  III-Nitride micropillar structures show great promise for applications in
micro light-emitting diodes and vertical power transistors due to their
excellent scalability and outstanding electrical properties. Typically,
III-Nitride micropillars are fabricated through a top-down approach using
reactive ion etch which leads to roughened, non-vertical sidewalls that results
in significant performance degradation. Thus, it is essential to remove this
plasma etch induced surface damage. Here, we show that potassium hydroxide
(KOH) acts as a crystallographic etchant for III-Nitride micropillars,
preferentially exposing the vertical <1-100> m-plane, and effectively removing
dry etch damage and reducing the structure diameter at up to 36.6 nm/min. Both
KOH solution temperature and concentration have a dramatic effect on this wet
etch progression. We found that a solution of 20% AZ400K (2% KOH) at 90 C is
effective at producing smooth, highly vertical sidewalls with RMS surface
roughness as low as 2.59 nm, ideal for high-performance electronic and
optoelectronic devices.
