and 40 nm, respectively, and lower aspect ratio Ge/Si FEAs with minimum tip radii of 50 nm were fabricated. The realized FEAs show good emission behavior with field emission characteristics straight related to tip geometry: low electric field threshold for silicon and germanium tips (<18 V/?m) and enhancement factor of more than 250 and 130, respectively; conversely for the epitaxial germanium we obtained 32 V/lm for electric field threshold and 70 for enhancement factor. Current emission time stability for silicon, for germanium and for Ge/Si field emitter arrays were demonstrated. © 2012 Elsevier B.V. All rights reserved.