Surface Control of Doping in Self-Doped Nanocrystals

Abstract

Self-doped nanocrystals raise great interest for infrared (IR) optoelectronics because their optical properties span from near to far IR. However, their integration for photodetection requires a fine understanding of the origin of their doping and also a way to control the magnitude of the doping. In this paper, we demonstrate that a fine control of the doping level between 0.1 and 2 electrons per dot is obtained through ligand exchange. The latter affects not only the interparticle coupling but also their optical properties because of the band-shift resulting from the presence of surface dipoles. We demonstrate that self-doping is a bulk process and that surface dipoles can control its magnitude. We additionally propose a model to quantify the dipole involved with each ligand. We eventually use the ligand design rule previously evidenced to build a near-infrared photodetector on a soft and transparent substrate. The latter significantly improves the performance compared to previously reported colloidal quantum dot-based photodetectors on plastic substrates operated in the telecom wavelength range.

Probing Charge Carrier Dynamics to Unveil the Role of Surface Ligands in HgTe Narrow Band Gap Nanocrystals

“…Among potential candidates, mercury chalcogenides (HgS 6,7 , HgSe [8][9][10] and HgTe 11 ) are the most mature materials, combining a tunable infrared absorption 12,13 with photoconductive 14 properties. In spite of huge progresses reported over the past decades 15 , which include the report of photovoltaic devices 16 , intraband transition based photodetector 1,17 , plasmonic devices 18,19 and multicolor devices 20,21 , no rational design of the material has been conducted.…”

Designing Photovoltaic Devices Using HgTe Nanocrystals for Short and Mid‐Wave Infrared Detection

“…Highly monodisperse HgTe nanocrystals can now be synthetized and present an atom‐like spectrum in the IR range . Synthetic progress also includes shape control with the synthesis of nanoplatelets and heterostructures . Another striking observation from a material point of view is the observation of self‐doping .…”

“…Because doping drives the presence of the intraband transition and the dark current magnitude, it must be controlled precisely to be exploited in IR‐sensing materials. The level of doping has been determined using methods such as (spectro) electrochemistry or photoemission and appears to be strongly dependent on the capping molecules …”

“…[14] Synthetic progress also includes shape control with the synthesis of nanoplatelets [15] and heterostructures. [16][17][18][19] Another striking observation from a material point of view is the observation of self-doping. [17,20] Mercury chalcogenides nanocrystals can present an air-stable intraband transition [21,22] in the mid-and far-IR.…”

“…[16][17][18][19] Another striking observation from a material point of view is the observation of self-doping. [17,20] Mercury chalcogenides nanocrystals can present an air-stable intraband transition [21,22] in the mid-and far-IR. For long, the observation of such transition was only achievable using optical and electrochemical [23] pumping.…”