Terahertz emission from GaAs and InAs in a magnetic field

We have studied terahertz (THz) emission from InAs and GaAs in a magnetic field, and find that the emitted radiation is produced by coupled cyclotron-plasma charge oscillations. Ultrashort pulses of THz radiation were produced at semiconductor surfaces by photoexcitation with a femtosecond Ti-sapphire laser. We recorded the integrated THz power and the THz emission spectrum as a function of magnetic field at fields up to 5.5 T, and as function of temperature for T=10–280K. The maximum observed THz power is ∼1.6×10^-13J/pulse (12 μW average power) from n-InAs(1.8×10¹⁶cm^-3) at B=3.2T. We compare our results to semiclassical models of magnetoplasma oscillations of bulk free carriers and damped motion of free carriers in a two-dimensional electron gas. The bulk model describes THz emission from n-GaAs at all magnetic fields, and InAs at B=0. It fails to describe THz emission from InAs at nonzero magnetic fields. We show that a model including both bulk plasma oscillations and THz emission from a surface accumulation layer describes THz emission from InAs in a moderate magnetic field, but this model does not completely describe emission at fields |B|>1.0T.