Carrier Density Modulation in PbSe Quantum Dot Films via In-Solution Ligand Exchange
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MRS Advances © 2020 Materials Research Society DOI: 10.1557/adv.2020.254
Carrier Density Modulation in PbSe Quantum Dot Films via In-Solution Ligand Exchange Tom Nakotte 1,2, Hongmei Luo 1, and Jeff Pietryga 2,* 1 Department of Chemical and Materials Engineering, New Mexico State University, Las Cruces, NM 88003.
2
Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
*
Correspondence [email protected]
ABSTRACT
In-solution ligand exchange of PbSe QDs is used to examine the effect of capping ligand on the carrier density of PbSe QD films. Results show that carrier density can be modulated by a factor of 5 by choice of ligand without any additional post deposition treatments. Proper fabrication and measurement conditions for calculating carrier densities from C-V measurements using a sandwich structure on P-doped Si/SiO2/Al2O3/QD/Au structure capacitance devices are outlined. Combining carrier density results with field-effect-transistor measurements, promising ligands which display lower carrier densities without having a significant drop off in carrier mobility are identified as candidates for photodetection purposes.
1
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INTRODUCTION PbSe quantum dots (QDs) have the potential to improve upon current photodetector technologies in the near-IR and mid-IR spectral regions [1, 2]. Size tunable emission ranging from 1-4 µm [3], the possibility of carrier multiplication [4], and various developed methods such as quantized Ostwald ripening [5] to improve the size distribution to as little 5% within an ensemble, are all advantageous properties for photodetection purposes. Improving capabilities in these regions is of significant consequence for applications such as; environmental monitoring [6], motion sensing [7], and fiber-optic communications [8]. Additionally the high Z number of PbSe QDs make them promising candidates for detection of higher energy photons such as X-rays and gamma rays, however for these purposes the development of thick uniform films is vital. Despite these promising properties early QD devices suffered in performance due to low carrier mobilities, resulting from the long insulating ligands that stabilize QDs when they are in colloidal solution but cause discontinuities between QDs when they are made into a film [9]. Layer-by-layer ligand exchange employed during QD film preparation, in which long native ligands in a thin QD film are replaced by shorter ligands through exposure to a solution containing more strongly binding short ligands, was an early solution to improve QD spacing issues within films [10, 11]. However layer-bylayer ligand exchange is only successful if the QD film is sufficiently thin to allow complete solution penetration, and can result in non-uniform films as it is performed repeatedly when prod
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