The MBE growth of lead tin selenides (Pb1-xSnxSe: LTS)/PbSe double layers was carried out, and the effects of reduced growth temperature on crystalline qualities of upper LTS layers and diffusion of dopants at the interface between LTS and PbSe were investigated. A few micrometer-thick PbSe epitaxial layers (undoped) were directly grown on the CaF2 (111) substrates at 485 degrees C and then the Bi or Bi2Se3; doped LTS layers were grown on top of PbSe at 200-485 degrees C. It was found that epitaxial temperature could be reduced to 200 degrees C. Reflection high energy electron diffraction (RHEED) patterns and full width at half maximum (FWHM) values of X-ray rocking curves in LTS indicated that crystalline qualities of LTS layers tended to degrade at lower temperature than similar to 300 degrees C. Deviation from the abrupt change in dopant concentrations at the interface was observed by secondary ion mass spectroscopy (SIMS) analysis, suggesting possible diffusion of dopant from LTS into PbSe. In the case of diffusion of Bi from LTS (n similar to 10(18) cm(-3)) into undoped PbSe (p similar to 10(17) cm(-3)), deviation was as small as 500 Angstrom and the value of diffusion coefficient was roughly estimated as that of the order of 10(-15) cm(2)/s at 300-400 degrees C.