  To explain the broad-band spectral energy distributions (SED) of Seyfert
nuclei and QSOs, we study the emission spectrum emerging from a vertical
disk-corona structure composed of a two-temperature plasma by solving
hydrostatic equilibrium and radiative transfer self-consistently. Our model can
nicely reproduce the soft X-ray excess with alpha (L_frequency proportional to
the frequency to the power of -alpha) of about 1.5 and the hard tail extending
to about 50 keV with alpha about 0.5. The different spectral slopes (alpha
about 1.5 below 2 keV and about 0.5 above) are the results of different
emission mechanisms: unsaturated Comptonization in the former and a combination
of Comptonization, bremsstrahlung, and reflection of the coronal radiation at
the disk-corona boundary in the latter.
