FTIR Characterization of IV-VI Semiconductors Grown by LPE on (100) BaF2

The recent development of a new liquid phase epitaxy (LPE) process for growth of narrow bandgap IV-VI semiconductor alloys on low cost BaF₂ substrates offers new opportunities to advance IV-VI semiconductor device technology. Fourier transform infrared (FTIR) absorption spectroscopic characterization of lattice-matched PbSe_0.78Te_0.22 layers grown by LPE on (100) BaF₂ substrates shows that the absorption edge varies from 213 meV at 4 K to 275 meV at room temperature. Characterization of quaternary Pb_0.95Sn_0.05Se_0.80Te_0.20 layers shows that the absorption edge varies from 118 meV at 10 K to 200 meV at room temperature. Strong Fabry-Perot interference fringes are also observed in the FTIR spectra which allow calculation of epilayer thicknesses. The FTIR data show that a double heterostructure (DH) laser fabricated from these materials, with the ternary alloy as cladding layers and the quaternary alloy as the active layer, will have band edge discontinuities of approximately 40 meV and a tuning range from 10.3 μm at 77 K to 6.4 μm at 300 K.