  Metastable wurtzite crystal phases of semiconductors comprise enormous
potential for high-performance electro-optical devices, owed to their extended
tunable direct band gap range. However, synthesizing these materials in good
quality and beyond nanowire size constraints has remained elusive. In this
work, the epitaxy of wurtzite InP microdisks and related geometries on
insulator for optical applications is explored. This is achieved by an
elaborate combination of selective area growth of fins and a zipper-induced
epitaxial lateral overgrowth, which enables co-integration of diversely shaped
crystals at precise position. The grown material possesses high phase purity
and excellent optical quality characterized by STEM and $\mu$-PL. Optically
pumped lasing at room temperature is achieved in microdisks with a lasing
threshold of 365 $\mu J/cm^2$, thus demonstrating promise for a wide range of
photonic applications.
