  The boson-fermion atomic bound states (composite fermion) and their roles for
the phase structures are studied in a bose-fermi mixed condensate of atomic gas
in finite temperature and density. The two-body scattering equation is
formulated for a boson-fermion pair in the mixed condensate with the
Yamaguchi-type potential. By solving the equation, we evaluate the binding
energy of a composite fermion, and show that it has small T-dependence in the
physical region, because of the cancellation of the boson- and fermion-
statistical factors in the equation. We also calculate the phase structure of
the BF mixed condensate under the equilibrium B+F -> BF, and discuss the role
of the composite fermions: the competitions between the degenerate state of the
composite fermions and the Bose-Einstein condensate (BEC) of isolated bosons.
The criterion for the BEC realization is obtained from the
algebraically-derived phase diagrams at T=0.
