  The BCS to Bose-Einstein condensation (BEC) crossover of electron-hole (e-h)
pairs in optically excited semiconductors is studied using the two-band Hubbard
model with both repulsive and attractive interactions. Applying the
self-consistent t-matrix approximation combined with a local approximation, we
examine the properties of a normal phase and an excitonic instability. The
transition temperature from the normal phase to an e-h pair condensed one is
studied to clarify the crossover from an e-h BCS-like state to an excitonic
Bose-Einstein condensation, which takes place on increasing the e-h attraction
strength. To investigate effects of the repulsive interaction and the e-h mass
difference, we calculate the transition temperature for various parameters of
the interaction strengths, the e-h particle density, and the mass difference.
While the transition temperature in the e-h BCS regime is sufficiently
suppressed by the repulsive interaction, that of the excitonic BEC is largely
insensitive to it. We also show quantitatively that in the whole regime the
mass difference leads to large suppression of the transition temperature.
