Localised etching of (100) GaAs via an AlAs sacrificial layer

(100) GaAs substrate was patterned in 7H3PO4 (85% w/w):7H2O2 (30% w/w): IODI H2O via an etching mask with dynamic edges. The mask consisted of a resist layer, a Ti layer, a GaAs top layer, and an AlAs sacrificial layer. [0-11]-oriented stripe patterns were defined in the resist and Ti layers. At first, the top GaAs layer was etched via the resist /Ti mask. Once the solution cut via the AlAs layer, the underlying GaAs began to be locally etched at laterally moving [0-11]-oriented edges of the AlAs layer that was etched concurrently. Mesas and ridges confined to side facets tilted at about 30deg were produced through such laterally changing mask patterns.