The role of bandgap energy excess in surface emission of terahertz radiation from semiconductors

We compare the emission power of GaAs, InGaAs and InAs as function of excitation photon energy. We find that the carrier excess excitation energy is more relevant to explain their performance difference than their mobilities. We conclude that ballistic transport after photoexcitation is the dominant mechanism for terahertz emission and that the relative importance of drift current in comparison to the ballistic motion depends on the comparison of the initial kinetic energy hv - E _bangap and the surface potential energy eV _pin .