Time-resolved pump–probe spectroscopic ellipsometry of cubic GaN II: Absorption edge shift with gain and temperature effects

We recently published a study concerning femtosecond pump–probe absorption edge spectroscopy of cubic GaN (fundamental bandgap: 3.23 eV), resulting in the transient dielectric function. In present study, we continue our investigations those measurements by determining time-dependent transition energy at Fermi-vector between conduction and valence bands. The generation electron–hole pairs 266 nm pump-beam (4.66 eV) shifts ≈500 meV within 1 ps due to many-body effects like band-filling bandgap renormalization. Modeling this ultra-fast change is achieved converting energies into free-carrier concentrations, assuming electron contributions be dominant. consider relaxation, recombination, diffusion free-carriers as well either an additional gain-recombination or temperature effects. This allows for describing on short time scales. Both models yield similar values characteristic relaxation (≈0.21 ps), recombination (≈25 coefficient (≈1 cm2/s).