Enhanced terahertz emission from GaAs substrates deposited with aluminum nitride films caused by high interface electric fields

We report on the enhanced terahertz (THz) emission from SI-GaAs and n-GaAs wafer surfaces grown with aluminum nitride (AlN) thin films, by more than a factor of 2 and 4, respectively. This is attributed to the increased GaAs surface electric field as confirmed by calculations and photoreflectance measurements. The deposition of AlN on an n-InAs substrate, however, produces no change in the THz emission despite the presence of a strong field as obtained from calculations. These results show that for semiconductors in which the THz radiation is primarily due to drift current, an increase in interface electric field results to an increase in the THz emission. For semiconductors whose primary source of THz radiation is carrier diffusion however, an increase in the interface electric field has a no effect in THz emission intensity.