Semiconductors are essential in the fabrication of many optical and electrical devices. Due to enhanced optical and electrical properties observed in nanoscale semiconducting materials, the focus of research has shifted from bulk materials to quantum dots (QDs). Many studies have been conducted on direct-gap semiconducting QDs, including CdSe and PbS, but these materials are highly toxic in comparison to Group IV materials, hindering practical applications in biomedical and advanced technological studies. Unfortunately, Group IV semiconductors have an indirect gap hindering light-interaction efficiency. To address this issue, the alloying of tin and quantum confinement effects have been examined to produced direct-gap, tunable Ge1-xSnx QDs which exhibit high absorption and photoluminescent efficiency, and improved electrical properties. Utilization of these enhanced properties for practical applications and devices requires the processing of these QDs into thin films. To create conducting, uniform thin films from the colloidally stable Ge1-xSnx QDs, a ligand exchange has been performed, replacing oleylamine (OLA) with a conducting metal chalcogenide (MCC) as the QD capping ligand. Comparison of the MCC-capped QDs to the OLA-capped QDs was studied to probe the effects of the exchange on crystal structure, size, composition, and energy gaps of the QDs. Upon the successful ligand exchange, the MCC-capped QDs were spin-coated onto a glass substrate to produce conducting Ge1-xSnx QD thin films. The electrical conductivity of these films was probed and compared to that of the conductivity of the OLA-capped QD films. The tunability of these films was also investigated. Herein, we will discuss the effects of the ligand exchange, deposition parameters, and QD composition on the morphology, crystal structure, thickness, and electrical conductivity of the Ge1-xSnx QD thin films.

Self-assembled Ge1–x Snx alloy nanocrystal thin films exhibiting tunable energy gaps and high electrical conductivity

ACS Spring 2022

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