Electrical and optical properties of Co-doped and undoped MoS2

Co-doped and undoped layered MoS2 crystals were grown by the chemical vapor transport method using iodine as the transport agent. Both reflectance and piezoreflectance measurements reveal two exciton transitions of the direct band edge around 1.86 and 2.06 eV for undoped MoS2 and 1.84 and 2.03 eV for Co-doped MoS2. Hall effect measurements show that the Co-doped MoS2 sample has a lower carrier concentration and mobility than the undoped sample. These differences between undoped and Co-doped MoS2 were attributed to the effect of cobalt atoms causing a small lattice distortion, lattice imperfections and/or impurity states that form trap states between the conduction band and valence band. Furthermore, photoconductivity (PC) and persistent PC results show that Co-doped MoS2 has a longer time constant and better responsivity than undoped MoS2. This work discusses the advantages of Co-doped MoS2 for photodetector applications. (C) 2016 The Japan Society of Applied Physics