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

Abstract

Wafer-scale and layered MoS₂ films are grown by sulfurizing amorphous MoS₂ films deposited on sapphire substrates by using a radio-frequency sputtering system. To verify the layer numbers of the multi-layer MoS₂ films, atomic layer etchings are adopted. Wafer-scale MoS₂ film growth with good layer number uniformity up to 30 is observed. A vertical device with 20-layer MoS₂ 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 MoS₂ layer can be separated and form photovoltaic responses. With the insertion of 5 nm MoO₃ carrier transport layer between the MoS₂ layer and the top Au electrode, enhanced photovoltaic responses are observed for the device. By using graphene as the carrier transport layer and MoS₂ as the light absorption layer, avalanche photocurrents are observed for planar MoS₂/graphene photoconductive devices. With the assist of the higher electron density in multi-layer MoS₂, an easier compensation in the loss of photo-excited electrons and therefore, charge neutrality in the MoS₂ 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 MoS₂ absorption layer.