Pyrolytic boron nitride double container and manufacture thereof

−1 −1 A pyrolytic boron nirtride double container for a source of molecular beams used in molecular beam epitaxy, wherein the transmissivity of an inner container of the pyrolytic boron nitride double container with respect to light having a wave number of 2600 cmto 6500 cmis 90% or less of that of an outer container. The pyrolytic boron nitride double container, which enables molecular beams to generate stably with good temperature controllability and high heat efficiency and which can be used in a stable manner, is provided through a simple process and at low cost, so that molecular beam epitaxial growth can be stabilized, quality of the epitaxial film can be improved, and even though the rise and drop in the temperature of the material melt is repeated, or even at an emergency suspension of the operation, the trouble due to breakage of the container can be prevented.