Probing the temperature dependent transport in colloidal MoS₂ nanocrystals

The quantum confinement effect leads to interesting phenomenon in colloidal MoS₂ nanocrystals (NCs), specifically, size-tuneable optical and electronic properties. In addition the ability to be solution processed makes the NCs ideal for commercial flexible and tuneable LEDs, photodetectors, solar cells and transparent electronic devices. In this work, we made temperature dependent (10K-350K) two probe I-V measurements on MoS₂ NC assemblies (without gate bias) to estimate parameters (from non-linear fitting) such as mobility, conductivity, activation energy, etc. and study their temperature and size dependence, which showed a transition from Nearest Neighbour Hopping (NNH) at higher temperatures (where Arrhenius like behaviour was seen) to Variable Range Hopping (VRH) at lower temperatures. Spontaneous phase transition of MoS₂ from trigonal prismatic to octahedral (which was monitored by X-ray photoelectron spectroscopy, Raman and UV-Vis spectroscopy), and restoration of 2H-phase by ex-situ thermal annealing was also studied. Our results indicate that for microelectronics, 1-T might be more suitable due to its higher mobility over 2-H, which remains the better choice for optoelectronics.