Colloidal Indium Arsenide Quantum dots: Precursor Chemistry, Synthesis strategies, and Core/Shell Architectures for Short-Wave Infrared Optoelectronics

Short-wave infrared (SWIR) technologies were historically developed for defense, aerospace, and scientific instrumentation, where their ability to operate under low-light conditions and penetrate atmospheric obscurants such as fog, smoke, and haze enabled critical functions including surveillance, night-time imaging, and target identification. For several decades, the development and deployment of SWIR technologies remained largely confined to these specialized sectors. Consequently, epitaxially grown III-V semiconductor detectors, particularly those based on indium gallium arsenide (InGaAs), became the dominant platform for SWIR technologies. In such stringent applications, performance requirements generally outweighed economic constraints, allowing the widespread use of these high-performance but costly detector technologies. However, in recent years the application landscape of SWIR technologies has expanded significantly beyond traditional defense applications toward industrial inspection, biomedical diagnostics, environmental monitoring, automotive sensing, and consumer electronics. This shift from specialized instrumentation to broader commercial deployment has created a strong demand for scalable and economically viable sensing technologies. The high fabrication costs associated with epitaxial semiconductor growth therefore represent a major barrier to large-scale adoption. Consequently, significant research efforts have focused on developing alternative material platforms capable of enabling lower-cost SWIR devices. Among these approaches, solution-processable nanomaterials have emerged as particularly promising candidates, as they offer compatibility with scalable manufacturing techniques and the potential to substantially reduce device fabrication costs while maintaining the desirable optoelectronic properties required for SWIR applications. Colloidal indium arsenide (InAs) quantum dots (QDs) are a leading class of RoHS-compliant infrared nanomaterials owing to their large exciton Bohr radius, which enables deep spectral tunability, as well as their high chemical stability. However, the synthesis of high-quality InAs QDs remains challenging because of the strong covalency of the In-As bond and the limited availability of suitable arsenic precursors. Current synthetic strategies rely predominantly on two arsenic sources: tris(trimethylsilyl)arsine ((TMS)3-As) and tris(dimethylamino)arsine (amino-As). Although substantial progress has been achieved using both approaches, each route still suffers from intrinsic limitations associated with precursor chemistry, reaction scalability and reproducibility, which collectively hinder the broader adoption of InAs QDs in commercial SWIR technologies. This thesis addresses the major bottlenecks associated with both the (TMS)3-As and amino-As routes by introducing mechanistic insights and innovative scientific modifications. Through these advancements, the work establishes pathways for producing high-quality InAs QDs with excitonic absorption and emission in the SWIR region, thereby laying the groundwork for scalable and industrially relevant InAs QD platforms for future infrared optoelectronic applications. The thesis is divided into three chapters: Chapter 1 provides the scientific and technological context for this thesis by introducing the SWIR spectral region and its rapidly expanding relevance across a wide range of applications, which is driving increasing commercial and consumer demand. It discusses current market trends and highlights how today’s SWIR technologies rely mainly on expensive epitaxial III-V semiconductors, motivating the need for solution-processable SWIR nanomaterials. The chapter then provides a brief history of colloidal nanomaterials and outlines the key principles governing their size-dependent properties, surface chemistry, ligand interactions, core-shell structures, and common synthesis strategies. Building on this foundation, it reviews the classes of nanomaterials that operate in the SWIR region, their historical development, and the role of RoHS compliance in guiding material choices. Finally, the chapter focuses on colloidal InAs QDs, summarizing their synthetic historical background, the precursors that have enabled their synthesis, and the remaining challenges that motivate the studies presented in Chapters 2 and 3. In Chapter 2, we investigate the synthesis of InAs QDs using the (TMS)3-As precursor and examine the mechanistic limitations associated with the procedures commonly employed in the literature. Although state-of-the-art methodologies based on this precursor can produce high-quality InAs QDs with excellent optical properties, they are hampered by the in-situ generation of water during the reaction, which necessitates extensive post-synthetic purification and complicates the workflow. Through a combination of optical, structural, and NMR analyses, we show that the commonly employed dioctylamine (DOA)-oleic acid system undergoes acid-base condensation, leading to the in-situ generation of water, that reacts with the silyl-precursors leading to TMS-derived impurities that contaminate the QDs. By substituting DOA with a tertiary amine, namely trioctylamine (TOA), we suppress these side reactions and obtain cleaner, higher-quality InAs QDs with markedly improved optical properties. The chapter further presents a systematic comparison between the conventional and modified synthetic approaches, providing clear experimental evidence that the proposed strategy effectively resolves the water-generation problem in a mechanistically informed manner. Despite the improved reaction control and enhanced optical quality achieved using the (TMS)3-As precursor, its high cost and extreme pyrophoricity pose significant challenges for large-scale and industrial implementation. These limitations motivate the work presented in Chapter 3, where we explore a safer and more economically viable arsenic precursor system as an alternative route for the synthesis of high-quality InAs quantum dots. In Chapter 3 we investigate the synthetic route based on amino-As precursor. Although this precursor has been explored as a safer alternative to (TMS)3-As, its use still presents intrinsic challenges that hinder the controlled growth of large InAs quantum dots. In this route, a reducing agent is required to convert As3+ to As3-, and the strength and stability of this reagent play a critical role in determining the nucleation and growth behavior of the nanocrystals. Conventional reducing agents are typically supplied in low-boiling solvents, which can cause boiling bursts during high-temperature injections, leading to safety concerns and poor reaction reproducibility. In this chapter, we introduced a new reducing agent, an amino-alane (TOA-AlH3), that overcomes key limitations of the amino-As route and enables more stable reaction conditions at elevated temperatures. Using this reagent in both hot-injection and seeded-growth methods, we synthesize large, monodisperse InAs cores that, after ZnSe shelling, exhibit efficient SWIR photoluminescence. The chapter also shows that TOA-AlH3 is fully compatible with ZnCl2, an essential additive for achieving high PLQY in InAs@ZnSe QDs. Together, these topics establish the scientific framework for the thesis, which aims to develop improved precursor chemistries and synthetic strategies for colloidal InAs quantum dots and their core/shell architectures, enabling high-quality SWIR nanomaterials suitable for future optoelectronic technologies.