We report evidence of a new long-range order in single-crystal ${\mathrm{Zn}}_3$${\mathrm{As}}_2$ grown epitaxially on lattice-mismatched InP and GaAs. The Raman activity of the layers confirm, in contrast to the bulk $C_{4v}^{12}$ symmetry, a space group of $D_{4h}^{15}$ for the epilayers. Thermodynamic considerations show that the dependence of the free energy on the lattice parameters may be sufficient to account for the stability of the new structure in the epilayer.

• Received 25 March 1988

DOI:https://doi.org/10.1103/PhysRevLett.62.551