Band Gap Energies and Refractive Indices of Epitaxial Pb1-xSrxTe Thin Films

Pb1-xSrxTe thin films with different strontium (Sr) compositions are grown on BaF2(111) substrates by molecular beam epitaxy (MBE). Using high resolution x-ray diffraction (HRXRD), we obtain Pb1-xSrxTe latticeconstants, which vary in the range 6.462--6.492 AA. According to the Vegard law and HRXRD data, Sr compositions in Pb1-xSrxTe thin films range from 0.0--8.0%. The Pb1-xSrxTe refractive index dispersions are attained from infrared transmission spectrum characterized by Fourier transform infrared (FTIR) transmission spectroscopy. It is found that refractive index decreases while Sr content increases in Pb1-xSrxTe. We also simulate the Pb1-xSrxTe transmission spectra theoretically to obtain the optical band gap energies which range between 0.320eV and 0.449eV. The simulated results are in good agreement with the FTIR data. Finally, we determine the relation between Pb1-xSrxTe band gap energies and Sr compositions (Eg=0.320+0.510x-0.930x2 +184x3(eV)).