A Chemical Etchant for the Selective Removal of GaAs Through SiO[sub 2] Masks

An etchant has been developed for etching selected regions of through windows in an mask. This etchant has been found to provide fiat etching profiles across the unmasked regions of the GaAs, and has considerably reduced undercutting commonly caused by attack of the . The chemical etching rates have been evaluated and have been found to depend strongly on the concentration of the etching solution and on the crystal orientation of the . The utility of the for device preparation has been demonstrated by its application to the fabrication of interdigitated bipolar transistors with 5 μm base‐emitter separation.