Effects of magnetic field and optical fluence on terahertz emission in gallium arsenide

The excitation density dependence of magnetic-field-enhanced terahertz $({\mathrm{T}\mathrm{H}\mathrm{z}=10\mathrm{}}^{12}$ Hz) emission from (100) GaAs is studied. It is found that THz power saturates at a higher optical-excitation density, when a magnetic field is applied. This observation explains the different magnetic field enhancements that have been reported recently. At low excitation densities the results are shown to be consistent with a simple model of carrier-carrier scattering, whilst at higher densities surface field screening becomes important.