High performance terahertz imaging devices have drawn wide attention due to their significant application in healthcare, security of food and medicine, and nondestructive inspection, as well as national security applications. Here we demonstrate a broadband terahertz photon-type up-conversion imaging device, operating around the liquid helium temperature, based on the gallium arsenide homojunction interfacial workfunction internal photoemission (HIWIP)-detector-LED up-converter and silicon CCD. Such an imaging device achieves broadband response in 4.2–20 THz and can absorb the normal incident light. The peak responsivity is 0.5 AW −1 . The light emitting diode leads to a 72.5% external quantum efficiency improvement compared with the one widely used in conventional up-conversion devices. A peak up-conversion efficiency of 1.14 × 10 −2 is realized and the optimal noise equivalent power is 29.1 pWHz −1/2 . The up-conversion imaging for a 1000 K blackbody pin-hole is demonstrated. This work provides a different imaging scheme in the terahertz band.

Terahertz imaging has many important potential applications. Due to the failure of Si readout integrated circuits (ROICs) and the thermal mismatch between the photo-detector arrays and the ROICs at temperatures below 40 K, there are big technical challenges to construct terahertz photo-type focal plane arrays. In this work, we report pixel-less photo-type terahertz imagers based on the frequency up-conversion technique. The devices are composed of terahertz quantum-well photo-detectors (QWPs) and near-infrared (NIR) light emitting diodes (LEDs) which are grown in sequence on the same substrates using molecular beam epitaxy. In such an integrated QWP-LED device, photocurrent in the QWP drives the LED to emit NIR light. By optimizing the structural parameters of the QWP-LED, the QWP part and the LED part both work well. The maximum values of the internal and external energy up-conversion efficiencies are around 20% and 0.5%. A laser spot of a homemade terahertz quantum cascade laser is imaged by the QWP-LED together with a commercial Si camera. The pixel-less imaging results show that the image blurring induced by the transverse spreading of photocurrent is negligible. The demonstrated pixel-less imaging opens a new way to realize high performance terahertz imaging devices.Terahertz imaging has many potential applications, such as deep space exploration, imaging of biological tissues, mail screening and fingerprint identification, and situation awareness in fire disasters 1 . Terahertz focal plane arrays (FPAs) are key components for real time terahertz imaging systems 2 . Several different FPAs working in the terahertz regime have been developed in recent years based on the phase change of VO x , the complementary metal-oxide-semiconductor transistor (CMOS) technology, and the pyroelectric effect of LiTaO 3 crystal 2,3 . However, photo-type terahertz FPAs are still absent now. Compared to the thermal and other FPAs, photo-type FPAs have advantages of high detection sensitivity, short response time, large linear response range, and high damage threshold 2 .In mid-and far-infrared spectral regimes, FPAs are constructed by flip-chip bonding photo-detector arrays to commercial Si readout integrated circuits (ROICs) 2 . HgCdTe and quantum well infrared photo-detector (QWIP) FPAs are in the dominant position in mid-and far-infrared regimes 4 . Terahertz photo-detectors based on inter-subband transition in one-and three-dimensional quantum confined semiconductor structures were demonstrated in the past decade 2,4 . GaAs/(Al,Ga)As quantum well photo-detectors (QWPs) operating in terahertz band were realized by Liu et al. 5 . At temperatures below 30 K, background-limited infrared performance (BLIP) is reached for terahertz QWPs in 3.0-7.0 THz 6 . Due to the high quality of molecular beam epitaxy (MBE) grown GaAs/(Al,Ga)As multi-layer structure and the mature III-V fabrication processing technique, it is possible to fabricate terahertz QWPs with uniform detection performance in a large area scale. However, there are two t...

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