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 $T=10\mathrm{}–280\mathrm{K}.$ The maximum observed THz power is $\sim 1.6\times {10}^{-13}\mathrm{J}/\mathrm{p}\mathrm{u}\mathrm{l}\mathrm{s}\mathrm{e}$ (12 μW average power) from $n-\mathrm{InAs}(1.8\mathrm{}\times {10}^{16}{\mathrm{cm}}^{\mathrm{-}3})$ at $B=3.2\mathrm{}\mathrm{T}.$ 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 $n-\mathrm{GaAs}$ at all magnetic fields, and InAs at $B=0.\mathrm{}$ 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 $|B|>1.0\mathrm{}\mathrm{T}.$