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.