Assessment of crystal quality and unit cell orientation in epitaxial Cu₂ZnSnSe₄ layers using polarized Raman scattering.

We use polarization-resolved Raman spectroscopy to assess the crystal quality of epitaxial kesterite layers. It is demonstrated for the example of epitaxial Cu₂ZnSnSe₄ layers on GaAs(001) that "standing" and "lying" kesterite unit cell orientations (c'-axis parallel / perpendicular to the growth direction) can be distinguished by the application of Raman tensor analysis. From the appearance of characteristic intensity oscillations when the sample is rotated one can distinguish polycrystalline and epitaxial layers. The method can be transferred to kesterite layers oriented in any crystal direction and can shed light on the growth of such layers in general.