Phase discrimination in CdSe structures by means of Raman scattering

Raman spectra of epitaxial layers of CdSe grown by molecular beam epitaxy have been measured for the cubic (zincblende) and hexagonal (wurtzite) phases. The Raman spectra are examined in the light of density functional calculations for these two highly similar structures. Characteristic Raman frequencies and spectral features associated with the different symmetry are discussed and reliable criteria for phase discrimination based on Raman spectroscopy are proposed. Although LO frequencies are virtually identical in both structures and may be affected by size effects, the observation of a low energy E2 mode at 33 cm−1 unambiguously identifies the wurtzite structure and can be used as a specific fingerprint to distinguish between these two phases in CdSe‐based nanostructures. The slightly lower LO frequency measured in the zincblende epitaxial layer is ascribed to residual tensile strain. For solar cell applications, the crystalline phase of CdSe [wurtzite °(W) or zincblende °(ZB)] is crucial. Discriminating between these two phases in nanostructured material is not straightforward using conventional XRD techniques. Here, Cuscó et al. propose Raman scattering as a convenient approach to differentiate between W and ZB phases. The observation of the strong, sharp low‐frequency E2 mode is an unambiguous fingerprint for the W phase.