Enhanced THz emission efficiency of composition-tunable InGaAs nanowire arrays

We report the terahertz (THz) emission properties of composition-tunable, intrinsically n-type InGaAs nanowire (NW) arrays using THz time-domain spectroscopy. By tuning the alloy composition of In_1-xGa_xAs NWs from pure InAs (x(Ga)=0) up to the intermediate composition (x(Ga)∼0.5), a substantially enhanced (>3-fold) THz emission efficiency is found, which is ascribed to a reduction in electron accumulation at the NW surface and respective electron scattering at donor-type surface defects. These findings are also confirmed by photoexcitation wavelength dependent measurements, while the THz emission characteristics are further found to be different from corresponding bulk-type planar InGaAs. In particular, NWs exhibit no distinct maxima in THz excitation spectra as caused by electron scattering to subsidiary conduction band valleys and commonly observed in the majority of bulk semiconductors. The wavelength-dependent emission spectra further reveal distinct signatures of modified intervalley scattering, revealing the underlying polytypism of intermixed wurtzite and zincblende phases in the investigated InGaAs NWs.