Layer Number Controllable Molybdenum Disulfide Film Growth and Its Applications in Vertical and Planar Photodetectors

Abstract Wafer‐scale and layered MoS 2 films are grown by sulfurizing amorphous MoS 2 films deposited on sapphire substrates by using a radio‐frequency sputtering system. To verify the layer numbers of the multi‐layer MoS 2 films, atomic layer etchings are adopted. Wafer‐scale MoS 2 film growth with good layer number uniformity up to 30 is observed. A vertical device with 20‐layer MoS 2 embedded in between Al (bottom) and Au (top) electrodes is fabricated. With different work functions of the metal electrodes, photo‐excited electrons and holes in the MoS 2 layer can be separated and form photovoltaic responses. With the insertion of 5 nm MoO 3 carrier transport layer between the MoS 2 layer and the top Au electrode, enhanced photovoltaic responses are observed for the device. By using graphene as the carrier transport layer and MoS 2 as the light absorption layer, avalanche photocurrents are observed for planar MoS 2 /graphene photoconductive devices. With the assist of the higher electron density in multi‐layer MoS 2 , an easier compensation in the loss of photo‐excited electrons and therefore, charge neutrality in the MoS 2 layer can be maintained. Significant reduction in the rise/fall times from >100 ms. to <10 ms. is also observed for the planar photodetector with 10‐layer MoS 2 absorption layer.