News Source：School of Optics and Photonics

Editor: Sheng Yun

Reviewer: Dong Liquan

Professor Chen Menglu and Professor Tang Xin, members of Professor Hao Qun’s team at the School of Optics and Photonics in BIT, have published a paper entitled "Mid-Infrared Intraband Photodetector via High Carrier Mobility HgSe Colloidal Dots" in the journal ACS NANO. It explains how to realize the low-cost mid-infrared intraband transition detection by using the 1Se to 1Pe transition in the low-cost colloidal quantum dot (CQDs) conduction band.

The research of infrared materials and devices is central to the development of infrared technology, and the realization of low-cost, high-performance infrared detectors is the future direction of development in this field. However, infrared materials are limited by the narrow-band semiconductor materials, due to the photoelectric effect. Using the intraband transition of materials can break the limitation of infrared photoelectric materials on band gap, greatly broaden the choice of infrared materials, enrich the preparation method of infrared materials, and is one of the effective ways to reduce the cost of infrared materials and devices. This work takes advantage of the synthesis and processing of the colloidal quantum dots and liquid phase, and develops a room-temperature mixed-phase ligand exchange method to obtain a relatively high carrier mobility (~1 cm2 /Vs) and precise regulation of doping in the conduction band, under the quantum confinement effect. This results in a 1000-fold improvement in response speed (several μs) and a 55-fold increase in responsivity of the intraband transition mid-infrared photodetector. Under the blackbody radiation, the mid-wave 5 µm increases, which is 1.7 x 109 Jones greater than the specific detectivity. This is the first thermal imaging has been obtained based on an intraband transition colloidal quantum dot infrared camera, and a CO2 gas sensor with a detection accuracy of 0.25 ppm to 2000 ppm has been achieved.

Figure 1. Mixed-phase ligand exchange process for intraband CQDs.

Figure 2. Spectro-electrochemistry of 7 nm diameter HgSe.

The intraband transition infrared material system places higher demands on precise doping control and carrier transport control. In this work, a mixed-phase ligand exchange method for intraband transition CQDs was developed (Figure 1), which can effectively reduce the spacing between CQDs, achieve precise doping control of surface dipoles, and make the material air-stable. A spectro-electrochemical platform (Figure. 2) has been built to obtain a detailed energy band structures of HgSe CQD, demonstrating that there is no obvious trapping state in the material.

Figure 3. Photoconductor characterization.

Figure 4. Gas detection.

Therefore a CQD intraband transition infrared camera is made, and it successfully implemented for thermal imaging (Figure 3). Compared to a low mobility intraband transition CQD detector, this detector has a 55-fold increase in responsivity, and a 10-fold increase in specifific detectivity, which is to 1.7× 109 Jones, and can achieve a fast response of several μs (Figure 4). Its mid-wave narrow-band detection and fast response enables sensitive detection of greenhouse gases. Taking CO2 as an example, in combination with a Michelson interferometer, a CO2 gas sensor with a sensitivity range of 0.25 ppm to 2000 ppm has successfully developed.

With the rapid development of artificial intelligence, automatic driving, smart cities, smart agriculture and other fields in recent years, the demand for infrared information in various fields is growing. This achievement takes advantage of the low cost and liquid phase processing of CQDs and proposes a new concept of using intraband transition to realize a infrared detector, and for the first time realizes a mid-infrared intraband photodetector with practical value, verifying its functions such as infrared camera and highly sensitive greenhouse gas detection. And this plays an important role in promoting the development of low-cost and high-performance infrared detectors.

Link to original article:https://doi.org/10.1021/acsnano.2c03631

About the authors:

Hao Qun ， a Distinguished Professor and Dean of the School of Optics and Photonics of BIT. She received her PhD in engineering from Tsinghua University in 1998, and was exceptionally promoted to professor in 2003 and was appointed as a doctoral supervisor in 2004. From 1999 to 2001, she was concurrently a visiting researcher at the University of Tokyo, Japan, and in 2011 she was concurrently a Chair Professor at Case Western Reserve University, U.S. She is also the head of the Innovation and Talent Introduction Base for Universities, the head of the Innovation Team of the Ministry of Science and Technology in key areas, the Cross-century Outstanding Talent of the Ministry of Education, the prestigious teacher of Beijing, and the national "women's contribution" pacesetter. She has long been engaged in teaching and scientific research in the field of new photoelectric imaging and sensing technology and photoelectric precision testing technology. Her main research directions include new photoelectric imaging technology, bionic photoelectric sensing technology, anti-vibration interferometry technology and instrumentation. She has led a number of national projects, including The National Natural Science Foundation of China (NSFC) Instrument Special/Key Projects, the Key R&D Program of the Ministry of Science and Technology, the Basic Strengthening Program, the GF Basic Research Major/Key Projects, and the National 863 Projects etc. She is the standing director of Chinese Optical Society and the chairman of the Photoelectric Committee, the standing director of China Instrument and Control Society, and the executive vice chairman of Opto-electromechanical Technology and System Integration Branch, the standing director of Chinese Society for Measurement, the director of China Ordnance Society, and the chairman of Committee for Optics, the director of the China Optics and Optoelectronics Association and the vice chairman of the Infrared Branch etc. Meanwhile, she is the deputy editor-in-chief of Defense Technology magazine.

Chen Menglu， a professor and PhD supervisor in the School of Optics and Photonics of BIT She was selected to the 2021 National Youth Talent Program (Overseas), the "Young Talent Support Project" of China Association for Science and Technology, Beijing "Science and Technology New Star" and other support programs. She received her Bachelor of Science degree from the University of Science and Technology of China (USTC) in 2015 and her PhD in Physics from the University of Chicago in 2020. She has long been engaged in the research of infrared detection and imaging of CQDs, and has obtained breakthrough results in the optimization of transport properties of infrared quantum dots, high performance mid-wave infrared detector at room temperature, and intraband transition narrow-band infrared detection and other areas. She has published more than 20 academic papers in SCI journals such as Nature Materials, ACS Nano etc.

Tang Xin， a professor and PhD supervisor in the School of Optics and Photonics of BIT. He has been selected for the 2019 National Youth Program for the Introduction of Overseas Top-level Talents and the "Young Talent Support Project" of the Chinese Association for Science and Technology. He has been engaged in the research and system development of new CQD infrared detectors and focal plane arrays, with a wave range covering short-wave, mid-wave and long-wave multiple important infrared atmospheric windows. His related results has been published as first author or corresponding author in Nature Photonics, Advanced Materials, ACS Nano and other journals. He is currently leading a number of projects, such as the key program of National Natural Science Foundation of China and the Key R&D Program of the Ministry of Science and Technology for Young Scientists.