In Situ Photoluminescence of Colloidal Quantum Dots During Gas Exposure—The Role of Water and Reactive Atomic Layer Deposition Precursors

Colloidal quantum dots (QDs) are a promising material for optoelectronic applications. Typically, device integration requires QDs to be embedded in a host material. Atomic layer deposition (ALD) is often considered as a deposition technique for such purposes. However, it is known that ALD and vacuum processes often influence the optical properties of QDs in a negative way. Here, we describe an in situ photoluminescence (PL) measurement setup and use it to monitor the PL of QDs under vacuum and during ALD. For CdSe-based core/shell QDs, a reduction in the QD PL was observed upon exposure to vacuum. Water was identified as crucial for maintaining a high PL as evidenced by re-exposure to different gases. Furthermore, we addressed the influence of vacuum, different plasmas (O₂, H₂O, H₂, H₂S/Ar, and Ar), precursors (trimethylaluminum, diethylzinc, tetrakis(dimethylamido)titanium, and tetrakis(ethylmethylamido)hafnium), reactants (H₂O, H₂S, and O₃), and ALD processes (Al₂O₃, TiO₂, HfO₂, and ZnS) on QDs. We observed a PL reduction by up to 90% upon plasma treatments. Furthermore, we found that trimethylaluminum and diethylzinc reduced the PL efficiency by more than 70% while exposure to tetrakis(dimethylamido)titanium and tetrakis(ethylmethylamido)hafnium lowered the PL by only 10-20%. Surprisingly, tetrakis(dimethylamido)titanium and H₂O, which by themselves had only a minor influence on the QD PL, still caused an 80% drop of the PL efficiency when combined as an ALD process. On the other hand, ALD growth of HfO₂ by combining tetrakis(ethylmethylamido)hafnium and O₃ preserved 80% of the initial PL quantum yield, making it a promising process for QD embedding. These results put forward in situ PL measurements as a versatile technique to identify suitable precursors, reactants and ALD processes for QD embedding and investigate the interaction between QDs and reactive gaseous species in general.