In recent years, infrared/terahertz detection technology has made remarkable progress. This review article will focus on the current infrared and terahertz detectors and make corresponding comments on their advantages and disadvantages. To meet the needs of the current level of technology, photon-type infrared/terahertz detectors required for high-speed detection have received extensive attention and research, but their disadvantages such as low operating temperature and narrow response spectral range limit the application scenarios. This article will mainly introduce and comment on the GaAs-based classical infrared/terahertz photon-type detectors based on aspects such as working principle, working mode, research progress, and band gap engineering. On this basis, the research progress of the quantum ratchet photodetector (QRPD) proposed by our research group is introduced in detail, and its advantages and feasibility are explained from the working principle to device structure of the QRPD device. By studying the working mechanism and quantum characteristics of QRPD under different impurity types, doping concentrations, growth processes, and band gap structures, the experimental results of different structural QRPD devices are listed and analyzed in this article.
Significance The ratchet structure can detect infrared radiation without an external electric field, and can achieve the property of spectrally tunable under a specific bias to achieve broadband detection. Further, the QRPD is integrated with the LED to prepare a quantum ratchet upconversion device, which can achieve ultra- broadband detection in the range of 4-200 THz, and the responsivity of the quantum ratchet upconversion detector can reach 0.4 A/W at 25 K. This study shows that the quantum ratchet detector can effectively increase the operating temperature and response spectral range of the device, and provides a new idea for high-temperature infrared/terahertz photon-type detectors.
Progress First, we introduced the advantages and disadvantages of the existing traditional infrared/terahertz detectors in the detection band, operating temperature, and response speed. We analyzed the detection band range and operating temperature of InGaAs, HgCdTe, InSb, QWIP, BIB, and Ge-based detectors, and found that although the current infrared photon-type detectors have a fast response speed and high sensitivity, the detection band range is limited and the operating temperature is low. Terahertz photon-type detectors are limited by extremely low temperature operating conditions and the diffraction limit, and related imaging technologies currently have no major breakthroughs.
Then, we introduced four kinds of GaAs-based infrared/terahertz detectors. Among them, the n-type QWP structure requires the design of the coupling structure to increase the complexity and cost of the preparation, and the response spectral range is very narrow, and broadband detection cannot be achieved. Like QWIP, QCD also faces the same problem. Due to the limit of experimental growth, the cutoff wavelength of HIWIP/HEIWIP detectors cannot be further increased, and the operating temperature is low. The responsivity of OPHED detectors is low, and the peak responsivity is only on the order of µA/W.
On these bases, we introduced the principle of quantum ratchet and the related research progress in recent years using the principle of optically responsive quantum ratchet. The related research progress of the GaAs-based quantum ratchet detector we recently proposed was introduced in detail. Due to the hot hole effect and the complexity of the valence band, the quantum ratchet ratchet detector breaks through the semiconductor band gap limit, and achieves an ultra-broadband response in the range of 4-300 THz. And due to the higher barrier in the ratchet structure, the overall dark current is reduced by more than three orders of magnitude compared with other traditional terahertz detectors. The asymmetry of the ratchet structure also causes the detector to produce a ratchet effect, that is, it can generate effective photocurrent even under zero bias, which is considered a new type of photovoltaic effect. The ratchet detector we proposed not only solves the problem of narrow spectral width and low operating temperature of traditional photon-type terahertz detectors, but also provides a new method for the study of optically responsive ratchets and quantum ratchets. We also tried different material epitaxial growth methods to prepare quantum ratchet detectors and presented the latest comparison results. In addition, for the aspect of high-temperature operation, our latest research results show that the highest response temperature of the terahertz band of the quantum ratchet structure upconversion device can reach 25 K.
Conclusions and Prospects We first introduce the key problems of current infrared/terahertz detectors in broadband, high temperature, and high speed. Then, we focus on introducing four common GaAs-based infrared/terahertz detectors, and makes comments on their working principles, device structures, advantages, and disadvantages. On this basis, we focus on introducing the research progress of the QRPD proposed by our research group. The superiority and feasibility of the QRPD are explained from the aspects of the basic principle of the device, the device structure, and the experimental characterization results. The quantum ratchet detector we proposed provides a new type of solution and idea for achieving high-speed, broadband, and high-temperature infrared/terahertz detection and upconversion. The realization of broadband response and high-temperature operation broadens the new idea of the detection technology band gap engineering design. Inspired by this, we can try to use different material structures for infrared detection, and optimize the device through the ratchet structure to achieve broadband, high-temperature and other characteristics. This work opens a new window for the traditional semiconductor band gap engineering to achieve high-performance infrared/terahertz detection.