Fast Near‐Infrared Photodetection Using III–V Colloidal Quantum Dots

• Published in: Advanced materials (Weinheim) Vol. 34; no. 33; pp. e2203039 - n/a
• Main Authors: Sun, Bin, Najarian, Amin Morteza, Sagar, Laxmi Kishore, Biondi, Margherita, Choi, Min‐Jae, Li, Xiyan, Levina, Larissa, Baek, Se‐Woong, Zheng, Chao, Lee, Seungjin, Kirmani, Ahmad R., Sabatini, Randy, Abed, Jehad, Liu, Mengxia, Vafaie, Maral, Li, Peicheng, Richter, Lee J., Voznyy, Oleksandr, Chekini, Mahshid, Lu, Zheng‐Hong, García de Arquer, F. Pelayo, Sargent, Edward H.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.08.2022; Wiley Blackwell (John Wiley & Sons)
• Subjects: Arsenic; Charge transport; fast photodetectors; heavy‐metal free; Indium arsenides; Materials science; near‐infrared; Permittivity; Photodiodes; Quantum dots; Quantum efficiency; Response time; Time response
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.202203039

Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II–VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III–Vs—if their surface chemistry can be mastered—offer a low permittivity and thus increase potential for high‐speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm2 V−1 s−1) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 ns—the fastest photodiode among previously reported CQD photodiodes—combined with an external quantum efficiency (EQE) of 30% at 940 nm. An amphoteric liganding strategy is developed to simultaneously address In and As dangling bonds on InAs colloidal quantum dot (CQD) surfaces, which provides passivation and charge transport for low‐permittivity CQD solids. The resulting photodiodes achieve a response time faster than 2 ns—the fastest photodiode among previously reported CQD photodiodes—combined with an external quantum efficiency of 30% at 940 nm.