  An ultrabroadband upconversion device is demonstrated by direct tandem
integration of a p-type GaAs/AlxGa1-xAs ratchet photodetector (RP) with a GaAs
double heterojunction LED (DH-LED) using the molecular beam epitaxy (MBE). An
ultrabroadband photoresponse from terahertz (THz) to near infrared (NIR) region
(4-200 THz) was realized that covers a much wider frequency range com-pared
with the existing upconversion devices. Broadband IR/THz radiation from 1000 K
blackbody is successfully upconverted into NIR photons which can be detected by
commercial Si-based device. The normal incidence absorption of the RP
simplifies the structure of the RP-LED device and make it more compact compared
with the inter-subband transition based upconverters. In addition to the
up-conversion function, the proposed upconverter is also tested as photovoltaic
detectors in the infrared region (15-200 THz) without an applied bias voltage
due to the ratchet effect.
