Effect of interface on mid-infrared photothermal response of MoS2 thin film grown by pulsed laser deposition

Here we report mid infrared (mid-IR) photothermal response of multi layer MoS2 thin film grown on crystalline (p-type silicon and c-axis oriented single crystal sapphire) and amorphous substrates (Si/SiO2 and Si/SiN) by pulsed laser deposition (PLD) technique. The photothermal response of the MoS2 films was measured as changes in the resistance of MoS2 films when irradiated with mid IR (7 to 8.2 {\mu}m) source. We show that it is possible to enhance the temperature coefficient of resistance (TCR) of the MoS2 thin film by controlling the interface through proper choice of substrate and growth conditions. The thin films grown by PLD were characterized using XRD, Raman, AFM, XPS and TEM. High-resolution transmission electron microscopy (HRTEM) images show that the MoS2 films grow on sapphire substrate in a layer-by-layer manner with misfit dislocations. Layer growth morphology is disrupted when grown on substrates with diamond cubic structure such as silicon due to growth twin formation. The growth morphology is very different on amorphous substrates such as Si/SiO2 or Si/SiN. The MoS2 film grown on silicon shows a very high TCR (-2.9% K-1), mid IR sensitivity (delR/R=5.2 %) and responsivity (8.7 V/W) as compared to films on other substrates.