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The BCS to Bose-Einstein condensation (BEC) crossover of electron-hole (e-h)pairs in optically excited semiconductors is studied using the two-band Hubbardmodel with both repulsive and attractive interactions. Applying theself-consistent t-matrix approximation combined with a local approximation, weexamine the properties of a normal phase and an excitonic instability. Thetransition temperature from the normal phase to an e-h pair condensed one isstudied to clarify the crossover from an e-h BCS-like state to an excitonicBose-Einstein condensation, which takes place on increasing the e-h attractionstrength. To investigate effects of the repulsive interaction and the e-h massdifference, we calculate the transition temperature for various parameters ofthe interaction strengths, the e-h particle density, and the mass difference.While the transition temperature in the e-h BCS regime is sufficientlysuppressed by the repulsive interaction, that of the excitonic BEC is largelyinsensitive to it. We also show quantitatively that in the whole regime themass difference leads to large suppression of the transition temperature.Comment: 8 pages, 7 figures, to be published in Phys. Rev.

Excitonic BCS-BEC crossover at finite temperature: Effects of repulsion and electron-hole mass difference