Molecular beam epitaxy of periodic BaF2/PbEuSe layers on Si(111)

Bragg reflector structures consisting of BaF2/PbEuSe stacks have been epita xially grown on CaF2/Si (111) substrates, The reflectors are centered at a wavelength of 4.0 mu m with a bandwidth of about 3.0 mu m. Reflectivity as high as 95% at the center wavelength has been achieved in three-stack refle ctors. Cracks were visible under an optical Normarski microscope in two-sta ck reflectors, The formation of cracks is probably due to the accumulation of the residual thermal strain in thick layers or the hindrance of dislocat ion glide at the BaF2/PbEuSe interfaces. (C) 1999 American Vacuum Society. [S0734-211X(99)06203-4].