  An ultra-broadband THz emitter covering a wide range of frequencies from 0.1
to 10 THz is highly desired for spectroscopy applications. So far, spintronic
THz emitters have been proven as one class of efficient THz sources with a
broadband spectrum while the performance in the lower frequency range (0.1 to
0.5 THz) limits its applications. In this work, we demonstrate a novel concept
of a current-enhanced broad spectrum from spintronic THz emitters combined with
semiconductor materials. We observe a 2-3 order enhancement of the THz signals
in a lower THz frequency range (0.1 to 0.5 THz), in addition to a comparable
performance at higher frequencies from this hybrid emitter. With a bias
current, there is a photoconduction contribution from semiconductor materials,
which can be constructively interfered with the THz signals generated from the
magnetic heterostructures driven by the inverse spin Hall effect. Our findings
push forward the utilization of metallic heterostructures-based THz emitters on
the ultra-broadband THz emission spectroscopy.
