  High performance Terahertz (THz) photodetector has drawn wide attention and
got great improvement due to its significant application in biomedical,
astrophysics, nondestructive inspection, 6th generation communication system as
well as national security application. Here we demonstrate a novel broadband
photon-type THz/infrared (IR) photodetector based on the GaAs/AlxGa1-xAs
ratchet structure. This kind of photodetector realizes a THz photon-response
based on the electrically pumped hot hole injection and overcomes the internal
workfunction related spectral response limit. An ultrabroadband photoresponse
from 4 THz to 300 THz and a peak responsivity of 50.3 mA/W are realized at
negative bias voltage of -1 V. The photodetector also presents a bias-tunable
photon-response characteristic due to the asymmetric structure. The ratchet
structure also induces an evident photocurrent even at zero bias voltage, which
indicates the detector can be regard as a broadband photovoltaic-like detector.
The rectification characteristic and high temperature operation possibility of
the photodetector are also discussed. This work not only demonstrates a novel
ultrabroadband THz/IR photodetector, but also provides a new method to study
the light-responsive ratchet.
