Many-body effects on optical carrier cooling in intrinsic semiconductors at low lattice temperatures

Based on the coupled density and energy balance equations, a dynamical model is proposed for exploring many-body effects on optical carrier cooling (not lattice cooling) in steady state in comparison with the earlier findings of current-driven carrier cooling in doped semiconductors [X. L. Lei and C. S. Ting, Phys. Rev. B 32, 1112 (1985)] and tunneling-driven carrier cooling through discrete levels of a quantum dot [H. L. Edwards , Phys. Rev. B 52, 5714 (1995)]. This dynamical carrier-cooling process is mediated by a photoinduced nonthermal electron-hole composite plasma in an intrinsic semiconductor under a thermal contact with a low-temperature external heat bath, which is a generalization of the previous theory for a thermal electron-hole plasma [H. Haug and S. Schmitt-Rink, J. Opt. Soc. Am. B 2, 1135 (1985)]. The important roles played by the many-body effects such as band-gap renormalization, screening, and excitonic interaction are fully included and analyzed by calculating the optical-absorption coefficient, spontaneous emission spectrum, and thermal-energy exchange through carrier-phonon scattering. Both the optical carrier cooling and heating are found with increasing pump-laser intensity when the laser photon energy is set below and above the band gap of an intrinsic semiconductor. In addition, the switching from carrier cooling to carrier heating is predicted when the frequency detuning of a pump laser changes from below the band gap to above the band gap.