Bandgap energies and refractive indices of Pb1−xSrxSe

Optical transmission measurements were carried out on Pb1−xSrxSe samples, grown by molecular beam epitaxy, with different Sr compositions (x) ranging from 0 to 1. Refractive indices were calculated for all the samples at room temperature and at 77 K by fitting the transmittance data. Bandgap energies of all compositions were calculated by fitting the absorption coefficients to theoretical models of direct and indirect transitions. A distinct bandgap inversion from the direct to the indirect was observed at a Sr composition of approximately x=0.20. The direct and indirect bandgaps of SrSe calculated from the experimental results were found to be 3.81 and 1.82 eV, respectively.