  We report a two-step process to obtain smooth and vertical {10-10} m-plane
facets in AlGaN/GaN separate confinement heterostructures designed to fabricate
UV lasers emitting at 355 nm. The process consists in a dry etching by RIE-ICP
combined with a crystallographic-selective wet etching process using a
KOH-based solution. The anisotropy in the wet etching rates between the
different crystallographic planes of the AlGaN structure, allows the
fabrication of flat and parallel facets without a degradation of the
multilayered ensemble. The optical performance of the lasers display a major
improved when using the two-step process for the definition of the cavity, in
comparison to cavities fabricated by mechanical cleaving, with the lasing
threshold under optical pumping being reduced to almost half.
