Negative Crystal-Field Splitting of the Valence Bands in CdSnP2

The polarization selection rules governing the band-edge electroreflectance and photoreflectance spectra of CdSn${\mathrm{P}}_2$ are opposite to those observed in wurtzite II-VI semiconductors and to theoretical predictions for similar chalcopyrite semiconductors. This result is explained by a new valence-band model with the essential feature that the sign of the crystal-field splitting is opposite to that observed in wurtzite II-VI semiconductors.