Abstract

Colloidal quantum dots (CQDs), and especially HgTe CQDs, have the potential to disrupt traditional solid-state manufacturing of sensitive infrared photodetectors. Here we produce a surface model for (111) HgTe surfaces present in tetrahedral CQDs and attempt to use density functional theory (DFT) to explore various issues in the fabrication and performance of HgTe CQD photodetectors. One such concern is the presence of mid-gap trap states that can hurt device performance. In this work, we demonstrate that an abundant source of these trap states is unpassivated mercury at the surface of the nanocrystal, which can be corrected with passivation procedures. Furthermore, we show that mercury vacancies, which contribute under-coordinated tellurium sites on the surface, do not appear to have an outsized impact on mid-gap states, unlike other II-VI CQD systems. This is likely a unique effect of the geometry of the tetrahedral nanocrystal. While tellurium vacancies were also explored, and preliminary results would indicate the presence of trap states, further simulation is warranted to verify this effect. We are also able to demonstrate a universal control of conduction type in the CQDs regardless of the synthesis employed. The use of mercury substitution reveals the ability of indium species to induce n-type doping, while silver tends to accumulate on the FCC sites of mercury rich surfaces and induces p-type doping. We expect that experimental procedures can be devised to adapt many common syntheses to exploit this effect. Furthermore, we confirm the observation of a ligand dipole dependent Fermi level, highlighting the need for further investigation, and potentially enabling higher performing devices with shorter ligands and precisely engineered band alignments.

Publication Date

8-2024

Document Type

Thesis

Student Type

Graduate

Degree Name

Materials Science and Engineering (MS)

Department, Program, or Center

Chemistry and Materials Science, School of

Advisor

Scott Williams

Advisor/Committee Member

Pratik Dholabhai

Advisor/Committee Member

Michael Pierce

Campus

RIT – Main Campus

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